2024-03-28T17:22:57Zhttps://ir.vanderbilt.edu/oai/requestoai:ir.vanderbilt.edu:1803/164882021-05-07T13:49:01Zcom_1803_569com_1803_66col_1803_685
Axionlike Dark Energy and Particle Decay in theFuture of the Accelerating Universe
Norton, Cameron
The 1998 discovery that the universe was accelerating in its expansion has yet to be explained
theoretically, meriting the continual theoretical and observational study of this phenomena.
In this thesis, we undergo a phenomenological study of the cosmological implications of this
“dark energy” in two different ways.
In the first part of this thesis, we examine the cosmological evolution of ultralight axionlike (ULA) scalar fields with potentials of the form V (φ) = m2f
2
[1 − cos (φ/f)]2
, with
particular emphasis on the deviation in their behavior from the corresponding small-φ powerlaw approximations to these potentials: V (φ) ∝ φ
2n
. We show that in the slow-roll regime,
when φ˙2/2 V (φ), the full ULA potentials yield a more interesting range of possibilities for
quintessence than do the corresponding power law approximations. For rapidly oscillating
scalar fields, we derive the equation of state parameter and oscillation frequency for the ULA
potentials and show how they deviate from the corresponding power-law values. We derive
an analytic expression for the equation of state parameter that better approximates the ULA
value than does the pure power-law approximation.
In the second part, we study particle decay in the future of the accelerating universe. We
generalize the result that in a cosmological constant dominated universe, the decay of matter
into relativistic particles can never cause radiation to once again dominate over matter. We
study both models of dark energy comprised of quintessence and cosmologies ending in a “big
rip” in this context.
Vanderbilt University. Dept. of Physics and Astronomy
2021-04-30
Thesis
en_US
http://hdl.handle.net/1803/16488
https://ir.vanderbilt.edu/bitstream/1803/16488/1/Cameron%20Norton%20Honors%20Thesis.pdf
b947f79dc75d015c0f91198cabb5634c
https://ir.vanderbilt.edu/bitstream/1803/16488/2/license.txt
49f58bf859518f166339cafac2e786df
Physics
oai:ir.vanderbilt.edu:1803/94722020-04-22T10:22:00Zcom_1803_569com_1803_66col_1803_685
LieART 2.0--An Improved Way to Compute Branching Rules
Saskowski, Robert
Kephart, Thomas
In this thesis, we present LieART 2.0 which contains substantial extensions to the Mathematica application
LieART (Lie Algebras and Representation Theory) for computations frequently encountered in Lie algebras and representation theory, such as tensor product decomposition and subalgebra branching of irreducible
representations. LieART 2.0 can now handle all classical and exceptional Lie algebras up through rank 15.
The basic procedure is unchanged–it computes root systems of Lie algebras, weight systems and several other properties of irreducible representations, but new features and procedures have been included to allow the extensions to be seamless. The new version of LieART continues to be user friendly. Some extended tables of branching rules of irreducible representations are included in the supplementary material for use without Mathematica software.
Vanderbilt University. Dept. of Physics and Astronomy
2019-04-18
Thesis
en_US
http://hdl.handle.net/1803/9472
https://ir.vanderbilt.edu/bitstream/1803/9472/1/Senior_Thesis__LieART_2_0_%27.pdf
943712dacff5339d0c585203efb80512
https://ir.vanderbilt.edu/bitstream/1803/9472/2/license.txt
8a4605be74aa9ea9d79846c1fba20a33
https://ir.vanderbilt.edu/bitstream/1803/9472/3/Senior_Thesis__LieART_2_0_%27.pdf.txt
4bdd55682ca0517c28827f779452d712
Lie algebra
Lie group
representation theory
irreducible representation
branching rule
GUT
model building
Mathematica
Physics
oai:ir.vanderbilt.edu:1803/50982020-04-22T08:11:57Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Dark radiation from particle decays during big bang nucleosynthesis
Menestrina, Justin
Scherrer, Robert J. (Robert Joseph), 1959-
Cosmic microwave background (CMB) observations suggest the possibility of an extra dark
radiation component, while the current evidence from big bang nucleosynthesis (BBN) is more
ambiguous. Dark radiation from a decaying particle can affect these two processes differently.
Early decays add an additional radiation component to both the CMB and BBN, while late
decays can alter the radiation content seen in the CMB while having a negligible effect on BBN.
Here we quantify this difference and explore the intermediate regime by examining particles
decaying during BBN, i.e., particle lifetimes τ_X satisfying 0.1 sec < τ_X < 1000 sec. We calculate the change in the effective number of neutrino species, Neff, as measured by the CMB, ΔN_CMB, and the change in the effective number of neutrino species as measured by BBN, ΔN_BBN, as a
function of the decaying particle initial energy density and lifetime, where DNBBN is defined in
terms of the number of additional two-component neutrinos needed to produce the same
change in the primordial 4He abundance as our decaying particle. As expected, for short
lifetimes (τ_X < 0.1 sec), the particles decay before the onset of BBN, and DNCMB = DNBBN,
while for long lifetimes (τ_X >1000 sec), ΔN_BBN is dominated by the energy density of the
nonrelativistic particles before they decay, so that ΔN_BBN remains nonzero and becomes
independent of the particle lifetime. By varying both the particle energy density and lifetime,
one can obtain any desired combination of N_BBN and ΔN_CMB, subject to the constraint that
DNCMB N_BBN. We present limits on the decaying particle parameters derived from
observational constraints on ΔN_CMB, and N_BBN.
