5,070 research outputs found
Molecular gas and star formation in early-type galaxies
We present new mm interferometric and optical integral-field unit (IFU)
observations and construct a sample of 12 E and S0 galaxies with molecular gas
which have both CO and optical maps. The galaxies contain 2 x 10^7 to 5 x 10^9
M\odot of molecular gas distributed primarily in central discs or rings (radii
0.5 to 4 kpc). The molecular gas distributions are always coincident with
distributions of optically-obscuring dust that reveal tightly-wound spiral
structures in many cases. The ionised gas always approximately corotates with
the molecular gas, evidencing a link between these two gas components, yet star
formation is not always the domi- nant ionisation source. The galaxies with
less molecular gas tend to have [O III]/H{\beta} emission-line ratios at high
values not expected for star formation. Most E/S0s with molecular gas have
young or intermediate age stellar populations based on optical colours,
ultraviolet colours and absorption linestrengths. The few that appear purely
old lie close to the limit where such populations would be undetectable based
on the mass fractions of expected young to observed old stars. The 8{\mu}m
polycyclic aromatic hydrocarbon (PAH) and 24{\mu}m emission yield similar star
formation rate estimates of E/S0s, but the total infrared overpredicts the rate
due to a contribution to dust heating from older stars. The radio-far infrared
relation also has much more scatter than for other star-forming galaxies.
However, despite these biases and additional scatter, the derived star
formation rates locate the E/S0 galaxies within the large range of the
Schmidt-Kennicutt and constant efficiency star formation laws. Thus the star
formation process in E/S0s is not overwhelmingly different than in other
star-forming galaxies, although one of the more reliable tracers (24{\mu}m)
points to a possible lower star-formation efficiency at a given gas surface
density.Comment: submitted to MNRA
A theorem on the absence of phase transitions in one-dimensional growth models with onsite periodic potentials
We rigorously prove that a wide class of one-dimensional growth models with
onsite periodic potential, such as the discrete sine-Gordon model, have no
phase transition at any temperature . The proof relies on the spectral
analysis of the transfer operator associated to the models. We show that this
operator is Hilbert-Schmidt and that its maximum eigenvalue is an analytic
function of temperature.Comment: 6 pages, no figures, submitted to J Phys A: Math Ge
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Investigating the impact of poverty on colonization and infection with drug-resistant organisms in humans: a systematic review
Background
Poverty increases the risk of contracting infectious diseases and therefore exposure to antibiotics. Yet there is lacking evidence on the relationship between income and non-income dimensions of poverty and antimicrobial resistance. Investigating such relationship would strengthen antimicrobial stewardship interventions.
Methods
A systematic review was conducted following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. PubMed, Ovid, MEDLINE, EMBASE, Scopus, CINAHL, PsychINFO, EBSCO, HMIC, and Web of Science databases were searched in October 2016. Prospective and retrospective studies reporting on income or non-income dimensions of poverty and their influence on colonisation or infection with antimicrobial-resistant organisms were retrieved. Study quality was assessed with the Integrated quality criteria for review of multiple study designs (ICROMS) tool.
Results
Nineteen articles were reviewed. Crowding and homelessness were associated with antimicrobial resistance in community and hospital patients. In high-income countries, low income was associated with Streptococcus pneumoniae and Acinetobacter baumannii resistance and a seven-fold higher infection rate. In low-income countries the findings on this relation were contradictory. Lack of education was linked to resistant S. pneumoniae and Escherichia coli. Two papers explored the relation between water and sanitation and antimicrobial resistance in low-income settings.
Conclusions
Despite methodological limitations, the results suggest that addressing social determinants of poverty worldwide remains a crucial yet neglected step towards preventing antimicrobial resistance
The structure and dynamics of a bright point as seen with Hinode, SoHO and TRACE
Our aim is to determine the plasma properties of a coronal bright point and
compare its magnetic topology extrapolated from magnetogram data with its
appearance in X-ray images. We analyse spectroscopic data obtained with
EIS/Hinode, Ca II H and G-band images from SOT/Hinode, UV images from TRACE,
X-ray images from XRT/Hinode and high-resolution/high-cadence magnetogram data
from MDI/SoHO. The BP comprises several coronal loops as seen in the X-ray
images, while the chromospheric structure consists of tens of small bright
points as seen in Ca II H. An excellent correlation exists between the Ca II
BPs and increases in the magnetic field, implying that the Ca II H passband is
a good indicator for the concentration of magnetic flux. Doppler velocities
between 6 and 15 km/s are derived from the Fe XII and Fe XIII lines for the BP
region, while for Fe XIV and Si VII they are in the range from -15 to +15 km/s.
The coronal electron density is 3.7x10^9 cm^-3. An excellent correlation is
found between the positive magnetic flux and the X-ray light-curves. The
remarkable agreement between the extrapolated magnetic field configuration and
some of the loops composing the BP as seen in the X-ray images suggests that a
large fraction of the magnetic field in the bright point is close to potential.
