Energy bounds for a system of gravitating bosons

Using a method in which the wave functions need not be calculated, we calculate the lower energy bound for a system of mutually gravitating bosons with any number n of particles. This method is based on using the geometric properties of triangles formed by particles. We find the limits for the coefficient C in the asymptotic expression for the nonrelativistic ground-state energy of the gravitational system.     

Kinetic equations in the method of two-time finite-temperature Green's functions. I. Renormalization of the collision integral

A system of equations that includes a generalized kinetic equation and equations for the static correlation functions is constructed for a normal quantum system of interacting Bose and Fermi particles with two-body interaction on the basis of the method of two-time finite-temperature Green's functions. The equations are in general valid for systems with arbitrary density of the particles. A method of successive approximation that makes it possible to go beyond the usual low-density expansion is discussed. The proposed method leads to a renormalization of the collision integral and makes it possible to obtain correlation functions for the total energy density, including its potential part.V. A. Steklov Mathematics Institute, Russian Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 96, No. 3, pp. 351–372, September, 1993.     

On the discrete kinetic theory for active particles. Mathematical tools

This paper deals with the development of a mathematical discrete kinetic theory to model the dynamics of large systems of interacting active particles whose microscopic state includes not only geometrical and mechanical variables (typically position and velocity), but also peculiar functions, called activities, which are able to modify laws of classical mechanics. The number of the above particles is sufficiently large to describe the overall state of the system by a suitable probability distribution over the microscopic state, while the microscopic state is discrete. This paper deals with a methodological approach suitable to derive the mathematical tools and structures which can be properly used to model a variety of models in different fields of applied sciences. The last part of the paper outlines some research perspectives towards modelling.     

Conservative numerical method for solving the averaged Boltzmann equation

A method is proposed for averaging the Boltzmann kinetic equation with respect to transverse velocities. A system of two integro-differential equations for two desired functions depending only on the longitudinal velocity is derived. The gas particles are assumed to interact as absolutely hard spheres. The integrals in the equations are double. The reduction in the number of variables in the desired functions and the low multiplicity of the integrals ensure the computational efficiency of the averaged equations. A numerical method of discrete ordinates is developed that effectively solves the gas relaxation problem based on the averaged equations. The method is conservative, and the number of particles, momentum, and energy are conserved automatically at every time step.     

Numerical method for a dynamic optimization problem arising in the modeling of a population of aerosol particles

A model coupling differential equations and a sequence of constrained optimization problems is proposed for the simulation of the evolution of a population of particles at equilibrium interacting through a common medium.The first order optimality conditions of the optimization problems relaxed with barrier functions are coupled with the differential equations into a system of differential-algebraic equations that is discretized in time with an implicit first order scheme. The resulting system of nonlinear algebraic equations is solved at each time step with an interior-point/Newton method. The Newton system is block-structured and solved with Schur complement techniques, in order to take advantage of its sparsity. Application to the dynamics of a population of organic atmospheric aerosol particles is given to illustrate the evolution of particles of different sizes. To cite this article: A. Caboussat, A. Leonard, C. R. Acad. Sci. Paris, Ser. I 346 (2008).     

On the holomorphic solutions of Hamiltonian equations of motion of point charges

The Maxwell–Lorenz system of electromagnetic fields interacting with charged particles (point charges) is studied in the Darwin approximation in which the Lagrangian and Hamiltonian of the particles are not coupled with the field. The solution of the equation of motion of particles with approximate Darwin Hamiltonian is found in a finite time interval by using the Cauchy theorem. The components of this solution are represented as holomorphic functions of time.     

Blow-up criteria for the three dimensional nonlinear dissipative system modeling electro-hydrodynamics

In this paper, we investigate some sufficient conditions for the breakdown of local smooth solutions to the three dimensional nonlinear nonlocal dissipative system modeling electro-hydrodynamics. This model is a strongly coupled system by the well-known incompressible Navier–Stokes equations and the classical Poisson–Nernst–Planck equations. We show that the maximum of the vorticity field alone controls the breakdown of smooth solutions, which reveals that the velocity field plays a more dominant role than the density functions of charged particles in the blow-up theory of the system. Moreover, some Prodi–Serrin type blow-up criteria are also established.     

