A volume and material handling cost based heuristic for designing cellular manufacturing cells

One of the major problems in a group technology or cellular manufacturing environment is the formation of part groups and machine cells. Because of the combinatorial nature of the cell formation problem, it is difficult to solve the problem optimally. Most of the procedures related to cell design in cellular manufacturing operate on the part-machine incidence matrix in an attempt to identify block diagonality. If complete block diagonality does not exist, the decision about cell configuration is left to the subjective judgement of the designer. These procedures are also generally based on part routing only, and do not consider part volume and material handling costs.In this paper we develop an integer programming model, as well as a heuristic to effectively assign machines to cells. In these procedures we consider component volumes, costs related to movement of components between and within cells, and penalty for not using all machines in a cell visited by a component. Since the integer programming formulation becomes large even for small problems, an efficient heuristic is developed to solve larger problems. The heuristic solutions to 180 randomly generated small problems were compared against the optimal solutions obtained by the integer programming model. The heuristic has been found to identify optimal solutions in all 180 cases.This heuristic is also compared to several well known algorithms on 900 larger test problems. These problems were generated to cover a wide range of environmental situations such as varying levels of block diagonality in the part-machine incidence matrix, and diversity in the component volumes and material handling costs. In 99% of the problems our heuristic generated solutions which are better or as good as the best solution obtained by other algorithms. Further, in situations where complete block diagonality in the part-machine incidence matrix did not exist, our heuristic produced even better results. Since the maximum number of iterations required in our heuristic is the number of machines in the problem, the heuristic is computationally efficient.     

Methods of cell formation in group technology: A framework for evaluation

Group technology is a manufacturing philosophy that attempts to provide some of the operational advantages of a line layout while maintaining some of the strategic advantages of the job shop layout. In designing a productive process that will adopt this manufacturing strategy, one of the primary problems encountered is the formation of component families and production cells. The production cell is a group of machines or processes of functionally dissimilar types that are placed together and dedicated to the manufacture of a specific range of component families.Several researchers in operations management have proposed methods of forming production cells and component families. These methods differ in terms of information requirements and also in terms of the final cell design. Furthermore, the objectives for each method are quite different and it thus seems that the focus has been on the method rather than its appropriateness in a particular situation. This article reviews some of the most publicized methods of group formation and analyzes the type of cells that could be formed using these methods. Subsequently, an evaluative framework is presented where the relative advantages of each type of production cell are discussed in terms of several strategic and operational factors. This framework is of particular use as it highlights the fact that in implementing a cellular manufacturing system, most organizations will face a trade-off of strategic and operational “costs.” Finally, the appropriateness of the cell types with respect to the degree of customer interaction is also discussed.     

农村环境效益审计探讨

文章针对我国当前社会主义新农村建设中面临的严峻的农村环境问题,率先提出开展农村环境效益审计.论文分析了当前阻碍我国农村环境效益审计发展的四个症结,给出相应的对策,并从角色定位、内容范围、组织实施、评价标准和技术方法五个方面,构筑了服务社会主义新农村建设的农村环境效益审计实施框架.     

Models of Quality‐Adjusted Life Years when Health Varies Over Time: Survey and Analysis

Abstract.  Quality‐adjusted life year (QALY) models are widely used for economic evaluation in the health care sector. In the first part of the paper, we establish an overview of QALY models where health varies over time and provide a theoretical analysis of model identification and parameter estimation from time trade‐off (TTO) and standard gamble (SG) scores. We investigate deterministic and probabilistic models and consider five different families of discounting functions in all. The second part of the paper discusses four issues recurrently debated in the literature. This discussion includes questioning the SG method as the gold standard for estimation of the health state index, re‐examining the role of the constant‐proportional trade‐off condition, revisiting the problem of double discounting of QALYs, and suggesting that it is not a matter of choosing between TTO and SG procedures as the combination of these two can be used to disentangle risk aversion from discounting. We find that caution must be taken when drawing conclusions from models with chronic health states to situations where health varies over time. One notable difference is that in the former case, risk aversion may be indistinguishable from discounting.     

