Thesis (Ph.D.)--University of Tulsa, 1992. / Bibliography: leaves 73-78.

Estoques são comuns a qualquer empresa, visto que são necessários para amortecer impactos de demandas não programadas e evitar rupturas entre processos, adicionando segurança entre diferentes elos de uma cadeia. Problemas de gerenciamento de estoques são corriqueiros, dado que as suas causas podem ser múltiplas, estando presentes em diferentes nós de uma cadeia e sendo originados por questões vinculadas ao fornecimento, à demanda, à informação, além de outros fatores possíveis. Devido à importância dos estoques para uma empresa, seja financeira, como concentração de ativos, ou seja por mitigar riscos no processo de suprimento, problemas de gerenciamento de estoques são periodicamente tratados na literatura. Entretanto, não existe consenso sobre o que são os problemas de gerenciamento e um método difundido para sua identificação e análise. Esta pesquisa concentra-se nesta lacuna, propondo um método de identificação e análise dos problemas de gerenciamento de estoques. Este método está ancorado em seis distintas etapas que foram aplicadas, na forma de um estudo de caso, em uma empresa da serra gaúcha. As etapas compreendem a identificação dos causadores do problema de gerenciamento de estoques, a modelagem e simulação do ambiente proposto e análises das iterações sob a perspectiva de três variáveis chave: saldo de estoques, escassez e uma função custo. Entre os resultados desta pesquisa encontram-se uma classificação de causadores de problemas de gerenciamento de estoques e o método proposto. Foi possível observar no estudo de caso que, entre as variáveis de entrada utilizada, quando manipulada a média aritmética da distribuição destas variáveis estocásticas, elas causaram maior variação sistemática ao resultado do modelo quando comparada a variação sistemática causada pela alteração da variância da distribuição desta mesma variável estocástica. / Inventories are common to any businesses, as they are needed to cushion impacts from unscheduled demands and avoid ruptures between processes, adding security between different tiers in a supply chain. Inventory management problems are common, as their causes can be multiple, and being present on different nodes of a chain, which can be caused by issues related to supply, demand, information, and other possible factors. Due to the importance of inventories for a business, whether financial - as assets - or its role in mitigating risks in the supply process, inventory management problems are frequently approached in the literature. However, there is no consensus on what are inventory management problems and there is no widespread method for identification and analysis of inventory management problems. This research focus on this gap by proposing a method of identification and analysis of inventory management problems. This method is anchored in six distinct steps that have been applied in the form of a case study on a company in south of Brazil. The steps include the identification of the causes of the inventory management problem, the modeling and simulation of the proposed environment and analysis of iterations from the perspective of three key variables: inventory balance, inventory shortages and a cost function. Among the results of this research are a classification of inventory management problems originators and the proposed method. It was observed in the case study that among the input variables, when manipulated the arithmetic mean of the stochastic distribution of these variables, they increased the systematic variation output of the model more than when were manipulated the variance of the stochastic distribution of the same variable.

Estoques são comuns a qualquer empresa, visto que são necessários para amortecer impactos de demandas não programadas e evitar rupturas entre processos, adicionando segurança entre diferentes elos de uma cadeia. Problemas de gerenciamento de estoques são corriqueiros, dado que as suas causas podem ser múltiplas, estando presentes em diferentes nós de uma cadeia e sendo originados por questões vinculadas ao fornecimento, à demanda, à informação, além de outros fatores possíveis. Devido à importância dos estoques para uma empresa, seja financeira, como concentração de ativos, ou seja por mitigar riscos no processo de suprimento, problemas de gerenciamento de estoques são periodicamente tratados na literatura. Entretanto, não existe consenso sobre o que são os problemas de gerenciamento e um método difundido para sua identificação e análise. Esta pesquisa concentra-se nesta lacuna, propondo um método de identificação e análise dos problemas de gerenciamento de estoques. Este método está ancorado em seis distintas etapas que foram aplicadas, na forma de um estudo de caso, em uma empresa da serra gaúcha. As etapas compreendem a identificação dos causadores do problema de gerenciamento de estoques, a modelagem e simulação do ambiente proposto e análises das iterações sob a perspectiva de três variáveis chave: saldo de estoques, escassez e uma função custo. Entre os resultados desta pesquisa encontram-se uma classificação de causadores de problemas de gerenciamento de estoques e o método proposto. Foi possível observar no estudo de caso que, entre as variáveis de entrada utilizada, quando manipulada a média aritmética da distribuição destas variáveis estocásticas, elas causaram maior variação sistemática ao resultado do modelo quando comparada a variação sistemática causada pela alteração da variância da distribuição desta mesma variável estocástica. / Inventories are common to any businesses, as they are needed to cushion impacts from unscheduled demands and avoid ruptures between processes, adding security between different tiers in a supply chain. Inventory management problems are common, as their causes can be multiple, and being present on different nodes of a chain, which can be caused by issues related to supply, demand, information, and other possible factors. Due to the importance of inventories for a business, whether financial - as assets - or its role in mitigating risks in the supply process, inventory management problems are frequently approached in the literature. However, there is no consensus on what are inventory management problems and there is no widespread method for identification and analysis of inventory management problems. This research focus on this gap by proposing a method of identification and analysis of inventory management problems. This method is anchored in six distinct steps that have been applied in the form of a case study on a company in south of Brazil. The steps include the identification of the causes of the inventory management problem, the modeling and simulation of the proposed environment and analysis of iterations from the perspective of three key variables: inventory balance, inventory shortages and a cost function. Among the results of this research are a classification of inventory management problems originators and the proposed method. It was observed in the case study that among the input variables, when manipulated the arithmetic mean of the stochastic distribution of these variables, they increased the systematic variation output of the model more than when were manipulated the variance of the stochastic distribution of the same variable.

