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Polarization degree differences for the 3p 2P3/2–3s 2S1/2 transition of N4+(3p 2P3/2) produced in N5+-He and N5+-H2 collisions

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Physical Review A 2010年第1期81卷 014702-014702页

作者： L. Liu Y. Q. Zhao J. G. Wang R. K. Janev H. Tanuma The Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Post Office Box 8009 People’s Republic of China Department of Physics and Key Laboratory for Atomic and Molecular Nanosciences Tsinghua University Beijing 100084 People’s Republic of China Macedonian Academy of Sciences and Arts Post Office Box 428 1000 Skopje Macedonia Department of Physics Tokyo Metropolitan University Tokyo 192–0397 Japan

The magnetic substate-selective single-electron-capture cross sections in collisions of N5+ with He and H2 are calculated using the two-center atomic orbital close-coupling method, and the polarization of emitted radiation from the excited state of N4+ is investigated for projectile energies between 1.2 and 7 keV/u. The polarization degrees for the 3p 2P3/2–3s 2S1/2 transition of N4+(3p 2P3/2) produced in N5++He and N5++H2 electron-capture collisions are in general agreement with the experimental measurements. It is found both experimentally and theoretically that there exists a large difference between the polarization degrees of this radiation resulting from the N5++He and N5++H2 electron-capture collisions, namely, ~0.25 and ~0, respectively. By studying the time evolution of electron-capture dynamics in the two systems we have found that this difference is caused mainly by the difference in the interactions in the two systems at relatively small internuclear distances, consistent with the molecular picture of the collision dynamics.

关键词： Quantum chemistry

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Electron collisions with the BH2 radical using the R-matrix method

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Physical Review A 2010年第6期82卷 062711-062711页

作者： Song Bin Zhang Jian Guo Wang R. K. Janev Xiang Jun Chen Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics University of Science and Technology of China Hefei 230026 China Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics P. O. Box 8009 Beijing 100088 China Macedonian Academy of Sciences and Arts P. O. Box 428 1000 Skopje Macedonia

Differential, integral, and momentum-transfer cross sections for the rotationally elastic and inelastic scattering of electron by the BH2 radical at low collision energies (0–8 eV) are reported in a 22-state molecular R-matrix method. The excitation cross sections from the ground X 2A1 state to the first two excited states 2B1 and 4A2 are calculated as well, for incident electron energies from the respective thresholds up to 8 eV. Configuration-interaction wave functions are used to represent the target states which account for the correlation effects. Four shape and three Feshbach resonances are detected. The Born-closure approximation is applied for the elastic and dipole-allowed transitions to account for the l>4 partial waves excluded from the R-matrix calculations.

关键词： Wave functions

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Dielectronic recombination in He-like, Li-like, and Be-like highly charged ions in the KLL and KLM manifolds

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Physical Review A 2010年第2期81卷 022712-022712页

作者： A. P. Kavanagh H. Watanabe Y. M. Li B. E. O’Rourke H. Tobiyama N. Nakamura S. McMahon C. Yamada S. Ohtani F. J. Currell Centre for Plasma Physics International Research Centre for Experimental Physics Queens University Belfast BT7 1NN UK Institute for Laser Science and Department of Applied Physics and Chemistry University of Electro-Communications Chofu Tokyo 182-8585 Japan Institute of Applied Physics and Computational Mathematics Post Office Box 8009 Beijing 100088 People’s Republic of China

This paper reports a systematic study of the dependence on atomic number of the dielectronic recombination resonance strengths for He-like, Li-like and Be-like ions. Recent measurements of dielectronic recombination resonance strengths for the KLL and KLM manifolds for iron, yttrium, iodine, holmium, and bismuth are also described. The resonance strengths were normalized to calculated electron impact ionization cross sections. The measured resonance strengths generally agree well with theoretical calculations using the distorted wave approximation. However, KLM resonance strength measurements on high atomic number open-shell ions gave higher values than those suggested by calculations. Using recently measured data, along with existing results, scaling laws have been generated as a function of atomic number for He-like, Li-like, and Be-like ions in the KLL and KLM manifolds.

