871 research outputs found
Nonlocal mechanism for cluster synchronization in neural circuits
The interplay between the topology of cortical circuits and synchronized
activity modes in distinct cortical areas is a key enigma in neuroscience. We
present a new nonlocal mechanism governing the periodic activity mode: the
greatest common divisor (GCD) of network loops. For a stimulus to one node, the
network splits into GCD-clusters in which cluster neurons are in zero-lag
synchronization. For complex external stimuli, the number of clusters can be
any common divisor. The synchronized mode and the transients to synchronization
pinpoint the type of external stimuli. The findings, supported by an
information mixing argument and simulations of Hodgkin Huxley population
dynamic networks with unidirectional connectivity and synaptic noise, call for
reexamining sources of correlated activity in cortex and shorter information
processing time scales.Comment: 8 pges, 6 figure
Nonlinear Impurity Modes in Homogeneous and Periodic Media
We analyze the existence and stability of nonlinear localized waves described
by the Kronig-Penney model with a nonlinear impurity. We study the properties
of such waves in a homogeneous medium, and then analyze new effects introduced
by periodicity of the medium parameters. In particular, we demonstrate the
existence of a novel type of stable nonlinear band-gap localized states, and
also reveal an important physical mechanism of the oscillatory wave
instabilities associated with the band-gap wave resonances.Comment: 11 pages, 3 figures; To be published in: Proceedings of the NATO
Advanced Research Workshop "Nonlinearity and Disorder: Theory and
Applications" (Tashkent, 2-6 Oct, 2000) Editors: P.L. Christiansen and F.K.
Abdullaev (Kluwer, 2001
Exact solution of a linear molecular motor model driven by two-step fluctuations and subject to protein friction
We investigate by analytical means the stochastic equations of motion of a
linear molecular motor model based on the concept of protein friction. Solving
the coupled Langevin equations originally proposed by Mogilner et al. (A.
Mogilner et al., Phys. Lett. {\bf 237}, 297 (1998)), and averaging over both
the two-step internal conformational fluctuations and the thermal noise, we
present explicit, analytical expressions for the average motion and the
velocity-force relationship. Our results allow for a direct interpretation of
details of this motor model which are not readily accessible from numerical
solutions. In particular, we find that the model is able to predict
physiologically reasonable values for the load-free motor velocity and the
motor mobility.Comment: 12 pages revtex, 6 eps-figure
myTunes: Digital music library users and their self-images
This investigation explored the relationships between individuals’ self-images and their interactions with their digital music collections via the commercially predominant program iTunes. Sixty-nine university students completed an internet-based Musical Self-Images Questionnaire (MSIQ) along with a series of questions concerning their iTunes collections. The majority of participants were highly engaged with music, regardless of their varied musical backgrounds. Factor analysis of the MSIQ data revealed two distinct self-image groups, which we label as ‘musical practitioner’ (linking ‘overall musician’, ‘performer’, ‘composer’, ‘teacher’, and ‘listener’) and ‘music consumer’ (linking ‘listener’, ‘fan’, and ‘technology user’). Participants used an average of seven attributes to categorize their music, and most consistently used one in particular to sort their collections. Those who rated themselves as higher level performers and fans used the playlist function (which involves compiling sequences of selected tracks) more often than those with lower self-ratings on those scales
Dopant-induced crossover from 1D to 3D charge transport in conjugated polymers
The interplay between inter- and intra-chain charge transport in bulk
polythiophene in the hopping regime has been clarified by studying the
conductivity as a function of frequency (up to 3 THz), temperature and doping
level. We present a model which quantitatively explains the observed crossover
from quasi-one-dimensional transport to three-dimensional hopping conduction
with increasing doping level. At high frequencies the conductivity is dominated
by charge transport on one-dimensional conducting chains.Comment: 4 pages, 2 figure
Music for all: Identifying, challenging and overcoming barriers