Vanderbilt University. Dept. of Physics and Astronomy
2012-04
Thesis
en_US
http://hdl.handle.net/1803/5098
https://ir.vanderbilt.edu/bitstream/1803/5098/1/Menestrina_thesis.pdf
e2e8c4aa06c432bda766aa87fe183ad3
https://ir.vanderbilt.edu/bitstream/1803/5098/5/license.txt
8ec8fd34acde2f4d8b37a78345cbcc36
https://ir.vanderbilt.edu/bitstream/1803/5098/6/Menestrina_thesis.pdf.txt
b174b560bb34779e01cb9ddbc27209ba
Cosmology
Big Bang Nucleosynthesis
Cosmic Microwave Background
Dark Radiation
Effective Neutrino Number
Cosmology
Cosmic background radiation
Big bang theory
Dark matter (Astronomy)
Dark energy (Astronomy)
Nucleosynthesis
Radioactive decay
oai:ir.vanderbilt.edu:1803/29502011-02-11T18:27:38Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Micro Programmable Object Navigation Gadget (micro-PONG) for Studying Electroosmotic Flow in PDMS Microchannel
Rohrman, Brittany Ann
Wikswo, John Peter
Precise control of fluid delivery in analytical devices may be achieved by harnessing electroosmotic flow (EOF) in oxidized
poly(dimethylsiloxane) microfluidic channels fabricated via soft lithography. However, the magnitude of this flow depends on a number
of parameters, including the geometry and surface chemistry of the channel walls, and is known to attenuate over time. In order to
characterize these parameters and calibrate the magnitude of EOF in our devices, we have developed a versatile automated control and
measurement system called micro-PONG (Micro Programmable Object Navigation Gadget). The system detects, controls, and measures the
movement of polystyrene beads caused by EOF in the channel. The micro-PONG system consists of a LabView program, a DAQ board, an external voltage switching circuit, and a camera. A computer
algorithm reverses the direction of the EOF each time the bead enters one of two user-specified "goalpost" areas, thus keeping the bead trapped and moving back and forth between the goalposts (similar to a game of ping pong) for extended periods of time. From the recorded motion of the bead, the three-dimensional velocity profile of the fluid in the channel may be estimated using a novel ImageJ macro for determining motion in three dimensions. This analysis may then be
used to determine the magnitude of the EOF, inertia, and response time of the system as well as the time-dependent effects of PDMS surface
properties on EOF. The micro-PONG system may also be useful for other purposes that require the automated manipulation of particles or
cells.
Vanderbilt University. Dept. of Physics and Astronomy
2009-04-20
Thesis
en_US
http://hdl.handle.net/1803/2950
https://ir.vanderbilt.edu/bitstream/1803/2950/1/RohrmanThesis_2.doc
ca3e5ea3ef7c185db558149b77634fc2
https://ir.vanderbilt.edu/bitstream/1803/2950/2/license.txt
c829f4f5351ddf2bd804d462dbfb36ad
https://ir.vanderbilt.edu/bitstream/1803/2950/3/RohrmanThesis_2.doc.txt
c498597300b9066af78da9d8e08736fc
Electrokinetic flow
Microfluidics
Poly(dimethylsiloxane)
Particle image velocimetry
Electroosmotic flow
Electrokinetics
Microfluidics
Electro-osmosis
oai:ir.vanderbilt.edu:1803/52032020-04-22T08:21:33Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
An anomalous measurement of delta m31 squared from neutrino oscillations at the Daya Bay Reactor Neutrino Experiment
Burroughs, Hunter
Ernst, David
In 2012, the collaboration overseeing the Daya Bay Reactor Neutrino
Experiment announced results which determined the magnitude of the mixing
angle \theta_{13} with unprecedented precision. However, no attempt was made
in the collaboration’s publications to predict the value of the most
relevant mass-squared difference to the observed oscillation, \delta
m^2_{31}. This paper presents the results of an analysis which suggests that
the Daya Bay data prefers a value of \delta m^2_{31} which is far greater
than its presently recognized value. Specifically, it is found that Daya Bay
predicts \delta m^2_{31} = 3.53_(-1.07)^(+.74) × 10^(-3) eV^2, where the
cited uncertainties correspond to the 99% confidence bounds. This
measurement excludes the most precise current measurement of \delta
m^2_{31}, the MINOS result, at a 99% confidence level and is in turn
excluded by the MINOS data at a 10 \sigma level. The possibility that
sterile neutrino effects are the cause of this anomalous result is
considered and used to suggest further work.
Vanderbilt University. Department of Physics and Astronomy
2013-04-22
Thesis
en_US
http://hdl.handle.net/1803/5203
https://ir.vanderbilt.edu/bitstream/1803/5203/1/Burroughs_Thesis.pdf
cde003b7f6531e5afce17ce5e1a98264
https://ir.vanderbilt.edu/bitstream/1803/5203/2/license.txt
8ec8fd34acde2f4d8b37a78345cbcc36
https://ir.vanderbilt.edu/bitstream/1803/5203/3/Burroughs_Thesis.pdf.txt
e17a91926f39710b615d8cd68b359129
neutrino mixing
neutrino oscillations
oscillation parameters
Daya Bay
sterile neutrino
theta 13
neutrino mass difference
Neutrinos
Oscillations
Neutrinos -- Mass
Nuclear reactors
Daya Wan he dian zhan (China)
oai:ir.vanderbilt.edu:1803/7332020-04-22T06:56:38Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Influence of patient size on dose to female breast tissue during routine computed tomography scans
Scully, Peter C.
Stabin, Michael
Monte Carlo methods are well suited to the evaluation of radiation transport phenomena. The scalable phantoms employed in this project permitted rapid creation of three models of similar geometry, but different body habitus. It is difficult at this point to draw any conclusions about the relationship between patient size and radiation dose to breast tissue during CT scans of the chest. However, the results of DeMarco et al. suggest that we may find a more complicated relationship between breast size and breast dose than we anticipated. Whatever the relationship, it is important that physicians and radiologists realize how dose delivered by CT varies with breast size, so that an effective balance of risks and benefits may be obtained for all patients in diagnostic CT imaging.
