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Post-irradiation flashes and continuous emission from solid deuterium

Physical Review B 1997年第2期55卷 906-906页

作者： J. A. Forrest R. L. Brooks Guelph-Waterloo Program for Graduate Work in Physics University of Guelph Guelph Ontario Canada N1G 2W1

Optical emission from proton-beam-irradiated solid deuterium near 800 nm has been studied after termination of the proton beam. The continuous red emission shows a residual intensity that persists over 30 min from termination of the beam. Optical flashes can also be thermally triggered over 10 min after termination of irradiation. Such triggered flashes are shown to quench the infrared absorption of Stark-shifted charge-induced features. Ultraviolet photons can stimulate this red emission after termination of irradiation with no measurable decrease in intensity for 40 min. The cause of this continuous emission and optical flashes is discussed in the light of these results.

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Nonexponential dynamic relaxation of randomly branched polymers in good solvents

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Physical Review E 1997年第6期56卷 7017-7017页

作者： Josh Kemp Zheng Yu Chen Guelph-Waterloo Program for Graduate Work in Physics and Department of Physics University of Waterloo Waterloo Ontario Canada N2L 3G1

Monte Carlo simulations were carried out to study the dynamics of randomly branched polymers in good solvents. Two types of time scales were observed: fast relaxation times corresponding to the internal contraction motions and slower relaxation times corresponding to the overall rotational motions of the polymers. The former is associated with autocorrelation functions that exhibit nonexponential decay behavior, a signature of the dynamics of random systems. The latter is associated with the usual exponential decay behavior, typical of linear or regularly branched polymers.

关键词： Molecular dynamics

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Charge-density waves and density of states in the intercalated tunnel structure TlxNb3Te4

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Physical Review B 1997年第3期56卷 1175-1175页

作者： F. W. Boswell G. A. Scholz J. C. Bennett Guelph-Waterloo Program for Graduate Work in Physics Waterloo Campus University of Waterloo Ontario Canada N2L 3G1

Tunnel structures, into which a variety of atoms can be intercalated, offer a promising approach for investigation of the interaction between charge-density waves (CDW’s) and foreign atoms. For this purpose single crystals of TlxNb3Te4 with 0<~x<~1 were prepared. CDW’s were observed below room temperature for all crystals, despite the wide range of Tl content. The wave vectors were determined by electron diffraction and the transition temperatures by resistivity measurements. For x<0.25 the transition temperatures were less than those of the pure material, while for x>0.25 both the transition temperatures and wave vectors increased strongly and passed through a maximum near x=0.75. The results were interpreted in terms of the crystal structure and the variation of the electron density of states at the Fermi level, as additional electrons were contributed to the host crystal with increasing Tl content. This is an example of a quasi-one-dimensional, inorganic system in which the transition temperature and CDW vector can be conveniently tuned by adjustments of the intercalate content.

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Surface-enhanced ordering and layer-thinning transitions in freely suspended smectic-A films

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Physical Review E 1997年第2期55卷 2030-2030页

作者： Y. Martínez-Ratón A. M. Somoza L. Mederos D. E. Sullivan Instituto de Ciencia de Materiales Consejo Superior de Investigaciones Científicas Cantoblanco Madrid E-28049 Spain Department of Physics and Guelph-Waterloo Program for Graduate Work in Physics University of Guelph Guelph Ontario Canada N1G 2W1

We propose a physical mechanism which leads to surface-enhanced smectic-A ordering (SESO) at the free surface of a model liquid crystal. We also provide an explanation, based on a density-functional theory, for recent experimental results for the melting behavior of freely suspended smectic (FSS) films. It is shown that stepwise layer-thinning transitions do not usually occur during melting of FSS films, despite the presence of SESO. We find that thinning transitions similar to those observed experimentally occur under conditions such that the film interior melts to a nematic rather than isotropic liquid phase.

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X-ray natural widths, level widths and Coster-Kronig transition probabilities

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AIP Conference Proceedings 1997年第1期389卷 431-446页

作者： T. Papp J. L. Campbell D. Varga Institute of Nuclear Research of the Hungarian Academy of Sciences Debrecen Bem tér 18/c P.f. 51 H-4001 Hungary Guelph-Waterloo Program for Graduate Work in Physics University of Guelph Guelph Ontario N1G2W1 Canada

A critical review is given for the K-N7 atomic level widths. The experimental level widths were collected from x-ray photoelectron spectroscopy (XPS), x-ray emission spectroscopy (XES), x-ray spectra fluoresced by synchrotron radiation, and photoelectrons from x-ray absorption (PAX). There are only limited atomic number ranges for a few atomic levels where data are available from more than one source. Generally the experimental level widths have large scatter compared to the reported error bars. The experimental data are compared with the recent tabulation of Perkins et al. and of Ohno et al. Ohno et al. performed a many body approach calculation for limited atomic number ranges and have obtained reasonable agreement with the experimental data. Perkins et al. presented a tabulation covering the K-Q1 shells of all atoms, based on extensions of the Scofield calculations for radiative rates and extensions of the Chen calculations for non-radiative rates. The experimental data are in disagreement with this tabulation, in excess of a factor of two in some cases. A short introduction to the experimental Coster-Kronig transition probabilities is presented. It is our opinion that the different experimental approaches result in systematically different experimental data.

