6,040 research outputs found
Atypical late-time singular regimes accurately diagnosed in stagnation-point-type solutions of 3D Euler flows
We revisit, both numerically and analytically, the finite-time blowup of the
infinite-energy solution of 3D Euler equations of stagnation-point-type
introduced by Gibbon et al. (1999). By employing the method of mapping to
regular systems, presented in Bustamante (2011) and extended to the
symmetry-plane case by Mulungye et al. (2015), we establish a curious property
of this solution that was not observed in early studies: before but near
singularity time, the blowup goes from a fast transient to a slower regime that
is well resolved spectrally, even at mid-resolutions of This late-time
regime has an atypical spectrum: it is Gaussian rather than exponential in the
wavenumbers. The analyticity-strip width decays to zero in a finite time,
albeit so slowly that it remains well above the collocation-point scale for all
simulation times , where is the singularity time.
Reaching such a proximity to singularity time is not possible in the original
temporal variable, because floating point double precision ()
creates a `machine-epsilon' barrier. Due to this limitation on the
\emph{original} independent variable, the mapped variables now provide an
improved assessment of the relevant blowup quantities, crucially with
acceptable accuracy at an unprecedented closeness to the singularity time:
$T^*- t \approx 10^{-140}.
On-site approximation for spin-orbit coupling in LCAO density functional methods
We propose a computational method that simplifies drastically the inclusion
of spin-orbit interaction in density functional theory implemented on localised
atomic orbital basis sets. Our method is based on a well-known procedure for
obtaining pseudopotentials from atomic relativistic 'ab initio' calculations
and on an on-site approximation for the spin-orbit matrix elements. We have
implemented the technique in the SIESTA code, and we show that it provides
accurate results for the overall band structure and splittings of group IV and
III-IV semiconductors as well as for 5d metals.Comment: 8 pages, 4 figures. Published in J. Phys.: Condens. Matter 18
7999-8013, 2006. Some errata correcte
A caducidade dos vÃnculos dos trabalhadores da Administração Pública Portuguesa
O presente artigo tem por objecto a análise do regime legal da caducidade dos vÃnculos dos trabalhadores da Administração Pública, seja por aposentação ou reforma do trabalhador, por impossibilidade do exercÃcio da actividade respeitante ao trabalhador ou ao empregador ou, finalmente, por verificação do termo nos contratos a prazo. Nesta última hipótese, analisa-se com particular destaque a questão da atribuição ou não (e, em caso afirmativo, em que termos) de uma indemnização ao trabalhador contratado a termo cujo contrato caduque.ABSTRACT: This article is focused in the legal regulation of contract expiry inside the public employment, produced by workers retirement, preclusion of working performance due to employee or employer or by term end, in temporary contracts. In this last case, it is analyzed the eventual payment of a compensation and, eventually, the terms according to witch that payment will be made.N/
Radial percolation reveals that cancer stem cells are trapped in the core of colonies
Using geometrical arguments, it is shown that Cancer Stem Cells (CSCs) must be con-fined inside solid tumors under natural conditions. Aided by an agent-based model and percolation theory, the probability of a CSC being positioned at the border of a colony is estimated. This probability is estimated as a function of the CSC self-renewal probability ps; i.e., the chance that a CSC remains undifferentiated after mitosis. In the most common situations ps is low, and most CSCs produce differentiated cells at a very low rate. The results presented here show that CSCs form a small core in the center of a cancer cell colony; they become quiescent due to the lack of space to proliferate, which stabilizes their population size. This result provides a simple explanation for the CSC niche size, dispensing with the need for quorum sensing or other proposed signaling mechanisms. It also supports the hypothesis that metastases are likely to start at the very beginning of tumor development.Fil: Barberis, Lucas Miguel. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Córdoba. Instituto de FÃsica Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de FÃsica Enrique Gaviola; Argentin
Emergence of a single cluster in Vicsek's model at very low noise
The classic Vicsek model [Phys. Rev. Lett. 75, 1226 (1995)PRLTAO0031-900710.1103/PhysRevLett.75.1226] is studied in the regime of very low noise intensities, which is shown to be characterized by a cluster [macrocluster (MC)] that contains a macroscopic fraction of the system particles. It is shown that the well-known power-law behavior of the cluster-size distribution loses its cutoff, becoming bimodal at very low noise intensities: A peak develops for larger sizes to settle the emergence of the MC. The average cluster number m∗ is introduced as a parameter that properly describes this change, i.e., a line in the noise-speed phase portrait can be identified to separates both regimes. Finite-size scaling analysis is performed to show that a phase transition to a macroscopic cluster is taking place. Consistency of the results with the literature is also checked and commented on.Fil: Barberis, Lucas Miguel. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Córdoba. Instituto de FÃsica Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de FÃsica Enrique Gaviola; Argentin
Magnitud, composición y patrones espaciotemporales de la mortalidad de vertebrados en las carreteras a escala regional