Vanderbilt University. Dept. of Physics & Astronomy
2008-04-21
Thesis
en_US
http://hdl.handle.net/1803/733
https://ir.vanderbilt.edu/bitstream/1803/733/1/PScullypdf.pdf
2eb77c35923bc1fc559fc6fba89deb59
https://ir.vanderbilt.edu/bitstream/1803/733/2/license.txt
b4a9adea1881018e2a4372e60ae40cf7
https://ir.vanderbilt.edu/bitstream/1803/733/3/PScullypdf.pdf.txt
e3003d749a3b4b3a6bfbf98735181a59
Radiation
Tomography
Breast
Dose
Breast -- Radiography
Radiation -- Dosage
Cancer -- Tomography
Body size
Monte Carlo method
Diagnostic imaging
oai:ir.vanderbilt.edu:1803/7352020-04-22T06:56:49Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Reflection and rotation for three dimensional microscopy of live cells
Wright, Charlie
Wikswo, John Peter
Confocal scanning laser microscopy and multiphoton microscopy provide 3D data from biological specimens, but with limited z-axis precision. Multiple microscale mirrors can be used to obtain more accurate 3D data on living cells while using classical widefield microscopy. Etched silicon wells coated with aluminum were used to obtain 3D images of budding yeast cells, with information along the z-axis provided by reflections from the angled sides of the well. To supplement measurements obtained with this method, work was also conducted on a system to allow for rotation of a cell attached to a pulled glass tip. Images of a yeast cell obtained from either method can be fit to a simple 3D surface due to the cell's roughly spheroidal shape, which should provide accurate measurements of the volume of an individual budding yeast cell as it progresses through the cell cycle.
Vanderbilt University. Dept. of Physics & Astronomy
2008-04-18
Thesis
en_US
William and Nancy McMinn Honor Scholarship,
Vanderbilt Institute for Integrative Biosystems
http://hdl.handle.net/1803/735
https://ir.vanderbilt.edu/bitstream/1803/735/1/CW%20Honors%20Thesis.pdf
fc14be1423e3c31a243dede2bf30b4e4
https://ir.vanderbilt.edu/bitstream/1803/735/2/license.txt
e0a411c78e609391b9f7f591376658cf
https://ir.vanderbilt.edu/bitstream/1803/735/3/CW%20Honors%20Thesis.pdf.txt
33abe661470aa2b2388d60bcbfc4133b
Reflection
3d microscopy
MPWs
Rotation
Yeast -- Analysis
Biological specimens
Cytology -- Technique
Confocal microscopy
Electron microscopy
Three-dimensional imaging in biology
oai:ir.vanderbilt.edu:1803/50922020-04-22T08:09:14Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Real-time real-space density functional theory calculations of electron scattering in materials
Wyatt, Benjamin
Varga, Kálmán, 1963-
Density functional theory is utilized in real-time,
real-space simulations of LEED measurements and attosecond electron
scattering. For LEED measurements, we find that our simulation results
agree well with experimental data and other theoretical approaches.
For attosecond electron scattering, we find that the wavefunction of
the scattered electron is not signficantly changed by the scattering
process, and the measured electron density seems to be related to the
initial form of the wave-packet. However, further investigation is
needed to confirm these results for different choices of initial form.
Vanderbilt University. Dept. of Physics and Astronomy
2012-05-04
Thesis
en_US
http://hdl.handle.net/1803/5092
https://ir.vanderbilt.edu/bitstream/1803/5092/1/Wyatt_Thesis.pdf
d40794a442ffe9060849fdce8e4c15cb
https://ir.vanderbilt.edu/bitstream/1803/5092/5/license.txt
8ec8fd34acde2f4d8b37a78345cbcc36
https://ir.vanderbilt.edu/bitstream/1803/5092/6/Wyatt_Thesis.pdf.txt
594b87671485d533a40515c72521d30c
density functional theory
low-energy electron diffraction
attosecond
electron
LEED measurements
Density functionals
Low energy electron diffraction
Electrons -- Scattering
oai:ir.vanderbilt.edu:1803/183112023-08-02T16:15:07Zcom_1803_569com_1803_66col_1803_685
Deformed Explicitly Correlated Gaussians
Beutel, Matthew
Strong coupling of cavity electromagnetic modes and molecules has emerged as
an area of intense theoretical and experimental interest. Such systems are of
particular interest due to their ability to modify the physical and chemical properties of materials. In this work, I use a stochastic variational method (SVM)
to construct optimized light-matter coupled wave function. By using SVMs to
select the best basis states, we are able to achieve highly accurate energies and
wave functions. In this work, I will be solving for the Pauli-Fierz (PF) nonrelativistic QED Hamiltonian. In this work I will introduce a new basis type
Deformed Explicitly Correlated Gaussians (DECGs). DECGs are a modified
form of explicitly correlated Gaussians (ECGs) where the basis is chosen such
that the dipole self-interaction term can be eliminated. These calculations will
be compared to those performed with traditional ECGs, demonstrating their
superiority in cases where a non-spherical potential exists, such as the dipole
self-interaction term.
