560 research outputs found
Kinematics of diffuse ionized gas in the disk halo interface of NGC 891 from Fabry-P\'erot observations
The properties of the gas in halos of galaxies constrain global models of the
interstellar medium. Kinematical information is of particular interest since it
is a clue to the origin of the gas. Here we report observations of the
kinematics of the thick layer of the diffuse ionized gas in NGC 891 in order to
determine the rotation curve of the halo gas. We have obtained a Fabry-P\'erot
data cube in Halpha to measure the kinematics of the halo gas with angular
resolution much higher than obtained from HI 21 cm observations. The data cube
was obtained with the TAURUS II spectrograph at the WHT on La Palma. The
velocity information of the diffuse ionized gas extracted from the data cube is
compared to model distributions to constrain the distribution of the gas and in
particular the halo rotation curve. The best fit model has a central
attenuation tau_H-alpha=6, a dust scale length of 8.1 kpc, an ionized gas scale
length of 5.0 kpc. Above the plane the rotation curve lags with a vertical
gradient of -18.8 km/s/kpc. We find that the scale length of the H-alpha must
be between 2.5 and 6.5 kpc. Furthermore we find evidence that the rotation
curve above the plane rises less steeply than in the plane. This is all in
agreement with the velocities measured in the HI.Comment: A&A, in press. 13 pages, 19 figure
Dependence of radio halo properties on star formation activity and galaxy mass
We investigate the relation between the existence and size of radio halos,
which are believed to be created by star formation (SF) related energy input
into the interstellar medium, and other galaxy properties, most importantly
star formation activity and galaxy mass. Based on radio continuum and H-alpha
observations of a sample of seven late-type spiral galaxies we find a direct,
linear correlation of the radial extent of gaseous halos on the size of the
actively star-forming parts of the galaxy disks. Data of a larger sample of 22
galaxies indicate that the threshold energy input rate into the disk ISM per
unit surface area for the creation of a gaseous halo depends on the mass
surface density of the galaxy, in the sense that a higher threshold must be
surpassed for galaxies with a higher surface density. Because of the good
prediction of the existence of a radio halo from these two parameters, we
conclude that they are important, albeit not the only contributors. The
compactness of the SF-related energy input is also found to be a relevant
factor. Galaxies with relatively compact SF distributions are more likely to
have gaseous halos than others with more widespread SF activity. These results
quantify the so-called "break-out" condition for matter to escape from galaxy
disks, as used in all current models of the interstellar medium and first
defined by Norman and Ikeuchi (1989).Comment: accepted for publication in Astronomy & Astrophysic
Implementation and Validation of Schapery-Rand Anisotropic Viscoelasticity Model for Super-Pressure Balloons
The thin film used for the NASA Ultra Long Duration Balloons (ULDB) shows con-siderable time-dependent behaviour. Furthermore, experiments on scaled ULDB balloons have revealed that wrinkles are present over a wide range of pressures. A numerical model has been developed describing the nonlinear anisotropic viscoelastic material behaviour by means of a Schapery-type model and this model has been extended to model wrinkling by means of a user-defined subroutine in the finite-element package ABAQUS. After a description of the viscoelastic modelling approach, a lobe of a 48 gore ULDB flat facet balloon is modelled and compared to experimental results. Additionally two test cases of anisotropic wrinkling are presented, one involving a flat membrane and one a cylindrical balloon structure. I
Physical Conditions in the Dwarf Local Group Irregular Galaxy IC10. I- Diffuse Ionized Gas
A detailed analysis on the physical conditions of the Interstellar Medium in
the main body of the Local Group dwarf irregular galaxy IC 10 is carried out
using long-slit spectroscopy. Maps of the excitation, the H flux,
[NII]/H and [SII]/H are presented. The Diffuse Ionized Gas
inside the galaxy is studied. We found that the spectral characteristics are
not similar to those for spiral galaxies: the values of the ratios
[NII]/H and [SII]/H are not as large as in spiral galaxies but
the excitation is much larger. These values, especially the large excitation,
can be explained by proposing an extra source of ionization. Different sources
are studied but any of the models at hand could be really fitted except a
combination of photons leaking from the HII regions in addition to the
ionization provided by the WR stars present in this galaxy. Shocks are not
needed for explaining the line intensity ratios except in a small part in the
west side of the galaxy.Comment: 12 pages, 12 figures, accepted for publication in A&
Positivity of the English language
Over the last million years, human language has emerged and evolved as a
fundamental instrument of social communication and semiotic representation.
