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- Active noise control (9)
- Acoustics (8)
- Acoustic (6)
- Energy density (6)
- Atomic physics (5)
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- ANC (4)
- Carbon nanotubes (4)
- Laser cooling (4)
- Noise (4)
- Sound power (4)
- Acoustic energy density (3)
- Acoustic intensity (3)
- Calcium (3)
- DSMC (3)
- Data storage (3)
- EUV (3)
- Interferometry (3)
- Nanoparticle (3)
- Optical constants (3)
- Rocket noise (3)
- Thin films (3)
- Ultracold plasma (3)
- Absorption coefficients (2)
- Acoustical (2)
- Active Noise Control (2)
- Algorithm (2)
- Architectural acoustics (2)
- Auralization (2)
- Beryllium (2)
- Carbon Nanotube (2)
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Articles 31 - 60 of 133
Full-Text Articles in Physical Sciences and Mathematics
Towards Stronger Coulomb Coupling In An Ultracold Neutral Plasma, Mary Elizabeth Lyon
Towards Stronger Coulomb Coupling In An Ultracold Neutral Plasma, Mary Elizabeth Lyon
Theses and Dissertations
Ultracold neutral plasmas are created by photoionizing laser-cooled atoms in a magneto-optical trap (MOT). Due to their large electrical potential energies and comparatively small kinetic energies, ultracold plasmas fall into a regime of plasma systems which are called “strongly coupled.” A priority in the field of ultracold plasmas is to generate plasmas with higher values of the strong coupling parameter Γ, which is given as the ratio of the nearest-neighbor Coulomb potential energy to the average kinetic energy. The equilibrium strong coupling in ultracold plasmas is limited by the ultrafast relaxation of the ions due to spatial disorder in the …
Introduction To The Development Of A Radio Astronomy System At Brigham Young University, Daniel Robert Blakley
Introduction To The Development Of A Radio Astronomy System At Brigham Young University, Daniel Robert Blakley
Theses and Dissertations
The intent of this project was founded upon the need to train students in the techniques of radio astronomy with the purpose of establishing a radio telescope in order to teach the principles and practice of radio astronomy.This document describes the theory, research, to establish the 1st generation radio telescope system within the Department of Physics and Astronomy at Brigham Young University. Included are introductions to: (1) The nature of star forming regions in the spiral arm structure of the galaxy, H I (the hydrogen spin-flip transition) and OH MASERS, (2) The of terminology used with the system components and …
Investigation Of A New Method Of Estimating Acoustic Intensity And Its Application To Rocket Noise, Benjamin Young Christensen
Investigation Of A New Method Of Estimating Acoustic Intensity And Its Application To Rocket Noise, Benjamin Young Christensen
Theses and Dissertations
An alternative pressure-sensor based method for estimating the acoustic intensity, the phase and amplitude gradient estimation (PAGE) method, is presented. This method is similar to the finite-difference p-p (FD) method, in which the intensity is estimated from pressure measurements made using an array of closely spaced microphones. The PAGE method uses the same hardware as the FD method, but does not suffer from the frequency-dependent bias inherent to the FD method. Detailed derivations of the new method and the traditional FD method are presented. Both methods are then compared using two acoustic fields: a plane wave and a three monopole …
Application Of An Isogeometric Boundary Element Method To The Calculation Of Acoustic Radiation Modes And Their Efficiencies, Candice Marie Humpherys
Application Of An Isogeometric Boundary Element Method To The Calculation Of Acoustic Radiation Modes And Their Efficiencies, Candice Marie Humpherys
Theses and Dissertations
In contrast to the structural modes, which describe the physical motion of vibrating structures, acoustic radiation modes describe the radiated sound power. Radiation modes are beneficial in active noise control because reducing an efficiently radiating radiation mode guarantees the reduction of radiated sound power. Much work has been done to calculate the radiation modes for simple geometries, where analytic solutions are available. In this work, isogeometric analysis (IGA) is used to provide a tool capable of analyzing the radiation modes of arbitrarily complex geometries. IGA offers increased accuracy and efficiency by using basis functions generated from Non-Uniform Rational B-Splines (NURBS) …
