Variable neighbourhood search for the minimum labelling Steiner tree problem

We present a study on heuristic solution approaches to the minimum labelling Steiner tree problem, an NP-hard graph problem related to the minimum labelling spanning tree problem. Given an undirected labelled connected graph, the aim is to find a spanning tree covering a given subset of nodes of the graph, whose edges have the smallest number of distinct labels. Such a model may be used to represent many real world problems in telecommunications and multimodal transportation networks. Several metaheuristics are proposed and evaluated. The approaches are compared to the widely adopted Pilot Method and it is shown that the Variable Neighbourhood Search that we propose is the most effective metaheuristic for the problem, obtaining high quality solutions in short computational running time

Heuristics based on greedy randomized adaptive search and variable neighbourhood search for the minimum labelling spanning tree problem

This paper studies heuristics for the minimum labelling spanning tree (MLST) problem. The purpose is to find a spanning tree using edges that are as similar as possible. Given an undirected labelled connected graph, the minimum labelling spanning tree problem seeks a spanning tree whose edges have the smallest number of distinct labels. This problem has been shown to be NP-complete. A Greedy Randomized Adaptive Search Procedure (GRASP) and different versions of Variable Neighbourhood Search (VNS) are proposed. They are compared with other algorithms recommended in the literature: the Modified Genetic Algorithm and the Pilot Method. Nonparametric statistical tests show that the heuristics based on GRASP and VNS outperform the other algorithms tested. Furthermore, a comparison with the results provided by an exact approach shows that we may quickly obtain optimal or near-optimal solutions with the proposed heuristics

Maximizing the hyperpolarizability of one-dimensional systems

Previous studies have used numerical methods to optimize the hyperpolarizability of a one-dimensional quantum system. These studies were used to suggest properties of one-dimensional organic molecules, such as the degree of modulation of conjugation, that could potentially be adjusted to improve the nonlinear-optical response. However, there were no conditions set on the optimized potential energy function to ensure that the resulting energies were consistent with what is observed in real molecules. Furthermore, the system was placed into a one-dimensional box with infinite walls, forcing the wavefunctions to vanish at the ends of the molecule. In the present work, the walls are separated by a distance much larger than the molecule's length; and, the variations of the potential energy function are restricted to levels that are more typical of a real molecule. In addition to being a more physically-reasonable model, our present approach better approximates the bound states and approximates the continuum states - which are usually ignored. We find that the same universal properties continue to be important for optimizing the nonlinear-optical response, though the details of the wavefunctions differ from previous result.Comment: 10 pages, 5 figure

Mejora de la exploración y la explotación de las heurísticas constructivas para el MLSTP

En este trabajo se proponen dos mejoras para aumentar la explotación y la exploración del clásico algoritmo constructivo MVCA para el problema del árbol generador etiquetado mínimo (Minimum Labelling Spanning Tree Problem; MLSTP). Se describe la aplicación de contrastes de hipótesis no paramétricos para contrastar tales mejoras. En el MLSTP se parte de un grafo conexo con aristas de distinto tipo y se trata de encontrar el árbol generador con las aristas más parecidas posible. Cada tipo de arista viene identificado por un color o etiqueta y el árbol generador óptimo es aquel que usa el menor número de colores. Los tiempos y soluciones obtenidas son comparables a los mejores resultados aparecidos en la literatura para el MLSTP

Diffusion dynamics on multiplex networks

We study the time scales associated to diffusion processes that take place on multiplex networks, i.e. on a set of networks linked through interconnected layers. To this end, we propose the construction of a supra-Laplacian matrix, which consists of a dimensional lifting of the Laplacian matrix of each layer of the multiplex network. We use perturbative analysis to reveal analytically the structure of eigenvectors and eigenvalues of the complete network in terms of the spectral properties of the individual layers. The spectrum of the supra-Laplacian allows us to understand the physics of diffusion-like processes on top of multiplex networks.Comment: 6 Pages including supplemental material. To appear in Physical Review Letter

