Inventory systems

This analytical study investigates the impact of time-dependent demand and pricing on inventory models, focusing on deteriorating items. Inventory management plays a critical role in operational efficiency and cost minimization. Understanding how demand and price fluctuations over time affect inventory models is crucial for optimizing stock levels and reducing waste. By reviewing recent advancements and methodologies, this study highlights key findings, identifies research gaps, and suggests areas for further investigation. The analysis encompasses various models and approaches, providing a comprehensive overview of the current state of research in this domain.

Inventory control management remains a cornerstone of operational efficiency in modern supply chain systems. This study explores the Economic Order Quantity (EOQ) model, a foundational inventory control technique, by comparing its application under two distinct demand scenarios: constant and variable demand rates. This research highlights how demand variability influences optimal order quantities, total inventory costs, and decisionmaking processes through a detailed theoretical framework, mathematical analysis, and practical implications. From recent literature in operations research and supply chain management, the article provides insights into the adaptability of the EOQ model across diverse demand conditions, offering a comprehensive guide for practitioners and researchers alike.

In this paper, we consider a single machine at which two types of orders with deterministic processing times arrive according to independent Bernoulli processes. When the machine switches from processing one type of order to another, fixed switch-over times are incurred. For both types of orders, we determine the delivery-time distribution for a periodic switching strategy and for an exhaustive service policy. Using these delivery-time distributions, we compare for these switching strategies both the average delivery time and the fraction of orders that are processed in time. Numerical examples show that a periodic switching strategy performs considerably worse than an exhaustive service policy. For the periodic switching strategy, however, delivery times of orders can be guaranteed, which is not the case for the exhaustive service policy. Hence, for this latter policy, we also determine the expected delivery times of orders iffor each state upon arrival of an order the promised delivery time has to be met with a certain probability. When this probability is high, the periodic switching strategy might outperform the exhaustive service policy. Finally, we compute the switching strategy that minimizes the number of orders at the machine, and compare it with the aforementioned switching strategies.

This paper explores the escalating adoption of Open-Source Software (OSS) and its implications on traditional software assets inventory practices. While OSS offers undeniable benefits in terms of flexibility and cost, it also introduces complexities, especially in managing intricate dependency structures within the software supply chain. In response to this, the concept of Software Bill of Materials (SBOM) is proposed as a potential solution, aiming to bring transparency by documenting software components and dependencies. This paper presents an empirical study that evaluates the effectiveness and efficiency of a set of SBOM generation tools across diverse IT infrastructures and software inventory tools. It highlights SBOM's tools advantages, such as discovering OSS components installed without reliance on OS package managers, and providing component dependencies' information. By addressing this, we aim to deepen the understanding of SBOM's significance in modern software management practices and provide insights for optimizing SBOM generation tools usage.

Sistem informasi akan sangat berguna jika didukung dengan sistem persediaan yang efisien, sehingga selain transaksi dapat dilakukan dengan lebih cepat, juga ada jaminan bahwa sistem persediaan akan menghemat biaya. Penelitian ini dilakukan di salah satu gudang komponen sepeda motor di Sulawesi Selatan. Komponen yang disimpan ada ratusan jenis karena selain menjualnya, pemilik juga membuka layanan perbaikan seeda motor. Saat ini gudang melakukan pemeriksaan dan pencatatan manual dalam melayani pelanggan. Terdapat kesulitan saat dilakukan pencarian karena tidak ada petunjuk yang jelas mengenai posisi barang tersebut, juga penataannya belum rapi. Pencarian dimulai dengan pemeriksaan buku catatan, yang juga masih disusun secara manual. Akibatnya, posisi persediaan juga sulit diperkirakan, yang akan mempengaruhi jumlah pesanan yang akan diberikan ke pemasok. Terkadang terjadi kekurangan persediaan yang menyebabkan pelanggan kecewa. Berdasarkan permasalahan di atas, maka dilakukan analisi...

The present research focuses on an Economic Production Quantity (EPQ) model with uncertain demand. To resemble it with reality, shortages are allowed and completely backordered. Besides the present EPQ model has included a two level credit scheme according to which both supplier and retailer are giving relaxation in payment to their respective customers in order to boost up the sales. To illustrate and justify the model five instances have taken and solved. Along with this a sensitivity analysis is done for different parameters.

