Influence of helicity on scaling regimes in model of passive scalar advected by the turbulent velocity field with finite correlation time

The advection of a passive scalar quantity by incompressible helical turbulent flow has been investigated in the frame of an extended Kraichnan model. Statistical fluctuations of the velocity field are assumed to have the Gaussian distribution with zero mean and defined noise with finite time-correlation. Actual calculations have been done up to two-loop approximation in the frame of the field-theoretic renormalization group approach. It turned out that the space parity violation (helicity) of a stochastic environment does not affect anomalous scaling which is the peculiar attribute of corresponding model without helicity. However, stability of asymptotic regimes, where anomalous scaling takes place, and the effective diffusivity strongly depend on the amount of helicity.     

Numerical evaluation of time-dependent reflected intensity from an anisotropically scattering semi-infinite atmosphere

A numerical scheme, designed to provide four or five digit accuracy for the reflected photon intensity from an anisotropically scattering semi-infinite medium, is presented. The atmosphere is characterized by both a mean free time between collisions and a mean time of temporal capture. Tables of reflected intensities for a test-phase function are included for use as benchmarks to which other numerical solutions can be compared.     

Universality in passively advected hydrodynamic fields: the case of a passive vector with pressure

Universality of statistical properties of passive quantities advected by turbulent velocity fields at changing the passive forcing mechanism is discussed. In particular, we concentrate on the statistical properties of an hydrodynamic system with pressure. We present theoretical arguments and preliminary numerical results which show that the fluxes of passive vector field and of the velocity field have the same scaling behavior. By exploiting such a property, we propose a way to compute the anomalous exponents of three dimensional turbulent velocity fields. Our findings are in agreement within 5% with experimental values of the anomalous exponents. Received 4 July 2001     

Massive μ pair production in a vector field theory model

We treat massive electrodynamics as a model for the production of massive μ pairs in high-energy hadronic collisions. The dominant diagrams in perturbation theory are identified and analyzed. These graphs have an eikonal structure which leads to enormous cancellations in the two-particle inclusive cross section but not in the n-particle production cross sections. Under the assumption that these cancellations are complete, a Drell-Yan structure appears in the inclusive cross section but the particles accompanying the μ pairs have a very different structure compared to the parton model. The pionization region is no longer empty of particles as in simple parton models.     

Multiple scaling regimes in simple aging models

We investigate aging in glassy systems based on a simple model, where a point in configuration space performs thermally activated jumps between the minima of a random energy landscape. The model allows us to show explicitly a subaging behavior and multiple scaling regimes for the correlation function. Both the exponents characterizing the scaling of the different relaxation times with the waiting time and those characterizing the asymptotic decay of the scaling functions are obtained analytically by invoking a "partial equilibrium" concept.     

有限振幅驻波声场中分岔的数值研究

对闭管中有限振幅气柱振动规律进行了数值研究,结果显示有限振幅驻波场具有强烈的非线性特性,在一定条件下会出现分岔混沌现象.倍周期分岔是有限振幅驻波场达到混饨的途径之一.     

Plasma instabilities in an anisotropically expanding geometry

We study (3+1)D kinetic (Boltzmann-Vlasov) equations for relativistic plasma particles in a one dimensionally expanding geometry motivated by ultrarelativistic heavy-ion collisions. We set up local equations in terms of Yang-Mills potentials and auxiliary fields that allow simulations of hard- (expanding-) loop dynamics on a lattice. We determine numerically the evolution of plasma instabilities in the linear (Abelian) regime and also derive their late-time behavior analytically, which is consistent with recent numerical results on the evolution of the so-called melting color-glass condensate. We also find a significant delay in the onset of growth of plasma instabilities which are triggered by small rapidity fluctuations, even when the initial state is highly anisotropic.     

Numerical simulation of particle motion in an ultrasound field using the lattice Boltzmann model

In this paper we investigate the motion of small particles suspended in a fluid through which an ultrasound field is propagating. The application of the lattice Boltzmann model to this problem is considered using a two dimensional model. Particles in an ultrasound field are observed to move with a mean particle motion. Further, the time-averaged force on a fixed cylinder is computed and found to be in good agreement with a theoretical expression for the radiation force. Simulations are performed with a single particle, although the approach can equally be applied for a larger number of particles.     

Coherent backscattering enhancement in highly anisotropically scattering media: Numerical solution

The problem of coherent backscattering enhancement in media with highly anisotropic scattering is considered within the scalar wave theory. A stable computational algorithm, suitable for the media of finite thickness, is formulated. Numerical simulations are performed, and the results are presented and discussed.     

Numerical simulation of particle motion in an ultrasound field using the lattice Boltzmann model

In this paper we investigate the motion of small particles suspended in a fluid through which an ultrasound field is propagating. The application of the lattice Boltzmann model to this problem is considered using a two dimensional model. Particles in an ultrasound field are observed to move with a mean particle motion. Further, the time-averaged force on a fixed cylinder is computed and found to be in good agreement with a theoretical expression for the radiation force. Simulations are performed with a single particle, although the approach can equally be applied for a larger number of particles.     

Numerical simulation of an uncharged droplet in a uniform electric field

The deformations of a real dielectric droplet subjected to a uniform alternating electric field and immersed in an insulating fluid are numerically studied by the Boundary Element Method. The alternating electric field time scale is taken much smaller than the hydrodynamic time scale of the droplet shape deformation. The influence of the frequency and the conductivity of the droplet upon the critical electric field, beyond which instabilities develop, are compared with the experimental measurements. Numerical results well account for experimental data while an unexpected good correspondence with Taylor's theory is found.     

Scattering of a Gaussian beam by an anisotropically coated circular cylinder

A solution to the problem of Gaussian beam scattering by an anisotropically coated circular cylinder is presented. The incident Gaussian beam source is expanded as an approximate expression in the simple form with a Tayor’s series. The transmitted field in the anisotropically coated region is expressed as a infinite summation of eigen plane waves with different polar angles. The unknown coefficients of the scattered fields are obtained with the aid of the boundary conditions. The infinite series can be truncated under the prerequisite of achieving the solution convergence. Only the case of transverse-electric polarization is discussed. The similar formulation of transverse-magnetic polarization can be obtained by adopting the similar method. Some numerical results are presented and discussed. The result is in agreement with that available as expected when the Gaussian beam degenerates to a plane wave incidence case.