689 research outputs found
Menos insumos, mais qualidade.
Estudo mostra que a produção integrada de maçã requer menos insumos e mais mão-de-obra para o monitoramento. Como resultado, maior rentabilidade e menos custos de pós-colheita.Possui tabela comparativa de custo anual de produção de macieiras cvs Gala e Fuji nos sistemas de Produção Integrada e produção convencional (mar. 2001)
Rate maintenance and resonance in the entorhinal cortex
Throughout the brain, neurons encode information in fundamental units of spikes. Each spike represents the combined thresholding of synaptic inputs and intrinsic neuronal dynamics. Here, we address a basic question of spike train formation: how do perithreshold synaptic inputs perturb the output of a spiking neuron? We recorded from single entorhinal principal cells in vitro and drove them to spike steadily at ∼5 Hz (theta range) with direct current injection, then used a dynamic-clamp to superimpose strong excitatory conductance inputs at varying rates. Neurons spiked most reliably when the input rate matched the intrinsic neuronal firing rate. We also found a striking tendency of neurons to preserve their rates and coefficients of variation, independently of input rates. As mechanisms for this rate maintenance, we show that the efficacy of the conductance inputs varied with the relationship of input rate to neuronal firing rate, and with the arrival time of the input within the natural period. Using a novel method of spike classification, we developed a minimal Markov model that reproduced the measured statistics of the output spike trains and thus allowed us to identify and compare contributions to the rate maintenance and resonance. We suggest that the strength of rate maintenance may be used as a new categorization scheme for neuronal response and note that individual intrinsic spiking mechanisms may play a significant role in forming the rhythmic spike trains of activated neurons; in the entorhinal cortex, individual pacemakers may dominate production of the regional theta rhythm
Dynamical response of the Hodgkin-Huxley model in the high-input regime
The response of the Hodgkin-Huxley neuronal model subjected to stochastic
uncorrelated spike trains originating from a large number of inhibitory and
excitatory post-synaptic potentials is analyzed in detail. The model is
examined in its three fundamental dynamical regimes: silence, bistability and
repetitive firing. Its response is characterized in terms of statistical
indicators (interspike-interval distributions and their first moments) as well
as of dynamical indicators (autocorrelation functions and conditional
entropies). In the silent regime, the coexistence of two different coherence
resonances is revealed: one occurs at quite low noise and is related to the
stimulation of subthreshold oscillations around the rest state; the second one
(at intermediate noise variance) is associated with the regularization of the
sequence of spikes emitted by the neuron. Bistability in the low noise limit
can be interpreted in terms of jumping processes across barriers activated by
stochastic fluctuations. In the repetitive firing regime a maximization of
incoherence is observed at finite noise variance. Finally, the mechanisms
responsible for spike triggering in the various regimes are clearly identified.Comment: 14 pages, 24 figures in eps, submitted to Physical Review
Ultracold-neutron infrastructure for the gravitational spectrometer GRANIT
The gravitational spectrometer GRANIT will be set up at the Institut Laue
Langevin. It will profit from the high ultracold neutron density produced by a
dedicated source. A monochromator made of crystals from graphite intercalated
with potassium will provide a neutron beam with 0.89 nm incident on the source.
The source employs superthermal conversion of cold neutrons in superfluid
helium, in a vessel made from BeO ceramics with Be windows. A special
extraction technique has been tested which feeds the spectrometer only with
neutrons with a vertical velocity component v < 20 cm/s, thus keeping the
density in the source high. This new source is expected to provide a density of
up to 800 1/cm3 for the spectrometer.Comment: accepted for publication in Proceedings International Workshop on
Particle Physics with Slow Neutron
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