24,051 research outputs found
Shear-melting of a hexagonal columnar crystal by proliferation of dislocations
A hexagonal columnar crystal undergoes a shear-melting transition above a
critical shear rate or stress. We combine the analysis of the shear-thinning
regime below the melting with that of synchrotron X-ray scattering data under
shear and propose the melting to be due to a proliferation of dislocations,
whose density is determined by both techniques to vary as a power law of the
shear rate with a 2/3 exponent, as expected for a creep model of crystalline
solids. Moreover, our data suggest the existence under shear of a line hexatic
phase, between the columnar crystal and the liquid phase
Mean field study of structural changes in Pt isotopes with the Gogny interaction
The evolution of the nuclear shapes along the triaxial landscape is studied
in the Pt isotopic chain using the selfconsistent Hartree-Fock-Bogoliubov
approximation based on the Gogny interaction. In addition to the
parametrization D1S, the new incarnations D1N and D1M of this force are also
included in our analysis to asses to which extent the predictions are
independent of details of the effective interaction. The considered range of
neutron numbers 88<N<26 includes prolate, triaxial, oblate and spherical ground
state shapes and serves for a detailed comparison of the predictions obtained
with the new sets D1N and D1M against the ones provided by the standard
parametrization Gogny-D1S in a region of the nuclear landscape for which
experimental and theoretical fingerprints of shape transitions have been found.
Structural evolution along the Pt chain is discussed in terms of the
deformation dependence of single particle energies.Comment: 18 pages, 10 figures. Accepted for publication in Phys. Rev.
Energy weighted sum rules for mesons in hot and dense matter
We study energy weighted sum rules of the pion and kaon propagator in nuclear
matter at finite temperature. The sum rules are obtained from matching the
Dyson form of the meson propagator with its spectral Lehmann representation at
low and high energies. We calculate the sum rules for specific models of the
kaon and pion self-energy. The in-medium spectral densities of the K and anti-K
mesons are obtained from a chiral unitary approach in coupled channels which
incorporates the S- and P-waves of the kaon-nucleon interaction. The pion
self-energy is determined from the P-wave coupling to particle-hole and
Delta-hole excitations, modified by short range correlations. The sum rules for
the lower energy weights are fulfilled satisfactorily and reflect the
contributions from the different quasi-particle and collective modes of the
meson spectral function. We discuss the sensitivity of the sum rules to the
distribution of spectral strength and their usefulness as quality tests of
model calculations.Comment: 19 pages, 6 figures; one figure added, enhanced discussion, version
to appear in PR
Kinetic Ising System in an Oscillating External Field: Stochastic Resonance and Residence-Time Distributions
Experimental, analytical, and numerical results suggest that the mechanism by
which a uniaxial single-domain ferromagnet switches after sudden field reversal
depends on the field magnitude and the system size. Here we report new results
on how these distinct decay mechanisms influence hysteresis in a
two-dimensional nearest-neighbor kinetic Ising model. We present theoretical
predictions supported by numerical simulations for the frequency dependence of
the probability distributions for the hysteresis-loop area and the
period-averaged magnetization, and for the residence-time distributions. The
latter suggest evidence of stochastic resonance for small systems in moderately
weak oscillating fields.Comment: Includes updated results for Fig.2 and minor text revisions to the
abstract and text for clarit
FÉRAL, Josette, Mise en scène et jeu de l’acteur : entretiens, Montréal/Carnières (Belgique), Éditions Jeu/Éditions Lansman, t. 2, 1998
Frugivorous birds are important seed dispersers and influence the recruitment of many plant species in the rainforest. The efficiency of this dispersal generally depends on environment quality, bird species, richness and diversity of resources, and low levels of anthropogenic disturbance. In this study, we compared the sighting number of dusky-legged guans (Penelope obscura) by km and their movement in two areas of Serra do Japi, one around the administrative base (Base) where birds received anthropogenic food and a pristine area (DAE) with no anthropogenic resource. We also compared the richness of native seeds in feces of birds living in these two areas. Although the abundance of P. obscura was higher in the Base, these individuals moved less, dispersed 80% fewer species of plants and consumed 30% fewer seeds than individuals from DAE. The rarefaction indicated a low richness in the