On the centralizer of generic braids

We study the centralizer of a braid from the point of view of Garside theory, showing that generically a minimal set of generators can be computed very efficiently, as the ultra summit set of a generic braid has a very particular structure. We present an algorithm to compute the centralizer of a braid whose generic-case complexity is quadratic on the length of the input, and which outputs a minimal set of generators in the generic case.Ministerio de Economía y CompetitividadFondo Europeo de Desarrollo Regiona

Preference and performance of Phyllocnistis citrella Stainton (Lepidoptera:Gracillariidae) on three citrus hosts: Laboratory and field assessment

The relationship between preference and performance is crucial to the ecology and evolution of plant-insect interactions. Oviposition preference and offspring performance were evaluated for a citrus pest, the leafminer Phyllocnistis citrella (Lepidoptera: Gracillariidae), on three of its host plants: lemon (Citrus limon L. Burm.), orange (Citrus sinensis L. Osbeck), and grapefruit (Citrus paradisi Macfadyen) in Tucumán province (northwest Argentina). Choice and no-choice tests were performed in open and enclosed environments, and performance parameters (development time, survival, pupal size, and sex ratio) were estimated from laboratory rearing and 3-yr field sampling data. Parasitism rates were studied in laboratory choice test and field assessments. Preference trends were inconsistent, with lemon receiving more eggs in some tests, whereas no preference was observed in others. Patterns of host use in the field did not show significant differences among species. Leafminer performance, including parasitism and predation rates, was generally homogeneous among host plants. From these results, lemon, orange, and grapefruit seem to represent intrinsically similar resources for P. citrella populations in northwest Argentina, a trend that was accompanied by a lack of consistent oviposition preferences in foraging females. Ecological conditions might be more important than physiological adaptation in shaping a probably labile host ranking in this pest species.La relación entre preferencia y rendimiento es crucial para la ecología y evolución de las interacciones insecto-planta. Se evaluó la preferencia de puesta y el rendimiento de la descendencia para una plaga de cítricos, el minador de la hoja Phyllocnistis citrella (Lepidoptera: Gracillariidae), sobre tres de sus plantas hospederas: limonero (Citrus limon [Linn.] Burm.), naranjo (Citrus sinensis [Linn.] Osbeck) y pomelo (Citrus paradisi Macfadyen) en la provincia de Tucumán (Noroeste de Argentina). Se realizaron pruebas con y sin elección en ambientes abiertos y cerrados, y se estimaron parámetros de rendimiento (tiempo de desarrollo, supervivencia, tamaño pupal y proporción de sexos) a partir de individuos criados en laboratorio y datos de tres años de muestreos de campo. Las tasas de parasitismo se estudiaron en pruebas de laboratorio con elección y evaluaciones en campo. Las tendencias de preferencia fueron inconsistentes, con limonero recibiendo más huevos en algunas pruebas, mientras que no se observó preferencia en otras. Los patrones de uso de hospedero en campo no mostraron diferencias significativas entre especies. El rendimiento del minador, incluyendo las tasas de parasitismo y depredación, fue generalmente homogéneo entre plantas hospederas. Con estos resultados, las plantas de limonero, naranjo y pomelo representarían intrínsecamente recursos similares para las poblaciones del minador de los cítricos en el NO de Argentina, tendencia que fue acompañada por la ausencia de preferencias consistentes en la puesta de huevos por parte de las hembras. Las condiciones ecológicas podrían ser más importantes que la adaptación fisiológica al moldear un rango de hospederos probablemente voluble en esta especie plaga.Fil: Goane, Lucía. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Valladares, Graciela Rosa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Willink, Eduardo. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; Argentin

Ab Initio studies of the atomic structure and electronic density of states of pure and hydrogenated a-Si

We propose a method to simulate a-Si and a-Si:H using an ab initio approach based on the Harris functional and thermally amorphisized periodically continued cells with at least 64 atoms, and calculate their radial distribution functions. Hydrogen incorporation was achieved via diffusive random addition. The electronic density of states (DOS) is obtained using density functional theory with the aid of both the Harris-functional and Kohn-Sham-LDA approaches. Two time steps are used, 2.44 and 10 fs for the pure, and 0.46 and 2 fs for the hydrogenated, to see their effect on the topological and DOS structure of the samples. The calculated long time-step radial features of a-Si are in very good agreement with experiment whereas for a-Si:H the short time-step partial and total radial features agree well; for the long time-step simulation molecular hydrogen appears during annealing.The long time-step a-Si has a well defined gap with two dangling bonds, that clears and increases upon hydrogen addition and relaxation, as expected. The short time-step structures have more defects, both dangling and floating bonds, that are less characteristic of a good sample; however the radial structures of a-Si:H are in better agreement with experiment indicating that the experimental work was done on defective samples.Comment: 11 pages, RevTeX, 16 figures, submitted to Phys. Rev. B 16 June 200

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The incidence of graft on developing-country firms

This paper measures the extent to which firms in developing countries are the target of bribes. Using new firm-level survey data from 33 African and Latin American countries, we first show that perceptions adjust slowly tofirms'experience with corrupt officials and hence are an imperfect proxy for the true incidence of graft. We then construct an experience-based index that reflects the probability that a firm will be asked for a bribe in order to complete a specified set of business transactions. On average, African firms are three times as likely to be asked for bribes as are firms in Latin America, although there is substantial variation within each region. Last, we show that graft appears to be more prevalent in countries with excessive regulation and where democracy is weak. In particular, our results suggest that the incidence of graft in Africa would fall by approximately 85 percent if countries in the region had levels of democracy and regulation similar to those that exist in Latin America.Public Sector Corruption&Anticorruption Measures,Corruption&Anitcorruption Law,Crime and Society,E-Business,Access to Finance

Primitive model electrolytes. A comparison of the HNC approximation for the activity coefficient with Monte Carlo data

Accuracy of the mean activity coefficient expression (Hansen-Vieillefosse-Belloni equation), valid within the hypernetted chain (HNC) approximation, was tested in a wide concentration range against new Monte Carlo (MC) data for +1:-1 and +2:-2 primitive model electrolytes. The expression has an advantage that the excess chemical potential can be obtained directly, without invoking the time consuming Gibbs-Duhem calculation. We found the HNC results for the mean activity coefficient to be in good agreement with the machine calculations performed for the same model. In addition, the thermodynamic consistency of the HNC approximation was tested. The mean activity coefficients, calculated via the Gibbs-Duhem equation, seem to follow the MC data slightly better than the Hansen-Vieillefosse-Belloni expression. For completeness of the calculation, the HNC excess internal energies and osmotic coefficients are also presented. These results are compared with the calculations based on other theories commonly used to describe electrolyte solutions, such as the mean spherical approximation, Pitzer's extension of the Debye-H\"uckel theory, and the Debye-H\"uckel limiting law.Comment: 15 pages, 6 figure

Communication Architecture for Tracking and Interoperable Services at Hospitals: A Real Deployment Experience

Any new hospital communication architecture has to support existing services, but at the same time new added features should not affect normal tasks. This article deals with issues regarding old and new systems’ interoperability, as well as the effect the human factor has in a deployed architecture. It also presents valuable information, which is a product of a real scenario. Tracking services are also tested in order to monitor and administer several medical resources