Narrow Results

This study presents an inventory management framework that integrates preservation technology investments with demand influenced by price and advertisement frequency, while also examining the impact of carbon tax policies. Two models are considered: (i) a baseline model without carbon policies and (ii) an advanced model incorporating carbon tax policies to mitigate environmental impacts. The analysis explores the interplay between preservation technology investments and carbon emissions, providing insights into optimal pricing and replenishment strategies for managing deteriorating inventory with varying initial reference prices. The results highlight the effectiveness of preservation technologies in reducing deterioration rates, stabilizing costs and enhancing inventory quality. To operationalize these strategies, a practical iterative algorithm is developed, and validated through detailed numerical examples and key parameter analyses.

In this paper, we discuss why it is appropriate maximize the profits, instead of minimizing the costs, in an inventory system with an inventory-level-dependent demand rate. In addition, we restate Urban's viewpoint that the restriction of zero ending-inventory is not necessary in an inventory-level-dependent demand model. Consequently, we amend Giri and Chaudhuri's inventory model for deteriorating items by changing the objective to maximize the profits and relaxing the restriction of zero ending-inventory. Finally, we provide a couple of examples to show that both the order quantity and the profit obtained from our proposed model are significantly larger than those in Giri and Chaudhuri's model, in which the objective is to minimize the costs.

For a finite planning horizon, there has been a considerable body of research papers in the area of operations management that dealt with four different inventory shortage models in the last two decades. In this paper, we establish the models to reflect the fact that the longer the waiting time, the smaller the backlogging rate. We then use maximizing profit as the objective to make an appropriate comparison among those four alternatives. The theoretical results reveal that Model 4 provides the highest profit only if the profit margin is sufficiently low. Otherwise, in general, Model 3 has the highest profit among them.

In this paper, we study an inventory system with partial backlogging, in which the backlogging rate is a continuous and nonincreasing two piece function. The total shortage cost includes three significant costs: the unit backorder cost (depending on the backorder time), the opportunity cost, and the goodwill cost. This model generalizes several inventory systems studied by other authors. The optimal policy is characterized through several results, which depend on the values of the known input parameters. Illustrative examples and a sensitivity analysis, which help us understand the theoretical results, are also given.

Inventory models with deteriorating items have received considerable attention in recent years. In considering the deteriorating inventory with permissible delay in payments, most researchers pay attention to a single warehouse. Under conditions of permissible delay in payments, this paper develops a model to determine the optimal cycle time for a single deteriorating item that is stored in two different warehouses. A rented warehouse (RW) is used to store the excess units over the fixed capacity W of the owned warehouse (OW). The rented warehouse is assumed to charge higher unit holding cost than the OW. In this paper, we propose a two-warehouse inventory model for deteriorating items under permissible delay in payments. It is assumed that the deterioration rate in RW is the same as in OW, and the holding cost in RW is greater than that in OW. The stocks of RW are transported to OW in continuous release pattern and the transportation cost is ignored. Three theorems are developed to determine the optimal cycle time and numerical examples are given to illustrate these theorems.

Manufacturers and suppliers offer temporary reductions (or permanent increases) in the price charged to the resellers for a variety of reasons. The trade promotion may be offered to the reseller at a single point in time or over a finite time-span. In addition, in reselling situations, the end demand tends to be sensitive to selling price. It is commonly found that under such trade promotion (or in stockpiling to an announced price increase), not all the quantity purchased by the reseller at discount may be passed on to the final consumer at a reduced selling price. In fact, previous studies have shown that it is optimal for the reseller to carry forward some of the quantity purchased at discount and sell it later at the regular price. It has been suggested in the literature that by placing a restriction on the reseller's purchase quantity, the supplier can restrict the reseller's forward buy quantity. In this paper, we evaluate this approach. In the rest of the paper, we present alternate schemes which are easy to administer and which insure that the supplier avoids the spike in demand that occurs in the unconstrained problem.

