| 1. |
- Ahani, Narges, et al.
(författare)
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Placement Optimization in Refugee Resettlement
- 2021
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Ingår i: Operations Research. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0030-364X .- 1526-5463. ; 69:5, s. 1468-1486
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Tidskriftsartikel (refereegranskat)abstract
- Every year, tens of thousands of refugees are resettled to dozens of host countries. Although there is growing evidence that the initial placement of refugee families profoundly affects their lifetime outcomes, there have been few attempts to optimize resettlement decisions. We integrate machine learning and integer optimization into an innovative software tool, Annie™ Matching and Outcome Optimization for Refugee Empowerment (Annie™ Moore), that assists a U.S. resettlement agency with matching refugees to their initial placements. Our software suggests optimal placements while giving substantial autonomy to the resettlement staff to fine-tune recommended matches, thereby streamlining their resettlement operations. Initial back testing indicates that Annie™ can improve short-run employment outcomes by 22%–38%. We conclude by discussing several directions for future work.
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| 2. |
- Amaldi, Edoardo, et al.
(författare)
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Solving Nonlinear Covering Problems Arising in WLAN Design
- 2011
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Ingår i: OPERATIONS RESEARCH. - : Informs. - 0030-364X .- 1526-5463. ; 59:1, s. 173-187
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Tidskriftsartikel (refereegranskat)abstract
- Wireless local area networks (WLANs) are widely used for cable replacement and wireless Internet access. Because the medium access control (MAC) scheme of WLANs has a strong influence on network performance, it should be accounted for in WLAN design. This paper presents AP location models that optimize a network performance measure specifically for the MAC scheme of WLANs that represents the efficiency in sharing the wireless medium. For these models, we propose a solution framework based on an effective integer-linear programming Dantzig-Wolfe reformulation. This framework is applicable to any nonlinear covering problem where the objective function is a sum of contributions over the groundset elements (users in WLANs). Extensive computational results show that our solution strategy quickly yields optimal or near-optimal solutions for WLAN design instances of realistic size.
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| 3. |
- Asmussen, Sören, et al.
(författare)
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On the tail of the waiting time in a Markov-modulated M/G/1 queue
- 2002
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Ingår i: Operations Research. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0030-364X .- 1526-5463. ; 50:3, s. 559-565
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Tidskriftsartikel (refereegranskat)abstract
- We show that the "exponential decay parameter" of the waiting time in a Markov-modulated M/G/1 queue is no larger than that of the corresponding M/G/1 queue with "averaged" parameters, and we give a necessary and sufficient condition for equality. We also explore the effect of speeding up the modulation process. A key tool is a Markov-modulated fluid model.
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| 4. |
- Axsäter, Sven
(författare)
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Exact and approximate evaluation of batch-ordering policies for two-level inventory systems
- 1993
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Ingår i: Operations Research. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0030-364X .- 1526-5463. ; 41:4, s. 777-785
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Tidskriftsartikel (refereegranskat)abstract
- We consider a two-level inventory system with one warehouse and N identical retailers. Lead times (transportation times) are constant and the retailers face independent Poisson demand. In a previous paper, we derived a recursive procedure for determining the policy costs for an average item in case of one-for-one replenishment policies. In this paper, we show how these results can be used for the exact or approximate evaluation of more general policies where both the retailers and the warehouse order in batches. We compare our methods to the method recently suggested by A. Svoronos and P. Zipkin.
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| 5. |
- Axsäter, Sven
(författare)
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On the feasibility of aggregate production plans
- 1986
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Ingår i: Operations Research. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0030-364X .- 1526-5463. ; 34:5, s. 796-800
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Tidskriftsartikel (refereegranskat)abstract
- We consider a situation in which a hierarchical planning system with two levels is applied to a multistage production process. The higher level aggregate production plan, expressed in terms of product groups, is disaggregated at the lower level into a detailed plan for individual items. We describe constraints imposed upon the aggregate level product groups that will guarantee the existence of a feasible disaggregation at the lower detailed level. The possibility of formulating suitable constraints is closely related to our choice of product groups and the aggregation of product data.
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| 6. |
- Axsäter, Sven, et al.