It is generally observed that the products losses its freshness with the course of time that stimulates depression in demand of the product. In these circumstances, price discounts are necessary to raise the market. This is why, when the product's the index of freshness reaches a certain level, we created an inventory model wherein price reductions are provided at a sale price. The main goal is to figure out what the best selling price and cycle time are in order to maximise profit. The meaning and uniqueness of an ideal model solution are incorporated into the circumstances. The next move is to use a simple algorithm to find an optimal solution. Finally, a numerical example is presented, followed by a sensitivity analysis.

The behaviour of prioritized backorders has been under-exposed in the literature as researchers rarely go beyond finding the proportions of backorders so as to enable the calculation of fill rate. Therefore, this paper used a high and low priority rationing spare parts inventory simulation model for slow moving parts using (S,S-1) policy to characterize the backorders. From the model, the results of the average number, mean response time and maximum queue length of backorders for four sensitive parameters (base stock level, critical stock level, high priority arrival rate and low priority arrival rate), were analysed. The results and analysis from this study will help in taking informed decision with regards to possible adjustment of inventory system so that huge backorder and consequently huge amount of money will not be tied down in inventory.

Neste artigo é apresentada a área de conservação e restauro do Museu Nacional de Etnologia e o seu desenvolvimento ao longo dos últimos anos. É feita a descrição breve de algumas das acções de gestão do acervo desenvolvidas, pondo em evidência a sua transversalidade e a estreita articulação com os diversos sectores do Museu. A atitude crítica e de constante reflexão que tem pautado a actuação deste sector do Museu é ilustrada por diferentes projectos, sendo aqui dada especial relevância aos vários modelos de formação adoptados e à colaboração com outras instituições.

The world has become global in the way goods and services are produced and marketed. The stiff global competition faced by these companies necessitates a need to embark on radical strategies in the form of World Class manufacturing philosophies to survive, make profit and remain competitive. While companies in developing countries strive to adopt these World Class Manufacturing (WCM) philosophies into their production process, there is often lack of a measure on their progress towards world class manufacturing status besides the improvement in productivity. This paper's focus is on how companies can assess their progress in terms of achieving a world class manufacturing status. The research starts with an assessment of the world class status of the company that has adopted best manufacturing practices. A Current State Radar Chart (CSRC) is drawn to see the company's position on the radar. Researches methods (questionnaires, interviews, company audit) are used to identify wastes according to WCM. WCM techniques were used to minimise wastes. A Future State Radar Chart (FSRC) is drawn to assess the improvements made. The company was operating its margarine production process at 35% of a world class process. The major waste identified was the downtime. Downtime contributed to 74% of the total available time leaving production only 26% of the available time. WCM techniques realised a reduction in downtime by 30% and increased the available time for production to 56%. These changes achieved a 56% of a world class process on the FRC drawn.

Kebutuhan Spare Parts unit Froklift Truck atau yang biasa disebut dengan Reach Truck saat ini dihadapkan pada sebuah risiko, tidak dapat memenuhi keinginan para pelanggannya. Persediaan bisa muncul ketika ada kebutuhan dan adanya sebuah perencanaan untuk mengadakan persediaan. Akibat yang ditimbulkan ketika sebuah perusahaan melakukan pengadaan tanpa ada perencanaan yaitu seringterjadinya tidak terjual akibat rendahnya jumlah permintaan sehingga mengakibatkan kinerja perusahaan menurun dan biaya yang tinggi. Teknik pengendalian persediaan akan memperkirakan berapa jumlah optimal tingkat persediaan yang diharuskan, serta kapan saatnya mulai mengadakan pemesanan kembali (reorder point). Perencanaan dengan pendekatan EOQ (Economic Order Quantity) merupakan solusi perencaaan persediaan yang optimal dalam memenuhi kebutuhan persediaan tetap lancar.

Control of inventory in production and operation systems is very important for better management and utilization of resources. In this paper, the optimal control of a periodic-review inventory system with items deterioration is considered. We are concerned with the problem of determining the production rate that minimizes a certain cost function. We deal with both cases where the deterioration coefficient is known and unknown. In the case where it is unknown, the recursive least squares algorithm is used to estimate this parameter. The main control objective is to maintain the inventory at a desired level in spite of the unknown model parameter and variable demand. The self-tuning optimal control is presented and the effectiveness of the proposed control algorithm is illustrated by simulation.

