27,719 research outputs found
Decay of distance autocorrelation and Lyapunov exponents
This work presents numerical evidences that for discrete dynamical systems
with one positive Lyapunov exponent the decay of the distance autocorrelation
is always related to the Lyapunov exponent. Distinct decay laws for the
distance autocorrelation are observed for different systems, namely exponential
decays for the quadratic map, logarithmic for the H\'enon map and power-law for
the conservative standard map. In all these cases the decay exponent is close
to the positive Lyapunov exponent. For hyperbolic conservative systems, the
power-law decay of the distance autocorrelation tends to be guided by the
smallest Lyapunov exponent.Comment: 7 pages, 8 figure
Characterizing Weak Chaos using Time Series of Lyapunov Exponents
We investigate chaos in mixed-phase-space Hamiltonian systems using time
series of the finite- time Lyapunov exponents. The methodology we propose uses
the number of Lyapunov exponents close to zero to define regimes of ordered
(stickiness), semi-ordered (or semi-chaotic), and strongly chaotic motion. The
dynamics is then investigated looking at the consecutive time spent in each
regime, the transition between different regimes, and the regions in the
phase-space associated to them. Applying our methodology to a chain of coupled
standard maps we obtain: (i) that it allows for an improved numerical
characterization of stickiness in high-dimensional Hamiltonian systems, when
compared to the previous analyses based on the distribution of recurrence
times; (ii) that the transition probabilities between different regimes are
determined by the phase-space volume associated to the corresponding regions;
(iii) the dependence of the Lyapunov exponents with the coupling strength.Comment: 8 pages, 6 figure
Comportamento fisiológico de sementes de açaí (Euterpe oleracea Mart.) submetidas à desidratação.
O presente trabalho, objetivando verificar os efeitos imediatos da desidratação sobre o comportamento fisiológico das sementes de açaí (Euterpe oleracea Mart.), utilizou lote oriundo de população de 25 progênies de meio-irmãos, pertencente à Coleção de Germoplasma da Embrapa Amazônia Oriental (Belém/PA). Anteriormente à secagem, foi determinado o grau de umidade das sementes e coletado o tratamento que continha o maior grau de umidade (45%). As demais sementes foram submetidas à secagem, em câmara com circulação de ar (30°C±2°C), visando à obtenção dos demais tratamentos com 39%, 33%, 27%, 22% e 15% de água. O efeito da desidratação sobre a qualidade das sementes foi avaliado através das seguintes determinações: grau de umidade, teste de germinação, índice de velocidade de emergência e emergência de plântulas. Foi verificado que desidratação até 39% de água não produz efeitos fisiológicos imediatos sobre as sementes de açaí; a partir de 33% de água, a dessecação favorece progressivamente a redução da germinação e, ao atingir 15% de água, a capacidade germinativa foi anulada.Trabalho também apresentado no 18º Congresso Brasileiro de Fruticultura, 2004, em Florianópolis
New thought experiment to test the generalized second law of thermodynamics
We propose an extension of the original thought experiment proposed by
Geroch, which sparked much of the actual debate and interest on black hole
thermodynamics, and show that the generalized second law of thermodynamics is
in compliance with it.Comment: 4 pages (revtex), 3 figure
Gravitational Collapse of Self-Similar and Shear-free Fluid with Heat Flow
A class of solutions to Einstein field equations is studied, which represents
gravitational collapse of thick spherical shells made of self-similar and
shear-free fluid with heat flow. It is shown that such shells satisfy all the
energy conditions, and the corresponding collapse always forms naked
singularities.Comment: 34 pages, 9 figures, late
Non-hexagonal-ring defects and structures induced by strain in graphene and in functionalized graphene
We perform {\textit ab initio} calculations for the strain-induced formation
of non-hexagonal-ring defects in graphene, graphane (planar CH), and graphenol
(planar COH). We find that the simplest of such topological defects, the
Stone-Wales defect, acts as a seed for strain-induced dissociation and
multiplication of topological defects. Through the application of inhomogeneous
deformations to graphene, graphane and graphenol with initially small
concentrations of pentagonal and heptagonal rings, we obtain several novel
stable structures that possess, at the same time, large concentrations of
non-hexagonal rings (from fourfold to elevenfold) and small formation energies
- …