基于马尔科夫过程的大型机组三状态可靠性研究

目的研究大型机组系统的可用度,在一定程度上对大型机组可靠性管理工作水平提供理论依据.方法利用马尔科夫过程理论,提出了大型机组三状态可靠性模型,根据Chapman-Kolmogorov方程,建立了线性方程组.结果通过求解方程组,绘制出状态转移图,计算出系统处于各种状态下的概率和系统可用度.结论根据大型机组处于三状态的概率...     

线截抽样中两个样本被同时抽中的概率及其协方差的研究

通过对线截抽样中样本间两两同时出现的概率进行研究，解决树木间的协方差问题，以便通过一条样线对总体作出估计     

林带有断空概率的模拟计算与最佳设计行数的推导

本文用概率论方法对林带行数、长度、保存率与林带完整性的关系做了系统的理论分析和验证,提出保证林带完整、连续的林带行数与保存率和带长有关;在理论推导的基础上建立了带状林最佳设计行数表;给出了带状林行数设计的理论根据和具体方法。     

A new contagion index to quantify spatial patterns of landscapes

A contagion index was proposed by O'Neill et al. (1988) to quantify spatial patterns of landscapes. However, this index is insensitive to changes in spatial pattern. We present a new contagion index that corrects an error in the mathematical formulation of the original contagion index. The error is identified mathematically. The contagion indices (both original and new) are then evaluated against simulated landscapes.     

对违约相关性计量模型的研究

对企业的违约相关性进行了说明，并介绍了违约相关性的两种传统分析方法，提出了一个改进的模型，对其结论作了详细分析。     

云南松林分与小蠹虫的竞争状态研究

云南松林遭小蠹虫危害以后,常由于林分抵御功能的不同而形成区域性的蠢害林分系统,即在"虫群区域"内存在着"衰退"和"发展"两种林分演变过程,若按"演变属性"来分析,则看到蓄积量下降、蓄积量停滞、蓄积量上升等3种林分演变过程是蠹害林分系统的普遍性特征,前2种属于"衰退状态",后1种属于"发展状态"。对3个蠢害林分系统的"演变属性"用二项分布P(衰退概率)+Q(发展概率)=1来描述,那么二项式(P+Q)3方程中的系数1、3、3、1成为系统中不同"演变属性"的概率论判断。由人为因素、虫群因素、环境因素引起的林分"衰退"和"发展"当然是随机的,但从分析中看到人的正、反两面行为都会引起林分与虫群相互作用的变化。     

Brown hyaenas on roads: Estimating carnivore occupancy and abundance using spatially auto-correlated sign survey replicates

Carnivore survey protocols that properly address spatial sampling and detectability issues are seldom feasible at a landscape-scale. This limits knowledge of large-scale patterns in distribution, abundance and their underlying determinants, hindering conservation of globally threatened carnivore populations. Occupancy analysis of data from logistically efficient sign surveys along consecutive road segments (spatially auto-correlated replicates) offers a potential solution. We adapted and applied this newly-developed method over 62,979 km² of human-modified land in South Africa. Our aims were to (1) generate unbiased estimates of brown hyaena occupancy and abundance (2) investigate two suspected determinants of occupancy using a combination of biological and socio-economic sampling techniques, and (3) use simulations to evaluate the effort required for abundance and occupancy estimates with acceptable bias, precision and power. Brown hyaena occupancy was estimated at 0.748 (±SE 0.1), and estimated overall density in agricultural land (0.15/100 km², ±SE 0.08) was an order of magnitude lower than in protected areas. Positive attitudes to carnivores and presence of wildlife farms exerted strong positive effects on occupancy, so changes in these factors may well exert monotonic impacts on local metapopulation status. Producing reliable occupancy and abundance estimates would require ?6 replicates and ?12 replicates per site respectively. Detecting 50% and 30% declines in brown hyaena occupancy with adequate power would require five annual surveys at ?65 sites and ?125 sites respectively. Our results suggest that protocols based on spatially auto-correlated sign survey replicates could be used to monitor carnivore populations at large, and possibly even country-wide spatial scales.     

Current statistical issues in Weed Research

The correct design of experimental studies, the selection of the appropriate statistical analysis of data and the efficient presentation of results are key to the good conduct and communication of science. The last Guidance for the use and presentation of statistics in Weed Research was published in 1988. Since then, there have been developments in both the scope of research covered by the journal and in the statistical techniques available. This paper addresses the changes in statistics and provides a reference work that will aid researchers in the design and analysis of their work. It will also provide guidance for editors and reviewers. The paper is organised into sections, which will aid the selection of relevant paragraphs, as we recognise that particular approaches require particular statistical analysis. It also uses examples, questions and checklists, so that non-specialists can work towards the correct approach. Statistics can be complex, so knowing when to seek specialist advice is important. The structure and layout of this contribution should help weed scientists, but it cannot provide a comprehensive guide to every technique. Therefore, we provide references to further reading. We would like to reinforce the idea that statistical methods are not a set of recipes whose mindless application is required by convention; each experiment or study may involve subtleties that these guidelines cannot cover. Nevertheless, we anticipate that this paper will help weed scientists in their initial designs for research, in the analysis of data and in the presentation of results for publication.     

协同DF-OFDM系统中基于MRC的机会中继研究

针对机会中继译码转发协同系统中未考虑直传链路的问题,提出一种由目的节点根据系统中断概率进行中继选择的方案,研究了将机会中继信号与直传信号在目的节点进行最大比合并时的系统性能,推导了采用最大比合并时的系统中断概率.研究结果表明,当直传链路存在时,通过目的节点的中继选择,可使系统性能得到进一步提高,其性能优于不考虑直传链路时的机会中继系统.     

马尔科夫链预测法对四川各地区人均GDP的研究

马尔科夫在近代物理学、生物学、公共服务事业、信息处理、制动控制、通信及计算机方面有广泛的预测应用.利用马尔可夫转移概率矩阵来对四川各地区人均GDP的研究,可以预测未来几年四川地区的小康情况.