| 1. |
- Axsäter, Sven
(author)
-
Evaluation of Unidirectional Lateral Transshipments and Substitutions in Inventory Systems
- 2003
-
In: European Journal of Operational Research. - 0377-2217. ; 149:2, s. 438-447
-
Journal article (peer-reviewed)abstract
- One interpretation of the model considered in this paper is a single-echelon inventory system consisting of a number of local warehouses, which normally replenish from an outside supplier. In case of a stockout at a warehouse an emergency lateral transshipment from another warehouse may be possible. However, such transshipments are only allowed in one direction, i.e., the flow structure is unidirectional. Such policies can be of interest if the warehouses have very different shortage costs. Another interpretation is substitution in an inventory system. We then instead consider different items in a single warehouse. When a demand for a low quality item cannot be met directly, the item can be replaced by another high quality item. We provide a simple and efficient approximate technique for policy evaluation in such systems. The performance of this technique is evaluated in a simulation study. Although the errors are not always negligible, the suggested method gives a good picture of how the considered lateral transshipments or substitutions affect the inventory system.
|
|
| 2. |
- Ohlsson, Mattias, et al.
(author)
-
An efficient mean field approach to the set covering problem
- 2001
-
In: European Journal of Operational Research. - 0377-2217. ; 133:3, s. 583-595
-
Journal article (peer-reviewed)abstract
- A mean field feedback artificial neural network (ANN) algorithm is developed and explored for the set covering problem. A convenient encoding of the inequality constraints is achieved by means of a multilinear penalty function. An approximate energy minimum is obtained by iterating a set of mean field equations, in combination with annealing. The approach is numerically tested against a set of publicly available test problems with sizes ranging up to 5 × 103 rows and 106 columns. When comparing the performance with exact results for sizes where these are available, the approach yields results within a few percent from the optimal solutions. Comparisons with other approximate methods also come out well, in particular given the very low CPU consumption required - typically a few seconds. Arbitrary problems can be processed using the algorithm via a public domain server.
|
|
| 3. |
- Skjott-Larsen, T, et al.
(author)
-
Logistics in the Oresund region after the bridge
- 2003
-
In: European Journal of Operational Research. - 0377-2217. ; 144:2, s. 247-256
-
Journal article (peer-reviewed)abstract
- The paper is based on a joint research project between Lund University and Copenhagen Business School. The main research question is: Can the Oresund region position itself as a leading logistics centre in Scandinavia in light of the new conditions created by the bridge? The purpose is to create a fundamental understanding of the new logistics conditions in the Oresund region by identifying drivers and barriers and suggesting future research topics. A theoretical frame of reference was developed combining four separate fields of theory and 47 personal interviews were carried out within four different categories of actors. The answers were grouped into: regional thinking, location to the Oresund region, importance of infrastructure, logistical competence and external factors. We found that most companies still use separate logistics structures for customers in Scania and in Zealand. However, all respondents agreed that the bridge at least has a psychological importance as a visible symbol of coherence. Educational institutions were considered to be the major possibility/driving factor for economic development. Identified barriers included: A lack of logistics competence, non-harmonised legislation and regulations, the absence of a logistical platform covering Denmark-Scania and industry-academia for the exchange of ideas, experiences and cultural differences. Several proposals for further research were formulated. (C) 2002 Elsevier Science B.V. All rights reserved.
|
|
| 4. |
- Aardal, Karen, et al.
(author)
-
On the resemblance between the Kornai-Liptak and cross decomposition techniques for block-angular linear programs
- 1990
-
In: European Journal of Operational Research. - : Elsevier BV. - 0377-2217 .- 1872-6860. ; 46:3, s. 393-398
-
Journal article (peer-reviewed)abstract
- In this paper the resemblance is demonstrated between the master- and subproblems generated by the Kornai-Liptak algorithm and the subproblems obtained by using the cross decomposition method on linear optimization problems with block-angular structure. The significance of the similarity between these two algorithms becomes apparent considering the main disadvantage attributed to cross decomposition. In cross decomposition a master problem has to be solved from time to time since the subproblems alone do not always give a converging sequence of primal and dual solutions. But if the cross decomposition algorithm is modified in such a way that the successive primal and dual subproblem solutions are taken into consideration with equal weights, this results in the Kornai-Liptak algorithm for which convergence is guaranteed
|
|
| 5. |
- Al-Najjar, Basim, 1954-, et al.
(author)
-
Enhancing a Company’s Profitability and Competitiveness Using Integrated Vibration-Based Maintenance : A Case Study
- 2004
-
In: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 157:3, s. 643-657
-
Journal article (peer-reviewed)abstract
- In this paper a model is developed for identifying, monitoring and improving the economic impact of vibration-based maintenance (VBM). This model provides an additional possibility of identifying where, why and how much capital should be invested, and judges whether or not the investment was cost-effective. The model is further utilised to develop relevant maintenance performance measures. When the model was tested in a Swedish paper mill, the main results were: the average yearly maintenance profit achieved using integrated VBM was at least 3.58 million Swedish kronor (SEK) (approximately USD 0.358 million), and average potential savings (economic losses) were around SEK 30 million (USD 3 million). Furthermore, the model facilitated identification of problem areas and recognition of where investments should be made. The major conclusion is that the better the data coverage and quality, the greater control is possible over direct maintenance costs, savings and further profits in maintenance. Moreover, using the model it would be easier and more reliable to detect deviations in the maintenance performance and eliminate their causes at an early stage.
|
|
| 6. |
- Aldin, Niklas, et al.
