5,926 research outputs found
Relationships between food resources, foraging patterns, and reproductive success in the water pipit, Anthus sp. spinoletta
A basic but rarely tested assumption in optimal foraging theory is that positive relationships exist between the foraging pattern of an animal, its short-term benefits in feeding, and its long-term fitness. We present evidence for these relationships for a central place foraging situation. We studied the foraging behavior of adult water pipits (Anthus sp. spinoletta) feeding nestlings in an Alpine habitat near Davos, Switzerland, with the following results: (1) searching effort decreases with increasing distance from the nest, (2) the amount of prey and the proportion of large items brought to the nest increases with increasing foraging distance, (3) water pipits do not forage according to habitat availability, but prefer vegetation types with the highest food density (mainly grass and herbs) and avoid those with the lowest, and (4) this selectivity is only expressed when the birds forage more than 50 m from the nest, i.e., usually outside the territory. Among the several potential interpretations of these results, the most parsimonious is that foraging decisions are based on profitability, i.e., on the net energy gain per time unit. Additionally, we found that food conditions translate into fitness: the number of fledglings per nest is related positively to the average prey biomass at the foraging place and negatively to the average distance between the foraging place and the nest. Maximum economic distances, which were predicted from this food-fitness relationship, agreed well with the actual foraging distances observed. This suggests a dose connection between foraging decisions and fitness. In addition to the theoretical issues, some conservation issues are also briefly discusse
Continuous optical loading of a Bose-Einstein Condensate in the Thomas-Fermi regime
We discuss the optical loading of a Bose-Einstein condensate in the
Thomas-Fermi regime. The condensate is loaded via spontaneous emission from a
reservoir of excited-state atoms. By means of a master equation formalism, we
discuss the modification of the condensate temperature during the loading. We
identify the threshold temperature, , above (below) which the loading
process leads to cooling (heating), respectively. The consequences of our
analysis for the continuous loading of an atom laser are discussed.Comment: 7 pages, 3 figure
Quantum gate in the decoherence-free subspace of trapped ion qubits
We propose a geometric phase gate in a decoherence-free subspace with trapped
ions. The quantum information is encoded in the Zeeman sublevels of the
ground-state and two physical qubits to make up one logical qubit with ultra
long coherence time. Single- and two-qubit operations together with the
transport and splitting of linear ion crystals allow for a robust and
decoherence-free scalable quantum processor. For the ease of the phase gate
realization we employ one Raman laser field on four ions simultaneously, i.e.
no tight focus for addressing. The decoherence-free subspace is left neither
during gate operations nor during the transport of quantum information.Comment: 6 pages, 6 figure
Mesoscopic atomic entanglement for precision measurements beyond the standard quantum limit
Squeezing of quantum fluctuations by means of entanglement is a well
recognized goal in the field of quantum information science and precision
measurements. In particular, squeezing the fluctuations via entanglement
between two-level atoms can improve the precision of sensing, clocks,
metrology, and spectroscopy. Here, we demonstrate 3.4 dB of metrologically
relevant squeezing and entanglement for ~ 10^5 cold cesium atoms via a quantum
nondemolition (QND) measurement on the atom clock levels. We show that there is
an optimal degree of decoherence induced by the quantum measurement which
maximizes the generated entanglement. A two-color QND scheme used in this paper
is shown to have a number of advantages for entanglement generation as compared
to a single color QND measurement.Comment: 6 pages+suppl, PNAS forma
Observational Evidence of Accretion Disk-Caused Jet Precession in Galactic Nuclei
We show that the observational data of extragalactic radio sources tend to
support the theoretical relationship between the jet precession period and the
optical luminosity of the sources, as predicted by the model in which an
accretion disk causes the central black hole to precess.Comment: 13 pages, 1 figure, accepted for publication in ApJ Letter
Long distance regularization in chiral perturbation theory with decuplet
We investigate the use of long distance regularization in SU(3) baryon chiral
perturbation theory with decuplet fields. The one-loop decuplet contributions
to the octet baryon masses, axial couplings, S-wave nonleptonic hyperon decays
and magnetic moments are evaluated in a chirally consistent fashion by
employing a cutoff to implement long distance regularization. The convergence
of the chiral expansions of these quantities is improved compared to the
dimensionally regularized version which indicates that the propagation of
Goldstone bosons over distances smaller than a typical hadronic size, which is
beyond the regime of chiral perturbation theory but included by dimensional
regularization, is removed by use of a cutoff.Comment: 31 page
Electroweak radiative corrections to deep-inelastic neutrino scattering - implications for NuTeV ?
We calculate the O(alpha) electroweak corrections to charged- and
neutral-current deep-inelastic neutrino scattering off an isoscalar target. The
full one-loop-corrected cross sections, including hard photonic corrections,
are evaluated and compared to an earlier result which was used in the NuTeV
analysis. In particular, we compare results that differ in input-parameter
scheme, treatment of real photon radiation and factorization scheme. The
associated shifts in the theoretical prediction for the ratio of neutral- and
charged-current cross sections can be larger than the experimental accuracy of
the NuTeV result.Comment: 19 pages late
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