81 research outputs found
Mixing in two magnetic OB stars discovered by the MiMeS collaboration
Recent observational and theoretical arguments suggest that magnetic OB stars
may suffer more mixing than their non magnetic analogs. We present the results
of an NLTE abundance study revealing a lack of CN-cycled material at the
surface of two magnetic stars discovered by the MiMeS project (NGC2244 #201 and
HD 57682). The existence of a strong magnetic field is therefore not a
sufficient condition for deep mixing in main-sequence OB stars.Comment: 2 pages, no figures. To appear in proceedings of IAUS272 'Active OB
Stars: Structure, Evolution, Mass Loss and Critical Limits
Pembrolizumab-induced massive hypereosinophilia associated with mononeuritis multiplex, brain microvascular lesions and intestinal eosinophilic infiltration in a melanoma patient
Être urbaniste en Suisse romande. Description d'un champ professionnel en mutation
Entre novembre 2017 et mars 2018, une vaste enquête par questionnaires a été lancée, par les Universités de Genève et Lausanne, auprès de 1375 personnes supposées avoir une activité en lien avec la production du territoire en Suisse romande. Dans un deuxième temps, 24 entretiens semi-directifs ont été réalisés auprès d'interlocuteurs représentatifs. Le portrait de l'urbaniste romand qui résulte de cette enquête est celui d'un-e géographe, architecte, aménagiste ou environnementaliste formé-e en Suisse. Plutôt jeune, il travaille à une courte majorité dans une administration. Peu engagé dans les associations professionnelles, il acquiert un sentiment d'identité professionnelle au moyen de sa discipline de formation. Il exerce dans un environnement plutôt ouvert, l'urbanisme étant conçu comme un domaine interprofessionnel, frappé du sceau de la coopération entre les différentes disciplines à l'origine des métiers de la ville. Les réponses au questionnaire montrent un tropisme plutôt classique dans l'identification des disciplines préparant le mieux aux métiers de l'urbanisme. On évoque ainsi, dans l'ordre, l'architecture, la géographie, l'architecture du paysage. Cette lecture somme toute conforme à l'histoire se manifeste également dans les propositions d'organisation des formations qui nous ont été faites. Le modèle plébiscité est celui d'une formation de type post-diplôme, qui parachèverait un parcours disciplinaire poussé en initiant les candidats aux arcanes des autres disciplines de l'urbanisme, de manière à favoriser le dialogue des disciplines dans le projet urbain. Si le portrait en chiffres de l'urbaniste romand est globalement proche de ce que l'histoire du domaine laissait supposer, il n'en demeure pas moins que le champ de l'urbanisme est, en Suisse francophone comme ailleurs, traversé de tensions qui le dynamisent. La pensée du projet, le durcissement de LAT, la nécessité de ne plus seulement faire la ville, mais de faire avec la ville ont conduit, d'une part, à l'intégration de nouveaux métiers, dont certains, mentionnés dans les entretiens, n'apparaissent même pas dans les réponses au questionnaire, comme le travail social ; d'autre part, à l'explicitation de nouvelles compétences cardinales dès lors que l'on veut être urbaniste, notamment celles liées au leadership, à la capacité de management ou encore à la communication
Isolating Clusters with Wolf-Rayet Stars in I Zw 18
We present UV images and spectra of the starburst galaxy I Zw 18, taken with
the Space Telescope Imaging Spectrograph. The high spatial resolution of these
data allows us to isolate clusters containing Wolf-Rayet stars of the subtype
WC. Our far-UV spectra clearly show CIV 1548,1551 and HeII 1640 emission of WC
stars in two clusters: one within the bright (NW) half of I Zw 18, and one on
the outskirts of this region. The latter spectrum is unusual, because the CIV
is seen only in emission, indicating a spectrum dominated by WC stars. These
data also demonstrate that the HI column in I Zw 18 is strongly peaked in the
fainter (SE) half of I Zw 18, with a column depth far larger than that reported
in previous analyses.Comment: 4 pages, Latex. 2 figures (1 color). Uses corrected version of
emulateapj.sty and apjfonts.sty (included). Accepted for publication in ApJ
Letters. Revised for typos and reversed labels in Fig 2 captio
Chemical abundances in an UV-selected sample of galaxies
We discuss the chemical properties of a sample of UV-selected
intermediate-redshift (0 < z < 0.4) galaxies in the context of their physical
nature and star formation history. This work represents an extension of our
previous studies (Treyer et al. 1998; Sullivan et al. 2000, 2001) on
UV-selected galaxies. We revisit the optical spectra of these galaxies and
perform further emission-line measurements restricting the analysis to those
spectra with the full set of emission lines required to derive chemical
abundances. Our final sample consists of 68 galaxies with heavy element