(author)
-
Electronic commerce, marketing channels and logistics platforms - a wholesaler perspective
- 2003
-
In: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 144:2, s. 270-279
-
Journal article (peer-reviewed)abstract
- Electronic commerce may impose new demands which the supply chain has to react to, while at the same time being an enabler of effective marketing and logistics. This paper describes alternative strategies for wholesalers conducting electronic commerce and how logistics may support the development of marketing channels and improve flexibility. Related issues with logistics implications are the decisions whether or not to use multiple channels and if intermediaries should totally bypass dealers, or rather collaborate by letting them manage the marketing relations and bypass them logistically. The concept of “logistics platforms” is discussed, based on empirical findings. Empirically the base is a case study of an intermediary with extensive use of business-to-business electronic commerce in a supply chain with independent dealers. The paper compares theoretical aspects with findings from the case and gives some indications of the potential of electronic commerce and logistics platforms.
|
|
| 7. |
- Ari, E. Aysen, et al.
(author)
-
Disaggregation under uncertainty in hierarchical production planning
- 1988
-
In: European Journal of Operational Research. - : Elsevier BV. - 0377-2217 .- 1872-6860. ; 35:2, s. 182-186
-
Journal article (peer-reviewed)abstract
- This study deals with a hierarchical planning system that is used for planning of a single-stage manufacturing system. We consider two decision levels, aggregate and detailed planning, and formulate a model for evaluation of aggregate plans and optimal disaggregation in case of independent stochastic demand. It is shown how the optimal solution can be obtained with the aid of a dynamic programming algorithm. Furthermore, we give conditions that will guarantee optimality of a simple intuitive disaggregation rule
|
|
| 8. |
- Asratian, Armen, et al.
(author)
-
A generalized class-teacher model for some timetabling problems
- 2002
-
In: European Journal of Operational Research. - : Elsevier. - 0377-2217 .- 1872-6860. ; 143:3, s. 531-542
-
Journal article (peer-reviewed)abstract
- We consider a theoretical model which extends the basic "class-teacher model" of timetabling and which corresponds to some situations which occur frequently in the basic training programs of universities and schools. We are given m teachers T1, ..., Tm and n classes C1, ..., Cn. The set of classes is partitioned into p disjoint subsets G1, ..., Gp in such a way that in addition to the lectures given by one teacher to one class, there are some lectures given by one teacher to the students of all classes in group Gl, 1 ≤ l ≤ p. Such lectures will be called group-lectures. The number alj of one hour group-lectures which teacher Tj must deliver to group Gl and the number bij of one hour class-teaching which Tj must give to class Ci are given. Is there a timetable of t hours (or length t), so that each class Ci and each group Gl receive all their lectures, but no student is scheduled to be taught by more than one teacher in each hour, and no teacher must teach to more than one group or class in each hour? We show that this problem is NP-complete and find some sufficient conditions for the existence of a timetable of length t. We also describe an algorithm for constructing a timetable corresponding to the requirement matrices A = (alj) and B = (bij) and show that under a natural assumption on A and B this algorithm finds a timetable within 7/6 of the optimum length
|
|
| 9. |
- Bergman, Bo, et al.
(author)
-
TTT-concept and replacements to extend system life
- 1987
-
In: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 28:3, s. 302-307
-
Journal article (peer-reviewed)abstract
- In a number of papers the current authors have illustrated how the Total Time on Test (TTT) concept can be used when analysing the ordinary age replacement problem and different generalization thereof. In this paper we show that the TTT-concept is very useful also when analysing another replacement problem discussed by C. Derman et al. in which the replacements of a vital component, for which there are n space units, are made with the goal of maximizing the expected system life. (12 refs.)
|
|
| 10. |
- Blomvall, Jörgen, et al.
(author)
-
A Riccati-based primal interior point solver for multistage stochastic programming
- 2002
-
In: European Journal of Operational Research. - Amsterdam, Netherlands : Elsevier. - 0377-2217 .- 1872-6860. ; 143:2, s. 452-461
-
Journal article (peer-reviewed)abstract
- We propose a new method for certain multistage stochastic programs with linear or nonlinear objective function, combining a primal interior point approach with a linear-quadratic control problem over the scenario tree. The latter problem, which is the direction finding problem for the barrier subproblem is solved through dynamic programming using Riccati equations. In this way we combine the low iteration count of interior point methods with an efficient solver for the subproblems. The computational results are promising. We have solved a financial problem with 1,000,000 scenarios, 15,777,740 variables and 16,888,850 constraints in 20 hours on a moderate computer. © 2002 Elsevier Science B.V. All rights reserved.
|
|
