37,491 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
The Pierre Auger Observatory: Results on Ultra-High Energy Cosmic Rays
The focus of this article is on recent results on ultra-high energy cosmic
rays obtained with the Pierre Auger Observatory. The world's largest instrument
of this type and its performance are described. The observations presented here
include the energy spectrum, the primary particle composition, limits on the
fluxes of photons and neutrinos and a discussion of the anisotropic
distribution of the arrival directions of the most energetic particles.
Finally, plans for the construction of a Northern Auger Observatory in
Colorado, USA, are discussed.Comment: Proceedings of the International Workshop on Advances in Cosmic Ray
Science, Waseda University, Shinjuku, Tokyo, Japan, March 2008; to be
published in the Journal of the Physical Society of Japan (JPSJ) supplemen
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
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