| 1. |
- Axsäter, Sven
(författare)
-
Evaluation of Unidirectional Lateral Transshipments and Substitutions in Inventory Systems
- 2003
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Ingår i: European Journal of Operational Research. - 0377-2217. ; 149:2, s. 438-447
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
- Ohlsson, Mattias, et al.
(författare)
-
An efficient mean field approach to the set covering problem
- 2001
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Ingår i: European Journal of Operational Research. - 0377-2217. ; 133:3, s. 583-595
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Tidskriftsartikel (refereegranskat)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.
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| 3. |
- Skjott-Larsen, T, et al.
(författare)
-
Logistics in the Oresund region after the bridge
- 2003
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Ingår i: European Journal of Operational Research. - 0377-2217. ; 144:2, s. 247-256
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Aardal, Karen, et al.
(författare)
-
On the resemblance between the Kornai-Liptak and cross decomposition techniques for block-angular linear programs
- 1990
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217 .- 1872-6860. ; 46:3, s. 393-398
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Tidskriftsartikel (refereegranskat)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
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| 5. |
- Al-Najjar, Basim, 1954-, et al.
(författare)
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Enhancing a Company’s Profitability and Competitiveness Using Integrated Vibration-Based Maintenance : A Case Study
- 2004
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Ingår i: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 157:3, s. 643-657
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Tidskriftsartikel (refereegranskat)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.
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| 6. |
- Aldin, Niklas, et al.
(författare)
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Electronic commerce, marketing channels and logistics platforms - a wholesaler perspective
- 2003
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Ingår i: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 144:2, s. 270-279
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Tidskriftsartikel (refereegranskat)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.
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| 7. |
- Ari, E. Aysen, et al.
(författare)
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Disaggregation under uncertainty in hierarchical production planning
- 1988
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217 .- 1872-6860. ; 35:2, s. 182-186
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Tidskriftsartikel (refereegranskat)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
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| 8. |
- Asratian, Armen, et al.
(författare)
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A generalized class-teacher model for some timetabling problems
- 2002
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Ingår i: European Journal of Operational Research. - : Elsevier. - 0377-2217 .- 1872-6860. ; 143:3, s. 531-542
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Tidskriftsartikel (refereegranskat)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
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| 9. |
- Bergman, Bo, et al.
(författare)
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TTT-concept and replacements to extend system life
- 1987
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Ingår i: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 28:3, s. 302-307
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Tidskriftsartikel (refereegranskat)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.)
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| 10. |
- Blomvall, Jörgen, et al.
(författare)
-
A Riccati-based primal interior point solver for multistage stochastic programming
- 2002
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Ingår i: European Journal of Operational Research. - Amsterdam, Netherlands : Elsevier. - 0377-2217 .- 1872-6860. ; 143:2, s. 452-461
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Tidskriftsartikel (refereegranskat)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.
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| 11. |
- Brännäs, Kurt, et al.
(författare)
-
Semiparametric estimation of heterogeneous count data models
- 1994
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217 .- 1872-6860. ; 76:2, s. 247-258
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Tidskriftsartikel (refereegranskat)abstract
- Unobserved heterogeneity in a stochastic model is usually represented by a mixing distribution. In this paper a semiparametric estimator is adapted to over-dispersed Poisson regression models. No assumptions are needed about the estimated mixing distribution. The parameters of included explanatory variables are estimated at the same time. The applicability and promising properties of the method are illustrated. Empirically the estimator is applied to a coffee purchase model and to a business travel frequency model subject to zero truncation. The approach is useful, e.g., in marketing research where socio-demographic variables as well as marketing instruments can be included as explanatory variables.
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| 12. |
- Carlsson, Christer, et al.
