Extremality and the global Markov property II: The global markov property for non-FKG maximal Gibbs measures

We give a condition on a Gibbs measure for an attractive Markov specification, which assures extremality and the global Markov property. As an example of application we consider the class of attractive Markov specifications defined on a compact configuration space over a two-dimensional lattice by the interaction Hamiltonians (assumed to have a finite set of periodic ground configurations) satisfying Peierl's condition. We prove that each extremal Gibbs measure for such a specification, at sufficiently low temperature, has the global Markov property.On leave of absence from the Institute of Theoretical Physics, University of Wrocaw, Poland.     

First-principles combinatorial design of transition temperatures in multicomponent systems: the case of Mn in GaAs

The transition temperature TC of multicomponent systems--ferromagnetic, superconducting, or ferroelectric--depends strongly on the atomic arrangement, but an exhaustive search of all configurations for those that optimize TC is difficult, due to the astronomically large number of possibilities. Here we address this problem by parametrizing the TC of a set of approximately 50 input configurations, calculated from first principles, in terms of configuration variables ("cluster expansion"). Once established, this expansion allows us to search almost effortlessly the transition temperature of arbitrary configurations. We apply this approach to search for the configuration of Mn dopants in GaAs having the highest ferromagnetic Curie temperature. Our general approach of cluster expanding physical properties opens the way to design based on exploring a large space of configurations.     

Renormalization group approach to exact sampling

In this Letter, we use a general renormalization-group algorithm to implement Propp and Wilson's "coupling from the past" approach to complex physical systems. Our algorithm follows the evolution of the entire configuration space under the Markov chain Monte Carlo dynamics from parts of the configurations (patches) on increasing length scales, and it allows us to generate "exact samples" of the Boltzmann distribution, which are rigorously proven to be uncorrelated with the initial condition. We validate our approach in the two-dimensional Ising spin glass on lattices of size 64 x 64.     

离化态原子基态电子结构特征与轨道竞争规律

离化态原子广泛存在于等离子体物质中,其相关性质是天体物理、受控核聚变等前沿科学研究领域的重要基础.基于独立电子近似,本文系统研究了扩展周期表元素(2 Z 119)所有中性和离化态原子的基态电子结构.基于设计的原子轨道竞争图,系统总结了各周期元素轨道竞争的规律,并结合离化态原子的局域自洽势阐明了其轨道竞争(即轨道塌陷)的机制;在此基础上,说明了部分元素性质与轨道竞争的关系.利用本文研究得到的离化态原子基态电子结构,可建立更精密计算相关原子的能级结构、跃迁几率等物理量之基础,从而满足高功率自由电子激光实验分析、原子核质量精密测量等前沿研究的需求.     

锆铌合金的特殊准随机结构模型的分子动力学研究

锆合金(如:锆铌(Zr-Nb)合金)的辐照损伤问题是裂变堆结构材料和燃料棒包壳材料设计的关键,而深入理解辐照损伤的物理机制,往往需借助于原子尺度的计算模拟,如:分子动力学和第一性原理等.针对随机置换固溶体合金的模拟,首先需构建能反映合金元素随机分布特征的大尺寸超胞,然而第一性原理计算量大,不宜使用过大(如≥200原子)超胞.通常第一性原理计算使用的是特殊准随机(SQS)超胞,SQS超胞可部分反映合金元素的随机分布特性,但对于特定组分只对应一种构型,这种模型是否能反映真实随机置换固溶体中多种局域构型的统计平均还有待进一步研究验证.分子动力学可在更大的尺度上进行计算模拟,能够通过随机取代(RSS)模型研究更多的合金构型,因此,本文基于RSS超胞模型及SQS扩展超胞模型,运用分子动力学方法对Zr-Nb合金进行了研究.首先通过构型误差分析确定了能真实反映固溶体合金性能统计性的RSS超胞的临界尺寸;然后计算比较了Zr-Nb合金SQS扩展超胞和一系列RSS超胞的晶格常数、形成能和能量—体积关系.研究表明,利用SQS超胞模拟得到的固溶体的晶格常数、形成能和能量体积曲线与一系列RSS超胞的对应统计值接近,因而SQS超胞可用于研究随机置换固溶体合金.     

