406 research outputs found
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
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.
Investigation of host liquid crystal composition on polymer stabilised blue phase properties
Polymer stabilised blue phase liquid crystals (PSBPLCs) have been investigated for photonics and display applications for the following reasons: optical isotropy in the dark state, ease of fabrication due to the omission of the alignment layer, and sub-millisecond response length. Major barriers to the commercialisation of PSBPLCs are: hysteresis, residual birefringence, and most significantly, high driving voltage. We have chosen to lower the driving voltage through optimization of the mixture (host LC, chiral dopant and monomer). In this paper, investigation of the contribution of the host liquid crystal to the phase stability and electro-optic characteristics of the PSBP will be discussed. The following cases have been investigated: a) A three component host liquid crystal (E8, PE-sCNF (4- Cyano-3-fluorophenyl 4-pentyl benzoate) and CPP-3FF (4-(trans-4-n-propyl cyclohexyl)-3',4'-difluoro-l,l'- biphenyl), LCC Corporation, Japan). For a ratio of E8:PE-CNF:CPP-3FF of 5:3:2, a large BPI window of >SO.4°C and low hysteresis was achieved, but the driving voltage was 79V, and b) A single host liquid crystal, 80CB with chiral dopant Clsl S. For a ratio for 80CB:CBls of 1:1, this mixture demonstrated a significantly lower driving voltage of 6SV, but exhibited a smaller BPI window of >27°C. Decrease in the ratio of 80CB:CBls also induced the presence of a BPII phase in the mixture. A single host liquid crystal has the advantage of simplicity of composition, and lowered driving voltage. However, the hysteresis and blue phase temperature range needs to be optimised. This investigation concludes upon the suggestion of liquid crystal characteristics which optimises the blue phase temperature range, low hysteresis, switching times and driving voltage
Linear stability analysis of retrieval state in associative memory neural networks of spiking neurons
We study associative memory neural networks of the Hodgkin-Huxley type of
spiking neurons in which multiple periodic spatio-temporal patterns of spike
timing are memorized as limit-cycle-type attractors. In encoding the
spatio-temporal patterns, we assume the spike-timing-dependent synaptic
plasticity with the asymmetric time window. Analysis for periodic solution of
retrieval state reveals that if the area of the negative part of the time
window is equivalent to the positive part, then crosstalk among encoded
patterns vanishes. Phase transition due to the loss of the stability of
periodic solution is observed when we assume fast alpha-function for direct
interaction among neurons. In order to evaluate the critical point of this
phase transition, we employ Floquet theory in which the stability problem of
the infinite number of spiking neurons interacting with alpha-function is
reduced into the eigenvalue problem with the finite size of matrix. Numerical
integration of the single-body dynamics yields the explicit value of the
matrix, which enables us to determine the critical point of the phase
transition with a high degree of precision.Comment: Accepted for publication in Phys. Rev.
Early warnings of the potential for malaria transmission in rural Africa using the hydrology, entomology and malaria transmission simulator (HYDREMATS)
<p>Abstract</p> <p>Background</p> <p>Early warnings of malaria transmission allow health officials to better prepare for future epidemics. Monitoring rainfall is recognized as an important part of malaria early warning systems. The Hydrology, Entomology and Malaria Simulator (HYDREMATS) is a mechanistic model that relates rainfall to malaria transmission, and could be used to provide early warnings of malaria epidemics.</p> <p>Methods</p> <p>HYDREMATS is used to make predictions of mosquito populations and vectorial capacity for 2005, 2006, and 2007 in Banizoumbou village in western Niger. HYDREMATS is forced by observed rainfall, followed by a rainfall prediction based on the seasonal mean rainfall for a period two or four weeks into the future.</p> <p>Results</p> <p>Predictions made using this method provided reasonable estimates of mosquito populations and vectorial capacity, two to four weeks in advance. The predictions were significantly improved compared to those made when HYDREMATS was forced with seasonal mean rainfall alone.</p> <p>Conclusions</p> <p>HYDREMATS can be used to make reasonable predictions of mosquito populations and vectorial capacity, and provide early warnings of the potential for malaria epidemics in Africa.</p
Thermochemical Investigations in the System Cadmium-Praseodymium Relevant for Pyrometallurgical Fuel Reprocessing
Biocompatibility of subretinal parylene-based Ti/Pt microelectrode array in rabbit for further artificial vision studies
To evaluate the biocompatibility of subretinal implanted parylene-based Ti/Pt microelectrode arrays (MEA). Eyes were enucleated 3 months after MEAs were implanted into the subretinal space of rabbits. Morphological changes of the retinas were investigated by H&E staining. Immunohistochemical staining for glial fibrillary acidic protein and opsin were performed to evaluate changes in Muller cells and photoreceptors in the retinas. Retina tissue around the array remained intact. Photoreceptor degeneration and glial cell activation were observed in the retina overlaying the MEA implant. However, the cells in the inner retinal layers were preserved. Photoreceptor degeneration and glial cell activation at the MEA–retina interface are expected to be a normal reaction to implantation. Material used in this experiment has good biocompatibility within the subretinal environment and is expected to be promising in the further retinal prosthesis studies
Cortical-Bone Fragility - Insights from sFRP4 Deficiency in Pyle's Disease
BACKGROUND
Cortical-bone fragility is a common feature in osteoporosis that is linked to non
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vertebral fractures. Regulation of cortical-bone homeostasis has proved elusive. The
study of genetic disorders of the skeleton can yield insights that fuel experimental
therapeutic approaches to the treatment of rare disorders and common skeletal
ailments.
METHODS
We evaluated four patients with Pyle’s disease, a genetic disorder that is characterized
by cortical-bone thinning, limb deformity, and fractures; two patients were examined
by means of exome sequencing, and two were examined by means of Sanger se
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quencing. After a candidate gene was identified, we generated a knockout mouse
model that manifested the phenotype and studied the mechanisms responsible for
altered bone architecture.
RESULTS
In all affected patients, we found biallelic truncating mutations in
SFR P4
, the gene
encoding secreted frizzled-related protein 4, a soluble Wnt inhibitor. Mice deficient
in
Sfrp4
, like persons with Pyle’s disease, have increased amounts of trabecular bone
and unusually thin cortical bone, as a result of differential regulation of Wnt and
bone morphogenetic protein (BMP) signaling in these two bone compartments. Treat
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ment of
Sfrp4-
deficient mice with a soluble Bmp2 receptor (RAP-661) or with anti
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bodies to sclerostin corrected the cortical-bone defect.
CONCLUSIONS
Our study showed that Pyle’s disease was caused by a deficiency of sFRP4, that cortical-
bone and trabecular-bone homeostasis were governed by different mechanisms, and
that sFRP4-mediated cross-regulation between Wnt and BMP signaling was critical
for achieving proper cortical-bone thickness and stability. (Funded by the Swiss Na
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tional Foundation and the National Institutes of Health.
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