Artículos (Estadística e Investigación Operativa)https://hdl.handle.net/11441/108442019-04-20T18:17:57Z2019-04-20T18:17:57ZNew models for the location of controversial facilities: A bilevel programming approachhttps://hdl.handle.net/11441/846532019-03-26T07:51:42Z2019-07-01T00:00:00ZNew models for the location of controversial facilities: A bilevel programming approach
Motivated by recent real-life applications in Location Theory in which the location decisions generate controversy, we propose a novel bilevel location
model in which, on the one hand, there is a leader that chooses among a number of fixed potential locations which ones to establish. Next, on the second hand, there is one or several followers that, once the leader location facilities have been set, chooses his location points in a continuous framework. The leader’s goal is to maximize some proxy to the weighted distance to the follower’s location points, while the follower(s) aim is to locate his location points as close as possible to the leader ones. We develop the bilevel location model for one follower and for any polyhedral distance, and we extend it for several followers and any ℓp-norm, p ∈ Q, p ≥ 1. We prove the NP-hardness of the problem and propose different mixed integer linear programming formulations. Moreover, we develop alternative Benders decomposition algorithms for the problem. Finally, we report some computational results comparing the formulations and the Benders decompositions on a set of instances.
2019-07-01T00:00:00ZGeneralized modified slash Birnbaum–Saunders distributionhttps://hdl.handle.net/11441/832342019-02-19T12:59:36Z2018-01-01T00:00:00ZGeneralized modified slash Birnbaum–Saunders distribution
In this paper, a generalization of the modified slash Birnbaum-Saunders (BS) distribution is introduced. The model is defined by using the stochastic representation of the BS distribution, where the standard normal distribution is replaced by a symmetric distribution proposed by Reyes et al. It is
proved that this new distribution is able to model more kurtosis than other extensions of BS previously proposed in the literature. Closed expressions are given for the pdf (probability density functio), along with their moments, skewness and kurtosis coefficients. Inference carried out is based on
modified moments method and maximum likelihood (ML). To obtain ML estimates, two approaches are considered: Newton-Raphson and EM-algorithm. Applications reveal that it has potential for doing well in real problems.
2018-01-01T00:00:00ZHeliostat field cleaning scheduling for Solar Power Tower plants: a heuristic approachhttps://hdl.handle.net/11441/827872019-04-03T05:54:05Z2019-02-01T00:00:00ZHeliostat field cleaning scheduling for Solar Power Tower plants: a heuristic approach
Soiling of heliostat surfaces due to local climate has a direct impact on their
optical efficiency and therefore a direct impact on the productivity of the Solar
Power Tower plant. Cleaning techniques applied are dependent on plant construction and current schedules are normally developed considering heliostat layout patterns, providing sub-optimal results. In this paper, a method to optimise cleaning schedules is developed, with the objective of maximising energy generated by the plant. First, an algorithm finds a cleaning schedule by solving an integer program, which is then used as a starting solution in an exchange heuristic. Since the optimisation problems are of large size, a p-median type heuristic is performed to reduce the problem dimensionality by clustering heliostats into groups to be cleaned in the same period.
2019-02-01T00:00:00ZRailway traffic disturbance management by means of control strategies applied to operations in the transit systemhttps://hdl.handle.net/11441/809592019-04-03T05:54:08Z2018-01-01T00:00:00ZRailway traffic disturbance management by means of control strategies applied to operations in the transit system
Railway systems in metropolitan areas support a high density of daily traffic that is exposed to different types of disturbances in the service. An interesting topic in the literature is to obtain action protocols in the presence of contingencies which can affect the system operation, avoiding the propagation of perturbation and minimizing its negative consequences.
Assume that, with a small margin of time (e.g. one day), the decision-maker of the transportation network is knowing that a part of the train fleet will become inoperative temporarily along a specific transit line and none additional vehicle will be able to restore the affected services. The decision to be taken in consequence will require to reschedule the existing services by possibly reducing the number of expeditions (line runs). This will affect travellers who regularly use the transit system to get around. Consider that the decision-maker aims to lose the least number of passengers as a consequence of
having introduced changes into the transit line. A strategy that could be applied in this context is to remove those line runs which are historically less used by travellers without affecting the remaining services. Another alternative strategy might be to reschedule the timetables of the available units, taking into account the pattern of arrivals of users to the boarding stations and the user behavior during waiting times (announced in situ).
The aim of this work consists of assessing the strategy of train rescheduling along the current transportation line when the supply must be reduced in order to reinforce the service of another line, exploited by the same public operator, which has suffered an incidence or emergency.
2018-01-01T00:00:00Z