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Functionally Graded Thermal Protection Systems for Future Space Vehicles

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Title:
Functionally Graded Thermal Protection Systems for Future Space Vehicles
Series Title:
Journal of Undergraduate Research
Creator:
Behnke, Marlana
Sankar, Bhavani ( Mentor )
Place of Publication:
Gainesville, Fla.
Publisher:
University of Florida
Publication Date:
Language:
English

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serial ( sobekcm )

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Abstract:
High thermal stresses develop when two different types of materials (such as a metal and ceramic) are bonded together. This is often the case in thermal protection systems (TPS) for reentry vehicles that need to be both insulative and structurally strong. The thermal stresses developed in a two-component composite that gradually changes from one material composition to another, also known as a functionally graded material (FGM), were studied to determine if there are advantages to using an FGM as part of a TPS. Finite element analysis was used to study the heat loads that occur during spacecraft reentry. These heat loads were applied to a three-dimensional finite element model of the FGM composed of 100% aluminum oxide in the top layer and 100% nickel alloy in the bottom layer, with either a linear or an elliptical functional variation between these outermost layers. Thermal stresses and strains were examined to determine the advantages of using an FGM. The study found that using an FGM does allow for material tailoring that will prevent failure. However, prevention of failure in the material is not guaranteed. Using von Mises stress failure criteria, the materials were shown to fail at certain percent compositions. If the sections of the material that failed are removed, failure can be prevented, but the material will not vary from 100% ceramic to 100% metal. It will only vary from 80% metal to 80% ceramic, for example. It is therefore plausible to use an FGM as part of a TPS.

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Functionally Graded Thermal Protection Systems for Future
Space Vehicles


Marlana Behnke


College of Engineering, University of Florida


High thermal stresses develop when two different types of materials (such as a metal and ceramic) are bonded
together. This is often the case in thermal protection systems (TPS) for reentry vehicles that need to be both insulative
and structurally strong. The thermal stresses developed in a two-component composite that gradually changes from one
material composition to another, also known as a functionally graded material (FGM), were studied to determine if
there are advantages to using an FGM as part of a TPS. Finite element analysis was used to study the heat loads that
occur during spacecraft reentry. These heat loads were applied to a three-dimensional finite element model of the FGM
composed of 100% aluminum oxide in the top layer and 100% nickel alloy in the bottom layer, with either a linear or
an elliptical functional variation between these outermost layers. Thermal stresses and strains were examined to
determine the advantages of using an FGM. The study found that using an FGM does allow for material tailoring that
will prevent failure. However, prevention of failure in the material is not guaranteed. Using von Mises stress failure
criteria, the materials were shown to fail at certain percent compositions. If the sections of the material that failed are
removed, failure can be prevented, but the material will not vary from 100% ceramic to 100% metal. It will only vary
from 80% metal to 80% ceramic, for example. It is therefore plausible to use an FGM as part of a TPS.


INTRODUCTION

The thermal protection system (TPS), or heat shield, is a
critical component of a spacecraft that enters an
atmosphere. When a spacecraft enters a planetary
atmosphere, it is travelling at hypersonic speeds, resulting
in significant aerodynamic heating that would destroy a
vehicle with no TPS. The high temperatures developed
over the vehicle result in structural deformations due to
large thermal loads. Currently there are two common types
of TPS: ablators and tiles and blankets. The former
Mercury, Gemini, and Apollo missions, as well as current
Soyuz missions, use an ablator that bums off of the vehicle
as it absorbs the heat. The Space Shuttle Orbiter currently
uses High Temperature Resistant Ceramic Tiles and
Blankets that act as insulators.
These types of TPS are structurally weak and can easily
become damaged, as in the Space Shuttle Columbia
accident (Wilson, 2003). Integrating a metal into the TPS
could improve the strength. However, abrupt transitions in
material composition and properties usually result in sharp
local stress concentrations (Suresh & Mortensen, 1998).
The large difference in coefficients of thermal expansion of
a metal and ceramic will lead to large thermal stresses
when a large heat flux is applied, as is the case during


reentry. These stresses can be reduced if the transition from
one material to the other is gradual. Therefore, the use of a
functionally graded material (FGM) is appropriate. An
FGM is a two-component composite that gradually
changes from one material composition to another (Ruys &
Sun, 2002). Suresh and Mortensen (1998) provide the
reader with an overview of FGM characteristics and
manufacturing processes. Figure 1 is an illustration of an
FGM in which the white could represent ceramic and the
black represents a metal. In an FGM, aside from magnitude
of the thermal stresses being minimized, the onset of
plastic yielding and failure can be delayed, large stress
concentrations can be suppressed, strength of the interfacial
bond can be increased, and crack propagation can be
reduced (Mortenson, 1998).
The purpose of the study described below is to deter-
mine to what extent the FGM is useful in reducing thermal
stresses for TPS applications. In Sankar and Tzeng (2002),
an elasticity solution showed that an FGM does reduce the
thermal stresses when modeled as a beam with an expo-
nential temperature variation that varies in the opposite
direction of the elastic constants. The thermal stresses in a
two-dimensional FGM (material composition changes in
two directions) modeled as a plate have also been studied
and shown to reduce thermal stresses (Nemat-Alla, 2003).


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





MARLANA BEHNKE


Table 1: Effective Property Formulas


Figure 1: Illustration of FGM such that white represents ceramic
and black represent metal (Aboudi, Pindera, & Arnold 2001)

This study focuses on analyzing a three-dimensional
plate that is functionally graded with respect to the
thickness. A heat flux similar to that undergone during
spacecraft reentry into Earth's atmosphere will be applied.
The plate will be functionally graded according to linear
and elliptical variations. The thermal stresses and strains
will be compared in these different types of configurations
to determine the advantages of using an FGM in a TPS. It
is expected that all of the variations being analyzed will
show that thermal stresses can be reduced and tailored with
an FGM.

METHODOLOGY

Material Selection
Aluminum oxide, or alumina, was chosen as the
ceramic because of its low conductivity and its high
strength relative to many ceramics (Materials, 2002)..
Nickel was chosen to be the metal because it is strong and
corrosive resistant. Nickel 200, which is 99.6% pure
wrought nickel, is very common in aerospace applications
(Nickel 200/201, 2009). This particular nickel alloy was
used for failure analysis.

Effective Properties of the Functionally Graded
Material
Each layer of an FGM will have a different material
composition. For example, one layer may have 100%
alumina and 0% nickel, while the layer below that may
have 90% alumina and 10% nickel. These percent
compositions are also known as volume fractions when
referring to composites. If there are two materials creating
one new material, the new material has effective material
properties that result in the combination of the material
properties of each individual material.
There are several ways to determine the effective
properties. The two most common methods are the rule of
mixtures and inverse rule of mixtures. For the analysis of


i""
I)
cLI Illr I~
ly:
L.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 | Spring 2010


Material Property Effective Property Formula
1 V1 V2
+-
Young's Modulus (E) E E E2
Coefficient of Thermal = +-
Expansion (a) _______ = F + _______

Density (p) + P-22
P1CA1V P2 Cp2cV2
Heat Capacity ( c,)

v = v 1V + v 2V
Poisson's Ratio


k=kl* 1+ 3(k2 k)
Thermal Conductivity (k) L 3(k1)(V2)+(k2 + 2 * k)(V,)


the FGM in this paper, either one of these methods was
used, or an empirical formula was used for thermal
conductivity, as described below (Nemat-Alla, 2003).
Table 1 shows the formula used for each material property,
where 1 represents alumina, 2 represents nickel, and V is
the volume fraction, which has a value that can range from
Oto 1.
The effective properties were found for each layer
based on the volume fractions associated with each
function described in the following section. The FGM will
be subjected to a large range of temperatures (300K-
1000K) during reentry. Therefore, temperature dependent
properties of both alumina and nickel were used.

Generation of Functional Variations
Three different functional variations of material were
studied. Each FGM had a layer of pure ceramic on the top
surface and a pure nickel layer on the bottom surface.
The first functional grade studied was a linear variation.
This FGM was 1 cm thick. It began with pure ceramic on
the outermost layer, which would be exposed to air. Then,
with each subsequent evenly spaced layer, 10% of the
alumina was taken away, and 10% of the nickel was added.
For example, the second layer had 90% alumina and 10%
nickel. The third layer had 80% alumina and 20% nickel.
This continued to change linearly through the thickness
(making a total of 11 layers) until the bottom layer
contained 100% nickel and 0% alumina.
The next configuration studied varied elliptically as in
Equation 1, where P is the material property, z is the





THERMAL PROTECTION SYSTEMS FOR FUTURE SPACE VEHICLES


-- More Nickel


---More Alumina


-Linear ()


4.5E+11



4E+11



co 3.5E+11
C,,

o 3E+11
v-,

> 2.5E+11



2E+11



1.5E+11
0 0.2 0.4 0.6 0.8 1
Volume Fraction


Figure 2: Three different volume fraction variations


position through the thickness, and h is the total thickness.
The subscripts 1 and 2 represent alumina and nickel,
respectively.

Z2
P=P + (P2-P1) 1-
h
Equation 1
The Young's Modulus was used to form this elliptical
equation. The effective Young's Modules was determined
at various heights. Knowing these heights, the volume
fraction at various layers was determined following the
inverse rule of mixtures. This configuration varied
elliptically and had a greater amount of alumina overall.
This configuration will be referred to as "elliptical
alumina." This FGM is comprised of 15 layers. There is
0.1 cm of alumina for the top layer. There is then 1 cm of
FGM that varies elliptically.
The final configuration tested was an inverse of the
configuration previously described. There was an elliptical


variation but a greater amount of nickel overall. This
configuration will be referred to as "elliptical nickel."
Figure 2 is a graph of the property variation with volume
fraction using Young's Modulus as an example.

Heat Transfer Analysis
After completing the analysis to determine the volume
fraction variations for each of the three configurations, a
heat transfer analysis was conducted to determine the
temperatures that the FGM would experience. The results
from this analysis are used in the next section to determine
the thermal stresses and strains. Bapanapalli, Sankar,
Haftka, Gogu, and Blosser (2007) demonstrated that a one-
dimensional heat transfer analysis is appropriate for this
type of problem. The temperature distributions did not vary
significantly between the two-dimensional and one-
dimensional problem. For this reason, a finite element one-
dimensional heat transfer problem was conducted to
determine the temperature distribution in the FGMs.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





MARLANA BEHNKE


z axis runs through the thickness of the plate. Using the
results from the heat transfer analysis (described below),
the temperature loads were applied. These temperatures
were prescribed to the entire plate through the thickness
because it was found that the temperature was almost
uniform throughout the thickness. Also, the same
temperature load was applied to each configuration due to
the fact that they all yielded similar results. Table 2 shows
the step time and temperature chosen.

Table 2


450 1575 2175
Time from Rentry, sec
Figure 3: Heat flux approximation during space
(Bapanapalli et al., 2007).


4500


shuttle reentry


ABAQUS, a commercial finite element modeling
program, was used for both the heat transfer and thermal
stress analysis. The heat transfer problem was modeled as
a wire. The material properties were prescribed as
discussed in the previous sections.
Boundary conditions were also applied. The boundary
condition at x = 0, where the TPS is attached to another
part of the spacecraft, is a radiation boundary condition in
which the emissivity is 0. This is not actually the case, but
rather a conservative assumption. The top layer that is
exposed to the air was prescribed a radiative and
convective boundary condition.
The heat loads were also prescribed to the one-
dimensional model. The analysis only deals with heat flux
loading. The heat flux applied was obtained from
Bapanapalli et al. (2007) and a graph of the heat flux
during a typical space shuttle reentry is shown in Figure 3.
After the one-dimensional model was formed, it was
meshed in elements of 0.0001 m. The quadratic heat
transfer analysis was then performed in order to determine
the temperature distribution in each of the three FGM
models.

Thermal Stress and Strain Analysis
Once the temperature distribution is determined from
the previous step, thermal analysis can be completed. First,
one quarter of a 30 cm x 30 cm x 1 cm (1.1 cm for
elliptical configuration) three-dimensional finite element
plate was modeled in ABAQUS. Three models were
analyzed: the linear model, the elliptical alumina model,
and the elliptical nickel model.
Symmetric boundary conditions and a boundary
condition in which displacement in the direction of the
thickness was inhibited were applied. The plate was
therefore free to expand in the x and y directions, where the


Step Duration (s) Temperature (K)
Initial --- 300
1 300 380
2 300 575
3 300 725
4 300 825
5 435 880
6 300 890


Given that only a temperature load was applied, the
only stress and strain on the three-dimensional plate is due
to thermal stresses. For the analysis, the plate was meshed
into elements that were approximately 0.0015 cm x 0.0015
cm x 0.0001 cm. A thermal stress analysis was then
performed for each material distribution to obtain the
thermal stresses and strains in each layer using 20-node
brick elements.
Failure analysis was conducted with the given
configurations and will be described in greater detail in the
results. It is important to note that the given material
distributions failed. Therefore, it was desired to analyze the
elliptical FGMs with a different number of layers. In both
the elliptical alumina and the elliptical nickel, a stress
concentration was noted in a certain area, in which an extra
layer was added to try to prevent the stress concentration.
After that analysis, some of the layers where failure was
occurring were removed in order to investigate if that
would lower the thermal stresses. The layers that were
added or taken away are explained in greater depth in the
results. The results of adding or taking away layers in the
elliptical alumina are presented simultaneously with the
results of the original configurations.

RESULTS

Heat Transfer Analysis
The one-dimensional heat transfer analysis was conducted
for the linear, elliptical alumina and elliptical nickel
configurations. The important results obtained from this
analysis are summarized in Table 3. Max AT refers to the


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





THERMAL PROTECTION SYSTEMS FOR FUTURE SPACE VEHICLES


Table 3


Functional Max
Variation Temperature (K) Max AT (K)
Linear 910 22
Elliptical
Alumina 890 10
Elliptical Nickel 886 3

maximum temperature difference that occurs at any time
during reentry between the top and bottom surface.
As mentioned previously, this analysis revealed that
the temperature does not vary significantly through the
thickness. Therefore, it was appropriate to assume a
uniform temperature load throughout the three-dimensional
plate at various time steps.

Thermal Stress and Strain Analysis
The thermal stresses were analyzed by looking at the
von Mises Stresses and the maximum principal strains
through the thickness at the center of each plate.

Linear Configuration. Figure 4 and Figure 5 show the
thermal stress and strain distributions through the thickness
of the linear FGM at the time of maximum stress.


0.01


0.008


0.006


0.004


0.002


Elliptical Alumina Configuration. Figure 6 and Figure 7
show the thermal stress and strain distributions through the
thickness of the elliptical alumina FGM at the time of
maximum stress. Note that the original configuration is
completely overlapped by the configuration with an extra
layer.

Elliptical Nickel Configuration. Figure 8 and Figure 9
show the thermal stress and strain distributions through the
thickness of the elliptical nickel FGM at the time of
maximum stress.

Stress and Strain Comparisons. Figure 10 is a
comparison of the original thermal stresses developed in
the three types of FGMs. Figure 11 is a comparison of the
original strains developed in the three types of FGMs,
being compared to the strains in the case where there was
only nickel or only alumina.
Figure 12 is a model of the deformation of an FGM
after the temperature loads have been applied. The various
colors represent different magnitudes of stress, where the
green represents the highest stress and the dark blue
represents the lower stress magnitudes. The various stress
magnitudes are caused by the interaction of different
material's properties. Each layer is expanding differently.


0.0 50.0 100.0 150.0 200.0 250.0 300.0
Mises Stress (MPa)

Figure 4: von Mises Stress at maximum thermal stress, linear





University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010


--






MARLANA BEHNKE


0.01



o 0.008

I-
1-
c 0.006

0
I-
o 0.004
Co


O 0.002



0
0.005 0.006 0.007 0.008 0.009 0.010

Strain

Figure 5: Maximum principal strain, linear





-- Original Config. ---Extra layer -A-Missing bottom 4 layers


0.010



w 0.008



S 0.006
0
C-


. 0.004
I-




0.002


0.000 ,

0.0 200.0 400.0 600.0 800.0 1,000.0
Stress (MPa)

Figure 6: von Mises Stress at maximum thermal stress, elliptical alumina







University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 | Spring 2010
6






THERMAL PROTECTION SYSTEMS FOR FUTURE SPACE VEHICLES


-*- Original Config. -- Extra Layer

0.012


S0.010



0.008
.2
I-
m 0.006

I-
S 0.004

.T
o 0.002


0.000
0.0060 0.0080 0.0100
Strain

Figure 7: Maximum principal strain, elliptical alumina


-- Missing bottom 4 layers


0.0120


0.0140


-- Original Config. -0- Extra Layer -- Missing top 4 layers



















0.00 0.0 100. 20.0 30.0 00.


0.012


0.010



0.008


0.006


0.004


0.002



0.000


0.0 100.0 200.0 300.0 400.0
Stress (MPa)

Figure 8: von Mises Stress at maximum thermal stress, elliptical nickel


500.0 600.0


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010
7





MARLANA BEHNKE


-*-Original Config. -*- Extra Layer - Missing top 4 layers


0.010


0.008


0.006


0.004


0.002


0.000


0.007


0.008 0.008 0.009 0.009 0.010 0.010
Strain


0.011


0.011


Figure 9: Maximum principal strain, elliptical nickel


Elliptical Alumina - Elliptical Nickel


0.8


0.6


0.4


0.2


Linear


0.0 100.0 200.0 300.0 400.0 500.0 600.0 700.0 80C
Stress (MPa)


Figure 10: Stress vs. thickness for three FGM types




University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010
8


).0


A,,


M"'


z


/


-


-


-





THERMAL PROTECTION SYSTEMS FOR FUTURE SPACE VEHICLES


-Elliptical Alumina
-100% Nickel


1

0.8

0.6


0.4 -

0.2 -

0
0.006


-Elliptical Nickel
100% Alumina


0.008 0.010 0.012
Strain


Figure 11: Strain comparison for three FGMs and case of no FGM


Figure 12: Model of FGM deformation after temperature change

Failure Analysis
Knowing the yield strengths of the two materials that
compose the FGM, the effective yield strength can be
estimated to determine if and when failure occurs in the
FGM. A common failure criterion used for FGMs is von
Mises failure (Lee, Kim, Ahn, DeJonghe, & Thomas,
2007).The effective yield strength was calculated with the
rule of mixtures. The yield strength of aluminum oxide is
approximately 300 MPa and the yield strength of nickel is
approximately 200 MPa. One purpose of adding nickel is
to increase the strength of the material. While the yield
strength of nickel is shown to be lower than that of
alumina, it is important to note that the strength found


experimentally for alumina is in ideal cases; it will
typically not be as strong. Also, once it cracks, damage will
occur very quickly in the alumina.
Figure 13 is a graph of the factor of safety through the
thickness for each of the three types of FGMs. The straight
line that occurs on the factor of safety of 1 represents the
point at which failure will occur. Any factor of safety less
than 1 also indicated failure. Note that the graph's x-axis
was adjusted to show a maximum factor of safety of 10.
There were sections of the FGM that had factors of safety
higher than this, but these points are not close to failure,
and thus they are not focused on.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010


*Linear







MARLANA BEHNKE


-Elliptical Alumina


1-


0.8
0.8 -6- - -


0.6


0.4



0.2


0


-Elliptical Nickel


Linear - Point of Failure, < 1


0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
Factor of Safety


Figure 13: Factor of safety through the thickness of the FGM for the three FGM types


CONCLUSIONS

Summary of Heat Transfer
The heat transfer analysis revealed that the temperature
through the thickness of the FGM was fairly uniform at all
times during reentry. The maximum temperature difference
in any of the FGMs at any given time was 22 K. This slight
difference is not expected to significantly affect the results
of the thermal stress analysis that followed.
It is also important to note that the given FGM is not
suitable for providing added insulative properties. Heat
travels through the thickness very quickly. The thermal
conductivity of both materials is relatively high, and the
FGM is also very thin.

Summary of Thermal Stress and Strain
The thermal stress analysis showed that the elliptical
alumina configuration had the largest peak thermal stress
of all of the FGMs, but the elliptical nickel had relatively
high peak stresses as well. The linear configuration had the
lowest magnitudes of thermal stress overall. The stresses in
the linear configuration were highest when a large volume
fraction of nickel was present.


The strain results revealed that elliptical alumina had
the largest peak strain but the lowest strain overall. The
elliptical nickel had the lowest peak strain but the largest
strain overall. The linear configuration fell between the two
other designs. To evaluate the significance of these results,
the failure analysis must be examined more closely.

Summary of Failure
After completing the failure analysis, it was found that
all three of the FGM configurations failed during
maximum stress situations. Failure of elliptical alumina
occurred at the bottom 10% of the FGM where the volume
fraction of nickel is .5. Failure of elliptical alumina occurs
at the bottom 15% of the FGM where the volume fraction
of nickel is .15. The linear configuration failed at both the
top and bottom 10% of the material where the volume
fraction of nickel is .1 and .9, respectively.
In order to decrease the stress magnitudes, an extra
layer was added where there was a stress concentration.
This had little to no impact on the magnitudes of the stress,
as shown in Figures 6 and 8.
Although adding a layer had a very slight impact,
removing layers where the FGM failed did result in an


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





THERMAL PROTECTION SYSTEMS FOR FUTURE SPACE VEHICLES


increase in the factor of safety overall. However, this was
likely because the layers where failure occurred were
removed. The overall stress magnitude of the layers that
remained did not change significantly.

Future Work
It was found that the FGM could potentially be used as
part of a TPS. However, the FGM is likely not best for an
entire TPS due to weight and insulation considerations.
The FGM can be tailored to reduce thermal stresses so as
to not have failure occur. However, layers may have to be
removed such that the FGM only transitions from 80%
metal and 20% ceramic to 20% metal and 80% ceramic, for
example.
Before an FGM could be used on a TPS, it is important
to note the future work that must be completed. The von
Mises failure stress used, as well as the effective yield
strength used found through the rule of mixtures, may not
be the ideal failure analysis to use. Other failure modes
should be investigated given the nature of this FGM
application. Crack propagation and delamination should
also be investigated.
Once the behavior of this type of composite is better
understood, it may become useful in many applications,
including in TPSs, aircraft turbine blades, and military
armor.

References

Aboudi, J., Pindera, M.J., & Arnold, S. M. (2001). Higher
Order Theory for Functionally Graded Materials.
Retrieved April 1, 2009, from NASA:
http://www.grc.nasa.gov/WWW/RT/RT2000/5000/592
Oamold3 .html

Bapanapalli, S. K., Sankar, B. V., Haftka, R. T., Gogu, C.,
& Blosser, M. L., (2007). "Design of an integrated
thermal protection system." Manuscript submitted for
publication.


Lee, C. S., Kim, S. G., Ahn, S. H., DeJonghe, L. C., &
Thomas, G., (2007). "Three dimensional analysis of
thermal stress and prediction of failure of
polytypoidally joined Si3n4-A12o3 functionally graded
material", Materials Transactions 48(9), 2489-2493.

Materials - Aluminum Oxide (A1203) Properties. (2002).
Retrieved April 1, 2009, from Accuratus Corporation:
http://www.accuratus.com/alumox.html

Nemat-Alla, M. (2003). Reduction of thermal stresses by
developing two-dimensional functionally graded
materials. International Journal of Solids and
Structures , 40(26), 7339-7356.

Nickel 200/201. (2009) Retrieved April 1, 2009, from Pai,
Inc.: www.painc.com/nickel_200_201 .htm

Ruys, A. & Sun, D. (2002). Functionally graded materials
and their production methods. AZo Journal of
Materials Online. Retrieved April 1, 2009, from
AZoM:
http://www.azom.com/Details.asp?ArticlelD=1592

Sankar, B. V., & Tzeng, J. T. (2002). Thermal Stresses in
Functionally Graded Beams. AIAA Journal, 40(6),
1228-1232.

Suresh, S. & Mortensen, A. (1998). Fundamentals of
functionally graded materials. London: Maney
Publishing.

Wilson, J., Ed. (2003, Aug.). Report of Columbia Accident
I, ' .r ig,,i, I Board, Volume I. Retrieved April 1,
2009, from NASA:
http://www.nasa.gov/columbia/home/CAIBVol 1 .html


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010







MSM Photodetectors on Germanium Substrates with SWNT Film

Electrodes


Keith Knauer,


College of Engineering, University of Florida


In this paper, Schottky-like behavior of single-walled carbon nanotube (SWNT) film contacts on Ge is demonstrated by the
fabrication and electrical characterization of metal-semiconductor-metal (MSM) photodetectors with SWNT film electrodes. In
addition, the effect of device geometry on the dark current is studied by scaling the active area, finger width, and finger spacing of
the MSM photodetectors. Finally, the dark current of the SWNT film devices is compared to the dark current of metal control
samples, demonstrating that the use of SWNT film electrodes results in a significant reduction in dark current. These experimental
results give insight into the electrical properties of the SWNT film-Ge interface while also demonstrating the use of SWNT film as
a transparent and conductive material for electronic applications.


I. INTRODUCTION


A. Carbon Nanotubes
Carbon nanotubes were discovered in 1991 by Sumio
Iijima at the NEC Tsukuba Research Laboratory using
high resolution transmission electron microscopy to study
the soot from fullerene synthesis by arc discharge [1].
Shown in Fig. 1, a carbon nanotube is a single graphite
plane, known as graphene, that has been rolled up into a
hollow cylinder. During formation, larger cylinders can
encapsulate tubes with smaller diameters and form a
multi-walled carbon nanotube (MWNT). However,
single-walled carbon nanotubes (SWNT) are of more
immediate electrical interest due to their outstanding
electrical and physical properties. They exhibit diameters
of 1 to 10 nm and can exceed several micrometers in
length [2]. Individual SWNTs have been used in
applications such as transistors and sensors, but their
widespread use has been hampered by a lack of control
over their diameter, location, chirality, and direction [3],
[4].
B. Single-Walled Carbon Nanotube Films
SWNT films consist of layers of interwoven SWNTs
forming a three-dimensional mesh. Due to averaging
effects, these films possess uniform and predictable
electronic properties independent of the varying
characteristics of the constituent nanotubes. SWNT films
can be created by vacuum filtration, deposited on
arbitrary substrates, and efficiently patterned, while
possessing low resistivity (on the order of 10-4 Q cm),
high mobility, and high transparency to visible and
infrared wavelengths. Thus, they are promising
candidates to be used as transparent, conductive
electrodes for various optoelectonic applications [5]-[9].
Fig. 2 contains an AFM image of a 20 nm thick SWNT
film patterned by photolithography with subsequent 02
plasma etching. Enabling electronic and optoelectronic


applications of SWNT films motivates the
characterization of SWNT film-semiconductor junctions
with various substrates. In this effort, it has been recently
shown that SWNT films make a Schottky contact on Si
and GaAs, but the nature of SWNT film on Ge remains
largely unexamined [10], [11].









C






Fig. 1 A SWNT can be thought of as a sheet of graphene
rolled into a hollow cylinder along a chiral vector, C. [1].


(b)


0

0 1 2 3 4
Distance (urn)


Fig. 2. (a) AFM image of SWNT film illustrating patterning by
02 plasma etching. The smooth surface between the film is the
SiO2 substrate where the film has been completely removed. (b)
Height of SWNT film shown by cross-section [9].


.**


1 ->
'A


4*
wg


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 | Spring 2010







Effects of Environmental Heterogeneity on Male-Male
Competitive Success, Size, and Scaling in a Cactus Bug
Narnia femorata (Hemiptera: Coreidae)

Fae Nageon de Lestang


The effects of environment on sexual selection, specifically male competition, have yet to be fully explored. We examined
the effects of natural environmental heterogeneity on male scaling, size, and competitive success in a cactus bug, Narnia
femorata. Male N femorata were raised in two alternate environments (cactus with fruits and cactus without fruits) from
the fifth instar and checked daily until they reached adulthood. Males raised in a treatment with both cactus pads and fruit
developed faster and weighed more overall. Upon reaching sexual maturity, a subset of males was randomly chosen,
paired by treatment, and placed with a virgin female. Then their behaviors were recorded for time intervals over a period
of 110 minutes. We observed matings in 8 of 29 contests, all by males raised in the treatment with both cactus pads and
fruit. Noneof the males raised on a treatment of just cactus pads mated. Successful males were larger and expressed
relatively larger sexually-selected traits for their body size. These results suggest that natural environmental variation has
a significant effect on male competitive success for the species.


