Burgers方程的激波解与激波位置(英文)

讨论了Burgers方程激波解和位置的转移 .认为 :对该类方程 ,当边值发生微小变化时 ,不仅激波解发生变化 ,而且激波位置将发生较大的变化 ,甚至从内层移到边界 .其激波解也会发生相应的变化 .     

半线性椭圆方程等值面过值问题解的极限性态

本文研究了半线性椭圆型方程当等值面边界缩小为一点时,解的极限性态．     

具有非线性吸收项和边界流的m,p-Laplacian抛物方程研究（英文）

本文研究了一类在■中的m,p-Laplacian抛物方程(p2,m1),其具有非线性内部吸收项(-λu~κ)和非线性边界流u~q.当qq~*时,任意解都是整体存在的.当qq~*时,根据初值的选取,爆破解和整体解都可能存在.在临界情形q=q~*,吸收项系数的大小在决定解的整体存在和爆破现象方面发挥决定性作用.当κ≤1时,所有解整体存在.当1κm(p-1)+p时,对于任意初值,大的λ可以导致解发生有限时刻爆破,即Fujita爆破,而小的λ可以导致解整体存在.而且,我们给出了系数大小的定量估计.当κm(p-1)+p时,爆破解和整体解都是可以存在的.     

简单闭环路网交通流定常解

基于在分岔路口满足用户均衡原理的假定,研究了由三条路段和两个交叉路口组成的简单闭环路网的交通流定常解问题,发现定常解参数及其性态依赖于路网上的车流总数:当车流总数不大于第一个临界值,或不小于第二个临界值时,定常解在每一条路段上均为密度取常数的平凡解;否则,在瓶颈路口（上游最大流量大于下游最大流量的路口）的上游路段将产生激波间断,呈排队等候现象.对分岔路口和交汇路口为瓶颈的情况,分别给出了完整的解析结果     

关于齐次四元Monge-Ampère方程的一些注记北大核心CSCD

本文考虑了四元数空间Hn中齐次四元Monge-Ampère方程的狄利克雷问题解的正则性.首先,当区域是边界为C1,1的强拟凸域时,作者给出了解的Lipschitz估计.其次,考虑了四元MongeAmpère算子的收敛性.最后,讨论了齐次四元Monge-Ampère方程的粘性次解与F-次调和函数之间的关系.     

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.     

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.     

可压缩流初边值问题的奇异极限

本文研究可压缩流初边值问题的奇异极限。利用方程组本身的特殊结构,采用相消法,克服了系数奇异(大参数)所带来的困难,通过能量估计得到了如下结果:1.当Mach数的倒数λ趋大时,局部光滑解存在唯一,且解的“生命跨度”(即延续时间)与参数λ无关。2.固壁特征边界和非特征边界可以得到统一处理。3.它的极限解满足不可压缩流的初边值问题。     

带不定权非线性边界的p-Laplacian问题解的存在性

研究了一类带不定权非线性边界的p-Laplacian椭圆方程.获得了当非线性边界的特征值参数小于第二特征值时,该方程存在非平凡解.主要工具为环绕定理.     

非特征边界的MHD方程的边界层

考查了小粘性时非特征边界情况下MHD方程在边界附近的性质,说明速度在边界上不为零.源于之前非特征边界条件下不可压缩Navier-Stokes方程边界层的工作,证明了边界层的存在性,并得到了当粘性收敛于零时,MHD方程的解收敛于理想MHD方程的解.     

GLOBAL SOLUTION TO 1D MODEL OF A COMPRESSIBLE VISCOUS MICROPOLAR HEAT-CONDUCTING FLUID WITH A FREE BOUNDARY

In this paper we consider the nonstationary 1D flow of the compressible viscous and heat-conducting micropolar fluid,assuming that it is in the thermodynamically sense perfect and polytropic.The fluid is between a static solid wall and a free boundary connected to a vacuum state.We take the homogeneous boundary conditions for velocity,microrotation and heat flux on the solid border and that the normal stress,heat flux and microrotation are equal to zero on the free boundary.The proof of the global existence of the solution is based on a limit procedure.We define the finite difference approximate equations system and construct the sequence of approximate solutions that converges to the solution of our problem globally in time.     

On improperly posed Caucfay problems and their approximate solution

It is well known that, in general, the Cauchy problem for theLaplace equation does not allow a solution and therefore isill-posed in both the Hadamard and the Tikhonov senses. Thepresent work focuses on the question whether the problem hasany meaningful approximate solution for arbitrary boundary conditions.Firstly, it is shown that it is possible to construct an analyticfunction which assumes some prescribed value on part of theboundary of a simply-connected domain. This problem is thenshown to be equivalent to the Cauchy problem under consideration,the solution to which can thus be invariably approximated toany degree of accuracy on the unit circle centred at the originwhen both the potential and the flux are specified as square-integrablefunctions over half the unit circle boundary. The uniquenessof the exact solution to the problem is also established. Theseresults are actually true for any simply-connected domain whichcan be conformally mapped onto the unit circle so that the partof its boundary with prescribed potential and flux correspondsto one-half of the unit circle boundary. Finally, the feasibilityof a boundary element formulation for a generic type of ill-posedboundary value problems is briefly discussed.     

