Physics and Astronomy

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Jeffery Anderson (Capstone, June 2013, Advisor: Dallin Durfee )

Abstract

Jordan Bell (Senior Thesis, April 2013, Advisor: David Allred )

Abstract

The thickness uniformity of thin films across a substrate's surface is of interest in many important applications, including the manufacture of multilayer mirrors and antireflective coatings. This thesis explores the thickness profile of films deposited by DC magnetron sputtering on large stationary substrates, then uses that data in a computer model to predict thickness uniformity for substrates undergoing "planetary" motion. We tested the ability of the model to make predictions by producing a sample under planetary rotation and measuring its thickness profile. We found that the model gave a good approximation to the actual thickness profile, but actually underestimated the thickness uniformity.

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Josh Bodon (Senior Thesis, August 2013, Advisor: Kent Gee )

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The radiation of finite-amplitude waves from the open end of a baffled, circular pipe is considered as a direct continuation of work begun by Kuhn, Blackstock, and Wright more than three decades ago [Kuhn et al., J. Acoust. Soc. Am. 63, S1, S84 (1978)]. Band-limited Gaussian noise, as well as 1 kHz, 1.5 kHz, and 2kHz sinusoidal pulses, with initial peak pressure amplitudes ranging from 0.5 – 1.2 kPa, have been propagated down a 6.1 m pipe, whose open end (5.1 cm inner diameter) has been placed off-center in a large rectangular baffle. As the steepened or shock-like waves exit the pipe, the measured waveforms are comprised of sharp impulses that are delta function-like in nature, particularly on axis. Although linear piston theory predicts similar waveform shapes, there is also evidence that nonlinear propagation of these impulses, which can exceed peak pressure amplitudes of 1.5 kPa near the pipe opening, is occurring.

Carla Carroll (Senior Thesis, April 2013, Advisor: Mike Joner )

Abstract

The environment surrounding supermassive black holes in active galaxies can be probed through the reverberation mapping technique. This technique requires the galactic nuclei to be simultaneously observed spectroscopically with a large 2m-class telescope and photometrically with a smaller telescope. Since obtaining large telescope time for long observing campaigns is difficult, we present a new broadband photometric reverberation mapping technique that can be performed on meter-class telescopes. Observations in the R and V band filters provide a measurement of time variable emission in Hα and Hβ respectively mixed with an observation of the continuum. The I band filter provides a continuum-only measurement. We obtained photometric observations in VRI on the 0.9-meter telescope at the West Mountain Observatory of the very broad-line Seyfert I galaxy Mrk 926 to test this technique. We found Mrk 926 relatively quiescent during the fall of 2012, though we originally selected Mrk 926 due to its strong emission lines and strong variability. This made estimation of Mrk 926's supermassive black hole mass impossible. Despite the quiescent results of Mrk 926, we produced high precision light curves from all filters over the period of several months. Our data are sufficient that had our target AGN\index{AGN} been variable, we would have been able to measure delay times between the BLR and the nucleus.

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Caleb Coburn (Senior Thesis, August 2013, Advisor: Michael Ware )

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We report the intensity measurement of a high intensity pulsed laser focus and the efficiency characterization of an optical signal collection system. We seek experimental confirmation that large free electron wave packets radiate like point particles. Our experiment requires intensities on the order of 1018 W/cm2 to produce red-shifted signal photons. The red shift is important in discriminating against a large background. We use time-of-flight spectroscopy to measure the charge to mass ratio of laser induced multiply ionized argon and compare the highest achieved charge state with known strong-field ionization intensities. We also use parametric down conversion to make an absolute efficiency measurement of our detection system. These measurements are necessary to ensure our apparatus is capable of producing the intensity dependent signal that we seek and allow us to calculate the total radiated signal. We measure a pulse intensity of at least 1:571018 W/cm2. The collection efficiency is 22:71%.

