37,587 research outputs found
Automatic programming methodologies for electronic hardware fault monitoring
This paper presents three variants of Genetic Programming (GP) approaches for intelligent online performance monitoring of electronic circuits and systems. Reliability modeling of electronic circuits can be best performed by the Stressor - susceptibility interaction model. A circuit or a system is considered to be failed once the stressor has exceeded the susceptibility limits. For on-line prediction, validated stressor vectors may be obtained by direct measurements or sensors, which after pre-processing and standardization are fed into the GP models. Empirical results are compared with artificial neural networks trained using backpropagation algorithm and classification and regression trees. The performance of the proposed method is evaluated by comparing the experiment results with the actual failure model values. The developed model reveals that GP could play an important role for future fault monitoring systems.This research was supported by the International Joint Research Grant of the IITA (Institute of Information Technology Assessment) foreign professor invitation program of the MIC (Ministry of Information and Communication), Korea
Constraining the Minimum Mass of High-Redshift Galaxies and Their Contribution to the Ionization State of the IGM
We model the latest HST WFPC3/IR observations of > 100 galaxies at redshifts
z=7-8 in terms of a hierarchical galaxy formation model with starburst
activity. Our model provides a distribution of UV luminosities per dark matter
halo of a given mass and a natural explanation for the fraction of halos
hosting galaxies. The observed luminosity function is best fit with a minimum
halo mass per galaxy of 10^{9.4+0.3-0.9} Msun, corresponding to a virial
temperature of 10^{4.9+0.2-0.7} K. Extrapolating to faint, undetected galaxies,
the total production rate of ionizing radiation depends critically on this
minimum mass. Future measurements with JWST should determine whether the entire
galaxy population can comfortably account for the UV background required to
keep the intergalactic medium ionized.Comment: 9 pages, 6 figures, submitted to ApJ, comments welcom
Cores in Dwarf Galaxies from Dark Matter with a Yukawa Potential
We show that cold dark matter particles interacting through a Yukawa
potential could naturally explain the recently observed cores in dwarf galaxies
without affecting the dynamics of objects with a much larger velocity
dispersion, such as clusters of galaxies. The velocity dependence of the
associated cross-section as well as the possible exothermic nature of the
interaction alleviates earlier concerns about strongly interacting dark matter.
Dark matter evaporation in low-mass objects might explain the observed deficit
of satellite galaxies in the Milky Way halo and have important implications for
the first galaxies and reionization.Comment: 6 pages, 2 figure
Action at a distance in classical uniaxial ferromagnetic arrays
We examine in detail the theoretical foundations of striking long-range
couplings emerging in arrays of fluid cells connected by narrow channels by
using a lattice gas (Ising model) description of a system. We present a
reexamination of the well known exact determination of the two-point
correlation function along the edge of a channel using the transfer matrix
technique and a new interpretation is provided. The explicit form of the
correlation length is found to grow exponentially with the cross section of the
channels at the bulk two-phase coexistence. The aforementioned result is
recaptured by a refined version of the Fisher-Privman theory of first order
phase transitions in which the Boltzmann factor for a domain wall is decorated
with a contribution stemming from the point tension originated at its
endpoints. The Boltzmann factor for a domain wall together with the point
tension is then identified exactly thanks to two independent analytical
techniques, providing a critical test of the Fisher-Privman theory. We then
illustrate how to build up the network model from its elementary constituents,
the cells and the channels. Moreover, we are able to extract the strength of
the coupling between cells and express them in terms of the length and width
and coarse grained quantities such as surface and point tensions. We then
support our theoretical investigation with a series of corroborating results
based on Monte Carlo simulations. We illustrate how the long range ordering
occurs and how the latter is signaled by the thermodynamic quantities
corresponding to both planar and three-dimensional Ising arrays.Comment: 36 pages, 19 figure
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