frugivorous diet of birds from the Base when compared to the populations from DAE. We conclude that human food supply can interfere in the behavior of these birds and in the richness of native seeds dispersed.Frugivorous birds are important seed dispersers and influence the recruitment of many plant species in the rainforest. The efficiency of this dispersal generally depends on environment quality, bird species, richness and diversity of resources, and low le75410081017sem informaçãosem informaçãoAves frugÃvoras são importantes dispersoras de sementes e influenciam no recrutamento de muitas espécies na floresta tropical. A eficiência dessa dispersão geralmente depende da qualidade do meio ambiente, das espécies de aves envolvidas, da riqueza e divWe thank the Graduate Program in Ecology of Unicampfor financial support through the discipline Topics in Field Ecology. The Research Base of Serra do Japi for lodging and authorizing research in the study area. We also thank E. Pereira for contributions
Universality in Glassy Low-Temperature Physics
We propose a microscopic translationally invariant glass model which exhibits
two level tunneling systems with a broad range of asymmetries and barrier
heights in its glassy phase. Their distribution is qualitatively different from
what is commonly assumed in phenomenological models, in that symmetric
tunneling systems are systematically suppressed. Still, the model exhibits the
usual glassy low-temperature anomalies. Universality is due to the collective
origin of the glassy potential energy landscape. We obtain a simple explanation
also for the mysterious {\em quantitative} universality expressed in the
unusually narrow universal glassy range of values for the internal friction
plateau.Comment: 4 pages, 5 figures, uses RevTeX
Exact solution of the lattice vertex model analog of the coupled Bariev XY chains
We present the algebraic Bethe Ansatz solution for the vertex model recently
proposed by Zhou as the classical analog of the Bariev interacting XY chains.
The relevant commutation rules between the creation fields contain the Hecke
symmetry pointed out recently by Hikami and Murakami. The eigenvalues of the
corresponding transfer matrix are explicitly given.Comment: Plain latex, 8 pag
Digital Availability of Product Information for Collaborative Engineering of Spacecraft
In this paper, we introduce a system to collect product information from
manufacturers and make it available in tools that are used for concurrent
design of spacecraft. The planning of a spacecraft needs experts from different
disciplines, like propulsion, power, and thermal. Since these different
disciplines rely on each other there is a high need for communication between
them, which is often realized by a Model-Based Systems Engineering (MBSE)
process and corresponding tools. We show by comparison that the product
information provided by manufacturers often does not match the information
needed by MBSE tools on a syntactic or semantic level. The information from
manufacturers is also currently not available in machine-readable formats.
Afterwards, we present a prototype of a system that makes product information
from manufacturers directly available in MBSE tools, in a machine-readable way.Comment: accepted at CDVE201
Ciclagem de nutrientes em cultivo de terceira soca de cana-de-açúcar.
Resumo: O objetivo do trabalho foi avaliar a liberação de macronutrientes em função de nÃveis de palhada mantida sobre o solo, na terceira soca de cana-de-açúcar, e sua contribuição para ciclos posteriores. O ensaio foi instalado em Araras ?SP, safra 2011-2012 (variedade RB-845210). Os tratamentos foram os nÃveis de palhada 25% - 50% - 75% - 100% (2,8 - 5,7 - 8,5 -11,3 t ha-1 em base seca) dispostos em blocos ao acaso, 4 repetições. Foi utilizado o método dos ?litter bags? para avaliar a decomposição da biomassa e sua respectiva ciclagem de nutrientes. Determinou-se as concentrações (g kg-1) de N, P, K, Ca, Mg e S e as quantidades (kg ha-1) liberadas após um ciclo de cultivo. Utilizou-se a análise de variância e regressão. As concentrações de N, P, Ca e S diferiram com nÃveis de palhada; já o K e Mg não responderam aos tratamentos. O modelo linear melhor se ajustou para as concentrações do N, P, K e Ca, com exceção do Mg e S. Houve maior liberação de nutrientes nos maiores nÃveis de palhada, porém esta diferença foi atribuÃda ao aumento da massa entre os tratamentos. Os elementos Ca, K e N, respectivamente, foram os mais liberados, independente dos tratamentos. Conclui-se que variações na quantidade de palhada deixadas sobre o solo apresentam comportamentos diferentes de mineralização de nutrientes durante um ciclo de cultivo da cana-de-açúcar. Há maior liberação de nutrientes nos maiores nÃveis de palhada, sendo os elementos Ca, K e N, respectivamente, os mais liberados
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