People use language in part to convey emotional information, leading to the
central and contingent questions: (1) What is the emotional spectrum of natural
language? and (2) Are natural languages neutrally, positively, or negatively
biased? Here, we report that the human-perceived positivity of over 10,000 of
the most frequently used English words exhibits a clear positive bias. More
deeply, we characterize and quantify distributions of word positivity for four
large and distinct corpora, demonstrating that their form is broadly invariant
with respect to frequency of word use.Comment: Manuscript: 9 pages, 3 tables, 5 figures; Supplementary Information:
12 pages, 3 tables, 8 figure
Near-field interactions between metal nanoparticle surface plasmons and molecular excitons in thin-films: part I: absorption
In this and the following paper (parts I and II, respectively), we systematically study the interactions between surface plasmons of metal nanoparticles (NPs) with excitons in thin-films of organic media. In an effort to exclusively probe near-field interactions, we utilize spherical Ag NPs in a size-regime where far-field light scattering is negligibly small compared to absorption. In part I, we discuss the effect of the presence of these Ag NPs on the absorption of the embedding medium by means of experiment, numerical simulations, and analytical calculations, all shown to be in good agreement. We observe absorption enhancement in the embedding medium due to the Ag NPs with a strong dependence on the medium permittivity, the spectral position relative to the surface plasmon resonance frequency, and the thickness of the organic layer. By introducing a low index spacer layer between the NPs and the organic medium, this absorption enhancement is experimentally confirmed to be a near field effect In part II, we probe the impact of the Ag NPs on the emission of organic molecules by time-resolved and steady-state photoluminescence measurements
Fast variables determine the epidemic threshold in the pairwise model with an improved closure
Pairwise models are used widely to model epidemic spread on networks. These include the modelling of susceptible-infected-removed (SIR) epidemics on regular networks and extensions to SIS dynamics and contact tracing on more exotic networks exhibiting degree heterogeneity, directed and/or weighted links and clustering. However, extra features of the disease dynamics or of the network lead to an increase in system size and analytical tractability becomes problematic. Various `closures' can be used to keep the system tractable. Focusing on SIR epidemics on regular but clustered networks, we show that even for the most complex closure we can determine the epidemic threshold as an asymptotic expansion in terms of the clustering coefficient.We do this by exploiting the presence of a system of fast variables, specified by the correlation structure of the epidemic, whose steady state determines the epidemic threshold. While we do not find the steady state analytically, we create an elegant asymptotic expansion of it. We validate this new threshold by comparing it to the numerical solution of the full system and find excellent agreement over a wide range of values of the clustering coefficient, transmission rate and average degree of the network. The technique carries over to pairwise models with other closures [1] and we note that the epidemic threshold will be model dependent. This emphasises the importance of model choice when dealing with realistic outbreaks
The Star Cluster Population of M51: II. Age distribution and relations among the derived parameters
We use archival {\it Hubble Space Telescope} observations of broad-band
images from the ultraviolet (F255W-filter) through the near infrared (NICMOS
F160W-filter) to study the star cluster population of the interacting spiral
galaxy M51. We obtain age, mass, extinction, and effective radius estimates for
1152 star clusters in a region of kpc centered on the
nucleus and extending into the outer spiral arms. In this paper we present the
data set and exploit it to determine the age distribution and relationships
among the fundamental parameters (i.e. age, mass, effective radius). Using this
dataset we find: {\it i}) that the cluster formation rate seems to have had a
large increase 50-70 Myr ago, which is coincident with the suggested
{\it second passage} of its companion, NGC 5195, {\it ii}) a large number of
extremely young ( 10 Myr) star clusters, which we interpret as a population
of unbound clusters of which a large majority will disrupt within the next
10 Myr, and {\it iii)} that the distribution of cluster sizescan be well
approximated by a power-law with exponent, , which is
very similar to that of Galactic globular clusters, indicating that cluster
disruption is largely independent of cluster radius. In addition, we have used
this dataset to search for correlations among the derived parameters. In
particular, we do not find any strong trends between the age and mass, mass and
effective radius, nor between the galactocentric distance and effective radius.
