不连续三阶两点边值问题的可解性

证明了非线性三阶两点边值问题u′″（t）-q（u″（t））f（t，u（t）），u（O）=a，u（1）=b，u″（0）=c解的一个存在定理．在这个问题中，f（t，u）是一个Carathéodory函数而边界条件是非齐次的．我们的结论表明该问题能够有一个解，只要在R。的某个有界集合上q（υ）的“本性高度”与f（t，u）的“最大高度”积分的乘积是适当的．     

共振条件下一类三阶m-点边值问题解的存在性

考虑共振情形下三阶微分方程m-点边值问题x＇＇＇（t）=f（t,x（t）,x＇（t）,x＂（t））＋p（t）,t∈（0,1）, x（0）=0,x＂（0）=0,x＇（0）=0,x＇（1）=∑i=1^m-2 aix＇（ξi）,其中ai≥0，0〈ξ1〈ξ2〈…〈ξm-2〈1且∑i=1^m-2 ai=1．利用Mawhin重合度拓展定理，得到该问题解存在性的新的结果．     

一类非线性抛物方程的初边值问题

本文研究了一类非线性抛物方程的初边值问题,即ut-f(u)xx=0,x∈R+,f'(u)＞0,u(0,t)=u_,t≥0;u(+∞,0)=u+.这里我们考虑一般情形,即u_≠u+.在某种小性条件下,我们证明了以上抛物方程的解存在且当时间充分大时,解趋近该问题的自相似解(-u)(x/√1+t).我们还进-步得到了解的最优衰减速度为(1+t)-1/4.     

一个摄动对称拟线性椭圆方程的多解

本文用变分方法考虑方程-Δpu=g（x,u）+f（x,u）无穷多解的存在性.这里Ω　Rn是一个具有光滑边界　Ω的有界域,g∈C（Ω×R）,g（x,t）关于t是奇的.     

一类二阶隐式微分方程的可解性

本文关注如下的二阶隐式微分方程f（t，u（t），u″（t））=0，a．e．t∈（O，1），边值条件为u（0）=u（1）=0．利用上下解方法和迭代技巧研究了该问题的可解性并得到了一些解的存在性结果．     

测度链上p-Laplacian边值问题的三个正对称解

该文研究了p-Laplacian动力边值问题（g（u^△（t）））△＋a（t）f（t，u（t））=0，t∈[0，T]T,u（0）=u（T）=w，u△（0）=-u^△（T）正解的存在性．其中W是非负实数，g（v）=｜v｜p-2v1 P＞1．根据对称技巧和五泛函不动点定理，证明了边值问题至少有三个正的对称解，同时，给出了一个例子验证了我们的结果。     

含反馈控制和参数的非线性泛函微分系统的正周期解的分析

我们研究下面具有反馈控制和参数的非线性微分系统的正周期解的存在性与不存在性：{dx/dt=-r（t）x（t）＋λF（t,xt,u（t-δ（t）））,du/dt=-h（t）u（t）＋g（t）x（t-σ（t））.在一定条件下通过应用Leggett．Williams不动点定理,证明该系统至少有三个正周期解;在另外的条件下,通过用反证法证明了该系统的正周期解不存在．     

一类多偏差变元的二阶微分方程周期解

本文利用重合度理论研究了一类二阶多偏差变元的微分方程 x＂（t）＋f（t,x（t）,x（t-τ0（t））,x＇（t））＋∑nj=1g（x（t-τj（t）））=p（t） 的周期解问题，得到了存在周期解的新的结果．     

非线性梁振动方程的周期解

一、引言考虑下述问题Ku″ A~2u M(‖A~1/2u‖~2)Au Au′=f(x,t),t>0,x∈Ω,(1.1)u|_t=0~=u_0(x),x∈Ω,(1.2)Ku′|_(t=0)=u_1(x),x∈Ω,(1.3)u=0,x∈(?)Ω,t≥0 (1.4)的ω-周期解的存在性.其中 Ω(?)R~n 为一有界光滑区域,u′=((?)u)/((?)t),u_″=((?)u)/((?)t)~2,K 为有界线性对称算子且满足(Ku,u)≥0,M∈C~1[0,∞),M(ξ)≥-β,ξ≥0.此模型最初由Woinowsky 和 Krieger 提出,方程形式为     

一类泛函微分方程的渐近性

主要讨论一类泛函微分方程x（t）=a（t）g（x（t））＋b（t）f（x1）（t≥0）解的渐近表现．建立非振动解和振动解趋于零的充分条件．     

REGULARIZATION OF AN ILL-POSED HYPERBOLIC PROBLEM AND THE UNIQUENESS OF THE SOLUTION BY A WAVELET GALERKIN METHOD

We consider the problem K(x)u xx = u tt , 0 < x < 1, t ≥ 0, with the boundary condition u(0,t) = g(t) ∈ L 2 (R) and u x (0, t ) = 0, where K(x) is continuous and 0 < α≤ K (x) < +∞. This is an ill-posed problem in the sense that, if the solution exists, it does not depend continuously on g. Considering the existence of a solution u(x, ) ∈ H 2 (R) and using a wavelet Galerkin method with Meyer multiresolution analysis, we regularize the ill-posedness of the problem. Furthermore we prove the uniqueness of the solution for this problem.     

