LQ optimal and reaching law-based sliding modes for inventory management systems

In this article, the theory of discrete sliding-mode control is used to design new supply strategies for periodic-review inventory systems. In the considered systems, the stock used to fulfil an unknown, time-varying demand can be replenished from a single supply source or from multiple suppliers procuring orders with different delays. The proposed strategies guarantee that demand is always entirely satisfied from the on-hand stock (yielding the maximum service level), and the warehouse capacity is not exceeded (which eliminates the cost of emergency storage). In contrast to the classical, stochastic approaches, in this article, we focus on optimising the inventory system dynamics. The parameters of the first control strategy are selected by minimising a quadratic cost functional. Next, it is shown how the system dynamical performance can be improved by applying the concept of a reaching law with the appropriately adjusted reaching phase. The stable, nonoscillatory behaviour of the closed-loop system is demonstrated and the properties of the designed controllers are discussed and strictly proved.     

Controlling general multi-echelon distribution supply chains with improved reorder decision policy utilizing real-time shared stock information

The objective of this paper is to introduce an improved reorder decision policy for controlling general multi-echelon distribution systems utilizing shared stock information. Since traditional reorder policies sometimes show poor performances when applied to distribution systems, the order risk policy, which utilizes shared stock information more accurately, was developed for the two-echelon distribution system in the previous research. In this paper, the order risk policy is extended to general multi-echelon systems. Since the calculation of the exact order risk for general multi-echelon systems is complex, a practical approximation method is developed. Through computational experiments, the superior performance of the order risk policy, compared to the existing reorder policies, is shown and the value of shared stock information varying with the characteristics of the supply chain is analyzed.     

供应链环境下的装备多级库存优化研究

研究了一个战役级、多个战术级仓库组成的树型多级库存系统,建立了战役级仓库分别采用等量等间隔、不等量等间隔订货策略的模型。采用自适应遗传算法实现了模型的求解,并用实例验证了算法的有效性。     

基于特定类的不完备决策系统的分布约简

现有的不完备决策系统的分布约简研究主要针对决策系统中的所有决策类,而某些实际应用中,人们往往仅关注于某个特定类的属性约简问题。基于这种考虑,首先提出了基于特定类的不完备决策系统的分布约简的理论框架,给出了在相容关系下的基于差别矩阵的约简算法,最后将该算法与基于所有决策类的不完备决策系统分布约简算法进行对比。实验结果表明,当决策类为特定类时,约简结果的平均长度相对较短,约简效率也有显著的提高。     

Automated sub-zoning of water distribution systems

Water distribution systems (WDS) are complex pipe networks with looped and branching topologies that often comprise thousands to tens of thousands of links and nodes. This work presents a generic framework for improved analysis and management of WDS by partitioning the system into smaller (almost) independent sub-systems with balanced loads and minimal number of interconnections. This paper compares the performance of three classes of unsupervised learning algorithms from graph theory for practical sub-zoning of WDS: (1) Global clustering – a bottom-up algorithm for clustering n objects with respect to a similarity function, (2) Community structure – a bottom-up algorithm based on the property of network modularity, which is a measure of the quality of network partition to clusters versus randomly generated graph with respect to the same nodal degree, and (3) Graph partitioning – a flat partitioning algorithm for dividing a network with n nodes into k clusters, such that the total weight of edges crossing between clusters is minimized and the loads of all the clusters are balanced. The algorithms are adapted to WDS to provide a practical decision support tool for water utilities. Visual qualitative and quantitative measures are proposed to evaluate models' performance. The three methods are applied for two large-scale water distribution systems serving heavily populated areas in Singapore.     

Expert systems for inventory control management

An expert system for inventory management is presented in this paper. The focus is on the development of a simple, user friendly tool that can be used by managers to increase the effectiveness of their inventory control systems. The expert system is capable of deriving input parameters by performing necessary analysis on databases, implementing a set of rules for the selection of inventory models, and present the output through tables. plots, or graphs. The scope of this paper is limited to the single item, single location problem.     

