Source-type solution to nonlinear Fokker-Planck equation in one dimension

In this paper, we consider the following equation ut=(um)xx+(un)x, with the initial condition as Dirac measure. Attention is focused on existence, nonexistence, uniqueness and the asymptotic behavior near (0,0) of solution to the Cauchy’s problem. The special feature of this equation lies in nonlinear convection effect, i.e., the equation possesses nonlinear hyperbolic character as well as degenerate parabolic one. The situation leads to a more sophisticated mathematical analysis. To our knowledge, the solvability of singular solution to the equation has not been concluded yet. Here based on the previous works by the authors, we show that there exists a critical number n0=m+2 such that a unique source-type solution to this equation exists if 0≤n相似文献   

A differential equation approach to nonlinear programming

A new method is presented for finding a local optimum of the equality constrained nonlinear programming problem. A nonlinear autonomous system is introduced as the base of the theory instead of usual approaches. The relation between critical points and local optima of the original optimization problem is proved. Asymptotic stability of the critical points is also proved. A numerical algorithm which is capable of finding local optima systematically at the quadratic rate of convergence is developed from a detailed analysis of the nature of trajectories and critical points. Some numerical results are given to show the efficiency of the method.     

A semismooth equation approach to the solution of nonlinear complementarity problems

In this paper we present a new algorithm for the solution of nonlinear complementarity problems. The algorithm is based on a semismooth equation reformulation of the complementarity problem. We exploit the recent extension of Newton's method to semismooth systems of equations and the fact that the natural merit function associated to the equation reformulation is continuously differentiable to develop an algorithm whose global and quadratic convergence properties can be established under very mild assumptions. Other interesting features of the new algorithm are an extreme simplicity along with a low computational burden per iteration. We include numerical tests which show the viability of the approach.     

A lattice Boltzmann model for the Fokker-Planck equation

In this paper, a lattice Boltzmann model is presented for solving one and two-dimensional Fokker-Planck equations with variable coefficients. In particular, it is efficient to simulate one-dimensional stochastic processes governed by the Fokker-Planck equation. Numerical results agree well with the exact solutions, which indicates that the proposed model is suitable for solving the Fokker-Planck equation.     

A nonlinear approach to absorbing boundary conditions for the semilinear wave equation

We construct a family of absorbing boundary conditions for the semilinear wave equation. Our principal tool is the paradifferential calculus which enables us to deal with nonlinear terms. We show that the corresponding initial boundary value problems are well posed. We finally present numerical experiments illustrating the efficiency of the method.

     

A nonlinear multiple scales approach to modelling almost third harmonic interfaces

The evolution of third harmonic resonant narrow bandwidth capillary-gravity waves on an interface of two fluids is considered. The method of multiple scales is utilised in order to derive a set of first order coupled nonlinear partial differential equations which model the evolution of the wavepacket. Some solution families are exhibited.     

A new approach to solving the stationary Fokker-Planck-Kolmogorov equation for a randomly oscillating nonlinear system

It is shown that the Fokker-Planck-Kolmogorov equation in terms of amplitude and phase may, in the stationary case, be reduced to a first order partial differential equation which we call the stationary reduced Fokker-Planck-Kolmogorov. A method for approximate solution of the reduced equation is presented which does not need assumptions on the smallness of nonlinearity of a system and intensity of random influences.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 44, No. 8, pp. 1123–1129, August, 1992.     

Bifurcation approach to a logistic elliptic equation with a homogeneous incoming flux boundary condition

In this paper, we consider a semilinear elliptic boundary value problem in a smooth bounded domain, having the so-called logistic nonlinearity that originates from population dynamics, with a nonlinear boundary condition. Although the logistic nonlinearity has an absorption effect in the problem, the nonlinear boundary condition is induced by the homogeneous incoming flux on the boundary. The objective of our study is to analyze the existence of a bifurcation component of positive solutions from trivial solutions and its asymptotic behavior and stability. We perform this analysis using the method developed by Lyapunov and Schmidt, based on a scaling argument.     

