4,620 research outputs found
Two distinct desynchronization processes caused by lesions in globally coupled neurons
To accomplish a task, the brain works like a synchronized neuronal network
where all the involved neurons work together. When a lesion spreads in the
brain, depending on its evolution, it can reach a significant portion of
relevant area. As a consequence, a phase transition might occur: the neurons
desynchronize and cannot perform a certain task anymore. Lesions are
responsible for either disrupting the neuronal connections or, in some cases,
for killing the neuron. In this work, we will use a simplified model of
neuronal network to show that these two types of lesions cause different types
of desynchronization.Comment: 5 pages, 3 figure
Adequação de métodos para estimar a população de Elasmopalpus lignosellus em condições de laboratório.
Tres metodos (extracao de ovos, contagem direta de ovos e emergencia de lagartas recem-eclodidas para determinar o potencial de infestacao de Elasmopalpus lignosellus, Zeller 1848 foram testados em laboratorio. Para o metodo de extracao de ovos a amostra de solo foi tratada com hipoclorito de sodio a 1% sendo posteriormente lavada em peneiras de 10, 20 e 100 mesh. Os residuos retirados na peneira de 100 mesh foram tratados com uma solucao saturada de sulfato de magnesio e deixados decantar; o liquido sobrenadante contendo os ovos foi filtrado com um filtro de organdi, e os ovos foram contados com o auxilio de uma lupa binocular. No metodo de contagem direta de ovos no solo foi utilizada uma lupa binocular, e no metodo de emergencia de lagartas utilizaram-se folhas de milho para atrair lagartas recem-eclodidas e afetou-se a contagem destas. Os resultados indicaram que em condicoes de laboratorio o metodo de contagem direta de ovos e mais eficiente do que o metodo de extracao de ovos; nas outras comparacoes, os metodos nao foram estatisticamente diferentes. Utilizando o metodo de extracao de ovos observou-se que os ovos postos pela largado diretamente no solo nao sao removidos com a mesma eficiencia que os ovos misturados manualmente no solo
Phase synchronization of coupled bursting neurons and the generalized Kuramoto model
Bursting neurons fire rapid sequences of action potential spikes followed by
a quiescent period. The basic dynamical mechanism of bursting is the slow
currents that modulate a fast spiking activity caused by rapid ionic currents.
Minimal models of bursting neurons must include both effects. We considered one
of these models and its relation with a generalized Kuramoto model, thanks to
the definition of a geometrical phase for bursting and a corresponding
frequency. We considered neuronal networks with different connection topologies
and investigated the transition from a non-synchronized to a partially
phase-synchronized state as the coupling strength is varied. The numerically
determined critical coupling strength value for this transition to occur is
compared with theoretical results valid for the generalized Kuramoto model.Comment: 31 pages, 5 figure
Finite Size Effects in Separable Recurrent Neural Networks
We perform a systematic analytical study of finite size effects in separable
recurrent neural network models with sequential dynamics, away from saturation.
We find two types of finite size effects: thermal fluctuations, and
disorder-induced `frozen' corrections to the mean-field laws. The finite size
effects are described by equations that correspond to a time-dependent
Ornstein-Uhlenbeck process. We show how the theory can be used to understand
and quantify various finite size phenomena in recurrent neural networks, with
and without detailed balance.Comment: 24 pages LaTex, with 4 postscript figures include
Optimal Cosmic-Ray Detection for Nondestructive Read Ramps
Cosmic rays are a known problem in astronomy, causing both loss of data and
data inaccuracy. The problem becomes even more extreme when considering data
from a high-radiation environment, such as in orbit around Earth or outside the
Earth's magnetic field altogether, unprotected, as will be the case for the
James Webb Space Telescope (JWST). For JWST, all the instruments employ
nondestructive readout schemes. The most common of these will be "up the ramp"
sampling, where the detector is read out regularly during the ramp. We study
three methods to correct for cosmic rays in these ramps: a two-point difference
method, a deviation from the fit method, and a y-intercept method. We apply
these methods to simulated nondestructive read ramps with single-sample groups
and varying combinations of flux, number of samples, number of cosmic rays,
cosmic-ray location in the exposure, and cosmic-ray strength. We show that the
y-intercept method is the optimal detection method in the read-noise-dominated
regime, while both the y-intercept method and the two-point difference method
are best in the photon-noise-dominated regime, with the latter requiring fewer
computations.Comment: To be published in PASP. This paper is 12 pages long and includes 15
figure
Intermingled basins in coupled Lorenz systems
We consider a system of two identical linearly coupled Lorenz oscillators,
presenting synchro- nization of chaotic motion for a specified range of the
coupling strength. We verify the existence of global synchronization and
antisynchronization attractors with intermingled basins of attraction, such
that the basin of one attractor is riddled with holes belonging to the basin of
the other attractor and vice versa. We investigated this phenomenon by
verifying the fulfillment of the mathematical requirements for intermingled
basins, and also obtained scaling laws that characterize quantitatively the
riddling of both basins for this system
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