The 7th
Annual
NC
Undergraduate
Summer Research Symposium
Physics REU program –
NCSU
Abstracts are listed in
alphabetical order by the last name of the corresponding author.
|
Aggarwal, Parv |
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Home Institution: |
Duke |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
Dave Aspnes/Physics Simon Lappi/Chemistry |
|
Title of Presentation: |
Reciprocal Space Analysis
of FTIR Spectroscopy |
Two fundamental constraints
encountered in Fourier Transform Infrared (FTIR) spectroscopy are apodization-related line broadening and resolution limitations,
both caused by finite mirror travel. While these constraints are often
mitigated by using large mirror travel distances (>1 m), such
implementations are often not feasible due to size and cost limitations, such
as in the Carbon Cycle Fourier Transform Spectrometer (CC-FTS) satellite
monitoring mission. Such cases require the use of numerical methods to
compensate, at least partially, instrumental constraints. In this study, we
analyze how reciprocal space transformations, used widely in Electro-reflectance
Spectroscopy and Spectroscopic Ellipsometry, can be
applied to overcome mirror travel constraints in FTIR spectroscopy.
|
Akerson, Adrian R. |
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Home Institution: |
Embry-Riddle Aeronautical
University |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
Albert Young/Physics |
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Title of Presentation: |
Measurement and Simulation
of the Temperature Profile for a Thick Si(Li) Detector System |
A measurement of the beta-asymmetry in the decay of polarized 19Ne
was performed at the Princeton cyclotron using two, segmented, lithium-drifted
silicon detectors, or Si(Li)'s. In this measurement, the timing
properties of the detectors were determined using Compton scattering of
gamma-rays from 60C decay. Because the spatial distribution of
the ionization produced by the beta-particles emitted following 19Ne
decay was quite different from the ionization distribution produced from the 60Co
calibration source, there was a residual systematic error in the timing
calibration for the beta-asymmetry measurement. To correct this
systematic error, accurate models of the pulse shapes for different ionization
distributions must be produced. This, in turn, requires an accurate
spatial temperature profile for the Si(Li) detectors. Because the
original detector was not available, our strategy was to determine an effective
temperature range for the detector by attaching silicon diode thermometers to
the surface of a silicon disk with similar dimensions to the original Si(Li)'s
(0.32 cm thick and 7.32 cm in diameter) in the cold finger and cryogenic
mounting arrangement used in the original beta-asymmetry
measurement. The measured thermal profile will then be mapped
to the actual Si(Li) detector thermal profiles through temperature distribution
models produced using the COSMO code. Our measurements suggest the
original Si(Li) detector had a temperature between 102 and 114 degrees at all
points within the detector. This temperature range is narrow enough to
constrain pulse-shape models (now being produced) and the resulting residual
systematic error in the timing calibration.
|
Allen, Cyril A. |
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Home Institution: |
NCSU |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
John M. Blondin/Physics |
|
Title of Presentation: |
Supernova Shear and
Magnetic Field Amplification |
A core collapse supernova
marks the death of a star over 8 times the size of the sun. Sometimes in the
aftermath of these explosions a spinning, magnetized, neutron star can be left
behind, also known as a pulsar. It has recently been discovered that pulsar
spins can arise through a spiral spherical accretion
shock instability (SASI) of a supernova. This instability produces a strong
shear flow inside the supernova shock wave, which might lead to amplification
of the star's magnetic field. To study
this possibility, hydrodynamic simulations have been modified to include a
tracer of the magnetic field by adding the magnetic induction equation to the
code. Diagnostics were added to the code to measure the overall field strength
and shear flow generated by the SASI. I
found the magnetic field could be amplified by a factor of 100 in only 20 milliseconds.
