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Full-Text Articles in Physics

A Measurement Of The [Tau Lepton] Polarization At The Z Resonance With The Delphi Detector At Lep , Antonio Wong Chan Jan 1993

A Measurement Of The [Tau Lepton] Polarization At The Z Resonance With The Delphi Detector At Lep , Antonio Wong Chan

Retrospective Theses and Dissertations

The polarization of [tau] leptons produced in the reaction e[superscript]+e[superscript]-→[tau][superscript]+[tau][superscript]- near the peak of the Z° resonance has been measured using a sample of 24904 [tau][superscript]+[tau][superscript]- events, with an estimated background of 1.5%. We have selected 4562 [tau]→ e[nu][macron][nu], 2218 [tau]→[pi][nu] and 5133 [tau]→[rho][nu] candidates. The mean value obtained is P[subscript][tau]=-0.176± 0.029. This corresponds to a ratio of the neutral current vector to the axial-vector coupling constants of the [tau] lepton of g[subscript]spV[tau]/g ...


Support Minimized Inversion Of Acoustic And Elastic Wave Scattering , Ali Safaeinili Jan 1993

Support Minimized Inversion Of Acoustic And Elastic Wave Scattering , Ali Safaeinili

Retrospective Theses and Dissertations

Inversion of limited data is common in many areas of NDE such as X-ray Computed Tomography (CT), Ultrasonic and eddy current flaw characterization and imaging;In many applications, it is common to have a bias toward a solution with minimum (L[superscript]2)[superscript]2 norm without any physical justification. When it is a priori known that objects are compact as, say, with cracks and voids, by choosing "Minimum Support" functional instead of the minimum (L[superscript]2)[superscript]2 norm, an image can be obtained that is equally in agreement with the available data, while it is more consistent ...


Vibrational And Acoustic Response Of Ribbed Plates , Ten-Bin Juang Jan 1993

Vibrational And Acoustic Response Of Ribbed Plates , Ten-Bin Juang

Retrospective Theses and Dissertations

A self-consistent mathematical formulation, using the Fourier transform method and a direct Gaussian numerical integration scheme, is developed and verified for analysis of both vibrational and acoustic responses of infinite submerged ribbed plates. Further steps developed from standard theories make structural intensity, acoustic intensity, and acoustic power calculations possible in the nearfield and farfield, and are demonstrated in this work;The direct numerical integration scheme adopted to obtain responses has proved to be straightforward and reliable. Although the double integration expression in some responses makes the technique infeasible, a practical way to overcome that difficulty is demonstrated using a standard ...


Frequency Conversion Analysis Of Noise In Heterojunction Bipolar Transistor Oscillators Including Periodically Modulated Noise Sources , Bradley Allen Kramer Jan 1993

Frequency Conversion Analysis Of Noise In Heterojunction Bipolar Transistor Oscillators Including Periodically Modulated Noise Sources , Bradley Allen Kramer

Retrospective Theses and Dissertations

A procedure which may be used to analyze the noise characteristics of HBT oscillators is presented. A large signal model of a HBT is developed based largely on the Gummel-Poon transistor model. A new base-emitter diffusion capacitance model is also generated which shows improved accuracy over conventional bipolar transistor models in characterizing HBTs. The large signal characteristics of the oscillator are then established using a time domain simulator. Conversion matrix theory is applied to the large signal model to generate an equivalent linear oscillator model which accounts for all of the frequency conversion effects which occur due to circuit nonlinearities ...


Synthesis, Characterization, Phase Diagrams And Superconducting And Normal State Magnetic Properties Of La[Subscript 2-X]Sr[Subscript X]Cuo4 (0 [Less Than Or Equal To] X [Less Than Or Equal To] 0.08) And Electrochemically Oxidized La[Subscript 2-X]Sr[Subscript X]Cuo[Subscript 4 + Delta] (0 [Less Than Or Equal To] X [Less Than Or Equal To] 0.33, 0 [Less Than Or Equal To Delta Less Than Or Equal To] 0.12) , Fangcheng Chou Jan 1993

