不可压双曲型液晶的Ericksen-Leslie方程的大Ericksen数的极限的形式分析

该文考虑了参数化的液晶的不可压双曲型的Ericksen-Leslie方程.形式上,让参数消失该文证明了这个极限方程存在一个局部的经典解.更进一步,该文形式上得出一个关于这个参数化的液晶的双曲型方程和极限方程的解的误差估计,这对应的是关于它们的经典解在L2空间中的一个形式上的能量估计.     

颗粒与流体混合物模型解的一致估计

该文利用能量方法和一致的Gronwall不等式,研究了一个颗粒与流体混合物模型解关于时间的一致估计,这个关于时间的一致估计有助于我们进一步研究解的渐近行为.     

不带Gilbert项的Landau-Lifshitz方程的一些精确爆破解（英文）

本文构造了柱坐标下多维Landau-Lifshitz方程的一些爆破解.在这些解中,存在两个球面S~2上有限初始能量的爆破解.对于非均质的各向同性的Landau-Lifshitz方程,给定有限能量的光滑初始条件,解能否发展出有限能量球面上的爆破解还是不清楚的.文章中的例子说明这种情形的爆破是可以发生的.     

The Legendre Collocation Spectral Method for the Ground State Solutions of the Bose-Einstein Condensates北大核心CSCD

近年来,有关Bose-Einstein凝聚态基态解的实验研究已经取得了一系列重要的成果.该文在相关研究成果的基础上,首先通过降维和无量纲化方法将Bose-Einstein凝聚态基态解问题转换成能量泛函极值问题,在离散该泛函时,尝试使用Legendre配置谱方法离散该能量泛函的一维和二维情形.其次,对该能量泛函极小值问题进行了数值模拟.最后,通过分析实验数据结果和图像得出,针对非旋转的Bose-Einstein凝聚态的基态解问题可以使用Legendre配置谱方法来求解,且数值结果的误差较小.     

耦合非线性Schrodinger方程组的Neumann问题

该文考虑一类耦合椭圆型非线性Schrodinger方程组的Neumann问题极小能量解(基态解)的存在性和集中性质.主要研究极小能量解的尖点,即最大值点的位置.利用Lin Tai-Chia和Wei Juncheng研究Dirichlet问题的方法,该文首先得到了相应Neumann问题的极小能量解的存在性.当相当于Planck常数的小参数趋于零时,该文证明了极小能量解的尖点向定义区域的边界靠近,并且能量集中在这些尖点处.另外,方程组解的两个分支解相互吸引或排斥时,它们的尖点也相互吸引或排斥.     

耦合非线性Schrödinger方程组的Neumann问题

该文考虑一类耦合椭圆型非线性Schr\"{o}dinger方程组的Neumann问题极小能量解（基态解）的存在性和集中性质. 主要研究极小能量解的尖点, 即最大值点的位置. 利用 Lin Tai-Chia 和 Wei Juncheng 研究 Dirichlet 问题的方法, 该文首先得到了相应Neumann问题的极小能量解的存在性. 当相当于Planck常数的小参数趋于零时, 该文证明了极小能量解的尖点向定义区域的边界靠近, 并且能量集中在这些尖点处. 另外, 方程组解的两个分支解相互吸引或排斥时, 它们的尖点也相互吸引或排斥.     

磁流体方程组弱解在负指标Besov空间中基于旋度和电流的正则性标准

本文研究了不可压磁流体方程组弱解的正则性准则,设(u(t,x),6(t,x))是不可压磁流体方程组在(O,T)上的光滑解,如果旋度和电流密度满足(▽× u,▽× b) ∈ L 2-a/2 (O, T;B-aa∞, ∞(R3)) ηL1-a/2(O,T;B-∞1,-a∞(R3)),0＜α＜1,则光滑解(u(t,x),b(t,x))可以连续延拓到(O,T'),T'＞T.而且这个条件可以保证满足能量不等式的弱解是(O,T)上的光滑解.     

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.     

带有强阻尼项的拟线性抛物方程整体解的存在性与指数增长

本文研究拟线性项与源项的竞争对具有强阻尼项的拟线性抛物方程解的影响.利用Galerkin方法给出局部解的存在性,结合势井方法和修改的能量泛函,在不同条件下证明整体解的存在性,并估计整体解的能量衰减.最后在初始能量为负或初始能量有一临界的正的下界,且时间t趋于无穷时,解的Lp范数将以指数形式增长.     

三阶Airy方程满足两个守恒律的非线性差分格式

近年来,学者们对发展型偏微分方程设计了一种能保持多个守恒律的数值方法,这类方法无论在解的精度还是长时间的数值模拟方面都表现出非常好的性质.将这类思想应用到三阶Airy方程,即三阶散射方程,对其设计了满足两个守恒律的非线性差分格式.该格式不仅计算数值解,同时计算数值能量,并且保证数值解和数值能量同时守恒.从数值结果可以看出,该格式在长时间的数值模拟中具有更好的保结构性质.     

