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Brigham Young University

2013

Articles 1 - 8 of 8

Full-Text Articles in Physics

Development And Validation Of An Automated Directivity Acquisition System Used In The Acquisition, Processing, And Presentation Of The Acoustic Far-Field Directivity Of Musical Instruments In An Anechoic Space, Nicholas J. Eyring Dec 2013

Development And Validation Of An Automated Directivity Acquisition System Used In The Acquisition, Processing, And Presentation Of The Acoustic Far-Field Directivity Of Musical Instruments In An Anechoic Space, Nicholas J. Eyring

Theses and Dissertations

A high spatial resolution acoustic directivity acquisition system (ADAS) has been developed to acquire anechoic measurements of the far field radiation of musical instruments that are either remote controlled or played by musicians. Building upon work performed by the BYU Acoustic Research Group in the characterization of loudspeaker directivity, one can rotate a musical instrument with sequential azimuthal angle increments under a fixed semicircular array of microphones while recording repeated notes or sequences of notes. This results in highly detailed and instructive directivity data presented in the form of high-resolution balloon plots. The directivity data and corresponding balloon plots may …

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Analyses Of Nonlinearity Measures In High-Amplitude Sound Propagation, Michael B. Muhlestein Jul 2013

Analyses Of Nonlinearity Measures In High-Amplitude Sound Propagation, Michael B. Muhlestein

Theses and Dissertations

Military aircraft generate high-amplitude noise which can cause injury to attending personnel. Efforts to mitigate the effects of this noise require a detailed understanding of the propagation of the noise, which was shown previously to be nonlinear. This thesis presents an analysis of high-amplitude noise propagation, emphasizing measures used to quantify the importance of considering nonlinearity. Two measures of the importance of nonlinearity are compared. These measures are the wave steepening factor and a skewness estimate. The wave steepening factor is a measure of how much nonlinear waveform steepening has occurred in a waveform. The skewness estimate is the skewness …

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Characterization Of Ingaas Quantum Dot Chains, Tyler Drue Park Jul 2013

Characterization Of Ingaas Quantum Dot Chains, Tyler Drue Park

Theses and Dissertations

InGaAs quantum dot chains were grown with a low-temperature variation of the Stranski-Krastanov method, the conventional epitaxial method. This new method seeks to reduce indium segregation and intermixing in addition to giving greater control in the growth process. We used photoluminescence spectroscopy techniques to characterize the quality and electronic structure of these samples. We have recently used a transmission electron microscope to show how the quantum dots vary with annealing temperature. Some questions relating to the morphology of the samples cannot be answered by photoluminescence spectroscopy alone. Using transmission electron microscopy, we verified flattening of the quantum dots with annealing …

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Simulation Of 810 Nm Light Propagation Through The Human Finger For Non-Invasive Blood Analysis, Nichole Millward Maughan Jun 2013

Simulation Of 810 Nm Light Propagation Through The Human Finger For Non-Invasive Blood Analysis, Nichole Millward Maughan

Theses and Dissertations

Non-invasive blood analysis devices that can measure characteristics less prominent than the oxygenation of hemoglobin are of interest in the medical community. An important step in creating these devices is to model the interaction of photons with human tissue in increasingly greater physiological detail. We have modeled, using a Monte Carlo technique, the interaction of photons through epidermis, blood and water arranged both in layers and in a homogeneous mixture. We confirm the expected linear relation between photon attenuation and material volumetric percentage in our two-layer models. We discovered that this relationship becomes non-linear in the homogeneously mixed models where …

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Cluster Expansion Models Via Bayesian Compressive Sensing, Lance Jacob Nelson May 2013

Cluster Expansion Models Via Bayesian Compressive Sensing, Lance Jacob Nelson

Theses and Dissertations

The steady march of new technology depends crucially on our ability to discover and design new, advanced materials. Partially due to increases in computing power, computational methods are now having an increased role in this discovery process. Advances in this area speed the discovery and development of advanced materials by guiding experimental work down fruitful paths. Density functional theory (DFT)has proven to be a highly accurate tool for computing material properties. However, due to its computational cost and complexity, DFT is unsuited to performing exhaustive searches over many candidate materials or for extracting thermodynamic information. To perform these types of …

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Experimental Analysis Of Energy-Based Acoustic Arrays For Measurement Of Rocket Noise Fields, Jarom Henry Giraud Mar 2013

Experimental Analysis Of Energy-Based Acoustic Arrays For Measurement Of Rocket Noise Fields, Jarom Henry Giraud

Theses and Dissertations

Microphone arrays are useful for measuring acoustic energy quantities (e.g. acoustic intensity) in the near-field of a full-scale solid rocket motor. Proper characterization of a rocket plume as a noise source will allow for more accurate predictions in engineering models that design for protection of structures, payloads and personnel near the rockets. Acoustic intensity and energy density quantities were measured in three rocket noise fields and have shown that the apparent source region of the rocket becomes smaller and moves upstream as frequency increases. Theoretical results accounting for some scattering and finite-difference errors arising in these types of energy-based measurements …

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Limit Of Strong Ion Coupling Due To Electron Shielding, M. Lyon, Scott D. Bergeson, M. S. Murillo Jan 2013

Limit Of Strong Ion Coupling Due To Electron Shielding, M. Lyon, Scott D. Bergeson, M. S. Murillo

Faculty Publications

We show that strong coupling between ions in an ultracold neutral plasma is limited by electron screening. While electron screening reduces the quasiequilibrium ion temperature, it also reduces the ion-ion electrical potential energy. The net result is that the ratio of nearest-neighbor potential energy to kinetic energy in quasiequilibrium is constant and limited to approximately 1 unless the electrons are heated by some external source. We support these conclusions by reporting measurements of the ion velocity distribution in an ultracold neutral calcium plasma. These results match previously reported simulations of Yukawa systems. Theoretical considerations are used to determine the screened …

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Versatile Rb Vapor Cells With Long Lifetimes, John F. Hulbert, Matthieu Giraud-Carrier, Tom Wall, Aaron R. Hawkins, Scott D. Bergeson, Jennifer Black, Holger Schmidt Jan 2013

Versatile Rb Vapor Cells With Long Lifetimes, John F. Hulbert, Matthieu Giraud-Carrier, Tom Wall, Aaron R. Hawkins, Scott D. Bergeson, Jennifer Black, Holger Schmidt

Faculty Publications

The authors report on an approach to the construction of long-lasting rubidium atomic vapor cells. The method uses pinch-off copper cold-welds, low temperature solders, and electroplated copper to create long-lasting hermetic seals between containment chambers of dissimilar geometries and materials. High temperature epoxy, eutectic lead/tin solder, and indium solder were considered as sealing materials. These seals were analyzed using accelerated lifetime testing techniques. Vapor cells with epoxy and bare metal solder seals had a decrease in the rubidium atomic density within days after being heated to elevated temperatures. They also exhibited broadened spectra as a result of rubidium reacting with …

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