1,987 research outputs found
Electronic Circuit to Mimic the Neural Network for the Saccade Controller
The proposed device is an electronic circuit that mimics the neural network controlling fast eye movements, or saccades. The device simulates the signals produced by each neuronal population during the control of a horizontal saccade and allows for observing and recording. It will serve as a valuable teaching tool in the field of neural control. Furthermore, the device will have applications in the realm of diagnosing and properly treating brain injury. Finally, this device could be incorporated into a system for controlling the eye movements of a realistic, artificially intelligent robot.
The FitzHugh-Nagumo model of the action potential is used as a foundation to mimic the signals produced by the neurons in question. This is a proven framework, and provides a simple empirical model that can be customized according to the properties of a given neuron. Each neuron will be printed on a circuit board that can be bypassed to simulate a lesion. A current pulse will serve as an input, but in the future, this may be replaced with feedback from a robot. This product is unique in that an analog circuit model of this neural network has not been built before
State-dependent diffusion: thermodynamic consistency and its path integral formulation
The friction coefficient of a particle can depend on its position as it does
when the particle is near a wall. We formulate the dynamics of particles with
such state-dependent friction coefficients in terms of a general Langevin
equation with multiplicative noise, whose evaluation requires the introduction
of specific rules. Two common conventions, the Ito and the Stratonovich,
provide alternative rules for evaluation of the noise, but other conventions
are possible. We show the requirement that a particle's distribution function
approach the Boltzmann distribution at long times dictates that a drift term
must be added to the Langevin equation. This drift term is proportional to the
derivative of the diffusion coefficient times a factor that depends on the
convention used to define the multiplicative noise. We explore the consequences
of this result in a number examples with spatially varying diffusion
coefficients. We also derive path integral representations for arbitrary
interpretation of the noise, and use it in a perturbative study of correlations
in a simple system.Comment: 18 pages, 8 figures, Accepted to PR
Path Integral Approach to 't Hooft's Derivation of Quantum from Classical Physics
We present a path-integral formulation of 't Hooft's derivation of quantum
from classical physics. The crucial ingredient of this formulation is Gozzi et
al.'s supersymmetric path integral of classical mechanics. We quantize
explicitly two simple classical systems: the planar mathematical pendulum and
the Roessler dynamical system.Comment: 29 pages, RevTeX, revised version with minor changes, accepted to
Phys. Rev.
Dynamics of a stretched nonlinear polymer chain
We study the relaxation dynamics of a coarse-grained polymer chain at
different degrees of stretching by both analytical means and numerical
simulations. The macromolecule is modelled as a string of beads, connected by
anharmonic springs, subject to a tensile force applied at the end monomer of
the chain while the other end is fixed at the origin of coordinates. The impact
of bond non-linearity on the relaxation dynamics of the polymer at different
degrees of stretching is treated analytically within the Gaussian
self-consistent approach (GSC) and then compared to simulation results derived
from two different methods: Monte-Carlo (MC) and Molecular Dynamics (MD).
At low and medium degrees of chain elongation we find good agreement between
GSC predictions and the Monte-Carlo simulations. However, for strongly
stretched chains the MD method, which takes into account inertial effects,
reveals two important aspects of the nonlinear interaction between monomers:
(i) a coupling and energy transfer between the damped, oscillatory normal modes
of the chain, and (ii) the appearance of non-vanishing contributions of a
continuum of frequencies around the characteristic modes in the power spectrum
of the normal mode correlation functions.Comment: 17 pages, 9 figure
The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe
The preponderance of matter over antimatter in the early Universe, the
dynamics of the supernova bursts that produced the heavy elements necessary for
life and whether protons eventually decay --- these mysteries at the forefront
of particle physics and astrophysics are key to understanding the early
evolution of our Universe, its current state and its eventual fate. The
Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed
plan for a world-class experiment dedicated to addressing these questions. LBNE
is conceived around three central components: (1) a new, high-intensity
neutrino source generated from a megawatt-class proton accelerator at Fermi
National Accelerator Laboratory, (2) a near neutrino detector just downstream
of the source, and (3) a massive liquid argon time-projection chamber deployed
as a far detector deep underground at the Sanford Underground Research
Facility. This facility, located at the site of the former Homestake Mine in
Lead, South Dakota, is approximately 1,300 km from the neutrino source at
Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino
charge-parity symmetry violation and mass ordering effects. This ambitious yet
cost-effective design incorporates scalability and flexibility and can
accommodate a variety of upgrades and contributions. With its exceptional
combination of experimental configuration, technical capabilities, and
potential for transformative discoveries, LBNE promises to be a vital facility
for the field of particle physics worldwide, providing physicists from around
the globe with opportunities to collaborate in a twenty to thirty year program
of exciting science. In this document we provide a comprehensive overview of
LBNE's scientific objectives, its place in the landscape of neutrino physics
worldwide, the technologies it will incorporate and the capabilities it will
possess.Comment: Major update of previous version. This is the reference document for
LBNE science program and current status. Chapters 1, 3, and 9 provide a
comprehensive overview of LBNE's scientific objectives, its place in the
landscape of neutrino physics worldwide, the technologies it will incorporate
and the capabilities it will possess. 288 pages, 116 figure
Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial
Background
Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy
Measuring the Neutrino Cross Section Using 8 years of Upgoing Muon Neutrinos Observed with IceCube
The IceCube Neutrino Observatory detects neutrinos at energies orders of magnitude higher than those available to current accelerators. Above 40 TeV, neutrinos traveling through the Earth will be absorbed as they interact via charged current interactions with nuclei, creating a deficit of Earth-crossing neutrinos detected at IceCube. The previous published results showed the cross section to be consistent with Standard Model predictions for 1 year of IceCube data. We present a new analysis that uses 8 years of IceCube data to fit the ν absorption in the Earth, with statistics an order of magnitude better than previous analyses, and with an improved treatment of systematic uncertainties. It will measure the cross section in three energy bins that span the range 1 TeV to 100 PeV. We will present Monte Carlo studies that demonstrate its sensitivity
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