(författare)
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Consensus in distributed soft environments
- 1992
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Ingår i: European Journal of Operational Research. - : Elsevier. - 0377-2217 .- 1872-6860. ; 61:1-2, s. 165-185
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies the problem of formalizing consensus reaching within a set of decision makers trying to find and agree upon a mutual decision. Decision makers produce their individual rankings, using their own pet decision schemas. Thus consensus reaching relies only on the aggregation of individual decisions rather than on individual decision procedures. The aggregation of the individual rankings is supported by an advising monitor which tries to contract the decision makers into a mutual decision through soft enforcement. Convergence to consensus then depends upon the decision makers' willingness to compromise. We use a topological approach to consensus where we can measure distances between decision makers. Within the approach we can also model the trade-off between a degree of consensus and a strength of majority.
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| 13. |
- Ekvall, Niklas
(författare)
-
A Lattice Approach for Pricing of Multivariate Contingent Claims
- 1996
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Ingår i: European Journal of Operational Research. - : Elsevier: 24 months. - 0377-2217. ; 91:2, s. 214-228
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Tidskriftsartikel (refereegranskat)abstract
- The lattice approach developed by Boyle, Evnine and Gibbs (BEG) is hitherto one of the most appealing, when it comes to pricing multivariate contingent claims. The BEG approach has, however, some problems, two of the major ones being that the method can lead to negative jump probabilities and has a slow rate of convergence. In this paper, a lattice approach (the NEK approach) is developed which avoids both of the aforementioned problems of the BEG approach. It is shown that the NEK approach has a very fast rate of convergence. The results are accurate enough for most needs with as few as ten time steps, and the results are astonishingly accurate with twenty time steps. Moreover, the NEK approach is simple and easy to understand, and also easy to implement. The latter property follows from the fact that all jump probabilities are equal and that the formulas for the jump sizes are extremely simple.
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| 14. |
- Forsberg, Rolf
(författare)
-
Exact evaluation of (R, Q)-policies for two-level inventory systems with Poisson demand
- 1997
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Ingår i: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 96:1, s. 130-138
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we show how to exactly evaluate holding and shortage costs for a two-level inventory system with one warehouse and N different retailers. Lead-times (transportation times) are constant, and the retailers face different Poisson demand processes. All facilities apply continuous review (R, Q)-policies. We express the policy costs as a weighted mean of costs for one-for-one ordering policies.
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| 15. |
- Forsberg, Rolf
(författare)
-
Optimization of order-up-to-S policies for two-level inventory systems with compound Poisson demand
- 1995
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Ingår i: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 81:1, s. 143-153
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Tidskriftsartikel (refereegranskat)abstract
- We consider a two-level inventory system with one warehouse and N retailers. Leadtimes are constant, and the retailers face different compound Poisson demand processes. All facilities apply order-up-to-S replenishment policies. We show how to evaluate holding and shortage costs exactly.
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| 16. |
- Gunnarsson, Claes, 1967-, et al.
(författare)
-
Charge the relationships and gain loyalty effects : turning the supply link alert to IT opportunities
- 2003
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Ingår i: European Journal of Operational Research. - Amsterdam : Elsevier. - 0377-2217 .- 1872-6860. ; 144:2, s. 257-269
-
Tidskriftsartikel (refereegranskat)abstract
- The main purpose of this paper is to explore and analyze interconnected effects related to the use of IT, and in so doing, provide an understanding of integrative logistics operations in a supply chain link. We take a theoretical point of departure in the three factors of relationship investments, formalization and trust. Thereafter we will expand and elaborate these factors by discussing embedded elements and mechanisms, related to relationships and loyalty, which result in an outlined model for empirical research focused on operational and strategic partnerships. Based on an empirical analysis we propose that the use of IT, expressed as digitization, can be seen as a driving force for bridging a gap between the actual and potential pattern of integrative logistics operations in a supply chain link. Digitization activates mechanisms in trust, commitment, and solidarity, which are related to loyalty and simultaneously enable heterogeneous influences in relationship characteristics.
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| 17. |
- Gunnarsson (Lidestam), Helene, et al.
