891 research outputs found
How training and testing histories affect generalization: a test of simple neural networks
We show that a simple network model of associative learning can\ud
reproduce three findings that arise from particular training and\ud
testing procedures in generalization experiments: the effect of 1)\ud
``errorless learning'' and 2) extinction testing on peak shift, and\ud
3) the central tendency effect. These findings provide a true test\ud
of the network model, which was developed to account for other\ud
penhomena, and highlight the potential of neural networks to study\ud
phenomena that depend on sequences of experiences with many stimuli.\ud
Our results suggest that at least some such phenomena, e.g.,\ud
stimulus range effects, may derive from basic mechanisms of\ud
associative memory rather than from more complex memory processes
The Bulge-Halo Connection in Galaxies: A Physical Interpretation of the Vcirc-sigma_0 Relation
We explore the dependence of the ratio of a galaxy's circular velocity,
Vcirc, to its central velocity dispersion, sigma_0, on morphology, or
equivalently total light concentration. Such a dependence is expected if light
traces the mass. Over the full range of galaxy types, masses and brightnesses,
and assuming that the gas velocity traces the circular velocity, we find that
galaxies obey the relation log(Vcirc/sigma_0)= 0.63-0.11*C28 where
C28=5log(r80/r20) and the radii are measured at 80 percent and 20 percent of
the total light. Massive galaxies scatter about the Vcirc = sqrt(2)*sigma_0
line for isothermal stellar systems. Disk galaxies follow the simple relation
Vcirc/sigma_0=2(1-B/T), where B/T is the bulge-to-total light ratio. For pure
disks, C28~2.8, B/T -> 0, and Vcirc~=2*sigma_0. Self-consistent equilibrium
galaxy models from Widrow & Dubinski (2005) constrained to match the
size-luminosity and velocity-luminosity relations of disk galaxies fail to
match the observed Vcirc/sigma_0 distribution. Furthermore, the matching of
dynamical models for Vcirc(r)/sigma(r) with observations of dwarf and
elliptical galaxies suffers from limited radial coverage and relatively large
error bars; for dwarf systems, however, kinematical measurements at the galaxy
center and optical edge suggest Vcirc(Rmax) > 2*sigma_0 (in contrast with past
assumptions that Vcirc = sqrt(2)*sigma_0 for dwarfs.) The Vcirc-sigma_0-C28
relation has direct implications for galaxy formation and dynamical models,
galaxy scaling relations, the mass function of galaxies, and the links between
respective formation and evolution processes for a galaxy's central massive
object, bulge, and dark matter halo.Comment: Accepted for publication in ApJL. Current version matches ApJL page
requiremen
Casimir Effect in Background of Static Domain Wall
In this paper we investigate the vacuum expectation values of energy-
momentum tensor for conformally coupled scalar field in the standard parallel
plate geometry with Dirichlet boundary conditions and on background of planar
domain wall case. First we calculate the vacuum expectation values of
energy-momentum tensor by using the mode sums, then we show that corresponding
properties can be obtained by using the conformal properties of the problem.
The vacuum expectation values of energy-momentum tensor contains two terms
which come from the boundary conditions and the the gravitational background.
In the Minkovskian limit our results agree with those obtained in [3].Comment: 8 Page
Testing the Magnetic-Core Memory System in a Computer
A working memory has a "safe" operating region in a multidimensional space whose coordinates consist of the significant operating parameters of the memory. Errors occur only with excursions of the operating point outside the safe volume; such excursions result from failure of the surrounding equipment to remain perfectly stable. The optimum operating point is determined by the nominal settings of all the parameters which permit operation with a minimum of errors. Reliability is then defined as the ratio of the number of memory cycles to the number of errors. This is, to a very close approximation,the reciprocal of the probability of the operating point to drift from its optimum setting into the region outside the safe volume.
The specific problems of finding an optimum point and evaluating the reliability of the 32 x 32 MTC memory have been facilitated by reduction of the number of significant variables to two: the driving current and the common bias of the sensing gate tubes. Optimum conditions were 475-ma X, Y, and Z driving currents (1/2 Im) and -30-v gate-tube bias. Since the probability distributions of the variables are not known, reliability can only be evaluated by optimizing the adjustments of the system and maintaining count of its errors
Towards hardware acceleration of neuroevolution for multimedia processing applications on mobile devices
This paper addresses the problem of accelerating large artificial neural networks (ANN), whose topology and weights can evolve via the use of a genetic algorithm. The proposed digital hardware architecture is capable of processing any evolved network topology, whilst at the same time providing a good trade off between throughput, area and power consumption. The latter is vital for a longer battery life on mobile devices. The architecture uses multiple parallel arithmetic units in each processing element (PE). Memory partitioning and data caching are used to minimise the effects of PE pipeline stalling. A first order minimax polynomial approximation scheme, tuned via a genetic algorithm, is used for the activation function generator. Efficient arithmetic circuitry, which leverages modified Booth recoding, column compressors and carry save adders, is adopted throughout the design
String cosmological model in the presence of a magnetic flux
A Bianchi type I string cosmological model in the presence of a magnetic flux
is investigated. A few plausible assumptions regarding the parametrization of
the cosmic string and magneto-fluid are introduced and some exact analytical
solutions are presented.Comment: 9 pages, 4 Figure
Empowering and assisting natural human mobility: The simbiosis walker
This paper presents the complete development of the Simbiosis Smart Walker. The device is equipped with a set of sensor subsystems to acquire user-machine interaction forces and the temporal evolution of user's feet during gait. The authors present an adaptive filtering technique used for the identification and separation of different components found on the human-machine interaction forces. This technique allowed isolating the components related with the navigational commands and developing a Fuzzy logic controller to guide the device. The Smart Walker was clinically validated at the Spinal Cord Injury Hospital of Toledo - Spain, presenting great acceptability by spinal chord injury patients and clinical staf
Cascading on extragalactic background light
High-energy gamma-rays propagating in the intergalactic medium can interact
with background infrared photons to produce e+e- pairs, resulting in the
absorption of the intrinsic gamma-ray spectrum. TeV observations of the distant
blazar 1ES 1101-232 were thus recently used to put an upper limit on the
infrared extragalactic background light density. The created pairs can
upscatter background photons to high energies, which in turn may pair produce,
thereby initiating a cascade. The pairs diffuse on the extragalactic magnetic
field (EMF) and cascade emission has been suggested as a means for measuring
its intensity. Limits on the IR background and EMF are reconsidered taking into
account cascade emissions. The cascade equations are solved numerically.
Assuming a power-law intrinsic spectrum, the observed 100 MeV - 100 TeV
spectrum is found as a function of the intrinsic spectral index and the
intensity of the EMF. Cascades emit mainly at or below 100 GeV. The observed
TeV spectrum appears softer than for pure absorption when cascade emission is
taken into account. The upper limit on the IR photon background is found to be
robust. Inversely, the intrinsic spectra needed to fit the TeV data are
uncomfortably hard when cascade emission makes a significant contribution to
the observed spectrum. An EMF intensity around 1e-8 nG leads to a
characteristic spectral hump in the GLAST band. Higher EMF intensities divert
the pairs away from the line-of-sight and the cascade contribution to the
spectrum becomes negligible.Comment: 5 pages, to be published as a research note in A&
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