9,335 research outputs found
Phenomenological model for symmetry breaking in chaotic system
We assume that the energy spectrum of a chaotic system undergoing symmetry
breaking transitions can be represented as a superposition of independent level
sequences, one increasing on the expense of the others. The relation between
the fractional level densities of the sequences and the symmetry breaking
interaction is deduced by comparing the asymptotic expression of the
level-number variance with the corresponding expression obtained using the
perturbation theory. This relation is supported by a comparison with previous
numerical calculations. The predictions of the model for the
nearest-neighbor-spacing distribution and the spectral rigidity are in
agreement with the results of an acoustic resonance experiment.Comment: accepted for publication in Physical Review
Viscous Cosmology
We discuss the possibility to implement a viscous cosmological model,
attributing to the dark matter component a behaviour described by bulk
viscosity. Since bulk viscosity implies negative pressure, this rises the
possibility to unify the dark sector. At the same time, the presence of
dissipative effects may alleviate the so called small scale problems in the
CDM model. While the unified viscous description for the dark sector
does not lead to consistent results, the non-linear behaviour indeed improves
the situation with respect to the standard cosmological model.Comment: Latex file, 7 pages, 6 figures. To appear in the proceedings of the
XIIth International Conference on Gravitation, Astrophysics and Cosmology,
June 28-July 5, 2015, PFUR, Moscow, Russi
Experimental analysis of lateral impact on planar brittle material: spatial properties of the cracks
The breakup of glass and alumina plates due to planar impacts on one of their
lateral sides is studied. Particular attention is given to investigating the
spatial location of the cracks within the plates. Analysis based on a
phenomenological model suggests that bifurcations along the cracks' paths are
more likely to take place closer to the impact region than far away from it, i.
e., the bifurcation probability seems to lower as the perpendicular distance
from the impacted lateral in- creases. It is also found that many observables
are not sensitive to the plate material used in this work, as long as the
fragment multiplicities corresponding to the fragmentation of the plates are
similar. This gives support to the universal properties of the fragmentation
process reported in for- mer experiments. However, even under the just
mentioned circumstances, some spatial observables are capable of distinguishing
the material of which the plates are made and, therefore, it suggests that this
universality should be carefully investigated
Aporte de serrapilheira ao solo em estágios sucessionais florestais na reserva biológica de Poço das Antas, Rio de Janeiro, Brasil.
Foram definidos mosaícos de fitofisionomias temporais em sistemas tropicais de baixada localizados na REBIO de Poço das Antas, RJ - Brasil. A serrapilheira foi quantificada com coletas quinzenais e determinada sua concentração de nutrientes via fração foliar em intervalos bimestrais. A floresta avançada apresentou o maior aporte de 6,9 mais ou menos 1,1 ton ha-1 ano-1 total, o estágio intermediário com 5,5 mais ou menos 0,5 ton ha-1 ano-1 total e para o plantio 3 mais ou menos 0,7 ton ha-1 ano-1 total. As concentrações via serrapilheira (fração foliar) dos nutrientes N, P, K e Ca foram maiores com o uso de Mimosa bimucronata (DC) O. kuntze nos reflorestamentos, demonstrando ser esta uma espécie de potencial elevado quanto ao conteúdo nutricional à recomposição de ecossistemas. Sua estratégia de renovação foliar ocorre sob o ritmo perenifólio, com maior contribuição na estação chuvosa e sincronizado a fase reprodutiva. A magnitude de transferência dos nutrientes na fração foliar para os estágios estudados segue a ordem de concentração: P < K < Mg < Ca < N < C. Não foram encontradas diferenças significativas quanto as concentrações de entrada dos nutrientes entre as estações nos estágios estudados. Gaps of temporal fitofisionoms were defined on lowland tropical systems localized in the Biologic Reserve of Poço das Antas RJ - Brazil. The litter-fall was quantificated by each fifteen days and was determinated the nutrient concentration of foliar fraction each two months. The oldest forest had the major litter-fall, 6.9 l l.l ton ha-1 total as the other fractions, when compared with the intermediate age forest with 5.5 1 0.5 ton ha-1 year-1 total. The plantation had the lowest values, 3.0 1 0.7 ton ha-1 year1 total. The foliar litter-fall concentration of N, P, K, Ca nutrients were bigger for Mimosa bimucronata (DC.). O. kuntze crop, showing then the great ecosystems nutritional recomposition potential of this specie with foliar renovation strategy occurs under perenifolial rhythm, mostly in the rain season synchronized to the reproduction phase. The transference rate of nutrients in the studied foliar fraction follows this concentration order: P < K < Mg < Ca < N < C.Parceria: UFRRJ
How can the nanostructure affect the charge transport in PLED?
In polymer light emitting diodes (PLEDs) each semiconducting polymer chain consists of a large number of conjugated segments linked by kinks or twists and each one of them behaves like a separated straight strand. The length and orientation of the conjugated strands relative to the electrodes surface depend on the deposition conditions used. Atomistic results have shown that the molecular properties of the conjugated strands
depend on their length, which can affect the electronic processes involved in PLEDs. The aim of this work is to study the influence of the average conjugation length within the polymer layer on charge injection, trapping and recombination in PLEDs for all polymer strand orientations relative to the electrodes surface obtained experimentally by different techniques. For that purpose we use a mesoscopic model that considers the morphology
and the molecular properties of the polymer. Our results show that by increasing the average conjugation length of the active polymer layer the amount of charge injected into the device increases and the recombination probability occurs preferentially in segments longer than the average conjugation length, both effects having implications on the performance of polymer LEDs.Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência , Tecnologia, Inovação” – POCTI/CTM/41574/2001, CONC-REEQ/443/EEI/2005 e SFRH/BD/22143/2005European Community Fund FEDE
Molecular Evaluation of exons 8 and 22 of the SHANK3 gene in Autism Spectrum Disorders
Autism spectrum disorders are a group of neurodevelopmental disorders with a complex and heterogeneous etiology. Studies have shown that genetic factors play an important role in the aetiology of these diseases. Recently, de novo mutations, frameshifts and deletions have been described in the SHANK3 gene, also known as ProSAP2 gene, which encodes a synaptic scaffolding protein. All the participants of this study had normal karyotypes and underwent screening for Fragile-X syndrome. Subsequently, they were analyzed by direct sequencing of different points of exons 8 and 22 of the SHANK3 gene. None of the study participants presented with changes in these regions. These findings may be due to the fact that mutations, deletions and duplications of the SHANK3 gene are rare
Analytical results for a Bessel function times Legendre polynomials class integrals
When treating problems of vector diffraction in electromagnetic theory, the
evaluation of the integral involving Bessel and associated Legendre functions
is necessary. Here we present the analytical result for this integral that will
make unnecessary numerical quadrature techniques or localized approximations.
The solution is presented using the properties of the Bessel and associated
Legendre functions.Comment: 4 page
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