热传导方程小波解的点态收敛

本文主要考虑热传导方程uxx=ut,0≤x<1,t≥0;u(1,t)=g(t),其中边界条件g(t)为已知函数．此定解问题为一不适定问题,也就是说当边界条件有微小扰动时,将会引起解大的扰动．本文将利用多分辨率分析构造一小波解,且证明此解是适定的,并给出所定义小波解与定解问题的真正解在点态意义下的误差估计．     

Lp-Lq Estimates for a Linear Perturbed Klein-Gordon Equation

We consider L^p-L^q estimates for the solution u(t,x) to tbe following perturbed Klein-Gordon equation ∂_{tt}u - Δu + u + V(x)u = 0 \qquad x∈ R^n, n ≥ 3 u(x,0) = 0, ∂_tu(x,0) = f(x) We assume that the potential V(x) and the initial data f(x) are compact, and V(x) is sufficiently small, then the solution u(t,x) of the above problem satisfies ||u(t)||_q ≤ Ct^{-a}||f||_p for t > 1 where a is the piecewise-linear function of 1/p and 1/q.     

Time periodic solutions of nonlinear wave equations

Existence and regularity of solutions of $$(1)u_{tt} - u_{xx} = \varepsilon K(x,t,u,u_t )0< x< \pi ,0 \leqslant t \leqslant 2\pi $$ together with the periodicity and boundary conditions $$(2)u(x,t + 2\pi ) = u(x,t),u(0,t) = 0 = u(\pi ,t)$$ is studied both with an without the dissipation u_t. A solution is a pair (χ, u). A main feature of interest here is an infinite dimensional biofurcation problem. Under appropriate conditions on K, global existence results are obtained by a combination of analytical and topological methods.     

非共振带阻尼半线性梁方程系统的存在性结果

本文讨论可能带阻尼项的半线性梁方程系统 utt uxxxx But=Au g( t,x,u) h( t,x)的周期边值问题 .借助 L yapunov- Schmidt方法 ,利用 Leray- Schauder不动点定理 ,在一定条件下证明了该系统至少存在一个解     

Polynomial bounds on the Sobolev norms of the solutions of the nonlinear wave equation with time dependent potential

Archiv der Mathematik - We consider the Cauchy problem for the nonlinear wave equation $$u_{tt} - \Delta _x u +q(t, x) u + u^3 = 0$$ with smooth potential $$q(t, x) \ge 0$$ having compact support...     

Pointwise convergence of the wavelet solution to the parabolic equation with variable coefficients

We consider the parabolic equation with variable coefficients k(x)uxx = ut,0,x ≤ 1,t ≥ 0, where 0 < α ≤ k(x) < +∞, the solution on the boundary x = 0 is a given function g and ux(0,t) = 0. We use wavelet Galerkin method with Meyer multi-resolution analysis to obtain a wavelet approximating solution, and also get an estimate between the exact solution and the wavelet approximating solution of the problem.     

Periodic Solutions of Nonlinear Wave Equations with Dissipative Boundary Conditions

Applying Nash-Moser's implicit function theorem, the author proves the existence of periodic solution to nonlinear wave equation u_{tt} - u_{xx} + εg(t, x, u, u_t, u_x, u_{tt}, u_{tx}, u_{xx}) = 0 with a dissipative boundary condition, provided ε is sufficiently small.     

Asymptotic behavior relative to a large parameter of the solution of the Fok-Klein-Gordon equation in the case of a discontinuous initial condition

One considers the problem of the asymptotic behavior for K→+∞ of the solution of the Cauchy problem $$u_{tt} - u_{xx} + \kappa ^2 u = 0; u|_{t = 0} = \theta (x), u_t |_{t = 0} = 0 (t > 0 - fixed)$$ Hereθ(x) is the Heaviside function. In the neighborhood of the characteristics x=±t function u(x,t)_?2 oscillates exceptionally fast (the wavelength is of order k^?2). Near the t axis the asymptotics of u(x,t) contains the Fresnel integral.     

Smoluchowski-Kramers approximation for a general class of SPDEs

We prove that the so-called Smoluchowski-Kramers approximation holds for a class of partial differential equations perturbed by a non-Gaussian noisy term. Namely, we show that the solution of the one-dimensional semi-linear stochastic damped wave equations , u(0) = u₀, u_t (0) = v₀, endowed with Dirichlet boundary conditions, converges as the parameter μ goes to zero to the solution of the semi-linear stochastic heat equation , u(0) = u₀, endowed with Dirichlet boundary conditions. Dedicated to Giuseppe Da Prato on the occasion of his 70th birthday