Observation of the condensation of a gas of interacting grains

We consider an ensemble of grains that interact through a dipole-dipole interaction. A granular gas is formed by the vertical motion of a piston at the bottom boundary of the system. The interaction between the grains is controlled by an horizontally applied magnetic field. When the speed of the piston is decreased, we observe a transition from a low density to a high density phase. When the interaction between grains is weak, the transition is continuous. It is discontinuous for stronger interaction. The phase diagram displays strong similarities with the ones observed for usual equilibrium phase transitions.     

Dependence of the characteristics of bubbles on types of sonochemical reactors

Computer simulations of bubble oscillations in liquid water irradiated by an ultrasonic wave have revealed that the characteristic of bubbles depends on types of sonochemical reactors: a horn-type reactor and a standing-wave type reactor. When the acoustic amplitude is large at 20 kHz, the bubble content is mostly water vapor even at the end of the bubble collapse and the temperature inside a bubble at the collapse is relatively low. On the other hand, when the acoustic amplitude is relatively low, the bubble content is mostly noncondensable gas at the end of the bubble collapse and the bubble temperature is relatively high. In a horn-type sonochemical reactor, the former type of bubbles are dominant because many bubbles exist near the horn-tip where the acoustic amplitude is large, while in a standing-wave type reactor the latter type of bubbles are dominant because the Bjerknes force gathers bubbles at a region where acoustic amplitude is relatively low.     

On the theory of the condensed states of heteropolymers

The collapse (globulization) of an ideal heteropolymer chain under the action of an external attractive field is considered. The problem of the collapse of different types of primary structures, including mobile, periodic, large-block, and statistical structures, is formulated. It is shown that for a random heteropolymer, the mathematical image of the globular state is the chain-length independence of the probability distribution of a random thermal distribution function of the end monomer coordinates. The free energy per monomer of a chain in a globular state and local densities of monomers of all types are shown to be a self-averaging quantities. An exactly solvable model is proposed for a globule formed by a statistical heteropolymer chain. In this model, different types of monomers are attracted to different centers by linear elastic forces with identical elastic constants. The modulus of elasticity is obtained for a heteropolymer globule with respect to the attraction of different types of monomers in different directions. It is shown that this modulus is higher for a short-periodic polymer than for a statistical one.     

Investigation of evaporation and boiling of liquids

It is shown experimentally that a minimum in the evaporation curve of water drops, a 5% aqueous solution of ethanol, and a 5% aqueous solution of n-butanol, i.e., the maximal evaporation rate of these liquids, is observed at a critical thermal load under boiling. Based on this finding, a method to determine the temperature of onset of the boiling crisis is suggested. It is found that the evaporation stages of drops of a liquid correlate with boiling regimes for this liquid.     

混合物状态方程的计算

多介质流体动力学过程的数值模拟往往涉及混合物状态方程的计算. 做图法和Newton 法是混合物状态方程计算常采用的方法, 前者虽直观精度却差, 后者计算效率高却只具有局部收敛性, 当解与其初始猜测值相差较远时Newton法不一定能够获得收敛解. 为此, 本文给出一种具有大范围收敛性的嵌入算法(imbedding method)求解混合物状态方程, 其基本思想是通过引入嵌入参数, 将待解的混合物状态方程和易解的混合物状态方程线性组合, 构成嵌入方程组, 当嵌入参数从0连续地变化到1 时, 嵌入方程组的解由易解的混合物状态方程的解连续地变化为待解的混合物状态方程的解. 嵌入方程组可由Newton法迭代求解, 也可转化为以嵌入参数为自变量的常微分方程组, 从而易于由成熟的计算方法如梯形法等进行求解. 进一步利用热力学基本关系, Maxwell形式的微分方程描述了压力和温度随嵌入参数的演化速率与应变速率和组分质量分数演化速率的关系. 对铅锡混合物热力学量的计算表明了本文算法的有效性.     

Evolution and Generation of Dynamics of Two-Mode Squeezed States of Time-Dependent Coupled Boson System

The system of the Hamiltonian involving a driving part, a single mode part, and a two-mode squeezed one and a two-mode coupled one is discussed using the Lewis-Riesenfeld invariant theory. The time evolution operator is obtained. When the initial state is a coherent state, the quantum fluctuation of the system is calculated, and it is dependent on the squeezed part and the two-mode coupled part, but not dependent on the driving one.     

Complete list of first integrals of dynamic equations of motion of a 4D rigid body in a nonconservative field under the assumption of linear damping

The dynamic part of equations of motion of a dynamically symmetric 4D rigid body, where the force field is concentrated on that part of the body that has the form of a two-dimensional disc, is investigated. In this case, the tensor of the angular velocity of such a body is six-dimensional, while the velocity of the center of mass is four-dimensional. Under certain conditions, a complete list of first integrals, which are expressed through elementary functions, is obtained.     