Spin And Orbital Moments And Magnetic Order In Fe3o4 Nanoparticle Assemblies, Yanping Cai
Spin And Orbital Moments And Magnetic Order In Fe3o4 Nanoparticle Assemblies, Yanping Cai
Theses and Dissertations
Fe3O4 magnetic nanoparticles of 5 to 11 nm in size were prepared by organic methods. Particle size was analyzed by both X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) techniques. Zero Field Cooling (ZFC) / Field Cooling (FC) and magnetization loop measurements were recorded by VSM, and they confirmed superparamagnetic behavior in the sample. The blocking temperature is found to be in the range of 30 K ~ 170 K. It has a dependence on the particle size. ZFC / FC curves also indicate the presence of magnetic coupling between particles. X-ray Magnetic Circular Dichroism (XMCD) measurements of these nanoparticles …
Estimating The Acoustic Power Of Sources In Nonideal Enclosures Using Generalized Acoustic Energy Density, Daniel Ryan Marquez
Estimating The Acoustic Power Of Sources In Nonideal Enclosures Using Generalized Acoustic Energy Density, Daniel Ryan Marquez
Theses and Dissertations
Sound power measurements of acoustic sources are generally made in reverberation or anechoic chambers using acoustic pressure measurements as outlined in specific ISO or other standards. A reverberation chamber produces an approximate diffuse-field condition, wherein the sound power is determined from the spatially averaged squared pressure. An anechoic chamber produces an approximate free-field condition, wherein the sound power is estimated from squared pressure over an enveloping measurement surface. However, in many cases it is desirable to estimate sound power within nonideal semi-reverberant spaces. In these environments, both direct and reverberant energies may contribute significantly to the total acoustic field. This …
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 …
Analyses Of Nonlinearity Measures In High-Amplitude Sound Propagation, Michael B. Muhlestein
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 …
Characterization Of Ingaas Quantum Dot Chains, Tyler Drue Park
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 …
Simulation Of 810 Nm Light Propagation Through The Human Finger For Non-Invasive Blood Analysis, Nichole Millward Maughan
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 …
Cluster Expansion Models Via Bayesian Compressive Sensing, Lance Jacob Nelson
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 …
Experimental Analysis Of Energy-Based Acoustic Arrays For Measurement Of Rocket Noise Fields, Jarom Henry Giraud
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 …
Investigation Of Low-Stress Silicon Nitride As A Replacement Material For Beryllium X-Ray Windows, David B. Brough
Investigation Of Low-Stress Silicon Nitride As A Replacement Material For Beryllium X-Ray Windows, David B. Brough
Theses and Dissertations
The material properties of low stress silicon nitride make it a possible replacement material for beryllium in X-ray windows. In this study, X-ray windows made of LPCVD deposited low stress silicon nitride are fabricated and characterized. The Young's modulus of the LPCVD low stress silicon nitride are characterized and found to be 226±23 GPa. The residual stress is characterized using two different methods and is found to be 127±25 MPa and 141±0.28 MPa. Two support structure geometries for the low stress silicon nitride X-ray windows are used. X-ray windows with thicknesses of 100 nm and 200 nm are suspended on …
Thin Films Of Carbon Nanotubes And Nanotube/Polymer Composites, Anthony D. Willey
Thin Films Of Carbon Nanotubes And Nanotube/Polymer Composites, Anthony D. Willey
Theses and Dissertations
A method is described for ultrasonically spraying thin films of carbon nanotubes that have been suspended in organic solvents. Nanotubes were sonicated in N-Methyl-2-pyrrolidone or N-Cyclohexyl-2-pyrrolidone and then sprayed onto a heated substrate using an ultrasonic spray nozzle. The solvent quickly evaporated, leaving a thin film of randomly oriented nanotubes. Film thickness was controlled by the spray time and ranged between 200-500 nm, with RMS roughness of about 40 nm. Also described is a method for creating thin (300 nm) conductive freestanding nanotube/polymer composite films by infiltrating sprayed nanotube films with polyimide.
