1,721,018 research outputs found
A mathematical model for the Multi-Levels Product Allocation Problem in a warehouse with compatibility constraints
No full textThe aim of this work is to address the products allocation problem in a multi-layers warehouse with compatibility constraints among the classes. The problem under study represents one of the most relevant topic in Logistics. The goal is to reduce, as much as possible, the delivery times; the inventories; the total logistic costs and to guarantee, at the same time, higher service levels (i.e., high customers satisfaction degree). In this work, a linear model to mathematically represent the problem is developed and its performance is evaluated on a set of instances, representing realistic situations. A sensitivity analysis is
also carried out by considering the most relevant parameters of the model. Finally, an Iterated Local Search based heuristic is defined in order to solve large scale scenarios in a reasonable amount of time. Numerical results show that the proposed heuristic is able to find
good quality solutions with a computational effort lower than that required to solve the proposed mathematical model
Solving Stochastic Linear Programs with Restricted Recourse using Interior Point Methods
No full textA Multistage Formulation for Generation Companies in a Multi-Auction Electricity Market
No full textIn this paper we deal with the definition of a decision model
for a producer operating in a multi-auction electricity
market. The decisions to be taken concern the commitment of the
generation plants and the quantity of energy required to offer to
each auction and to cover the bilateral contracts. We propose a
Multistage Stochastic Programming model in which the randomness
of the clearing prices is represented by means of a scenario tree.
The risk is modelled using a Conditional Value at Risk term in the
objective function. Experimental results are reported to show the
validity of our model and to discuss the influence of the risk
parameters on the optimal value
A class of label-correcting methods for the K shortest paths problem
No full textIn this paper we deal with the problem of finding the first K shortest paths from a single origin node to all other nodes of a directed graph. In particular, we define the necessary and sufficient conditions for a set of distance label vectors, on the basis of which we propose a class of methods which can be viewed as an extension of the generic label-correcting method for solving the classical single-origin all-destinations shortest path problem. The data structure used is characterized by a set of K lists of candidate nodes, and the proposed methods differ in the strategy used to select the node to be extracted at each iteration. The computational results show that: 1. some label-correcting methods are generally much faster then the double sweep method of Shier (1979); 2. the most efficient node selection strategies, used for solving the classical single-origin all-destinations shortest path problem, have proved to be effective also in the case of the K shortest paths
A wise cost-effective supplying bandwidth policy for multilayer wireless cognitive networks
No full textInventory management is one of the most important research areas in Operations Research and Logistics. It mainly aims to efficiently manage inventories at different facilities (for example, warehouses and plants in Supply Chains (SCs)), minimizing the total cost and satisfying the service levels. Some exact inventories management approaches are successfully proposed and applied to different real scenarios, traditionally related to the SCs, even if the extreme versatility of these techniques could make them attractive to new challenging scenarios such as those related to telecommunications networks. Starting from this vision, the focus of this paper is to show the new benefits of applying an adaptive period inventory management policy to a wireless cognitive telecommunication scenario in which radio transmission resources are treated as short-term life time goods which supplies wisely in order to maximize both economic profit and quality of service offered to wireless users. The system behavior is tested using an agent-based simulator and computational results show that introducing this wise control on the bandwidth supplying mechanism guarantees a more reactive and effective telecommunication network, reaching a good compromise between the total profit and the service levels
Solving a Complex Public Waste Collection Problem in Southern Italy
No full textWe conducted a study on solid waste collection for the Health Department of the Municipality of Castrovillari, a town located in Southern Italy. The main difficulties we had to tackle depended on a number of constraints imposed by road network features, traffic congestion and equipment. As these aspects are quite common in Europe, we expected to find some related methodology (or, at least, some case studies) in the literature. Surprisingly, most issues of our problem were not addressed by any existing paper. We therefore carried out a research project whose outcome was a computerized system which allowed one to avoid overtime and to accomplish a reduction of about 8% in total cost. We estimate that, if applied by other Italian municipalities, this kind of analysis could save hundreds of millions of Euro every year
MUTANTI pnc IN ESCHERICHIA COLI K-12
No full textMutans of E. coli K12 deficient in the recycling pathway of NAD were isolated. Nutritional properties of
mutants provide elucidations regarding NAD turnover and utilization of exogenous NAD
Solving the shortest path tour problem
No full textIn this paper, we study the shortest path tour problem in which a
shortest path from a given origin node to a given destination node must be found in a directed graph with non-negative arc lengths. Such path needs to across a sequence of node subsets that are given in a fixed order. The subsets are disjoint and may be different-sized. A polynomial reduction of the problem to a classical shortest path problem over a modified digraph is described and two solution approaches based on the above reduction and Dynamic Programming, respectively, are proposed and compared with the state-of-the-art solving procedure. The proposed approaches are tested on existing datasets for this problem and on a large class of new benchmark instances. The computational experience shows that both the proposed approaches exhibit a consistent improved performance in terms of computational time with respect to the existing solving method
Allocating Production Batches to Subcontractors by Fuzzy Goal Programming
Full text linkAllocating production batches to subcontractors arises frequently in industry. When subcontractors
operate different equipment, batch assignment is a complex decision that must take into account both
throughput and quality of finished goods. In this paper, aMixed Integer Linear Goal Programming Model,
where productivity uncertainty is taken into account through Fuzzy Set Theory, is developed. Our study
was motivated by a real-world application arising in an Italian textile company. Computational results
show that this method outperforms the hand-made solutions put to use by the management so far
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