INTRODUCTION

Sexual selection has been a greatly debated concept
since it was first defined by Darwin in 1871. Darwin
originally described sexual selection as an advantage in
reproductive success among individuals (Darwin, 1871;
Andersson, 1994). Traits from successful individuals
would presumably be passed on to their offspring, and thus
the process of sexual selection would ensue (Pagel, 2002).
An important facet of sexual selection, intrasexual
selection, involves competition between members of the
same sex for access to the opposite sex and is generally
most intense in males. Intersexual selection (mate choice)
occurs when individuals select mates based upon preferred
traits. Females are often the choosier sex; hence, this
process is commonly termed female choice (or female
preference). The products of sexual selection are usually a
combination of both intrasexual and intersexual selection
(Moore & Moore, 1999; Hunt et al., 2009).
The factors that determine the success of an individual
may be more complex than initially imagined. While
heredity undeniably affects sexual selection, we have only
recently begun to address effects of natural environmental
variation on the processes and outcomes of sexual
selection. Recent empirical research has shown both social
and physical environments to impact male competitive
success in contests across many taxa, yet our understanding
of male combat and environmental heterogeneity is still
incomplete (Hubbell & Johnson, 1987; Young & Stanton,


1990; Clark et al., 1997). In this study, we explored
influences of natural environmental variation on male
development, size, shape, and competitive success. The
following question was addressed in our research: what
effect does environmental variation have on individual
morphology, and consequently, male contest outcome?
Based on results from other species (Miller & Emlen,
2010), we predicted that natural environmental variation
would have a significant effect on all aspects of male
growth and development and ultimately affect competitive
success.
We tested our prediction using Namia femorata, a
species of cactus bug in the family Coreidae. Coreids, or
leaf-footed bugs, are diverse and commonly have enlarged
and ornate hind legs (Rodriguez, 2005). Males often use
their hind legs to fight for access to females (Miyatake,
1997; Eberhard, 1998). Although Coreids are a very
diverse and interesting group, they have been largely
overlooked as a study group (an exception, however, is
Miller & Emlen, 2010).
The study species, N femorata, is found primarily in
Central America, the southwestern United States, and, most
recently, Florida (Baranowski & Slater, 1986). N femorata
feeds primarily on prickly pear and cholla cactus in the
genus Opuntia,both on the cactus cladodes (or pads) and its
reproductive structures (flowers and fruit). Females lay
eggs directly along the spines of cactus, and juveniles
aggregate on the cactus cladodes until they mature.
Juveniles reach adulthood in five nymphal instars. There


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





SEASONAL DIFFERENCES IN NUTRIENT ALLOCATION OF ARCTIC TUNDRA VEGETATION


effect on adult weight that the small initial disparity does
not likely account for the large difference in adult weights.
Males raised in the fruit treatment developed signif-
icantly faster than males raised in the no-fruit treatment.
Insects were sorted into the two treatments for only the
final stage of development; thus, effects of food treatment
would have likely been much more pronounced had food
treatment lasted for their entire development (Nageon de
Lestang & Miller, 2009).

Competitive and mating behaviors
Treatment had no effect on attack behavior in males
(Table 2). However, it is possible that males had already
established dominancy roles within the container prior to
observation, making the likelihood of observing an attack
improbable (Crespi, 1986). We found that males raised on
the fruit treatment were more likely to approach females
(P= 0.0345) but not more likely to contact or mount
females over the observed period (P= 0.7554) (Table 2).
There are a few possible explanations for this phenomenon.
It is possible that males from the fruit treatment were more
active overall than males from the no-fruit treatment due to
their more nutrient-rich diet (Sillanpaa, 2008; Low et al.,
2009). Males from the fruit treatment may have already
established dominancy within the arena, discouraging
males from the no-fruit treatment from approaching the
female and risking a potentially energy-intensive fight.
Males raised without 0. humifusa fruit were introduced to
the arenas 24 hours before any observations were taken and
may have been feeding on the fruit during this period.
Thus, males from the no-fruit treatment could have been
less active overall because they were digesting the fruit
they had previously ingested. Males raised with a more
complete diet may have had heightened sensory
capabilities, therefore making them more likely to locate
and contact females within the arena. Many studies have
shown a relationship between quality of diet and sensory
capabilities in insects (Chapman & Lee, 1991; Bernays &
Chapman, 1998; Triseleva & Safonkin, 2006).
Ultimately, males from the two treatments were
equally likely to mount a female within the given
observation period, yet only males raised with access to
cactus fruit successfully copulated with females (n=8,
Figure 2). This surprising result indicates the considerable
impact of food treatment and, more broadly, natural
environmental variation on competitive success for males
in this species. Given this information, we can assume that
female preference may have played a large role in the
results obtained (Hunt et al., 2009). Nevertheless,
measuring mating success provides us with a strong
indicator of reproductive success and, ultimately,
competitive success of the individual.


Body and weapon size
Male N femorata that mated with females during the
competitions were all from the fruit treatment and had a
significantly larger body size based on pronotum width
(Figure 3). The allometric relationship between femur
width and body size also differed across treatments. Males
from the fruit treatment had proportionately larger femurs
than males in the no-fruit treatment when comparing femur
width to body size. Because male femurs are used as
weapons and may also be ornaments, these results indicate
that males from the fruit treatment may have a considerable
advantage over males from the no-fruit treatment. This
evident disparity between insects from the two treatments
could be due to the higher quality of nutrition insects from
the fruit treatment experienced. Males raised with access to
0. humifusa fruit were presumably able to allocate more
energy and/or resources to developing this secondary sex
trait, indicating the importance of developmental environ-
ment for morphology in this species. The correlation we
found in body and leg size was not only due to apparent
success in male N femorata, but also reflects the effects of
treatment on the morphology of the insects. A random
sample of measurements from males raised on the two food
treatments showed similar morphological differences (CW
Miller, unpublished data).
We found environmental variation to have a significant
effect on the morphology, weight, development, and
behavior of male N femorata. Though we tested our
hypotheses by administering two different food treatments
to the N. femorata test population, it is important to realize
that these treatments represent two drastically different
environments to the species. Moreover, it is extremely
likely that juveniles living in close proximity will develop
in one of these two environmental conditions.
Other studies investigating effects of environmental
heterogeneity have found natural environment variation to
have a significant impact on male competitive success in a
broad spectrum of organisms (Eberhard & Gutierrez, 1991;
Folstad & Karter, 1992; von Schantz, 1999; Garant et al.,
2001). Such results indicate that environmental variation
may have far-reaching implications in the field of sexual
selection.
In conclusion, we found natural environment variation
to have staggering effects on the morphology, weight,
development, and competitive success of male N femorata.
These results suggest alternate environments may affect the
process of sexual selection for the species. More research is
still needed to further examine the impact of environmental
variation on the many aspects of sexual selection

REFERENCES CITED

Andersson M, 1994. Sexual Selection. Princeton, New
Jersey: Princeton University Press.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





MSM PHOTODETECTORS ON GERMANIUM SUBSTRATES WITH SWNT FILM ELECTRODES


various dimensions were then patterned using S1813
positive photoresist and subsequently etched to the
substrate by wet etching in 6:1 BOE. A SWNT film of
approximately 50 nm that was prepared by vacuum
filtration was then deposited. Following the film
deposition, interdigitated finger electrodes were patterned
by photolithography with S1813. The electrode fingers
were then etched by inductively coupled plasma etching
on a Unaxis Shuttlelock RIE-ICP using an 02 etching
chemistry. The etch parameters included 100W on the
substrate RF supply, 300W on the ICP RF supply, a
chamber pressure of 45 mtorr, and an 02 flow rate of 20
sem. In addition, a helium flow rate of 10 seem was used
to cool the substrate. After resist removal, the metal
contact pads were patterned using a double resist
photolithography step with S1813 and LOR3B. Here
LOR3B was used to facilitate the final metal lift-off.
Metal contact stacks of 30nm titanium and 70nm gold
were deposited using an Edwards e-beam evaporator.
Lift-off was then performed using PG photoresist
remover. Control samples with metal finger electrodes of
30nm Ti and 70nm gold were also fabricated for
comparison using identical process steps.
Fig. 6 shows optical microscope images of a
completed MSM photodetector with SWNT film
electrodes and a control sample of identical dimensions.
Various devices with differing active area length (AL),
active area width (AW), finger spacing (S), and finger
width (W) were fabricated to determine the dependence
of the dark current on device geometry. Furthermore,
four-point structures were also fabricated to determine the
SWNT film resistance.


III. RESULTS & DISCUSSION


A. Film Resistivity

First, the resistivity of the SWNT film was
determined by four-point probe measurements taken
using a parameter analyzer at room temperature. An
optical microscope image of a four-point probe structure
fabricated on the SWNT film sample with length L = 600
Ipm, width W = 20 Ipm, and thickness t = 50 nm is shown
in Fig.7(a). In taking these measurements, a current is
forced through the outer contacts and the voltage is
measured across the inner contacts. The resitivity, p, is
determined by the formula
L
R = p

where R is the resistance taken from the slope of I-V
curves [Fig. 7(b)]. The I-V curve of this device is shown
in Fig. 7(c), from which it is determined that the film
resistivity is approximately 4.7 x 10'3 0 cm.


3


A
W


. 0
r-

|-40

-80


Fig. 6 [(a)-(b)] Optical images of completed MSM devices. (a)
Photodetector with SWNT film electrodes. (b) Control sample
with metal electrodes for comparison.


-2.0 -1.0 0.0 1.0 2.0

Voltage (V)


Fig. 7 [(a)-(c)] Extraction of SWNT film resistivity (a) Optical
image of a four-point probe structure with SWNT film
electrodes. (b) Illustration of film dimensions. (c) I-V curve of
the four-point probe structure.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





MARLANA BEHNKE


z axis runs through the thickness of the plate. Using the
results from the heat transfer analysis (described below),
the temperature loads were applied. These temperatures
were prescribed to the entire plate through the thickness
because it was found that the temperature was almost
uniform throughout the thickness. Also, the same
temperature load was applied to each configuration due to
the fact that they all yielded similar results. Table 2 shows
the step time and temperature chosen.

Table 2


450 1575 2175
Time from Rentry, sec
Figure 3: Heat flux approximation during space
(Bapanapalli et al., 2007).


4500


shuttle reentry


ABAQUS, a commercial finite element modeling
program, was used for both the heat transfer and thermal
stress analysis. The heat transfer problem was modeled as
a wire. The material properties were prescribed as
discussed in the previous sections.
Boundary conditions were also applied. The boundary
condition at x = 0, where the TPS is attached to another
part of the spacecraft, is a radiation boundary condition in
which the emissivity is 0. This is not actually the case, but
rather a conservative assumption. The top layer that is
exposed to the air was prescribed a radiative and
convective boundary condition.
The heat loads were also prescribed to the one-
dimensional model. The analysis only deals with heat flux
loading. The heat flux applied was obtained from
Bapanapalli et al. (2007) and a graph of the heat flux
during a typical space shuttle reentry is shown in Figure 3.
After the one-dimensional model was formed, it was
meshed in elements of 0.0001 m. The quadratic heat
transfer analysis was then performed in order to determine
the temperature distribution in each of the three FGM
models.

Thermal Stress and Strain Analysis
Once the temperature distribution is determined from
the previous step, thermal analysis can be completed. First,
one quarter of a 30 cm x 30 cm x 1 cm (1.1 cm for
elliptical configuration) three-dimensional finite element
plate was modeled in ABAQUS. Three models were
analyzed: the linear model, the elliptical alumina model,
and the elliptical nickel model.
Symmetric boundary conditions and a boundary
condition in which displacement in the direction of the
thickness was inhibited were applied. The plate was
therefore free to expand in the x and y directions, where the


Step Duration (s) Temperature (K)
Initial --- 300
1 300 380
2 300 575
3 300 725
4 300 825
5 435 880
6 300 890


Given that only a temperature load was applied, the
only stress and strain on the three-dimensional plate is due
to thermal stresses. For the analysis, the plate was meshed
into elements that were approximately 0.0015 cm x 0.0015
cm x 0.0001 cm. A thermal stress analysis was then
performed for each material distribution to obtain the
thermal stresses and strains in each layer using 20-node
brick elements.
Failure analysis was conducted with the given
configurations and will be described in greater detail in the
results. It is important to note that the given material
distributions failed. Therefore, it was desired to analyze the
elliptical FGMs with a different number of layers. In both
the elliptical alumina and the elliptical nickel, a stress
concentration was noted in a certain area, in which an extra
layer was added to try to prevent the stress concentration.
After that analysis, some of the layers where failure was
occurring were removed in order to investigate if that
would lower the thermal stresses. The layers that were
added or taken away are explained in greater depth in the
results. The results of adding or taking away layers in the
elliptical alumina are presented simultaneously with the
results of the original configurations.

RESULTS

Heat Transfer Analysis
The one-dimensional heat transfer analysis was conducted
for the linear, elliptical alumina and elliptical nickel
configurations. The important results obtained from this
analysis are summarized in Table 3. Max AT refers to the


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010







Information Recall in Compensated Adult Dyslexics: Does

Repetition Help?


Pamela J. Carvajal, Lori J. P. Altmann, Linda J. Lombardino


University of Florida


Most research on dyslexia has studied the elementary population. However, the effects of dyslexia do not disappear with age, although
the manifestation of the core deficits in dyslexia may change over time. Underlying phonological deficits in adults with developmental
dyslexia (DD) may impair their ability to encode and recall auditory information. This study examined recall of auditory information
in compensated adults with DD when responses were written or oral. As expected, the DD group had poorer recall than control
subjects, with the difference in recall more obvious after the second recall attempt. Amount of information recall correlated with
executive function measures of processing speed rather than memory. Results from this study identify impairments in individuals with
DD that might impact classroom performance.


Introduction

Developmental dyslexia (DD) is a disorder that is
neurobiological in origin (Hudson, High, & Otaiba, 2007),
which has been defined by the World Federation of
Neurology as a disorder manifested by difficulty in
learning to read despite conventional instruction, adequate
intelligence, and sociocultural opportunity (Brosnan et al.,
2002). Badian (1984) reported that dyslexia is the most
prevalent developmental disorder, affecting around 5-10%
of the population of the Western world (as cited in Smith-
Spark & Fisk, 2007; Bronson et al., 2002). Dyslexia is
characterized by difficulties with accurate and/or fluent
word recognition and poor spelling and decoding abilities
(Lyon, Shaywitz, & Shaywitz, 2003). Research has shown
that students do not outgrow dyslexia; it is a persistent and
chronic problem (Bruck, 1992). However, the focus of
research on dyslexia has been on reading-related skills in
the elementary population, with comparatively little
research on the manifestations of dyslexia in adults (Rath
& Royner, 2002). Considering the increasing number of
students entering postsecondary institutions, more research
on the effects of dyslexia on college students is necessary
(Kirby, Silvestri, Allingham, Parrila, & La Fave, 2008).
The current study examines the performance of a group of
college students with developmental dyslexia (DD) and
their normal reading peers (NR) on a task meant to mimic
classroom experience, a story retell task. In this task,
participants heard a paragraph and had to repeat it in
writing and, after hearing it again, repeat it orally. To
foreshadow our results, the group with dyslexia
remembered less overall than the normal readers; however,
unexpectedly, those with DD did not show significantly
improved memory after hearing the passage twice, a robust
effect among normal readers. Moreover, passage recall was
predicted by executive function scores rather than working
memory scores.


One of the core deficits in dyslexia is impaired
phonological processing (Miles, Thierry, Roberts &
Schiffeldrin, 2006). This phonological deficit has
pervasive effects on many aspects of language, including
the acquisition of reading, writing, and spelling (Lyon et
al., 2003). Moreover, the phonological impairment in DD
may also be the proximal cause of deficits in working
memory in this population (de Jong, 1998). Working
memory is defined as a limited capacity system allowing
the temporary storage and manipulation of information
necessary for such complex tasks as language
comprehension, verbal learning, and reasoning (Baddeley,
2000). Baddeley describes working memory as a four-
component system, consisting of the phonological loop,
visuospatial sketchpad, episodic buffer, and central
executive. The phonological loop is a temporary storage of
auditory input, which decays over a period of a few
seconds unless retrieved by articulatory rehearsal or, in
other words, short-term verbatim memory. The
visuospatial sketchpad maintains a short-term record of
visual and spatial information. The episodic buffer is
defined as a limited-capacity temporary system, which is
capable of integrating information from different
subsystems. Finally, the central executive controls and
integrates the information and function of the other three
components. Smith-Spark and Fisk (2007) studied working
memory function in adults with dyslexia and reported
distinct deficits in the phonological, visuospatial, and
central executive domains of working memory.
Research has also suggested individuals with dyslexia
may have difficulties with executive function. Broadly
defined, executive functioning refers to a range of
cognitive abilities including initiation, planning and
prioritizing, decision making, and task switching
(Altemeier, Abbot, & Berninger, 2008; Spreen & Strauss,
1998). Importantly, other aspects of cognition, such as
processing speed, have been associated with both working


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010







CARVAJAL ET AL.


Discussion

This study demonstrated that the reported deficits in
short-term memory in adults with DD also manifest in
poorer recall of auditory discourse. Moreover, even after
hearing the passage a second time, recall of information by
the DD group was significantly impaired compared to NRs.
Consequently, our initial prediction that recall would only
be impaired in the first retelling was not supported. In fact,
recall was only significantly impaired in the individuals
with DD relative to NRs during the second recall attempt,
in which individuals with DD failed to show a significant
increase in the amount of information recalled.
Interestingly, recall scores correlated with executive
function measures targeting speed of complex processing
(i.e. Trails B and Digit Symbol Substitution). This suggests
that speed of processing limitations may interact with poor
phonological encoding in individuals with dyslexia to
impair cumulative recall of information.
Consistent with another initial prediction, participants
from both groups who had the writing task first had poorer
recall than those who did the oral retell task first. Because
both groups were affected, similarly there was no
interaction of task order with group, as had been predicted.
However, as shown in Figure 1, individuals with DD who
had the written task first recalled very little information.
Writing requires the activation and coordination of several




30


25


E 20


0 15-


S10
0
a-


linguistic skills including, but not limited to, semantics,
syntax, and writing conventions (Puranik, Lombardino &
Altmann, 2006). Consequently, it has been suggested that
the cognitive demands of writing decrease the amount of
cognitive resources available for recalling auditory
information (Piolat, Olive, & Kellogg, 2004). Also,
transcribing auditory information requires connecting the
phonological representations for words with their
corresponding orthography, a skill that is specifically
impaired in dyslexia (Lyon, Shaywitz, S., & Shaywitz B.,
2003). Therefore, the additional working memory and
executive demands inherent in writing (Piolatet al., 2005),
as well as the memory demands of the story recall task,
likely contributed to the extremely poor performance of the
DD group when written recall was the first task.
One of the most important findings in this study was
the relationship between recall and executive function
tasks, usually considered to measure speed of processing,
Trails B and Digit Symbol Substitution. Limitations in
speed of processing could certainly restrict the amount of
information an individual with DD could encode from an
auditory message. In an educational context, for example,
slowed processing speeds could lead to a processing
bottleneck, particularly in lecture classes that emphasize
the ability to quickly encode and integrate incoming
auditory information. This could lead to failure to encode
whole chunks of information. Deficits in speed of


ITask 2 (written) Task 1 (written) I Task 2 (oral)
Oral 1st Written-1st


Figure 1: Number of propositions recalled by task number in each order, by modality of recall.

University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010







Methods on Defining the Center and Spatial Analysis of the Orion
Nebula Cluster


Karl Jaehnig


University of Florida


Using observational data from the Chandra Orion Ultradeep Project (COUP), we develop and refine methods by which a center can be
defined through a robust process that removes the bias in arbitrarily choosing a center. In previous research, most massive O type star,
0 1 Ori C, has been used as the center for analyses on the Orion Nebula Cluster (ONC). The new center, which is defined from the
final method, is slightly above 0 1 Ori C, at R.A. =83.8157 and DEC=-5.37905. Using this new center, spatial analyses are developed
and applied to the ONC in order to give some method of spherocity, as current theories on nebular dynamical evolution predict that
the ONC is spherical towards the center, more so because of its relatively young age of 1Myr. Linearization was used with a divided
cluster and compared with the total distribution, and statistical tests give a measure of probability that the section belongs to the
whole. Linearization as a function and radii and angle reveal contradicting conclusions, with the center becoming more aspherical with
the radial linearization and the angular linearization revealing that the center becomes more spherical, in line with current theories.


1. Introduction


Research on the Orion Nebula Cluster (ONC) has
proven to be of exceptional value over the last couple of
years. Due to the cluster's young age of IMyr and its
nearby distance to the Earth, the ONC has served as an
efficient and indispensable source of data to augment
theories on stellar nebula evolution as well as the
dynamics of stellar nebula evolution. Until recently,
much of the research done on the ONC to determine
cluster membership has been rather limited due to a
cloud of gas and dust that does not allow optical imaging
(e.g. Hillenbrand & Hartmann 1998; Bally, O'Dell, &
McCaughrean 2000), infrared photometry (e.g.
Carpenter, Hillenbrand, & Skrutskie 2001; Lada et al.
2004), and infrared spectroscopy (Slesnick, Hillenbrand,
& Carpenter 2004) to fully penetrate and catalogue the
cluster members.
Using the Chandra X-ray observatory, the Chandra
Orion Ultradeep Project (COUP) provides the most up-
to-date catalogue of ONC cluster members, detecting a
total of 1616 X-ray sources (Feigelson et al. 2005). Of
these 1616 sources, 1315 stars have confirmed cluster
membership, leaving 285 X-ray sources, further
catalogued into 51 lightly and 234 heavily obscured
sources. The 51 lightly obscured sources are divided into
three groups: 16 likely new members, 2 appearing to be
X-rays produced at the bow shocks of Herbig-Haro
outflows and the remaining 33 possibly spurious weak
sources. The 234 heavily obscured objects have 75
COUP sources, likely being embedded cloud members
with membership for 42 confirmed and the remaining
159 sources being extragalactic (Feigelson et al. 2005).


2. Defining the Center

The majority of research and data on the analyses of
the spatial structure of stellar structures rely on a center
from which various processes can take place. Usually,
the center is defined as an object or star taken to be in
the visual origin of the cluster. For the ONC, the most
widely used origin star is 0 1 Ori C, a massive 07 type
star z45Msun. 0 1 Ori C resides in a central area known
as the Trapezium, consisting of the five most massive
stars in the ONC. The arbitrary choosing of a center


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010







Quantification of Lacune Volume in Alzheimer's Disease and
Small Vessel Vascular Dementia

Lauren P. Kelley

Understanding pathological markers seen on brain magnetic resonance imaging (MRI) may improve dementia
diagnosis and treatment approaches. This study sought to examine total brain MRI lacunes volume in
Alzheimer's disease (AD) and small vessel vascular dementia (sVD) as well as AD and sVD group differences
in lacune volume within regional white and gray matter. We hypothesized greater total lacune volume in
vascular dementia, with the greatest volume in the basal ganglia. Lacune volumes were measured on brain
MRIs diagnosed clinically with AD (n=42) or sVD (n=28). A trained rater (reliability, r = 0.93-0.98) measured
the volume of all lacunes 2mm in diameter or larger. Separate volumes were calculated for lacunes in white and
gray matter regions. Perivascular spaces were excluded. Results revealed that lacune volume did not differ
between sVD and AD (mean s.d: AD= 9.99 24.19 mm3; sVD= 9.87 13.62mm3 and sVD group (t(68) = -
0.11; p = 0.91); and in each region measured, the mean lacunes volume did not differ between sVD and AD
white matter regions (t(68) = 0.46, p = 0.65) or those found in subcortical gray matter structures (t(68) = -0.68,
p = 0.50). For all gray and white matter regions, the lacune volume was comparable and both sVD and AD
patients presented with evidence of vascular disease. Future studies should examine regional lacune volume and
cognition in these patient groups.


Introduction


Dementia is the severe impairment of intellectual
capacity and personality due to the loss of or damage to
neurons in the brain that inhibit activities of daily living
(NINDS, 2008). Dementia, although not a diagnosis, is a
descriptive term encompassing the many disorders
interfering with brain function. The risk of dementia
increases significantly with age, and "the number of people
affected by dementia is estimated to double every 20 years
to 81.1 million by 2040." (Xie, Brayne & Matthews, 2008,
p. 258) As the aging population increases, the frequency of
dementia diagnoses increases, encompassing a large
variety of syndromes. Some dementia patients demonstrate
similar clinical presentations, thus influencing the
complexity of diagnosis. Alzheimer's disease (AD) and
small vessel vascular dementia (sVD) are the two most
commonly diagnosed forms of dementia; however, the
differential diagnosis of these specific dementia syndromes
presents a challenge due to similarities in their clinical
presentations. Many researchers are currently investigating
the various influences and their relationship to the
diagnosis. In this study, we examined patients with AD and


sVD to determine whether lacunes, a sVD pathology
marker, are a possible differentiating factor between the
two dementias.
Dementia encompasses a variety of syndromes, with
AD being the most commonly diagnosed form. Many
people suffering with AD experience a slow and gradual
progression of decline, with memory difficulty as the first
noticeable symptom. This is believed to occur because the
pathological processes of AD typically begin in the medial
temporal lobes, specifically the hippocampal region, a
structure critical to memory consolidation. Damage to this
region of the brain often interferes with the connections
that influence language, particularly semantic fluency and
object naming tasks.
By performing post-mortem brain dissections on his
patients, German neurophysiologist Alois Alzheimer was
the first to identify the two defining characteristics of AD:
amyloid plaques and neurofibrillary tangles. Amyloid
plaques are an accumulation of beta-amyloid protein that
builds up between neurons and interferes with cell-to-cell
communication, eventually resulting in neuronal death
(Alzheimer's Association, 2008; Loring, 2005). As
functional communication is lost, it is thought that the
neurons become disengaged and take on a self-destructive


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 4 I Summer 2009





MEASUREMENT OF GROUNDWATER AND CONTAMINANT FLUX IN FRACTURED ROCK MEDIA WITH A PASSIVE FLUX METER


Table 4: The volume of water and alcohol solution in each vial
depending on its designated dilution. Vials included 0%, 20%,
40%, 60%, 70%, 80%, 90%, and 95% dilutions.

Vial # Water Volume (mL) Solution Volume (mL)
1 0 40
2 8 32
3 16 24
4 16 24
5 24 16
6 28 12
7 28 12
8 32 8
9 36 4
10 38 2


Table 5: Tracers and their corresponding volumetric contribution
to the pure alcohol mixture and their final concentration in the
tracer solution for the first batch experiment concerning AC Felt
1300 only.

Volumetric
Volume Concentration
Contribution to
in Tracer
Alcohol Tracer Tracer Mixture
(mL) Solution (ppm)
(mL)
2-butanol 5.0 125
1-butanol 5.0 125
3-pentanol 5.0 125
1-pentanol 8.3 200
1-hexanol 25.0 620
2,4-DMP 25.0 620
1-heptanol 33.3 830
Total 106.6 2645


Figure 5: 40mL EPA glass vials on the rotator to ensure
complete exposure of fabric to the alcohol tracers.


AC Felt was selected as the best option after analyzing
the results from this batch experiment with three fabrics,
and a batch experiment with just AC Felt 1300 ensued with
two modifications. Initial alcohol tracer concentrations
were reduced, and the felt was cut into 2cm x 6cm strips
instead of the square centimeter pieces; then two strips
were deposited into each vial. One consecutive piece of
fabric more closely mimics field conditions by reducing
layering of fabric and the length of exposed edges. Similar
to Table 3, the new tracer mixture and solution recipes are
given in Table 5. At first glance, these concentrations may
not seem significantly reduced, but it is important to note
that the first batch test was done with a total of 6cm2 of


fabric per vial while the second batch test was done with
12cm2 of fabric per vial. Save these two modifications, the
methodology for the first batch test using only AC Felt
1300 was identical to the methodology utilized during the
batch test for AC Felt 1300, Polyorgs, and FM 100.
As shown in the Results & Discussion section, the
consequential sorption isotherm curves for AC Felt 1300
followed an obvious trend for the three longest-chain
alcohols, yet the four shorter-chain tracers showed
unpredictability. In response to this dilemma, a second
batch test was conducted for AC Felt 1300 in which the
fabric strips were exposed to one solution containing 2-
butanol and 1-butanol, and different fabric strips were
exposed to a solution containing 3-pentanol and 1-
pentanol.
Two different alcohol tracer solutions were made. The
first solution consisted of 0.lmL of 2-butanol and 1-
butanol in 0.5L of water (160ppm each). The second
solution included 0.lmL of 3-pentanol and 1-pentanol in
0.5L of water (160ppm each). A set often 40mL EPA glass
vials was allocated to each solution. As shown in Figure 6,
one 2cm x 6cm strip of fabric was placed in each vial along
with increasingly diluted alcohol tracer solution. The
weight of each vial was taken before and after the addition
of fabric. Once again, the vials were rotated for 48 hours
and then allowed to settle for 24 hours. Disposable glass
pipettes were used to deliver the resulting aqueous solution
from the 40mL EPA vials to 2mL auto injection GC vials.
The 2mL samples were analyzed by the GC to determine
the equilibrium concentration of tracers in the aqueous
phase. With these data, a fourth set of sorption isotherm
curves was created.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010
5







KARLJAEHNIG


References

Bally, J., O'Dell, C. R., and McCaughrean, M. J.. "Disks,
microjets, windblown bubbles and outflows in the Orion
Nebula." The Astrophysical Journal, 2000: 2919-2959.

Carpenter,J. M. Hillenbrand, L. A., and Skrutskie, M. F..
"Near-Infrared photometric variability of stars toward the
Orion A Molecular Cloud." The Astrophysical Journal,
2001: 3160-3190.

Feigelson, E. D. et al. "Global X-Ray properties of the Orion
Nebula region." The Astrophysical Journal, 2005: 379-
389.

Hillenbrand, L. A., and Hartmann, L. W.. "A preliminary
study of the Orion Nebula Cluster structure and
dynamics." The Astrophysical Journal, 1998: 540-553.

Lada, C. J., Muench, A. A., Lada, E. A., and Alves, J. F..
"Deep 3.8 micron observations of the Trapezium Cluster."
The Astrophysical Journal, 2004: 1254-1264.