Synthesis, Characterization, Phase Diagrams And Superconducting And Normal State Magnetic Properties Of La[Subscript 2-X]Sr[Subscript X]Cuo4 (0 [Less Than Or Equal To] X [Less Than Or Equal To] 0.08) And Electrochemically Oxidized La[Subscript 2-X]Sr[Subscript X]Cuo[Subscript 4 + Delta] (0 [Less Than Or Equal To] X [Less Than Or Equal To] 0.33, 0 [Less Than Or Equal To Delta Less Than Or Equal To] 0.12) , Fangcheng Chou

Retrospective Theses and Dissertations

La[subscript] 2-xSr[subscript] xCuO[subscript]4 (0 ≤ x ≤ 0.15) can all be intercalated with oxygen by an novel electrochemical oxidation method. Bulk superconductivity is found with an onset T[subscript] c ≈ 40 K for the whole range 0.01 ≤ x ≤ 0.15; for x = 0.25 and 0.33, the electrochemical oxidation did not improve the superconducting properties. The magnetic susceptibility [chi](T = 50-320 K) data for La[subscript]2CuO[subscript]4.11 and La[subscript]1.92Sr[subscript]0.08CuO[subscript]4.07 are nearly identical with those of conventionally prepared La[subscript]1.85Sr[subscript]0 ...


Theoretical Study Of The Noble Metals On Semiconductor Surfaces And Ti-Base Shape Memory Alloys , Yungui Ding Jan 1993

Theoretical Study Of The Noble Metals On Semiconductor Surfaces And Ti-Base Shape Memory Alloys , Yungui Ding

Retrospective Theses and Dissertations

The electronic and structural properties of the (√3 x √3) R30° Ag/Si(111) and (√3 x √3) R30° Au/Si(111) surfaces are investigated using first principles total energy calculations. We have tested almost all experimentally proposed structural models for both surfaces and found the energetically most favorable model for each of them. The lowest energy model structure of the (√3 x √3) R30° Ag/Si(111) surface consists of a top layer of Ag atoms arranged as "honeycomb-chained-trimers" lying above a distorted "missing top layer" Si(111) substrate. The coverage of Ag is 1 monolayer (ML). We find ...


Acoustically Driven Integrated Microstrip Antennas And Electromagnetic Radiation From Piezoelectric Devices , Charles Forrest Campbell Jan 1993

Acoustically Driven Integrated Microstrip Antennas And Electromagnetic Radiation From Piezoelectric Devices , Charles Forrest Campbell

Retrospective Theses and Dissertations

For a receiver system to be considered integrated, the antenna and electronics need to be fabricated on a single semiconductor wafer. To avoid EMI problems, the circuitry must somehow be shielded from the environment where the antenna resides. The required shielding may be accomplished by separating the antenna on one side of the wafer from the electronics on the other side with a conducting ground plane. Energy may be acoustically coupled from the antenna to the circuitry through the ground plane via thin film piezoelectric transducers on either side of the wafer. The radiating side of the wafer would then ...


An Experimental Method For Structural Intensity And Source Location , Yong Zhang Jan 1993

An Experimental Method For Structural Intensity And Source Location , Yong Zhang

Retrospective Theses and Dissertations

This study investigates the structural intensity and the force distribution function as tools to study vibrating plates. A laser Doppler vibrometer is used in measuring the plate normal velocity for the calculation of the structural intensity and the force distribution function. Several examples show the possibility of locating sources and studying the influence of ribs and damping material attached to the plate surface;There have been many studies on structural intensity. This thesis shows that the differences between two commonly used formulations are the assumptions that are used in deriving the formulas;The force distribution function is introduced in this ...


