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Articles 151 - 180 of 204
Full-Text Articles in Astrophysics and Astronomy
Error Sensor Strategies For Active Noise Control And Active Acoustic Equalization In A Free Field, Ryan T. Chester
Error Sensor Strategies For Active Noise Control And Active Acoustic Equalization In A Free Field, Ryan T. Chester
Theses and Dissertations
Several measurements may be used as error signals to determine how to appropriately control a sound field. These include pressure, particle velocity, energy density and intensity. In this thesis, numerical models are used to show which signals perform best in is free-field active noise control (ANC) using error sensors located in the near field of the sound sources. The second is equalization in a free field and a semi-free field. Minimized energy density total power output (MEDToPO) plots are developed; these indicate the maximum achievable attenuation for a chosen error sensor as a function of location. A global listening area …
Improving Performance Of The Filtered-X Least Mean Square Algorithm For Active Control Of Noise Contatining Multiple Quasi-Stationary Tones, Stephan P. Lovstedt
Improving Performance Of The Filtered-X Least Mean Square Algorithm For Active Control Of Noise Contatining Multiple Quasi-Stationary Tones, Stephan P. Lovstedt
Theses and Dissertations
The Filtered-X Least-Mean-Square (FXLMS) algorithm is widely used in active noise control due to its robustness, simplicity, and ability to be implemented in real time. In a feedforward implementation of the FXLMS algorithm, a reference signal that is highly correlated with the noise to be controlled is filtered with an estimate of the transfer function of the secondary path. The convergence characteristics of the FXLMS algorithm have been well studied. A convergence parameter is used to optimize the convergence of the algorithm. However, the optimal value for the convergence parameter is frequency dependent. Thus for noise containing multiple tones at …
Multi-Channel Digital Receiver Data Acquisition System For The Arecibo Radar System, Ryan Seal
Multi-Channel Digital Receiver Data Acquisition System For The Arecibo Radar System, Ryan Seal
Theses and Dissertations
Digital Receivers are commercially available, cost effective solutions that are becoming commonplace in modern data acquisition systems (MDAS). The digital receiver has the ability to be reconfigured via software, making MDAS flexible for a variety of applications. This thesis describes the design and implementation of a complete MDAS using a general purpose computer (GPC) equipped with a digital receiver card. This system will replace the older DAS (baseband sampling) used by the Space and Atmospheric Science (SAS) group at the Arecibo Observatory (AO). Emphasis is placed on a generic system easily adaptable to a specific application with minimal effort. A …
Solid Phase Crystallization Of Vanadium Dioxide Thin Films And Characterization Through Scanning Electron Microscopy, Felipe Rivera
Solid Phase Crystallization Of Vanadium Dioxide Thin Films And Characterization Through Scanning Electron Microscopy, Felipe Rivera
Theses and Dissertations
Crystalline films of vanadium dioxide were obtained through thermal annealing of amorphous vanadium dioxide thin films sputtered on silicon dioxide. An annealing process was found that yielded polycrystalline vanadium dioxide thin films, semi-continuous thin films, and films of isolated single-crystal particles. Orientation Imaging Microscopy (OIM) was used to characterize and study the phase and the orientation of the vanadium dioxide crystals obtained, as well as to diferentiate them from other vanadium oxide stoichiometries that may have formed during the annealing process. There was no evidence of any other vanadium oxides present in the prepared samples. Indexing of the crystals for …
Scandium Oxide Thin Films And Their Optical Properties In The Extreme Ultraviolet, Guillermo Antonio Acosta
Scandium Oxide Thin Films And Their Optical Properties In The Extreme Ultraviolet, Guillermo Antonio Acosta
Theses and Dissertations
This study reports on the physical and optical characterization of scandium oxide thin films. Thin films of scandium oxide, 20-40 nm thick, were deposited on silicon wafers, quartz slides, and silicon photodiodes by reactively sputtering scandium in an oxygen environment. These samples were characterized using ellipsometry, high-resolution transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray analysis. A 28.46 nm thick scandium oxide thin film was measured in the Extreme Ultraviolet (EUV) from 2.7 to 50 nm (459.3 to 24.8 eV) using synchrotron radiation at the Advanced Light Source Beamline 6.3.2 at the Lawrence Berkeley National Laboratory. In …
Construction Of A Calcium Matter-Wave Interferometer, Christopher Joseph Erickson
Construction Of A Calcium Matter-Wave Interferometer, Christopher Joseph Erickson
Theses and Dissertations
I describe the construction of a calcium matter-wave interferometer. The interferometer is based on a Ramsey-Borde scheme, and uses a thermal beam of atoms excited by an optical-frequency transition in calcium. In our experiment four pi/2 pulses of light are delivered to the atoms, which split and recombine the wave functions of the atoms. Our experimental design minimizes first-order Doppler shifts, and allows for the cancellation of systematic errors including phase shifts due to rotation and acceleration. I describe the individual components of the interferometer and its assembly. The requirements for the electronics used in the experiment as well as …
