The laser-induced vibrational excitation of an adatom bound to a harmonic lattice at T =0 K is studied by integrating the classical generalized Langevin equation numerically. The anharmonicity of the adatom-surface bo...
The laser-induced vibrational excitation of an adatom bound to a harmonic lattice at T =0 K is studied by integrating the classical generalized Langevin equation numerically. The anharmonicity of the adatom-surface bond plays an important role in inducing quasiperiodic and chaotic adatom motion.
Recent Dirac-Hartree-Slater and Dirac-Hartree-Fock calculations of ionization cross-sections, fluorescence and Coster-Kronig yields and X-ray emission rates offer a “self-consistent” theoretical data base for relati...
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Recent Dirac-Hartree-Slater and Dirac-Hartree-Fock calculations of ionization cross-sections, fluorescence and Coster-Kronig yields and X-ray emission rates offer a “self-consistent” theoretical data base for relative intensities of proton-induced L X-rays. Interpolation schemes for use with tables of these quantities are described. Theoretical intensity ratios for major line groups agree with compiled experimental data to within a few percent, justifying use of the data base in PIXE.
A theory of the longitudinal electron spin susceptibility χs for an antiferromagnetic superconductor (AFS) has been given. For the AFS, we have assumed a homogeneous superconducting order parameter and a one-dimensio...
A theory of the longitudinal electron spin susceptibility χs for an antiferromagnetic superconductor (AFS) has been given. For the AFS, we have assumed a homogeneous superconducting order parameter and a one-dimensional electron band that satisfies the nesting condition ɛk=-ɛk+Q, where Q is the wave vector characterizing the antiferromagnetic (AF) order. First we have studied the dependence of χs on the scattering rates for the scattering of conduction electrons from the nonmagnetic, spin-orbit, and magnetic impurities by regarding HQ as a parameter and neglecting the spin-fluctuation effects (HQ is the AF field). The effect of impurities is found to be significant. Then we have investigated the temperature dependence of χs by taking TN
We propose a finite-size scaling hypothesis for the ‘‘singular’’ part of the free-energy density, f(s)(T,H;L), and the correlation function, G(R,T,H;L), of a system with O(n) symmetry (n≥2), confined to geometry ...
We propose a finite-size scaling hypothesis for the ‘‘singular’’ part of the free-energy density, f(s)(T,H;L), and the correlation function, G(R,T,H;L), of a system with O(n) symmetry (n≥2), confined to geometry Ld−d’×∞d’ (d>4, d’≤2) and subjected to periodic boundary conditions. On the basis of this hypothesis, we predict finite-size effects in the zero-field susceptibility, χ(T;L), the correlation length, ξ(T;L), and the ‘‘singular’’ part of the specific heat, c(s)(T;L), in the region of first-order phase transition (T
A numerical integration of the equations of motion of a 17-particle chain with nearest-neighbor linear and cubic forces has been carried out in quadruple-precision FORTRAN over a period of 600 model time units. The ch...
A numerical integration of the equations of motion of a 17-particle chain with nearest-neighbor linear and cubic forces has been carried out in quadruple-precision FORTRAN over a period of 600 model time units. The chain has clamped ends and is excited initially in the 11th mode. The data obtained from the integration constitute a reversible time ensemble. Equilibrium mode energy distributions in this ensemble prove to have a Maxwell-Boltzmann form, and in addition the calculated mode temperatures agree with those obtained from the double-precision statistical ensemble previously reported for the same system and same model parameters [B. I. Henry and J. Grindlay, Physica D 28, 49 (1987)]. It follows that statistical-ensemble averages and time-ensemble averages are equal, and hence the ergodic hypothesis holds for these two data banks.
The present work examines two aspects of metallic liquid–glass transitions. First, a computerexperiment, consisting of a temperature‐quench Monte Carlo calculation for the liquid–glass transition of Ca0.7Mg0.3, is ...
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The present work examines two aspects of metallic liquid–glass transitions. First, a computerexperiment, consisting of a temperature‐quench Monte Carlo calculation for the liquid–glass transition of Ca0.7Mg0.3, is carried out. A comparison with such calculations for monatomic metals indicates that there is a significant difference in the Wendt and Abraham criterion for monatomic metals and metallic alloys. In addition, a comparison with laboratory experiments indicates that the discrepancies between the Wendt–Abraham parameters obtained in these laboratory experiments and in the computerexperiments can be ascribed to different cooling rates. Second, an analytic study of the pair distribution function near the transition temperature is presented and reproduces the linear temperature dependence of the Wendt–Abraham parameter. This gives a physical picture for this parameter and indicates that the liquid–glass transition is more likely to be a first‐order transition than a second‐order one.
A scaling hypothesis is set up for the magnetization m(T,H;L) and susceptibility χ(T,H;L) of a finite-sized system, with O(n) symmetry (n≥2), confined to geometry Ld−d’×∞d’(2<d<4,d’≤2) and subjected ...
A scaling hypothesis is set up for the magnetization m(T,H;L) and susceptibility χ(T,H;L) of a finite-sized system, with O(n) symmetry (n≥2), confined to geometry Ld−d’×∞d’(2
Using proton‐beam irradiation at 15 MeV, the emission spectra from 3He and 4He doped samples of solid hydrogen and deuterium have been observed from 350–750 nm at 4.2 K. Such samples simulate the conditions of solid...
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Using proton‐beam irradiation at 15 MeV, the emission spectra from 3He and 4He doped samples of solid hydrogen and deuterium have been observed from 350–750 nm at 4.2 K. Such samples simulate the conditions of solid tritium or tritiated hydrogens after about six days of helium accretion. The spectra are very similar to pure helium gas spectra acquired at 4.2 K and closer still to spectra acquired using helium gas in the upper portion of a sample cell partially filled with solid hydrogen. The helium collects as macroscopically large bubbles whose pressure has been determined. The pure 4He gas spectrum at 4.2 K contains a band near 460 nm previously assigned to an unspecified excimer–dimer radiative transition. The pressure and isotope dependence of this band is presented which lends support to that interpretation. A mechanism is proposed for the transition.
Emission spectra of three isotopomers of helium hydride (4HeH, 3HeH, and 3HeD) in the visible spectral region have been acquired using proton‐beam irradiation of dense helium gas (150 Torr) at 4.2 K in the presence o...
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Emission spectra of three isotopomers of helium hydride (4HeH, 3HeH, and 3HeD) in the visible spectral region have been acquired using proton‐beam irradiation of dense helium gas (150 Torr) at 4.2 K in the presence of some solid hydrogen or deuterium. Besides the previously reported D? 2Σ+→A? 2Σ+ transition, near 550 nm, a second transition near 640 nm, identified as the D? 2Σ+→B? 2Π, has been acquired and analyzed. The spectroscopic constants for both transitions have been obtained and compared to the theoretical results based on the latest published potential curves. Further insight into the mechanism for forming HeH will be presented, which indicates that the formation process is sensitive to the hydrogen vapor pressure above the solid.
There are numerous materials and techniques for the fabrication of optical waveguides and opto-electronic circuits, however all structures require knowledge of the guiding properties for the realization of practical d...
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There are numerous materials and techniques for the fabrication of optical waveguides and opto-electronic circuits, however all structures require knowledge of the guiding properties for the realization of practical devices. We have studied in detail the guiding properties of the planar thin film waveguide, from the most basic, three-layer structure to multilayer waveguides. In sections II and III we describe general formulas for the field distributions, the eigenvalue equations from which the propagation constant can be found, and the generalized dispersion properties, which tell us the variation in effective index with respect to any physical parameter upon which the refractive index or thickness of any layer may depend.
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