Two-component Bose-Einstein condensates

Recently, coupled systems of nonlinear Schrödinger equations have been used extensively to describe Bose-Einstein condensates. In this paper, we study the structure of vortices of the coupled nonlinear equations for two-component Bose-Einstein condensates (BEC) in a three-dimensional space. We show that vortices is 1-rectifiable set, and give its mean curvature. In particular, we show that large interspecies scattering length causes vortices for two-component BEC.     

The self-similar expanding curve for the curvature flow equation

We study a two-point free boundary problem for the curvature flow equation. By studying the corresponding nonlinear initial value problem, we obtain the existence and uniqueness of the forward self-similar solution of this problem. The corresponding curve is called the self-similar expanding curve. We also derive the asymptotic stability of this curve.

     

Subcritical nonlinear heat equation

We study asymptotic behavior in time of small solutions to nonlinear heat equations in subcritical case. We find a new family of self-similar solutions which change a sign. We show that solutions are stable in the neighborhood of these self-similar solutions.     

Stable self-similar blowup in the supercritical heat flow of harmonic maps

We consider the heat flow of corotational harmonic maps from \(\mathbb {R}^3\) to the three-sphere and prove the nonlinear asymptotic stability of a particular self-similar shrinker that is not known in closed form. Our method provides a novel, systematic, robust, and constructive approach to the stability analysis of self-similar blowup in parabolic evolution equations. In particular, we completely avoid using delicate Lyapunov functionals, monotonicity formulas, indirect arguments, or fragile parabolic structure like the maximum principle. As a matter of fact, our approach reduces the nonlinear stability analysis of self-similar shrinkers to the spectral analysis of the associated self-adjoint linearized operators.     

Self-Similar Parabolic Optical Solitary Waves

We study solutions of the nonlinear Schrödinger equation (NLSE) with gain, describing optical pulse propagation in an amplifying medium. We construct a semiclassical self-similar solution with a parabolic temporal variation that corresponds to the energy-containing core of the asymptotically propagating pulse in the amplifying medium. We match the self-similar core through Painlevé functions to the solution of the linearized equation that corresponds to the low-amplitude tails of the pulse. The analytic solution accurately reproduces the numerically calculated solution of the NLSE.     

Asymptotic behavior of nonlinear waves in elastic media with dispersion and dissipation

In the case of nonlinear elastic quasitransverse waves in composite media described by nonlinear hyperbolic equations, we study the nonuniqueness problem for solutions of a standard self-similar problem such as the problem of the decay of an arbitrary discontinuity. The system of equations is supplemented with terms describing dissipation and dispersion whose influence is manifested in small-scale processes. We construct solutions numerically and consider self-similar asymptotic approximations of the obtained solution of the equations with the initial data in the form of a “spreading” discontinuity for large times. We find the regularities for realizing various self-similar asymptotic approximations depending on the choice of the initial conditions including the dependence on the form of the functions determining the small-scale smoothing of the original discontinuity. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 147, No. 2, pp. 240–256, May, 2006.     

Two-Dimensional and Three-Dimensional Thermal Structures in a Medium with Nonlinear Thermal Conductivity

The article considers self-similar solutions of the nonlinear heat equation with a three-dimensional source that evolve in a blow-up setting. The self-similar problem is a boundary-value problem for a nonlinear equation of elliptical type that has a nonunique solution. We investigate the eigenfunction spectrum of the self-similar problem in two- and three-dimensional space. The problem is solved on a grid by Newton’s iteration method. The implementation of Newton’s method requires analysis of a linearized equation and construction of initial approximations. The eigenfunctions are continued in a parameter. Structures of various symmetry are obtained. New types of multidimensional structures are observed: these are multiply connected three-dimensional heat localization regions.__________Translated from Prikladnaya Matematika i Informatika, No. 17, pp. 84–111, 2004.     

A Counterexample to C 2,1 Regularity for Parabolic Fully Nonlinear Equations

We address the self-similar solvability of a singular parabolic problem and show that solutions to parabolic fully nonlinear equations are not expected to be C ^2,1.     

非线性发展方程的自相似解

本文着力于给出非线性发展方程的自相似解的一些最新的研究进展．借助于调和分析的方法(特别是利用Littlewood-Paley理论、时空估计等)，通过非线性发展方程的Cauchy问题的研究来获得自相似解．主要技术是将初始状态空间X推广到非自反的Banach空间(使得X包含那些具自相似结构的初始函数)，相应地将适定性中解在t=0处的连续性放宽成弱连续．另一方面，用Scaling的方法来分析时空可积空间的形式、非线性增长与空间X的选取等．这对非线性发展方程Cauchy问题的研究是至关重要的，它本质上给出了研究非线性发展方程Cauchy问题的工作空间．进而，对于自相似解的结构、自相似解作用(可以是某些整体解的大尺度极限)亦给出了一些具体的分析．     