(författare)
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Supply chain modelling of forest fuel
- 2004
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Ingår i: European Journal of Operational Research. - 0377-2217. ; 158:1, s. 103-123
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Tidskriftsartikel (refereegranskat)abstract
- We study the problem of deciding when and where forest residues are to be converted into forest fuel, and how the residues are to be transported and stored in order to satisfy demand at heating plants. Decisions also include whether or not additional harvest areas and saw-mills are to be contracted. In addition, we consider the flow of products from saw-mills and import harbors, and address the question about which terminals to use. The planning horizon is one year and monthly time periods are considered. The supply chain problem is formulated as a large mixed integer linear programming model. In order to obtain solutions within reasonable time we have developed a heuristic solution approach. Computational results from a large Swedish supplying entrepreneur are reported.
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| 18. |
- Haftor, Darek, 1969-, et al.
(författare)
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A framework for the constitution of modelling processes : a proposition
- 2003
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Ingår i: European Journal of Operational Research. - : Elsevier. - 0377-2217 .- 1872-6860. ; 145:1, s. 202-215
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Tidskriftsartikel (refereegranskat)abstract
- Given that the quality of models significantly affects the outcome of their application, it is important to reflect on the process by which they are actually constructed. This is addressed by the proposed Framework for the Constitution of Modelling Processes, which is presented here along with a few examples of its practical application. This framework is founded on Projective Constructivist Epistemology and provides a generic description of modelling processes, including their purpose, behaviour and structure. The framework may serve as a meta-model for the understanding, classification, use and development of the many different contributions to the field of modelling. Over the past five years, the framework has been actively researched, developed and applied in a variety of practical contexts, including the public, military and business sectors.
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| 19. |
- Hartman, Thomas, 1957-, et al.
(författare)
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Allocative Efficiency in Branch Banking
- 2001
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Ingår i: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 134:2, s. 232-242
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Tidskriftsartikel (refereegranskat)abstract
- Bank branch efficiency and organization change is analyzed using data from 50 savings bank branches in Sweden. First, technical and allocative efficiencies are analyzed, using non-priced and priced inputs. Secondly, by grouping the branches according to their organizational designation, efficiency is examined by level of service. Trends in performance over two time periods are also analyzed.
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| 20. |
- Heshmati, Almas
(författare)
-
Quality adjusted measures of services in public schools
- 2002
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Ingår i: European Journal of Operational Research. - : Elsevier B.V. - 0377-2217 .- 1872-6860. ; 136:3, s. 655-670
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Tidskriftsartikel (refereegranskat)abstract
- This study considers specification and estimation of cost functions in public schools. A number of production characteristics are included in the specification to control for observable differences between municipalities in the provision of their school services. Both parametric and non-parametric approaches are used to take into account the quality differences in school services. These approaches are then compared to the alternative output measure without any adjustment for quality differences. The sensitivity of different elasticities and returns to scale (RTS) measures with respect to alternative model specifications and quality adjustments are also analyzed. In the empirical section we examine performances of 286 Swedish municipalities in the production of primary and secondary school education during the 1992/3-1994/5 school years. ©2002 Elsevier Science B.V. All rights reserved.
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| 21. |
- Kumar, Dhananjay, et al.
(författare)
-
Maintenance scheduling under age replacement policy using proportional hazards model and TTT-plotting
- 1997
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Ingår i: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 99:3, s. 507-515
-
Tidskriftsartikel (refereegranskat)abstract
- The failure characteristics of a system may depend on the total operating time, operating time since the last repair, failure history, operating conditions or on the values of monitored variables. A reliability based approach which takes into consideration values of monitored variables is suggested for estimating the optimum maintenance (or replacement) time interval for a system or threshold values of monitored variables under the age replacement policy. The maintenance cost equation is formed on the basis of the planned and unplanned maintenance costs and the values of monitored variables. The proportional hazards model is used to identify the importance of monitored variables. The reliability function is estimated considering the values of monitored variables. A total time on test (TTT) plot based on this estimate of the reliability function is used to estimate the optimum maintenance (or replacement) time interval for a system or threshold values of monitored variables. This approach is illustrated with an example.
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| 22. |
- Larsson, Torbjörn, et al.