Challenges in Chagas Disease Drug Discovery: a review

Chagas disease or American trypanosomiasis is a neglected tropical disease caused by the parasite Trypanosoma cruzi. Although the number of infected individuals has decreased, about 6-7 million people are infected worldwide. The chemotherapy drugs currently used are limited to benznidazole and nifurtimox. They are effective in acute phase, congenital transmission and children with chronic infection; however, recent clinical trials have shown limitations in adults with chronic infection, presenting drawbacks during the treatment. Thus, there is an urgent need for new effective, safe and affordable drugs to fight against this complex disease. There were high expectations for azole derivatives as they appeared to be the most promising drugs for the treatment of Chagas disease during the last decade; however, the disappointing results obtained so far in clinical trials evidenced the lack of correlation between preclinical and clinical development. Therefore, the feedback obtained from these studies should define the starting point for addressing a roadmap for the drug discovery process in the fight against this disease. To tackle this challenge, it is important to keep in mind the drug target profile, already defined by panels of experts, and the coordinated work involving multi-disciplinary networks focusing not only on the discovery of new drugs but also on the standardization of the protocols that would allow acceleration in the Chagas disease drug discovery process

Desarrollo ontogénico y cambio socioambiental en la comarca Lozoya- Somosierra (Madrid). 1981-1996.

This work aims to describe and to analyse the effects of socio-environmental changes on bioanthropological characteristics in the Lozoya-Somosierra area (Madrid) during 15 years. Several statistical techniques were carried out on the cense, interviews and mesure data of a schoolchildren sample. Results show a favorable effect of socio-economic improve, population hetero * Sección de Antropología. Facultad de Ciencias Biológicas. Universidad Complutense de Madrid. 223 M. D. Marrodán, et al. Desarrollo ontogénico y cambio socioambiental... genicity and nutritional and sanitary accesibility over the growth and maduration of children. These results are similar in other studies and they are in the same sense that the general idea about the human biological susceptibibility of the environment. RÉSUMÉ Le présent travail a pour objetif l'analyse de l'influence des changements socioenvironnementals qui ont eu place sur les charactéristiques bioantropologiques dans la région de Lozoya-Somosierra (Madrid) pendant 15 années. Les donnés, lesquels sont venues des registres censés, des enquêtes et des mesures sur un échantillon représentatif de la population scolaire, ont été analysées avec plusieurs techniques statistiques. Les résultats montre que les changements pour le progrès socioéconomique, la variabilité génétique et la accessibilité aux ressources nutritionnelles et sanitation, ont été un effet positif sur la croissance et la maduration de la population infantile. Ces resultats sont pareil avec d'autres études et avec la réflexion généralisée de la subceptibilité biologique humaine en face a l'environnement immédiat. 1.Este estudio describe y analiza las consecuencias bioantropológicas del cambio socioambiental acontecido en la comarca Lozoya-Somosierra (Madrid) durante 15 años. Los datos, procedentes de registros censales, encuestas y medición de una muestra representativa de la población escolar, se han analizado matemáticamente, empleando diferentes técnicas estadísticas. Los resultados indican que el cambio socioambiental que ha tenido lugar en la comarca entre los años 1981 y 1996, en el sentido de la mejora socioeconómica, la heterogenicidad poblacional y la accesibilidad a los recursos nutricionales y sanitarios, ha supuesto una repercusión positiva en el crecimiento y maduración de la población infantil. Son resultados en consonancia con otros estudios y con la reflexión generalizada de la susceptibilidad biológica humana frente a su entorno inmediato

