9,779 research outputs found
Memory effects on the statistics of fragmentation
We investigate through extensive molecular dynamics simulations the
fragmentation process of two-dimensional Lennard-Jones systems. After
thermalization, the fragmentation is initiated by a sudden increment to the
radial component of the particles' velocities. We study the effect of
temperature of the thermalized system as well as the influence of the impact
energy of the ``explosion'' event on the statistics of mass fragments. Our
results indicate that the cumulative distribution of fragments follows the
scaling ansatz , where is
the mass, and are cutoff parameters, and is a scaling
exponent that is dependent on the temperature. More precisely, we show clear
evidence that there is a characteristic scaling exponent for each
macroscopic phase of the thermalized system, i.e., that the non-universal
behavior of the fragmentation process is dictated by the state of the system
before it breaks down.Comment: 5 pages, 8 figure
Transport on exploding percolation clusters
We propose a simple generalization of the explosive percolation process
[Achlioptas et al., Science 323, 1453 (2009)], and investigate its structural
and transport properties. In this model, at each step, a set of q unoccupied
bonds is randomly chosen. Each of these bonds is then associated with a weight
given by the product of the cluster sizes that they would potentially connect,
and only that bond among the q-set which has the smallest weight becomes
occupied. Our results indicate that, at criticality, all finite-size scaling
exponents for the spanning cluster, the conducting backbone, the cutting bonds,
and the global conductance of the system, change continuously and significantly
with q. Surprisingly, we also observe that systems with intermediate values of
q display the worst conductive performance. This is explained by the strong
inhibition of loops in the spanning cluster, resulting in a substantially
smaller associated conducting backbone.Comment: 4 pages, 4 figure
A time-dependent density functional theory scheme for efficient calculations of dynamic (hyper)polarizabilities
We present an efficient perturbative method to obtain both static and dynamic
polarizabilities and hyperpolarizabilities of complex electronic systems. This
approach is based on the solution of a frequency dependent Sternheimer
equation, within the formalism of time-dependent density functional theory, and
allows the calculation of the response both in resonance and out of resonance.
Furthermore, the excellent scaling with the number of atoms opens the way to
the investigation of response properties of very large molecular systems. To
demonstrate the capabilities of this method, we implemented it in a real-space
(basis-set free) code, and applied it to benchmark molecules, namely CO, H2O,
and paranitroaniline (PNA). Our results are in agreement with experimental and
previous theoretical studies, and fully validate our approach.Comment: 9 pages, 4 figure
Elliptic Flow and Dissipation in Heavy-Ion Collisions at E_{lab} = (1--160)A GeV
Elliptic flow in heavy-ion collisions at incident energies
(1--160)A GeV is analyzed within the model of 3-fluid dynamics (3FD). We show
that a simple correction factor, taking into account dissipative affects,
allows us to adjust the 3FD results to experimental data. This single-parameter
fit results in a good reproduction of the elliptic flow as a function of the
incident energy, centrality of the collision and rapidity. The experimental
scaling of pion eccentricity-scaled elliptic flow versus
charged-hadron-multiplicity density per unit transverse area turns out to be
also reasonably described. Proceeding from values of the Knudsen number,
deduced from this fit, we estimate the upper limit the shear
viscosity-to-entropy ratio as at the SPS incident energies.
This value is of the order of minimal observed in water and liquid
nitrogen.Comment: 10 pages, 7 figures, version accepted by Phys. Rev.
Estudo da oferta e comercialização de repolho na CEAPE no período de 1999 a 2005.
bitstream/item/26141/1/f-11.pd
Fracturing highly disordered materials
We investigate the role of disorder on the fracturing process of
heterogeneous materials by means of a two-dimensional fuse network model. Our
results in the extreme disorder limit reveal that the backbone of the fracture
at collapse, namely the subset of the largest fracture that effectively halts
the global current, has a fractal dimension of . This exponent
value is compatible with the universality class of several other physical
models, including optimal paths under strong disorder, disordered polymers,
watersheds and optimal path cracks on uncorrelated substrates, hulls of
explosive percolation clusters, and strands of invasion percolation fronts.
Moreover, we find that the fractal dimension of the largest fracture under
extreme disorder, , is outside the statistical error bar of
standard percolation. This discrepancy is due to the appearance of trapped
regions or cavities of all sizes that remain intact till the entire collapse of
the fuse network, but are always accessible in the case of standard
percolation. Finally, we quantify the role of disorder on the structure of the
largest cluster, as well as on the backbone of the fracture, in terms of a
distinctive transition from weak to strong disorder characterized by a new
crossover exponent.Comment: 5 pages, 4 figure
Dinâmica populacional de Ctenarytaina spatulata (Hemiptera: Psyllidae) em Eucaluptus grandis com novos registros de ocorrência.
Dentre os fatores físicos que exercem influência sobre os insetos, os mais importantes são a temperatura, a umidade, luz e o vento. Quanto à temperatura, os insetos, de um modo geral, desenvolvem-se melhor em temperaturas próximas a 25o C, podendo, no entanto, viver numa larga faixa de temperaturas. Dentro da faixa favorável, os insetos apresentam estreitas faixas de melhor desenvolvimento. De forma análoga à temperatura, as exigências de água pelos insetos variam muito, principalmente devido seus hábitos alimentares. A luz é um dos fatores limitantes aos seres vivos, podendo influenciar na reprodução, dispersão, emergência, alimentação e escolha do hospedeiro (BRENNAN & WEINBAUM 2001d). O vento, além de afetar a temperatura e umidade do ambiente, auxilia os insetos nos processos de dispersão e migração, principalmente quando procuram novo habitat, para alimentação e reprodução (LARA, 1979)
Utilização de caldas orgânicas fermentadas no controle do Mal-do-Panamá da bananeira.
A banana é uma das culturas mais importantes no cenário agrícola nacional, tendo cerca de 520 mil hectares de área plantada. Dentre as doenças que ocorre na cultura da bananeira, o mal-do-Panamá, causado pelo fungo Fusariumoxysporum f. sp. cubense (Foc) é considerada a mais destrutiva
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