关键词： Impact ionization

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Precision calculation of low-energy electron-impact excitation cross sections of sodium

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Physical Review A 2010年第2期81卷 022703-022703页

作者： Xiang Gao Xiao-Ying Han Lan Voky Nicole Feautrier Jia-Ming Li Department of Physics Shanghai Jiao Tong University Shanghai 200240 People’s Republic of China The Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing 100088 People’s Republic of China LERMA UMR 8112 du CNRS Observatoire de Paris 92915 Meudon Cedex France Key Laboratory of Atomic and Molecular Nanosciences of Education Ministry Department of Physics Tsinghua University Beijing 100084 People’s Republic of China

The collision cross sections of sodium from the ground state to the first four excited states at the incident energy ranging from 0 to 5.4 eV are calculated using the R-matrix method. The convergences of the cross sections are checked systematically by using four sets of high-quality target states, i.e., 5, 9, 14, and 19 physical target states. The influence of the Rydberg target states on the collision cross sections is also elucidated at higher incident energies; i.e., the amplitude of resonance structures will decrease with respect to the effective quantum number υ of the Rydberg target states. This result is very useful for the calculations of these cross sections at intermediate energy with finite target states by combining the partial-wave-expansion methods valid at low energy with the first Born approximation method valid at high energy, which would be of great importance in obtaining complete cross-section data for related scientific fields.

关键词： Excited states

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Theory of ice premelting in porous media

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Physical Review E 2010年第3期81卷 031604-031604页

作者： Hendrik Hansen-Goos J. S. Wettlaufer Department of Geology and Geophysics Yale University New Haven Connecticut 06520 USA Department of Physics Yale University New Haven Connecticut 06520 USA Program in Applied Mathematics Yale University New Haven Connecticut 06520 USA

Premelting describes the confluence of phenomena that are responsible for the stable existence of the liquid phase of matter in the solid region of its bulk phase diagram. Here we develop a theoretical description of the premelting of water ice contained in a porous matrix, made of a material with a melting temperature substantially larger than ice itself, to predict the amount of liquid water in the matrix at temperatures below its bulk freezing point. Our theory combines the interfacial premelting of ice in contact with the matrix, grain-boundary melting in the ice, and impurity and curvature induced premelting, with the latter occurring in regions which force the ice-liquid interface into a high curvature configuration. These regions are typically found at points where the matrix surface is concave, along contact lines of a grain boundary with the matrix, and in liquid veins. Both interfacial premelting and curvature induced premelting depend on the concentration of impurities in the liquid, which, due to the small segregation coefficient of impurities in ice are treated as homogeneously distributed in the premelted liquid. Our principal result is an equation for the fraction of liquid in the porous medium as a function of the undercooling, which embodies the combined effects of interfacial premelting, curvature induced premelting, and impurities. The result is analyzed in detail and applied to a range of experimentally relevant settings.

关键词： Ice

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Dynamics of O6+ + H electron capture in Debye plasmas and properties of resulting O5+(nl) emission spectra

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Physical Review A 2010年第2期82卷 022701-022701页

作者： Y. Q. Zhao L. Liu J. G. Wang R. K. Janev P. Xue Department of Physics and Key Laboratory of Atomic and Molecular Nanosciences Tsinghua University Beijing 100084 China Institute of Applied Physics and Computational Mathematics P.O. Box 8009 Beijing 100088 China Macedonian Academy of Sciences and Arts P.O. Box 428 1000 Skopje Macedonia

The electron capture in O6+-H collisions is studied by the two-center atomic orbital close-coupling (TC-AOCC) method when the interactions of charged particles are screened and have a Yukawa form. Atomic orbitals and eigenenergies of n ⩽ 6 states on O5+ and n ⩽ 2 states on H are calculated as a function of the interaction screening parameter and used in the AOCC dynamics scheme to calculate the electron capture cross sections in the energy range 1–200 keV/u. It is shown that the degree of interaction screening reduces the electron binding energies, the number of open electron capture channels, and the strength of exchange couplings, thus affecting the entire collision dynamics and the magnitude and energy behavior of electron capture cross sections. The state-selective electron capture cross sections in this collision system, as well as the intensities of a number of charge exchange spectral lines, for a number of representative interaction screening strengths are presented and discussed.

关键词： Quantum chemistry

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Geometrical ambiguity of pair statistics: Point configurations

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Physical Review E 2010年第1期81卷 011105-011105页

作者： Y. Jiao F. H. Stillinger S. Torquato Department of Chemistry Princeton University Princeton New Jersey 08544 USA Princeton Institute for the Science and Technology of Materials Princeton University Princeton New Jersey 08544 USA Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA and Princeton Center for Theoretical Physics Princeton University Princeton New Jersey 08544 USA