伴有靶核核心激发的氘核削裂反应

本文研究了在氘核削裂反应中伴随有靶核核心激发的情况。在这种情况下,假定由于核子-核子剩余相互作用,靶核的组态除了通常壳模型组态外,还混杂有核心激发的组态。同样,剩余核的组态主要是某一种核心激发的组态,但也还混杂有别种组态。在这假定下,给出了所考虑的反应过程的微分截面表示式。它表明,反应截面主要由靶核的组态混合所贡献。一般说来,组态的混合程度不大,故可预期截面数值是较小的。公式还表明,反应角分布的特征峯是由核心在激发后留下来的空穴态的轨道角动量量子数所决定的。这二点结论与这类反应的实验结果是一致的。运用这公式具体估计了六个反应事例的核谱因子,在实验误差内,理论值和从实验的估计值大致相合。     

Structural,electronic, magnetic properties and critical behavior of the equiatomic quaternary Heusler alloy CoFeTiSn

In this article, we study the exchange coupling interactions of the equiatomic quaternary Heusler alloy CoFeTiSn, using the two methods: Monte Carlo simulations and the ab-initio method. In a first step, we use the ab-initio calculations to investigate the structural, the electronic and the magnetic properties of this alloy under the GGA method. The analysis of the energy dependence on the lattice parameter a (Å) of the equiatomic quaternary Heusler alloy CoFeTiSn, is discussed for different atomic configurations. The ferromagnetic configuration is found to be the more stable one, with an optimal lattice parameter value 6.00 Å. On the other hand, the electronic structure results show that the compound CoFeTiSn exhibits a half-metallic character and a spin polarization of 100% at the Fermi-level. The total magnetic moment of this alloy is found to be equal to 2.00 μ_B which follows the Slater Pauling rule. Our results support the half-metallic behavior of the studied material. In order to complete this study, we reported the dependence of the critical transition temperature as a function of the parameter α of the equiatomic quaternary Heusler alloy CoFeTiSn. We showed that the critical temperature increases almost linearly with an increase of the values of the parameter α.     

Influence of fillers concentration on electrical properties of polystyrene matrix doped by gold nanoparticles and 8HQ

The analysis of the electrical properties of polystyrene films containing gold nanoparticles capped with 1-dodecanethiol and 8-hydroxyquinoline molecules is reported. The conductivity of the nanocomposite as a function of the doping level has been investigated both in planar and stacked configurations. While the former configuration evidenced low field tunneling between nanoparticles in the polymer matrix, stacked devices allowed us to investigate the main phenomena ruling the transport properties when switching effects are present close to critical electric fields. In particular, through the analysis of current-voltage characteristics we studied the charge transport at different fillers concentrations and sketched a physical picture of conductivity in such nanocomposite systems.     

一维对心碰撞恢复系数的讨论

本文深入讨论了两球对心碰撞时,速度恢复系数、冲量恢复系数、能量恢复系数3种恢复系数的不同定义,并且讨论了3种定义之间的关系,总结了影响恢复系数的各种因素;同时,分析了恢复系数不同取值时的物理意义.研究这3种定义时,我们发现了一个共同特点是经典理论中都将恢复系数看作只与材料有关的常数.但是实际碰撞过程恢复系数不是仅仅依赖于材料的一种固有属性,它还与摩擦、撞击物和被撞击物的材料、接触面的几何性质以及碰撞的位形、初始速度等因素有关.本文仅限于考虑与材料特性有关的经典理论研究.     

Phase diagrams,electronic and magnetic properties of the quaternary Heusler alloy NbRhCrAl

In this paper, we are studying the quaternary Heusler alloy NbRhCrAl, using the full potential linearized augmented plane wave and the generalized gradient approximation of the exchange and correlation potential methods. For this purpose, we established the electronic and magnetic properties of this quaternary Heusler alloy. We investigated the density of states (DOS) and the band structure of this Heusler compound.This material contains three magnetic atoms: Nb, Rh and Cr modeled by the spin moments S = 1, P = 5/2 and Q = 3/2, respectively. In a first step, we elaborated the ground state phase diagrams in different physical parameter planes to explore the existing stable configurations. On the other hand, we used the MONTE CARLO simulations (MCS) to investigate the thermal behavior of the magnetizations of this system. Also, we have investigated the effect of varying the crystal field and the external magnetic field on the total magnetizations. To complete this study, we illustrated and discussed the hysteresis loops as a function of the external magnetic field, when fixing the values of the studied physical parameters.     

