Classical and quantum kinetic equations with exact conservation laws

Stationary and dynamic properties of reduced density matrices can be determined from formal or approximate closures of an infinite hierarchy of equations. The local macroscopic conservation laws place weak but important constraints on the reduced density matrices which should be respected by any closure. For pairwise additive forces conditions on the closure of the one- and two-particle equations are obtained that preserve the exact functional dependence of the conserved densities and their fluxes on the reduced density matrices. To illustrate the nature of these conditions, a closure approximation suitable for a quantum gas is given, yielding an extension of the time-dependent Hartree-Fock equations for the dynamics of a nuclear fluid to include collisions.     

Solid-state effects on the asymmetry parameter and on the partial photoionization cross section of ag4d valence-band at the cooper minimum

We present experimental determinations of the partial photoionization cross section (σ) and the asymmetry parameter (β) for Ag atoms deposited at room temperature and at submonolayer coverages onto a Si (111) substrate and for metallic (polycrystalline) Ag in the photon-energy range of hv = 75–200 eV. The hv dependence of σ and β from Ag atoms on Si compare favorably with the atomic σ and β, where σ and β from metallic Ag are severely distorted. An interpretation scheme is suggested to connect the differences in the cross sections to the solid-state effects on the initial-state wave functions and to connect the differences in the asymmetry parameters to the solid-state effects on both the initial-state and the final-state wave functions.     

Nano- and Pico-Scale Transport Phenomena in Fluids

A new theoretical approach to describe pre-hydrodynamic stages of evolution in nonequilibrium fluids is presented. The local density, velocity, and temperature fields are expressed as integrals over Green's functions that depend on initial-state ensemble averages of dynamical quantities. For systems in which the initial states are nonuniform in only one spatial direction, explicit expressions for the Green's functions are derived in terms of initial-state ensemble averages of moments of particle displacements and products of particle velocities and particle displacements.     

Transverse-momentum and collision-energy dependence of high-pT hadron suppression in Au+Au collisions at ultrarelativistic energies

We report high statistics measurements of inclusive charged hadron production in Au+Au and p+p collisions at sqrt[s(NN)]=200 GeV. A large, approximately constant hadron suppression is observed in central Au+Au collisions for 5相似文献   

Light-induced ejection of alkali atoms in polysiloxane coated cells

Summary An intense laser-induced fluorescence of sodium and of other alkali atoms (K, Rb) at room and lower temperatures has been observed in polysiloxanecoated cells, producing a vapor density of the metal which is much higher than that corresponding to the thermal equilibrium between the vapor and the condensed phase. This enhancement is attributed to the light-induced ejection of atoms absorbed by the polysiloxane coating. The atomic density of the vapor can be manipulated by changing either the laser power or frequency. The dependence of the atomic density on these and other parameters as well as its time-dependent behavior are studied experimentally. A tentative interpretation of the phenomenon is discussed in terms of the properties of solutions of the alkali metals in several solvents.     

Interpretation of the electronic spectra of phthalocyanines with transition metals from quantum-chemical calculations by the density functional method

Using the time-dependent formalism of the density functional theory (time-dependent density functional theory (TDDFT)), the energies and intensities of the electronic transitions of some metal phthalocyanines of transition metals and of their anionic forms with different electron localization are studied quantum chemically. It is shown that, in all the cases studied, calculations using the B3LYP functional with even a comparatively narrow basis set (6–31G) are quite consistent with the previous calculations of the same objects by the ZINDO/S-CI semiempirical method taking into account double excitations. For a number of particular examples, it is shown that a lack of consideration of doubly excited configurations in the calculation of excited states by the TDDFT method can be compensated by the contribution from single excitations, which proves to be more significant due to the presence of the correlation component of the exchange-correlation functional.     

xF (or y)-Dependence of Nuclear Absorption and Energy Loss Effects onJ/ψ Production

By means of the nuclear parton distribution studied only with lepton deep-inelastic scattering experimental data, the J/ψ ``normal nuclear absorption' and energy loss effects are studied in a Glauber formalism at HERA and RHIC energies. Assuming that the absorption cross section σ_abs increases with thecharmonium-nucleon center of mass energy, the results reveal a significant dependence of the σ_abs on rapidity y at RHIC energies. The initial-state energy loss effect, which is found important only at HERA energies, is also considered, and its influence should be eliminated when we studied the absorption effect at low collision energies. Finally, we also present the theoretical prediction for LHC.     

Exact density-functional potentials for time-dependent quasiparticles

We calculate the exact Kohn-Sham potential that describes, within time-dependent density-functional theory, the propagation of an electron quasiparticle wave packet of nonzero crystal momentum added to a ground-state model semiconductor. The potential is observed to have a highly nonlocal functional dependence on the charge density, in both space and time, giving rise to features entirely lacking in local or adiabatic approximations. The dependence of the nonequilibrium part of the Kohn-Sham electric field on the local current and charge density is identified as a key element of the correct Kohn-Sham functional.     

