The 8th
Annual
NC
Undergraduate
Summer Research Symposium
Physics REU abstracts
Abstracts are listed in
alphabetical order by the last name of the corresponding author.
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Bemelmans, Norman L. |
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Home Institution: |
NCSU |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Chemistry |
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Research Mentor(s): |
Thomas P. Pearl/Physics Pengshun Luo/Physics |
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Title of Presentation: |
DNA Insertion into Alkanethiolate
Self-assembled Monolayers Grown on Au(111) |
Biological molecules and
biomimetic systems are prized in certain applications for their specific
chemical recognition properties. As such, experiments investigating the
structure and electronics of surface-immobilized DNA are high-impact in the
fields of nanotechnology and biosensing. In this study we have used a
custom-built ambient scanning tunneling microscope (STM) to observe and
characterize thiol- functionalized double-strand (ds) DNA inserted into one of
several alkanethiolate (e.g. decanethiolate, cyclohexanethiolate)
self-assembled monolayers (SAMs), which consist of a single layer of
alkanethiol species chemisorbed to a Au(111) substrate via a robust Au-S bond.
We have recorded STM images of these monolayers before and after DNA insertion
via solution phase deposition and they offer powerful topographical evidence of
disordered areas within the monolayer (i.e. vacancy sites and domain
boundaries) as preferential DNA insertion
sites. The degree to which molecules like DNA can be isolated at the single
molecule level determines how well molecular-level characteristics can be
determined; i.e., the ability to
investigate the properties of solitary DNA molecules is limited by the level of
deposition control at the surface. Although the research to date is promising,
more work is needed in order to realize the full potential of these
experiments.
|
Boyne, Philip P. |
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Home Institution: |
NCSU |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research Mentor(s): |
John M. Blondin/Physics |
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Title of Presentation: |
A Dense CSM Model For SN
2002ic |
Type Ia supernovae (SNe) are
created by the thermonuclear explosion of a white dwarf star, releasing a
tremendous amount of energy into their surroundings. Before the SN explosion,
the white dwarf and/or companion star are expected to blow stellar wind(s)
outwards and accumulate circumstellar material (CSM). As we learn more about
the interaction of the SN shockwave with this material, we better understand
the origin of Ia SNe. Most Type Ia SNe interact weakly with the CSM; one of the
few examples of strong circumstellar interaction is SN 2002ic. Chugai et al.
proposed a model in which the observational properties (the bolometric light
curve, quasi-continuum, and Ca II emission features) of this SN are produced by
a blastwave propagating through a dense CSM environment. They hypothesize that
under these conditions the shell of shocked ejecta will fragment due to the
nonlinear thin-shell instability. The instability matches with the observed
round-topped Hα line profile and the high luminosity of Ca II
features. Using two- and three-dimensional hydrodynamics code, we model this
scenario and vary the time after explosion as well as the total mass and energy
released. We will include radiative cooling as a result of the dense
environment and examine its effect on the stability of the shocked ejecta.
|
Burkey,
Mary T. |
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Home Institution: |
NCSU |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research Mentor(s): |
Stephen P. Reynolds/Physics Kazimierz Borkowski/Physics |
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Title of Presentation: |
An Analysis of Abnormal Behavior in Kepler's Supernova Remnant
|
Type Ia supernovas are widely used as standards for
interstellar distances because of their supposed uniformity and predictability.
However, there is very little knowledge regarding type Ia supernova
progenitors. An initial analysis of a 750 ks Chandra x-ray observation of SN
1604 (Kepler’s Supernova Remnant) revealed that it is interacting with material
lost from its progenitor, thus producing a modified circumstellar medium (CSM).