This raises the possibility that shear-induced field amplification might be
able to contribute to the energy of the supernova explosion and explain the
high magnetic fields of the pulsar left behind.
|
Brown, Andrew D. Lynch, I. |
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Home Institution: |
NCSU |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Mechanical Engineering Physics |
|
Research |
Jacqueline Krim / Physics / Nanotribology |
|
Title of Presentation: |
Microtransporting: Tracking the Motion of Microspheres
on Quartz Crystal Microbalances |
In this study 5 µm diameter polystyrene spheres were deposited onto the
electrode of a quartz crystal microbalance (QCM). The QCM was driven at varying
drive voltages in orientations normal and parallel to gravity, producing a
frequency response that correlates to the crystal amplitude (“decoupling
curve”). The relationship between the frequency response and the crystal
amplitude gives rise to the calculation of slip time, which can be used to
derive a velocity dependent frictional force between the particles and the
surface. A high resolution camera was used to capture the movement of spheres,
which showed that the particle motion was dependent on the direction of
oscillation of the QCM and gravity in the orientations parallel with gravity.
|
Canty, Timothy M. |
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Home Institution: |
NCSU |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
Stephen Reynolds/Physics |
|
Title of Presentation: |
Kepler's Supernova Remnant: An Algorithmic Approach to
X-ray Spectral Classification |
In a type Ia supernova, a white dwarf gains mass
exceeding a critical limit and explodes. As type Ia
supernovae are used as standard luminosity candles for cosmological research, study of their remnants has wide astrophysical
application. Kepler's supernova remnant gives us a
unique chance to observe a young (~400 yrs) and nearby type Ia remnant. Although Kepler
is clearly a Ia event, our
long observation with the Chandra X-ray Observatory shows a few regions that
have spectra similar to circumstellar material (CSM),
not typical of a standard Ia explosion. In addition
to the CSM dominated by oxygen and magnesium lines, there are two other
distinct spectral classes: line-free continuum regions caused by
non-thermal bremsstrahlung and synchrotron radiation,
and regions with strong iron and silicate lines indicative of hot gas ejected
in the explosion. We are adapting an Expectation Maximization Gaussian Mixture
Model algorithm commonly used in medical imaging to identify regions of
contrasting spectral character. This algorithm effectively removes the subjectivity
used in previous visual classifications. It also produces a complete set of
similar regions; this improves the signal to noise ratio of the resulting
spectra which allows for better statistical data. We are attempting to separate
non-thermal emission from thermal emission and also identify areas of CSM. By
automating this process, we show the algorithm can correctly identify important
regions and aim to use this approach to gain insight on why Kepler's
supernova differs from other Ia
events.
|
Fisher, Alexander A. |
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Home Institution: |
St. Lawrence |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
Hans Hallen/Physics |
|
Title of Presentation: |
Voltage-Assisted
Photoemission Using Ultraviolet Near-Field Scanning Optical Microscopy |
Near-field scanning optical
microscopy (NSOM) can be used to provide us with high resolution images of
photoelectron production as well as optical and electrical data. We used a
tunable ultraviolet to create photoelectrons which we then collected with the
metal coating on the NSOM tapered optical fiber tip. The close proximity of the
tip and sample allowed us to create an extremely high electric field with only
modest (few volt) bias between the tip and sample. These high fields can change
the local work function of the material and thus aid the removal of the
electrons. This NSOM configuration permits variations of laser wavelength,
tip-sample distance, collection voltage, and lateral position on a sample,
enabling robust model testing of voltage-assisted photoemission.
|
Fox, Christopher J. |
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Home Institution: |
Harvey Mudd
College |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
Karen E. Daniels/Physics |
|
Title of Presentation: |
Determining the Rate of
Capillary Ridge Spreading via Laser Line Profiling |
Surfactant applied to a thin
fluid film is known to reduce the surface tension and form a capillary ridge
centered on the point of insertion. Understanding the mechanics of this
phenomenon in detail requires the ability to track the concentration of the surfactant
across the fluid surface while simultaneously measuring the rate of change of
the fluid’s height profile. The purpose of this REU research was to
measure the rate of spreading of the capillary ridge using laser imaging
techniques. By carefully extracting the displacement of a thin laser line
from a time series of photographs and calibrating, we have developed a precise
and non-invasive means to resolve the height profile of a thin fluid layer
along a desired axis. Measured at regular time intervals, these height
profiles allow us to determine the velocity of the capillary ridge during
spreading.
|
Gibson, Clint M. |
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Home Institution: |
NCSU |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
John M. Blondin/Physics |
|
Title of Presentation: |
Formation of the Ring of
Pearls Around SN 1987A |
Observations of Supernova
(SN) 1987A indicate the existence of a deformity in the ring of shocked gas surrounding
the supernova. We have investigated the possibility that a non-linear thin shell instability (NTSI) is accountable
for this deformity. The NTSI occurs under certain conditions, in shells
comprised of shocked medium, where the fluctuation parallel to the flow
direction is greater in size than the thickness of the shell itself. This
instability could produce fingers protruding inward of the shell. As the
blast wave propagates outward from the core, it would hit these fingers first.
