Motivated by a study of the logistics systems used to manage consumable service parts for the U.S. military, we consider a static threshold-based rationing policy that is useful when pooling inventory across two demand classes characterized by different arrival rates and shortage (stockout and delay) costs. The scheme operates as a (Q, r) policy with the following feature. Demands from both classes are filled on a first-comefirst-serve basis as long as on-hand inventory lies above a threshold level K. Once on-hand inventory falls below this level, low priority (i.e., low shortage cost) demand is backordered while high priority demand continues to be filled. We analyze this static policy first under the assumption that backorders are filled according to a special threshold clearing mechanism. Structural results for the key performance measures are established to enable an efficient solution algorithm for computing stock control and rationing parameters (i.e., Q, r, and K). Numerical results confirm that the solution under this special threshold clearing mechanism closely approximates that of the priority clearing policy. We next highlight conditions where our policy offers significant savings over traditional 'round-up' and 'separate stock' policies encountered in the military and elsewhere. Finally, we develop a lower bound on the cost of the optimal rationing policy. Numerical results show that the performance gap between our static threshold policy and the optimal policy is small in environments typical of the military and high technology industries.
A irline flight delays have come under increased scrutiny lately in the popular press, with the Federal Aviation Administration data revealing that airline on-time performance was at its worst level in 13 years in 2007. Flight delays have been attributed to several causes such as weather conditions, airport congestion, airspace congestion, use of smaller aircraft by airlines, etc. In this paper, we examine the impact of the scheduled block time allocated for a flight, a factor controlled by airlines, on on-time arrival performance. We analyze empirical flight data published by the Bureau of Transportation Statistics to estimate the scheduled on-time arrival probability of each commercial domestic flight flown in the United States in 2007 by a major carrier. The structural estimation approach from econometrics is then used to impute the overage to underage cost ratio of the newsvendor model for each flight. Our results show that airlines systematically "underemphasize" flight delays, i.e., the flight delay costs implied by the newsvendor model are less than the implied costs of early arrivals for a large fraction of flights. Our results indicate that revenue drivers (e.g., average fare) and competitive measures (e.g., market share) have a significant impact on the scheduled on-time arrival probability. We also show that the scheduled on-time arrival probability is not positively affected by the total number of passengers on the aircraft rotation who could be affected by a flight delay, or the number of incoming and outgoing connecting passengers on a flight. Operational characteristics such as the hub and spoke network structure also have a significant impact on the scheduled on-time arrival probability. Finally, full-service airlines put a higher weight on the cost of late arrivals than do low-cost carriers, and flying on the lowest fare flight on a route results in a drop in the scheduled on-time arrival probability.
An increasing number of manufacturers have started to pursue a strategy that promotes inventory sharing among the dealers in their distribution network. In this paper we analyze a decentralized dealer network in which each independent dealer is given the flexibility to share his inventory. We model inventory sharing as a multiple demand classes problem in which each dealer faces his own customer demand with high priority, and inventory-sharing requests from other dealers with low priority. Assuming that each dealer uses a base-stock and threshold-rationing policy for his inventory-stocking and inventory-sharing decisions, we explicitly model the interactions between the dealers through inventory sharing and obtain a closed-form cost function for each dealer based on the steady-state distribution of the inventory levels at the two dealers. We then provide a detailed supermodularity analysis of the inventory-sharing and inventory-rationing game in which each dealer has a two-dimensional strategy set (stocking level and rationing level). We show that the full-sharing game (in which dealers precommit to sharing all of their on-hand inventory) and the fixed-sharing-level game (in which dealers precommit to sharing a portion of their on-hand inventory) are supermodular, and thus a pure-strategy Nash equilibrium is guaranteed to exist. For the rationing game (in which dealers precommit to their stocking levels), we show that there exists a dominant strategy equilibrium on the dealers' sharing (rationing) levels. Finally, a comprehensive computational study is conducted to highlight the impact of the manufacturer's incentives, subsidies, and/or transshipment fees on the dealers' sharing behavior.inventory sharing and rationing, inventory competition, decentralized supply chains, noncooperative games
Firms have recently vertically integrated with suppliers to ensure corporate social and environmental responsibility (CSER) in sourcing. We investigate the conditions under which CSER concerns will drive vertical integration, and how actions of nongovernmental organizations (NGOs) impact CSER. This paper is inspired by Taylor Guitars’s acquisition of an ebony mill in Cameroon to ensure CSER. Whereas the majority of the responsible sourcing literature focuses on auditing as a mechanism for addressing CSER, we study vertical integration as an alternative. Our analysis confirms that CSER can be a potential driver of vertical integration aside from other well-known drivers. We analyze game-theoretical models where a firm can vertically integrate to potentially eliminate CSER risks. Two innovative features of our models are demand externalities (namely, a firm’s CSER violation can positively or negatively affect its competitor’s demand) and horizontal sourcing (namely, a vertically integrated firm can sell responsibly sourced supply to a competitor). We show that a firm’s CSER strategy depends on the risk of a CSER violation exposure, the level of demand externalities (positive or negative), and whether horizontal sourcing is feasible. We find that in industries where horizontal sourcing is unlikely, firms stay disintegrated under a low CSER violation exposure risk and vertically integrate under a moderate CSER violation exposure risk. Surprisingly, firms may stay disintegrated under a high CSER violation exposure risk combined with strongly negative demand externalities. In contrast, firms vertically integrate under moderate-to-high CSER violation exposure risk when horizontal sourcing is possible but may not share responsibly sourced supply through horizontal sourcing under strongly positive demand externalities. We show that firms should be conscious about demand externalities and the possibility of horizontal sourcing in the industry when considering vertical integration for CSER. We also provide guidance to NGOs interested in promoting CSER. When horizontal sourcing is unlikely, NGOs should specify both violating and nonviolating firms in their reports, but not over-scrutinize firms; whereas when horizontal sourcing is possible, NGOs should allocate more resources for scrutinizing firms’ CSER violations and create industry-wide violation reports, while avoiding naming of specific firms in their reports. This paper has been accepted for the Manufacturing & Service Operations Management Special Issue on Value Chain Innovations in Developing Economies.
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