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1.
The atomic dynamics of liquid lead at the temperature T = 600 K has been simulated on the basis of the embedded atom model potential (the “embedded” atom model making it possible to effectively take into account the many-particle interactions) in order to study the mechanisms of formation of the atomic collective excitations. Spectra of the dynamic structure factor S(k, ω) and the spectral densities of the time correlation functions of the longitudinal \(\tilde C_L\) (k, ω) and transverse \(\tilde C_T\) (k, ω) currents have been calculated for the wavenumber region 0.11 Å?1 ≤ k ≤ 2.01 Å?1. It has been established that the dynamics of density fluctuations is characterized by two dispersion “acoustic-like” branches of the longitudinal and transverse polarization. 相似文献
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M. A. González C. Mondelli C. Cabrillo R. Fernández-Perea F. J. Bermejo F. Albergamo E. Enciso C. Carbajo M. J. Torralvo 《The European physical journal. Special topics》2007,141(1):35-38
The spectrum of collective excitations of liquid deuterium
in the bulk and confined within a MCM-41 matrix having pores of an
average diameter of 2.4 nm has been studied by means of neutron
scattering and molecular dynamics simulations. The main effects of
confining liquid D2 consist in a shift of the characteristic
frequencies associated with damped density oscillations to higher
energies. A strong decrease in diffusivity is also observed upon
confinement. 相似文献
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Bermejo FJ Kinugawa K Cabrillo C Bennington SM Fak B Fernandez-Diaz MT Verkerk P Dawidowski J Fernandez-Perea R 《Physical review letters》2000,84(23):5359-5362
The origin of the well-defined collective excitations found in liquid para-H2 by recent experiments is investigated. The persistence of their relatively long lifetimes down to microscopic scales is well accounted for by calculations carried out by means of path-integral-centroid molecular dynamics. In contrast only overdamped excitations are found in calculations carried within the classical limit. The results provide fully quantitative evidence of quantum effects on the dynamics of a simple liquid. 相似文献
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The investigation of the ion dynamics in the liquid alloy K52Cs48, which has the same electron density as Rb, was carried out by neutron inelastic scattering. Well defined collective excitations were observed up to the maximum value of momentum transfer of the experiment. A scaling of the dispersion relation data was found to hold between K-Cs alloys, Rb and Cs. The suggested scaling points out the key role of the conduction electron density in the collective dynamics of alkali metals. 相似文献
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We present a parameter-free theory of the collective excitations in simple liquids such as liquid metals or rare gases. The
theory is based on the mode-coupling theory (MCT), which has been previously applied successfully for explaining the liquid-to
glass transition. The only input is the liquid structure factor. We achieve good agreement both for the liquid dispersion
(maximum of the longitudinal current spectrum) and width (damping) with experimental findings. The time-dependent memory function
predicted by MCT has a two-step exponential decay as previously found in computer simulations. Furthermore MCT predicts a
scaling of the liquid dispersion with the effective hard-sphere diameter of the materials. This scaling is obeyed by the available
experimental data. 相似文献
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The role of antisymmetric tensor fields in the gauging of groups is related to theorems on cohomology theory, and Cartan integrable systems are discussed. Examples are given. Various possibilities to gauge d = 11 supergravity by decontracting its underlying group are considered. In particular the simple supergroups Osp (1 | 64) and SU(32 | 1) yield a negative result, but a certain non-semisimple supergroup containing Osp (1 | 32) is proposed as a viable candidate. The corresponding action would no longer contain the 3-index photon Aμν?, but instead a second spin field ημ and boson fields and . A first order formalism for d = 11 is presented. It is to be used for an improved form of dimensional reduction. 相似文献
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P. von Brentano C. Fransen A. Gade A. Lisetskiy N. Pietralla 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):99-103
Due to the recent development of radioactive beam production, various direct reaction studies in reversed kinematics have
been made to investigate the behavior of the N = 20 shell closure in the neutron-rich region. Coulomb excitation, proton inelastic scattering, and fragmentation of unstable
nuclei have been studied with γ-ray detection.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: motobaya@rikkyo.ne.jp 相似文献
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Intersubband resonances in a semiconductor quantum well (QW) display fascinating features involving various collective excitations such as Fermi-edge singularity (FES) and intersubband plasmon (ISP). Using a density matrix approach, we treated many-body effects such as depolarization, vertex correction, and self-energy consistently for a two-subband system. We found a systematic change in resonance spectra from FES- to ISP-dominated features, as QW width or electron density is varied. Such an interplay between FES and ISP significantly changes both line shape and peak position of the absorption spectrum. We found that a cancellation of FES and ISP undresses the resonant responses and recovers the single-particle features of absorption for semiconductors with a strong nonparabolicity such as InAs, leading to a dramatic broadening of the absorption spectrum. 相似文献
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B. M. Nyakó J. Gizon V. Barci A. Gizon S. André D. Barnéoud D. Curien J. Genevey J. C. Merdinger 《Zeitschrift für Physik A Hadrons and Nuclei》1989,334(4):513-514
Collective bands have been identified for the first time in the nucleus127Ce using in- beam spectroscopic techniques. A band developed up to spin 51/2 is proposed to be based on an h11/2 neutron hole configuration. The observed backbend is produced by the alignment of an h11/2 proton pair. Another level sequence is very likely generated by ag7/2 or d5/2 neutron- hole. 相似文献
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We report on a mechanism of dynamic dipolar coupling in magnetic superlattices via long-wavelength nonevanescent fields. In the spin excitation spectra of our heterophase stripe structures, such interactions mediate a singlet<-->doublet crossover in the frequency regime driven by the orientation of an external static field. This crossover is a new feature observed in collective behavior of superlattices, though there is some analogy of this phenomenon with birefringence taking place in optical superlattices. We envision applying the collective effects described here in microwave photonic devices. 相似文献
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V. M. Kolomietz A. G. Magner V. A. Plujko 《Zeitschrift für Physik A Hadrons and Nuclei》1993,345(2):131-136
We expand the nonmarkovian collision integral in terms of multipolarities of the distortion of the Fermi surface. It is shown that damping of zero-sound is determined by all multipolarities of the Fermi-surface deformation. For large zero-sound velocity with respect to the Fermi velocity the relaxation time is related to the quadrupole deformation of the Fermi surface. The contributions of collisions to the total widths of the giant multipole resonances are calculated in a semiclassical macroscopic nuclear model. 相似文献
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V. S. Anikeev 《Russian Physics Journal》1968,11(12):68-71
Collective excitations of exciton type are considered. The oscillator strength of a collective excitation is expressed in terms of the oscillator strengths of the one-electron transitions. The scope for negative absorption is discussed. 相似文献
20.
Keshav M. Dani Jerome Tignon Michael Breit Daniel S. Chemla Eleftheria G. Kavousanaki Ilias E. Perakis 《Physica E: Low-dimensional Systems and Nanostructures》2006,34(1-2):206
Using the non linear optical technique of 3-pulse 4-wave mixing, we study the dynamics of the collective excitations of the quantum Hall system. We excite the system with 100 fs pulses propagating in directions k1 and k3 and then probe its time evolution with a delayed pulse k2. We measure the non-linear optical response from the lowest Landau level along the direction k1+k2−k3. As function of the time delay of pulse k2, this signal shows striking beats for short time delays (500 fs), followed by a rise (20 ps) and then a decay (100 ps). We identify the microscopic origin of this dynamics by extending the standard theory of ultra fast nonlinear optics to include the effects of the correlations. 相似文献