A self-consistent field method applied to the dynamics of viscous suspensions

A method for the approximate solution of the problem of many bodies of spherical form in a viscous fluid is developed in the Stokes approximation. Using a purely hydrodynamic approach, based on the use of the concept of a self-consistent field, the classical boundary value problem is reduced to a formal procedure for solving a linear system of algebraic equations in the tensor coefficients, which occur in the solution obtained for the velocity field and pressure of the liquid. A procedure for the approximate solution of this system of equations is constructed for the case of dilute suspensions, when the ratio of the size of the dispersed particles to the characteristic distance between them is a small parameter. Finally, the initial boundary value problem is reduced to solving a recurrent system of equations, in which each subsequent approximation for all the required quantities depends solely on the previous approximations. The system of recurrent equations obtained can be solved analytically in any specified approximation with respect to a small parameter. It is shown that this system of equations contains in itself all possible physical formulations of the problems, and, within the frameworks of the mathematical procedure constructed, they are distinguished solely by a set of specified and required functions. The practical possibilities of the method are in no way limited by the number of dispersed particles in the fluid.     

The Wigner semi-circle law and eigenvalues of matrix-valued diffusions

Summary A system of stochastic differential equations for the eigenvalues of a symmetric matrix whose components are independent Ornstein-Uhlenbeck processes is derived. This corresponds to a diffusion model of an interacting particles system with linear drift towards the origin and electrostatic inter-particle repulsion. The associated empirical distribution of particles is shown to converge weakly (as the number of particles tends to infinity) to a limiting measure-valued process which may be characterized as the weak solution of a deterministic ODE. The Wigner semi-circle density is found to be one of the equilibrium points of this limiting equation.     

Permittivity and one-particle distribution functions in the thermodynamics of a coulomb system

Using the grand canonical distribution and the virial theorem, we show that the Gibbs thermodynamic potential of a nonrelativistic system of charged particles is uniquely determined by its permittivity and the distribution functions of electrons and nuclei without using perturbation theory. This means that consistent approximations for the permittivity and one-particle distribution functions of electrons and nuclei must be used to calculate thermodynamic functions of the Coulomb system. To construct such selfconsistent approximations, we propose using a decoupling procedure based on separating the “connected” and “regular” parts of the temperature Green’s functions in the equations of motion. We consider the self-consistent Hartree-Fock approximation corresponding to this procedure.     

Multidimensional high-field limit of the electrostatic Vlasov-Poisson-Fokker-Planck system

In this paper, the high-field limit of the Vlasov-Poisson-Fokker-Planck system for charged particles is rigorously derived. The first result is obtained in any space dimension by using modulated energy techniques. It requires the smoothness of the solutions of the limit problem. In dimension 2, it is possible to handle more general data by using methods developed for a diagonal defect measures theory. The convergence of the concentration of particles is obtained in the space of bounded measures. In both cases, the limit of the sequence of densities of distribution functions is shown to solve a nonlinear system of partial differential equations which is related to Ohm's law.     

Analyticity for Some Operator Functions from Statistical Quantum Mechanics

For rather general thermodynamic equilibrium distribution functions the density of a statistical ensemble of quantum mechanical particles depends analytically on the potential in the Schr?dinger operator describing the quantum system. A key to the proof is that the resolvent to a power less than one of an elliptic operator with non-smooth coefficients, and mixed Dirichlet/Neumann boundary conditions on a bounded up to three-dimensional Lipschitz domain boundedly maps the space of square integrable functions to the space of essentially bounded functions. Dedicated to Günter Albinus Submitted: November 21, 2008. Accepted: March 31, 2009.     

