184 research outputs found
Infrared dust emission in the outer disk of M51
We examine faint infrared emission features detected in Spitzer Space
Telescope images of M51, which are associated with atomic hydrogen in the outer
disk and tidal tail at R greater than R_25 (4.9', ~14 kpc at d=9.6 Mpc). The
infrared colors of these features are consistent with the colors of dust
associated with star formation in the bright disk. However, the star formation
efficiency (as a ratio of star formation rate to neutral gas mass) implied in
the outer disk is lower than that in the bright disk of M51 by an order of
magnitude, assuming a similar relationship between infrared emission and star
formation rate in the inner and outer disks.Comment: 13 pages in manuscript form, 2 figures; download PDF of manuscript
with original-resolution Figure 1 at
http://www.eg.bucknell.edu/physics/thornley/thornleym51.pd
Discovery of a detached HI gas shell surrounding alpha Orionis
We report the detection of the HI line at 21 cm in the direction of alpha Ori
with the Nancay Radiotelescope and with the Very Large Array. The observations
confirm the previous detection of HI emission centered on alpha Ori, but
additionally reveal for the first time a quasi-stationary detached shell of
neutral atomic hydrogen ~4 arcmin. in diameter (0.24 pc at a distance of 200
pc). The detached shell appears elongated in a direction opposite to the star's
space motion. A simple model shows that this detached atomic gas shell can
result from the collision of the stellar wind from alpha Ori with the local
interstellar medium (ISM). It implies that alpha Ori has been losing matter at
a rate of ~ 1.2x10^-6 solar masses per year for the past 8x10^4 years. In
addition, we report the detection of atomic hydrogen associated with the
far-infrared arc located 6 arcmin. north-east of alpha Ori, that has been
suggested to trace the bow shock resulting from the motion of the star through
the ISM. We report also the detection by the Galaxy Evolution Explorer (GALEX)
of a far-UV counterpart to this arc.Comment: Accepted for publication in the Monthly Notices; version with full
resolution figures available at
http://aramis.obspm.fr/~lebertre/paper-alphaOri_MNRAS.pd
Cool gas and dust in M33: Results from the Herschel M33 extended survey (HERM33ES)
We present an analysis of the first space-based far-IR-submm observations of
M 33, which measure the emission from the cool dust and resolve the giant
molecular cloud complexes. With roughly half-solar abundances, M33 is a first
step towards young low-metallicity galaxies where the submm may be able to
provide an alternative to CO mapping to measure their H content. In this
Letter, we measure the dust emission cross-section using SPIRE and
recent CO and \HI\ observations; a variation in is present from a
near-solar neighborhood cross-section to about half-solar with the maximum
being south of the nucleus. Calculating the total H column density from the
measured dust temperature and cross-section, and then subtracting the \HI\
column, yields a morphology similar to that observed in CO. The H/\HI\ mass
ratio decreases from about unity to well below 10% and is about 15% averaged
over the optical disk. The single most important observation to reduce the
potentially large systematic errors is to complete the CO mapping of M 33.Comment: 5 pages, 5 figures Accepted for publication in Astronomy and
Astrophysic
Metal production in M33: space and time variations
Nearby galaxies are ideal places to study in detail metallicity gradients and
their time evolution. We consider chemical abundances of a new sample of \hii\
regions complemented with previous literature data-sets. We compare \hii\
region and PN abundances obtained with a common set of observations taken at
MMT. With an updated theoretical model, we follow the time evolution of the
baryonic components and chemical abundances in the disk of M33, assuming that
the galaxy is accreting gas from an external reservoir. Supported by a uniform
sample of nebular spectroscopic observations, we conclude that: {\em i}) the
metallicity distribution in M33 is very complex, showing a central depression
in metallicity probably due to observational bias; {\em ii}) the metallicity
gradient in the disk of M33 has a slope of -0.037 0.009 dex kpc in
the whole radial range up to 8 kpc, and -0.044 0.009 dex kpc
excluding the central kpc; {\em iii}) there is a small evolution of the slope
with time from the epoch of PN progenitor formation to the present-time.}Comment: A&A accepted, 15 Pags, 13 Figs, language correctio
X Her and TX Psc: Two cases of ISM interaction with stellar winds observed by Herschel
The asymptotic giant branch (AGB) stars X Her and TX Psc have been imaged at
70 and 160 microns with the PACS instrument onboard the Herschel satellite, as
part of the large MESS (Mass loss of Evolved StarS) Guaranteed Time Key
Program. The images reveal an axisymmetric extended structure with its axis
oriented along the space motion of the stars. This extended structure is very
likely to be shaped by the interaction of the wind ejected by the AGB star with
the surrounding interstellar medium (ISM). As predicted by numerical
simulations, the detailed structure of the wind-ISM interface depends upon the
relative velocity between star+wind and the ISM, which is large for these two
stars (108 and 55 km/s for X Her and TX Psc, respectively). In both cases,
there is a compact blob upstream whose origin is not fully elucidated, but that
could be the signature of some instability in the wind-ISM shock. Deconvolved
images of X Her and TX Psc reveal several discrete structures along the
outermost filaments, which could be Kelvin-Helmholtz vortices. Finally, TX Psc
is surrounded by an almost circular ring (the signature of the termination
shock?) that contrasts with the outer, more structured filaments. A similar
inner circular structure seems to be present in X Her as well, albeit less
clearly.Comment: 11 pages, Astronomy & Astrophysics, in pres
Investigation into the material properties of wooden composite structures with in-situ fibre reinforcement using additive manufacturing
In contrast to subtractive manufacturing techniques, additive manufacturing processes are known for their high efficiency in regards to utilisation of feedstock. However the various polymer, metallic and composite feedstocks used within additive manufacturing are mainly derived from energy consuming, inefficient methods, often originating from non-sustainable sources. This work explores the mechanical properties of additively manufactured composite structures fabricated from recycled sustainable wood waste with the aim of enhancing mechanical properties through glass fibre reinforcement.
