10,231 research outputs found
Are the input parameters of white-noise-driven integrate-and-fire neurons uniquely determined by rate and CV?
Integrate-and-fire (IF) neurons have found widespread applications in
computational neuroscience. Particularly important are stochastic versions of
these models where the driving consists of a synaptic input modeled as white
Gaussian noise with mean and noise intensity . Different IF models
have been proposed, the firing statistics of which depends nontrivially on the
input parameters and . In order to compare these models among each
other, one must first specify the correspondence between their parameters. This
can be done by determining which set of parameters (, ) of each model
is associated to a given set of basic firing statistics as, for instance, the
firing rate and the coefficient of variation (CV) of the interspike interval
(ISI). However, it is not clear {\em a priori} whether for a given firing rate
and CV there is only one unique choice of input parameters for each model. Here
we review the dependence of rate and CV on input parameters for the perfect,
leaky, and quadratic IF neuron models and show analytically that indeed in
these three models the firing rate and the CV uniquely determine the input
parameters
Topological Transitions for Lattice Bosons in a Magnetic Field
We study the Hall response of the Bose-Hubbard model subjected to a magnetic
field. We show that the Hall conductivity is proportional to the particle
density plus an integer. The phase diagram is intersected by topological
transitions between different integer values. These transitions originate from
points in the phase diagram with effective charge conjugation symmetry, and are
attributed to degeneracies in the many body spectrum which serve as sources for
the Berry curvature. We find that extensive regions in the phase diagram
exhibit a negative Hall conductivity, implying that flux flow is reversed in
these regions - vortices there flow upstream. We discuss experimental
implications of our findings.Comment: 11 pages, 7 figure
Optical distributed sensors for feedback control: Characterization of photorefractive resonator
The aim of the project was to explore, define, and assess the possibilities of optical distributed sensing for feedback control. This type of sensor, which may have some impacts in the dynamic control of deformable structures and the monitoring of small displacements, can be divided into data acquisition, data processing, and control design. Analogue optical techniques, because they are noninvasive and afford massive parallelism may play a significant role in the acquisition and the preprocessing of the data for such a sensor. Assessing these possibilities was the aim of the first stage of this project. The scope of the proposed research was limited to: (1) the characterization of photorefractive resonators and the assessment of their possible use as a distributed optical processing element; and (2) the design of a control system utilizing signals from distributed sensors. The results include a numerical and experimental study of the resonator below threshold, an experimental study of the effect of the resonator's transverse confinement on its dynamics above threshold, a numerical study of the resonator above threshold using a modal expansion approach, and the experimental test of this model. A detailed account of each investigation, including methodology and analysis of the results are also included along with reprints of published and submitted papers
Leptogenesis in models with keV sterile neutrino dark matter
We analyze leptogenesis in gauge extensions of the Standard Model with keV
sterile neutrino dark matter. We find that both the observed dark matter
abundance and the correct baryon asymmetry of the Universe can simultaneously
emerge in these models. Both the dark matter abundance and the leptogenesis are
controlled by the out of equilibrium decays of the same heavy right handed
neutrino.Comment: 6 pages, 1 figur
Distributed control for COFS 1
An overview is given of the work being done at NASA LaRC on developing the Control of Flexible Structures (COFS) 1 Flight Experiment Baseline Control Law. This control law currently evolving to a generic control system software package designed to supply many, but not all, guest investigators. A system simulator is also described. It is currently being developed for COFS-1 and will be used to develop the Baseline Control Law and to evaluate guest investigator control schemes. It will be available for use whether or not control schemes fall into the category of the Baseline Control Law. First, the hardware configuration for control experiments is described. This is followed by a description of the simulation software. Open-loop sinusoid excitation time histories are next presented both with and without a local controller for the Linear DC Motor (LDCM) actuators currently planned for the flight. The generic control law follows and algorithm processing requirements are cited for a nominal case of interest. Finally, a closed-loop simulation study is presented, and the state of the work is summarized in the concluding remarks
Neutrino Masses and Absence of Flavor Changing Interactions in the 2HDM from Gauge Principles
We propose several Two Higgs Doublet Models with the addition of an Abelian
gauge group which free the usual framework from flavor changing neutral
interactions and explain neutrino masses through the seesaw mechanism. We
discuss the kinetic and mass-mixing gripping phenomenology which encompass
several constraints coming from atomic parity violation, the muon anomalous
magnetic moment, rare meson decays, Higgs physics, LEP precision data,
neutrino-electron scattering, low energy accelerators and LHC probes.Comment: 54 pages, 10 figure
Signatures of axion-like particles in the spectra of TeV gamma-ray sources
One interpretation of the unexplained signature observed in the PVLAS
experiment invokes a new axion-like particle (ALP) with a two-photon vertex,
allowing for photon-ALP oscillations in the presence of magnetic fields. In the
range of masses and couplings suggested by PVLAS, the same effect would lead to
a peculiar dimming of high-energy photon sources. For typical parameters of the
turbulent magnetic field in the galaxy, the effect sets in at E_gamma >~ 10
TeV, providing an ALP signature in the spectra of TeV gamma sources that can be
probed with Cherenkov telescopes. A dedicated search will be strongly motivated
if the ongoing photon regeneration experiments confirm the PVLAS particle
interpretation.Comment: 8 pages, 1 eps figure; typos corrected, matches published versio
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