This is unusual for a type Ia supernova, as such behavior is usually
characterized by a Core-Collapse supernova (CC). I am working to complete a
separation and analysis of the CSM as well as the shocked ejecta in SN 1604
utilizing the same Chandra dataset. X-ray images will be used to illustrate
results. By learning the composition, whereabouts, and quantity of Kepler’s
CSM, the overall knowledge of type Ia supernovas will be furthered. The
analysis includes using advanced statistical techniques such as Gaussian
Mixture Models to identify regions with comparable spectral properties within
energy slices ranging from 0.3 to 8.0 keV. Segmented images are being employed
to minimize noise. DS9 RGB images will also serve as a tool for identifying
regions.
|
Bushwick, Sophie M. |
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Home Institution: |
Carleton College |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research Mentor(s): |
Robert Riehn/Physics Keith Weninger/Physics Carlos P. Ortiz/Physics |
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Title of Presentation: |
Hydrodynamic Focusing of
Biological Molecules |
We are developing a method for
tracking biological reaction kinetics in a microfluidic device. The device produces hydrodynamic focusing of
a central stream to allow fast mixing of reagents and spatial mapping of the
reaction coordinate. While this stream
flows down the center of an x-junction in the microfluidics device, two other
streams enter through the sides of the junction, “pinching” the central
flow. The application of the side
streams decreases the lateral dimension of the central stream, giving it a
small width and thus short diffusion time between the central and side
streams. We can use the shortened
diffusion time to precisely determine reaction time. The detection of this reaction’s kinetics is
done via Fluorescence Resonance Energy Transfer (FRET). The FRET technique is a spectroscopic tool to
detect conformational change in a biological molecule, which is tagged at known
sites with two dyes, an energy donor and an acceptor. The dyes absorb light energy and then emit it
as fluorescence, with the wavelength of the emitted light varying with the
molecule’s conformational changes.
Before tracking a biological molecule with FRET, we are testing our
concept with a fast chemical system which lets us explore the achievable time
resolution. In particular, we run the
pH-sensitive dye fluorescein through the central channel, with side streams of
a different pH. Because the intensity of
the fluorescein changes after the central stream mixes with the side streams,
we can calculate diffusion and reaction times.
|
Cetnar, Ashley |
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Home Institution: |
Grove City College |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research Mentor(s): |
Albert Young/Nuclear
Physics Robert Pattie/Nuclear Physics |
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Title of Presentation: |
Development of a
Conversion Electron Source for Timing Measurements and the Determination of
Angle Dependent Detector Response in the UCNA Experiment |
The beta-asymmetry from polarized
neutron beta-decay is proportional to (v/c)AcosΘ, where Θ
is the emission angle of the beta particles, A is the beta-asymmetry parameter (with a small energy dependence),
and v is the speed of the
beta-particle. In the Ultra-Cold Neutron A-correlation experiment (UCNA),
ideally, the average value of cosΘ = ˝ and the
detected energy of the electrons determines the v/c factor. Scattering and energy loss in non-active materials in
the trajectory of the emitted electrons introduces an angular dependence to the
efficiency and response of the detectors. This deviation is corrected for in
the UCNA experiment based on results from Monte Carlo simulations. In order to
directly establish the angle dependent corrections we have developed a timing
source that can be placed into the 1T magnetic fields in the beta spectrometer.
An avalanche photodiode detects Auger electrons emitted in coincidence with
conversion electrons from 113Sn, providing the time of flight for the
conversion electrons. Because the conversion electrons are essentially
mono-energetic, the time of flight is determined by the pitch angle of the
trajectories in the spectrometer magnetic field. We present an evaluation of
the performance of the timing source and expected response in the UCNA
experiment.
