共查询到20条相似文献,搜索用时 156 毫秒
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非自治时滞微分方程的扰动全局吸引性* 总被引:1,自引:1,他引:0
考虑具有扰动项的非自治时滞微分方程x>(t)=-a(t)x(t-τ)+F(t,xt),t≥0(*)其中F:[0,∞)×C[-δ,0]→R且连续,C[-δ,0]表示将[-δ,0]映射到R的所有连续函数集合.F(t,0)≡0,a(t)∈C((0,∞),(0,∞)),τ≥0.通常文献对a(t)不依赖于t即a(t)为自治情形,研究了方程(*)零解的局部或全局渐近性质[1~5,7].本文对a(t)为非自治即依赖于t之情形,获得了方程(*)零解全局吸引的充分条件,所得结论在某种意义上说是不可改进的.本文改进和推广了已有文献的相应结果,同时本文采用的方法可应用到非自治非线性扰动方程. 相似文献
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本文主要讨论三维Boussinesq方程当扩散系数κ=0时光滑解的爆破准则.利用Littlewood-Paley分解和能量方法证明了如果方程关于水平速度场ū=(u1,u2,0)的水平导数满足▽hū=(1ū,1ū,0)∈L1(0,T;B0∞,∞(R3)).则解(u,θ)可以连续到T1>T. 相似文献
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首先对广义Pochhammer-Chre方程(PC方程)utt-uttxx+ruxxt-(a1u+a2u2+a3u3)xx=0(r≠0)(Ⅰ)的孤波解u(ξ)建立了公式∫-∞+∞[u'(ξ)]2dξ=1/12rv(C+-C-)3[3a3(C++C-)+2a2]。由此推知:广义PC方程(Ⅰ)不可能有钟状孤波解,只可能有扭状孤波解;而广义PC方程utt-uttxx-(a1u+a2u2+a3u3)xx=0(Ⅱ)可能既有钟状孤波解又有渐近值满足3a3(C++C-)+2a2=0的扭状孤波解。进一步求出了广义PC方程(Ⅰ)的扭状孤波解,求出了广义PC方程(Ⅱ)的钟状孤波解和渐近值满足2a3(C++C-)+2a2=0的扭状孤波解。最后给出了广义PC方程utt-uttxx-(a1u+a3u3+a5u5)xx=0(Ⅲ)的显式孤波解。 相似文献
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本文利用由三维弹性力学方程,通过几何小参数α=r0/R0摄动得到的厚环壳渐近方程,求得了厚环壳在内压q作用下的应力和变形解。 相似文献
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一般地,二元二次方程F(x,y)=0(*)表示圆锥曲线.如果方程(*)能化成:(x-m)2/a2 (y-n)2/b2=0.的形式,则(*)表示 相似文献
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考虑了在极小测度集Mc0唯一遍历时,Hamilton-Jacobi方程的黏性解uc:M→R关于平均作用量c的连续性.证明了在相差一个常数的意义下,黏性解uc(X)(■x∈M)关于c是连续的. 相似文献
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求强非线性系统次谐共振解的MLP方法 总被引:10,自引:0,他引:10
定义了一个新的参数变换α=α(ε,nω0/m,ω1),扩展了改进的LP方法的应用范围,使该方法能够求强非线性系统的次谐共振解.研究了Duffing方程的1/3亚谐和3次超谐共振解以及Vander Pol-Mathieu方程1/2亚谐共振解,这些例子说明近似解和数值解相当吻合. 相似文献
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本文考虑如下拟线性薛定谔方程:-Δu+(κu)/2△u2=λ|u|p-2u,x∈Ω,这里u∈H(Ω),2
0,N≥3且Ω是有界区域.结合变分方法和摄动讨论,作者证明了存在常数κ0> 0,使得对任何的κ∈(0,κ0),这类特征值问题有解(λ,u).特别地,如果限制|u|pp=α,作者发现对任何的κ> 0,存在α0> 0,使得在α <α0时,该特征值问题的解总是存在的.此外,作者采用不同于Morse迭代的方法构造出了常数κ0和α0的精确表达式. 相似文献
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本文对微分方程组其中a(t)>0,r(t)>0,t≥t0;f(x)对x>0正值递减;g(y)>0,给出存在正规解,有界正规解或两类无穷区间[c,∞)(c≥t0)上边值问题解的充要条件.同时给出若干例子说明结果的条件. 相似文献
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A note on geometric ergodicity of autoregressive conditional heteroscedasticity (ARCH) model 总被引:1,自引:0,他引:1
Zudi Lu 《Statistics & probability letters》1996,30(4):305-311
For the pth-order linear ARCH model, , where 0 > 0, i 0, I = 1, 2, …, p, {t} is an i.i.d. normal white noise with Et = 0, Et2 = 1, and t is independent of {Xs, s < t}, Engle (1982) obtained the necessary and sufficient condition for the second-order stationarity, that is, 1 + 2 + ··· + p < 1. In this note, we assume that t has the probability density function p(t) which is positive and lower-semicontinuous over the real line, but not necessarily Gaussian, then the geometric ergodicity of the ARCH(p) process is proved under Et2 = 1. When t has only the first-order absolute moment, a sufficient condition for the geometric ergodicity is also given. 相似文献
