纳米晶体线的晶格动力学格林函数及晶格振动

通过求解差分方程,推导了纳米晶体线的晶格动力学格林函数,分析了其晶格振动,并推导了声子数表象中的原子位移及晶格振动哈密顿公式.研究结果表明,纳米晶体线的晶格振动能带分裂为一系列的子带,格波只能沿纳米晶体线的纵向传播,沿纳米晶体线的横截面只存在驻波.     

Light-induced cross transport phenomena in a single-component gas

The cross transport processes that occur in a single-component gas in a capillary and are caused by resonance laser radiation and pressure and temperature gradients are studied. An expression for entropy production is derived using a system of kinetic Boltzmann equations in a linear approximation. The kinetic coefficients that determine the transport processes are shown to satisfy the Onsager reciprocal relations at any Knudsen numbers and any character of the elastic interaction of gas particles with the capillary surface. The light-induced baro- and thermoeffects that take place in a closed heat-insulated system in the field of resonance laser radiation are considered. Analytical expressions are obtained for the Onsager coefficients in an almost free-molecular regime. The light-induced pressure and temperature gradients that appear in a closed heat-insulated capillary under typical experimental conditions are numerically estimated.     

单波驱动的过渡粒子效应

本文讨论单波在环等离子体中引起的过渡粒子及其有关效应。 关键词：     

A review of commonly used analytical and empirical formulae for predicting sound diffracted by a thin screen

This paper reviews some useful analytical and empirical formulae that are used for the calculation of sound diffracted by a barrier. A brief historic overview of the study of spherical waves diffracted by a rigid half plane is presented also. The physical principles of sound diffraction by a thin plane are explained. The mathematical expressions are cast in a convenient form for ease of numerical implementation. Accurate analytical solutions are expressed in terms of standard mathematical functions that can be computed readily. Among the approximate solutions quoted, quite a few empirical formulations are adequate for most engineering purposes. The information presented in this paper should also be helpful for those who are interested in the study of sound diffracted by a barrier in a room or in a long industrial space.     

Propagation of a decentered astigmatic partially coherent beam in a turbulent atmosphere

Propagation properties of a decentered general astigmatic partially coherent beam (i.e., decentered twisted anisotropic Gaussian Schell-model beam) in a turbulent atmosphere are investigated. Analytical formulas for the cross-spectral density and decentered parameter of a decentered astigmatic partially coherent beam propagating in a turbulent atmosphere are derived. Irradiance properties of a decentered astigmatic partially coherent beam in a turbulent atmosphere are studied graphically, and are found to be quite different from its properties in free space.     

Frequency-division multiplexing of optical-fibre sensors using a frequency-modulated source

Three basic configurations, namely, (i) parallel with a common reference, (ii) parallel with separate references and (iii) series, are studied for a multiplexed system of optical-fibre sensors. With a frequency-modulated laser source, each sensor of a different predetermined path imbalance results in a different beat frequency at the detector and signals are multiplexed in the frequency domain. The cross-term problem arising from undesired interference associated with more than one sensor is described. A series configuration has more cross terms than a parallel configuration if there are four sensors or more and, consequently, suffers more signal power reduction if there are seven sensors or more. Several schemes are presented, which ensures the separation of cross terms from desired signals. In a parallel system with a common reference, signals and cross terms are allocated in the lower and in the higher region, respectively, or to every other line in the frequency domain. In a parallel system with separate references, sensors are made incoherent to each other to produce no cross terms. In a series system, more elaborate schemes are necessary. The estimated maximum number of sensors indicates that a parallel configuration should be used if there are 10 sensors or more to be multiplexed.     

Thermodynamics of electrons in the graphene bilayer

Some problems of the thermodynamics of electrons in a doped graphene bilayer are considered. Analytical expressions are derived for chemical potential and specific heat in the limiting cases of low and high temperatures. The Seebeck and Thomson coefficients are estimated. Landau levels are studied using a semi-classical approach. An expression for thermodynamic potential is obtained and the de Haas-van Alphen oscillations are studied. The oscillations of magnetic entropy and electron temperature in a magnetic field, i.e., the oscillating magnetocaloric effect, are investigated. For all parameters, the cases of graphene bilayer and monolayer are compared.     