There is, however, a strong correlation between the age of a cluster and its
extinction, with younger clusters being more heavily reddened than older
clusters.Comment: 21 pages, 20 figures, accepted A&
Assessment and Treatment Recommendations for Pediatric Pain: The Influence of Patient Race, Patient Gender, and Provider Pain-Related Attitudes
Previous studies have documented that racial minorities and women receive poorer pain care than their demographic counterparts. Providers contribute to these disparities when their pain-related decision-making systematically varies across patient groups. Less is known about racial and gender disparities in children with pain or the extent to which providers contribute to these disparities. In a sample of 129 medical students (henceforth referred to as "providers"), Virtual Human methodology and a pain-related version of the Implicit Association Test (IAT) were used to examine the effects of patient race/gender on providers’ pain assessment/treatment decisions for pediatric chronic abdominal pain, as well as the moderating role of provider implicit pain-related race/gender attitudes. Findings indicated that providers rated Black patients as more distressed (mean difference [MD] = 2.33, P < .01, standard error [SE] = .71, 95% confidence interval [CI] = .92, 3.73) and as experiencing more pain-related interference (MD = 3.14, P < .01, SE = .76, 95% CI = 1.63, 4.64) compared to White patients. Providers were more likely to recommend opioids for Black patients than White patients (MD = 2.41, P < .01, SE = .58, 95% CI = 1.05, 3.76). Female patients were perceived to be more distressed by their pain (MD = 2.14, P < .01, SE = .79, 95% CI = .58, 3.70) than male patients, however there were no gender differences in treatment recommendations. IAT results indicated that providers held implicit attitudes that Black Americans (M = .19, standard deviation [SD] = .29) and males (M = .38, SD = .29) were more pain-tolerant than their demographic counterparts; however, these implicit attitudes did not significantly moderate their pain assessment/treatment decisions. Future studies are needed to elucidate specific paths through which the pain experience and care of children differ across racial and gender groups
Deep 1.1 mm-wavelength imaging of the GOODS-S field by AzTEC/ASTE - I. Source catalogue and number counts
[Abridged] We present the first results from a 1.1 mm confusion-limited map
of the GOODS-S field taken with AzTEC on the ASTE telescope. We imaged a 270
sq. arcmin field to a 1\sigma depth of 0.48 - 0.73 mJy/beam, making this one of
the deepest blank-field surveys at mm-wavelengths ever achieved. Although our
GOODS-S map is extremely confused, we demonstrate that our source
identification and number counts analyses are robust, and the techniques
discussed in this paper are relevant for other deeply confused surveys. We find
a total of 41 dusty starburst galaxies with S/N >= 3.5 within this uniformly
covered region, where only two are expected to be false detections. We derive
the 1.1mm number counts from this field using both a "P(d)" analysis and a
semi-Bayesian technique, and find that both methods give consistent results.
Our data are well-fit by a Schechter function model with (S', N(3mJy), \alpha)
= (1.30+0.19 mJy, 160+27 (mJy/deg^2)^(-1), -2.0). Given the depth of this
survey, we put the first tight constraints on the 1.1 mm number counts at
S(1.1mm) = 0.5 mJy, and we find evidence that the faint-end of the number
counts at S(850\mu m) < 2.0 mJy from various SCUBA surveys towards lensing
clusters are biased high. In contrast to the 870 \mu m survey of this field
with the LABOCA camera, we find no apparent under-density of sources compared
to previous surveys at 1.1 mm. Additionally, we find a significant number of
SMGs not identified in the LABOCA catalogue. We find that in contrast to
observations at wavelengths < 500 \mu m, MIPS 24 \mu m sources do not resolve
the total energy density in the cosmic infrared background at 1.1 mm,
demonstrating that a population of z > 3 dust-obscured galaxies that are
unaccounted for at these shorter wavelengths potentially contribute to a large
fraction (~2/3) of the infrared background at 1.1 mm.Comment: 21 pages, 9 figures. Accepted to MNRAS
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