DRP分销管理系统的设计与实现

DRP是管理企业的分销网络系统，目的是使企业具有对订单和供货具有快速反应和持续补充库存的能力。通过互联网将供应商与经销商有机地联系在一起，DRP为企业的业务经营及与贸易伙伴的合作提供了一种全新的模式。该文使用Java作为开发语言，采用Struts2框架技术搭建整个系统，数据库采用SQL2000，Eclipse5．11作为开发工具，设计并实现了DRP分销管理系统。     

Time delay systems with distribution dependent dynamics

General delay dynamical systems in which uncertainty is present in the form of probability measure dependent dynamics are considered. Several motivating examples arising in biology are discussed. A functional analytic framework for investigating well-posedness (existence, uniqueness and continuous dependence of solutions), inverse problems, sensitivity analysis and approximations of the measures for computational purposes is surveyed.     

Analyzing information-enabled stockout management under vendor-managed inventory

We develop a mechanism under vendor-managed inventory (VMI) by which a manufacturer provides an incentive contract to a retailer to convert lost sales stockouts into backorders. An incentive contract is required since the retailer’s efforts are not directly observable. We first show that when there are no limits on order quantities or inventory levels imposed on the manufacturer, the manufacturer will push inventory onto the retailer. The manufacturer minimizes the possibility for lost sales stockouts by maintaining high inventory levels at the retailer rather than by paying incentives to the retailer. However, modern information systems (IS), such as radio frequency identification (RFID), allow the retailer to monitor inventory at its premises and to enforce limits on order quantities. With strict limits on order quantities, the manufacturer will provide incentives to the retailer to convert lost sales stockouts to backorders. We analyze the conditions under which these incentive payments are likely to be highest.     

基于混合需求的供应链多级库存协同订货模型

针对供应链多级库存系统存在混合需求的情况,建立了基于混合需求的多级库存协同订货模型。该模型假设在供应链中只有最下游节点面临的需求是独立需求,而其他上游节点面临的需求都是与之相关的相关需求。由于相关需求是一种块状需求,其库存成本构成与独立需求明显不同。因此,通过对多级库存系统的库存成本构成进行重新分析,分别给出了需求确定时不允许缺货和允许缺货的协同订货模型。另外,还通过对安全库存的分析给出了需求不确定时的协同订货模型。最后,给出了模型求解的遗传算法,并进行了实例仿真分析,展示了这种协同订货模型在混合需求的供应链中的实用性。     

Resource management in open Linda systems

Coordination systems, in particular Linda, have established themselves as important tools for the development of applications to open systems such as the Internet. This paper shows how to tackle a forgotten, but crucial problem in open coordination systems: memory management. As with any system which intends to be of wide use and because memory is a finite resource, coordination systems must address the problems of memory exhaustion. This paper first explores the orthogonality between coordination and computation in order to make it clear that the problem of memory exhaustion in coordination systems cannot be solved using garbage collection schemes implemented at the computation language—a garbage collection scheme must exist in the coordination environment as well. Following the explanation on orthogonality, the paper will focus on describing a garbage collection scheme for the Linda family of coordination systems. It is expected that the solution in Linda can be adapted to other coordination systems as long as they are based on tuple space communication. Copyright © 2003 John Wiley & Sons, Ltd.     

Data management in executive information systems

Data management is important in developing and maintaining executive information systems (EISs). An EIS can fail due to the lack of an adequate data infrastructure for this `data intensive' application. From the literature, discussions with developers, consulting experiences, and eight case studies, a set of key data management issues were identified. Three – data security, ownership, and standards – were further studied, using survey data collected from 85 organizations. Canonical correlation analysis was used to investigate the relationship between these issues and potentially related variables. The breadth and depth of information provided were found to be correlated with the difficulty of the issues. The degree of support from key individuals was also found to be correlated with the level of difficulty.     

Efficient tag detection in RFID systems

Recent technological advances have motivated large-scale deployment of RFID systems. However, a number of critical design issues relating to efficient detection of tags remain unresolved. In this paper, we address three important problems associated with tag detection in RFID systems: (i) accurately detecting RFID tags in the presence of reader interference (reader collision avoidance problem); (ii) eliminating redundant tag reports by multiple readers (optimal tag reporting problem); and (iii) minimizing redundant reports from multiple readers by identifying a minimal set of readers that cover all tags present in the system (optimal tag coverage problem). The underlying difficulties associated with these problems arise from the lack of collision detection mechanisms, the potential inability of RFID readers to relay packets generated by other readers, and severe resource constraints on RFID tags. In this paper we present a randomized, distributed and localized Reader Collision Avoidance (RCA) algorithm and provide detailed probabilistic analysis to establish the accuracy and the efficiency of this algorithm. Then, we prove that the optimal tag coverage problem is NP-hard even with global knowledge of reader and tag locations. We develop a distributed and localized Redundant Reader Elimination (RRE) algorithm, that efficiently identifies redundant readers and avoids redundant reporting by multiple readers. In addition to rigorous analysis of performance and accuracy, we provide results from elaborate simulations for a wide range of system parameters, demonstrating the correctness and efficiency of the proposed algorithms under various scenarios.     

