248 research outputs found
Are group- and cluster-scale dark matter halos over-concentrated?
We investigate the relationship between the halo mass, M_200, and
concentration, c, for a sample of 26 group- and cluster-scale strong
gravitational lenses. In contrast with previous results, we find that these
systems are only ~ 0.1 dex more over-concentrated than similar-mass halos from
dark matter simulations; the concentration of a halo with M_200 = 10^14 M_sun
is log c = 0.78\pm0.05, while simulations of halos with this mass at similar
redshifts (z ~ 0.4) predict log c ~ 0.56 - 0.71. We also find that we are
unable to make informative inference on the slope of the M_200-c relation in
spite of our large sample size; we note that the steep slopes found in previous
studies tend to follow the slope in the covariance between M_200 and c,
indicating that these results may be measuring the scatter in the data rather
than the intrinsic signal. Furthermore, we conclude that our inability to
constrain the M_200-c slope is due to a limited range of halo masses, as
determined by explicitly modelling our halo mass distribution, and we suggest
that other studies may be producing biased results by using an incorrect
distribution for their halo masses.Comment: 8 pages; accepted to MNRA
A rapid review of communication strategies for physical activity guidelines and physical activity promotion: A review of worldwide strategies
BACKGROUND: To support the strategy development for communication of the updated physical activity (PA) guidelines, the UK Chief Medical Officers’ Expert Panel for Communication was created.
METHODS: To help inform this process a rapid review was performed to identify and describe how other nations are communicating their PA guidelines and PA generally. Elements of the Health enhancing physical activity (HEPA) policy audit tool (PAT) created by the World Health Organization (WHO) were used to investigate all 195 countries.
RESULTS: Seventy-seven countries had their own guidelines, 53 used the WHO guidelines, and for 65 countries no guidelines could be found. For the communication, 27 countries used infographics, 56 had government policies/documents, and 11 used a mass media campaign. Only 6 of these had been evaluated. Although many countries used infographics, there were no associated evaluations. As such any future communication strategies should incorporate an evaluation. Mass media campaigns had the strongest evidence base, proving to be an effective strategy, particularly when incorporating aspects of social marketing.
CONCLUSION: This review provides an insight into strategies countries worldwide have taken to communicate PA guidelines and PA promotion. These should be carefully considered when deciding how best to communicate and promote PA
guidelines
Calibration and sensitivity of the Virgo detector during its second science run
The Virgo detector is a kilometer-length interferometer for gravitational
wave detection located near Pisa (Italy). During its second science run (VSR2)
in 2009, six months of data were accumulated with a sensitivity close to its
design. In this paper, the methods used to determine the parameters for
sensitivity estimation and gravitational wave reconstruction are described. The
main quantities to be calibrated are the frequency response of the mirror
actuation and the sensing of the output power. Focus is also put on their
absolute timing. The monitoring of the calibration data as well as the
parameter estimation with independent techniques are discussed to provide an
estimation of the calibration uncertainties. Finally, the estimation of the
Virgo sensitivity in the frequency-domain is described and typical
sensitivities measured during VSR2 are shown.Comment: 30 pages, 23 figures, 1 table. Published in Classical and Quantum
Gravity (CQG), Corrigendum include
Search for Gravitational Wave Bursts from Six Magnetars
Soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are thought to be magnetars: neutron stars powered by extreme magnetic fields. These rare objects are characterized by repeated and sometimes spectacular gamma-ray bursts. The burst mechanism might involve crustal fractures and excitation of non-radial modes which would emit gravitational waves (GWs). We present the results of a search for GW bursts from six galactic magnetars that is sensitive to neutron star f-modes, thought to be the most efficient GW emitting oscillatory modes in compact stars. One of them, SGR 0501+4516, is likely similar to 1 kpc from Earth, an order of magnitude closer than magnetars targeted in previous GW searches. A second, AXP 1E 1547.0-5408, gave a burst with an estimated