3,068 research outputs found
Anisotropy and inflation in Bianchi I brane worlds
After a more general assumption on the influence of the bulk on the brane, we
extend some conclusions by Maartens et al. and Santos et al. on the asymptotic
behavior of Bianchi I brane worlds. As a consequence of the nonlocal
anisotropic stresses induced by the bulk, in most of our models, the brane does
not isotropize and the nonlocal energy does not vanish in the limit in which
the mean radius goes to infinity. We have also found the intriguing possibility
that the inflation due to the cosmological constant might be prevented by the
interaction with the bulk. We show that the problem for the mean radius can be
completely solved in our models, which include as particular cases those in the
references above.Comment: 10 pages, improved discussion on the likeliness of
non-isotropization, completed list of references, matches version to appear
in Class. Quantum Gra
Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in the Globular Cluster M15: II. Kinematical Analysis and Dynamical Modeling
We analyze HST/STIS spectra (see Paper I) of the central region of the dense
globular cluster M15. We infer the velocities of 64 individual stars,
two-thirds of which have their velocity measured for the first time. This
triples the number of stars with measured velocities in the central 1 arcsec of
M15 and doubles the number in the central 2 arcsec. Combined with existing
ground-based data we obtain the radial profiles of the projected kinematical
quantities. The RMS velocity sigma_RMS rises to 14 km/s in the central few
arcsec, somewhat higher than the values of 10-12 km/s inferred previously from
ground-based data. To interpret the results we construct dynamical models based
on the Jeans equation, which imply that M15 must have a central concentration
of non-luminous material. If this is due to a single black hole, then its mass
is M_BH = (3.9 +/- 2.2) x 10^3 solar masses. This is consistent with the
relation between M_BH and sigma_RMS that has been established for galaxies.
Also, the existence of intermediate-mass black holes in globular clusters is
consistent with several scenarios for globular cluster evolution proposed in
the literature. Therefore, these results may have important implications for
our understanding of the evolution of globular clusters, the growth of black
holes, the connection between globular cluster and galaxy formation, and the
nature of the recently discovered `ultra-luminous' X-ray sources in nearby
galaxies. Instead of a single black hole, M15 could have a central
concentration of dark remnants (e.g., neutron stars) due to mass segregation.
However, the best-fitting Fokker-Planck models that have previously been
constructed for M15 do not predict a central mass concentration that is
sufficient to explain the observed kinematics.[ABRIDGED]Comment: 43 pages, LaTeX, with 14 PostScript figures. Astronomical Journal, in
press (Dec 2002). Please note that the results reported here are modified by
the Addendum available at astro-ph/0210158 (Astronomical Journal, in press,
Jan 2003). This second version submitted to astro-ph is identical to first,
with the exception of the preceeding remar
3-D Photoionization Structure and Distances of Planetary Nebulae II. Menzel 1
We present the results of a spatio-kinematic study of the planetary nebula
Menzel 1 using spectro-photometric mapping and a 3-D photoionization code. We
create several 2-D emission line images from our long-slit spectra, and use
these to derive the line fluxes for 15 lines, the Halpha/Hbeta extinction map,
and the [SII] line ratio density map of the nebula. We use our photoionization
code constrained by these data to derive the three-dimensional nebular
structure and ionizing star parameters of Menzel 1 by simultaneously fitting
the integrated line intensities, the density map, and the observed morphologies
in several lines, as well as the velocity structure. Using theoretical
evolutionary tracks of intermediate and low mass stars, we derive a mass for
the central star of 0.63+-0.05 Msolar. We also derive a distance of 1050+_150
pc to Menzel 1.Comment: To be published in ApJ of 10th February 2005. 12 figure
Subpopulations of bovine WC1+ γδ T cells rather than CD4+CD25highFoxp3+ T cells act as immune regulatory cells ex vivo
Regulatory T cells (Treg) are regarded essential components for maintenance of immune homeostasis. Especially CD4+CD25high T cells are considered to be important regulators of immune reactivity. In humans and rodents these natural Treg are characterized by their anergic nature, defined as a non-proliferative state, suppressive function and expression of Foxp3. In this study the potential functional role of flowcytometry-sorted bovine white blood cell populations, including CD4+CD25high T cells and γδ T cell subpopulations, as distinct ex vivo regulatory cells was assessed in co-culture suppression assays. Our findings revealed that despite the existence of a distinct bovine CD4+CD25high T cell population, which showed Foxp3 transcription/expression, natural regulatory activity did not reside in this cell population. In bovine co-culture suppression assays these cells were neither anergic nor suppressive. Subsequently, the following cell populations were tested functionally for regulatory activity: CD4+CD25low T cells, WC1+, WC1.1+ and WC1.2+ γδ T cells, NK cells, CD8+ T cells and CD14+ monocytes. Only the WC1.1+ and WC1.2+ γδ T cells and CD14+ monocytes proved to act as regulatory cells in cattle, which was supported by the fact that these regulatory cells showed IL-10 transcription/expression. In conclusion, our data provide first evidence that cattle CD4+CD25highFoxp3+ and CD4+CD25low T cells do not function as Treg ex vivo. The bovine Treg function appears to reside in the γδ T cell population, more precisely in the WC1.1+ and the WC1.2+ subpopulation, major populations present in blood of cattle in contrast to non-ruminant species
Straylight Measurements in Two Different Apodized Diffractive Multifocal Intraocular Lenses
Quantum Gravity in Large Dimensions
Quantum gravity is investigated in the limit of a large number of space-time
dimensions, using as an ultraviolet regularization the simplicial lattice path
integral formulation. In the weak field limit the appropriate expansion
parameter is determined to be . For the case of a simplicial lattice dual
to a hypercube, the critical point is found at (with ) separating a weak coupling from a strong coupling phase, and with degenerate zero modes at . The strong coupling, large , phase is
then investigated by analyzing the general structure of the strong coupling
expansion in the large limit. Dominant contributions to the curvature
correlation functions are described by large closed random polygonal surfaces,
for which excluded volume effects can be neglected at large , and whose
geometry we argue can be approximated by unconstrained random surfaces in this
limit. In large dimensions the gravitational correlation length is then found
to behave as , implying for the universal
gravitational critical exponent the value at .Comment: 47 pages, 2 figure
Interventions with potential to reduce sedentary time in adults:Systematic review and meta-analysis
Context: Time spent in sedentary behaviours (SB) is associated with poor health, irrespective of the level of physical activity. The aim of this study was to evaluate the effect of interventions which included SB as an outcome measure in adults.