Queue systems are essential in the modelling of transport systems. Increasing requirements from the beneficiaries of logistic services have led to a broadening of offerings. Consequently, models need to consider transport entities with priorities being assigned in relation to the costs corresponding to different classes of customers and/or processes. Waiting lines and queue disciplines substantially affect queue system performance. This paper aims to identify a solution for decreasing the waiting time, the total time in the system, and, overall, the cost linked to queueing delays. The influence of queue discipline on the waiting time and the total time in the system is analysed for several cases: (i) service for priority classes at the same rate of service with and without interruptions, and (ii) service for several priority classes with different service rates. The presented analysis is appropriate for increasing the performance of services dedicated to freight for two priority cla...

This paper addresses a tactical planning problem for a three-echelon, reparable-parts service network characterized by a capacitated repair facility and local opportunities for inventory pooling. The problem is to find the optimal total system stock. The model proposed is appropriate for high-cost, high-criticality, low-demand-rate parts for which transport times are short and for which optimization-based stock allocation is performed in the distribution system. The model includes parameters that characterize design and management decisions in the resupply system. The model can be solved in time that is nlog(n) in the number of part number-location combinations, making it a practical technique for large-scale inventory problems. One implication of this approach is to emphasize the importance of optimization-based stock allocation and repair priority routines in inventory management execution systems.

This paper addresses a tactical planning problem for a three-echelon, reparable-parts service network characterized by a capacitated repair facility and local opportunities for inventory pooling. The problem is to find the optimal total system stock. The model proposed is appropriate for high-cost, high-criticality, low-demand-rate parts for which transport times are short and for which optimization-based stock allocation is performed in the distribution system. The model includes parameters that characterize design and management decisions in the resupply system. The model can be solved in time that is nlog(n) in the number of part number-location combinations, making it a practical technique for large-scale inventory problems. One implication of this approach is to emphasize the importance of optimization-based stock allocation and repair priority routines in inventory management execution systems.

In this paper, we propose a new method for the localization of RFID tags, by deploying off-the-shelf RFID equipment on a robotic platform. The constructed robot is capable to perform Simultaneous Localization (of its own position) and Mapping (SLAM) of the environment and then locate the RFID tags around its path. The proposed method is based on properly treating the measured phase of the backscattered signal by each tag at the reader's antenna, located on top of the robot. More specifically, the measured phase samples are reconstructed, such that the 2π discontinuities are eliminated (phase-unwrapping). This allows for the formation of an optimization problem, which can be solved rapidly by standard methods. The proposed method is experimentally compared against the SAR/imaging methods, which represent the accuracy benchmark in prior-art, deploying off-the-shelf equipment. It is shown that the proposed method solves exactly the same problem as holographic-imaging methods, overcoming the grid-density constraints of the latter. Furthermore, the problem, being calculations-grid-independent, is solved orders of magnitude faster, allowing for the applicability of the method in real-time inventorying and localization. It is also shown that the state-of-the-art SLAM method, which is used for the estimation of the trace of the robot, also suffers from errors, which directly affect the accuracy of the RFID localization method. Deployment of reference RFID tags at known positions, seems to significantly reduce such errors.

In this paper, we propose a novel method for the three dimensional (3D) localization of RFID tags, by deploying a single RFID antenna on a robotic platform. The constructed robot is capable of performing Simultaneous Localization (of its own position) and Mapping (SLAM) of the environment and then locating the tags around its path. The proposed method exploits the unwrapped measured phase of the backscattered signal, in such manner that the localization problem can be solved rapidly by standard optimization methods. Three dimensional solution is accomplished with a single antenna on top of the robot, by forcing the robot to traverse non-straight paths (e.g. s-shaped) along the environment. It is proven theoretically and experimentally that any non-straight path reduces the locus of possible solutions to only two points along the 3D space, instead of the circle that represents the corresponding locus for typical straight robot trajectories. As a consequence, by applying our proposed method "Phase Relock" along the known half-plane of the search-space, the unique solution is rapidly found. We experimentally compare our method against the "holographic" method, which represents the accuracy benchmark in priorart, deploying commercial off-the-shelf (COTS) equipment. Both algorithms find the unique solution, as expected. Furthermore, "Phase ReLock" overcomes the calculations-grid constraints of the latter. Thus, better accuracy is achieved, while, more importantly, Phase-Relock is orders of magnitude faster, allowing for the applicability of the method in real-time inventorying and localization.

