851 research outputs found
Adaptability of great cormorants Phalacrocorax carbo in a coastal environment demonstrated by their exploitation of introduced prey species and use of artificial breeding sites
An analysis of the contents of regurgitations of great cormorant Phalacrocorax carbo chicks at two coastal colonies in South Africa, one on an offhore island (St Croix) and the other at a saltworks in an estuary (Swartkops), revealed that the diet was dominated by introduced freshwater and estuarine fish. Most other prey species were indigenous euryhaline fish, and from the size ranges of the estuary-dependent species it was clear that they had been obtained in estuaries. Great cormorants in this coastal environment have learned to exploit introduced fish species, but use offshore islands as safe breeding sites, unless suitably safe artificial sites are created near their preferred foraging areas.Keywords: chick regurgitations, diet, St Croix Island, Swartkops RiverAfrican Journal of Marine Science 2002, 24: 317–32
Positive tension 3-branes in an bulk
In this work, we review and extend the so-called consistency conditions for
the existence of a braneworld scenario in arbitrary dimensions in the
Brans-Dicke (BD) gravitational theory. After that, we consider the particular
case of a five-dimensional scenario which seems to have phenomenological
interesting implications. We show that, in the BD framework, it is possible to
achieve necessary conditions pointing to the possibility of accommodating
branes with positive tensions in an AdS bulk by the presence of the additional
BD scalar field, avoiding in this way the necessity of including unstable
objects in the compactification scheme. Furthermore, in the context of time
variable brane tension, it is shown that the brane tension may change its sign,
following the bulk cosmological constant sign.Comment: 15 pages, new version to appear in JHE
On measurement of top polarization as a probe of production mechanisms at the LHC
In this note we demonstrate the use of top polarization in the study of resonances at the LHC, in the possible case where the dynamics implies
a non-zero top polarization. As a probe of top polarization we construct an
asymmetry in the decay-lepton azimuthal angle distribution (corresponding to
the sign of ) in the laboratory. The asymmetry is non-vanishing
even for a symmetric collider like the LHC, where a positive axis is not
uniquely defined. The angular distribution of the leptons has the advantage of
being a faithful top-spin analyzer, unaffected by possible anomalous
couplings, to linear order. We study, for purposes of demonstration, the case
of a as might exist in the little Higgs models. We identify kinematic cuts
which ensure that our asymmetry reflects the polarization in sign and
magnitude. We investigate possibilities at the LHC with two energy options:
TeV and TeV, as well as at the Tevatron. At the
LHC the model predicts net top quark polarization of the order of a few per
cent for GeV, being as high as for a smaller mass
of the of GeV and for the largest allowed coupling in the model, the
values being higher for the TeV option. These polarizations translate to a
deviation from the standard-model value of azimuthal asymmetry of up to about
() for () TeV LHC, whereas for the Tevatron, values as high as
are attained. For the TeV LHC with an integrated luminosity of 10
fb, these numbers translate into a sensitivity over a large
part of the range GeV.Comment: 28 page, LaTeX, requires JHEP style file, 12 figures. Typos corrected
and references adde
Top Quarks as a Window to String Resonances
We study the discovery potential of string resonances decaying to
final state at the LHC. We point out that top quark pair production is a
promising and an advantageous channel for studying such resonances, due to
their low Standard Model background and unique kinematics. We study the
invariant mass distribution and angular dependence of the top pair production
cross section via exchanges of string resonances. The mass ratios of these
resonances and the unusual angular distribution may help identify their
fundamental properties and distinguish them from other new physics. We find
that string resonances for a string scale below 4 TeV can be detected via the
channel, either from reconstructing the semi-leptonic
decay or recent techniques in identifying highly boosted tops.Comment: 22 pages, 6 figure
The holographic principle
There is strong evidence that the area of any surface limits the information
content of adjacent spacetime regions, at 10^(69) bits per square meter. We
review the developments that have led to the recognition of this entropy bound,
placing special emphasis on the quantum properties of black holes. The
construction of light-sheets, which associate relevant spacetime regions to any
given surface, is discussed in detail. We explain how the bound is tested and
demonstrate its validity in a wide range of examples.
