301 research outputs found
Oscillator neural network model with distributed native frequencies
We study associative memory of an oscillator neural network with distributed
native frequencies. The model is based on the use of the Hebb learning rule
with random patterns (), and the distribution function of
native frequencies is assumed to be symmetric with respect to its average.
Although the system with an extensive number of stored patterns is not allowed
to get entirely synchronized, long time behaviors of the macroscopic order
parameters describing partial synchronization phenomena can be obtained by
discarding the contribution from the desynchronized part of the system. The
oscillator network is shown to work as associative memory accompanied by
synchronized oscillations. A phase diagram representing properties of memory
retrieval is presented in terms of the parameters characterizing the native
frequency distribution. Our analytical calculations based on the
self-consistent signal-to-noise analysis are shown to be in excellent agreement
with numerical simulations, confirming the validity of our theoretical
treatment.Comment: 9 pages, revtex, 6 postscript figures, to be published in J. Phys.
Stochastic transitions of attractors in associative memory models with correlated noise
We investigate dynamics of recurrent neural networks with correlated noise to
analyze the noise's effect. The mechanism of correlated firing has been
analyzed in various models, but its functional roles have not been discussed in
sufficient detail. Aoyagi and Aoki have shown that the state transition of a
network is invoked by synchronous spikes. We introduce two types of noise to
each neuron: thermal independent noise and correlated noise. Due to the effects
of correlated noise, the correlation between neural inputs cannot be ignored,
so the behavior of the network has sample dependence. We discuss two types of
associative memory models: one with auto- and weak cross-correlation
connections and one with hierarchically correlated patterns. The former is
similar in structure to Aoyagi and Aoki's model. We show that stochastic
transition can be presented by correlated rather than thermal noise. In the
latter, we show stochastic transition from a memory state to a mixture state
using correlated noise. To analyze the stochastic transitions, we derive a
macroscopic dynamic description as a recurrence relation form of a probability
density function when the correlated noise exists. Computer simulations agree
with theoretical results.Comment: 21 page
Vibrational effect on the fragmentation dynamics of the C K-shell excited CF2CH2
Photoabsorption cross-sections of CF2CH2 were measured in the carbon K-edge region and linear time-of-flight mass spectra were acquired at some photon energies across the two π* peaks. The kinetic energy distributions of CH2+ and CF2+ with two components were deduced from the analysis of the mass spectra. The CH2+ ion with high kinetic energies increases with the extent of vibrational excitation of the CF 1s-1π* state, indicating that molecular vibrations play an important role in the photofragmentation of the inner-shell excited molecule
Sugar metabolism in expanding husk leaves of flint corn (Zea mays L.) genotypes differing in husk leaf size
Relationships between leaf expansion and MeOH-soluble (cytosol) and cell-wall fractions, and their sugar composition prior to silking in flint corn lines were studied. A greater husk leaf area of one genotype, X-15 is mainly due to prolonged and higher rate of expansion. Prior to rapid expansion of husk leaf area, neutral sugars in the cytosol fraction accounted for most of the non-starch carbohydrates (56-62%), while hemicellulose and cellulose fractions accounted for less than 20%.0 In mature leaf parts, however, sugars in the cytosol fraction decreased but those in hemicellulose and cellulose fractions increased by 30 0x1.e499cp-891nd 42%, respectively. The predominant sugar in the cytosol fraction was glucose (Glc), while in the hemicellulose fraction xylose (Xyl) and arabinose (Ara) dominated. During rapid expansion of husk leaves, 13C was incorporated at a higher rate into hemicellulose than cellulose, and this process was more active in X-15 than in other genotypes. During an identical period, 13C atom 0.000000e+00xcess in Xyl increased markedly in the hemicellulose fraction, however it remained low in the cytosol one. The current results suggest that synthesis of Xyl and xylan plays an important role in renewal of hemicellulose, which may be required for expansion
Adenomatous Polyposis Coli Regulates Axon Arborization and Cytoskeleton Organization via Its N-Terminus
Conditional deletion of APC leads to marked disruption of cortical development and to excessive axonal branching of cortical neurons. However, little is known about the cell biological basis of this neuronal morphological regulation. Here we show that APC deficient cortical neuronal growth cones exhibit marked disruption of both microtubule and actin cytoskeleton. Functional analysis of the different APC domains revealed that axonal branches do not result from stabilized β-catenin, and that the C-terminus of APC containing microtubule regulatory domains only partially rescues the branching phenotype. Surprisingly, the N-terminus of APC containing the oligomerization domain and the armadillo repeats completely rescues the branching and cytoskeletal abnormalities. Our data indicate that APC is required for appropriate axon morphological development and that the N-terminus of APC is important for regulation of the neuronal cytoskeleton
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