Accurate tail-to-peak intensity ratios are extracted from the spectra produced in a Si(Li) detector by x-rays of energies 2-1. keV. The widely used model of a surface layer of incomplete charge collection fails to exp...
Accurate tail-to-peak intensity ratios are extracted from the spectra produced in a Si(Li) detector by x-rays of energies 2-1. keV. The widely used model of a surface layer of incomplete charge collection fails to explain the energy dependence of these data. The model is augmented to include loss of photoelectrons travelling back into the ICC layer from an interaction in the active silicon region;this gives excellent agreement with experiment. It is shown that the detection efficiency in the region of low x-ray energy may be deduced from the tail-to-peak ratios, together with measurement of the thicknesses of the beryllium window and the metal contact;a potential source of error in measuring the latter by the popular fluorescence technique is demonstrated.
The guelph proton microprobe has provided several thousand spot analyses of mineralogical, geochemical and metallurgical specimens, mainly through contract arrangements. User-friendly target chamber design with color ...
The guelph proton microprobe has provided several thousand spot analyses of mineralogical, geochemical and metallurgical specimens, mainly through contract arrangements. User-friendly target chamber design with color TV viewing of the incident beam spot at magnification x 300 is crucial in this {1.. A new PC-based data accumulation system for both spot analysis and elemental mapping is described. Various enhancements to the GUPIX software for spectrum fitting and standardization are reviewed.
First-principles theoretical results are reported for the specific heats and closely related thermodynamic quantities, required in the determination of the characteristics of the supercooled metallic liquids, for Al, ...
详细信息
First-principles theoretical results are reported for the specific heats and closely related thermodynamic quantities, required in the determination of the characteristics of the supercooled metallic liquids, for Al, Rb and Ca0.7Mg0.3 metals. Of these results, those for the specific heats are fully analyzed and discussed by considering computer-simulation results on the atomic motion in the supercooled-liquid region. It now appears that the specific heat at constant pressure behaves as a monotonically increasing function of temperature in decreasing from the melting temperature to the glass-transition temperature for those supercooled metallic liquids that have high glass-forming ability.
A first-principles thermodynamic calculation appropriate for metallic glasses is first proposed and is then carried out for the metals Al and Ca0.7Mg0.3. The calculated results are compared with previously obtained re...
详细信息
A first-principles thermodynamic calculation appropriate for metallic glasses is first proposed and is then carried out for the metals Al and Ca0.7Mg0.3. The calculated results are compared with previously obtained results for the supercooled-liquid states of pure Al metal. It now appears that, because of the significant change in the derivative of the volume with respect to temperature on going through the liquid-glass transition, the thermodynamic quantities vary drastically in this region, for those metals that can form glasses in the laboratory through the liquid-quenching process.
We present a Monte Carlo simulation of X-ray interaction with a Si(Li) detector which includes for the first time both a detailed description of the atomic excitation and de-excitation and also a physically realistic ...
We present a Monte Carlo simulation of X-ray interaction with a Si(Li) detector which includes for the first time both a detailed description of the atomic excitation and de-excitation and also a physically realistic model of the frontal region of incomplete charge collection. Simulated lineshapes are in good agreement with those measured by using monoenergetic X-rays of energy 1.1. keV and by varying the two parameters of the model we can generate lineshapes very similar to those reported in the literature for other Si(Li) detectors.
The electric modulus representation is used to display conductivity and dielectric relaxation occurring in poly(propylene glycol)-4000 (PPG) complexed with LiCF3SO3, as the ether oxygen to lithium (O:Li) ratio is vari...
详细信息
The electric modulus representation is used to display conductivity and dielectric relaxation occurring in poly(propylene glycol)-4000 (PPG) complexed with LiCF3SO3, as the ether oxygen to lithium (O:Li) ratio is varied from 300:1.to 1.:1. The frequency range covered is 1. to 1.(7) Hz. Results are obtained for temperatures above the glass transition temperature appropriate for each PPG-LiCF3SO3 complex. For O:M = 300:1. the conductivity peak and the alpha and alpha' relaxation are clearly resolved. As the concentration is increased, there is a coupling between the structural and the conductivity relaxations;the various peaks begin to overlap. The coupling is greatest for an O:Li ratio in the range 30:1.to 1.:1. where the highest conductivity is measured. Below room temperature, the 30:1.complex has the highest conductivity, above room temperature the 1.:1.complex has the highest. At any particular temperature there is a concentration above which the conductivity drops. This drop is due to reduced ion mobility resulting from a dramatic increase in viscosity to values above approximately 1.0 poise.
