Entropy and irreversibility in a dilute gas of hard disks

The partition of the canonical entropy (invariant of motion) into a thermodynamic part 5th and a nonthermodynamic oneS _nonth, respectively increasing and decreasing functions of time for a system approaching equilibrium, was proposed by Prigogine and co-workers. This viewpoint is critically examined in the special case of an initially uncorrelated gas of hard disks. BothSth and the leading term ofS _nonth are evaluated for finite assemblies of 400,1600, and 6400 disks, by the method of molecular dynamics. There is good evidence that, in the limit of an infinite system, the Prigogine scheme is verified.On leave of absence from the University of Brussels, Belgium.     

Phase diagrams in mixed spin-3/2 and spin-2 Ising system with two alternative layers within the effective-field theory

The phase diagrams in the mixed spin-3/2 and spin-2 Ising system with two alternative layers on a honeycomb lattice are investigated and discussed by the use of the effective-field theory with correlations. The interaction of the nearest-neighbour spins of each layer is taken to be positive (ferromagnetic interaction) and the interaction of the adjacent spins of the nearest-neighbour layers is considered to be either positive or negative (ferromagnetic or anti-ferromagnetic interaction). The temperature dependence of the layer magnetizations of the system is examined to characterize the nature (continuous or discontinuous) of the phase transitions and obtain the phase transition temperatures. The system exhibits both second-and first-order phase transitions besides triple point (T P ), critical end point (E), multicritical point (A), isolated critical point (C) and reentrant behaviour depending on the interaction parameters. We have also studied the temperature dependence of the total magnetization to find the compensation points, as well as to determine the type of behaviour, and N-type behaviour in N′eel classification nomenclature existing in the system. The phase diagrams are constructed in eight different planes and it is found that the system also presents the compensation phenomena depending on the sign of the bilinear exchange interactions.     

Association of mono- and dimethyl ethers of chlorine 6 in ethanol-water solutions

The association of γ-mono- and 6,γ-dimethyl ethers of chlorin e₆ (I and II) in mixtures of a phosphate buffer and ethanol is studied. The number of molecules in associates and the dimerization constants are determined. The formation of the dimers of compound I and dimers and associates of a higher order for II is established. It is found that, unlike I, the shift of the Q absorption band of the dimer toward larger wavelengths is rather great as compared to the monomer band for II; it exceeds 30 nm, which is uncommon for porphyrins. This difference of spectral changes in association of I and II is attributed to the dissimilar character of interaction of their molecules with each other and with the molecules of the surroundings, and also to the structural features of the dimers. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 440–444, July–August, 2000.     

R600a/R23两级自动复叠制冷系统降温特性研究

以R600 a/R23两级自动复叠制冷系统为例,研究了不同配比条件下,制冷系统中的特征点温度在降温过程中变化特性。试验表明混合制冷剂的配比是自动复叠制冷系统关键问题,通过控制关键点的温度可以判断混合制冷剂的最佳配比。     

Spectral densities of response functions for the O(3) symmetric Anderson and two channel Kondo models

The O(3) symmetric Anderson model is an example of a system which has a stable low energy marginal Fermi liquid fixed point for a certain choice of parameters. It is also exactly equivalent, in the large U limit, to a localized model which describes the spin degrees of freedom of the linear dispersion two channel Kondo model. We first use an argument based on conformal field theory to establish this precise equivalence with the two channel model. We then use the numerical renormalization group (NRG) approach to calculate both one-electron and two-electron response functions for a range of values of the interaction strength U. We compare the behaviours about the marginal Fermi liquid and Fermi liquid fixed points and interpret the results in terms of a renormalized Majorana fermion picture of the elementary excitations. In the marginal Fermi liquid case the spectral densities of all the Majorana fermion modes display a dependence on the lowest energy scale, and in addition the zero Majorana mode has a delta function contribution. The weight of this delta function is studied as a function of the interaction U and is found to decrease exponentially with U for large U. Using the equivalence with the two channel Kondo model in the large U limit, we deduce the dynamical spin susceptibility of the two channel Kondo model over the full frequency range. We use renormalized perturbation theory to interpret the results and to calculate the coefficient of the ln divergence found in the low frequency behaviour of the T=0 dynamic susceptibility. Received 29 January 1999     

