Physical Sciences and Mathematics Commons^™

Collisional Effects In The Absorption Spectra Of The Oxygen A Band And Nitric Oxide Fundamental Band, Robert S. Pope

Theses and Dissertations

Fourier transform spectroscopy was used to measure pressure broadening coefficients in the absorption spectra of both the oxygen A band and the nitric oxide fundamental band. Oxygen spectra were recorded with O₂, N₂, CO, CO₂, SF₆ and noble gas collision partners, while nitric oxide spectra were recorded using noble gas collision partners. Pressure broadening coefficients were determined in the P and R branches for every resolved line for each of the fifteen collision pairs studied. In addition, broadening coefficients and qualitative evidence of line coupling were found for the Q branch of NO …

Optimal Atmospheric Compensation For Anisoplanatism In Adaptive-Optical Systems, Matthew R. Whiteley

Theses and Dissertations

Anisoplanatism in adaptive optics (AO) systems is a performance-degrading effect that arises whenever light from the wave-front sensor beacon and light from the object of interest sample different volumes of optical turbulence. This effect occurs if there is either a spatial separation between the object and the beacon, or a spatial separation between the wave-front sensor and phase-compensation aperture, or if both types of separation are present in the AO system. Anisoplanatism results in an increased value of the aperture-averaged residual phase variance after AO compensation, which causes an exponential decrease in system performance. This dissertation offers a theoretical framework …

Emissivity Measurements And Modeling Of Silicon Related Materials And Structures, Sufian Abedrabbo

Dissertations

The objective of this dissertation is to investigate the major issues concerning applications of pyrometry for applications in rapid thermal processing (RTP) of silicon related materials. The research highlights of this work are:

Establishment of spectral ernissometry as a novel, reliable and reproducible technique for:

Determination of wavelength and temperature dependent reflectivity, transmissivity, emissivity and temperature, simultaneously, of silicon related materials and structures. The emissometer operates in the wavelength range of 1-20mm and temperature range of 300-1200K. The analysis of the influence of morphological effects on the radiative properties by measurement of (a) front-smooth incidence versus backside-rough incidence of singleside …

Angle-Resolved Studies Of Inner Shell Excitations For Argon, Krypton And Xenon Using Third Generation Synchrotron Sources, Ahmad H. Farhat

Dissertations

This dissertation, which is in the area of atomic physics, concentrates on the study of the interaction between VUV-soft X-ray radiation and atoms in the gas phase. The main area of interest is the study of Auger decay in atoms utilizing the process known as the resonance Auger effect, where an inner shell electron is excited to an unfilled orbital followed by the ejection of an Auger electron. The measurements in this thesis were performed by using the high resolution Atomic, Molecular and Optical Physics undulator beam line, which utilizes a spherical grating monochromator at the Advanced Light Source at …

Effects Of Randomness And Spatially Dependent Relaxation On Sandpile Models, Isiaka O. Akanbi

Electronic Dissertations and Theses

Random deposition represents the simplest growth model. From a randomly chosen site over the surface, a particle falls vertically until it reaches the top of the interface, whereupon it sticks irreversibly. To include surface relaxation, we allow the deposited particle to diffuse along the surface up to a finite distance, stopping when it finds the position with the lowest height. As a result of the relaxation process, the final interface will be smooth, compared to the model without relaxation. In this research we investigate two types of randomness in the relaxation of sandpile models when the slop at some point …

Vortex Wake And Exhaust Plume Interaction, Including Ground Effect, Ihab Gaber Adam

Mechanical & Aerospace Engineering Theses & Dissertations

Computational modeling and studies of the near-field wake-vortex turbulent flows, far-field turbulent wake-vortex/exhaust-plume interaction for subsonic and High Speed Civil Transport (HSCT) airplane, and wake-vortex/exhaust-plume interaction with the ground are carried out. The three-dimensional, compressible Reynolds-Averaged Navier-Stokes (RANS) equations are solved using the implicit, upwind, Roe-flux-differencing, finite-volume scheme. The turbulence models of Baldwin and Lomax, one-equation model of Spalart and Allmaras and two-equation shear stress transport model of Menter are implemented with the RANS solver for turbulent-flow modeling.

For the near-field study, computations are carried out on a fine grid for a rectangular wing with a NACA-0012 airfoil section and …

A Study Of The Knowledge Structure Of Expert, Intermediate, And Novice Subjects In The Domain Of Physics, Jennifer L. Discenna

Dissertations

The objective of this research was to investigate the knowledge structure in physics by describing the knowledge of experts, intermediates, and novices. A review of the literature on expertise, physics knowledge, and conceptual structure provided two competing representations of physics knowledge: one defined as a hierarchy of models arranged from general to specific models, the second defined by theories which link knowledge together.

