Retardation of dislocations by the Cherenkov mechanism in crystals with a soft mode

The retardation mechanism of dislocations in crystals with a soft mode on account of Cherenkov emission of soft optical phonons is considered in the present work. The conditions in which this retardation mechanism appears are examined for various orientations of the wave vector q_c characterizing structural phase transition. It is shown that the threshold velocity of the retardation mechanism in the case where q_c¦V (V is the velocity of motion of the dislocations) decreases on approaching the phase-transition temperature T_c in proportion to ¦t_c–T_c¦. The dependence of the dynamic retardation coefficient B on the velocity V and the closeness to the point of structural phase transition is obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 59–64, December, 1988.     

微平行管道内Jeffrey流体的非定常电渗流动

研究了微平行管道内线性黏弹性流体的非定常电渗流动, 其中线性黏弹性流体的本构关系是由Jeffrey流体模型来描述的. 利用Laplace变换法, 求解了线性化的Poisson-Boltzmann方程、 非定常的柯西动量方程和Jeffrey流体本构方程, 给出了黏弹性Jeffrey流体电渗速度的解析表达式, 分析了无量纲弛豫时间λ₁和滞后时间λ₂对速度剖面的影响. 发现滞后时间为零时, 弛豫时间越小, 速度剖面图越接近牛顿流体的速度剖面图; 随着弛豫时间和滞后时间的增加, 速度振幅也变得越来越大, 随着时间的增加, 速度逐渐趋于恒定. 关键词： 双电层 微平行管道 Jeffrey流体 非定常电渗流动     

Settling velocity of equiaxed dendrites in a tube

The settling velocity of equiaxed dendrites can cause macrosegregation and influence the structure of the equiaxed zone during the casting solidification process. So an understanding of the settling characteristics is needed to predict the structure and segregation in castings. The settling velocity of NH4Cl equiaxed dendrites of non-spherical geometry was studied experimentally in an NH4Cl-70wt.%H2O solution. A calculation formula was proposed to calculate the settling velocity of sediment equiaxed dendrites in a tube filled with saturated solution at a moderate Reynolds number region. The retardation effects of the wall and morphology of the equiaxed dendrite on the settling velocity were taken into account in the development of the calculation formula, and the correction function B of the drag coefficient with consideration of the retardation effects of the wall and morphology of the equiaxed dendrite on the settling velocity of the equiaxed dendrite was calibrated according to the experimental results. A comparison showed that the formula has a good accordance with the experimental results.     

Microwave detection of spatial-dispersion effects in superconductors

A microwave method based on the use of microstrip retardation systems for detecting spatial-dispersion effects in superconductors is proposed. Strong phase velocity retardation in a microstrip resonator has been revealed, which is explained by the influence of sharp strip edges, near which high curvature occurs for the coordinate system introduced to search for wave solutions. This circumstance leads to a spatial dependence of the phase velocity on the scale factors of the curvilinear coordinate system and may significantly reduce the phase velocity. Comparative estimates of the spatial effects in samples of a single-crystal high-temperature superconductor (YBaCuO), Nb, and Cu have been obtained from measurements of the total value and increment of the resonance frequency during the transition of the cooling helium from the liquid to gaseous state, depending of the sample position in the field of the microstrip resonator.     

Charged Nanoparticle Transport in Polymer-Grafted Nanochannels

Molecular dynamics simulations were used to investigate the electric field-induced migration of nanoparticles in a nanochannel grafted with a polymer brush. The distribution of nanoparticles, brush monomer density and migration velocity are addressed at different electric field strengths and grafting densities. The increase of the grafting density leads to a decrease of the effective radius of the nanochannel. At high grafting density, the distribution of nanoparticles is shifted significantly towards the center of the channel. Enhancing the electric field leads to a very slight change of brush monomer density. The migration velocity increases with the electric field rapidly at weak electric fields, while a slow increase is observed at strong electric fields. Additionally, it is found that the migration velocity of nanoparticles exhibits a nonlinear dependence on the grafting density.     

Kontamination und Schutz Des Grundwassers in Der Nähe Von Atomkraftwerken

Abstract

The influence of diffusion, dispersion, retardation and their correlation with groundwater velocities, porosity and radioactivity is discussed in relation to nuclear power plants and their potential influence on groundwater pollution.     

Experimental study of different modes of block sliding along interface. Part 1. Laboratory experiments

This paper is the first part of an experimental work on studying the formation of different deformation modes of rock discontinuities under laboratory and field conditions. The formation conditions of different sliding modes were studied under laboratory conditions for several types of discontinuities, such as rigid surface contact and cracks filled with quartz sand, talc, and clay. A wide range of shear deformation modes were experimentally reproduced—from dynamic slip with a maximum velocity of tens of mm/s to stable sliding with a velocity of 1 µm/s. The behavior of a crack with a clay-containing gouge drastically changes after its wetting. The larger is the content of clay, the longer is the slip duration. The motion of a block consists of a long phase (~100 s) in which displacement velocity smoothly increases, and a retardation phase of almost the same duration in which displacement velocity decreases down to a few tens of µm/s. The used sensors detected no acoustic emission prior to the beginning of block sliding as well as on all stages of block motion until its full stop. It is shown that slow slip events have all stages typical for stick-slip motion: acceleration, long sliding, retardation, arrest, and quiescence. The conducted laboratory experiments substantiate the earlier statement that all types of deformation processes in the Earth’s crust produce a common range of phenomena.     

