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1.
王琴  李治明  刘连寿   《中国科学A辑》2000,30(7):639-643
用随机级联模型对高能碰撞中的非热相变作了仔细研究 ,用MonteCarlo模拟得到了表征相变的特征参数λ q 与矩阶数q之间的关系 ,证实了自相似多粒子系统中存在两相 ,求出了相变点q =qc 对起伏参数α的依赖关系 ,并和NA2 2实验结果进行了比较 .在中心极限近似下用解析计算作了同样的研究 .对中心极限近似的适用程度进行了讨论 .  相似文献
2.
利用△E-E望远镜及北京Q3D磁谱仪系统.在HI-13串列加速器提供的35MeVα离子轰击下,测量了56Fe(аd)58Co核反应的精细能谱和微分截面角分布.借助全微观DEBA理论分析,相应于核反应俘获的p-n核子对具有(lg9/2)2组态,观测到迄今所能看到的最高拉长态(lg9/2,lg9/2)_9.还对6.4 MeV高激发能级核反应截面的反常增强,而p-n核子对耦合成最小角动量的实验证据进行了讨论,并且确认了6.4MeV能级为非自然宇称态,自旋字称值Jл=1+.  相似文献
3.
本文描述了400 keV离子注入机中磁分析器的特殊设计。在设计中采用了不对称双聚焦条件,并使磁分析器的横向物点是实的,纵向物点是虚的,然后用静电二元四极透镜来实现离子源初聚系统与磁分析器之间的光路匹配。这样设计的磁分析器体积小、质量分辨率高。本机的质量分辨率为200,即能分辨汞离子的六个同位素,实际的测试结果与分辨率的计算值很一致,这表明理论计算是相当成功的。  相似文献
4.
This paper is concerned with stochastic Lotka–Volterra models perturbed by Lévy noise. Firstly, stochastic logistic models with Lévy noise are investigated. Sufficient and necessary conditions for stochastic permanence and extinction are obtained. Then three stochastic Lotka–Volterra models of two interacting species perturbed by Lévy noise (i.e., predator–prey system, competition system and cooperation system) are studied. For each system, sufficient and necessary conditions for persistence in the mean and extinction of each population are established. The results reveal that firstly, both persistence and extinction have close relationships with Lévy noise; Secondly, the interaction rates play very important roles in determining the persistence and extinction of the species.  相似文献
5.
A stochastic Lotka-Volterra system under regime switching is proposed and investigated. First, sufficient conditions for stochastic permanence and extinction of the solution are established. Then the lower- and upper-growth rates of the positive solution are investigated. In addition, the superior limit of the average in time of the sample path of the solution is estimated. The results show that these properties have close relationships with the stationary probability distribution of the Markov chain. Finally, the main results are illustrated by several examples and figures. Some recent results are extended and improved.  相似文献
6.
In this paper, we propose and investigate a stochastic two-prey one-predator model. Firstly, under some simple assumptions, we show that for each species x i , i=1,2,3, there is a π i which is represented by the coefficients of the model. If π i <1, then x i goes to extinction (i.e., lim t→+∞ x i (t)=0); if π i >1, then x i is stable in the mean (i.e., $\lim_{t\rightarrow+\infty}t^{-1} \int_{0}^{t}x_{i}(s)\,\mathrm {d}s=\mbox{a positive constant}$ ). Secondly, we prove that there is a stationary distribution to this model and it has the ergodic property. Thirdly, we establish the sufficient conditions for global asymptotic stability of the positive solution. Finally, we introduce some numerical simulations to illustrate the theoretical results.  相似文献
7.
A stochastic logistic model under regime switching is proposed and investigated. Sufficient conditions for extinction, non-persistence in the mean, weak persistence and stochastic permanence are established. The threshold between weak persistence and extinction is obtained. Then we show that this threshold also is the threshold between stochastic permanence and extinction under a simple additional condition. The results show that firstly, the stationary probability distribution of the Markov chain plays a key role in determining the permanence and extinction of the population. Secondly, different types of environmental noises have different effects on the permanence and extinction of the population. Thirdly, the more the stochastic noises, the easier the population goes to extinction.  相似文献
8.
This paper is concerned with a stochastic non-autonomous Gilpin-Ayala model. First, it is shown that this model has a global positive solution. Then sufficient conditions for extinction, non-persistence in the mean, weak persistence and stochastic permanence of the solution are established. The critical number between weak persistence and extinction is obtained. Finally, the lower- and upper-growth rate of the solution are investigated. Several numerical figures are introduced to illustrate the results. Some recent results are improved and generalized.  相似文献
9.
A two-species stochastic non-autonomous predator–prey model is investigated. Sufficient criteria for extinction, non-persistence in the mean and weak persistence in the mean are established. The critical value between persistence and extinction is obtained for each species in many cases. It is also shown that the system is globally asymptotically stable under some simple conditions. Some numerical simulations are introduced to illustrate the main results.  相似文献
10.
In this paper, sufficient criteria for global asymptotic stability of a general stochastic Lotka-Volterra system with infinite delays are established. Some simulation figures are introduced to support the analytical findings.  相似文献
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