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Electrodynamic Properties of Single-Crystal and Thin-Film Strontium Titanate

Description: The authors present a comparative study of broadband electrodynamic properties of coplanar waveguides made from nonlinear dielectric single-crystal and thin-film SrTiO{sub 3} (STO) with high-temperature superconducting thin-film YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} electrodes. The waveguides that use single-crystal STO exhibit a monotonic increase in refractive index, dielectric nonlinearity, and dissipation with decreasing temperature (from 80 K to 20 K), whereas those based on thin-film STO show similar but weaker effects with increasing temperature. Under dc bias, both types of waveguides show reduced refractive index, but dissipation increases in the case of single-crystal STO, while it decreases in the case of STO thin-films.
Date: May 13, 1999
Creator: Findikoglu, A.T.; Jia, Q.; Reagor, D.W.; Kwon, C. & Rasmussen, K.O.
Partner: UNT Libraries Government Documents Department


Description: The objective of this research was to demonstrate that electrokinetics can be used to remove colloidal coal and mineral particles from coal-washing ponds and lakes without the addition of chemical additives such as salts and polymeric flocculants. The specific objectives were: Design and develop a scaleable electrophoresis apparatus to clarify suspensions of colloidal coal and clay particles; Demonstrate the separation process using polluted waste water from the coal-washing facilities at the coal-fired power plants in Centralia, WA; Develop a mathematical model of the process to predict the rate of clarification and the suspension electrical properties needed for scale up.
Date: December 18, 1999
Creator: Davis, E. James
Partner: UNT Libraries Government Documents Department

High-Resolution Measurements of the K-Shell Spectral Lines of Hydrogenlike and Heliumlike Xenon

Description: With the implementation of a transmission-type curved crystal spectrometer at the Livermore high-energy electron beam ion trap (SuperEBIT) the window on sub-eV level measurements of the ground-state quantum electrodynamics and the two-electron quantum electrodynamics of high-Z ions has been opened. High-resolution spectroscopic measurements of the K{alpha} spectra of hydrogenlike Xe{sup 53+} and heliumlike Xe{sup 52+} are presented. The electron-impact excitation cross sections have been determined relative to the radiative recombination cross sections. The electron-impact energy was 112 keV which is about 3.7 times the excitation threshold for the n = 2 {yields} 1 transitions. Although the relative uncertainties of the measured electron-impact excitation cross sections range from about 20% to 50%, significant disagreement between the measured and calculated cross section values has been found for one of the heliumlike xenon lines. Overall, the comparison between experiment and theory shows that already for xenon (Z=54) the Breit interaction plays a significant part in the collisional excitation process. The measured cross sections for the hydrogenlike transitions are in good agreement with theoretical predictions. Additionally, the Xe{sup 53+} Ly-{alpha}{sub 1} transition energy has been measured utilizing the K{alpha} emission of neutral cesium and barium for calibration. Surprisingly, the experimental result, (31279.2 {+-} 1.5) eV, disagrees with the widely accepted theoretically predicted value of (31283.77 {+-} 0.09) eV. However, this disagreement does not (yet) call for any correction in respect to the theoretical values for the transition energies of the hydrogenlike isoelectronic sequence. It rather emphasizes the need for a reevaluation of the commonly used x-ray wavelengths table for atomic inner-shell transitions, in particular, for the cesium K{alpha} lines.
Date: September 13, 1999
Creator: Windman, K.; Beiersdorfer, P.; Brown, G.V.; Crespo, J.R.; Osterheld, A.L.; Reed, K.J. et al.
Partner: UNT Libraries Government Documents Department

Feynman-Schwinder representation approach to nonperturbative physics

Description: The Feynman-Schwinger representation provides a convenient framework for the calculation of nonperturbative propagators. In this paper the authors first investigate an analytically solvable case, namely the scalar QED in 0+1 dimension. With this toy model they illustrate how the formalism works. The analytic result for the self energy is compared with the perturbative result. Next, using a {chi}{sup 2} {phi} interaction, they discuss the regularization of various divergences encountered in this formalism. The ultraviolet divergence, which is common in standard perturbative field theory applications, is removed by using a Pauli-Villars regularization. They show that the divergence associated with large values of Feynman-Schwinger parameter s is spurious and it can be avoided by using an imaginary Feynman parameter is.
Date: June 1, 1999
Creator: Savkli, C.; Tjon, J. & Gross, F.
Partner: UNT Libraries Government Documents Department

The equation of motion of an electron

Description: We review the current status of understanding of the equation of motion of an electron. Classically, a consistent, linearized theory exists for an electron of finite extent, as long as the size of the electron is larger than the classical electron radius. Nonrelativistic quantum mechanics seems to offer a fine theory even in the point particle limit. Although there is as yet no convincing calculation, it is probable that a quantum electrodynamical result will be at least as well-behaved as is the nonrelativistic quantum mechanical results. {copyright} {ital 1999 American Institute of Physics.}
Date: July 1, 1999
Creator: Kim, K. & Sessler, A.M.
Partner: UNT Libraries Government Documents Department