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Micro-PIXE analysis of silicate reference standards for trace Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo and Pb, with emphasis on Ni for application of the Ni-in-garnet geothermometer

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Canadian Mineralogist 1996年第1期34卷 37-37页

作者： Campbell, J.L. Teesdale, W.J. Kjarsgaard, B.A. Cabri, L.J. University of Guelph Guelph-Waterloo Program for Graduate Work in Physics Guelph ON Canada

Trace-element analysis is a powerful tool for studying numerous processes of research interest in the Earth Sciences; as well, it has important applications of interest to the mineral exploration community. Here, we present the results of a comprehensive study of five internationally recognized silicate reference standards (BHVO-1, GXR-5, GSR-5, MAG-1 and GSD-50) utilizing micro-PIXE analysis. Results of trace analyses for Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo and Pb are presented. Measured data for the five standards exhibit agreement within + or -10%, and commonly better, with recommended levels of concentration in the 50-400 ppm range. Detection limits (for a typical 3- to 4-minute analysis of an accumulated charge of 2.5 microCoulombs) are in the range of 2-10 ppm, with precisions of 1-10%. A detailed study of the X-ray spectra in the vicinity of the Fe, Ni and Co lines illustrates that the GUPIX software is able to correctly fit the complex spectra and thus provide accurate Ni concentrations. Further tests on Ni in garnet are reported, in the context of current application of the Ni-in-garnet geothermometer in diamond exploration; it appears important to resolve the difference between the two published calibrations of this important geothermometer.

关键词： Acccuracy Garnet Geostandards Glasses Micro-PIXE analysis Ni-in-garnet geothermometer Trace elements

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Direct use of variational principles as an approximation technique in classical mechanics

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AMERICAN JOURNAL OF physics 1996年第9期64卷 1177-1184页

作者： Gray, CG Karl, G Novikov, VA Guelph‐Waterloo Program for Graduate Work in Physics and Department of Physics University of Guelph Guelph Ontario N1G 2W1 Canada

The Hamilton least action principle, a reformulated Maupertuis least action principle, and their reciprocals, are shown to be useful as direct methods for approximate solutions of dynamics problems. We discuss applications to trajectories of all types, i.e., periodic, quasiperiodic, chaotic, scattering, and arbitrary segments of arbitrary trajectories. The analogy with the standard technique used in quantum mechanics is very striking, especially in one of the reformulations (extremization of the mean energy), and in the calculational procedure (Rayleigh-Ritz type). (C) 1996 American Association of physics Teachers.

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Acoustic emission from modulated laser beam welding of materials

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JOURNAL OF LASER APPLICATIONS 1996年第4期8卷 205-210页

作者： Gu, HP Duley, WW Guelph‐Waterloo Program for Graduate Work in Physics University of Waterloo Waterloo Ontario Canada N2L 3G1

Acoustic emission during the laser welding of metals with a modulated CO2 laser beam has been investigated. Sharp resonances at many frequencies in the acoustic emission spectra have been observed. This was most noticeable when the average laser power was high enough to produce full penetration welds whose acoustic emission at high harmonics with frequencies that overlap with bands of vibrational frequencies corresponding to eigenmodes of the keyhole are greatly enhanced. Lower harmonics were not clearly observed. However, in partial penetration welding, many harmonic components were observed. These results are not affected by a surface coating of the metal as in the galvanized steel sheet sample. This observation indicates that the keyhole and its surrounding liquid layer act as a frequency selective amplifier for pressure fluctuations induced by changes in the interaction of the laser radiation with the walls of the keyhole. When a continuous wave (CW) beam is used, random fluctuations with frequencies within these allowed bands are amplified to produce a spectrum consisting of a large number of overlapping but discrete frequency components. When the laser beam is modulated, a forced response is elicited resulting in a much simplified emission spectrum.

关键词： laser welding acoustic monitoring

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Reflected-light, photoluminescence and OBIC imaging of solar cells using a confocal scanning laser MACROscope/microscope

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SOLAR ENERGY MATERIALS AND SOLAR CELLS 1996年第4期44卷 439-450页

作者： Ribes, AC Damaskinos, S Tiedge, HF Dixon, AE Brodie, DE Guelph-Waterloo Program for Graduate Work in Physics Waterloo Campus University of Waterloo Waterloo Ont. Canada N2L 3G1

This paper describes a confocal scanning beam MACROscope/Microscope which can image specimens up to 7x7 cm in size using reflected light, photoluminescence and optical beam induced current. The MACROscope provides a 10 mu m spot size at various wavelengths and generates 512 x 512 pixel images in less than 5 s. When used in combination with a conventional confocal scanning laser microscope sub-micron spot sizes become possible providing resolutions as high as 0.25 mu m laterally and 0.5 mu m axially in reflected light. The main function of this imaging system is to spatially resolve any defects within solar cells and similar devices. Several reflected-light, photoluminescence and OBIC images of CdS/CuInSe2 and CdZnS/CuInSe2 thin film solar cells are presented.

关键词： confocal macroscope OBIC photoluminescence

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Spherical particle size determination by analytical inversion of the UV-visible NIR extinction spectrum

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APPLIED OPTICS 1996年第1期35卷 193-197页

作者： Wang, JH Hallett, FR []The authors are with the Guelph–Waterloo Program for Graduate Work in Physics Department of Physics University of Guelph Guelph Ontario N1G 2W1 Canada

An analytic inversion method, based on the anomalous diffraction approximation for nonabsorbing spherical particles, was developed to retrieve the size distribution from the optical turbidity or extinction spectrum. This method makes use of a differential Fourier cosine transform approach and provides a simple and fast inversion by means of fast Fourier transform and the Savitzky-Golay filter. The applicability of this algorithm was tested on the extinction data generated by the Mie solution. The effects of noise, modality, band limits, and data set size were analyzed by comparison with simulated data. This method can be used to reconstruct the original monomodal and bimodal distributions from 10% noise-corrupted data. The peak position and ratio of peak heights can be recovered with 10% or less deviation. The experiments with latex spheres showed that the inversion result from this method compares favorably with that from the dynamic light scattering measurement. (C) 1996 Optical Society of America

关键词： particle size measurement turbidity optical characterization inverse problem and light scattering

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