应用Bulk时空流形对宇宙学常数的研究

宇宙学常数的物理学起源问题被视为现代物理中最重大的疑难之一.从额外维的流形出发,给出了宇宙学常数的Bulk时空流形起源的理论.从而得到了不同情况下宇宙学常数的取值和宇宙学常数随时间变化的函数,并且得到了可拟合现代天文观测的宇宙学常数.     

Coupling, spectral gap and related topics (Ⅲ)

THIS is the last one of a series of three papers. Here, we discuss six topics related to the spectral gap: the gradient estimate, the heat kernel and Harnack inequality, the logarithmic Sobolev inequality, the convergence in total variation, the algebraic convergence and the infinite-dimensional case. The perturbation of spectral gap and the logarithmic Sobolev constant under a linear transform is given (Theorem 5). A new proof for computing the logarithmic Sobolev constant in a basic case is also presented (Theorem 7).     

Global view of Hopf bifurcations of a van der Pol oscillator with delayed state feedback

This paper presents both analytical and numerical studies on the global view of Hopf bifurcations of a van der Pol oscillator with delayed state feedback. Based on a detailed analysis of the stability switches of the trivial equilibrium of the system, the stability charts are given in a parameter space consisting of the time delay and the feedback gains. The center manifold reduction and the normal form method are used to study Hopf bifurcations with respect to the time delay. To gain an insight into the pe...     

非紧流形上抛物方程的椭圆型梯度估计

给出完备非紧黎曼流形M上的抛物方程ut=△u＋Xu＋hu的正解的全局梯度估计,该估计与M的维数n无关.这里X是任意非零C 1向量场;h是定义在M×（0,＋∞）上的非负函数,对于自变量x是C 1函数.作为应用,我们将给出该方程的解的Harnack估计.     

存在共圆Killing向量场的拟共形黎曼流形

本文推广了《关于无穷小共圆运动几个定理》(罗崇善)的若干结果,得到:若一个拟共形平坦(拟共形半对称或拟共形循环)流形M~n(n≥4)存在一个共圆Killing向量场,则M~n是常曲率流形,或拟常曲率流形或ρ的梯度是M~n的平行向量场。     

A perturbation-incremental scheme for studying Hopf bifurcation in delayed differential systems

A new method,called perturbation-incremental scheme (PIS),is presented to investigate the periodic solution derived from Hopf bifurcation due to time delay in a system of first-order delayed differential equations.The method is summarized as three steps,namely linear analysis at critical value,perturbation and increment for continuation.The PIS can bypass and avoid the tedious calculation of the center manifold reduction (CMR) and normal form.Meanwhile,the PIS not only inherits the advantages of the method ...     

Einstein流形及其全脐超曲面

本文研究Ｅｉｎｓｔｅｉｎ流形及其全脐超曲面，得到具正截曲率Ｅｉｎｓｔｅｉｎ流形的一个特征及其超曲面成为全脐的条件。     

发动机排气歧管热负荷数值模拟

某发动机运行期间，由于不合理的结构设计导致排气歧管关键部位的热疲劳失效，为此采用CFD技术模拟排气歧管工作时的外流场；通过热力学计算得到排气歧管的入口和出口边界条件。计算排气歧管的三维瞬态内流场；将内外流场计算的等效传热边界条件影射到排气歧管的内外表面生成传热边界条件，计算出结构温度场；将固体边界的温度作为流场边界条件重新进行内外流场计算，反复迭代多次，最后，求解结构的热应力．对原方案提出了改进意见，结构改进后，排气歧管热疲劳失效得到排除．     

解空间结构与几何空间中线面关系的判定

讲述了如何通过分析线性方程组导出组的解空间结构去判定几何空间中的线面关系.