A Semenov approach to the modelling of thermal runaway of damp combustible material

Semenov theory for the self-heating of a reactive slab is extendedto take account of the presence of water vapour. In this paper,mass changes due to evaporation/condensation are neglected butheat exchange is retained in the energy equation. By doing this,a simple easily solvable set of equations can be set up to representthe thermal behaviour of the slab. No account is taken of possiblewet exothermic reactions in this paper. The aim is simply tounderstand the effects of evaporation/condensation on the overallthermal history. Using a simple model which treats the masschanges within the material as negligible, the competitive effectsof condensation and evaporation are shown to produce a two-timesituation which depends crucially on the surface mass transfer/heattransfer ratio h_m. Either self-heating occurs at a lower ratethan that due to dry oxidation, or else a maximum temperatureis reached before a lower equilibrium steady-state temperatureis achieved. Thus, compared to the dry case, in general terms,evaporation certainly encourages stability. However, the finalstrictly subcritical steady state will not always be achieveddue to the competitive process between recondensation and evaporationloss at the surface at medium timescales. A set of quasi-steadystates is identified which yield plots of a more restrictivecritical value of temperature against the Frank-Kamenetskiiparameter (proportional to the thickness of the slab and itsreactivity). If the value of h_m is such that the maximum temperaturereaches this critical value, then thermal runaway can stilltake place even though the starting value of temperature wasstrictly below the true (damp) final steady-state critical value.     

A unique solution to a nonlinear elliptic equation

The purpose of this paper is to prove the existence of a unique, classical solution to the nonlinear elliptic partial differential equation −∇⋅(a(u(x))∇u(x))=f(x) under periodic boundary conditions, where u(x₀)=u₀ at x₀∈Ω, with Ω=TN, the N-dimensional torus, and N=2,3. The function a is assumed to be smooth, and a(u(x))>0 for , where G⊂R is a bounded interval. We prove that if the functions f and a satisfy certain conditions, then a unique classical solution u exists. The range of the solution u is a subset of a specified interval . Applications of this work include stationary heat/diffusion problems with a source/sink, where the value of the solution is known at a spatial location x₀.     

Convergence to equilibrium for linear spatially homogeneous Boltzmann equation with hard and soft potentials: A semigroup approach in L1‐spaces

We investigate the large time behavior of solutions to the spatially homogeneous linear Boltzmann equation from a semigroup viewpoint. Our analysis is performed in some (weighted) L¹‐spaces. We deal with both the cases of hard and soft potentials (with angular cut‐off). For hard potentials, we provide a new proof of the fact that, in weighted L¹‐spaces with exponential or algebraic weights, the solutions converge exponentially fast towards equilibrium. Our approach uses weak‐compactness arguments combined with recent results of the second author on positive semigroups in L¹‐spaces. For soft potentials, in L¹‐spaces, we exploit the convergence to ergodic projection for perturbed substochastic semigroup to show that, for very general initial datum, solutions to the linear Boltzmann equation converges to equilibrium in large time. Moreover, for a large class of initial data, we also prove that the convergence rate is at least algebraic. Notice that, for soft potentials, no exponential rate of convergence is expected because of the absence of spectral gap.     

A spline collocation approach for the numerical solution of a generalized nonlinear Klein-Gordon equation

In this paper, a finite element collocation approach using cubic B-splines is employed for the numerical solution of a generalized form of the nonlinear Klein-Gordon equation. The efficiency of the method is tested on a number of examples that represent special cases of the extended equation including the sine-Gordon equation. The numerical results are compared with existing numerical and analytic solutions and the outcomes confirm that the scheme yields accurate and reliable results even when few nodes are used at the time levels.     

Long-time behavior for a nonlinear plate equation with thermal memory

We consider a nonlinear plate equation with thermal memory effects due to non-Fourier heat flux laws. First we prove the existence and uniqueness of global solutions as well as the existence of a global attractor. Then we use a suitable ?ojasiewicz-Simon type inequality to show the convergence of global solutions to single steady states as time goes to infinity under the assumption that the nonlinear term f is real analytic. Moreover, we provide an estimate on the convergence rate.