In the first instance, samples were formed by pouring formulation of wood waste (wood flour) and thermosetting binder (urea formaldehyde), with and without glass fibres, into a mould. The same formulations were used to additively manufacture samples via a layered deposition technique. Samples manufactured using each technique were cured and subsequently tested for their mechanical properties. Additively manufactured samples had superior mechanical properties, with up to 73% increase in tensile strength compared to moulded composites due to a densification of feedstock/paste and fibre in-situ directional alignment
Rescue of Dystrophic Skeletal Muscle by PGC-1α Involves a Fast to Slow Fiber Type Shift in the mdx Mouse
Increased utrophin expression is known to reduce pathology in dystrophin-deficient skeletal muscles. Transgenic over-expression of PGC-1α has been shown to increase levels of utrophin mRNA and improve the histology of mdx muscles. Other reports have shown that PGC-1α signaling can lead to increased oxidative capacity and a fast to slow fiber type shift. Given that it has been shown that slow fibers produce and maintain more utrophin than fast skeletal muscle fibers, we hypothesized that over-expression of PGC-1α in post-natal mdx mice would increase utrophin levels via a fiber type shift, resulting in more slow, oxidative fibers that are also more resistant to contraction-induced damage. To test this hypothesis, neonatal mdx mice were injected with recombinant adeno-associated virus (AAV) driving expression of PGC-1α. PGC-1α over-expression resulted in increased utrophin and type I myosin heavy chain expression as well as elevated mitochondrial protein expression. Muscles were shown to be more resistant to contraction-induced damage and more fatigue resistant. Sirt-1 was increased while p38 activation and NRF-1 were reduced in PGC-1α over-expressing muscle when compared to control. We also evaluated if the use a pharmacological PGC-1α pathway activator, resveratrol, could drive the same physiological changes. Resveratrol administration (100 mg/kg/day) resulted in improved fatigue resistance, but did not achieve significant increases in utrophin expression. These data suggest that the PGC-1α pathway is a potential target for therapeutic intervention in dystrophic skeletal muscle
100 mum and 160 mum emission as resolved star-formation rate estimators in M33 (HERM33ES)
Over the past few years several studies have provided estimates of the SFR
(star-formation rate) or the total infrared luminosity from just one infrared
band. However these relations are generally derived for entire galaxies, which
are known to contain a large scale diffuse emission that is not necessarily
related to the latest star-formation episode. We provide new relations to
estimate the SFR from resolved star-forming regions at 100 mum and 160 mum. We
select individual star-forming regions in the nearby (840 kpc) galaxy M33. We
estimate the SFR combining the emission in Halpha and at 24 mum to calibrate
the emission at 100 mum and 160 mum as SFR estimators, as mapped with
PACS/Herschel. The data are obtained in the framework of the HERM33ES open time
key project. There is less emission in the HII regions at 160 mum than at 100
mum. Over a dynamic range of almost 2 dex in Sigma(SFR) we find that the 100
mum emission is a nearly linear estimator of the SFR, whereas that at 160 mum
is slightly superlinear. The behaviour of individual star-forming regions is
surprisingly similar to that of entire galaxies. At high Sigma(SFR), star
formation drives the dust temperature, whereas uncertainties and variations in
radiation-transfer and dust-heated processes dominate at low Sigma(SFR).
Detailed modelling of both galaxies and individual star forming regions will be
needed to interpret similarities and differences between the two and assess the
fraction of diffuse emission in galaxies.Comment: 5 pages, 3 figures, accepted for publication in the A&A Herschel
special issu
High-Resolution Melting Analysis as a Powerful Tool to Discriminate and Genotype Pseudomonas savastanoi Pathovars and Strains
Pseudomonas savastanoi is a serious pathogen of Olive, Oleander, Ash, and several other Oleaceae. Its epiphytic or endophytic presence in asymptomatic plants is crucial for the spread of Olive and Oleander knot disease, as already ascertained for P. savastanoi pv. savastanoi (Psv) on Olive and for pv. nerii (Psn) on Oleander, while no information is available for pv. fraxini (Psf) on Ash. Nothing is known yet about the distribution on the different host plants and the real host range of these pathovars in nature, although cross-infections were observed following artificial inoculations. A multiplex Real-Time PCR assay was recently developed to simultaneously and quantitatively discriminate in vitro and in planta these P. savastanoi pathovars, for routine culture confirmation and for epidemiological and diagnostical studies. Here an innovative High-Resolution Melting Analysis (HRMA)-based assay was set up to unequivocally discriminate Psv, Psn and Psf, according to several single nucleotide polymorphisms found in their Type Three Secretion System clusters. The genetic distances among 56 P. savastanoi strains belonging to these pathovars were also evaluated, confirming and refining data previously obtained by fAFLP. To our knowledge, this is the first time that HRMA is applied to a bacterial plant pathogen, and one of the few multiplex HRMA-based assays developed so far. This protocol provides a rapid, sensitive, specific tool to differentiate and detect Psv, Psn and Psf strains, also in vivo and against other related bacteria, with lower costs than conventional multiplex Real-Time PCR. Its application is particularly suitable for sanitary certification programs for P. savastanoi, aimed at avoiding the spreading of this phytopathogen through asymptomatic plants
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