162 research outputs found
Application of Time Transfer Function to McVittie Spacetime: Gravitational Time Delay and Secular Increase in Astronomical Unit
We attempt to calculate the gravitational time delay in a time-dependent
gravitational field, especially in McVittie spacetime, which can be considered
as the spacetime around a gravitating body such as the Sun, embedded in the
FLRW (Friedmann-Lema\^itre-Robertson-Walker) cosmological background metric. To
this end, we adopt the time transfer function method proposed by Le
Poncin-Lafitte {\it et al.} (Class. Quant. Grav. 21:4463, 2004) and Teyssandier
and Le Poncin-Lafitte (Class. Quant. Grav. 25:145020, 2008), which is
originally related to Synge's world function and enables to
circumvent the integration of the null geodesic equation. We re-examine the
global cosmological effect on light propagation in the solar system. The
round-trip time of a light ray/signal is given by the functions of not only the
spacial coordinates but also the emission time or reception time of light
ray/signal, which characterize the time-dependency of solutions. We also apply
the obtained results to the secular increase in the astronomical unit, reported
by Krasinsky and Brumberg (Celest. Mech. Dyn. Astron. 90:267, 2004), and we
show that the leading order terms of the time-dependent component due to
cosmological expansion is 9 orders of magnitude smaller than the observed value
of , i.e., ~[m/century]. Therefore, it is not possible
to explain the secular increase in the astronomical unit in terms of
cosmological expansion.Comment: 13 pages, 2 figures, accepted for publication in General Relativity
and Gravitatio
High-Speed Cylindrical Collapse of Two Perfect Fluids
In this paper, the study of the gravitational collapse of cylindrically
distributed two perfect fluid system has been carried out. It is assumed that
the collapsing speeds of the two fluids are very large. We explore this
condition by using the high-speed approximation scheme. There arise two cases,
i.e., bounded and vanishing of the ratios of the pressures with densities of
two fluids given by . It is shown that the high-speed approximation
scheme breaks down by non-zero pressures when are bounded
below by some positive constants. The failure of the high-speed approximation
scheme at some particular time of the gravitational collapse suggests the
uncertainity on the evolution at and after this time. In the bounded case, the
naked singularity formation seems to be impossible for the cylindrical two
perfect fluids. For the vanishing case, if a linear equation of state is used,
the high-speed collapse does not break down by the effects of the pressures and
consequently a naked singularity forms. This work provides the generalisation
of the results already given by Nakao and Morisawa [1] for the perfect fluid.Comment: 11 pages, 1 figure, accepted for publication in Gen. Rel. Gra
Critical Collapse of Cylindrically Symmetric Scalar Field in Four-Dimensional Einstein's Theory of Gravity
Four-dimensional cylindrically symmetric spacetimes with homothetic
self-similarity are studied in the context of Einstein's Theory of Gravity, and
a class of exact solutions to the Einstein-massless scalar field equations is
found. Their local and global properties are investigated and found that they
represent gravitational collapse of a massless scalar field. In some cases the
collapse forms black holes with cylindrical symmetry, while in the other cases
it does not. The linear perturbations of these solutions are also studied and
given in closed form. From the spectra of the unstable eigen-modes, it is found
that there exists one solution that has precisely one unstable mode, which may
represent a critical solution, sitting on a boundary that separates two
different basins of attraction in the phase space.Comment: Some typos are corrected. The final version to appear in Phys. Rev.
Cosmological expansion and local systems: a Lema\^{i}tre-Tolman-Bondi model
We propose a Lema\^{i}tre-Tolman-Bondi system mimicking a two-body system to
address the problem of the cosmological expansion versus local dynamics. This
system is strongly bound but participates in the cosmic expansion and is
exactly comoving with the cosmic substratum
States and transitions in black-hole binaries
With the availability of the large database of black-hole transients from the
Rossi X-Ray Timing Explorer, the observed phenomenology has become very
complex. The original classification of the properties of these systems in a
series of static states sorted by mass accretion rate proved not to be able to
encompass the new picture. I outline here a summary of the current situation
and show that a coherent picture emerges when simple properties such as X-ray
spectral hardness and fractional variability are considered. In particular,
fast transition in the properties of the fast time variability appear to be
crucial to describe the evolution of black-hole transients. Based on this
picture, I present a state-classification which takes into account the observed
transitions. I show that, in addition to transients systems, other black-hole
binaries and Active Galactic Nuclei can be interpreted within this framework.
The association between these states and the physics of the accretion flow
around black holes will be possible only through modeling of the full time
evolution of galactic transient systems.Comment: 30 pages, 11 figures, To appear in Belloni, T. (ed.): The Jet
Paradigm - From Microquasars to Quasars, Lect. Notes Phys. 794 (2009
Impact of tetanus-diphtheria-acellular pertussis immunization during pregnancy on subsequent infant immunization seroresponses : follow-up from a large randomized placebo-controlled trial
Background: Pertussis immunization during pregnancy results in high pertussis antibody concentrations in young infants but may interfere with infant immune responses to post-natal immunization. Methods: This phase IV, multi-country, open-label study assessed the immunogenicity and safety of infant primary vaccination with DTaP-HepB-IPV/Hib and 13-valent pneumococcal conjugate vaccine (PCV13). Enrolled infants (6\u201314 weeks old) were born to mothers who were randomized to receive reduced-antigen-content diphtheria-tetanus-three-component acellular pertussis vaccine (Tdap group) or placebo (control group) during pregnancy (270/7\u2013366/7 weeks\u2019 gestation) with crossover immunization postpartum. All infants received 2 or 3 DTaP-HepB-IPV/Hib and PCV13 doses according to national schedules. Immunogenicity was assessed in infants pre- and 1 month post-primary vaccination. The primary objective was to assess seroprotection/vaccine response rates for DTaP-HepB-IPV/Hib antigens 1 month post-primary vaccination. Results: 601 infants (Tdap group: 296; control group: 305) were vaccinated. One month post-priming, seroprotection rates were 100% (diphtheria; tetanus), 6598.5% (hepatitis B), 6595.9% (polio) and 6594.5% (Hib) in both groups. Vaccine response rates for pertussis antigens were significantly lower in infants whose mothers received pregnancy Tdap (37.5\u201377.1%) versus placebo (90.0\u201399.2%). Solicited and unsolicited adverse event rates were similar between groups. Serious adverse events occurred in 2.4% (Tdap group) and 5.6% (control group) of infants, none were vaccination-related. Conclusions: Pertussis antibodies transferred during pregnancy may decrease the risk of pertussis infection in the first months of life but interfere with the infant's ability to produce pertussis antibodies, the clinical significance of which remains unknown. Safety and reactogenicity results were consistent with previous experience
Early-Stage Development of Novel Cyclodextrin-siRNA Nanocomplexes Allows for Successful Postnebulization Transfection of Bronchial Epithelial Cells
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Biological and physical characterization of the seabed surrounding Ascension Island from 100–1000 m
- …