611 research outputs found
Applicability of the Fisher Equation to Bacterial Population Dynamics
The applicability of the Fisher equation, which combines diffusion with
logistic nonlinearity, to population dynamics of bacterial colonies is studied
with the help of explicit analytic solutions for the spatial distribution of a
stationary bacterial population under a static mask. The mask protects the
bacteria from ultraviolet light. The solution, which is in terms of Jacobian
elliptic functions, is used to provide a practical prescription to extract
Fisher equation parameters from observations and to decide on the validity of
the Fisher equation.Comment: 5 pages, 3 figs. include
Opinion and community formation in coevolving networks
In human societies opinion formation is mediated by social interactions,
consequently taking place on a network of relationships and at the same time
influencing the structure of the network and its evolution. To investigate this
coevolution of opinions and social interaction structure we develop a dynamic
agent-based network model, by taking into account short range interactions like
discussions between individuals, long range interactions like a sense for
overall mood modulated by the attitudes of individuals, and external field
corresponding to outside influence. Moreover, individual biases can be
naturally taken into account. In addition the model includes the opinion
dependent link-rewiring scheme to describe network topology coevolution with a
slower time scale than that of the opinion formation. With this model
comprehensive numerical simulations and mean field calculations have been
carried out and they show the importance of the separation between fast and
slow time scales resulting in the network to organize as well-connected small
communities of agents with the same opinion.Comment: 10 pages, 5 figures. New inset for Fig. 1 and references added.
Submitted to Physical Review
State of the science and the way forward for the ecotoxicological assessment of contaminated land.
Durante as Ăşltimas duas dĂ©cadas, ecotoxicologistas de solo tĂŞm feito progressos ao utilizar conceitos básicos e avanços da zoologia e ecologia do solo. Os mĂ©todos existentes tĂŞm sido aplicados, e tĂŞm-se desenvolvido novas ferramentas para avaliar de que modo a contaminação quĂmica pode afetar o ecossistema terrestre, inclusive pela degradação ou destruição da qualidade do solo e dos habitats ou pela redução da biodiversidade edáfica. Os ecotoxicologistas de solo utilizam um conjunto de protocolos padronizados, originalmente desenvolvidos como testes de laboratĂłrio com compostos quĂmicos simples como os pesticidas e, posteriormente, adaptados em termos de abordagens e mĂ©todos, para a avaliação de áreas contaminadas. No entanto, a relevância ecolĂłgica de algumas abordagens permanece questionável. Neste artigo, os autores discutem os recentes desafios para uma avaliação ecotoxicolĂłgica coerente do ecossistema solo em áreas contaminadas e apresentam recomendações de como integrar os efeitos das propriedades fĂsicoquĂmicas do solo, as variações na diversidade de invertebrados do solo e, as interações entre organismos dos vários nĂveis trĂłficos. SĂŁo analisadas novas abordagens e mĂ©todos de avaliação, usando-se exemplos de trĂŞs continentes (particularmente o trabalho desenvolvido no Brasil), e sĂŁo dadas recomendações de como aumentar a relevância ecolĂłgica na avaliação ecotoxicolĂłgica de áreas contaminadas
Experimental evidence of stochastic resonance without tuning due to non Gaussian noises
In order to test theoretical predictions, we have studied the phenomenon of
stochastic resonance in an electronic experimental system driven by white non
Gaussian noise. In agreement with the theoretical predictions our main findings
are: an enhancement of the sensibility of the system together with a remarkable
widening of the response (robustness). This implies that even a single resonant
unit can reach a marked reduction in the need of noise tuning.Comment: 4 pages, 3 figure
Enhancement of Stochastic Resonance in distributed systems due to a selective coupling
Recent massive numerical simulations have shown that the response of a
"stochastic resonator" is enhanced as a consequence of spatial coupling.
Similar results have been analytically obtained in a reaction-diffusion model,
using "nonequilibrium potential" techniques. We now consider a field-dependent
diffusivity and show that the "selectivity" of the coupling is more efficient
for achieving stochastic-resonance enhancement than its overall value in the
constant-diffusivity case.Comment: 10 pgs (RevTex), 4 figures, submitted to Phys.Rev.Let
Entropic sampling dynamics of the globally-coupled kinetic Ising model
The entropic sampling dynamics based on the reversible information transfer
to and from the environment is applied to the globally coupled Ising model in
the presence of an oscillating magnetic field. When the driving frequency is
low enough, coherence between the magnetization and the external magnetic field
is observed; such behavior tends to weaken with the system size. The time-scale
matching between the intrinsic time scale, defined in the absence of the
external magnetic field, and the extrinsic time scale, given by the inverse of
the driving frequency, is used to explain the observed coherence behavior.Comment: 8 page
Oxygen and Carbon Dioxide Rhythms Are Circadian Clock Controlled and Differentially Directed by Behavioral Signals
This is the author accepted manuscript. The final version is available from Elsevier (Cell Press).Daily rhythms in animal physiology are driven by endogenous circadian clocks in part through rest-activity and feeding-fasting cycles. Here, we examined principles that govern daily respiration. We monitored oxygen consumption and carbon dioxide release, as well as tissue oxygenation in freely moving animals to specifically dissect the role of circadian clocks and feeding time on daily respiration. We found that daily rhythms in oxygen and carbon dioxide are clock controlled and that time-restricted feeding restores their rhythmicity in clock-deficient mice. Remarkably, day-time feeding dissociated oxygen rhythms from carbon dioxide oscillations, whereby oxygen followed activity, and carbon dioxide was shifted and aligned with food intake. In addition, changes in carbon dioxide levels altered clock gene expression and phase shifted the clock. Collectively, our findings indicate that oxygen and carbon dioxide rhythms are clock controlled and feeding regulated and support a potential role for carbon dioxide in phase resetting peripheral clocks upon feeding.British Heart FoundationEuropean Research CouncilEuropean Union, Seventh Framework Program, Marie Curie Action
Le roman d'entreprise: breaking the silence
This article looks at three recent French novels novels in order to explore key themes in what has become known as the roman d’entreprise: Pierre Mari’s Résolution (2005), Nathalie Kuperman’s Nous étions des êtres vivants (2010) and Thierry Beinstingel’s Retour aux mots sauvages (2010). The figure of the entreprise functions both as a fictional representation of the post-Fordist workplace environment in companies such as France Télécom, and also as a means of tackling wider issues of work and social organisation in an era of neoliberal managerialism. The concepts of capitalist realism, organisational miasma and virtuality are used to analyse the ways in which the three novels convey the distinctive affective landscape of the contemporary entreprise. Fiction is used to consider the prolix and self-referential nature of the managerialist entreprise, which enables it to exert a significant influence on the individual and collective subjectivities of employees. The three novels focus on the capacity of the entreprise to capture language and impose an affect of silence on employees
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