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．     

一类具时滞的Rayleigh型泛函微分方程反周期解的存在性

应用Leray Schauder不动点定理,研究了一类具时滞的Rayleigh型泛函微分方程： x″（t）＋f（x′（t））＋g（x（t-τ（t）））=e（t）的反周期解问题,得到了反周期解存在的新的结果。     

三阶常系数拟线性泛函微分方程的周期解

研究了一个三阶泛函微分方程周期解的存在唯一性和全局吸引性：x′′′（t）＋ax′′（t）＋bx′（t）＋cx（t）＋g（t,x（tτ））=p（t）.这是一个常系数拟线性泛函微分方程.通过将这个方程转变为三维的拟线性微分方程（组）,得到了这个方程存在唯一周期解的充分条件;通过选取适当的李雅普诺夫函数,推导了这个方程解的全局吸引性;进一步,得到了此方程周期解的全局吸引性.最后,举出了两个应用实例.     

Newton方程周期解存在性的构造性证明

本文在条件n2≤α（t）≤gx（t，x）≤b（t）≤（n＋1）2下，构造性地证明了Newton方程x″（t）十g（t，x（t））＝0的2π－周期解的存在唯一性，证明过程同时提供了一种数值计算周期解的方法．     

一类具分布时滞的高阶泛函微分方程的周期解存在性问题

利用Fourier级数理论。伯努利数理论和重合度理论研究了一类具分布时滞的高阶泛函微分方程x^（m）（t）＋f（x^（m-1）（t）＋g（∫-r^0x（t＋s）da（s））=p^（t）的周期解问题，得到了周期解存在的一些新结果．     

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．     

具偏差变元的Rayleigh型p-Laplacian方程的周期解

研究了一类具偏差变元的Rayleigh型p-Laplacian方程（φp（x′（t）））′＋f（t,x′（t））＋g（t,x（t-τ（t）））=e（t）的周期解问题.利用拓扑度理论和一个先验估计,获得了一些新的结果,同时也改进并推广了已有文献中的一些结果.     

二阶非自治Hamilton 系统周期解的新结果

研究了二阶非自治Hamilton系统（t）-B（t）x（t）＋▽H（t,x（t））=0,在局部超二次条件下周期解的存在性问题,利用山路定理和局部环绕定理得到了新的存在性定理,改进了已有结果.     

周期系数的高维Riccati方程的周期解

本文研究了周期系数的高维Riccati方程X’＝X·A（t）·X＋B（t）·X＋C（t）,其中X∈R(n×1)A（t）∈R(1×n),B（t）∈R(n×n),C（t）E∈R(n×1);A（t）,B（t）,C（t）均是以2π为周期的实连续矩阵或向量函数,建立了该方程存在广义周期解的一个充要条件和存在周期解的两个充分条件,推广了周期系数的Riccati方程存在周期解的一些结论．     

一类脉冲微分方程正周期解存在的充要条件

考虑非线性脉冲微分方程{x＇（t）=x（t）[a（t）-b（t）x^p（t）],t≠tk, △x｜t=tk=ckx（tk）,k∈N.得到了该方程存在正周期解的充要条件为m∏k=1（1＋ck）^pexp（p∫^w 0）a（σ）dσ）＞1.     

Determining a Rotation of a Tetrahedron from a Projection

The following problem, arising from medical imaging, is addressed: Suppose that T is a known tetrahedron in ?³ with centroid at the origin. Also known is the orthogonal projection U of the vertices of the image ?T of T under an unknown rotation ? about the origin. Under what circumstances can ? be determined from T and U?     

Symmetry-based solution of a model for a combination of a risky investment and a riskless investment

Benth and Karlsen [F.E. Benth, K.H. Karlsen, A note on Merton's portfolio selection problem for the Schwartz mean-reversion model, Stoch. Anal. Appl. 23 (2005) 687-704] treated a problem of the optimisation of the selection of a portfolio based upon the Schwartz mean-reversion model. The resulting Hamilton-Jacobi-Bellman equation in 1+2 dimensions is quite nonlinear. The solution obtained by Benth and Karlsen was very ingenious. We provide a solution of the problem based on the application of the Lie theory of continuous groups to the partial differential equation and its associated boundary and terminal conditions.     

On a mapping of a projective space into a sphere

We obtain an exact estimate for the minimum multiplicity of a continuous finite-to-one mapping of a projective space into a sphere for all dimensions. For finite-to-one mappings of a projective space into a Euclidean space, we obtain an exact estimate for this multiplicity for n = 2, 3. For n ≥ 4, we prove that this estimate does not exceed 4. Several open questions are formulated.     

Calculating a function of a matrix with a real spectrum

Let T be a square matrix with a real spectrum, and let f be an analytic function. The problem of the approximate calculation of f(T) is discussed. Applying the Schur triangular decomposition and the reordering, one can assume that T is triangular and its diagonal entries t_ii are arranged in increasing order. To avoid calculations using the differences t_ii ? t_jj with close (including equal) t_ii and t_jj, it is proposed to represent T in a block form and calculate the two main block diagonals using interpolating polynomials. The rest of the f(T) entries can be calculated using the Parlett recurrence algorithm. It is also proposed to perform some scalar operations (such as the building of interpolating polynomials) with an enlarged number of significant decimal digits.

     

Approaching a vertex in a shrinking domain under a nonlinear flow

We consider here the homogeneous Dirichlet problem for the equation , in a noncylindrical domain in space-time given by . By means of matched asymptotic expansion techniques we describe the asymptotics of the maximal solution approaching the vertex x=0, t=T, in the three different cases p>1/2, p=1/2(vertex regular), p<1/2 (vertex irregular).     

Folding a surface to a polygon

A concept of folding for compact connected surfaces, involving the partition of the surface into combinatorially identical n-sided topological polygons, is defined. The existence of such foldings for given n and given surfaces is explored, with definitive results for the sphere and the torus. We obtain necessary conditions for the existence of such foldings in all other cases.Supported by Kuwait University Grant SM 043.