分子动力学模拟玻璃微球充气保气性能的机理

为了探讨载能重粒子辐照改善惯性约束聚变中所用玻璃微球的充气性能,以及热弛豫过程中改善其保气性能的微观机制,利用分子动力学的方法对载能重粒子辐照前后的SiO₂玻璃在内部形成气体扩散微通道的机理进行了模拟研究。结果表明,重粒子辐照可以在SiO₂玻璃中形成明显的扩散通道,说明辐照后的玻璃更适合通入Ar等较大尺寸气体;在高温高压的条件下,形成的扩散通道有逐渐关闭的趋势,辐照产生的缺陷能够在一定程度上得到修复。因此,利用重粒子辐照的方法,可在玻璃体中产生充气的微通道,该通道在高温高压下可实现关闭,从而起到开关的作用。模拟结果可为实验上通过重粒子辐照提升微球玻璃充气保气性能的方法提供理论支持,说明该方法具有可行性。     

Dynamic magnetic properties in the kinetic mixed spin-2 and spin-5/2 Ising model under a time-dependent magnetic field

We extend the recent paper [W. Jiang, V-C. Lo, B-D. Bai, J. Yang, Physica A 389 (2010) 2227-2233] to present a study, within a mean-field approach, the dynamic magnetic properties of the mixed spin-2 and spin-5/2 Ising ferrimagnetic system, which corresponds the molecular-based magnetic materials AFe^IIFe^III(C₂O₄)₃ [ A=N(n-C_nH_2n+1)₄, n=3-5], by using the Glauber-type stochastic dynamics. This mixed Ising ferrimagnetic system is used on a layered honeycomb lattice in which Fe^II (S=5/2) and Fe^III (σ=2) occupy sites. First, we investigate the time variations of average order parameters to find the phases in the system and then the thermal behavior of the dynamic order parameters to obtain the dynamic phase transition (DPT) points as well as to characterize the nature (first-or second-order) phase transitions. We also present the dynamic phase diagrams and study the dynamic magnetic hysteresis loop behaviors of the kinetic mixed spin-2 and spin-5/2 Ising ferrimagnetic system. The results are compared with some experimental and theoretical works and a good overall agreement is found.     

氢及其同位素宽区状态方程的核量子效应

应用大规模第一性原理分子动力学数值模拟方法,系统研究了氢及其同位素在极端条件下的分子解离规律及状态方程,并给出了参数化的解函数拟合公式。结合分子、原子流体量子振动的一阶修正,揭示了氢及其同位素的核量子效应,解析获得了氢、氘分子在温稠密区域分子解离规律的差别。由第一性原理状态方程给出了雨贡纽曲线,与气炮、化学炸药、磁驱动、高能激光等实验数据相符合,并详细讨论了由核量子效应导致的氢、氘雨贡纽曲线的同位素效应。     

Dynamics of ionization mechanisms in relativistic collisions involving heavy and highly-charged ions

The dynamics of mechanisms associated with the ionization of inner-shell electrons in relativistic collisions involving heavy and highly-charged ions is investigated within a nonperturbative approach formulated explicitly in the time domain. The theoretical treatment is based on the exact numerical solution of the time dependent Dirac equation for two Coulomb centers on a lattice in momentum space. We present results for ionization in encounters between 100 MeV/u Au⁷⁹⁺ projectile ions impinging on a hydrogen-like uranium target. By directly visualizing the collision dynamics we identify a new ionization mechanism in which electrons are emitted from the internuclear region preferentially in the transverse direction with respect to the projectile trajectory. A striking characteristic of this ionization mechanism is that the velocity of the electron is higher than the projectile velocity. Received 26 June 2001 and Received in final form 27 November 2001     

Combination of two basic types of synchronization in a coupled semiconductor laser system

Combination of two basic types of synchronization, anticipatory synchronization and lagged synchronization, is investigated numerically between two coupled semiconductor lasers. It is found that lagged synchronization produced by a backward coupling with a suitable delay can combine with the originally hidden anticipatory synchronization and produce a type of synchronization overcoming the original lagged synchronization produced by a forward coupling. We study the combination synchronization phenomenon when the delay of the backward coupling is different from that of the original anticipatory synchronization. Our results suggest that the synchronization combination phenomenon might allow an interpretation of an experimental observation by Sivaprakasam et al. [Phys. Rev. Lett. 87, 154101 (2001)] that the anticipating time is irrespective of the external-cavity round trip time, which to date remains to be understood.     

