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991.
用量子化学从头算方法研究H2BO分子的稳定结构、异构化反应和脱氢反应及其热力学性质,较完整地阐述了H2BO在位能面上的重排和离解过程,用UHF/3-21G和MP2/3-21G优化了稳定构型和寻找过渡态。 相似文献
992.
993.
J.C. Gimel T. Nicolai D. Durand J.M. Teuler 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):91-97
Dynamic properties of Brownian particles immersed in a periodic potential with two barriers V1 and V2 (symmetric bistable potential) are studied by using the Fokker-Planck equation which we solve numerically by the matrix continued
fraction method. This study will therefore serve to demonstrate the influence of this form of potential, which is of great
interest for superionic conductors and for many other solid systems, on the diffusion process. Thus, we have calculated the
full width at half maximum (FWHM) ) of the quasi-elastic line of the dynamic structure factor, for a large range of values of the wave-vectors q. Our results show clearly that, by varying the ratio of the barriers strictly between and 1, the Fokker-Planck equation describes a diffusive process which has some characteristic of jump and
liquid-like regimes. While in the limit cases, i.e. when tends to or 1, the diffusion process can be described only by a simple jump motion. However, the jump-lengths corresponding
to each limit case are not equal. In general the change of the ratio is found to have a significant effect on the character
of the diffusive motion. We have also performed Fokker-Planck dynamics calculations of the diffusion coefficient in a bistable
potential. We have found a good agreement between numerical calculations and analytical approximation results obtained in
the high friction limit.
Received 25 May 1998 and Received in final form 15 November 1998 相似文献
994.
M. Grifoni E. Paladino U. Weiss 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):719-729
The dynamics of the reduced density matrix of the driven dissipative two-state system is studied for a general diagonal/off-diagonal
initial state. We derive exact formal series expressions for the populations and coherences and show that they can be cast
into the form of coupled nonconvolutive exact master equations and integral relations. We show that neither the asymptotic
distributions, nor the transition temperature between coherent and incoherent motion, nor the dephasing rate and relaxation
rate towards the equilibrium state depend on the particular initial state chosen. However, in the underdamped regime, effects
of the particular initial preparation, e.g. in an off-diagonal state of the density matrix, strongly affect the transient dynamics. We find that an appropriately tuned external ac-field
can slow down decoherence and thus allow preparation effects to persist for longer times than in the absence of driving.
Received 23 October 1998 and Received in final form 26 February 1999 相似文献
995.
G. Abramson J.L. Vega 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(2):361-364
Multifractal critical phenomena with infinite-temperature critical point and with complex coexistence of the infinite and
finite temperature critical points are considered and it is shown that strange attractors generated by cascades of period-doubling
bifurcations (Feigenbaum scenario) as well as fields of velocity differences in fluid turbulence belong to the former subclass
of the multifractal critical phenomena, while the real traffic processes and real currency exchange processes belong to the
last (complex) subclass of the multifractal critical phenomena. Data obtained by different authors are used for this purpose.
Received 5 February 1999 相似文献
996.
X.-F. Pang 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):415-428
The influence of a soliton on the properties of the M?ssbauer effect resulting from the gamma-active nuclei situated at lattice
sites in quasi-one-dimensional anharmonically organic molecular chains, in which the active nuclei emit gamma-photons, has
been theoretically studied by a quantum vibrational model. An expression for the gamma-radiated M?ssbauer transition probability
as a function of the temperature and non-linear interaction has been obtained. Finally we give some new properties of this
effect from numerical calculation in such a case, which present a way to experimentally confirm the soliton existence in molecular
crystals.
Received 9 April 1998 and Received in final form 11 December 1998 相似文献
997.
G. Bazalgette M. Büchner C. Champenois G. Trenec J. Vigué 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(2):193-200
We describe the first saturation spectroscopy experiment concerning the A-X transition of ICl with considerably better resolution
than previous works. Form our data, improved constants for the hyperfine structure of the excited state are determined. The
A-X transition of ICl could be used to develop a set of secondary frequency standards and its metrologic qualities are discussed.
Received: 27 July 1998 / Received in final form: 30 November 1998 相似文献
998.
J. Torrès T. Martin 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):319-322
In the light of the recent analogs of the Hanbury-Brown and Twiss experiments [1] in mesoscopic beam splitters, negative current
noise correlations are recalled to be the consequence of an exclusion principle. Here, positive (bosonic) correlations are
shown to exist in a fermionic system, composed of a superconductor connected to two normal reservoirs. In the Andreev regime,
the correlations can either be positive or negative depending on the reflection coefficient of the beam splitter. For biases
beyond the gap, the transmission of quasiparticles favors fermionic correlations. The presence of disorder enhances positive
noise correlations. Potential experimental applications are discussed.
Received 1 June 1999 相似文献
999.
N. Vandewalle M. Ausloos Ph. Boveroux A. Minguet 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(2):355-359
We present a method for visualizing the pattern which we believe to be a precursor signature of financial crashes (or ruptures).
The log-periodicity of the pattern is investigated through the envelope function technique. Three periods of the Dow Jones
Industrial Average (DJIA) are investigated: 1982-1987, 1992-1997 and 1993-1998. The presence of a rupture in the end of 1998
is outlined from data taken before the end of August 1998.
Received 15 October 1998 and Received in final form 19 November 1998 相似文献
1000.
A. Wobst D. Weinmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):159-167
The curvatures of two-particle energy levels with respect to the enclosed magnetic flux in mesoscopic disordered rings are
investigated numerically. We find that the typical value of the curvatures is increased by interactions in the localised regime
and decreased in the metallic regime. This confirms a prediction by Akkermans and Pichard (Eur. Phys. J. B 1, 223 (1998)). The interaction-induced changes of the typical curvatures at different energies and disorder strengths exhibit
one-parameter scaling with a conductance-like single parameter. This suggests that interactions could influence the conductance
of mesoscopic systems similarly.
Received 24 August 1998 相似文献