This would produce intermittent spurts of light around center of the SN, as is
the effect observed in the case of SN 1987A. This study uses a three
dimensional hydrodynamics code to model the circumstellar
shell formed by the progenitor star of SN 1987A. The values known from
observations of SN 1987A are used in the production, keeping the model as
accurate as possible. We first show that spherical shells are susceptible
to the NTSI, provided that the Mach number of both shocks is > 5. We
then use the original model of Martin and Arnett to explain the circumstellar shells of 1987A. We find that when we
apply their model to 3-D, the inner rig is deformed by the NTSI.
|
Lamar, Tyra A. |
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Home Institution: |
North Carolina Central University |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
Robert Riehn/Physics |
|
Title of Presentation: |
Assembling Synthetic Genes
with Custom Epigenetic Modifications |
The recent
study of epigenetics, inheritable alterations in gene
expression that do not change DNA sequences, has given researchers greater
insight into the growth of several types of cancer. As a result of this developing field, scientists
have discovered that cancer cells are caused by chemical changes in gene
behavior, as opposed to mutations in the genes themselves. One frequently
studied epigenetic mechanism used by cancer is DNA methylation,
which is the addition of a methyl group to a DNA strand to partially suppress
gene function. The goal of this research is to methylate
synthetically assembled genes and to study the methylation’s
physical effects on the DNA strands. These genes of known length and known
sequence can consequently serve as a standard for future methylated
DNA studies. I constructed the synthetic genes using Polymerase Chain
Reaction (PCR), a method of replicating single-stranded DNA primers to form
double-stranded DNA. To measure the length of my PCR genes, I ran the PCR
solution through gel electrophoresis. I then amplified this nucleotide
solution using a second PCR reaction to increase the DNA concentration,
measuring this DNA length as well. This higher concentration DNA solution was methylated using BST-1 antibodies. Once the methylation has been optimized, I aim to bind antibodies to
the DNA in an effort to visualize the methylation
sites. Finally, I will analyze the methylated DNA
using gel electrophoresis in hopes of detecting the methylated
areas of the genes and studying their properties.
|
Learner, Christopher M. Zhang, Y. Sandin, A. Wu, D. |
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Home Institution: |
NCSU |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
Jack E. Rowe/Physics |
|
Title of Presentation: |
Low Energy Electron
Diffraction and Atomic Force Microscopy of Epitaxial
Zinc Oxide Films |
Single Crystal Zinc Oxide
films have many interesting technological applications. They can be used to
make p-n junctions which are used in LED’s and transistors. Zinc Oxide is a TCO
or Transparent Conducting Oxide. This property allows for applications in LCD
screens, thin-film solar cells, and flat-panel displays. The purpose of the
current thin-film Zinc Oxide research is to develop ways of growing very
uniform heteroepitaxial thin films of ZnO. The goal is to eventually be able to consistently
produce perfectly smooth single crystal films. We use Low Energy Electron
Diffraction (LEED) to investigate the periodicity of the ZnO
samples produced. LEED works by shooting an approximately 1mm diameter beam of
electrons at the sample under UHV conditions and projecting the diffracted
electrons onto a phosphor screen. The phosphor emits visible light when the
scattered electrons hit it. The pattern that appears on the screen is then a
representation of the inverse lattice of the material. The ZnO
LEED displays a hexagonal inverse lattice which gives a real-space lattice
constant of 2.21 Angstroms. We also use Atomic Force Microscopy (AFM) to
measure the topography of the samples, from which we can gather information
about the domain size of the ZnO crystals. These
domains appear to range in length from approximately 300-700nm, width from
180-270nm, and height from 20-50 nm. Optical microscopy has been used to gain a
qualitative understanding of the differences in surface features and domain
sizes on different areas of the surface. Analysis of the data has shown that
the diffraction patterns are from single crystal orientation epitaxial films. We have also found that there are sample
charging effects that occur during LEED measurements. The sample charging
effects vary according to electron energy and range from 26 to 43 Volts.