Daniel Craft (Senior Thesis, April 2013, Advisor: John Colton )

Abstract

Electron spins in InAs quantum dots have been studied using a pump-probe technique that normally yields the T1 spin lifetime, the time required for initially polarized electrons to relax and randomize. Using a circularly polarized laser tuned to the wavelength response of the quantum dots, the spins are "pumped" into alignment. After alignment, the spins are detected using a second, linearly polarized "probe" laser. The spin response over time is traced out by changing the delay between the two lasers. In contrast with other samples (bulk GaAs and a GaAs quantum well), where the spin response decays exponentially with time, initial data on the quantum dots has shown an unexpected, exponentially decaying sinusoid. This exponentially decaying sinusoid has a decay constant of 190 ns and oscillation frequency of 4.17 MHz, independent of both temperature and magnetic field.

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Eric Gibbs (Senior Thesis, August 2013, Advisor: Branton Campbell )

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Symmetry-mode analysis (SMA) has proven to be an effective tool in solving a nuclear crystal structure from powder diffraction data. The principles of SMA have also been applied to magnetic structures though previous work has been limited to the set of modes associated with a single k vector. Here we demonstrate the capabilities of fully-general SMA by solving both the nuclear and magnetic structures of La_0.5Ca_0.5MnO_3 from data collected at the POWGEN beam line at the Spallation Neutron Source at Oak Ridge Tennessee. The low-temperature antiferromagnetic structure of La_0.5Ca_0.5MnO_3 (LCMO) combines many k vectors and possesses a monoclinic 2√2×2√2×2 supercell relative to the cubic-perovskite parent. Starting with a P21/m-symmetry model for the nuclear structure, based on previous work, symmetry-mode inclusion/exclusion cycles added considerable detail to the final result. A list of candidate active magnetic modes were initially determined in P1 symmetry, which indicated magnetic space-group Pa21/m (also consistent with previous work), where 9 magnetic degrees of freedom are present. Constrained by this symmetry, subsequent simulated-annealing runs yielded several distinct structures with comparable fits resulting due to the pseudo-orthorhombic metric of LCMO. Physical considerations then guide our choice of the final structure.

Erin Gilmartin (Senior Thesis, December 2013, Advisor: Gus Hart )

Abstract

The hardness of platinum and palladium alloys can be signicantly improved by precipitate hardening. One application of this is in Pt/Pd jewelery alloys where only small amounts of the alloying agent may be added (less than 5 wt.-%). For these alloys, one needs to identify platinum- and palladium-rich ordered phases that will form precipitates in nearly pure alloys. Using first principles calculations, we identified 22 systems where a platinum- or palladium-rich phase (prototype Pt8 Ti) is stable but has not yet been observed. In the case of Pt-Mo, we constructed a cluster expansion and predicted the order-disorder transition temperature. Using our results as a guide, further experimental work may well turn up additional elements that will be useful for precipitate hardening in Pt-rich and Pd-rich alloys.

Landon Goggins (Capstone, June 2013, Advisor: )

Abstract

Vesicle fusion is a highly studied topic in many biological fields, as it is extremely important in the nervous system at the synapses. While the protein machinery behind vesicle fusion is well-studied and understood, the effect of lipid order and stability on vesicle fusion is not. In our research, we attempt to see what effect fusogenic proteins have on lipid order by measuring the phase transition temperature of artificial vesicles using a Differential Scanning Calorimeter. To do so, we prepared the instrument extensively by calibrating it and finding its optimal parameters that will allow for many further uses and experiments. We found that while changing the buffer solution the vesicles are contained in significantly reduced the melting temperature, the addition of Syntaxin (a fusogenic protein) into the vesicle membranes may have only slightly reduced it.

Matthew Groesbeck (Senior Thesis, August 2013, Advisor: Michael Ware )

Abstract

We describe the motivation for a research project measuring decay rates of various beta decay-type isotopes. Recent publications have suggested that nuclear decay rates show an unexpected slight annual oscillation. The unknown factor causing this fluctuation is hypothesized to be the variable flux of solar neutrinos through the earth. Our experiment is designed to test these claims by tracking the counts of ten beta-decay samples over a period of up to ten years. The samples will be measured by multiple radiation detectors under strict environmental controls. The central LabView control program is also described in depth.