Slesnick, C. L., Hillenbrand, L. A., and Carpenter, J. M. "The
spectroscopically determined substellar mass function of
the Orion Nebula Cluster." The Astrophysical Journal,
2004: 1045-1063.



































University of Florida I Journal of Undergraduate Research | Volume 10, Issue 2 | Spring 2010






STEPHANIE ISHII


a. 2-butanol

2
18 -
1 6 ,
S14
1 2 -
S1 AC Felt 1300
I 08 1
06
0 04 *
1 02
0
0 50 100 150
Equ. Conc., mg/L


b. 1-butanol

4 ,
5 35
3 3 -
1 25 p
S15AC Felt 1300
1 5
Q 1
i 05
0 I
0 50 100 150
Equ. Conc., mg/L


c. 3-pentanol

6 -

5 p

4 *

3 AC Felt 1300


I 1

0 0
0 20 40 60 80 100 120
Equ. Conc., mg/L


d. 1-pentanol

16 |
14 -
S12 -

8 AC Felt 1300
6 ----------------
S4
! 2
6 0
0 50 100 150 200

Equ. Conc., mg/L


e. 1-hexanol

80

70
60
S50
S40 AC Felt 1300
S30'
*20
010
0
0 50 100 150 200 250 300
Equ. Conc., mg/L


f. 2,4-DMP

t80
70 -
60
5 50
40 I AC Felt 1300
S30 -
220
110
0

0 50 100 150 200 250
Equ. Conc., mg/L


g. 1-heptanol

160
140 -
, 120 -

S8*
100 o
80 ,* *AC Felt 1300
60 -
40
S20
20

0 20 40 60 80
Equ. Conc., mg/L


Figure 9: Sorption isotherm curves from the first batch
test data concerning only AC Felt 1300. Each graph
represents a different tracer, going from shortest chain
alcohol (highest aqueous solubility) to longest chain
alcohol (highest tendency to sorb). Tracers represented
by graphs a-d show more unpredictability, while tracers
represented by graphs e-g demonstrate clear trends.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010
10









-5.2



-5.3

o
-5.4
U


5.5



-C R


ONC Total Distribution







.- '', ' : ,


84.0 85.9 B5.8
R.A J2000


Figure 4: Enlarged plot of the centers
1A


8.1 835.6


calculated via method


Another iteration of the mean-based center instead
changes the center used to define the sample when the
aperture is decreased. After the first sample is calculated
using the first mean, which is the same as the first mean
center for the entire sample, the new mean is calculated
from the decreased sample of stars. Before the next
distance is defined, and the current sample is decreased
further, the new center is taken to be the mean center
calculated from the current samples size.
This replacement continues as the sample is
decreased further. The centers were then plotted to show
their relative position in the ONC as well as an enlarged
view, which displays the mean center of the decreased
sample as well as the center from which that mean center
was calculated. The movement of this mean-based center
does not show any pattern or tendency to head toward a
certain area, which may have been called the center
region of the ONC (Table 2) (Figure 4=centers/enlarged
view) (Figure 5=centers/total view).



Table 2
Method 1B Center Movement
Aperture R.A. DEC RAx DECy
Full 83.8177 -5.38684 null null
.1 83.8176 -5.38162 83.8177 -5.38684
.08 83.8177 -5.38020 83.8176 -5.38162
.06 83.8187 -5.37918 83.8177 -5.38020
.04 83.8187 -5.37915 83.8187 -5.27918
.02 83.8168 -5.37975 83.8187 -5.37915
.009 83.8163 -5.37961 83.8168 -5.27975
.007 83.8159 -5.37944 83.8163 -5.37961


S.AM/


.009


83.8'90 83-8185 83.8180 83.8175 83.81/0 83.8165 83.8160 83-8!b5
R.A J2000


Figure 5: Total ONC distribution with method 1B centers

2.2 Method 1B for Defining the Center: Spatial
Distribution
The second method used to define a center is not
vulnerable to the location of the arbitrary center usually
chosen. Instead, the method seeks to define the center as
being in the area of greatest star/area density. This
method employs a process in which a loop runs
continuously. This loop defines every star in the ONC
sample (1408 total) as the center. As each star is taken to
be the center, each sample belonging to the star that is its
center is defined as all stars that lie at or within the
radius (in decimal degrees) distance defined. Then all
neighbors within this individual sample are counted and
this is the number C for that star.
The loop continues for all stars in the entire ONC.
The max C is then taken to be the 'winner' and the
associated R.A. and DEC of the star to which this C
belongs is then marked as the center (Figure 6). Unlike
the mean-based center, all the centers defined using the
spatial density processes are real stars in the ONC. The
mean-based stars were all virtual objects that serve as
central markers but don't actually exist.
One vulnerability of using the spatial density as a
means of defining the center is that at certain apertures,
primarily at the minimum useful range or radii, two or
even three centers would be defined (Figure 7).
This complication of defining multiple centers arises
because of the smaller radii used to define C. The
number C is so small that numerous stars throughout the
ONC contain that amount of stars within its sample. To
avoid the problem of multiple centers being defined, an
acceptable value for each sample that defines C should
be 20 < C <40 stars. This also overturns the problem of
there being sufficient stars in the value of C for which
the poisson error is no longer a concern. Overall, there
are four apertures that only have 1 max C to be defined
as the center (Table 3).


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010


ONC Cente' Movement


.08

.1







Measurement of Groundwater and Contaminant Flux in Fractured

Rock Media with a Passive Flux Meter: An Evaluation of Sorptive

Materials with Alcohol Tracers


Stephanie Ishii


College of Engineering, University of Florida


Groundwater hydrologists must accurately estimate water and contaminant fluxes in aquifers in order to predict risk, regulation
compliance, and contaminant attenuation. A new direct method for the simultaneous measurement of cumulative groundwater and
contaminant flux in fractured rock aquifers through the use of a fractured rock passive flux meter (FRPFM) is under development.
This paper identifies a sorptive material and a range of resident alcohol tracers that can be used in combination as part of the FRPFM
to quantify the aforementioned fluxes. When exposed to groundwater flow, the resident alcohol tracers are eluted from the fabric at
rates relative to the magnitude of the groundwater flux. In order to quantify the groundwater flux based on the removal of tracers, the
partition coefficient for each tracer between water and the sorptive material must be known. This paper presents sorption isotherm
curves from several laboratory experiments. These curves contribute to the determination of the final partition coefficient, KD, for each
tracer when exposed to water and the selected sorptive material AC Felt 1300.


Introduction

Groundwater is withdrawn from aquifers for municipal,
agricultural, and industrial purposes. Eventually,
groundwater becomes naturally incorporated in surface
water due to discharge at locations such as springs and
seeps. Should this groundwater become contaminated, it
poses a threat to human and environmental health via direct
consumption and indirect pathl\ a s such as vapor intrusion
[1].
Because groundwater is ubiquitous, it is therefore
necessary for groundwater hydrologists to accurately
estimate water and contaminant fluxes in aquifers. Truthful
measurements of water and contaminant mass fluxes are of
great significance due to the fact that they lend themselves
to the prediction of risk, regulation compliance, and
contaminant attenuation. Despite the importance of these
measurements, accurate estimations of subsurface
contaminant mass flows are difficult. Many methodologies
represent short-term evaluations that reflect aquifer
conditions at one instant in time and not long-term trends.
These measurements do not account for variability in
concentrations and flow rates over a period of time [2].
In response to this dilemma, the passive flux meter
(PFM) was introduced. This new method is a simultaneous
direct in situ point measurement of time-averaged water
and contaminant fluxes in porous media [3]. However, the
hydrology of a porous media aquifer is extremely different
than that of a fractured rock aquifer. Hence, the latter
remains a field in which minimal research has been
published. This research contributes to the expansion of the
PFM from porous media to fractured rock aquifers.


The Passive Flux Meter
As used in porous media, the PFM is a self-contained
permeable cylinder that is inserted into a well or boring.
The meter can remain in the ground for a time period
ranging from days to months. While in the borehole, the
meter passively intercepts groundwater flow without
retaining it. As shown in Figure 1, the groundwater flow
first comes into contact with a thin, non-reactive layer of
permeable material that functions as a boundary layer.
After passing the external layer, the water is intercepted by
packed granular activated carbon. The granular activated
carbon serves two purposes: to retain various organic
contaminants from the groundwater flowing through the
meter and to release non-toxic 'resident tracers' at rates
proportional to the amount of water flowing through the
meter. The resident tracers are known amounts of various
alcohols that the granular activated carbon is pretreated
with prior to deployment. Each tracer is water soluble, but
to a different degree. The short-chain alcohols have a
stronger tendency to exist in the aqueous phase, and thus
are released first when exposed to water flow. The long-
chain alcohols are more strongly sorbed to the granular
activated carbon and require a larger amount of
groundwater flow to be released [4].
Once the period of deployment is complete, the meters
are carefully removed from the ground and the granular
activated carbon is placed in an extraction solution to
quantify the remaining amount of each tracer. Then a
secondary extraction is performed to quantify the
intercepted contaminants. Contaminant mass is used to
determine the cumulative contaminant flux during the
given time period, and the residual resident tracer mass is


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





SEASONAL DIFFERENCES IN NUTRIENT ALLOCATION OF ARCTIC TUNDRA VEGETATION


DISCUSSION
Woody species were the dominant functional group
at our field site, comprising over half of the total
aboveground community composition and over seven-
eighths of the vascular plant community. In addition,
mosses and lichens are known to have lower uptake of
nitrogen relative to vascular plants (Gordon et al., 2001;
Hyvarinen and Crittenden, 1998; Kume et al., 2008).
The belowground community at our field site is
overwhelmingly comprised of woody roots and
rhizomes. As such, the nitrogen cycling of this sort of
tundra ecosystem is dominated by the nitrogen dynamics
of the woody functional group.

Nitrogen Concentrations
As described in Chapin (1980), deciduous woody
species have higher maximum leafN concentrations than
evergreen species. This pattern was present in our own
data, as V. uliginosum had consistently higher leaf N
concentrations than either V. vitis-idaea or R.
subarcticum. Graminoids also followed this pattern,
having higher shoot N concentrations than the woody
evergreen species but lower N concentrations than the
deciduous V. uliginosum. These patterns in leaf N
concentrations are likely part of the adaptive life history
strategies of these plants, as deciduous species must
allocate high N levels to the production of a full set of
new leaves each season, while evergreen species must
only produce a partial set of new leaves and allocate a
small proportion of N to maintenance (Chapin 1980).
Evergreen leaves also tend to be better defended than
deciduous leaves, so the extra carbon inherent in
structural and some chemical defenses also lowers the
apparent N concentration in these plants (Chapin et al.,
2002). The N concentrations in stems for all three woody
species were roughly equivalent, but varied throughout
the season coupled with changes in leafN concentration.
Seasonal effects on leaf N concentrations were
strongest in graminoids and the deciduous woody plant
V. uliginosum. The seasonal trend present in the
graminoid shoots (and the concurrent decline in
belowground root and rhizome N concentration)
suggests initial allocation of N to shoots from the
beginning of the season through late June, with a
reduction of N concentration in shoots by August. The
large spring decrease in the belowground N
concentration of graminoids is consistent with previous
findings of up to a 54% decrease across the growing
season (Chapin, 1980). In V. uliginosum, the early June
leaf N concentrations were very high relative to other
species but fell drastically thereafter. This finding
suggests a high initial allocation to the production of
new leaves during leaf-out and subsequent re-allocation
of N for other purposes. This fits the deciduous life
history model well because V. uliginosum has a fleeting
investment in ephemeral foliage.


Evergreen species exhibited a different trend due to
their different life history strategy. The evergreen R.
subarcticum exhibited a modest peak in N concentration
in the middle of the growing season in order to take
advantage of peak light and temperature for
photosynthesis (Zhang et al., 1997). Stem N
concentration changes for R. subarcticum were coupled
with leaf N changes in an opposing manner, which
suggests N from stems supplied the increase in leaf N
concentrations. For V. vitis-idaea, leaf N concentrations
experienced a slight increase near the end of the growing
season. This increase was not significant, but it was
matched by a concurrent opposing change in stem N
concentrations. Such a trend toward continuing N
allocation to leaves may be attributable to the wetter-
than-average summer, as V. vitis-idaea has been found
to significantly increase leaf area and thus
photosynthetic rate relative to other species with
increased water availability (Shetsova et al., 1997). As
with R. subarcticum, changes in stem N concentration
were closely coupled with changes in leaf N
concentration, suggesting that stems were the primary
source of N supplying increased leafN concentrations.
Woody root N concentrations declined slightly over
the course of the season, likely as annual fine roots
matured and accumulated carbon. Woody rhizome N
concentrations stayed relatively constant across the
season, suggesting that N deposits to or w ithdira al1
from these storage organs were balanced or matched by
concurrent changes in carbohydrate storage.

Nitrogen Pools
For arctic vascular plant species, two strategies
dominate: evergreen and deciduous (Chapin, 1980).
Deciduous species tend to have large persistent storage
reserves, from which they produce their annual
photosynthetic growth, while evergreen species have
much smaller reserves, instead investing in the
maintenance of persistent photosynthetic material
(Chapin, 1980). In the Alaskan tundra, we see examples
of both strategies.
In our tundra site, the deciduous strategy is
employed by two phylogenetically disparate functional
groups. Members of the deciduous graminoid functional
group have a large belowground nitrogen pool, much of
which is allocated to shoots in the first half of the
growing season and then reabsorbed before shoots
senesce. The deciduous V. uliginosum is the only woody
species to have a larger N pool in stems than in leaves,
with almost three-quarters of the aboveground N pool in
stems. This is consistent with the deciduous life history
strategy, as annual leaves receive only a small proportion
of the total plant N pool. Since deciduous shrubs
typically have greater belowground biomass than
evergreens (Chapin, 1980), the majority of the rhizomal
N storage evident in the woody belowground community


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 1 I Fall 2009
5





STEPHANIE ISHII

REFERENCES

[1] Department of Health and Human Services, Agency for
Toxic Substances and Disease Registry. "Evaluation of
Environmental Contamination, Exposure Pathways, and the
Public Health Implications." Retrieved March 15, 2009,
from ATSDR Web site:


[2] Hatfield, K. "Demonstration and Validation of a Fractured
Rock Passive Flux Meter (FRPFM)." Research Proposal
prepared for the Department of Defense.

[3] Hatfield, K., Annable, M., Cho, J., Rao, P., & Klammler, H.
(2i" '-4. "A direct passive method for measuring water and
contaminant fluxes in porous media." Journal of
Contaminant Hydrology, vol. 75, pp. 155-181.

[4] Weber, W., McGinley, P., & Katz, L. (1990). "Sorption
phenomena in subsurface systems concepts, models and
effects on contaminant fate and transport." Water Resources,
vol. 25 (no. 5), pp. 499-528.

[5] Stauffer, P. (2006). "Flux flummoxed: A proposal for
consistent usage." Ground Water Technical Commentary,
vol. 44 (no. 2), pp. 125-128.

[6] U.S. Geological Survey. (2008). "Octanol-Water Partition
Coefficient (Kow)." Retrieved February 4, 2009, from USGS
Web site:


[7] Brandsgaard, J., Granada, B., Myers, A., & Van Hoosen.
"Bioremediation: Sorption Isotherm." Retrieved February 4,
2009, from D. Woodrow Wilson National Fellowship
Foundation Web site:
/isotherm.htm>

[8] Chern, J. & Wu, C.. (2001). "Desorption of dye from
activated carbon beds: effects of temperature, pH, and
alcohol." Water Research, vol. 35 (no. 17), pp. 4159-4165.





















University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010







Seasonal Differences in Nutrient Allocation of Arctic Tundra

Vegetation

Chase M. Mason, Caitlin E. Hicks Pries, and Edward A. G. Schuur University of Florida

Arctic tundra ecosystems are under increasing pressure from rising temperatures and nutrient deposition. As nutrient cycling is altered
in the face of such pressures, it is important to understand ecosystem functioning in minimally impacted tundra. This study
investigates differences in nitrogen allocation among plant functional groups and species. It also investigates the sources and
pathways of nitrogen uptake among functional groups. Distinct patterns in nitrogen allocation were observed between evergreen and
deciduous life history strategies. Deciduous species such as graminoids and Vaccinium uliginosum were found to invest heavily in
storage organs and to allocate nitrogen to foliage in a fleeting pulse. Evergreen species such as Rhododendron subarcticum and
Vaccinium vitis-idaea were found to invest a much higher amount of nitrogen in persistent leaf biomass, with a lower proportion of
nitrogen allocated to storage. Available nitrogen was found to be partitioned between functional groups by source, with graminoids
favoring ammonium and woody species favoring nitrate. The description of tundra nitrogen dynamics afforded by this study provide a
baseline for further study into the impacts of change on nutrient cycling in this threatened ecosystem.


INTRODUCTION

As arctic temperatures rise due to global climate
change, large swathes of tundra are losing one of their
defining characteristics: shallow permafrost (Billings et al.,
1982). Permafrost underlies over 24 percent
(approximately 22.8 million km2) of the land area in the
Northern Hemisphere (Armstrong et al., 2001). Tundra
ecosystems comprise roughly half this, which is nearly 8.5
percent of Earth's total land area (Shantz, 1954). With the
thawing of superficial permafrost comes a thickening of the
active layer-the depth of soil that thaws during the
growing season (Hinzman et al., 1991). This thickening of
the active layer heralds many changes, including increased
soil water capacity, bulk groundwater flow, decomposition,
and microbial nutrient cycling (Hinzman et al., 1991;
Nadelhoffer et al., 1991). These changes directly impact
plant function, including rooting depth as well as water and
nutrient availability (Hinzman et al., 1991). Along with
changes to permafrost, arctic ecosystems face threats from
atmospheric nitrogen deposition that may also affect plant
function (Jaffe and Zukowski, 1993).
Altered plant functioning has the potential to change
nutrient cycling dynamics in tundra ecosystems. To
observe shifts in nutrient cycling, one can monitor changes
in nutrient allocation. The patterns by which plants budget
nutrients to particular organs is strongly linked to life
history strategies and adaptations to the rigors of their
habitat (Chapin et al., 2002). Plants exhibit a consistent
pattern of nutrient allocation that maximizes both net
primary productivity and continued nutrient uptake
(Chapin et al., 2002). However, these patterns of allocation
between plant parts can be altered by changes in the


environment, including increased nutrient availability
(J6nsd6ttir et al., 1995). Such increases in nutrient
availability to arctic plant communities come from both
nutrient deposition and a thickening active layer (J6nsd6ttir
et al., 1995; Gordon et al., 2001; Hinzman et al., 1991).
These changes could potentially impact community
composition in a warming arctic by differentially favoring
certain species (J6nsd6ttir et al., 1995). In order to fully
understand the impacts of these changes, we need to
understand how nutrient allocation functions in tundra
environments where nutrient availability is not changing.
This study examines the seasonal differences in
nutrient allocation among plant tissues in the three
ecologically dominant functional groups of tundra plants:
mosses, graminoids, and shrubs. Specifically, we
investigate how nitrogen allocation to below- and
aboveground biomass varies throughout the growing
season. This study also addresses seasonal effects on
nutrient allocation to leaves and stems of three dominant
woody species: Rhododendron subarcticum, Vaccinium
vitis-idaea, and Vaccinium uliginosum. In addition, we
investigate 615N differences among the leaf tissue from
plant functional groups to evaluate the potential sources
and uptake pathrl a% s used to obtain nitrogen.
It is predicted that nutrient allocation will differ
throughout the growing season, as plants produce new
foliage and lengthen stems and roots. We expect the
nitrogen concentrations of ephemeral plant tissues
(deciduous leaves and graminoid shoots) to peak in the
middle of the growing season and then drop prior to
autumn abscission (Chapin, 1980). Similarly, more
nutrients are predicted to be allocated to roots as they
lengthen in order to take advantage of water and nutrients


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010
1





THERMAL PROTECTION SYSTEMS FOR FUTURE SPACE VEHICLES


Table 3


Functional Max
Variation Temperature (K) Max AT (K)
Linear 910 22
Elliptical
Alumina 890 10
Elliptical Nickel 886 3

maximum temperature difference that occurs at any time
during reentry between the top and bottom surface.
As mentioned previously, this analysis revealed that
the temperature does not vary significantly through the
thickness. Therefore, it was appropriate to assume a
uniform temperature load throughout the three-dimensional
plate at various time steps.

Thermal Stress and Strain Analysis
The thermal stresses were analyzed by looking at the
von Mises Stresses and the maximum principal strains
through the thickness at the center of each plate.

Linear Configuration. Figure 4 and Figure 5 show the
thermal stress and strain distributions through the thickness
of the linear FGM at the time of maximum stress.


0.01


0.008


0.006


0.004


0.002


Elliptical Alumina Configuration. Figure 6 and Figure 7
show the thermal stress and strain distributions through the
thickness of the elliptical alumina FGM at the time of
maximum stress. Note that the original configuration is
completely overlapped by the configuration with an extra
layer.

Elliptical Nickel Configuration. Figure 8 and Figure 9
show the thermal stress and strain distributions through the
thickness of the elliptical nickel FGM at the time of
maximum stress.

Stress and Strain Comparisons. Figure 10 is a
comparison of the original thermal stresses developed in
the three types of FGMs. Figure 11 is a comparison of the
original strains developed in the three types of FGMs,
being compared to the strains in the case where there was
only nickel or only alumina.
Figure 12 is a model of the deformation of an FGM
after the temperature loads have been applied. The various
colors represent different magnitudes of stress, where the
green represents the highest stress and the dark blue
represents the lower stress magnitudes. The various stress
magnitudes are caused by the interaction of different
material's properties. Each layer is expanding differently.


0.0 50.0 100.0 150.0 200.0 250.0 300.0
Mises Stress (MPa)

Figure 4: von Mises Stress at maximum thermal stress, linear





University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010


--





STEPHANIE ISHII


Groundwater
Flow
Direction
*-*------*
w


r L

I
Permeable i
Flux Meter
Sorbent
Boundary
sy


Figure 1: Cross-sectional illustration of a passive flux meter
(PFM) of radius r [3]

used to determine the cumulative water flux based on
predetermined sorption and desorption behavior [3].

Fractured Rock Passive Flux Meter
Although this new technology has already confirmed
its worth in porous media, the hydrology of a fractured
rock aquifer is decidedly more complex. Unlike in porous
media, the groundwater flow is highly heterogeneous [2].
These complex hydrogeologic conditions result in difficult
characterization of groundwater flow and contamination;
however, these measurements are essential to evaluating
contaminant risk, regulation compliance, and attenuation.
With some modification, the porous media PFM may
be able to be extended to fractured rock. The ability to
obtain cumulative fluxes in fractured rock aquifers under
ambient closed-hole conditions would accomplish
estimating contaminant mass discharge from source zones
with much greater ease. In turn, assessment of long-term
risk, evaluation of remedial performance, and regulatory
compliance could be done with an increased level of
accuracy and promptness. Significant cost savings can be
realized with a cumulative measurement by eliminating the
need to take numerous concentration samples over time
and recognizing when a fractured rock site poses little off-
site risk due to its own natural attenuation [2].
This paper addresses one modification to the original
PFM. In lieu of the loose granular activated carbon, an
activated carbon impregnated fabric will be used. The
fabric will be designed such that it intercepts contaminants
as groundwater flow passes through it and releases the
alcohol tracers it has been pre-saturated with at rates
proportional to groundwater flow. The purpose of this
paper is to evaluate the feasibility of various sorptive
fabrics and tracers that could be used in combination to
measure water flux at sites consisting of fractured rock


media. In order to realize this objective, a relationship
regarding sorptive capacity must be established between
the fabric and its tracers. This relationship is given by the
partition coefficient, KD. Equations describing the
correlation between the partition coefficient, residual tracer
amounts, and their corresponding groundwater flux are
given elsewhere [2], [3].

Definition of Flux
For the purposes of this paper, flux shall be defined as
the flow rate per unit area. Thus, a mass flux would have SI
units ofkg/(m2s) [5].

Materials & Methodology

The primary objective is to determine a sorptive media
that may be used in combination with a range of alcohol
tracers to indicate the magnitude and direction of
groundwater flow in a given fracture. This fabric, when
pretreated with the alcohol tracers and exposed to
groundwater flow, should gradually elute the tracers from
itself. The rate at which elution occurs for each tracer is
dependent upon the magnitude of the groundwater flow.
Once the meter is removed from the ground, a residual
tracer distribution can be generated, as shown in Figure 2.


Uniformly
Distributed
/ Tracers


Tracers have been
washed away

SZ


-------o
qTr s


Tracers Remaining


Figure 2: A cross-sectional illustration of the residual tracer
distribution on the sorptive material after being exposed to
groundwater flow qo. The cross-section is for the case of a
perpendicular intersection of borehole and fracture plane [2].

Activated Carbon Impregnated Fabrics
The first materials to be identified for this study were
an assortment of possible activated carbon impregnated
fabrics. Nine different fabrics, as shown in Figure 3, were
collected as possible sorptive materials.
The fabrics were separated into two main categories:
activated carbon (AC) felt and cloth. The fabrics char-
acterized as AC felts are thicker (thicknesses were approx-
imately 3mm) and have more structural integrity, while the
cloths are thin and very flexible. Some of the clothes (BET
1000, BET 1300, and BET 1500) were thin enough for
light to shine through. Table 1 presents the commercial
name for each fabric as well as the labels that are used to
refer to each fabric for the remainder of this paper.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





MARLANA BEHNKE


Table 1: Effective Property Formulas


Figure 1: Illustration of FGM such that white represents ceramic
and black represent metal (Aboudi, Pindera, & Arnold 2001)

This study focuses on analyzing a three-dimensional
plate that is functionally graded with respect to the
thickness. A heat flux similar to that undergone during
spacecraft reentry into Earth's atmosphere will be applied.
The plate will be functionally graded according to linear
and elliptical variations. The thermal stresses and strains
will be compared in these different types of configurations
to determine the advantages of using an FGM in a TPS. It
is expected that all of the variations being analyzed will
show that thermal stresses can be reduced and tailored with
an FGM.

METHODOLOGY

Material Selection
Aluminum oxide, or alumina, was chosen as the
ceramic because of its low conductivity and its high
strength relative to many ceramics (Materials, 2002)..
Nickel was chosen to be the metal because it is strong and
corrosive resistant. Nickel 200, which is 99.6% pure
wrought nickel, is very common in aerospace applications
(Nickel 200/201, 2009). This particular nickel alloy was
used for failure analysis.

Effective Properties of the Functionally Graded
Material
Each layer of an FGM will have a different material
composition. For example, one layer may have 100%
alumina and 0% nickel, while the layer below that may
have 90% alumina and 10% nickel. These percent
compositions are also known as volume fractions when
referring to composites. If there are two materials creating
one new material, the new material has effective material
properties that result in the combination of the material
properties of each individual material.
There are several ways to determine the effective
properties. The two most common methods are the rule of
mixtures and inverse rule of mixtures. For the analysis of


i""
I)
cLI Illr I~
ly:
L.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 | Spring 2010


Material Property Effective Property Formula
1 V1 V2
+-
Young's Modulus (E) E E E2
Coefficient of Thermal = +-
Expansion (a) _______ = F + _______

Density (p) + P-22
P1CA1V P2 Cp2cV2
Heat Capacity ( c,)

v = v 1V + v 2V
Poisson's Ratio


k=kl* 1+ 3(k2 k)
Thermal Conductivity (k) L 3(k1)(V2)+(k2 + 2 k)(V,)


the FGM in this paper, either one of these methods was
used, or an empirical formula was used for thermal
conductivity, as described below (Nemat-Alla, 2003).
Table 1 shows the formula used for each material property,
where 1 represents alumina, 2 represents nickel, and V is
the volume fraction, which has a value that can range from
Oto 1.
The effective properties were found for each layer
based on the volume fractions associated with each
function described in the following section. The FGM will
be subjected to a large range of temperatures (300K-
1000K) during reentry. Therefore, temperature dependent
properties of both alumina and nickel were used.

Generation of Functional Variations
Three different functional variations of material were
studied. Each FGM had a layer of pure ceramic on the top
surface and a pure nickel layer on the bottom surface.
The first functional grade studied was a linear variation.
This FGM was 1 cm thick. It began with pure ceramic on
the outermost layer, which would be exposed to air. Then,
with each subsequent evenly spaced layer, 10% of the
alumina was taken away, and 10% of the nickel was added.
For example, the second layer had 90% alumina and 10%
nickel. The third layer had 80% alumina and 20% nickel.
This continued to change linearly through the thickness
(making a total of 11 layers) until the bottom layer
contained 100% nickel and 0% alumina.
The next configuration studied varied elliptically as in
Equation 1, where P is the material property, z is the





MEASUREMENT OF GROUNDWATER AND CONTAMINANT FLUX IN FRACTURED ROCK MEDIA WITH A PASSIVE FLUX METER


AC FELT


CLOTH


Figure 3: Nine activated carbon impregnated fabrics chosen for
testing and separated into activated carbon (AC) felt and cloth
categories. Fabrics characterized as felts are thicker and have
more structural integrity.