An inventory model is discussed with generalized ramp-type demand where the time to deterioration follows Weibull distribution. Shortages of inventories are allowed and completely backlogged. Total cost is derived by trading off setup cost, holding cost, deterioration cost, and shortage cost. The optimal replenishment policy for a single period is derived by minimizing the total cost per unit time over infinite time horizon. A numerical example is presented and sensitivity analysis is also carried out. The rationale for generalized ramp-type demand is discussed.

In the classical economic order quantity (EOQ) inventory model, it was assumed that the retailer must pay for the received items immediately. However, in practice, the supplier not only allows retailer to settle the account after a certain fixed period but also may offer a cash discount to encourage the retailer to pay for his purchases as soon as possible. On the other hand, it is common practice in most inventory systems to hold excess stocks in a rented warehouse whenever the storage capacity of the owned warehouse is insufficient. Therefore, the purpose of this paper is to establish an EOQ model with limited storage capacity, in which the supplier provides cash discount and permissible delay in payments for the retailer. In the model, we develop some useful theorems to characterize the optimal solution and provide a simple method to find the optimal replenishment cycle time and payment time. Finally, several numerical examples are given to illustrate the theoretical results and some managerial insights are also obtained.

This paper presents a stylized model to determine the optimal strategy for the integrated supplier-retailer inventory model under the condition that both the supplier and retailer have adopted a trade credit strategy. By analyzing the total channel profit function, we develop an algorithm to simultaneously determine the retailer's optimal order quantity and the number of shipment per production run from the supplier to the retailer. Our results demonstrate that the trade credit strategy is effective to supply chain system performance when customers are sensitive to the credit period length offered by the retailer. Moreover, when customers are sensitive to the credit period, if the retailer conveys partial advantage gained from the trade credit offered by the supplier to customers by suitably adjusting the customer's credit period then the entire system and every channel partner can benefit.

Since the publication of the Goyal model in 1985, research on the modeling of inventory lot-size under trade credits has resulted in a body of literature. In this paper, we present a review of the advances in inventory literature under conditions of permissible delay in payments since 1985. We classify all related previous articles into five categories based on: (a) without deterioration, (b) with deterioration, (c) with allowable shortage, (d) linked to order quantity, and (e) with inflation. The motivations, extensions and weaknesses of various previous models have been discussed in brief to bring out pertinent information regarding model developments in the past two decades.

In today's business environment, a supplier usually offers customers a permissible delay for settling outstanding account balance for the goods supplied. However, a supplier on occasion may allow this permissible delay in payments to be more than the usual during a given specified period. In this paper, we establish an appropriate model for a customer to determine its optimal special order quantity when the supplier offers a special extended permissible delay for one time only during a specified period. We then establish two theorems for a customer to find the optimal special order quantity. Finally, several numerical examples are given to illustrate the theoretical results.

A single item, single cycle economic production quantity model for perishable products is proposed where the demand is two-component and stock dependent. The production inventory scenario of products like cake, bread, fast foods, fishes, garments, cosmetics etc in the festival season is considered. The profit function is formulated under the assumption that the time period of the festival seasons is fixed and the display capacity of the produced item is limited. In the formulation process, to introduce more flexibility, a goal programming technique is incorporated to achieve the producer's desired profit and stock of as much inventory as possible below the display capacity level. A numerical example is presented to illustrate the proposed model. A sensitivity analysis of the model is also carried out.

This paper analyzes a continuous-review inventory system with random supply interruptions and stochastic lead time. In such a system, a monopolistic supplier alternates between random ON and OFF periods. The variable (r,q)-policy is used. With a constant demand rate, the leadtime may be interrupted by a random number of OFF periods of the supplier. Using the regenerative cycle analysis, a long-run average cost function is obtained and shown to have some important properties. Accordingly, an effective search algorithm is proposed to find the sub-optimal inventory policy. In the end, we also investigate the effects on the average cost of the uncertain order delay which attribute to both the supply interruptions and the random leadtime. Numerical examples are presented to demonstrate the effectiveness of the search algorithm.

