一个耦合双曲-抛物系统的全局光滑解

考虑一个源自生物学的耦合双曲-抛物模型的初边值问题.当动能函数为非线性函数以及初始值具有小的L~2能量但其H~2能量可能任意大时,得到了初边值问题光滑解的全局存在性和指数稳定性.而且,如果假定非线性动能函数满足一定的条件,在对初值没任何小条件假定下得到光滑解的全局存在性.通过构造一个新的非负凸熵和做精细的能量估计得到了结果的证明.     

双曲空间上的Landau-Lifshitz-Gilbert方程解的全局存在性与自相似爆破解

应用Hasimoto变换,给出了双曲空间H~2上的Landau-Lifshitz-Gilbert(LLG)方程的一等价系统.基于该等价模型,证明了在小初值条件下LLG方程解的全局存在性.到目前为止,还未见到有文章在双曲空间下给出带阻尼项方程的精确解.基于导出的等价方程,首次构造了一显式小初值的整体解.另外,也给出了等价系统的自相似有限时间爆破解.在作者发表的论文[25]中,构造了在H~2上没有吉尔伯特阻尼项方程的有限时间爆破解.带阻尼项的LLG方程的有限能量解能否在H~2上演化出有限时间爆破或全局光滑这一问题尚不清楚.该文给出的自相似有限时间爆破解是在整个空间区域上的有限能量解.该例子给出了这个问题的一个回答.     

三维Brinkman-Forchheimer方程强解的全局吸引子的存在性

研究了三维有界区域上Brinkman-Forchheimer方程■-γ△u+au+b|u|u+c|u|~βu+▽p=f强解的存在唯一性及强解的全局吸引子的存在性.首先证明了当5/2≤β≤4及初始值u_0∈H_0~1(Ω)时强解的存在唯一性.接着对强解进行了一系列一致估计,基于这些一致估计,借助半群理论证明了方程的强解分别在H_1~1(Ω)和H~2(Ω)空间中具有全局吸引子,并证明了H_0~1(Ω)中的全局吸引子实际上便是H~2(Ω)中的全局吸引子.     

基于一个新的NCP函数的光滑牛顿法求解非线性互补问题

本文研究了非线性互补的光滑化问题.利用一个新的光滑NCP函数将非线性互补问题转化为等价的光滑方程组,并在此基础上建立了求解P0-函数非线性互补问题的一个完全光滑化牛顿法,获得了算法的全局收敛性和局部二次收敛性的结果.并给出数值实验验证了理论分析的正确性.     

带有线性记忆的波方程在R~n上的时间依赖吸引子

本文基于Conti M,Di Plinio F等人提出的关于时间依赖全局吸引子的概念,研究了无界域上带有线性记忆的波方程解的长时间行为.利用尾部估计和压缩函数的方法证明了过程的渐近紧性,进而获得了H~1(R~n)×L~2(R~n)×L_u~2(R~+;H~1(R~n))上时间依赖吸引子的存在性.     

解约束优化的分段线性有理NCP函数

本文给出新的NCP函数,这些函数是分段线性有理正则伪光滑的,且具有良好的性质.把这些NCP函数应用到解非线性优化问题的方法中.例如,把求解非线性约束优化问题的KKT点问题分别用QP-free方法,乘子法转化为解半光滑方程组或无约束优化问题.然后再考虑用非精确牛顿法或者拟牛顿法来解决该半光滑方程组或无约束优化问题.这个方法是可实现的,且具有全局收敛性.可以证明在一定假设条件下,该算法具有局部超线性收敛性.     

箱式约束变分不等式的一类新光滑gap函数

针对箱式约束变分不等式问题,利用一类积分型全局最优性条件,提出了一个新光滑gap函数.该光滑gap函数形式简单且具有较好的性质.利用该gap函数,箱式约束变分不等式可转化为等价光滑优化问题进行求解.进一步地,讨论了可保证等价光滑优化问题的任意聚点为箱式约束变分不等式问题解的条件.以一个简单的摩擦接触问题为例阐释了该方法的应用.最后,利用标准的变分不等式考题验证了方法的有效性.     

3-分片线性NCP函数的滤子QP-free算法

本文定义一个3-分片线性的NCP函数,并对非线性约束优化问题,提出了带有这分片NCP函数的QP-free非可行域算法.根据优化问题的一阶KKT条件,利用乘子和NCP函数,得到非光滑方程,本文给出一个非光滑方程的迭代算法.这算法包含原始-对偶变量,在局部意义下,可看成关于一阶KKT最优条件的的扰动拟牛顿迭代算法.在线性搜索时,这算法采用滤子方法.本文给出的算法是可实现的并具有全局收敛性,且在适当假设下具有超线性收敛性.     

半离散Schr?dinger-BBM型方程的全局吸引子

主要研究用Crank-Nicolson格式对时间t半离散化的Schr?dinger-BBM方程组的长时间行为,证明了该半离散化方程全局吸引子的正则性.首先证明半离散方程在H~1×H~1空间上生成一个离散无穷维动力系统,并且在H(3/2-ε)×H~2拥有一个全局吸引子A_τ;然后证明该全局吸引子A_τ是正则的,即A_τH~(3/2-ε)×H~2是有界的并且是紧的.     

不等式约束优化问题的低阶精确罚函数的光滑化算法

对不等式约束优化问题提出了一个低阶精确罚函数的光滑化算法. 首先给出了光滑罚问题、非光滑罚问题及原问题的目标函数值之间的误差估计,进而在弱的假
设之下证明了光滑罚问题的全局最优解是原问题的近似全局最优解. 最后给出了一个基于光滑罚函数的求解原问题的算法,证明了算法的收敛性,并给出数值算例说明算法的可行性.     