Vanderbilt University. Dept. of Physics and Astronomy
2022-12
Thesis
en_US
http://hdl.handle.net/1803/18311
https://ir.vanderbilt.edu/bitstream/1803/18311/1/honors_thesis%20%282%29.pdf
a3b48d631229e2b8dde25588157e40fe
https://ir.vanderbilt.edu/bitstream/1803/18311/2/honors%20thesis.zip
1aa1c652aab70257ccf67f73a91c6a45
https://ir.vanderbilt.edu/bitstream/1803/18311/3/license.txt
49f58bf859518f166339cafac2e786df
Quantum Information Science
Cavity QED
Deformed Explicitly Correlated Gaussians
Physics
oai:ir.vanderbilt.edu:1803/75632020-04-22T06:07:04Zcom_1803_569com_1803_66col_1803_685
Nanoscale dolmen structure exhibiting a tunable Fano resonance
Beier, Nicholas
Haglund, Richard F., Jr., 1942-
A Fano resonance is an asymmetric, resonant scattering phenomenon which occurs in a multitude of fields, such as atomic physics, nuclear physics, nonlinear optics, and nanophotonics. The Fano resonance is a many-particle excitation arising from a single-particle excitation, and occurs due to the interference of a narrow discrete resonance overlapping with a spectrally broad resonance. Multi-element nanoparticles are explored as a means to realize this resonance type, which has a characteristic, steep dispersion useful in sensors, among other devices. A gold dolmen nanostructure consisting of a bright, radiative, dipolar mode coupled with a dark, quadrupolar mode is investigated, which produces the plasmonic analogue of electromagnetically induced transparency through the interference of the bright and dark modes. Additionally, the plasmonic resonance of a metallic nanostructure is extremely sensitive to its local dielectric environment. Vanadium dioxide exhibits a large change in its dielectric function during its metal to insulator phase transition. The combination of the gold dolmen nanostructure with vanadium dioxide produces a tunable Fano resonance. The dimensions of the structure are optimized such that the resonance is near symmetric in shape and located in the near infrared to allow for spectroscopic measurement. The author is unable to obtain experimental results of this hybrid structure, but previous work, combined with simulation data, suggest the proposed structure will exhibit the expected result.
Vanderbilt University. Dept. of Physics and Astronomy
2016-05-02
Thesis
en_US
United States. Department of Energy. Office of Science (DE-FG02-01ER45916).
http://hdl.handle.net/1803/7563
https://ir.vanderbilt.edu/bitstream/1803/7563/1/Nicholas%20Beier%20Honors%20Thesis.pdf
c3c2a33bd6ed2597eb0a73ad1ff8ac19
https://ir.vanderbilt.edu/bitstream/1803/7563/2/license.txt
ece5a9f3b88102a1eb9b2ff22411c299
https://ir.vanderbilt.edu/bitstream/1803/7563/3/Nicholas%20Beier%20Honors%20Thesis.pdf.txt
c17b882e5df6e54c335db5077d62cd7e
Plasmonics
Metal Nanoparticles
Vanadium Dioxide
Fano Resonance
Nanoparticles
Nanostructured materials
Nanophotonics
Plasmons (Physics)
Vanadium oxide
Resonance
oai:ir.vanderbilt.edu:1803/41052020-04-22T08:11:19Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Investigation of Electroosmotic Flow in Various Microfluidic Structures
Diggins, Patrick
Wikswo, John Peter
Enclosed microfluidic devices provide excellent systems for the study of
biological processes such as cell-cell, paracrine, and autocrine signaling
systems. By minimizing the fluid volume within the chambers, microfluidic
devices diminish the dilution of secreted products which makes the detection
of the secreted products a more straightforward task. A major design problem
associated with the construction of microfluidic devices for biological
research is the need to provide well-controlled fluidic transportation for
cells, the nutrients that the cells need, and waste removal. Most precision
syringe pumps which can accurately provide low flow rates are expensive and
constitute a barrier to experiment design. Electroosmotic pumps could
potentially provide a valuable alternative as a low volume flow rate pumping
system for many types of microfluidic devices. We have developed a
poly(dimethylsiloxane) (PDMS) microfluidic device that incorporates both
electroosmotic flow and pressure driven flow. The device is designed to
increase the relative strength of the electroosmotic flow (EOF) component of
the total flow through the use of an array of small volume parallel pumping
channels which provide higher passive resistance to pressure driven flow
than a larger volume single-channel EOF pump. Using a novel microfluidic
instrumentation device which we call the "Micro Programmable Object
Navigation Gadget" (µ-PONG), we investigate how different properties and
geometries of the device affect the EOF rate. In addition, we demonstrate
that fluid flow driven by a small hydraulic pressure head can be completely
canceled by an user initiated EOF in the pumping channels which are
incorporated into a microfluidic device. The ability to modulate the flow
and to create "stop flow" conditions in microfluidic devices is also
important for biological research.
Vanderbilt University. Dept. of Physics and Astronomy
2010-04
Thesis
en_US
http://hdl.handle.net/1803/4105
https://ir.vanderbilt.edu/bitstream/1803/4105/1/Diggins_Thesis_5_6.pdf
e8ada8985b686c05753055cd71394fa3
https://ir.vanderbilt.edu/bitstream/1803/4105/2/license.txt
51f53f829d8a6beaa78c0f1be5919701
https://ir.vanderbilt.edu/bitstream/1803/4105/3/Diggins_Thesis_5_6.pdf.txt
c080975a672329d0b78c4a79d5684918
Electrokinetic flow
Electroosmotic flow
Poiseuille flow
MEMS, Poly(dimethylsiloxane)
Particle imaging
Microfluidic devices
Microfluidics
Fluid dynamics
oai:ir.vanderbilt.edu:1803/48432020-04-22T07:58:32Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Engineering a perfusion-enabled mechanical compressor for long-duration immobilization and microscopy of cells and small organisms
Jiang, Liwei
Janetopoulos, Christopher
The study of living specimens is essential to the understanding of
organismal behavior. Unfortunately, a major difficulty in the study of
live organisms is that many move in and out of the field of view or
focal plane during microscopy. The present work seeks to combat this
considerable problem by developing a mechanical microcompressor that
immobilizes living cells and small organisms for long-duration optical
microscopy. The device, dubbed the "Commodore Compressor," features
two key innovations: (1) the integration of a perfusion system to keep
the trapped specimen alive over several hours, as well as permitting
the addition of chemoattractants, drugs, and other chemicals; (2) the
incorporation of an optional patterned PDMS platform to improve the
efficacy of immobilization in a targeted, organism-specific manner.
One application of the Commodore Compressor is in monitoring the
change in protein bioluminescence intensity in many trapped
Saccharomyces cerevisiae cells during synchronized cell cycles. The
experiment's feasibility and key techniques have been well
demonstrated, although bioluminescence cannot currently be visualized.
