467 research outputs found
An outer shade of Pal: Abundance analysis of the outer halo globular cluster Palomar 13
At a Galactocentric distance of 27 kpc, Pal 13 is an old globular cluster
(GC) in the outer halo. We present a chemical abundance analysis of this remote
system from high-resolution spectra obtained with Keck/HIRES. Owing to the low
signal-to-noise ratio of the data, our analysis is based on a coaddition of the
spectra of 18 member stars. We are able to determine integrated abundance
ratios for 16 species of 14 elements, of -elements (Mg,Si,Ca,Ti),
Fe-peak (Sc,Mn,Cr,Ni,Cu,and Zn), and n-capture elements (Y,Ba). While the mean
Na abundance is found to be slightly enhanced and halo-like, our method does
not allow us to probe an abundance spread that would be expected in this light
element if multiple populations are present in Pal 13. We find a metal-poor
mean metallicity of (statistical) 0.22 (systematic),
confirming that Pal 13 is a typical metal-poor representative of the outer
halo. While there are some differences between individual -elements,
such as halo-like Mg and Si versus the mildly lower Ca and Ti abundances, the
mean [/Fe] of 0.340.06 is consistent with the marginally lower
component of the halo field and GC stars. We discuss our results in
the context of other objects in the outer halo and consider which of these
objects were likely accreted. We also discuss the properties of their
progenitors. While chemically, Pal 13 is similar to Gaia-Enceladus and some of
its GCs, this is not supported by its kinematic properties. Moreover, its
chemodynamical similarity with NGC 5466, a progeny of the Sequoia accretion
event, might indicate a common origin in this progenitor. However, the
ambiguities in the full abundance space of this comparison emphasize the
difficulties in unequivocally labeling a single GC as an accreted object, let
alone assigning it to a single progenitor. (Abridged)Comment: 10 pages, 7 figures, accepted for publication in Astronomy &
Astrophysic
Relation entre l'accĆØs Ć des services pour des problĆØmes de santĆ© mentale et le partage de matĆ©riel dāinjection chez des utilisateurs de drogue par injection Ć MontrĆ©al
Objectif : Cette eĢtude voulait examiner l'association entre l'acceĢs aĢ des services pour des probleĢmes de santeĢ mentale et le partage reĢceptif de mateĢriel dāinjection dans une cohorte d'utilisateurs de drogue par injection (UDIs) aĢ MontreĢal. De plus, elle eĢtudiait le possible effet modificateur de la deĢtresse psychologique (DP).
MeĢthodologie : Les participants de la cohorte HEPCO vus entre 2011 et 2015 (n = 358) ont compleĢteĢ des questionnaires aux 3 mois. Le partage reĢceptif de mateĢriel dāinjection eĢtait deĢfini comme eĢtant sāeĢtre injecteĢ avec une seringue ou tout autre mateĢriel dāinjection deĢjaĢ utiliseĢ par quelquāun dāautre dans les 3 derniers mois. LāacceĢs aĢ des services pour des probleĢmes mentaux eĢtait deĢfini comme ayant visiteĢ au moins un professionnel de la santeĢ pour des probleĢmes mentaux dans les 3 derniers mois. La DP eĢtait mesureĢe par le Kessler Psychological Distress Scale.
ReĢsultats : En analyses multivarieĢes, une association significative a eĢteĢ trouveĢe entre le partage reĢceptif de mateĢriel dāinjection et lāacceĢs aux services pour des probleĢmes de santeĢ mentale. LāaĢge et le sexe masculin sont associeĢs aĢ de plus faibles probabiliteĢs de partage, tandis que lāutilisation dāopioiĢdes et avoir partageĢ dans les 3 mois preĢceĢdant lāentrevue dāentreĢe sont associeĢs avec de plus grandes chances de partager. Aucune eĢvidence que la DP ne vient modifier cette association nāa eĢteĢ trouveĢe.
Conclusion : Dans cet eĢchantillon, une association protectrice existe entre lāacceĢs aĢ des services pour des probleĢmes de santeĢ mentale et le partage reĢceptif, peu importe le degreĢ de deĢtresse psychologique.Objective: The main objective of the present study was to assess the association between
access to services for mental health problem and receptive sharing of injection material among
people who inject drugs (PWID) in MontrƩal. Moreover, it wanted to examine the potential
modifying effect by the level of psychological distress (PD).
