Optimal policies in hybrid manufacturing/remanufacturing systems with product substitution

In hybrid control systems for simultaneous remanufacturing of used products and manufacturing of new ones, the two operations are not directly interconnected if remanufactured items are downgraded and have to be sold in markets different from those for new products. Sometimes a connection between these markets is given by a downward substitution property which allows the producer to offer a new item instead of a remanufactured one in case of a shortage of a remanufactured product. Thus, shortage costs can be avoided, but a loss in profit due to sale of a high-graded product at the price of a low-graded one has to be accepted. For a single-period problem with stochastic returns of used products and stochastic demands of serviceable ones, it is shown how the manufacturing and remanufacturing decisions have been coordinated in order to maximize the total expected profit. It turns out that under strictly proportional costs and revenues a medium-simple ‘order-up-to policy’ with two parameters and two parameter functions is optimal. However, optimal policies in situations where manufacturing leadtimes exceed leadtimes for remanufacturing turn out to be different from those in the opposite leadtime case. The research presented combines methods for policy analysis in stochastic manufacturing/remanufacturing problems and in stochastic inventory control problems with substitutable products.     

An economic production and remanufacturing model with learning effects

Managing inventory in reverse logistics has been receiving much attention in recent years. One inventory problem that has been of interest to researchers is the production and remanufacturing model, where used items are collected and remanufactured to satisfy customer demand. The available models in the literature do not discuss the learning effects in production and remanufacturing processes. This may not be true in industries where labour costs and learning costs are expensive. By modelling these learning effects, management may use established learning models to better utilize capacity, manage inventories, and coordinate production and distribution throughout the chain.This paper extends the production, remanufacture, and waste disposal model by assuming learning to occur in both production and remanufacturing processes. However, this paper also assumes that improvements due to learning require capital investment. Mathematical models are developed, numerical examples are provided, and results are discussed.     

Robust optimal policies of production and inventory with uncertain returns and demand

We consider an inventory and production planning problem with uncertain demand and returns, in which the product return process is integrated into the manufacturing process over a finite planning horizon. We first propose an inventory control model for the return and remanufacturing processes with consideration of the uncertainty of the demand and returns. Then a robust optimization approach is applied to deal with the uncertainty of the problem through formulating a robust linear programming model. Moreover, properties on the robust optimization model are studied, and an equivalent robust optimization model based on duality theory is obtained which allows the solutions to be derived more efficiently. Finally, we provide a set of numerical examples to verify the effectiveness of the approach and analyze the effects of the key parameters on the solutions.     

Demand chain alignment competence — delivering value through product life cycle management

This paper endorses demand chain alignment as a competence that supports effective product life cycle (PLC) management. Demand chain alignment integrates the demand creation (historic domain of marketing) and demand fulfilment processes (domain of supply chain management), to develop and to deliver products that convey superior customer value while deploying resources efficiently. So far, the relationship between demand chain alignment and PLC management has only been addressed from an operations and demand/supply chain perspective, but not from a marketing perspective. Three research propositions, on the relationship between both concepts, are derived from a literature review and applied to a case study from a global player in the tobacco industry. The findings do not support the current view that the product life cycle is a market-oriented classification variable for demand chain strategies. Instead, demand chain alignment needs to link customer needs-based segments with the supply chain. Moreover, PLC management and demand chain alignment have a mutually reinforcing relationship, in which PLC management can facilitate the competence development, ensures a dynamic perspective and, at the same time, benefits from aligned demand creation and fulfilment processes. Based on the findings, a model integrating demand chain alignment and PLC management is proposed.     

Applying fuzzy linguistic quantifier to select supply chain partners at different phases of product life cycle

Owing to rapidly growing global competition, enterprises are increasingly focusing on their core competencies. The focal company faces the challenge of creating alliances with more suppliers to create outsourcing synergy and provide heterogeneous products for customers. This study proposes a fuzzy multiple attribute decision making (FMADM) method based on the fuzzy linguistic quantifier. An attempt is made to ensure that the evaluation results satisfy the current product competition strategies, and also improve the effectiveness and efficiency of the entire supply chain. The fuzzy concept is applied to both the ordinal and cardinal information. Furthermore, the fuzzy linguistic quantifier guided order-weighted aggregation (FLQG-OWA) operator can be used to satisfy the enterprise product development strategy based on different phases of product life cycle.     