In order to investigate the two representations described above, a reiterative categorization task was employed. This task resulted in a hierarchical sort with larger piles at the top of the hierarchy and smaller piles at the bottom …

Electron Emission Following The Interaction Of Slow Highly Charged Ions With Solids, Joseph W. Mcdonald

Dissertations

The interaction of highly-charged ions with surfaces involves many excitation processes of the surface atoms and the bulk material. One such process, the emission of electrons from surfaces due to the potential energy of the incident ions has been studied. The experimental results presented here confirm that the majority of electrons emitted as a result of highly-charged ions interacting with a solid surface have energies of about 20 eV. Auger processes contribute a smaller fraction of the total emitted electrons with increasing Z o f the projectile. This contribution to the total electron emission yield is found to be less …

Measuring The Bunch-Length Of An Electron Beam By Utilizing The Laser Heterodyne Technique, Katrina L. Carter

Electronic Dissertations and Theses

The focus of this project was to develop an apparatus that would aid in measuring the bunch-length of an electron beam at the interaction point of the Stanford Linear Collider (SLC) by utilizing the laser heterodyne technique. This technique involves the superposition of two laser pulses of slightly different frequencies. As a result, a traveling fringe pattern is created, and a bunch-to-bunch variation of the Compton rate would be introduced. The magnitude of this variation depends on the best wavelength and on Fourier transform of the longitudinal bunch distribution. The laser heterodyne technique is implemented by the addition of a …

All-Sky Measurements Of The Mesospheric "Frontal Events" From Bear Lake Observatory, Utah, Seon-Hee Seo

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Studies of internal gravity waves in the earth's upper atmosphere are of considerable interest. These waves play a very important role in the dynamics of the mesosphere and lower thermosphere (ML T) region where they can transfer large amounts of energy and momentum from the lower atmosphere via wave saturation and dissipation. In particular, small-scale short-period ( < 1 hour) waves of the type regularly recorded by all-sky nightglow imagers operated by Utah State University (USU) are known to be very important contributors. In this thesis attention is focused on a subset of small-scale wave phenomena recently discovered using such image data, the so called "frontal events." Frontal events have distinguishable characteristics from usual short-period ( < 1 hour) gravity waves. The principal characteristics are a well defined leading "front, " which exhibits a sharp change in intensity followed by a coherent wave trail (often extending from horizon to horizon) and relatively high phase speeds ( > 50ms^-1) Another unusual characteristic of "frontal events" is an apparent reversal in contrast of the wave structures as imaged in the hydroxyl (OH) emission (peak altitude - 87 km) when compared with the oxygen (OJ) "green line" (557.7 nm) emission (peak …

The Effects Of Fabry-Perot Fringing On The Sensitivity Of A Wavelength Modulation Experiment, Patrick C. Shea

Electrical & Computer Engineering Theses & Dissertations

Parasitic Fabry-Perot etaloning plagues many experiments which use wavelength modulation spectroscopy. This fringing, which is an artifact that almost always appears in such experiments, arises from multiple reflections in the optical elements in the experimental apparatus. The etaloning plays a detrimental role and limits the ultimate sensitivity of wavelength modulation spectroscopy experiments. The research described in this thesis investigates this phenomenon. Experimental results are presented which show that when the Q-factor of the parasitic etalon is smaller that that of the absorption line being measured, significant improvement in the Signal to Fringe Noise Ratio can be obtained through the use …

Optical Physics Of Microcavity Surface Emitting Lasers, Michael J. Noble

Theses and Dissertations

This dissertation consists of an in-depth theoretical analysis of the optical impact of transverse index confinement on the lasing modes of microcavity surface emitting lasers. Two different variational techniques were employed to calculate the relevant optical laser parameters: (1) modal resonance, field profile, (2) confinement factor, and (3) threshold gain. Through a semianalytic field analysis, two new confinement related effects were discovered: (1) a polarization dependent change in mirror reflectance with aperture radius, and (2) a mode dependent blueshift. Through a numerical field analysis, the physical mechanisms governing diffraction were ascertained. These are: (1) the transverse confinement of the optical …

Linear Reconstruction Of Non-Stationary Image Ensembles Incorporating Blur And Noise Models, Stephen D. Ford

