Conductivity of a two-dimensional model of a structurally anisotropic composite with a system of scratches

The conductivity of a two-dimensional model of a structurally anisotropic composite, an isotropic matrix with nonconducting inclusions in the form of parallel scratches, is considered. The centers of the scratches are randomly distributed over the (x, y) plane. An approximate method is applied to derive an expression for the effective conductivity tensor, which satisfactorily describes of the electric conductivity of the model over a wide range of concentrations.     

Electrical conductivity of a two-dimensional model for a structurally anisotropic composite

The electrical conductivity of a two-dimensional structurally anisotropic model for a composite is considered. The model represents an isotropic matrix with a system of nonconducting inclusions in the form of infinitely thin straight line segments (scratches). The scratches make an angle θ or −θ with a preferred axis (for definiteness, axis y) at the same probability, and their centers are chaotically distributed. An approximate effective medium method is used to obtain a general expression for the effective conductivity tensor $ \hat \sigma _e $ \hat \sigma _e of this model that is valid over a wide concentration range. In this approximation, both components of tensor are $ \hat \sigma _e $ \hat \sigma _e shown to vanish at the same percolation threshold, which is expressed explicitly. The conductivity of the model in a critical region is considered in terms of the similarity hypothesis.     

Vertex calculation for a composite particle

The classical treatment and the quantization of composite relativistic systems is given a manifestly covariant formulation in presence of constraints. A particular formulation of Feynman's quantum mechanics is used to treat the scattering of composite relativistic systems. A covariant harmonic oscillator model is employed to calculate vertices of interactions: the results are similar to the corresponding ones in the usual field theories, but the presence of some convergence factors gives hope that a theory with composite particles may be finite.     

Bias voltage effect on electron tunneling across a junction with a ferroelectric-ferromagnetic two-phase composite barrier

The effect of bias voltage on electron tunneling across a junction with a ferroelectric-ferromagnetic composite barrier is investigated theoretically. Because of the inversion symmetry breaking of the spontaneous ferroelectric polarization, bias voltage dependence of the electron tunneling shows significant differences between the positive bias and the negative one. The differences of spin filtering or tunnel magnetoresistance increase with the increasing absolute value of bias voltage. Such direction preferred electron tunneling is found intimately related with the unusual asymmetry of the electrical potential profile in two-phase composite barrier and provides a unique change to realize rectifying functions in spintronics.     

Superposition rule for light scattering by a composite particle

A superposition rule for light scattering by composite particles is presented that expresses the scattering amplitude of a composite particle as a superposition of that of the host particle and those of the shadowed inclusions. The superposition rule is derived for a soft composite particle but also provides insight into light scattering by a general composite scatterer. Favorable comparison with an exact numerical method demonstrates the usefulness of the rule in analyzing light scattering by composite particles such as biological cells.     

一维Hulthén势场中Klein-Gordon粒子的透射共振

用Heaviside函数构造出一维对称的Hulthén势垒,求解了其满足的Klein-Gordon方程. 散射态的精确解可以由超几何函数表示, 透射系数T和反射系数R能由Klein-Gordon 方程满足的边界条件得到.并由流密度守恒推导出低动量粒子发生透射共振的条件. 关键词： Klein-Gordon方程 Hulthén势垒 散射态 透射共振     

Diffusion of a chemically active colloidal particle in composite channels

Diffusion of colloidal particles in microchannels has been extensively investigated, where the channel wall is either a no-slip or a slip-passive boundary. However, in the context of active fluids, driving boundary walls are ubiquitous and are expected to have a substantial effect on the particle dynamics. By mesoscale simulations, we study the diffusion of a chemically active colloidal particle in composite channels, which are constructed by alternately arranging the no-slip and diffusio-osmotic boundary walls. In this case, the chemical reaction catalyzed by the active colloidal particle creates a local chemical gradient along the channel wall, which drives a diffusio-osmotic flow parallel to the wall. We show that the diffusio-osmotic flow can significantly change the spatial distribution and diffusion dynamics of the colloidal particle in the composite channels. By modulating the surface properties of the channel wall, we can achieve different patterns of colloidal position distribution. The findings thus propose a novel possibility to manipulate colloidal diffusion in microfluidics, and highlight the importance of driving boundary walls in dynamics of colloidal particles in microchannels.     

Scattering of Hawking photons as a barrier to particle absorption by black holes

Electromagnetic scattering interactions between photons emanating from a Schwarzschild black hole and an incident charged particle should generate a repulsive force between the particle and black hole. The net scattering cross-section is calculated here as a function of the mass M of the black hole and the mass m of the particle for scenarios in which the particle is point-like and initially stationary, with proper energy ε=m, at some location far from the black hole. It follows from comparing the repulsive scattering force to the corresponding gravitational force that, in order for the particle to be drawn to the black hole, ε/Tbh must be greater than a certain lower bound that is of the order ¹⁰−3 for spin-1/2 or spin-0 particles with unit-charge. Although the scattering restriction is weaker than the requirement ε/Tbh?1 obtained independently from field-theoretic and thermodynamic treatments, the recurrence of a lower bound on the Boltzmann factor ε/Tbh in limitations on particle absorption suggests a physical unity whose nature is fundamentally thermodynamic.     

