458 research outputs found
Cortisol levels are positively associated with pup-feeding rates in male meerkats
In societies of cooperative vertebrates, individual differences in contributions to offspring care are commonly substantial. Recent attempts to explain the causes of this variation have focused on correlations between contributions to care and the protein hormone prolactin, or the steroid hormone testosterone. However, such studies have seldom considered the importance of other hormones or controlled for non-hormonal factors that are correlative with both individual hormone levels and contributions to care. Using multivariate statistics, we show that hormone levels explain significant variation in contributions to pup-feeding by male meerkats, even after controlling for non-hormonal effects. However, long-term contributions to pup provisioning were significantly and positively correlated with plasma levels of cortisol rather than prolactin, while plasma levels of testosterone were not related to individual patterns of pup-feeding. Furthermore, a playback experiment that used pup begging calls to increase the feeding rates of male helpers gave rise to parallel increases in plasma cortisol levels, whilst prolactin and testosterone levels remained unchanged. Our findings confirm that hormones can explain significant amounts of variation in contributions to offspring feeding, and that cortisol, not prolactin, is the hormone most strongly associated with pup-feeding in cooperative male meerkats
Searching Data: A Review of Observational Data Retrieval Practices in Selected Disciplines
A cross-disciplinary examination of the user behaviours involved in seeking
and evaluating data is surprisingly absent from the research data discussion.
This review explores the data retrieval literature to identify commonalities in
how users search for and evaluate observational research data. Two analytical
frameworks rooted in information retrieval and science technology studies are
used to identify key similarities in practices as a first step toward
developing a model describing data retrieval
Two-body correlations in Bose condensates
We formulate a method to study two-body correlations in a condensate of N
identical bosons. We use the adiabatic hyperspheric approach and assume a
Faddeev like decomposition of the wave function. We derive for a fixed
hyperradius an integro-differential equation for the angular eigenvalue and
wave function. We discuss properties of the solutions and illustrate with
numerical results. The interaction energy is for N~20 five times smaller than
that of the Gross-Pitaevskii equation
Effective Field Theories on Non-Commutative Space-Time
We consider Yang-Mills theories formulated on a non-commutative space-time
described by a space-time dependent anti-symmetric field .
Using Seiberg-Witten map techniques we derive the leading order operators for
the effective field theories that take into account the effects of such a
background field. These effective theories are valid for a weakly
non-commutative space-time. It is remarkable to note that already simple models
for can help to loosen the bounds on space-time
non-commutativity coming from low energy physics. Non-commutative geometry
formulated in our framework is a potential candidate for new physics beyond the
standard model.Comment: 22 pages, 1 figur
Neutron-H potentials and the H-properties
The continuum resonance spectrum of H (H++) is investigated by
use of the complex scaled hyperspherical adiabatic expansion method. The
crucial H-neutron potential is obtained by switching off the Coulomb part
from successful fits to He-proton experimental data. These two-body
potentials must be expressed exclusively by operators conserving the
nucleon-core mean field angular momentum quantum numbers. The energies
and widths of the ground-state resonance and the lowest two
excited and -resonances are found to be MeV,
MeV and MeV, respectively. These results agree with
most of the experimental data. The energy distributions of the fragments after
decay of the resonances are predicted.Comment: 26 pages, 8 tables, 7 figures. Accepted for publication in Nucl.
Phys.
Dipole excited states in Li with complex scaling
The 1 excitations of the three--body halo nucleus Li are
investigated. We use adiabatic hyperspherical expansion and solve the Faddeev
equations in coordinate space. The method of complex scaling is used to compute
the resonance states. The Pauli forbidden states occupied by core neutrons are
excluded by constructing corresponding complex scaled phase equivalent two-body
potentials. We use a recently derived neutron--core interaction consistent with
known structure and reaction properties of Li and Li. The
computed dipole excited states with , , and
have energies ranging from 0.6 MeV to 1.0 MeV and widths between
0.15 MeV and 0.65 MeV. We investigate the dependence of the complex energies of
these states on the Li spectrum. The finite spin 3/2 of the core and the
resulting core-neutron spin-spin interaction are important. The connection with
Coulomb dissociation experiments is discussed and a need for better
measurements is pointed out.Comment: 28 pages, 6 figures, Nuclear Physics A, in pres
Comprehensive calculations of three--body breakup cross sections
We present in detail a theoretical model for fragmentation reactions of
three--body halo nuclei. The different reaction mechanisms corresponding to the
different processes are described and discussed. Coulomb and nuclear
interactions are simultaneously included and the method is therefore applicable
for any target, light, intermediate and heavy. Absolute values of many
differential cross sections are then available as function of beam energy and
target. We apply the method to fragmentation of He and Li on C, Cu
and Pb. A large variety of observables, cross sections and momentum
distributions, are computed. In almost all cases we obtain good agreement with
the available experimental data.Comment: 41 pages, 10 figures, to be published in Nucl. Phys.
Pentaquark as Kaon-Nucleon Resonance
Several recent experiments have reported evidence for a narrow feature in the
K(+)-neutron system, an apparent resonant state ~ 100 MeV above threshold and
with a width < 25 MeV. This state has been labelled as Theta(+) (previously as
Z(*)), and because of the implied inclusion of a anti-strange quark, is
referred to as a pentaquark, that is, five quarks within a single bag. We
present an alternative explanation for such a structure, as a higher angular
momentum resonance in the isospin zero K(+) -N system. One might call this an
exit channel or a molecular resonance. In a non-relativistic potential model we
find a possible candidate for the kaon-nucleon system with relative angular
momentum L=3, while L=1 and 2 states possess centrifugal barriers too low to
confine the kaon and nucleon in a narrow state at an energy so high above
threshold. A rather strong state-dependence in the potential is essential,
however, for eliminating an observable L=2 resonance at lower energies.Comment: 4 page
Decay of Z into Two Light Higgs Bosons
If the standard electroweak gauge model is extended to include two or more
Higgs doublets, there may be a neutral Higgs boson which is light (with a
mass of say 10 GeV) but the coupling is suppressed so that it has so far
escaped experimental detection. However, the effective coupling is
generally unsuppressed, hence the decay of Z into two light Higgs bosons plus a
fermion-antifermion pair may have an observable branching fraction, especially
if decays invisibly as for example in the recently proposed doublet Majoron
model.Comment: 10 pages, LaTex, figures available upon request to
[email protected]
The t W- Mode of Single Top Production
The t W- mode of single top production is proposed as an important means to
study the weak interactions of the top quark. While the rate of this mode is
most likely too small to be observed at Run II of the Fermilab Tevatron, it is
expected to be considerably larger at the CERN LHC. In this article the
inclusive t W- rate is computed, including O(1 / log (m_t^2 / m_b^2))
corrections, and when combined with detailed Monte Carlo simulations including
the top and W decay products, indicate that the t W- single top process may be
extracted from the considerable t tbar and W+ W- j backgrounds at low
luminosity runs of the LHC.Comment: 16 pages, 4 figure
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