Theses and Dissertations

Two new linear reconstruction techniques are developed to improve the resolution of images collected by ground-based telescopes imaging through atmospheric turbulence. The classical approach involves the application of constrained least squares (CLS) to the deconvolution from wavefront sensing (DWFS) technique. The new algorithm incorporates blur and noise models to select the appropriate regularization constant automatically. In all cases examined, the Newton-Raphson minimization converged to a solution in less than 10 iterations. The non-iterative Bayesian approach involves the development of a new vector Wiener filter which is optimal with respect to mean square error (MSE) for a non-stationary object class degraded …

Performance Of Imaging Laser Radar In Rain And Fog, Kathleen M. Campbell

Theses and Dissertations

The Air Force is currently developing imaging laser radar systems (ladar) for use on precision guided munitions and other imaging systems. Scientists at Eglin Air Force Base, in conjunction with Wright Laboratories, are testing a 1.06-um wavelength ladar system and need to understand the weather effects on the ladar images. As the laser beam propagates through the atmosphere, fog droplets and raindrops can cause image degradation, and these image degradations are manifested as either dropouts or false returns. An analysis of the dropouts and false returns helped to quantify the performance of the system in adverse weather conditions. Statistical analysis …

Regression Analysis Of Radar Measured Optical Turbulence With Synoptic Scale Meteorological Variables, Diana L. Hajek

Theses and Dissertations

A key issue to the USAF's Airborne Laser (ABL) program is the ability to accurately predict the level of optical turbulence that the ABL will encounter at its flight levels. The optical turbulence must be characterized so that the range and range variation of the ABL can be determined. Gravity wave spectra resulting from frontal or jet stream passage are presumed to cause layers of optical turbulence; however, exact relationships between optical turbulence and synoptic scale meteorological phenomena are unclear. This study assesses the statistical relationship between optical turbulence and synoptic scale variables through multiple linear regression. The optical turbulence …

Spectroscopy Of Charge-Coupled Devices, Lars Mündermann

Dissertations and Theses

A systematic study of persistent, or residual, images occurring in CCD imagers and a systematic study of dark current generation in CCD imagers are presented. These effects are a source of unwanted signal in frames, and should be considered where very exact, low light-level signal processing is necessary. For both studies explanatory models and statistical analysis techniques have been developed which enable the derivation of the densities and the characteristic energies. Furthermore the importance of understanding these phenomena in the context of today's low light-level imaging is discussed.

Impurity sites are found to be responsible for residual images. Photoelectrons are …

Microscale And Nanoscale Testing Of Materials Using Scanning Probe Technologies, Mark Phelan

Theses

Understanding solid surfaces and their properties is of crucial importance for many sectors of industry. This interest stems from the fact that solid surfaces are the working interface between a solid material and its environment and in many cases it is this interface which determines both the suitability and life span of a mechanical component. Furthermore the modification of surface properties using coatings and multi-layered materials has grown significantly, particularly in the case of data storage, optics and microelectronics. The demands of these and other sectors have provided the impetus for the development of material testing techniques applicable to coatings …

Searches For Exotic Matter, David Lee Morgan

Dissertations, Theses, and Masters Projects

This research encompasses two quite distinct searches for exotic matter. The first half concerns exotic matter on the scale of elementary particles. In this chapter, I consider the production of gluinos, the supersymmetric partner of the gluon, in models where the gluino is very light. Cross sections are calculated for electroproduction and hadroproduction of gluinos and the results indicate that existing accelerators are capable of probing the region of gluino masses between 1.0 and 2.0GeV with lifetimes between 10{dollar}\sp{lcub}-10{rcub}{dollar} and 10{dollar}\sp{lcub}-6{rcub}{dollar} seconds. Such experiments could find a light gluino if it exists, or to close this unexplored mass-lifetime window. The …

A Search For Lepton Flavor Violation In The Neutral Kaon System, Christopher Henry Hoff

Dissertations, Theses, and Masters Projects

The conservation of separate lepton number is an ad hoc conservation principle in the Standard Model but several non-Standard Model theories allow violation of separate lepton number conservation. A very sensitive search for lepton flavor violation in the neutral kaon system, via the decay K0L→me , was undertaken by Brookhaven National Laboratory Experiment 871 (E871) during the 1995 and 1996 AGS HEP running periods. No K0L→me decays were observed and a single event sensitivity (SES) of 1.97x10-12 was achieved. This single event sensitivity corresponds to an upper limit on the branching fraction of BK0L→m e<4.53+/-0.21+/-0.46x 10-12 at a 90% confidence level.

