584 research outputs found
Building a Spiking Neural Network Model of the Basal Ganglia on SpiNNaker
We present a biologically-inspired and scalable model of the Basal Ganglia (BG) simulated on the SpiNNaker machine, a biologically-inspired low-power hardware platform allowing parallel, asynchronous computing. Our BG model consists of six cell populations, where the neuro-computational unit is a conductance-based Izhikevich spiking neuron; the number of neurons in each population is proportional to that reported in anatomical literature. This model is treated as a single-channel of action-selection in the BG, and is scaled-up to three channels with lateral cross-channel connections. When tested with two competing inputs, this three-channel model demonstrates action-selection behaviour. The SpiNNaker-based model is mapped exactly on to SpineML running on a conventional computer; both model responses show functional and qualitative similarity, thus validating the usability of SpiNNaker for simulating biologically-plausible networks. Furthermore, the SpiNNaker-based model simulates in real time for time-steps 1 ms; power dissipated during model execution is & #x2248;1.8 W
A study of supercooling of the disordered vortex phase via minor hysteresis loops in 2H-NbSe_2
We report on the observation of novel features in the minor hysteresis loops
in a clean crystal of NbSe_2 which displays a peak effect. The observed
behavior can be explained in terms of a supercooling of the disordered vortex
phase while cooling the superconductor in a field. Also, the extent of spatial
order in a flux line lattice formed in ascending fields is different from (and
larger than) that in the descending fields below the peak position of the peak
effect; this is attributed to unequal degree of annealing of the state induced
by a change of field in the two cases.Comment: 5 pages of text + 6 figures, submitted to Phys. Rev.
Deformation effects in Ni nuclei produced in Si+Si at 112 MeV
Velocity and energy spectra of the light charged particles (protons and
-particles) emitted in the Si(E = 112 MeV) + Si
reaction have been measured at the Strasbourg VIVITRON Tandem facility. The
ICARE charged particle multidetector array was used to obtain exclusive spectra
of the light particles in the angular range 15 - 150 degree and to determine
the angular correlations of these particles with respect to the emission angles
of the evaporation residues. The experimental data are analysed in the
framework of the statistical model. The exclusive energy spectra of
-particles emitted from the Si + Si compound system are
generally well reproduced by Monte Carlo calculations using spin-dependent
level densities. This spin dependence approach suggests the onset of large
deformations at high spin. A re-analysis of previous -particle data
from the Si + Si compound system, using the same spin-dependent
parametrization, is also presented in the framework of a general discussion of
the occurrence of large deformation effects in the A ~ 60 mass region.Comment: 25 pages, 6 figure
Experiences, information and knowledge on hygiene promotion
Experiences, information and knowledge on hygiene promotio
Bouncing Brane Cosmologies from Warped String Compactifications
We study the cosmology induced on a brane probing a warped throat region in a
Calabi-Yau compactification of type IIB string theory. For the case of a BPS
D3-brane probing the Klebanov-Strassler warped deformed conifold, the cosmology
described by a suitable brane observer is a bouncing, spatially flat
Friedmann-Robertson-Walker universe with time-varying Newton's constant, which
passes smoothly from a contracting to an expanding phase. In the
Klebanov-Tseytlin approximation to the Klebanov-Strassler solution the
cosmology would end with a big crunch singularity. In this sense, the warped
deformed conifold provides a string theory resolution of a spacelike
singularity in the brane cosmology. The four-dimensional effective action
appropriate for a brane observer is a simple scalar-tensor theory of gravity.
In this description of the physics, a bounce is possible because the relevant
energy-momentum tensor can classically violate the null energy condition.Comment: 20 pages, 2 figures; v2, references added and minor correction
Particle motion in the field of a five-dimensional charged black hole
In this paper, we have investigated the geodesics of neutral particles near a
five-dimensional charged black hole using a comparative approach. The effective
potential method is used to determine the location of the horizons and to study
radial and circular trajectories. This also helps us to analyze the stability
of radial and circular orbits. The radius of the innermost stable circular
orbits have also been determined. Contrary to the case of massive particles for
which, the circular orbits may have up to eight possible values of specific
radius, we find that the photons will only have two distinct values for the
specific radii of circular trajectories. Finally we have used the dynamical
systems analysis to determine the critical points and the nature of the
trajectories for the timelike and null geodesics.Comment: 15 pages, accepted for publication in Astrophysics and Space Scienc
Weak Field Black Hole Formation in Asymptotically AdS Spacetimes
We use the AdS/CFT correspondence to study the thermalization of a strongly
coupled conformal field theory that is forced out of its vacuum by a source
that couples to a marginal operator. The source is taken to be of small
amplitude and finite duration, but is otherwise an arbitrary function of time.
When the field theory lives on , the source sets up a
translationally invariant wave in the dual gravitational description. This wave
propagates radially inwards in space and collapses to form a black
brane. Outside its horizon the bulk spacetime for this collapse process may
systematically be constructed in an expansion in the amplitude of the source
function, and takes the Vaidya form at leading order in the source amplitude.
This solution is dual to a remarkably rapid and intriguingly scale dependent
thermalization process in the field theory. When the field theory lives on a
sphere the resultant wave either slowly scatters into a thermal gas (dual to a
glueball type phase in the boundary theory) or rapidly collapses into a black
hole (dual to a plasma type phase in the field theory) depending on the time
scale and amplitude of the source function. The transition between these two
behaviors is sharp and can be tuned to the Choptuik scaling solution in
.Comment: 50 pages + appendices, 6 figures, v2: Minor revisions, references
adde
Sub- and above barrier fusion of loosely bound Li with Si
Fusion excitation functions are measured for the system Li+Si
using the characteristic -ray method, encompassing both the sub-barrier
and above barrier regions, viz., = 7-24 MeV. Two separate experiments
were performed, one for the above barrier region (= 11-24 MeV) and
another for the below barrier region (= 7-10 MeV). The results were
compared with our previously measured fusion cross section for the
Li+Si system. We observed enhancement of fusion cross section at
sub-barrier regions for both Li and Li, but yield was substantially
larger for Li. However, for well above barrier regions, similar type of
suppression was identified for both the systems.Comment: 8 pages, 6 figures, as accepted for publication in Eur.Phys.J.
Measurement of the form-factor ratios for D+ --> K* l nu
The form factor ratios rv=V(0)/A1(0), r2=A2(0)/A1(0) and r3=A3(0)/A1(0) in
the decay D+ --> K* l nu, K* -->K-pi+ have been measured using data from charm
hadroproduction experiment E791 at Fermilab. From 3034 (595) signal
(background) events in the muon channel, we obtain rv=1.84+-0.11+-0.09,
r2=0.75+-0.08+-0.09 and, as a first measurement of r3, we find 0.04+-0.33
+-0.29. The values of the form factor ratios rv and r2 measured for the muon
channel are combined with the values of rv and r2 that we have measured in the
electron channel. The combined E791 results for the muon and electron channels
are rv=1.87+-0.08+-0.07 and r2=0.73+-0.06+-0.08.Comment: 9 pages + 3 figures ; submitted to PL
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