Purpose: One of the most usual indicators to measure the performance of any inventory policy is the mean stock level. In the generalized base stock, periodic review policy, the expected mean stock during the replenishment cycle is usually estimated by practitioners and researchers with the traditional Hadley-Whitin approximation. However it is not accurate enough and exact methods suggested on the related literature focus on specific demand distributions. This paper proposes a generalized method to compute the exact value of the expected mean stock to be used when demand is modelled by any uncorrelated, discrete and stationary demand pattern. Design/methodology/approach: The suggested method is based on computing the probability of every stock level at every point of the replenishment cycle for which it is required to know the probability of any stock level at the beginning of the cycle and the probability transition matrix between two consecutive periods of time. Furthermore, the traditional Hadley-Whitin approximation is compared with the proposed exact method over different discrete demand distributions Findings: This paper points out the lack of accuracy that the Hadley-Whitin approximation shows over a wide range of service levels and discrete demand distributions.

This article is about adaptive production control policies based on Kanban and CONWIP. First, it is shown that the Extended Kanban and the Generalized Kanban control policies, which have not been considered up to now in the relevant literature, actually fall within the category of adaptive card-based production control policies. Moving further, two novel adaptive production control policies are proposed, the Adaptive Generic Kanban and the Adaptive Extended Kanban. The proposed policies along with Extended Kanban and Generalized Kanban are compared in a simulation study to five existing adaptive approaches for controlling Kanban and CONWIP systems. It is noted that a comparative evaluation of these five existing adaptive policies is also absent from the relevant bibliography. The set of nine policies is tested in a tri-objective optimization problem, i.e. minimizing mean Work-In-Process, mean finished goods inventory and mean length of backorders queue under three different demand patterns. A multi-objective evolutionary algorithm is used to find optimal or near-optimal parameters for the control policies, and the resulting Pareto fronts are compared in terms of several metrics. In this experimental trial, the Extended Kanban, the Generalized Kanban and Adaptive Extended Kanban policies achieve the highest ranking.

This paper studies the effect of two service-level measures on the design of a critical-level policy for fast-moving items, where rationing is used to provide differentiated service levels to two classes of demand-high priority and low priority. Using the threshold-clearing mechanism under a strictly increasing non-negative demand to allocate backorders when multiple outstanding orders exist, we formulate service-level problems under type-I, fill-rate, and mixed service-level constraints to determine the optimal parameters of a continuous review (Q, r) policy with constant threshold value C to rationing the low-priority class. Based on several monotone properties, we proposed global search algorithms to solve the service-level problems, which guarantee reaching the globally optimal solution for any desired level of accuracy. Further results and a computational study demonstrate how these different models fare against each other in practice.

In this article, we consider an indoor simultaneous localization and mapping (SLAM) problem for a mobile robot measuring the phase of the signal backscattered by a set of passive radio ultra high frequency identification (ID) tags, deployed in unknown position on the ceiling of the environment. The solution approach is based on the introduction, for each radio frequency identification (RFID) tag observed, of a multihypothesis extended Kalman filter (MHEKF) which, based on the measured phases and on the wheel encoder readings, provides an estimate of the range and of the bearing of the observed tag with respect to the robot. This information is then used in an extended Kalman filter (EKF) solving the SLAM problem. Since an effective range and bearing estimate is available only after some steps, a resilient module is added to the algorithm to evaluate the reliability of the position estimate of each observed tag. As shown through numerical and experimental results, this makes the proposed approach robust with respect to several kinds of unmodeled disturbances, like multipath effects or even the unexpected change of the position of a tag.

In this paper, we consider the integrated planning of resources in a service maintenance logistics system in which spare parts supply and service engineers deployment are considered simultaneously. The objective is to determine close-tooptimal stock levels as well as the number of service engineers that minimize the total average costs under a maximum total average waiting time constraint. When a failure occurs, a spare part and a service engineer are requested for the repair call. In case of a stock-out at spare parts inventory, the repair call will be satisfied entirely via an emergency channel with a fast replenishment time but at a high cost. However, if the requested spare part is in stock, the backlogging policy is followed for engineers. We model the problem as a queueing network. An exact method and two approximations for the evaluation of a given policy are presented. We exploit evaluation methods in a greedy heuristic procedure to optimize this integrated planning. In a numerical study, we show that for problems with more than five types of spare parts it is preferable to use approximate evaluations as they become significantly faster than exact evaluation.