The effect of backlog queue and load-building processing in a multi-echelon inventory network

A continuous-review, two-echelon inventory system with one central warehouse and an arbitrary number of non-identical retailers is considered in this study. Retailers face independent Poisson demands and apply standard (r, Nq) policies. Filled orders at the central warehouse must be consolidated into loads before shipping to the retailer level. New modeling options for the backorder processing and load-building processes are considered. Employing simulation, a set of experiments is performed to illustrate how different processing rules for the backlogging and load-building queues affect the lead-time experienced at the retailer level. Simulation results indicate that there are cases where considerable improvements can be gained from using different processing rules in backlogging and load-building queues.     

Asymptotic stability in distribution of stochastic systems with semi-Markovian switching

This paper investigates the asymptotic stability in distribution of stochastic systems with semi-Markovian switching whose transition rates are time varying, which are more general than stochastic systems with Markovian switching. Some sufficient conditions for the asymptotic stability in distribution of stochastic systems with semi-Markovian switching are established and those conditions are employed to design the state-feedback controllers in terms of linear matrix inequalities. Finally, several examples are given to illustrate the effectiveness of the theoretical results.     

多级集群式供应链跨链库存合作及鲁棒优化算法

以四级两单链的集群式供应链为研究对象,在两个单链相巨竞合条件下,建立了两单链问两零售商跨链问库存协作的时变鲁棒控制系统模型,以及牛鞭效应的弱化方法,并用H∞优化算法来求解动态最优决策.通过实例分析表明,集群式供应链跨链间协调及鲁棒优化能有效抑制牛鞭效应、降低库存水平,在减小订货波动的同时可提高对集群市场的响应速度.     

DRP分销管理系统的设计与实现

DRP是管理企业的分销网络系统,目的是使企业具有对订单和供货具有快速反应和持续补充库存的能力。通过互联网将供应商与经销商有机地联系在一起,DRP为企业的业务经营及与贸易伙伴的合作提供了一种全新的模式。该文使用Java作为开发语言,采用Struts2框架技术搭建整个系统,数据库采用SQL2000,Eclipse5.1[1]作为开发工具,设计并实现了DRP分销管理系统。     

Limiting zero distribution of sampled systems

In this paper, we consider the sampling of a continuous time system with possibly a non-rational transfer function. Limiting zero distribution of the sampled system represented by an FIR model is derived. It is shown that the zeros of the FIR sampled system converge evenly to the unit circle or to the unit disk plus unstable roots of the reciprocal polynomials depending on assumptions.     

Peaking demand factor-based reliability analysis of water distribution systems

Water demands vary and consideration of the probabilistic nature of the variations should lead to more instructive assessments of the performance of water distribution systems. Water consumption data for several households were analysed using the chi-square technique and it was found that distributions worth considering under certain circumstances include the normal and lognormal.Reliability values were calculated for a range of critical demand values and the corresponding confidence levels determined from the probability distributions. Water consumption was assumed to be pressure dependent and the modelling of the water distribution system was carried out accordingly. This peaking factor approach coupled with the statistical modelling of demands provides a more realistic way of incorporating variations in demands in the evaluation and reporting of system performance than the traditional single demand value approach in that the extent to which a network can satisfy any demand and the probability that the demand will occur can be recognized explicitly. The method is illustrated by an example.     

Parameters of cache systems based on a Zipf-like distribution

The object of this paper is to explain a system of Internet traffic caching. The task is to create an analytical model of a cache system linking its size with other parameters by boundary conditions. A definition of a dynamic cache model is introduced. The parameters of a cache system are calculated using the Zipf's first law and Zipf-like distribution. The correspondence between size of a cache system and aggregated bandwidth of external links is derived.