17,844 research outputs found
Constraints on the distribution of supernova remnants with Galactocentric radius
Supernova remnants (SNRs) in the Galaxy are an important source of energy
injection into the interstellar medium, and also of cosmic rays. Currently
there are 294 known SNRs in the Galaxy, and their distribution with
Galactocentric radius is of interest for various studies. Here I discuss some
of the statistics of Galactic SNRs, including the observational selection
effects that apply, and difficulties in obtaining distances for individual
remnants from the `Sigma-D' relation. Comparison of the observed Galactic
longitude distribution of a sample of bright Galactic SNRs -- which are not
strongly affected by selection effects -- with those expected from models is
used to constrain the Galactic distribution of SNRs. The best-fitting
power-law/exponential model is more concentrated towards the Galactic centre
than the widely used distribution obtained by Case & Bhattacharya (1998).This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stv188
A methodology for full-system power modeling in heterogeneous data centers
The need for energy-awareness in current data centers has encouraged the use of power modeling to estimate their power consumption. However, existing models present noticeable limitations, which make them application-dependent, platform-dependent, inaccurate, or computationally complex. In this paper, we propose a platform-and application-agnostic methodology for full-system power modeling in heterogeneous data centers that overcomes those limitations. It derives a single model per platform, which works with high accuracy for heterogeneous applications with different patterns of resource usage and energy consumption, by systematically selecting a minimum set of resource usage indicators and extracting complex relations among them that capture the impact on energy consumption of all the resources in the system. We demonstrate our methodology by generating power models for heterogeneous platforms with very different power consumption profiles. Our validation experiments with real Cloud applications show that such models provide high accuracy (around 5% of average estimation error).This work is supported by the Spanish Ministry of Economy and Competitiveness under contract TIN2015-65316-P, by the Gener-
alitat de Catalunya under contract 2014-SGR-1051, and by the European Commission under FP7-SMARTCITIES-2013 contract 608679 (RenewIT) and FP7-ICT-2013-10 contracts 610874 (AS- CETiC) and 610456 (EuroServer).Peer ReviewedPostprint (author's final draft
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Search for radio emission from the exoplanets Qatar-1b and WASP-80b near 150 MHz using the giant metrewave radio telescope
We present radio observations made towards the exoplanets Qatar-1b and
WASP-80b near 150~MHz with the Giant Meterwave Radio Telescope. These targets
are relatively nearby irradiated giant exoplanets, a hot Jupiter and a hot
Saturn, with sizes comparable to Jupiter but different masses and lower
densities. Both the targets are expected to host extended H/He envelopes like
Jupiter, with comparable or larger magnetic moments. No radio emission was
detected from these exoplanets, with 3sigma limits of 5.9 and 5.2 mJy for
Qatar-1b and WASP-80b, respectively, from these targeted observations. These
are considerably deeper limits than those available for exoplanets from wide
field surveys at similar frequencies. We also present archival VLA observations
of a previously reported radio source close to Vir 61 (which has three
exoplanets). The VLA observations resolve the source, which we identify as an
extragalactic radio source, i.e. a chance association with Vir 61.
Additionally, we cross-match a recent exoplanet catalogue with the TIFR GMRT
Sky Survey ADR1 radio catalogue, but do not find any convincing associations
Patterns of quark mass matrices in a class of Calabi-Yau models
We study a class of superstring models compactified in the 3-generation
Calabi-Yau manifold of Tian and Yau. Our analysis includes the complete
-singlet sector, which has been recently evaluated using techniques of
spectral and exact sequences. We use the discrete symmetries of the models to
find flat directions of symmetry breaking that leave unbroken a low energy
matter parity and make all leptoquarks heavy while preserving light Higgs
fields. Then we classify the patterns of ordinary quark mass matrices and show
that (without invoking effects due to nonrenormalizable terms) only one
structure can accommodate the observed value of fermion masses and mixing
angles, with preference for a heavy {\it top} quark ( GeV for
). The model, which unifies perturbatively and predicts a
realistic structure of quark mass matrices with texture zeroes, is one of the
many possible string vacua. However, in contrast with what is often assumed in
the search for realistic unified scenarios, it is highly nonminimal near the
unification scale and the predicted mass matrices have no simple symmetry
properties.Comment: 30 (including Tables and Figures), UG-FT-38/9
GMRT 610-MHz observations of the faint radio source population – and what these tell us about the higher radio-frequency sky
We present 610-MHz Giant Metrewave Radio Telescope observations of 0.84 deg of the AMI001 field (centred on 002310, +31°53′) with an rms noise of 18 μJy beam in the centre of the field. A total of 955 sources are detected, and 814 are included in the source count analysis. The source counts from these observations are consistent with previous work. We have used these data to study the spectral index distribution of a sample of sources selected at 15.7 GHz from the recent deep extension to the Tenth Cambridge (10C) survey. The median spectral index, α, (where S ∝ ν) between 0.08</mJy<0.2 is 0.32 ± 0.14, showing that star-forming galaxies, which have much steeper spectra, are not contributing significantly to this population. This is in contrast to several models, but in agreement with the results from the 10C ultradeep source counts; the high-frequency sky therefore continues to be dominated by radio galaxies down to S = 0.1 mJy.The GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. IHW thanks the Science and Technologies Facilities Council for a studentship. IHW and MJJ acknowledge support from the Square Kilometre Array South Africa. IHW thanks the South African Astronomical Observatory, where some of this work was carried out
Identifying consistent biomechanical parameters across rising-to-walk subtasks to inform rehabilitation in practice: A systematic literature review