A second application involves fluorescence imaging of the neural
network development of immobilized Caenorhabditis elegans over many
hours. The development of new patterned PDMS platform designs, aided
by the innovative use of established techniques, has driven the
present work toward accomplishing the goal, but true long-term
viability remains elusive. The Commodore Compressor may be directly
used or easily adapted for many other specimen types and experimental
scenarios.
Vanderbilt University. Dept. of Physics and Astronomy
2011-04
Thesis
en_US
http://hdl.handle.net/1803/4843
https://ir.vanderbilt.edu/bitstream/1803/4843/1/Jiang_thesis.pdf
4648537c16f20157bfb691b46f5b5b15
https://ir.vanderbilt.edu/bitstream/1803/4843/2/license.txt
8ec8fd34acde2f4d8b37a78345cbcc36
https://ir.vanderbilt.edu/bitstream/1803/4843/3/Jiang_thesis.pdf.txt
2151fcd116787aa9f6cbc6737e6237cd
compressor
immobilization
microscopy
microfabrication
polydimethylsiloxane
PDMS
Caenorhabditis elegans
Saccharomyces cerevisiae
yeast
nematode
Microscopy
Microscopy -- Technique
Organisms
oai:ir.vanderbilt.edu:1803/29482020-04-22T08:19:41Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Measurement of Energy Spectrum of Electrons Field-Emitted from Diamond Field-Emitter Arrays
Stewart, Christopher L.
Brau, Charles A., 1938-
A retarding mesh analyzer was used to measure the electron energy spectrum field emitted from a single tip of a Diamond Field Emitter Array. The emission was dominated by adsorbed gas
atoms and molecules on the surface which were both spatially and temporally unstable. As a result, the spectra taken had highly variant spectral features and there was an order of magnitude span in the emitted current. The spectrum from a clean surface roughly obeyed the thermal field emission model and was consistent with reported spectra from a nitrogen-doped, diamond-like carbon film.
Vanderbilt University. Dept. of Physics and Astronomy
2009-04-20
Thesis
en_US
http://hdl.handle.net/1803/2948
https://ir.vanderbilt.edu/bitstream/1803/2948/1/CLStewartThesis.pdf
f2db40127912e65a5a9d3b6039e5e942
https://ir.vanderbilt.edu/bitstream/1803/2948/2/license.txt
70f528d37b6dd43dd176cece1919d57f
https://ir.vanderbilt.edu/bitstream/1803/2948/3/CLStewartThesis.pdf.txt
a8f1e790d5f42c87f83b0c4a746b572c
Fowler-Nordheim
Field emission
Diamond
Electron energy spectrum
Field emission
Electron spectroscopy
Electrons -- Emission
Diamond thin films
oai:ir.vanderbilt.edu:1803/66312020-04-22T06:08:18Zcom_1803_569com_1803_66col_1803_685
Emittance and entropy of electron beams
Erickson, Collin
Brau, Charles A., 1938-
Creating high-brightness electron beams, which have many practical
applications, is done with cathodes in regions with large electric
field by field emission. The brightness is high when the current is
high and the volume of the beam in phase space is small. An estimate
of the phase space volume is the rms emittance. The simulations
described in this report show that the beam emitted by a gated diamond
field emitter of the type fabricated at Vanderbilt has an exquisitely
small emittance, on the order of a few nm. This is probably too small
to measure. The rms emittance is generally thought to be constant for
a beam or increasing in the presence of aberrations in the beam
optics, but simulations show that this is not true. The rms emittance
rises and falls according to the geometry that surrounds the beam.
The entropy of an electron beam can be calculated, and should be
constant if done in six dimensional phase space, and approximately
constant in four dimensions. Calculations show that the entropy is not
constant in two nor four dimensions. Rather, the entropy changes over
time with a shape similar to how the emittance changes, which includes
a local maxima at the entrance to an aperture and minima on either
side. It is not clear if the fault is with the calculations or
theory. To our knowledge, this is the first time that the entropy of a
particle beam has been computed and used in a quantitative
fashion. Future research should explore the applications and
limitations of this concept.
Vanderbilt University. Department of Physics and Astronomy
2014-04
Thesis
en_US
http://hdl.handle.net/1803/6631
https://ir.vanderbilt.edu/bitstream/1803/6631/1/Erickson_Thesis_20140502.pdf
59e1f0644cbb27926567026980669d8e
https://ir.vanderbilt.edu/bitstream/1803/6631/3/license.txt
ece5a9f3b88102a1eb9b2ff22411c299
https://ir.vanderbilt.edu/bitstream/1803/6631/4/Erickson_Thesis_20140502.pdf.txt
dfcc3b906b4d4a0dc07483cbd80ff48f
CC0 1.0 Universal
electron beams
high-brightness electron beams
emittance
rms emittance
field emission cathode
entropy
beam entropy
Electron beams
Beam emittance (Nuclear physics)
Field emission cathodes
Particle beams
High-brightness accelerators
Phase space (Statistical physics)
Entropy
oai:ir.vanderbilt.edu:1803/48412020-04-22T08:00:28Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Perturbation Theory for Thin Cladding Layers on Silicon Photonic Systems
Phare, Christopher
Weiss, Sharon M., 1977-
I develop a perturbation theory for resonant frequency shifts caused by thin
layer of material added to dielectric systems. This development can be used
to effectively model photonic surface-sensing systems, which use this
resonance shift to measure the presence of, e.g., biomolecules attached to
the sensor system. Direct modeling was previously intractable due to
extremely long simulation times required to account for the cladding
layers. The developed theory is verified against a special-case direct
simulation and by measuring the shift caused by silicon dioxide deposited on
a fabricated ring-resonator sensor.