Stability Of Quark-Antiquark Models Of Mesons: A Study On The Validity Of The Spectator, Dirac, And Salpeter Equations, Michael Uzzo

Dissertations, Theses, and Masters Projects

Mesons are made of quark-antiquark pairs held together by the strong force. The one channel spectator, Dirac, and Salpeter equations can each be used to model this pairing. We look at cases where the relativistic kernel of these equations corresponds to a linear combination of scalar exchange and vector exchange. The vector exchange will be either the time-like component or the full four vector. The systems covered here are referred to as quasirelativistic, which means retardation, regularization, and form factors are not included. Since the model used in this paper describes mesons which cannot decay physically, the equations must describe …

The Role Of Adsorbed Oxygen In Secondary Emission From Metallic Substrates, Scott Gregory Walton

Dissertations, Theses, and Masters Projects

Low energy, ion- and photon-induced secondary electron and anion emission from metallic substrates has been investigated as a function of adsorbate coverage. Sodium positive ions (Na+), with kinetic energies up to 500 eV, and photons, with energies up to 23 eV, are utilized to initiate secondary emission. The principal adsorbate is oxygen with coverages ranging from none to a few monolayers.;For ion-induced emission, the secondary electron and negative ion absolute and relative yields from 302 stainless steel and polycrystalline tungsten (W) have been measured as a function of both impact energy and oxygen coverage. Additionally, the yields from a "technical" …

First Observation Of The Very Rare Decay Neutral Kaon(Long) Going To Electron Positron, Robert David Martin Iii

Dissertations, Theses, and Masters Projects

Brookhaven National Laboratory AGS Experiment 871 (E871) has carried out a search for the very rare, GIM and helicity suppressed decay of the long-lived neutral kaon into an electron-positron pair. This decay is predicted within the Standard Model to occur with a branching ratio of {dollar}(9.0 \pm 0.4)\times 10\sp{lcub}-12{rcub}.{dollar} Data were taken during the 1995 and 1996 AGS HEP running periods on the B5 beamline. A signal of (4 {dollar}\pm{dollar} 2) {dollar}K\sbsp{lcub}L{rcub}{lcub}0{rcub} \to e\sp+e\sp-{dollar} events is seen with a physics background expectation of 0.2 events. The ratio of the partial decay widths {dollar}\Gamma(K\sbsp{lcub}L{rcub}{lcub}0{rcub} \to e\sp+e\sp-)/\Gamma(K\sbsp{lcub}L{rcub}{lcub}0{rcub}\to\mu\sp+\mu\sp-){dollar} is determined to be {dollar}(1.3\sbsp{lcub}-0.6{rcub}{lcub}+0.8{rcub} …

Electroproduction Of The S(11)Meson(1535) Resonance At High Momentum Transfer, Christopher Stephen Armstrong

Dissertations, Theses, and Masters Projects

The amplitude of the $S\sb{11}$(1535) resonance at values of four-momentum transfer $Q\sp2 > 0$ is not explained by the nonrelativistic constituent quark model, and is currently a topic of theoretical interest; in addition, the large branching fraction of this resonance to the proton-$\eta$ decay channel is not well understood. There is also controversy concerning the $Q\sp2$ regime in which perturbative QCD becomes important in describing nucleon resonances such as the $S\sb{11}$. The $p(e, e\sp\prime p)\eta$ reaction is an excellent system in which to study this resonance and address the issue of possible perturbative effects: the $p\eta$ channel is not accessible to …

The Green Dyadic Formulation For Radiation Problems With Arbitrary Sources Embedded In Stratified Multi-Layer Structures : Application To Molecular Fluorescence Problems, Robert Lyle Hartman

Dissertations and Theses

The Green Dyadic method for computing fields due to current sources between parallel interfaces of dielectric materials is studied. Computer implementation of the method as presented in a well-known article leads to the conclusion that significant errors are present. Two dissimilar methods of solution lead to corrected formulations which are shown to be equivalent. The same correction is found in the research literature. For confirmation, computations are performed in examples involving an emitting dipole by both the Green dyadic method and Sommerfeld' s Hertz vector method. Finally, the computational examples are used to compute fluorescence decay rates for emitting dipoles …

Coherent Neutral Pion Photoproduction On The Deuteron, David G. Meekins

Dissertations, Theses, and Masters Projects

The differential scattering cross section for the process gd→dp0 was measured, as part of experiment E89-012 at Thomas Jefferson National Accelerator Facility. The experiment was performed in Hall C during the Spring of 1996 as the commissioning experiment for the Hall C cryogenic target. The High Momentum Spectrometer was used to detect the recoil deuteron and no effort was made to detect the p0 or its decay photons. The differential cross section was measured at a number of incident photon energies between 0.8 GeV and 4.0 GeV for the deuteron center-of-mass angles of 90?? and 136??. The data were found …