Unique Covering Problems with Geometric Sets

The Exact Cover problem takes a universe U of n elements, a family F of m subsets of U and a positive integer k, and decides whether there exists a subfamily(set cover) F' of size at most k such that each element is covered by exactly one set. The Unique Cover problem also takes the same input and decides whether there is a subfamily F' subset of F such that at least k of the elements F' covers are covered uniquely(by exactly one set). Both these problems are known to be NP-complete. In the parameterized setting, when parameterized by k, Exact Cover is W1]-hard. While Unique Cover is FPT under the same parameter, it is known to not admit a polynomial kernel under standard complexity-theoretic assumptions. In this paper, we investigate these two problems under the assumption that every set satisfies a given geometric property Pi. Specifically, we consider the universe to be a set of n points in a real space R-d, d being a positive integer. When d = 2 we consider the problem when. requires all sets to be unit squares or lines. When d > 2, we consider the problem where. requires all sets to be hyperplanes in R-d. These special versions of the problems are also known to be NP-complete. When parameterizing by k, the Unique Cover problem has a polynomial size kernel for all the above geometric versions. The Exact Cover problem turns out to be W1]-hard for squares, but FPT for lines and hyperplanes. Further, we also consider the Unique Set Cover problem, which takes the same input and decides whether there is a set cover which covers at least k elements uniquely. To the best of our knowledge, this is a new problem, and we show that it is NP-complete (even for the case of lines). In fact, the problem turns out to be W1]-hard in the abstract setting, when parameterized by k. However, when we restrict ourselves to the lines and hyperplanes versions, we obtain FPT algorithms.

Role of upward leaders in modifying the induced currents in solitary down-conductors during a nearby lightning strike to ground

Electromagnetic field produced by a lightning strike to ground causes significant induction to tall objects in the vicinity. The frequency of occurrence of such nearby ground strikes can be higher than the number of direct strikes. Therefore, a complete knowledge on these induced currents is of practical relevance. However, limited efforts towards the characterisation of such induced currents in tall down-conductors could be seen in the literature. Due to the intensification of the background field caused by the descending stepped leader, tall towers/down-conductors can launch upward leaders of significant length. The nonlinearity in the conductance of upward leader and the surrounding corona sheath can alter the characteristics of the induced currents. Preliminary aspects of this phenomenon have been studied by the author previously and the present work aims to perform a detailed investigation on the role of upward leaders in modifying the characteristics of the induced currents. A consistent model for the upward leader, which covers all the essential electrical aspects of the phenomena, is employed. A first order arc model for representing the conductance of upward leader and a field dependant quadratic conductivity model for the corona sheath is employed. The initial gradient in the upward leader and the field produced by the return stroke forms the excitation. The dynamic electromagnetic response is determined by solving the wave equation using thin-wire time-domain formulation. Simulations are carried out initially to ascertain the role of individual parameters, including the length of the upward leader. Based on the simulation results, it is shown that the upward leader enhances the induced current, and when significant in length, can alter the waveshape of induced current from bipolar oscillatory to unipolar. The duration of the induced current is governed by the length of upward leader, which in turn is dependant on the return stroke current and the effective length of the down-conductor. If the current during the upward leader developmental phase is considered along with that after the stroke termination to ground, it would present a bipolar current pulse. (C) 2015 Elsevier Ltd. All rights reserved.

Fruit Trait Preference in Rhesus Macaques (Macaca mulatta) and its Implications for Seed Dispersal

