一类二阶非线性泛函微分方程的振动性

本文讨论二阶非线性泛函微分方程(a(t)y′(t))′+p(t)y′(t-τ(t))-q(t)f(y(t))=0,t≥t₀,(1)(a(t)y′(t))′-p(t)y′(t+τ(t))-q(t)f(y(t))=0,t≥t₀,(2)获得了方程(1)和(2)振动的充分性判据,推广和改进了已知的一些结果.     

空间情形下旋转体体积的计算

运用定积分中的元素法,给出了空间曲线绕空间直线旋转一周所成的旋转曲面与垂直于旋转轴的两个平面所围成的旋转体体积的计算公式:V=π(m2+n2+p2)23∫tt12{[p(y(t)-b)-n(z(t)-c)]2+[m(z(t)-c)-p(x(t)-a)]2+[n(x(t)-a)-m(y(t)-b)]2}m.x′(t)+n.y′(t)+p.z′(t)dt从而将平面图形的旋转体体积推广到了空间情形.     

TWO POSITIVE SOLUTIONS FOR A CLASS OF SINGULAR BOUNDARY VALUE PROBLEMS

An existence theorem of two positive solutions of the singular BVP1/(p(t))(p(t)y′(t))′+λα(t)f(y(t))=0,t∈(0,1),αy(0)-βp(t)y′(t)=0=γy(1)+δp(t)y′(t)was established by using topological degree theory.     

纠正《高等数学》(同济四版)的一个错误

《高等数学》[1]中关于两类曲线积分关系的推导是错误的 .关于两类曲线积分关系有一个熟知的公式 ,即∫LP(x,y) dx+Q(x,y) dy=∫L [P(x,y) cosα+Q(x,y) cosβ]ds,(1 )其中 cosα,cosβ为有向弧段 L的切向量的方向余弦 .但《高等数学》中关于 (1 )的推导是错误的 .它给出曲线弧 L的参数方程x=φ(t) ,　 y=ψ(t) (2 )(注意从 (2 )中体现不出弧的方向 ) ,它又假定有向弧起点和终点的参数分别为 α和 β,然后下式成立∫LP(x,y) dx+Q(x,y) dy=∫βα {P[φ(t) ,ψ(t) ]φ′(t) +Q[φ(t) ,ψ(t) ]ψ′(t) }dt. (3)它又设有向弧切向量为t={…     

一类广泛的二阶泛函数分方程解的振动性和非振动性定理

The purpose of this paper is to give some sufficient conditions on / and g for ensuring that all solutions or all bounded solutions of general second order functional differential equation 〔r(t)g(y′(t))〕′+ f(t,y(t),y(p(t)),y′(t),y′(q(t)))=0 are oscillatory, or it has at least one bounded nonoscillatory solution.     

The Oscillation and Nonoscillation Theorems for A Class of General Second Order Functional Differential Equations

The purpose of this paper is to give some sufficient conditions on f andg for ensuring that all solutions or all bounded solutions of general secondorder functional dlfferential equation 〔r(t)g(y′(t))〕′+ f(t,y(t),y(p(t)),y′(t),y′(q(t)))=0are oscillatory,or it has at least one bounded nonoscillatory solution.     

二阶带偏差变元的微分方程的解的振动性

本文讨论下述二阶带偏差变元的非线性微分方程[r(t)y′(t)]′+f(t,y(t),y(g(t)),y′(t),y′(h(t)))=0为振动的充分性与必要性条件,其中g(t)与h(t)当t趋于无穷时均趋于无穷,非线性项f为“端有界”。 本文得到的振动的充分性与必要性条件,对于f是超线性,亚线性,拟线性的情形也适用,适用范围比文[1—4]广。本文还区分了情形,又区分了g(t)是滞后与超步的情形。     

非线性中立型延迟微分方程稳定性分析

This paper is devoted to the stability analysis of both the true solution and the numerical approximations for nonlinear systems of neutral delay differential equations(NDDEs) of the general form y′(t)=F(t，y(t)，G(t，y(t-τ-(t))，y′(t-τ-(t)))). We first present a sufficient condition on the stability and asymptotic stability of theoretical solution for the nonlinear systems. This work extends the results recently obtained by A.Bellen et al. for the form y′(t)=F(t，y(t)，G(t，y(t-τ-(t))，y′(t-τ-(t)))). Then numerical stability of Runge-Kutta methods for the systems of neutral delay differential equations is also investigated. Several numerical tests listed at the end of this paper to confirm the above theoretical results.     

CAUCHY PROBLEM FOR LINEARIZED SYSTEM OF TWO-DIMENSIONAL ISENTROPIC FLOW WITH AXISYMMETRICAL INITIAL DATA IN GAS DYNAMICS

§1IntroductionIn the present paper,we are interested in solving the Cauchy problem for linearizedsystem of two-dimensional isentropic flow with initial data in gas dynamicsρt+ρ0xu+yv=0,ut+p′(ρρ00)xρ=0,vt+p′(ρ0ρ0)yρ=0,(1.1)t=0:(ρ,u,v)=(ρ0(r),u0(r),v0(r)),(1.2)whereρis the density,(u,v)is the velocity,ρ0is a positive constant,p=p(ρ)is theequation of state satisfying p′(ρ0)>0,(r,θ)is the polar coordinate such thatx=rcosθ,y=rsinθ,0≤r<+∞,0≤θ≤2π…     

ON THE EXISTENCE OF NONTRIVIAL PERIODIC SOLUTIONS OF DIFFERENTIAL DIFFERENCE EQUATIONS

This paper cosiders the existence of nontrivial periodic solutions of the differentialdifference equationsx′(t)=-f(x(t-1)),x′(t)=-(f(x(t-1)+f(x(t-2))),and(x′(t)=f(x(t),y(t),x(t-1),y(t-1)),y′(t)=g(x(t),y(t),x(t-1),y(t-1)).)Some new existence criteria are obtained.