Control of inventory in production and operation systems is very important for better management and utilization of resources. In this paper, the optimal control of a periodic-review inventory system with items deterioration is considered. We are concerned with the problem of determining the production rate that minimizes a certain cost function. We deal with both cases where the deterioration coefficient is known and unknown. In the case where it is unknown, the recursive least squares algorithm is used to estimate this parameter. The main control objective is to maintain the inventory at a desired level in spite of the unknown model parameter and variable demand. The self-tuning optimal control is presented and the effectiveness of the proposed control algorithm is illustrated by simulation.

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In this paper, we consider a spare parts inventory problem faced by a manufacturer of electronic machines with expensive parts that are located at various customer locations. The parts fail infrequently according to a Poisson process. To serve customers when a failure occurs, the manufacturer operates a central warehouse and many field depots that stock spare parts. The central warehouse acts as a repair facility and replenishes stock at the field depots. There is a centralized decision maker who manages the inventory in both the central warehouse and the field depots. We develop a continuous review, base stock policy for this two-echelon, multi-item spare parts inventory system. We formulate a model to minimize the system-wide inventory cost subject to a response time constraint at each field depot. We present an efficient heuristic algorithm and study its computational effectiveness.

A normalização documental nos sistemas de informação dos museus tem sido, nos últimos sete anos, a nossa principal área de actividade profissional e de investigação. Verificamos que dada a inexistência de uma normalização de estrutura dos sistemas de informação de museus, ...

Maintaining the continuity of operations becomes increasingly important for systems that are subject to disruptions due to various reasons. In this paper, we study an inventory system operating under a (q, r) policy, where the supply can become inaccessible for random durations. The availability of the supply is modeled by assuming a single supplier that goes through ON and OFF periods of stochastic duration, both of which are modeled by phase-type distributions (PTD). We provide two alternative representations of the state transition probabilities of the system, one with integral and the other employing Kolmogorov differential equations. We then use an efficient formulation for the analytical model that gives the optimal policy parameters and the long-run average cost. An extensive numerical study is conducted, which shows that OFF time characteristics have a bigger impact on optimal policy parameters. The ON time characteristics are also important for critical goods if disasters can happen.

Maintaining the continuity of operations becomes increasingly important for systems that are subject to disruptions due to various reasons. In this paper, we study an inventory system operating under a (q, r) policy, where the supply can become inaccessible for random durations. The availability of the supply is modeled by assuming a single supplier that goes through ON and OFF periods of stochastic duration, both of which are modeled by phase‐type distributions (PTD). We provide two alternative representations of the state transition probabilities of the system, one with integral and the other employing Kolmogorov differential equations. We then use an efficient formulation for the analytical model that gives the optimal policy parameters and the long‐run average cost. An extensive numerical study is conducted, which shows that OFF time characteristics have a bigger impact on optimal policy parameters. The ON time characteristics are also important for critical goods if disasters c...

Dá-se a conhecer o sistema de inventário e de gestão das colecções do Museu da Indústria de Chapelaria de S. João da Madeira, tendo especial atenção aos aspectos relacionados com as utilizações possíveis desse sistema. Tais utilizações são as internas do museu, as de investigadores externos e as do público em geral. Nestas perspectivas, descrevem-se as principais funcionalidades do sistema.

Se estudian modelos EOQ de inventarios, en los que, durante el período de escasez, se considera que una proporción de la demanda se pierde y el resto se atiende con la llegada del siguiente pedido. La fracción de demanda no satisfecha en el período de rotura se supone que es una función dependiente del tiempo que los clientes deberían esperar hasta la recepción del artículo. El objetivo es encontrar el tamaño del lote que maximiza el beneficio por unidad de tiempo. Este beneficio medio se calcula teniendo en cuenta los ingresos obtenidos por las ventas y los costes de compra, mantenimiento, rotura y pedido. El coste unitario de compra es constante y conocido, el coste de almacenamiento es una función lineal basada en el inventario promedio y el coste de realizar un pedido es constante e independiente del tamaño del pedido. Los costes unitarios de rotura son funciones afines que dependen del tiempo que los clientes deben o deberían esperar hasta la llegada del siguiente pedido. Se desarrolla un procedimiento para caracterizar la política óptima de reposición y el beneficio máximo asociado. Este trabajo extiende diversos modelos de inventario estudiados por otros autores.

