Critical exponents predicted by grouping of Feynman diagrams in φ4 model

Different perturbation theory treatments of the Ginzburg‐Landau phase transition model are discussed. This includes a criticism of the perturbative renormalization group (RG) approach and a proposal of a novel method providing critical exponents consistent with the known exact solutions in two dimensions. The usual perturbation theory is reorganized by appropriate grouping of Feynman diagrams of φ⁴ model with O(n) symmetry. As a result, equations for calculation of the two‐point correlation function are obtained which allow to predict possible exact values of critical exponents in two and three dimensions by proving relevant scaling properties of the asymptotic solution at (and near) the criticality. The new values of critical exponents are discussed and compared to the results of numerical simulations and experiments.     

Direct Numerical Simulation of Three-Dimensional Richtmyer--Meshkov Instability

Direct numerical simulation （DNS） is used to study flow characteristics after interaction of a planar shock with a spherical media interface in each side of which the density is different. This interracial instability is known as the Richtmyer-Meshkov （R-M） instability. The compressible Navier-Stoke equations are discretized with group velocity control （GVC） modified fourth order accurate compact difference scheme. Three-dimensional numerical simulations are performed for R-M instability installed passing a shock through a spherical interface. Based on numerical results the characteristics of 3D R-M instability are analysed. The evaluation for distortion of the interface, the deformation of the incident shock wave and effects of refraction, reflection and diffraction are presented. The effects of the interracial instability on produced vorticity and mixing is discussed.     

Numerical analysis of three-colour HgCdTe detectors

The performance of three-colour HgCdTe photovoltaic heterostructure detector is examined theoretically. In comparison with two-colour detectors with two back-to-back junctions, three-colour structure contains an absorber of intermediate wavelength placed between two junctions and electronic barriers are used to isolate this intermediate region. This structure was first proposed by British workers. Three-detector structures with different localizations of separating barriers are analyzed. The calculation results are presented in the form of spatial distributions of bandgap energy and quantum efficiency. Enhanced original computer programs are applied to solve the system of non-linear continuity equations for carriers and Poisson equations. In addition, the numerical analysis includes the dependence of absorption coefficient on Burstein effect as well as interference effects in heterostructure with metallic electrical contacts. It is shown that the performance of the detector is critically dependent on the barrier’s doping level and position in relation to the junction. This behaviour is serious disadvantage of the considered three-colour detector. A small shift of the barrier location and doping level causes serious changes in spectral responsivity.     

Development and testing of a numerical simulation method for thermally nonequilibrium dissociating flows in ANSYS Fluent

Various issues of numerical simulation of supersonic gas flows with allowance for thermochemical nonequilibrium on the basis of fluid dynamic equations in the two-temperature approximation are discussed. The computational tool for modeling flows with thermochemical nonequilibrium is the commercial software package ANSYS Fluent with an additional userdefined open-code module. A comparative analysis of results obtained by various models of vibration-dissociation coupling in binary gas mixtures of nitrogen and oxygen is performed. Results of numerical simulations are compared with available experimental data.     

Numerical simulation of quasi-multifractal diffusion process

The properties of quasi-multifractal diffusion process are discussed. A discrete model of the process is constructed, and a method is proposed for calculating the quasi-multifractal spectrum, based on statistical processing of its realizations. An analysis of multifractal properties performed by numerical simulation of the quasi-multifractal spectrum is qualitatively substantiated by examining realizations of the simulated process. The results of numerical simulations suggest that there are three distinct scaling regions. Special attention is given to comparative analyses between numerical and analytical results and between realizations of the proposed process and the well-known multifractal random walk.     

N-body integral equations and four-nucleon calculations

N-body extension of the Faddeev three-body theory is formulated in a novel approach. Comparison with other formulations is performed and first numerical results for the⁴He nucleus are briefly discussed.     

Period doubling toward chaos in a driven magnetic macrospin

The Landau-Lifshitz-Gilbert equation is analyzed in the case of a configuration involving easy plane isotropy under the influence of a sinusoidally oscillating magnetic field and a demagnetizing field. Through the use of numerical techniques, chaotic behavior is found and analyzed. By reducing the system to a discrete map (numerically), bifurcation diagrams for the system are computed. The system is found to exhibit a period doubling cascade route to chaos, and it obeys certain convergence rules for chaotic transitions outlined by Feigenbaum. A connection is drawn between the route to chaos and the geometry of the system, and comparisons are made with similar systems. Within the chaotic regime, windows of arbitrarily large period are suspected to exist, and explicitly illustrated and discussed for a period three window.     