Primates constitute 25-40 % of the frugivore biomass of tropical forests. Primate fruit preference, as a determinant of seed dispersal, can therefore have a significant impact on these ecosystems. Although the traits of fruits included in primate diets have been described, fruit trait preference has been less studied with respect to fruit availability. We examined fruit trait preference and its implications for seed dispersal in the rhesus macaque (Macaca mulatta), a dietarily flexible species and important seed disperser, at the Buxa Tiger Reserve, India. Over a year, we monitored the phenology of selected trees in the study area, observed the feeding behavior of rhesus macaques using scans and focal animal sampling, and documented morphological traits of the fruits/seeds consumed. Using generalized linear modeling, we found that the kind of edible tissue was the chief determinant of fruit consumption, with M. mulatta feeding primarily on fruits with juicy-soft pulp and acting as seed predators for those with no discernible pulp. Overall, the preferred traits were external covers that could be easily pierced by a fingernail, medium to large seeds, true stone-like seeds, and juicy-soft edible tissue, thereby implying that fruit taxa with these traits had a higher probability of being dispersed. Macaques were more selective during the high fruit availability period than the low fruit availability period, preferentially feeding on soft-skinned fruits with juicy-soft pulp. We suggest that further studies be conducted across habitats and time to understand the consistency of interactions between primates and fruits with specific traits to determine the degree of selective pressure (if any) that is exerted by primates on fruit traits.

Polymers with aligned carbon nanotubes: Active composite materials

We review the current state of the polymer-carbon nanotube composites field. The article first covers key points in dispersion and stabilization of nanotubes in a polymer matrix, with particular attention paid to ultrasonic cavitation and shear mixing. We then focus on the emerging trends in nanocomposite actuators, in particular, photo-stimulated mechanical response. The magnitude and even the direction of this actuation critically depend on the degree of tube alignment in the matrix; in this context, we discuss the affine model predicting the upper bound of orientational order of nanotubes, induced by an imposed strain. We review how photo-actuation in nanocomposites depend on nanotube concentration, alignment and entanglement, and examine possible mechanisms that could lead to this effect. Finally, we discuss properties of pure carbon nanotube networks, in form of mats or fibers. These systems have no polymer matrix, yet demonstrate pronounced viscoelasticity and also the same photomechanical actuation as seen in polymer-based composites. © 2008 Elsevier Ltd. All rights reserved.

Archaeometric evidence for the authenticity of the Jehoash inscription tablet

A gray, fine-grained arkosic sandstone tablet bearing an inscription in ancient Hebrew from the First Temple Period contains a rich assemblage of particles accumulated in the covering patina. Two types of patina cover the tablet: a thin layer of black to orange iron-oxide-rich layer, a product of micro-biogenic processes, and a light beige patina that contains feldspars, carbonate, iron oxide, subangular quartz grains, carbon ash particles and gold globules (1 to 4 microns [1 micron = 0.001 millimeter] in diameter). The patina covers the rock surface as well as the engraved lettering grooves and blankets and thus post-dates the incised inscription as well as a crack that runs across the stone and several of the engraved letters. Radiocarbon analyses of the carbon particles in the patina yield a calibrated radiocarbon age of 2340 to 2150 Cal BP. The presence of microcolonial fungi and associated pitting in the patina indicates slow growth over many years. The occurrence of pure gold globules and carbon ash particles is evidence of a thermal event in close proximity to the tablet (above 1000 degrees Celsius). This study supports the antiquity of the patina, which in turn, strengthens the contention that the inscription is authentic.

