Critical behavior in the layered organic–inorganic hybrid(CH_3NH_3)_2CuCl_4

The critical properties and the nature of the ferromagnetic–paramagnetic phase transition in the 2D organic-inorganic hybrid(CH_3NH_3)_2 CuCl_4 single crystal have been investigated by dc magnetization in the vicinity of the magnetic transition. Different techniques were used to estimate the critical exponents near the ferromagnetic–paramagnetic phase transition such as modified Arrott plots, the Kouvel–Fisher method, and the scaling hypothesis. Values of β = 0.22, γ = 0.82, and δ = 4.4 were obtained. These critical exponents are in line with their corresponding values confirmed through the scaling hypothesis as well as the Widom scaling relation, supporting their reliability. It is concluded that this 2D hybrid compound possesses strong ferromagnetic intra-layer exchange interaction as well as weak interlayer ferromagnetic coupling that causes a crossover from 2D to 3D long-range interaction.     

Post-Newtonian parameter γ in generalized non-local gravity

We investigate the post-Newtonian parameter γ and derive its formalism in generalized non-local(GNL) gravity, which is the modified theory of general relativity(GR) obtained by adding a term m~(2n-2)R□(-n)R to the Einstein-Hilbert action. Concretely,based on parametrizing the generalized non-local action in which gravity is described by a series of dynamical scalar fields φ~i in addition to the metric tensor g_(μν), the post-Newtonian limit is computed, and the effective gravitational constant as well as the post-Newtonian parameters are directly obtained from the generalized non-local gravity. Moreover, by discussing the values of the parametrized post-Newtonian parameters γ, we can compare our expressions and results with those in Hohmann and Jrv et al.(2016), as well as current observational constraints on the values of γ in Will(2006). Hence, we draw restrictions on the nonminimal coupling terms F around their background values.     

Non-Achievability of Metal-Insulator Transition in Two-Dimensional Systems

We present a simple demonstration of the nonfeasibility of metal-insulator transition in an exactly two-dimensional （2D） system. The Hartree-Fock potential in the 3D system is suitably modified and presented for the 2D case. The many body effects are included in the screening function, and binding energies of a donor are obtained as a function of impurity concentration so as to find out the possible way leading metal-insulator transition in the 2D system. While solving for the binding energy for a shallow donor in an isolated well of a GaAs/Ga1-x Als As superlattice system within the effective mass approximation, it leads to unphysical results for higher concentrations. It shows that the phase transition, the bound electron entering into the conduction band whereby （H）min=0, is not possible beyond this concentration. The results suggest thai a phase transition is impossible in 213 systems, supporting the scaling theory of localization. The results are compared with the existing data available and discussed in the light of existing literature.     

Interaction between many parallel screw dislocations and a semi-infinite crack in a magnetoelectroelastic solid

Based on the fundamental equations of magnetoelectroelastic material and the analytic theory, and using the Muskhelishvili-introduced well-known elastic techniques combined with the superposition principle, the closed form solution of the generalized stress field of the interaction between many parallel screw dislocations and a semi-infinite crack in an infinite magnetoelectroelastic solid is obtained, on the assumption that the surface of the crack is impermeable electrically and magnetically. Besides, the Peach–Koehler formula of n parallel screw dislocations is given. Numerical examples show that the generalized stress varies with the position of point z and is related to the material constants. The results indicate that the stress concentration occurs at the dislocation core and the tip of the crack. The result of interaction makes the system stay in a lower energy state.     

A simplified Parisi ansatz

Based on simple combinatorial arguments, we formulate a generalized cavity method where the Random Overlap Structure(ROSt) probability space of Aizenmann, Sims and Starr is obtained in a constructive way, and we use it to give a simplified derivation of the Parisi formula for the free energy of the Sherrington–Kirkpatrick model.     

Landau damping and frequency-shift of a quadrupole mode in a disc-shaped rubidium Bose–Einstein condensate

The damping and frequency-shift in Landau mechanism of a quadrupole mode in a disc-shaped rubidium Bose–Einstein condensate are investigated by using the Hartree–Fock–Bogoliubov approximation. The practical relaxations of the elementary excitations and the orthometric relation among them are taken into account to obtain advisable calculation formula for damping as well as frequency-shift. The first approximation of Gaussian distribution function is employed for the ground-state wavefunction to suitably eliminate the divergence of the analytic three-mode coupling matrix elements.According to these methods, both Landau damping rate and frequency-shift of the quadrupole mode are analytically calculated. In addition, all the theoretical results agree with the experimental ones.     

On dynamics of elastic rod based on exact Cosserat model

The analysis of kinematics and dynamics of an elastic rod with circular cross section is studied on the basis of exact Cosserat model under consideration of the tension and shear deformation of the rod. The dynamical equations of a rod with arbitrary initial shape are established in general form. The dynamics of a straight rod under axial tension and torsion is discussed as an example. In discussion of static stability in the space domain the Greenhill criteria of stability and the Euler load are corrected by the influence of tension and shear strain. In analysis of dynamical stability in the time domain it is shown that the Lyapunov and Euler stability conditions of the rod in space domain are the necessary conditions of Lyapunov's stability in the time domain. The longitudinal, torsional and lateral vibrations of a straight rod based on exact model are discussed, and an exact formula of free frequency of lateral vibration is obtained. The free frequency formulas of various simplified models, such as the Rayleigh beam, the Kirchhoff rod, and the Timoshenko beam, can be seen as special cases of the exact formula under different conditions of simplification.     