Shadowing effects in nuclear parton distributions for small values ofx

The shadowing corrections to gluon and quark distributions in nuclei in the region of small values ofx are discussed. They are related to parton distributions in a pomeron which are in principle measurable in hard diffractive processes on the nucleon target. Multiple scattering corrections to shadowing are considered in a model dependent way. The perturbative QCD evolution of shadowing is also taken into account. Various possibilities of the partonic content of a pomeron are considered. It is shown in particular that the conventional parametrizations of parton distributions in a pomeron which are based on the assumption that it consists mostly of gluons imply substantial nuclear shadowing in gluon distributions in heavy nuclei. Possible phenomenological implications of shadowing corrections in nuclear parton distributions for various semi-hard processes with nuclear targets are briefly discussed.     

Propagation and scattering of light in stratified media

The propagation and scattering of light in stratified media are considered. Based on the Maxwell equations, the present approaches to the solution of these problems are formulated in a unified way. The particular features of the wave propagation in stratified media are discussed. Scalar and vector fields are considered. Media with small-and large-scale regular inhomogeneities are examined. The construction of the Green’s function of the wave equation in a spatially homogeneous medium is discussed. Stratified isotropic and anisotropic media are analyzed. The scattering of light in a stratified medium is studied with emphasis on the Kirchhoff method, as this makes it possible to obtain calculation formulas in a form convenient for comparing the theory with the experiment. The propagation of waves in photonic crystals and the formation of forbidden zones in such objects are briefly considered.     

The classification of displacements and rotations in a cellular space—Time

The implications of the lack of continuity in space-time brought about by every observation process are discussed in connection with the need for finding new observables based on realisable measuring processes. Displacements in a cellular space are defined and their rules of combination are formulated. Rotations in a cellular space are defined in terms of a set of radius displacements and in terms of a set of instructions which tell how these radii should be used.     

Probe studies of silicon p-n junctions

The results of single-probe studies of thick and thin silicon p-n junctions are described. The electric fields in a diode with a p⁺-n junction and in a stabilitron with a p-n junction in the forward and reverse directions are studied. Measurements are made at various currents and temperatures. The p-n junctions are analyzed on the basis of the probe measurements.     

Characterisation of valves as sound sources: Structure-borne sound

Taps and other valves are major sound sources in piping systems and can cause unacceptable noise levels in buildings. The noise results from the fluid-, structure- and air-borne sound emission. At present the acoustic emission of water appliances is tested according to a European standard, the shortcomings of which are apparent as a result of a round robin test of different European laboratories. As a result, there are currently neither acceptable measurement methods for water appliances available nor input data for prediction models. This paper considers methods of characterizing water appliances as sources of structure-borne sound. The concepts of mobility and free velocity are employed for a source characterisation based on power. Taps are considered alone and also in combination with a basin, where again the mobility and free velocity are used. A reception plate method is assessed as an alternative. The two methods each provide an independent characterisation of a structure-borne sound source as a single value. The values are on a power basis and provide input data suitable for prediction of the installed structure-borne power and thence the resultant sound pressure in adjacent rooms. Measured and predicted values of sound pressure level, caused by a wash-basin installed in an adjacent room, are compared.     

Transport of polarized neutrons through magnetic noncoplanar layered systems

The transport of neutrons through noncoplanar systems is shown to have a partly unidirectional character. To this end, the transmission of a three-layer magnetic film with a noncoplanar magnetization in the absence of applied magnetic field and the transmission of a two-layer magnetic film with a noncollinear magnetization in the presence of a magnetic field are calculated. The calculations demonstrate that, if the losses in the films are neglected, the transmissions in two opposite directions differ only for processes with and without spin flip. If these losses are taken into account, the total transmissions of a nonpolarized neutron beam in two opposite directions are also different. The consequences of these specific features of noncoplanar systems are discussed.     