Anticoncepción poscoital. Características de la demanda

ObjetivoConocer el perfil de las mujeres que demandan anticoncepción poscoital (APC).DiseñoDescriptivo transversal. Emplazamiento. Centro de Orientación Familiar (COF), Área 4 del Instituto Madrileño de Salud. Madrid.ParticipantesTodas las mujeres que acudieron en el año 2000 para requerir APC (n = 404).MedicionesSe realizó una encuesta con variables sociodemográficas relacionadas con la APC y con la vida sexual.ResultadosLa edad media fue de 23,9 años (límites, 14–49); el 9,9% era menor de edad. La media de coitos al mes era de 6,7, el número de años de relaciones sexuales era de 4,9 y el primer coito se produjo, de media, a los 18 años. El 90,9% afirmaba tener pareja estable. Tenía estudios secundarios o universitarios un 75%. El 55,7% manifestaba no haber recibido información sobre anticonceptivos. El 19,5% utilizó APC en otra ocasión. El 6,5% había tenido alguna interrupción voluntaria de embarazo y de éstas, el 36% había utilizado APC anteriormente. Los motivos de consulta fueron: rotura de preservativo (69,3%), preservativo retenido (16,9%) y coito sin protección (12%). El 7% tuvo otros coitos de riesgo en el mismo ciclo. Un 33,2% las remitía su equipo de atención primaria, acudió por conocidos el 19% y desde servicios de urgencias el 16%. Conocía el COF un 26,1%. En el 12,2% no se prescribió APC por mínimo riesgo de embarazo. Realizaron la valoración una enfermera (52,6%), médicos residentes (34,4%) y una ginecóloga (13%).ConclusionesFalta información sobre métodos anticonceptivos. La mayoría de las pacientes son derivadas por otros servicios sanitarios.ObjectiveDefine the profile of the women that ask for emergency contraception (EC).DesignTransversal descriptive investigation.SettingFamiliar Planning Center of 4th Area of Instituto Madrileño de Salud. in Madrid. Participants. All the women that went in the year 2000 requiring EC (n=404).MeasurementsWas carried out a survey with sociodemographic variables, related with the EC and with the sexual life.ResultsThe average age was of 23.9 years (age range 14 to 49) were inquired, 9.9 were under 18. They had an average of 6.7 intercourses per month, the first intercourse when they were 18 years old on average, and 4.9 years of sexual relationships. 90.9% stated to have a couple. 75% were graduated from high school or university, and 55.7% said they had never received information about contraceptives. For 19.5% this was not the first time they asked for EC. 6.5% had interrupted on purpose pregnancy and 36% of them had used EC before. The reasons to demand EC were: condom break (69.3%), held condom (16.9%) and intercourse without any protection (12%). 7% acknowledged other risky intercourses during the same period. 33.2% had been sent by a General Practitioner, 26.1% knew the center, 19% were sent by acquaintances and 16% from Emergency Services. EC was not prescribed in 12.2% of the cases because of minimum risk to pregnancy. The evaluation was made by a nurse (52.6%), by a doctor (34.4%) and by a gynecologist (13%).ConclusionsThere is a lack of information about contraceptive methods. Most of the patients are sent from other sanitary services

Molecular heterogeneity of large-conductance calcium-activated potassium channels in canine intracardiac ganglia

Large conductance calcium-activated potassium (BK) channels are widely expressed in the nervous system. We have recently shown that principal neurons from canine intracardiac ganglia (ICG) express a paxilline- and TEA-sensitive BK current, which increases neuronal excitability. In the present work, we further explore the molecular constituents of the BK current in canine ICG. We found that the β1 and β4 regulatory subunits are expressed in ICG. Single channel voltage-dependence at different calcium concentrations suggested that association of the BKα with a particular β subunit was not enough to explain the channel activity in this tissue. Indeed, we detected the presence of several splice variants of the BKα subunit. In conclusion, BK channels in canine ICG may result from the arrangement of different BKα splice variants, plus accessory β subunits. The particular combinations expressed in canine IC neurons likely rule the excitatory role of BK current in this tissue

Zircon to monazite phase transition in CeVO4

X-ray diffraction and Raman-scattering measurements on cerium vanadate have been performed up to 12 and 16 GPa, respectively. Experiments reveal that at 5.3 GPa the onset of a pressure-induced irreversible phase transition from the zircon to the monazite structure. Beyond this pressure, diffraction peaks and Raman-active modes of the monazite phase are measured. The zircon to monazite transition in CeVO4 is distinctive among the other rare-earth orthovanadates. We also observed softening of external translational Eg and internal B2g bending modes. We attributed it to mechanical instabilities of zircon phase against the pressure-induced distortion. We additionally report lattice-dynamical and total-energy calculations which are in agreement with the experimental results. Finally, the effect of non-hydrostatic stresses on the structural sequence is studied and the equations of state of different phases are reported.Comment: 45 pages, 8 figures, 8 table