|
Lease, Christopher A. |
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Home Institution: |
State University of New
York at New Paltz |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
Jack E.Rowe/Physics |
|
Title of Presentation: |
Spherical Microwave
Confinement of Plasma for Fusion Reactions |
Spherical Microwave
Confinement uses electrostatics and microwaves to confine a
plasma. Previous attempts at this provided insight for modifications
that could be made in order for this to occur. The plasma, in this
situation, is a low density, low temperature plasma that is slightly ionized in
air. Under fusion conditions it will become fully ionized. The
ultimate goal will be to use deuterium as a fuel, instead of air, with the
modified antennas. The helical antennas used in the trial need to be
modified from their initial version. A first trial uses Polyclay
to fill the center of the antennas. The surfaces of them have a silicon
sealant. Aluminum foil is wrapped around the base of the antennas to
prevent any undesirable plasma formation at the base. The next antenna design
uses copper conical coils molded in vinyl ester resin and coated with
ceramic. We added an improved grid and coated the inner surface of the
sphere with ceramic to prevent a current between the grid and the sphere.
To obtain optimal results in fusion experiments the pressure inside of the
sphere needs to be as low as possible before backfill to 1 to 10 mTorr. We installed a turbo molecular pump and
replaced most of the plumbing that was plastic with metal and will use this in
future trials.
|
Martin, Kyle J. |
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Home Institution: |
NCSU |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
Stephen P.
Reynolds/Physics |
|
Title of Presentation: |
X-ray Emission from Iron
in Kepler’s Supernova Remnant |
Supernova remnants (SNRs) are the bright and gaseous remains of exploded stars
that are expanding at several thousand kilometers per second. One of the more
prominently studied of these objects is the remnant of Kepler’s
supernova of 1604 AD. Kepler’s SNR has similar
features to a Type Ia event, which is characterized
by an exploding white dwarf and a lack of hydrogen in the spectra. In addition,
Kepler’s SNR has a very strong iron presence in the
spectra. This is important because the location, velocity, and physical
conditions of the iron give information on the explosion mechanism and
progenitor system, and can be studied through a spectral feature in the x-ray
region of the spectrum, the K alpha line. This analysis focuses on
characteristics of the iron K emission line between 5.7 and 7 keV. In early 2006, the Chandra X-ray Observatory spent 741
thousand seconds observing this object and recording data with its ACIS-S CCD
camera. In analyzing the data, the spectra were plotted and fitted with the
Gaussian and thermal Bremsstrahlung models. These
models allowed for the measurement of characteristics such as the line energy,
line width, and temperature of the selected region in the SNR. From this
information, other information such as the velocities of the ejected matter
(from Doppler shifts), and ionization states of the iron can be determined. The
result of this research will yield a better understanding of the SNR
phenomenon.
|
Pfeiffer, Erik W. |
|
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Home Institution: |
Rowan University |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
|
Research |
Jack E. Rowe/Physics |
|
Title of Presentation: |
Clustering and Coalescence
of Nanoscale Islands on CoSi2 and TiSi2 Surfaces |
Transition metal silicide (CoSi2, TiSi2) islands can be formed by deposition
on a silicon wafer. At high annealing temperatures (>1000°C) these islands will undergo the late-stage effects
of Ostwald Ripening and coalescence. Measurable values such as the
density, size, and height of the islands, combined with known values such as
annealing temperature and annealing time, will reveal necessary insight into
separate projects involving nano-scale bridges and
other technology. The samples themselves were made previously by graduate
students in the Surface Science Lab at NCSU. Measurements were taken
using an auto-probe Atomic Force Microscope, which is accurate down to the
Angstrom scale. AFMs measure topography and
error signal by monitoring frequency oscillations between the probe-tip and the
sample. A photo-detector also measures angular changes in a laser which
is reflected off of the tip, effectively detecting minute changes in the
z-direction. Image analysis is done using AutoProbe-Image
software. This poster will reveal how annealing temperature directly
affects the density of islands, whether a preferred island size exists for any
annealing temperature, and whether the shape of the islands differs in regards
to the crystal structure of the film. Preliminary data suggests a mode of
two CoSi2 islands per 5x5 micrometer area in ~1200º C annealing areas,
while in ~1150º C areas, the amount of islands increases substantially
to an average of 28 islands. The density of the region can suggest whether
material was lost or gained during coalescence. Islands in the former
region have an average width of one micrometer, and a height of 85 nanometers,
while the latter tends to support islands of only 300 nanometers in width and
approximately twelve nanometers in height. Other trends such as island
dominance (islands which significantly vacate their surrounding region),
tendency towards preferred size, height, and ellipticity
will be discussed.
