Enrique Cabrera

A Hybrid Approach Using an Artificial Bee Algorithm with Mixed Integer Programming Applied to a Large-Scale Capacitated Facility Location Problem

We present a hybridization of two different approaches applied to the well-known Capacitated Facility Location Problem (CFLP). The Artificial Bee algorithm (BA) is used to select a promising subset of locations (warehouses) which are solely included in the Mixed Integer Programming (MIP) model. Next, the algorithm solves the subproblem by considering the entire set of customers. The hybrid implementation allows us to bypass certain inherited weaknesses of each algorithm, which means that we are able to find an optimal solution in an acceptable computational time. In this paper we demonstrate that BA can be significantly improved by use of the MIP algorithm. At the same time, our hybrid implementation allows the MIP algorithm to reach the optimal solution in a considerably shorter time than is needed to solve the model using the entire dataset directly within the model. Our hybrid approach outperforms the results obtained by each technique separately. It is able to find the optimal solution in a shorter time than each technique on its own, and the results are highly competitive with the state-of-the-art in large-scale optimization. Furthermore, according to our results, combining the BA with a mathematical programming approach appears to be an interesting research area in combinatorial optimization.

Insatisfacción corporal en los trastornos de la conducta alimentaria: un estudio comparativo

Antecedentes: La insatisfaccion corporal (IC) es considerada factor predisponente, desencadenante, perpetuante y pronostico de los trastornos alimentarios (TCA). Objetivos: Comparar la presencia de IC y caracteristicas psicopatologicas/conductuales entre mujeres con y sin TCA. Metodo: A 52 pacientes con TCA y 51 estudiantes sin TCA, se les aplico comparativamente el Test de Actitudes Alimentarias (EAT-40), el Inventario de Desordenes Alimentarios (EDI) y el Cuestionario de Silueta Corporal (BSQ). Resultados: Las pacientes alcanzaron puntajes significativamente mas elevados que las estudiantes en el BSQ, EAT-40, EDIy sub escalas (p = < 0,001), excepto perfeccionismo (p = 0,015). La IC medida por el EDI (17 versus 4; p < 0,001) y el BSQ (152 versus 58,5; p < 0,001) arrojo puntajes significativamente mas altos en las pacientes, principalmente las anorecticas en el EAT-40, BSQ, IC, sentimientos de inutilidad personal y perfeccionismo (p < 0,001); las bulimicas en el EDI global, motivacion por la delgadez, consciencia interoceptiva, bulimia, temor a la madurez y desconfianza interpersonal (p < 0,001). El item IC del EDI mostro un OR de 1,17, versus el BSQ (OR= 1,05) (p < 0,001). El puntaje global del EAT-40 se correlaciono directa y significativamente con el BSQ (r = 0,672; p < 0,001) en las pacientes y estudiantes con el item IC del EDI (r = 0,639; p < 0,001). Conclusiones: La IC esta presente en grado extremo en todos los subtipos de TCA. Las anorecticas mostraron mayor IC acompanada de sentimientos de inutilidad personal y perfeccionismo. Una mayor IC se relaciona positivamente con una mayor sintomatologia compatible con TCA. El riesgo de padecerlo de una joven que exhibe algun grado de IC es altisimo.

Evaluación de la respuesta antioxidante en Chiton granosus Frembly, 1928 (Mollusca: Polyplacophora) a contaminantes oxidativos

Oxidative stress is the damage at cellular, tissue or organic level produced by reactive oxygen species, that are produced as a result of the exposition to polluting agents, the ingestion through diet, UV radiation or to the oxygen metabolic processes. Chiton granosus is an intertidal organism abundant in Valparaiso, region of Chile. The objective of studying this species, by its abundance, is oriented to its use as biomarkers of oxidative polluting agents and so to evaluate its possible role as a monitoring species of the presence of these polluting agents. To evaluate, gonads, radular and digestive systems were analyzed from Chiton granosus collected from Torpederas, a highly polluted public sector, and Montemar (control area). Two hundreds and fifty nine individuals of Chiton granosus were collected; 133 from Torpederas and 126 from Montemar. The results indicate that no differences due to the sex exists in enzyme activity: catalase in the gonads, superoxide dismutase (SOD) in the radular and digestive systems. No influence of the sampling site was observed, nevertheless the lipoperoxidative damage was concordant with a greater oxidation level in females in the more polluted sector. Total antioxidant capacity exhibited significant differences due to sex and oxidative pollution.