A stochastic model for solidification

A 3-dimensional (2-space, 1-time) model relating the diffusion of heat and mass to the kinetic processes at the solid-liquid interface, using a stochastic approach is presented in this paper. This paper is divided in two parts. In the first part the basic set of equations describing solidification alongwith their analysis and solution are given. The process of solidification has a stochastic character and depends on the net probability of transfer of atoms from liquid to the solid phase. This has been modeled by a Markov process in which knowledge of the parameters at the initial time only is needed to evaluate the time evolution of the system. Solidification process is expressed in terms of four coupled equations, namely, the diffusion equations for heat and mass, the equations for concentration of the solid phase and for rate of growth of the solid-liquid interface. The position of the solid-liquid interface is represented with the help of a delta function and it is defined as the surface at which latent heat is evolved. A numerical method is used to solve the equations appearing in the model. In the second part the results i.e. the time evolution of the solid-liquid interface shape and its concentration, rate of growth and temperature are given.     

Thermodynamic analysis of the quantum critical behavior of Ce-lattice compounds

A systematic analysis of low-temperature magnetic phase diagrams of Ce compounds is performed in order to recognize the thermodynamic conditions to be fulfilled by those systems to reach a quantum critical regime or, alternatively, to identify other kinds of low-temperature behavior. Based on specific heat (C _m ) and entropy results, three different types of phase diagrams are recognized: (i) with the entropy involved in the ordered phase (S _MO) decreasing proportionally to the ordering temperature (T _MO); (ii) those showing a transference of degrees of freedom from the ordered phase to a non-magnetic component, with their C _m (T _MO) jumps (ΔC _m ) vanishing at finite temperature; and (iii) those ending at a critical point at finite temperature because their ΔC _m do not decrease sufficiently with T _MO, producing an entropy accumulation at low temperature.

Only those systems belonging to the first case, i.e. with S _MO?→?0 as T _MO?→?0, can be regarded as candidates for quantum critical behavior. Their magnetic phase boundaries deviate from the classical negative curvature below T?≈?2.5?K, denouncing monotonic misleading extrapolations down to T?=?0. Different characteristic concentrations are recognized and analyzed for Ce-ligand alloyed systems. In particular, a pre-critical region is identified where the nature of the magnetic transition undergoes significant modifications, with its ?C _m /?T discontinuity strongly affected by the magnetic field and showing an increasing remnant entropy at T?→?0. Physical constraints arising from the third law at T?→?0 are discussed and recognized from experimental results.     

Pulse radar reflectometry for fusion plasma diagnostics

A basic principle of pulse radar reflectometry is considered in this paper. A numerical analysis is performed in order to study errors appearing due to the expansion of a microwave pulse reflected from the plasma.A block diagram of the basic pulse radar scheme and its overall performance is presented. The first experimental results obtained on T11-M tokamak are discussed.An improved pulse radar scheme with cross-detection is considered. The results of bench test experiments and future applications of this scheme are discussed.     

Dynamic properties of phase diagram in cylindrical ferroelectric nanotubes

The dynamic properties of phase diagrams in cylindrical ferroelectric nanotubes were investigated by utilizing the effective-field theory with correlations. Three different structure mechanisms are discussed by performing three different interaction functions. Effects of structure factors of the ferroelectric nanotubes are shown in phase diagrams. A linear relation between the crossover value of transverse field in inner-layer of nanotube and the exchange interaction are revealed. Moreover, for the first time, the phase transition characteristics are shown both in 2-D and 3-D phase diagrams by comparing the variations of the ferroelectric region and the morphology vividly. In comparison, results of the usual mean-field approximation are also presented in some phase diagrams, it suggest that the differential operator technique with correlations reduces some extent of the ferroelectric features of the ferroelectric nanotube.     

激光二极管抽运的GaAs被动Q开关Nd：YVO4激光器

利用固体可饱和吸收体砷化镓（GaAs）作为被动调Q元件，实现了激光二极管抽运平－凹腔掺钕钒酸钇（Nd:YVO4）激光调Q运转，详细测量了砷化镓被动调QNd:YVO4激光输出特性，获得脉宽15ns，重复频率470kHz，光束质量M^2=1.31的激光输出，调Q激光运转阈值为500mW，并数值求解了砷化镓被动调Q速率方程，讨论了被动调Q机理以及调Q脉冲宽度和脉冲重复频率对抽运速率的依赖关系，理论计算结果与实验结果相一致。     

Bistability in dual-frequency nematic liquid crystals

Different modes of bistable switching in liquid crystals with frequency inversion of the dielectric anisotropy sign are discussed. The study is performed by numerical simulation and experimentally. It is shown that dual frequency driving can be effectively used to control switching between topologically equivalent and non-equivalent director field distributions. The experimental results on temperature performance of the dual-frequency switching and possible driving methods for energy consumption and expanding the temperature range are presented.     