Nathan Gundlach (Senior Thesis, April 2013, Advisor: Justin Peatross )

Abstract

We use the Dirac equation to model electron behavior in a strong laser field. We also present simulations of the density of spin expectation as the Gaussian wave packet undergoes complex relativistic motion. This work extends an analytic technique for computing a Gaussian wave packet in an intense laser field to the case of a Dirac electron. This technique previously had only been applied to the Klein-Gordon equation.

David Hart (Senior Thesis, April 2013, Advisor: Traci Neilsen )

Abstract

The two-source model for jet noise holds that turbulent mixing noise in jets is generated by uncorrelated, fine-scale (FSS) and partially correlated, large-scale (LSS) turbulent structures [Tam et al., J. Fluid Mech. 615, 253-292, (2008)]. The noise from an F-22A Raptor is modeled with an equivalent source consisting of two line arrays of monopole sources. These arrays, one correlated and one uncorrelated, with Rayleigh-distributed amplitudes, account for both FSS and LSS sound propagation [J. Morgan et al., J. Acoust. Soc. Am. 129, 2442 (2011)]. The equivalent source parameters are selected based on a Bayesian optimization implemented with simulated annealing and fast Gibbs sampler algorithms. This method yields the best fit parameters, and the sensitivity of the solution is indicated by the estimated posterior probability distributions. This equivalent source model can generate results up to approximately 1 kHz and accurately predict both near-field and far-field measurements. Analysis of the resulting equivalent sources shows that the directional, correlated line array has a greater effect on the near-field sound. Additionally, the sensitivity of the model parameters appears to increase as the frequency increases. These and other findings give insight into the physical nature of the jet noise source.

David Hoagland (Capstone, August 2013, Advisor: )

Abstract

The purpose of this project is to design and test a helical insert that will be used in the snow sports industry to affix retention bindings to downhill snow skis. The goal is to produce a product that will exceed the current tensile strength standard for the industry as well as provide greater freedom to the consumer. ASTM International provides several standards for the testing of sports equipment that were used as the basis of this research. My project is accomplished through combining research in ski design and manufacturing, emphasis coursework in manufacturing engineering and business management, and experimental procedures learned from physics. The product was tested on cross-section samples of snow skis that consist of sandwiched layers of plastic and composites wrapped around a core material of wood, foam, or a combination of both with epoxy resin. A variation of ASTM Standard F474-98 was used to verify the results. The results of this research proved that both goals were attained.

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Jarom Jackson (Senior Thesis, April 2013, Advisor: Dallin Durfee )

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This thesis describes the work done to set up two external cavity diode lasers to be used in an ion interferometer. These lasers will be used to trap and cool atoms and to manipulate and probe their energy states. The main cooling laser is generated using a doubled IR laser, but is very unstable due to the various stages—diode, external cavity, doubling crystal and cavity—that all need feedback to lock the frequency. The probe laser is much simpler because the wavelength needed matches that of a readily available laser diode. The stability and scanning ranges of both lasers are presented.

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Brian James (Senior Thesis, August 2013, Advisor: Lawrence Rees )

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With the global supply of He-3 in short supply and an increased need for neutron detectors, Cd-based detectors provide an attractive alternative. I have done research on various possible designs using Monte Carlo methods to optimize detectors for efficient neutron capture.By examining Cd-based detectors with the highest neutron capture rate will be better able to distinguish neutrons and gamma rays in order decrease the possibility of false neutron detection.

