3,358 research outputs found
Identifying disparity to improve outcomes: Diabetes-related knowledge assessment among primary health care providers in Armenia
High-latitude HF Doppler observations of ULF waves. 1. Waves with large spatial scale sizes
Accelerating Cosmic Microwave Background map-making procedure through preconditioning
Estimation of the sky signal from sequences of time ordered data is one of
the key steps in Cosmic Microwave Background (CMB) data analysis, commonly
referred to as the map-making problem. Some of the most popular and general
methods proposed for this problem involve solving generalised least squares
(GLS) equations with non-diagonal noise weights given by a block-diagonal
matrix with Toeplitz blocks. In this work we study new map-making solvers
potentially suitable for applications to the largest anticipated data sets.
They are based on iterative conjugate gradient (CG) approaches enhanced with
novel, parallel, two-level preconditioners. We apply the proposed solvers to
examples of simulated non-polarised and polarised CMB observations, and a set
of idealised scanning strategies with sky coverage ranging from nearly a full
sky down to small sky patches. We discuss in detail their implementation for
massively parallel computational platforms and their performance for a broad
range of parameters characterising the simulated data sets. We find that our
best new solver can outperform carefully-optimised standard solvers used today
by a factor of as much as 5 in terms of the convergence rate and a factor of up
to in terms of the time to solution, and to do so without significantly
increasing the memory consumption and the volume of inter-processor
communication. The performance of the new algorithms is also found to be more
stable and robust, and less dependent on specific characteristics of the
analysed data set. We therefore conclude that the proposed approaches are well
suited to address successfully challenges posed by new and forthcoming CMB data
sets.Comment: 19 pages // Final version submitted to A&
Radio emission models of Colliding-Wind Binary Systems
We present calculations of the spatial and spectral distribution of the radio
emission from a wide WR+OB colliding-wind binary system based on
high-resolution hydrodynamical simulations and solutions to the radiative
transfer equation. We account for both thermal and synchrotron radio emission,
free-free absorption in both the unshocked stellar wind envelopes and the
shocked gas, synchrotron self-absorption, and the Razin effect. The
applicability of these calculations to modelling radio images and spectra of
colliding-wind systems is demonstrated with models of the radio emission from
the wide WR+OB binary WR147. Its synchrotron spectrum follows a power-law
between 5 and 15 GHz but turns down to below this at lower and higher
frequencies. We find that while free-free opacity from the circum-binary
stellar winds can potentially account for the low-frequency turnover, models
that also include a combination of synchrotron self-absorption and Razin effect
are favoured. We argue that the high-frequency turn down is a consequence of
inverse-Compton cooling. We present our resulting spectra and intensity
distributions, along with simulated MERLIN observations of these intensity
distributions. From these we argue that the inclination of the WR147 system to
the plane of the sky is low. We summarise by considering extensions of the
current model that are important for models of the emission from closer
colliding wind binaries, in particular the dramatically varying radio emission
of WR140.Comment: 18 pages, 18 figures; Accepted by Astronomy and Astrophysics, July 8,
200
Submillimeter Follow-up of WISE-Selected Hyperluminous Galaxies
We have used the Caltech Submillimeter Observatory (CSO) to follow-up a
sample of WISE-selected, hyperluminous galaxies, so called W1W2-dropout
galaxies. This is a rare (~ 1000 all-sky) population of galaxies at high
redshift (peaks at z=2-3), that are faint or undetected by WISE at 3.4 and 4.6
um, yet are clearly detected at 12 and 22 um. The optical spectra of most of
these galaxies show significant AGN activity. We observed 14 high-redshift (z >
1.7) W1W2-dropout galaxies with SHARC-II at 350 to 850 um, with 9 detections;
and observed 18 with Bolocam at 1.1 mm, with five detections. Warm Spitzer
follow-up of 25 targets at 3.6 and 4.5 um, as well as optical spectra of 12
targets are also presented in the paper. Combining WISE data with observations
from warm Spitzer and CSO, we constructed their mid-IR to millimeter spectral
energy distributions (SEDs). These SEDs have a consistent shape, showing
significantly higher mid-IR to submm ratios than other galaxy templates,
suggesting a hotter dust temperature. We estimate their dust temperatures to be
60-120 K using a single-temperature model. Their infrared luminosities are well
over 10^{13} Lsun. These SEDs are not well fitted with existing galaxy
templates, suggesting they are a new population with very high luminosity and
hot dust. They are likely among the most luminous galaxies in the Universe. We
argue that they are extreme cases of luminous, hot dust-obscured galaxies
(DOGs), possibly representing a short evolutionary phase during galaxy merging
and evolution. A better understanding of their long-wavelength properties needs
ALMA as well as Herschel data.Comment: Will be Published on Sep 1, 2012 by Ap
325-MHz observations of the ELAIS-N1 field using the Giant Metrewave Radio Telescope
We present observations of the European Large-Area {\it ISO} Survey-North 1
(ELAIS-N1) at 325 MHz using the Giant Metrewave Radio Telescope (GMRT), with
the ultimate objective of identifying active galactic nuclei and starburst
galaxies and examining their evolution with cosmic epoch. After combining the
data from two different days we have achieved a median rms noise of Jy beam, which is the lowest that has been achieved at this
frequency. We detect 1286 sources with a total flux density above Jy. In this paper, we use our deep radio image to examine the spectral
indices of these sources by comparing our flux density estimates with those of
Garn et al. at 610 MHz with the GMRT, and surveys with the Very Large Array at
1400 MHz. We attempt to identify very steep spectrum sources which are likely
to be either relic sources or high-redshift objects as well as inverted-spectra
objects which could be Giga-Hertz Peaked Spectrum objects. We present the
source counts, and report the possibility of a flattening in the normalized
differential counts at low flux densities which has so far been reported at
higher radio frequencies.Comment: The paper contains 15 figures and 5 tables. Accepted for publication
in MNRA
Apparatus for a Search for T-violating Muon Polarization in Stopped-Kaon Decays
The detector built at KEK to search for T-violating transverse muon
polarization in K+ --> pi0 mu+ nu (Kmu3) decay of stopped kaons is described.
