3,087 research outputs found
Cryptanalysis of a computer cryptography scheme based on a filter bank
This paper analyzes the security of a recently-proposed signal encryption
scheme based on a filter bank. A very critical weakness of this new signal
encryption procedure is exploited in order to successfully recover the
associated secret key.Comment: 6 pages, 1 figur
Unveiling First Order CMR Transitions in the Two-Orbital Model for Manganites
Large scale Monte Carlo simulation results for the two-orbital model for
manganites, including Jahn-Teller lattice distortions, are here presented. At
hole density x=1/4 and in the vicinity of the region of competition between the
ferromagnetic metallic and spin-charge-orbital ordered insulating phases, the
colossal magnetoresistance (CMR) phenomenon is observed with a
magnetoresistance ratio ~10,000% Our main result is that this CMR transition is
found to be of first order in some portions of the phase diagram, in agreement
with early results from neutron scattering, specific heat, and magnetization,
thus solving a notorious discrepancy between experiments and previous
theoretical studies. The first-order characteristics of the transition survive,
and are actually enhanced, when weak quenched disorder is introduced.Comment: 4 pages, 4 figure
Phase Diagram of a Model for Diluted Magnetic Semiconductors Beyond Mean-Field Approximations
A lattice spin-fermion model for diluted magnetic semiconductors (DMS) is
investigated numerically, improving on previously used mean-field (MF)
approximations. Curie temperatures are obtained varying the Mn-spin x and hole
n densities, and the impurity-hole exchange J in units of the hopping amplitude
t. Optimal values are found in the subtle intermediate regime between itinerant
and localized carriers. Our main result is the behavior of the Curie
temperature at large J/t, where a "clustered" state is observed and
ferromagnetism is suppressed. Formal analogies between DMS and manganites are
also discussed.Comment: Revtex4, 4 pages, 4 figures. New figures, emphasis change
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