Electronic structure of the NiMnSb-semiconductor (110) interface

The electronic structure and magnetic properties of the (110) interface between the half-metallic Heusler alloy NiMnSb and semiconductors with different configurations of contact atoms have been calculated in terms of the density functional theory. It has been shown that spin polarization depends substantially on the configuration of atoms at the contacts. The nature of the interface states at the contacts under consideration has been analyzed. A nearly 100% spin polarization is obtained for the configuration with nickel and antimony, which in the alloy occupy the corresponding sites of the anion and the cation in the semiconductor. The evaluation of the adhesion energy at the interfaces has demonstrated that contacts with a maximum spin polarization also have the highest energy and are energetically favorable and stable.     

Stability of Quark Star Models

In this paper,we investigate the stability of quark stars with four different types of inner matter configurations;isotropic,charged isotropic,anisotropic and charged anisotropic by using the concept of cracking.For this purpose,we have applied local density perturbations technique to the hydrostatic equilibrium equation as well as on physical parameters involved in the model.We conclude that quark stars become potentially unstable when inner matter configuration is changed and electromagnetic field is applied.     

Quantum turbulence: Theoretical and numerical problems

The term “quantum turbulence” (QT) unifies the wide class of phenomena where the chaotic set of one dimensional quantized vortex filaments (vortex tangles) appear in quantum fluids and greatly influence various physical features. Quantum turbulence displays itself differently depending on the physical situation, and ranges from quasi-classical turbulence in flowing fluids to a near equilibrium set of loops in phase transition. The statistical configurations of the vortex tangles are certainly different in, say, the cases of counterflowing helium and a rotating bulk, but in all the physical situations very similar theoretical and numerical problems arise. Furthermore, quite similar situations appear in other fields of physics, where a chaotic set of one dimensional topological defects, such as cosmic strings, or linear defects in solids, or lines of darkness in nonlinear light fields, appear in the system. There is an interpenetration of ideas and methods between these scientific topics which are far apart in other respects. The main purpose of this review is to bring together some of the most commonly discussed results on quantum turbulence, focusing on analytic and numerical studies. We set out a series of results on the general theory of quantum turbulence which aim to describe the properties of the chaotic vortex configuration, starting from vortex dynamics. In addition we insert a series of particular questions which are important both for the whole theory and for the various applications. We complete the article with a discussion of the hot topic, which is undoubtedly mainstream in this field, and which deals with the quasi-classical properties of quantum turbulence. We discuss this problem from the point of view of the theoretical results stated in the previous sections. We also included section, which is devoted to the experimental and numerical suggestions based on the discussed theoretical models.     

The cubic period-distance relation for the Kate reversible pendulum

We describe the correct cubic relation between the mass configuration of a Kater reversible pendulum and its period of oscillation. From an analysis of its solutions we conclude that there could be as many as three distinct mass configurations for which the periods of small oscillations about the two pivots of the pendulum have the same value. We also discuss a real compound Kater pendulum that realizes this property.     

Opto-mechatronic configurations to maximize dynamic range and optimize resolution of optical instruments

We developed a new mechanical configuration which combines various optical techniques to maximize dynamic range and to optimize resolution in optical instruments. We assessed various optical configurations by looking at such variables as electronic signal processing and mechanical construction. Previous configurations developed over the last 10 years are discussed. In our new configuration, we adopted and integrated devices such as a microscopic, an interferometer, an electronic speckle pattern interferometer, and a photon tunneling microscope. We examined the impact of our new configuration on future opto-mechatronic systems design. Our new configuration can be an effective and versatile optical metrology tool for enhancing the performance of MEMS and NEMS devices.     