Vanderbilt University. Dept. of Physics and Astronomy
2011-04
Thesis
en_US
http://hdl.handle.net/1803/4841
https://ir.vanderbilt.edu/bitstream/1803/4841/1/Phare_Thesis.pdf
db9327b9666a74e7f8b9abbeb11075f8
https://ir.vanderbilt.edu/bitstream/1803/4841/2/license.txt
8ec8fd34acde2f4d8b37a78345cbcc36
https://ir.vanderbilt.edu/bitstream/1803/4841/3/Phare_Thesis.pdf.txt
2d647bd04cdeb7e1c6a4126e50b2da7b
photonics
ring resonator
perturbation theory
photonic crystal
sensing
Perturbation (Mathematics)
Photonics
Dielectric films
Thin films
Dielectric resonators
oai:ir.vanderbilt.edu:1803/48392020-04-22T06:07:04Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Finite-Element Analysis of Low-Power Laser Heating in Gold::Vanadium Dioxide Nanocomposites
MacQuarrie, Evan
Haglund, Richard F., Jr., 1942-
Finite element modeling was performed using COMSOL Multiphysics to study the
thermal dynamics of gold::vanadium dioxide (VO$_{2}$) nanocomposites. These
simulations were done to understand the data from transient absorption pump
probe measurements taken over the previous two years by the author. The
various parameters contributing to the dynamics of the system were
systematically varied within the simulation in order to understand how the
various properties of the nanocomposite affect the thermodynamics of the
system. It was determined that the background temperature and the optical
properties of the film make the dominant contributions to the system
response. The simulation was able to predict the maximum change in
transmission measured in experiment fairly well but could not predict the
speed at which the system responded to the pump laser. Steps to improve
upon the agreement between experiment and simulation are proposed.
Vanderbilt University. Dept. of Physics and Astronomy
2011-04
Thesis
en_US
http://hdl.handle.net.proxy.library.vanderbilt.edu/1803/4839
https://ir.vanderbilt.edu/bitstream/1803/4839/1/MacQuarrie_2011Thesis.pdf
40389b351335f5669cf9d3391aa9fa63
https://ir.vanderbilt.edu/bitstream/1803/4839/2/license.txt
8ec8fd34acde2f4d8b37a78345cbcc36
https://ir.vanderbilt.edu/bitstream/1803/4839/3/MacQuarrie_2011Thesis.pdf.txt
10ae22c8d8e24d84beda514ce05f28c9
Finite element analysis
vanadium dioxide
metal nanoparticles
optical limiter
plasmonic modulator
Finite element method
Vanadium oxide
Vanadium compounds
Metals -- Heating
Nanocomposites (Materials)
oai:ir.vanderbilt.edu:1803/66292020-04-22T06:11:49Zcom_1803_569com_1803_66col_1803_685
The quadratic approximation for quintessence with arbitrary initial conditions
Swaney, Jeffrey
Scherrer, Robert J. (Robert Joseph), 1959-
We examine models of quintessence in which a minimally-coupled scalar field
phi evolves near a
local extremum of its potential V ( phi) at phi_*. Assuming that (1/V
)(dV/dphi) is small and w ~ -1, we
Taylor expand the potential about phi_* and derive a general expression for
w(a). The dynamics of this
field are determined by the initial and final equation of state parameters
w_i and w_0, the quantity
V''( phi_*)/V(phi_*), and the direction of \dot\phi_i in relation to
\dot\phi _0. This approximation is then tested for six
values of V''( phi_*)/V(phi_*) and shown to lie within 2% of the exact
solution for five of these cases.
However, the model becomes less precise near certain values of V''(
phi_*)/V(phi_*) where \dot\phi
becomes very large.
Vanderbilt University. Department of Physics and Astronomy
2014-04
Thesis
en_US
http://hdl.handle.net/1803/6629
https://ir.vanderbilt.edu/bitstream/1803/6629/1/Jeff_Swaney_thesis.pdf
8c44709360bc5d929ace766666f62f32
https://ir.vanderbilt.edu/bitstream/1803/6629/3/license.txt
ece5a9f3b88102a1eb9b2ff22411c299
https://ir.vanderbilt.edu/bitstream/1803/6629/4/Jeff_Swaney_thesis.pdf.txt
f151f56af673b49bf2a10791ff23a2cf
CC0 1.0 Universal
Dark energy
Quintessence
w(a)
Dark energy (Astronomy)
Dark energy (Astronomy) -- Mathematical models
Dark matter (Astronomy)
Scalar field theory
oai:ir.vanderbilt.edu:1803/94432020-04-22T10:32:38Zcom_1803_569com_1803_66col_1803_685
Probing Heavy Spin-2 Bosons with γγ final states from Vector Boson Fusion Processes at the LHC
Guo, Yuhan
New massive spin-2 particles are predicted in theoretical extensions to the Standard Model (SM) attempting to solve the hierarchy problem. Such theories postulate that gravity is diluted compared to the other fundamental forces because it can propagate in extra spatial dimensions. While such theoretical models are of high experimental interest because they predict massive spin-2 particles (Y2) potentially detectable by collider experiments, searches at the Large Hadron Collider (LHC) have thus far produced no significant evidence for their existence. This work considers a hypothetical physics scenario where low coupling strengths between the Y2 and quarks/gluons is the underlying reason behind the null Y2 search results at the LHC, which have mainly relied on Drell-Yan and gluon-gluon fusion production mechanisms. The focus of this paper is a feasibility study to search for Y2 particles using vector boson fusion (VBF) processes at the LHC. In the context of an effective field theory approach with varying couplings κV between Y2 and the weak bosons of the SM, we consider the Y2 → γγ decay mode to show that the requirement of a diphoton pair combined with two high pT forward jets with large dijet mass and with large separation in pseudorapidity can significantly
√ reduce the SM backgrounds. Assuming proton-proton collisions at present the total VBF production cross sections, Y2 decay widths, and Y2 → γγ branching ratios as a function of m(Y2), considering universal and non-universal couplings to the SM particles. The unitarity-violating phase space is described. The proposed VBF Y2 → γγ search is expected to achieve a discovery reach with signal significance greater than 5σ for Y2 masses up to 4.4 TeV and κV couplings down to 0.5.