Resident Alcohol Tracers
In order to choose appropriate tracers for the PFM, the
octanol-water partition coefficients and carbon chain
lengths of several alcohols were analyzed. The tendency
for a tracer to remain sorbed to a fabric increases with both
the chain length and the octanol-water partition coefficient,
Kow. The Kow value is the ratio of a chemical's
concentration in octanol and in water at equilibrium and at
a constant temperature [6]. Hence, a low Kow value denotes
a chemical's increased tendency to exist in the aqueous
phase. These values must differ for each tracer so that each
tracer has a different affinity for water and is therefore
released from the fabric at various rates. These various
rates can then be used as an indication of the magnitude of
groundwater flow passing through the fabric. For example,
a strong flux of groundwater may result in the removal of
2-butanol, 1-butanol, 3-pentanol, and 1-pentanol, while a
weak flux of groundwater may only result in the partial
removal of 2-butanol; 1-heptanol, which has the highest
sorption affinity, will exhibit the lowest rate of elution.
Table 2 displays the Kow values for the range of alcohol
tracers used as well as their molecular weight as an
indicator of chain length.


Table 1: The commercial names of the nine activated carbon
impregnated fabrics chosen for testing. The labels given for each
fabric are used throughout this paper in lieu of their commercial
name.

Fabric Type Commercial Name Label
AC Felt AmeriAsia BET AC Felt 1000
1000 felt
AC Felt AmeriAsia BET AC Felt 1300
1300 felt
AC Felt AmeriAsia BET AC Felt 1500
1500 felt
AC Felt Polyorgs Activated Polyorgs
Carbon Fabric
Cloth Calgon Carbon FM 10
Zorflex cloth
FM 10
Cloth Calgon Carbon FM 100
Zorflex cloth
FM 100
Cloth AmeriAsia MY- BET 1000
QW-011, BET
1000 cloth
Cloth AmeriAsia MY- BET 1300
QW-013, BET
1300 cloth
Cloth AmeriAsia MY- BET 1500
QW-015, BET
1500 cloth

Table 2: Alcohols used as resident tracers with their
corresponding octanol-water partition coefficients and molecular
weights. Increasing property values indicate increasing
tendencies to sorb and remain sorbed to the fabric.

Chemical CAS Log( Kow) Molecular
Name Number Weights
2-butanol 78-92-2 0.6 74.1
1-butanol 71-36-3 0.9 74.1
3-pentanol 584-02-1 1.21 88.2
1-pentanol 71-41-0 1.40 88.2
1-hexanol 111-27-3 2.03 102.2
2,4- dimethyl- 600-36-2 2.31 116.203
3-pentanol
(DMP)
1-heptanol 111-70-6 2.34-2.62 116.2


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010
3






INFORMATION RECALL


completed four tasks measuring executive function: trail-
making test B (Trails B), Digit Symbol Copying and Digit
Symbol Substitution tests, and a Stroop test. Used to
measure processing speed, attention, and sequence
maintenance (Cui et al., 2007; Spreen & Strauss, 1998),
Trails B is a timed paper and pencil task involving numeric
and alphanumeric sequencing (Cui et al., 2007). The test
consists of 25 circles with numbers (1-13) and letters (A-
L). Participants were instructed to connect the circles in
ascending order, alternating between the numbers and
letters. The task was timed until the participant connected
the last circle. Results of Trails B are used to measure
processing speed, attention, and sequence maintenance
(Cui et al., 2007; Spreen & Strauss, 1998). The Digit
Symbol Copying and Digit Symbol substitution tests are
also timed paper and pencil tasks. In the Digit Symbol
Copying test, symbols are printed in the upper half of a
box. Participants were instructed to copy the symbol in the
upper half of the box into the lower half of the box as fast
as they could and was timed until they completed all of the
boxes. The Digit Symbol Substitution test pairs numbers 1-
9 with symbols. This is followed by a grid of 100 boxes
showing the symbol in the top half. The participant must
fill in the lower portion of the box with the corresponding
number. The score is the time to complete the entire grid.
Both Digit Symbol Copying and Substitution tasks are also
measures of processing speed (Joy, Kaplan, & Fein, 2004).
The Stroop test is an executive function task measuring
inhibition (Kofman, Meiran, Greenberg, Balas, & Cohen,
2006). Its first task asks participants to name the color of
sets of XXXXs in five columns on the paper. Its second
task presents color words shown in a different color ink
(e.g., the word "blue" printed in red ink) and requires
participants to name the color in which the word is printed
rather than reading the actual word. Scoring for both
Stroop tasks is based on the number of correct responses in
45 seconds.
To measure working memory, participants also
completed a two-back test in which computer displayed
capital letters, one at a time, on the screen, and the
participant was instructed to indicate whether or not the
symbol on the screen matched the symbol that appeared
two screens back. All responses were made by clicking on
the left and right buttons on a mouse, indicating yes and no
responses, respectively. There were 100 total trials, of
which 15 were "critical" NO trials. Scores were the percent
of critical trials that were correctly detected.
The experimental task was a story retell task
administered twice in two different modalities. A narrative
story (shown in the Appendix A) was used for the story re-
tell task. Each participant was instructed to listen to the


story carefully, then to orally repeat the story back to the
examiner. The same story was then read aloud by the ex-
perimenter a second time, and the participant was instruct-
ed to reproduce the story through writing. The order of the
modality of responses, written or oral, was counterbalanced
across all subjects, and there was no time limit for either
task. The oral samples were digitally recorded and
transcribed verbatim by a trained research assistant.
Written samples were also transcribed verbatim. No
grammar or spelling corrections were made in the verbatim
transcripts. Transcripts were scored for the number of
propositions accurately recalled, with a maximum score of
30 (see Appendix B). The dependent variable was the
amount of information recalled by the subject.
Analyses examined the effect of task number (Task 1,
Task 2) and task order (written first, oral first) as well as
group.
Our analyses used a three-way, mixed model ANOVA
with Group as a between subjects variable and Task
number (Task 1, Task 2) and Modality order (Oral-1st,
Written-1st) as within subjects, repeated measures
variables. In addition, planned comparisons explicitly
compared Group differences on Task 1 and Task 2.

Results

In the three-way ANOVA, there was a main effect of
group, F(1,38)= 8.072, p < .01, 2 = .18. The DD group
overall produced fewer propositions (M = 12.62, SE =
1.10) than the NR group (M= 16.89, SE= 1.03). There was
also a main effect of task number F(1,38) = 12.402, p <
.002, n2 = .25. As expected, people remembered more
propositions the second time they were asked. The task
number by group interaction was marginally significant,
F(1, 38) = 2.743, p < .11, n2 = .25. Compared to Task 1,
individuals with DD did not show significantly improved
recall in Task 2, t(18) = 1.463, p > .15, while NRs' recall
improved significantly in Task 2, t(21) = 3.675, p < .002.
Planned comparisons showed that individuals with DD
and NRs performed similarly in oral recall, t(39) < 1, but
the group with DD tended to produce less information than
NRs when the task required writing, t(39) = 1.740, p < .10.
In addition, recall scores of the two groups did not differ in
task 1, t(39) = 0.841, p > .4; however, the NRs recalled
significantly more information in task 2, t(39) = 3.542, p <
.002.
The amount of information recalled at the first retelling
correlated with Trails B (r = -36, p < .05) and digit symbol
substitution scores (r = -.39, p < .03). The number of
propositions recalled in the second retelling correlated with
Trails B scores (r = -.36,p < .04).


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010







VOLUMETRIC QUANTIFICATION OF LACUNES IN AD AND SVD


H, Edt T,, Wm*, alty ft*, T,,, H,
L 11IT I I J A 1 -4 1> 14110-41 P*
2.9T MRC20405 A Nk H
Ex: 1
tl_ mprage_ra
S. 3/8
Im 871160
Ax 129.4,"COI) Acq TrT
256 x 144
Mag: 5.6x


R




ET 1
TR: 2500.0
T E: 4.4
1.0thki-1,0sp
VV:263 L 119 P D'


Figure 3: The image demonstrates the on-screen ruler across the
diameter of the lacune.

matter; the periventricular region was comprised of the
area V2 cm around the lateral ventricles; and deep was
between the infracortical and periventricular regions. The
subcortical gray matter structures that were assessed were
the caudate, thalamus, and basal ganglia. Each of the
lacunes was recorded in a spreadsheet according to the
region they were located as well as the left or right
orientation of the brain.


Results

Intraclass correlation coefficients revealed high intra-
rater and inter-rater reliability for the visual rating scale (r
=0.98 and r = 0.93, respectively).

University of Florida I Journal of Undergraduate


Aim 1: A t-test was conducted comparing AD and sVD
on lacune volume. No statistical difference was found
between total lacune volume in AD (M = 9.99, SD = 24.19;
see Table 2) and sVD group (M = 9.87, SD = 13.62; t(68)
= -0.11; p = 0.91; see Figure 4). A power analysis was
performed to determine if the sample size was indicative of
the non-significant findings. These analyses revealed that
at least 840,128 subjects would be needed for the minimal
effect size (d = 0.1176) to reach statistical significance.
Aim 2: Individual t-tests were performed looking at
between group differences in lacunes by region and found
no significance (see Tables 3 and 4). Since the current
sample size was insufficient for analyzing the seven
regions of interest individually, we combined lacunes that
were found in subcortical white matter (e.g.,
periventricular, deep, infracortical, and internal capsule) to
compare to those found in subcortical gray matter
structures (e.g., caudate, thalamus, and basal ganglia).
Independent t-tests revealed no significant differences
between patients with AD and sVD lacunes in white matter
regions (t(68) = 0.46, p = 0.65) or those found in
subcortical gray matter structures (t(68) = -0.68, p= 0.50).
The power analysis for Aim 2 revealed lacunes in the white
matter (d = 0.1176) would require 2, 272 subjects and
lacunes in the gray matter (d = 0.1655) would require 1,150
before an effect of this magnitude would reach statistical
significance.


Figure 4: The relationship between total lacune volumes in AD
and sVD with the standard deviation.

Table 2: Mean and Standard Deviation of Total Lacunar
Volume (mm3)
Group Mean SD
Alzheimer's disease (n=42) 9.99 + 24.19
Small vessel vascular disease (n=28) 9.87 13.62


Research I Volume 10, Issue 4 I Summer 2010





PUJA PATEL


frequencies to those of the mimicked versions in each
environment. A difference in frequency of the mimicked
and actual cardinal song would tell us that the cardinal
increased the pitch of its songs in urban areas. On the other
hand, cardinals may not increase their pitch, but rather the
urban mockingbirds increase the pitch of the mimicked
version.
We can also investigate how important a
mockingbird's ability to adjust his song to improve signal
transmission is for mating. For example, males in louder
territories that cannot adjust their song frequency may have
a harder time attracting and keeping their females and
retaining their territory. We can band all males and females
at each study site and follow them from year to year to
correlate their noise environment and song adjustment with
rates of mate and territory fidelity.


Gill, F. B. 2007. Ornithology, 3rd Edition. W.H. Freeman and Company, New
York, New York.

Marzluff, J.M., R. Bowman, and R. Donnelly. 2001. Avian ecology and
conservation in an urbanizing world. Kluwer Academic Publishers, Boston.

Slabbekoom, H. and M. Peet. 2003. Birds sing at a higher pitch in urban noise.
Nature 424: 267-268.

Slabbekoom, H. and T.B. Smith. 2002. Habitat-dependent song divergence in the
Little Greenbul: an analysis of environmental selection pressures on acoustic
signals. Evolution 56: 1849-1858.
Warren, P.S, M. Katti, M. Ermann, and A. Brazel. 2006. Urban bioacoustics: it's
not just noise. Animal Behavior 71: 491-502.
Wiley, R.H. 1991. Associations of song properties with habitats for territorial
oscine birds of eastern North America. American Naturalist 138: 973-993.
Wood, W.E. and S.M. Yezerinac. 2006. Song Sparrow (Melospzza melodia) song
varies with urban noise. Auk 123: 650-659.


Conclusions
Since urbanization has caused an increase in ambient
noise and birds continue to rely on vocal signaling as their
primary method of communication, it is important to assess
how song characteristics are affected by noise. Now that
we have established that mockingbirds sing at a higher
minimum frequency in urban areas, we can further tease
apart the reasons for this song adjustment. Mockingbirds
mimic avian songs and non-avian sounds found in their
environment and build a diverse song repertoire. This is
interesting because we can use their diverse repertoire to
analyze their song composition: which species they mimic,
how those species' songs are similar or different, and how
mimicking those species or background noise affects the
transmission of a mockingbird's song in its environment.
We can also begin to assess consequences of this song
adjustment on mate attraction and mate and territory
retention to gain a more complete understanding of how
urban noise affects the fitness of songbirds.

ACKNOWLEDGMENTS

University Scholars Program contributed financial
assistance for the research equipment. I thank Christine
Stracey, Jill Jankowski, and Dr. Scott Robinson for
mentoring and assisting me with this research. I thank
Aaron Spalding for constructing part of the apparatus used
for making the recordings.

REFERENCES

Derrickson, K.C. and R. Breitwisch. 1992. Northern Mockingbird (Mzmnus
polyglottos). In The Birds of North America, No. 7. A. Poole, P. Stettenheim and
F. Gill (Eds). The Academy of Natural Sciences, Philadelphia, PA; and the
American Orithologists' Union, Washington, D.C.
Fuller, R.A., P.H. Warren, and K.J. Gaston. 2007. Daytime noise predicts
nocturnal singing in urban robins. Biology Letters 3: 368-370.

University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010







MARLANA BEHNKE


-Elliptical Alumina


1-


0.8
0.8 -6- -


0.6


0.4



0.2


0


-Elliptical Nickel


Linear Point of Failure, < 1


0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
Factor of Safety


Figure 13: Factor of safety through the thickness of the FGM for the three FGM types


CONCLUSIONS

Summary of Heat Transfer
The heat transfer analysis revealed that the temperature
through the thickness of the FGM was fairly uniform at all
times during reentry. The maximum temperature difference
in any of the FGMs at any given time was 22 K. This slight
difference is not expected to significantly affect the results
of the thermal stress analysis that followed.
It is also important to note that the given FGM is not
suitable for providing added insulative properties. Heat
travels through the thickness very quickly. The thermal
conductivity of both materials is relatively high, and the
FGM is also very thin.

Summary of Thermal Stress and Strain
The thermal stress analysis showed that the elliptical
alumina configuration had the largest peak thermal stress
of all of the FGMs, but the elliptical nickel had relatively
high peak stresses as well. The linear configuration had the
lowest magnitudes of thermal stress overall. The stresses in
the linear configuration were highest when a large volume
fraction of nickel was present.


The strain results revealed that elliptical alumina had
the largest peak strain but the lowest strain overall. The
elliptical nickel had the lowest peak strain but the largest
strain overall. The linear configuration fell between the two
other designs. To evaluate the significance of these results,
the failure analysis must be examined more closely.

Summary of Failure
After completing the failure analysis, it was found that
all three of the FGM configurations failed during
maximum stress situations. Failure of elliptical alumina
occurred at the bottom 10% of the FGM where the volume
fraction of nickel is .5. Failure of elliptical alumina occurs
at the bottom 15% of the FGM where the volume fraction
of nickel is .15. The linear configuration failed at both the
top and bottom 10% of the material where the volume
fraction of nickel is .1 and .9, respectively.
In order to decrease the stress magnitudes, an extra
layer was added where there was a stress concentration.
This had little to no impact on the magnitudes of the stress,
as shown in Figures 6 and 8.
Although adding a layer had a very slight impact,
removing layers where the FGM failed did result in an


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





Do MOCKINGBIRDS CHANGE THEIR SONG TO COMPENSATE FOR URBAN NOISE?


Non-urban


Urban


Habitat


Figure 2: Minimum frequencies of mockingbird songs in urban versus
non-urban areas (with standard error bars).


20 30 40 50 60
Low Frequency Ambient Power (dB)
Figure 3: Relationship between the minimum frequency of mockingbird
songs and the average power of low-frequency ambient noise.

DISCUSSION

The results of our experiment support our hypotheses
that mockingbirds adjust their song according to the
ambient noise in their habitat. Mockingbirds in urban areas
sing at a higher minimum frequency than those in non-
urban areas. This shift in frequency prevents their songs
from being masked by the low-frequency urban noise,
thereby improving the transmission of their signal. Thus,
even with the loud noises characteristic of an urban
environment, mockingbirds are able to adjust their song to
more effectively communicate with each other.
Mockingbirds are highly territorial and typically pair
monogamously; therefore, the ability to alter their song
should help them in territory defense, mate attraction, and
mate retention (Derrickson and Breitwisch 1992).


Mockingbirds' ability to compensate for increased urban
noise may be a factor that allows them to successfully
inhabit urban areas.
Since mockingbirds mimic other birds, the fact that
they sing at a higher minimum frequency in urban areas
may be explained three ways. First, the bird species found
in urban areas differ substantially from those species found
in non-urban environments (Marzluff et al. 2001). It is
possible that the species in urban areas on average
naturally sing at higher frequencies than the species found
in non-urban areas. Thus, the suite of songs urban
mockingbirds are exposed to are of a higher frequency.
Second, mockingbirds may simply be choosing to mimic
higher frequency noises, including songs, from their
environment because those are the sounds they can best
hear over the urban ambient noise. Finally, because
mockingbirds mimic other birds in their environment, the
shift in frequency of mockingbird songs may reflect similar
responses in other urban birds, as these species may also be
responding to the urban noise.

Future Directions
To obtain more accurate results of the differences in
minimum frequency of urban and non-urban mockingbirds,
we should average the minimum frequencies of each
phrase within a recording rather than using the lowest note
throughout the entire recording to dictate the minimum
frequency at which the bird sings. In this case, a phrase
would be a group of repeated syllables (Gill 2007); finding
the minimum of each phrase would provide a more
accurate value for the minimum frequency at which the
bird predominately sings.
Since we now know that mockingbirds adjust their
song according to their habitat, we can explore how they
mimic avian songs. We can compare the species of birds in
each habitat that the mockingbird could mimic. To
determine if the songs differ because the species
compositions differ, we can list the species that make up
urban and non-urban bird communities. We can calculate
the minimum frequency at which each species naturally
sings and determine the average across species in urban
areas and compare that to the average across species in
non-urban areas. Alternatively, if mockingbird songs differ
because they are preferentially mimicking high frequency
songs, we can analyze the mockingbird's song recording to
figure out which species it actually mimics. We can then
compare the frequency of mimicked versus non-mimicked
songs in each habitat.
Finally, we can determine if mockingbirds mimic
songs of other birds verbatim or if they alter the frequency
of the mimicked version. For example, mockingbirds
frequently mimic the song of the Northern Cardinal in both
urban and non-urban habitats. We could record cardinal
songs in each environment and compare their average


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010


I- Fit EI 95% Colidaice LimtsI


00
0



0
O


0 o





THERMAL PROTECTION SYSTEMS FOR FUTURE SPACE VEHICLES


-Elliptical Alumina
-100% Nickel


1

0.8

0.6


0.4 -

0.2 -

0
0.006


-Elliptical Nickel
100% Alumina


0.008 0.010 0.012
Strain


Figure 11: Strain comparison for three FGMs and case of no FGM


Figure 12: Model of FGM deformation after temperature change

Failure Analysis
Knowing the yield strengths of the two materials that
compose the FGM, the effective yield strength can be
estimated to determine if and when failure occurs in the
FGM. A common failure criterion used for FGMs is von
Mises failure (Lee, Kim, Ahn, DeJonghe, & Thomas,
2007).The effective yield strength was calculated with the
rule of mixtures. The yield strength of aluminum oxide is
approximately 300 MPa and the yield strength of nickel is
approximately 200 MPa. One purpose of adding nickel is
to increase the strength of the material. While the yield
strength of nickel is shown to be lower than that of
alumina, it is important to note that the strength found


experimentally for alumina is in ideal cases; it will
typically not be as strong. Also, once it cracks, damage will
occur very quickly in the alumina.
Figure 13 is a graph of the factor of safety through the
thickness for each of the three types of FGMs. The straight
line that occurs on the factor of safety of 1 represents the
point at which failure will occur. Any factor of safety less
than 1 also indicated failure. Note that the graph's x-axis
was adjusted to show a maximum factor of safety of 10.
There were sections of the FGM that had factors of safety
higher than this, but these points are not close to failure,
and thus they are not focused on.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010


*Linear





PUJA PATEL


and Breitwisch 1992). Thus, mockingbirds represent a
unique opportunity to examine the effects of urban noise
on song properties, song composition, and even the song
patterns of other birds.

Hypotheses
Given previous studies (Slabbekoom and Peet 2003;
Fuller et al. 2007), we hypothesized that mockingbirds
adjust their song frequencies based on the background
noise in their environment to improve song transmission.
Since urban areas typically have more low frequency
ambient noise (Warren et al. 2006) than non-urban areas,
we hypothesized that mockingbirds in urban areas sing at a
higher minimum frequency than those in non-urban areas.

METHODS

Song Recordings
We looked for male mockingbirds in areas within and
around Gainesville, FL between April and July 2008. Our
study sites included two pastures (University of Florida
Beef Research Unit and Boston Farm Santa Fe River
Ranch Beef Unit), two parking lots (Oaks Mall and Butler
Plaza), three residential areas (Capri, Duck Pond, and
Gateway at Gainesville Apartments), and one biological
preserve (Ordway-Swisher Biological Station). We located
singing males and recorded each mockingbird's song for
15 minutes, obtaining a total of 22 mockingbird song
recordings. If the bird stopped singing part way through,
we returned to it at a later time to get a total 15-minute
recording. In order to compare the mockingbird's song to
the noise in the environment, we also recorded the ambient
noise in each mockingbird's environment for five minutes
directly following the song recording.
We recorded mockingbird songs and ambient noise
using a Fostex FR-2LE 2-Channel Compact Flash Field
Recorder and a ME62 Omni-Directional Condenser
Microphone attached to a plastic Telinga parabolic dish.
We detached the parabolic dish when recording the
ambient noise. The volume input level for ambient
recordings was standardized. For the song recordings, we
did not standardize the input volume or the distance to the
bird; therefore, we cannot compare the amplitude
(loudness) of the songs.

Song Processing and Analyses
We used the program Raven Pro v1.4 to display
spectrograms of all recordings on the computer. We
listened to each song recording and studied the respective
spectrogram to select parts of each song recording in which
only the targeted mockingbird was singing. We also
avoided parts of the song that were polluted with other
background noises, such as cows, buses, cars, and
mechanical noises.


For each song recording, we found the frequency at
which the lowest note was sung within the selections
previously made for that file. In cases where there were
multiple parts of recordings (multiple files adding up to 15
minutes of song), we took the average of all of the file
minimums for each bird. We then compared the average
minimum frequencies of urban mockingbirds to those of
non-urban mockingbirds using a t-test. All analyses were
performed in SAS version 9.2.
Because we were particularly interested in the low-
frequency ambient noise, we limited our analysis of
ambient noise to the lower range of mockingbird songs. As
an upper limit to our low frequency range, we used the
highest minimum frequency value (1.662 kHz) from all
songs. We then selected the noise in each five-minute
ambient recording from 0 to 1.662 kHz as our measure of
low-frequency ambient noise. We used Raven Pro to
calculate the average power of that selection. Power is a
measure of the loudness of the background noise in
decibels (dB). We compared the average power of low-
frequency ambient noise in urban areas to that in non-urban
areas. We also did a linear regression of minimum
frequency of all recorded males versus the average power
(loudness) of their respective ambient recording.

RESULTS

Urban environments have significantly louder low-
frequency noise than do non-urban environments (t19 -
4.75, p = 0.0001; Fig.l). Mockingbirds in urban areas sing
at a significantly higher minimum frequency than those in
non-urban areas (t19 = -3.75, p = 0.002; Fig. 2). Song
differs not only in urban versus non-urban environments,
but also as low frequency ambient noise (between 0 and
1.662 kHz) changes. As the background noise gets louder,
the birds sing at a higher frequency (F1,19 = 15.31, p
0.0009, r2 = 0.45; Fig. 3).


60
9 50
-a
S40
S30 -
20 -
20
I-J

S10
0


I


Non-urban


Urban


I Habitat

Figure 1: Average power of low-frequency ambient noise in urban
versus non-urban areas (with standard error bars).


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010







CARVAJAL ET AL.


Brosnan, M., Demetre, J., Hamill, S., Robson, K., Shepherd,
H., & Cody, G. (2002). Executive functioning
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Kirby, J., Silvestri, R., Allingham, B., Parrila, R., & La Fave,
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500270913

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doi: 10.1080/03075070600572173


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 | Spring 2010





FAE NAGEON DE LESTANG


are approximately two generations of N. femorata per year
(Baranowski & Slater, 1986). Females spend the majority
of their time feeding on cactus fruits, and males establish
and defend territories on the cactus fruit against other
males. Males have enlarged femurs complete with spurs
and use their large hind legs in combat, kicking other
males, or even gripping and squeezing the opposing male's
abdomen with their femurs during conflict. Prior to mating,
males typically touch females with their antennae and
proceed to mount them. Whether or not mating occurs from
this point is largely under female control.
Opuntia fruits are a favorite food of many animals,
such as deer, rodents, gophers, and rabbits, and are
removed quickly from cactus patches (Hellgren, 1994; CW
Miller, unpublished data). Also, because most Opuntia
species produce fruit only once per year, some generations
of N. femorata develop without Opuntia fruit. N. femorata
juveniles do not have wings until they reach adulthood, and
thus are largely immobile, leaving many juveniles without
access to Opuntia fruit for large parts or all of their
development. Previous work examining effects of food
treatment on N. femorata as of the first instar found that
95% of nymphs reared with fruit and cactus cladodes had
reached adulthood at 10 weeks of development, while only
7% of nymphs raised without cactus fruit reached
adulthood (Nageon de Lestang & Miller, 2009).
To mimic two different natural environments N.
femorata experience during maturation, we raised two
groups ofN. femorata from the fifth instar to adulthood on
either Opuntia humifusa cladodes and fruit or 0. humifusa
cladodes only. We hypothesized that males raised on a diet
of 0. humifusa cladodes and fruit would be more
competitively successful, be larger in size and weight, and
have faster development (Nageon de Lestang & Miller,
2009; CW Miller, unpublished data). We recorded weights
and development timing of N femorata from the fifth
instar to adulthood. After males were sexually mature, we
randomly paired them by treatment and allowed them to
compete for access to a female. Morphology and body size
were recorded for all competitions in which a male mated
with the female.

METHODS

We collected over 40 adult N femorata adults and
ample 0. humifusa cactus pads and fruits over the span of a
40-hectare area to ensure genetic diversity of the lab
population at Ordway-Swisher Biological Station,
University of Florida (820W, 29041'N) in September, 2008.
Males and females were paired, placed into separate
containers with cactus and fruits, and allowed to mate.
Each day we checked containers for egg clutches. Clutches
were placed into discrete containers where groups of
nymphs hatched and developed with ample cactus and


cactus fruit available. All insects were raised in a
greenhouse with natural lighting supplemented with
artificial lighting for a 13-hour photoperiod and a
temperature range of 21 to 380 C. All containers included
both 0. humifusa cladodes and fruits, planted in a mixture
of potting soil and topsoil. Within 24 hours of reaching the
fifth instar, we weighed each nymph within 0.001 g and
randomly transferred each juvenile to a plastic container
with a treatment of 0. humifusa with or without cactus
fruit. Fifth instars were checked daily until reaching
adulthood and were then weighed for the second time as
new adults within 24 hours. A small subset was weighed
after 72 hours. The weights and weight gain of these
individuals did not differ significantly from those weighed
after 24 hours; thus, they were included in all analyses.
From these 296 new adults, we randomly selected 58
sexually mature male N femorata for competitions. When
these 58 males were from two- to five-week-old adults, we
randomly paired and placed them into an arena. We
allowed males 24 hours to acclimate to the arena and
establish dominancy roles before any observations were
taken. None of the males used in the experiment had been
exposed to females since their fifth instar. Arenas consisted
of a plastic deli container (11.5 cm top diameter, 9.0 cm
bottom diameter, 14.0 cm height) holding one potted O.
humifusa cladode with a fruit positioned on top of the
cladode. We first marked each male's pronotum with a
paint pen for individual identification and then transferred
the males to the arenas. Markings were made with Zebra
All-Purpose Markers (Neon Orange), Elmer's Opaque
Paint Markers (Lime Green), or Sharpie Permanent Marker
(Metallic).
After 24 hours, we placed a three- to five-week-old
adult virgin female N femorata into each arena. The
greenhouse temperature was approximately 29 C during
behavioral trials. We allowed insects fifteen minutes to
adjust to the new circumstances before beginning
observations. We recorded observations for intervals of one
minute every 11 minutes, for a total of ten time intervals
(110 minutes total). Both the location of the males and
their behaviors were recorded out of the 29 total
competitions run. Descriptions of each behavior recorded
are listed in Table 1.
We measured males from containers where mating
occurred (n=8). These live insects (n=16) were measured
within 0.01mm with Mitutoyo digital calipers. Based on
behavioral interactions among insects in this species and
related species (Miller, 2007), we considered male hind
legs to be weapons. Hind femur width was determined by
taking the mean of the measurements of both hind legs at
the third distal spine. This measurement includes both the
width of the femur itself and the length of the spine. We
used the widest part of the male femur as the measurement
point, which contacts the abdomens of rival males during


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





FAE NAGEON DE LESTANG


Effects of natural dietary differences on
competitive and mating behaviors
We observed matings in eight of the 29 containers, and
males reared with cactus fruits were significantly more
likely to mate (Table 2). In fact, not a single male reared
without cactus fruits mated during the observation window
(Figure 2). Surprisingly, no males attempted to mount a
mating pair in any of the trials, and only three males out of
all 29 trials attacked the other male during observation.
During our observation period, males reared with
cactus fruits were not more likely to be sighted on cactus
fruits than males raised on just cactus cladodes; nor were
they more likely to attack other males. However, the males
reared with cactus fruits had a greater activity level. They
were more often observed to be walking and were more
likely to approach females. Regardless, the probability of
males contacting and mounting females did not differ
across the treatments.

