Production planning and inventory control with remanufacturing and disposal

In this paper we consider a stochastic inventory system with production, remanufacturing, and disposal operations. Customer demands must either be fulfilled from the production of new products or by the remanufacturing of used products. Used products are either remanufactured or disposed of. To coordinate production, remanufacturing and disposal operations efficiently, we extend the PUSH and PULL strategies that Van der Laan et al. developed to control a system in which all returned products are remanufactured and no planned disposals occur. The other contributions of this paper are to indicate when and why planned disposals are economically beneficial, and to compare the PUSH-disposal strategy to the PULL-disposal strategy. In addition, we investigate the robustness of the control parameters of the PUSH- and PULL-disposal strategy over the different stages of a product life-cycle

Exact and approximation algorithms for the operational fixed interval scheduling problem

The Operational Fixed Interval Scheduling Problem (OFISP) is characterized as the problem of scheduling a number of jobs, each with a fixed starting time, a fixed finishing time, a priority index, and a job class. The objective is to find an assignment of jobs to machines with maximal total priority. The problem is complicated by the restrictions that: (i) each machine can handle only one job at a time, (ii) each machine can handle only jobs from a prespecified subset of all possible job classes, and (iii) preemption is not allowed. It follows from the above that OFISP has both the character of a job scheduling problem and the character of an assignment problem. In this paper we discuss the occurrence of the problem in practice, and we present newly developed exact and approximation algorithms for solving OFISP. Finally, some computational results are shown

Product remanufacturing and disposal: A numerical comparison of alternative control strategies

In this paper we consider a single-product, single-echelon production and inventory system with product returns, product remanufacturing, and product disposal. For this system we consider three different procurement and inventor

A DSS for capacity planning of aircraft maintenance personnel

In this paper we describe a Decision Support System (DSS) that has been developed for the aircraft maintenance department of the Dutch national airline company at the main airport in the Netherlands. The aircraft maintenance department is responsible for carrying out the regular short inspections of aircraft between their arrival at and their consecutive departure from the airport. The main resource of the aircraft maintenance department is its workforce. The DSS that has been developed can be used to support the management of the maintenance department in solving several capacity planning problems related to the size and the composition of the workforce. In this paper we give a description of the capabilities of the DSS. Furthermore, we describe the solution technique that is applied within the DSS for determining the required size and composition of the workforce

Strategic Issues in Product Recovery Management

This article examines strategic production and operations management issues in product recovery management (PRM). PRM encompasses the management of all used and discarded products, components, and materials for which a manufacturing company is legally, contractually, or otherwise responsible. The objective of PRM is to recover as much of the economic (and ecological) value of used and discarded products, components, and materials as reasonably possible, thereby reducing the ultimate quantities of waste to a minimum. This article also discusses the relevance of PRM to durable products manufacturers. It contains a categorization of PRM decisions. A case study based on the PRM system of a multinational copier manufacturer is presented to illustrate a set of specific production and operations management issues. The experiences of two other pro-active manufacturers (BMW and IBM) are also discusse

Allocation of Railway Rolling Stock for Passenger Trains

For a commercially operating railway company, providing a high level of service for the passengers is of utmost importance. The latter requires a high punctuality of the trains and an adequate rolling stock capacity. Unfortunately, the latter is currently (2002) one of the bottlenecks in the service provision by the main Dutch railway operator NS Reizigers. Especially during the morning rush hours, many passengers cannot be transported according to the usual service standards due to a shortage of the ro

An (s,Q) inventory model with remanufacturing and disposal

In this paper we analyse an (s, Q) inventory model in which used products can be remanufactured to new ones. We develop two approximations for the average costs and compare their performance with that of an approximation suggested by Muckstadt and Isaac. Next we extend the model with the option to dispose returned products and present a heuristic optimisation procedure which is checked with full enumeration

Planning the Size and Organization of KLM's Aircraft Maintenance Personnel

Develops a decision support system (DSS) for the aircraft maintenance department of KLM Royal Dutch Airlines at Schiphol Airport in Amsterdam, Netherlands. Tasks of the department; Support provided by the DSS to management; Analyzing several capacity planning problems related to the size and the organization of the workforce

Routing Trains through railway stations: model formulation and algorithms

In this paper we consider the problem of routing trains through railway stations. This problem occurs as a subproblem in a project which the authors are carrying out in cooperation with the Dutch railways. The project involves the analysis of future infrastructural capacity requirements in the Dutch railway network, Part of this project is the automatic generation and evaluation of timetables. To generate a timetable a hierarchical approach is followed: at the upper level in the hierarchy a tentative timetable is generated, taking into account the specific scheduling problems of the trains at the railway stations at an aggregate level. At the lower level in the hierarchy it is checked whether the tentative timetable is feasible with respect to the safety rules and the connection requirements at the stations. To carry out this consistency cheek, detailed schedules for the trains at the railway yards have to be generated. In this paper we present a mathematical model formulation for this detailed scheduling problem, based on the Node Packing Problem (NPP). Furthermore, we describe a solution procedure for the problem, based on a branch-and-cut approach. The approach is tested in an empirical study with data from the station of Zwolle in The Netherlands

New first trimester crown-rump length's equations optimized by structured data collection from a French general population

--- Objectives --- Prior to foetal karyotyping, the likelihood of Down's syndrome is often determined combining maternal age, serum free beta-HCG, PAPP-A levels and embryonic measurements of crown-rump length and nuchal translucency for gestational ages between 11 and 13 weeks. It appeared important to get a precise knowledge of these scan parameters' normal values during the first trimester. This paper focused on crown-rump length. --- METHODS --- 402 pregnancies from in-vitro fertilization allowing a precise estimation of foetal ages (FA) were used to determine the best model that describes crown-rump length (CRL) as a function of FA. Scan measures by a single operator from 3846 spontaneous pregnancies representative of the general population from Northern France were used to build a mathematical model linking FA and CRL in a context as close as possible to normal scan screening used in Down's syndrome likelihood determination. We modeled both CRL as a function of FA and FA as a function of CRL. For this, we used a clear methodology and performed regressions with heteroskedastic corrections and robust regressions. The results were compared by cross-validation to retain the equations with the best predictive power. We also studied the errors between observed and predicted values. --- Results --- Data from 513 spontaneous pregnancies allowed to model CRL as a function of age of foetal age. The best model was a polynomial of degree 2. Datation with our equation that models spontaneous pregnancies from a general population was in quite agreement with objective datations obtained from 402 IVF pregnancies and thus support the validity of our model. The most precise measure of CRL was when the SD was minimal (1.83mm), for a CRL of 23.6 mm where our model predicted a 49.4 days of foetal age. Our study allowed to model the SD from 30 to 90 days of foetal age and offers the opportunity of using Zscores in the future to detect growth abnormalities. --- Conclusion --- With powerful statistical tools we report a good modeling of the first trimester embryonic growth in the general population allowing a better knowledge of the date of fertilization useful in the ultrasound screening of Down's syndrome. The optimal period to measure CRL and predict foetal age was 49.4 days (9 weeks of gestational age). Our results open the way to the detection of foetal growth abnormalities using CRL Zscores throughout the first trimester