Radiative corrections to chiral amplitudes in quasiperipheral kinematics

Chiral amplitudes for two-jet processes in quasiperipheral kinematics are calculated at the Born and one-loop correction levels. The amplitudes of subprocesses describing the interaction of a virtual and a real photon with the creation of a charged fermion pair for various chiral states are considered in detail. Similar results are presented for the Compton subprocess with a virtual photon. Contributions of the emission of virtual, soft, and hard real additional photons are explicitly taken into account. The relevant cross sections expressed in terms of impact factors are in agreement with the structure function approach in the leading logarithmic approximation. Contributions of the next-to-leading terms are represented in analytic form. Estimation of accuracy is discussed. The text was submitted by the authors in English.     

A completely integrable case in three-particle problems with homogeneous potentials

Trajectory equations are considered for classical three-particle problems on a straight line with potentials that are homogeneous coordinate functions. It is proposed to consider the case of a zero total energy as a completely integrable one in a generalized sense, since in it the order of the differential trajectory equation is lowered to the first one, the variables in the Hamiltonian-Jacobi equation are separated, there are additional first integral and invariant tori, in spite of the fact that the system cannot be integrable by the Liouville-Arnold theorem. The solutions are constructed (i) in a parametric form, (ii) in the form of a convergent perturbative series of a new type, and (iii) as a convergent Fourier series.     

Direct conversion of mixed phase into free hadronic gas and transverse pion momenta in ultra-relativistic nuclear collisions

The deflagration model is developed for a physically substantiated situation when free pions are radiated directly from a time-like hypersurface formed by a rarefaction shock wave. It is shown that the shock front and pion collective flow velocities are enhanced in this approach as compared to the standard deflagration model. Exotic regimes are also possible. The stability conditions are investigated and analytic solutions are found. We calculate the pion transverse momentum spectra in ultra-relativistic nuclear collisions and indicate their behavior in the region 0.2 GeV/c<p _⊥<1 Gev/c. The spectra are essentially different in this region depending on whether or not longitudinal collective flows are in a mixed phase.     

Radial motion of a solid spherical body in a magnetic field

The object of the present paper is to investigate the radial motion of a solid spherical body, assumed to be homogeneous, isotropic and elastic, in presence of a magnetic field in the azimuthal direction. The body is assumed to be in a state of initial stress which is hydrostatic in nature. This theory of radial motion of a solid spherical body in a magnetic field has been utilised to find the small radial motion of a solid Earth assumed to be homogeneous isotropic elastic sphere in presence of a magnetic field in the azimuthal direction. Considering the effect of gravity and the initial stress produced by slow process of creep due to extra masses over the surface of the Earth, the fundamental equations of motion are derived which are non-linear in character and are solved. The times of a desired radial displacement are calculated in presence of a magnetic field only and in presence of the same magnetic field, initial stress and gravitational field, which are compared and exhibited numerically.     

PREDICTION OF DYNAMIC CHARACTERISTICS USING UPDATED FINITE ELEMENT MODELS

Model updating techniques are used to update a finite element model of a structure so that an updated model predicts the dynamics of a structure more accurately. The application of such an updated model in dynamic design demands that it also predict the effects of structural modifications with a reasonable accuracy. This paper deals with updating of a finite element model of a structure and its subsequent use for predicting the effects of structural modifications. Updated models have been obtained by a direct model updating method and by an iterative method of model updating based on the frequency response function (FRF) data. The suitability of updated models for predicting the effect of structural modifications is evaluated by some computer and laboratory experiments. First a study is performed using a simulated fixed-fixed beam. Cases of complete, incomplete and noisy data are considered. Updated models are obtained by the direct and the FRF-based method in each of these cases. These models are then used for predicting the changes in the dynamic characteristics brought about due to a mass and a beam modification. The simulated study is followed by a study involving actual measured data for the case of an F-shape test structure. The updated finite element models for this structure are obtained again by the direct and the FRF-based method. Structural modifications in terms of mass and beam modifications are then introduced to evaluate the updated model for its usefulness in dynamic design. It is found that the predictions based on the iterative method based updated model are reasonably accurate and, therefore, this updated model can be used with reasonable accuracy to perform dynamic design. The predictions on the basis of the direct method based updated model are found to be reasonably accurate in the lower portion of the updating frequency range but the predictions are in a significant error in the remaining portion of the updating frequency range. It is concluded that the updated models that are closer to the structure physically are likely to perform better in predicting the effects of structural modification.