434 research outputs found
Parallel Perceptrons, Activation Margins and Imbalanced Training Set Pruning
The final publication is available at Springer via http://dx.doi.org/10.1007/11492542_6Proceedings of Second Iberian Conference, IbPRIA 2005, Estoril, Portugal, June 7-9, 2005, Part IIA natural way to deal with training samples in imbalanced class problems is to prune them removing redundant patterns, easy to classify and probably over represented, and label noisy patterns that belonging to one class are labelled as members of another. This allows classifier construction to focus on borderline patterns, likely to be the most informative ones. To appropriately define the above subsets, in this work we will use as base classifiers the so–called parallel perceptrons, a novel approach to committee machine training that allows, among other things, to naturally define margins for hidden unit activations. We shall use these margins to define the above pattern types and to iteratively perform subsample selections in an initial training set that enhance classification accuracy and allow for a balanced classifier performance even when class sizes are greatly different.With partial support of Spain’s CICyT, TIC 01–572, TIN2004–0767
Experimental Study of Noise-induced Phase Synchronization in Vertical-cavity Lasers
We report the experimental evidence of noise-induced phase synchronization in
a vertical cavity laser. The polarized laser emission is entrained with the
input periodic pump modulation when an optimal amount of white, gaussian noise
is applied. We characterize the phenomenon, evaluating the average frequency of
the output signal and the diffusion coefficient of the phase difference
variable. Their values are roughly independent on different waveforms of
periodic input, provided that a simple condition for the amplitudes is
satisfied. The experimental results are compared with numerical simulations of
a Langevin model
Energy radiation of moving cracks
The energy radiated by moving cracks in a discrete background is analyzed.
The energy flow through a given surface is expressed in terms of a generalized
Poynting vector. The velocity of the crack is determined by the radiation by
the crack tip. The radiation becomes more isotropic as the crack velocity
approaches the instability threshold.Comment: 7 pages, embedded figure
Weak-winner phase synchronization: a curious case of weak interactions
We report the observation of a nontrivial emergent state in a chain of nonidentical, heterogeneously coupled oscillators where a set of weakly coupled oscillators becomes phase synchronized while the strongly coupled ones remain drifting. This intriguing “weak-winner” synchronization phenomenon can be explained by the interplay between nonisochronicity and the natural frequency of the oscillator, as coupling strength is varied. Furthermore, we present sufficient conditions under which the weak-winner phase synchronization can occur for limit cycles as well as chaotic oscillators. Employing a model system from ecology as well as a paradigmatic model from physics, we demonstrate that this phenomenon is a generic feature for a large class of coupled oscillator systems. The realization of this peculiar, yet quite generic weak-winner dynamics can have far-reaching consequences in a wide range of scientific disciplines that deal with the phenomenon of phase synchronization, including synchronization of networks. Our results also highlight the role of nonisochronicity (shear) as a fundamental feature of an oscillator in shaping emergent dynamical patterns in complex networks
Gravitational excitons from extra dimensions
Inhomogeneous multidimensional cosmological models with a higher dimensional
space-time manifold are investigated under dimensional reduction. In the
Einstein conformal frame, small excitations of the scale factors of the
internal spaces near minima of an effective potential have a form of massive
scalar fields in the external space-time. Parameters of models which ensure
minima of the effective potentials are obtained for particular cases and masses
of gravitational excitons are estimated.Comment: Revised version --- 12 references added, Introduction enlarged, 20
pages, LaTeX, to appear in Phys.Rev.D56 (15.11.97
Reliability of fluctuation-induced transport in a Maxwell-demon-type engine
We study the transport properties of an overdamped Brownian particle which is
simultaneously in contact with two thermal baths. The first bath is modeled by
an additive thermal noise at temperature . The second bath is associated
with a multiplicative thermal noise at temperature . The analytical
expressions for the particle velocity and diffusion constant are derived for
this system, and the reliability or coherence of transport is analyzed by means
of their ratio in terms of a dimensionless P\'{e}clet number. We find that the
transport is not very coherent, though one can get significantly higher
currents.Comment: 14 pages, 5 figure
Universally Coupled Massive Gravity, II: Densitized Tetrad and Cotetrad Theories
Einstein's equations in a tetrad formulation are derived from a linear theory
in flat spacetime with an asymmetric potential using free field gauge
invariance, local Lorentz invariance and universal coupling. The gravitational
potential can be either covariant or contravariant and of almost any density
weight. These results are adapted to produce universally coupled massive
variants of Einstein's equations, yielding two one-parameter families of
distinct theories with spin 2 and spin 0. The theories derived, upon fixing the
local Lorentz gauge freedom, are seen to be a subset of those found by
Ogievetsky and Polubarinov some time ago using a spin limitation principle. In
view of the stability question for massive gravities, the proven non-necessity
of positive energy for stability in applied mathematics in some contexts is
recalled. Massive tetrad gravities permit the mass of the spin 0 to be heavier
than that of the spin 2, as well as lighter than or equal to it, and so provide
phenomenological flexibility that might be of astrophysical or cosmological
use.Comment: 2 figures. Forthcoming in General Relativity and Gravitatio
Dynamical measure and field theory models free of the cosmological constant problem
Summary of abstract Field theory models including gauge theories with SSB are
presented where the energy density of the true vacuum state (TVS) is zero
without fine tuning. The above models are constructed in the gravitational
theory where a measure of integration \Phi in the action is not necessarily
\sqrt{-g} but it is determined dynamically through additional degrees of
freedom. The ratio \Phi/\sqrt{-g} is a scalar field which can be solved in
terms of the matter degrees of freedom due to the existence of a constraint. We
study a few explicit field theory models where it is possible to combine the
solution of the cosmological constant problem with: 1) possibility for
inflationary scenario for the early universe; 2) spontaneously broken gauge
unified theories (including fermions). The models are free from the well known
problem of the usual scalar-tensor theories in what is concerned with the
classical GR tests. The only difference of the field equations in the Einstein
frame from the canonical equations of the selfconsistent system of Einstein's
gravity and matter fields, is the appearance of the effective scalar field
potential which vanishes in TVS without fine tuning.Comment: Extended version of the contribution to the fourth Alexander
Friedmann International Seminar on Gravitation and Cosmology; accepted for
publication in Phys. Rev. D; 31 page
From weak-scale observables to leptogenesis
Thermal leptogenesis is an attractive mechanism for generating the baryon
asymmetry of the Universe. However, in supersymmetric models, the parameter
space is severely restricted by the gravitino bound on the reheat temperature
. For hierarchical light neutrino masses, it is shown that thermal
leptogenesis {\it can} work when GeV. The low-energy
observable consequences of this scenario are . For higher , thermal leptogenesis works in a
larger area of parameter space, whose observable consequences are more
ambiguous. A parametrisation of the seesaw in terms of weak-scale inputs is
used, so the results are independent of the texture chosen for the GUT-scale
Yukawa matrices.Comment: a few references adde
The Refederalization of American Health Care
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69090/2/10.1177_107755878704400103.pd
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