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Zachary Jensen (Senior Thesis, April 2013, Advisor: Scott Sommerfeldt )

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Acoustic enclosures are commonly used to attenuate the noise radiated from a sound source. A model to accurately predict the insertion loss of an enclosure can quickly become complicated for complex configurations and have uncertainties over different frequency ranges. In many such situations, a reliable, simple method of predicting insertion loss with reasonable accuracy would be valuable if a quick estimation is needed for a certain enclosure. An insertion loss model was tested using a Design of Experiments (DOE) approach, which incorporated a range of apertures, absorptive treatment, and obstructions, with varying surface areas and positions in order to span a large design space. This paper discusses the insertion loss measurements of the DOE test configurations and compares the measurements with an attempted fit of all 36 configurations. Nearly 80% of the configurations fell below an error of 2.5 dB, and 100% fell below 4.5 dB, which was deemed to provide a reasonable rough estimate of insertion loss.

Jorge Jimenez Blanco (Senior Thesis, April 2013, Advisor: Bret Hess )

Abstract

MRI is widely used in medical imaging. Unlike x-ray and Computed Tomography, MRI uses no ionizing (x-ray) radiation, and is thus less damaging. However, MRI suffers from compara- tively long scan times for some applications. MRI data is sampled in the Fourier domain, and the sampling required for a full image can be quite time consuming in comparison to other medical imaging techniques. The use of certain schemes that allow us to reconstruct full images from under-sampled MRI data may potentially solve this problem. This thesis first provides an in- troduction to the basic principles behind MRI to serve as a foundation for understanding image reconstruction. The mathematical theory of compressed sensing is then presented, which allows images to be reconstructed from randomly under-sampled Fourier domain data. A description of how compressed sensing can be used in MRI to greatly accelerate image acquisition is then pro- vided. Finally, a variety of different MRI acquisition strategies using compressed sensing were simulated, and results are presented. A maximum reduction of 66% of scan time was achieved by the strategies explored with very little loss of image quality.

Adam Konneker (Senior Thesis, April 2013, Advisor: Robert Davis )

Abstract

Here we report the synthesis of vertically aligned and three-dimensional patterned silicon-carbide nanowires (SiCNWs). The SiCNWs were formed by thermally annealing silicon-carbon core-shell nanotubes (Si/CNTs) in argon. The Si/CNTs were fabricated based on a carbon nanotube templated microfabrication process (CNT-M), in which a vertically aligned and patterned carbon nanotube (CNT) growth was followed by low pressure chemical vapor deposition (LPCVD) of silicon. The carbon nanotube forests were grown from a patterned catalyst layer resulting in high aspect ratio three dimensional microscale structures up to 500 microns tall with vertical sidewalls. Silicon LPCVD layers were deposited conformally, coating the nanotubes well into the interior of the structure. A thermal annealing of the structure converts the Si/CNTs to SiCNWs. This combination of CNT-M fabrication, LPCVD silicon deposition, and annealing yields a unique fabrication approach resulting in porous three dimensional silicon carbide structures with precise control over shape and porosity.

Tess Larson (Senior Thesis, August 2013, Advisor: Denise Stephens )

Abstract

The exoplanet research group at BYU has been observing and reducing data taken of objects on the Kepler planetary candidate list. We observed KOI667.01 at West Mountain Observatory (WMO) and realized that it was a false positive. Because the field we were interested in was very crowded we could not use aperture photometry to analyze the data. We used DAOPHOT in order to reduce the data and compute accurate light curves. We were able to determine which object within our crowded field was the eclipsing binary.

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Tyler Lee (Capstone, June 2013, Advisor: )

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Cellular exocytosis is driven by the formation of SNARE complexes between synaptobrevin (VAMP), SNAP25, and syntaxin on the plasma membrane. These SNARE proteins work together to drive fusion, but the individual effects of each of these proteins are still undetermined. We show that syntaxin can be reconstituted into the membranes of artificial vesicles for in vitro fusion experiments. The nystatin/ergosterol fusion assay was used to measure individual fusion events of artificial vesicles to a planar lipid bilayer formed on hole of a plastic cup. We found that reconstituted syntaxin has a possible hindering effect on fusion in the absence of other SNARE proteins, but further testing is necessary to confirm this hypothesis. Furthermore, we suggest that syntaxin keeps vesicles from sticking together, allowing the vesicles to diffuse more readily in solution.