A matheuristic approach combining local search and mathematical programming

A novel matheuristic approach is presented and tested on a well-known optimisation problem, namely, capacitated facility location problem (CFLP). The algorithm combines local search and mathematical programming. While the local search algorithm is used to select a subset of promising facilities, mathematical programming strategies are used to solve the subproblem to optimality. Proposed local search is influenced by instance-specific information such as installation cost and the distance between customers and facilities. The algorithm is tested on large instances of the CFLP, where neither local search nor mathematical programming is able to find good quality solutions within acceptable computational times. Our approach is shown to be a very competitive alternative to solve large-scale instances for the CFLP.

Improving Tabu Search Performance by Means of Automatic Parameter Tuning

A common problem when performing (meta)heuristic techniques over complex combinatorial optimization problems is parameter tuning. Finding the right parameter values can lead to significant improvements in terms of the best solution objective value found by the heuristic, heuristic reliability, and heuristic convergence, among others. Unfortunately, this is usually a tedious and complicated task if done manually. Furthermore, parameter values usually depend on the problem that is going to be solved. In this paper, we propose a framework that is based on the genetic programming (GP) technique to fine tune a key parameter of the well-known tabu search (TS) algorithm. Several experiments are performed over a set of small instances of the well-known capacitated facility location problem. The results have shown that adjusting the probability of acceptance of the best neighbor ρ in the TS algorithm using GP leads to an average value of the obtained solution that is closer to the optimal solution than the average value obtained by the simple TS algorithm with an a priori selected value for ρ. More importantly, standard deviation of the algorithm is greatly improved by our approach, which makes it much more reliable if time limitations are present. Finally, we confirm that the value of the parameter ρ largely depends on the problem that is attempted to solve.

Local Search Algorithms for the Beam Angles’ Selection Problem in Radiotherapy

One important problem in radiation therapy for cancer treatment is the selection of the set of beam angles radiation will be delivered from. A primary goal in this problem is to find a beam angle configuration (BAC) that leads to a clinically acceptable treatment plan. Further, this process must be done within clinically acceptable times. Since the problem of selecting beam angles in radiation therapy is known to be extremely hard to solve as well as time-consuming, both exact algorithms and population-based heuristics might not be suitable to solve this problem. In this paper, we compare two matheuristic methods based on local search algorithms, to approximately solve the beam angle optimisation problem (BAO). Although the steepest descent algorithm is able to find locally optimal BACs for the BAO problem, it takes too long before convergence, which is not acceptable in clinical practice. Thus, we propose to use a next descent algorithm that converges quickly to good quality solutions although no (local) optimality guarantee is given. We apply our two matheuristic methods on a prostate case which considers two organs at risk, namely, the rectum and the bladder. Results show that the matheuristic algorithm based on the next descent local search is able to quickly find solutions as good as the ones found by the steepest descent algorithm.