Effects of natural dietary differences on body size
and weapon size
In contests in which a male mated with the female,
males that completed development with cactus fruits
available were larger than males deprived of cactus fruits
in both pronotum width (body size; F1,13 = 141.02, P <
0.001) and mean hind femur width (weapon size; F1,13 =
200.49, P < 0.001, Figure 3). The slopes of the scaling
relationships between hind femur width and pronotum
width were not significantly different according to
experimental treatment (F1,11 = 0.98, P > 0.50). Therefore,
we proceeded to look for effects of the environmental
treatment on scaling intercept. We found a significant
effect of treatment on the scaling intercept between body
size and weapon size (Fl,12 = 7.96, P =0.015, Figure 3).
Males reared with cactus fruits during the final stage of
development had wider hind femurs for a given body size.





Table 2: Results of GLIMMIX models for competitive and courting
behaviors. Mating behavior was analyzed with a paired t-test.

Behavior d.f For t***
insect on fruit 1,28 <0.001
attacking male 1, 28 1.23
walking 1, 28 6.38**
approaching female 1, 28 4.94*
contacting female 1,28 0.1
mounting female 1, 28 0.22
mating 1, 28 2.05**
*P < 0.05, **P <0.02


Fruit


Without fruit


Environmental treatment
Figure 2: Males reared with fruit for the final stage of development
(grey bar) had a greater probability of mating during our observation
period than males reared without fruit.


1.5
E 1.4
1.3
1.2
S1.1
1.0

C 0.8
0.7


0.0






-r<
0


i 0



o800

2.8 3.0 3.2
P


3.4 3.6 3.8 4.0
ronotum width (mm)


4.2 4.4 4.6


Figure 3: Males achieving matings during our observation period
(closed circles) were larger and had a greater scaling intercept between
pronotum width (body size) and hind femur width (weapon size) than
males that did not achieve matings (open circles). All males that
achieved matings had been reared with cactus fruits for the final stages
of development. Cactus illustrations feature cladodes with and without
cactus fruits. Illustrations by David Tuss.

DISCUSSION

Weight and development
Males raised with fruit gained considerably more
weight over the fifth instar than males in the no-fruit
treatment (Figure 1). Juvenile males sorted into the fruit
treatment weighed more than males in the no-fruit
treatment initially, even though insects were randomly
selected for treatment. While this weight difference is
unusual and unexpected, treatment had such a profound


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





SEASONAL DIFFERENCES IN NUTRIENT ALLOCATION OF ARCTIC TUNDRA VEGETATION


REFERENCES

Armstrong RL, Brodzik MJ, Dyurgerov M, Maslanik JA,
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,.1 ,. i,, State of the Cryosphere: Response of the
Cryosphere to global warming. Glaciological Data:
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Billings WD, Luken JO, Mortenesen DA, Peterson KM. Arctic
tundra: a source or sink for atmospheric carbon dioxide
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Eckstein RL, Karlsson PS, Weih M. The ;.. ,i .. _, ,, of
resorption of leafresources for shoot growth in evergreen
and deciduous woody plants from a subarctic
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Nadelhoffer KJ, Giblin AE, Shaver GR, Laundre JA. Effects of
temperature and substrate quality on element
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253.

Shantz HL. The place ofgrasslands in the Earth's cover.
Ecology. 1954; 35:143-145.

Shetsova A, Haukioja E, Ojala A. Growth response of
subarctic dwarfshrubs, Empetrum nigrum and Vaccinium
vitis-idaea, to manipulated environmental conditions and
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Zhang T, Osterkamp TE, Stamnes K. Effects of climate on the
active layer and permafrost on the north slope ofAlaska,
U.S.A. Permafrost and Periglacial Processes. 1997; 8:45-
67.


Chapin FS, III. Nutrient allocation and responses to
defoliation in tundra plants. Arctic and Alpine Research.
1980; 12:553-563.

Chapin FS, III, Matson PA, Mooney HA. Principles of
Terrestrial Ecosystem Ecology. Springer-Verlag; 2002.

Gordon C, Wynn JM, Woodin SJ. Impacts of increased
nitrogen supply on high Arctic heath: the importance of
bryophytes and phosphorus availability. New Phytologist.
2001; 149:461-471.

Hinzman LD, Kane DL, Gieck RE, Everett KR. Hydrologic
and thermal properties of the active layer in the Alaskan
Arctic. Cold Regions Science and Technology. 1991;
19:95.

Hyvarinen M, Crittenden P. Relationships between
atmospheric nitrogen inputs and the vertical nitrogen and
phosphorus concentration gradients in the lichen
Cladonia portentosa. New Phytologist. 1998; 140:519-
530.

Jaffe DA, Zukowski MD. Nitrate deposition to the Alaskan
snowpack. Atmospheric Environment. 1993; 27A:2935-
2941.

J6nsd6ttir IS, Callaghan TV, Lee JA. Fate of added nitrogen
in a moss-sedge Arctic community and effects of
increased nitrogen deposition. The Science of the Total
Environment. 1995; 160:677-685.

Kume A, Bekku YS, Hanba YT, Nakano T, Kanda H.
,. -. .,. concentration within %S,, i O,'-,i oppositifolia in
different successional stages on a glacier foreland in the
high Arctic. Polar Science. 2008; 2:143-147.

Miller AE, Bowman WD. Variation in nitrogen-15 natural
abundance and nitrogen uptake traits among co-
occurring alpine species: do species partition by nitrogen
form? Oecologia. 2002; 130:609-616.



University of Florida I Journal of Undergraduate Research I Volume 10, Issue 1 I Fall 2009
7





KEITH KNAUER


C. Metal-Semiconductor-Metal Photodetectors
In this work, the SWNT film-Ge junction is studied
by the fabrication and electrical characterization of metal-
semiconductor-metal (MSM) photodetectors with SWNT
film electrodes on Ge substrates. Photodetector research
has broad implications due to the widespread use of
photodetectors in modem technologies such as high-
speed optical communication systems. An MSM
photodetector converts optical energy into an electrical
current and consists of two back-to-back Schottky
contacts on a semiconductor substrate. Illustrated in Fig.
3, MSM devices possess two metal contacts with
interdigitated finger electrodes. By applying a negative
bias to one contact and a positive bias to the other, a
depletion region and electric field are established. When
photons are incident on the semiconductor, electron-hole
pairs are generated and the electric field sweeps the
carriers out of the depletion region, giving rise to the
photocurrent. Increasing the bias can increase the speed
and collection efficiency of the device, but it can also
sharply increase thermionic emission and tunneling at the
Schottky contacts collectively referred to as the dark
current. In order to minimize power dissipation and
maximize sensitivity, the dark current must be minimized.
MSM photodetectors can be monolithically fabricated for
use in optoelectronic applications and have many
advantages over other types of photodetectors, including
low cost, simplicity of operation, and ease of fabrication
[12], [13]. A major limitation of MSM photodetectors is
their low responsivity due to light being reflected from
the surfaces of their metal electrodes, as depicted in Fig.
4 [13]. This motivates the use of transparent conductive
SWNT film as the electrode material to provide more
active area to incident light.
In this paper, MSM photodetectors with SWNT
film electrodes on Ge substrates are fabricated and
electrically characterized. A comparison of the dark
current of the SWNT film devices and metal control
samples is conducted, revealing that the use of SWNT
film electrodes reduces the dark current significantly.
Lastly, the dependence of the dark current on device
geometry is studied by varying device active area, finger
width, and finger spacing. These experimental results
give insight into the electrical properties of the SWNT
film-Ge interface while also demonstrating the use of
SWNT film as a transparent and conductive material for
electronic applications.

II. EXPERIMENTAL PROCEDURE

A multilayered mask and a Karl Suss MA-6 contact
mask aligner were used to photolithographically pattern
and fabricate the MSM devices. The process steps are
shown in Fig. 5. Following surface cleansing with
solvents, a 100 nm thick isolation layer of SiO2 was
deposited by plasma-enhanced chemical vapor deposition
(PECVD) in an STS 310PC PECVD. Active areas of


light ,


==


Fig. 3. MSM photodetector consisting of two contacts with
interdigitated finger electrodes. Light incident on the
semiconductor surface causes a photocurrent to flow between
the biased contacts. Adapted from [13].


I Incident


Reflected








Fig. 4. Incident light upon metal electrodes is reflected, leading
to decreased responsivity. Transparent conductive SWNT film
electrodes may allow some of this reflected light to be
transmitted to the substrate and contribute to the photocurrent
[13].


SiO2.


SWNT film
\


Ti/Au \


Fig. 5 [(a)-(d)] Fabrication steps used for MSM photodetectors
with SWNT film electrodes as seen through the cross section of
a single finger electrode. (a) Ge substrate prepared by cleaning
with solvents. (b) Isolation Si02 layer deposited by PECVD.
(c) Active area windows wet etched to surface. (d) SWNT film
prepared by vacuum filtration deposited across substrate. (e)
Interdigitated fingers etched in SWNT film by 02 plasma
etching. (f) Ti/Au contacts deposited by e-beam evaporation
with subsequent lift-off.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





CHASE MASON


in the seasonally thickening active layer (Chapin, 1980;
Hinzman et al., 1991). For winter-persistent stems and
rhizomes, the opposite is expected, as nutrient reserves are
shunted into new ephemeral growth during the growing
season and reabsorbed before autumn (Chapin, 1980).
Rhizomes are expected to experience increased nutrient
content at the end of the growing season, when other plant
parts are undergoing senescence and winter is approaching.
This study should help shed light on the dynamics of
nutrient cycling in pristine tundra ecosystems.

METHODS

Sampling
We collected samples for this study on June 4, June 26,
and August 9, 2008 from tundra near Eight-Mile Lake,
Healy, Alaska. Three 0.25 m2 plots were randomly
sampled at each time point from tundra sites with minimal
permafrost thaw. We harvested all above- and
belowground biomass within plots, including stems, leaves,
rhizomes, and all roots >1 mm. Belowground biomass was
harvested to the depth of soil thaw. After collection, we
dried biomass for three days at 60 OC. We then divided
aboveground plant biomass by functional group into
mosses, graminoids, and non-graminoid vascular plants.
Three ubiquitous plants were further identified and
separated to species level: Vaccinium uliginosum,
Vaccinium vitis-idaea, and Rhododendron subarcticum
(formerly Ledum decumbens). Belowground plant biomass
was separated into woody roots, woody rhizomes, and
graminoid roots and rhizomes. Above- and belowground
biomass was weighed with a Mettler Toledo AX204 digital
scale for each functional group or species. Leaves and
stems were weighed separately for woody vascular plants.

Nutrient Analysis
All vascular species and functional groups were
chopped into a fine powder with a Wiley mill. Mosses
were finely chopped with scissors. Once powdered,
between 2 and 5 mg (dependent on estimated nitrogen and
carbon concentrations) of homogenized material from each
sample were weighed with a Sartorius Pro II digital scale
and rolled in Costech 4x6 mm tins for analysis. We
measured nitrogen and carbon concentrations in each
sample using a Costech Instruments EC54010 elemental
analyzer. Using a ThermoFinnigan Delta-plus XL mass
spectrometer, samples were combusted at 1020 OC to
measure 15N isotope signatures in order to evaluate the
primary source and pathway from which each plant
acquired nitrogen.

Statistical Analysis
Means and standard errors were calculated using
Microsoft Excel. Statistical tests (one- and two-way


ANOVAs and Tukey post-hoc tests) were performed using
JMP 7 software by SAS.

RESULTS

Community Composition
Aboveground plant communities in sampled plots were
mostly (>50%) woody species, including R. subarcticum,
V. vitis-idaea, V. uliginosum, and other woody species
(Betula nana, Rubus chamaemorus, Empetrum nigrum,
etc.) (Figure 1). Graminoids (Eriophorum and Carex
species) comprised less than ten percent of the
aboveground biomass, with mosses making up an
equivalent amount (Figure 1). Lichens comprised the
remaining roughly thirty percent. Three-quarters of
belowground biomass was made up of woody rhizomes.
The remaining quarter of belowground biomass was
divided evenly between woody roots and graminoid tissue
(roots and rhizomes).

Nitrogen Concentrations
Many distinct trends in growing season N
concentration exist for the tested plant tissues. Graminoid
shoots had their highest N concentration of 2.4% in the
middle of the season (Figure 2). Graminoid shoot June 26
and August 9 sample means are statistically different (one-
way ANOVA, f=6.12, p=0.046). Mosses do not experience
a significant change in N concentration across the growing
season, with tissue concentrations hovering around 0.7%
(one-way ANOVA, f=0.03, p=0.97) (Figure 2). Nitrogen
concentrations for R. subarcticum leaves peaked in late
June, reaching 1.4%. R. subarcticum stems displayed an
opposing trend, with their lowest concentration was in late
June, covering a span from about 0.6-0.5% (Figure 2).
Though variation across the season is not significant for R.
subarcticum stems or


Aboveground Mean Community Composition


Graminoid
Moss
O Lichen
OR subarcticum
"V uliginosum
oV vitis-idaea
U Other Plants


Figure 1: Aboveground community composition for the entire season
(the mean of all time points). Bold outlines indicate woody species.
Sample size for each species/functional groups is (n=8), with the
exception of V. uliginosum, which has a sample size of (n=7).


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010
2







KARLJAEHNIG


Table 4
Radial Comparison Data
(prob) Distance


D.0125
5.02649e-009
1.29590e-005
0.0311638
0.000407571
2.98120e-005
8.28566e-016
9.40134e-010
1.32297e-005
2.53991e-005
0.00274500
2.23450e-011
1.32707e-008


D.025
4.03383e-021
7.36067e-010
4.17003e-005
7.65775e-007
1.48352e-010
1.89378e-026
2.13127e-027
2.83600e-008
4.32433e-010
6.75427e-007
1.25539e-013
1.38110e-017


D.05
2.44161e-025
2.95477e-013
9.67269e-007
1.12354e-006
7.23266e-014
2.37464e-023
2.64501e-026
1.34639e-008
2.47053e-007
6.76513e-007
2.02101e-012
1.71377e-019


D.075
7.60807e-018
1.42820e-009
5.74405e-005
3.33289e-005
1.36466e-009
1.49368e-015
1.73619e-014
1.55457e-007
3.31928e-005
6.28134e-006
5.42930e-007
1.94955e-013


D.1
6.94558e-010
1.55129e-005
5.44195e-005
4.76625e-005
1.17768e-007
8.93262e-008
1.09335e-008
0.000145615
0.00233548
0.00958955
2.65583e-005
1.74551e-006


The probabilities do show a tendency to increase as
radial distance closes in toward the center, as would
have been expected if the ONC was spherical. Some
quadrants showed a higher probability of being part of
the total distribution (Figure 10). However, some sectors
showed a decrease going from some radial distance to a
smaller radial distance. It is unknown whether this is due
to the small amount of objects that were used to
calculate the value P for the innermost sector bins, which
were in the single digits (Figure 11).


Sect' 3 .05


00 o 001 0.02 003
erees(coo2000)


Figure 10: Here are the first three sectors from the northeast
quadrant of the ONC, showing each sector's probability as a
function of distance.
sector


10o ~-
03 A,
50 J^/


epeg2000)


Figure 11: This is an enlarged plot of the innermost region of
the ONC. The number of stars/bin does not exceed 20 at this
distance.


4. Analyzing Structure as a Function of Angle

We previously analyzed the structure of the ONC by
statistically comparing a set amount of individual bins to
the entire distribution in order to gain some measure of
how apsherical the ONC is internally. Since the arrays
containing the value D were integers, we compared the
unsorted values of the x distances for both the sample
bin and the entire distribution. The values of the
distances provide a measure of distribution when
compared to the complete distribution, which show how
small or how large the differences are between both sets
of radial distances. Here we analyze the structure of the
ONC as a function of angular position relative to the
origin. Moving counterclockwise from the north line,
extending downward through the origin and going all the
way to the same line, the angle 0 has a value of 0 < 0 <
27n rad.
This means, however, that the spatial configuration
used is to be annular sectors that either extend from the
origin to some radial distance outward or annular rings
that extend from one distance to another, dividing the
ONC into 5-6 annular rings and 5-6 annular samples.
The use of bins as in 2.1 is not useful, since the entire
angular position of the ONC must be compared through
the whole range of the unit circle; sector bins would
simply remove any useable data. Since the arrays of
angular positions are sorted out when produced, they
cannot be compared as was done with the x-distances in
2.1. Instead, a uniform distribution needs to be generated
that has equal number of objects at equal angles around
an origin as well as all the objects having equal radial
distances from the center. When linearly analyzed using
either radial distances or angular positions, the linearized
plot is a straight line.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 | Spring 2010


sector
1
2
3
4
5
6
7
8
9
10
11
12


D.25
0.0628336
0.00779168
0.543415
0.216930
0.411573
0.0493635
0.109060
0.393800
0.476098
0.844455
0.000750447
0.0120352


on


0..


0.04 0-.0


o0.0 o 10





MARLANA BEHNKE


-*-Original Config. -*- Extra Layer Missing top 4 layers


0.010


0.008


0.006


0.004


0.002


0.000


0.007


0.008 0.008 0.009 0.009 0.010 0.010
Strain


0.011


0.011


Figure 9: Maximum principal strain, elliptical nickel


Elliptical Alumina Elliptical Nickel


0.8



0.6



0.4



0.2


Linear


0.0 100.0 200.0 300.0 400.0 500.0 600.0 700.0 80C

Stress (MPa)


Figure 10: Stress vs. thickness for three FGM types




University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010
8


).0


A ,,iii I


z


/


-



-



-







processing and executive function could also interfere
with a student's ability to monitor the amount of
information they are missing and their understanding of
the information they were able to recall. Lack of
awareness of missed or misunderstood information could
prevent students from asking questions to clarify gaps in
their understanding.
The current practice of accommodations for
individuals with dyslexia requires that they receive
lecture notes prior to class. However, in most cases, no
further strategies are provided to students for getting the
full benefit of this accommodation (Rath & Royer,
2002). Kirby et al. (2008) suggested that explicit
instruction in strategies to minimize the effects of
dyslexia might benefit these students. They analyzed the
learning strategies of postsecondary students with
dyslexia, and found that, although students with dyslexia
do use learning strategies, they may need considerably
more instruction and strategy to execute these strategies
efficiently. In particular, Kirby et al. (2008) suggested an
intervention approach specifically targeting skills such
as main idea identification and note taking. Rath and
Royer (2002) suggested that once students acquired
explicit strategies for overcoming their academic
deficits, they become more confident as learners. One
type of intervention they proposed, self-advocacy, is a
training approach that raises students' awareness of their
disabilities and personal limitations. Helping students
gain awareness of their weaknesses would help them to
anticipate and plan for potentially difficult situations,
such as might arise in a large lecture class or with a
particularly hard to understand professor. Increased
awareness of their deficits would also allow them to
better inform their professors in order to get the
assistance they need and perhaps make them more
willing to take advantage of the accommodations
available to them.
Other strategies for minimizing resource demands
during classes might include reading over the lecture
notes before the class began. This strategy would also
help familiarize the student with the lecture material, and
familiarity with the material could alleviate some of the
cognitive demands imposed by note taking. Of course,
completing suggested readings prior to class could also
help the student gain familiarity with the subject matter
of the lecture. More cognitive resources could then be
made available for efforts in recalling, integrating, and
understanding the information. Additionally, recording
class lectures could allow the student to go back over
class notes. Recording lectures would make material
available to listen to several times, allowing the student
to shift concentration from memorization to
comprehension. Another possible approach that might be
beneficial to students with dyslexia would be choosing


seminars rather than lecture-based classes. Learning
through seminars rather than lectures would help the
student be less dependent on the online encoding of
auditory information. By actively engaging the student,
seminars could eliminate interference imposed by
language deficits.
The participants in the current study were all
enrolled in college and consequently can be considered
to be highly compensated individuals with DD.
Nevertheless, the results from this study revealed
significant deficits in recall of auditory information in
adults with DD, even when the information was
presented twice in context. Moreover, our results linked
this impairment in reproducing auditory information to
executive function deficits, particularly those associated
with speed of processing, rather than working memory.
Executive function deficits can also interfere with the
ability to develop compensatory strategies. Therefore,
we suggest that specific instruction in strategies to
minimize the effects of deficits in phonological encoding
and deficits in auditory processing speed may be
particularly helpful for college students with dyslexia.
Exactly which strategies would provide the most benefit
needs further research (Rath & Royer, 2002).

Acknowledgments

We would like to thank Cynthia Puranik for helping
with the design. We also like to thank SueAnn Eidson
and Becky Wiseheart for helping with the evaluations,
and Kathy Shepard, Ansley Myrick, and Jordan
Ginsburg for doing the experimental testing.


References
Altemeier, L., Jones, J., Abbott, R., & Berninger, V. (2006).
Executive functions in becoming writing readers and
reading writers: note taking and report writing in third and
fifth graders. Developmental Neuropsychology, 29(1),
161-173. doi:10.1207/sl 5, 2;-'42din2901_8
Altemeier, L., Abbott, R., & Berninger, V. (2008, July).
Executive functions for reading and writing in typical
literacy development and dyslexia. Journal of Clinical
and Experimental Neuropsychology, 30(5), 588-606.
doi:10.1080/13803390701562818
Baddeley, A. (2000, November). The episodic buffer: A new
component of working memory? Trends in C.,;,, a,.-
Sciences, 4(11), 417-423. doi:10.1016/S1364-6613
(00)01538-2
Berninger, V., Abbott, R., Thomson, J., Wagner, R., Swanson,
H., Wijsman, E., & Raskind, W. (2006). Modeling
phonological core deficits within a working memory
architecture in children and adults with developmental
dyslexia. Scientific Studies ofReading, 10(2), 165-198.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





KEITH KNAUER


B. Dark Current
Next, the dark current of the SWNT film and control
samples were measured at room temperature. Fig. 8(a)
shows the I-V curve for an MSM photodetector with
SWNT film electrodes, with AL=AW=200 pm and
W=S=15 lim. The I-V curve for the corresponding metal
control sample is shown in Fig 8(b). Schottky-like
behavior can be readily observed, but the curve does not
saturate at large voltages as would be expected due to the
back-to-back Schottky diode making up the MSM
photodetectors. More analysis is required to determine
the cause of this behavior, but it is evident from the
symmetry of these curves that the SWNT film acts as a
uniform material. In addition, Fig. 9 shows a comparison
of the dark current of these two devices on a log scale,
showing that the dark current of the MSM device with
SWNT film electrodes is nearly two orders of magnitude
lower than that of the control sample.
Finally, the effect of device scaling on dark current at
room temperature was studied. The dark current I-V
curves for MSM devices with W=S=20 pm and
decreasing AL=AW are displayed in Fig. 10 (a). The dark
current is shown to uniformly decrease with decreasing
AL=AW. This is expected as reducing the active length
and the number of fingers will lead to a lower dark
current. Fig. 10 (b) shows the room temperature dark
current I-V curves of MSM devices with AL=AW=300
pm and increasing S=W. The dark current decreases
uniformly with increasing S=W. This is because
increasing the finger spacing and width decreases the
total number of fingers, which decreases the dark current.
1.5
1.0 a)
S0.5
E
0.0
|-0.5
S-1.0
-1.5
-2.0 -1.0 0.0 1.0 2.0
Voltage (V)


1.E-02
1.E-03
1.E-04
1.E-05
1.E-06
1.E-07
1.E-08
1.E-09


S-I --- CNT Film
S...... Control


1.0
Voltage (V)


Fig. 9 Dark current comparison on a log scale plot showing the
use of SWNT film electrodes results in a dark current reduction
of nearly two orders of magnitude.


a)
....... AL= AW =400pm
- AL=AW=300pm
----AL=AW=200pm ..

.." s

^... -* ,- ,' . .1

0.0 0.5 1.0 1.5 2.0
Voltage (V)


80 b)
S...... S=W =1Om10
60 -S=W=20im
----S=W=504m


Voltage (V)


- 0.0

S-20.0


Fig. 8 [(a)-(b)]
AL=AW=200pm
electrodes (b) m
evident.


b)


Fig. 10 [(a)-(b)] I-V curves showing the effects of device
scaling on the dark current. (a) Scaling of AL=AW when
W=S=20 pm (b) Scaling S=W when AL=AW=300 pm.



IV. CONCLUSIONS


.U MSM photodetectors with SWNT film electrodes on
-2.0 -1.0 0.0 1.0 2.0 Ge substrates have been fabricated and characterized.
Voltage (V) Schottky-like behavior is observed from room

Scurves of MSM photodetectors having temperature dark current measurements, but more
I-V curves of MSM photodetectors having .
and W=S=15pm with (a) SWNT film analysis is required to fully understand the underlying
letal electrodes. Schottky-like behaviour is physical causes of this behavior. Insight could be gained
from future studies focusing on extracting the Schottky
University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010


-14





STEPHANIE ISHII


Preliminary Tests
As a preliminary test, eight of the nine fabrics were
tested for usability. BET 1500 was automatically
eliminated based on its thinness. Sorption isotherm curves,
as described later in this paper and elsewhere [7], were
generated for each fabric. Alcohol tracer solution was
prepared consisting of tracer concentrations ranging from
800ppm (2-butanol) to 600ppm (1-heptanol), which was
used to treat incrementally increasing amounts of fabric
(varying number of square centimeter pieces), as shown in
Figure 4. Based on these results, the nine fabrics were
reduced to three: Polyorgs, FM 100, and AC Felt 1300.


Figure 4: Varying amounts of activated carbon fabrics (square
centimeter pieces) being treated with constant concentrations of
alcohol tracers for the first preliminary test.

These three fabrics were tested in a similar fashion, but
in lieu of varying amounts of fabric, each vial contained a
constant amount of fabric and various dilutions of the
alcohol tracer solution. The original solution included
tracer concentrations ranging from 150ppm (2-butanol) to
1000ppm (1-heptanol). Dilutions ranged from 100%
original alcohol tracer solution to 5% tracer solution with
95% water. From these results, AC Felt 1300 was deemed
the most viable.

Tests for Felt 1300
For the previous batch test concerning AC Felt 1300,
Polyorgs, and FM 100, in which AC Felt 1300 was deemed
the most plausible, a tracer mixture was made according to
the measurements presented in the second column of Table
3. Each tracer was individually pipetted into one glass
bottle. Once all tracers had been deposited, the glass bottle
was tightly sealed with a screw cap and Teflon septum.
The mixture was allowed to equilibrate for 45 minutes to
an hour while being shaken every ten minutes. After all the
tracers had been thoroughly combined, 4.4mL of tracer
mixture and a magnetic stir bar were added to 1L of water


in a 1L volumetric flask to obtain the concentrations
presented in column 3 of Table 3. A glass stopper was
placed into the flask and wrapped with Teflon tape in order
to ensure minimal volatilization of tracers. The solution
was placed on a stir plate and allowed to mix until all
alcohol ganglia had disappeared and the tracers were
thoroughly dissolved.

Table 3: Tracers and their corresponding volumetric contribution
to the pure alcohol mixture and their final concentration in the
tracer solution, which consisted of the mixture and water.

Volumetric Concentration in
Contribution to
Alcohol Tracer r Tracer Solution
Tracer Mixture
(mL) (ppm)
2-butanol 1.3 150
1-butanol 1.8 200
3-pentanol 1.8 200
1-pentanol 3.1 350
1-hexanol 7.0 800
2,4-DMP 7.0 800
1-heptanol 8.8 1000
Total 30.8 3500

Ten 40mL Environmental Protection Agency (EPA)
glass vials with plastic caps and Teflon septa were labeled
and their empty weights recorded. AC Felt 1300 was cut
into one square centimeter pieces, six of which were placed
into each vial; the weights were again recorded to deduce
the exact weight of fabric in each vial. Specific amounts of
water were then transferred into each vial with a
volumetric pipette according to the vial's corresponding
dilution factor. After the water had been added, the
remaining fraction of the 40mL volume was filled with
alcohol solution via volumetric pipette. Water was first
pipetted into each vial to avoid volatilization of alcohol
tracers. Table 4 provides the dilution information for each
vial. Once filled with water and solution, the vial weights
were recorded.
The vials were then placed on a rotator (see Figure 5)
set at 20rpm for 48 hours to fully expose all areas of the
fabric to the alcohol tracers. After the rotation period, the
vials were removed from the rotator and allowed to settle
for 24 hours. It is important to note that during this time,
the vials were not refrigerated, as sorption behavior is
heavily influenced by changes in temperature [8]. Samples
of the resulting aqueous solution were transferred into 2mL
auto sample vials with disposable glass pipettes for
analysis using a gas chromatograph (GC). The GC
analyzed the samples for the remaining concentration of
tracers in the aqueous solution. Due to conservation of
mass, the difference between the original concentration and
the remaining concentration for each tracer was assumed to
have sorbed onto the AC Felt 1300.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 | Spring 2010





SEASONAL DIFFERENCES IN NUTRIENT ALLOCATION OF ARCTIC TUNDRA VEGETATION


Table 1: Behaviors recorded over each observation period.

