Sotirios Papachristos

University of Ioannina | UOI · Department of Mathematics

In this paper, we consider a two warehouse inventory model, an owned one (OW) and a rented one (RW). Inventory deteriorates in the two warehouses at different constant rates, demand rate is a general ramp-type function of time and shortages are partially backlogged at a constant rate. Existence and uniqueness of the optimal solution is discussed. A...

We consider a single-echelon inventory installation under the classical EOQ (with backorders) paradigm to study the effects of supply quality on cost performance. Previous research on imperfect supply quality has focused on variants of the proportional (deterministic or random) yield problem, where supply batches are all accepted and then used, aft...

In this paper an order level inventory model for deteriorating items with general ramp type demand rate under conditions of permissible delay in payments is proposed. In this model shortages are allowed and partially backlogged. The backlogging rate is variable and dependent on the waiting time for the next replenishment. Its study requires explori...

A build-to-order (BTO) product is produced according to customers' requirements and specifications. Returning such a product is generally not allowed. However, if a return policy is offered, the producer may gain significant competitive advantages. The producer can gain the advantage of the return policy if the product design is highly modular. Mod...

In this paper, an inventory model with general ramp type demand rate, time dependent (Weibull) deterioration rate and partial backlogging of unsatisfied demand is considered. The model is studied under the following different replenishment policies: (a) starting with no shortages and (b) starting with shortages. The model is fairly general as the d...

In this paper, the traditional inventory lot-size model is extended to allow not only for general partial backlogging rate but also for inflation. The assumptions of equal cycle length and constant shortage length imposed in the model developed by Moon et al. [Moon, I., Giri, B.C., Ko, B., 2005. Economic order quantity models for ameliorating/deter...

This paper deals with a joint EOQ and EPQ model where the stationary demand call be satisfied by remanufactured and newly purchased products. The model assumes that a proportion of the already used products is Collected from customers and later is recovered for reuse. The remanufactured products tire regarded as perfect as new ones. For this model...

The paper deals with the problem of determining the economic order quantity under conditions of permissible delay in payments. A new credit period scheme is proposed under which the supplier offers to the buyer a fixed base level credit period in settling the account, plus additional delay time depending on the quantity ordered. The optimal repleni...

In this article, we revisit the paper by Teunter, R.H. [2004. Lot-sizing for inventory systems with product recovery. Computers and Industrial Engineering 46 (3), 431-441]. The solution algorithm proposed there, is partly heuristic and so it leads to an approximate policy. Computational experience shows that this algorithm behaves very well and giv...

We study a single-item periodic-review inventory model in a fluctuating environment with a fixed lead time of λ periods. The state of the environment at the beginning of each period is described by a homogeneous Markov chain. Ordering, holding, penalty costs and the distributions of random variables representing the customer's demand and the suppli...

This article considers a production/inventory system where each lot of items received or produced contains a random proportion of defective units, items of imperfect quality. The purchaser contacts a 100% inspection in order to identify the perfect (acceptable) quality items. The model examines the following two options for the imperfect quality it...

In this paper a periodic review inventory model with finite horizon and remanufacturing, manufacturing options is studied. It is assumed that demand and cost parameters are constant and a sufficiently large quantity of used products is available at the beginning of the horizon. The model is studied within the class of policies with given remanufact...

In this article, a single-product recovery system is studied. Used products are collected from customers and kept at the recoverable inventory warehouse for future recovery. The constant demand rate can be satisfied either by newly produced products or by recovered ones (serviceable inventory), which are regarded as perfectly as the new ones. Exces...

In this paper, we first look at the issue of non-shortages in models with proportional imperfect quality, when the proportion of the imperfects is a random variable. More specifically we revisit the papers of Salameh and Jaber (Int. J. Prod. Econom. 64 (2000) 59) and Chan et al. (Prod. Plann. Control 14 (2003) 588) and we point out that the suffici...

We consider the single-product lot-sizing problem over a finite planning horizon. Demand at each period is constant, and excess demand is completely backlogged. Holding and backlogging costs are proportional to the amount of inventory stocked or backlogged, while ordering cost is fixed, independent of the quantity ordered. The optimal policy target...

In this paper we present four inventory control models under the following assumptions. Planning horizon is finite and demand is a general logconcave function of time. The models allow for deterioration of items over time and shortages partially backlogged at an exponential rate. For each of the models we establish the existence of a unique optimal...

Wee (International Journal of Production Economics 59 (1999) 511), in his interesting paper presented a deterministic inventory model with the following characteristics. Quantity discount schemes for the unit cost, partial backlogging at a fixed rate, deterioration of stock in time and demand rate being a linear function of the selling price. In th...

Yan and Cheng (J. Operational Res. Soc. 49 (1998), 1288–1295) presented a general production–inventory model with production rate, product demand rate and deterioration rate, all considered as functions of the time. Their model allows for shortages and partial backlogging of the unsatisfied demand at a constant rate. In this paper, we extend the re...

In a recent paper Yang et al. extended the lot-size models to allow for inflation and fluctuating demand. For this model they proved that the optimal replenishment schedule exists and is unique. They also proposed an algorithm to find the optimal policy. The present paper provides examples, which show that the optimal replenishment schedule and con...

In this paper we study a continuous review inventory model. Five costs are considered as significant: deterioration, holding, shortage, opportunity cost due to the lost sales and the replenishment cost per replenishment which is linear dependent on the lot size. The deterioration of items occurs at a fixed rate independent of time. Demand rate is d...

We study a continuous review inventory model over a finite-planning horizon with deterministic varying demand and constant deterioration rate. The model allows for shortages, which are partially backlogged at a rate which varies exponentially with time. For this model an optimal replenishment policy is established.

In this paper we present rules concerning the optimal policy and stability regions for the single product periodic review inventory problem with stationary demands, over a finite horizon. The key parameter to the whole study is the Lot-Sizing Index (LSI) introduced by Blackburn and Millen. Two algorithms are presented. The first one constructs stab...

In this paper we present rules concerning the optimal policy and stability regions for the single product periodic review inventory problem with stationary demands, over a finite horizon. The key parameter to the whole study is the Lot-Sizing Index (LSI) introduced by Blackburn and Millen. Two algorithms are presented. The first one constructs stab...

In this paper we examine the performance of several commonly used heuristics for the single-level lot-sizing problem, for products with stationary demand and cost parameters. A particular combination of demand and cost combination, introduced by Blackburn and Millen, called the lot-sizing index (LSI), is shown to be an excellent predictor of heuris...

We point out some errors in Iglehart's paper, "The Dynamic Inventory Problem with Unknown Demand Distribution," published in Management Science in 1964.