The close correlation between the positive magnetic flux and the X-ray emission
suggests that energy released by magnetic reconnection is stimulated by flux
emergence or cancellation.Comment: 10 pages with 11 figures. Accepted in Astronomy and Astrophysic
First 230 GHz VLBI Fringes on 3C 279 using the APEX Telescope
We report about a 230 GHz very long baseline interferometry (VLBI) fringe
finder observation of blazar 3C 279 with the APEX telescope in Chile, the
phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory
(ARO). We installed VLBI equipment and measured the APEX station position to 1
cm accuracy (1 sigma). We then observed 3C 279 on 2012 May 7 in a 5 hour 230
GHz VLBI track with baseline lengths of 2800 M to 7200 M and
a finest fringe spacing of 28.6 micro-arcseconds. Fringes were detected on all
baselines with SNRs of 12 to 55 in 420 s. The correlated flux density on the
longest baseline was ~0.3 Jy/beam, out of a total flux density of 19.8 Jy.
Visibility data suggest an emission region <38 uas in size, and at least two
components, possibly polarized. We find a lower limit of the brightness
temperature of the inner jet region of about 10^10 K. Lastly, we find an upper
limit of 20% on the linear polarization fraction at a fringe spacing of ~38
uas. With APEX the angular resolution of 230 GHz VLBI improves to 28.6 uas.
This allows one to resolve the last-photon ring around the Galactic Center
black hole event horizon, expected to be 40 uas in diameter, and probe radio
jet launching at unprecedented resolution, down to a few gravitational radii in
galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in
detail, follow-up observations with APEX and five other mm-VLBI stations have
been conducted (March 2013) and are being analyzed.Comment: accepted for publication in A&
Use of sonic tomography to detect and quantify wood decay in living trees.
Premise of the studyField methodology and image analysis protocols using acoustic tomography were developed and evaluated as a tool to estimate the amount of internal decay and damage of living trees, with special attention to tropical rainforest trees with irregular trunk shapes.Methods and resultsLiving trunks of a diversity of tree species in tropical rainforests in the Republic of Panama were scanned using an Argus Electronic PiCUS 3 Sonic Tomograph and evaluated for the amount and patterns of internal decay. A protocol using ImageJ analysis software was used to quantify the proportions of intact and compromised wood. The protocols provide replicable estimates of internal decay and cavities for trees of varying shapes, wood density, and bark thickness.ConclusionsSonic tomography, coupled with image analysis, provides an efficient, noninvasive approach to evaluate decay patterns and structural integrity of even irregularly shaped living trees
The stellar host in blue compact dwarf galaxies: the need for a two-dimensional fit
The structural properties of the low surface brightness stellar host in blue
compact dwarf galaxies are often studied by fitting r^{1/n} models to the outer
regions of their radial profiles. The limitations imposed by the presence of a
large starburst emission overlapping the underlying component makes this kind
of analysis a difficult task. We propose a two-dimensional fitting methodology
in order to improve the extraction of the structural parameters of the LSB
host. We discuss its advantages and weaknesses by using a set of simulated
galaxies and compare the results for a sample of eight objects with those
already obtained using a one-dimensional technique. We fit a PSF convolved
Sersic model to synthetic galaxies, and to real galaxy images in the B, V, R
filters. We restrict the fit to the stellar host by masking out the starburst
region and take special care to minimize the sky-subtraction uncertainties. In
order to test the robustness and flexibility of the method, we carry out a set
of fits with synthetic galaxies. Furthermore consistency checks are performed
to assess the reliability and accuracy of the derived structural parameters.
The more accurate isolation of the starburst emission is the most important
advantage and strength of the method. Thus, we fit the host galaxy in a range
of surface brightness and in a portion of area larger than in previous
published 1D fits with the same dataset. We obtain robust fits for all the
sample galaxies, all of which, except one, show Sersic indices n very close to
1, with good agreement in the three bands. These findings suggest that the
stellar hosts in BCDs have near-exponential profiles, a result that will help
us to understand the mechanisms that form and shape BCD galaxies, and how they
relate to the other dwarf galaxy classes.Comment: 22 pages, 15 figures (low resolution), accepted for publication in
A&A. A higher resolution version of the figures can be provided upon reques
Spin-filtering and charge- and spin-switching effects in a quantum wire with periodically attached stubs
Spin-dependent electron transport in a periodically stubbed quantum wire in
the presence of Rashba spin-orbit interaction (SOI) is studied via the
nonequilibrium Green's function method combined with the Landauer-Buttiker
formalism. The coexistence of spin filtering, charge and spin switching are
found in the considered system. The mechanism of these transport properties is
revealed by analyzing the total charge density and spin-polarized density
distributions in the stubbed quantum wire. Furthermore, periodic spin-density
islands with high polarization are also found inside the stubs, owing to the
interaction between the charge density islands and the Rashba SOI-induced
effective magnetic field. The proposed nanostructure may be utilized to devise
an all-electrical multifunctional spintronic device.Comment: 4 pages, 4 figure
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