(författare)
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A Lagrangean heuristic for the capacitated concave minimum cost network flow problem
- 1994
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217 .- 1872-6860. ; 78:1, s. 116-129
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Tidskriftsartikel (refereegranskat)abstract
- We propose a heuristic solution technique for the capacitated concave minimum cost network flow problem based on a Lagrangean dualization of the problem. Despite its dual character the algorithm guarantees the generation of primal feasible solutions which are local optima and therefore candidates of being the global optimum. The Lagrangean dual is solved by a subgradient search procedure and provides a lower bound to the optimal value. The lower bound is, in general, stronger than the one obtained by a linear approximation of the original problem. It can be used as a judgement of the quality of the solution or in a branch and bound procedure. Computational results from randomly generated problems are presented
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| 23. |
- Larsson, Torbjörn, 1957-, et al.
(författare)
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On the convergence of conditional e-subgradient methods for convex programs and convex-concave saddle-point problems
- 2003
-
Ingår i: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 151:3, s. 461-473
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Tidskriftsartikel (refereegranskat)abstract
- The paper provides two contributions. First, we present new convergence results for conditional e-subgradient algorithms for general convex programs. The results obtained here extend the classical ones by Polyak [Sov. Math. Doklady 8 (1967) 593, USSR Comput. Math. Math. Phys. 9 (1969) 14, Introduction to Optimization, Optimization Software, New York, 1987] as well as the recent ones in [Math. Program. 62 (1993) 261, Eur. J. Oper. Res. 88 (1996) 382, Math. Program. 81 (1998) 23] to a broader framework. Secondly, we establish the application of this technique to solve non-strictly convex-concave saddle point problems, such as primal-dual formulations of linear programs. Contrary to several previous solution algorithms for such problems, a saddle-point is generated by a very simple scheme in which one component is constructed by means of a conditional e-subgradient algorithm, while the other is constructed by means of a weighted average of the (inexact) subproblem solutions generated within the subgradient method. The convergence result extends those of [Minimization Methods for Non-Differentiable Functions, Springer-Verlag, Berlin, 1985, Oper. Res. Lett. 19 (1996) 105, Math. Program. 86 (1999) 283] for Lagrangian saddle-point problems in linear and convex programming, and of [Int. J. Numer. Meth. Eng. 40 (1997) 1295] for a linear-quadratic saddle-point problem arising in topology optimization in contact mechanics.
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| 24. |
- Migdalas, Athanasios, et al.
(författare)
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Sector modeling for the prediction and evaluation of Cretan olive oil
- 2004
-
Ingår i: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 152:2, s. 454-464
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Tidskriftsartikel (refereegranskat)abstract
- Greece is a major international olive oil producer. Olive oil varieties constitute the major crops for Greek farmers growing certain oriental olive oil varieties. Currently, the olive oil sector in Greece is undergoing substantial changes and the response of farmers and consumers to this will be a vital factor in its success. Throughout the application of the common agriculture policy (CAP), mechanisms, such as production aid, subsidies and marketing orders, were employed to support both producers and consumers. A possible reform of CAP aimed at eliminating or reducing production aid or any kind of subsidies could have a considerable effect on producer and consumer marketing behaviour. In this study a formulated mathematical problem for the olive oil sector on the island of Crete based on the welfare concept and the simulation of the olive oil market equilibrium, subject to specified policy interventions and circumstances was adopted. According to the results obtained, it was concluded that future olive oil policies should not impinge on mechanisms that influence olive oil farmers and consumer behaviour but should emphasize the greater cost effectiveness of production and marketing policies
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| 25. |
- Olhager, Jan, 1955-, et al.
(författare)
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Enterprise resource planning survey of Swedish manufacturing firms
- 2003
-
Ingår i: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 146:2, s. 365-373
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Tidskriftsartikel (refereegranskat)abstract
- Enterprise resource planning (ERP) systems are the new type of information systems for enterprise integration. By adding functionality to previous manufacturing resource planning systems, the aim is to integrate functions and processes within a manufacturing firm. In this paper, we present a survey of ERP implementation in Swedish manufacturing firms, concerned with ERP system penetration, the pre-implementation process, implementation experience, ERP system configuration, benefits, and future directions. ⌐ 2002 Elsevier Science B.V. All rights reserved.
