2,144 research outputs found
New insight into the relation between star formation activity and dust content in galaxies
(Abridged) We assemble a sample of 3258 low-redshift galaxies from the SDSS
DR6 with complementary photometric observations by GALEX, 2MASS and IRAS at
far-ultraviolet and infrared wavelengths. We use a recent, simple but
physically motivated model to interpret the observed spectral energy
distributions of the galaxies in this sample in terms of statistical
constraints on physical parameters describing the star formation history and
dust content. The focus on a subsample of 1658 galaxies with highest S/N
observations enables us to investigate most clearly several strong correlations
between various derived physical properties of galaxies. We find that the
typical dust mass of a star-forming correlates remarkably well with the star
formation rate (SFR). We also find that the dust-to-stellar mass ratio, the
ratio of dust mass to star formation rate and the fraction of dust luminosity
contributed by the diffuse interstellar medium all correlate strongly with
specific SFR. A comparison with recent models of chemical and dust evolution of
galaxies suggests that these correlations could arise, at least in part, from
an evolutionary sequence. As galaxies form stars, their ISM becomes enriched in
dust, while the drop in gas supply makes the specific SFR decrease.
Interestingly, as a result, a young, actively star-forming galaxy with low
dust-to-gas ratio may still be highly dusty because it contains large amounts
of interstellar gas. This may be important for the interpretation of the
infrared emission from young, gas-rich star-forming galaxies at high redshift.
Our study provides a useful local reference for future statistical studies of
the star formation and dust properties of galaxies at high redshifts.Comment: 15 pages, 10 figures, accepted for publication in MNRAS.
Full-resolution figures available from
http://users.physics.uoc.gr/~dacunha/paper_dacunha.pd
Optical vs. infrared studies of dusty galaxies and AGN: (I) Nebular emission lines
Optical nebular emission lines are commonly used to estimate the star
formation rate of galaxies and the black hole accretion rate of their central
active nucleus. The accuracy of the conversion from line strengths to physical
properties depends upon the accuracy to which the lines can be corrected for
dust attenuation. For studies of single galaxies with normal amounts of dust,
most dust corrections result in the same derived properties within the errors.
However, for statistical studies of populations of galaxies, or for studies of
galaxies with higher dust contents such as might be found in some classes of
"transition" galaxies, significant uncertainty arises from the dust attenuation
correction. We compare the strength of the predominantly unobscured mid-IR
[NeII]15.5um + [NeIII]12.8um emission lines to the optical H alpha emission
lines in four samples of galaxies: (i) ordinary star forming galaxies, (ii)
optically selected dusty galaxies, (iii) ULIRGs, (iv) Seyfert 2 galaxies. We
show that a single dust attenuation curve applied to all samples can correct H
alpha emission for dust attenuation to a factor better than 2. Similarly, we
compare mid-IR [OIV] and optical [OIII] luminosities to find that [OIII] can be
corrected to a factor better than 3. This shows that the total dust attenuation
suffered by the AGN narrow line region is not significantly different to that
suffered by the starforming HII regions in the galaxy. We provide explicit dust
attenuation corrections, together with errors, for [OII], [OIII] and H alpha.
The best-fit average attenuation curve is slightly greyer than the Milky-Way
extinction law, indicating either that external galaxies have slightly
different typical dust properties to the Milky Way, or that there is a
significant contribution from scattering. Finally, we uncover an intriguing
correlation between Silicate absorption and Balmer decrement.Comment: 19 pages, 9 figures, accepted for publication in MNRA
Sleep quality in middle-aged and elderly Chinese: distribution, associated factors and associations with cardio-metabolic risk factors
Background
Poor sleep quality has been associated with increased risk of heart disease, diabetes and mortality. However, limited information exists on the distribution and determinants of sleep quality and its associations with cardio-metabolic risk factors in Chinese populations. We aimed to evaluate this in the current study.
Methods
A cross-sectional survey conducted in 2005 of 1,458 men and 1,831 women aged 50–70 years from urban and rural areas of Beijing and Shanghai. Using a questionnaire, sleep quality was measured in levels of well, common and poor. Comprehensive measures of socio-demographical and health factors and biomarkers of cardio-metabolic disease were recorded. These were evaluated in association with sleep quality using logistic regression models.
Results
Half of the population reported good sleep quality. After adjusting for potential confounders, women and Beijing residents had almost half the probability to report good sleep quality. Good physical and mental health (good levels of self-rated health (OR 2.48; 95%CI 2.08 to 2.96) and no depression (OR 4.05; 95%CI 3.12 to 5.26)) related to an increased chance of reporting good sleep quality, whereas short sleep duration (<7 hrs OR 0.10; 95%CI 0.07 to 0.14)) decreased it substantially. There were significant associations between levels of sleep quality and concentrations of plasma insulin, total and LDL cholesterol, and index of insulin resistance.