Impedance Spectroscopy And Nmr Studies Of Fast Ion Conducting Chalcogenide Glasses , Hitendra Kumar Patel Jan 1993

Impedance Spectroscopy And Nmr Studies Of Fast Ion Conducting Chalcogenide Glasses , Hitendra Kumar Patel

Retrospective Theses and Dissertations

Two fully automated, temperature controlled, impedance spectroscopy workstations have been developed for this project. Impedance spectroscopy studies of glasses have been performed over the wide frequency (1 Hz-1 GHz) and wide temperature (100-500 K) range;This study yields the first-ever full compositional (three decades) range examination of the Na[subscript]2S + B[subscript]2S[subscript]3 and K[subscript]2S + B[subscript]2S[subscript]3 systems. The activation energy is modeled using a modified Anderson-Stuart model that predicts well the results for the low alkali glasses. a.c. conductivity is examined through the electrical modulus formalism and the Kohlrausch-Williams-Watts decay ...


Scattering Investigation Based On Acoustical Holography , Ming-Te Cheng Jan 1993

Scattering Investigation Based On Acoustical Holography , Ming-Te Cheng

Retrospective Theses and Dissertations

The objective of this research is to investigate sound scattering by an object using a two-surface measurement technique that separates the incident field and the scattered field. The separation technique is developed in cartesian and cylindrical coordinates. The decomposition method in the cartesian coordinate system is based on the principle that any wave form can be decomposed into plane-wave components by using a two dimensional spatial Fourier transform. For the cylindrical coordinate system, a two plane separation technique is based on decomposing the sound field into cylindrical waves. Numerical simulations are performed and the effect of various parameters are investigated ...


Investigation Of The Phase Equilibria And Phase Transformations Associated With The Bi2sr2cacu2oy Superconductor , Terry George Holesinger Jan 1993

Investigation Of The Phase Equilibria And Phase Transformations Associated With The Bi2sr2cacu2oy Superconductor , Terry George Holesinger

Retrospective Theses and Dissertations

Compositional measurements of the Bi[subscript]2Sr[subscript]2CaCu[subscript]2O[subscript]y (2212) solid solution region were performed in the TEM in order to separate intergrowth and solid solubility effects. Most of the solid solubility is accounted for by changes in the Sr and Ca concentrations. Changes in the Bi concentration account for the rest. Based on these results, two substitution schemes were determined to occur. The first is just the interchange between Sr and Ca. The second involves the substitution of Bi for Sr or Ca. It appears to be unfavorable for Sr or Ca to substitute for ...


Carbon In Fly Ash Analysis Using Photoacoustic Spectroscopy , Jeffrey Raymond Dykstra Jan 1993

Carbon In Fly Ash Analysis Using Photoacoustic Spectroscopy , Jeffrey Raymond Dykstra

Retrospective Theses and Dissertations

Photoacoustic absorption spectroscopy (PAS) was investigated as a method for on-line monitoring of carbon in fly ash from coal-fired boilers. PAS is based on the periodic heating of a gas when amplitude-modulated radiation is absorbed by the gas or by particles suspended in the gas. This periodic heating produces an acoustical wave that can be detected by a microphone. Because the PAS signal is based solely on the absorption of radiation (by carbon) and not scattering of radiation (by mineral matter), it has the potential for distinguishing unburned carbon from mineral matter suspended in the flue gas. Two radiation sources ...


Quantum Dynamical Phenomena Of Independent Electrons In Semiconductor Superlattices Subject To A Uniform Electric Field , Ann Marie Bouchard Jan 1993

Quantum Dynamical Phenomena Of Independent Electrons In Semiconductor Superlattices Subject To A Uniform Electric Field , Ann Marie Bouchard

Retrospective Theses and Dissertations

We solve the time-dependent Schrodinger equation for independent electrons in both periodic and aperiodic semiconductor superlattices with a superimposed static uniform electric field, F, using both analytical and numerical methods. In the case of periodic superlattices, in suitable circumstances the electron exhibits Bloch oscillations in the form of long-lived and virtually time-periodic sinusoidal center-of-mass oscillations. Depending on the miniband structure of the superlattice, the value of F, and the detailed form of the initial wave function, other dynamical phenomena can occur which can coexist with or even totally mask the Bloch oscillations. These include a nearly time-periodic coherent breathing mode ...