Method: At 3-month intervals, between March 2011 and December 2015, participants (n =
358) answered an interviewer-administered questionnaire eliciting information on
sociodemographic characteristics, substance use and related behaviours, utilization of
services, and mental health indicators. Receptive sharing was defined as having injected with
previously used injection material. Access to services for mental health problems was defined
as at least one visit to various professionals for mental health problems. PD was measured by
the Kessler Psychological Distress Scale (K10). General estimating equation (GEE) analyses
were performed.
Results: In multivariate analyses, a significant association was found between receptive
sharing of injection material and access to services for mental health problems. Age (per 5
years increased) and male gender are associated with a lower likelihood of receptive sharing,
while opioids consumption and receptive sharing in the past 3 months at baseline are
associated with a higher likelihood of receptive sharing. No evidence of effect modification by
psychological distress was found.
Conclusion: Among PWID, access to services for mental health problems was associated with
a lower likelihood of receptive sharing, regardless of the level of psychological distress
Complex microwave conductivity of PrCeCuO thin films using a cavity perturbation method
We report a study of the microwave conductivity of electron-doped
PrCeCuO superconducting thin films using a
cavity perturbation technique. The relative frequency shifts obtained for the
samples placed at a maximum electric field location in the cavity are treated
using the high conductivity limit presented recently by Peligrad
Using two resonance modes, TE (16.5 GHz) and TE
(13 GHz) of the same cavity, only one adjustable parameter is needed
to link the frequency shifts of an empty cavity to the ones of a cavity loaded
with a perfect conductor. Moreover, by studying different sample
configurations, we can relate the substrate effects on the frequency shifts to
a scaling factor. These procedures allow us to extract the temperature
dependence of the complex penetration depth and the complex microwave
conductivity of two films with different quality. Our data confirm that all the
physical properties of the superconducting state are consistent with an order
parameter with lines of nodes. Moreover, we demonstrate the high sensitivity of
these properties on the quality of the films
Galaxies at the extremes: Ultra-diffuse galaxies in the Virgo Cluster
We report the discovery of three large (R29 >~ 1 arcminute) extremely low
surface brightness (mu_(V,0) ~ 27.0) galaxies identified using our deep,
wide-field imaging of the Virgo Cluster from the Burrell Schmidt telescope.
Complementary data from the Next Generation Virgo Cluster Survey do not resolve
red giant branch stars in these objects down to i=24, yielding a lower distance
limit of 2.5 Mpc. At the Virgo distance, these objects have half-light radii
3-10 kpc and luminosities L_V=2-9x10^7 Lsun. These galaxies are comparable in
size but lower in surface brightness than the large ultradiffuse LSB galaxies
recently identified in the Coma cluster, and are located well within Virgo's
virial radius; two are projected directly on the cluster core. One object
appears to be a nucleated LSB in the process of being tidally stripped to form
a new Virgo ultracompact dwarf galaxy. The others show no sign of tidal
disruption, despite the fact that such objects should be most vulnerable to
tidal destruction in the cluster environment. The relative proximity of Virgo
makes these objects amenable to detailed studies of their structural properties
and stellar populations. They thus provide an important new window onto the
connection between cluster environment and galaxy evolution at the extremes.Comment: 7 pages, 4 figures, to appear in ApJ Letters. Updated with minor
revisions to match accepted versio
Galaxies at the extremes: Ultra-diffuse galaxies in the Virgo Cluster
We report the discovery of three large (R29 >~ 1 arcminute) extremely low
surface brightness (mu_(V,0) ~ 27.0) galaxies identified using our deep,
wide-field imaging of the Virgo Cluster from the Burrell Schmidt telescope.