Error Sensor Placement For Active Control Of An Axial Cooling Fan, Benjamin M. Shafer
Error Sensor Placement For Active Control Of An Axial Cooling Fan, Benjamin M. Shafer
Theses and Dissertations
Recent experimental achievements in active noise control (ANC) for cooling fans have used near-field error sensors whose locations are determined according to a theoretical condition of minimized sound power. A theoretical point source model, based on the condition previously stated, reveals the location of near-field pressure nulls that may be used to optimize error sensor placement. The actual locations of these near-field pressure nulls for both an axial cooling fan and a monopole loudspeaker were measured over a two-dimensional grid with a linear array of microphones. The achieved global attenuation for each case is measured over a hemisphere located in …
Development Of A Method For Calculating Delta Scuti Rotational Velocities And Hydrogen Beta Color Indices, Tabitha Christi Buehler
Development Of A Method For Calculating Delta Scuti Rotational Velocities And Hydrogen Beta Color Indices, Tabitha Christi Buehler
Theses and Dissertations
To add to the understanding of the structure and evolution of Delta Scuti stars, 167 Delta Scutis north of -01 degrees declination and brighter than 13th magnitude have been observed spectroscopically. A method for calculating rotational velocity values and Hydrogen-Beta color indices for the stars in the data set with no previously published values is developed, using the stars in the data set brighter than 7th magnitude. Rotational velocity values for four stars with previously unknown values and Hydrogen-Beta index values for five stars with previously unknown values are calculated.
Optimization Of Control Source And Error Sensor Locations In Free Field Active Noise Control, Connor Raymond Duke
Optimization Of Control Source And Error Sensor Locations In Free Field Active Noise Control, Connor Raymond Duke
Theses and Dissertations
Previous work has shown that active noise control (ANC) can be applied to axial cooling fans. Optimization of the control source and error sensor placement is desired to maximize the attenuation using ANC. A genetic algorithm was developed to find the optimal placement of control sources for a given primary source. The optimal configuration of control sources around a single primary source was shown to be a linear arrangement of the sources. This holds true for both two-dimensional as well as three-dimensional configurations. The higher-order radiation of the linear arrangement has also been verified experimentally, but the improvement in the …
Development Of A New Ca Ii H And K Spectrophotometric Temperature Index, Kathleen Elizabeth Moncrieff
Development Of A New Ca Ii H And K Spectrophotometric Temperature Index, Kathleen Elizabeth Moncrieff
Theses and Dissertations
We are developing a new spectrophotometric temperature index based on the Ca II H and K lines. Because these lines are present even in very cool stars and because the Ca II H line is blended with the H-epsilon line in hot stars, this index should cover a very broad range of spectral types. Our data set consisted of 95 stars with spectral types ranging from O9 to M1. We examined five different indices based on the Ca II H + H-epsilon and K lines, as well as single-wavelength indices centered on each of the H-delta and H-gamma lines, which …
The Effect Of Nonlinear Propagation On Near-Field Acoustical Holography, Micah Raymond Shepherd
The Effect Of Nonlinear Propagation On Near-Field Acoustical Holography, Micah Raymond Shepherd
Theses and Dissertations
Near-field acoustical holography (NAH) has been used extensively for acoustical imaging of infinitesimal-amplitude (or small-amplitude) sources. However, recent interests are in the application of NAH to image finite-amplitude (or high-amplitude) sources such as jets and rockets. Since NAH is based on linear equations and finite-amplitude sources imply nonlinear effects, which cause shock formation and consequently an altered spectral shape, a feasibility study is carried out to determine the effect of nonlinear propagation on NAH. Jet and rocket sources typically have a distinct spectral shape resembling a ‘haystack’ and center frequencies varying from 30 to 300 Hz. To test the effect …
On Stability And Evolution Of Solutions In General Relativity, Stephen M. Taylor
On Stability And Evolution Of Solutions In General Relativity, Stephen M. Taylor
Theses and Dissertations
This thesis is concerned with several problems in general relativity and low energy string theory that are pertinent to the time evolution of the gravitational field. We present a formulation of the Einstein field equations in terms of variational techniques borrowed from geometric analysis. These equations yield the evolution equations for the Cauchy problems of both general relativity and low energy string theory. We then proceed to investigate the evolutionary linear stability of Schwarzschild-like solutions in higher dimensional relativity called black strings. These objects are determined to be linearly unstable. This motivates a further stability analysis of the charged p-brane …
Development Of A Mevva Based Beryllium-7 Plasma Source, David K. Olson
Development Of A Mevva Based Beryllium-7 Plasma Source, David K. Olson
Theses and Dissertations
