8,435 research outputs found

    Magnetic field dependence of the density of states in the multiband superconductor β\beta-Bi2_2Pd

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    We present very low temperature scanning tunneling microscopy (STM) experiments on single crystalline samples of the superconductor β\beta-Bi2_2Pd. We find a single fully isotropic superconducting gap. However, the magnetic field dependence of the intervortex density of states is higher than the one expected in a single gap superconductor, and the hexagonal vortex lattice is locked to the square atomic lattice. Such increase in the intervortex density of states and vortex lattice locking have been found in superconductors with multiple superconducting gaps and anisotropic Fermi surfaces. We compare the upper critical field Hc2(T)H_{c2}(T) obtained in our sample with previous measurements and explain available data within multiband supercondutivity. We propose that β\beta-Bi2_2Pd is a single gap multiband superconductor. We anticipate that single gap multiband superconductivity can occur in other compounds with complex Fermi surfaces.Comment: 8 pages, 7 figure

    The Dynamical Behaviour of Test Particles in a Quasi-Spherical Spacetime and the Physical Meaning of Superenergy

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    We calculate the instantaneous proper radial acceleration of test particles (as measured by a locally defined Lorentzian observer) in a Weyl spacetime, close to the horizon. As expected from the Israel theorem, there appear some bifurcations with respect to the spherically symmetric case (Schwarzschild), which are explained in terms of the behaviour of the superenergy, bringing out the physical relevance of this quantity in the study of general relativistic systems.Comment: 14 pages, Latex. 4 figures. New references added. Typos corrected. To appear in Int. J. Theor. Phy

    Análise multivariada de características de carcaça e qualidade da carne de ovinos.

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    Resumo: Técnicas de análise multivariada foram utilizadas para avaliação de características de carcaça e qualidade da carne de cordeiros: Morada Nova (MN), Somalis Brasileira (SB), Santa Inês (SI) e ½ Dorper x ½ Morada Nova (F1). Na análise fatorial, os cinco primeiros fatores extraídos por componentes principais explicaram 80 % da variância total dos dados. Os escores calculados para cada fator foram utilizados na análise de variância. Houve efeito significativo do grupo genético para os fatores 1, 3 e 4. O primeiro fator é o processo que representa às características morfométricas da carcaça, os pesos ao abate e da carcaça, os pesos dos cortes comerciais e a área de olho de lombo, sendo a raça SI superior às raças SB e MN, porém similar ao genótipo F1. Esse fator explica 52,65 % da variância total dos dados. Quanto ao terceiro (espessura de gordura e intensidade de vermelho da carne) e ao quarto fator (índice de quebra por resfriamento e perda de peso por cocção) a raça SB apresentou maior especificidade, diferindo dos demais grupos. Para o segundo fator (pH medido 24 horas post mortem, luminosidade da carne e intensidade de amarelo) e para o quinto (força de cisalhamento) não houve diferença entre os grupos genéticos. Através da análise exploratória dos dados foi possível reduzir a dimensionalidade do conjunto de informações e identificar diferenças entre grupos considerando o processo formado pelas combinações lineares das características mais associadas entre si (fatores). [Multivariate analysis of carcass and meat quality traits in sheep]. Abstract: Multivariate analyzes were used for evaluation of carcass and meat quality traits of lambs: Morada Nova (MN), Brazilian Somalis (BS), Santa Inês (SI) and ½Dorper x ½Morada Nova (F1). In the factor analysis, the first five factors extracted by principal components explained 80 % of total variance. The factor scores were used in the analysis of variance. The first factor is the process that represents the carcass morphometric traits, to slaughter weights and commercial cuts weights and loin eye area, and SI breed similar to genotype F1, but higher than the races SB and MN. This factor explained 52.65% of the total variance. The third (fat thickness and redness of meat) and the fourth factor (drip loss and cooking loss), SB genotype showed higher specificity, differing from other groups. For the second factor (pH measured 24 hours post mortem, lightness of meat and yellowness of meat) and the fifth factor (shear force) there was no difference between genotypes. Through exploratory analysis of the data was possible to reduce the dimensionality of the information and identify differences among genotypes considering the process formed by linear combinations of the traits more associated with each other (factors)

    Explainable Artificial Intelligence (XAI): Concepts, Taxonomies, Opportunities and Challenges toward Responsible AI