Methods: Thirteen databases, including The Cochrane Library, MEDLINE and SPORTDiscus, trial registers and reference lists, were searched for randomised controlled trials until January 2014. Study selection, data extraction and quality assessment were performed independently. Primary outcomes included SB, proxy measures of SB and patterns of accumulation of SB. Secondary outcomes were cardiometabolic health, mental health and body composition. Intervention types were categorised as SB only, physical activity (PA) only, PA and SB or lifestyle interventions (PA/SB and diet).
Results: Of 8087 records, 51 studies met the inclusion criteria. Meta-analysis of 34/51 studies showed a reduction of 22 min/day in sedentary time in favour of the intervention group (95% CI −35 to −9 min/day, n=5868). Lifestyle interventions reduced SB by 24 min/day (95% CI −41 to −8 min/day, n=3981, moderate quality) and interventions focusing on SB only by 42 min/day (95% CI −79 to −5 min/day, n=62, low quality). There was no evidence of an effect of PA and combined PA/SB interventions on reducing sedentary time.
Conclusions: There was evidence that it is possible to intervene to reduce SB in adults. Lifestyle and SB only interventions may be promising approaches. More high quality research is needed to determine if SB interventions are sufficient to produce clinically meaningful and sustainable reductions in sedentary time
Increasing Short-Stay Unplanned Hospital Admissions among Children in England; Time Trends Analysis '97-'06
BACKGROUND: Timely care by general practitioners in the community keeps children out of hospital and provides better continuity of care. Yet in the UK, access to primary care has diminished since 2004 when changes in general practitioners' contracts enabled them to 'opt out' of providing out-of-hours care and since then unplanned pediatric hospital admission rates have escalated, particularly through emergency departments. We hypothesised that any increase in isolated short stay admissions for childhood illness might reflect failure to manage these cases in the community over a 10 year period spanning these changes.
METHODS AND FINDINGS: We conducted a population based time trends study of major causes of hospital admission in children 2 days. By 2006, 67.3% of all unplanned admissions were isolated short stays <2 days. The increases in admission rates were greater for common non-infectious than infectious causes of admissions.
CONCLUSIONS: Short stay unplanned hospital admission rates in young children in England have increased substantially in recent years and are not accounted for by reductions in length of in-hospital stay. The majority are isolated short stay admissions for minor illness episodes that could be better managed by primary care in the community and may be evidence of a failure of primary care services
Dynamical Instabilities of the Randall-Sundrum Model
We derive dynamical equations to describe a single 3-brane containing fluid
matter and a scalar field coupling to the dilaton and the gravitational field
in a five dimensional bulk. First, we show that a scalar field or an arbitrary
fluid on the brane cannot evolve to cancel the cosmological constant in the
bulk. Then we show that the Randall-Sundrum model is unstable under small
deviations from the fine-tuning between the brane tension and the bulk
cosmological constant and even under homogeneous gravitational perturbations.
Implications for brane world cosmologies are discussed.Comment: 12 pages, 2 figure
Axisymmetric metrics in arbitrary dimensions
We consider axially symmetric static metrics in arbitrary dimension, both
with and without a cosmological constant. The most obvious such solutions have
an SO(n) group of Killing vectors representing the axial symmetry, although one
can also consider abelian groups which represent a flat `internal space'. We
relate such metrics to lower dimensional dilatonic cosmological metrics with a
Liouville potential. We also develop a duality relation between vacuum
solutions with internal curvature and those with zero internal curvature but a
cosmological constant. This duality relation gives a solution generating
technique permitting the mapping of different spacetimes. We give a large class
of solutions to the vacuum or cosmological constant spacetimes. We comment on
the extension of the C-metric to higher dimensions and provide a novel solution
for a braneworld black hole.Comment: 36 pages, LaTeX (JHEP), 4 figures, section added (published version
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