62 research outputs found
Fluctuations in network dynamics
Most complex networks serve as conduits for various dynamical processes,
ranging from mass transfer by chemical reactions in the cell to packet transfer
on the Internet. We collected data on the time dependent activity of five
natural and technological networks, finding that for each the coupling of the
flux fluctuations with the total flux on individual nodes obeys a unique
scaling law. We show that the observed scaling can explain the competition
between the system's internal collective dynamics and changes in the external
environment, allowing us to predict the relevant scaling exponents.Comment: 4 pages, 4 figures. Published versio
Nonuniversality in the pair contact process with diffusion
We study the static and dynamic behavior of the one dimensional pair contact
process with diffusion. Several critical exponents are found to vary with the
diffusion rate, while the order-parameter moment ratio m=\bar{rho^2}
/\bar{rho}^2 grows logarithmically with the system size. The anomalous behavior
of m is traced to a violation of scaling in the order parameter probability
density, which in turn reflects the presence of two distinct sectors, one
purely diffusive, the other reactive, within the active phase. Studies
restricted to the reactive sector yield precise estimates for exponents beta
and nu_perp, and confirm finite size scaling of the order parameter. In the
course of our study we determine, for the first time, the universal value m_c =
1.334 associated with the parity-conserving universality class in one
dimension.Comment: 9 pages, 5 figure
Entropy-based analysis of the number partitioning problem
In this paper we apply the multicanonical method of statistical physics on
the number-partitioning problem (NPP). This problem is a basic NP-hard problem
from computer science, and can be formulated as a spin-glass problem. We
compute the spectral degeneracy, which gives us information about the number of
solutions for a given cost and cardinality . We also study an extension
of this problem for partitions. We show that a fundamental difference on
the spectral degeneracy of the generalized () NPP exists, which could
explain why it is so difficult to find good solutions for this case. The
information obtained with the multicanonical method can be very useful on the
construction of new algorithms.Comment: 6 pages, 4 figure
Small world effects in evolution
For asexual organisms point mutations correspond to local displacements in
the genotypic space, while other genotypic rearrangements represent long-range
jumps. We investigate the spreading properties of an initially homogeneous
population in a flat fitness landscape, and the equilibrium properties on a
smooth fitness landscape. We show that a small-world effect is present: even a
small fraction of quenched long-range jumps makes the results indistinguishable
from those obtained by assuming all mutations equiprobable. Moreover, we find
that the equilibrium distribution is a Boltzmann one, in which the fitness
plays the role of an energy, and mutations that of a temperature.Comment: 13 pages and 5 figures. New revised versio
Detrended Fluctuation Analysis of Systolic Blood Pressure Control Loop
We use detrended fluctuation analysis (DFA) to study the dynamics of blood
pressure oscillations and its feedback control in rats by analyzing systolic
pressure time series before and after a surgical procedure that interrupts its
control loop. We found, for each situation, a crossover between two scaling
regions characterized by exponents that reflect the nature of the feedback
control and its range of operation. In addition, we found evidences of
adaptation in the dynamics of blood pressure regulation a few days after
surgical disruption of its main feedback circuit. Based on the paradigm of
antagonistic, bipartite (vagal and sympathetic) action of the central nerve
system, we propose a simple model for pressure homeostasis as the balance
between two nonlinear opposing forces, successfully reproducing the crossover
observed in the DFA of actual pressure signals
Shortest paths on systems with power-law distributed long-range connections
We discuss shortest-path lengths on periodic rings of size L
supplemented with an average of pL randomly located long-range links whose
lengths are distributed according to P_l \sim l^{-\xpn}. Using rescaling
arguments and numerical simulation on systems of up to sites, we show
that a characteristic length exists such that for
. For small p we find
that the shortest-path length satisfies the scaling relation
\ell(r,\xpn,p)/\xi = f(\xpn,r/\xi). Three regions with different asymptotic
behaviors are found, respectively: a) \xpn>2 where , b)
1<\xpn<2 where 0<\theta_s(\xpn)<1/2 and, c) \xpn<1 where
behaves logarithmically, i.e. . The characteristic length is
of the form with \nu=1/(2-\xpn) in region b), but depends
on L as well in region c). A directed model of shortest-paths is solved and
compared with numerical results.Comment: 10 pages, 10 figures, revtex4. Submitted to PR
Statistical mechanics of complex networks
Complex networks describe a wide range of systems in nature and society, much
quoted examples including the cell, a network of chemicals linked by chemical
reactions, or the Internet, a network of routers and computers connected by
physical links. While traditionally these systems were modeled as random
graphs, it is increasingly recognized that the topology and evolution of real
networks is governed by robust organizing principles. Here we review the recent
advances in the field of complex networks, focusing on the statistical
mechanics of network topology and dynamics. After reviewing the empirical data
that motivated the recent interest in networks, we discuss the main models and
analytical tools, covering random graphs, small-world and scale-free networks,
as well as the interplay between topology and the network's robustness against
failures and attacks.Comment: 54 pages, submitted to Reviews of Modern Physic
Influência de diferentes tipos de clarificantes na coloração e conteúdo de compostos fenólicos do hidromel.
Objetivou-se avaliar o efeito de diferentes clarificantes sobre a coloração e conteúdo de compostos fenólicos do hidromel. Foram elaborados sete tratamentos, baseados na adição dos clarificantes durante o processo de sestabilização a frio do hidromel(4ºC): A0(sem adição de clarificante); A1(bentonite 0,8g/L); A2(bentonite 0,8g/L+carvão 0,5g/L); A3(bentonite 0,8g/L+Polivinilpolipirrolidona-PVPP 0,1g/L); A4(sílica 0,5g/L); A5(sílica 0,5g/L+carvão 0,5g/L); A6(sílica 0,5g/L+PVPP 0,1g/L)
Transcultural adaptation of the Emotion Matching Task: an emotion neuropsychological assessment
Emotions play a central role in children’s relationships. Deficits in emotional understanding have been associated with several neuropsychiatric disorders. In Brazil, however, few psychological instruments are available to assess young children’s emotional development. The objective of the present study was to make a transcultural adaptation of the Emotion Matching Task (EMT). The EMT was translated and adapted by a team of bilingual researches and then back-translated to English. The preliminary versions were assessed by EMT’s authors and by Brazilians specialized judges. The final version was applied in a sample of 50 children between three and six years of age and answered by nine judges in three Brazilian states. The results indicate good semantic equivalence and good agreement with the answers provided (κ= 0.88, Z=95.2, p<0.001). The final version of the EMT was considered appropriate and satisfactory
Web 2.0 como estruturante dos processos de produção e difusão científica em um grupo de pesquisa: o TWIKI e o GEC
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