Analysis of a batch machine fed by an unreliable discrete machine

This paper analyses the behaviour of a manufacturing line consisting of two machines in series where the first machine processes lots one at a time, and is subject to failure and takes a random amount of time to repair when it fails, and the second machine is a perfectly reliable batch machine. A control limit policy is adopted to determine lot sizes for the batch machine. When the batch machine completes processing, if the number of lots in the buffer is greater than or equal to the critical number (Q?), all the lots in the buffer are loaded immediately, otherwise the batch machine waits until Q lots are accumulated. An embedded discrete time Markov-chain approach is proposed, and recursive approaches are developed to derive necessary performance measures. A numerical example explains how to obtain the optimal value of a critical number minimizing the cost functions.     

Parking slot assignment for urban distribution: Models and formulations

A key element to enhance urban distribution is the adequate management of parking space, particularly for loading and unloading operations. An in-advance booking system able to be adjusted to users needs can be a very useful tool for city councils. Such a tool should be fed with criteria for allocating requests to time slots. In this paper we discuss alternative criteria for the parking slot assignment problem for urban distribution and we propose the use of mathematical programming formulations to model them. Several models are proposed, analyzed and compared among them. Extensive computational experience is presented with a detailed analysis and comparison, which provides quantitative indicators of the quality of each of the proposed models.     

A note on “The EPQ with partial backordering and phase-dependent backordering rate”

Pentico et al. [The EPQ with partial backordering and phase-dependent backordering rate. Omega 2011;39(5):574-7] recently proposed an EPQ model with partial backordering. They tried to determine the minimum average total cost per year from the three cases: to lose all sales, to meet all demand, and to allow stockouts with partial backordering. In this paper, we solve the same model without differential calculus and present a different decision procedure. Without the comparison of those costs, a numerical example is illustrated to determine the optimal production policy by our criteria.     

城市停车难与机械式立体停车设备

阐述了我国汽车发展的形势及城市停车难问题的现状,对停车难问题从大城市向中小经济发达城市拓延的态势进行了分析,提出推动机械式立体停车库发展解决停车难问题的思考.文中还介绍了机械式立体停车库的结构型式及特点.     

MRP Planned Orders in a Multiple‐Supplier Environment with Differing Lead Times

This study examines a deterministic material requirements planning (MRP) problem where lead times at subsequent ordering moments differ. Adequate replenishment methods that can cope with lead time differences are lacking because of the order crossover phenomenon, that is, replenishment orders are not received in the sequence they are ordered. This study specifies how to handle order crossovers and recalculate planned order releases after an update of gross requirements. The optimal (s, S) policy is based on dynamic programing. The state space is kept to a minimum due to three fundamental insights. The performance of the optimal solution approach is compared with two heuristics based on relaxations and a benchmark approach in which order crossovers are ignored. A numerical analysis reveals that average cost savings up to 25% are possible if the optimal policy is used instead of the benchmark approach. The contribution of this study is threefold: (1) it generalizes theory on MRP ordering, allowing for lead time differences and order crossovers; (2) it develops new fundamental insights and an optimal solution procedure, leading to substantial cost saving; and (3) it provides good‐performing heuristics for a general and realistic replenishment problem that can replace the current replenishment methods within MRP.     

基于批量流的多阶段生产系统的优化问题研究

考虑一个多阶段生产系统,在每个阶段上生产批量被分成若干个子批量进行加工,子批量可以相等也可以不相等,同时每个阶段上在相邻子批量之间可以有空闲。每个阶段上子批量的数目可以不相等。文中首先以系统总变动成本为目标函数对这样一个系统建立对应的模型,提出了求解这一问题的启发式方法,通过数值算例验证了这一方法的有效性。此外,还讨论了重启成本、空闲成本和对应于子批量的调整成本对系统总变动成本、生产批量以及子批量数目的影响。     

郑和下西洋反思

通过对十五世纪中、西方远航船队的比较 ,昭示世人郑和船队的伟大。通过对郑和下西洋目的的辨析 ,阐明了明成祖朱棣和明宣宗朱瞻基派遣郑和下西洋的真实意图 ,追求“天下共主”的虚名和“贸采琛异”的耗费 ,给明朝社会经济带来了沉重打击。这是“埋葬”伟大郑和船队的根本原因     

民主选举方式的伦理价值新探

投票选举,就其自身来说,符合按照德才分配政治职务的原则,因而是善的;但就其结果来说,却使被选举权为精英垄断,赋予官吏和政治权力以极大的重要性,最终难免精英篡夺最高权力,使“选举”成为“选主”,因而罪莫大焉。因此,投票选举“自身善”与“结果恶”的净余额是极大的恶,属于纯粹恶范畴,是不应该的、恶的和具有负价值的民主选举方式。相反,抽签选举,就其自身来说,违背按照德才分配政治职务的原则,因而是恶;但就其结果来说,不但保障了每个人都平等享有选举权和被选举权,而且还具有破除精英垄断政权、扼杀专制者于摇篮和降低官吏的价值,因而善莫大焉。因此,抽签选举“自身恶”与“结果善”的净余额是极大的善,属于必要恶范畴,是应该的、善的和具有正价值的民主选举方式。     

古希腊悲剧三题

古希腊悲剧光辉灿烂,至今仍洋溢着旺盛的生命力,其理论与创作实践,对我们仍有着参考和借鉴之处。本文主要论述了古希腊悲剧中悲剧主人公的创造,悲剧反映社会生活矛盾的规律,以及悲剧的命运观等三个问题。     

配额——交易机制下动态批量生产和减排投资策略研究

随着我国碳排放交易市场的建立和发展,在碳排放约束下逐步降低单位产出的碳排放水平成为企业生产经营管理中的中长期约束性目标。本文在一个多周期决策模型中研究了配额-交易机制下企业的最优动态批量生产、碳排放权交易和减排投资联合决策问题。生产商在整个决策周期期初决定是否进行减排投资以及投资规模,根据每个周期的生产计划决定减排设备的运行计划。根据节能减排技术的特点,本文假设生产商运行减排设备时不仅降低了产品的单位生产碳排放量,而且降低了产品的单位生产成本。本文基于广义Benders分解法对模型进行了最优性分析,得到了最优生产决策和最优减排投资决策的一些基本性质,并通过数值实验分析了碳排放配额和碳排放权价格对生产商总成本、总排放以及减排投资决策的影响。本文的数值实验分析结果发现:(1)当碳交易市场上的碳排放权充足时,减少碳排放配额或改变碳排放配额的分配方式并不能影响生产商的碳排放水平;(2)碳排放权价格是影响生产商的碳排放水平和减排投资规模的关键因素;(3)随着碳排放权价格的上升,即使拥有足够的碳排放配额,生产商仍会不断提高减排投资规模以获得减排收益。研究结果对碳排放交易体系下生产企业进行减排技术投资具有较强的管理启示。