A production/remanufacture model with returns’ subassemblies managed differently

This paper considers a production-remanufacturing inventory model for a single product, where constant demand is satisfied from the inventory of newly produced and remanufactured items. Although the available models in the literature imply that collected used units (or returns) are disassembled for recovery purposes, these models really do not treat them as such. Contrary, the returns are assumed to be recovered as whole units, perhaps, for simplicity. This assumption may not capture the benefits reaped from product recovery programs. This paper addresses this limitation in the literature and assumes that each unit of a used product is collected and disassembled into components, where these components are sorted into subassemblies, which are fed back into the production-remanufacturing process. The returned subassemblies are remanufactured and reassembled to represent a second source of as-good-as-new units of the end-product. For this multi-component inventory problem, the question that needs to be answered is whether, or not, extreme strategies of either pure remanufacturing or pure production are more economical than a mixed strategy (one that combines both strategies). A mathematical model is developed that accounts for the inventories of subassemblies. The results suggested that not accounting for the disassembled components of a product leads to inappropriate inventory decisions that are not environmentally sound.     

An inventory model with non-resuming randomly interruptible lead time

We assume that an unreliable supplier in a single-item stochastic inventory system alternates randomly between two possible states (i.e., available and unavailable), following a two-state continuous-time homogeneous Markov chain. For a compound Poisson stream of demands and Erlang lead times, our model considers the scenario where the processing of the outstanding order (if any) is interrupted at every supplier's transition epoch from the available to the unavailable state, and is restarted from the outset upon the supplier's regaining its available state. We derive the stationary distribution of the on-hand inventory under a continuous-review policy and provide some numerical results.     

Business cycle stylized facts and inventory behaviour: New evidence for the Euro area

The purpose of this paper is for the first time to use Business Tendency Survey data, first, to identify new facts that are useful for the interpretation of the decline in the volatility of real activity in the Euro area, and, second, to test the inventory management hypothesis as an explanation for the Great Moderation in Europe. We present stylized facts from the Business Tendency data on series for inventories, current production, current orders, and expected production for the Euro area, emphasizing the decline in the volatility of the series. Further, we investigate whether the decline in inventory volatility can be attributed to an endogenous change in the persistence of shocks to the accumulation dynamics of inventories or to an exogenous change in the shocks hitting the inventory optimisation process. Our results at Euro level generally indicate that there is no evidence of a break in the inventory accumulation process. On the contrary, the impact of exogenous shocks on inventory volatility appears to be steadily declining over time, beginning from the mid-1980s.     

An inventory and order admission control policy for production systems with two customer classes

In this paper we examine a Markovian single-stage system producing a single item to satisfy demand of two different customer classes. A simple threshold type heuristic policy is proposed for the joint control of inventories and backorders. Explicit forms of the steady-state probabilities under this policy are derived and used to assess the average profit rate of the system and determine the optimal control parameters. Certain properties of the average profit rate are established and used to develop computationally efficient algorithms for finding the optimal control parameter values. Numerical results show that the proposed policy is a very good approximation of the optimal policy and outperforms other commonly used policies.     

A serial mixed produce-to-order and produce-in-advance inventory model with multiple retailers

We formulate a general mixed produce-to-order and produce-in-advance inventory model having multiple stocking echelons and multiple retailers. We show that the problem to find an optimal inventory policy for such a model with a uniform or a normal demand distribution can be reduced to a general constrained optimization problem.     

