Optimal Ordering Policies for Inventory Systems with Emergency Ordering

This paper considers dynamic single- and multi-product inventory problems in which the demands in each period are independent and identically distributed random variables. The problems considered have the following common characteristics. At the beginning of each period two order quantities are determined for each product. A “normal order” quantity with a constant positive lead time of λ _n periods and an “emergency order” quantity with a lead time of λ _e periods, where λ _e = λ _n - 1. The ordering decisions are based on linear procurement costs for both methods of ordering and convex holding and penalty costs. The emergency ordering costs are assumed to be higher than the normal ordering costs. In addition, future costs are discounted.For the single-product problem the optimal ordering policy is shown to be the same for all periods with the exception of the last period in the N-period problem. For the multi-product problem the one- and N-period optimal ordering policy is characterized where it is assumed that there are resource constraints on the total amount that can be ordered or produced in each period.     

基于灰色预测模型的核事故医学应急装备使用保障费用分析

建立了核事故医学应急装备使用保障费用分析模型,且通过GM(1,1)灰色预测模型对核事故医学应急装备使用保障费用进行预测分析,解决了传统方法因数据缺乏而预测精度不足的问题。并用实际数据对预测模型进行了精度验证,结果表明该方法具有很好的预测精度,可用于核事故医学应急装备使用保障费用的预测和估算,为相关部门经费分配提供决策支持,对加强核事故医学应急装备全系统、全寿命的经济技术可行性论证,提高决策水平、计划的科学性和经费整体使用效益都具有重要意义.     

Systems Analysis

Journal of the Operational Research Society -     

震后应急物流系统中带时间窗的模糊动态LRP

针对震后应急物流系统中多层次设施定位－运输路线安排问题(LRP),考虑系统中的动态性、时效性、路网连通性、需求不确定性等特点,建立了一个带时间窗的模糊动态LRP优化模型,据此进行救援过程中不同周期灾区外围应急物资集散点和灾区应急配送中心的定位以及应急物资运输路线安排的联合决策。针对该模型的特点,提出了一种基于动态规划的改进遗传算法,为防遗传算法过早收敛问题,使用了随机遍历抽样法、重组策略和变化变异率法,并通过特定实值编码、罚函数法和物资需求量分割策略处理模型中的约束条件。最后,通过算例分析验证了该模型和算法的有效性。     

城市医疗急救绩效分析研究

为了准确评估城市医疗急救(120急救)系统的救援绩效,面向救护车救援调度过程,通过将救护车状态定义为空闲或繁忙建立救护车队的救援状态空间,基于条件概率的乘法规则以及生灭过程平衡方程,构造求解各救护车工作强度(救护车处在繁忙状态的时间占比)的近似线性方程组及其迭代求解算法,由此提出了救护车工作强度近似模型。基于救护车工作强度,给出了救护车跨区救援比例、响应时间等救援绩效计算方法。为了验证上述模型,评价了苏州市区120急救系统的绩效指标,据此改善了救护车救援系统配置方案。研究表明,救护车工作强度近似模型克服了以往救护车数量较多时(大于20辆)难以求解的困难;根据救援距离设置救护车指派优先级能够实现救护车共享、平衡各救护车工作强度以及跨区救援比例;在不增加救护车总数的情况下,基于救援绩效能够改善救护车分布以及急救辖区划分从而有效缩短医疗急救响应时间。     

传染性公共卫生突发事件的应急物资布局分析

公共卫生突发事件是突发事件中重要的一类,而公共卫生突发事件往往具有传梁性,传染性是指一个地区发生某种突发事件,周围其他地区也可能会发生同类事件.因此针对于具有传染效应的公共卫生突发事件,考虑其发生的不同级别引发周边其他地区不同突发事件的情况,将问题分为事件初始发生以及引发两个阶段进行分析,同时考虑选址和物资配置以满足两个阶段对应急物资的需求,建立模型,求解并给出算例.     

需求不确定下应急医疗服务站鲁棒配置模型与算法

大型突发事件发生后需要快速启动应急救灾网络,合理配置应急医疗服务站。本文考虑各应急医疗服务站选址节点需求的不确定性,引入三个不确定水平参数,构建四类不确定需求集合(box, ellipsoid, polyhedron和interval-polyhedron)对应的应急医疗服务站鲁棒配置模型,运用分支-切割算法求解,最后,进行需求扰动比例的灵敏度分析。算例结果表明,四类不确定需求集下的鲁棒配置模型中,ellipsoid不确定需求集合配置模型开放设施较少,总成本最小,鲁棒性较好。决策者还可以根据风险偏好选择不确定水平和需求扰动比例的组合,以使得总成本最小。     