Conclusion
Levels of good sleep quality in middle-age and elderly Chinese were low. Gender, geographical location, self-rated health, depression and sleep quantity were major factors associated with sleep quality. Prospective studies are required to distil the factors that determine sleep quality and the effects that sleep patterns exert on cardio-metabolic health
Nucleation phenomena in protein folding: The modulating role of protein sequence
For the vast majority of naturally occurring, small, single domain proteins
folding is often described as a two-state process that lacks detectable
intermediates. This observation has often been rationalized on the basis of a
nucleation mechanism for protein folding whose basic premise is the idea that
after completion of a specific set of contacts forming the so-called folding
nucleus the native state is achieved promptly. Here we propose a methodology to
identify folding nuclei in small lattice polymers and apply it to the study of
protein molecules with chain length N=48. To investigate the extent to which
protein topology is a robust determinant of the nucleation mechanism we compare
the nucleation scenario of a native-centric model with that of a sequence
specific model sharing the same native fold. To evaluate the impact of the
sequence's finner details in the nucleation mechanism we consider the folding
of two non- homologous sequences. We conclude that in a sequence-specific model
the folding nucleus is, to some extent, formed by the most stable contacts in
the protein and that the less stable linkages in the folding nucleus are solely
determined by the fold's topology. We have also found that independently of
protein sequence the folding nucleus performs the same `topological' function.
This unifying feature of the nucleation mechanism results from the residues
forming the folding nucleus being distributed along the protein chain in a
similar and well-defined manner that is determined by the fold's topological
features.Comment: 10 Figures. J. Physics: Condensed Matter (to appear
LOFAR/H-ATLAS: The low-frequency radio luminosity - star-formation rate relation
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.Radio emission is a key indicator of star-formation activity in galaxies, but the radio luminosity-star formation relation has to date been studied almost exclusively at frequencies of 1.4 GHz or above. At lower radio frequencies the effects of thermal radio emission are greatly reduced, and so we would expect the radio emission observed to be completely dominated by synchrotron radiation from supernova-generated cosmic rays. As part of the LOFAR Surveys Key Science project, the Herschel-ATLAS NGP field has been surveyed with LOFAR at an effective frequency of 150 MHz. We select a sample from the MPA-JHU catalogue of SDSS galaxies in this area: the combination of Herschel, optical and mid-infrared data enable us to derive star-formation rates (SFRs) for our sources using spectral energy distribution fitting, allowing a detailed study of the low-frequency radio luminosity--star-formation relation in the nearby Universe. For those objects selected as star-forming galaxies (SFGs) using optical emission line diagnostics, we find a tight relationship between the 150 MHz radio luminosity () and SFR. Interestingly, we find that a single power-law relationship between and SFR is not a good description of all SFGs: a broken power law model provides a better fit. This may indicate an additional mechanism for the generation of radio-emitting cosmic rays. Also, at given SFR, the radio luminosity depends on the stellar mass of the galaxy. Objects which were not classified as SFGs have higher 150-MHz radio luminosity than would be expected given their SFR, implying an important role for low-level active galactic nucleus activity.Peer reviewedFinal Published versio
Cold gas accretion in galaxies
Evidence for the accretion of cold gas in galaxies has been rapidly
accumulating in the past years. HI observations of galaxies and their
environment have brought to light new facts and phenomena which are evidence of
ongoing or recent accretion:
1) A large number of galaxies are accompanied by gas-rich dwarfs or are
surrounded by HI cloud complexes, tails and filaments. It may be regarded as
direct evidence of cold gas accretion in the local universe. It is probably the
same kind of phenomenon of material infall as the stellar streams observed in
the halos of our galaxy and M31. 2) Considerable amounts of extra-planar HI
have been found in nearby spiral galaxies. While a large fraction of this gas
is produced by galactic fountains, it is likely that a part of it is of
extragalactic origin. 3) Spirals are known to have extended and warped outer
layers of HI. It is not clear how these have formed, and how and for how long
the warps can be sustained. Gas infall has been proposed as the origin. 4) The
majority of galactic disks are lopsided in their morphology as well as in their
kinematics. Also here recent accretion has been advocated as a possible cause.
In our view, accretion takes place both through the arrival and merging of
gas-rich satellites and through gas infall from the intergalactic medium (IGM).
The infall may have observable effects on the disk such as bursts of star
formation and lopsidedness. We infer a mean ``visible'' accretion rate of cold
gas in galaxies of at least 0.2 Msol/yr. In order to reach the accretion rates
needed to sustain the observed star formation (~1 Msol/yr), additional infall
of large amounts of gas from the IGM seems to be required.Comment: To appear in Astronomy & Astrophysics Reviews. 34 pages.