We have designed a new type of plasma gun ion source for a Malmberg-Penning trap based on Metal Vapor Vacuum Arc (MeVVA) ion source designs. Our primary intent with this MeVVA-type source is to create a confinable beryllium-7 (7-Be) plasma. 7-Be is a peculiar isotope due to its varying radioactive decay half-life in different electro-chemical configurations. It is also found in an unexpected abundance at high altitudes of the Earth's atmosphere. It is possible ioniziation affects the radioactivity of the isotope, partly explaining this discrepancy with atmospheric models. The short half-life of 7-Be requires us to replace the sample inside …
Extreme Ultraviolet Polarimetry With Laser-Generated High-Order Harmonics, Nicole Brimhall
Extreme Ultraviolet Polarimetry With Laser-Generated High-Order Harmonics, Nicole Brimhall
Theses and Dissertations
We developed an extreme ultraviolet (EUV) polarimeter, which employs laser-generated high-order harmonics as the light source. This relatively high-flux directional EUV source has available wavelengths between 8 nm and 62 nm and easily rotatable linear polarization. The polarimeter will aid researchers at BYU in characterizing EUV thin films and improving their understanding of materials for use in EUV optics. This first-time workhorse application of laser high harmonics enables polarization-sensitive reflection measurements not previously available in the EUV. We have constructed a versatile positioning system that places harmonics on the microchannel plate detector with an accuracy of 0.3 mm, which allows …
Coupling Down Converted Light Into Single Mode Fibers, David A. Niemi
Coupling Down Converted Light Into Single Mode Fibers, David A. Niemi
Theses and Dissertations
We investigate the influence of the pump and collection mode parameters on the collection efficiency of Type I down converted photons into single mode fibers. For best single and coincidence counting rates, we find that the mode sizes should be close to the same size and that the mode waists should be located near the down-conversion crystal. Larger collection waists give higher collection efficiencies, but lower singles counts.
Development Of An H-Alpha Index For The Detection Of Pms Candidates In Young Open Clusters, Liberty Rae Evanko
Development Of An H-Alpha Index For The Detection Of Pms Candidates In Young Open Clusters, Liberty Rae Evanko
Theses and Dissertations
One phase of formation of medium- and low-mass stars is the optically visible phase known as the pre-main-sequence or PMS phase. In order to further the understanding of this phase, more of these PMS objects need to be identified and classified. Previous techniques have used photometry to identify possible PMS objects by their characteristic Hα emission. Once identified these objects can be studied spectroscopically yielding complete PMS classification. This study develops a method to locate these emission objects that overcomes two limitations of previous techniques. The first limitation is the need for the creation of reddening maps. It is eliminated …
In-Situ And Simultaneous Measurements Of Size And Charge Distributions Of Dust On Mars: Instrumentation And Analysis, Praveen Kumar Srirama
In-Situ And Simultaneous Measurements Of Size And Charge Distributions Of Dust On Mars: Instrumentation And Analysis, Praveen Kumar Srirama
Theses and Dissertations
Martian dust characterization is important for minimizing the effects of abrasion, adhesion, corrosion, and damage to mission hardware, and also to reduce the effect on human health during future robotic and human exploratory missions. Characterizing the particle size and charge on Mars dust will help in the development of techniques for dust mitigation. Presently there is no miniature instrument which is capable of in-situ and real time measurements on Mars. In order to simultaneously analyze the particle size and charge of Mars dust, a Dust Particle Analyzer (DPA) has been developed and tested which is based on a Laser Doppler …
Computationally Modeling The Effects Of Surface Roughness On Soft X-Ray Multilayer Reflectors, Jedediah Edward Jensen Johnson
Computationally Modeling The Effects Of Surface Roughness On Soft X-Ray Multilayer Reflectors, Jedediah Edward Jensen Johnson
Theses and Dissertations
Electromagnetic scattering from a rough two dimensional homogeneous scatterer has been computationally modeled. The scatterer is intended to simulate reflection from a two interface multilayer. The rough scatterer was created from Gaussian random points centered about an ideal interface. The points were connected with a third order spline interpolant which accounts for correlation between neighboring surface atoms. The scalar electric field integral equation (EFIE) and magnetic field integral equation (MFIE) were solved using the Nystrom method to obtain the reflected intensity as a function of observation angle. Verification of the accuracy of the code was obtained by means of comparison …
A Statistical Analysis Of Wide Binary Evolution, Kyle Burton Johnston
A Statistical Analysis Of Wide Binary Evolution, Kyle Burton Johnston
Theses and Dissertations
Post main sequence (MS) mass loss causes orbital separation amplification in fragile (i.e. common proper motion) binary star systems. Components typically have separations around -1000 a.u. Such wide pairs experience negligible tidal interactions and mass transfer between companions; they evolve as two separate but coeval stars. In this paper we will attempt to model how post-MS mass loss statistically distorts a frequency distribution of fragile binary separations. Understanding this process provides a robust test of current theories of stellar evolution and sets constraints on the dynamics of the Galactic disk.