The Post-NEWTONian Effect of Gravitation and the Retardation of the Gravitational Potential in Classical and Relativistic Theories of Gravitation

For planetary motions the post-NEWTON ian approximations of classical, special-relativistic, and general-covariant theories are compared. It is shown that, in this approximation, the anisotropy terms, which occur in the effective interaction potential in classical and special-relativistic theories, suggest a retardation of gravitation. In the post-NEWTON ian approximation of general-covariant theories the fixation of a retardation velocity is equivalent to coordinate conditions. – All post-NEWTON ian corrections are dipole-like ones, while, according to GAUSS , the classical perturbation theory generally leads to quadrupole-like corrections of the perturbation potential.     

温度梯度区域熔化作用下熔池迁移的元胞自动机模拟

本文采用耦合凝固和熔化效应的二维元胞自动机(cellular automaton, CA)模型,对温度梯度区域熔化(temperature gradient zone melting, TGZM)效应引起的熔池在固液两相区中的迁移现象进行模拟研究.模拟分析了抽拉速度、熔池初始位置、温度梯度和合金成分等因素对TGZM动力学的影响,并将模拟结果与解析模型的预测结果进行比较验证.通过模拟发现,在温度梯度作用下,熔池总是向着高温方向迁移;当抽拉速度低于或高于临界抽拉速度时,熔池朝向移动的液相线或固相线迁移;对于给定的抽拉速度,位于糊状区内临界位置以上的熔池会迁移进入液相,而位于临界位置以下的熔池会逐步靠近固相线.此外,温度梯度越高,合金成分越低,熔池的迁移速度越快.     

On the notion of thermophoretic velocity

The phenomenology of thermal diffusion of a particle in a solvent involves the Soret coefficient of the particle/solvent mixture. It is usually considered that the migration velocity of the particle in the solvent is proportional to the Soret coefficient. I show here that this view is wrong because ordinary diffusion contributes to migration if the solvent is not homogeneous. I examine several examples (NaCl in water, polystyrene in ethylbenzene, maghemite nanoparticles) to show that this contribution can be sufficiently strong to change the sign of the migration velocity and vitiate the interpretation of experimental data, measurement of the Soret coefficient, the comparison of experiment with theory and inter-experimental comparisons.     

Instability of single-walled carbon nanotubes conveying Jeffrey fluid

We report instability of the single-walled carbon nanotubes(SWCNT) filled with non-Newtonian Jeffrey fluid.Our objective is to get the influences of relaxation time and retardation time of the Jeffrey fluid on the vibration frequency and the decaying rate of the amplitude of carbon nanotubes.An elastic Euler-Bernoulli beam model is used to describe vibrations and structural instability of the carbon nanotubes.A new vibration equation of an SWCNT conveying Jeffrey fluid is first derived by employing Euler-Bernoulli beam equation and Cauchy momentum equation taking constitutive relation of Jeffrey fluid into account.The complex vibrating frequencies of the SWCNT are computed by solving a cubic eigenvalue problem based upon differential quadrature method(DQM).It is interesting to find from computational results that retardation time has significant influences on the vibration frequency and the decaying rate of the amplitude.Especially,the vibration frequency decreases and critical velocity increases with the retardation time.That is to say,longer retardation time makes the SWCNT more stable.     

Solid phase epitaxy amorphous silicon re-growth: some insight from empirical molecular dynamics simulation

The modelling of interface migration and the associated diffusion mechanisms at the nanoscale level is a challenging issue. For many technological applications ranging from nanoelectronic devices to solar cells, more knowledge of the mechanisms governing the migration of the silicon amorphous/crystalline interface and dopant diffusion during solid phase epitaxy is needed. In this work, silicon recrystallisation in the framework of solid phase epitaxy and the influence on orientation effects have been investigated at the atomic level using empirical molecular dynamics simulations. The morphology and the migration process of the interface has been observed to be highly dependent on the original inter-facial atomic structure. The [100] interface migration is a quasi-planar ideal process whereas the cases [110] and [111] are much more complex with a more diffuse interface. For [110], the interface migration corresponds to the formation and dissolution of nanofacets whereas for [111] a defective based bilayer reordering is the dominant re-growth process. The study of the interface velocity migration in the ideal case of defect free re-growth reveals no difference between [100] and [110] and a decrease by a mean factor of 1.43 for the case [111]. Finally, the influence of boron atoms in the amorphous part on the interface migration velocity is also investigated in the case of [100] orientation.     