Equivalent representation of orthogonal-field electrodynamics by system of covariant lines of force

It is shown that the electrodynamics of orthogonal magnetic and electric fields can be represented as the dynamics of covariant lines of force. Such a representation is provided for the Lienard-Wichert field of an arbitrary moving charge and the field of a charge that moves uniformly about a circle. The four vector of the electric lines of force is written as the sum of the four vector of the charge and the radius four vector directed along the light cone to the observation point. This vector is a solution of an equation that formally coincides with the equation of motion of the magnetic moment in external fields for a zero intrinsic magnetic moment. The electromagnetic field is reconstructed according to a system of lines that correspond to the total equation of motion of the magnetic moment. Such a field for a uniformly circulating charge is examined.Erevan Physics Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, Nos. 3, 4, pp. 313–323, March–April, 1992.     

Application of the method of smooth perturbations to the solution of problems of optical tomography of strongly scattering objects containing absorbing macroinhomogeneities

Monochromatic small-angle Fraunhofer diffraction from a spiral is studied as a function of its stretching. A simple relation between locations of the principal maxima and geometrical parameters of a spiral is obtained. Diffraction from a spiral is analyzed theoretically in the linear approximation of the boundaries of the profile of a periodic unit. An analytical expression for the light intensity at any point of a screen is derived, and analytical relations between locations of the principal maxima and geometrical parameters of a spiral, which are identical to the relations established experimentally, are obtained. The possibility for utilizing the results obtained in the development of systems of automatic control of the main geometrical parameters of spiral objects in the process of their production is demonstrated by the example of the analysis of diffraction patterns from a standard metallic screw and a twisted capron fiber.     

Design of a Reflective Aspherical Surface of a Compact Beam-Shaping Device

A compact beam-shaping device with a reflective aspherical surface is proposed. The device converts a circular symmetric Gaussian beam from a laser into a uniform distribution on a target plane. The device consists of a laser, a reflective aspherical surface formed on the base plane inclined by 45° against the optical axis, and a spacer. The surface is designed for an optical device used as a transmitter of indoor wireless optical communication, which is one of the promising applications. The designed surface is obtained by approximation using polynomial. Beam shaping of a simulated surface and a uniform intensity distribution on the target plane is obtained. The intensity distribution generated by the surface is numerically simulated and evaluated if the surface is misaligned. It is clarified that the generated distribution is tolerable for the misalignment.     

Some mechanisms of excitation of a railway wheel

Railway wheel vibrations are caused by a number of mechanisms. Two of these are considered: (a) gravitational load reaction acting on different points of the wheel rim, as the wheel rolls on, and (b) random fluctuating forces generated at the contact patch by roughness on the mating surfaces of the wheel and rail. The wheel is idealized as a thin ring, and the analysis is limited to a single wheel rolling on a rail. It is shown that the first mechanism results in a stationary pattern of vibration, which would not radiate any sound. The acceleration caused by roughness-excited forces is much higher at higher frequencies, but is of the same order as that caused by load reaction at lower frequencies. The computed acceleration level (and hence the radiated SPL) caused by roughness is comparable with the observed values, and is seen to increase by about 10 dB for a doubling of the wagon speed. The driving point impedance of the periodic rail-sleeper system at the contact patch, which is used in the analysis, is derived in a companion paper.     

扭摆系统中扭杆的等效转动惯量——圆柱杆扭转振动的研究

研究扭摆系统中扭杆的质量或转动惯量对扭摆运动的影响,引入一个概念:扭摆系统中扭杆的等效转动惯量.纠正了一些文献在相关问题上的误解.     

Gravitational interaction of a vector field with account of the nonmetricity of space-time

The gravitational interaction of a vector field is investigated in a space with the nonmetricity described by the Weyl vector. The analogue of the Coulomb law for the electrostatic field of a point charge is found in such a space. It is shown that taking account of the nonmetricity of space-time leads to the appearance of a nonlinearity in a massive vector field, resulting in the sine-Gordon and shine-Gordon equations. The screening of the vector-field mass as a consequence of its interaction with the nonmetricity is clarified. The solution for the Reissner-Nordström problem in a Weyl space is obtained, which asymptotically coincides with the solution of the same problem in general relativity, but nowhere does it possess singularities apart from at the origin. The obtained results show that it is reasonable to take account of the nonmetricity when describing the gravitational interaction of a vector field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 50–54, August, 1984.     

Measurement of the Elasticity of Biological Soft Tissue of Finite Thickness

Elasticity is of profound significance to evaluating the function of a biological soft tissue.When the elasticity of a tissue is macroscopically changed,it means that the biological function of the tissue is abnormal and some disease or injury may occur.In the present work,an elastometer is developed to measure the elasticity of biological soft tissues.The measurement is based on the indentation method and the force is measured by the bending of the cantilever.The force-indentation data of the soft tissue is experimentally measured by this elastometer and Young's modulus of the tissue is calculated using the Hertz-Sneddon model.For comparison,a numerical model for the indentation method is established using the finite element method.The difference between the actual modulus and the measured modulus is discussed.The effect of the thickness of the specimen on the measurement is investigated.Young's moduli of beef,porcine liver and porcine kidney are experimentally measured.The results indicate that our elastometer is effective in measuring Young's modulus of a soft tissue quantitatively.     

