The wide spread use of advanced information systems such as Material Requirements Planning (MRP) has significantly altered the practice of dependent demand inventory management. Recent research has focused on development of multi-level lot sizing heuristics for such systems. In this paper, we develop an optimal procedure for the multi-period, multi-product, multi-level lot sizing problem by modeling the system as a constrained generalized network with fixed charge arcs and side constraints. The network permits us to relax some of the more restrictive assumptions of previous models such as those designed for product structures with single sources or successors. The solution to the resulting minimum cost flow problem yields optimal lot sizing decisions for all purchases as well as manufactured goods and components in all periods over a finite planning horizon. A simple illustration, beginning with a master production schedule and bills of material, illustrates the suitablility of this approach for modeling complex requirements planning systems. Optimal solutions obtained by this method may also be useful in comparing results obtained from future heuristic approaches which may be more computationally efficient.network/graphs: applications, inventory/production, material requirements planning

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An important problem confronting health care administration is cost containment in hospitals. Much of the current high costs can be traced directly to outdated procedures in materials management leading to waste, excessive inventory and unnecessary obsolescence of expensive short shelf life items. In this paper, we illustrate how a modern requirements planning system for surgical supplies was developed for a private hospital in Houston and used to effectively hold inventory levels to the minimum required to support a detailed schedule of surgical procedures. We also discuss some specific problems involved in the transfer of manufacturing technology to the hospital setting.

IS an account cf Goseromei't sponsored Rork ^either the I . nor cmv persoa acttsg on behalf of tho Commisston INTRODUCTIONThe general availability of radioisotopes has placed a powerful tool in the hands of investigators in many fields of science, and it is the purpose of this report to aid these workers in the design of meaningful experiments utilizing radioactivity. An understanding of the various factors which may contribute to errors in measurement is essential for the choice of appropriate techniques and measuring devices and for the proper evaluation of experimental data. This report is not intended as a treatise on the measurement of radioactivity, but it is hoped that the presentation of a handy guide to some of the problems involved and the techniques generally employed in avoiding or correcting for them, together with references to the pertinent literature, will provide an adequate orientation and introduction to the subject. GENERAL CONSIDERATIONSAlthough the discussion here will be limited to counting methods of radioactive assay, which are of more general interest, a variety of techniques are available, e.g., photographic, calorimetric, charge collection, colloid deposition, crystal coloring, etc. Different techniques may, of course, involve somewhat different error analyses; however, the problems associated with the determination of the absolute disintegration rate of a radioactive source by counting techniques afford an excellent example of the commonly encountered difficulties. Such a determination involves a knowledge of the decay scheme of the rachoactive nuclide and the efficiency of the detector for the particles or rays emitted by the source. It is thus necessary to know the fraction of the radiation leaving the source which enters the sensitive volume of the detector ("geometry factor") and the intrinsic efficiency of the detector for the radiation. The interactions of radiation with matter alter the simple geometrical relationship between the source and detector by processes of absorption and scattering in the material of the sample itself, its support, any covering material, the space between the sample and the counter, the counter window, and the housing of the detector unit. These effects are complex and depend critically on the size and m.aterial of the sample and its support and on the energy and type of the radiation. Special techniques are required to minimize these effects for the determination of disintegration rates to a few percent accuracy.For many purposes an experiment can be designed so that relative counting rates of samples of a particular nuclide will suffice. It is then only necessary to coxmt under nearly identical conditions to obtain precisions of the order of one to two percent. This criterion, in practice, is relatively simple to meet and, whenever possible, comiparative cotmting is therefore recommended. Of course, if it is necessary to compare the activity of sources which differ in chemical or physical nature or in the energy of their radiations, these differe...

Within the past several years, considerable research has been devoted to the aggregate production planning problem starting with the pioneering work of Holt et al. (1955)and the resulting Linear Decision Rule (LDR). However, researchers have also recognized that developing optimal aggregate production plans, per se, is not sufficient for solving real problems; these plans have to be disaggregated into specific schedules for specific products. Consequently, the thrust of current research is on the 'disaggregation' problem. Simultaneously a number of companies have been installing MRP systems with reports of significant improvements in inventory control, production planning, work force scheduling and production costs. This paper reports on an experiment which was designed and conducted to compare the effectiveness of the 'aggregate-disaggregate' and MRP approaches to production planning in a simulation environment. LDR was used as the optimal aggregate technique in the aggregate-disaggregate approach. The results appeared to favour the MRP approach.