536 research outputs found
Action Potential Onset Dynamics and the Response Speed of Neuronal Populations
The result of computational operations performed at the single cell level are
coded into sequences of action potentials (APs). In the cerebral cortex, due to
its columnar organization, large number of neurons are involved in any
individual processing task. It is therefore important to understand how the
properties of coding at the level of neuronal populations are determined by the
dynamics of single neuron AP generation. Here we analyze how the AP generating
mechanism determines the speed with which an ensemble of neurons can represent
transient stochastic input signals. We analyze a generalization of the
-neuron, the normal form of the dynamics of Type-I excitable membranes.
Using a novel sparse matrix representation of the Fokker-Planck equation, which
describes the ensemble dynamics, we calculate the transmission functions for
small modulations of the mean current and noise noise amplitude. In the
high-frequency limit the transmission function decays as ,
where surprisingly depends on the phase at which APs are
emitted. In a physiologically plausible regime up to 1kHz the typical response
speed is, however, independent of the high-frequency limit and is set by the
rapidness of the AP onset, as revealed by the full transmission function. In
this regime modulations of the noise amplitude can be transmitted faithfully up
to much higher frequencies than modulations in the mean input current. We
finally show that the linear response approach used is valid for a large regime
of stimulus amplitudes.Comment: Submitted to the Journal of Computational Neuroscienc
Fingerprints of classical diffusion in open 2D mesoscopic systems in the metallic regime
We investigate the distribution of the resonance widths
and Wigner delay times for scattering from two-dimensional
systems in the diffusive regime. We obtain the forms of these distributions
(log-normal for large and small , and power law in the
opposite case) for different symmetry classes and show that they are determined
by the underlying diffusive classical dynamics. Our theoretical arguments are
supported by extensive numerical calculations.Comment: 7 pages, 3 figure
An Examination of Adult Bullying in the K-12 Workplace: Implications for School Leaders
The issue of bullying in K-12 schools usually brings images of students to mind, but a recent quantitative study of a sample from K-12 school personnel in Michigan showed that 27.8% of adults in the K-12 workplace consider themselves the target of an adult bully. This study calls for school leadership to recognize and proactively address the issue of workplace bullying in K-12 schools through policy, procedures, training, prevention, enforcement, and positive resolution to provide a safe, non-threatening environment in which to work and learn
Levy Flights in Inhomogeneous Media
We investigate the impact of external periodic potentials on superdiffusive
random walks known as Levy flights and show that even strongly superdiffusive
transport is substantially affected by the external field. Unlike ordinary
random walks, Levy flights are surprisingly sensitive to the shape of the
potential while their asymptotic behavior ceases to depend on the Levy index
. Our analysis is based on a novel generalization of the Fokker-Planck
equation suitable for systems in thermal equilibrium. Thus, the results
presented are applicable to the large class of situations in which
superdiffusion is caused by topological complexity, such as diffusion on folded
polymers and scale-free networks.Comment: 4 pages, 4 figure
Anomalous diffusion as a signature of collapsing phase in two dimensional self-gravitating systems
A two dimensional self-gravitating Hamiltonian model made by
fully-coupled classical particles exhibits a transition from a collapsing phase
(CP) at low energy to a homogeneous phase (HP) at high energy. From a dynamical
point of view, the two phases are characterized by two distinct single-particle
motions : namely, superdiffusive in the CP and ballistic in the HP. Anomalous
diffusion is observed up to a time that increases linearly with .
Therefore, the finite particle number acts like a white noise source for the
system, inhibiting anomalous transport at longer times.Comment: 10 pages, Revtex - 3 Figs - Submitted to Physical Review
Metal-insulator transitions in cyclotron resonance of periodic nanostructures due to avoided band crossings
A recently found metal-insulator transition in a model for cyclotron
resonance in a two-dimensional periodic potential is investigated by means of
spectral properties of the time evolution operator. The previously found
dynamical signatures of the transition are explained in terms of avoided band
crossings due to the change of the external electric field. The occurrence of a
cross-like transport is predicted and numerically confirmed
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