isotropic energy >10(44) erg which is comparable to the giant flares. We find no evidence of GWs associated with a sample of 1279 electromagnetic triggers from six magnetars occurring between 2006 November and 2009 June, in GW data from the LIGO, Virgo, and GEO600 detectors. Our lowest model-dependent GW emission energy upper limits for band-and time-limited white noise bursts in the detector sensitive band, and for f-mode ringdowns (at 1090 Hz), are 3.0 x 10(44)d(1)(2) erg and 1.4 x 10(47)d(1)(2) erg, respectively, where d(1) = d(0501)/1 kpc and d(0501) is the distance to SGR 0501+4516. These limits on GW emission from f-modes are an order of magnitude lower than any previous, and approach the range of electromagnetic energies seen in SGR giant flares for the first time.United States National Science FoundationScience and Technology Facilities Council of the United KingdomMax-Planck-SocietyState of Niedersachsen/GermanyItalian Istituto Nazionale di Fisica NucleareFrench Centre National de la Recherche ScientifiqueAustralian Research CouncilCouncil of Scientific and Industrial Research of IndiaIstituto Nazionale di Fisica Nucleare of ItalySpanish Ministerio de Educacion y CienciaConselleria d'Economia Hisenda i Innovacio of the Govern de les Illes BalearsFoundation for Fundamental Research on Matter supported by the Netherlands Organisation for Scientific ResearchPolish Ministry of Science and Higher EducationFoundation for Polish ScienceRoyal SocietyScottish Funding CouncilScottish Universities Physics AllianceNational Aeronautics and Space Administration NNH07ZDA001-GLASTCarnegie TrustLeverhulme TrustDavid and Lucile Packard FoundationResearch CorporationAlfred P. Sloan FoundationRussian Space AgencyRFBR 09-02-00166aIPN JPL Y503559 (Odyssey), NASA NNG06GH00G, NASA NNX07AM42G, NASA NNX08AC89G (INTEGRAL), NASA NNG06GI896, NASA NNX07AJ65G, NASA NNX08AN23G (Swift), NASA NNX07AR71G (MESSENGER), NASA NNX06AI36G, NASA NNX08AB84G, NASA NNX08AZ85G (Suzaku), NASA NNX09AU03G (Fermi)Astronom
Directional limits on persistent gravitational waves using LIGO S5 science data
The gravitational-wave (GW) sky may include nearby pointlike sources as well
as astrophysical and cosmological stochastic backgrounds. Since the relative
strength and angular distribution of the many possible sources of GWs are not
well constrained, searches for GW signals must be performed in a
model-independent way. To that end we perform two directional searches for
persistent GWs using data from the LIGO S5 science run: one optimized for
pointlike sources and one for arbitrary extended sources. The latter result is
the first of its kind. Finding no evidence to support the detection of GWs, we
present 90% confidence level (CL) upper-limit maps of GW strain power with
typical values between 2-20x10^-50 strain^2 Hz^-1 and 5-35x10^-49 strain^2
Hz^-1 sr^-1 for pointlike and extended sources respectively. The limits on
pointlike sources constitute a factor of 30 improvement over the previous best
limits. We also set 90% CL limits on the narrow-band root-mean-square GW strain
from interesting targets including Sco X-1, SN1987A and the Galactic Center as
low as ~7x10^-25 in the most sensitive frequency range near 160 Hz. These
limits are the most constraining to date and constitute a factor of 5
improvement over the previous best limits.Comment: 10 pages, 4 figure
The similarity of the stellar mass fractions of galaxy groups and clusters
We employ a large sample of 20171 optically-selected groups and clusters at
0.15 < z < 0.4 in the SDSS to investigate how the stacked stellar mass fraction
varies across a wide range of total mass, . Our study improves upon
previous observational studies in a number of important ways, including having
a much larger sample size, an explicit inclusion of the intracluster light
(ICL) component, and a thorough examination of the accuracy of our total mass
estimates via comparisons to simulations and weak lensing observations. We find
that the stellar mass fraction depends only weakly on total mass and that the
contribution of ICL to the total stellar mass fraction is significant
(typically 20-40 per cent). Both of these findings are in excellent accordance
with the predictions of cosmological simulations. Under the assumption of a
Chabrier (Salpeter) IMF, the derived star formation efficiency
(/, where ) is relatively low at 8 per
cent (14 per cent) and is consistent with the global star formation efficiency
of semi-analytic models that reproduce the galaxy stellar mass function. When
our measured stellar mass fractions are combined with the observed relation
between hot gas mass fraction and total mass from X-ray observations, our
