The Experts below are selected from a list of 19554 Experts worldwide ranked by ideXlab platform
Hermann Gehring - One of the best experts on this subject based on the ideXlab platform.
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a two phase hybrid metaheuristic for the vehicle routing problem with time windows
European Journal of Operational Research, 2005Co-Authors: Jorg Homberger, Hermann GehringAbstract:Abstract The subject of this paper is a two-phase hybrid metaheuristic for the vehicle routing problem with time windows and a central depot (VRPTW). The objective function of the VRPTW considered here combines the minimization of the number of vehicles (primary Criterion) and the total travel distance (Secondary Criterion). The aim of the first phase is the minimization of the number of vehicles by means of a ( μ , λ )-evolution strategy, whereas in the second phase the total distance is minimized using a tabu search algorithm. The two-phase hybrid metaheuristic was subjected to a comparative test on the basis of 356 problems from the literature with sizes varying from 100 to 1000 customers. The derived results show that the proposed two-phase approach is very competitive.
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two evolutionary metaheuristics for the vehicle routing problem with time windows
Infor, 1999Co-Authors: Jorg Homberger, Hermann GehringAbstract:AbstractThe vehicle routing problem with time windows (VRPTW) is an extension of the well-known vehicle routing problem with a central depot. The objective is to design an optimal set of routes that services all customers and satisfies the given constraints, especially the time window constraints. The objective function considered here combines the minimization of the number of vehicles (primary Criterion) and the total travel distance minimization (Secondary Criterion). In this paper, two evolution strategies for solving the VRPTW are proposed. The evolution strategies were tested on 58 problems from the literature with sizes varying from 100 to 417 customers and 2 to 54 vehicles. The generated new best known solutions indicate that evolution strategies are effective in reducing both the number of vehicles and the total travel distance
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a parallel hybrid evolutionary metaheuristic for the vehicle routing problem with time windows
1999Co-Authors: Hermann GehringAbstract:The vehicle routing problem with time windows (VRPTW) is an extension of the well-known vehicle routing problem with a central depot. The objective function of the VRPTW considered here combines the minimization of the number of vehicles (primary Criterion) and the total travel distance (Secondary Criterion). In this paper, a two-phase procedural approach for solving the VRPTW is parallelized. The aim of the first phase is the minimization of the number of vehicles by means of a (1, λ)-evolution strategy, whereas in the second phase the total distance is minimized using a tabu search algorithm. The parallelization of this sequential hybrid procedure follows the concept of cooperative autonomy, i.e., several autonomous sequential solution procedures cooperate through the exchange of solutions. However, exchanges of solutions lead to the corresponding jumps in the solution space only if certain acceptance conditions are met. The good performance of both the sequential and the parallel approach is demonstrated by means of well-known and new benchmark problems.
Tadeusz Sawik - One of the best experts on this subject based on the ideXlab platform.
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a lexicographic approach to bi objective scheduling of single period orders in make to order manufacturing
European Journal of Operational Research, 2007Co-Authors: Tadeusz SawikAbstract:This paper presents a lexicographic approach and integer programming formulations for a dual-objective, long-term production scheduling in make-to-order manufacturing environment. The problem objective is to assign single-period customer orders for various product types to planning periods to complete all the orders with minimum number of tardy orders as a primary Criterion and to level the aggregate production or the total capacity utilization over a planning horizon as a Secondary Criterion. Each order must be completed during one planning period. The basic integer programming formulation has been strengthened by the addition of some cutting constraints derived by relating the demand on required capacity to available capacity for each subset of orders with the same due date. The approach has been applied to optimize production schedules in a flexible flowshop made up of several processing stages in series, with identical, parallel machines, and an output buffer of limited capacity for holding completed products before delivery to the customers. Numerical examples modeled after a real-world make-to-order flexible assembly line in the electronics industry are provided and some computational results are reported.
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discrete optimization a lexicographic approach to bi objective scheduling of single period orders in make to order manufacturing
2007Co-Authors: Tadeusz SawikAbstract:AbstractThis paper presents a lexicographic approach and integer programming formulations for a dual-objective, long-termproduction scheduling in make-to-order manufacturing environment. The problem objective is to assign single-period cus-tomer orders for various product types to planning periods to complete all the orders with minimum number of tardyorders as a primary Criterion and to level the aggregate production or the total capacity utilization over a planning horizonas a Secondary Criterion. Each order must be completed during one planning period. The basic integer programming for-mulation has been strengthened by the addition of some cutting constraints derived by relating the demand on requiredcapacity to available capacity for each subset of orders with the same due date. The approach has been applied to optimizeproduction schedules in a flexible flowshop made up of several processing stages in series, with identical, parallel machines,and an output buffer of limited capacity for holding completed products before delivery to the customers. Numerical exam-ples modeled after a real-world make-to-order flexible assembly line in the electronics industry are provided and some com-putational results are reported. 2006 Elsevier B.V. All rights reserved.
Jorg Homberger - One of the best experts on this subject based on the ideXlab platform.