Behavior Description
Male rapidly approached and
Attacking contacted the other male
Male walked around arena
Walking without apparent direction
Feeding Male fed on 0. humifusa
Sedentary Male did not move
Mating Male mated with the female
Male was in physical contact
Touching with the female
Male walked directly and rapidly
Approaching female towards the female
Mounting female Male mounted the female
Male mounted a copulating
Mounting pair female


escalated male-male competitions (CW Miller, personal
observation). We used pronotum width as a metric of body
size because it is easy to measure accurately and is a
common proxy for body size in insects.


Statistical analysis
We tested for an effect of the experimental treatment
(males reared with or without cactus fruit for the final stage
of development) on insect morphology with analyses of
variance (SPSS 15.0). Next, we examined the effect of
treatment on the scaling relationship allometryy) between
body size and hind femur width using ANCOVA with
pronotum width as the covariate. We first performed a
separate ANCOVA for hind femur width to test for effects
of experimental treatment on the slope of the scaling
relationship between body size and hind femur width,
indicated by a significant interaction with pronotum width.
If slopes did not differ according to pronotum width, we
examined effects of experimental treatment on the intercept
of the scaling relationship (i.e. trait size when controlling
for body size). The effect of experimental treatment on
developmental timing, weight at fifth instar, adult weight,
and weight gain between early fifth instar and adulthood
were tested using ANOVA (SPSS 15.0).
We employed multiple logistic regression analyses in
mixed models using the GLIMMIX macro of SAS to look
for associations between the natal experimental treatment
and the occurrences of each behavior. For probability of
mating, we used a paired t-test because GLIMMIX models
did not converge.


RESULTS


Effects of natural dietary differences on weight
and development
Treatment had a significant effect on development time
between insects from the two treatments. Insects raised in
the fruit treatment matured from the fifth instar to
adulthood in 9.5 days on average, while insects raised in
the no-fruit treatment took on average 13.5 days to mature.
Surprisingly, we did find a marginal difference in the
fifth instar weights of males and females selected for the
fruit treatment versus those selected for the no-fruit
treatment (F1,249 = 3.722, P = 0.055, Figure 1). Though
juveniles were randomly selected, those intended for the
fruit treatment weighed more in the fifth instar than those
intended for the no-fruit treatment. This initial difference is
small in comparison to the weight difference of adults
reared in the alternate treatments. Both males and females
reared for their final instar with access to fruits were much
heavier than those reared without access to fruits over this
developmental stage (F1,181 = 192.011, P < 0.001, Figure
1). Males with access to fruits gained on average 122%
more mass in their final instar than those deprived of fruits,
which gained only 50% more mass on average. Overall,
females gained more weight in their final instar than males.
Females with access to fruit gained an average of 129%
more mass in their final instar than those raised without
fruits, which gained 60% more mass on average in their
last instar.


0.09

0.08

0.07
05)
S0.06
_E
0)
S0.05

0.04

0.03

0.02


--- Females without fruit
-0-- Females with fruit
-- Males without fruit
A Males with fruit


Fifth instar


Adult


Developmental stage
Figure 1: Fifth-instar nymphs randomly chosen for the fruit treatment
initially weighed slightly more than nymphs deprived of fruits. During
the fifth instar, insects provided with cactus fruits gained substantially
more weight than insects deprived of fruits.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010







VOLUMETRIC QUANTIFICATION OF LACUNES IN AD AND SVD


Figure 1: A diagram exhibiting the process of subcortical vascular disease.


of small arteriole vessels deep within the brain, affecting
primarily the subcortical regions. Once a vessel becomes
damaged, irreversible tissue death occurs that is detectable
through brain imaging and appears as dark, spherical holes.
The tissue death results in the decline of memory, cognitive
ability, and executive functioning, defined as dementia
(Libon et al., 2004). In our investigation, we decided to
isolate and quantify this brain variable to see if it is only
associated with sVD. If so, then lacunes could serve as a
differentiating marker between AD and sVD.
In this study, we examined the presence of lacunes as a
brain variable on MRI by comparing total and regional
lacune volume in patients diagnosed with sVD and AD.
MR imaging was determined the most appropriate method
for the volumetric quantification of lacunes. As AD and
sVD are the two most prevalent forms of dementia, this
study is intended to examine the increased presence of
these representative markers believed to influence
cognitive and memory decline. Because AD and sVD may
share similar pathological markers, it is imperative that
research be carried out to help understand the relationship


of vascular brain deficits in order to provide information
needed to help establish prevention for dementia.

Specific Aims and Hypothesis
Aim 1: To examine total lacunes volume, a marker of
vascular disease, on brain MRIs in individuals with
clinically diagnosed AD or sVD.
The first aim of this study is to focus on total lacunes
volume, a more commonly associated sVD marker, and
determine its prevalence in AD patients. We hypothesize
that sVD will have a greater volume of lacunes; however,
an alternative hypothesis is that similar lacune volumes
may be found between the AD and sVD patients, as the
likelihood of a pure diagnosis of either is now known to be
rare due to overlap in pathology.
Aim 2: To investigate regional lacunes volume in four
white matter and three gray matter regions between
diagnoses.
It is hypothesized that lacunes are more prevalent in
the basal ganglia region of the brain due to blood supplied
through the lenticular striate arteries, which feed blood


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 4 I Summer 2009
3


I E. I r~oru rrr (krrr i
ILI" hr1P1 l W6;6x k? TC (I
fig, F, LA*$Al' of alaw dwnr, *lr

nb fdwIt port tw 4., "tr y






KARLJAEHNIG


ONC Complete Distribution pop:1408stors

.'.', '4



&.--o
:. .
":.. ,;. ... ... .. .
.

". . .







.


.0 83.9 83.8 83.7 82
R.A J2000


show the movement of the mean center as the aperture
and the sample size decreased. Overall, the movement of
the center does not show any discernible pattern to make
any conclusions.

Table 1


Figure 1: Plot of the ONC, as seen from the Chandra X-ray
Observatory.

from which to conduct spatial analyses fails to account
for the entirety of the stellar structure. The structure of
the ONC, while assumed to be spherical, does not
readily show this due to the aperture of the Chandra X-
ray observatory, which only absorbed data through its
diamond-shaped aperture (Figure 1).


2.1 Method 1A for Defining the Center: Mean
Based
This method follows the center as the aperture is
decreased and the sample size goes from 1408 all the
way to 123 stars at .0125 decimal degrees from the
center. The center is first taken to be the mean R.A. and
mean DEC of the entire sample. Using this center, the
first sample consists of all objects within a distance of.l1
decimal degrees. All other samples with a distance
greater than or equal to .1 decimal degrees are excluded
using the distance formula,

D = J((Xi_Xn)2 + ((' )2), where x is
R.A. and y is DEC.


After the new sample size has been created, the mean
center is the coordinates of the mean R.A. and the DEC
calculated to give a center, which represents the relative
center of this sample based on star location. The sample
size is further decreased, calculating new mean centers
in each consecutive sample, until the sample size is only
-123 stars, where the statistical noise is too large to
decrease the sample any further (Table 1) (Figure 2,
center movement) (Figure 3, mean centers/overall). The
centers are then plotted on an enlarged area graph to


- 5J8r


.

-7


83.8180 eBs 81 l
RA J2OC


Figure 2: Enlarged plot of center movement
method 1A


ONC Total Distribution








: I
.< ,7 ,


, r . .. . a


84.0 8..9 83.8
R.A J2000

Figure 3: Centers from method 1A
distribution.


calculated via


83.7 83.6


within the complete


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010


Method 1A Center Movement
aperture R.A. DEC
.1 83.8182 5.38335
.08 83.8175 5.38323
.06 83.8182 5.38575
.04 83.8167 5.38764
.02 83.8182 5.38942
.009 83.8185 5.38941
.007 83.8184 5.38882


ONC Center Movement:


83.8185


J.8110 83s1W6bi





SEASONAL DIFFERENCES IN NUTRIENT ALLOCATION OF ARCTIC TUNDRA VEGETATION


Graminoids and Mosses
S--Graminold Shoots
5 Mosses

2



1-







5 -
4.5 T I^^^Y


3.5 -
3 -
2.5 .
2-
1.5
0










0.5
0
June 4 June 26 August 9
Vaccinium uliginosum
5

^. 4 Leaws
-.-Stems

S 3-
S2.5
2 2
z 1.5

0.5

June 4 June 26 August 9


Rhododenron subarcticum
2
1 8 Leaes
-1 Stems




2 08
z 06
04
02
0
June 4 June 26 August 9

Belowground Community


June 4 June 26 August 9


Vaccinium vitis-idaea
1
0.9
0.8
S0.7

0.5
S0.4
0.3 -*-Leales
.2 ---tems

0.1
0
June 4 June 26 August 9

Figure 2: Aboveground mean nitrogen
concentrations by weight for graminoid shoots
and mosses, Rhododendron subarcticum leaves
and stems, Vaccinium vitis-idaea leaves and
stems, and Vaccinium uliginosum leaves and
stems. Error bars represent SE. Sample sizes
differ between June 4 and August 9 (n=3) and
June 26 (n=2). The June 26 time point for V.
uliginosum has a single sample (n=l) and thus
lacks error bars. Belowground mean nitrogen
concentrations by weight for graminoid tissues
and woody roots and rhizomes. Error bars
represent SE. Each time point has the same
sample size (n=3).


leaves, differences between tissues are highly significant
and the interaction effect between date and tissue
approaches significance (two-way ANOVA, date effect
f=0.87, p=0.45; tissue effect f=114, p<0.05; date x tissue
f=3.03, p=0.09). Nitrogen concentrations for V. vitis-idaea
leaves showed a v-shaped relationship, with the lowest
sample mean of 0.78% on June 26 (Figure 2). As with R.
subarcticum, the V. vitis-idaea stem concentration showed
an opposing relationship to that of the leaves (Figure 2).
Variation across the season was nonsignificant for V. vitis-
idaea leaves and stems; however, there was a significant
tissue effect (two-way ANOVA, date effect f=1.63,
p=0.24; tissue effect f=21.3, p<0.05; date x tissue f=0.5,
p=0.62). For V. uliginosum, leaf N concentrations were
highest in the beginning of the season, 3.6%, and declined
through August (Figure 2). Stem N concentrations for V.
uliginosum remained relatively stable throughout the
season, but were lower than leaf N (Figure 2). V.
uliginosum June 26 data were excluded due to the presence
of only one sample, but there was still a significant
difference between June 4 and August samples and
significant differences between tissues (two-way ANOVA,
date effect f=14, p<0.05, tissue effect f=34.0, p<0.05, date
x tissue f=11.0, p<0.05).
All belowground tissue (woody roots rhizomes, and
graminoid tissue) N concentrations decreased as the season
progressed (Figure 2). The most dramatic decline (roughly
0.5%) occurred in graminoid roots and rhizomes, with a
more gentle dip of about 0.1% in woody roots and


rhizomes (Figure 2). Though apparent as trends, there were
no statistically significant differences between tissues or
across the season (two-way ANOVA, date effect f=2.29,
p=0.13; tissue effect f=1.81 p=0.19; date x tissue f=0.55
p=0.70).



Nitrogen Pools
Plant species and functional groups exhibited a number
of trends in their nitrogen pools. Graminoids were divided
into shoot and belowground (roots and rhizomes) tissue
pools, and these two N pools demonstrated different trends
(Figure 3). The graminoid shoot N pool peaked in the
middle of the growing season at 39.5 g/m2 and declined
slightly by August (Figure 3). The belowground N pool
remained relatively stable from the start through the middle
of the growing season, hovering at 22 g/m2 before
declining by August (Figure 3). These trends did not reach
significance (two-way ANOVA, date effect f=0.95,
p=0.42; tissue effect f=0.95, p=0.35; date x tissue f=1.67,
p=0.23).
For the three woody species, aboveground pools were
divided between leaves and stems. Leaf N pools for R.
subarcticum peaked at 27.8 g/m2 in the middle of the
growing season, while stem N pools experienced a gradual
increase of roughly 15 g/m2 throughout the growing season
(Figure 3). The variation across the growing season is
statistically significant (two-way ANOVA, date effect
f=6.1, p<0.05; tissue effect f=0.89, p=0.38; date x tissue


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010
3






CARVAJAL ET AL.


memory and executive function in individuals with
dyslexia and other populations (Cui, Lyness, Tu, King &
Caine, 2007; Salthouse, Atkinson, & Berish, 2003; Urso,
2008). There is much debate over whether the
characteristic phonological deficits in dyslexia can be
attributed to working memory and executive function
impairments or whether the phonological deficits in
dyslexia contribute to working memory and executive
function impairments.

Effects of DD on Education and Writing
Higher education emphasizes skills that are
particularly vulnerable in individuals with dyslexia. For
example, higher education demands competence not only
in reading, but also in writing, auditory memory, auditory
processing and note-taking, all of which may be impaired
in dyslexia. Prior research on dyslexia has shown much
focus on reading problems; but with the growing
documentation of the weaknesses in writing, the need for
further research in this area is becoming more evident (e.g.,
Beminger, Nielsen, Abbott, Wijsman, & Raskind, 2008).
Mortimore and Crozier (2006) surveyed male college
students with dyslexia who admitted that expressing ideas
in writing was the third highest self-reported difficulty.
Simmerman and Risemberg (1997) characterized writing as
a controlled process in which self-initiation of thought and
planning behaviors are used to attain writing goals (as cited
in Altemeier et al., 2008). Considering these task demands,
the deficits in executive function and working memory in
dyslexia may underlie some of their difficulties with
writing (Altemeier, Jones, Abbot, & Beminger, 2006;
Altemeier et al., 2008). The students with dyslexia
surveyed by Mortimore and Crozier (2006) also reported
that note taking was the most difficult skill for them to
master. Similarly, Kirby et al. (2008) examined how
weaknesses in the phonological processing of individuals
with dyslexia manifested in the classroom and affected
their academic performance. They found that students with
dyslexia experienced the most difficulty with tasks such as
taking lecture notes, writing essays, and comprehending
large quantities of complex text (Kirby et al., 2008). Note
taking during a lecture requires the written recall of
auditory information, especially in a lecture-based
environment (Mortimore & Crozier, 2006), and
maintenance of this information while transcribing the
salient points. Academic writing requires working memory
for activating several thoughts at once and executive
function for manipulating these thoughts into a logical
order. Therefore, considering the demands that note-taking
makes on both phonological encoding and working
memory, and that writing itself requires working memory
and executive function, it is not surprising that note-taking


and writing might be particularly difficult for individuals
with dyslexia.
The current study investigated how the
characteristic phonological impairments in DD might
manifest itself in lecture-based settings. In the study,
individuals with DD and NRs were required to recall an
auditory passage both orally and in writing. The current
study also investigated whether relationships existed
between recall abilities, working memory, and/or executive
function. We predicted that individuals with DD would
have more difficulty overall with the task than NRs,
especially in the written task, but might perform similarly
to NRs on oral recall. Furthermore, we predicted that
individuals with DD would perform extremely poorly
when they were instructed to complete the written recall
task first. Finally, we predicted that individuals with DD
would recall less than the NRs the first time they heard the
passage but, after the second hearing, would demonstrate
similar levels of recall as the NRs.

Method

Participants
Nineteen individuals with DD and 23 NRs
participated in this experiment. All participants were
enrolled in college and ranged in ages from 16-28. NRs
were recruited from a participant pool at the University of
Florida and received course credit for participating.
Participants with DD were recruited from the the Disability
Resource Center at the University of Florida (UF), a local
community college, and the UF Speech and Hearing Clinic.
The DD group was compensated $7.50/hr for their time.
Each of the dyslexic participants completed a two-hour
evaluation to confirm their diagnosis. Licensed speech
pathologists from the UF Speech and Hearing Clinic
conducted the evaluations, which included Test of Word
Reading Efficiency; Comprehensive Test of Phonological
Processing; word identification, word attack, and passage
comprehension subtests of the Woodcock Reading Mastery
Test-Revised; and the spelling subtest from the Wide Range
Achievement Test. All participants were required to score at
least one standard deviation (SD) below the mean on word
reading, non-word decoding, or reading fluency, and score
no lower than one SD below the mean on reading
comprehension to qualify for participation. A questionnaire
regarding early educational history and family history was
also evaluated by a specialist in dyslexic diagnosis.

Procedure
Participants completed a battery that included, among
other tasks, tests of executive function, working memory,
and the experimental passage recall task. Participants


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 | Spring 2010





FAE NAGEON DE LESTANG


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Chapman RF, and Lee JC, 1991. Environmental-effects on
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Hunt J, Breuker CJ, Sadowski JA, and Moore AJ, 2009.
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Low C, Wood SN, and Nisbet RM, 2009. The effects of
group size, leaf size, and density on the performance of a leaf-
mining moth. J Anim Ecol 78:152-160.
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Miller, CW and Moore AJ. 2007. A potential resolution to
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Miyatake T, 1997. Functional morphology of the hind legs
as weapons for male contests in Leptoglossus australis
(Heteroptera: Coreidae). J Insect Behav 10:727-735.

Moore AJ, and Moore PJ, 1999. Balancing sexual selection
through opposing mate choice and male competition. Proc R Soc
B 266:711-716.

Nageon de Lestang F, and Miller CW, 2009. Effects of diet
on the development and survivorship of Narniafemorata nymphs
(Hemiptera: Coreidae). Fl Ent 95:511-512.

Pagel M ,editor, 2002. Encyclopedia of Evolution. New
York, New York: Oxford University Press.

Sillanpaa S, 2008. How do food quality and larval crowding
affect performance of the autumnal moth, Epirrita autumnata?
Entomol Exp Appl 129:286-294.

Triseleva TA, and Safonkin AF, 2006. Variation in antennal
sensory system in different phenotypes of large fruit-tree tortrix
Archips podana Scop. (Lepidoptera: Tortricidae). Biol Bull
33:568-572.

Young HJ, and Stanton ML, 1990. Influence of
environmental quality on pollen competitive ability in wild
radish. Science 248:1631-1633.


Hubbell SP, and Johnson LK, 1987. Environmental variance
in lifetime mating success, mate choice, and sexual selection. Am
Nat 130:91-112.















University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010






MSM PHOTODETECTORS ON GERMANIUM SUBSTRATES WITH SWNT FILM ELECTRODES


barrier height of the SWNT film-Ge junction from dark
current measurements taken as a function of temperature,
as well as determination of the carrier type by measuring
the dark current of fingerless MSM structures with
asymmetric SWNT film contact areas [10]. Moreover, it
has been demonstrated that MSM photodetectors with
SWNT film electrodes have significantly lower dark
current than metal control samples and that their dark
current scales rationally with device geometry. A
comparison of the photocurrent and responsivity of the
MSM devices with SWNT film electrodes versus metal
control samples would be of interest in fully assessing the
advantages of using SWNT film electrodes for MSM
photodetectors on Ge substrates. These experimental
results give insight into the electrical properties of the
SWNT film-Ge interface while also demonstrating the
use of SWNT film as a transparent and conductive
material for electronic applications.

ACKNOWLEDGMENTS
The author would like to thank Dr. Ant Ural for
supervising this research project and providing invaluable
guidance. This work would also not have been possible
without the training from and discussions with the
members of the Nanotechnology Group at the University
of Florida, including Jason Johnson, Ashkan Behnam,
Yongho Choi, Karthik Vishwanathan, and Nischal
Radhakrishna. This work was completed through UF's
University Scholars Program.


REFERENCES
[1] A. Loiseau, et al., Ed., Understanding Carbon Nanotubes: From Basics
to Apphcations (Lecture Notes in Physics 677). Berlin, Germany:
Springer, 2006.
[2] R. Waser, Ed., Nanoelectronics and Information Theory: Advanced
Electronic Materials and Novel Devices, 2nd ed., Weinheim, Germany:
Wiley-VCH, 2005.
[3] A. Javey, J. Guo, Q. Wang, M. Lundstrom, and H. Dai, "Ballistic carbon
nanotube field-effect transistors," Nature, vol. 424, no. 6949, pp. 654-
657, Aug. 2003.
[4] K. Besteman, J. Lee, F. Wiertz, H. Heering, and C. Dekker, "Enzyme-
coated carbon nanotubes as single-molecule biosensors," Nano Letters,
vol. 3, no. 6, pp. 727-730, Jun. 2003.
[5] Z. Wu, et al. "Transparent, conductive carbon nanotube films," Science,
vol. 305, no. 5688, pp. 1273-1276, Aug. 2004.
[6] E.S. Snow, J.P. Novak, P. M. Campbell, and D. Park, "Random
networks of carbon nanotubes as an electronic material," Apphed
F: ..,. Letters, vol. 82, no. 13, pp. 2145-2147, Mar. 2003.
[7] Y. Zhou, L. Hu, and G. Grfiner, "A method of printing carbon nanotube
thin films,"Apphedi -: ., .. Letters, vol. 88, 123109, Mar. 2006.
[8] E. Bekyarova, et al. "Electronic properties of single-walled carbon
nanotube networks," Journal of the American Chemical Society, vol.
127, no. 16, pp. 5990-5995. Apr. 2005.
[9] A. Behnam, et al., "Nanolithographic patterning of transparent,
conductive single-walled carbon nanotube films by inductively coupled
plasma reactive ion etching," Journal of Vacuum Science & Technology
B, vol. 25, no. 2, 348-354, Mar/Apr. 2007.
[10] A. Behnam, et al., "Metal-semiconductor-metal photodetectors based on
single-walled carbon nanotube film-GaAs Schottky contacts," Journal
ofApphed ';*.., ... vol. 103, 114315, Jun. 2008.
[11] A. Behnam, et al., "Experimental characterization of single-walled
carbon nanotube film-Si Schottky contacts using metal-semiconductor-
metal structures," Apphedi : .. Letters. vol. 92, 243116, Jun. 2008.
[12] K. Brennan, J. Haralson, J. Parks, and A. Salem, "Review of reliability
issues of metal-semiconductor-metal and avalanche photodiode
photonic detectors," Microelectronics Rehability, vol. 39, no. 12, pp.
1873-1883, Dec. 1999.
[13] L. Noriega, "Fabrication of novel metal-semiconductor-metal
photodetectors by nanolithographic patterning of single-walled carbon
nanotube films," M.S. thesis, University of Florida, Gainesville, 2006.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





MEASUREMENT OF GROUNDWATER AND CONTAMINANT FLUX IN FRACTURED ROCK MEDIA WITH A PASSIVE FLUX METER


a. 2-butanol

3

25 -

2
SAC Felt 1300
1 5 Polyorgs
1 FM 100

05
0 --
0 5 ---- i---- i---- ----
o 0
0 50 100 150 200
Equ. Conc., mg/L


b. 1-butanol


r
B 5

S* AC Felt 1300
S3 -- Polyorgs
S* FM 100

1

SO
0 50 100 150 200 250
Equ. Conc., mg/L


c. 3-pentanol

8
7 -
6
5 AC Felt 1300
4 -- m Polyorgs
3 FM 100
22
1
0

0 50 100 150 200 250
Equ. Conc., mg/L


d. 1-pentanol

20
18
16 *
14
12 *AC Felt 1300
10 Polyorgs
8 FM 100
6
4I

I 0
0 100 200 300 400
Equ. Conc., mg/L


e. 1-hexanol

80
70
60
50 AC Felt 1300
40 m Polyorgs
S30 (- FM 100
S20
10 1

0 100 200 300 400 500 600
Equ. Conc., mg/L


f. 2,4-DMP

80-
70 -
60
50 AC Felt 1300
S40 Polyorgs
t 30 FM 100
2 20
1 10 ,I
10
olI
0 200 400 600 800
Equ. Conc., mg/L


g. 1-heptanol

1180
160
140 -
S120 AC Felt 1300
100 -*
SPolyorgs
S 80
l __--60--------- m FM 100
40 f-
4 20
20

0 100 200 300 400
Equ. Conc., mg/L




Figure 8: Sorption isotherm curves from the second
preliminary test data concerning three fabric choices.
Each graph represents a different tracer, going from
shortest chain alcohol (highest aqueous solubility) to
longest chain alcohol (highest tendency to sorb). AC Felt
1300 shows the highest sorption affinity for the alcohol
tracers and was therefore chosen as the most viable
option.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





MEASUREMENT OF GROUNDWATER AND CONTAMINANT FLUX IN FRACTURED ROCK MEDIA WITH A PASSIVE FLUX METER

Conclusion

Thus far, these data have shown that AC Felt 1300 can
be feasibly used in a FRPFM with regard to the sorption of
the seven aforementioned alcohol tracers. As shown in
graphs e, f, and g in Figure 9 and graphs a, b, c, and d in
Figure 10, there is an initial linear relationship for each
tracer between its existence in either the aqueous or sorbed
phase. The slope of the linear portion of each sorption
isotherm represents the partition coefficient, KD Further
research is needed to more clearly define KD via additional
batch experiments at different initial tracer concentrations
as well as tests involving actual water flow.
Once the partition coefficient for each tracer is
determined, tests must be conducted with surrogate
contaminants to evaluate their sorption behavior when
exposed to AC Felt 1300. These results would allow AC
Felt 1300 to serve as an indicator of water flux by means of
tracer elution and as an indicator of contaminant flux
through contaminant sorption.

Acknowledgments

I would like to extend my sincerest gratitude to my
mentors, Dr. Mark Newman and Dr. Jaehyun Cho, for
sharing their extensive knowledge and skills with me. You
both have shown me the importance of thinking big while
taking baby steps and the necessity in treating obstacles as
creative opportunities. Thank you for introducing me to the
world of research as mentors and friends.




























University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010






METHODS ON DEFINING THE CENTER AND SPATIAL ANALYSIS OF THE ORION NEBULA CLUSTER


4.1 Annular Sectors Extending Radial Outward
from the Center
Setting the origin to be R.A.=83.8157, DEC=-
5.37905, we limit the sample as we have done
previously using the distance formula and removing all
stars not at or within a set radial distance from the center
of the ONC. Running another programmed algorithm, a
line rotates from the north line counterclockwise from 0
to 27n radians, storing the angular position of each star
relative to the north line running through the origin.
Naturally, this array of values is already in ascending
order and does not need to be sorted as was done with
the radial distances.
Another loop is created that then performs a similar
process to the radial linearization in 2.1, where a line
runs counterclockwise from the north line and counts
how many stars are at each angular position until it gets
to 27n radians. This array of T is then stored and
normalized. The programmed algorithm and the angular
position loop are then executed over the uniform
distribution, producing an array of angular positions that
extend over the range of the unit circle in equal angular
increments. This array will not change when compared
to all other angular sectors and annular rings. Both
arrays of the current annular sector and of the uniform
distribution are then compared using the Kolmogorov-
Smimov statistical test for two distributions. The
probability P is then a measure of how close the annular
sector is to being uniform in angular distribution (Table
5). The probabilities show, as radial distance extends
inward toward the center, that the ONC becomes more
like the uniform distribution, that is, more spherical as
the central region is approached. The low value of p is
for the entire distribution within a large annular sector
that encompasses it all. It has value P= 4.34896E-05


Table 5


The central region had the highest value of P, for
which its value was P= .291896.


4.2 Annular Rings of Some Radial Length.
Setting the origin as before, we now determine the
sample of stars within each annular ring as being n < r <
m, where n is the minimum of r in the annulus, m is the
maximum value of r, and r is the radial distance from the
center. Six Annuli are created on which the angular
position algorithm and loop are run and then compared
to the array of the uniform distribution to calculate the
probability P (Table 6). Like the annular sectors, the
value of P for the annuli shows a tendency to increase as
radial distance approaches the central region. However,
at annulus 4, for which r is .025 < r < .05, P drops to P=
.000157721. As the annuli approach the center, the value
of P once again increases. The value of the innermost
sector and the innermost annulus is the same since they
have same value of r, where 0.0 < r < .0125.

Table 6
Angular Final Data(Annuli)

Annulus Prob D
1 0.000109248 0.120982
2 0.000286393 0.150718
3 0.0467696 0.0885942
4 0.000157721 0.122550
5 0.0224349 0.109556
6 0.291896 0.0878821


5. Conclusion

The results do not conclusively show that the ONC
becomes more spherical approaching the center.
However, both the radial and angular analyses give
another measure of the spherocity within the ONC, and
this gives data that can be modeled and compared to
King model equations used to predict the dynamics of
stellar evolution. More so, the robust method of defining
the center with the ONC can be applied to other nebular
clusters as well, which can give a standardized method
of choosing a center from which to run analysis on
spatial structure instead of arbitrary choice.

Acknowledgments

I thank Dr. Jonathan C. Tan (University of Florida)
for mentoring and direction in the research project as
well as Audra Hemandez and Mike Butler for assistance
in using the programming language IDL for the
development of the algorithms.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010


Angular Final Data(Spherical)
Sample Prob D
4.34896e-005 4.34896e-005
0.00196265 0.0597223
0.00238646 0.0645293
0.0388893 0.0573619
0.0827593 0.0722484
0.291896 0.0878821
6






MARLANA BEHNKE


0.01



o 0.008

I-
1-
c 0.006

0
I-
o 0.004
Co


O 0.002



0
0.005 0.006 0.007 0.008 0.009 0.010

Strain

Figure 5: Maximum principal strain, linear





-- Original Config. ---Extra layer -A-Missing bottom 4 layers


0.010



w 0.008



S 0.006
0
C-


0.004
I-




0.002


0.000 ,

0.0 200.0 400.0 600.0 800.0 1,000.0
Stress (MPa)

Figure 6: von Mises Stress at maximum thermal stress, elliptical alumina







University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 | Spring 2010
6





THERMAL PROTECTION SYSTEMS FOR FUTURE SPACE VEHICLES


-- More Nickel


---More Alumina


-Linear ()


4.5E+11



4E+11



co 3.5E+11
C,,

o 3E+11
v-,

> 2.5E+11



2E+11



1.5E+11
0 0.2 0.4 0.6 0.8 1
Volume Fraction


Figure 2: Three different volume fraction variations


position through the thickness, and h is the total thickness.
The subscripts 1 and 2 represent alumina and nickel,
respectively.

