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Many real problems in supervised classification involve high-dimensional feature data measured for individuals of known origin from two or more classes. When the dimension of the feature vector is very large relative to the number of individuals, it presents formidable challenges to construct a discriminant rule (classifier) for assigning an unclassified individual to one of the known classes. One way to handle this high-dimensional problem is to identify highly relevant differential features for constructing a classifier. Here a new approach is considered, where a mixture model with random effects is used firstly to partition the features into clusters and then the relevance of each feature variable for differentiating the classes is formally tested and ranked using cluster-specific contrasts of mixed effects. Finally, a non-par...
Comment: 23 pages, 6 figures: Fig.2 has been replaced (in the preceding version it was identical to Fig.1)
Comment: Journal: Theory and Practice of Logic Programming Journal Acronym: TPLP Category: Paper for Special Issue (Verification and Computational Logic) Submitted: 18 March 2002, revised: 14 Januari 2003, accepted: 5 September 2003
Analyses of marine carbonates through the interval 63.9 to 65.4 million years ago indicate a near-constant flux of extraterrestrial helium-3, a tracer of the accretion rate of interplanetary dust to Earth. This observation indicates that the bolide associated with the Cretaceous-Tertiary (K-T) extinction event was not accompanied by enhanced solar system dustiness and so could not have been a member of a comet shower. The use of helium-3 as a constant-flux proxy of sedimentation rate implies deposition of the K-T boundary clay in (10 ± 2) × 10^3 years, precluding the possibility of a long hiatus at the boundary and requiring extremely rapid faunal turnover.
Comment: 4 pages, 3 figures; published version
We develop a new analytic approach for the study of lattice heteropolymers, and apply it to copolymers with correlated Markovian sequences. According to our analysis, heteropolymers present three different dense phases depending upon the temperature, the nature of the monomer interactions, and the sequence correlations: (i) a liquid phase, (ii) a ``soft glass'' phase, and (iii) a ``frozen glass'' phase. The presence of the new intermediate ``soft glass'' phase is predicted for instance in the case of polyampholytes with sequences that favor the alternation of monomers. Our approach is based on the cavity method, a refined Bethe Peierls approximation adapted to frustrated systems. It amounts to a mean field treatment in which the nearest neighbor correlations, which are crucial in the dense phases of heteropolymers, are handled exac...
Late Cretaceous (100–73 Ma) pelagic limestones were measured for helium concentration and isotopic composition to characterize the interplanetary dust flux using ^(3)He as a tracer. In the Bottaccione section near Gubbio, Italy, three intervals of elevated 3He concentration were detected: K1 in the Campanian stage at ∼79 Ma, K2 in the Santonian stage at ∼85 Ma, and K3 in the Turonian stage at ∼91 Ma. All three of these episodes are associated with high ^(3)He/^(4)He and ^(3)He/non-carbonate ratios, consistent with their derivation from an enhanced extraterrestrial ^(3)He flux rather than decreased carbonate sedimentation or dissolution. While K2 is modest in magnitude and duration and thus is of limited significance, K1 and K3 are each identified by a few myr interval with an ∼4-fold enhancement in mean 3He flux compared with pre-event...
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