Stochastic Dynamics and Hierarchy for the Boltzmann Equation with Arbitrary Differential Scattering Cross Section

The stochastic dynamics for point particles that corresponds to the Boltzmann equation with arbitrary differential scattering cross section is constructed. We derive the stochastic Boltzmann hierarchy the solutions of which outside the hyperplanes of lower dimension where the point particles interact are equal to the product of one-particle correlation functions, provided that the initial correlation functions are products of one-particle correlation functions. A one-particle correlation function satisfies the Boltzmann equation. The Kac dynamics in the momentum space is obtained.__________Published in Ukrains’kyi Matematychnyi Zhurnal, Vol. 56, No. 12, pp. 1629–1653, December, 2004.     

Lagrangian coherent structures,transport and chaotic mixing in simple kinematic ocean models

Methods of dynamical system’s theory are used for numerical study of transport and mixing of passive particles (water masses, temperature, salinity, pollutants, etc.) in simple kinematic ocean models composed with the main Eulerian coherent structures in a randomly fluctuating ocean—a jet-like current and an eddy. Advection of passive tracers in a periodically-driven flow consisting of a background stream and an eddy (the model inspired by the phenomenon of topographic eddies over mountains in the ocean and atmosphere) is analyzed as an example of chaotic particle’s scattering and transport. A numerical analysis reveals a non-attracting chaotic invariant set Λ that determines scattering and trapping of particles from the incoming flow. It is shown that both the trapping time for particles in the mixing region and the number of times their trajectories wind around the vortex have hierarchical fractal structure as functions of the initial particle’s coordinates. Scattering functions are singular on a Cantor set of initial conditions, and this property should manifest itself by strong fluctuations of quantities measured in experiments. The Lagrangian structures in our numerical experiments are shown to be similar to those found in a recent laboratory dye experiment at Woods Hole. Transport and mixing of passive particles is studied in the kinematic model inspired by the interaction of a current (like the Gulf Stream or the Kuroshio) with an eddy in a noisy environment. We demonstrate a non-trivial phenomenon of noise-induced clustering of passive particles and propose a method to find such clusters in numerical experiments. These clusters are patches of advected particles which can move together in a random velocity field for comparatively long time. The clusters appear due to existence of regions of stability in the phase space which is the physical space in the advection problem.     

Point interactions in the problem of three quantum particles with internal structure

A system of three quantum particles with internal structure in which the two-body interactions are point interactions and are described in terms of two-channel Hamiltonians is considered. It is established that in the cases when the parameters of the model are such that the total Hamiltonian of the three-particle system is semibounded the Faddeev equations are Fredholm equations. Boundary conditions are formulated for the differential Faddeev equations whose solutions are the scattering wave functions.Joint Institute for Nuclear Research, Dubna. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 102, No. 2, pp. 258–282, February, 1995.     

Quasicontinuous approximation in classical statistical mechanics

Within the framework of classical statistical mechanics, we consider infinite continuous systems of point particles with strong superstable interaction. A family of approximate correlation functions is defined to take into account solely the configurations of particles in the space \mathbb R^d {{\mathbb R}^d} that contain at most one particle in each cube of a given partition of the space \mathbb R^d {{\mathbb R}^d} into disjoint hypercubes of volume a ^d : It is shown that the approximations of correlation functions thus defined are pointwise convergent to the exact correlation functions of the system if the parameter of approximation a approaches zero for any positive values of the inverse temperature β and fugacity z: This result is obtained both for two-body interaction potentials and for many-body interaction potentials.     

A Formal Extension of the Pad? Table to Include Two Point Pad? Quotients

A new system of rational functions, obtained from the convergentsof continued fractions which correspond to two power seriessimultaneously, is introduced. This system is shown to includethe well known Pad? quotients for each of the two series individually.In addition it contains rational functions which, when informationabout a function at two points is known in the form of finiteor infinite power series expansions, can provide interpolatingrational approximations to the function.     

广义数及其应用(Ⅰ)

本文在文献[2]的基础上引进广义数系统,定义了以广义数为基础的广义函数(本质不同于L.Schwartz的分布),研究了勒贝格积分的推广,将这理论应用于分布,便得到对σ函数等的自然理解,对广义数应用于量子场论中,也作了一些尝试性的工作。