The dc-conductivity, plasma frequency and the specific heat are calculated as a function of doping for La2-xSrxCuO4 and related compounds. There is good quantitative agreement with experimental data. The volume includ...
详细信息
The dc-conductivity, plasma frequency and the specific heat are calculated as a function of doping for La2-xSrxCuO4 and related compounds. There is good quantitative agreement with experimental data. The volume included by the Fermi surface obeys Luttinger Theorem. The calculations are based on quasiparticles whose energy spectrum has tight binding form renormalized by strong correlations and originating from the t-t'-J model. We have used the relaxation time approximation.
Deuterium nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times were determined in order to study the dynamics of t-butyl groups in butylated hydroxytoluene. The results are consistent with a mode...
详细信息
Deuterium nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times were determined in order to study the dynamics of t-butyl groups in butylated hydroxytoluene. The results are consistent with a model first proposed by Beckmann et al. [J. Magn. Reson. 36, 1.9 (1.79)], where there is an inequivalence between the methyl groups within each t-butyl group. While two methyl groups reorient rapidly relative to the whole t-butyl rotation, the remaining methyl group is more restricted in its motion, reorienting at a rate comparable to that of the t-butyl group itself. The spin-lattice relaxation data show two T1.minima, the high temperature minimum (40-degrees-C) corresponding to the combined t-butyl and "slow" methyl rotations, and the low temperature minimum corresponding to "fast" methyl group rotation. Using an explicitly defined T1.fitting function, the T1.data yield activation energies of 2.2 and 6.0 kcal/mol for the fast methyl and t-butyl rotations, respectively, both in agreement with Beckmann's values obtained from proton T1.experiments. It was also possible to simulate the low temperature deuterium NMR spectra from T = - 1.0-degrees-C to T = - 80-degrees-C using the aforementioned dynamical inequivalence between the t-butyl methyl groups. While the fast methyl group rotation was in the motional narrowing region for T > - 1.0-degrees-C, it was possible, from the simulations, to determine the t-butyl exchange rates to within 1.%. The jump rates are remarkably close to the values predicted from the T1.results. Above - 80-degrees-C, the spectra could not be simulated, implying that a third motion must be present to further alter the high temperature line shapes. The effective axial asymmetry of the T > - 20-degrees spectra indicates that the additional motion involves a two site exchange.
The resistivity and T(c) of Bi2Sr2CaCu2O8+delta can be reversibly modified at room temperature using an electrochemical cell. Whereas reducing with up to 0.02 mole fraction of charge enhances the T(c) systematically f...
详细信息
The resistivity and T(c) of Bi2Sr2CaCu2O8+delta can be reversibly modified at room temperature using an electrochemical cell. Whereas reducing with up to 0.02 mole fraction of charge enhances the T(c) systematically from about 73 K to 88 K, further reduction decreases the T(c) again and eventually goes on to suppress superconductivity altogether. Above 0.1. mole fraction p(T) loses its metallic character and assumes a negative slope which, above 0.50 mole fraction, can be modeled in terms of a semiconductor with an activation energy of 30 +/- 2 meV. Oxidizing the latter material restores superconductivity, albeit the reversibility is not complete. Electrochemical and EDX data are compatible with the reversible solid state diffusion of copper;we propose that copper is intercalating.
作者：
SIMPSON, JJDepartment of Physics
University of Guelph and Guelph-Waterloo Program for Graduate Work in Physics Guelph Ontario Canada N1G 2W1
It is suggested that the late neutrino events from supernova SN1.87A detected by the Kamiokande and IMB detectors can be understood as arising from massive neutrinos decaying in flight. If the neutrino mass is 1. keV,...
It is suggested that the late neutrino events from supernova SN1.87A detected by the Kamiokande and IMB detectors can be understood as arising from massive neutrinos decaying in flight. If the neutrino mass is 1. keV, the estimated mean life is (0.6-1.6) x 1.(4) s. The shorter prompt pulse then implies an upper limit to the mass of the lightest neutrino of 1. eV.
暂无评论