Theoretical Studies Of Zirconium And Carbon Clusters With Molecular Dynamics Simulations , Bulin Zhang Jan 1993

Theoretical Studies Of Zirconium And Carbon Clusters With Molecular Dynamics Simulations , Bulin Zhang

Retrospective Theses and Dissertations

With the aim of understanding the anomalous phonon behavior near the martensitic phase transition in Zr, we have simulated the dynamics of atomic motion in the high temperature bcc phase of Zr using an embedded-atom potential. The calculated dynamical structure factors reproduce the strong asymmetry in the scattering cross-sections in different Brillouin zones observed in inelastic neutron scattering experiments. From the real-space atomic picture, we observed the phase fluctuations between bcc and low temperature phase hcp. It is found that the anomalous phonon behavior arises from the incompleteness of the phase fluctuations;Combining an efficient simulated annealing scheme for generating ...


Circular Magnetic X-Ray Dichroism In Rare Earth Compounds , Jonathan Clark Lang Jan 1993

Circular Magnetic X-Ray Dichroism In Rare Earth Compounds , Jonathan Clark Lang

Retrospective Theses and Dissertations

Circular magnetic x-ray dichroism (CMXD) has been used to probe the magnetic properties of rare earth compounds. This study has been undertaken in two distinct parts. First, the angular dependence of the CMXD signal has been examined in order to determine the multiple nature of the transitions involved. Second, the nature of the dichroic spectra of amorphous and crystalline GdFe[subscript]2 has been probed. CMXD offers a unique probe of the magnetic properties of amorphous materials providing information that is not available from any other technique;Previous CMXD measurements at the L edges of rare earth materials have demonstrated ...


Rheed Studies Of The Nucleation, Growth, And Mobility Of Ag Atoms On The Si(111)7x7 Surface , Kelly Ryan Roos Jan 1993

Rheed Studies Of The Nucleation, Growth, And Mobility Of Ag Atoms On The Si(111)7x7 Surface , Kelly Ryan Roos

Retrospective Theses and Dissertations

The low temperature and flux dependent growth of ultrathin Ag films on the Si(111)7 x 7 surface is studied with Reflection High-Energy Electron Diffraction (RHEED). The grazing incidence geometry of RHEED allows for an incident molecular beam normal to the surface, and makes it an ideal surface probe for studying ultrathin film growth in real time. Short-lived oscillations in the diffracted intensity are observed during Ag deposition at 150 K, indicating quasi-layer-by-layer growth mediated by adatom mobility. When the 150 K growth is performed over a wide range of deposition rates F, the peak intensity is observed to ...


Growth And Characterization Of Polysilicon Films Deposited By Reactive Plasma Beam Epitaxy , Behnam Moradi Jan 1993

Growth And Characterization Of Polysilicon Films Deposited By Reactive Plasma Beam Epitaxy , Behnam Moradi

Retrospective Theses and Dissertations

Polycrystalline silicon was deposited at low temperatures (400-550°C) by using a new technique, reactive plasma beam epitaxy. The technique consists of using an intense flux of hydrogen radicals, generated by an electron cyclotron resonance (ECR) source to promote nucleation and crystallinity at low temperatures. The film structure could be smoothly changed from polysilicon to amorphous by changing the flux of incoming H radicals on the surface of the sample. The flux of hydrogen radicals can be controlled by changing the deposition pressure, with lower pressures leading to a higher H radical flux and greater degree of crystallinity. The effect ...


Density Functional Studies: First Principles And Semi-Empirical Calculations Of Clusters And Surfaces , Susan Buthaina Sinnott Jan 1993

Density Functional Studies: First Principles And Semi-Empirical Calculations Of Clusters And Surfaces , Susan Buthaina Sinnott

Retrospective Theses and Dissertations

In the research presented here, various theoretical electronic structure techniques are utilized to analyze widely different systems from silicon clusters to transition metal solids and surfaces. For the silicon clusters, first principles density functional methods are used to investigate Si[subscript] N for N = 2-8. The goal is to understand the different types of bonding that can occur in such small clusters where the coordination of the atoms differs substantially from that of the stable bulk tetrahedral bonding. Such uncoordinated structures can provide a good test of more approximate theories that can be used eventually to model silicon surfaces, of ...


