1,279 research outputs found
Rotifers in the Schelde estuary (Belgium): a test of taxonomic relevance
To investigate the reaction of the zooplankton community to improving water quality in the Schelde estuary, we studied the relationship between rotifer species distribution and environmental factors, and the feasibility of using a coarser level of taxonomic resolution. Fifty-two taxa, belonging to 26 genera, were identified, including 22 taxa new for the Schelde. Brachionus calyciflorus, Keratella cochlearis and B. angularis were the most abundant species. The highest diversity and abundances were observed in the freshwater reach. Redundancy analyses (RDA) showed that the main environmental factors explaining rotifer distribution were chlorinity and seasonal factors (discharge levels, cyclopoid abundance). Analysis carried out with data at the species and the genus level gave similar ordination plots, but the positioning of a genus relative to environmental factors did not always adequately represent the associations between the various species within the genus and environmental factors. Similar patterns in space and time were observed using taxonomic richness and diversity indices for analyses at species or genus level. Thus, in the context of the restoration of the Schelde estuary, the identification of rotifer species is very informative, but not essential for detecting important ecological associations
Study of relativistic bound states for scalar theories in Bethe-Salpeter and Dyson-Schwinger formalism
The Bethe-Salpeter equation for Wick-Cutkosky like models is solved in
dressed ladder approximation. The bare vertex truncation of the Dyson-Schwinger
equations for propagators is combined with the dressed ladder Bethe-Salpeter
equation for the scalar S-wave bound state amplitudes. With the help of
spectral representation the results are obtained directly in Minkowski space.
We give a new analytic formula for the resulting equation simplifying the
numerical treatment. The bare ladder approximation of Bethe-Salpeter equation
is compared with the one with dressed ladder. The elastic electromagnetic form
factors is calculated within the relativistic impulse approximation.Comment: 30 pages, 10 figures, accepted for publication in Phys. Rev.
Lattice calculations for A=3,4,6,12 nuclei using chiral effective field theory
We present lattice calculations for the ground state energies of tritium,
helium-3, helium-4, lithium-6, and carbon-12 nuclei. Our results were
previously summarized in a letter publication. This paper provides full details
of the calculations. We include isospin-breaking, Coulomb effects, and
interactions up to next-to-next-to-leading order in chiral effective field
theory.Comment: 38 pages, 11 figures, final publication versio
Evidence for orbital ordering in LaCoO3
We present powder and single crystal X-ray diffraction data as evidence for a
monoclinic distortion in the low spin (S=0) and intermediate spin state (S=1)
of LaCoO3. The alternation of short and long bonds in the ab plane indicates
the presence of eg orbital ordering induced by a cooperative Jahn-Teller
distortion. We observe an increase of the Jahn-Teller distortion with
temperature in agreement with a thermally activated behavior of the Co3+ ions
from a low-spin ground state to an intermediate-spin excited state.Comment: Accepted to Phys. Rev.
A limited sampling strategy for estimation of the area under the curve (0 to 8 hours) of mycophenolic acid administered three times daily to liver transplant recipients
Measurement of the Charged Pion Electromagnetic Form Factor
Separated longitudinal and transverse structure functions for the reaction
1H(e,eprime pi+)n were measured in the momentum transfer region Q2=0.6-1.6
(GeV/c)**2 at a value of the invariant mass W=1.95 GeV. New values for the pion
charge form factor were extracted from the longitudinal cross section by using
a recently developed Regge model. The results indicate that the pion form
factor in this region is larger than previously assumed and is consistent with
a monopole parameterization fitted to very low Q2 elastic data.Comment: 5 pages, 3 figure
Signatures of three-nucleon interactions in few-nucleon systems
Recent experimental results in three-body systems have unambiguously shown
that calculations based only on nucleon-nucleon forces fail to accurately
describe many experimental observables and one needs to include effects which
are beyond the realm of the two-body potentials. This conclusion owes its
significance to the fact that experiments and calculations can both be
performed with a high accuracy. In this review, both theoretical and
experimental achievements of the past decade will be underlined. Selected
results will be presented. The discussion on the effects of the three-nucleon
forces is, however, limited to the hadronic sector. It will be shown that
despite the major successes in describing these seemingly simple systems, there
are still clear discrepancies between data and the state-of-the-art
calculations.Comment: accepted for publication in Rep. Prog. Phy
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