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| 26. |
- Papahristodoulou, Christos
(författare)
-
Option Strategies with linear programming
- 2004
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Ingår i: European Journal of Operational research. - 0377-2217. ; 157:1, s. 246-256
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Tidskriftsartikel (refereegranskat)abstract
- In practice, all option strategies are decided in advance, given the investor’s belief of the stock price. In this paper, instead of deciding in advance the most appropriate hedging option strategy, an LP problem is formulated, by considering all significant Greek parameters of the Black-Scholes formula, such as delta, gamma, theta, rho and kappa. The optimal strategy to select will be simply decided by the solution of that model. The LP model is applied to Ericsson’s call and puts options.
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| 27. |
- Penttinen, Markku
(författare)
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Myopic and stationary solutions for stochastic cash balance problems
- 1991
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Ingår i: European Journal of Operational Research. - Amsterdam : Elsevier. - 0377-2217 .- 1872-6860. ; 52:2, s. 155-166
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents constructive solutions to stochastic cash balance problems. The model studied is in a periodic review framework with convex holding and shortage costs levied both in the beginning and at the end of each period. Transaction costs are linear, with the possibility of unequal fixed and proportional parts for orders and disposals. Optimal myopic solutions are presented for convex and linear costs. The application of an integral of the cumulative demand distribution yields simple formulae for solving the exact values of the policy parameters. The logistic distribution is used to obtain results readily applicable in day-to-day decision-making. Approximations of the Wilson formula type are developed and compared with earlier contributions. Conditions for the optimality of myopic policies are also presented. Stationary solutions are developed, and compared with myopic results in order to evaluate the amount of suboptimality. The stationary distribution and the optimal policy are given for the bilateral exponential demand distribution case. All results have been programmed and tested against the local finance market data.
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| 28. |
- Skriver, A.J.V., et al.
(författare)
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Bicriteria network location (BNL) problems with criteria dependent lengths and minisum objectives
- 2004
-
Ingår i: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 156:3, s. 541-549
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Tidskriftsartikel (refereegranskat)abstract
- We present a new location model, which is a generalization of the bicritera median problem. We introduce two sum objectives and criteria dependent edge lengths. For this script N sign P complete problem a solution method finding all the efficient solutions is presented. The method is a two-phases approach, which can easily be applied as an interactive method. In Phase 1 the supported solutions are found, and in Phase 2 the unsupported solutions are found. This method can be thought of as a general approach to bi-objective combinatorial optimization (BOCO) problems. © 2003 Elsevier B.V. All rights reserved.
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| 29. |
- Tambour, Magnus, et al.
(författare)
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Productivity and customer satisfaction in Swedish pharmacies : A DEA network model
- 1999
-
Ingår i: European Journal of Operational Research. - : Elsevier. - 0377-2217. ; 115:3, s. 449-458
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a Data Envelopment Analysis (DEA) network model that allows inclusion of customer satisfaction in efficiency and productivity measures. The network consists of a production node and a consumption node and offers flexibility in modelling the production and consumption process where a firm-specific allocation of input resources to production and customer oriented activities is allowed. The proposed model is applied on a sample of Swedish pharmacies with organizational objectives that necessitates a monitoring of efficiency and productivity as well as customer satisfaction. Estimation results from the network model and a direct productivity model (without customer satisfaction) are compared and indicate that the technical efficiency is lower under the network model. The productivity results indicate productivity progress under both models, albeit with a slower rate of change under the network model.
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| 30. |
- Tari, M.H., et al.
(författare)
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Optimisation modelling of industrial energy systems using MIND introducing the effect of material storage
- 2002
-
Ingår i: European Journal of Operational Research. - 0377-2217 .- 1872-6860. ; 142:2, s. 419-433
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Strategic decisions regarding industrial energy systems should ideally involve the entire plant. Systems analysis using optimisation methods identifies the minimum cost solution among numerous alternatives. In the deregulated Swedish (and European) energy market, there are large variations in electricity contracts. These contracts affect the possibilities of industrial energy systems to react not only through the price level but also through the price structure. Material storage can affect an industrial system in many ways. One of them is that material storage can prevent a situation in which different parts of an industrial system with different production rates counteract each other. In this paper, the influence on energy costs of the use of material storage is discussed. The importance of modelling material storage has been shown, especially in situations where there are time-of-use-prices of electricity. A case study from the pulp and paper industry has been used to confirm this. © 2002 Elsevier Science B.V. All rights reserved.