Vanderbilt University. Dept. of Physics and Astronomy
2019
Thesis
en_US
http://hdl.handle.net/1803/9443
https://ir.vanderbilt.edu/bitstream/1803/9443/1/Yuhan_Guo_Physics_Honors_Thesis.pdf
fbe485e35d3d999da7c5f8b9cd22d975
https://ir.vanderbilt.edu/bitstream/1803/9443/2/license.txt
8a4605be74aa9ea9d79846c1fba20a33
https://ir.vanderbilt.edu/bitstream/1803/9443/3/Yuhan_Guo_Physics_Honors_Thesis.pdf.txt
5708aa84f9f08992316adcdceec9b5f1
Vector Boson Fusion Processes
Standard Model
Partical Physics
Large Hadron Collider
Physics
oai:ir.vanderbilt.edu:1803/41062020-04-22T08:10:58Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Multipole mixing ratios of transitions out of high spin gamma vibrational states in neutron rich Mo, Ru isotopes
Fenker, Benjamin
Hamilton, Joseph H.
Current models of nuclear structure describe nuclear states in terms of
collective vibrations and rotations of a ground state. - One such quadrupole
vibrational band is the gamma-band formed by vibrations of the short sides
of a deformed nucleus. - When a nucleus that is in this mode decays to its
ground state, the electromagnetic radiation is predicted to be entirely
quadrupole in nature. - This prediction has been well documented in a wide
range of nuclei. - However, a recent study of neutron rich molybdenum and
ruthenium isotopes found a few gamma-band to ground-band transitions that
contained almost no quadrupole radiation. - This work utilizes the
Gammasphere detector array to examine the angular correlations in the
de-excitations of the secondary fission fragments of 252Cf in order to make
independent measurements of these results. - This work also uses the same
technique to measure the multipole mixing ratios of gamma-band to
ground-band transitions originating in states with spin-parity as high as
9+. - The results demonstrate that in these nuclei, electric quadrupole
radiation is strongly favored in gamma to ground band transitions as has
been predicted by theory.
Vanderbilt University. Dept. of Physics and Astronomy
2010-04-27
Thesis
en_US
http://hdl.handle.net/1803/4106
https://ir.vanderbilt.edu/bitstream/1803/4106/1/ben_thesis.pdf
b23544cb5b8e6cbcc1e4f8d39658a8c1
https://ir.vanderbilt.edu/bitstream/1803/4106/5/license.txt
e73896de3e9c049a2e2c39e415310251
https://ir.vanderbilt.edu/bitstream/1803/4106/6/ben_thesis.pdf.txt
4ce91370ea1235fad91986defc9f71ca
Nuclear deformation
Neutron-rich
Multipole mixing ratios
High spin
Gamma vibrational states
Mo, Ru isotopes
Spontaneous fission
Angular correlations (Nuclear physics)
Nuclear structures
Nuclear shapes
Molybdenum -- Isotopes
Ruthenium -- Isotopes
oai:ir.vanderbilt.edu:1803/48402020-04-22T08:03:37Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Developing High-Brightness Electron Beam Sources for Producing Quantum Degenerate Electron Beams
Kohler, Jonathan
Brau, Charles A., 1938-
The Pauli Exclusion Principle places a fundamental limit on the brightness
of an electron beam. Developing a cathode which can reach this limit is
useful for achieving maximum operation in current applications of electron
beams, but also opens new areas of physics to be explored. When the phase
space of the electron beam is filled to the maximum density, the electrons
will experience a degeneracy pressure, similar to that which keeps a neutron
star from collapsing. One promising source for a quantum degenerate beam is
field emission from adsorbates on carbon nanotubes. Adsorbates have been
shown to provide several orders of magnitude enhancement to emission
brightness, which approaches the degeneracy limit. We have developed
experiments to test various adsorbates, in order to find those which bind
tightest and provide the largest enhancement in brightness. Continuing work
to discover better adsorbates should soon allow for the generation of a
quantum degenerate electron beam.
Vanderbilt University. Dept. of Physics and Astronomy
2011-04
Thesis
en_US
http://hdl.handle.net/1803/4840
https://ir.vanderbilt.edu/bitstream/1803/4840/1/Kohler_thesis.pdf
2f168273089919a0f5e80a30af0a325b
https://ir.vanderbilt.edu/bitstream/1803/4840/2/license.txt
8ec8fd34acde2f4d8b37a78345cbcc36
https://ir.vanderbilt.edu/bitstream/1803/4840/3/Kohler_thesis.pdf.txt
488e0c168098a2f5dcf2b9f19722c8e7
high brightness cathode
electron beam
carbon nanotube
field emission
quantum degeneracy
resonant tunneling
Electron beams
High-brightness accelerators
Field emission cathodes
Particle beams
oai:ir.vanderbilt.edu:1803/51912020-04-22T08:21:31Zcom_1803_561com_1803_559com_1803_3706com_1803_569com_1803_66col_1803_831col_1803_685
Simulations of Nano-Structures in Time Dependent External Fields
Atkinson, Mackenzie
Varga, Kálmán, 1963-
Time Dependent Density Functional Theory is used to probe the
structure of matter. Coulomb explosion of small hydrocarbons driven by
strong laser pulses and electron holography of molecules are studied
in a theoretical framework. The spectra of the ejected protons
obtained computationally is in good agreement with experimental data
of Coulomb explosion. TDDFT allowed us to obtain time-dependent data,
giving us a deeper understanding of the process. Our computational
approach to electron holography provides 3-d reconstructions of simple
molecules. Further investigation is needed in order to reconstruct
larger molecules.