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David Ludlow (Capstone, June 2013, Advisor: )

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Spencer Lyon (Capstone, August 2013, Advisor: Derek Thomas )

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I describe the creation of a Python interface to the HSF C++ library. HSF stands for hierarchal spline forests and the C++ library is used to represent surfaces or volumes of arbitrary complexity in terms of hierarchal splines. This library is under active development by BYU faculty in the Physics, Engineering, Mathematics, and Information Technology departments. I will defend the choice of using Python as the high-level interface. I will also describe projects that facilitate wrapping compiled languages (like C, C++ or Fortran) in Python. Among them are SWIG, Boost.Python, Cython, and a relatively new project – XDress. XDress blends an expressive typesystem, C/C++ source code parsers, and code generating utilities into an easy to use system for constructing Python wrappers for C or C++ code via Cython.

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Thayne McCombs (Senior Thesis, August 2013, Advisor: Joseph Moody )

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The Remote Observatory for Variable Object Research (ROVOR) has a backlog of three years of observations that have not been reduced or analyzed. In this Thesis we discuss software we developed to improve the data reduction pipeline and automate many of the necessary steps in re- ducing astronomical data. Specifically, we developed the RedROVOR python package to perform the tasks necessary for reducing data from ROVOR, as well as an online web interface (RovorWeb) which provides an easy to use interface to the RedROVOR toolset, as well as an online observation log management system to keep track of observations made with the ROVOR observatory.

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Josh Olson (Senior Thesis, July 2013, Advisor: Justin Peatross )

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We employ an interferometric technique to diagnose the plasma density in an intense laser focus that ionizes neon gas. A probe beam, arriving after the ionizing pulse, experiences a phase shift as it travels through the refractive index of the plasma. The phase shift is apparent when the probe beam interferes with a reference beam that avoids the plasma. The plasma density is characterized as a function of delay over several nanoseconds after the 35- femtosecond ionizing laser pulse. Our data shows a 50% drop in density after 4.5 ns.

David Perkins (Senior Thesis, August 2013, Advisor: Ross Spencer )

Abstract

The National Spherical Torus Experiment (NSTX), underway at Princeton Plasma Physics Laboratory (PPPL), investigates the plasma dynamics in a spherical tokamak to understand the device’s potential as a fusion power generator. Temperature anisotropy, a characteristic that could have substantial effects on the plasma’s overall dynamics, is not well-known in NSTX. The particle code GTC- NEO, a particle-in-cell simulation developed at PPPL, allows for computational diagnosis of temperature anisotropy. The code simulates a tokamak plasma in the neoclassical limit. We present here a computational study of temperature anisotropy in NSTX using GTC- NEO, including spatial temperature anisotropy profiles in varied regimes of particle collision frequency. Results show that anisotropy is less than 5% in NSTX. We observed that temperature anisotropy peaks near the edge of the plasma on the outboard side of the device. The magnitude of this peak varies inversely with collision frequency.

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Lukas Pritchett (Senior Thesis, April 2013, Advisor: Justin Peatross )

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We investigate time-resolved quantum field theory (QFT), which seeks the time evolution of QFT states. Time-resolution in the Schrödinger picture is possible with commonly available computational resources. In demonstration of this, we have developed a time-resolution method and applied it to problems in phi-4. We detail the method and provide some example computation times. The study of time-resolved QFT can provide insight into the structure of QFT and also an alternative method for solving familiar problems.

Nicole Quist (Senior Thesis, May 2013, Advisor: Lawrence Rees )

Abstract

The double pulse response of the Gadolinium Lithium Borate Cerium detector suggested its effectiveness for applications in Laboratory Nuclear Astrophysics, specifically in sparse neutron spectroscopy amidst the competition of background radiation. Using Cf-252 as a neutron source, a time of flight facility was built to determine the efficiency of the LGB detector. The detector has a $10\%$ efficiency in neutron detection, however, the energy detection efficiency is $2\%$. Thus, the total efficiency for neutron spectroscopy is $0.2\%$. Therefore, the LGB detector is not a good choice for neutron spectroscopy.