液体速度电化学测试法传质解

1引言在电化学过程中，电迁移作用的存在使得离子的传质问题复杂化，这是因为近电极处的电势梯度与溶液中的各种高于分布有关。Newman［‘，‘］等曾研究过电化学溶液中离子迁移效应对离子传质的影响，并采用数值计算方法讨论了静止溶液中几种不同电报过程中的传质状况。对流场参数测量电极而言，理论分析的目的是希望得到可测量（电流）与流场参数的函数关系，故数值计算法不大适用。作者［’，‘］提出的稀电解质溶液中传递现象电化学测试法，给出了一种得到近似理论解的方法。本文进一步给出了迁移作用存在下驻点区域的传质理论解并将其…     

Retardation effect in microstrips and microwave detection of spatial dispersion in superconductors

Effect of significant retardation of the phase velocity in a microwave microstrip resonator has been found and utilized for detection of spatial-dispersion phenomena in superconductors, which should be pronounced when the phase velocity became less than the Fermi velocity. The effect is explained by the influence of the fine fringes of a strip near of which the high values of curvature can appear for the system of coordinates introduced to find solutions. This leads to a spatial dependence of the phase velocity on the Lamé coefficients (metric coefficients) of the curvilinear system of coordinates and can decrease the velocity significantly. Comparative estimates of the spatial effects for single-crystal high-T_c (YBaCuO), Nb, and Cu samples were obtained from measurements of the resonant frequency depending on a position of the sample in the field.     

Motile parameters of cell migration in anisotropic environment derived by speed power spectrum fitting with double exponential decay

Cell migration through anisotropic microenvironment is critical to a wide variety of physiological and pathological processes.However,adequate analytical tools to derive motile parameters to characterize the anisotropic migration are lacking.Here,we proposed a method to obtain the four motile parameters of migration cells based on the anisotropic persistent random walk model which is described by two persistence times and two migration speeds at perpendicular directions.The key process is to calculate the velocity power spectra of cell migration along intrinsically perpendicular directions respectively,then to apply maximum likelihood estimation to derive the motile parameters from the power spectra fitting with double exponential decay.The simulation results show that the averaged persistence times and the corrected migration speeds can be good estimations for motile parameters of cell migration.     

Promotion of cooperation by aspiration-induced migration

In this paper, we study an aspiration-induced migration model, in which each individual plays the prisoner’s dilemma game with those being within a circle of radius r centered on himself/herself. An individual will migrate to a randomly chosen place with the velocity v if his/her payoff is below the aspiration level. We report that cooperative behavior is favored when the aspiration level and interaction radius are moderate, and the migration velocity is slow.     

Generation of elliptically polarized terahertz waves from laser-induced plasma with double helix electrodes

By applying a helical electric field along a plasma region, a revolving electron current is formed along the plasma and an elliptically polarized far-field terahertz wave pattern is observed. The observed terahertz wave polarization reveals the remarkable role of velocity retardation between optical pulses and generated terahertz pulses in the generation process. Extensive simulations, including longitudinal propagation effects, are performed to clarify the mechanisms responsible for polarization control of air-plasma-based terahertz sources.     

理想条件下氦氡团簇离子垂直移动速度的理论计算

在论述了氦氡团簇形成机理的基础上，根据传统力学理论，进一步推导了氦氡团簇离子移动速度计算公式，并对氦氡团簇向上和向下移动的极限速度以及达到极限速度的时间进行了讨论. 关键词： 团簇 氡运移 最大速度     

Decommissioning of a Nuclear Power Plant: Determination of Site-Specific Sorption Coefficients for Co-60 and Cs-137

Abstract

Assessment of radiological risks in strategies for decommissioning of nuclear installations have to consider not only technical concepts such as cutting and decontamination techniques but, even more important, requirements for input of reliable information on the hydrological situation and retardation capabilities of relevant radionuclides specific to the respective decommissioning operation.

In this paper we describe appropriate methods for obtaining site-specific sorption data and present results achieved from a case study performed as a commercial contractual work preliminary to the planned decommissioning of a nuclear power plant. A detailed mineralogical study of the sediment used in our sorption experiment highlights the necessity of a thorough sample homogenization and characterization. Batch experiments using radiotracer techniques for the determination of site-specific sorption coefficients show significant retardation for Co-60 and Cs-137 after only 2h of equilibration between the preconditioned groundwater and sediment. Sorption is more effective in the groundwater of a deeper aquifer containing a higher amount of colloidal clay (illite) particles < 0.63 μn. The Co-60 radiotracer is more completely sorbed than the Cs-137 radiotracer. Equilibration of radionuclide distribution is slow, particularly for Co-60. Presence of EDTA reduces sorption of Co-60 efficiently while Cs-137 sorption remains unaffected.     

Theory and application of cyclone with impulse electrostatic excitation for cleaning molecular gas

This paper introduces the structure, characteristics and operating principle of a cyclone impulse electrostatic precipitation (CIESP), and presents the solid–gas separation mechanism of CIESP. The hydromechanics equations of particles in solid–gas separation are set up with the goal of analyzing the characteristics of impulse corona discharge. The application of CIESP for cleaning molecular gas in a catalyst plant is explained. We conclude that CIESP is very suitable for cleaning sticky dust particles from exhaust gases of molecular sieve catalyst plant, and has high overall collection efficiency, while the migration velocity is approximately twice that of the electrostatic precipitation (up to 0.15–0.18 m/s). The theoretical formula for particle migration velocity is experimentally verified.