19,240 research outputs found
Critical and resonance phenomena in neural networks
Brain rhythms contribute to every aspect of brain function. Here, we study
critical and resonance phenomena that precede the emergence of brain rhythms.
Using an analytical approach and simulations of a cortical circuit model of
neural networks with stochastic neurons in the presence of noise, we show that
spontaneous appearance of network oscillations occurs as a dynamical
(non-equilibrium) phase transition at a critical point determined by the noise
level, network structure, the balance between excitatory and inhibitory
neurons, and other parameters. We find that the relaxation time of neural
activity to a steady state, response to periodic stimuli at the frequency of
the oscillations, amplitude of damped oscillations, and stochastic fluctuations
of neural activity are dramatically increased when approaching the critical
point of the transition.Comment: 8 pages, Proceedings of 12th Granada Seminar, September 17-21, 201
Hydro-wind balance in daily electricity markets : a case-study
ABSTRACT: The European Union has been one of the major drivers of the development of renewable energy. In Portugal, renewable generation is subject to specific licensing requirements and benefits from a feed-in-tariff. This paper pays special attention to wind and hydroelectric technologies. Typically, wind farms produce more energy during the night (off-peak periods), when the demand is lower, contributing to a reduction of the market price. Hydroelectric power plants use off-peak periods to pump water, and produce energy in the periods of a 24 hour day where the prices of electricity are higher (peak periods). This paper presents a case study aiming at analyzing the behavior of hydroelectric power producers—that is, in power systems with large renewable generation, producers typically use the periods of the day with lower energy prices for pumping, and the other periods (with higher energy prices) to produce electricity. The simulations are performed using MATREM (for Multi-Agent Trading in Electricity Markets). The results confirm (and rebate) the typical behavior of hydroelectric power producers.info:eu-repo/semantics/publishedVersio
Diagnóstico sobre a conservação on farm de variedades locais de abóboras no Tocantins e Mato Grosso.
Com a finalidade de realizar um diagnóstico sobre a ocorrência e as condições de conservação on farm de espécies de Cucurbita em áreas de agricultores familiares do Tocantins e Mato Grosso, conduziu-se esse trabalho.bitstream/item/84979/1/bpd-97.pd
Chemical composition and activity of a biofilm during the start-up of an airlift reactor
For the successful operation of a biofilm reactor, it is important to characterise the fixed biomass,
its activity and composition. The purpose of this research was to monitor the biofilm characteristics of an
airlift reactor, namely its composition in terms of exopolymers (polysaccharides and proteins), attached
biomass, thickness, total proteins, as well as its activity in terms of substrate consumption rates. During the
early phases of biofilm development, a high exopolymer production was observed, which helped in
promoting the initial cell adhesion. The high turbulence with strong abrasive conditions might also trigger the
excretion of those polymers. Low levels of extracellular proteins were detected, showing that the proteins in
the biofilm were mainly intracellular. The biofilm accumulation on the carrier was accompanied by an
increased biological activity; however, at the end of the experiment, the specific substrate consumption rate
decreased, probably because of a reduction of the cell density within the biofilm.Fundação para a Ciência e a Tecnologia (FCT) – PRAXIS XXI/BM/6699/95
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