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Drake Ranquist (Senior Thesis, April 2013, Advisor: Victor Migenes Gaetan )

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Magnetic reconnection is the leading mechanism for energy release in solar eruptions. The coronal magnetic field cannot be measured remotely or in situ, which makes modeling difficult. Using NIMROD, an extended magnetohydrodynamics simulation code, we have developed an indirect method to obtain the asymmetry of the magnetic field during observed solar eruptions. We analyzed the eruptions on 6/7 Dec 2010 and 7 Mar 2011 with the Atmospheric Imaging Assembly. We traced post-flare loops and found the asymmetric reconnection models that best fit the observations using rotation and chi-squared algorithms. To further constrain the results, we rotated these fits onto the observations from the Solar Terrestrial Relations Observatory. We estimated that the 2010 event had a magnetic field asymmetry of 4:1 and the 2011 event an asymmetry of 1.5:1. In combination with other signatures of asymmetric magnetic reconnection, this can yield a method for determining the upstream magnetic field ratios during solar eruptions.

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Emily Ranquist (Senior Thesis, August 2013, Advisor: Denise Stephens )

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Magnitudes are the quantitative measurements of a star’s brightness. By analyzing a plot of the magnitude over time, known as a light curve, one can detect objects with fluctuating light output, such as variable stars, eclipsing binaries, and stars with transiting planets. To obtain magnitudes, we must go through a time consuming process called photometry on multiple images for every star we wish to plot. Through the use of the command language and scripting tools in NOAO’s Image Reduction and Analysis Facility (IRAF), we have been able to develop a program called brightER that greatly reduces the amount of time spent on photometric procedures. BrightER is a compilation of multiple scripts, each designed to automate a specific part of the process. Using this program, we have been able to reproduce light curves in less than an hour that originally took days to create. The ease and efficiency of brightER allows us to focus less on data acquisition and more on the results.

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Brent Reichman (Senior Thesis, April 2013, Advisor: Scott Sommerfeldt )

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Active noise control (ANC) uses a control signal to effectively cancel out unwanted sound. Applying ANC to snoring presents an interesting challenge because of its unpredictable nature and the close distance between the source and the desired region of cancellation. This experiment focuses on two factors: How much attenuation can be achieved in a standard bed using different microphone and speaker setups and how large is the "zone of silence" that is created.

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Shanell Reynolds (Capstone, April 2013, Advisor: Traci Neilsen Kent Gee )

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Aircraft maintenance workers can be exposed to high noise levels while working around military aircraft. Near-field measurements of an F-22 Raptor at different engine conditions provide information regarding the noise dosage experienced in the vicinity of the aircraft. Level weighting curves, which account for different aspects of hearing perception, have been applied to the overall sound pressure level data from locations where personnel might stand. Hearing protection attenuations are applied to the A-weighted overall sound pressure levels to determine the exposure levels while wearing properly inserted ear plugs and muffs. It is found that significant reduction is achieved by the required dual hearing protection used for this project. The dual hearing protection can provide around 40 dB of attenuation in the overall exposure level. These results can be used by the military to make informed decisions regarding acceptable exposure times for maintenance personnel.

Danny Ritter (Capstone, June 2013, Advisor: )

Abstract

To gain insight as to how proteins affect the stability of artificial vesicles (AVs) and therefore their fusion with lipid bilayers, we used Differential Scanning Calorimetry (DSC). DSC uses constant temperature change at a specified rate to determine phase transition temperatures of the sample being scanned. Though DSC has been a common technique in biophysics for a few decades, we had to find optimal calibration constants, scan rates, and sample concentrations that worked best for our experiments. Upon comparing results of DSC scans of dipalmitoylphosphatidylcholine (DPPC) vesicles with no infused proteins with scans of syntaxin-infused DPPC vesicles, we saw no apparent change in the phase transition temperature of the vesicles. One would expect the protein-infused vesicles to have a lower degree of order, which contributes to stability. Lower stability results in lower phase transition temperature. The lack of phase transition temperature change, therefore, is somewhat surprising. More experiments should be done to determine the reproducibility of this result, and to check the accuracy of our calorimeter.