The Bertrand Duopoly model for demand in economics is a well-used model. Although this model has important insights towards pricing strategy, it does not accurately depict true market behaviors. In this paper, we will examine the advantages and disadvantages of the current model and its assumptions.We then take a whole new approach towards modeling this phenomena, using Poisson processes to model the demand of goods. We will discuss why this is a better approach and explain how we can extend this to better understand pricing strategies and market dynamics. We then apply our findings to the newsvendor problem, a commonly used problem in inventory management. Using non-homogeneous Poisson processes we explain how to find an optimal pricing strategy and an optimal inventory level for the newsvendor problem.In this paper we explain how to extend the newsvendor problem to a newsvendor duopoly problem. Again we show how to find the optimal pricing strategies and inventory levels for multiple goods in a market. Having found the optimal pricing strategy and inventory level, we then examine the market dynamics in more details. We explore monopolistic and duopolistic markets where the goods range from complements to substitutes and homogeneous to differentiated goods. We discuss how to model the progression of the inventory probabilities and then explain how to price inventory options.

Supply chain management is one of the fundamental topics in the field of operations research, and a vast literature exists on the subject. Many recent developments in the field are rapidly narrowing the gap between the systems handled in the literature and the real-life problems companies need to solve on a day-to-day basis. However, there are certain features often observed in real-world systems that elude even these most recent developments. In this thesis, we consider a number of these features, and propose some new heuristics together with methodologies to evaluate their performance. In Chapter 2, we consider a general two-echelon distribution system consisting of a depot and multiple sales outlets which face random demands for a given item. The replenishment process consists of two stages: the depot procures the item from an outside supplier, while the retailers' inventories are replenished by shipments from the depot. Both of the replenishment stages are associated with a given facility-specific leadtime. The depot as well as the retailers face a limited inventory capacity. We propose a heuristic for this class of dynamic programming models to obtain an upper bound on optimal costs, together with a new approach to generate lower bounds based on Lagrangian relaxation. We report on an extensive numerical study with close to 14,000 instances which evaluates the accuracy of the lower bound and the optimality gap of the various heuristic policies. Our study reveals that our policy performs exceedingly well almost across the entire parameter spectrum. In Chapter 3, we extend the model above to deal with distribution systems involving several items. In this setting, two interdependencies can arise between items that considerably complicate the problem. First, shared storage capacity at each of the retail outlets results in a trade-off between items; ordering more of one item means less space is available for another. Second, economies of scope can occur in the order costs if several items can be ordered from a single supplier, incurring only one fixed cost. To our knowledge, our approach is the first that has been proposed to handle such complex, multi-echelon, multi-item systems. We propose a heuristic for this class of dynamic programming models, to obtain an upper bound on optimal costs, together with an approach to generate lower bounds. We report on an extensive numerical study with close to 1,200 instances that reveals our heuristic performs excellently across the entire parameter spectrum. In Chapter 4, we consider a periodic-review stochastic inventory control system consisting of a single retailer which faces random demands for a given item, and in which demand forecasts are dynamically updated (for example, new information observed in one period may affect our beliefs about demand distributions in future periods). Replenishment orders are subject to fixed and variable costs. A number of heuristics exist to deal with such systems, but to our knowledge, no general approach exists to find lower bounds on optimal costs therein. We develop a general approach for finding lower bounds on the cost of such systems using an information relaxation. We test our approach in a model with advance demand information, and obtain good lower bounds over a range of problem parameters. Finally, in Appendix A, we begin to tackle the problem of using these methods in real supply chain systems. We were able to obtain data from a luxury goods manufacturer to inspire our study. Unfortunately, the methods we developed in earlier chapters were not directly applicable to these data. Instead, we developed some alternate heuristic methods, and we considered statistical techniques that might be used to obtain the parameters required for these heuristics from the data available.