|
Pope, Thomas C. |
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Home Institution: |
NCSU |
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Program: |
Physics REU program – NCSU |
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College: |
PAMS |
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Department(s): |
Physics |
|
Research |
John M. Blondin/Physics |
|
Title of Presentation: |
Bondi-Hoyle-Lyttleton Accretion: Questions for Flip-flopping |
The night sky is full of
point sources of X-rays, most of which are black holes or neutron stars gaining
matter. The fundamental mechanism behind this accretion was first theorized by Bondi and Hoyle in 1939. The two considered the scenario in
which a compact object travels through a cloud of interstellar medium in order
to understand how it would gain material. Once it was theorized that accretion
may lead to gaining angular momentum Fryxell and Taam began using hydrodynamic simulations to show that if a
density gradient is introduced perpendicular to the incident flow, the shock
behind the compact object will 'flip-flop' and even flip over the object,
resulting in the formation of an accretion disk. The disk spins one direction,
disappears, and is later formed again, spinning in the counter direction.
Several authors since have noticed errors inherent in the simulations from
which this result was found. These include poor numerical resolution,
inappropriate boundary conditions upstream, and an unrealistically large accretor. My research seeks to find more accurate results
using a more complete computer code which will account for the aforementioned
errors. I've found that the 'flip-flop' instability occurs when the
adiabatic index of the gas is 4/3 but these oscillations dampen out completely
when the adiabatic index is set to 5/3. Also, the instability only appears so
long as the density asymmetry parameter is small. A critical point seems to
exist between .005 and .0625 beyond which the instability no longer occurs.
|
Will, David A. |
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Home Institution: |
Heidelberg College |
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Program: |
Physics REU program – NCSU |
|
College: |
PAMS |
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Department(s): |
Astrophysics |
|
Research |
John Blondin/Astrophysics |
|
Title of Presentation: |
Bridging the Gap Between
Binary Systems and Thermonuclear Supernovae |
Thermonuclear supernovae
(known as Type Ia
supernovae) are thought to stem from binary star systems. This project intends
to build upon current knowledge of binary systems through 3D analysis of a red
giant-white dwarf binary system (RG+WD). Of particular interest will be the
interaction of the stellar winds between the two stars (often referred to as a
colliding wind phenomenon). Here, we consider a red giant at the origin of a
spherical coordinate system and a white dwarf in orbit around it. Using a
hydrodynamic code evolving the fluid equations over time, a working 3D model
can be produced that will provide insight into the cause of such supernovae.
|
Woody, Michael S. |
|
|
Home Institution: |
University of North
Carolina, Chapel Hill |
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Program: |
Physics REU program – NCSU |
|
College: |
PAMS |
|
Department(s): |
Physics |
|
Research |
Thomas P. Pearl/Physics Pengshun Luo/Physics |
|
Title of Presentation: |
Observation,
Characterization, and Modeling of Molecular Rings Formed from DNA Deposited
on Au(111) |
A method of measuring the sequence dependent
properties of surface bound single and double stranded DNA may be possible
using scanning probe microscopy, providing researchers an additional method for
obtaining and verifying sequencing data. DNA deposited on a Au(111)
surface of various strand lengths, sequences, and surface anchoring chemistry
has been successfully imaged using scanning tunneling microscopy (STM) and
atomic force microscopy (AFM). For one particular short, 45 base pair
long DNA segment chemically anchored on the gold surface, with a specific
sequence containing a 15 bp AT spacer, ring-like
structures have been observed. Understanding the composition and
formation mechanisms of these structures may lead to an improved ability to
image DNA with STM on Au(111) as well as a better method for preparing
individually isolated DNA molecules on surfaces. During the course of the
experiment, parameters such as DNA concentration, exposure time, and buffer
solution were varied. Concentration and exposure time appeared to have
some impact on the rings’ appearance and the number of rings observed. In
an attempt to gain more insight into the structures, a computer model was
constructed based on electrostatic interaction between the DNA molecules.
This model should provide additional information about the composition and
formation mechanisms of the ring structures.
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Last modified July 2008 by Sharon E. Hunt