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971.
M. Vatasescu F. Masnou-Seeuws 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(2):191-204
The paper contains a time-dependent investigation of the tunneling effect observed in the photoassociation spectrum of Cs2 and attributed to the 0g
-(6s, 6p
3/2) double well. When by photoassociation of two cold cesium atoms a vibrational level of the outer well is populated, tunneling
is an efficient mechanism for transferring the population to the inner well (R < 15a
0), where spontaneous emission may lead to formation of cold molecules in low vibrational levels of the a
3Σ+
u(6s, 6s) electronic state. This tunneling effect is analyzed by wavepackets propagation, first considering the double well potential
alone, and following a packet made by a superposition of states initially located at large distances. Characteristic times
for the vibration dynamics, corresponding to a beating phenomenon between the two wells, to partial “revival” at large distances,
and to maxima in the population localized in the inner well are reported and discussed. Second, we simulate the two-channels
a
3Σ+
u(6s, 6s)↦0g
-(6s, 6p
3/2) photoassociation at detunings around 2.9 cm-1: the inner well can be populated either by the excitation of a vibrational level of the external well (resonant excitation),
or by tuning the photoassociation laser at the energy of the inner well level which displays tunneling (“off-resonance excitation”).
In the first case the photoassociation is efficient, while the tunneling probability is small; in the second, the tunneling
probability is large, so that despite the poor efficiency of the photoassociation process, more population can be transferred
to the inner well. This second choice is shown to be very sensitive to the laser intensity, which could be used to control
the population of the inner well and hence the formation of ultracold molecules in low vibrational levels.
Received 19 April 2002 Published online 1st October 2002
RID="a"
ID="a"e-mail: francoise.masnou@lac.u-psud.fr 相似文献
972.
R. Ramaswamy 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):339-343
Integrable dynamical systems, namely those having as many independent conserved quantities as freedoms, have all Lyapunov
exponents equal to zero. Locally, the instantaneous or finite time Lyapunov exponents are nonzero, but owing to a symmetry,
their global averages vanish. When the system becomes nonintegrable, this symmetry is broken. A parallel to this phenomenon
occurs in mappings which derive from quasiperiodic Schr?dinger problems in 1-dimension. For values of the energy such that
the eigenstate is extended, the Lyapunov exponent is zero, while if the eigenstate is localized, the Lyapunov exponent becomes
negative. This occurs by a breaking of the quasiperiodic symmetry of local Lyapunov exponents, and corresponds to a breaking
of a symmetry of the wavefunction in extended and critical states.
Received 25 October 2001 / Received in final form 8 December 2001 Published online 2 October 2002
RID="a"
ID="a"e-mail: r.ramaswamy@mail.jnu.ac.in 相似文献
973.
Bershtein V. A. Egorov V. M. Zgonnik V. N. Melenevskaya E. Yu. Vinogradova L. V. 《Journal of Thermal Analysis and Calorimetry》2000,59(1-2):23-31
Segmental dynamics around Tg in the 4- and 6-arm fullerene (C60) core star-like polystyrenes with different preset arm lengths was studied by DSC as compared to that in the linear PS and PS/C60 blend. The anomalies in glass transition behavior were found for the stars including both suppression and facilitation of segmental motion, and pronounced dynamic heterogeneity within a transition range. The results are interpreted in terms of breakdown of intermolecular cooperativity of segmental motions and PS-C60 interactions.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
974.
A. A. Hakhoumyan V. Zh. Tovmasyan H. S. Haroyan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2008,43(3):125-130
Possibility to record B-FSK signals with use of stochastic resonance is studied. A Schmidt trigger is employed as bistable stochastic resonator. A digital model of the detector is proposed and quantitative results are obtained by means of simulations. Dependence of the probability of correctly detected bits on the added noise power and on the low-pass filter cutoff frequency is studied. Also the stability of the detector with respect to channel-introduced phase shifts is revealed. 相似文献
975.
Kaźmierkiewicz R Czaplewski C Lammek B Ciarkowski J 《Journal of computer-aided molecular design》1999,13(1):21-33
Subject of this work is the analysis of molecular dynamics (MD) trajectories of neurophysins I (NPI) and II (NPII) and their complexes with the neurophyseal nonapeptide hormones oxytocin (OT) and vasopresssin (VP), respectively, simulated in water. NPs serve in the neurosecretory granules as carrier proteins for the hormones before their release to the blood. The starting data consisted of two pairs of different trajectories for each of the (NPII/VP)2 and (NPI/OT)2 heterotetramers and two more trajectories for the NPII2 and NPI2 homodimers (six trajectories in total). Using essential dynamics which, to our judgement, is equivalent to factor analysis, we found that only about 10 degrees of freedom per trajectory are necessary and sufficient to describe in full the motions relevant for the function of the protein. This is consistent with these motions to explain about 90% of the total variance of the system. These principal degrees of freedom represent slow anharmonic motional modes, clearly pointing at distinguished mobility of the atoms involved in the protein's functionality. 相似文献
976.
We study a stochastic neural-network model in which neurons and synapses change with a priori probability p and 1–p, respectively, in the limit p0. This implies neuron activity competing with fast fluctuations of the synaptic connections—in fact, random oscillations around values given by a learning (for example, Hebb's) rule. The consequences for the system performance of a dynamics constantly checking at random the set of memorized patterns is thus studied both analytically and numerically. We describe various nonequilibrium phase transitions whose nature depends on the properties of fluctuations. We find, in particular, that under rather general conditions locally stable mixture states do not occur, and pattern recognition and retrieval processes are substantially improved for some classes of synaptic fluctuations. 相似文献
977.
Fracture experiments on symmetric-tilt grain boundaries in Cu are interpreted using the Peierls-Nabarro continuum model of dislocation nucleation as a starting point. Good agreement is found only when the continuum model is modified according to the results of atomistic simulations. The same experiments are also reproduced by direct Molecular Dynamics simulations of fracture propagation and dislocation emission from a microcrack placed in the interface plane of the symmetric-tilt (221)(221) grain boundary in fcc Cu. Direction-dependent fracture response is observed, namely the microcrack advancing by brittle fracture along the [11
] direction and being blunted by dislocation emission along the opposite [
4] direction. Moreover, the simulations allow us to establish important differences with respect to the continuum-model predictions due to the shielding of the stress field at the crack-tip and to the presence of the residual stress at the interface. 相似文献
978.
979.
980.
用雷诺应力模型计算旋风分离器中气-固两相流动 总被引:6,自引:0,他引:6
针对分离器内部的复杂的三维强旋转、气-固两相湍流运动,采用雷诺应力模型(SSG),利用贴体网格技术,模拟计算了分离器内部流动,并将计算结果与实验数据进行分析、比较。分离器内的固体颗粒运动采用涉及湍流扩散影响的随机轨道模型和确定轨道模型,在流场计算的基础上,模拟了不同直径的颗粒在分离器内的运动规律及颗粒分离效率,并同理论和实验得到的数据进行了比较。 相似文献