9,078 research outputs found
Synchronization and oscillatory dynamics in heterogeneous mutually inhibited neurons
We study some mechanisms responsible for synchronous oscillations and loss of
synchrony at physiologically relevant frequencies (10-200 Hz) in a network of
heterogeneous inhibitory neurons. We focus on the factors that determine the
level of synchrony and frequency of the network response, as well as the
effects of mild heterogeneity on network dynamics. With mild heterogeneity,
synchrony is never perfect and is relatively fragile. In addition, the effects
of inhibition are more complex in mildly heterogeneous networks than in
homogeneous ones. In the former, synchrony is broken in two distinct ways,
depending on the ratio of the synaptic decay time to the period of repetitive
action potentials (), where can be determined either from the
network or from a single, self-inhibiting neuron. With ,
corresponding to large applied current, small synaptic strength or large
synaptic decay time, the effects of inhibition are largely tonic and
heterogeneous neurons spike relatively independently. With ,
synchrony breaks when faster cells begin to suppress their less excitable
neighbors; cells that fire remain nearly synchronous. We show numerically that
the behavior of mildly heterogeneous networks can be related to the behavior of
single, self-inhibiting cells, which can be studied analytically.Comment: 17 pages, 6 figures, Kluwer.sty. Journal of Compuational Neuroscience
(in press). Originally submitted to the neuro-sys archive which was never
publicly announced (was 9802001
Comprehensive theory of the relative phase in atom-field interactions
We explore the role played by the quantum relative phase in a well-known
model of atom-field interaction, namely, the Dicke model. We introduce an
appropriate polar decomposition of the atom-field relative amplitudes that
leads to a truly Hermitian relative-phase operator, whose eigenstates correctly
describe the phase properties, as we demonstrate by studying the positive
operator-valued measure derived from it. We find the probability distribution
for this relative phase and, by resorting to a numerical procedure, we study
its time evolution.Comment: 20 pages, 4 figures, submitted to Phys. Rev.
Pilot study of vegetation in the Alchichica-Perote region by remote sensing
A study of the application of satellite images to the identification of vegetation in a small area corresponding to the arid zone of Veracruz and part of Puebla is presented. This study is accomplished by means of images from the LANDSAT satellite obtained on January 19 and May 23, 1973. The interpretation of the different maps is made on the basis of information from the data bank of the Flora de Veracruz program, and various surveys made by land and air
Dissipative vortex solitons in 2D-lattices
We report the existence of stable symmetric vortex-type solutions for
two-dimensional nonlinear discrete dissipative systems governed by a
cubic-quintic complex Ginzburg-Landau equation. We construct a whole family of
vortex solitons with a topological charge S = 1. Surprisingly, the dynamical
evolution of unstable solutions of this family does not alter significantly
their profile, instead their phase distribution completely changes. They
transform into two-charges swirl-vortex solitons. We dynamically excite this
novel structure showing its experimental feasibility.Comment: 4 pages, 20 figure
The all-particle energy spectrum of cosmic rays from 10 TeV to 1 PeV measured with HAWC
The HAWC observatory is an air-shower detector, which is designed to study
both astrophysical gamma-rays in the TeV region and galactic cosmic rays in the
energy interval from 1 TeV to 1 PeV. This energy regime is quite interesting
for cosmic ray research, since indirect observations overlap with direct
measurements, which offers the opportunity for cross calibration and studies of
experimental systematic errors in both techniques. One quantity that could help
for this purpose is the all-particle energy spectrum of cosmic rays. In this
work, we present an update of HAWC measurements on the total cosmic-ray energy
spectrum between 10 TeV and 1 PeV. The spectrum was obtained from an unfolding
analysis of almost two years of HAWC's data, which was collected from January,
2018 to December, 2019. For the energy estimation, we employed the high-energy
hadronic interaction model QGSJET-II-04. As in a previous work of HAWC,
published in 2017, we observed the presence of a knee-like feature in the
region of tens of TeV.Comment: Submission to SciPos
Morphological number-count and redshift distributions to I < 26 from the Hubble Deep Field: Implications for the evolution of Ellipticals, Spirals and Irregulars
We combine the photometric redshift data of Fernandez-Soto et al. (1997) with
the morphological data of Odewahn et al. (1996) for all galaxies with I < 26.0
detected in the Hubble Deep Field. From this combined catalog we generate the
morphological galaxy number-counts and corresponding redshift distributions and
compare these to the predictions of high normalization zero- and passive-
evolution models. From this comparison we conclude the following: (1) E/S0s are
seen in numbers and over a redshift range consistent with zero- or minimal
passive- evolution to I = 24. Beyond this limit fewer E/S0s are observed than
predicted implying a net negative evolutionary process --- luminosity dimming,
disassembly or masking by dust --- at I > 24. (2) Spiral galaxies are present
in numbers consistent with zero- evolution predictions to I = 22. Beyond this
magnitude some net- positive evolution is required. Although the number-counts
are consistent with the passive-evolution predictions to I=26.0 the redshift
distributions favor number AND luminosity evolution. (3) There is no obvious
explanation for the late-type/irregular class and this category requires
further subdivision. While a small fraction of the population lies at low
redshift (i.e. true irregulars), the majority lie at redshifts, 1 < z < 3. At z
> 1.5 mergers are frequent and, taken in conjunction with the absence of normal
spirals at z > 2, the logical inference is that they represent the progenitors
of normal spirals forming via hierarchical merging.Comment: Accepted for publication in ApJ Letters, colour plates available from
http://www.phys.unsw.edu.au/~spd/bib.htm
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