Synchronization of chaotic systems: Transverse stability of trajectories in invariant manifolds

We examine synchronization of identical chaotic systems coupled in a drive/response manner. A rigorous criterion is presented which, if satisfied, guarantees that synchronization to the driving trajectory is linearly stable to perturbations. An easy to use approximate criterion for estimating linear stability is also presented. One major advantage of these criteria is that, for simple systems, many of the calculations needed to implement them can be performed analytically. Geometrical interpretations of the criterion are discussed, as well as how they may be used to investigate synchronization between mutual coupled systems and the stability of invariant manifolds within a dynamical system. Finally, the relationship between our criterion and results from control theory are discussed. Analytical and numerical results from tests of these criteria on four different dynamical systems are presented. (c) 1997 American Institute of Physics.     

Growth and collapse of laser-induced bubbles in glycerol--water mixtures

Comprehensive numerical and experimental analyses of the effect of viscosity on cavitation oscillations are performed. This numerical approach is based on the Rayleigh-Plesset equation. The model predictions are compared with experimental results obtained by using a fibre-optic diagnostic technique based on optical beam deflection （OBD）. The maximum and minimum bubble radii as well as the oscillation times for each oscillation cycle are determined according to the characteristic signals. It is observed that the increasing of viscosity decreases the maximum bubble radii but increases the minimum bubble radii and the oscillation time. These experimental results are consistent with numerical results.     

IONIZATION OF THE HYDROGEN NEGATIVE ION IN A UNIFORM ELECTRIC FIELD

The ionized Lifetime of the hydrogen negativeion in a uniform electric field is again calculated by using improved perturbation theory.The choice of the H^--ion wave function and the normalization of wave function of continuous state are discussed. The numerical calculations by using Rotenberg-Stein wave function with five parameters are performed. Comparison of our results with experimental results obtained by G. M. Stinson et al. is given.     

Oscillation characteristics of a laser-induced cavitation bubble in water at different temperatures

Comprehensive numerical and experimental analyses of the effect of temperature on cavitation oscillations are performed. In the experimental study, the oscillation of a laser-generated single cavitation bubble near a rigid boundary is obtained using a fiber-optic diagnostic technique based on optical beam detection (OBD). The maximum and minimum bubble radii as well as the oscillation times for each oscillation cycle are determined according to the characteristic signals. And cavitation bubble tests are performed using water at different temperatures, and its temperature ranges from freezing point (0 °C) to near boiling. Furthermore, a modified Rayleigh-Plesset equation is derived for calculating the temporal development of the bubble radius at different temperatures. Both the experimental and the numerical results show that the maximum bubble radius and bubble lifetime both increase as temperature increases. The mechanism behind it has also been discussed.     

Formation of black hole and emission of gravitational waves

Numerical simulations were performed for the formation process of rotating black holes. It is suggested that Kerr black holes are formed for wide ranges of initial parameters. The nature of gravitational waves from a test particle falling into a Kerr black hole as well as the development of 3D numerical relativity for the coalescing binary neutron stars are discussed.     

通过单电子泵实现对单电子运动的控制及其相图分析

介绍了单电子泵的工作原理，讨论了如何利用库仑阻塞和单电子隧穿实现对单电子泵中单个电子运动的控制，从而给出它的相图，并由此得到了单电子泵的一个重要用途，即控制微小电流.指出栅极可能引入的随机电荷对单电子泵的应用并无影响. 关键词： 单电子泵 库仑阻塞 相图     

A molecular dynamics study on iridium

In this study, molecular dynamics simulations are performed by using a modified form of Morse potential function in the framework of the Embedded Atom Method (EAM). Temperature-and pressure-dependent behaviours of bulk modulus, second-order elastic constants (SOEC), and the linear-thermal expansion coefficient is calculated and compared with the available experimental data. The melting temperature is estimated from 3 different plots. The obtained results are in agreement with the available experimental findings for iridium.