(författare)
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Optimal "Position-Based" Warehouse Ordering in Divergent Two-Echelon Inventory Systems
- 2008
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Ingår i: Operations Research. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0030-364X .- 1526-5463. ; 56:4, s. 976-991
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Tidskriftsartikel (refereegranskat)abstract
- A continuous-review two-echelon inventory system with one central warehouse and a number of nonidentical retailers is considered. The retailers face independent Poisson demand and apply standard (R, Q) policies. The retailer order quantities are fixed integer multiples of a certain batch size, representing the smallest pallet or container size transported in the system. A warehouse order may consist of one or several such batches. We derive a new policy for warehouse ordering, which is optimal in the broad class of position-based policies relying on complete information about the retailer inventory positions, transportation times, cost structures, and demand distributions at all facilities. The exact analysis of the new policy includes a method for determining the expected total inventory holding and backorder costs for the entire system. The class of position-based policies encompasses both the traditional installation-stock and echelon-stock (R, Q) policies, as well as the more sophisticated policies recently analyzed in the literature. The value of more carefully incorporating a richer information structure into the warehouse ordering policy is illustrated in a numerical study.
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| 7. |
- Axsäter, Sven
(författare)
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Simple solution procedures for a class of two-echelon inventory problems
- 1990
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Ingår i: Operations Research. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0030-364X .- 1526-5463. ; 38:1, s. 64-69
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Tidskriftsartikel (refereegranskat)abstract
- We consider an inventory system with one warehouse and N retailers. Lead times are constant and the retailers face independent Poisson demand. Replenishments are one-for-one. We provide simple recursive procedures for determining the holding and shortage costs of different control policies
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| 8. |
- Bergman, Bo, et al.
(författare)
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The total time on test concept and its use in reliability theory
- 1984
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Ingår i: Operations Research. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0030-364X .- 1526-5463. ; 32:3, s. 596-606
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Tidskriftsartikel (refereegranskat)abstract
- More than 30 years ago, Epstein and Sobel introduced the Total Time on Test (TTT-) concept. During the last 10 years different generalizations of this concept have been defined and studied, e.g. the TTT-transform and the TTT-plot; a basic paper was presented by Barlow and Campo in 1975. Many of these generalizations have proven to be very useful in different areas of reliability, both from a theoretical and a practical point of view. The purpose of this expository paper is to present some of these generalizations and illustrate their value.
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| 9. |
- Berling, Peter, 1973-, et al.
(författare)
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Optimal Inventory Policies when Purchase Price and Demand are Stochastic
- 2011
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Ingår i: Operations Research. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0030-364X .- 1526-5463. ; 59:1, s. 109-124
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we consider the problem of a firm that faces a stochastic (Poisson) demand and must replenishfrom a market in which prices fluctuate, such as a commodity market. We describe the price evolution as acontinuous stochastic process and we focus on commonly used processes suggested by the financial literature,such as the geometric Brownian motion and the Ornstein-Uhlenbeck process. It is well-known that under variablepurchase price, a price-dependent base-stock policy is optimal. Using the single-unit decomposition approach, weexplicitly characterize the optimal base-stock level using a series of threshold prices. We show that the base-stocklevel is first increasing and then decreasing in the current purchase price. We provide a procedure for calculatingthe thresholds, which yields closed-form solutions when price follows a geometric Brownian motion and implicitsolutions under the Ornstein-Uhlenbeck price model. In addition, our numerical study shows that the optimalpolicy performs much better than inventory policies that ignore future price evolution, because it tends to placelarger orders when prices are expected to increase.
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| 10. |
- Eriksson, Kimmo, et al.
(författare)
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Optimal Expected Rank in a Two-Sided Secretary Problem
- 2007
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Ingår i: Operations Research. - : Institute for Operations Research and the Management Sciences (INFORMS). - 0030-364X .- 1526-5463. ; 55:5, s. 921-931
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Tidskriftsartikel (refereegranskat)abstract
- In a two-sided version of the famous secretary problem, employers search for a secretary at the same time as secretaries search for an employer. Nobody accepts being put on hold, and nobody is willing to take part in more than N interviews. Preferences are independent, and agents seek to optimize the expected rank of the partner they obtain among the N potential partners. We find that in any subgame perfect equilibrium, the expected rank grows as the square root of N (whereas it tends to a constant in the original secretary problem). We also compute how much agents can gain by cooperation.
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