Kinetic theory of point vortices in two dimensions: analytical results and numerical simulations

We develop the kinetic theory of point vortices in two-dimensional hydrodynamics and illustrate the main results of the theory with numerical simulations. We first consider the evolution of the system “as a whole” and show that the evolution of the vorticity profile is due to resonances between different orbits of the point vortices. The evolution stops when the profile of angular velocity becomes monotonic even if the system has not reached the statistical equilibrium state (Boltzmann distribution). In that case, the system remains blocked in a quasi stationary state with a non standard distribution. We also study the relaxation of a test vortex in a steady bath of field vortices. The relaxation of the test vortex is described by a Fokker-Planck equation involving a diffusion term and a drift term. The diffusion coefficient, which is proportional to the density of field vortices and inversely proportional to the shear, usually decreases rapidly with the distance. The drift is proportional to the gradient of the density profile of the field vortices and is connected to the diffusion coefficient by a generalized Einstein relation. We study the evolution of the tail of the distribution function of the test vortex and show that it has a front structure. We also study how the temporal auto-correlation function of the position of the test vortex decreases with time and find that it usually exhibits an algebraic behavior with an exponent that we compute analytically. We mention analogies with other systems with long-range interactions.     

Homogeneous and heterogeneous clustering in the accretion regime

Condensation of nano-droplets in a supersaturating vapor decomposes in two steps: the formation of a nucleation center, also called critical nuclei or nucleation seed, and the growth sequence, by accretion of further atoms on the nucleation center. These two steps have been investigated separately through the clustering of homogeneous particles Na_n and heterogeneous particles Na_nX in a helium buffer gas (X = (Na₂O)₂ or (NaOH)₂). The growth sequence is analyzed with preformed molecules X injected in a supersaturating sodium vapor and driving production of Na_nX clusters. Cluster distribution mean sizes are controlled by sodium concentration and by the condensation cell effective length. The signal intensities observed for homogeneous and heterogeneous clusters are proportional to the homogeneous and heterogeneous nucleation center numbers respectively. We can measure the efficiency for the homogeneous nucleation center production versus sodium concentration. This process is the onset of the condensation phase transition.     

Single crystals and thin film growth in Bi(Pb)-SrCaCuO system by the flux method

We present ab initio calculations for Si ad-atom kinetics on surfactant (As, Sb) covered Si(111) considering the structures experimentally found during homoepitaxy. On As-covered Si(111), one exclusively finds islands with double-step height which always show the equilibrium (1 2 1)-structure. On the other hand, on Sb-covered Si(111) large Si islands with single-step height appear with (1 2 1)-structure, on which smaller islands nucleate which show the ( $ \sqrt{3} \times \sqrt{3} $ )-structure of the Sb-covered terraces. The competition between diffusion of ad-atoms on top of the surfactant layer and incorporation into the layer by exchange with a surfactant atom, and the consequences for the island development on the different structures are discussed.     

The numerical simulation and analysis of three-dimensional seawater intrusion and protection projects in porous media

For the three-dimensional seawater intrusion and protection system, the model of dynamics of fluids in porous media and the modified upwind finite difference fractional steps schemes are put forward. Based on the numerical simulation of the practical situation in the Laizhou Bay Area of Shandong Province, predictive numerical simulation and analysis of the consequence of protection projects, underground dams, tidal barrage projects and the applied modular form of project adjustment have been finished. By using the theory and techniques of differential equation prior estimates, the convergence results have been got. Supported by the Major State Basic Research Program of China (Grant No. 19990328), the National Tackling Key Problem (Grant No. 2005020069), the National Natural Sciences Foundation of China (Grant Nos. 10771124 and 10372052), and the Doctorate Foundation of the Ministry of Education of China (Grant No. 20030422047)     