Parameter Tuning for Local-Search-Based Matheuristic Methods

Algorithms that aim to solve optimisation problems by combining heuristics and mathematical programming have attracted researchers’ attention. These methods, also known as matheuristics, have been shown to perform especially well for large, complex optimisation problems that include both integer and continuous decision variables. One common strategy used by matheuristic methods to solve such optimisation problems is to divide the main optimisation problem into several subproblems. While heuristics are used to seek for promising subproblems, exact methods are used to solve them to optimality. In general, we say that both mixed integer (non)linear programming problems and combinatorial optimisation problems can be addressed using this strategy. Beside the number of parameters researchers need to adjust when using heuristic methods, additional parameters arise when using matheuristic methods. In this paper we focus on one particular parameter, which determines the size of the subproblem. We show how matheuristic performance varies as this parameter is modified. We considered a well-known NP-hard combinatorial optimisation problem, namely, the capacitated facility location problem for our experiments. Based on the obtained results, we discuss the effects of adjusting the size of subproblems that are generated when using matheuristics methods such as the one considered in this paper.

Efecto de la radiación ultravioleta B en la producción de polifenoles en la microalga marina Chlorella sp.

Marine algae are an important source of antioxidant compounds (phenols and polyphenols), generated as defense mechanisms against stress factors (UV radiation, temperature, herbivory). The aim of this study was to evaluate the strategy of adaptation to the effect of ultraviolet B radiation (UV-B, 280-315 nm) in the marine microalga Chlorella sp. through, the production of polyphenols and total antioxidant capacity. Chlorella sp. cultures were exposed to UV-B radiation (470 μW cm -2 ) over increasing time periods. We evaluated the total antioxidant capacity DPPH, total polyphenols, chlorophyll-a and b, and cell densities in exposed and unexposed cultures. The results indicated that UV-B caused a decrease in cell density in cultures irradiated for the first time (1st stage), with a significant increment (P < 0.05, lower than the control) in the 2nd and 3rd stages only through the 4th stage (day 7), corresponding to a dose of 16,920 J m -2 . The production of total phenols increased significantly (P < 0.05) for the IVth extract with respect to the control, confirming that the exposure to UV-B caused a reaction in the microalgae, generating higher levels of photoprotector substances. Total antioxidant capacity and total polyphenols did not show a significant correlation (R 2 = 0.72) due to the lack of specificity of the DPPH assay for this type of antioxidant, but a very similar trend was observed. Although the amounts of antioxidant compounds were not high, their synthesis corresponded to the

ESTUDIO COMPARATIVO ENTRE LA MASA OSEA EVALUADA POR PROTOCOLOS KINEANTROPOMETRICOS V/S DENSIDAD OSEA MEDIDA POR DENSITOMETRIA FOTONICA DUAL: COMPARATIVE STUDY AMONG KINANTHROPOMETRIC BONE MASS V/S DUAL FOTONIC BONE DENSITY

Bone mass (BM) determination according to kineantropometric methods is usually made on each model of a new corporal fractionation. The cadaverous validation of these methods is scarce, except from the model of KERR (1988) and the cadaverous study of Brussels, CLARYS et al. (1984), therefore, to attain a validation according to modern methodology and up to date could contribute important background in the study of the osteo-calcic metabolism. Nowadays, the evaluation of the bone mineral density (BMD) and the bone mineral content (BMC) by means of the fotonic dual absorciometry, widely known as osseous densitometry (OD) are recognised; consequently, the validation of the antropometric formulae of MO v/s DO could contribute reliable data of the osseous condition of the body. The subjects are 19 volleyball players, 10 men and 9 women, from university teams, whom were first kineantropometrically evaluated-according to the rules of the International Society for Advances in Kineatropometry (ISAK)- and, immediately after, underwent a full-length DO in a Fotonic Dual Densytometer (NORLAND XR 26, Mark II, 1994). We set up the correlations between the BMC and the BMD v/s the following antropometric estimations of MO: D. Kerr, Von Dobeln and Makiegka modified by A. Martin (1984). The results show correlations statistically significant among the different models v/s DO (p<0.05); however, the determination coefficient (r2) do not reach 50%. These results suggest that when there is a relation statistically significant, the MO antropometric models for the estimation of the MO could not estimate BMC nor BMD, this is because the concept of the osseous density is not related with the osseous weight in a 100%, since this one, apart from containing minerals, contains water and organic matter