Achieving factory automation through Group Technology principles

This article illustrates the use of Group Technology (GT) principles for integrating the various elements of Computer Integrated Manufacturing (CIM). Several observations are made regarding the current state of batch manufacturing in the U.S. in light of these principles. Following a brief historical background, the various elements of GT are described as they occur in the manufacturing cycle. Since the main prerequisite to GT is part family identification, the various classification and coding systems for identifying part families, and also non-codification systems, are briefly described.The benefits of design rationalization and variety reduction are then explained in the context of CAD, CAM, and CAPP. Next, cellular manufacturing, currently the major problem area in the U.S. regarding GT, is discussed. The discussion includes new production technologies and concepts such as economies of scope. Materials management and operation scheduling are discussed next, highlighting the GT/MRP interface. The effect of GT and other new technologies on quality is then addressed and the significant impacts here are noted. Next, the effects on related areas such as personnel and accounting are described, including worker satisfaction, incentive schemes, and cost tracking.Last, an assessment of the current status of batch manufacturing is undertaken. Academic approaches, as well as industry crusades such as just-in-time (JIT) production, are reviewed and the current problems in adopting cellular layouts are addressed.     

基于PC的开放式控制系统在开方机上的应用

对开方机的主要组成和功能进行了描述,介绍了倍福控制系统的构成和工作原理。针对开方机的具体控制要求,完成了控制系统的架构配置、控制软件框架设计、主要程序流程设计、软件代码的编写和模拟调试。     

Argumatics: a text analysis procedure for supporting problem formulation

Problem formulation is the most critical phase of the decision making process. This, particularly in the case of high level multi-stakeholder problems, is not trivial, as the problems do not come “neatly packaged”. The procedure presented in this paper aims to support (i) the exploration of the stakeholders' mental constructs, and (ii) the generation, comparison and synthesis of alternative problem formulations. The suggested procedure — while using the decision analytic approach of the traditional text analysis procedures, follows an inverse, bottom-up direction of analysis: first the individual arguments inherent in the text are explored, then taking them as a starting point, the structures behind the arguments are identified.     

Efficient tests for the presence of a pair of complex conjugate unit roots in real time series

We introduce a framework which allows us to draw a clear parallel between the test for the presence of seasonal unit roots and that for unit root at frequency 0 (or π$\pi$). It relies on the properties of the complex conjugate integrated of order one processes which are implicitly at work in the real time series. In the same framework as that of Phillips and Perron (Biometrica 75 (1988) 335), we derive tests for the presence of a pair of conjugate complex unit roots. The asymptotic distribution we obtain are formally close to those derived by these authors but expressed with complex Wiener processes. We then introduce sequences of near-integrated processes which allow us to study the local-to-unity asymptotic of the above test statistics. We state a result on the weak convergence of the partial sum of complex near-random walks which leads to complex Orstein–Uhlenbeck processes. Drawing on Elliott et al. (Econometrica 64 (1996) 813) we then study the design of point-optimal invariant test procedures and compute their envelope employing local-to-unity asymptotic approximations. This leads us to introduce new feasible and near efficient seasonal unit root tests. Their finite sample properties are investigated and compared with the different test procedures already available (J. Econometrics 44 (1991) 215; 62 (1994) 415; 85 (1998) 269) and those introduced in the first part of the paper.     

The design and use of effective employee participation groups: Implications for human resource management

The use of employee participation groups is an increasingly widespread response to unrelenting environmental demands for higher levels of organizational performance. Guidelines for the design of participation groups are suggested, based on a study of participation group programs in nine organizational units of a major corporation. In order to be most effective, participation groups should include or have access to adequate skills and knowledge for systematic problem solving, should use formalized procedures, should be integrated horizontally and vertically with the rest of the organization, and should be a regular part of the organization rather than special entities. The appropriateness of using participation groups as a part of a larger human resource strategy is explored.     