带梯度吸收项的快扩散方程的自相似奇性解

研究一类带有非线性梯度吸收项的快速扩散方程的自相似奇性解．通过自相似变换,该自相似奇性解满足一个非线性常微分方程的边值问题,再利用打靶法技巧研究该常微分方程初值问题解的存在唯一性并根据初值的取值范围对其解进行了分类．通过对这些解类的性质的分析研究,得出了自相似强奇性解存在唯一性的充分必要条件,此时自相似奇性解就是强奇性解．     

Radial equivalence for the two basic nonlinear degenerate diffusion equations

In this paper we prove that there exists an explicit correspondence between the radially symmetric solutions of two well-known models of nonlinear diffusion, the porous medium equation and the p-Laplacian equation. We establish exact correspondence formulas between these solutions. We also study in detail the application of the results in the important case of self-similar solutions. In particular, we derive the existence of new self-similar solutions for the evolution p-Laplacian equation.     

Coupled nonlinear Schrödinger systems with potentials

Coupled nonlinear Schrödinger systems describe some physical phenomena such as the propagation in birefringent optical fibers, Kerr-like photorefractive media in optics and Bose-Einstein condensates. In this paper, we study the existence of concentrating solutions of a singularly perturbed coupled nonlinear Schrödinger system, in presence of potentials. We show how the location of the concentration points depends strictly on the potentials.     

An estimate of the Hausdorff dimension of a weak self-similar set

We propose an estimate to quantitatively evaluate the Hausdorff dimension of a self-similar set based on a system of weak contractions each of whose contraction coefficient is not a constant but a function of a parameter. Using the estimate, we investigate the topological structures specific to this weak self-similar set.     

具有多重非线性的非牛顿多方渗流方程的整体存在性与非存在性

考虑了一个具有多重非线性的抛物模型中,非线性扩散项、非线性反应项和非线性边界流三种非线性机制之间的相互作用.通过构造自相似上解和自相似下解,获得了临界整体存在性曲线和临界Fujita曲线.     

Rotating Two-Component Bose-Einstein Condensates

Recently, coupled systems of nonlinear Schr?dinger equations have been used extensively to describe Bose-Einstein condensates. In this paper, we study the structure of vortices for rotating two-component Bose-Einstein condensates (BEC) in a three-dimensional domain. We show that vortices is 1-rectifiable set, and give its mean curvature in the strong coupling (Thomas-Fermi) limit. In particular, we study effect of rotating term acting on the vortices.     

Solitary Waves for Linearly Coupled Nonlinear Schrödinger Equations with Inhomogeneous Coefficients

Motivated by the study of matter waves in Bose–Einstein condensates and coupled nonlinear optical systems, we study a system of two coupled nonlinear Schrödinger equations with inhomogeneous parameters, including a linear coupling. For that system, we prove the existence of two different kinds of homoclinic solutions to the origin describing solitary waves of physical relevance. We use a Krasnoselskii fixed point theorem together with a suitable compactness criterion.     

Global smooth solution to a coupled Schrödinger system in atomic Bose-Einstein condensates with two-dimensional spaces

We obtain the global smooth solution of a nonlinear Schrödinger equations in atomic Bose-Einstein condensates with two-dimensional spaces. By using the Galerkin method and a priori estimates, we establish the global existence and uniqueness of the smooth solution.     

Asymptotically self-similar global solutions of a general semilinear heat equation

We consider the general nonlinear heat equation on where and g satisfies certain growth conditions. We prove the existence of global solutions for small initial data with respect to a norm which is related to the structure of the equation. We also prove that some of those global solutions are asymptotic for large time to self-similar solutions of the single power nonlinear heat equation, i.e. with Received: 23 July 1999 / Accepted: 14 December 2000 / Published online: 23 July 2001     

Special two-soliton solution of the generalized Sine–Gordon equation with a variable coefficient

A new special two-soliton solution to the generalized Sine–Gordon equation with a variable coefficient is constructed analytically, by using the self-similar method and Hirota bilinear method. To construct this special solution, we do not utilize the pairs of one-soliton solutions, as is customarily done when solving the Sine–Gordon equation, but introduce two auxiliary self-similar variables in Hirota’s procedure. We also study features of this solution by choosing different self-similar variables. The results obtained confirm that the behavior of such Sine–Gordon solitons can be easily controlled by the selection of the self-similar variables.     

Orbital stability of bound states of nonlinear Schrödinger equations with linear and nonlinear optical lattices

We study the orbital stability and instability of single-spike bound states of semi-classical nonlinear Schrödinger (NLS) equations with critical exponent, linear and nonlinear optical lattices (OLs). These equations may model two-dimensional Bose-Einstein condensates in linear and nonlinear OLs. When linear OLs are switched off, we derive the asymptotic expansion formulas and obtain necessary conditions for the orbital stability and instability of single-spike bound states, respectively. When linear OLs are turned on, we consider three different conditions of linear and nonlinear OLs to develop mathematical theorems which are most general on the orbital stability problem.