Fatih Mutlu

A comparison of outbound dispatch policies for integrated inventory and transportation decisions

This paper investigates the impact of alternative outbound dispatch policies on integrated stock replenishment and transportation decisions. The logistics literature reports that two different types of such policies are popular in current practice. These are time-based and quantity-based dispatch policies. Considering the case of stochastic demand, the paper presents analytical and numerical results showing that the cost savings obtained through quantity-based policies can be substantial. However, under a quantity-based policy, a specific delivery time cannot be quoted when the customer places an order. Hence, the paper also investigates the cost and customer waiting time implications of hybrid policies and demonstrates that hybrid policies are superior to time-based policies in terms of the resulting costs. Furthermore, although hybrid policies are not superior to quantity-based policies in terms of the resulting costs, they are superior in terms of a service measure which is quantified by the long-run average cumulative waiting time.

An Analytical Model for Computing the Optimal Time-and-Quantity-Based Policy for Consolidated Shipments

The logistics literature reports that three different types of shipment consolidation policies are popular in current practice. These are time-based, quantity-based and Time-and-Quantity (TQ)-based consolidation policies. Although time-based and quantity-based policies have been studied via analytical modeling, to the best of the authors knowledge, there is no exact analytical model for computing the optimal TQ-based policy parameters. Considering the case of stochastic demand/order arrivals, an analytical model for computing the expected long-run average cost of a consolidation system implementing a TQ-based policy is developed. The cost expression is used to analyze the optimal TQ-based policy parameters. The presented analytical results prove that: (i) the optimal TQ-based policy outperforms the optimal time-based policy; and (ii) the optimal quantity-based policy is superior to the other two (i.e., optimal time-based and TQ-based) policies in terms of cost. Considering the expected maximum waiting time as a measure of timely delivery performance, however, it is numerically demonstrated that the TQ-based policies improve on the quantity-based policies significantly with only a slight increase in the cost.

An integrated resource allocation and distribution model for pre-disaster planning

We model a disaster preparedness problem for the supply of a commodity.We consider an integrated pre- and post-disaster preparedness planning model.The use of multiple supply points reduces supply deprivations at the demand points.Deprivation cost structure significantly affect the proportion of pre- and post-disaster allocations. In this paper, a three-echelon network model is proposed for integrated emergency preparedness and response planning for the distribution of emergency supplies. The model minimizes the social cost to identify a set of potential supply points (SPs) at the highest echelon, where supply items are consolidated and sent to the prepositioning facilities. The sum of logistics and deprivation costs incurred by the population due to the lack of access to goods or services, is considered as the social cost in this model. The deprivation cost is assumed to increase exponentially with the deprivation time. The model also considers pre-disaster and post-disaster purchasing decisions at the SPs, and allows direct shipments from SPs and prepositioned facilities to the demand points. Numerical analysis shows that multiple supply sources can ensure efficient distribution of the supplies and reduce the deprivation costs. The results also indicate that partial prepositioning and post-disaster purchasing can reduce the shortage in emergency supplies.

Projection of Diabetes Burden through 2025 and Contributing Risk Factors of Changing Disease Prevalence: An Emerging Public HealthProblem

Background: The Middle East region is predicted to have one of the highest prevalence of diabetes mellitus (DM) in the world. This is the first study in the region to forecast the burden of diabetes. Aim: This study aims to estimate the projected prevalence of type 2 diabetes mellitus [T2DM] among adults in Qatar over the period 2012 to 2025 using national data, and to quantify the potential effect of a suggested preventive intervention program. Design: It is an observational cohort study. Setting: The survey was based on registry at the Hamad General Hospital and Primary Health Care (PHC) centers in the State of Qatar. Subjects: This study consisted of patients above 25 years of age with diagnosed diabetes mellitus registered at Hamad General Hospital and Primary Health Care (PHC) centers during January 2006 to December 2012. Methods: We developed a dynamic model in which actual incidence, prevalence, and life expectancy data are used and alternative assumptions about future trends in these parameters can be incorporated. Linear regression model has been performed to forecast the burden of diabetes in oil - rich country. Result: According to the dynamic model, a 10% increased in the number of diabetic patients in the State of Qatar from 37000 in 2006 to 122,000 in 2012 (about 1% annually). The annual diabetes incidence rate was higher in women than in men during a period between 2006 to 2012 years. The static model forecasted as 10% increase over 10 years. The relative increase in prevalence of diabetes and number of diabetic people is higher in women than in men (16.6%; 17.5% and 18.4% in men vs. 22.6%; 23.8% and 25.1% in women). Most of the increase in prevalence of diabetes is projected to occur in younger age groups where it is estimated to increase among age groups of 50-59 years and above 60 years, respectively. Conclusion: The burden of diabetes in Qatar is markedly larger than proposed by IDF estimations- suggesting that Qatar would be one of the top ten countries worldwide in diabetes prevalence. Family history of diabetes, consanguinity marriages’, hereditary gene-environment interactions, poor nutrition in utero and in early life plus over nutrition in later life may also contribute to the current diabetes epidemic in Qatari’s Arab populations. In planning future health care, monitoring of trends in incidence, prevalence, remission, and mortality or life expectancy is a necessary prerequisite.