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Student Author(s): |
Davis, Bryce F. |
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Home Institution: |
NCSU |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research Mentor(s): |
Thomas P. Pearl/Physics Katie M. Andrews/Physics |
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Title of Presentation: |
Organization of the
Nucleobase Adenine on Ag(111) |
In recent years scanning
tunneling microscopy (STM) has been used extensively to characterize surfaces
at the nanoscale because of its high level of spatial resolution. The limit of this
resolution however, is often found at the submolecular level, and because of
this it is not always simple to determine molecular organization using STM
alone. We have studied a system which illustrates this case precisely: the
growth of monolayers of the nucleobase adenine (C5H5N5)
on Ag(111). It is particularly difficult to image the submolecular features of
adenine, owing mostly to the delocalization of electronic states typical of a
ringed compound, but also to the relatively round shape and small size of the
molecule. Furthermore, adenine molecules can hydrogen bond to each other in
many different configurations, several of which have similar stabilization
energies. Consequently, several pieces of information must be collated before a
viable postulation of its organization on the surface can be made. In this
study we observed the organization of adenine on Ag(111), with ultrahigh
vacuum, low temperature STM. We present reasonable conjecture on the
arrangement of the molecules on the surface based on correlation of the
observed structures with crystallographic directions of the underlying silver
lattice, investigation of the spatial dimensions of the features of the
observed structures, and comparison with past density functional calculations.
|
Dinolov, Georgi S. |
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Home Institution: |
Harvey Mudd College |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research Mentor(s): |
Karen E. Daniels/Physics Michael
Shearer/Mathematics Rachel Levy/Mathematics,
Harvey Mudd College David W. Fallest/Physics |
|
Title of Presentation: |
Inward Spreading of
Non-soluble Surfactants on Thin Liquid Films |
Surfactants are widely used
in industry for their ability to lower surface tension, and there remain many
open questions about how to mathematically model their dynamics. A droplet of surfactant on a liquid surface spreads
away from itself due to imbalance of forces
at its leading edge. These forces
also act on the liquid to create an expanding surface wave. Our experiment tracks a radially symmetric,
inward-moving wave and the surfactant which induced it. We directly image the surfactant by using
lipid molecules containing fluorescent functional groups which glow under
ultraviolet light. We also measure the location of the surface wave ridge by
refraction of a laser line. By combining
these two novel experimental techniques, and employing a digital camera, we
simultaneously capture the surfactant spreading and wavefront movement on a
millimeter-thick liquid film. Our
apparatus further allows us to collect results from both stationary and
spinning substrates. Use of a spincoater
gives us the ability to form thinner liquid films, as well as to exert forces
opposing those which drive surface spreading.
We compare our results to mathematical models, which predict power-law behavior with an exponent of 1/4,
for outward-moving waves.
|
Dulin, Davis |
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Home Institution: |
NCSU |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research Mentor(s): |
John Blondin/Physics |
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Title of Presentation: |
What Drives the SASI in Supernovae? |
The spherical accretion
shock instability (SASI) is now understood to be an important ingredient in
launching a shock wave out of the stellar core and driving a supernova explosion.
Furthermore, the SASI could indirectly be the explanation of the rapid rotation
of young radio pulsars (Blondin & Mezzacappa 2007) and the high space
velocity of a subset of pulsars (Scheck et al 2004, 2006). The origin of the
SASI, however, is debated. In one theory the SASI is associated with an
acoustic wave propagating along the inside surface of the postbounce accretion
shock in a core-collapse supernovae. An alternate perspective proposed by
Foglizzo et al. (2007) can be taken, which describes the SASI as a result of a
vortical-acoustic instability in which all propagation is purely radial.
This debate may be settled by using hydrodynamic simulations to study the
interaction of acoustic waves with strong shocks. The current analysis is being
done on a Standing Strong Shock simulation ran by VH-1, which is a
multidimensional ideal compressible gas-dynamics code. This code has been
manipulated in order to create a stationary shock, and have a perpendicular
sinusoidal oscillation of the lower y-boundary in order to create an acoustic
wave propagation on the inside surface of a 2-Dimensional recreation of a postbounce
accretion shock. These created waves were then analyzed for relatively large
time intervals, and current runs show that the waves began to grow, which
corresponds to our hypothesis.