La génesis del matrimonio civil

Resumen: Es insuficiente para comprender adecuadamente las causas sociales, políticas e ideológicas de la incorporación del matrimonio civil obligatorio a nuestra legislación, el analizar el período histórico próximo a la sanción de la ley 2.393. Por ello hemos organizado la investigación en tres capítulos: “Los matrimonios entre personas de distinta religión”, “Católicos y liberales” y “La Ley de Matrimonio Civil”. El primero abarca la problemática, las distintas soluciones y la legislación aplicable, en el Río de la Plata, desde el tiempo de la colonia hasta la sanción del Código Civil. El segundo, la concepción filosófica de los hombres de la generación del ochenta, protagonistas de la sanción de la ley 2.393, las dos corrientes de pensamiento enfrentadas por su concepto del hombre, la libertad y el Estado, la posición de la prensa, los criterios sustentados por los doctorandos de la época, el fenómeno inmigratorio y el proceso de secularización. Por último, el proyecto de ley, sus repercusiones en la sociedad, en la prensa, el clero y la opinión pública; y su tratamiento en el Congreso de la Nación. Buscamos discernir las causas verdaderas y principales y las ficticias que llevaron a la introducción del matrimonio civil en el derecho argentino, para ello no solo hemos consultado las fuentes habituales, sino que hemos examinado gran cantidad de fuentes originales de la época. Entre ellas, a) la totalidad de los artículos publicados en los diarios La Prensa y La Nación durante el período 1870–1888; b) las Cartas remitidas por el Obispo de Buenos Aires, Monseñor Aneiros y por el Obispo de Córdoba, Fray Reginaldo al Senado de la Nación; c) Actas de las Sesiones de las Cámaras de Diputados y Senadores y d) las tesis doctorales de Francisco Barroetaveña, Daniel Goytia, Julio Sánchez Viamonte, Leopoldo Tahiér, Federico Valdez, Alejandro González Vélez y Alejandro Garramuño.

Una introducción a temas y tensiones presentes en el documento

Resumen: El artículo recorre los antecedentes que dieron origen al Documento de la Comisión Teológica Internacional sobre ley natural, con particular referencia a las intervenciones de Juan Pablo II y Benedicto XVI. Presenta sucintamente algunos temas del documento, a saber: la búsqueda de un patrimonio ético común a la humanidad en las tradiciones culturales; la cuestión de la experiencia moral y la llamada interior a hacer el bien; la justificación filosófica de la ley natural; el orden político de la sociedad y el tema de Jesucristo, plenitud de la ley natural. También se consideran las tensiones que subyacen al mismo, con particular referencia a las problemáticas de modernidad ilustrada y posmodernidad, laicismo y laicidad y iusnaturalismo y positivismo jurídico.

Computer Simulation Of Random Sphere Packing In An Arbitrarily Shaped Container

Most simulations of random sphere packing concern a cubic or cylindric container with periodic boundary, containers of other shapes are rarely studied. In this paper, a new relaxation algorithm with pre-expanding procedure for random sphere packing in an arbitrarily shaped container is presented. Boundaries of the container are simulated by overlapping spheres which covers the boundary surface of the container. We find 0.4 similar to 0.6 of the overlap rate is a proper value for boundary spheres. The algorithm begins with a random distribution of small internal spheres. Then the expansion and relaxation procedures are performed alternately to increase the packing density. The pre-expanding procedure stops when the packing density of internal spheres reaches a preset value. Following the pre-expanding procedure, the relaxation and shrinking iterations are carried out alternately to reduce the overlaps of internal spheres. The pre-expanding procedure avoids the overflow problem and gives a uniform distribution of initial spheres. Efficiency of the algorithm is increased with the cubic cell background system and double link data structure. Examples show the packing results agree well with both computational and experimental results. Packing density about 0.63 is obtained by the algorithm for random sphere packing in containers of various shapes.

Collective evolution characteristics and computer simulation of short fatigue cracks

Fatigue testing was conducted using a kind of triangular isostress specimen to obtain the short-fatigue-crack behaviour of a weld low-carbon steel. The experimental results show that short cracks continuously initiate at slip bands within ferrite grain domains and the crack number per unit area gradually increases with increasing number of fatigue cycles. The dispersed short cracks possess an orientation preference, which is associated with the crystalline orientation of the relevant slip system. Based on the observed collective characteristics, computer modelling was carried out to simulate the evolution process of initiation, propagation and coalescence of short cracks. The simulation provides progressive displays which imitate the appearance of experimental observations. The results of simulation indicate that the crack path possesses a stable value of fractal dimension whereas the critical value of percolation covers a wide datum band, suggesting that the collective evolution process of short cracks is sensitive to the pattern of crack site distribution.

A review of dynamic fracture mechanics in China

This paper summarizes the recent development of dynamic fracture in China. The review covers analytical and numerical results on elastodynamic crack fields in 3D and layered media; experimental and theoretical research on dynamic mechanical properties of rocks and advanced materials; transient effects on ideally plastic crack-tip fields when the inertia forces are not negligible.

