22,009 research outputs found
Hamming distance and mobility behavior in generalized rock-paper-scissors models
This work reports on two related investigations of stochastic simulations
which are widely used to study biodiversity and other related issues. We first
deal with the behavior of the Hamming distance under the increase of the number
of species and the size of the lattice, and then investigate how the mobility
of the species contributes to jeopardize biodiversity. The investigations are
based on the standard rules of reproduction, mobility and predation or
competition, which are described by specific rules, guided by generalization of
the rock-paper-scissors game, valid in the case of three species. The results
on the Hamming distance indicate that it engenders universal behavior,
independently of the number of species and the size of the square lattice. The
results on the mobility confirm the prediction that it may destroy diversity,
if it is increased to higher and higher values.Comment: 7 pages, 9 figures. To appear in EP
A geometric technique to generate lower estimates for the constants in the Bohnenblust--Hille inequalities
The Bohnenblust--Hille (polynomial and multilinear) inequalities were proved
in 1931 in order to solve Bohr's absolute convergence problem on Dirichlet
series. Since then these inequalities have found applications in various fields
of analysis and analytic number theory. The control of the constants involved
is crucial for applications, as it became evident in a recent outstanding paper
of Defant, Frerick, Ortega-Cerd\'{a}, Ouna\"{\i}es and Seip published in 2011.
The present work is devoted to obtain lower estimates for the constants
appearing in the Bohnenblust--Hille polynomial inequality and some of its
variants. The technique that we introduce for this task is a combination of the
Krein--Milman Theorem with a description of the geometry of the unit ball of
polynomial spaces on .Comment: This preprint does no longer exist as a single manuscript. It is now
part of the preprint entitled "The optimal asymptotic hypercontractivity
constant of the real polynomial Bohnenblust-Hille inequality is 2" (arXiv
reference 1209.4632
Anomalous diffusion in correlated continuous time random walks
We demonstrate that continuous time random walks in which successive waiting
times are correlated by Gaussian statistics lead to anomalous diffusion with
mean squared displacement ~t^{2/3}. Long-ranged correlations of the
waiting times with power-law exponent alpha (0<alpha<=2) give rise to
subdiffusion of the form ~t^{alpha/(1+alpha)}. In contrast correlations
in the jump lengths are shown to produce superdiffusion. We show that in both
cases weak ergodicity breaking occurs. Our results are in excellent agreement
with simulations.Comment: 6 pages, 6 figures. Slightly revised version, accepted to J Phys A as
a Fast Track Communicatio
The antikaon nuclear potential in hot and dense matter
The antikaon optical potential in hot and dense nuclear matter is studied
within the framework of a coupled-channel self-consistent calculation taking,
as bare meson-baryon interaction, the meson-exchange potential of the J\"ulich
group. Typical conditions found in heavy-ion collisions at GSI are explored. As
in the case of zero temperature, the angular momentum components larger than
L=0 contribute significantly to the finite temperature antikaon optical
potential at finite momentum. It is found that the particular treatment of the
medium effects has a strong influence on the behavior of the antikaon potential
with temperature. Our self-consistent model, in which antikaons and pions are
dressed in the medium, gives a moderately temperature dependent antikaon
potential which remains attractive at GSI temperatures, contrary to what one
finds if only nuclear Pauli blocking effects are included.Comment: 30 pages, 8 figures, references added. Accepted for publication in
PR
The origin of power-law distributions in deterministic walks: the influence of landscape geometry
We investigate the properties of a deterministic walk, whose locomotion rule
is always to travel to the nearest site. Initially the sites are randomly
distributed in a closed rectangular ( landscape and, once
reached, they become unavailable for future visits. As expected, the walker
step lengths present characteristic scales in one () and two () dimensions. However, we find scale invariance for an intermediate
geometry, when the landscape is a thin strip-like region. This result is
induced geometrically by a dynamical trapping mechanism, leading to a power law
distribution for the step lengths. The relevance of our findings in broader
contexts -- of both deterministic and random walks -- is also briefly
discussed.Comment: 7 pages, 11 figures. To appear in Phys. Rev.
Crossover of thermal to shot noise in chaotic cavities
We study the crossover between thermal and shot-noise power in a chaotic
quantum dot in the presence of non-ideal contacts at finite temperature. The
result explicitly demonstrates that the temperature affect the
suppression-amplification effect present in the main quantum noise. In
particular, the weak localization contribution to the noise has an anomalous
thermal behavior when one let the barriers vary, indicating the presence of a
critical point related to specific value of the tunneling barriers. We also
show how to get to the opaque limit of the quantum dot at finite temperature.Comment: 6 pages, 5 figures. To be published in Europhysics Letter
Incidência de fungos fitopatogênicos em sementes de caupi em Petrolina-PE, em diferentes temperaturas.
Suplemento, ref. 224. Edição dos Resumos do XXXV Congresso Paulista de Fitopatologia, Jaguariúna, fev. 2012
Emissão de óxido nitroso originária de excretas bovina em pastagem sob integração lavoura-pecuária.
O N perdido do sistema, originado das excretas dos animais, pode dar origem a significativos fluxos de N2O, colaborando para aumentar a concentração desse gás na atmosfera. O objetivo deste trabalho é estudar o impacto das excretas bovinas (fezes e urina) sobre as emissões de N2O em pastagem, sob integração lavoura-pecuária na região de cerrado
Dry Matter Production of Shoots and Root Density of Two Cultivars of \u3ci\u3eLablab purpureus\u3c/i\u3e (L.) Sweet
This experiment was conducted in green house conditions to evaluate the DM accumulation in the shoots and in the roots of two cultivars of Lablab purpureus (L.) Sweet. A 2x3 factorial (two cultivars and three evaluation dates) was conducted according to a randomized complete block design with four replications, being the cultivars Highworth and Rongai evaluated at 42, 56, and 70 days after seedling emergence (DASE). The results indicated that the cvs. Highworth and Rongai have the same pattern of DM accumulation in the shoots. In the upper layer of the soil (0-0.20 m) it was found 38.83% and 43.64% of the DM accumulated in the roots down to 2.00 m depth, in the cvs. Highworth and Rongai, respectively. In the deepest layer (1.80-2.00 m) it was found 3.02% and 1.5% of the DM accumulated in the roots of the cvs. Highworth and Rongai, respectively. The root density showed a striking decrease upper layer from the soil (0-0.2 m) down to the depth of 0.60 - 0.80 m (from 10.83 to 1.75 cm.cm-3 in the cv. Highworth and from 10.76 to 1.28 cm.cm-3 in the cv. Rongai). At the bottom layer (1.80-2.00 m) the root density values were 0.98 cm.cm-3 and 0.59 cm.cm-3, respectively for the cvs. Highworth and Rongai. The root/shoot ratios were similar in both cvs. and decreased from 42 to 70 DASE showing that the cvs. evaluated had the same dynamics of DM accumulation
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