Sound Absorption And Sound Power Measurements In Reverberation Chambers Using Energy Density Methods, David B. Nutter
Sound Absorption And Sound Power Measurements In Reverberation Chambers Using Energy Density Methods, David B. Nutter
Theses and Dissertations
Measurements in a reverberation chamber use spatially averaged squared pressure to calculate sound absorption, sound power, and other sound measurements. While a reverberation chamber provides an approximation of a diffuse sound field, variations in the measurements introduce uncertainty in measurement results. Room qualification procedures require a sufficient number of source-receiver locations to obtain suitable measurements. The total acoustic energy density provides greater spatial uniformity than squared pressure, which requires fewer source-receiver positions to produce similar or better accuracy in measurement results. This paper explores the possibility of using energy density in place of squared pressure, using methods outlined in current …
Feedback Applications In Active Noise Control For Small Axial Cooling Fans, Matthew J. Green
Feedback Applications In Active Noise Control For Small Axial Cooling Fans, Matthew J. Green
Theses and Dissertations
Feedback active noise control (ANC) has been applied as a means of attenuating broadband noise from a small axial cooling fan. Such fans are used to maintain thermal stability inside of computers, projectors, and other office equipment and home appliances. The type of low-level noise radiated from axial cooling fans has been classified as harmful to productivity and human well being. Previous research has successfully implemented feed-forward ANC, targeting specific narrow-band fan noise content related to the blade passage frequency (BPF) of the fan. The reference signal required for a feed-forward algorithm limits its ability to attenuate much of the …
Optimization Of Active Noise Control For Small Axial Cooling Fans, Brian B. Monson
Optimization Of Active Noise Control For Small Axial Cooling Fans, Brian B. Monson
Theses and Dissertations
Previous work has shown that active noise control is a feasible solution to attenuate tonal noise radiated by small axial cooling fans, such as those found in desktop computers. One such control system reduced noise levels of a baffled 80-mm fan in the free field with four small loudspeakers surrounding the fan. Due to industry specified spatial constraints, a smaller fan and speaker configuration was desirable. The smaller configuration maintains similar control performance, further facilitating practical implementation of the control system. The smaller control system employs a smaller fan running at a higher speed. Different loudspeaker configurations for control exist …
A Search For Low-Amplitude Variability Among Population I Main Sequence Stars, Michael Benjamin Rose
A Search For Low-Amplitude Variability Among Population I Main Sequence Stars, Michael Benjamin Rose
Theses and Dissertations
The detection of variable stars in open clusters is an essential component of testing stellar structure and evolution theories. The ability to detect low-amplitude variability among cluster members is directly related to the quality of the photometric results. Point Spread Function (PSF) fitting is the best method available for measuring accurate magnitudes within crowded fields of stars, while high-precision differential photometry is the preferred technique for removing the effects of atmospheric extinction and variable seeing. In the search for new variable stars among hundreds or thousands of stars, the Robust Median Statistic (RoMS) is proven more effective for finding low-amplitude …
Mechanisms Of The Wurtzite To Rock Salt Phase Transitions In Galium Nitride, Jesse Z. Gunter
Mechanisms Of The Wurtzite To Rock Salt Phase Transitions In Galium Nitride, Jesse Z. Gunter
Theses and Dissertations
We studied the wurtzite to rock salt phase transition in gallium nitride ( GaN ). Using the mapping algorithm of COMSUBS we found 435 possible mechanisms for this transition. We then used FIREBALL to do density functional theory calculations and found enthalpy barrier heights for the transition pathway. We used this to determine the mechanisms that are the most favorable for GaN. The most favorable mechanisms for GaN are those that break no bonds during the phase transition. The bond-preserving mechanisms involve bilayer sliding of (010) hexagonal plane in the plus or minus [100] hexagonal direction.