A ground hydrologic model with inclusion of a layer of vegetation canopy that can interact with general-circulation model

In this paper, a ground hydrologic model(GHM) is presented in which the vapor, heat and momentum exchanges between ground surface covers (including vegetation canopy) and atmosphere is described more realistically. The model is used to simulate three sets of field data and results from the numerical simulation agree with the field data well. GHM has been tested using input data generated by general circulation model (GCM) runs for both the North American regions and the Chinese regions, The results from GHM are quite different from those of GHMs in GCMs. It shows that a more active concerted effort on the land surface process study to provide a physically realistic GHM for predicting the exchange between land and atmosphere is important and necessary.

The changing behaviour of the term structure of post-war US

Using U.S. interest rate data covering the period 1950:1-1992:7, this paper tests the rational expectations model of the term structure of interest rates. We show evidence that the rational expectations model of the term structure is supported by the data during the seventies and a period lasting from the mid-eighties to the end of the sample. However, during the …fties, sixties and a period that covers most of the Volcker’s office term (from September 1979 to April 1986) the term structure model is rejected by the data. Moreover, wefind evidence of regime changes in the short-term rate process and the term structure of interest rates. These regime switches roughly coincide with changes in the Federal Reserve chairman. The switches in monetary policy taking place when the chairmanship of the Federal Reserve changes therefore seem to play an important role in characterizing the term structure of interest rates.

The effect of flexibility in working hours on fertility: A comparative analysis of selected european countries

The main aim of this paper is to measure the extent to which part-time work enhances fertility for married or cohabiting women of fertile age. The study covers eleven European countries. The data used are a pool sample of five waves of the European Community Household Panel. Given that we believe that the decisions concerning fertility and labor market status are taken jointly, we carry out a simultaneous estimation approach. Results suggest that policy makers wishing to implement adequate part-time schedules so as to enhance fertility should look at the part-time schedules available in Belgium, Ireland and The Netherlands, which enhance fertility for women who take advantage of this flexibility measure so as to reconcile family and work.

Capacidades directivas y aprendizaje en las pymes exportadoras

[ES] La importancia de las percepciones de la dirección de la empresa ante la exportación puede afectar de manera significativa al comportamiento exportador de las pymes. En concreto, este aspecto puede incidir sobre el hecho de comenzar una política de exportación en la empresa, así como en políticas de consolidación de dichas exportaciones. El trabajo presentado analiza empíricamente estos dos hechos. En primer lugar en qué medida la percepción de la dirección ante la exportación afecta al hecho de comenzar la exportación. En segundo lugar, en caso de ya ser pymes exportadoras, se estudian qué percepciones directivas ayudan a consolidar dicho compromiso exportador. Para ello se desarrollan y validan ciertas escalas que miden la percepción de las ventajas y las barreras a la exportación mediante el empleo de ecuaciones estructurales. Ambos estudios se efectúan teniendo en cuenta la condición de familiar o no de las pymes objeto de estudio, con el fin de efectuar un análisis exploratorio sobre la potencial incidencia de este hecho.

Los Recursos Humanos en las Pymes: Análisis empírico de la formación, rotación y estructura de propiedad

[ES] Este trabajo tiene como objetivo presentar los principales resultados de un estudio que pretende acercarse a la realidad de las pequeñas y medianas empresas riojanas, tanto familiares como no familiares, ya que son mayoría abrumadora en la Comunidad. Se ha realizado un análisis descriptivo de algunos aspectos relevantes de la gestión de los recursos humanos como la formación y el desarrollo de sus trabajadores y directivos, la estabilidad laboral y la estructura de propiedad. En el presente trabajo ofrecemos los principales resultados con respecto a estas cuestiones, esbozando una descripción y valoración de estas empresas, así como un perfil de sus percepciones principales en relación a las cuestiones analizadas.