|
Student Author(s): |
Fender, Melissa L. |
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Home Institution: |
NCSU |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
Karen E. Daniels/Physics Pedro Reis/Mathematics, MIT Frederic Lechenault/Physics |
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Title of Presentation: |
Interactions of Propagating Cracks |
When the edges of an elastic plate are pulled apart,
two cracks on opposite sides of the plate will propagate like single cracks
until they pass and begin to attract, cutting out a lens shape. In this experiment, we study this interaction
between two nearby cracks in a gelatin plate as a function of their initial
separation by applying a pulling force
on a plate with two precut cracks of known initial separation, s. By changing s and measuring the dimension and
shape of the lens we show that the size of the lens is proportional to s. By tracking the tips of the cracks as they
propagate we can characterize the dynamics of the crack formation. We observe
that the crack speeds slow approximately exponentially in time and that the
data from runs with different s values can be collapsed by s and the pulling
speed to a single curve. In addition, we
interpret the dynamics in light of a central force model.
|
Finch, Sean W. |
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Home Institution: |
NCSU |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research Mentor(s): |
Henning O. Back/Physics |
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Title of Presentation: |
A High Sensitivity Radon
Detector for the Kimballton Underground Research Facility |
Low count rate nuclear
physics experiments, such as those involving double beta decay, direct dark
matter detection, and solar neutrino physics, require low levels of background
radiation. Radon gas, present in the
air, decays into radioactive daughters which can plate out on detector
components and contribute to the background radiation. A goal for the Kimballton Underground
Research Facility (KURF) is to monitor, lower, and control the radon
levels. The radon levels desired for
these experiments are below the minimum detection level for most commercially
available detectors. This project
focuses on the construction of a radon detector designed to measure the radon
level accurately at the mBq/m3 level. The detector uses a Hamamatsu Si PIN
photodiode to detect the alpha decay of 218Po, the daughter nuclei
of 222Rn. In order to pull
the negatively charged polonium atoms out of the air and towards the
photodiode, the Si chip and its amplifier circuit were biased at positive high
voltage. A multi-channel analyzer is
used to collect data from the detector.
From the number of counts in the 218Po alpha peak we can
calculate the efficiency of the detector and calibrate it to represent the
corresponding radon level. This radon
detector should provide excellent data on the background radon levels in KURF,
and will be in integral part of future work to lower the radon levels at
KURF.
|
Kenny, Samuel G. |
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Home Institution: |
NCSU |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research |
John M. Blondin/Physics |
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Title of Presentation: |
Numerical Simulations of
Tilted Accretion Disks |
Hercules X-1 is a Low Mass
X-ray Binary system which consists of a neutron star and a donor star. These
two bodies are orbiting each other so close that the neutron star's gravity is
causing material to be ejected from the donor star by a process called
Roche-Lobe Overflow. Observational studies reveal a quasi-periodic oscillation
in the X-ray luminosity from Hercules X-1 on the order of 35 days. This is
thought to occur as a result of the existence of a tilted, precessing, and
possibly warped accretion disk orbiting its companion star HZ Herculis. We
present a 3D hydrodynamic numerical simulation of fluid flow in such a system
scaled to the values of Hercules X-1 and quantify various aspects of the
system.
|
Marcus, Aaron L. |
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Home Institution: |
NCSU |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research Mentor(s): |
John M. Blondin/Physics |
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Title of Presentation: |
3D Hydrodynamic
Simulations of Colliding Stellar Winds |
Current theories for the
progenitors of Type Ia supernovae (SNe) involve close binary systems containing
a white dwarf and a companion donor star. Such systems are expected to have
substantial circumstellar material at the time of the supernova explosion, yet
almost all Ia SNe show no signs of circumstellar interaction. We want to know
where this circumstellar material ends up. Using the VH-1 hydrodynamics code,
we run a 3D simulation of colliding winds in binary star systems separated by a
distance between 1 and 200 AU. The companion star blows slow, dense winds
towards the fast, sparse winds of the white dwarf. We want to know the
characteristics of progenitors that evolve into a system where no wind from the
companion star is present at the time of the explosion. Knowing these
characteristics will help us better understand both the system and the
supernova explosion.
|
Mauney, Christopher M. |
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Home Institution: |
NCSU |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research Mentor(s): |
John M. Blondin/Physics |
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Title of Presentation: |
Scalable Poisson Solver
for a 3D Spherical Grid |
Simulations of core-collapse
supernovae use a wide range of physics, and require massive computing power.