The lack of coordination in supply chains can cause various inefficiencies like bullwhip effect and inventory instability. Extensive researches quantified the value of sharing and forecasting of customer demand, considering that all the supply chain partners can have access to the same information. However, only few studies devoted to identify the value of limited collaboration or information visibility, considering their impact on the overall supply chain performances for local and global service level. This paper attempts to fill this gap by investigating the interaction of collaboration and coordination in a fourechelon supply chain under different scenarios of information sharing level. The results of the simulation study show to what extent the bullwhip effect and the inventory variance increase and amplify when a periodic review order-up-to level policy applies, noting that more benefits generate when coordination starts at downstream echelons. A factorial design confirmed the importance of information sharing and quantified its interactions with inventory control parameters, proving that a poor forecasting and definition of safety stock levels have a significant contribution to the instability across the chain. These results provide useful implications for supply chain managers on how to control and drive supply chain performances.

Demand signal processing contributes significantly to the bullwhip effect and inventory instability in supply chains. Most previous studies have been attempting to evaluate the impact of available traditional forecasting methods on the bullwhip effect. Recently, some researchers have employed SPC control charts for developing forecasting and inventory control systems that can regulate the reaction to short-run fluctuations in demand. This paper evaluates a SPC forecasting system denoted as SPC-FS that utilizes a control chart approach integrated with a set of simple decision rules to counteract the bullwhip effect whilst keeping a competitive inventory performance. The performance of SPC-FS is evaluated and compared with moving average and exponential smoothing in a four-echelon supply chain employs the order-up-to (OUT) inventory policy, through a simulation study. The results show that SPC-FS is superior to the other traditional forecasting methods in terms of bullwhip effect and inventory variance under different operational settings. The results confirm the previous researches that the moving average achieves a lower bullwhip effect than the exponential smoothing, and we further extend this conclusion to the inventory variance.

Inventory replenishment rules contribute significantly to the bullwhip effect and inventory instability in supply chains. Smoothing replenishment rules have been suggested as a mitigation solution for the bullwhip effect but dampening the bullwhip effect might increase inventory instability. This paper evaluates a real-time inventory replenishment system denoted as SPC that utilizes a control chart approach to counteract the bullwhip effect whilst achieving competitive inventory stability. The SPC employs two control charts integrated with a set of decision rules to estimate the expected demand and adjust the inventory position, respectively. The first control chart works as a forecasting mechanism and the second control chart is devoted to control the inventory position variation whilst allowing order smoothing. A simulation analysis has been conducted to evaluate and compare SPC with a generalized (R, S) policy in a four-echelon supply chain, under various operational settings in terms of demand process, lead-time and information sharing. The results show that SPC is superior to the traditional (R, S) and comparable to the smoothing one in terms of bullwhip effect, inventory variance, and service level. Further managerial implications have been obtained from the results.

Bullwhip effect represents the amplification and distortion of demand variability as moving upstream in a supply chain, causing excessive inventories, insufficient capacities and high operational costs. A growing body of literature recognizes ordering policies and the lack of coordination as two main causes of the bullwhip effect, suggesting different techniques of intervention. This paper investigates the impact of information sharing on ordering policies through a comparison between a traditional (R, S) policy and a coordination mechanism based on ordering policy (a combination of (R, D) and (R, S) policies). This policy relies on a slow, easy to implement, information sharing to overcome drawbacks of the effect, in which replenishment orders are divided into two parts; the first is to inform the upstream echelons about the actual customer demand and the second is to inform about the adjustment of the inventory position, smoothing at the same time the orders of the different levels of the supply chain. A simulation model for a multi-echelon supply chain quantifies the supply chain dynamics under these different policies, identifying how information sharing succeeds to achieve an acceptable performance in terms of both bullwhip effect and inventory variance.