Conrad Rosenbrock (Senior Thesis, April 2013, Advisor: Bret Hess )

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Artificial neural networks have been effective in reducing computation time while achieving remarkable accuracy for a variety of difficult physics and materials science problems. Neural networks are trained iteratively by adjusting the size and shape of sums of non-linear functions by varying the function parameters to fit results for complex non-linear systems. For smaller structures, ab initio simulation methods can be used to determine absorption spectra under field perturbations. However, these methods are impractical for larger structures. Designing and training an artificial neural network with simulated data from density functional theory may allow time-dependent perturbation effects to be calculated more efficiently. I investigate the design considerations of neural network implementations for calculating perturbation-coupled electron oscillations in small molecules. The neural network structure presented is eventually shown to be flawed because it mishandled the complex-valued inputs and outputs that it was trained on. As a result, important complex behavior, required for an accurate approximation of the time-evolution for the system, was ignored. Despite this, valid theory and design considerations are discussed in connection with a new complex-valued network structure that may be adequate to solve the problem.

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Ryan Sandberg (Senior Thesis, August 2013, Advisor: Justin Peatross )

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We present the 3D visualization of an electron wave packet in an intense laser field. Our visualization is based on a virtual camera model. The camera can be rotated around the wave packet, allowing the wave packet to be seen from any angle. The camera program integrates probability density along the line of sight and displays the calculated wave packet as a cloud. The probability density relies on a formula for calculating the wave packet in an intense laser field that was developed previously. To improve the 3D perspective of the images, we display coordinate lines in the wave packet visualization. We apply our camera model to an electron in an intense laser field and show frames from the movies we made. Features of note include the helical path of the wave packet in circularly polarized light and the multi-peaked structure that develops when the wave packet reaches the size of a laser wavelength.

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James Schwab (Capstone, April 2013, Advisor: David Allred )

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Brigham Young University's Department of Physical and Astronomy's Thin Film Research Group has been studying the apparent expansion of yttrium oxide and scandium oxide when exposed to 7.27 eV excimer lamp. These films have more than tripled their initial thickness because of the exposure. Such expansion is quite unexpected. The excimer lamp used is very similar to UV cleaning lamps used to clean films and semiconductors in industry. It is therefore very important to understand this phenomenon. It has been previously found that reactively sputtered samples exhibit this expansion. Samples were grown and then analyzed using a tunneling electron microscope, ellipsometry, and spectral analysis. More samples were prepared and tested in various atmospheres in an attempt to isolate the catalysts or reactants needed for the phenomenon to occur. Evidence suggests that the presence of a gaseous species; perhaps oxygen or ozone is required in addition to the lamp for growth to occur.

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Michelle Spencer (Senior Thesis, May 2013, Advisor: Mike Joner )

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This thesis will cover the research behind the recent supernovae SN 2010hh, 2011dh, 2011fe and 2012aw. The different types of supernovae will be introduced and discussed. The data gathering and processing will be described. The light curve resulting from Type IIb supernova 2011dh will be compared to the template.The light curve for Type II-P supernova 2012aw will be discussed. Finally, the Type Ia supernovae 2010hh and 2011fe will be used to calculate their distance modulus and thus the distance to their respective galaxies NGC 6524 and M101.

Trevor Stout (Senior Thesis, August 2013, Advisor: Kent Gee )

Abstract

Acoustic intensity measurements of the F-22A Raptor are analyzed as part of ongoing efforts to characterize the noise radiation from military jet aircraft. Data were recorded from a rig of microphones and an attached tetrahedral intensity probe at various locations to the sideline and aft of the aircraft. Numerical analysis of the intensity at one-third octave band center frequencies along various measurement planes and at a 23 m radius arc reveals the magnitude and directionality of the vector acoustic intensity. Differences in the trends for low-frequency and high-frequency data are discussed and, via a simple ray tracing method from maximum intensity regions, interpreted in terms of far-field behavior and source location. In particular, the extended source region contracts and moves upstream with increasing frequency, and vector directionalities point farther toward the sideline.

