4,338 research outputs found
Statistical Communication Theory
Contains research objectives and reports on five research projects.National Science Foundation (Grant GP-2495)National Institutes of Health (Grant MH-04737-04)National Aeronautics and Space Administration (Grant NsG-496
Images of the Dark Soliton in a Depleted Condensate
The dark soliton created in a Bose-Einstein condensate becomes grey in course
of time evolution because its notch fills up with depleted atoms. This is the
result of quantum mechanical calculations which describes output of many
experimental repetitions of creation of the stationary soliton, and its time
evolution terminated by a destructive density measurement. However, such a
description is not suitable to predict the outcome of a single realization of
the experiment were two extreme scenarios and many combinations thereof are
possible: one will see (1) a displaced dark soliton without any atoms in the
notch, but with a randomly displaced position, or (2) a grey soliton with a
fixed position, but a random number of atoms filling its notch. In either case
the average over many realizations will reproduce the mentioned quantum
mechanical result. In this paper we use N-particle wavefunctions, which follow
from the number-conserving Bogoliubov theory, to settle this issue.Comment: 8 pages, 6 figures, references added in version accepted for
publication in J. Phys.
Towards an Axiomatization of Simple Analog Algorithms
International audienceWe propose a formalization of analog algorithms, extending the framework of abstract state machines to continuous-time models of computation
Functional diversity of marine ecosystems after the Late Permian mass extinction event
Article can be accessed from http://www.nature.com/ngeo/journal/v7/n3/full/ngeo2079.htmlThe Late Permian mass extinction event was the most severe such crisis of the past 500 million years and occurred during an episode of global warming. It is assumed to have had significant ecological impact, but its effects on marine ecosystem functioning are unknown and the patterns of marine recovery are debated. We analysed the fossil occurrences of all known Permian-Triassic benthic marine genera and assigned each to a functional group based on their inferred life habit. We show that despite the selective extinction of 62-74% of marine genera there was no significant loss of functional diversity at the global scale, and only one novel mode of life originated in the extinction aftermath. Early Triassic marine ecosystems were not as ecologically depauperate as widely assumed, which explains the absence of a Cambrian-style Triassic radiation in higher taxa. Functional diversity was, however, significantly reduced in particular regions and habitats, such as tropical reefs, and at these scales recovery varied spatially and temporally, probably driven by migration of surviving groups. Marine ecosystems did not return to their pre-extinction state, however, and radiation of previously subordinate groups such as motile, epifaunal grazers led to greater functional evenness by the Middle Triassic
Critical Review of Theoretical Models for Anomalous Effects (Cold Fusion) in Deuterated Metals
We briefly summarize the reported anomalous effects in deuterated metals at
ambient temperature, commonly known as "Cold Fusion" (CF), with an emphasis on
important experiments as well as the theoretical basis for the opposition to
interpreting them as cold fusion. Then we critically examine more than 25
theoretical models for CF, including unusual nuclear and exotic chemical
hypotheses. We conclude that they do not explain the data.Comment: 51 pages, 4 Figure
Vitrification of a monatomic 2D simple liquid
A monatomic simple liquid in two dimensions, where atoms interact
isotropically through the Lennard-Jones-Gauss potential [M. Engel and H.-R.
Trebin, Phys. Rev. Lett. 98, 225505 (2007)], is vitrified by the use of a rapid
cooling technique in a molecular dynamics simulation. Transformation to a
crystalline state is investigated at various temperatures and the
time-temperature-transformation (TTT) curve is determined. It is found that the
transformation time to a crystalline state is the shortest at a temerature 14%
below the melting temperature Tm and that at temperatures below Tv = 0.6 Tm the
transformation time is much longer than the available CPU time. This indicates
that a long-lived glassy state is realized for T < Tv.Comment: 5pages,5figures,accepted for publication in CEJ
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