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| 31. |
- Althin, Rikard, et al.
(författare)
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Swedish employment offices: A new model for evaluating effectiveness
- 2010
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Ingår i: European Journal of Operational Research. - : Elsevier. - 0377-2217 .- 1872-6860. ; 207:3, s. 1535-1544
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Tidskriftsartikel (refereegranskat)abstract
- We measure how well Swedish employment offices perform in delivering the services required of them by the Swedish government. In contrast to earlier studies we use a dynamic efficiency framework, which allows us to better model the intertemporal nature of these services, explicitly allowing for placements of intermediate nature across periods. Rather than using second stage analysis to assess the effects of varying local labor market conditions and differences in client characteristics on performance, we include a measure of the office’s expected work load directly in the model. This measure, derived from duration analysis, is designed to capture the variation across offices in resources needed before an average individual can obtain employment. It is estimated from the characteristics of all unemployed individual and local labor market conditions.The empirical results demonstrate an increase in the office’s expected work loads over time and point to substantial differences in performance across offices. The results also point toward more than optimal placements in intermediate outputs such as non-matching jobs, training, and continued unemployment.
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| 32. |
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| 33. |
- Andersson, Jonas, et al.
(författare)
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Exact analysis of One-Warehouse-Multiple-Retailer inventory systems with quantity restricted deliveries
- 2023
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217. ; 309:3, s. 1161-1172
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Tidskriftsartikel (refereegranskat)abstract
- Joint consideration and coordination of inventory and shipment decisions is an important challenge in the quest for sustainable distribution systems. This paper addresses this issue by presenting a method for exact analysis of the inventory level distributions in a centralized One-Warehouse-Multiple-Retailer (OWMR) inventory system with quantity restricted deliveries from the warehouse. The system is characterized by continuous review (R,nQ) policies, complete backordering, and compound Poisson demand. The class of quantity restricted delivery policies we consider is motivated by a common desire in practice to ship full load carriers. It generalizes the assumption of unrestricted partial deliveries often used in the literature, and allows the warehouse to only ship retailer specific delivery batch quantities to the different retailers. The delivery batches typically represent package or pallet sizes, containers, or full truckloads. An attractive feature of our approach is that it does not add to the computational effort of analyzing the special case of unrestricted partial deliveries available in the existing literature. A numerical study shows that accounting for quantitative delivery restrictions used in transportation and handling operations when optimizing the reorder points in multi-echelon systems can be very important. Failure to do so can lead to high backorder costs and inadequate customer service.
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| 34. |
- Ang, Frederic
(författare)
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Decomposing the Luenberger-Hicks-Moorsteen Total Factor Productivity indicator: An application to US agriculture
- 2017
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217. ; 260, s. 359-375
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a decomposition of the additively complete Luenberger-Hicks-Moorsteen Total Factor Productivity indicator into the usual components: technical change, technical inefficiency change and scale inefficiency change. Our approach is general in that it does not require differentiability or convexity of the production technology. Using a nonparametric framework, the empirical application focuses on the agricultural sector at the state-level in the U.S. over the period 1960-2004. The results show that Luenberger-Hicks-Moorsteen productivity increased substantially in the considered period. This productivity growth is due to output growth rather than input decline, although the extent depends on the convexity assumption of the technology. Technical change is the main driver, while the role of technical inefficiency change and scale inefficiency change also depends on the convexity assumption of the technology. (C) 2016 Elsevier B.V. All rights reserved.