Jane Tanner (Senior Thesis, April 2013, Advisor: John Colton )

Abstract

As the first step in creating a real-time system that can inexpensively and efficiently measure glass sheet in a production setting, we determined whether current technology, which implements ray tracing from specular reflections from the glass surface, is sufficient to characterize the flatness of the glass sheets. This measurement consists of an optical image of a uniform pattern of vertical stripes as reflected from the sheet of glass, and subsequent ray-trace modeling in order to determine the glass sheet shape that will produce the observed amount of pattern distortion. The system can detect changes as small as 25 um, and can measure amplitudes up to 5 mm accurately. Based on experiments performed, the system shows promise as on online measurement tool for industry.

Daniel Thrasher (Senior Thesis, August 2013, Advisor: Scott Bergeson )

Abstract

This thesis reports amplitude and frequency noise measurements of a Titanium:sapphire (Ti:sapphire) laser that is injection-locked with a low power diode laser. We use a heterodyne technique to frequency off-set lock a home built injection-locked Ti:sapphire laser with a low noise, commercial, injection-locked Ti:sapphire laser. Frequency noise measurements are made using the full-width-half-max of the two lasers’ beat note. Amplitude noise measurements are made using the root mean square (rms) of the output of a photo diode. Under optimal conditions the rms amplitude noise is 1.0% and the frequency noise is 300 kHz . The noise of our laser system depends on the feedback system characteristics. My contributions were the design and fabrication of a microwave interferometer, including its software and hardware, for the purpose of frequency off-set locking the two lasers. I also contributed to the data acquisition and analysis.

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Matea Trevino (Senior Thesis, August 2013, Advisor: Karine Chesnel )

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In this thesis, we will discuss the fabrication of magnetite (Fe3O4) nanoparticles, their structural characterization through X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM), and their magnetic characterization through Vibrating Sample Magnetometer (VSM). XRD will give us information about the crystallite quality of the nanoparticles and their average size. TEM will allow us to visualize the nanoparticles, when deposited on a substrate. We will then do bulk magnetization characterization using the VSM. For when they are small enough, magnetite nanoparticles follow a special magnetic behavior called superparamagnetism. This behavior is characterized by a blocking temperature, below which the particles are magnetically frozen. We learn that our nanoparticles show different structural and magnetic properties depending on the preparation method.

Seth Van Orden (Capstone, August 2013, Advisor: Harold Stokes )

Abstract

Existing web applications that generate lists of isotropy subgroups of crystallographic space groups are either not user friendly or are unnecessarily complicated. We developed a web application, ISOSUBGROUP, which we will show is simple and easy to use. The software development included the assembly of FORTRAN subroutines and an HTML user interface enhanced by CSS, resulting in a visually appealing environment.

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Brace White (Capstone, April 2013, Advisor: Traci Neilsen )

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I built an open-closed tube demonstration under the direction of Dr. Neilsen and Dr. Gee. We used the structure to model brass instruments and to explore the changes in sound properties of tubes with the addition of a variety of bells. The project will be used in acoustics classes to help students visualize and better understand the associated principles.

Josh Wilson (Senior Thesis, August 2013, Advisor: Scott Bergeson )

Abstract

It has been shown that under certain conditions, the characteristics of ultracold neutral plasmas, can be reproduced in laser-produced plasmas at room temperature. We are attempting to see more fully how true this is, by trying to control the electron temperature in a laser-produced plasma. We expected that by decreasing the intensity of our laser when we ionize our gas we would see the expansion of our plasma slow down, and hence deduce that the electron temperature had been lowered. We had difficulty observing this result experimentally. We modeled the system and found that if we increase our laser intensity, we should be able to observe the phenomenon we had hypothesized. The experimental and modeling processes are here outlined, as well as thoughts on how to improve the experiment in the future.

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