相对论重离子碰撞中的软探针和硬探针

简要回顾了高能核碰撞中夸克胶子等离子体的软探针和硬探针的一些最新进展,主要内容集中在相对论重离子对撞机和大型强子对撞机实验中各向异性集体流和喷注淬火的理论和唯象研究,对小系统中集体流的来源也做了简要的讨论。对于软探针,讨论了初态三维涨落和碰撞几何各向异性、相对论流体力学演化、末态各向异性集体流以及集体流的涨落、关联和纵向去关联等。通过与实验数据作系统的比较,可以探测重离子碰撞中夸克胶子等离子体的动力演化和各种输运性质。对于硬探针,集中讨论了部分子能量损失和喷注淬火对部分子味道的依赖性、重味夸克在夸克胶子等离子体中的强子化、整体喷注在核介质中的演化以及核介质对喷注的响应等。细致分析相关的观测量,可以帮助我们更全面地了解相对论核碰撞中喷注与核介质的相互作用以及重味粒子的生成。对于小系统,讨论初态和末态效应在解释小系统中轻强子和重味强子的集体流方面的贡献,这有助于我们理解大碰撞系统中集体流的起源成因。     

Two-photon double ionization of helium by chirped few-cycle attosecond pulses:From nonsequential to sequential regime

The two-photon double ionization(TPDI) dynamics of helium by chirped attosecond pulses are theoretically studied by solving the two-electron time-dependent Schr o¨dinger equation in its full dimensions. We show that both the differential and the total double ionization probability can be significantly controlled by adjusting the chirp. The dependence of the TPDI on the chirp can be quite different for different photon energies, relying on the central photon energy being in the sequential region, nonsequential region, or translation region. The physics which lead to the chirp dependence for different photon energies are addressed. Present findings are well reproduced by a model based on the second-order time-dependent perturbation theory.     

Transverse-momentum distribution of J/Ψ's in Pb-Pb collisions and gluon rescattering

We study anomalous J/Ψ suppression and p _t broadening in the model of prompt gluons. The anomalous suppression can be successfully described in this model. The transverse-momentum dependence of J/Ψ suppression in relativistic heavy-ion collisions is calculated from initial-state gluon rescattering with both nucleons and prompt gluons produced in nucleon-nucleon collisions in the early phase of the reaction. It seems impossible to describe simultaneously anomalous suppression and p _t broadening in Pb-Pb collisions within the model of prompt gluons with reasonable values of the parameters. Received: 27 September 2001 / Accepted: 12 November 2002 / Published online: 17 January 2003 RID="a" ID="a"e-mail: zhuangpf@mail.singhua.edu.cn Communicated by A. Molinari     

Pulse shape and molecular orientation determine the attosecond charge migration in Caffeine

The recent reduction of laser pulse duration down to the attosecond regime offers unprecedented opportunities to investigate ultrafast changes in the electron density before nuclear motion sets in. Here, we investigate the hole dynamics in the Caffeine molecule that is induced by an ionizing XUV pulse of 6 fs duration using the approximate time-dependent density functional theory method TD-DFTB. In order to account for ionization in a localized atomic orbital basis we apply a complex absorbing potential to model the continuum. Propagation of the time-dependent Kohn–Sham equations allows us to extract the time-dependent hole density taking the pulse shape explicitly into account. Results show that the sudden ionization picture, which is often used to motivate an uncorrelated initial state, fails for realistic pulses. We further find a strong dependence of the hole dynamics on the polarization of the laser field. Notwithstanding, we observe fs charge migration between two distant functional groups in Caffeine even after averaging over the molecular orientation.     

Nearly linear mappings and their applications

A simple 2-dimensional mapping is considered, both analytically and numerically, for which all nonlinear effects are of the same order as the perturbations and of the same origin. Properties of the stochastic instability are investigated, taking the beam-beam interaction in a storage ring as an important particular example of a dynamic system that can be modelled with such a mapping. The special case of time-dependent mappings is discussed. It is shown that low-frequency time dependence sharply decreases the critical perturbation strength for the stochastic transition.     

Energy loss of fast quarks in nuclei

We report an analysis of the nuclear dependence of the yield of Drell-Yan dimuons from the 800 GeV/c proton bombardment of 2H, C, Ca, Fe, and W targets. Employing a new formulation of the Drell-Yan process in the rest frame of the nucleus, this analysis examines the effect of initial-state energy loss and shadowing on the nuclear-dependence ratios versus the incident proton's momentum fraction and dimuon effective mass. The resulting energy loss per unit path length is -dE/dz = 2.32+/-0.52+/-0.5 GeV/fm. This is the first observation of a nonzero energy loss of partons traveling in a nuclear environment.     

