418 research outputs found
An Exact Calculation of the Energy Density of Cosmological Gravitational Waves
In this paper we calculate the Bogoliubov coefficients and the energy density
of the stochastic gravitational wave background for a universe that undergoes
inflation followed by radiation domination and matter domination, using a
formalism that gives the Bogoliubov coefficients as continous functions of
time. By making a reasonable assumption for the equation of state during
reheating, we obtain in a natural way the expected high frequency cutoff in the
spectral energy density.Comment: 12 pages+5 figures, uuencoded file,DF/IST-2.9
Survey measurements of community norms on adolescent girls and young women's (AGYW) sexual behaviour and use of condoms for HIV prevention in Manicaland, East Zimbabwe
Background: Qualitative data suggest pre-marital sex stigma presents a major obstacle to AGYW's use of HIV prevention methods. Lack of social acceptability therefore is included as a barrier to motivation to use condoms in HIV prevention cascades. Representative survey data on community norms are rare but necessary to test the validity of this assumption and measure their contributions to gaps in prevention cascades. Methods: General-population survey participants in Manicaland (agesâ„15,N = 9803) were asked if they agreed/disagreed with statements on social norms. AGYW were asked whether community views are an obstacle to their using condoms. Proportions agreeing/disagreeing with these statements were calculated, variations in community membersâ views were investigated in multivariable logistic-regression models, and the association between AGYW's perceiving negative community norms and condom use was measured. Results: 93.5%(95%CI,93%-94%) of respondents agreed that âMany young women have sex before marriage these daysâ. 57%(56%-59%) of men and 70%(69%-71%) of women disagreed that âIf I have a teenage daughter and she has sex before marriage, I would be ok with thisâ; and 41%(40%-43%) of men and 57%(56%-59%) of women disagreed that âIf I have a teenage daughter, I would tell her about condomsâ. Fathers but not mothers were more likely to disagree with their daughters having sex before marriage (Figure). Similar proportions of parents and other community members were against telling daughters about condoms. 68%(61%-75%) of sexually-active unmarried AGYW said negative community views were unimportant in decisions to use condoms. Condom use didn't differ between those who agreed/disagreed that negative community views are important (46.9% vs. 50.0%; AOR = 0.88, 95%CI, 0.48â1.62; N = 202). Conclusions: Community resistance to condom promotion based on pre-marital sex stigma may be weakening as a barrier to AGYW's motivation to use condoms in Manicaland. Community-led interventions to accelerate this dynamic in social norms and support AGYW's agency could reduce HIV incidence
The diet of red-throated divers (Gavia stellata) overwintering in the German Bight (North Sea) analysed using molecular diagnostics
In Europe, the German Bight is one of the most important non-breeding areas for protected red-throated divers (Gavia stellata). It is unclear what attracts the birds to this area, especially as the food composition of seabirds outside the breeding season is notoriously difficult to study. To obtain information on prey species composition of red-throated divers in this area, faecal samples from 34 birds caught alive were analysed using DNA metabarcoding. Prey DNA was detected in 85% of the samples with a mean number of 4.2â±â0.7 taxa per sample (nâ=â29). Altogether, we found a broad prey spectrum with 19 fish taxa from 13 families dominated by five groups: clupeids, mackerel, gadoids, flatfish and sand lances with clupeids being the most frequently detected prey. Our results indicate that red-throated divers are generalist opportunistic feeders in the German Bight, but pelagic schooling fish that aggregate at frontal zones and have a high energetic value might be favoured. Atlantic mackerel appears to be a more important prey for red-throated divers in this area than previously thought. The precision achievable using metabarcoding has revealed a number of prey species that are consumed by red-throated divers in the German Bight, which helps to explain the selection of this area by divers in winter and spring
Post-Inflationary Reheating
We study a model for reheating that has been much investigated for parametric
resonance, having a quartic interaction of the scalar inflaton with another
scalar field. Attention is particularly on the quantum excitations of the
inflaton field and the metric perturbation with a smooth transition from
quantum to classical stochastic states, followed through from a specific
inflation model to a state including a relativistic fluid. The scalar fields
enter non-perturbatively but the metric enters perturbatively, and the validity
of this latter is assessed. In this model our work seems to point the large
scale curvature parameter changing.Comment: 25 pages, 6 figures. Coding error(misprint) corrected:figures and
some conclusions change
Nucleonic resonance excitations with linearly polarized photon in
In this work, an improved quark model approach to the meson
photo-production with an effective Lagrangian is presented. The {\it t}-channel
{\it natural}-parity exchange is taken into account through the Pomeron
exchange, while the {\it unnatural}-parity exchange is described by the
exchange. With a very limited number of parameters, the available experimental
data in the low energy regime can be consistently accounted for. We find that
the beam polarization observables show sensitivities to some {\it s}-channel
individual resonances in the quark model symmetry limit.