Sensitivity to the transverse polarization component is obtained from
reconstruction of the decay plane by tracking the mu+ through a toroidal
spectrometer and detecting the pi0 in a segmented CsI(Tl) photon calorimeter.
The muon polarization was obtained from the decay positron asymmetry of muons
stopped in a polarimeter. The detector included features which minimized
systematic errors while maintaining high acceptance.Comment: 56 pages, 30 figures, submitted to NI
No Detectable Fertility Benefit from a Single Additional Mating in Wild Stalk-Eyed Flies
Background: Multiple mating by female insects is widespread, and the explanation(s) for repeated mating by females has been the subject of much discussion. Females may profit from mating multiply through direct material benefits that increase their own reproductive output, or indirect genetic benefits that increase offspring fitness. One particular direct benefit that has attracted significant attention is that of fertility assurance, as females often need to mate multiply to achieve high fertility. This hypothesis has never been tested in a wild insect population.Methodology/Principal Findings: Female Malaysian stalk-eyed flies (Teleopsis dalmanni) mate repeatedly during their lifetime, and have been shown to be sperm limited under both laboratory and field conditions. Here we ask whether receiving an additional mating alleviates sperm limitation in wild females. In our experiment one group of females received a single additional mating, while a control group received an interrupted, and therefore unsuccessful, mating. Females that received an additional mating did not lay more fertilised eggs in total, nor did they lay proportionately more fertilised eggs. Female fertility declined significantly through time, demonstrating that females were sperm limited. However, receipt of an additional mating did not significantly alter the rate of this decline.Conclusions/Significance: Our data suggest that the fertility consequences of a single additional mating were small. We discuss this effect (or lack thereof), and suggest that it is likely to be attributed to small ejaculate size, a high proportion of failed copulations, and the presence of X-linked meiotic drive in this species
Santorini, Another Meteorite on Mars and Third of a Kind
The Mars Exploration Rover (MER) Opportunity has been studying Meridiani Planum for five years. On sol 1634 of its mission, Opportunity left Victoria crater after investigating it for approximately 682 sols [1] and is now on a journey towards Endeavour, a 24 km diameter crater about 12 km southeast of Victoria. A priority along the way is the investigation of cobbles, which in the jargon of the MER science team denotes any loose rock fragment larger than a couple of centimeters. Cobbles investigated thus far are of diverse origin [2] and provide the only means to investigate material other than the ubiquitous sulfate-rich outcrop, basaltic sand or hematiterich spherules dubbed blueberries. Some of these cobbles are meteorites [3]. Meteorites on Mars are not just a curiosity that make Mars a more Earth-like planet. Metallic iron in meteorites, for example, may be used as a more sensitive tracer for volatile surface interactions compared to igneous minerals [4]. Between sols 1713 and 1749, including the period of Mars solar conjunction, Opportunity investigated a cobble informally named Santorini. Its chemical and mineralogical composition is very similar to Barberton and Santa Catarina, two cobbles that were identified as meteorites and which are probably related to each other [3]. Santorini was investigated with the rover s Panoramic Camera (Pancam), Microscopic Imager (MI), Alpha-Particle X-ray Spectrometer (APXS) and Moessbauer (MB) spectrometer. The miniature Thermal Emission Spectrometer (mini-TES) was not operational at the time. The Rock Abrasion Tool (RAT) could not be used to brush off potential dust coatings because of unfavorable geometry
GMASS Ultradeep Spectroscopy of Galaxies at 1.4<z<2. II. Superdense passive galaxies: how did they form and evolve ?
We combine ultradeep optical spectroscopy from the GMASS project ("Galaxy
Mass Assembly ultradeep Spectroscopic Survey") with GOODS multi-band photometry
and HST imaging to study a sample of passive galaxiesat 1.39<z<1.99 selected at
4.5 microns. A stacked spectrum with an equivalent integration time of ~500
hours was obtained is publicly released. The spectral and photometric SED
properties indicate very weak or absent star formation, moderately old stellar
ages of ~1 Gyr (for solar metallicity) and stellar masses in the range of
10^{10-11} solar masses, thus implying that the major star formation and
assembly processes for these galaxies occurred at z>2. These galaxies have
morphologies that are predominantly compact and spheroidal.However, their sizes
(R_e <~ 1 kpc) are much smaller than those of spheroids in the present--day
Universe. Their stellar mass surface densities are consequently higher by ~1
dex if compared to spheroids at z~0 with the same mass. Their rest-frame B-band
surface brightness scales with the effective radius, but the offset with
respect to the surface brightness of the local Kormendy relation is too large
to be explained by simple passive evolution. At z~1, a larger fraction of
passive galaxies follows the z~0 size -- mass relation. Superdense relics with
R_e~1 kpc are extremely rare at z~0 with respect to z>1, and absent if R_e<1
kpc. Because of the similar sizes and mass densities, we suggest that the
superdense passive galaxies at 1<z<2 are the remnants of the powerful
starbursts occurring in submillimeter--selected galaxies at z>2. The results
are compared with theoretical models and the main implications discussed in the
framework of massive galaxy formation and evolution.Comment: 22 pages, 23 figures, Astronomy & Astrophysics, in pres
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