Full-resolution version available at
http://www.astron.nl/~oosterlo/accretionRevie
Empirical Near Infrared colors for low-mass stars and brown dwarfs in the Orion Nebula Cluster
Atmospheric and evolutionary models for low-mass stars rely on approximate
assumptions on the physics of the stellar structure and the atmospheric
radiative transfer. This leads to biased theoretical predictions on the
photospheric Spectral Energy Distributions of Pre-Main Sequence (PMS) stars,
and affects the derivation of stellar parameters from photometric data. Our
goal is to correct the biases present in the theoretical predictions for the
near-IR photometry of low-mass PMS stars. Using empirical intrinsic IR colors,
we assess the accuracy of current synthetic spectral libraries and evolutionary
models. We consider a sample of ~300 PMS stars in the Orion Nebula Cluster (age
1 Myr) with measured luminosities, temperatures and photospheric JHKs
photometry. By analyzing the photospheric colors of our sample of stars, we
find that the synthetic JHKs photometry provided by theoretical spectral
templates for late spectral types (>K6) are accurate at the level of ~0.2 mag,
while colors are accurate at ~0.1 mag. We tabulate the intrinsic photospheric
colors, appropriate for the Orion Nebula Cluster, in the range K6-M8.5. They
can be conveniently used as templates for the intrinsic colors of other young
(age<5 Myr) stellar clusters. An empirical correction of the atmospheric
templates can fix the discrepancies between expected and observed colors.
Still, other biases in the evolutionary models prevent a more robust comparison
between observations and theoretical absolute magnitudes. In particular, PMS
evolutionary models seem to consistently underestimate the intrinsic
near-infrared flux at the very late spectral types, and this may introduce
spurious features in the low-mass end of the photometrically-determined Initial
Mass Function of young clusters.Comment: Accepted by A&
Improving education in primary care: development of an online curriculum using the blended learning model
<p>Abstract</p> <p>Background</p> <p>Standardizing the experiences of medical students in a community preceptorship where clinical sites vary by geography and discipline can be challenging. Computer-assisted learning is prevalent in medical education and can help standardize experiences, but often is not used to its fullest advantage. A blended learning curriculum combining web-based modules with face-to-face learning can ensure students obtain core curricular principles.</p> <p>Methods</p> <p>This course was developed and used at The Case Western Reserve University School of Medicine and its associated preceptorship sites in the greater Cleveland area. Leaders of a two-year elective continuity experience at the Case Western Reserve School of Medicine used adult learning principles to develop four interactive online modules presenting basics of office practice, difficult patient interviews, common primary care diagnoses, and disease prevention. They can be viewed at <url>http://casemed.case.edu/cpcp/curriculum</url>. Students completed surveys rating the content and technical performance of each module and completed a Generalist OSCE exam at the end of the course.</p> <p>Results</p> <p>Participating students rated all aspects of the course highly; particularly those related to charting and direct patient care. Additionally, they scored very well on the Generalist OSCE exam.</p> <p>Conclusion</p> <p>Students found the web-based modules to be valuable and to enhance their clinical learning. The blended learning model is a useful tool in designing web-based curriculum for enhancing the clinical curriculum of medical students.</p
Measuring large-scale structure with quasars in narrow-band filter surveys
We show that a large-area imaging survey using narrow-band filters could
detect quasars in sufficiently high number densities, and with more than
sufficient accuracy in their photometric redshifts, to turn them into suitable
tracers of large-scale structure. If a narrow-band optical survey can detect
objects as faint as i=23, it could reach volumetric number densities as high as
10^{-4} h^3 Mpc^{-3} (comoving) at z~1.5 . Such a catalog would lead to
precision measurements of the power spectrum up to z~3-4. We also show that it
is possible to employ quasars to measure baryon acoustic oscillations at high
redshifts, where the uncertainties from redshift distortions and nonlinearities
are much smaller than at z<1. As a concrete example we study the future impact
of J-PAS, which is a narrow-band imaging survey in the optical over 1/5 of the
unobscured sky with 42 filters of ~100 A full-width at half-maximum. We show
that J-PAS will be able to take advantage of the broad emission lines of
quasars to deliver excellent photometric redshifts, \sigma_{z}~0.002(1+z), for
millions of objects.Comment: Matches version published in MNRAS (2012
Facial expressions depicting compassionate and critical emotions: the development and validation of a new emotional face stimulus set
Attachment with altruistic others requires the ability to appropriately process affiliative and kind facial cues. Yet there is no stimulus set available to investigate such processes. Here, we developed a stimulus set depicting compassionate and critical facial expressions, and validated its effectiveness using well-established visual-probe methodology. In Study 1, 62 participants rated photographs of actors displaying compassionate/kind and critical faces on strength of emotion type. This produced a new stimulus set based on N = 31 actors, whose facial expressions were reliably distinguished as compassionate, critical and neutral. In Study 2, 70 participants completed a visual-probe task measuring attentional orientation to critical and compassionate/kind faces. This revealed that participants lower in self-criticism demonstrated enhanced attention to compassionate/kind faces whereas those higher in self-criticism showed no bias. To sum, the new stimulus set produced interpretable findings using visual-probe methodology and is the first to include higher order, complex positive affect displays
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