High-Spin [Gamma]-Ray Spectroscopy In 198bi, Superdeformation In 191au, And Multi-Photon Resonances In Low Energy E+E- Scattering , Duc Ta Vo Jan 1993

High-Spin [Gamma]-Ray Spectroscopy In 198bi, Superdeformation In 191au, And Multi-Photon Resonances In Low Energy E+E- Scattering , Duc Ta Vo

Retrospective Theses and Dissertations

The properties of low-and high-spin levels in [superscript]198Bi have been studied with the [superscript]181Ta([superscript]22Ne,5n)[superscript]198Bi reaction at 116 MeV and 120 MeV bombarding energies. Levels along and near the yrast lines, including one isomer, were established up to spin J ≈ 30\hbar. The main configurations of these states are suggested to be [pi] h[subscript]9/2 coupled to the known excited states in [superscript]197Pb. A sequence of states built on the excitation of the odd proton (coupled to one, two, or three quasi neutron-holes) was observed. In addition, at least two collective ...


Relativistic Two-Body Wave Equations , Alan James Sommerer Jan 1993

Relativistic Two-Body Wave Equations , Alan James Sommerer

Retrospective Theses and Dissertations

The history and conceptual development of relativistic two-body formalisms leading up to the Bethe-Salpeter equation are reviewed. The various three dimensional reductions of the Bethe-Salpeter equation, in particular the quasipotential equations, and methods for solving them are discussed. Previous studies which attempted to assess the relative merits of the various equations are examined, and a new criterion for judging the equations is proposed. The bound state energy predictions of the traditional quasipotential equations are compared with the predictions of fourth order perturbation theory at small coupling. The equations are ranked according to how well they reproduce perturbation theory at low ...


An Axial Approach To Detection In Capillary Electrophoresis , John Aaron Taylor Jan 1993

An Axial Approach To Detection In Capillary Electrophoresis , John Aaron Taylor

Retrospective Theses and Dissertations

The purpose of this research has been to develop and demonstrate visualization schemes which further the capabilities of capillary electrophoresis instrumentation. Our approach involves on-axis illumination of the compounds inside the capillary detection region and is applied to absorbance and fluorescence detection;Absorbance measurements were accomplished by focussing an incident beam of laser light into one end of the separation capillary. By utilizing signals collected over the entire length of the analyte band, this technique enhances the analytical path length of conventional absorbance detection sixty fold. The demonstrated instrument offers a fifteen-fold improvement in concentration limits of detection;Three fluorescence ...


Effects Of Randomly Rough Surfaces On Ultrasonic Inspection , Mehmet Bilgen Jan 1993

Effects Of Randomly Rough Surfaces On Ultrasonic Inspection , Mehmet Bilgen

Retrospective Theses and Dissertations

Surface finish of an industrial part affects its ultrasonic inspection and consequently the surfaces are often machined smooth before the evaluation. Ultrasonic inspection through smooth surfaces has been well studied and understood. A theoretical basis has been established for the characterization of interior cracks, voids and inclusions, and vast amount of literature exists. However, much less is known about quantitative ultrasonic inspection of such flaws in parts with rough surfaces, e.g. machine marks or "as-cast" surfaces. A question arises "When can an industrial part with randomly rough surfaces be inspected robustly using ultrasound?" This dissertation is aimed at answering ...


Topics In Electroweak Baryogenesis: The Sphaleron And T-Violation , Seungkoog Lee Jan 1993

Topics In Electroweak Baryogenesis: The Sphaleron And T-Violation , Seungkoog Lee

Retrospective Theses and Dissertations

Assuming that beyond the standard model physics can be parametrized in terms of high dimensional operators, we examine their effects on the energy of the sphaleron and the classical solution of the gauge and Higgs fields. In the absence of fermions, all of the six dimension 6 operators which are SU(2) symmetric have a small effect when calculated perturbatively. However, calculated non-perturbatively, one of the operators alters the boundary conditions of the equations of motion of the Higgs and gauge fields involved, and another operator gives rise to an abrupt change in the sphaleron energy at a small but ...