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Articles 1 - 11 of 11

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 ...


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 ...


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 ...


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 ...


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 ...


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 ...


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 ...


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 ...


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 ...