Studies of Nonlinear QED in Collisions of 46.6 Electrons with Intense LaserPulses

Description: We report on measurements of quantum electrodynamic processes in an intense electromagnetic wave, where nonlinear effects (both multiphoton and vacuum polarization) are prominent. Nonlinear Compton scattering and electron-positron pair production have been observed in collisions of 46.6 GeV and 49.1 GeV electrons of the Final Focus Test Beam at SLAC with terawatt pulses of 1053 nm and 527 nm wavelengths from a Nd:glass laser. Peak laser intensities of approximately 0.5 x 10{sup 18} W/cm{sup 2} have been achieved, corresponding to a value of approximately 0.4 for the parameter {eta} = eE{sub rms}/m{omega}{sub 0}c, and to a value of approximately 0.25 for the parameter {Upsilon}{sub e} = E{sub rms}/E{sub crit} = eE{sub rms}{h_bar}/m{sup 2}c{sup 3}, where E{sub rms} is the rms electric field strength of the laser in the electron rest frame. We present data on the scattered electron spectra arising from nonlinear Compton scattering with up to four photons absorbed from the field. A convolved spectrum of the forward high energy photons is also given. The observed positron production rate depends on the fifth power of the laser intensity, as expected for a process where five photons are absorbed from the field. The positrons are interpreted as arising from the collision of a high-energy Compton scattered photon with the laser beam. The results are found to be in agreement with theoretical predictions.
Date: February 16, 1999
Creator: McDonald, Kirk T.
Partner: UNT Libraries Government Documents Department

Light-front-quantized QCD in Covariant Gauge

Description: The light-front (LF) canonical quantization of quantum chromodynamics in covariant gauge is discussed. The Dirac procedure is used to eliminate the constraints in the gauge-fixed front form theory quantum action and to construct the LF Hamiltonian formulation. The physical degrees of freedom emerge naturally. The propagator of the dynamical {psi}{sub +} part of the free fermionic propagator in the LF quantized field theory is shown to be causal and not to contain instantaneous terms. Since the relevant propagators in the covariant gauge formulation are causal, rotational invariance--including the Coulomb potential in the static limit--can be recovered, avoiding the difficulties encountered in light-cone gauge. The Wick rotation may also be performed allowing the conversion of momentum space integrals into Euclidean space forms. Some explicit computations are done in quantum electrodynamics to illustrate the equivalence of front form theory with the conventional covariant formulation. LF quantization thus provides a consistent formulation of gauge theory, despite the fact that the hyperplanes x{sup {+-}} = 0 used to impose boundary conditions constitute characteristic surfaces of a hyperbolic partial differential equation.
Date: June 17, 1999
Creator: Srivastava, Prem P.
Partner: UNT Libraries Government Documents Department

Basic Engineering Research for D&D of R. Reactor Storage Pond Sludge: Electrokinetics, Carbon Dioxide Extraction, and Supercritical Water Oxidation

Description: Collaborating researchers at the University of South Carolina (USC), Clemson University (CU), and the Savannah River Site (SRS) are investigating the fundamentals of a combined extraction and destruction process for the decontamination and decommissioning (D&D) of PCB-contaminated materials as found at DOE sites. Currently, the volume of PCBs and PCB contaminated wastes at DOE sites nationwide is approximately 19,000 m3. While there are a number of existing and proposed processes for the recovery and/or destruction of these persistent 4 pollutants, none has emerged as the preferred choice. Therefore, this research focuses on combining novel processes to solve the problem. The research objectives are to investigate benign dense-fluid extraction with either carbon dioxide (USC) or hot water (CU), followed by destruction of the extracted PCBs via either electrochemical (USC) or hydrothermal (CU) oxidation. Based on the results of these investigations, a combined extraction and destruction process that incorporates the most successful elements of the various processes will be recommended for application to contaminated DOE sites.
Date: June 1, 1999
Creator: Hamilton, Edward A.; Bruce, David A.; Oji, Lawrence; White, Ralph E.; Matthews, Michael A. & Thies, Mark C.
Partner: UNT Libraries Government Documents Department

Quantum-Classical Correspondence in Nonrelativistic Electrodynamics

Description: A form of classical electrodynamic field exists which gives exact agreement with the operator field of quantum electrodynamics (QED) for the Lamb shift of a harmonically bound point electron. Here it is pointed out that this form of classical theory with its physically acceptable interpretation is the result of an unconventional resolution of a mathematically ambiguous term in classical field theory. Finally a quantum-classical correspondence principle is shown to exist in the sense that the classical field and expectation value of the QED operator field are identical if retardation is neglected in the latter.
Date: October 14, 1999
Creator: Ritchie, A.B. & Weatherford, C.A.
Partner: UNT Libraries Government Documents Department