27,104 research outputs found
Neural networks with dynamical synapses: from mixed-mode oscillations and spindles to chaos
Understanding of short-term synaptic depression (STSD) and other forms of
synaptic plasticity is a topical problem in neuroscience. Here we study the
role of STSD in the formation of complex patterns of brain rhythms. We use a
cortical circuit model of neural networks composed of irregular spiking
excitatory and inhibitory neurons having type 1 and 2 excitability and
stochastic dynamics. In the model, neurons form a sparsely connected network
and their spontaneous activity is driven by random spikes representing synaptic
noise. Using simulations and analytical calculations, we found that if the STSD
is absent, the neural network shows either asynchronous behavior or regular
network oscillations depending on the noise level. In networks with STSD,
changing parameters of synaptic plasticity and the noise level, we observed
transitions to complex patters of collective activity: mixed-mode and spindle
oscillations, bursts of collective activity, and chaotic behaviour.
Interestingly, these patterns are stable in a certain range of the parameters
and separated by critical boundaries. Thus, the parameters of synaptic
plasticity can play a role of control parameters or switchers between different
network states. However, changes of the parameters caused by a disease may lead
to dramatic impairment of ongoing neural activity. We analyze the chaotic
neural activity by use of the 0-1 test for chaos (Gottwald, G. & Melbourne, I.,
2004) and show that it has a collective nature.Comment: 7 pages, Proceedings of 12th Granada Seminar, September 17-21, 201
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
A dynamical point of view of Quantum Information: entropy and pressure
Quantum Information is a new area of research which has been growing rapidly
since last decade. This topic is very close to potential applications to the so
called Quantum Computer. In our point of view it makes sense to develop a more
"dynamical point of view" of this theory. We want to consider the concepts of
entropy and pressure for "stationary systems" acting on density matrices which
generalize the usual ones in Ergodic Theory (in the sense of the Thermodynamic
Formalism of R. Bowen, Y. Sinai and D. Ruelle). We consider the operator
acting on density matrices over a finite
-dimensional complex Hilbert space where and , are
operators in this Hilbert space. is not a linear operator. In
some sense this operator is a version of an Iterated Function System (IFS).
Namely, the , , play the role of the
inverse branches (acting on the configuration space of density matrices )
and the play the role of the weights one can consider on the IFS. We
suppose that for all we have that . A
family determines a Quantum Iterated Function System
(QIFS) , $\mathcal{F}_W=\{\mathcal{M}_N,F_i,W_i\}_{i=1,...,
k}.
A dynamical point of view of Quantum Information: Wigner measures
We analyze a known version of the discrete Wigner function and some
connections with Quantum Iterated Funcion Systems. This paper is a follow up of
"A dynamical point of view of Quantum Information: entropy and pressure" by the
same authors
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
A Thermodynamic Formalism for density matrices in Quantum Information
We consider new concepts of entropy and pressure for stationary systems
acting on density matrices which generalize the usual ones in Ergodic Theory.
Part of our work is to justify why the definitions and results we describe here
are natural generalizations of the classical concepts of Thermodynamic
Formalism (in the sense of R. Bowen, Y. Sinai and D. Ruelle). It is well-known
that the concept of density operator should replace the concept of measure for
the cases in which we consider a quantum formalism. We consider the operator
acting on the space of density matrices over a finite
-dimensional complex Hilbert space where and ,
are linear operators in this Hilbert space. In some sense this
operator is a version of an Iterated Function System (IFS). Namely, the
, , play the role of the inverse branches
(i.e., the dynamics on the configuration space of density matrices) and the
play the role of the weights one can consider on the IFS. In this way a
family determines a Quantum Iterated Function System
(QIFS). We also present some estimates related to the Holevo bound
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