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a two phase hybrid metaheuristic for the vehicle routing problem with time windows
European Journal of Operational Research, 2005Co-Authors: Jorg Homberger, Hermann GehringAbstract:Abstract The subject of this paper is a two-phase hybrid metaheuristic for the vehicle routing problem with time windows and a central depot (VRPTW). The objective function of the VRPTW considered here combines the minimization of the number of vehicles (primary Criterion) and the total travel distance (Secondary Criterion). The aim of the first phase is the minimization of the number of vehicles by means of a ( μ , λ )-evolution strategy, whereas in the second phase the total distance is minimized using a tabu search algorithm. The two-phase hybrid metaheuristic was subjected to a comparative test on the basis of 356 problems from the literature with sizes varying from 100 to 1000 customers. The derived results show that the proposed two-phase approach is very competitive.
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two evolutionary metaheuristics for the vehicle routing problem with time windows
Infor, 1999Co-Authors: Jorg Homberger, Hermann GehringAbstract:AbstractThe vehicle routing problem with time windows (VRPTW) is an extension of the well-known vehicle routing problem with a central depot. The objective is to design an optimal set of routes that services all customers and satisfies the given constraints, especially the time window constraints. The objective function considered here combines the minimization of the number of vehicles (primary Criterion) and the total travel distance minimization (Secondary Criterion). In this paper, two evolution strategies for solving the VRPTW are proposed. The evolution strategies were tested on 58 problems from the literature with sizes varying from 100 to 417 customers and 2 to 54 vehicles. The generated new best known solutions indicate that evolution strategies are effective in reducing both the number of vehicles and the total travel distance
K A Lehmann - One of the best experts on this subject based on the ideXlab platform.
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analgesic efficacy and safety of tramadol enantiomers in comparison with the racemate a randomised double blind study with gynaecological patients using intravenous patient controlled analgesia
Pain, 1995Co-Authors: Stefan Grond, T Meuser, D Zech, Ulrike Hennig, K A LehmannAbstract:Abstract The opioid analgesic tramadol is a racemate and consists of 50% (+)- and 50% (−)-enantiomer. This study investigated analgesic efficacy and safety of both enantiomers after intravenous (i.v.) injection in comparison with the racemate. Ninety-eight patients recovering from major gynaecological surgery under opioid-free halothane anaesthesia were treated in a randomised, double-blind study with (+)-tramadol, (−)-tramadol or the racemate. Following an individualised i.v. loading dose up to a maximum of 200 mg, patient-controlled analgesia with demand doses of 20 mg was made available for 24 h. The primary Criterion of efficacy was the decrease of pain intensity on a 5-point verbal rating scale from severe or maximum pain to mild or no pain within the first hour after the loading dose. The Secondary Criterion was patient satisfaction with pain relief during the 24-h observation period stated in the final interview. Patients who terminated the study prematurely were evaluated as non-responders. Of patients treated with (+)-tramadol, tramadol racemate, and (−)-tramadol, 12%, 15% and 53% of treated patients, respectively, terminated the study prematurely because of inefficacy. Of patients treated with (+)-tramadol, racemate or (−)-tramadol 67%, 48% and 38%, respectively, were considered responders regarding the primary Criterion of efficacy ( P = 0.061), and 82%, 76% or 41% with respect to the Secondary Criterion ( P = 0.001). Assessment of laboratory screening, adverse events, vital signs and blood gas monitoring showed no serious drug-related events. Nausea and vomiting were the most frequently reported non-serious side effects and were most often seen with (+)-tramadol. Taking into account both efficacy and safety aspects, the racemate seems to be superior to either enantiomer alone.
F A Allaert - One of the best experts on this subject based on the ideXlab platform.
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comparison of 1 and 3 polidocanol foam in ultrasound guided sclerotherapy of the great saphenous vein a randomised double blind trial with 2 year follow up the 3 1 study
European Journal of Vascular and Endovascular Surgery, 2007Co-Authors: C Hameldesnos, P Ouvry, J P Benigni, G Boitelle, M Schadeck, P Desnos, F A AllaertAbstract:Objectives To compare 1% and 3% POL foam in treating the great saphenous vein (GSV) by ultrasound guided sclerotherapy. Design Multicentre, prospective, randomised, double-blind trial with 2 year-follow-up. Patients and methods 148 patients with GSV reflux (saphenous trunk diameter 4–8 mm) were randomised to undergo ultrasound guided foam sclerotherapy using either 1% or 3% POL foam in a single session. Foam production was standardised using a sterile disposable syringe kit including sterile air and the Turbofoam® machine. Duplex ultrasonography was used to assess the outcome at 3 weeks, 6 months, 1 year, 18 months and 2 years. The main Criterion of success was the disappearance of the venous reflux. The length of occlusion of the vein (only measured at 3 week-echography assessment) was a Secondary Criterion. Side effects were assessed. Results 74 patients were included in each group. The mean volume of foam injected was 4.4 ml for the 3% group and 4.6 ml for the 1% group. After 3 weeks, reflux was abolished in 96% (71 patients) of the 3% group and 88% (68 patients) of the 1% group (NS). The mean occlusion length of the vein was 38 cm for the 3% group and 34 for the 1% group (NS). After 2-years, reflux was absent in 69% of the 3% group and 68% of the 1% group (NS). 14 patients were lost to follow-up at 2 years. Conclusion This study demonstrates equivalent efficacy for 1% POL and 3% POL foam in sclerotherapy of the GSV where the trunk is less than 8 mm in diameter. These data obtained two years of follow-up confirm our previously reported 6 month-follow-up data published in 2005.