22,364 research outputs found
2D Bayesian automated tilted-ring fitting of disk galaxies in large HI galaxy surveys: 2DBAT
We present a novel algorithm based on a Bayesian method for 2D tilted-ring
analysis of disk galaxy velocity fields. Compared to the conventional
algorithms based on a chi-squared minimisation procedure, this new
Bayesian-based algorithm suffers less from local minima of the model parameters
even with highly multi-modal posterior distributions. Moreover, the Bayesian
analysis, implemented via Markov Chain Monte Carlo (MCMC) sampling, only
requires broad ranges of posterior distributions of the parameters, which makes
the fitting procedure fully automated. This feature will be essential when
performing kinematic analysis on the large number of resolved galaxies expected
to be detected in neutral hydrogen (HI) surveys with the Square Kilometre Array
(SKA) and its pathfinders. The so-called '2D Bayesian Automated Tilted-ring
fitter' (2DBAT) implements Bayesian fits of 2D tilted-ring models in order to
derive rotation curves of galaxies. We explore 2DBAT performance on (a)
artificial HI data cubes built based on representative rotation curves of
intermediate-mass and massive spiral galaxies, and (b) Australia Telescope
Compact Array (ATCA) HI data from the Local Volume HI Survey (LVHIS). We find
that 2DBAT works best for well-resolved galaxies with intermediate inclinations
(20 deg < i < 70 deg), complementing three-dimensional techniques better suited
to modelling inclined galaxies.Comment: Accepted for publication in MNRAS; 46 pages, 33 figure
Impact of surface roughness in nanogap plasmonic systems
Recent results have shown unprecedented control over separation distances
between two metallic elements hundreds of nanometers in size, underlying the
effects of free-electron nonlocal response also at mid-infrared wavelengths.
Most of metallic systems however, still suffer from some degree of
inhomogeneity due to fabrication-induced surface roughness. Nanoscale roughness
in such systems might hinder the understanding of the role of microscopic
interactions. Here we investigate the effect of surface roughness in coaxial
nanoapertures resonating at mid-infrared frequencies. We show that although
random roughness shifts the resonances in an unpredictable way, the impact of
nonlocal effects can still be clearly observed. Roughness-induced perturbation
on the peak resonance of the system shows a strong correlation with the
effective gap size of the individual samples. Fluctuations due to fabrication
imperfections then can be suppressed by performing measurements on structure
ensembles in which averaging over a large number of samples provides a precise
measure of the ideal system's optical properties
Sustainable farming with native rocks: the transition without revolution.
The development process which humanity passed through favored a series of conquests, reflected in the better quality of life and longevity, however, it also provoked upsets and severe transformation in the environment and in the human food security. Such process is driving the ecosystems to be homogeneous, and, therefore,the nutrients� supply, via nourishment. To change this panorama, the present work discusses the gains of incorporating the stonemeal technique as a strategic alternative to give back the essential fertile characteristics to the soils. This technology has the function of facilitating the rejuvenation of the soils and increasing the availability of the necessary nutrients to the full development of the plants which is a basic input for the proliferation of life in all its dimensions
An HI study of the collisional ring galaxy NGC 922
We present new atomic hydrogen (HI) observations of the collisional ring
galaxy NGC 922 obtained using the Australia Telescope Compact Array. Our
observations reveal for the first time the vast extent of the HI disc of this
galaxy. The HI morphology and kinematics of NGC 922 show that this galaxy is
not the product of a simple drop-through interaction, but has a more complex
interaction history. The integrated HI flux density of NGC 922 from our
observations is 24.7 Jy km s, which is within the error of the flux
value obtained using the -m Parkes radio telescope. This flux density
translates to a total HI mass of M and corresponds to
an HI to total mass fraction (M/M) of approximately . The
gaseous structures of NGC 922 are more extended to the north and include an HI
tail that has a projected physical length of kpc. Gas warps are also
evident in the velocity field of NGC 922 and are more prominent on the
approaching and the western side of the disc. In comparison with a large sample
of star-forming galaxies in the local Universe, NGC 922 possesses a high gas
fraction relative to galaxies with a similar stellar mass of ~
M, and exhibits a high specific star formation rate.Comment: 11 pages, 8 figures, published in MNRA
14-01 Exploring the Equity Dimensions of US Bicycle Sharing Systems
Research over the past several decades has made it increasingly clear that livable communities are inextricably linked with the provision of opportunities for active and/or non-motorized transportation; i.e., walking, cycling and their variants. An emerging phenomena that is working within the broader movement of active transportation is public bicycle sharing systems (BSS). Such systems have grown considerably in the US in recent years and, in some cases, are dramatically changing the ecology of urban transport. Alongside celebrations of the early successes of US BSS, have been criticisms that these systems have not been adequately integrated into lower-income communities; a pattern that mirrors (motorized) transportation injustices-both past and present-that have burdened lower-income while simultaneously advantaging middle to higher-income communities. And while diverse communities are embracing non-motorized transportation, there is valid concern that traditionally underserved populations will again be marginalized or unable to share in the full benefits of existing and future bicycle- and pedestrian-oriented infrastructure including BSS. This research explores the spatial arrangements and allocations of US BSS and examines the extent to which lower-income communities experience differential access to bike-sharing infrastructure. Spatial regression models are employed to examine the degree to which race, ethnicity and/or economic hardship explain variations in the distribution of bike-sharing stations
The size and structure of the spheroid of IC 1613
Nearby galaxies, spirals as well as irregulars, have been found to be much
larger than previously believed. The structure of the huge spheroid surrounding
dwarf galaxies could give clues to their past gravitational history. Thanks to
wide field imagers, nearby galaxies with diameter of dozens of arcmin can be
effectively surveyed.
We obtain, from the CFHT archives, a series of i' and g' MegaCam images of IC
1613 in order to determine the stellar surface density of the field and
determine the shape of its spheroid. From the colour magnitude diagram we
select some 36,000 stars, in the first three magnitudes of the red giant
branch. The spatial distribution of these stars is used to establish the
structure of the spheroid.
The position angle of the major axis of the stellar spheroid is found to be
, some 30 from the major axis of the HI cloud
surrounding IC 1613. The surface density profile of the spheroid is not
exponential over all the length of the major axis. A King profile, with a core
radius of 4.5' and a tidal radius of 24' fits the data. The tidal truncation of
the spheroid suggests that IC 1613 is indeed a satellite of M31.Comment: accepted : A
Can vitamin D prevent acute respiratory infections?
Review of: Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. 2017;356:i6583.Can vitamin D prevent acute respiratory infections? A systematic review and meta-analysis says Yes, but the dosages used may not be what you'd expect. PRACTICE CHANGER: Reduce acute respiratory tract infections in those with significant vitamin D deficiency (circulating 25-hydroxyvitamin D levels < 10 ng/mL) with daily or weekly vitamin D supplementation--not bolus vitamin D treatment. STRENGTH OF RECOMMENDATION A: Based pm a systematic review and meta-analysis of 25 trials.Bob Marshall, MD, MPH, MISM, FAAFP; Nick Bennett, DO; Ashley Smith, MD; Robert Oh, MD, MPH, FAAFP; Jeffrey Burket, MD, MBA, FAAFP Madigan Family Medicine Residency, Gig Harbor, Was
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