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1.
研究一类具有时滞和基于比率的三种群食物链捕食-被捕食动力学模型.证明了该系统在适当条件下的一致持久性;通过构造Lyapunov泛函,得到了该系统正平衡点全局渐近稳定的充分条件.  相似文献
2.
二阶非线性微分方程的振动准则   总被引:43,自引:0,他引:43       下载免费PDF全文
王其如 《数学学报》2001,44(2):371-376
本文给出关于二阶非线性常微分方程和时滞微分方程的一些新的振动准则.  相似文献
3.
Continuous-Time Mean-Variance Portfolio Selection: A Stochastic LQ Framework   总被引:43,自引:0,他引:43  
This paper is concerned with a continuous-time mean-variance portfolio selection model that is formulated as a bicriteria optimization problem. The objective is to maximize the expected terminal return and minimize the variance of the terminal wealth. By putting weights on the two criteria one obtains a single objective stochastic control problem which is however not in the standard form due to the variance term involved. It is shown that this nonstandard problem can be ``embedded' into a class of auxiliary stochastic linear-quadratic (LQ) problems. The stochastic LQ control model proves to be an appropriate and effective framework to study the mean-variance problem in light of the recent development on general stochastic LQ problems with indefinite control weighting matrices. This gives rise to the efficient frontier in a closed form for the original portfolio selection problem. Accepted 24 November 1999  相似文献
4.
Benson Proper Efficiency in the Vector Optimization of Set-Valued Maps   总被引:34,自引:0,他引:34  
This paper extends the concept of cone subconvexlikeness of single-valued maps to set-valued maps and presents several equivalent characterizations and an alternative theorem for cone-subconvexlike set-valued maps. The concept and results are then applied to study the Benson proper efficiency for a vector optimization problem with set-valued maps in topological vector spaces. Two scalarization theorems and two Lagrange multiplier theorems are established. After introducing the new concept of proper saddle point for an appropriate set-valued Lagrange map, we use it to characterize the Benson proper efficiency. Lagrange duality theorems are also obtained  相似文献
5.
On adjacent-vertex-distinguishing total coloring of graphs   总被引:32,自引:0,他引:32  
In this paper, we present a new concept of the adjacent-vertex-distinguishing total coloring of graphs (briefly, AVDTC of graphs) and, meanwhile, have obtained the adjacent-vertex-distinguishing total chromatic number of some graphs such as cycle, complete graph, complete bipartite graph, fan, wheel and tree.  相似文献
6.
Geometric processes and replacement problem   总被引:30,自引:0,他引:30  
In this paper, we introduce and study the geometric process which is a sequence of independent non-negative random variablesX 1,X 2,... such that the distribution function ofX n isF (a n–1 x), wherea is a positive constant. Ifa>1, then it is a decreasing geometric process, ifa<1, it is an increasing geometric process. Then, we consider a replacement model as follows: the successive survival times of the system after repair form a decreasing geometric process or a renewal process while the consecutive repair times of the system constitute an increasing geometric process or a renewal process. Besides the replacement policy based on the working age of the system, a new kind of replacement policy which is determined by the number of failures is considered. The explicit expressions of the long-run average costs per unit time under each replacement policy are then calculated, and therefore the corresponding optimal replacement policies can be found analytically or numerically.  相似文献
7.
Convergence properties of the Fletcher-Reeves method   总被引:29,自引:0,他引:29  
This paper investigates the global convergence properties ofthe Fletcher-Reeves (FR) method for unconstrained optimization.In a simple way, we prove that a kind of inexact line searchcondition can ensure the convergence of the FR method. Severalexamples are constructed to show that, if the search conditionsare relaxed, the FR method may produce an ascent search direction,which implies that our result cannot be improved.  相似文献
8.
二阶扩张状态观测器的误差分析   总被引:25,自引:0,他引:25  
本文利用分片光滑的Lyapunov函数来进行扩张状态观测器的误差分析,指出了非线性扩张状态观测器有更好的估计精度能力,给出了为提高估计精度扩张状态观测器的参数所满足的条件.  相似文献
9.
An Efficient Hybrid Conjugate Gradient Method for Unconstrained Optimization   总被引:21,自引:0,他引:21  
Recently, we propose a nonlinear conjugate gradient method, which produces a descent search direction at every iteration and converges globally provided that the line search satisfies the weak Wolfe conditions. In this paper, we will study methods related to the new nonlinear conjugate gradient method. Specifically, if the size of the scalar k with respect to the one in the new method belongs to some interval, then the corresponding methods are proved to be globally convergent; otherwise, we are able to construct a convex quadratic example showing that the methods need not converge. Numerical experiments are made for two combinations of the new method and the Hestenes–Stiefel conjugate gradient method. The initial results show that, one of the hybrid methods is especially efficient for the given test problems.  相似文献
10.
Electronic structure of ZnO and its defects   总被引:21,自引:0,他引:21  
The electronic structure of ZnO and its native point defects has been calculated using full potential linear Muffin-tin orbital ( FP-LMTO) method for the first time. The results show that Zn3d electrons play an important role in the bonding of ZnO. Vacant Zn (Vzn) and interstitial O (Oi) produce the shallow acceptor levels at 0.3 eV and 0.4 eV above the top of the valence band (VB), while interstitial Zn (Zni) produces a shallow donor level at 0.5 eV bellow the bottom of the conduction band (CB). However, Vacant O (Vo) produces a deep donor level at 1.3 eV below the bottom of CB. On the basis of these results, we confirm that Zni is the main factor to induce the native n-type conductivity in ZnO  相似文献
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