Point configurations have been widely used as model systems in condensed-matter physics, materials science, and biology. Statistical descriptors, such as the n-body distribution function gn, are usually employed to characterize point configurations, among which the most extensively used is the pair distribution function g2. An intriguing inverse problem of practical importance that has been receiving considerable attention is the degree to which a point configuration can be reconstructed from the pair distribution function of a target configuration. Although it is known that the pair-distance information contained in g2 is, in general, insufficient to uniquely determine a point configuration, this concept does not seem to be widely appreciated and general claims of uniqueness of the reconstructions using pair information have been made based on numerical studies. In this paper, we present the idea of the distance space called the D space. The pair distances of a specific point configuration are then represented by a single point in the D space. We derive the conditions on the pair distances that can be associated with a point configuration, which are equivalent to the realizability conditions of the pair distribution function g2. Moreover, we derive the conditions on the pair distances that can be assembled into distinct configurations, i.e., with structural degeneracy. These conditions define a bounded region in the D space. By explicitly constructing a variety of degenerate point configurations using the D space, we show that pair information is indeed insufficient to uniquely determine the configuration in general. We also discuss several important problems in statistical physics based on the D space, including the reconstruction of atomic structures from experimentally obtained g2 and a recently proposed “decorrelation” principle. The degenerate configurations have relevance to open questions involving the famous traveling salesman problem.

关键词： Inverse problems

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Direct probing of electronic density distribution of a Rydberg state by high-order harmonic generation in a few-cycle laser pulse

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Physical Review A 2010年第4期82卷 043422-043422页

作者： Zhen Zhai Jing Chen Zong-Chao Yan Panming Fu Bingbing Wang Laboratory of Optical Physics Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China Center for Nonlinear Studies Institute of Applied Physics and Computational Mathematics Beijing 100088 China Department of Physics University of New Brunswick P.O. Box 4400 Fredericton New Brunswick E3B 5A3 Canada

We demonstrate that the electronic density distribution of a Rydberg state can be probed directly using a broadband harmonic spectrum in a few-cycle laser pulse. Taking advantage of the large orbital radius of a Rydberg state, we show that the Rydberg electron can be accelerated directly toward the core under the influence of a few-cycle laser pulse, leading to recombination and emission of harmonic photons. In this case the initial position of the electron and the harmonic order form a one-to-one correspondence, resulting in a realization of direct probing of the density distribution of the initial Rydberg state.

关键词： Rydberg states

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Electron–hydrogen-atom elastic and inelastic scattering with screened Coulomb interaction around the n=2 excitation threshold

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Physical Review A 2010年第3期81卷 032707-032707页

作者： Song Bin Zhang Jian Guo Wang R. K. Janev Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics University of Science and Technology of China Hefei 230026 People’s Republic of China Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics P. O. Box 8009 Beijing 100088 People’s Republic of China Macedonian Academy of Sciences and Arts P. O. Box 428 1000 Skopje Macedonia

The effects of Coulomb interaction screening on electron–hydrogen-atom elastic and excitation scattering around the n=2 threshold have been investigated by using the R-matrix method with pseudostates. The elastic and excitation collision strengths show dramatic changes when the interaction screening length D varies from ∞ to 3.8 a.u., as a result of the convergence of 1,3S Feshbach resonances to the varying 2s threshold and of the transformation of 1,3P and 1D Feshbach resonances into shape-type resonances when they pass across the 2s and 2p threshold at certain critical value of D, respectively [S. B. Zhang et al., Phys. Rev. Lett. 104, 023203 (2010)]. The resonance parameters for a large number of D in the range D=∞–3.8 a.u. are presented. It is observed that the 1,3P and 1D resonance contributions to the elastic and excitation collision strengths decrease rapidly with decreasing D after the resonance passes the critical D value. The contribution of a 1Se Feshbach resonance to the elastic or excitation collision strength changes into a cusp after the resonance merges into its parent 2s state and immerses into the background with the further decrease of D.

关键词： Excited states

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Maximal Potential Energy Transport: A Variational Principle for Solidification Problems

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Physical Review Letters 2010年第25期105卷 254502-254502页

作者： A. J. Wells J. S. Wettlaufer S. A. Orszag Department of Geology and Geophysics Yale University New Haven Connecticut 06520 USA Program in Applied Mathematics Yale University New Haven Connecticut 06520 USA Department of Physics Yale University New Haven Connecticut 06520-8109 USA Department of Mathematics Yale University New Haven Connecticut 06520-8283 USA

We analyze numerically the mechanisms controlling the spacing of chimneys—channels devoid of solid—in two-dimensional mushy layers formed by solidifying a binary alloy. Chimneys are the principal conduits through which buoyancy effects material transport out of the mushy layer and into the liquid from which it formed. Experiments show a coarsening of chimney spacing; we pursue the hypothesis that the spacing adjusts to optimize material transport and hence maximize the rate of removal of potential energy stored in the mushy layer. The optimal solute flux increases approximately linearly with the mush Rayleigh number. However, for spacings below a critical value, the chimneys collapse and solute fluxes cease, revealing a hysteresis between chimney convection and no flow. The results are consistent with a variational principle controlling the dynamics of this dissipative system.

关键词： Potential energy

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