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We consider context-free grammars of the form G = {f → fb1+b2+1ga1+a2, g → fb1 ga1+1},where ai and bi are integers sub ject to certain positivity conditions. Such a grammar G gives rise to triangular arrays {T(n, k)}0≤k≤n satisfying a three-term recurrence relation. Many combinatorial sequences can be generated in this way. Let Tn (x) =∑nk=0T(n, k)xk. Based on the differential operator with respect to G, we define a sequence of linear operators Pn such that Tn+1(x) = Pn(Tn(x)). Applying the characterization of real stability preserving linear operators on the multivariate polynomials due to Borcea and Br?ndén, we obtain a necessary and sufficient condition for the operator Pn to be real stability preserving for any n. As a consequence, we are led to a sufficient condition for the real-rootedness of the polynomials defined by certain triangular arrays, obtained by Wang and Yeh.Moreover, as special cases we obtain grammars that lead to identities involving the Whitney numbers and the Bessel numbers. 相似文献
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In this paper we investigate the behaviour of the solutions of equations ΣI=1n aixi = b, where Σi=1n, ai = 0 and b ≠ 0, with respect to colorings of the set N of positive integers. It turns out that for any b ≠ 0 there exists an 8-coloring of N, admitting no monochromatic solution of x3 − x2 = x2 − x1 + b. For this equation, for b odd and 2-colorings, only an odd-even coloring prevents a monochromatic solution. For b even and 2-colorings, always monochromatic solutions can be found, and bounds for the corresponding Rado numbers are given. If one imposes the ordering x1 < x2 < x3, then there exists already a 4-coloring of N, which prevents a monochromatic solution of x3 − x2 = x2 − x1 + b, where b ε N. 相似文献
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U. G. Abdullaev 《Applied Mathematics Letters》1994,7(6):85-89
We consider the nonlinear parabolic equation ut = (k(u)ux)x + b(u)x, where u = u(x, t, x ε R1, t > 0; k(u) ≥ 0, b(u) ≥ 0 are continuous functions as u ≥ 0, b (0) = 0; k, b > 0 as u > 0. At t = 0 nonnegative, continuous and bounded initial value is prescribed. The boundary condition u(0, t) = Ψ(t) is supposed to be unbounded as t → +∞. In this paper, sufficient conditions for space localization of unbounded boundary perturbations are found. For instance, we show that nonlinear equation ut = (unux)x + (uβ)x, n ≥ 0, β >; n + 1, exhibits the phenomenon of “inner boundedness,” for arbitrary unbounded boundary perturbations. 相似文献
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H. Galeana-Snchez 《Discrete Mathematics》1992,110(1-3):251-255
A directed graph D with vertex set V is called cyclically h-partite (h2) provided one can partition V=V0+V1++Vh−1 so that if (u, υ) is an arc of D then uεVi, and υεVi+1 (notation mod h). In this communication we obtain a characterization of cyclically h-partite strongly connected digraphs. As a consequence we obtain a sufficient condition for a digraph to have a h-kernel. 相似文献
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设K/F_q是整体函数域,l是与q互素的素数,ξ_1是K的固定代数闭包中的本原l次单位根.对于a,b∈K~*-(K~*)~l,本文主要讨论了根式扩域K(a~(1/2))与K(a~(1/l),(b~(1/l))的性质,利用Kummer理论给出了K(a~(1/l))/K与K(a~(1/l),b~(1/l))/K不是几何扩张的充要条件.当a,b是l-无关时,对于K的素除子P及对应的离散赋值环θ_P,利用这两类扩张的性质,通过分析a,b生成循环群(θ_P/P)~*的充要条件,本文明确给出了满足使得a,b生成循环群(θ_P/P)~*的全体素除子集合M_(a,b)的Dirichlet密度公式. 相似文献