86 research outputs found
r-modes in Relativistic Superfluid Stars
We discuss the modal properties of the -modes of relativistic superfluid
neutron stars, taking account of the entrainment effects between superfluids.
In this paper, the neutron stars are assumed to be filled with neutron and
proton superfluids and the strength of the entrainment effects between the
superfluids are represented by a single parameter . We find that the
basic properties of the -modes in a relativistic superfluid star are very
similar to those found for a Newtonian superfluid star. The -modes of a
relativistic superfluid star are split into two families, ordinary fluid-like
-modes (-mode) and superfluid-like -modes (-mode). The two
superfluids counter-move for the -modes, while they co-move for the
-modes. For the -modes, the quantity is
almost independent of the entrainment parameter , where and
are the azimuthal wave number and the oscillation frequency observed by an
inertial observer at spatial infinity, respectively. For the -modes, on
the other hand, almost linearly increases with increasing . It
is also found that the radiation driven instability due to the -modes is
much weaker than that of the -modes because the matter current associated
with the axial parity perturbations almost completely vanishes.Comment: 14 pages, 4 figures. To appear in Physical Review
Poly-essential and general Hyperelastic World (brane) models
This article provides a unified treatment of an extensive category of
non-linear classical field models whereby the universe is represented (perhaps
as a brane in a higher dimensional background) in terms of a structure of a
mathematically convenient type describable as hyperelastic, for which a
complete set of equations of motion is provided just by the energy-momentum
conservation law. Particular cases include those of a perfect fluid in
quintessential backgrounds of various kinds, as well as models of the elastic
solid kind that has been proposed to account for cosmic acceleration. It is
shown how an appropriately generalised Hadamard operator can be used to
construct a symplectic structure that controles the evolution of small
perturbations, and that provides a characteristic equation governing the
propagation of weak discontinuities of diverse (extrinsic and extrinsic) kinds.
The special case of a poly-essential model - the k-essential analogue of an
ordinary polytropic fluid - is examined and shown to be well behaved (like the
fluid) only if the pressure to density ratio is positive.Comment: 16 pages Latex, Contrib. to 10th Peyresq Pysics Meeting, June 2005:
Micro and Macro Structures of Spacetim
Disappearing Dark Matter in Brane World Cosmology: New Limits on Noncompact Extra Dimensions
We explore cosmological implications of dark matter as massive particles
trapped on a brane embedded in a Randall-Sundrum noncompact higher dimension
space. It is an unavoidable consequence of this cosmology that massive
particles are metastable and can disappear into the bulk dimension. Here, we
show that a massive dark matter particle (e.g. the lightest supersymmetric
particle) is likely to have the shortest lifetime for disappearing into the
bulk. We examine cosmological constraints on this new paradigm and show that
disappearing dark matter is consistent (at the 95% confidence level) with all
cosmological constraints, i.e. present observations of Type Ia supernovae at
the highest redshift, trends in the mass-to-light ratios of galaxy clusters
with redshift, the fraction of X-ray emitting gas in rich clusters, and the
spectrum of power fluctuations in the cosmic microwave background. A best concordance region is identified corresponding to a mean lifetime for
dark matter disappearance of Gyr. The implication
of these results for brane-world physics is discussed.Comment: 7 pages, 7 figures, new cosmological constraints added, accepted for
publication in PR
Slowly Rotating General Relativistic Superfluid Neutron Stars with Relativistic Entrainment
Neutron stars that are cold enough should have two or more
superfluids/supercondutors in their inner crusts and cores. The implication of
superfluidity/superconductivity for equilibrium and dynamical neutron star
states is that each individual particle species that forms a condensate must
have its own, independent number density current and equation of motion that
determines that current. An important consequence of the quasiparticle nature
of each condensate is the so-called entrainment effect, i.e. the momentum of a
condensate is a linear combination of its own current and those of the other
condensates. We present here the first fully relativistic modelling of slowly
rotating superfluid neutron stars with entrainment that is accurate to the
second-order in the rotation rates. The stars consist of superfluid neutrons,
superconducting protons, and a highly degenerate, relativistic gas of
electrons. We use a relativistic - mean field model for the
equation of state of the matter and the entrainment. We determine the effect of
a relative rotation between the neutrons and protons on a star's total mass,
shape, and Kepler, mass-shedding limit.Comment: 30 pages, 10 figures, uses ReVTeX
Syndrome herpétique mortel chez des singes atèle nés en captivité
Un syndrome herpétique mortel a été mis en évidence chez des singes atèle dans un zoo du centre-ouest de la France. Le virus isolé, du groupe 1 de Melnick, semble proche des Herpesvirus Ateles ou Saimirí. Il n'a vrai semblablement pas été contracté par les animaux en France et est présent à l’état latent dans la colonie.A fatal herpetic syndrome had been identified on spieder-monkeys in a french zoological garden. The isolated virus belongs to Melnick group 1, and seems to be related Ateles or Saimirí Herpesvirus. Probably, the ani mals did not get it in France but were already carrying it in a silent state
WMAP and Supergravity Inflationary Models
We study a class of N=1 Supergravity inflationary models in which the
evolution of the inflaton dynamics is controlled by a single power in the
inflaton field at the point where the observed density fluctuations are
produced, in the context of the braneworld scenario, in light of WMAP results.