© 2020 Elsevier B.V. Background: :The best approach to rehabilitate the control of everyday whole-body movement (e.g. rise-to-walk) after pathology remains unclear in part because the associated controlled performance variables are not known. Rise-to-walk can be performed fluidly (sit-to-walk) or non-fluidly (sit-to-stand, proceeded by gait-initiation). Biomechanical variables that remain consistent in health regardless of how rise-to walk is performed represent controlled performance variable candidates which could monitor rehabilitative change. Research Question: :To determine if any biomechanical parameters remain consistent across rising-to-walk (RTW) subtasks (sit-to-stand, gait-initiation, and sit-to-walk) in healthy adults for purposes of movement control assessment in clinical practice. Methods: :Data sources included Medline, Cinahl, and Scopus databases, and the grey literature. Study selection was based on eligibility criteria and must have reported spatiotemporal, kinematic and/or kinetic biomechanical parameters featuring >1 RTW subtask. Data extraction and synthesis; standardised-mean-differences (SMDs) were calculated (pooled if replicated in >1 study) for each parameter. Consistency was determined if SMD95 %CIs included the zero-effect line. Results: :Nine studies (n = 99) were included (40 ± 7.5yrs). Seven parameters were replicated in >1 study and subjected to meta-analysis (fixed-effect model). Two were consistent between sit-to-stand and sit-to-walk: flexion-momentum time (M(95 %CI) = 0.055(-0.423 to 0.533); p = 0.823) and peak whole-body-centre-of-mass vertical velocity (M(95 %CI)= -0.415(-0.898 to 0.069); p = 0.093); and centre-of-pressure to whole-body-centre-of-mass distance at toe-off (M(95 %CI)= -0.137(-0.712 to 0.439); p = 0.642) between gait-initiation and sit-to-walk. Another 20 parameters were consistent based on single-study SMDs. Significance: :Consistent parameters might exist across RTW subtasks. However, the evidence is based on few studies with small samples and variable RTW protocols. Future studies designed to confirm consistency using a standardised RTW protocol are needed
The faint radio source population at 15.7 GHz-IV. The dominance of core emission in faint radio galaxies
We present 15-GHz Karl G. Jansky Very Large Array observations of a complete
sample of radio galaxies selected at 15.7 GHz from the Tenth Cambridge (10C)
survey. 67 out of the 95 sources (71 per cent) are unresolved in the new
observations and lower-frequency radio observations, placing an upper limit on
their angular size of ~2 arcsec. Thus compact radio galaxies, or radio galaxies
with very faint jets, are the dominant population in the 10C survey. This
provides support for the suggestion in our previous work that low-luminosity
() radio galaxies are core-dominated, although
higher-resolution observations are required to confirm this directly. The 10C
sample of compact, high-frequency selected radio galaxies is a mixture of
high-excitation and low-excitation radio galaxies and displays a range of radio
spectral shapes, demonstrating that they are a mixed population of objects
Neuromuscular Electrical Stimulation as a Potential Countermeasure for Skeletal Muscle Atrophy and Weakness During Human Spaceflight
This is the final version. Available on open access from Frontiers Media via the DOI in this recordHuman spaceflight is associated with a substantial loss of skeletal muscle mass and muscle strength. Neuromuscular electrical stimulation (NMES) evokes involuntary muscle contractions, which have the potential to preserve or restore skeletal muscle mass and neuromuscular function during and/or post spaceflight. This assumption is largely based on evidence from terrestrial disuse/immobilization studies without the use of large exercise equipment that may not be available in spaceflight beyond the International Space Station. In this mini-review we provide an overview of the rationale and evidence for NMES based on the terrestrial state-of-the-art knowledge, compare this to that used in orbit, and in ground-based analogs in order to provide practical recommendations for implementation of NMES in future space missions. Emphasis will be placed on knee extensor and plantar flexor muscles known to be particularly susceptible to deconditioning in space missions
Major and minor flares on Cygnus X-3 revisited
Intense flares at cm-wavelengths reaching levels of tens of Jy have been
observed from Cygnus X-3 for many years. This active high mass X-ray binary
also has periods of quenching before major outbursts, and has minor flares at
levels of a few hundred mJy. In this paper we show that the minor flares have
much shorter rise times and durations suggesting more rapid expansion of the
synchrotron radiation emitting material than in the strong flares. They also
appear closer to the binary, whereas the large flares form a more developed
jet. Calculations of physical conditions show that the minor out-bursts have
lower minimum power but have larger magnetic fields and energy densities than
the major flares. Minor flares can occur while a major flare is in progress,
suggesting an indirect coupling between them. The spectral evolution of the
minor flares can be explained by either an expanding synchrotron source or a
shock model. The possibility that there is a brightening zone as in SS433 is
explored
Finite temperature stability and dimensional crossover of exotic superfluidity in lattices
We investigate exotic paired states of spin-imbalanced Fermi gases in
anisotropic lattices, tuning the dimension between one and three. We calculate
the finite temperature phase diagram of the system using real-space dynamical
mean-field theory in combination with the quantum Monte Carlo method. We find
that regardless of the intermediate dimensions examined, the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state survives to reach about one third
of the BCS critical temperature of the spin-density balanced case. We show how
the gapless nature of the state found is reflected in the local spectral
function. While the FFLO state is found at a wide range of polarizations at low
temperatures across the dimensional crossover, with increasing temperature we
find out strongly dimensionality-dependent melting characteristics of shell
structures related to harmonic confinement. Moreover, we show that intermediate
dimension can help to stabilize an extremely uniform finite temperature FFLO
state despite the presence of harmonic confinement.Comment: 5 pages, 3 figure
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