This work presents an extension of the classical EOQ model for items with a fixed shelf life and a declining demand rate due to a reduction in the quality of the item in the course of its shelf-life. The demand rate, reflecting consumer preference for fresh items, is a polynomial function of the remaining time until the expiry date of the item. A mathematical model is developed to maximize the average profit per unit time, subject to shelf-life and marginal profit limitations. We prove that based on these limitations the model has a unique optimal solution and suggest a procedure for finding the optimal cycle length. A numeric example, including a sensitivity analysis, illustrates the model.

In this paper, an inventory model for deteriorating items with ramp-type time and price dependent consumption rate over a finite planning horizon is considered. In contrast to the traditional deterministic inventory model with static price over the entire planning horizon or fixed number of price changes over the finite time horizon, an alternative model is derived in which prices and the number of price change are to be decision variables. We show that the total profit function is concave. With the concavity, a solution procedure is presented to determine optimal prices, optimal number of pricing cycles and optimal lot size and optimal profit. We illustrate the model with numerical examples. Sensitivity analysis of the model is also carried out.

The purpose of this article is to construct a stochastic-demand inventory model which assumes that the whole period is stockout and the goods supply is at the end of the period. Furthermore, it also assumes that the waiting willingness of the customer depends on the length of waiting time. Based on these assumptions, the optimal supply cycle is then found so that the profit per unit time is maximized.

This study develops a mathematical inventory model for deteriorating item taking into account a vertical integration of a three-echelon supply chain (one supplier, one distributor, and one retailer) through strategic alliances. The objective is to minimize the joint total relevant cost for the integrated inventory model. A simple but efficient heuristic technique is used to derive the optimal solution. A numerical example and sensitivity analysis on the optimal results are presented to validate the results of the proposed integrated model. The proposed mathematical model has demonstrated how an integrated approach to decision making can achieve a global optimum and outperform three typically individual models (i.e., independent model, dominant supplier's model and dominant retailer's model).

In this paper, a two-warehouse inventory model for items with imperfect quality and all-unit quantity discounts was developed. In practice, the supplier usually offers quantity discounts to encourage the retailer ordering larger lot sizes and thus, extra storage space is needed for the retailer. Two levels of storages, owned-warehouse and rented warehouse, are considered in this study to store bulk quantities. We develop two algorithms to determine the optimal lot size and purchasing cost: one is based on the work of Render et al. (2003) and the other is similar to the method proposed by Goyal (1995). Two numerical examples are provided for illustration, in which we show that our algorithms require fewer iterations than that of the modified procedures based on the work of Render et al. (2003).

In this article, we generalize Lev and Weiss's (1990) finite horizon economic order quantity (EOQ) model with cost change to the inventory system with deterioration. Supplier announces some or all of cost parameters may change after a decided time. Depending on whether the inventory is depleted at the time of the last opportunity to purchase before some or all of the cost parameters may change, there are two types of inventory models to be discussed. The main objective of this paper is to identify the optimal ordering policy of the inventory system by comparing the minimum cost of the two types of models. We suggest a finite horizon EOQ model to combine the above two types and propose a theorem that can quickly identify the optimal policy of the suggested model. In considering temporary price discount problem and discrete-time EOQ problem, in general, there are integer operators in mathematical models, but our approach offers a closed-form solution to these kinds of problems. Numerical examples are presented to demonstrate the results of the proposed properties and theorem.

We introduce a method for maximizing the run-out time for a system where the number of components available to make repairs is finite, and some of the components may be substituted for one another. The objective is to maximize the time at which the earliest run-out of any component occurs. The approach proposed here is to find the minimum time horizon such that no feasible allocation exists for a related linear programming problem. An adaptive version of this algorithm is proposed as a heuristic for the stochastic problem.