In particular, we find that the bounds on the spectral index and its running
constrain the parameter space both for models where the inflationary potential
is dominated by a quadratic term and by a cubic term in the inflaton field. We
also find that is required for the quadratic model whereas
for the cubic model. Moreover, we have determined an upper bound
on the five-dimensional Planck scale, M_5 \lsim 0.019 M, for the quadratic
model. On the other hand, a running spectral index with on large scales
and on small scales is not possible in either case.Comment: 7 pages, 4 eps figures, references corrected, version to appear in
Phys. Rev.
Bayesian multinomial probit modeling of daily windows of susceptibility for maternal PM2.5 exposure and congenital heart defects
Epidemiologic studies suggest that maternal ambient air pollution exposure during critical periods of pregnancy is associated with adverse effects on fetal development. In this work, we introduce new methodology for identifying critical periods of development during post-conception gestational weeks 2–8 where elevated exposure to particulate matter less than 2.5 µm (PM2.5) adversely impacts development of the heart. Past studies have focused on highly aggregated temporal levels of exposure during the pregnancy and have failed to account for anatomical similarities between the considered congenital heart defects. We introduce a multinomial probit model in the Bayesian setting that allows for joint identification of susceptible daily periods during pregnancy for 12 types of congenital heart defects with respect to maternal PM2.5 exposure. We apply the model to a dataset of mothers from the National Birth Defect Prevention Study where daily PM2.5 exposures from post-conception gestational weeks 2–8 are assigned using predictions from the downscaler pollution model. This approach is compared with two aggregated exposure models that define exposure as the average value over post-conception gestational weeks 2–8 and the average over individual weeks, respectively. Results suggest an association between increased PM2.5 exposure on post-conception gestational day 53 with the development of pulmonary valve stenosis and exposures during days 50 and 51 with tetralogy of Fallot. Significant associations are masked when using the aggregated exposure models. Simulation study results suggest that the findings are robust to multiple sources of error. The general form of the model allows for different exposures and health outcomes to be considered in future applications
Variational description of multi-fluid hydrodynamics: Uncharged fluids
We present a formalism for Newtonian multi-fluid hydrodynamics derived from
an unconstrained variational principle. This approach provides a natural way of
obtaining the general equations of motion for a wide range of hydrodynamic
systems containing an arbitrary number of interacting fluids and superfluids.
In addition to spatial variations we use ``time shifts'' in the variational
principle, which allows us to describe dissipative processes with entropy
creation, such as chemical reactions, friction or the effects of external
non-conservative forces. The resulting framework incorporates the
generalization of the entrainment effect originally discussed in the case of
the mixture of two superfluids by Andreev and Bashkin. In addition to the
conservation of energy and momentum, we derive the generalized conservation
laws of vorticity and helicity, and the special case of Ertel's theorem for the
single perfect fluid.
We explicitly discuss the application of this framework to thermally
conducting fluids, superfluids, and superfluid neutron star matter. The
equations governing thermally conducting fluids are found to be more general
than the standard description, as the effect of entrainment usually seems to be
overlooked in this context. In the case of superfluid He4 we recover the
Landau--Khalatnikov equations of the two-fluid model via a translation to the
``orthodox'' framework of superfluidity, which is based on a rather awkward
choice of variables. Our two-fluid model for superfluid neutron star matter
allows for dissipation via mutual friction and also ``transfusion'' via
beta-reactions between the neutron fluid and the proton-electron fluid.Comment: uses RevTeX 4; 20 pages. To appear in PRD. v2: removed discussion of
charged fluids and coupling to electromagnetic fields, which are submitted as
a separate paper for a clearer presentation v3: fixed typo in Eq.(9), updated
some reference
Le diagnostic anténatal modifie-t-il la prise en charge néonatale et le devenir à 1 an des enfants suivis pour atrésie de l’œsophage de type III ?
OBJECTIVE:
Evaluate neonatal management and outcome of neonates with either a prenatal or a post-natal diagnosis of EA type III.
STUDY DESIGN:
Population-based study using data from the French National Register for EA from 2008 to 2010. We compared children with prenatal versus post-natal diagnosis in regards to prenatal, maternal and neonatal characteristics. We define a composite variable of morbidity (anastomotic esophageal leaks, recurrent fistula, stenosis) and mortality at 1 year.
RESULTS:
Four hundred and eight live births with EA type III were recorded with a prenatal diagnosis rate of 18.1%. Transfer after birth was lower in prenatal subset (32.4% versus 81.5%, P<0.001). Delay between birth and first intervention was not significantly different. Defect size (2cm vs 1.4cm, P<0.001), gastrostomy (21.6% versus 8.7%, P<0.001) and length in neonatal unit care were higher in prenatal subset (47.9 days versus 33.6 days, P<0.001). The composite variables were higher in prenatal diagnosis subset (38.7% vs 26.1%, P=0.044).
CONCLUSION:
Despite the excellent survival rate of EA, cases with antenatal detection have a higher morbidity related to the EA type (longer gap). Even if it does not modify neonatal management and 1-year outcome, prenatal diagnosis allows antenatal parental counseling and avoids post-natal transfer
SPHERE/ZIMPOL observations of the symbiotic system R Aquarii. I:Imaging of the stellar binary and the innermost jet clouds
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