Vanderbilt University. Department of Physics and Astronomy
2013-04-22
Thesis
en_US
http://hdl.handle.net/1803/5191
https://ir.vanderbilt.edu/bitstream/1803/5191/1/mack_thesis.pdf
55a7d29a163fbbef5f7049f0e7a9e06d
https://ir.vanderbilt.edu/bitstream/1803/5191/2/license.txt
8ec8fd34acde2f4d8b37a78345cbcc36
https://ir.vanderbilt.edu/bitstream/1803/5191/3/mack_thesis.pdf.txt
decb3756996947aaae15e2c0e0a0eba9
DFT
TDDFT
Time dependence
Coulomb explosion
Nanostructures
Density functionals
Electron holography
Coulomb excitation
oai:ir.vanderbilt.edu:1803/169962022-01-13T23:56:30Zcom_1803_569com_1803_66col_1803_685
Analytic Solutions of Two Electrons in Harmonic Confinement in an Optical Cavity
Huang, Chenhang
The possibility to control quantum systems with photons has stimulated
recent interest in the study of quantum optical systems. While
simple classical quantum systems admit well-known solutions, analysis
of light-coupling quantum regimes remains lacking. In this work,
we obtain analytic solutions for a light-coupling electron pair in harmonic
confinement in a cavity by separating center-of-mass (CM) and
relative motions. The CM part can be calculated in closed form or
by exact diagonalization of the Hamiltonian, and the relative part is
quasi-exactly solvable. We analyze the 2D results produced by the
exact diagonalization method and reach conclusions on the effects of
different system parameters. We also present 1D numerical simulations
by Stochastic Variational Method (SVM) using Explicitly Correlated
Gaussian (ECG) bases, which agree with our analysis in 2D. Our analytic
solutions may provide a valuable calibration point for simulations
in the quantum optical regime.
Vanderbilt University. Dept. of Physics and Astronomy
2021-12
Thesis
en_US
http://hdl.handle.net/1803/16996
https://ir.vanderbilt.edu/bitstream/1803/16996/1/Honor_Thesis_of_Physics.pdf
afd9cfd40f9c019739a319866117fc42
https://ir.vanderbilt.edu/bitstream/1803/16996/2/license.txt
49f58bf859518f166339cafac2e786df
physics
honors thesis
condensed matter physics
material physics
Physics
oai:ir.vanderbilt.edu:1803/52292020-04-22T08:22:12Zcom_1803_569com_1803_66col_1803_685
Simulation and optimization of pulsed Chemical Exchange Saturation Transfer for clinical application at 3T
Dewey, Blake
Smith, Seth A.
Chemical Exchange Saturation Transfer (CEST) is often overlooked as a method
for the investigation of metabolites in vivo due to the time required to
obtain a full spectrum. We investigated the feasibility and optimization of
a pulsed CEST technique that interleaves an echo planer imaging (EPI)
readout with saturation in order to reduce time. In addition, we
incorporated a multi-shot EPI sequence that reduces distortions. To achieve
this, computer simulations based on the Bloch equations were used to
optimize scan parameters while keeping scan time in the clinical timeframe.
To analyze the data, a number of Lorentizian fitting algorithms were
investigated to evaluate their ability to isolate CEST contrast. By using a
30 ms pulse at 2 μT, we were able to achieve CEST contrast on the order of
2% and could provide APT maps based on an adapted Lorentzian fitting method.
In the process of this fitting, it was also discovered that MTR contrast
could also be recovered from the CEST data, allowing for MT and CEST to be
acquired at the same time.
Vanderbilt University. Deptartment of Physics and Astronomy
2013-04-22
Thesis
en_US
http://hdl.handle.net/1803/5229
https://ir.vanderbilt.edu/bitstream/1803/5229/1/blake_thesis.pdf
c6bd6d6df6849b73a3992aee75979455
https://ir.vanderbilt.edu/bitstream/1803/5229/2/license.txt
8ec8fd34acde2f4d8b37a78345cbcc36
https://ir.vanderbilt.edu/bitstream/1803/5229/3/blake_thesis.pdf.txt
f8fa828d8f276f64eedf504c85eaaf2f
MRI
Magnetic Resonance
CEST
Chemical Exchange Saturation Transfer
Pulsed CEST
MT
simulation optimization
Magnetic resonance imaging
Magnetic resonance imaging -- Mathematics
oai:ir.vanderbilt.edu:1803/103662020-08-17T06:10:13Zcom_1803_569com_1803_66col_1803_685
A web-based application of the Cellular Force Inference Toolkit (CellFIT)
Xu, Xiaojia
Given an image of an epithelial cell sheet, CellFIT can infer cellular forces by segmenting the image into individual cells, constructing equilibrium equations for the points where cells meet at triple junctions, and finding a least-squares solution for the tensions at cell-cell interfaces. Similarly, cellular pressures can be estimated by constructing Laplace equations that relate the edge tensions, curvatures and cellular pressure differences. Despite these capabilities, the accessibility of CellFIT to scientists of all backgrounds is not yet optimized. We will present an updated web-based application of CellFIT that allows users to access the software from a browser. The updated version includes improved error handling and the implementation of additional functionality for reading and processing image stacks. Application of the web-based CellFIT to time-resolved image stacks of wound healing in Drosophila epithelia demonstrates spatial and temporal variations in cellular forces as the wounds close.
Vanderbilt University. Dept. of Physics and Astronomy
2019-04-18
Thesis
en_US
Department of Physics and Astronomy, Vanderbilt University
http://hdl.handle.net/1803/10366
https://ir.vanderbilt.edu/bitstream/1803/10366/1/Xu_Honors_Thesis05.pdf
0680c11d620c6c8d26a89d9b22f760cc
https://ir.vanderbilt.edu/bitstream/1803/10366/2/license.txt
49f58bf859518f166339cafac2e786df
https://ir.vanderbilt.edu/bitstream/1803/10366/3/Xu_Honors_Thesis05.pdf.txt
2ebb078e8e56fb0f255443c9248e0221
biophysics
collective behavior
active matter
wound healing
Physics