Z2
P=P + (P2-P1) 1-
h
Equation 1
The Young's Modulus was used to form this elliptical
equation. The effective Young's Modules was determined
at various heights. Knowing these heights, the volume
fraction at various layers was determined following the
inverse rule of mixtures. This configuration varied
elliptically and had a greater amount of alumina overall.
This configuration will be referred to as "elliptical
alumina." This FGM is comprised of 15 layers. There is
0.1 cm of alumina for the top layer. There is then 1 cm of
FGM that varies elliptically.
The final configuration tested was an inverse of the
configuration previously described. There was an elliptical


variation but a greater amount of nickel overall. This
configuration will be referred to as "elliptical nickel."
Figure 2 is a graph of the property variation with volume
fraction using Young's Modulus as an example.

Heat Transfer Analysis
After completing the analysis to determine the volume
fraction variations for each of the three configurations, a
heat transfer analysis was conducted to determine the
temperatures that the FGM would experience. The results
from this analysis are used in the next section to determine
the thermal stresses and strains. Bapanapalli, Sankar,
Haftka, Gogu, and Blosser (2007) demonstrated that a one-
dimensional heat transfer analysis is appropriate for this
type of problem. The temperature distributions did not vary
significantly between the two-dimensional and one-
dimensional problem. For this reason, a finite element one-
dimensional heat transfer problem was conducted to
determine the temperature distribution in the FGMs.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





MEASUREMENT OF GROUNDWATER AND CONTAMINANT FLUX IN FRACTURED ROCK MEDIA WITH A PASSIVE FLUX METER


a. 3-pentanol

30 0

25 0
20 0

150 I IAC Felt 1300

100
S50

00
00 50 100 150 200
Equ. Conc., mg/L


b. 1-pentanol

300 -

250
' 20 0

S150 ACFelt 1300

100 -
t 50
N
S00
00 20 40 60 80 100
Equ. Conc., mg/L


c. 2-butanol

l 25 0

200 -
15' *



50









250
H r *










200

150 I 1

100

50

00
00 100 200 30 0 40 500
Equ. Conc., mg/L
S 250-----
al 200 -----





S 5 0 ---------------



Equ. Cone., mg/L


Figure 10: Sorption isotherm curves from the second
batch test data concerning only AC Felt 1300. Each
graph represents a different tracer that previously
showed inconsistent sorption behavior. For this batch
test, AC Felt 1300 was treated with one solution
containing just 2-butanol and 1-butanol, and in separate
vials it was treated with a solution containing just 3-
pentanol and 1-pentanol.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





STEPHANIE ISHII


Figure 6: 40mL EPA glass vial containing one 2 cm x 6 cm strip
of fabric and a solution with known alcohol tracer
concentrations.


Results & Discussion

The sorption isotherms constructed from the
preliminary test data are shown in Figure 7 (a-g). As with
all sorption isotherm curves displayed in this paper, the
independent variable represents the equilibrium
concentration of tracer remaining in the aqueous phase
after being exposed to a sorptive material, and the
dependent variable is the mass of tracer sorbed per unit
mass of material. The partition coefficient, KD, is estimated
as the slope of the initial linear portion of the curve.
Preliminary test data confirm that the alcohol tracers
with higher Kow values and longer-chain lengths are more
readily sorbed by all of the sorptive materials. These data
also show that when the aqueous equilibrium concentration
is high, the amount of sorbed tracer per sorbent tends to
decrease. If the aqueous concentration of tracer is high, a
tracer's affinity for the sorbed phase may be overwhelmed
by its affinity for itself and the strong sorption affinities of
the other longer-chained alcohols. From these data, it was
determined that a subsequent batch test had to be
conducted with lower initial concentrations of tracers.
Additionally, the eight sorptive materials from the first
preliminary test were reduced to three choices: AC Felt
1300, Polyorgs, and FM 100. These fabrics were selected
based on their trend-like sorption behavior with most of the
tracers. These fabrics were also chosen due to physical


characteristics, including structural integrity and a
substantial thickness. BET 1000, BET 1300, and BET 1500
all had thicknesses of approximately 1 mm. In order to
intercept contaminants and elute tracers, water must flow
through the fabric. If the fabric is too thin, groundwater
streamlines may bypass the fabric by flowing around it in
the borehole. FM 10 was eliminated due to excessive
fraying during testing procedures. AC Felt 1000 and AC
Felt 1500 both possessed desirable thicknesses, but during
testing procedures they displayed physical degradation. If
Figure 4 is given a closer look, suspended particles of
activated carbon that have been divorced from AC Felt
1500 can be seen. On the contrary, Figure 6 is a close-up of
a vial containing AC Felt 1300 and there is a significant
decrease in the amount of suspended carbon.
Figure 8 (a-g) presents the sorption isotherms for AC
Felt 1300, Polyorgs, and FM 100. For this batch test, the
initial concentration of each tracer was reduced in order to
avoid high aqueous equilibrium concentrations that would
conflict with the normal partitioning of tracers on fabric.
These data show that all three fabrics result in trend-like
sorption behavior, but AC Felt 1300 was chosen as the
superior sorptive material because it had the highest
sorption capacity.
The results for a subsequent batch experiment
concerning only AC Felt 1300 are presented in Figure 9 (a-
g). The initial tracer concentrations were again reduced in
an effort to focus on the initial linear portion of the
sorption isotherm. It was during this batch experiment that
the square centimeter pieces of fabric were replaced with
two 2cm x 6cm pieces of fabric to more closely mimic
field conditions. Graphs e, f, and g in Figure 9 include the
initial linear portion of each sorption curve from which the
partition coefficient is derived as well as a progression
toward maximum capacity. Graphs a, b, c, and d have less
defined trends, and instead of asymptotically approaching
maximum capacity, these sorption curves appear to be
returning to zero. On their own, the short-chain alcohols
have a low affinity for sorption onto the solid phase, and
this affinity decreases even more when undergoing
competition. In the presence of long-chain alcohols (i.e. 1-
heptanol), which have a high tendency to sorb to the solid
phase, the true partitioning of 1-butanol, 2-butanol, 3-
pentanol, and 1-pentanol between water, and the AC Felt
1300 becomes impossible to determine. In response to this
dilemma, a second batch test was conducted for AC Felt
1300 in which the fabric strips were exposed to one
solution containing 2-butanol and 1-butanol and different
fabric strips were exposed to a solution containing 3-
pentanol and 1-pentanol. Figure 10 displays the sorption
curves for the four short-chained tracers when separated.
The behavior showed a much higher level of predictability,
and the curves appear to be approaching maximum
capacity.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010







METHODS ON DEFINING THE CENTER AND SPATIAL ANALYSIS OF THE ORION NEBULA CLUSTER


3. Analysis of Structure: Aspherocity,
Asymmetries in Structure

Studying the structure of the ONC allows for the
strengthening or weakening of current stellar evolution
theories. The ONC, considered to be a relatively young
nebula cluster, is presumed to be of a spherical shape,
according to current theories on stellar nebulae. Using
the position data of the 1408 confirmed stars in the ONC
from the COUP (Feigelson et al. 2005), the analysis of
the structure of the ONC can reveal how spherical the
ONC really is and provide a measure by which to
calibrate equations, such as King models, that predict
stellar evolution based on current data.

3.1 Linearization as a Function or Radii
Using the distance formula, the distance each star has
to the center is calculated and stored. This array of R.A.
and DEC values is then sorted into an ascending array.
Running a loop, an algorithm is then used to find how
many stars are at or within a certain distance of each
value in this array. The loop counts how many stars are
at or within each value and stores each of them into an
array of scalar values, D. Plotting the sorted distances
and the values of D (which are also ascending as well), a
histogram shows an increment of one star per every
stored distance (Figure 8). This is appropriate since each
value of the distance was calculated from one star that
was at that distance, so the loop would find as many
stars as there are values for the array of distance. In
order to compare multiple radial linearizations on the
same plot, normalization is required for each array. This
simply requires that the values of the count array D be
divided by the maximum value of D, so that the
maximum value for N in the plot is 1.


-5.370


-5.375

-5.380

-5.385

-5.390


ONC


3.1 Bin-based Linearization as a Function of
Radial Distance
Dividing the ONC into bins with equal angles
provides a detailed look at the interior of the ONC. This
analysis can be extended to look into this structure as
radial distance decreases and heads toward the central
region in order to provide a look at the total distribution
in detail. The ONC is divided into 12 angular bins of
7r/3rads starting from a north line running through the
origin of the ONC and rotating counterclockwise. The
counterclockwise motion compensates for the reversed
east/west orientation of the ONC in the aperture of the
Chandra X-ray Observatory. The counterclockwise mo-
tion is really clockwise in the normal west/east motion in
the direction of an increasing angle, as in the Unit Circle.
A loop is created that runs counterclockwise, running
the linearization algorithm on the sample within the bin,
and then stores this information within an array. Once
this cycle is complete, the linearization algorithm then
executes for the complete distribution of the ONC. The
unsorted arrays of the distance for both the bin sample
and the complete sample of stars are then compared
using the Kolmogorov-Smimov statistical test for two
samples. The value P, where 0 < P < 1, is the probability
that the bin sample belongs to the complete distribution.
The more a sector bin belongs to the total distribution,
the more symmetrical the distribution of stars and thus
the higher the spherocity. The bins, which currently
divide the distribution into 12 angularly equal slices, are
then individually cut into six sections. The total amount
of bins that will be compared to the total distribution are
now 72. Each individual bin sector is now linearly
analyzed and compared to the total distribution, resulting
in 72 values of P (Table 4).
Due to the very small values of P for some bin
sectors, the log of each value P is taken in order to
compute a mean for each complete sector as well as each
bin sector at the same radial distance. The normalized
plots of each bin can also be compared visually to the
normalized plot of the total distribution (Figure 9).


7-7


3. 830 83.825 83.820 83.815 83.810 83.805 83.800 Figure 9: This is an example of one of the graphical com-
RA deg J2000 prisons of a sector to the total distribution. Here Sector 3 is
Figure 8: Radial Histogram for Bin 1, sector .1, where sector being compared to the total distribution, both compared only
designation lists the distance at which the bin was formed at a radial distance of .05 decimal degrees from the center.
University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010


ol oos 0.06 ~CI
~eEIYI (JII-YnCC


I.., O 00






KARLJAEHNIG


-5.4


-5.5
-5.6
84.0


83.9


83.8
RA J2000


83.7


Figure 6: Single Center chosen via method 1B





Table 3


Method 1B Calculated Center


Aper R.A. DEC
ture (j2000) (j2000)

.06 83.8115 -5.37728


.04 83.8223 -5.37660


.02 83.8111 -5.38383


.009 83.8133 -5.38175





They are average values, being in between the largest
apertures and the smallest apertures. There are multiple
centers at both extremes of the range used to define the
individual samples. The distribution of the centers within
the ONC shows that they are concentrated within the
central region of the ONC. A mean of these centers can
be used, but by choosing which apertures are useful, the
robustness of the method is lost.


-5.6 r
84.0


83.8
RA J2000


Figure 7: Multiple centers chosen via method 1B







2.3 Method 2: An Integration of Method 1A and
1B
The final method uses the robust elements of both
method 1A and method 1B in order to define a center
that is free of the bias in arbitrarily choosing a center to
begin with as well as the bias in choosing apertures that
provide an appropriate center. Employing method 2, and
executing the loop at the first aperture, the C values are
calculated and the top ten values of C are stored. This is
done for the eight apertures at the high range. In total, 8
sets of 10 C values are stored. The mean of each set is
calculated, and these virtual points are plotted within an
enlarged view of the ONC central region. The mean
centers from the replacing center iteration of method 1A
are plotted alongside the objects from method lB. This
then shows that both converge toward a small region that
lies above the trapezium star region, including 0 1 Ori C.
Taking the central five method 1B objects, which are
closest to the revolving center method 1A, and
calculating the mean of their R.A. and DEC, we now
have a center that is virtual but robust in its location due
to it being based off of spatial density in the central
region as well as the total distribution throughout the
ONC. The new center for the ONC, which is used
throughout this paper as the center of all following
analyses, is at R.A. = 83.8157, and DEC= -5.37905.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010


' ~ ' ''' ' ' ' ' ' '

.: .
i ;.: ~...
I~I :~
~t.'-:
.. ~. . 4~
- ; "
-
""I.~:'
:"' '
"
I :`L'rr~y~,. i;
i ..
'' '~
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: :: : 1::c ..
: ; r r.
;

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LAUREN P. KELLEY


Table 1: Demographic Information (N=70)
Alzheimer's disease (n=42)
Age
Education
MMSE
GDS
Small vessel vascular disease (n=28)
Age
Education
MMSE
GDS


Minimum
66
2
16
0
Minimum
65
4
14
0


Figure 2: An MRI scan demonstrating lacunes.


primarily to the subcortical nuclei, including the basal
ganglia. These lenticular striate arterioles are the smallest
in the intracranial region; thus they are prone to acute
changes in blood pressure. Therefore, it is predicted that
the basal ganglia in the sVD diagnosed patients will
present with a greater lacune volume.


Methods

Participants
The data collection was selected from a sample of 158
volumetric T-1 weighted brain MRI scans of dementia
patients enrolled in the University of Medicine and
Dentistry of New Jersey, Community Memory Disorder
Center. Seventy brains were analyzed-42 with the
diagnosis of AD and 28 with sVD. The patients were
recruited from an outpatient memory disorder clinic after
being seen consecutively as part of a memory assessment
program. All subjects with a history of major strokes and
serious psychiatric disorders were excluded from the study


Maximum
90
16
29
6
Maximum
91
20
27
10


Mean
79.45
12.35
23.02
2.20
Mean
81.36
12.00
22.11
3.71


Std. Deviation
5.21
2.79
3.17
1.86
Std. Deviation
5.59
2.99
2.99
3.52


(Table 1). Informed written consent was obtained
according to Institutional Review Board guidelines and the
Declaration of Helsinki with identifiable information
blinded.

Procedure for Data Collection
A 1.5 Tesla Siemens magnetic scanner was used to
obtain brain MRI data on the outpatient dementia
participants. The volumetric analysis of lacunes was
performed using a visual rating method on Efilm Lite, a
MRI radiological visualization tool. A trained rater
manually measured the diameter of each lacune using an
on-screen mouse-driven ruler. The intra-rater reliability
was r = 0.98 and inter-rater reliability was r = 0.93. The
trained rater was blinded to the patient diagnosis and
demographics to avoid biases. Each of the individual slices
of the T-1 weighted image was scanned for lacunes. On
slices where the largest diameter of the lacunes was
present, the trained rater marked a digital line across the
diameter with an on-screen mouse-driven ruler (see Figure
3). The lacunes volume was estimated using the formula
for the volume of a sphere, and the volumes of all the
lacunes in the single brain were summed to obtain an
overall volume. A more detailed explanation of the lacune
volumes can be found in the Appendix.
Due to difficulty in the differentiation between
perivascular space and lacunes, the following criterion was
used. Only well-defined, dark lesion lacunes with a
diameter > 2 mm that held a stationary position between
slices were graded. This method has been used in other
studies reported in the literature (e.g., Liem et al., 2007).
The location and orientation of the lacunes were then
recorded. The axial brain image was divided into seven
specific areas of interest-four white matter and three gray
matter. The white matter regions consisted of the
infracortical region, periventricular space, deep region, and
the anterior limb of the internal capsule. The infracortical
region was defined as the area V2 cm under the cortical gray


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 4 I Summer 2010






LAUREN P. KELLEY


course, leading to degeneration (Raff, Whitmore, & Finn,
2002). As the dead neurons accumulate, they become
entangled within the plaque, enlarging the mass and
damaging the surrounding tissue (Jekabsone, Mander,
Tickler, Sharpe, & Brown, 2006). In contrast,
neurofibrillary tangles are composed of a protein called
tau, which creates parallel structures within the cell's
nucleus to allow for optimal transport. When tangles occur
the tau becomes twisted, preventing the nutrients and
essential elements from entering the cell, leading to
neuronal malnourishment and death. These tangles tend to
aggregate throughout the course of AD, accumulating in
the cortex associated with cognitive domains (Binder,
Guillozet-Bongaarts, Garcia-Sierra, & Berry, 2004). As
AD progresses, a typical pattern of amyloid plaque and
tangles begin occurring, specifically around the cortex in
the amygdala and hippocampus region. These amyloid
plaques and neurofibrillary tangles deplete brain tissue,
resulting in forgetfulness and confusion (Anderton, 1997),
and increase in number as the disease progresses, gradually
spreading outward to other areas pfthe cortex.
A subtype of vascular dementia, sVD affects the brain
by interrupting the brain's blood vessels, thereby resulting
in tissue death of the area supplied by the vessel (see
Figure 1). Clinically, these patients present with executive
dysfunction, slowed information processing, and
subsequent cognitive impairment (Libon, Price, Garrett, &
Giovannetti, 2004). Strokes occur when a major vessel
hemorrhages or becomes obstructed and damages a
significant amount of surrounding tissue. In contrast, sVD
typically includes small, "silent," or "mini" strokes. These
strokes can occur without noticeable symptoms. On
magnetic resonance imaging (MRI), these appear as small
holes called lacunes (see Figure 2). Over time, an
accumulation of these lacunes is believed to disrupt brain
function in a pattern that can be confused for AD by some
general physicians.
Increasing research illustrates the complexity of AD
and sVD diagnosis due to their overlapping pathological
markers (Roman, 2004; Barker et al., 2005) and has
revealed that the actual number of true AD cases is
significantly lower than previously recorded (Victoroff,
Mack, Lyness, & Chui, 1995). Bowler, Munoz, Merskey,
and Hachinski (1998) supported this finding after
reassessing 307 previously diagnosed AD patients. They
found that there were two underlying fallacies contributing
to the increased positive predictive value for diagnosis of
AD. The first was due to "verification bias,"- the inability
to wait for the AD population to die in order to reveal true
diagnoses, as definite AD can only be diagnosed at
autopsy. The second factor attributes to co-morbidity, or
underlying diseases occurring in conjunction with AD.
This poses a serious issue, especially in the drug therapy


treatment used with AD patients. Depending upon the
progression of the confounding disease and its effect on
cognition, the drug therapy may not address the proper
disease. At the conclusion of the study, the original
positive predictive value of 78% reduced to 44% taking
these two factors into effect, thus supporting the difficulty
in differential diagnosis for AD.
Furthermore, another study showed that 86% of the
patients diagnosed with AD had an additional underlying
cause contributing to the dementia, with a substantial
amount due to cerebrovascular factors (Helzner et al.,
2009). This means that many patients with AD may have
evidence of vascular damage contributing to their cognitive
decline as well. Barba et al. (2000) and DeCarli (2003) are
in agreement that vascular disease contributes to the
increased diagnosis of vascular dementia and AD. They
found that stroke, hyperinsulinemia, diabetes mellitus,
current smoking, and hypertension are linked with an
increased risk of AD, and only high cholesterol and low
density lipoprotein cholesterol increase vascular dementia
risks (Helzner et al., 2009). In fact, the results of the study
showed that the contributing vascular factors increased the
progression of AD and are thought to "increase oxidative
stress or activate a neuroinflammatory response, triggering
amyloid production" (Helzner et al., 2009, p. 346). As the
formation of amyloid is a common characteristic associated
with AD, this result further illustrates the complexity of
diagnosing these two disorders.
Patients diagnosed with sVD may also present with
significant cortical and hippocampal atrophy, two defining
characteristics of AD (Laakso et al., 1996; Fein et al.,
2000). Furthermore, there are a number of diagnostic
criteria used to identify patients with varying levels of
sensitivity and specificity; for example, a patient may be
diagnosed with sVD with one method but not qualify using
a different set of criteria (i.e. the Alzheimer's Disease
Diagnostic and Treatment Centers [ADDCT] and the
National Institute of Neurological Disorders and Stroke
and Association Internationale pour la Recherche et
l'Enseignement en Neurosciences [NINDS-AIREN])
(Pohjasvaara, Mantyla, Ylikoski, Kaste, & Erkinjuntti,
2000; Consentino et al., 2004).
Due to the difficulty differentiating AD and sVD, our
group investigated lacunes, a vascular associated marker,
to determine if lacunes were also present in AD patients.
As mentioned above, lacunes are silent strokes that cause
necrosis of brain tissue, potentially producing memory and
other cognitive deficits (Desmond, Moroney, Sano, &
Stem, 2002). Lacunes result from an occlusion or rupture


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 4 I Summer 2010
2





SEASONAL DIFFERENCES IN NUTRIENT ALLOCATION OF ARCTIC TUNDRA VEGETATION


Graminoids
80 Shoots
70 : Roots and Rhizomes










80 6
70
e 60


0
50


0
0
z20
10

0
June 4 June 26 Aug 9

Vaccinium uliginosum
80-

70
7 Leaves
e' 60 m stems

2 50
0
o. 40

030
20

10

0
June 4 June 26 Aug 9


Rhododendron subarcticum
60 -
Leaves
Stems
50 4 stems

, 40
0
1 30


S20
z
10

0
June 4 June 26 Aug 9

Community Woody Belowground
160

140 .

120

9 100
0
- 80

0 60
40
20 40

20

June 4 June 26 Aug 9


Vaccinium vitis-idaea


20
Ci4
E


0.
'15

10
2
z5


0
June 4


Figure 3:_Division of nitrogen pools for
aboveground biomass between stems and leaves
for Rhododendron subarcticum, Vaccinium
vitis-idaea, Vaccinium uliginosum; between
aboveground shoots ,belowground roots, and
rhizomes in case of graminoids; and between
woody community roots and rhizomes. Error
bars represent SE. Sample sizes differ for
aboveground biomass between June 4 and
August 9 (n=3) and June 26 (n=2), with the
June 4 time point for V. uliginosum having
(n=2). The June 26 time point for V.
uliginosum has a single sample (n=1) and thus
lacks error bars. Belowground biomass for
graminoids has the same sample size (n=3) at
each time point, as did the woody belowground
community roots and rhizomes.


June 26


f=2.15, p=0.17). Leaf N pools for V vitis-idaea peaked
at 16.8 g/m2 in the middle of the growing season,
concurrently with stem N pools, which peaked at 5.3
g/m2 (Figure 3). Variation across the growing season was
significant, as were differences between tissue and the
interaction between date and tissue (two-way ANOVA,
date effect f=14.2, p<0.05; tissue effect f=10.3, p<0.05;
date x tissue f=4.2, p<0.05). Leaf N pools for V.
uliginosum did not vary strongly across the season, but
they had a slight decline of about 4 g/m2 between June 4
and August 9 (Figure 3). Stem N pools also declined
across the growing season, and the differences between
tissues approached significance (two-way ANOVA, date
effect f=0.71, p=0.42; tissue effect f=4.73, p=0.07, date
x tissue f=0.05, p=0.82).
For woody belowground tissues, roots and rhizomes
had opposing trends. Woody root N pools decreased by
almost 28 g/m2 across the growing season, while woody
rhizome N pools increased by over 102 g/m2 (Figure 3).
This large increase in the rhizome pool drove the overall
large increase in the woody belowground pool. Variation
across the season and tissue differences were significant,
as was the interaction effect between them (two-way
ANOVA, date effect f=5.8, p<0.05; tissue effect f=42.0,
p<0.05; date x tissue f=l1.1, p=0.05).


15N Isotope Analysis
Significant differences exist in "N enrichment
between every species and functional group (one-way
ANOVA, f=178.9, p<0.0001). Graminoids are the most
enriched, with a mean of 1.03 (Figure 4). Mosses were
somewhat depleted, with a mean of -4.14 (Figure 4). The
three woody species R. subarcticum, V vitis-idaea, and
V uliginosum were the most depleted, with means of -
8.40, -9.92, and -5.56, respectively (Figure 4).


o0

-2

-4

-6

-8

10

-12
Graminoid L decumbens V. uliginosum


Figure 4: 15N enrichment differences between functional
group/species.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010
4


Aug 9






INFORMATION RECALL


Appendix B


Mom, in spite of being in the middle of working on the
computer, called Anna to the phone. Anna and Rick, her
brother, were invited to a pool party given by a friend.
Mom said they could go if it did not rain. The afternoon
of the pool party arrived. The children, who had finished
their homework before dressing for the party, were very
excited. At the last minute, Anna called her friend and
explained that they would have been able to go except
for the weather.


P # Written Oral
1 Mom in middle of 2
2 working on computer
3 Mom called Anna
4 3 to phone
5 Despite 1, 3
6 Anna and Rick
7 Rick is brother of Anna
8 6 were invited
9 8 to party
10 Pool party
11 10 given by friend
12 Mom said 15
13 6 could go to party
14 no rain
15 If 14, 13
16 Afternoon of party
17 16 arrived
18 Children were excited
19 Very 18
20 The children dressed
21 20 for party
22 Children finished
homework
23 22 before 20
24 Anna called friend
25 At the last minute 24
26 Anna explained 27
27 Would have been able to 28
28 They go to party
29 27 except for 30
30 Weather

Total


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010


APPENDIX A







LAUREN P. KELLEY


Desmond, D. W., Moroney, J. T., Sano, M., & Stern, Y.
(2002). Mortality in patients with dementia after ischemic stroke.
Neurology, 59, 537-543.

Fein, G., Di Sclafani, V., Tanabe, J., Cardenas, V., Weiner,
M. W., Jagust W. J., et al. (2000). Hippocampal and cortical
atrophy predict dementia in subcortical ischemic vascular
disease. Neurology, 55, 1626-1635.

Helzner, E. P., Luchsinger, J. A., Scarmeas, N., Cosentino,
S., Brickman, A. M., Glymour, M. M, et al. (2009). Contribution
of vascular risk factors to the progression in Alzheimer disease.
Archives oJ ... in. I. ..-,; 66(3), 343-348.

Jekabsone, A., Mander, P. K., Tickler, A., Sharpe, M., &
Brown, G. C. (2006). Fibrillar beta-amyloid peptide A31-40
activates microglial proliferation via stimulating TNF-a release
and H202 derived from NADPH oxidase: a cell culture study.
Journal ofNeuroinflammation, 3(24).

Laakso, M. P., Partanen, K., Riekkinen, P., Lehtovirta, M.,
Helkala, E. L., Hallikainen, M., et al. (1996). Hippocampal
volumes in Alzheimer's disease, Parkinson's disease with and
without dementia, and in vascular dementia: An MRI study.
Neurology, 46(3), 678-681.

Libon, D. J., Price, C. C., Garrett, K. D. & Giovannetti, T.
t211 i4). From Binswanger's disease to leuokoaraiosis: What we
have learned about subcortical vascular dementia. The Clinical
Neuropsychologist, 18(1), 83-100.

Libon, D. J., Price, C. C., Giovannetti, T., Swenson, R.,
Bettcher, B. M., Heilman, K. M., et al. (2008). Linking MRI
hyperintensities with patterns of neuropsychological impairment:
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Liem, M. K., van der Grond, J., Haan, J., van den Boom, R.,
Ferrari, M.D., Knaap, Y. M., et al.
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cognitive dysfunction in CADASIL. Stroke, 38, 923-928.

Loring, J. F. (2005). Stem cells as delivery vehicles to target
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asp

Mohs, R. C., Doody, R. S., Mooris, J. C., leni, J. R., Rogers,
S. L., Perdomo, C. A., et al. (2001). A 1-year, placebo-controlled
preservation of function survival study of donepezil in AD
patients. Neurology, 57, 481-488.

National Institute of Neurological Disorders and Stroke
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27, 2008, from
http://www.ninds.nih.gov/disorders/dementias/dementia.htm


Nagy, Z., Esiri, M. M., Jobst, K. A., Morris, J. H., King, E.
M., McDonald, B., et al. (1997). The effects of additional
pathology on the cognitive deficit in Alzheimer disease. Journal
of .,i,, /.'' I,. '.-.-\' & Experimental Neurology, 56(2), 165-170.

Pohjasvaara, T., Mantylii, R., Ylikoski, R., Kaste, M., &
Erkinjuntti, T. (2000). Comparison of different clinical criteria
(DSM-III, ADDTC, ICD-10, NINDS-AIREN, DSM-IV) for the
diagnosis of vascular dementia. Stroke, 31, 2952-2957.

Price, C. C., Jefferson, A. L., Merino, J. G., Heilman, K. M.,
& Libon, D. J. (2005). Subcortical vascular dementia: Integrating
neuropsychological and neuroradiologic data. Neurology, 65(3),
376-382.

Raff, M. C., Whitmore, A. V., & Finn, J. T. (2002). Axonal
self-destruction and neurodegeneration. Science, 296(5569), 868-
871.

Roman, G. C. (2"'14). Facts, myths, and controversies in
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2), 49-52.