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| 35. |
- Armerin, Fredrik, 1971-
(författare)
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Investments with declining cost following a Levy process
- 2023
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217 .- 1872-6860. ; 304:3, s. 1052-1062
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Tidskriftsartikel (refereegranskat)abstract
- We consider an optimal investment problem in which the cost of the investment decreases over time. This decrease is modelled using the negative of a non-decreasing Levy process. The decreasing cost is a way of modelling that innovations drive down the cost of the investment. We present general results on how to compute both the value of the investment, as well as the optimal time at which the investment should be done. Several explicit examples of how different Levy processes influence the value of the investment are given as illustrations of the general results. The main tools used are fluctuation theory for Levy processes and inversion of Laplace transforms. When the inversion can be done analytically, we can present analytical solutions where in some cases only numerical solution has previously been known.
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| 36. |
- Athanasopoulos, George, et al.
(författare)
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Forecasting with temporal hierarchies
- 2017
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Ingår i: European Journal of Operational Research. - : Elsevier. - 0377-2217 .- 1872-6860. ; 262:1, s. 60-74
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces the concept of Temporal Hierarchies for time series forecasting. A temporal hierarchy can be constructed for any time series by means of non-overlapping temporal aggregation. Predictions constructed at all aggregation levels are combined with the proposed framework to result in temporally reconciled, accurate and robust forecasts. The implied combination mitigates modelling uncertainty, while the reconciled nature of the forecasts results in a unified prediction that supports aligned decisions at different planning horizons: from short-term operational up to long-term strategic planning. The proposed methodology is independent of forecasting models. It can embed high level managerial forecasts that incorporate complex and unstructured information with lower level statistical forecasts. Our results show that forecasting with temporal hierarchies increases accuracy over conventional forecasting, particularly under increased modelling uncertainty. We discuss organisational implications of the temporally reconciled forecasts using a case study of Accident & Emergency departments.
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| 37. |
- Axsäter, Sven
(författare)
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A Heuristic for Triggering Emergency Orders in an Inventory System
- 2007
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217. ; 176:2, s. 880-891
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers a single-echelon inventory system with a warehouse facing compound Poisson customer demand. Normally the warehouse replenishes from an outside supplier according to a continuous review reorder point policy. However, it is also possible to use emergency orders. Such orders incur additional costs but have a much shorter lead time. We consider standard holding and backorder costs as well as ordering costs. A heuristic decision rule for triggering emergency orders is suggested. The decision rule minimizes the expected costs under the assumption that there is only a single possibility for an emergency replenishment, but the rule is used repeatedly as a heuristic. Given a certain reorder point policy for normal replenishments, our decision rule will always reduce the expected costs. A simulation study illustrates that the suggested technique performs well under different conditions.
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| 38. |
- Axsäter, Sven
(författare)
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A Simple Procedure for Determining Order Quantities under a Fill Rate Constraint and Normally Distributed Lead-Time Demand
- 2006
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217. ; 174:1, s. 480-491
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Tidskriftsartikel (refereegranskat)abstract
- One of the most common practical inventory control problems is considered. A single-echelon inventory system is controlled by a continuous review (R,Q) policy. The lead-time demand is normally distributed. We wish to minimize holding and ordering costs under a fill rate constraint. Although, it is not especially complicated to derive the optimal solution, it is much more common in practice to use a simple approximate two-step procedure where the order quantity is determined from a deterministic model in the first step. We provide an alternative, equally simple technique, which is based on the observation that the considered problem for each considered fill rate has a single parameter only. The optimal solution for a grid of parameter values is stored in a file. When solving the problem for an item we use interpolation, or for parameter values outside the grid special approximations. The approximation errors turn out to be negligible. As an alternative to the interpolation we also provide polynomial approximations.
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| 39. |
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| 40. |
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| 41. |
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| 42. |
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| 43. |
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| 44. |
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| 45. |
- Axsäter, Sven, et al.