Especially, the two resonances and , which belong
to the representation , have dominant contributions
over other excited states. Concerning the essential motivation of searching for
"missing resonances" in meson photo-production, this approach provides a
feasible framework, on which systematic investigations can be done.Comment: 16 pages, Revtex, 9 eps figures, to appear in PR
Vector Meson Photoproduction with an Effective Lagrangian in the Quark Model
A quark model approach to the photoproduction of vector mesons off nucleons
is proposed. Its starting point is an effective Lagrangian of the interaction
between the vector meson and the quarks inside the baryon, which generates the
non-diffractive s- and u- channel resonance contributions. Additional t-channel
and exchanges are included for the and
production respectively to account for the large diffractive behavior in the
small region as suggested by Friman and Soyeur. The numerical results are
presented for the and productions in four isospin channels with
the same set of parameters, and they are in good agreement with the available
data not only in and productions but also in the charged
productions where the additional t-channel exchange does not
contribute so that it provides an important test to this approach. The
investigation is also extended to the photoproduction, and the initial
results show that the non-diffractive behavior of the productions in the
large region can be described by the s- and u- channel contributions with
significantly smaller coupling constants, which is consistent with the findings
in the similar studies in the QHD framework. The numerical investigation has
also shown that polarization observables are essential for identifying
so-called "missing resonances".Comment: 36 pages, 10 PS figures, extended version of nucl-th/9711061 and
nucl-th/9803021, submitted to PR
Environmental impact of wind energy:Synthesis and Review
One purpose of wind turbines is to provide pollution-free electric power at a reasonable price in an environmentally sound way. In this focus issue the latest research on the environmental impact of wind farms is presented. Offshore wind farms affect the marine fauna in both positive and negative ways. For example, some farms are safe havens for porpoises while other farms show fewer harbor porpoises even after ten years. Atmospheric computer experiments are carried out to investigate the possible impact and resource of future massive installations of wind turbines. The following questions are treated. What is the global capacity for energy production by the wind? Will the added turbulence and reduced wind speeds generated by massive wind farms cool or heat the surface? Can wind farms affect precipitation? It is also shown through life-cycle analysis how wind energy can reduce the atmospheric emission of eight air pollutants. Finally, noise generation and its impact on humans are studied
An Unified Approach To Pseudo Scalar Meson Photoproductions Off Nucleons In The Quark Model
An unified approach to the pseudo scalar meson (, and )
photoproduction off nucleons are presented. It begins with the low energy QCD
Lagrangian, and the resonances in the s- and u- channels are treated in the
framework of the quark model
The duality hypothesis is imposed to limit the number of the t-channel
exchanges. The CGLN amplitudes for each reaction are evaluated, which include
both proton and neutron targets. The important role by the S-wave resonances in
the second resonance region is discussed, it is particularly important for the
and photoproductions.Comment: 31 pages in Latex fil
Prognostically useful gene-expression profiles in acute myeloid leukemia
BACKGROUND: In patients with acute myeloid leukemia (AML) a combination of
methods must be used to classify the disease, make therapeutic decisions,
and determine the prognosis. However, this combined approach provides
correct therapeutic and prognostic information in only 50 percent of
cases. METHODS: We determined the gene-expression profiles in samples of
peripheral blood or bone marrow from 285 patients with AML using
Affymetrix U133A GeneChips containing approximately 13,000 unique genes or
expression-signature tags. Data analyses were carried out with Omniviz,
significance analysis of microarrays, and prediction analysis of
microarrays software. Statistical analyses were performed to determine the
prognostic significance of cases of AML with specific molecular
signatures. RESULTS: Unsupervised cluster analyses identified 16 groups of
patients with AML on the basis of molecular signatures. We identified the
genes that defined these clusters and determined the minimal numbers of
genes needed to identify prognostically important clusters with a high
degree of accuracy. The clustering was driven by the presence of
chromosomal lesions (e.g., t(8;21), t(15;17), and inv(16)), particular
genetic mutations (CEBPA), and abnormal oncogene expression (EVI1). We
identified several novel clusters, some consisting of specimens with
normal karyotypes. A unique cluster with a distinctive gene-expression
signature included cases of AML with a poor treatment outcome.
CONCLUSIONS: Gene-expression profiling allows a comprehensive
classification of AML that includes previously identified genetically
defined subgroups and a novel cluster with an adverse prognosis
- âŠ