共查询到20条相似文献,搜索用时 15 毫秒
1.
Adopting the standard mathematical framework for describing reduced dynamics, we derive two formal identities for the density operator of an open quantum system. Each of these is equivalent to the old Nakajima-Zwanzig equation. The first identity is local in time. It contains the inverse of the dynamical map which govern the evolution of the density operator. We indicate a time interval on which this inverse exists. The second identity constitutes a suitable starting point for going beyond the Markov approximation in a controlled way. On the basis of the Bloch equations we argue once more that in studying quantum dissipation one has to pay attention to the von Neumann conditions. In the Nakajima-Zwanzig equation we make the first Born approximation. The ensuing master equation possesses the correct weak-coupling limit. While proving this rather obvious but at the same time important statement, we elucidate the mathematical methods which underlie the weak-coupling limit. Moving to a two-dimensional Hilbert space, we find that both for short and for long times our approximate master equation respects the von Neumann conditions. Assuming exponential decay for correlation functions, we propose a physical limit in which the solutions for the density operator become Markovian in character. We confirm the well-known statement that, as seen from a macroscopic standpoint, the system starts from an effective initial condition. The approach to equilibrium is exponential. The accessory relaxation constants can differ from the usual Bloch parameters and by more than 50%. 相似文献
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V. E. Tarasov A. E. Kudryavtsev A. I. Romanov V. M. Weinberg 《Physics of Atomic Nuclei》2012,75(12):1536-1543
The $\bar pp$ -annihilation reactions $\bar pp \to \eta \eta \eta$ and $\bar pp \to \eta {\rm K}\bar {\rm K}$ at rest are considered in the tree approximation in the framework of SU(3) chiral effective theory at leading order. The calculated branchings are compared with the data. The results for neutral (????, $\eta {\rm K}^0 \bar {\rm K}^0$ ) and charged (??K + K ?) channels are essentially different. 相似文献
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Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 6, pp. 966–971, December, 1991. 相似文献
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《Physics letters. A》1988,133(9):489-492
We indicate some inconsistencies in the application of the long-wavelength approximation in the standard derivation of Davydov solitons. Consistent approach indicates that the scope of applicability of the theory is much smaller than previously thought. 相似文献
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It is shown that the Wigner-Weisskopf theory is an example of what Walls has called the ladder approximation in quantum optics. 相似文献
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Z. A. Tagiev R. Dzh. Kasumova R. A. Salmanova N. V. Kerimova 《Optics and Spectroscopy》2001,91(6):909-912
The operation of a dispersion interferometer with intracavity location of a medium under study is analyzed in the constant intensity approximation taking into account the reciprocal influence of a harmonic on the phase of the exciting wave. This approximation allows the effects of phase mismatch and losses in a medium on the course of a nonlinear process to be taken into account simultaneously. Intensity minima of the harmonic (as opposed to the constant field approximation) in the constant intensity approximation are shown to depend on dispersion of the refractive index of the medium under study, which makes it possible to determine dispersion of the refractive index of the substance under study directly and accurately 相似文献
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Based on the laminar combustion of gases and the filtration combustion of porous condensed compounds, some general approaches to the study of their mathematical models are demonstrated that simplify their quantitative analysis. Processes in a wide circle of phenomena proceed under conditions of a weakly disturbed pressure field, though providing macroscopic convective transfer. Under conditions of the substantially changed temperature field, in contrast to condensed media, gaseous media change their specific volume and increase mobility, which should be considered in combustion processes. The suggested quasi-stationary consideration of reacting medium flows simplifies their computation and analysis. 相似文献
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M. K. Balyan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2012,47(5):241-247
On the basis of eikonal approximation a theory of X-ray moiré formation is presented in the case where deformations are present in all three plates of the interferometer. The role of each plate of the interferometer in the process of moiré formation is revealed. The theory can be applied for the general case of weak deformations. 相似文献
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R. Engel A. Schiller V. G. Serbo 《The European Physical Journal C - Particles and Fields》2011,71(1):651-658
We consider coherent electromagnetic processes for colliders with short bunches, in particular the coherent bremsstrahlung (CBS). CBS is the radiation of one bunch particles in the collective field of the oncoming bunch. It can be a potential tool for optimizing collisions and for measuring beam parameters. A new simple and transparent method to calculate CBS is presented based on the equivalent photon approximation for this collective field. The results are applied to the??-factoryDA??NE. For this collider about 5·1014 d E ??/E ?? photons per second are expected in the photon energyE ?? range from the visible light up to 25 eV. 相似文献
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We consider coherent electromagnetic processes for colliders with short bunches, in particular the coherent bremsstrahlung (CBS). CBS is the radiation of one bunch particles in the collective field of the oncoming bunch. It can be a potential tool for optimizing collisions and for measuring beam parameters. A new simple and transparent method to calculate CBS is presented based on the equivalent photon approximation for this collective field. The results are applied to theφ-factoryDAΦNE. For this collider about 5·1014 d E γ/E γ photons per second are expected in the photon energyE γ range from the visible light up to 25 eV. 相似文献
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We consider coherent electromagnetic processes for colliders with short bunches, in particular the coherent bremsstrahlung
(CBS). CBS is the radiation of one bunch particles in the collective field of the oncoming bunch. It can be a potential tool
for optimizing collisions and for measuring beam parameters. A new simple and transparent method to calculate CBS is presented
based on the equivalent photon approximation for this collective field. The results are applied to theφ-factoryDAΦNE. For this collider about 5·1014
d
E
γ/E
γ photons per second are expected in the photon energyE
γ range from the visible light up to 25 eV. 相似文献
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《Physics letters. A》1986,118(9):471-474
The Rosen-Zener formula, for transition probabilities in the atomic two-level problem, is used to develop a many-level treatment of the surface-ion-neutralization probability. 相似文献
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Physics of the Solid State - The effect of the linear approximation of the electronic spectrum of single-layer graphene (low-energy approximation) on the magnitude of charge transfer between an... 相似文献
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