An empirical analysis of inventory turnover behaviour in Greek retail sector: 2000-2005

In this study we investigate the determinants of inventory turnover. The study is based on an econometric analysis of inventory behaviour using an inventory turnover model. The empirical implementation of the model was conducted on a sample of financial data for 566 Greek retail firms for the period 2000-2005. By employing panel data techniques it was found that inventory turnover ratio is negatively correlated with gross margin and positively correlated with capital intensity and a measure of sales surprise.Decomposing the variance into its components associated with year, firm and retail segment effects, we found that a substantial amount of inventory turns variability is due to segment-wise effects. Moreover, the inventory turnover reaction to different sales changes was also studied. It was estimated that changes in sales bring on bigger changes when firms operate in sales-declined region. These results are useful in identifying methods and applications to improve inventory performance among firms and over time.     

Agglomeration and clustering over the industry life cycle: Toward a dynamic model of geographic concentration

Research on agglomeration finds that either a higher survival rate of incumbent firms or a higher founding rate of new entrants, or both, can sustain an industry cluster. The conditioning effects of time on the two distinct mechanisms of survival and founding are, however, rarely examined. We argue that the forces driving geographic concentration vary across the industry life cycle. Data from Ontario's winery industry from 1865 to 1974 demonstrates a dynamic model of geographic concentration: agglomeration attracts more new entry in the growth stage only, whereas it contributes to firm survival in the mature stage only. The results not only establish the importance of understanding the temporal dynamics underlying agglomeration externalities, but also provide a possible explanation for the mixed empirical results found in previous studies. Copyright © 2013 John Wiley & Sons, Ltd.     

建设项目全寿命期精益成本管理研究

简要介绍了建设项目全寿命期成本管理和精益成本管理的概念，并对全寿命期和全过程成本管理方式进行了比较。在此基础上总结出全寿命期精益成本管理的概念，并对其特点进行了介绍，包括全员性、集成性、动态性和综合性。提出了建设项目全寿命期精益成本管理的体系框架，明确其成本最小化和顾客满意最大化的管理目标。分别从投资决策、设计、招投标、施工、竣工验收和运营养护6个阶段论述了全寿命精益成本管理的具体措施。     

基于生命周期理论评价建筑物能耗及环境影响

生命周期评价方法（LCA）能够分析整个建筑物各个环节对全社会的能耗和环境的影响,其分析结果可使项目各参与者清楚地了解建设项目各环节的能耗和环境影响。借助生命周期评价方法研究江苏某教学楼从原材料生产到建筑物修建完成整个过程中的能耗及环境影响,发现合理地利用分析结果有助于优化项目的设计、生产和运输方案。从节约资源、能源,保护环境的角度出发提出了扩大生命周期评价方法应用领域的研究方向。     

An extended production/recycling model with stationary demand and return rates

A production–recycling system is investigated. A constant demand can be satisfied with production and recycling. The used items are bought back and then recycled. The non-recycled products are disposed of. Two types of models will be analyzed. The first model examines the EOQ-related costs and minimizes the relevant costs. The second model generalizes the first model with the introduction of the cost function with linear waste disposal, recycling, production and buyback costs. It is asked whether the pure (either production or recycling) or mixed strategies are optimal and it will be shown that under these circumstances the mixed strategies are dominated by the pure strategies. The paper generalizes a former model proposed by the authors for the case of one recycling and one production batch to the case of arbitrary batch numbers.     

An inventory reservation problem with nesting and fill rate-based performance measures

In many inventory settings companies wish to provide customer-differentiated service levels. These may, for example, be motivated by differences in the perceived customer lifetime value or by specific contractual agreements. One approach to provide differentiated service levels is to reserve some portion of the available inventory exclusively for specific customer classes. Existing approaches to inventory reservation are typically based on the assumption that a company can assign a customer specific revenue or penalty cost to any order or unit of demand filled or unfulfilled. In practice, however, it is usually extremely difficult to accurately estimate (especially long term) monetary implications of meeting or not meeting customer demand and corresponding service level requirements. The research presented in this paper addresses the problem of setting appropriate inventory reservations for different customer classes based on fill rate-based performance measures. We model a single period inventory reservation problem with two customer classes and nesting. We develop exact expressions for two conflicting performance measures: (1) the expected fill rate of high priority customers and (2) the expected loss in the system fill rate induced by inventory reservation. With these expressions a decision maker can analyze the tradeoff between the loss in overall system performance and the higher expected fill rates for prioritized customers. We provide analytical insights into the effects of nesting and the impact of relevant problem parameters on these two performance measures. The analytical insights are illustrated and highlighted through a set of numerical examples. Although we limit our analysis to a single period inventory reservation problem, we expect that our results can be utilized in a wide range of problem settings in which a decision maker has to ration a perishable resource among different classes of customers.     