results imply that galaxy groups have significantly lower baryon fractions than
massive clusters. Ejection of gas due to energetic AGN feedback (most likely at
high redshift) provides a plausible mechanism for explaining the trends we
observe.Comment: accepted to MNRAS; minor revision
Dusty MgII absorbers: population statistics, extinction curves and gamma-ray burst sightlines
We present a new determination of the dust content and
near-ultraviolet/optical extinction curves associated with a sample of ~8300
strong (equivalent width > 1A) Mg II absorbers, with redshifts 0.4<z<2.2,
identified in Sloan Digital Sky survey (SDSS) spectra of quasars. Taking into
account the selection effects that result from dust extinction, including the
reduction in the signal-to-noise ratio of an absorber appearing in a reddened
quasar spectrum, we find a stronger dependence of E(B-V) on absorber rest
equivalent width (EW) than in other published work. The dependence of the
median reddening on EW can be reproduced by a power-law model:
E(B-V)=.8+/-3*10-4 * EW^(3.48+/-0.3) for 1.0A<EW<5.0A. Observed Mg II samples,
derived from flux-limited quasar surveys, are shown to suffer from significant
incompleteness at the level of 24+/-4 per cent for absorbers with EW>1A and
34+/-2 per cent for absorbers with EW>2A. Direct determination of the shape of
the near-ultraviolet extinction curves for absorbers as a function of E(B-V)
show evidence for systematic changes in the form of the extinction curves. At
low E(B-V) (>0.05), the extinction curve is well represented by a Small
Magellanic Cloud-like extinction curve. For intermediate E(B-V)s (<0.2),
approximately a third of MgII absorbers show evidence for a 2175A feature
similar to that of the Large Magellanic Cloud. For the small number of high
E(B-V) (>0.3) absorbers, the majority of which exhibit strong CaII 3935,3970
absorption, there is evidence for a 2175A feature as strong as that found in
the Milky Way. Application of the new results on the dust content of strong Mg
II absorbers shows that dusty absorbers can account for a significant
proportion, up to a factor of two, of the observed overdensity of absorbers
seen towards Gamma-Ray Burst (GRB) sightlines, compared to sightlines towards
quasars in flux-limited samples. (Abridged)Comment: 21 pages, 20 figures, 2 tables, accepted for publication in MNRA
Macrophages promote angiogenesis in human breast tumour spheroids in vivo
An in vivo model has been established to study the role of macrophages in the initiation of angiogenesis by human breast tumour spheroids in vivo. The extent of the angiogenic response induced by T47D spheroids implanted into the dorsal skinfold chamber in nude mice was measured in vivo and compared to that induced by spheroids infiltrated with human macrophages prior to implantation. Our results indicate that the presence of macrophages in spheroids resulted in at least a three-fold upregulation in the release of vascular endothelial growth factor (VEGF) in vitro when compared with spheroids composed only of tumour cells. The angiogenic response measured around the spheroids, 3 days after in vivo implantation, was significantly greater in the spheroids infiltrated with macrophages. The number of vessels increased (macrophages vs no macrophages 34±1.9 vs 26±2.5, P<0.01), were shorter in length (macrophages vs no macrophages 116±4.92 vs 136±6.52, P<0.008) with an increased number of junctions (macrophages vs no macrophages 14±0.93 vs 11±1.25, P<0.025) all parameters indicative of new vessel formation. This is the first study to demonstrate a role for macrophages in the initiation of tumour angiogenesis in vivo
Properties of galaxies reproduced by a hydrodynamic simulation.
Previous simulations of the growth of cosmic structures have broadly reproduced the 'cosmic web' of galaxies that we see in the Universe, but failed to create a mixed population of elliptical and spiral galaxies, because of numerical inaccuracies and incomplete physical models. Moreover, they were unable to track the small-scale evolution of gas and stars to the present epoch within a representative portion of the Universe. Here we report a simulation that starts 12 million years after the Big Bang, and traces 13 billion years of cosmic evolution with 12 billion resolution elements in a cube of 106.5 megaparsecs a side. It yields a reasonable population of ellipticals and spirals, reproduces the observed distribution of galaxies in clusters and characteristics of hydrogen on large scales, and at the same time matches the 'metal' and hydrogen content of galaxies on small scales
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