2,282 research outputs found
Three atmospheric dispersion experiments involving oil fog plumes measured by lidar
The Wave Propagation Lab. participated with the U.S. Environmental Protection Agency in a series of experiments with the goal of developing and validating dispersion models that perform substantially better that models currently available. The lidar systems deployed and the data processing procedures used in these experiments are briefly described. Highlights are presented of conclusions drawn thus far from the lidar data
Cryptic female choice via sperm dumping favours male copulatory courtship in a spider
Males of many animals perform 'copulatory courtship' during copulation, but the possible reproductive significance of this behaviour has seldom been investigated. In some animals, including the spider Physocyclus globosus (Pholcidae), the female discards sperm during or immediately following some copulations. In this study, we determined which of several variables associated with copulation correlated with paternity success in P. globosus when two males mate with a single female. Then, by determining which of these variables also correlated with sperm dumping, we inferred which variables may affect paternity via the mechanism of sperm dumping. Male abdomen vibration (a copulatory courtship behaviour) and male genitalic squeezing both correlated with both paternity and sperm dumping; so, these traits may be favoured by biased sperm dumping. Biased sperm dumping may also be the mechanism by which possible cryptic female choice favours another male trait that was the subject of a previous study, responsiveness to female stridulation. © 2009 European Society For Evolutionary Biology.Fil: Peretti, Alfredo Vicente. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; ArgentinaFil: Eberhard, W. G.. Universidad de Costa Rica; Costa Ric
Exact-Exchange Kohn-Sham formalism applied to one-dimensional periodic electronic systems
The Exact-Exchange (EXX) Kohn-Sham formalism, which treats exchange
interactions exactly within density-functional theory, is applied to
one-dimensional periodic systems. The underlying implementation does not rely
on specific symmetries of the considered system and can be applied to any kind
of periodic structure in one to three dimensions. As a test system,
-polyacetylene, both in form of an isolated chain and in the bulk
geometry has been investigated. Within the EXX scheme, bandstructures and
independent particle response functions are calculated and compared to
experimental data as well as to data calculated by several other methods.
Compared to results from the local-density approximation, the EXX method leads
to an increased value for the band gap, in line with similar observations for
three-dimensional semiconductors. An inclusion of correlation potentials within
the local density approximation or generalized gradient approximations leads to
only negligible effects in the bandstructure. The EXX band gaps are in good
agreement with experimental data for bulk -polyacetylene. Packing
effects of the chains in bulk -polyacetylene are found to lower the band
gap by about 0.5 eV
The hub as a launching platform: rapid movements of the spider Leucauge mariana (Araneae: Tetragnathidae) as it turns to attack prey
Shaping Robust System through Evolution
Biological functions are generated as a result of developmental dynamics that
form phenotypes governed by genotypes. The dynamical system for development is
shaped through genetic evolution following natural selection based on the
fitness of the phenotype. Here we study how this dynamical system is robust to
noise during development and to genetic change by mutation. We adopt a
simplified transcription regulation network model to govern gene expression,
which gives a fitness function. Through simulations of the network that
undergoes mutation and selection, we show that a certain level of noise in gene
expression is required for the network to acquire both types of robustness. The
results reveal how the noise that cells encounter during development shapes any
network's robustness, not only to noise but also to mutations. We also
establish a relationship between developmental and mutational robustness
through phenotypic variances caused by genetic variation and epigenetic noise.
A universal relationship between the two variances is derived, akin to the
fluctuation-dissipation relationship known in physics
Spiral Defect Chaos in Large Aspect Ratio Rayleigh-Benard Convection
We report experiments on convection patterns in a cylindrical cell with a
large aspect ratio. The fluid had a Prandtl number of approximately 1. We
observed a chaotic pattern consisting of many rotating spirals and other
defects in the parameter range where theory predicts that steady straight rolls
should be stable. The correlation length of the pattern decreased rapidly with
increasing control parameter so that the size of a correlated area became much
smaller than the area of the cell. This suggests that the chaotic behavior is
intrinsic to large aspect ratio geometries.Comment: Preprint of experimental paper submitted to Phys. Rev. Lett. May 12
1993. Text is preceeded by many TeX macros. Figures 1 and 2 are rather lon
Quantum entanglement with acousto-optic modulators: 2-photon beatings and Bell experiments with moving beamsplitters
We present an experiment testing quantum correlations with frequency shifted
photons. We test Bell inequality with 2-photon interferometry where we replace
the beamsplitters by acousto-optic modulators, which are equivalent to moving
beamsplitters. We measure the 2-photon beatings induced by the frequency
shifts, and we propose a cryptographic scheme in relation. Finally, setting the
experiment in a relativistic configuration, we demonstrate that the quantum
correlations are not only independent of the distance but also of the time
ordering between the two single-photon measurements.Comment: 14 pages, 16 figure
Incidence, Timing, and Correlates of Stent Thrombosis With the Polymeric Paclitaxel Drug-Eluting Stent
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The evolution of prey‐wrapping behaviour in spiders
We traced the evolution of silk use by spiders in attacks on prey by combining previous publications with new observations of 31 species in 16 families. Two new prey‐wrapping techniques are described. One, in which the spider holds a tense line (often covered with viscid silk) with both legs IV and applies it to the prey with a simultaneous movement of both legs, may be a synapomorphy linking Theridiidae, Nesticidae, and Synotaxidae. The other, in which the spider stands over the prey and turns in place, is apparently very ancient; it occurs in Theraphosidae, Tengellidae, and Agelenidae. The use of legs IV to wrap prey is described for the first time in Filistatidae and Scytodidae. Using a recent phylogeny of spiders, we propose that prey wrapping with legs IV has evolved convergently at least four times. We propose that prey wrapping originally evolved from egg‐sac construction behaviour.Instituto Smithsoniano de Investigaciones Tropicales (STRI)Universidad de Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí
Quantum correlations versus Multisimultaneity: an experimental test
Multisimultaneity is a causal model of relativistic quantum physics which
assigns a real time ordering to any set of events, much in the spirit of the
pilot-wave picture. Contrary to standard quantum mechanics, it predicts a
disappearance of the correlations in a Bell-type experiment when both analysers
are in relative motion such that, each one in its own inertial reference frame,
is first to select the output of the photons. We tested this prediction using
acousto-optic modulators as moving beam-splitters and interferometers separated
by 55 m. We didn't observe any disappearance of the correlations, thus refuting
Multisimultaneity.Comment: 4 pages, 3 figures, RevTex 4 versio
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