Characteristic features of the development of two-stream instability of electron beams in the presence of spatially localized perturbations

A study is made of the evolution of a spatially localized perturbation in the form of a Gaussian packet during two-stream instability in a plasma. It is shown that, on the whole, the moving perturbation is decelerated and its shape is distorted; moreover, the higher the group velocity of the packet, the higher the deceleration rate.     

Excitation of the half-frequency of the input signal in theresponse of an antenna immersed in a plasma

The nonlinear response of a cylindrical monopole antenna immersed in a steady-state collisionless magnetic-field-free plasma and driven by a single-frequency RF source is investigated. The thickness of the ion sheath surrounding the antenna is controlled by a DC bias applied to the latter. It is found that at frequencies of the driving signal close to twice the frequency of a sheath wave resonance, the 1/2-subharmonic is excited, provided that the input power level is sufficiently high. The dependence of this process on the sheath thickness and on the electron plasma density is studied in the vicinity of several sheath wave resonances. This nonlinear effect is interpreted as a parametric excitation due to the periodic modulation of the sheath thickness, and hence its capacitance, by the applied RF signal. A similar effect can be obtained by replacing the antenna-sheath-plasma structure in the measuring circuit by a variable capacitance diode. A numerical analysis of the differential equation describing the current waveform in a microwave network modeling the antenna-sheath-plasma system is presented. It confirms the fact that a periodically modulated capacitance embedded in a linear circuit is responsible for the observed excitation of the half-frequency of the input signal     

Thermodynamics of Phase Transitions of a Kerr Nonlinear Blackbody

We study the thermodynamics of phase transitions of a blackbody whose interior is filled by a Kerr nonlinear crystal. There is a transition temperature To, above which the Kerr nonlinear blackbody is in the normal thermal radiation state, and below which it is in the squeezed thermal radiation state. At To, the Gibbs free energy of the two phases is continuous but the entropy density of the two phases is discontinuous. Hence, there is a jump in the entropy density and this leads to a latent heat density. The photon system undergoes a first-order phase transition from the normal to the squeezed thermal radiation state.     

Micromechanism of the deformation process of macromolecular systems

The mechanism of cold drawing is described by a model of inhomogeneous deformation. The fundamental assumption of the model is that a random polymer coil subjected to an external stress forms a highly oriented strand and a residual rest coil that remains isotropic after a phase of elastic deformation. In this coil-strand transition model, the strand is growing during deformation by reduction of the volume part of the rest coil. In the volume-creating model, the constant orientation difference between rest coil and strand gives rise to a linear energy and entropy law and thus to a constant tensile stress. In the volume-conserving model, a decreasing power law for the stress-strain relationship is found, which is able to explain certain features of the cold drawing process.     

Synergetics of macrostructure evolution of a new phase

The status of the theory of nucleation of a new phase is reviewed. Special attention is devoted to the relation between the micro- and macroscopic levels. A systematic exposition is given of the methods developed by Cahn, Cook, Langer, and Mazenko for describing the spatiotemporal correlation of the order-parameter field for the continuous (spinodal) mechanism of formation of a new phase. The time dependence of the characteristic size L(t) is found for the cases of nonconserved and conserved order parameters as well as for the coalescence process. It is shown that in the case of the intermittent (binodal) formation mechanism a critical nucleus of a new phase can be represented as the soliton solution of the field equation. It is found that the appearance of sharp interphase boundaries results in a transition from spinodal to heterophase kinetics, represented as a loss of ergodicity. The nonergodicity parameter is determined as a function of the interatomic interaction and anharmonicity within the Ginzburg-Landau scheme. Coalescence in the presence of intense external noise is investigated for systems with a conserved order parameter. A stochastic equation is derived for the size distribution function of precipitates of the new phase and the effect of intensity fluctuations and supersaturation of the limiting component on the solution of this equation is investigated.Sumskii Physicotechnological Institute of the Scientific and Industrial Enterprise RÉTO. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 90–122, January, 1993.     

Four contemporary interpretations of the nature of science

Instrumentalism is an approach to science that treats a theory as a tool and only as a tool for computation; it dispenses with the concept of truth.Conventionalism treats a theory as true by convention if it forms a pattern of observations from which correct predictions can be made.Operationalism denies meaning to the concepts of a theory unless they can be defined operationally. It is argued in this paper that truth-value is indispensable to science, because a theory can be rejected only if an empirical consequence is false and if falsity of a conclusion entails falsity of a premise. This undermines the above positions. The fourth interpretation isinduction. Induction, by contrast, uses the notion of truth-value. What is focused on here is its reliance on the ultimacy ofobservation. The present thesis is that instrumentalism, conventionalism, and induction are different attempts to handle observations. The common problem is the gap between data and theory.All these interpretations share a philosophy of observationalism. The aim of this paper is to show that the several orthodox interpretations of science all fail to solve the problem of the data-theory gap, and to show that they all presuppose a philosophy of observation.