A conservation law with spatially localized sublinear damping

We consider a general conservation law on the circle, in the presence of a sublinear damping. If the damping acts on the whole circle, then the solution becomes identically zero in finite time, following the same mechanism as the corresponding ordinary differential equation. When the damping acts only locally in space, we show a dichotomy: if the flux function is not zero at the origin, then the transport mechanism causes the extinction of the solution in finite time, as in the first case. On the other hand, if zero is a non-degenerate critical point of the flux function, then the solution becomes extinct in finite time only inside the damping zone, decays algebraically uniformly in space, and we exhibit a boundary layer, shrinking with time, around the damping zone. Numerical illustrations show how similar phenomena may be expected for other equations.     

Nonclassical boundary value problem for the transport equation

We consider a nonclassical boundary value problem for the transport equation. The particle transport process is described by a stationary linear integro-differential equation, and the outgoing particle flux density on some part of the boundary is specified as the boundary condition. We find the particle flux density for a given outgoing flux and known coefficients of the equation. We show that, under some restrictions on the medium, there exists a unique solution of the problem, which can be represented by an infinite convergent series.     

On the Stationary Navier–Stokes Equations in the Half-Plane

We consider the stationary incompressible Navier–Stokes equation in the half-plane with inhomogeneous boundary condition. We prove the existence of strong solutions for boundary data close to any Jeffery–Hamel solution with small flux evaluated on the boundary. The perturbation of the Jeffery–Hamel solution on the boundary has to satisfy a nonlinear compatibility condition which corresponds to the integral of the velocity field on the boundary. The first component of this integral is the flux which is an invariant quantity, but the second, called the asymmetry, is not invariant, which leads to one compatibility condition. Finally, we prove the existence of weak solutions, as well as weak–strong uniqueness for small data and provide numerical simulations.     

A general solution of the diffusion equation for semiinfinite geometries

The solution of the time-dependent diffusion equation in a semiinfinite planar, cylindrical, or spherical geometry with common initial and asymptotic boundary conditions is considered. It is shown that this boundary value problem may be described by a single equation which involves only a first order spatial derivative and a half order time derivative. The replacement is exact in the planar and spherical geometry cases but approximate in the cylindrical case. This replacement permits the solution of the original boundary value problem to be written for any boundary condition at the origin. It also leads to a simple relationship between the boundary flux and the boundary intensive variable, which does not require a calculation of the intensive variable at all positions and times.     

A PRACTICAL PARALLEL DIFFERENCE SCHEME FOR PARABOLIC EQUATIONS

A practical parallel difference scheme for parabolic equations is constructed as follows: to decompose the domain Ω into some overlapping subdomains, take flux of the last time layer as Neumann boundary conditions for the time layer on inner boundary points of subdomains, solve it with the fully implicit scheme on each subdomain, then take correspondent values of its neighbor subdomains as its values for inner boundary points of each subdomain and mean of its neighbor subdomain and itself at overlapping points. The scheme is unconditionally convergent. Though its truncation error is O(τ h), the convergent order for the solution can be improved to O(τ h2).     

Continuous dependence on the heat source and non-linear stability for convection with internal heat generation

It is shown that the solution to the boundary-initial value problem for a heat-conducting viscous fluid depends continuously on changes in the heat supply function, for the improperly posed backward in time problem. A non-linear convection threshold is also determined for the problem of a layer of fluid heated internally (non-uniformly), with zero neat flux on the lower boundary and constant-temperature upper surface.     

Drift-diffusion in electrochemistry: thresholds for boundary flux and discontinuous optical generation

We consider an extension of the classical drift-diffusion model, which incorporates thermodynamic switching rules for generation and boundary flux. The motivation is the important case of the splitting of water molecules upon photonic irradiation of a semiconductor electrode located in an electrochemical cell. The solid state electrode forms the spatial domain of the model. The rules are motivated by the fact that the valence band of the semiconductor, which supplies positive charge to solution, has to be located at a lower energy level than the electrochemical potential of O₂ evolution in solution, and the conduction band, which supplies electrons to solution, has to be positioned at a higher energy level than the electrochemical potential of H₂ evolution. This defines thresholds in terms of electrochemical potentials before boundary flux is activated. The optical generation rate is affected, due to the increased carrier relaxation time, when these thresholds are crossed, and may be discontinuous. We thus consider a self-consistent model, in which ‘switching’ occurs only in principal variables. The steady-state model is considered, and trapping regions are derived for the solutions.     

Critical Quenching Exponents for Heat Equations Coupled with Nonlinear Boundary Flux

We discuss the quenching phenomena for a system of heat equations coupled with nonlinear boundary flux. We determine a critical value for the exponents in the boundary flux, such that only in the super critical case the simultaneous quenching can happen for any solution.