Although roadkill studies on a large scale are challenging, they can provide valuable information to assess the impact of road traffic on animal populations. Over 22 months (between July 2009–June 2010, and April 2011–March 2012) we surveyed 45 road sections of 10 km within a global biodiversity hotspot in Andalusia (87,000 km2), in southern Spain. We divided the region into five ecoregions differing in environmental conditions and landscape characteristics and recorded the relative magnitude, composition and spatiotemporal patterns of vertebrate (birds, mammal, amphibians, and reptiles) mortality. We used roadkill data from monthly surveys of road stretches with different speed limits, traffic volume, road design, and adjacent landscape composition. Roadkills varied over time and were not randomly distributed across ecoregions and road types. Overall, the groups most frequently encountered were mammals (54.4% of total roadkills) and birds (36.2%). Mortality rates in these two groups were higher on highways than on national or local roads, whereas those of amphibians (4.6%) and reptiles (4.3%) did not differ between road types. Except for mammals, the observed variation in vertebrate roadkills across ecoregions reflects the patterns of species richness previously described in the literature. Roadkills were concentrated over relatively short periods and this pattern was repeated over study periods and for all vertebrate classes. Our findings provide baseline information about road types, time periods and taxa with a higher probability of roadkills across an extensive region. These data represent an essential step towards the future implementation of broad–scale mitigation measures.A pesar de que los estudios a gran escala sobre mortalidad de animales en las carreteras son complejos, pueden aportar información valiosa para evaluar la incidencia del tráfico en las poblaciones de animales. Durante 22 meses (entre julio de 2009 y junio de 2010 y entre abril de 2011 y marzo de 2012), muestreamos 45 tramos de carretera de 10 km de longitud distribuidos en una zona con una gran diversidad en la región de AndalucÃa (87.000 km2), en el sur de España. La región se dividió en cinco ecorregiones con diferentes condiciones ambientales y caracterÃsticas del paisaje, y se analizaron la magnitud, la composición y los patrones espaciotemporales de la mortalidad de vertebrados (aves, mamÃferos, anfibios y reptiles). Usamos datos de atropellos obtenidos durante muestreos mensuales en tramos de carretera con diferentes lÃmite de velocidad, volumen de tráfico, diseño de la carretera y composición del paisaje adyacente. Los animales atropellados fueron distintos en el tiempo y no se distribuyeron aleatoriamente entre ecorregiones ni entre tipos de carretera. En total, los grupos que se encontraron con mayor frecuencia fueron los mamÃferos (el 54,4% de los atropellos registrados) y las aves (el 36,2%). La tasa de mortalidad observada en estos dos grupos fue mayor en autopistas que en carreteras nacionales o locales, mientras que la mortalidad de anfibios (el 4,6%) y de reptiles (el 4,3%) no presentó diferencias entre tipos de carretera. A excepción de los mamÃferos, la variación observada de la mortalidad en las carreteras entre las diferentes ecorregiones refleja los patrones de riqueza de especies descritos en las publicaciones cientÃficas. Los atropellos se concentraron en perÃodos de tiempo relativamente cortos y este patrón se repitió en las dos temporadas de estudio y con respecto a todas las clases de vertebrados. Nuestros resultados proporcionan información de referencia sobre los tipos de carretera, los perÃodos de tiempo y los taxones con una mayor probabilidad de morir por atropello en una extensa región, lo que supone un paso esencial para la implementación de medidas de mitigación a gran escala.Fil: Canal Piña, David. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina. Consejo Superior de Investigaciones CientÃficas; EspañaFil: Camacho, Carlos. Consejo Superior de Investigaciones CientÃficas; EspañaFil: MartÃn, Beatriz. Complejo Huerta Grande; EspañaFil: de Lucas, Manuela. Consejo Superior de Investigaciones CientÃficas; EspañaFil: Ferrer, Miguel. Consejo Superior de Investigaciones CientÃficas; Españ
Effects of flooding on mental health: a case-control study
3rd International Congress on Neurobiology, Psychopharmacology & Treatment guidance (May 30th - June 2nd, 2013)Background: Post-disaster mental health problems may affect population in different ways.
Population exposure to a natural disaster has been associated with psychological distress, in
particular, in the development of Posttraumatic Stress Disorder (PTSD).
Most people experience distress after their exposure to an extreme event. For people with good psychosocial resilience and access to social support, mental health problems can be relatively less important since supporting relationships and inner capabilities may begin the adaptation processes. Mental disorders occur often, but less commonly than dis-tress, and in some cases they may require intensive and long term continuing interventions and treatment
Experimental evaluation of big data querying tools
Nos últimos anos, o termo Big Data tornou-se um tópico bastanta debatido em várias
áreas de negócio. Um dos principais desafios relacionados com este conceito é como lidar
com o enorme volume e variedade de dados de forma eficiente. Devido à notória
complexidade e volume de dados associados ao conceito de Big Data, são necessários
mecanismos de consulta eficientes para fins de análise de dados. Motivado pelo rápido
desenvolvimento de ferramentas e frameworks para Big Data, há muita discussão sobre
ferramentas de consulta e, mais especificamente, quais são as mais apropriadas para
necessidades analÃticas especÃfica. Esta dissertação descreve e compara as principais
caracterÃsticas e arquiteturas das seguintes conhecidas ferramentas analÃticas para Big Data:
Drill, HAWQ, Hive, Impala, Presto e Spark. Para testar o desempenho dessas ferramentas
analÃticas para Big Data, descrevemos também o processo de preparação, configuração e
administração de um Cluster Hadoop para que possamos instalar e utilizar essas ferramentas,
tendo um ambiente capaz de avaliar seu desempenho e identificar quais cenários mais
adequados à sua utilização. Para realizar esta avaliação, utilizamos os benchmarks TPC-H e
TPC-DS, onde os resultados mostraram que as ferramentas de processamento em memória
como HAWQ, Impala e Presto apresentam melhores resultados e desempenho em datasets de
dimensão baixa e média. No entanto, as ferramentas que apresentaram tempos de execuções
mais lentas, especialmente o Hive, parecem apanhar as ferramentas de melhor desempenho
quando aumentamos os datasets de referência
Pre or Post-Softmax Scores in Gradient-based Attribution Methods, What is Best?
Gradient based attribution methods for neural networks working as classifiers
use gradients of network scores. Here we discuss the practical differences
between using gradients of pre-softmax scores versus post-softmax scores, and
their respective advantages and disadvantages.Comment: 8 pages, 2 figures. A version of this paper has been accepted for
presentation in The IEEE International Conference on Pattern Recognition
Systems (ICPRS-23
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