Antisymmetrisation effects in composite particle scattering

Several approximations for the determination of the real part of the heavy-ion optical potential have been studied. The results of these approximations for α-α scattering have been compared with the equivalent local potential determined by an inverse scattering method from a fully antisymmetrised “exact” calculation and some general conclusions are given.     

Quasielastic barrier distributions: role of particle transfer channels

The barrier distributions extracted from quasielastic excitation functions are analyzed in terms of a semiclassical model that incorporates both the excitation of the surface degrees of freedom and the exchange of neutrons and protons. It is shown that quasielastic cross sections receive sizable contributions from transfer reactions in all measured energy range.     

Laser ultrasonics detection of an embedded crack in a composite spherical particle

Laser ultrasonics was applied to the manufacturing control of the integrity (no failure) of coated spherical particles designed for High Temperature Reactors (HTR). This control is of major importance, since the coating of the nuclear fuel kernel is designed to prevent from the diffusion of fission products outside the particle during reactor operation. The SiC layer composing the coating is particularly important, since this layer must be an impenetrable barrier for fission products. The integrity of the SiC shell (no crack within the shell) can be assessed by the ultrasonic vibration spectrum of the HTR particle, which is significantly changed, compared to the reference spectrum of a defect-free particle. Spheroidal vibration modes of defect-free dummy particles with a zirconium dioxide (ZrO₂) core were observed in the 2-5 MHz range. A theoretical analysis is presented to account for the observed vibration spectra of defect-free or cracked HTR particles.     

Pauli-correct separable potentials for composite particle interactions

Experimental totalβ-decay energies for short-lived isotopes of gallium and germanium are presented. The sources were produced as mass-separated fission products at the OSIRIS on-line separator at Studsvik. By applyingβ-γ-coincidence methodsQ _α-values were determined for^80,81Ga and^79,81,82Ge. For these nuclei on or close to the shellN =50 and in the vicinity of ther-process “seed”, the atomic mass excess is derived and compared with predictions from mass formulae.     

Collision geometry and particle production in high energy heavy ion collision experiments

An overview of research status of soft physics in high energy heavy-ion collision experiments and recent experimental results are presented.This paper includes four parts:1)Theoretical predictions of quarkgluon plasma and introduction for high energy heavy ion collision experiments.2)Experimental status on collision geometry.3)Experimental status on particle production.4)Conclusion and outlook for research status of soft physics in LHC/ALICE.     

Collision geometry and particle production in high energy heavy ion collision experiments

An overview of research status of soft physics in high energy heavy-ion collision experiments and recent experimental results are presented. This paper includes four parts: 1) Theoretical predictions of quark-gluon plasma and introduction for high energy heavy ion collision experiments. 2) Experimental status on collision     

Oscillator with a centrifugal barrier

We study the wave functions and energy levels of a one-dimensional oscillator with a centrifugal barrier of the form s(s+1)/x². It is shown that a barrier of this kind automatically implies the point potential A(s)(x)/x. It is also shown that two different sets of even states are physically admissible, but that only one of these sets transforms continuously into the set of states of harmonic oscillator when the centrifugal barrier is allowed to vanish and is preferable for this reason.Translated from Izvestiya Vysshkh Uchebnykh Zavedenii, Fizika, No. 5, pp. 35–39, May, 1987.The authors acknowledge useful discussions with B. M. Bolotovskii, B. A. Lysov, and O. A. Khrustalev.     

Deep inelastic scattering by a composite particle in the scale-invariant Quark model

A method that sums the asymptotes of Feynman diagrams is used to consider the deep inelastic scatter of leptons by a pion, treated as a bound state of a quark and antiquark. It is shown that the form of the structure functions depends only on the number and type of quarks, but is independent of the bound state which they form. An estimate is obtained for the magnitude of the quark -gluon interaction constant at small distances.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 59–66, December, 1976.In conclusion we would like to thank A. V. Efremov for many fruitful discussions and much assistance, and Professor D. Ivanenko for discussing the paper in his seminar.     

Collision of a 1-D column of beads with a wall

An experimental study of the collision of a column of N beads () with a fixed wall is presented. For a fixed height of fall and a rigid wall, we show that the maximum force felt by the wall is independent of the number of beads N. The duration of impact, the velocity of the deformation wave in the column and an effective restitution coefficient of the column are also measured as a function of N. For a soft wall, we show that the maximum force depends on N. A non-dissipative numerical model, based on a nonlinear interaction law between nearest neighbours, gives results in agreement with the experimental data. Moreover, we show that, after the compression phase, the beads of the top of the column separate one after the other from the column with a velocity greater than the initial one. The beads at the bottom then bounce upwards in block, with a velocity smaller than the initial one. We emphasize that this detachment effect results from the energy redistribution within the whole system during the collision and not from any dissipative effect. Received: 6 February 1998 / Revised and accepted: 26 May 1998