A universal relation between geometry and information is thus uncovered. It
has yet to be explained. The holographic principle asserts that its origin must
lie in the number of fundamental degrees of freedom involved in a unified
description of spacetime and matter. It must be manifest in an underlying
quantum theory of gravity. We survey some successes and challenges in
implementing the holographic principle.Comment: 52 pages, 10 figures, invited review for Rev. Mod. Phys; v2:
reference adde
Localization of gravity on a de Sitter thick braneworld without scalar fields
In this work we present a simple thick braneworld model that is generated by
an intriguing interplay between a 5D cosmological constant with a de Sitter
metric induced in the 3-brane without the inclusion of scalar fields. We show
that 4D gravity is localized on this brane, provide analytic expressions for
the massive Kaluza-Klein (KK) fluctuation modes and also show that the spectrum
of metric excitations displays a mass gap. We finally present the corrections
to Newton's law due to these massive modes. This model has no naked
singularities along the fifth dimension despite the existence of a mass gap in
the graviton spectrum as it happens in thick branes with 4D Poincare symmetry,
providing a simple model with very good features: the curvature is completely
smooth along the fifth dimension, it localizes 4D gravity and the spectrum of
gravity fluctuations presents a mass gap, a fact that rules out the existence
of phenomenologically dangerous ultralight KK excitations in the model. We
finally present our solution as a limit of scalar thick branes.Comment: 11 pages in latex, no figures, title and abstract changed, a new
section and some references adde
Psychophysiological measures of stress in caregivers of individuals with autism spectrum disorder: a systematic review
Purpose: Parents of children with autism spectrum disorder (ASD) often self-report heightened levels of stress and physical health problems. This paper reviewed studies assessing physiological measures of stress among parents of children with ASD.
Methods: Systematic database searches identified 15 studies meeting inclusion criteria. Studies were reviewed to determine: (a) control group characteristics; (b) caregiver and care recipient characteristics; (c) setting; (d) physiological measures employed; (e) physiological outcomes; and (f) stressor type. A measure of methodological quality was also applied.
Results: Salivary cortisol was the most common physiological measure employed. A pattern of blunted physiological activity emerged within the reviewed studies, though some studies reported normal or even higher physiological activity among this population.
Conclusions: Findings suggested dysfunction of the hypothalamic-pituitary-adrenal-axis and autonomic nervous system for some, but not all, parents of children with ASD. Further research is warranted
Genetics, recombination and clinical features of human rhinovirus species C (HRV-C) infections; interactions of HRV-C with other respiratory viruses
To estimate the frequency, molecular epidemiological and clinical associations of infection with the newly described species C variants of human rhinoviruses (HRV), 3243 diagnostic respiratory samples referred for diagnostic testing in Edinburgh were screened using a VP4-encoding region-based selective polymerase chain reaction (PCR) for HRV-C along with parallel PCR testing for 13 other respiratory viruses. HRV-C was the third most frequently detected behind respiratory syncytial virus (RSV) and adenovirus, with 141 infection episodes detected among 1885 subjects over 13 months (7.5%). Infections predominantly targeted the very young (median age 6–12 months; 80% of infections in those <2 years), occurred throughout the year but with peak incidence in early winter months. HRV-C was detected significantly more frequently among subjects with lower (LRT) and upper respiratory tract (URT) disease than controls without respiratory symptoms; HRV-C mono-infections were the second most frequently detected virus (behind RSV) in both disease presentations (6.9% and 7.8% of all cases respectively). HRV variants were classified by VP4/VP2 sequencing into 39 genotypically defined types, increasing the current total worldwide to 60. Through sequence comparisons of the 5′untranslated region (5′UTR), the majority grouped with species A (n = 96; 68%, described as HRV-Ca), the remainder forming a phylogenetically distinct 5′UTR group (HRV-Cc). Multiple and bidirectional recombination events between HRV-Ca and HRV-Cc variants and with HRV species A represents the most parsimonious explanation for their interspersed phylogeny relationships in the VP4/VP2-encoding region. No difference in age distribution, seasonality or disease associations was identified between HRV-Ca and HRV-Cc variants. HRV-C-infected subjects showed markedly reduced detection frequencies of RSV and other respiratory viruses, providing evidence for a major interfering effect of HRV-C on susceptibility to other respiratory virus infections. HRV-C's disease associations, its prevalence and evidence for interfering effects on other respiratory viruses mandates incorporation of rhinoviruses into future diagnostic virology screening
Supersymmetric Monojets at the Large Hadron Collider
Supersymmetric monojets may be produced at the Large Hadron Collider by the
process qg -> squark neutralino_1 -> q neutralino_1 neutralino_1, leading to a
jet recoiling against missing transverse momentum. We discuss the feasibility
and utility of the supersymmetric monojet signal. In particular, we examine the
possible precision with which one can ascertain the neutralino_1-squark-quark
coupling via the rate for monojet events. Such a coupling contains information
on the composition of the neutralino_1 and helps bound dark matter direct
detection cross-sections and the dark matter relic density of the neutralino_1.
It also provides a check of the supersymmetric relation between gauge couplings
and gaugino-quark-squark couplings.Comment: 46 pages, 10 figures. The appendix has been rewritten to correct an
error that appears in all previous versions of the appendix. This error has
no effect on the results in the main body of the pape
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