Optimal spare parts management strategies allow sustaining a system's availability, while ensuring timely and effective maintenance. Following a systemic perspective, this paper starts from the Multi-Echelon Technique for Recoverable Item Control (METRIC) to investigate the potential use of a Weibull distribution for modelling items' demand in case of failure. Adapting the analytic formulation of METRIC through a Discrete Weibull distribution, this study originally proposes a METRIC-based model (DW-METRIC) to be used for modelling the stochastic demand in multi-item systems, in order to ensure process sustainability. The DW-METRIC has been tested in a case study related to an industrial plant constituted by 98 items in a passive redundancy configuration. Comparing the results via a simulation model, the outcomes of the study allow defining applicability criteria for the DW-METRIC, in those settings where the DW-METRIC offers more accurate estimations than the traditional METRIC.

Inventory replenishment rules have been recognized as a major cause of the bullwhip effect and inventory instability in multi-echelon supply chains. There is a trade-off between bullwhip effect and inventory stability where mitigating the bullwhip effect through order smoothing might increase inventory instability. Therefore, there is a substantial need for inventory control policies that can cope with supply chains dynamics. This paper attempts to formulate an inventory control system based on a statistical control chart approach to handle the trade-off between order variability amplification and inventory stability. The proposed replenishment system, namely IR-SPC, incorporates individual control charts to control both the inventory position and the placed orders. A simulation study has been conducted to evaluate and compare the IR-SPC with a generalized order-up-to that has order smoothing mechanism. The comparisons showed that the IR-SPC outperforms both the smoothing order-up-to policy and the Min-Max inventory policy in terms of bullwhip effect and inventory performances.

This research aim to discover and analyze whether operational audit of sales within the company have been implemented adequately, if the sale has been implemented effectively on the company, and to know how to audit roles ini supporting the operational effectiveness of sales. This research using a sample as many as 43 people respondent which is a population of employees on the object of research. Method of data collection is carried out directly by using questionnaires and interviews to company management. While the analysis is used to determine the relationship of variables (X) Audit of operational variables bound (Y) that sales effectivensss is a simple linear regression analysis. This research result indicates that the answers respondents for variables operational audit the average score 52,33 and 51,2% answer% of respondents below average, so can be concluded that the audit operational on PT. Uber Anugerah Motor Bandar Lampung. And for variables effetiveness sales the average sc...

Because of globalisation and an associated global manufacturing environment, cost competitiveness has become necessary. In order to survive, the manufacturing firms have to provide a high level of service to the customers and a high level of throughput with the lowest Work-In-Process (WIP) inventory among other factors. It often becomes difficult to achieve all the objectives by a company management. Implementation of the manufacturing techniques like just-in-time (JIT) or pull production techniques may give the solution. Selection of optimal policy among various JIT policies is another issue which requires a trade-off among performance measures. The most widely used method in the decision making is analytic hierarchy process (AHP). The present paper is devoted to a literature review concerning the applications of AHP in JIT manufacturing environment.

We analyze the joint optimization of spare parts inventories and workforce allocation in a single-site maintenance system. In this system, for each failure, a service engineer with a necessary replacement part has to be allocated. If one of the required resources is not available, the incoming failure request is routed to an external provider, such as a centralized repair facility or a subcontractor. We study multiple failure types (related to failing components) with exponentially distributed inter-failure times. The system repair times and the replenishment times of the spare parts inventory are also exponentially distributed. The inventory replenishment is done according to a Base-Stock policy. The objective is to minimize the total system cost consisting of annual holding costs of the spare parts and the service engineers, and incidental outsourcing costs. For the joint optimization of the resources, we propose a Mixed-Integer Programming (MIP) formulation using the balance equations of the Markov Chain representation of the system. Furthermore, we provide a simple and efficient heuristic that produces close-to-optimal (< 0.3% difference) results, for solving larger instances. Using the proposed optimization methods and real-life data, we analyze the optimal balance between the costs of the resources and the outsourcing costs and show how the outsourcing rates and the total costs behave for different system parameters.

This paper presents an approach for achieving a trade-off between pull and push production control principles. A mathematical model of the operation of a production system is suggested, which incorporates different options for inventory control strategies. The model covers several types of disruptions: resource breakdown, product quality loss and demand fluctuation. The optimal solution minimizes the total cost objective function and can be push, one of the classic pull control systems (kanbans, conwip, basestock) or any possible combination/ superimposition of them. The approach is illustrated in an example, for which optimal pull/ push combination is found and its evolution is shown under several scenarios with disruptions.