(författare)
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Sustainable Multi-echelon Inventory Control with Shipment Consolidation and Volume Dependent Freight Costs
- 2018
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217. ; 267:3, s. 904-916
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides exact analysis of a model for sustainable control of a one-warehouse-N-retailer inventory system with time based shipment consolidation. The model is motivated by discussions with industry, and involves the possibility to reserve intermodal transportation capacity in combination with truck transports available on demand. Inventories are reviewed continuously while shipments from the warehouse are consolidated for groups of retailers and dispatched periodically. A key result is the derivation of the probability mass functions for the number of units on each shipment. This allows for realistic volume dependent freight cost structures and transportation emissions to be included in the model. We show how to jointly optimize the reorder levels, shipment intervals and capacity reservation quantities to minimize the total expected costs. Transportation emissions are taken into consideration by use of a side constraint or by introducing emissions costs. A numerical example illustrates how the model can be used for evaluating the cost impact of reducing transportation emissions. The analysis is applicable to both single- and multi-item systems.
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| 46. |
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| 47. |
- Bandaru, Sunith, et al.
(författare)
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Generalized higher-level automated innovization with application to inventory management
- 2015
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Ingår i: European Journal of Operational Research. - : Elsevier. - 0377-2217 .- 1872-6860. ; 243:2, s. 480-496
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Tidskriftsartikel (refereegranskat)abstract
- This paper generalizes the automated innovization framework using genetic programming in the context of higher-level innovization. Automated innovization is an unsupervised machine learning technique that can automatically extract significant mathematical relationships from Pareto-optimal solution sets. These resulting relationships describe the conditions for Pareto-optimality for the multi-objective problem under consideration and can be used by scientists and practitioners as thumb rules to understand the problem better and to innovate new problem solving techniques; hence the name innovization (innovation through optimization). Higher-level innovization involves performing automated innovization on multiple Pareto-optimal solution sets obtained by varying one or more problem parameters. The automated innovization framework was recently updated using genetic programming. We extend this generalization to perform higher-level automated innovization and demonstrate the methodology on a standard two-bar bi-objective truss design problem. The procedure is then applied to a classic case of inventory management with multi-objective optimization performed at both system and process levels. The applicability of automated innovization to this area should motivate its use in other avenues of operational research.
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| 48. |
- Barrow, Devon, et al.
(författare)
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The impact of special days in call arrivals forecasting : A neural network approach to modelling special days
- 2018
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Ingår i: European Journal of Operational Research. - : Elsevier. - 0377-2217 .- 1872-6860. ; 264:3, s. 967-977
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Tidskriftsartikel (refereegranskat)abstract
- A key challenge for call centres remains the forecasting of high frequency call arrivals collected in hourly or shorter time buckets. In addition to the complex intraday, intraweek and intrayear seasonal cycles, call arrival data typically contain a large number of anomalous days, driven by the occurrence of holidays, special events, promotional activities and system failures. This study evaluates the use of a variety of univariate time series forecasting methods for forecasting intraday call arrivals in the presence of such outliers. Apart from established, statistical methods, we consider artificial neural networks (ANNs). Based on the modelling flexibility of the latter, we introduce and evaluate different methods to encode the outlying periods. Using intraday arrival series from a call centre operated by one of Europe's leading entertainment companies, we provide new insights on the impact of outliers on the performance of established forecasting methods. Results show that ANNs forecast call centre data accurately, and are capable of modelling complex outliers using relatively simple outlier modelling approaches. We argue that the relative complexity of ANNs over standard statistical models is offset by the simplicity of coding multiple and unknown effects during outlying periods.
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| 49. |
- Bekiros, Stelios, et al.
(författare)
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Information diffusion, cluster formation and entropy-based network dynamics in equity and commodity markets
- 2017
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Ingår i: European Journal of Operational Research. - : Elsevier. - 0377-2217 .- 1872-6860. ; 256:3, s. 945-961
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the dynamic causal linkages among U.S. equity and commodity futures markets via the utilization of complex network theory. We make use of rolling estimations of extended matrices and time-varying network topologies to reveal the temporal dimension of correlation and entropy relationships. A simulation analysis using randomized time series is also implemented to assess the impact of de-noising on the data dependence structure. We mainly show evidence of emphasized disparity of correlation and entropy-based centrality measurements for all markets between pre- and post-crisis periods. Our results enable the robust mapping of network influences and contagion effects while incorporating agent expectations.
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| 50. |
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