Toward an Application Guide for Safety Integrity Level Allocation in Railway Systems

The work in the article presents the development of an application guide based on feedback and comments stemming from various railway actors on their practices of SIL allocation to railway safety‐related functions. The initial generic methodology for SIL allocation has been updated to be applied to railway rolling stock safety‐related functions in order to solve the SIL concept application issues. Various actors dealing with railway SIL allocation problems are the intended target of the methodology; its principles will be summarized in this article with a focus on modifications and precisions made in order to establish a practical guide for railway safety authorities. The methodology is based on the flowchart formalism used in CSM (common safety method) European regulation. It starts with the use of quantitative safety requirements, particularly tolerable hazard rates (THR). THR apportioning rules are applied. On the one hand, the rules are related to classical logical combinations of safety‐related functions preventing hazard occurrence. On the other hand, to take into account technical conditions (last safety weak link, functional dependencies, technological complexity, etc.), specific rules implicitly used in existing practices are defined for readjusting some THR values. SIL allocation process based on apportioned and validated THR values is finally illustrated through the example of “emergency brake” subsystems. Some specific SIL allocation rules are also defined and illustrated.     

Building a mutually beneficial partnership to ensure backup supply

In today׳s complex global environment, it is very important for a firm to possess backup supply resource when facing unpredictable disruptions from its primary supply resource. To ensure the actual arrival of backup supply in cases of primary supply disruptions, a purchasing firm needs to work with its backup supplier to forge a strong partnership that not only protects itself, but also assures the backup supplier׳s economic benefit. In this research, we establish the structure of such a partnership based on real business practices. The interactions between the purchasing firm and the backup supplier are examined through a decision-tree approach that takes disruption situations at all levels into consideration. We then design the backup supply contract, find the Nash equilibrium contract parameters, and identify the critical conditions under which such a contractual partnership will be valuable. The contract parameters we find are functions of the moments of the demand distribution, which are independent of specific demand distributions and are easy to be estimated in practice. Our numerical tests support our theoretical results and demonstrate the robustness of the contract with respect to various demand distributions.     

An efficient algorithm for finding the M most probable configurationsin probabilistic expert systems

A probabilistic expert system provides a graphical representation of a joint probability distribution which enables local computations of probabilities. Dawid (1992) provided a flow- propagation algorithm for finding the most probable configuration of the joint distribution in such a system. This paper analyses that algorithm in detail, and shows how it can be combined with a clever partitioning scheme to formulate an efficient method for finding the M most probable configurations. The algorithm is a divide and conquer technique, that iteratively identifies the M most probable configurations.     

Edge Estimation in the Population of a Binary Tree Using Node-Sampling

Suppose a finite population of several vertices, each connected to single or multiple edges. This constitutes a structure of graphical population of vertices and edges. As a special case, the graphical population like a binary tree having only two child vertices associated to parent vertex is taken into consideration. The entire binary tree is divided into two sub-graphs such as a group of left-nodes and a group of right-nodes. This paper takes into account a mixture of graph structured and population sampling theory together and presents a methodology for mean-edge-length estimation of left sub-graph using right edge sub-graph as an auxiliary source of information. A node-sampling procedure is developed for this purpose and a class of estimators is proposed containing several good estimators. Mathematical conditions for minimum bias and optimum mean squared error of the class are derived and theoretical results are numerically supported with a test of 99% confidence intervals. It is shown that suggested class has a sub-class of optimum estimators, and sample-based estimates are closer to the true value of the population parameter.     

基于实物期权法的矿区生态补偿额核算研究——以湖南花垣锰矿区为例

确定补偿资标准是矿产开发生态补偿机制构建的关键,也是难点。实物期权二叉树模型能比较精确地计算出项目预期收益,而项目预期收益与实际收益的差额就是生态补偿额中的发展机会成本。运用此模型对湖南花垣县生态补偿额度中发展机会成本的年补偿额进行核算得知,目前矿区生态补偿额的征收标准过低,远远不能满足生态补偿的要求,因此,国家应增加生态补偿资金的拨付或加大税费征收力度,以达到对矿产资源的有偿使用和合理利用。     

论《醒世姻缘传》的树形结构

《醒世姻缘传》的结构神似树形,因果观是树形结构之根,晁源和狄希陈的前生后世的婚姻是树形结构的主干,晁夫人的后半世是树形结构的次干,诸多大小轶事构成树形结构的枝叶。依托树形结构,整部小说以惧内故事为主要讲述对象,展示明代中后期乡村及城市中下层各色人物和社会生活,其结构颇具特色。     

樟树意象的文化象征

樟树作为文化符号所遭遇的古冷今热的现象很值得研究。作为自然生长的南方树种,其实用价值表现多多,但是在芬芳比德、植物象征极为盛行的古代,樟树却没能获得应有的文化品质,这与其不幸生长在非政治中心的南方区域且隐居深山幽谷有关。至而今,尤其是近十余年来,樟树已被37个地级市选作市树,其符号价值迅速飙升,而主要的实用价值反而在无意间被忽略了。樟树作为市树确实让城市更美了,不过,它们展示的只是其亮丽的外表。     

喷树增产耐贮剂对沙糖桔树上及采后的保鲜效果

于沙糖桔果实转色期喷施＂喷树增产耐贮剂＂,可提高采前保果率、总糖、可溶性固形物和谷胱甘肽的含量,显著降低因干冷和湿冷引起的伤果和落果率.该处理可显著减少采后贮藏期总糖、可溶性固形物和水分的损失,减少烂果率,有助于维持果品的产量和质量.     

北京大学校园内植树碑考证

在北京大学未名湖旁有两块植树碑,一块是清朝乾隆皇帝丁未年（1788）所立,一块是民国十一年（1922）燕京大学教育系壬戌班所立,本文对这两块碑的碑文进行了考证。     

Parallelizing computation of expected values in recombinant binomial trees

Recombinant binomial trees are binary trees where each non-leaf node has two child nodes, but adjacent parents share a common child node. Such trees arise in option pricing in finance. For example, an option can be valued by evaluating the expected payoffs with respect to random paths in the tree. The cost to exactly compute expected values over random paths grows exponentially in the depth of the tree, rendering a serial computation of one branch at a time impractical. We propose a parallelization method that transforms the calculation of the expected value into an embarrassingly parallel problem by mapping the branches of the binomial tree to the processes in a multiprocessor computing environment. We also discuss a parallel Monte Carlo method and verify the convergence and the variance reduction behavior by simulation study. Performance results from R and Julia implementations are compared on a distributed computing cluster.