REMARKS ON THE LIFESPAN FOR THE SOLUTION TO NONLINEAR WAVE EQUATIONS IN THREE SPACE DIMENSIONS

The authors consider the Cauchy problem for the following nonlinear wave equationswhere x ∈ R3, t ≥ 0, ε > 0 is a small parameter, and obtain the sharp bounds for the lifespan of solution to (0.1). Specially, it is proved that there exist two constants C1 and C2, which are independent of ε, then the lifespan T(ε) satisfies the folowing inequalities

SPHERICAL NONLINEAR PULSES FOR THE SOLUTIONS OF NONLINEAR WAVE EQUATIONSⅡ, NONLINEAR CAUSTIC

This article discusses spherical pulse like solutions of the system of semilinear wave equations with the pulses focusing at a point and emerging outgoing in three space variables. In small initial data case, it shows that the nonlinearities have a strong effect at the focal point. Scattering operator is introduced to describe the caustic crossing. With the aid of the L^∞ norms, it analyzes the relative errors in approximate solutions.

Focusing of Spherical Nonlinear Pulses for Nonlinear Wave Equations Ⅲ. Subcritical Case

This paper studied spherical pulses of solutions of the system of semilinear wav e equations with the pulses focusing at a point in three space variables. It is shown that there is no nonlinear effect at leading terms of pulses, when the ini tial data is subcritical.

Sharpness on the Lower Bound of the Lifespan of Solutions to Nonlinear Wave Equations

This paper is devoted to proving the sharpness on the lower bound of the lifespan of classical solutions to general nonlinear wave equations with small initial data in the case n = 2 and cubic nonlinearity （see the results of T. T. Li and Y. M. Chen in 1992）. For this purpose, the authors consider the following Cauchy problem： { where □=δt^2-∑i=1n δx^^2 is the wave operator, g（x）（≡/） 0 is a smooth non-negative function with compact support, and ε 〉 0 is a small parameter. It is shown that the solution blows up in a finite time, and the lifespan T（ε） of solutions has an upper bound T（ε） ≤ exp（Aε-2） with a positive constant A independent of ε, which belongs to the same kind of the lower bound of the lifespan.

Focusing of Spherical Nonlinear Pulses for Nonlinear Wave Equations

This paper describes the behavior of spherical pulse solutions of a system of semilinear wave equations in three space variables. Away fi＇om the focal point, we describe solutions with nonlinear geometric optics. We show that the approximation given by nonlinear geometric optics is valid before and after the focal point. We obtain a global asymptotic description including an approximation which is a solution of the linear wave equations near the caustic.

Blow-Up Result for a Semi-Linear Wave Equation with a Nonlinear Memory Term of Derivative Type

In this paper,we study the blow-up of solutions to a semi-linear wave equation with a nonlinear memory term of derivative type.By using methods of an iteration argument and di erential inequalities,we obtain the blow-up result for the semi-linear wave equation when the exponent of p is under certain conditions.Meanwhile,we derive an upper bound of the lifespan of solutions to the Cauchy problem for the semi-linear wave equation.

SPHERICAL SYMMETRIC SOLUTIONS FOR THE MOTION OF RELATIVISTIC MEMBRANES AND NULL MEMBRANES IN THE REISSNER-NORDSTRM SPACE-TIME

In this article, we concern the motion of relativistic membranes and null mem- branes in the Reissner-Nordstrom space-time. The equation of relativistic membranes moving in the Reissner-Nordstrom space-time is derived and some properties are discussed. Spherical symmetric solutions for the motion are illustrated and some interesting physical phenomena are discovered. The equations of the null membranes are derived and the exact solutions are also given. Spherical symmetric solutions for null membranes are just the two horizons of Reissner-NordstrSm space-time.

THE ASYMPTOTIC BEHAVIOUR OF SOLUTIONS FOR A CLASS OF QUASILINEAR WAVE EQUATIONS WITH CUBIC NONLINEARITY IN TWO SPACE DIMENSIONS

For a class of quasilinear wave equations with small initial data, first we give the lower bound of lifespan of classical solutions, then we discuss the long time asymptotic behaviour of solutions away from the blowup time.

n维非线性波动方程对应的线性方程Cauchy问题的解

在n维非线性波动方程Cauchy问题的迭代解法中 ,每一个迭代步骤都需要求解一个相应的n维线性波动方程的Cauchy问题。对于n维线性波动方程Cauchy问题而言 ,只要初值适当光滑 ,其解也必适当光滑 ,且在整个半空间t≥ 0上是整体存在的。从较简单的n维线性波动方程Cauchy问题出发 ,利用球面平均法和降维法分别求出n为奇数 (n >1)和n为偶数时其解的表达式。并利用叠加原理求得了一般的n维线性齐次方程Cauchy问题和线性非齐次方程Cauchy问题的解 。

论球面波波动方程

基于准确的有限变形力学理论，本文建立了无限弹性介质中点爆炸震源产生的球面波非线性波动方程，从而揭示了球面波的振幅和波形演化现象。研究揭示经典的球面波波动方程只对固定振幅相成立，即只描述了相的运动方程，其波速为相速度。本文以变参数外尔斯特拉斯双周期椭圆函数给出精确波动方程解析解，从理论上阐明了地震子波（雷克子波）演化的弹性动力学本质，对于用地震勘探方法解决生产勘探问题具有理论指导意义。

关于三维波动方程(~2u/t^2)=a^2((~2u/x^2)+(~2u/y^2)+(~2u/z^2))

本文利用球面平均法u(r,t)=(1/4πr2)∫∫ SrM0u(M,t)ds=(1/4π)∫∫SrM0u(M,t)dΩ将三维波动方程(~2u/t^2)=a^2((~2u/x^2)+(~2u/y^2)+(~2u/z^2))化为关于平均值-u(r,t)的一维方程(2/t2)[ru-(r,t]=a2(2/r2)[ru-(r,t]

具有非线性记忆项的半线性双波动方程解的全局非存在性

研究了具有非线性记忆项的半线性双波动方程解的全局非存在性.通过建立辅助函数,运用非线性积分不等式相关的迭代方法,得到了解的生命跨度上界估计.

一类波动方程解的生命跨度的估计

在外区域上研究一类变系数且带组合非线性项的波动方程,其中空间维数满足n(n≥2)。首先,分别考虑带幂次非线性项|u|^(p)与导数非线性项|u_(t)|^(p)的问题。运用检验函数方法和Kato引理,导出Riccati方程,证明了解会破裂,结合叠加原理给出其生命跨度的上界估计。其次,选取适当的检验函数,采用Kato引理即给出生命跨度的上界估计。通过比较,给出生命跨度的最佳上界估计。

球面平均值函数及其微分方程的推导

三维波动方程初值问题是数学物理方法课程的重要教学内容.本文讨论球面平均法求解该问题时,球面平均值的定义及其满足的偏微分方程的建立过程.在教材常见推导的基础上,本文提出了球面平均值方程一种更简洁的推导方法.本文的讨论有利于澄清球面平均值函数的含义,为球面平均法以及球坐标系下数学物理方程的教学提供参考.

Derivative estimates of averaging opera tors and extension

We study the derivative operator of the generalized spherical mean S^γt. By considering a more general multiplier m^Ωγ,b=Vn-2/2+γ(|ξ|)|ξ|^bΩ(ξ') and finding the smallest γ such that m^Ωγ,b is an Hp multiplier, we obtain the optimal range of exponents (γ,β,p)to ensure the H^p(R^n) boundedness of a^βS^γ1f(x). As an application, we obtain the derivative estimates for the solution for the Cauchy problem of the wave equation on H^p(R^n) spaces.