Development And Comparison Of Highly Directional Loudspeakers, Gordon Robert Dix
Development And Comparison Of Highly Directional Loudspeakers, Gordon Robert Dix
Theses and Dissertations
Highly directive loudspeakers have long been important tools for sound system designers, experimental acousticians, and many other professionals in the audio industry. They allow sound engineers to more easily manipulate the radiation pattern of their loudspeakers to accommodate the purpose of the venue. Many commercially available products, while exhibiting good directivity at mid and high frequencies, generally lack control in the low frequency range. A new method for controlling the radiation pattern of a loudspeaker at low frequencies has been developed and modeled extensively. Prototypes have been built and tested in an anechoic chamber. Results from computer modeling and experimental …
Direct Observation Of Laser Filamentation In High-Order Harmonic Generation, John Charles Painter
Direct Observation Of Laser Filamentation In High-Order Harmonic Generation, John Charles Painter
Theses and Dissertations
We investigate the spatial evolution of an intense laser pulse as it generates high-order harmonics in a long gas cell, filled with 80 torr of helium. A thin foil separates the gas-filled region of the cell from a subsequent evacuated region. The exit plane of the gas cell can be scanned along the laser axis so that the evolution of the laser throughout the focus can be observed (full scanning range of 9 cm). We constructed an apparatus that images the laser radial energy profile as it exits the cell. The high harmonics, odd orders ranging from 45 to 91, …
The Violation Of Bell's Inequality In A Deterministic But Nonlocal Model, Stephanie Allred Magleby
The Violation Of Bell's Inequality In A Deterministic But Nonlocal Model, Stephanie Allred Magleby
Theses and Dissertations
This thesis investigates the violation of Bell's Inequality through the use of nonlocal measurement schemes as encapsulated in a quasi-deterministic toy model. This toy model, called the Q Box, is reminiscent of Mermin's Box in that it describes a system that appears to be deterministic yet produces the statistics of a quantum type system. [1] The workings of the Q Box are detailed both as a thought experiment and as a computer simulation. Nonlocal measurement protocols similar to those which generate a violation of Bell's Inequality in the Q Box are also applied to Mermin's Box, with comparable results. [1] …
Prediction Of Flight-Level Radiation Hazards Due To Solar Energetic Protons, Matthew P. Sattler
Prediction Of Flight-Level Radiation Hazards Due To Solar Energetic Protons, Matthew P. Sattler
Theses and Dissertations
The radiation environment at aircraft altitudes is caused primarily by high-energy particles originating from outside the near-earth environment. These particles generally come from outside our solar system and are called galactic cosmic rays. Occasionally however, a transient solar event will also accelerate energetic protons toward the earth. If these protons reach the upper atmosphere, they produce secondary particles via collisions, resulting in increased radiation levels in the atmosphere. Air crews and electronic systems flying at high altitudes during one of these events are subjected to these increased levels of radiation which can result in health problems for personnel and soft …
Electromagnetism In Gravitational Collapse, Craig Ernest Skinfill
Electromagnetism In Gravitational Collapse, Craig Ernest Skinfill
Theses and Dissertations
A numerical approach to including electromagnetism with general relativity is developed using GRAXI as a starting point. We develop a mathematical model describing electromagnetism coupled to a scalar field in an evolving axisymmetric spacetime. As there are numerous formulations of electromagnetism, we evalute different formulations in a limited flat space case. The full curved space system is then developed, using the flat case as a guide to implementing electromagnetism. This model is then implemented using GRAXI as a code base.
Acoustics Of The Salt Lake Tabernacle: Characterization And Study Of Spatial Variation, Sarah Rollins
Acoustics Of The Salt Lake Tabernacle: Characterization And Study Of Spatial Variation, Sarah Rollins
Theses and Dissertations
In order to preserve the acoustics of the Salt Lake Tabernacle after the seismic renovation of 2005-2006, it was necessary to characterize these acoustics immediately preceding the renovation. This thesis discusses the characterization process that began with the measurement of hundreds of impulse responses for five different source positions and several receiver locations throughout the hall seating areas. The acoustics were further characterized by deriving various parameters from these responses that correlate with subjective preferences for music and speech. Impulse responses were also generated by a CATT-Acoustic™ computer model of the Tabernacle for the same purpose. The parameter values were …