Thomas, D.A., Libon, J.D., & Ledakis, G.E., (2005).
Treating dementia patients with vascular lesions with donepezil:
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Victoroff, J., Mack, W.J., Lyness, S.A., & Chui, H.C.
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Zarow, C., Barron, E., Chui, H. C., & Perlmutter, L. S.
(1997). Vascular basement membrane pathology and
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147)., New York: New York Academy of Sciences.

Appendix

Lacune Measurement. Initially, the volumetric analysis
of lacunes was performed using a visual rating method on
Efilm Lite, a MRI radiological visualization tool. Once the
image was loaded, it was important to adjust the contrast to
better visualize the structures in the brain and the lacunes.
With the contrast adjusted, each slice was systematically
analyzed to identify the dark spherical lacunes. When a
lacune was located, the magnifying glass on the tool bar
was used to zoom in. Zooming provided better accuracy
when measuring the diameter of the lacunes. The next step


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 4 I Summer 2010
8







VOLUMETRIC QUANTIFICATION OF LACUNES IN AD AND SVD


demonstrated a significant improvement in working
memory tests and delayed recognition memory, both of
which continued to improve over time. Similarly, the
patients with AD also showed improvement on the working
memory tests. However, in patients with AD, dopenezil
functions primarily to maintain cognitive functioning and
delay progressive declines. These findings are imperative
for determining the impact of these medications between
diagnoses. Knowing the effects and the improvements from
medications such as donepezil on individuals with varying
levels of vascular disease may lead to improvements in
quality of life for patients as well as less burden for
caregivers.
The current study has a number of strengths. First, the
measurement approach to quantifying lacune volume was
highly reliable among an individual's multiple ratings as
well as between different raters. This reliability provides
researchers a defined method for lacunes quantification, as
the existing literature to date is vague on a methodological
approach. In addition, each rater was blinded to clinical
diagnosis to minimize bias. Finally, power analysis based
on the effect size of these data revealed that an unattainable
sample size would be necessary to find statistical
significance, thus supporting the non-significant results.
The current study presents a few limitations. First, we
assume healthy people do not have lacunes; however, a
control group of healthy adults would provide a
comparison group for determining if variability exists
among healthy older adults. Given the relatively large
amount of variability observed in the current patient
sample, particularly among those diagnosed with AD (see
Figure 4), it would be informative to know if this widely
variable pattern occurs in relatively healthy older adults as
well. Second, relevant medical history data were
unavailable for this patient sample and may have helped
explain the similarities between the two diagnostic groups
and some of the variability observed. Despite these
limitations, we believe this study provides convincing
evidence of vascular pathology in a group of AD as well as
sVD patients.
In summary, our study further demonstrated the
complexity involved in the differential diagnosis of AD
and sVD and how these two disease processes are
commonly occurring simultaneously. Moreover, the use of
MRI markers has become a productive area of
investigation for separating these two diseases. Lacune
volume, the investigated variable in our study, did not
prove significant alone; however, it is known to have an
effect on cognition. The combined impact of LA and
lacune volume on cognitive abilities in patients with
dementia will require further investigation in the future.


References

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Parallel organization of functionally
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Alzheimer's Association (2008). What is Alzheimer's?
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http://www.alz.org/alzheimers_diseasewhat is alzheimers.asp

Anderton, B. H. (1997). Changes in the ageing brain in
health and disease. Philosophical Transactions of the Royal
Society B: Biological Sciences, 352(1363), 1781-1792.

Barba, R., Martinez-Espinosa, S., Rodriguez-Garcia, E.,
Pondal M., Vivancos, J., & Del Ser, T.
(2000). Post stroke dementia: clinical features and risk
factors. Stroke, 31(7), 1494-1501.

Barker, W. W., Luis, C., Harwood, D., Loewenstein, D.,
Bravo, M., Ownby, R., et al. (2005).
The effect of a memory screening program on the early
diagnosis of Alzheimer disease. Alzheimer Disease and
Associated Disorders, 19(1), 1-7.

Binder, L. I., Guillozet-Bongaarts, A. L., Garcia-Sierra, F.,
& Berry, R. W. (2005, Jan.). Tau, tangles, and Alzheimer's
disease. Biochimica et BiophysicaActa, 1739(2-3), 216-223.

Bowler, J. V., Munoz, D. G., Merskey, H., & Hachinski, V.
H. (1998). Fallacies in the pathological confirmation of the
diagnosis of Alzheimer's disease. Journal of Neurology,
Neurosurgery, andPsychiatry, 64(1), 18-24.

Burns, A., Rossor, M., Hecker, J., Gauthier, S., Petit, H.,
Miller, H. J., et al. (1999). The effect of donepezil in
Alzheimer's disease: Results from a multinational trial. Dementia
and Geriatric C. .g'~in Disorders, 10(3), 237-244.

Cosentino, S. A., Jefferson, A. L., Carey, M., Price, C. C.,
Davis-Garrett, K., Swenson, R., et al. (2003). The clinical
diagnosis of vascular dementia: A comparison among four
classification systems and a proposal for a new paradigm. The
Clinical Neuropsychologist, 18(1), 6-21.

Crystal, H. A., Dickson, D., Davies, P., Masur, D., Grober,
E., & Lipton, R. B. (2000). The relative frequency of "Dementia
of Unknown Aetiology" increases with age and is nearly 50% in
nonagenarians. Archives oj .,.i .. .. -, 57(5), 713-719.

DeCarli, C. (2003). The role of cerebrovascular disease in
dementia. The Neurologist, 9(3), 123-136.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 4 I Summer 2010





THERMAL PROTECTION SYSTEMS FOR FUTURE SPACE VEHICLES


increase in the factor of safety overall. However, this was
likely because the layers where failure occurred were
removed. The overall stress magnitude of the layers that
remained did not change significantly.

Future Work
It was found that the FGM could potentially be used as
part of a TPS. However, the FGM is likely not best for an
entire TPS due to weight and insulation considerations.
The FGM can be tailored to reduce thermal stresses so as
to not have failure occur. However, layers may have to be
removed such that the FGM only transitions from 80%
metal and 20% ceramic to 20% metal and 80% ceramic, for
example.
Before an FGM could be used on a TPS, it is important
to note the future work that must be completed. The von
Mises failure stress used, as well as the effective yield
strength used found through the rule of mixtures, may not
be the ideal failure analysis to use. Other failure modes
should be investigated given the nature of this FGM
application. Crack propagation and delamination should
also be investigated.
Once the behavior of this type of composite is better
understood, it may become useful in many applications,
including in TPSs, aircraft turbine blades, and military
armor.

References

Aboudi, J., Pindera, M.J., & Arnold, S. M. (2001). Higher
Order Theory for Functionally Graded Materials.
Retrieved April 1, 2009, from NASA:
http://www.grc.nasa.gov/WWW/RT/RT2000/5000/592
Oamold3 .html

Bapanapalli, S. K., Sankar, B. V., Haftka, R. T., Gogu, C.,
& Blosser, M. L., (2007). "Design of an integrated
thermal protection system." Manuscript submitted for
publication.


Lee, C. S., Kim, S. G., Ahn, S. H., DeJonghe, L. C., &
Thomas, G., (2007). "Three dimensional analysis of
thermal stress and prediction of failure of
polytypoidally joined Si3n4-A12o3 functionally graded
material", Materials Transactions 48(9), 2489-2493.

Materials Aluminum Oxide (A1203) Properties. (2002).
Retrieved April 1, 2009, from Accuratus Corporation:
http://www.accuratus.com/alumox.html

Nemat-Alla, M. (2003). Reduction of thermal stresses by
developing two-dimensional functionally graded
materials. International Journal of Solids and
Structures 40(26), 7339-7356.

Nickel 200/201. (2009) Retrieved April 1, 2009, from Pai,
Inc.: www.painc.com/nickel_200_201 .htm

Ruys, A. & Sun, D. (2002). Functionally graded materials
and their production methods. AZo Journal of
Materials Online. Retrieved April 1, 2009, from
AZoM:
http://www.azom.com/Details.asp?ArticlelD=1592

Sankar, B. V., & Tzeng, J. T. (2002). Thermal Stresses in
Functionally Graded Beams. AIAA Journal, 40(6),
1228-1232.

Suresh, S. & Mortensen, A. (1998). Fundamentals of
functionally graded materials. London: Maney
Publishing.

Wilson, J., Ed. (2003, Aug.). Report of Columbia Accident
I, .r ig,,i, I Board, Volume I. Retrieved April 1,
2009, from NASA:
http://www.nasa.gov/columbia/home/CAIBVol 1 .html


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010







VOLUMETRIC QUANTIFICATION OF LACUNES IN AD AND SVD


was to select the ruler on the tool bar to calculate the size
of the individual lacune. This was accomplished by placing
the cursor on the right side of the lacune and dragging the
cursor across the widest diameter point. A number was
displayed that indicated the calculated diameter in
centimeters. The images below illustrate how lacunes
appear in their original size and after the image has been
enlarged to better visualize them for measurement.
Next, in each individual lacune with a diameter greater
than 0.2 cm, the measured diameter was used to calculate
the estimated lacune volume using the standard formula for
the volume of the sphere (volume= 4/37rr3). Once all of the
lacune volumes were calculated, each was recorded
according to region.
The location and orientation of the lacunes were then
recorded. The axial brain image was divided into seven
specific regions of interest-four in white matter regions
and three in subcortical gray matter structures. The white
matter regions consisted of infra-cortical, periventricular,
deep, and the anterior limb of the internal capsule. The
infracortical region was defined as the area V cm under the
cortical gray matter; the periventricular region was
comprised of the area V2 cm around the lateral ventricles;
deep was between the infracortical and periventricular
regions. The subcortical gray matter structures of interest
assessed were the caudate, thalamus, and basal ganglia
(specifically, the putamen and globus pallidus). Each of the
lacunes was recorded in a spreadsheet according to the
region where they were located as well as the left or right
orientation of the brain.


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University of Florida I Journal of Undergraduate Research I Volume 10, Issue 4 I Summer 2010







Functionally Graded Thermal Protection Systems for Future
Space Vehicles


Marlana Behnke


College of Engineering, University of Florida


High thermal stresses develop when two different types of materials (such as a metal and ceramic) are bonded
together. This is often the case in thermal protection systems (TPS) for reentry vehicles that need to be both insulative
and structurally strong. The thermal stresses developed in a two-component composite that gradually changes from one
material composition to another, also known as a functionally graded material (FGM), were studied to determine if
there are advantages to using an FGM as part of a TPS. Finite element analysis was used to study the heat loads that
occur during spacecraft reentry. These heat loads were applied to a three-dimensional finite element model of the FGM
composed of 100% aluminum oxide in the top layer and 100% nickel alloy in the bottom layer, with either a linear or
an elliptical functional variation between these outermost layers. Thermal stresses and strains were examined to
determine the advantages of using an FGM. The study found that using an FGM does allow for material tailoring that
will prevent failure. However, prevention of failure in the material is not guaranteed. Using von Mises stress failure
criteria, the materials were shown to fail at certain percent compositions. If the sections of the material that failed are
removed, failure can be prevented, but the material will not vary from 100% ceramic to 100% metal. It will only vary
from 80% metal to 80% ceramic, for example. It is therefore plausible to use an FGM as part of a TPS.


INTRODUCTION

The thermal protection system (TPS), or heat shield, is a
critical component of a spacecraft that enters an
atmosphere. When a spacecraft enters a planetary
atmosphere, it is travelling at hypersonic speeds, resulting
in significant aerodynamic heating that would destroy a
vehicle with no TPS. The high temperatures developed
over the vehicle result in structural deformations due to
large thermal loads. Currently there are two common types
of TPS: ablators and tiles and blankets. The former
Mercury, Gemini, and Apollo missions, as well as current
Soyuz missions, use an ablator that bums off of the vehicle
as it absorbs the heat. The Space Shuttle Orbiter currently
uses High Temperature Resistant Ceramic Tiles and
Blankets that act as insulators.
These types of TPS are structurally weak and can easily
become damaged, as in the Space Shuttle Columbia
accident (Wilson, 2003). Integrating a metal into the TPS
could improve the strength. However, abrupt transitions in
material composition and properties usually result in sharp
local stress concentrations (Suresh & Mortensen, 1998).
The large difference in coefficients of thermal expansion of
a metal and ceramic will lead to large thermal stresses
when a large heat flux is applied, as is the case during


reentry. These stresses can be reduced if the transition from
one material to the other is gradual. Therefore, the use of a
functionally graded material (FGM) is appropriate. An
FGM is a two-component composite that gradually
changes from one material composition to another (Ruys &
Sun, 2002). Suresh and Mortensen (1998) provide the
reader with an overview of FGM characteristics and
manufacturing processes. Figure 1 is an illustration of an
FGM in which the white could represent ceramic and the
black represents a metal. In an FGM, aside from magnitude
of the thermal stresses being minimized, the onset of
plastic yielding and failure can be delayed, large stress
concentrations can be suppressed, strength of the interfacial
bond can be increased, and crack propagation can be
reduced (Mortenson, 1998).
The purpose of the study described below is to deter-
mine to what extent the FGM is useful in reducing thermal
stresses for TPS applications. In Sankar and Tzeng (2002),
an elasticity solution showed that an FGM does reduce the
thermal stresses when modeled as a beam with an expo-
nential temperature variation that varies in the opposite
direction of the elastic constants. The thermal stresses in a
two-dimensional FGM (material composition changes in
two directions) modeled as a plate have also been studied
and shown to reduce thermal stresses (Nemat-Alla, 2003).


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010





CHASE MASON


is probably driven by V. uliginosum. This storage
allows V. uliginosum to leaf out quickly after spring
thaw and to enjoy both rapid growth and high
photosynthetic capacity (Chapin et. al, 1980).
Evergreen shrubs like R. subarcticum and V. vitis-
idaea take an opposing strategy, maintaining large stores
of N in their perennial leaves and much less in storage
organs relative to deciduous species (Chapin et al.,
1980). Such species invest both nutrients and carbon in
the defense and maintenance of their leaves, and as such
they do not need the large pulse of spring nutrients
afforded by deciduous storage organs (Chapin et al.,
2002). Evergreen species do, however, produce new
foliage each year, but they do so at a later date than
deciduous shrubs (Chapin, 1980), allocating extra N to a
handful of new leaves in order to better take advantage
of favorable photosynthetic conditions (Zhang et al.,
1997). Both species in this study showed a peak in leaf
N pools in the middle of the growing season. However,
the large fluctuation in the V. vitis-idaea leaf N pool
across the season was likely due to undersampling, but
the relative proportion of leaf:stem pool sizes is
consistent with a delayed production of new foliage.
The evergreen strategy employed by both R.
subarcticum and V. vitis-idaea involves the production
of a much larger leaf biomass, and thus these species
maintain a much larger yet diffuse N pool in their leaves.
This runs counter to the deciduous approach, whereby V.
uliginosum maintains a higher leaf N concentration in a
smaller pool of photosynthetic biomass, achieving an
equivalent level of functionality.
While no overall trends have been found
distinguishing the evergreen and deciduous strategies
with regard to nitrogen reabasorption efficiency,
individually V. uliginosum has been found to be 3.5
times as efficient in reabsorbing leaf N than V. vitis-
idaea (Eckstein et al., 1998). This efficiency may in part
help explain the large persistent stem N pool in V.
uliginosum as well as partially explain a mechanistic
difference in the life history strategies of these
congenitors.

Nitrogen Sources and Pathways
The strong differences in 15N isotope signatures
between graminoids, mosses, and woody species are best
explained by disparities in N source and uptake pathway.
Miller and Bowman (2002) found that 15N enrichment
was highly correlated with higher ammonium (NH4)
uptake relative to nitrate (N03), which suggests that the
graminoids in our study were likely getting the bulk of
their nitrogen from NH4. The woody species in our
study had depleted 15N signatures, suggesting both a
source and a pathway of nitrogen uptake. The species
tested in Miller and Bowman (2002) that had a depleted
15N signature preferentially took up N03 over NH4 at a
ratio of 3:2. Another cause of this depletion is that R.


subarcticum, V. vitis-idaea, and V. uliginosum are all in
the family Ericaceae and possess ericoid
ectomycorrhizal fungi. The extra biochemical reactions
needed to acquire nutrients via ectomycorrhizae, each of
which selects against the heavier isotope, results in
depletion of leaf 15N signatures.

A Changing Arctic
The Arctic today faces a milieu of challenges, most
anthropogenic in nature. Nitrogen deposition in low-
nutrient tundra ecosystems has increased fourfold in
northern Alaskan over the past 100 years (Jaffe and
Zukowski, 1993). Such inputs of nutrients threaten taxa
adapted to low nitrogen levels, particularly bryophytes
and lichens (Gordon et al., 2001). The competitive
balance between evergreen and deciduous species would
also likely shift in favor of deciduous species, as high
leaf longevity is most beneficial in low-resource
environments (Chapin et al., 2002). Species adapted to
take up nitrogen well from only one source would be at a
competitive disadvantage, a likely scenario in the highly
resource-partitioned tundra (Jonsd6ttir et al., 1995).
Temperature shifts also threaten nutrient dynamics, as an
increased active layer allows for more leaching
(Hinzman et al., 1991) and higher soil temperatures
increase rates of nitrogen and phosphorus mineralization
by microorganisms (Nadelhoffer et al., 1991). Arctic
plant communities are potentially highly sensitive to
even small changes in nitrogen cycling, whether via
inputs from afar or through faster soil turnover.
The information on tundra plant nitrogen allocation
supplied by this study provides a useful baseline for
further investigation into the effects of temperature
increase, permafrost thaw, nutrient deposition, and many
other factors. Such study is needed to predict the
ultimate fate of increased nitrogen inputs in this system,
the allocation dynamics of other limiting nutrients like
phosphorus, and the makeup of arctic plant
communities.

ACKNOWLEDGMENTS
I would first like to thank my graduate student
mentor Caitlin Hicks, without whom none of this would
be possible. In addition to the long hours spent in the
field collecting the samples used in this study, Caitlin
devoted countless hours of advice and guidance to this
work, including thoughtful explanation of novel and
complex scientific concepts, editorial supervision, and a
grounding perspective. I also thank Grace Crummer for
cheerful assistance with elemental analysis and mass
spectroscopy as well as general lab procedure. I, of
course, thank my faculty advisor Ted Schuur and the
Ecosystem Dynamics Research Lab at the University of
Florida for access to lab equipment, guidance, and
editorial input.


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010
6






LAUREN P. KELLEY


Table 3: Mean and Standard Deviation of Lacunar Volume by
Regions (mm3)
White matter region Alzheimer's Vascular
disease (n=42) dementia
(n=28)
Infracortical region 0.53 + 2.49 0.98 + 3.19
Periventricular region 1.47 6.25 1.49 4.04
Deep region 1.89 7.00 1.50 4.48
Internal capsule 1.51 3.90 0.08 + 0.41
Total white matter lacunes 5.40 + 14.19 4.05 + 7.88
Gray matter region
Caudate 0.20 + 1.29 0.15 + 0.79
Thalamus 0.13 0.86 0.29 1.06
Basal ganglia 4.33 17.52 7.09 17.23
(putamen, globus pallidus)
Total gray matter lacunes 4.66 17.55 7.53 17.12



Table 4: T-test (df=68) Results for Separated White and Gray
Matter Regions
White matter region AD vs. sVD
Infracortical region t = -0.66; p = 0.51
Periventricular region t = -0.11; p = 0.99
Deep region t = 0.26; p = 0.80
Internal capsule t = 1.92; p = 0.06
Total white matter lacunes t(68) = 0.46, p = 0.65
Gray matter region
Caudate t = 0.70; p = 0.86
Thalamus t = -0.68; p = 0.50
Basal ganglia t = -0.65; p = 0.52
(putamen, globus pallidus)
Total gray matter lacunes t(68) = -0.68, p = 0.50



Discussion

In this study, the results reveal no significant difference
in lacune volume among a moderate dementia group of
individuals diagnosed clinically with AD and sVD. Thus,
these data lend support to recent studies reporting
increasing vascular disease in patients with AD (Crystal et
al., 2000; Nagy et al., 1997). In addition, this study goes
beyond looking at total lacune volume alone: separate
brain regions were examined that have distinct, small
vessel vascular supplies, and no significant differences
were found between the two patient groups in any of these
regions of interest.
Contrary to expectations, there was similar lacune
volume in the deep white matter regions of the brain as
well as in subcortical gray matter nuclei such as the
thalamus, basal ganglia, and caudate. These regions have
key connections to the gray matter of the frontal lobes as
they are important for maintaining concentration,
sustaining effort over time, and information processing


speed (Alexander, DeLong, & Strick, 1986). Traditionally,
sVD has been considered a disease process affecting only
the deep white matter and subcortical nuclei, with a relative
sparing of these regions in pure AD or early stage AD.
Lacunes within these regions in AD patients can potentially
result in disruption to frontal subcortical path\\ an s Future
studies need to examine if the extent of lacune volume in
these regions for AD patients contributes to a decline in
frontal functions, thereby making them look clinically
similar to sVD patients.
Although lacunes were the area of interest for this
study, different markers of vascular pathology seen on MR
imaging have been investigated. Leukoaraiosis (LA)
specifically appears on MR imaging as hyperintense areas
within the white matter of the brain. LA has been known to
occur in healthy older adults but greater amounts appear in
dementia. Previous research has shown that at least 25% of
the brain's white matter needs to contain LA in order for
cognitive decline to occur (Price et al., 2005; Libon et al.,
2008). To date, no research has examined the combined
impact of LA and lacunes; however, this examination
would be advantageous if all brain variables could be
measured and examined in comparison to brain functions.
Overall, this study suggests that individuals with
clinically diagnosed AD also present with vascular disease
marker of lacunae throughout the brain. Existing literature
also supports these findings. Romin (2004) supports our
suggesting that vascular dementia is an underlying factor in
AD, as vascular disease generally increases with age. This
is supported by recent observations that AD patients in
their 70s and 80s often have vascular disease in addition to
other pathologies (Helzner et al., 2009). Recent research
has also suggested that sVD may accelerate or facilitate
other AD-like pathology, thus increasing overlap in
pathology between the two diagnoses (Zarow, Barron,
Chui, & Perlmutter, 1997).
Imaging evidence of vascular disease in AD may be
clinically relevant. There are some suggestions that patients
with vascular disease may respond better to memory
medications (Thomas, Libon, & Ledakis, 2005). \ Thomas
et al. (2005) study examined the efficacy of donepezil
hydrochloride, also known as AriceptTM, a frequently
prescribed drug for AD known to inhibit
acetylcholinesterase, on slowing the cognitive and
functional loss in AD. Other research has shown that in
patients with AD show improvement in preserving
cognitive and functional abilities after a 16-week treatment
(Burs et al., 1999), and the normal decline slowed by five
months (Mohs et al., 2001). This is the finding with
donepezil in AD, however, as increasing literature suggests
overlap in pathologies between AD and sVD. Thomas et al.
(2005) study examined the influence of donepezil in both
of these patient groups. The patients with sVD


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 4 I Summer 2010
6






STEPHANIE ISHII


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"w *+ FM 100
S0 FOLYORGS

-10
Equ. Conc., mg/L



c. 3-pentanol

35
30 BET 1000
25 BET 1300
20 -B
S.15 ACFELT1000
10 AC FELT 1300
"5.S x ACFELT1500
S5 *FMO--
S0 FM 10p
+ _______+___ FM100
"5 t I j- 'a 1t F,,
S -FOLYORGS
H 10
-15
Equ. Conc., mg/L



d. 1-pentanol


35
30 *BET 100
25 BET 1300
20 t
.U ACFELT 1000
15 *
f AC FELT 1300
1 10 -- -----
5 x AC FELT 1500
FM10
0 di + FM 100
S "5 t' J j ij i, I'l, a t + FMl.
S10 FOLYORGS

-15
Equ. Conc., mglL


e. 1-hexanol

100

80 z BET 1000
*BET 1300
S60 AC FELT 1000
c40 AC FELT 1300
40 ------
S -' x AC FELT 1500
20-- FM 10
+ FM 100
0 FOLYORGS

-20
Equ. Conc., mg/L



f. 2,4-DMP


90
80 - BET 100
70 BET1300
60 ACFELT 1000
50 AC FELT 1300
S40 x AC FELT 1500
t 30 FM10
S20 + FM 100
S10 IFOLYORGS
0 l
0 200 400 600 800
Equ. Conc., mg/L



g. 1-heptanol

300
BET 1000
250 BET 1300

200 AC FELT 1000
1, AC FELT 1300
S150--*---
1 x AC FELT 1500
100 -' -- FM10

I FOLYORGS

0 100 200 300 400 500 600
Equ. Conc., mg/L




Figure 7: Sorption isotherm curves from the preliminary
test data concerning all nine fabric choices. Each graph
represents a different tracer, going from shortest-chain
alcohol (highest aqueous solubility) to longest-chain
alcohol (highest tendency to sorb).


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010

8







Do Northern Mockingbirds Change Their Songs to Compensate for

Urban Noise?


Puja Patel


College of Liberal Arts and Sciences, University of Florida


Urban environments are characterized by increased anthropogenic noise. This increased low-frequency urban noise may interfere with
the song transmission of resident birds. Because birds use songs for communication, territory defense, mate attraction, and predator
avoidance, they must be able to adapt their songs to be heard in noisy areas to keep their territories and retain their mates. Based on
previous studies of the adjustment of song in other bird species, we hypothesized that Northern Mockingbirds (Mimus Ip.1. 1-.m
adjust their song according to their habitat and urban mockingbirds sing at a higher minimum frequency than do non-urban
mockingbirds. Singing male mockingbirds and ambient noise were recorded in urban (residential areas, parking lots) and non-urban
(pastures and biological preserve) areas in and around Gainesville, FL. All recordings were digitally analyzed using the program
Raven Pro, and the minimum frequency at which each male sang was calculated. The average power of low-frequency ambient noise
(all sounds below 1.662 kHz, the highest minimum frequency at which any mockingbird sang) was calculated for urban and non-urban
environments. We found that urban areas were significantly louder in low-frequency ambient noise than non-urban areas and that
urban birds sang at a significantly higher minimum frequency than non-urban birds. In addition, there was a significant correlation
between low-frequency ambient noise level and minimum frequency of mockingbird songs. Therefore, mockingbirds are able to adjust
their song to more effectively communicate with each other, which should help them in territory defense, mate attraction, and mate
retention. Thus, mockingbirds' ability to compensate for increased urban noise may be a factor that allows them to successfully
inhabit urban areas.


INTRODUCTION

As humans have urbanized natural habitats, they have
increased ambient noise levels in those areas. If this
increased noise is of the same frequency as the songs of
birds, then it may interfere with song transmission.
Because song is an important component of bird life and
functions in territory defense, mate attraction, and predator
avoidance (Warren et al. 2006), the ability of birds to
compensate for background noise in their environment
could be quite important.
For species that occur in a wide range of natural
habitats, their vocal signals have been shown to differ in
ways that maximize the transmission of the signal and thus
likely represent adaptations to different habitats (e.g. Wiley
1991; Slabbekoor and Smith 2002). In urban
environments, urban great tits (Parus major) have been
shown to sing at a higher frequency to overcome low-
frequency ambient noise (Slabbekoor and Peet 2003),
while urban European Robins (Erithacus rubecula) resort
to nocturnal singing in areas that are noisy during the day
(Fuller et al. 2007). Studies in North America have shown
that in noisier locations Song Sparrows (Melospiza
melodia) sing higher frequency low notes (Wood and
Yezerinac 2006).


It is possible, however, that bird species unable to
adjust their song frequencies to overcome urban noise
avoid dwelling in urban areas, thus decreasing species
diversity and abundance there. Since birds sing to
communicate, an inability to transmit one's song can make
it difficult to hold a territory and attract and retain a mate,
which would have fitness consequences for these
individuals.

Study System
I studied the variation in song frequencies (as a
measure of pitch, in Hz) of the Northern Mockingbird
(Mimus polyglottos) in urban versus non-urban areas.
Unlike other birds that have been previously studied,
mockingbirds mimic songs of the local birds in each
territory and build a diverse repertoire based on the
surrounding bird community and noises from the
environment (e.g. mechanical sounds and sounds of non-
avian species). Individuals learn sounds throughout life and
integrate them into their existing songs to carry an
extensive vocal repertoire as adults (Derrickson and
Breitwisch, 1992). Males often display vocal repertoires
containing more than 150 different song types; however,
vocal repertoires ranging from as low as 45 to as high as
203 different song types have been estimated (Derrickson


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010






THERMAL PROTECTION SYSTEMS FOR FUTURE SPACE VEHICLES


-*- Original Config. -- Extra Layer

0.012


S0.010



0.008
.2
I-
m 0.006

I-
S 0.004

.T
o 0.002


0.000
0.0060 0.0080 0.0100
Strain

Figure 7: Maximum principal strain, elliptical alumina


-- Missing bottom 4 layers


0.0120


0.0140


-- Original Config. -0- Extra Layer -- Missing top 4 layers



















0.00 0.0 100. 20.0 30.0 00.


0.012


0.010



0.008


0.006


0.004


0.002



0.000


0.0 100.0 200.0 300.0 400.0
Stress (MPa)

Figure 8: von Mises Stress at maximum thermal stress, elliptical nickel


500.0 600.0


University of Florida I Journal of Undergraduate Research I Volume 10, Issue 2 I Spring 2010
7