Parametrization of Barrier Characteristics for Spherical-Oblate Systems in any Configuration of Colliding Nuclei

The behaviors of barrier characteristics are analyzed for spherical-oblate systems over different configurations of colliding nuclei. For this purpose, we have extended our previous study [Phys. Rev. C 89(2014) 054607], it is devoted to optimum "cold" and "hot" configuration] to analyze the same reaction systems in various configurations.The investigation on some chosen systems reveals that the barrier height and its position can be parameterized in times of the different orientations.     

Calculating a local oscillating quasiparticle’s lifetime at screened defects in solids

We report on a novel approach to calculate quasiparticle lifetimes of localized initial states, which decay into the continuum of underlying quasi-free quasiparticle states in the vicinity of point defects and steps in solids. By using this interpretation of the inelastic damping of wavefunctions, the lifetime becomes a local property. In particular, we consider electrons, which are injected by a scanning tunneling microscope tip into the surface state of a noble metal surface. We investigate numerically the configuration of a single scatterer, a chain of scatterers, and a triangular quantum corral. As compared to an exponential increase of the damping from prior theories, we find an oscillating damping together with a linear background of the resulting measurement signal. The different configurations show increased lifetimes with increasing dimensionality as their scattering phase space is decreased.     

Transverse momentum distribution and elliptic flow of charged hadrons in $$$$ collisions at $$\sqrt{s_{NN}}=193$$sNN=193 GeV using HYDJET++

Recent experimental observations of the charged hadron properties in \(U+U\) collisions at 193 GeV contradict many of the theoretical models of particle production including two-component Monte Carlo Glauber model. The experimental results show a small correlation between the charged hadron properties and the initial geometrical configurations (e.g. body–body, tip–tip etc.) of \(U+U\) collisions. In this article, we have modified the Monte Carlo HYDJET++ model to study the charged hadron production in \(U+U\) collisions at 193 GeV center-of-mass energy in tip–tip and body–body initial configurations. We have modified the hard as well as soft production processes to make this model suitable for \(U+U\) collisions. We have calculated the pseudorapidity distribution, transverse momentum distribution and elliptic flow distribution of charged hadrons with different control parameters in various geometrical configurations possible for \(U+U\) collision. We find that HYDJET++ model supports a small correlation between the various properties of charged hadrons and the initial geometrical configurations of \(U+U\) collision. Further, the results obtained in modified HYDJET++ model regarding \(dn_{ch}/d\eta \) and elliptic flow (\(v_{2}\)) suitably matches with the experimental data of \(U+U\) collisions in minimum bias configuration.     

Experimental characterization of vibrated granular rings

We report an experimental study of the statistical properties of vibrated granular rings. In this system, a linked rod and bead metallic chain in the form of a ring is collisionally excited by a vertically oscillating plate. The dynamics are driven primarily by inelastic bead-plate collisions and are simultaneously constrained by the rings' physical connectedness. By imaging many instances of the ring configurations, we measure the ensemble averages and distributions of several physical characteristics on the scale of individual beads and composite ring. We study local properties such as inter-bead separation and inter-bonds angles, and global properties such as the radius of gyration and center-of-mass motion. We characterize scaling with respect to the size of the chain.     

用物理化学方法鉴别砷化镓中最主要深能级EL2的本性

本文应用半导体物理化学方法(借助某些物理测试手段)研究GaAs材料中最主要深施主能级EL2映陷的形成及其转化的一些规律。首先归纳了鉴别EL2本性的三个重要依据(化学计量比、与位错关系和低温光猝灭行为),然后着重阐述三元络合物A_(SGa)V_(As)V_(Ga)作为EL2缺陷构型的形成反应、应变模型形成机理和亚稳态机理,并利用该模型来解释EL2的主要物理和化学性质,对文献报道的EL2其它可能构型如As_(Ga)、As_(Ga)Asi、As_(Ga)V_(As)、As_(Ga)V_(Ga)、(Asi)_4、(As_(Ga))_n、V_(Ga)V_(As)和As_(Ga)V_(Ga)V_(As)等作了评述。最后还讨论了EL2与GaAs中其它深能级的关系,其中包括EL2族现象。