桩柱式桥台位移计算以及软弱地基时对其的影响

本文首先以工程实例计算简述桩柱式桥台台顶位移的计算过程,由此引申当基础为软弱基础时引起的桥台位移对于桥梁上部结构安全的影响,并概要介绍了其设计时应考虑的要素。     

Parametric bootstrap tests for continuous and discrete distributions

Statistical procedures based on the estimated empirical process are well known for testing goodness of fit to parametric distribution families. These methods usually are not distribution free, so that the asymptotic critical values of test statistics depend on unknown parameters. This difficulty may be overcome by the utilization of parametric bootstrap procedures. The aim of this paper is to prove a weak approximation theorem for the bootstrapped estimated empirical process under very general conditions, which allow both the most important continuous and discrete distribution families, along with most parameter estimation methods. The emphasis is on families of discrete distributions, and simulation results for families of negative binomial distributions are also presented.     

Business process architectures: overview,comparison and framework

With the uptake of business process modelling in practice, the demand grows for guidelines that lead to consistent and integrated collections of process models. The notion of a business process architecture has been explicitly proposed to address this. This paper provides an overview of the prevailing approaches to design a business process architecture. Furthermore, it includes evaluations of the usability and use of the identified approaches. Finally, it presents a framework for business process architecture design that can be used to develop a concrete architecture. The use and usability were evaluated in two ways. First, a survey was conducted among 39 practitioners, in which the opinion of the practitioners on the use and usefulness of the approaches was evaluated. Second, four case studies were conducted, in which process architectures from practice were analysed to determine the approaches or elements of approaches that were used in their design. Both evaluations showed that practitioners have a preference for using approaches that are based on reference models and approaches that are based on the identification of business functions or business objects. At the same time, the evaluations showed that practitioners use these approaches in combination, rather than selecting a single approach.     

Toward an overarching multi-level conceptualization of emergent leadership: Perspectives from social identity,and implicit leadership theories

Organizational leadership research has typically focused on hierarchal top-down leadership where the leader has legitimate authority over organizational tasks and roles. However, rather recently, research has emphasized the emergence of leaders within teams and groups, which is referred to as emergent or horizontal leadership. Due to its infancy, the concept has limited theoretical development and coherence. To further extend our understanding of the topic, we draw on social identity, and implicit leadership theories and offer a multi-level conceptualization of emergent leadership. We first compare emergent leadership to various leadership concepts and through a detailed review, identify mechanisms through which emergent leadership can be identified. Following that, we design an organizing framework based on existing research and then offer propositions presenting a multi-level conceptual model highlighting how different factors at different levels relate to informal leader emergence. We hope that by reforming the research of leadership emergence with a multi-level approach, we renovate the idea considering contextual factors and process mechanisms.     

Decision-making under risk: Editing procedures based on correlated similarities, and preference overdetermination

This paper studies editing procedures based on similarity relations in an expected utility maximization context. It shows that these procedures are compatible both with a family of difference-correlated similarities on the prize space and with a set of families (one for each probability) of ratio-correlated similarity relations on the probability space. In view of the properties satisfied by these families of correlated similarities, it is suggested that Rubinstein's preference overdetermination problem can be avoided. Received: 17 April 1996 / Accepted: 24 September 1998     

The empirical determination of technology and expectations: A simplified procedure

This paper makes three principal contributions to the growing body of empirically oriented research on dynamic factor demand systems that are based on the adjustment cost model of the firm. First, a simplified procedure is described for deriving demand and supply functions which are amenable to empirical estimation and which are consistent with intertemporal expected profit maximization and a general expectations formation process for future prices. Second, it is pointed out that estimation of a complete system of demand and supply functions permits the empirical identification of both the firm's technology and its expectations formation process. Finally, the procedure is applied to aggregate annual U.S. manufacturing data for the 1947-1977 period and the consistency of the data with the theoretical framework is investigated.     