This paper presents the strategy adopted by the Instituto de Investigação Científica Tropical (Tropical Research Institute), in Lisbon, to access and conserve the natural history collections under its care, specifically fluid-preserved zoological and botanical collections, through the creation and implementation of the interdisciplinary project "Promotion of Tropical Knowledge". We discuss key issues and planned interventions, taking into account the need to preserve the chemical structure and the morphology of the specimens in the best possible way. The article focuses on the importance of maintaining the integrity of the containers which house the specimens and the fluid composition and its appropriate levels, creating a protective microenvironment around the specimens. Reference is also made to the importance of computer processing of collections, allowing its availability to the scientific community and acting as a form of long term preservation, since this means of safeguarding information may last even longer than the specimens themselves. Resumo Neste artigo apresenta-se a estratégia seguida pelo Instituto de Investigação Científica Tropical, em Lisboa, para o acesso e conservação das colecções de história natural à sua guarda, especificamente, as colecções zoológicas e botânicas em meio líquido, através da criação e implementação do projecto interdisciplinar "Promoção do Saber Tropical". Discutem-se os principais problemas e intervenções previstas, com o objectivo de preservar a estrutura química e a morfologia dos espécimes. Foca-se, em particular, a importância da manutenção da integridade dos recipientes que albergam os espécimes e do líquido de preservação em níveis e composição apropriados, criando um microambiente protector à volta dos exemplares. Faz-se também referência à importância do tratamento informático das colecções, que facilita o acesso à informação por parte da comunidade científica, potenciando a investigação, e que funciona como uma forma de preservação de longo prazo, pois esse meio de salvaguarda da informação pode durar ainda mais tempo que os próprios espécimes.

As after sales services become more and more popular, particularly preventive or corrective maintenance, the intervention and repair of the customer’s goods in a timely and efficient manner ensure customer satisfaction and contribute to the establishment of brand image in the market of the suppliers. The availability and quality of spare parts are key elements of this strategy while ensuring minimal management costs. The reuse of spare parts retrieved from customer systems is a growing maintenance strategy practice which impacts the traditional spare parts supply chain. This reuse is primarily driven by extending the economic life of goods, initially regarded as waste and therefore without added value, by transforming them into valuable spare parts that can be reused; secondly, for environmental or regulatory reasons, demanding responsibility for the treatment of products at the end of their life; and thirdly, to improve the availability of parts for maintenance, especially parts th...

This technical report provides a concise overview of the extensive process implemented by the DICRC team for the mapping of several traditional and vernacular buildings of India. The Building Mapping is an approach towards identifying, understanding and developing a detailed inventory for different types of Traditional and Vernacular Buildings, their Elements (Interior Architecture elements, Furniture, Objects and Accessories) as well as the Space Making Crafts (SMC) and Surface Narrative Crafts (SNC) integrated within it; spread across India. The Building Mapping is an inclusive system of recording through photographic survey, form based inventory and interviews. It is the first of its kind visual-based mapping technique in India conducted using interactive mobile tablet survey. A specific mobile application has been developed by the researchers at DICRC to conduct this survey. The data generated out of this mapping process is categorized and it is taken further in preparing an in-depth Traditional Building Portfolio (TBP), Traditional Building Elements Catalogue (TBEC) and Interactive Online Map; all being disseminated through various online platforms.

We propose an analytically tractable approach for studying the transient behavior of multi-server queueing systems and feedforward networks with deterministic routing. We model the queueing primitives via polyhedral uncertainty sets inspired by the limit laws of probability. These uncertainty sets are characterized by parameters that control the degree of conservatism of the model. Assuming the inter arrival and service times belong to such uncertainty sets, we obtain closed form expressions for the worst case transient system time in multi-server queues and feedforward networks with deterministic routing. These analytic formulas offer rich qualitative insights on the dependence of the system times as a function of fundamental quantities in the queueing system. Moreover, we break new grounds and present an algorithm which appropriately averages worst case values obtained at different degrees of conservatism. This methodology achieves significant computational tractability and provides good approximations for the expected system time relative to simulation.