Comparing Theory And Experiment For Analyte Transport In The First Vacuum Stage Of The Inductively Coupled Plasma Mass Spectrometer, Matthew R. Zachreson
Comparing Theory And Experiment For Analyte Transport In The First Vacuum Stage Of The Inductively Coupled Plasma Mass Spectrometer, Matthew R. Zachreson
Theses and Dissertations
The Direct Simulation Monte Carlo algorithm as coded in FENIX is used to model the transport of trace ions in the first vacuum stage of the inductively coupled plasma mass spectrometer. Haibin Ma of the Farnsworth group at Brigham Young University measured two radial trace density profiles: one 0.7 mm upstream of the sampling cone and the other 10 mm downstream. We compare simulation results from FENIX with the experimental results. We find that gas dynamic convection and diffusion are unable to account for the experimentally-measured profile changes from upstream to downstream. Including discharge quenching and ambipolar electric fields, however, …
Modeling Radial Bernstein Modes In A Finite-Length Axisymmetric Non-Neutral Plasma, Mark Andrew Hutchison
Modeling Radial Bernstein Modes In A Finite-Length Axisymmetric Non-Neutral Plasma, Mark Andrew Hutchison
Theses and Dissertations
Axisymmetric radial Bernstein modes are known to exist in non-neutral plasmas and have been studied theoretically and computationally in 1D, but detection of these modes has still proven to be difficult due to self-shielding. To help advance the work on this front we created a 2D particle-in-cell (PIC) code that simulates a non-neutral plasma in a Malmberg-Penning trap. A detailed description of the PIC code itself has been included that highlights the benefits of using an $r^2$--$z$ grid and how it can be tested. The focus of the PIC simulation was to discover how best to drive and detect these …
Advanced Numerical Methods In General Relativistic Magnetohydrodynamics, Michael J. Besselman
Advanced Numerical Methods In General Relativistic Magnetohydrodynamics, Michael J. Besselman
Theses and Dissertations
We show our work to refine the process of evolutions in general relativistic magnetohydrodynamics. We investigate several areas in order to improve the overall accuracy of our results. We test several versions of conversion methodologies between different sets of variables. We compare both single equation and two equations solvers to do the conversion. We find no significant improvement for multiple equation conversion solvers when compared to single equation solvers. We also investigate the construction of initial data and the conversion of coordinate systems between initial data code and evolution code. In addition to the conversion work, we have improved some …
Researching Effective Methods For Teaching The Phases Of The Moon, Heather Patti Jones
Researching Effective Methods For Teaching The Phases Of The Moon, Heather Patti Jones
Theses and Dissertations
This study investigated the effectiveness of commonly used instructional methods for teaching the phases of the Moon to fifth and sixth grade students. The instructional methods investigated were the use of diagrams, animations, and models. The effectiveness of each method was tested by measuring students' understanding of Moon phases with a pre and post-assessment after receiving instruction with a specific method or combination of methods. These methods were then evaluated for their ability to help students learn essential concepts, reinforce relevant vocabulary and discourage misconceptions. Results showed that students had better scores with less prevalence of misconception when they were …
Nanoscale Surface Patterning And Applications: Using Top-Down Patterning Methods To Aid Bottom-Up Fabrication, Anthony Craig Pearson
Nanoscale Surface Patterning And Applications: Using Top-Down Patterning Methods To Aid Bottom-Up Fabrication, Anthony Craig Pearson
Theses and Dissertations
Bottom-up self-assembly can be used to create structures with sub-20 nm feature sizes or materials with advanced electrical properties. Here I demonstrate processes to enable such self-assembling systems including block copolymers and DNA origami, to be integrated into nanoelectronic devices. Additionally, I present a method which utilizes the high stability and electrical conductivity of graphene, which is a material formed using a bottom-up growth process, to create archival data storage devices. Specifically, I show a technique using block copolymer micelle lithography to fabricate arrays of 5 nm gold nanoparticles, which are chemically modified with a single-stranded DNA molecule and used …
Curious Growth Of A Buried Sio2 Layer, Thomas O. Mcconkie
Curious Growth Of A Buried Sio2 Layer, Thomas O. Mcconkie
Theses and Dissertations
Initial investigation of Moxtek wire grid polarizers composed of Al and coated with SiO2 - SiX - SiO2 (where SiX is used to indicate a Si rich layer whose complete composition is not to be disclosed for proprietary reasons) showed a growth of 3x in the inner (closest to Al) SiO2 layer after baking. Upon removing the X and varying rib composition and layering composition and geometries in 12 sets of before and after samples, no obvious growth was observed. Even baking the original unbaked sample yielded no growth. Our data suggest that the initial conclusion of buried oxide growth …