Validation of the Wiedemann–Franz law in a granular s-wave superconductor in the nanometer scale

The present study tries to evaluate the validity of the Wiedemann–Franz law in a granular s-wave superconductor in the presence of concentrated impurities. By using Green's function method and the Kubo formula technique, three distinct contributions of the Aslamazov–Larkin, the Maki–Thompson and, the density of states are calculated for both the electrical conductivity and the thermal conductivity in a granular s-wave superconductor. It is demonstrated that these different contributions to the fluctuation conductivity depend differently on the tunneling because of their different natures. This study examines the transport in a granular superconductor system in three dimensions in the limit of large tunneling conductance,which makes it possible to ignore all localization effects and the Coulomb interaction. We find that the tunneling is efficient near the critical temperature and that there is a crossover to the characteristic behavior of a homogeneous system.When it is far from the critical temperature, the tunneling is not effective and the system behaves as an ensemble of real zero-dimensional grains. The results show that the Wiedemann–Franz law is violated in both temperature regions.     

Research and experiments of mutual radiation impedance effect on array directivity

The mutual radiation impedance ignored in conventional array directivity formula is introduced into the calculation of array radiation sound field,and a modified array directivity formula considering the mutual radiation impedance is gained according to the superposition principle.Results of computer simulation and experiments for a uniform linear array and a uniform planar array show superior performance on the present of the practical directivity pattern of the modified formula in this paper in comparison to the conventional one.     

An Efficient Simulated Sea Slope Model for Backscattering from a Non-Gaussian Sea Surface

Based on the double superimposition model, a sea slope model is obtained on the basis of the generated oceanic surface instead of being assumed as a Gaussian distribution model. Then, a summation formula of the backscattering coefficient is derived from the Bass Fuks two-scale model and its application is extended to the non-Gaussian oceanic surface with the help of simulated sea slopes, which can adequately reflect the non-Gaussian configuration of the sea surface. Finally, this scattering model is employed to describe the baekscattering configuration of sea surfaces in different sea states and wind directions, and is confirmed by several numerical examples.     

Vacuum Effects on Massive Spinor Fields: S 1× R 3 Topology

The aim of this work was to investigate the role played by an external field on the Casimir energy density for massive fermions under S ¹× R ³ topology. Both twisted- and untwisted-spin connections are considered and the calculation in a closed form is performed using an alternative approach based on the combination of the analytic regularization method and the Euler–Maclaurin summation formula. It is shown that no mass scale appears in the final result and, therefore, Casimir effect arises only from the boundary conditions and vacuum fluctuations induced by the coupling with the external field. PACS numbers: 11.10.Wx     

Extended Feynman formula for time-dependent forced harmonic oscillator

Horváthy's modification of Feynman's path integral formula is generalized to the time-dependent forced harmonic oscillator. The propagator at caustics is then obtained by using its modified semi-group property. Finally, with our new formula, the propagator for a charged particle in a time-dependent electromagnetic field is evaluated exactly beyond and at caustics.     

修正的莫比乌斯反演公式在晶体对势计算中的应用

将陈-莫比乌斯公式作了进一步推广。用修正的莫比乌斯反演公式解决了Ewald求和的反问题——由晶体中原子所受的总势求得原子间的对势。对几种典型晶体结构,提出了基于迭代法的算法及相应的存储结构。分析了算法的稳定性及误差,并进行了试算。 关键词：     

The transformation between the mode representation and the generalized ray representation of a sound field

The “mode generation function” φ(ν), and the “generalized ray generation function” B(u) are introduced for a stratified wave-guide. It is proved that φ(ν) and B(u) are a Fourier transform pair when lateral waves do not appear. Mode representation and the “generalized ray” representation satisfy the Poisson summation formula. Furthermore, the “local conversion” relation between the mode and the ray is considered from the point of view of “member selection”. It is found that “local conversion” is just the result of using the stationary phase approximation in the Fourier transformation of φ(ν) and B(u). This is the same result as obtained by “selective processing” in which the constructive interference between adjoining members (of the ray or mode families) is used.     

非水平直圆管中黏性流体层流流量公式的推导及实验验证

通过牛顿粘滞定律和修正后的伯努利方程对非水平直圆管中黏性流体作层流运动时的流量公式进行了推导。指出将泊肃叶公式中的压强视作广义压强,则文中的推导公式与泊肃叶公式完全一致。说明泊肃叶公式可以用来求解非水平直圆管中黏性流体作层流运动时的流量。本文通过实验验证了推导公式。     

关于推广的KdV方程的孤波解

修正了文献[5]中推广的KdV方程传播波解的形变理论,并提出了一个相关的代数方程有非零实根的充要条件,从而指出了文献[5]中的一个分析错误。最后直接从推广的KdV方程本身给出了由形变理论生成的孤波解的显式公式。 关键词：     

Wightman function and vacuum polarization in models with non-trivial topology in the presence of boundaries

Wightman function and the vacuum expectation value of the scalar field squared are studied in models with a compact subspace in the presence of parallel plane boundaries, on which the field obeys Robin boundary conditions. By means of the generalized Abel-Plana summation formula we have explicitly extracted from the vacuum expectation values the parts induced by the boundaries. As a simple example, a one-dimensional internal space is considered compactified on a circle.     

Determination by quantum beat spectroscopy of fine-structure intervals in a series of highly excited sodium D states

Using the quantum beat method in conjunction with stepwise excitation, we have measured the absolute value of the fine-structure (fs) intervals in a series of highly excited sodium nD states (n=9 to 16). Preliminary Stark effect measurements of these levels also indicate that the fs is inverted. Our results and those previously obtained on the lowest D intervals (n=3 to 6) agree with an empirical formula giving the fs constant as an expansion in odd powers of n^?1. This formula allows the prediction of the as yet not measured 7D and 8D intervals.