Disentangling preferences and limited attention: Random-utility models with consideration sets

This paper presents a model of choice with limited attention. The decision-maker forms a consideration set, from which she chooses her most preferred alternative. Both preferences and consideration sets are stochastic. While we present axiomatisations for this model, our focus is on the following identification question: to what extent can an observer retrieve probabilities of preferences and consideration sets from observed choices? Our first conclusion is a negative one: if the observed data are choice probabilities, then probabilities of preferences and consideration sets cannot be retrieved from choice probabilities. We solve the identification problem by assuming that an “enriched” dataset is observed, which includes choice probabilities under two frames. Given this dataset, the model is “fully identified”, in the sense that we can recover from observed choices (i) the probabilities of preferences (to the same extent as in models with full attention) and (ii) the probabilities of consideration sets. While a number of recent papers have developed models of limited attention that are, in a similar sense, “fully identified”, they obtain this result not by using an enriched dataset but rather by making a restrictive assumption about the default option, which our paper avoids.     

Optimal maintenance center inventories for fault-tolerant repairable systems

In many military and commercial contexts, complex equipment which is expected to perform very reliably is often designed to be fault-tolerant, that is, able to function although some of the parts have failed. A popular fault-tolerant design is the m-out-of-n system, where there are n identical parts, at least m of which must be functional for machine operation. Complex equipment of this type often undergoes scheduled maintenance overhauls at regular intervals during which all failed components are replaced. Failure to have replacements on hand for failed parts requires emergency measures at premium cost. When repairable parts are highly reliable and expensive, both holding and shortage costs are high. A reasonable objective is to choose initial spares inventory to minimize the sum of holding costs and expected shortage costs.We first develop a model to determine the optimal repairable parts inventory for a maintenance center servicing machines containing a single m-out-of-n system. The model is then extended to handle a related problem, finding optimal maintenance center inventories for machines containing several m-out-of-n systems of different parts, minimizing total expected costs subject to a constraint on total inventory investment.We assume that there is a fleet of machines, which experience identical workloads. There is a cycle time of T days between overhauls for an individual machine. A machine arrives at the maintenance center for overhaul each day. At the overhaul, all failed parts are removed and sent to a repair shop, from which they eventually return to the maintenance center to be used again as spares. The total number of spares undergoing repair and on hand is a constant. There are no backorders; if the number on-hand spares is insufficient to meet demand at an overhaul, a shortage penalty is assessed which depends on the number and type of spares required.While computing holding costs is straightforward, computing expected shortage costs is more complex. Expected shortage costs are dependent upon several factors, including component failure rates, the values of m and n, part repair rates, and the initial number of spares on hand. We assume that the system of interest is well specified, so that the parameters of the model are known except for the number of initial spares of each type, which are the decision variables. We model the on-hand inventory of each type of part as a Markov chain with the number of spares on hand at the end of each day as the states, under the assumptions that failure rates are constant and repair times follow independent exponential distributions. We then calculate the steady-state probabilities of stockout of various numbers of spares, as a function of the initial spares inventory. The expected shortage costs for a given type of spare may then be calculated by finding the product of the penalty cost for lacking p spares and the probability of lacking p spares and summing over all possible p values.Solutions to the problem of finding optimal initial inventory level for a machine containing a single m-out-of-n system may be found easily by enumeration. Solutions to the constrained problem where the machine contains several independent m-out-of-n systems, may be found by dynamic programming. Sensitivity analysis of costs to changes in the inventory investment constraint is clear, and computational effort is reasonable. A simple example is included to illustrate the solution method for both problems.     

The use of time series processes to model the error structure of earnings in a longitudinal data analysis

This study presents an error structure that offers a rich statistical framework for panel data analysis. It includes as special cases most of the error specifications found in longitudinal studies of wages and earnings. A general set of procedures for choosing a specification of this error structure and estimating its parameters appears in the first part of this study. The last section applies these procedures to fit an error structure for wages and earnings of prime-age males using data from the Michigan Panel of Income Dynamics.     

供应链委托代理问题的一阶有效性研究

供应链的最优契约设计经常可以归结为一个委托代理问题．该问题所涉及的模型是一个特殊形式的二层优化问题。目前对该问题的研究非常困难。在经济学领域，解决委托代理模型常用的方法是一阶条件方法，但该方法通常是无效的。文章的主要创新点在于给出了两类满足单调似然率（MLRP）和凸性条件（CDFC）概率分布函数，这两类函数是满足一阶条件的。文章的研究拓广了一阶条件方法有效性的应用范围。