Quantum Dynamics Using Lie Algebras, With Explorations In The Chaotic Behavior Of Oscillators, Ryan Thomas Sayer
Quantum Dynamics Using Lie Algebras, With Explorations In The Chaotic Behavior Of Oscillators, Ryan Thomas Sayer
Theses and Dissertations
We study the time evolution of driven quantum systems using analytic, algebraic, and numerical methods. First, we obtain analytic solutions for driven free and oscillator systems by shifting the coordinate and phase of the undriven wave function. We also factorize the quantum evolution operator using the generators of the Lie algebra comprising the Hamiltonian. We obtain coupled ODE's for the time evolution of the Lie algebra parameters. These parameters allow us to find physical properties of oscillator dynamics. In particular we find phase-space trajectories and transition probabilities. We then search for chaotic behavior in the Lie algebra parameters as a …
Array-Based Characterization Of Military Jet Aircraft Noise, David William Krueger
Array-Based Characterization Of Military Jet Aircraft Noise, David William Krueger
Theses and Dissertations
Since the 1950s the jet aeroacoustics community has been involved in predicting and measuring the noise distribution in jets. In this work, cylindrical and planar Fourier near-field acoustical holography are used to investigate radiation from a full-scale, installed jet engine. Practical problems involving measurement aperture and the highly directional nature of the source are addressed. Insights from numerical simulations reveal usable reconstruction regions. A comparison of cylindrical and planar NAH for the respective measurement apertures shows cylindrical NAH outperforms planar NAH on reconstructions both towards and away from the source.
Analog Feedback Control Of Broadband Fan Noise, Cole Victor Duke
Analog Feedback Control Of Broadband Fan Noise, Cole Victor Duke
Theses and Dissertations
Active noise control (ANC) has been implemented using analog filters to reduce broadband noise from a small axial cooling fan. Previous work successfully attenuated narrow-band, tonal portions of the noise using a digital controller. The practical performance limits of this system were reached and it was desirable to attenuate the noise further. Additional research, therefore, sought to attenuate broadband noise from the fan using a digital controller, but performance was limited by the group delay inherent in the digital signal processor (DSP). Current research attempts to further attenuate broadband noise and improve performance of the system by combining the tonal …
Active Noise Control Of A Centrifugal Fan Mounted In A Mock Laptop Enclosure, John J. Esplin
Active Noise Control Of A Centrifugal Fan Mounted In A Mock Laptop Enclosure, John J. Esplin
Theses and Dissertations
Noise from information technology (IT) equipment is a significant problem in today's modern society. Active Noise Control (ANC) has shown promise in reducing the effect of IT fan noise on users. Though ANC has been applied to axial fans (such as those found in desktop computers), it has not been applied to centrifugal fans, such as those found in laptop computers. This work applies an ANC method to a centrifugal fan mounted in a mock laptop enclosure. This method is applied in four steps. First, secondary sources are placed in the vicinity of the fan. Second, an accurate model of …
Electron Microscopy Characterization Of Vanadium Dioxide Thin Films And Nanoparticles, Felipe Rivera
Electron Microscopy Characterization Of Vanadium Dioxide Thin Films And Nanoparticles, Felipe Rivera
Theses and Dissertations
Vanadium dioxide (VO_2) is a material of particular interest due to its exhibited metal to insulator phase transition at 68°C that is accompanied by an abrupt and significant change in its electronic and optical properties. Since this material can exhibit a reversible drop in resistivity of up to five orders of magnitude and a reversible drop in infrared optical transmission of up to 80%, this material holds promise in several technological applications. Solid phase crystallization of VO_2 thin films was obtained by a post-deposition annealing process of a VO_{x,x approx 2} amorphous film sputtered on an amorphous silicon dioxide (SiO_2) …
Measurement Of Plasma Density In A Gas-Filled Ionizing Laser Focus, Nathan Edward Heilmann
Measurement Of Plasma Density In A Gas-Filled Ionizing Laser Focus, Nathan Edward Heilmann
Theses and Dissertations
We use an interferometric method for measuring the plasma density in a laser-induced plasma as a function of time. Any changes in the density within 5 ns of generation is due plasma expansion and not recombination. The analytic solution for plasma expansion derived for ultracold Neutral Plasmas describes the expansion of our laser produced Neon plasma of densities up to approximately 40 Torr. A model for the utlracold neutral plasmas, in comparison with measurements of our plasmas, can be used to extract an electron temperature. Currently our plasmas have shown to have an electron temperature of approximately 44 eV.