Supercomputers of petaflops speeds, running hundreds of thousands processing
units are currently used. An important component of these simulations is an
efficient, scalable Poisson solver in three dimensions. An algorithm for a numerical solution of
Poisson's equation in two and three dimensions is implemented on a local
compute cluster to analyze accuracy and evaluate efficiency. The algorithm is
based on the multipole expansion technique, and takes advantage of the
recursive relations of Legendre polynomials and spherical harmonics, in two
dimensions and three dimensions respectively. An exact solution for an
ellipsoid of homogeneous density is known, and will be the model for error
analysis of the algorithm. The effect of simulation parameters on the algorithm
will also be discussed.
|
Port, Rachel T. |
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Home Institution: |
NCSU |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research Mentor(s): |
Thomas P. Pearl/Physics Shawn M. Huston/Physics |
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Title of Presentation: |
Combination FM-AFM and STM
Microscope Built for Operation in UHV and Low Temperatures |
The design and construction
of a combination frequency-modulated atomic force and scanning tunneling microscope
(AFM/STM) head that operates in ultra-high vacuum and at low temperatures will
be presented. The combination AFM/STM
was built by adding a quartz tuning fork assembly to a classic Besocke-style
STM microscope head. A sharpened
metallic tip attached to the free prong of the quartz crystal tuning fork acts
as a force sensor. The tip is
electrically isolated from the tuning fork electrodes so that both STM and AFM
measurements can be taken simultaneously. Preliminary images of pentacene
molecules on a clean Ag(111) surface in a low-density coverage at 77K will be
presented to demonstrate the stability of the microscope assembly as an
STM. Pentacene has interesting
electrical properties due to the conjugated network present in the fused rings
and the surface energetics of a low-density coverage regime on a noble metal
surface like Ag(111) have not yet been explored. Also, because the properties of pentacene
have been investigated on other surfaces and in different coverage regimes, the
properties of the pentacene adsorbate layer will serve as a point of comparison
in future experiments with halogenated conjugated molecules deposited on
Ag(111). Ultimately, complementary STM
and AFM measurements will allow for correlations to be made between the electrical
and topograghical properties of these molecules, thereby furthering our
understanding of molecular organization on surfaces.
|
Sharrits, Blake |
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Home Institution: |
NCSU |
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Program: |
Physics
REU Program |
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College: |
PAMS |
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Department(s): |
Physics |
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Research Mentor(s): |
John Blondin/Physics |
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Title of Presentation: |
Numerical Simulations
of the Superhump Phenomenon |
The superhump phenomenon
in close binary systems
is a periodic luminosity variation. This phenomenon has been observed in
many SU UMa-type dwarf novae
such as in the OY Car system. This superhump period is a few per cent
longer than the orbital
period of the system. From a theoretical standpoint the superhump
is powered by a tidal instability in the accretion disc, a
resonance around the 3:1 radius in the outer reaches of an eccentric
disc. This resonance occurs when the frequency of the radial motion of a
particle is roughly equal to the angular
frequency of the donor star. I will use high-resolution 2D and 3D
gas-dynamical simulations to study the superhump phenomenon and test the
hypothesis that the 3:1 resonance can explain this behavior. These
simulations will include a self-consistent tidal stream in order to study the
effects of the stream/disk interaction. I will be running these
simulations for several million computational cycles in order to look at the
entire evolution of the superhump phenomenon. The eccentricity of the disk is
quantified by taking a Fourier decomposition of the radial velocities
throughout the disk. By comparing both the 2D and 3D simulations it
become apparent that the 3D cases are needed to get a full understanding of
these systems.
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Last modified July 2009 by Sharon E. Hunt