Energy Variance in Decoherence

We study the effect of the initial-state energy variance to the short-time behavior of the Loschmidt echo(LE) in a purely dephasing model. We find that the short-time LE behaves as a Gaussian function with the width determined by the initial-state energy variance of the interaction Hamiltonian, while it is a quartic decaying function with the width determined by the initial-state energy variance of the commutator between the interaction Hamiltonian and the environmental Hamiltonian when the initial state is an eigenstate of the interaction Hamiltonian.Furthermore, the Gaussian envelope in the temporal evolution of LE in strong coupling regime is determined by the inband variance. We will also verify the above conclusion in the XY spin model(as environment).     

Plasma expansions with a time-dependent electron temperature

The fundamental of ion acceleration from the laser-solid interactions is the theory for describing plasma expansions into a vacuum. In the time interval of tens of femtoseconds after the laser pulse reaches the target, the plasma reaches local-thermal equilibrium and then hydrodynamic equations are available. However, it cannot reach macro-thermal equilibrium and does not satisfy Boltzmann distribution. The plasma is non-quasi-neutral and a strong charge separation exists. In fact, the electron temperature is time-dependent and the changing law is governed by the energy transfer between electrons and ions. In this Letter, an analytical solution is obtained for plasma expansions into a vacuum to describe the ion acceleration with a time-dependent electron temperature. It is obtained that the dependence of the plasma density on the potential is different from Boltzmann distribution in the time-dependent case. The time-dependent electron temperature also induces the unsteady ablation rate of the ablation plane, which is defined as the interface between the plasma and the solid (or liquid or gas). The electric field is also obtained and discussed in detail. The particular solution is given to show the influence of the time-dependent electron temperature on the laser-ion acceleration in a particular case: the electron temperature is proportional to the square of time. From that, it is concluded that laser-ion acceleration is more efficient in the time-increasing electron-temperature case than that in the isothermal case. The time-dependence of electron temperature comes from the time-dependence of laser intensity and induces the different efficiency of the laser-ion acceleration. At the ablation plane, the electron density and velocity are also predicted and explained reasonably.     

Energy shift of photoemission spectra for organics-passivated CdSe nanoparticles: The final-state effect

Size-dependent energy shift of photoemission spectra with respect to bulk sample has been examined for colloidally prepared CdSe nanoparticles with a series of particle sizes. The core-level shifts are well described by a theoretical calculation based on a final-state effect model, whereas an additional initial-state effect due to quantum confinement is required to elucidate the valence-band edge shifts. The results indicate that the interaction between the photohole and the dielectric background in the final state has to be considered in photoemission measurements for organics-passivated nanoparticles. The calculated results in the literature appear to overestimate the initial-state effect compared to our experimental observation.     

Dense colloidal suspensions under time-dependent shear

We consider the nonlinear rheology of dense colloidal suspensions under a time-dependent simple shear flow. Starting from the Smoluchowski equation for interacting Brownian particles advected by shearing (ignoring fluctuations in fluid velocity), we develop a formalism which enables the calculation of time-dependent, far-from-equilibrium averages. Taking shear stress as an example, we derive exactly a generalized Green-Kubo relation and an equation of motion for the transient density correlator, involving a three-time memory function. Mode coupling approximations give a closed constitutive equation yielding the time-dependent stress for arbitrary shear rate history. We solve this equation numerically for the special case of a hard sphere glass subject to step strain.     

Controllable coupling and quantum correlation dynamics of two double quantum dots coupled via a transmission line resonator

We propose a theoretical scheme to generate a controllable and switchable coupling between two double-quantum-dot (DQD) spin qubits by using a transmission line resonator (TLR) as a bus system. We study dynamical behaviors of quantum correlations described by entanglement correlation (EC) and discord correlation (DC) between two DQD spin qubits when the two spin qubits and the TLR are initially prepared in X-type quantum states and a coherent state, respectively. We demonstrate that in the EC death regions there exist DC stationary states in which the stable DC amplification or degradation can be generated during the dynamical evolution. It is shown that these DC stationary states can be controlled by initial-state parameters, the coupling, and detuning between qubits and the TLR. We reveal the full synchronization and anti-synchronization phenomena in the EC and DC time evolution, and show that the EC and DC synchronization and anti-synchronization depends on the initial-state parameters of the two DQD spin qubits. It is shown that the initial quantum correlation may be suppressed completely when the evolution time approaches to the infinity in the presence of dissipation. These results shed new light on dynamics of quantum correlations.