Development Of A Strontium-87 Ion Interferometer, Christopher Joseph Erickson
Development Of A Strontium-87 Ion Interferometer, Christopher Joseph Erickson
Theses and Dissertations
I present the construction of a low-velocity intense source (LVIS) of laser-cooled neutral strontium using permanent ring magnets. The LVIS consists of a magneto-optical trap from which cold strontium is extracted in a well-collimated beam. I also present the development and implementation of a full suite of low-noise, high-bandwidth laser control electronics including a microcontroller unit. This microcontroller remotely controls and monitors the current driver, temperature controller, and PID lock circuit for each diode laser simultaneously. The current driver output is accurate to within 2 micro-amps and repeatable to with a few nano-amps. The noise spectral density of the current …
Electron Screening And Disorder-Induced Heating In Ultracold Neutral Plasmas, Mary Elizabeth Lyon
Electron Screening And Disorder-Induced Heating In Ultracold Neutral Plasmas, Mary Elizabeth Lyon
Theses and Dissertations
Disorder-induced heating (DIH) is a nonequilibrium, ultrafast relaxation process that occurs when laser-cooled atoms are photoionized to make an ultracold plasma. Its effects dominate the ion motion during the first 100 ns of the plasma evolution. Using tools of atomic physics we study DIH with ns time resolution for different plasma densities and temperatures. By changing the frequency of the laser beam we use to probe the ions, we map out the time evolution of the velocity distribution. We can compare this to a fluorescence simulation in order to more clearly determine the relationship between the fluorescence signal and the …
A Search For And Characterization Of Young Stellar Objects In N206, An H Ii Complex In The Large Magellanic Cloud, Tabitha Christi Buehler
A Search For And Characterization Of Young Stellar Objects In N206, An H Ii Complex In The Large Magellanic Cloud, Tabitha Christi Buehler
Theses and Dissertations
I have identified 51 young stellar object candidates in N206, an H II complex in the nearby Large Magellanic Cloud galaxy. Using archival images from the Spitzer Space Telescope, supplemented with other infrared and optical images, I located point sources in this region. I distinguished possible young stellar objects based on their spectral energy distributions, morphologies, and locations in color-magnitude space. I classified the young stellar object candidates based on their likelihood of being young stellar objects and based on their apparent evolutionary stages. The spatial distribution of these candidates in N206 indicates that star formation is being triggered …
Fabrication And Application Of Vertically Aligned Carbon Nanotube Templated Silicon Nanomaterials, Jun Song
Fabrication And Application Of Vertically Aligned Carbon Nanotube Templated Silicon Nanomaterials, Jun Song
Theses and Dissertations
A process, called carbon nanotube templated microfabrication (CNT-M) makes high aspect ratio microstructures out of a wide variety of materials by growing patterned vertically aligned carbon nanotubes (VACNTs) as a framework and then infiltrating various materials into the frameworks by chemical vapor deposition (CVD). By using the CNT-M procedure, a partial Si infiltration of carbon nanotube frameworks results in porous three dimensional microscale shapes consisting of silicon-carbon nanotube composites. The addition of thin silicon shells to the vertically aligned CNTs (VACNTs) enables the fabrication of robust silicon nanostructures with edibility to design a wide range of geometries. Nanoscale dimensions are …