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    In the last few years, Artificial Intelligence (AI) has achieved a notable momentum that, if harnessed appropriately, may deliver the best of expectations over many application sectors across the field. For this to occur shortly in Machine Learning, the entire community stands in front of the barrier of explainability, an inherent problem of the latest techniques brought by sub-symbolism (e.g. ensembles or Deep Neural Networks) that were not present in the last hype of AI (namely, expert systems and rule based models). Paradigms underlying this problem fall within the so-called eXplainable AI (XAI) field, which is widely acknowledged as a crucial feature for the practical deployment of AI models. The overview presented in this article examines the existing literature and contributions already done in the field of XAI, including a prospect toward what is yet to be reached. For this purpose we summarize previous efforts made to define explainability in Machine Learning, establishing a novel definition of explainable Machine Learning that covers such prior conceptual propositions with a major focus on the audience for which the explainability is sought. Departing from this definition, we propose and discuss about a taxonomy of recent contributions related to the explainability of different Machine Learning models, including those aimed at explaining Deep Learning methods for which a second dedicated taxonomy is built and examined in detail. This critical literature analysis serves as the motivating background for a series of challenges faced by XAI, such as the interesting crossroads of data fusion and explainability. Our prospects lead toward the concept of Responsible Artificial Intelligence, namely, a methodology for the large-scale implementation of AI methods in real organizations with fairness, model explainability and accountability at its core. Our ultimate goal is to provide newcomers to the field of XAI with a thorough taxonomy that can serve as reference material in order to stimulate future research advances, but also to encourage experts and professionals from other disciplines to embrace the benefits of AI in their activity sectors, without any prior bias for its lack of interpretability

    Glacial geomorphology between the Gran Campo Nevado and Estrecho de Magallanes, Chile (52–53°S, 73°W)

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    We present the first extensive high-resolution glacial geomorphic map west of the Andean Cordillera in southernmost Chile (52.8–53.1°S, 73.0–73.9°W). The map extends over 1565 km2 and is based on high-resolution satellite images and aerial photographs. At selected locations, the remotely mapped geomorphology was corroborated by field observations. The study area is dominated by glacial erosional landforms (77%) over depositional landforms (23%), with published submarine depositional landforms having been included (e.g. moraines). Glacial drift, kettle kame topography and lateral and frontal moraines form the primary depositional landforms and sediment associations. Glacial cirques, wide U-shaped valleys, whalebacks, roches moutonnées and scoured bedrock characterize most of the mapped area. The spatial distribution of whalebacks and roches moutonnées in the study area indicates a lack of lithological control on their formation and a warm-based, dynamic ice velocity and thickness regime during Patagonian Ice Sheet cover and retreat during the last glacial cycle

    Unwrapping Closed Timelike Curves

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    Closed timelike curves (CTCs) appear in many solutions of the Einstein equation, even with reasonable matter sources. These solutions appear to violate causality and so are considered problematic. Since CTCs reflect the global properties of a spacetime, one can attempt to change its topology, without changing its geometry, in such a way that the former CTCs are no longer closed in the new spacetime. This procedure is informally known as unwrapping. However, changes in global identifications tend to lead to local effects, and unwrapping is no exception, as it introduces a special kind of singularity, called quasi-regular. This "unwrapping" singularity is similar to the string singularities. We give two examples of unwrapping of essentially 2+1 dimensional spacetimes with CTCs, the Gott spacetime and the Godel universe. We show that the unwrapped Gott spacetime, while singular, is at least devoid of CTCs. In contrast, the unwrapped Godel spacetime still contains CTCs through every point. A "multiple unwrapping" procedure is devised to remove the remaining circular CTCs. We conclude that, based on the two spacetimes we investigated, CTCs appearing in the solutions of the Einstein equation are not simply a mathematical artifact of coordinate identifications, but are indeed a necessary consequence of General Relativity, provided only that we demand these solutions do not possess naked quasi-regular singularities.Comment: 29 pages, 9 figure

    Neuropathic Pain in Dogs and Cats: Current Evaluation and Treatment Perspectives: Review

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    Abstract: During the past decade, the number of scientific papers on the recognition and multimodal management of pain in small animals increased exponentially. However, the variable of neuropathic pain, or adaptive disorder, has not yet been characterized completely. Its genesis is related to several diseases and injuries of the nervous system that change the neuroanatomical structures that participate in pain processing. Finding novel neurobiological mechanisms and the development of techniques for diagnosis and treatment in Human Medicine, are opening great opportunities for research and the understanding of neuropathic pain in pets

    Stability and collapse of localized solutions of the controlled three-dimensional Gross-Pitaevskii equation

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    On the basis of recent investigations, a newly developed analytical procedure is used for constructing a wide class of localized solutions of the controlled three-dimensional (3D) Gross-Pitaevskii equation (GPE) that governs the dynamics of Bose-Einstein condensates (BECs). The controlled 3D GPE is decomposed into a two-dimensional (2D) linear Schr\"{o}dinger equation and a one-dimensional (1D) nonlinear Schr\"{o}dinger equation, constrained by a variational condition for the controlling potential. Then, the above class of localized solutions are constructed as the product of the solutions of the transverse and longitudinal equations. On the basis of these exact 3D analytical solutions, a stability analysis is carried out, focusing our attention on the physical conditions for having collapsing or non-collapsing solutions.Comment: 21 pages, 14 figure
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