Exact and approximate calculation of the cycle service level in periodic review inventory policies

The parameters of stock policies are usually determined to minimize costs while satisfying a target service level. In a periodic review policy the time between reviews can be selected to minimize costs while the order-up-to-level is based on the fulfilment of a target service level. Generally, the calculation of this service measurement is obtained using approximations based on an additional hypothesis related to the demand pattern. Previous research has shown that there is a substantial difference between exact and approximate calculations in some general circumstances, so in these cases the service level is not accomplished or the stock level is overestimated. Although an exact calculation of CSL was developed in previous work, the computational effort required to apply it in practical environments leads to the proposal of two approximate methods (PI and PII) that, with the classic approximation, are analysed and evaluated in this paper. This analysis points out the risks of using the classic approximation and leads one to suggest PII as the most suitable and accurate enough procedure to compute the CSL straightforwardly in practice. Additionally, a heuristic approach based on PII is proposed to accept or reject an inventory policy in terms of fulfilling a given target CSL. This paper focuses on uncorrelated, discrete and stationary demand with a known distribution pattern and without backlog.     

Stage of the organizational life cycle and competition as mediators of problem perception for small businesses

An empirical study based upon a sample of 645 small businesses assesses the relationship that life cycle stage and level of competition exhibit with the problems perceived to constrain small business strategic planning. Problems have been identified as either internal (cash flow) or external (competition); they have further been classified as either situational or core problems. Among the most prevalent problems reported by decision makers are customer contact, market knowledge, marketing planning, location, and adequacy of capital. A total of 16 problem areas were identified. Traditional wisdom offers the scenario where problems faced will vary as the organization progresses through the life cycle. Much of this research refutes conventional wisdom in that level of competition was determined to have more of an impact on problem perception.     

基于利益相关者和生命周期的建设项目动态风险管理研究

建设项目的实施贯穿于项目全生命周期过程,且涉及不同的利益相关者,使得风险具有动态性特征。本文在综合国内外现有研究成果的基础上,提出了基于利益相关者和生命周期的动态风险管理体系。分别从利益相关者和生命周期两个角度探讨了风险的动态性特征,将项目风险、项目利益相关者和生命周期有机结合,系统地阐述了实施建设项目动态风险管理思想并提出实现动态风险管理的建议。     

Impact of RFID information-sharing strategies on a decentralized supply chain with reverse logistics operations

The integration of environmental practices in a supply chain has been study for the past few decades. However, most of the work relies on centralized decisions made by one player. Few papers address the complex dynamics of environmental decentralized supply chains and how these dynamics can affect environmental and economic outcomes. To study this problem, we consider a supply chain with a manufacturer and two different suppliers: a recycled-material and a raw-material supplier. The players make individual inventory decisions to satisfy demand and reduce cost. Further, this supply chain encompasses stochastic elements such as in demands, returns, and collection leadtimes. These decentralized decisions and random factors can cause underperforming results; therefore, new inventory models and technologies are needed to help companies increase coordination within these systems. We model the implementation of Radio Frequency Identification (RFID) in the supply chain to determine if real-time inventory monitoring and information sharing can help the system attain higher environmental benefits (more returns) and higher economic benefits (less cost). We study two scenarios through a simulation-based analysis: No RFID and RFID. Numerical studies show that environmental benefits are significantly increased with the attainment of more returns. However, although economic benefits are realized, they are less significant than the environmental benefits. Further regression and sensitivity analyses on the cost performance measures reveal that economic benefits depend on several drivers inside the system. We present managerial insights that illustrate what configurations within this complex system can lead to the achieving of environmental as well as economic benefits.