Global well‐posedness of classical solutions with large oscillations and vacuum to the three‐dimensional isentropic compressible Navier‐Stokes equations

We establish the global existence and uniqueness of classical solutions to the Cauchy problem for the isentropic compressible Navier‐Stokes equations in three spatial dimensions with smooth initial data that are of small energy but possibly large oscillations with constant state as far field, which could be either vacuum or nonvacuum. The initial density is allowed to vanish, and the spatial measure of the set of vacuum can be arbitrarily large; in particular, the initial density can even have compact support. These results generalize previous results on classical solutions for initial densities being strictly away from vacuum and are the first for global classical solutions that may have large oscillations and can contain vacuum states. © 2012 Wiley Periodicals, Inc.     

Global analysis of smooth solutions to a hyperbolic-parabolic coupled system

We investigate a model arising from biology, which is a hyperbolic- parabolic coupled system. First, we prove the global existence and asymptotic behavior of smooth solutions to the Cauchy problem without any smallness assumption on the initial data. Second, if the Hs ∩ Ll-norm of initial data is sufficiently small, we also establish decay rates of the global smooth solutions. In particular, the optimal L2 decay rate of the solution and the almost optimal L2 decay rate of the first-order derivatives of the solution are obtained. These results are obtained by constructing a new nonnegative convex entropy and combining spectral analysis with energy methods.     

GLOBAL EXISTENCE AND CONVERGENCE RATES OF SMOOTH SOLUTIONS FOR THE 3-D COMPRESSIBLE MAGNETOHYDRODYNAMIC EQUATIONS WITHOUT HEAT CONDUCTIVITY

In this paper, we are concerned with the global existence and convergence rates of the smooth solutions for the compressible magnetohydrodynamic equations without heat conductivity, which is a hyperbolic-parabolic system. The global solutions are obtained by combining the local existence and a priori estimates if H3-norm of the initial perturbation around a constant states is small enough and its L1-norm is bounded. A priori decay-in-time estimates on the pressure, velocity and magnetic field are used to get the uniform bound of entropy. Moreover, the optimal convergence rates are also obtained.     

EXISTENCE OF GLOBAL SMOOTH SOLUTION TO INITIAL BOUNDARY VALUE PROBLEM FOR A VISCOELASTIC MODEL WITH RELAXATION

This paper is concerned with the initial boundary value problem for a vis-coelastic model with relaxation. Under the only assumption that the C^0-norm of theinitial data is small, without smallness hypothesis for the C^1-norm, the existence of theglobal smooth solution to the corresponding initial boundary value problem is proved.The analysis is based on some a priori estimates obtained by the “maximum principle” offirst-order quasilinear hyperbolic system.     

Global Existence and Convergence Rates of Smooth Solutions for the 3-D Compressible Magnetohydrodynamic Equations Without Heat Conductivity

In this paper, we are concerned with the global existence and convergence rates of the smooth solutions for the compressible magnetohydrodynamic equations without heat conductivity, which is a hyperbolic-parabolic system. The global solutions are obtained by combining the local existence and a priori estimates if H³-norm of the initial perturbation around a constant states is small enough and its L¹-norm is bounded. A priori decay-in-time estimates on the pressure, velocity and magnetic field are used to get the uniform bound of entropy. Moreover, the optimal convergence rates are also obtained.     

Global Smooth Solutions to the 2-D Inhomogeneous Navier-Stokes Equations with Variable Viscosity

Under the assumptions that the initial density ρ0 is close enough to 1 and ρ0 -- 1∈ H^s＋1（R^2）, u0 ∈ H^s（R^2） ∩ H^-ε（R^2） for s 〉 2 and 0 〈 ε 〈 1, the authors prove the global existence and uniqueness of smooth solutions to the 2-D inhomogeneous Navier-Stokes equations with the viscous coefficient depending on the density of the fluid. Furthermore, the L^2 decay rate of the velocity field is obtained.     

Self-similar solutions for active scalar equations in Fourier–Besov–Morrey spaces

We are concerned with a family of dissipative active scalar equation with velocity fields coupled via multiplier operators that can be of positive-order. We consider sub-critical values for the fractional diffusion and prove global well-posedness of solutions with small initial data belonging to a framework based on Fourier transform, namely Fourier–Besov–Morrey spaces. Since the smallness condition is with respect to the weak norm of this space, some initial data with large \(L^{2}\) -norm can be considered. Self-similar solutions are obtained depending on the homogeneity of the initial data and couplings. Also, we show that solutions are asymptotically self-similar at infinity. Our results can be applied in a unified way for a number of active scalar PDEs like 1D models on dislocation dynamics in crystals, Burgers’ equation, 2D vorticity equation, 2D generalized SQG, 3D magneto-geostrophic equations, among others.     

Global existence and convergence rates of smooth solutions for the compressible magnetohydrodynamic equations

In this paper, we are concerned with the global existence and convergence rates of the smooth solutions for the compressible magnetohydrodynamic equations in R³. We prove the global existence of the smooth solutions by the standard energy method under the condition that the initial data are close to the constant equilibrium state in H³-framework. Moreover, if additionally the initial data belong to L^p with , the optimal convergence rates of the solutions in L^q-norm with 2≤q≤6 and its spatial derivatives in L²-norm are obtained.     

Mathematical aspects of the Maxwell problem

We study the large-time behaviour of global smooth solutions to the Cauchy problem for hyperbolic regularization of conservation laws. An attracting manifold of special smooth global solutions is determined by the Chapman projection onto the phase space of consolidated variables. For small initial data we construct the Chapman projection and describe its properties in the case of the Cauchy problem for moment approximations of kinetic equations. The existence conditions for the Chapman projection are expressed in terms of the solvability of the Riccati matrix equations with parameter.