This thesis presents a study of stochastic models of continuous review of inventory systems of perishable and non-perishable products, as well as inventory systems operating in random environment. It contains five chapters. The first chapter is introductory in nature, containing the motivation for the study and the techniques required for the analysis of respective models described in the remaining chapters. Chapter 2 provides a model of perishable product inventory system operating in a random environment. For the sake of simplicity, the stochastic environment is considered to alternate randomly over time between two states 0 and 1 according to an alternating renewal process. When the environment is in state k, the items in inventory have a perishable rate ìk, the demand rate is ëk and the replenishment cost is CRk. The performance of various measures of the system evolution are obtained, assuming instantaneous replenishment at the epoch of the first demand after the stock-out and associating a Markov renewal process with the inventory level. In Chapter 3, a continuous review single product perishable inventory model is considered. Items deteriorate in two phases and then perish. Independent demands occur at constant rates for items in phase I and in phase II. Demand that occurs for an item in phase I during its stock-out period is satisfied by an item in phase II with some probability. However a demand for an item in phase II occurring during its stock-out period is lost. The reordering policy is an adjustable (S,s) policy with the lead-time following an arbitrary distribution. Identifying the stochastic process as a renewal process, the probability distribution of the inventory level at any arbitrary instant of time is obtained. The expressions for the mean stationary rates of demands lost, demands substituted, perished units and scrapped units are also derived. A numerical example is considered to highlight the results obtained. Chapter 4 is a study of a two-commodity inventory system under continuous review. The maximum storage capacity for the i-th item is Si (i=1, 2). The demand points for each commodity are assumed to form an independent Poisson process, with unit demand for one item and bulk demand for the other. The order level is fixed as si for the i-th commodity (i=1, 2) and the ordering policy is to place an order for Qi (= Si – si , i = 1,2) items for the i-the commodity when both the inventory levels are less than or equal to their respective reorder levels. The lead-time is assumed to be exponential. The joint probability distribution for both commodities is obtained in both transient and steady state cases. Various measures of systems performance and the total expected cost rate in the steady state are derived. The results are illustrated with numerical examples. Chapter 5 provides an analysis of a continuous review of two-product system with two types of demands and with individual (S,s) ordering policy. The lead-time distribution of product 1 is arbitrary and that of product 2 exponential. Two types of demands occur at constant rates either for both products or for product 2 alone. Expressions for the stationary distribution of the inventory level are obtained by identifying the underlying stochastic processes as a semi-regenerative process. The mean stationary rates of the lost demands, the demands that are satisfied and the number of reorders are obtained and these measures are used to provide an expression for the cost rate. The main objective of this thesis is to improve the state of art of continuous review inventory systems. The salient features of the thesis are summarized below: <ul>(a) Consideration of</ul> <ul>(i) The impact of the stochastic environment on inventory systems;</ul> <ul>(ii) The interactions existing among the products in multi-product systems;</ul> <ul>(iii) Individual and joint-ordering policies;</ul> <ul>(b) Discussion of inventory systems with perishable products; </ul> <ul>(c) Effective use of the regeneration point technique to derive expressions for various system measures;</ul> <ul>(d) Illustration of the various results by extensive numerical work;</ul> <ul>(e) Relevant optimization problems</ul> / Thesis (PhD (Industrial Engineering))--University of Pretoria, 2006. / Industrial and Systems Engineering / unrestricted

M. Tech. (Industrial Engineering, Faculty of Engineering and Technology) Vaal University of Technology| / Implementing either periodic or continuous inventory review model within most manufacturing-companies-supply chains, as a management tool, incurs higher costs. These high costs affect the system flexibility which in turn affects the level of service required to satisfy customers. However, these effects are not clearly understood. This may be due to the fact that lead time and demand which are important input parameters of the manufacturing supply chain are not designed to be fully utilized under different and uncertain conditions such as seasonality, poor manufacturing, poor supplies and delivery performance, etc. Coming up with a hybrid inventory model which may combine, in some sense a continuous (r, Q) and a periodic (R, S) inventory review models can be useful in dealing with such problem. Therefore, more attention should be first devoted to formulating accurate models for lead time and demand that incorporate uncertainty. This study presents a simulation based approach that assesses the effect of uncertainty on the cost of implementing a continuous (r, Q), periodic (R, S) and hybrid inventory review models while considering appropriate constraint such as customer service and system flexibility. The stochastic representations of demand and lead time are proposed and used in the simulation models. Results reveal that under a unique situation, implementing a continuous (r, Q) inventory review model may cause manager to under-budget while the use of a periodic (R, S) inventory review models may lead to over budget and vice versa. Further investigation shows that the cost of implementing the hybrid inventory model, although higher at the beginning of operation, seems to be the most cost effective one over time. The result also reveal optimal re-order point path and optimal review interval path which when followed, should lead to optimal inventory cost path as demand and lead time fluctuate. Thus, a management guide is proposed that can be used by managers in making inventory decision.