Burden of diabetes mellitus attributable to demographic levels in Qatar: An emerging public health problem

BACKGROUND Diabetes is one of the main contributors to ill health and premature mortality worldwide and its prevalence has been rising during the last decades. AIM The aim of the present study was to quantify the burden of disease in terms of deaths and loss of healthy life years (DALYs) attributed to diabetes by its demographic levels in the State of Qatar. MATERIALS AND METHODS The methods were largely based on the established Global Burden of Disease methodology and use the burden of disease in terms of disability adjusted life years (DALYs) and the years lost due to disability (YLD) as the outcome measure. We calculated years lost due to disability (YLD) and years life lost (YLL) attributable to diabetes. The study was conducted during the period from June 2013 to January 2014. RESULTS The study findings revealed that disability adjusted life years (DALYs) has been increasing across the years and reached to 4.35 in 2011 from 2.58 in 2007. DALYs for men was remarkably higher than women during the period (2007-2011). Diabetes mellitus was the 6th leading cause of disease burden in Qatar (3.8%). The YLD showed a sharp increase in men (2.52 in 2011 from 1.34 in 2007) and women (1.05 in 2011 from 0.33 in 2007) during the year 2011. YLL portion of women enlarged considerably in 2011 (0.10) compared to 2010 (0.04). YLL for men and women was fluctuating across the years with a decrease in 2011 (18%) from 2007 (35%). Men and women in the age group 30-44 years had the highest peak across the years. CONCLUSION The study findings revealed that diabetes disease burden was considerably high in Qatar, particularly in the working age group. DALYs has been increasing across the years.

A comprehensive annual delivery program for upstream liquefied natural gas supply chain

Developing a cost-effective annual delivery program (ADP) is a challenging task for liquefied natural gas (LNG) suppliers, especially for LNG supply chains with large number of vessels and customers. Given significant operational costs in LNG delivery operations, cost-effective ADPs can yield substantial savings, adding up to millions. Providing an extensive account of supply chain operations and contractual terms, this paper aims to consider a realistic ADP problem faced by large LNG suppliers; suggest alternative delivery options, such as split-delivery; and propose an efficient heuristic solution which outperforms commercial optimizers. The comprehensive numerical study in this research demonstrates that contrary to the common belief in practice, split-delivery may generate substantial cost reductions in LNG supply chains.

On the service performance of alternative shipment consolidation policies

Abstract In order to compare the performances of alternative shipment consolidation policies, we develop closed-form expressions of the distribution of the maximum waiting time and the average order delay. We examine the tradeoff between the expected delivery frequency, as measured by the expected shipment consolidation cycle length, and the average order delay. The previous analytical results regarding shipment consolidation are aimed at optimizing the performances of alternative policies using cost-based criteria whereas our results are useful under service-based criteria.

The impact of production scheduling policies and buffer zone size in process synchronization an application in the primary aluminum industry

A hybrid process structure, a continuous flow followed by a batch process, is used in the primary aluminum production. The continuous flow provides a steady stream of Work-In-Process (WIP) to the process; but the WIP is usually delayed before it can move to the batch process. This leads to increased flow times, increased inventories, and inefficient use of resources. In such hybrid structures, process synchronization can be achieved by carefully scheduling the production and allocating the resources. We study the performances of two alternative production-scheduling policies and two alternative resource allocation mechanisms in the primary aluminum production process, which is a hybrid process. First, we build a simulation model that can represent a nearly realistic primary aluminum production setting under various design parameters. Second, we show that the production scheduling policy led by the latter stage of the production, significantly improves the process performance compared to a decentralized policy, in which each stage makes its own schedule. Third, we show that the amount of resources at the buffer zone in between the two stages of the process is very critical for the process performance; and we quantify its benefits through numerical work. Finally, we suggest that dedicating common resources, such as trucks, to individual stages of the process slightly improves the process performance as opposed to pooling those resources.