Complementary data from the Next Generation Virgo Cluster Survey do not resolve
red giant branch stars in these objects down to i=24, yielding a lower distance
limit of 2.5 Mpc. At the Virgo distance, these objects have half-light radii
3-10 kpc and luminosities L_V=2-9x10^7 Lsun. These galaxies are comparable in
size but lower in surface brightness than the large ultradiffuse LSB galaxies
recently identified in the Coma cluster, and are located well within Virgo's
virial radius; two are projected directly on the cluster core. One object
appears to be a nucleated LSB in the process of being tidally stripped to form
a new Virgo ultracompact dwarf galaxy. The others show no sign of tidal
disruption, despite the fact that such objects should be most vulnerable to
tidal destruction in the cluster environment. The relative proximity of Virgo
makes these objects amenable to detailed studies of their structural properties
and stellar populations. They thus provide an important new window onto the
connection between cluster environment and galaxy evolution at the extremes.Comment: 7 pages, 4 figures, to appear in ApJ Letters. Updated with minor
revisions to match accepted versio
The ACS Fornax Cluster Survey. III. Globular Cluster Specific Frequencies of Early-Type Galaxies
The globular cluster (GC) specific frequency (), defined as the number
of GCs per unit galactic luminosity, represents the efficiency of GC formation
(and survival) compared to field stars. Despite the naive expectation that star
cluster formation should scale directly with star formation, this efficiency
varies widely across galaxies. To explore this variation we measure the z-band
GC specific frequency () for 43 early-type galaxies (ETGs) from the
Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) Fornax Cluster
Survey. Combined with the homogenous measurements of in 100 ETGs from
the HST/ACS Virgo Cluster Survey from Peng et al. (2008), we investigate the
dependence of on mass and environment over a range of galaxy
properties. We find that behaves similarly in the two galaxy
clusters, despite the clusters' order-of-magnitude difference in mass density.
The is low in intermediate-mass ETGs (), and increases
with galaxy luminosity. It is elevated at low masses, on average, but with a
large scatter driven by galaxies in dense environments. The densest
environments with the strongest tidal forces appear to strip the GC systems of
low-mass galaxies. However, in low-mass galaxies that are not in strong tidal
fields, denser environments correlate with enhanced GC formation efficiencies.
Normalizing by inferred halo masses, the GC mass fraction,
, is constant for ETGs with stellar masses
, in agreement with previous
studies. The lack of correlation between the fraction of GCs and the nuclear
light implies only a weak link between the infall of GCs and the formation of
nuclei.Comment: 16 pages, 7 figures, 6 tables; accepted by Ap
The ACS Virgo Cluster Survey. XVII. The Spatial Alignment of Globular Cluster Systems With Early-Type Host Galaxies
We study the azimuthal distribution of globular clusters (GCs) in early-type
galaxies and compare them to their host galaxies using data from the ACS Virgo
Cluster Survey. We find that in host galaxies with visible elongation (epsilon
> 0.2) and intermediate to high luminosities (M_z<-19), the GCs are
preferentially aligned along the major axis of the stellar light. The red
(metal-rich) GC subpopulations show strong alignment with the major axis of the
host galaxy, which supports the notion that these GCs are associated with
metal-rich field stars. The metal-rich GCs in lenticular galaxies show signs of
being more strongly associated with disks rather than bulges. Surprisingly, we
find that the blue (metal-poor) GCs can also show the same correlation. If the
metal-poor GCs are part of the early formation of the halo and built up through
mergers, then our results support a picture where halo formation and merging
occur anisotropically, and where the present day major axis is an indicator of
the preferred merging axis.Comment: 8 pages, 7 figures, accepted for publication in The Astrophysical
Journa
Sensory afferents use different coding strategies for heat and cold
Primary afferents transduce environmental stimuli
into electrical activity that is transmitted centrally to
be decoded into corresponding sensations. However, it remains unknown how afferent populations
encode different somatosensory inputs. To address
this, we performed two-photon Ca2+ imaging from
thousands of dorsal root ganglion (DRG) neurons in
anesthetized mice while applying mechanical and
thermal stimuli to hind paws. We found that approximately half of all neurons are polymodal and that
heat and cold are encoded very differently. As temperature increases, more heating-sensitive neurons
are activated, and most individual neurons respond
more strongly, consistent with graded coding at population and single-neuron levels, respectively. In
contrast, most cooling-sensitive neurons respond
in an ungraded fashion, inconsistent with graded
coding and suggesting combinatorial coding, based
on which neurons are co-activated. Although individual neurons may respond to multiple stimuli, our results show that different stimuli activate distinct
combinations of diversely tuned neurons, enabling
rich population-level coding
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