The major purpose of this study was to evaluate the impact of a science course for prospective elementary teachers on their perceptions of the learning environment, attitudes towards science, and understandings of the nature of science. The sample consisted of 525 female students enrolled in 27 classes of A Process Approach to Science (SCED 401) at a large urban university in Southern California. Also comparisons were made between SCED 401 and the students' previous laboratory course with regard to the learning environment and attitudes. Perceptions of the learning environment were measured using scales from the Science Laboratory Environment Inventory (Open-Endedness and Material Environment) and the What Is Happening In this Class? (Student Cohesiveness, Instructor Support, Cooperation, Investigation). Attitudes towards science were assessed using the Enjoyment of Science Lessons scale from the Test of Science-Related Attitudes (TOSRA). Students completed the Nature of Scientific Knowledge Survey (NSKS) based on their entire science education experience-not just the one laboratory class which they had taken previously. Comparisons were then made with their understandings after having completed SCED 401. Finally, associations between the learning environment and the student outcomes of attitudes and understandings of the nature of science were explored. This study embraced the current trend in classroom learning environments research of combining quantitative and qualitative methods. Qualitative components included items from the open-ended questionnaire, Views of Nature of Science, interviews with students, and an analysis of concept maps. The qualitative findings expanded and complemented the quantitative results and, in several cases, supported the construct validity of scales assessing the learning environment and attitudes. / Another purpose of this study was to investigate the effects of using real research data for growth rates of four species of Antarctic seabirds (i.e., implementing an 'intervention') in six classes of SCED 401. The objective of the intervention was to increase the authenticity and quality of an experimental design project. In addition, the wildlife biologist who collected the data guided the students during the project. Although the intervention did not lead to an appreciable improvement in students' perceptions of the learning environment, differences between intervention and nonintervention classes were statistically significant for Enjoyment of Science Lessons from the TOSRA and for Creative from the NSKS (effect sues were 2.64 and 2.06 standard deviations, respectively). Results of this study indicated that during a factor analysis, the large majority of learning environment items belonged to their a priori scale (43 out of 46 items had factor loadings above 0.40) A valid instrument for use with prospective elementary teachers was produced by combining relevant scales from the Science . Laboratory Environment Inventory and the What Is Happening In this Class? A weaker factor structure was found for the Nature of Scientific Knowledge Survey. However, by moving close to half of the -faulty' items from the NSKS, the internal consistency reliability of scales improved considerably. This study also found large and statistically significant differences between students' previous laboratory class and SCED 401 for all six leaning environment scales. The largest difference was found for the level of Open-Endedness (effect size was 6.74 standard deviations). / A statistically significant difference also was found for Enjoyment of Science Lessons (effect size was 2.98 standard deviations). Differences were not as dramatic with regard to understandings of the nature of science, although differences for two scales (Creative and Unified) from the NSKS were positive and statistically significant. This study replicated past research by finding statistically significant positive correlations between all six learning environment scales and Enjoyment of Science Lessons. However, by far, Instructor Support had the largest independent association with enjoyment, using both the individual and class mean as the units of analysis. A positive link between a favorable leaning environment and the student outcome of understanding nature of science also was found. This research makes a distinctive contribution to the learning environments field because it is the first study to investigate laboratory classroom environments at the university level with prospective elementary teachers. The study is also the first to build a bridge between the classroom learning environment and the student outcome of understanding the nature of science. The study has implications for undergraduate laboratory course instructors, for science teacher educators who develop and instruct in elementary teacher preparation programs, and for future elementary teachers and the science learning of their future students.

The main goal of research is analysis of the inventory accounting methodics, to research the problems of inventory accounting in theory and practice and to make suggestions for improvement of inventory accounting by managing them. The aims of this research are: 1. To analyze the scientific and economical sources or literature and different legal bases, international and national standards concerning inventory accounting and its management. 2. To research the problems and their solutions linked with inventory accounting and its management. 3. To make suggestions for improving the methodics of inventory accounting and its management. The research methodics incorporates such methods: monographic, observation, logical analysis and synthesis, comparable analysis and diagrammatical. While exploring scientific and economical literature, national and international standards of accounting the problems concerning inventory accounting ant its management were obtained and solved.

The thesis deals with the issue of inventories in companies. The thesis describes inventories according to the current and amended legislation in the Czech Republic. Subsequently, the thesis describes accounting operations, activities and processes associated with inventories in practice. Focusing on two companies characterized by their cooperation, but different in their activities, the thesis analyzes the chosen fields of inventories and related activities, including the specifics resulting from mutual cooperation.