A great deal of change has occurred within UK music education over the past decade. There were good intentions behind some of the changes; for example, the government had an ambition to provide everyone with access to music education during their school years. The timing of such initiatives, however, was unfortunate. Within the context of financial austerity and the subsequent cuts to public spending, education budgets came under increasing pressure. This article examines the current challenges facing music education within England and raises questions for researchers to consider as the future direction of research in the field starts to take shape
Inter- and Intragranular Effects in Superconducting Compacted Platinum Powders
Compacted platinum powders exhibit a sharp onset of diamagnetic screening at
mK in zero magnetic field in all samples investigated. This
sharp onset is interpreted in terms of the intragranular transition into the
superconducting state. At lower temperatures, the magnetic ac susceptibility
strongly depends on the ac field amplitude and reflects the small intergranular
critical current density . This critical current density shows a strong
dependence on the packing fraction f of the granular samples. Surprisingly,
increases significantly with decreasing f ( A/cm for f = 0.67 and A/cm for f
= 0.50). The temperature dependence of shows strong positive curvature
over a wide temperature range for both samples. The phase diagrams of inter-
and intragranular superconductivity for different samples indicate that the
granular structure might play the key role for an understanding of the origin
of superconductivity in the platinum compacts.Comment: 11 pages including 9 figures. To appear in Phys. Rev. B in Nov. 0
Mitochondrial myopathy presenting as fibromyalgia: a case report
<p>Abstract</p> <p>Introduction</p> <p>To the best of our knowledge, we describe for the first time the case of a woman who met the diagnostic criteria for fibromyalgia, did not respond to therapy for that disorder, and was subsequently diagnosed by biochemical and genetic studies with a mitochondrial myopathy. Treatment of the mitochondrial myopathy resulted in resolution of symptoms. This case demonstrates that mitochondrial myopathy may present in an adult with a symptom complex consistent with fibromyalgia.</p> <p>Case presentation</p> <p>Our patient was a 41-year-old Caucasian woman with symptoms of fatigue, exercise intolerance, headache, and multiple trigger points. Treatment for fibromyalgia with a wide spectrum of medications including non-steroidal anti-inflammatory drugs, antidepressants, gabapentin and pregabalin had no impact on her symptoms. A six-minute walk study demonstrated an elevated lactic acid level (5 mmol/L; normal < 2 mmol/L). Biochemical and genetic studies from a muscle biopsy revealed a mitochondrial myopathy. Our patient was started on a compound of coenzyme Q10 (ubiquinone) 200 mg, creatine 1000 mg, carnitine 200 mg and folic acid 1 mg to be taken four times a day. She gradually showed significant improvement in her symptoms over a course of several months.</p> <p>Conclusions</p> <p>This case demonstrates that adults diagnosed with fibromyalgia may have their symptom complex related to an adult onset mitochondrial myopathy. This is an important finding since treatment of mitochondrial myopathy resulted in resolution of symptoms.</p
Density-dependence of functional development in spiking cortical networks grown in vitro
During development, the mammalian brain differentiates into specialized
regions with distinct functional abilities. While many factors contribute to
functional specialization, we explore the effect of neuronal density on the
development of neuronal interactions in vitro. Two types of cortical networks,
dense and sparse, with 50,000 and 12,000 total cells respectively, are studied.
Activation graphs that represent pairwise neuronal interactions are constructed
using a competitive first response model. These graphs reveal that, during
development in vitro, dense networks form activation connections earlier than
sparse networks. Link entropy analysis of dense net- work activation graphs
suggests that the majority of connections between electrodes are reciprocal in
nature. Information theoretic measures reveal that early functional information
interactions (among 3 cells) are synergetic in both dense and sparse networks.
However, during later stages of development, previously synergetic
relationships become primarily redundant in dense, but not in sparse networks.
Large link entropy values in the activation graph are related to the domination
of redundant ensembles in late stages of development in dense networks. Results
demonstrate differences between dense and sparse networks in terms of
informational groups, pairwise relationships, and activation graphs. These
differences suggest that variations in cell density may result in different
functional specialization of nervous system tissue in vivo.Comment: 10 pages, 7 figure
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