Results 31 - 40 of 134535
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[en] In this paper we provide a detailed analysis of heat generation in a solid-state laser medium. The fractional thermal loadings are different for different physical processes in a laser medium, including the fluorescence process, stimulated emission, energy transfer up-conversion and excited-state absorption. Applying this theoretical analysis in a diode-end-pumped Nd:GdVO4 laser at 1342 nm, and using a simple and efficient method to measure the thermal loading of the solid-state laser medium presented, the experimental results are in good agreement with the theoretically calculated results. (paper)
[en] Vibrational excitation: The previous evaluation by Itikawa was based on an earlier evaluation by Brunger, Buckman, and Elford. Since these evaluations, new and more accurate experimental data have been published. For the vibrational excitation from the ground v=0 to the first excited level v=1 of N2, the recommended differential cross-sections are the ones measured by M. Allan. In this study, the differential cross-section for the v=0 → v=1 excitation was measured for scattering angles q=45o, 135o, and 180o for energies between 0.3 and 5.5 eV. The measured cross-section was not resolved rotationally, i.e. a sum over all rotational levels has been measured. The region of resonances between 1.9 and 3.7 eV is well resolved. The same study gave also the differential cross sections for the v=0 → v=1 excitation as a function of the scattering angle for several values of scattering energies, E=0.8, 1.988, and 5 eV. Rotational excitation: The previous evaluation by Itikawa for rotational excitation from j=0 → j=2 and from j=0 → j=4 used the data from an earlier evaluation by Brunger, Buckman, and Elford, which was based on swarm experiment data. Since these evaluations, another accurate theoretical calculation by Sulc et al. has been published. The resulting cross section for the j=0 → j=2 transition is in good agreement with the previous evaluation for energies <1 eV. Therefore, we recommend to keep the data recommended by Itikawa for the j=0 → j=2 and j=0 → j=4 transition. New measurements and/or theoretical calculations of the rotational excitation of N2 are needed for low (<1 eV) and higher (>1 eV) energies starting with ground and excited rotational level of N2
[en] The Kitaev-Heisenberg model is source of a topological quantum spin liquid with Majorana fermions and gauge flux excitations as fractional quasiparticles. The material -RuCl is composed of weakly van der Waals bound honeycomb layers of edge sharing RuCl octahedra which has recently emerged as a prime candidate for realising such physics. We studied -RuCl by means of thermal transport measurements, a valuable tool to probe elementary excitations of systems with low dimensional spin structure. While the in-plane, longitudinal heat transport is governed by heat conduction of phonons that strongly scatter off the magnetic excitations present in the system, studying the thermal Hall effect (Rhighi-Leduc effect) opens up a new path towards detecting a direct contribution of unconventional magnetic excitations to entropy transport. We have observed a sizeable transversal heat conductivity , the agreement of which with the theoretical predictions for the pure Kitaev model being suggestive of heat transport by fractionalised quasiparticles in -RuCl.
[en] We consider the symmetric single-impurity Anderson model in the presence of pairing fluctuations. In the isotropic limit, the degrees of freedom of the local impurity are separated into hybridizing and non-hybridizing modes. The self-energy for the hybridizing modes can be obtained exactly, leading to two subbands centered at ±U/2. For the non-hybridizing modes, the second order perturbation yields a singular resonance of the marginal Fermi liquid form. By multiplicative renormalization, the self-energy is derived exactly, showing the resonance is pinned at the Fermi level, while its strength is weakened by renormalization. (author)
[en] We extend to finite temperature a Green's-function method that was previously proposed to evaluate ground-state properties of mesoscopic clouds of noninteracting fermions moving under harmonic confinement in one dimension. By calculations of the particle and kinetic-energy density profiles, we illustrate the role of thermal excitations in smoothing out the quantum shell structure of the cloud and in spreading the particle spill out from quantum tunnel at the edges. We also discuss the approach of the exact density profiles to the predictions of a semiclassical model often used in the theory of confined atomic gases at finite temperature
[en] We investigate the influence of low-energy recoils with respect to the electronic excitation of solids generated in atomic collision cascades. It is found that the electronic friction experienced by recoil atoms moving with kinetic energies below 10 eV contributes substantially to the total excitation energy dissipated into electronic degrees of freedom. The collision dynamics, on the other hand, remain virtually unchanged if the friction loss of these particles is switched on or off. This is illustrated by looking at the yield, emission sites and energies of sputtered surface atoms
[en] Highlights: • High resolution L1-L2,3M Coster-Kronig spectra in Ar are obtained by electron impact. • Many features are due to the autoionizing decay of neutral doubly excited states. • Energy analysis of ejected electrons ruled out hypothesis of the state origins. - Abstract: The ejected electron spectra between 25 and 56 eV kinetic energy in Ar have been measured at several electron impact energies. When the incident energy is above the Ar 2s ionization potential the peaks due to the L1-L2,3M1 and L1-L2,3M2,3 Coster-Kronig (CK) transitions are expected to occur in this region of kinetic energy, but we observe a series of other narrow structures that overlap and sometime dominate the spectrum due to the CK transitions. These features have been attributed to the autoionizing decay of inner valence doubly excited states to the Ar + ground state.
[en] The relativistic Multi-Reference Møller–Plesset (MR-MP) many-body perturbation theory was applied to calculate the energies of all excited states within the 3s3p, , 3s3d, 3p3d and configurations for every ion of the Mg isoelectronic sequence (). The results are compared with previous calculations and available experimental data. The MR-MP excitation energies agree with experiment typically within 100 ppm over a wide range of , particularly for mid- and high-range . Experimental data for highly charged ions in this isoelectronic sequence are limited and the complete and accurate dataset presented here is expected to ease the identification process upon measurements.
[en] Let E(B,Z,N) denote the ground state energy of an atom with N electrons and nuclear charge Z in a homogeneous magnetic field B. We study the asymptotics of E(B,Z,N) as B→∞ with N and Z fixed but arbitrary. It is shown that the leading term has the form (ln B)2 e(Z,N), where e(Z,N) is the ground state energy of a system of N bosons with delta interactions in one dimension. This extends and refines previously known results for N=1 on the one hand, and N,Z→∞ with B/Z3→∞ on the other hand. (orig.)
[en] The constrained minimization independent-fermion kinetic-energy kernel, δ2Ts[ρ]/δρ(r)δρ(r'), has a zero mode for all ρ(r), while it is non-negative for ρ(r) noninteracting v representable. copyright 1996 The American Physical Society