Solutions of the Boltzmann equation with infinite energy: Existence, stability and long time behavior

This paper is devoted to studying a class of solutions to the nonlinear Boltzmann equation having infinite kinetic energy, these solutions have an upper Maxwellian bound with infinite kinetic energy. Firstly, the existence and stability of this kind of solutions are established near vacuum. Secondly, it is proved that this kind of solutions are stable for any initial data, as a consequence, the Boltzmann equation has at most one solution with infinite kinetic energy. Finally, the long time behavior of the solutions is also established.     

Energy identity of the heat flow of H-systems at finite singular time

It is well known that there exists a global solution to the heat flow of H-systems.If the solution satisfies a certain energy inequality,it is global regular with at most finitely many singularities. Under the same energy inequality,we can show the energy identity of the heat flow of H-systems at finite singular time.The most interesting thing in our proof is that we find the singular points can only occur in the interior of the set in some sense.     

Evolution by Non-Convex Functionals

We establish a semi-group solution concept for flows that are generated by generalized minimizers of non-convex energy functionals. We use relaxation and convexification to define these generalized minimizers. The main part of this work consists in exemplary validation of the solution concept for a non-convex energy functional. For rotationally invariant initial data it is compared with the solution of the mean curvature flow equation. The basic example relates the mean curvature flow equation with a sequence of iterative minimizers of a family of non-convex energy functionals. Together with the numerical evidence this corroborates the claim that the non-convex semi-group solution concept defines, in general, a solution of the mean curvature equation.     

On the acceleration of shock waves and concentration of energy

By a series of simple examples related to exact solutions of problems in gas dynamics and magnetohydrodynamics, possible mechanisms of acceleration of shock waves and concentration of energy are elucidated. The acceleration of a shock wave is investigated in the problem of motion of a plane piston at a constant velocity in the case when the initial density of the medium drops in the presence of constant counterpressure. It is shown that in this situation a “blow-up” regime is induced by a shock wave going to infinity in finite time even for limited work of the piston. A simple spherically symmetric solution with a converging shock wave is constructed and shown to lead to the concentration of energy. A general method for solving one-dimensional non-self-similar problems related to matching the equilibrium state to a motion with homogeneous deformation on a shock wave is discussed; this method leads to a solution in quadratures.     

Weak solution of incompressible Euler equations with decreasing energy

Weak solution of incompressible Euler equations are L²-vector fields, satisfying integral relations, which express the mass and momentum balance. They are believed to describe the turbulent fluid motion at high Reynolds numbers. We justify this conjecture by constructing a weak solution with decreasing kinetic energy. The construction is based on Generalized Flows, introduced by Y. Brenier.     

Optimal time decay of the Boltzmann equation with frictional force

In this paper, we use the combination of energy method and Fourier analysis to obtain the optimal time decay of the Boltzmann equation with frictional force towards equilibrium. Precisely speaking, we decompose the equation into macroscopic and microscopic partitions and perform the energy estimation. Then, we construct a special solution operator to a linearized equation without source term and use Fourier analysis to obtain the optimal decay rate to this solution operator. Finally, combining the decay rate with the energy estimation for nonlinear terms, the optimal decay rate to the Boltzmann equation with frictional force is established.     

Nonradial positive solutions of the ‐Laplace Emden–Fowler equation with sign‐changing weight

In this paper we study the p‐Laplace Emden–Fowler equation with a radial and sign‐changing weight in the unit ball under the Dirichlet boundary condition. We show that if the weight function is negative in the unit ball except for a small neighborhood of the boundary and positive at somewhere in this neighborhood, then no least energy solution is radially symmetric. Therefore the equation has both a positive radial solution and a positive nonradial solution. Moreover, we prove in the one dimensional case that if the neighborhood is large, then a positive solution is unique.     

Global existence and nonexistence of generalized coupled reaction‐diffusion systems

In this paper, we consider the initial boundary value problem for a class of reaction‐diffusion systems with generalized coupled source terms. The assumption on the coupled source terms refers to the single equations and includes many kinds of polynomial growth cases. Under this assumption, the reaction‐diffusion systems have a variational structure, which is the foundation of constructing the potential wells to classify the initial data. In subcritical energy level and critical energy level, which are divided from potential well theory, the global existence solution, blow‐up in finite time solution, and asymptotic behavior of solution are obtained, respectively. Furthermore, we show the sufficient conditions of global well posedness with supercritical energy level by combining with comparison principle and semigroup theory.     

On the continuity of the time derivative of the solution to the parabolic obstacle problem with variable coefficients

This paper is devoted to continuity results of the time derivative of the solution to the one-dimensional parabolic obstacle problem with variable coefficients. Under regularity assumptions on the obstacle and on the coefficients, we prove that the time derivative of the solution is continuous for almost every time. When the solution is nondecreasing in time this result holds for every time. We also give an energy criterion which characterizes the continuity of the time derivative of the solution at a point of the free boundary. Such a problem arises in the pricing of American options in generalized Black–Scholes models of finance. Our results apply in financial mathematics.     

Global nonexistence of positive initial energy solution for coupled quasilinear system

In this paper, we consider global nonexistence of a solution for coupled quasilinear system with damping and source under Dirichlet boundary condition. We obtain a global nonexistence result of solution by using the perturbed energy method, where the initial energy is assumed to be positive. Copyright © 2017 John Wiley & Sons, Ltd.