1,553 research outputs found
Decorrelation of neural-network activity by inhibitory feedback
Correlations in spike-train ensembles can seriously impair the encoding of
information by their spatio-temporal structure. An inevitable source of
correlation in finite neural networks is common presynaptic input to pairs of
neurons. Recent theoretical and experimental studies demonstrate that spike
correlations in recurrent neural networks are considerably smaller than
expected based on the amount of shared presynaptic input. By means of a linear
network model and simulations of networks of leaky integrate-and-fire neurons,
we show that shared-input correlations are efficiently suppressed by inhibitory
feedback. To elucidate the effect of feedback, we compare the responses of the
intact recurrent network and systems where the statistics of the feedback
channel is perturbed. The suppression of spike-train correlations and
population-rate fluctuations by inhibitory feedback can be observed both in
purely inhibitory and in excitatory-inhibitory networks. The effect is fully
understood by a linear theory and becomes already apparent at the macroscopic
level of the population averaged activity. At the microscopic level,
shared-input correlations are suppressed by spike-train correlations: In purely
inhibitory networks, they are canceled by negative spike-train correlations. In
excitatory-inhibitory networks, spike-train correlations are typically
positive. Here, the suppression of input correlations is not a result of the
mere existence of correlations between excitatory (E) and inhibitory (I)
neurons, but a consequence of a particular structure of correlations among the
three possible pairings (EE, EI, II)
Signatures of current loop coalescence in solar flares
The nonlinear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic emission as well as the characteristics of 2-D microwave images obtained during a solar flare. The physical characteristics of the explosive coalescence of currents are presented in detail through computer simulation and theory. Canonical characteristics of the explosive coalescence are: (1) a large amount of impulsive increase of kinetic energies of electrons and ions; (2) simultaneous heating and acceleration of electrons and ions in high and low energy spectra; (3) ensuing quasi-periodic amplitude oscillations in fields and particle quantities; and (4) the double peak (or triple peak) structure in these profiles, participate in the coalescence process, yielding varieties of phenomena
Chemistry on the inside: green chemistry in mesoporous materials
An overview of the rapidly expanding area of tailored mesoporous solids is presented. The synthesis of a wide range of the materials is covered, both inorganically and organically modified. Their applications, in particular those relating to green chemistry, are also highlighted. Finally, potential future directions for these materials are discussed
太陽フレアーにおける融合不安定
Double sub-peak structures in the quasi-periodic oscillations found in the time profiles of two solar flares on 1980 June 7 and 1982 November 26 are well explained in terms of the coalescence instability of two current loops. This interpretation is supported by the observations of two microwave sources and their interaction for the November 26 flare. The difference of both sub-peak structures and time scales between the two flares are discussed from the viewpoint of different plasma parameters in our computer simulations
Fermionic field theory for directed percolation in (1+1) dimensions
We formulate directed percolation in (1+1) dimensions in the language of a
reaction-diffusion process with exclusion taking place in one space dimension.
We map the master equation that describes the dynamics of the system onto a
quantum spin chain problem. From there we build an interacting fermionic field
theory of a new type. We study the resulting theory using renormalization group
techniques. This yields numerical estimates for the critical exponents and
provides a new alternative analytic systematic procedure to study
low-dimensional directed percolation.Comment: 20 pages, 2 figure
ソーラーフレアーにおける電流ループのコアレッセンス
The nonlinear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic emission as well as the characteristics of 2-D microwave images obtained during a solar flare. The physical characteristics of the explosive coalescence of currents are presented in detail through computer simulation and theory.Canonical characteristics of the explosive coalescence are: (1) a large amount of impulsive increase of kinetic energies of electrons and ions, (2) simultaneous heating and acceleration of electrons and ions in high and low energy spectra, (3) ensuing quasi-periodic amplitude oscillations in fields and particle quantities, (4) the double peak (or triple peak) structure in these profiles, and (5) characteristic break in energy spectra of electrons and ions. A single pair of currents as well as multiple currents may participate in the coalescence process, yielding varieties of phenomena. These physical properties seem to underlie in some of impulsive solar flares.In particular, double sub-peak structures in the quasi-periodic oscillations found in the time profiles of two solar flares on June 7, 1980 and November 26, 1982 are well explained in terms of the coalescence instability of two current loops. This interpretation is supported by the observations of two microwave sources and their interaction for the November 26, 1982 flare.Some more details as well as a generalization of the present model to solar flares with the coalescence as an elementary process in the flare phenomenon are presented
太陽フレアーにおけるCoalescence不安定
The non-linear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic emission as well as the characteristics of 2-D microwave images obtained during a flare. The plasma compressibility leads to the explosive phase of loop coalescence and its overshoot results in amplitude oscillations in temperatures by adiabatic compression and decompression. We note that the presence of strong electric fields and super-Alfvenic flows during the course of the instabilty paly an important role in the production of non-thermal particles. A qualitative explanation on the physical processes taking place during the non-linear stages of the instability is given
Mutual Information of Population Codes and Distance Measures in Probability Space
We studied the mutual information between a stimulus and a large system
consisting of stochastic, statistically independent elements that respond to a
stimulus. The Mutual Information (MI) of the system saturates exponentially
with system size. A theory of the rate of saturation of the MI is developed. We
show that this rate is controlled by a distance function between the response
probabilities induced by different stimuli. This function, which we term the
{\it Confusion Distance} between two probabilities, is related to the Renyi
-Information.Comment: 11 pages, 3 figures, accepted to PR
速い無衝突磁気再結合の計算機によるモデル化
Particle simulations of collisionless tearing, reconnection and coalescence of magnetic fields for a sheet-pinch configuration show that reconnection is Sweet-Parker like in the tearing and island formation phase. It is much faster to explosive in the island coalescence stage. Island coalescence is the most energetic process arrl leads to large ion temperature increase and oscillations in the merged state. Similar phenomena have been observed in equivalent MHD simulations.Coalescence and its effects, as observed in our simulations, may explain many of the features of solar flares and coronal X-ray brightening
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