79,419 research outputs found
Dynamic flexoelectric effect in perovskites from first principles calculations
Using the dynamical matrix of a crystal obtained from ab initio calculations,
we have evaluated for the first time the strength of the dynamic flexoelectric
effect and found it comparable to that of the static bulk flexoelectric effect,
in agreement with earlier order-of-magnitude estimates. We also proposed a
method of evaluation of these effects directly from the simulated phonon
spectra. This method can also be applied to the analysis of the experimental
phonon spectra, being currently the only one enabling experimental
characterization of the static bulk flexoelectric effect
Ground-state landscape of 2d +-J Ising spin glasses
Large numbers of ground states of two-dimensional Ising spin glasses with
periodic boundary conditions in both directions are calculated for sizes up to
40^2. A combination of a genetic algorithm and Cluster-Exact Approximation is
used. For each quenched realization of the bonds up to 40 independent ground
states are obtained.
For the infinite system a ground-state energy of e=-1.4015(3) is
extrapolated. The ground-state landscape is investigated using a finite-size
scaling analysis of the distribution of overlaps. The mean-field picture
assuming a complex landscape describes the situation better than the
droplet-scaling model, where for the infinite system mainly two ground states
exist. Strong evidence is found that the ground states are not organized in an
ultrametric fashion in contrast to previous results for three-dimensional spin
glasses.Comment: 9 pages, revtex, 11 figures, 51 reference
Output Stream of Binding Neuron with Feedback
The binding neuron model is inspired by numerical simulation of
Hodgkin-Huxley-type point neuron, as well as by the leaky integrate-and-fire
model. In the binding neuron, the trace of an input is remembered for a fixed
period of time after which it disappears completely. This is in the contrast
with the above two models, where the postsynaptic potentials decay
exponentially and can be forgotten only after triggering. The finiteness of
memory in the binding neuron allows one to construct fast recurrent networks
for computer modeling. Recently, the finiteness is utilized for exact
mathematical description of the output stochastic process if the binding neuron
is driven with the Poissonian input stream. In this paper, the simplest
networking is considered for binding neuron. Namely, it is expected that every
output spike of single neuron is immediately fed into its input. For this
construction, externally fed with Poissonian stream, the output stream is
characterized in terms of interspike interval probability density distribution
if the binding neuron has threshold 2. For higher thresholds, the distribution
is calculated numerically. The distributions are compared with those found for
binding neuron without feedback, and for leaky integrator. Sample distributions
for leaky integrator with feedback are calculated numerically as well. It is
oncluded that even the simplest networking can radically alter spikng
statistics. Information condensation at the level of single neuron is
discussed.Comment: Version #1: 4 pages, 5 figures, manuscript submitted to Biological
Cybernetics. Version #2 (this version): added 3 pages of new text with
additional analytical and numerical calculations, 2 more figures, 11 more
references, added Discussion sectio
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