Supporting decision making to improve the performance of an Italian Emergency Medical Service

An Emergency Medical Service (EMS) plays a fundamental role in providing good quality health care services to citizens, as it provides the first answer in distressing situations. Early response, one of the key factors in a successful treatment of an injury, is strongly influenced by the performance of ambulances, which are sent to rescue the patient. Here we report the research carried on by the authors on the ambulance location and management in the Milano area (Italy), as a part of a wider research project in collaboration with the EMS of Milano and funded by Regione Lombardia. The question posed by the EMS managers was clear and, at the same time, tricky: could decision making tools be applied, based on the currently available data, to provide suggestions for decision makers? To answer such a question, three different studies have been carried on: first the evaluation of the current EMS system performance through statistical analysis; then the study of operational policies which can improve the system performance through a simulation model; and finally the definition of an alternative set of posts through an optimization model. This paper describes the methodologies underlying such studies and reports on how their main findings were crucial to help the EMS in changing its organization model.     

A Non-linear Multi-criteria Programming Approach for Determining County Emergency Medical Service Ambulance Allocations

In this paper an integer, non-linear mathematical programming model is developed to allocate emergency medical service (EMS) ambulances to sectors within a county in order to meet a government-mandated response-time criterion. However, in addition to the response-time criterion, the model also reflects criteria for budget and work-load, and, since ambulance response is best described within the context of a queueing system, several of the model system constraints are based on queueing formulations adapted to a mathematical programming format. The model is developed and demonstrated within the context of an example of a county encompassing rural, urban and mixed sectors which exhibit different demand and geographic characteristics. The example model is solved using an integer, non-linear goal-programming technique. The solution results provide ambulance allocations to sectors within the county, the probability of an ambulance exceeding a prespecified response time, and the utilization factor for ambulances per sector.     

Multiscale Analysis in Many-Body Systems

This paper is an introduction to a multiscale analysis approach to derive mathematical models for systems with finite and infinite degrees of freedom whose fundamental dynamics is stochastic and described by a chemical master equation.     

Systems Analysis and the Computer

The words ‘systems analysis’ are used in at least two senses in the literature. Whilst the general nature of the topic is well understood in the O.R. community, the nature of the term as used by computer scientists is less familiar. In this paper, the nature of systems analysis as it relates to computer-based systems is examined from the point of view that the computer system is an automaton embedded in a human system, and some facets of this are explored. It is concluded that O.R. analysts and computer analysts have things to learn from each other and that this ought to be reflected in their education. The important role played by change in the design of systems is also highlighted, and it is concluded that, whilst the application of techniques developed in the ‘artificial intelligence’ field have considerable relevance to constructing automata able to adapt to change in the environment, study of the human factors affecting the overall systems within which the automata are embedded has an even more important role.     

Vibration Analysis of Gyroscopic Systems

Mechanical structures which can vibrate about a state of mean rotation or translation may constitute gyroscopic dynamic systems that are related by the mathematical similarity of their governing equations of motion. Considering as examples a rotating circular ring and an axially travelling string, the analogy of those systems is demonstrated. The linear vibrations obtained by superposing small perturbations on the stationary solution are analyzed. Assuming time-varying speeds, the effect of non-constant stress resultants on the dynamic stability of gyroscopic systems is investigated and the results are compared to those found in literature where the stress resultants of axially moving continua are commonly taken as constant. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

An Analysis of Fast-Slow Systems

This paper discusses the construction of an approximate solutionto the standard fast-slow system of equations. The usual representationin terms of a fast vector and a slow vector is shown to be satisfactoryonly when certain matrices are neither ill conditioned nor near-orthogonal.Applications of the results to certain control problems areinvestigated. This paper was written while on Leave of Absence at the Departmentof Mathematics, University of Salford, Salford.     

Variational Analysis of Toda Systems

The author surveys some recent progress on the Toda system on a two-dimensional surface Σ,arising in models from self-dual non-abelian Chern-Simons vortices,as well as in differential geometry.In particular,its variational structure is analysed,and the role of the topological join of the barycentric sets of Σ is shown.     

Coderivative Analysis of Variational Systems

The paper mostly concerns applications of the generalized differentiation theory in variational analysis to Lipschitzian stability and metric regularity of variational systems in infinite-dimensional spaces. The main tools of our analysis involve coderivatives of set-valued mappings that turn out to be proper extensions of the adjoint derivative operator to nonsmooth and set-valued mappings. The involved coderivatives allow us to give complete dual characterizations of certain fundamental properties in variational analysis and optimization related to Lipschitzian stability and metric regularity. Based on these characterizations and extended coderivative calculus, we obtain efficient conditions for Lipschitzian stability of variational systems governed by parametric generalized equations and their specifications.