Wilson and Kadowaki-Woods ratios in heavy fermions

Recently we have shown that a one-parameter scaling, , describes the physical behavior of several heavy fermions in a region of their phase diagram. In this paper we fully characterize this region, obtaining the uniform susceptibility, the resistivity and the specific heat in terms of the coherence temperature . This allows for an explicit evaluation of the Wilson and the Kadowaki-Woods ratios in this regime. These quantities turn out to be independent of the distance to the quantum critical point (QCP). The theory of the one-parameter scaling corresponds to a local interacting model. Although spatial correlations are irrelevant in this case, time fluctuations are critically correlated as a consequence of the quantum character of the transition. Received 23 December 1998 and Received in final form 10 June 1999     

Physical realization and possible identification of topological excitations in quantum Heisenberg anti-ferromagnet on a two dimensional lattice

Physical spin configurations corresponding to topological excitations, expected to be present in the XY limit of a quantum spin 1/2 Heisenberg anti-ferromagnet, are probed on a two dimensional square lattice. Quantum vortices (anti-vortices) are constructed in terms of coherent staggered spin field components, as limiting case of meronic (anti-meronic) configurations. The crucial role of the associated Wess-Zumino-like (WZ-like) term is highlighted in our procedure. The time evolution equation of coherent spin fields used in this analysis is obtained by applying variational principle on the quantum Euclidean action corresponding to the Heisenberg anti-ferromagnet on lattice. It is shown that the WZ-like term can distinguish between vortices and anti-vortices only in a charge sector with odd topological charges. Our formalism is distinctly different from the conventional approach for the construction of quantum vortices (anti-vortices).     

Non-Fermi liquid behavior in the stripe phase of the extended Hubbard model

Within a strong-coupling perturbative approach, based on a Cumulant Expansion of the extended single-band Hubbard model, we show that the on-shell inverse scattering time deviates from the normal Fermi-liquid behavior near the points of the Fermi surface connected by the characteristic wave-vector of an incommensurate charge density wave. The violation of the Fermi liquid behavior is associated with a square root behavior of the inverse quasiparticle lifetime in proximity of a stripe phase. Some relevant features observed in ARPES experiments on Bi2212 are qualitatively reproduced. Received 28 February 2002 / Received in final form 7 May 2002 Published online 9 July 2002     

Pattern formation in reaction-diffusion system in crossed electric and magnetic fields

We consider a reaction-diffusion system in crossed electric and magnetic fields lying on the reaction plane. It is shown that a charge separation along the direction normal to the reaction plane resulting in a diffusional flux may cause a differential flow induced chemical instability and stationary pattern formation on a homogeneous steady state. This pattern is generically different from a Turing pattern modified by the crossed fields. The special role of magnetic field is emphasized. Our theoretical analysis is corroborated by numerical simulation on a reaction-diffusion system in three dimensions.     

A new scaling analysis of the susceptibility and the specific heat of the non-Fermi liquid system with and 0.5

The usual scaling equations at a phase transition, employed out of their usual validity range, with T_c a negative constant, fit properties observed in correlated electron systems with unmatched accuracy. We illustrate this behavior with our data in Ce(Ru_1-xRh_x)₂Si₂ for x = 0.4 and 0.5 and comment these results and what they imply physically. Received 22 June 1998 and Received in final form 29 September 1998     

Critical size and surface effect of the hydrogen interaction of palladium clusters

Metal hydrides are used for electrochemical or gaseous storage of hydrogen because considerable amounts of hydrogen are reversibly absorbed and desorbed at interstitial sites. Palladium is often used as a model system. Nanophase material is of interest because properties related to the hydrogen absorption are size dependent. In this study, clusters from the size of 55 to 1415 atoms are investigated and compared with bulk Pd. It turns out that not only the amount of hydrogen per palladium that can be intercalated changes but also kinetics and chemical potentials are dependent on the cluster size. The clusters used for this study were chemically synthesised and stabilised by a ligand shell. Received 9 October 1998 and Received in final form 10 May 1999