abundance ratios and both UV and CCD B-band photometry. Diagnostics based on
emission-line ratios show that all but one of the galaxies in our sample are
powered by hot, young stars rather than by an AGN. Oxygen-to-hydrogen (O/H) and
nitrogen-to-oxygen (N/O) abundance ratios are compared to those for various
local and intermediate-redshift samples. Our UV-selected galaxies span a wide
range of oxygen abundances, from 0.1 Zsun to solar, intermediate between
low-mass HII galaxies and massive starburst nuclei. For a given oxygen
abundance, most have strikingly low N/O values. Moreover, UV-selected and HII
galaxies systematically deviate from the usual metallicity-luminosity relation
in the sense of being more luminous by 2-3 magnitudes. Adopting the
"delayed-release" chemical evolution model, we propose our UV-selected sources
are observed at a special stage in their evolution, following a powerful
starburst which enriched their ISM in oxygen and temporarily lowered their
mass-to-light ratios. We discuss briefly the implications of our conclusions on
the nature of similarly-selected high-redshift galaxies.Comment: 17 pages, 10 figures, and 2 tables. Accepted for publication in MNRA
Detection of Wolf-Rayet stars of WN and WC subtype in Super Star Clusters of NGC 5253
We present spectroscopic observations of the central star clusters in NGC
5253 the aim of which is to search for WC stars. Our observations show the
presence of Wolf-Rayet (WR) stars not only of WN but also of WC subtype in two
star forming regions corresponding to the maximum optical and UV emission. The
massive star population we derive is consistent with young bursts of ~3 and 4
Myr. The region of maximum optical emission is found to provide the dominant
contribution of the ionizing flux as opposed to the less extinguished region of
maximum UV brightness. The presence of WR stars near the N-enriched regions
found by Walsh & Roy (1987, 1989) and Kobulnicky et al. (1997) suggests they
are a possible source of N. It is presently unclear whether or not our
detection of WC stars is compatible with the normal observed He/O and C/O
abundance ratios.Comment: Accepted by ApJ Letters. 10 pages, including 2 Figures. LaTeX using
aas2pp4 and psfig macros. Also available at
http://www.stsci.edu/ftp/science/starburst
Fundamental Properties of O-Type Stars
We present a comprehensive analysis of high-resolution, far-UV HST/STIS,
FUSE, and optical spectra of 17 O stars in the SMC. Our analysis is based on
NLTE metal line-blanketed model atmospheres calculated with our NLTE code
TLUSTY. We systematically explore the sensitivity of various UV and optical
lines to different stellar parameters. We have obtained consistent fits of the
UV and the optical spectrum to derive the effective temperature, surface
gravity, surface composition, and microturbulent velocity of each star. Stellar
radii, masses, luminosities and ages then follow. Similarly to more limited
recent studies, we derive cooler temperatures than the standard Teff
calibration of O stars. We propose a new calibration between the spectral type
and effective temperature based on our results from UV metal lines as well as
optical hydrogen and helium lines. For stars of the same spectral subtype, we
find a general good agreement between Teff determinations obtained with TLUSTY,
CMFGEN, and FASTWIND models. We derive ionizing luminosities that are smaller
by a factor of 3 compared to luminosities inferred from previous standard
calibrations. The chemical composition analysis reveals that the surface of
about 3/4 of the program stars is moderately to strongly enriched in nitrogen,
while showing the original helium, carbon, and oxygen abundances. Our results
support the new stellar evolution models that predict that the surface of fast
rotating stars becomes N-rich during the main sequence phase because of
rotationally-induced mixing. Most stars exhibit the ``mass discrepancy''
problem. This discrepancy too is a result of fast rotation which lowers the
measured effective gravity. Our study thus emphasizes the importance of
rotation in our understanding of the properties of massive stars. (abridged)Comment: Submitted to Astrophysical Journal; 69 page
Aged-engineered nanoparticles effect on sludge anaerobic digestion performance and associated microbial communities
To investigate the potential effect of aged engineered nanoparticles (a-ENPs) on sludge digestion performance, 150 L pilot anaerobic digesters (AD) were fed with a blend of primary and waste activated sludge spiked either with a mixture of silver oxide, titanium dioxide and zinc oxide or a mixture of their equivalent bulk metal salts to achieve a target concentration of 250, 2000, and 2800 mg kg− 1 dry weight, respectively. Volatile fatty acids (VFA) were 1.2 times higher in the spiked digesters and significantly different (p = 0.05) from the control conditions. Specifically, isovaleric acid concentration was 2 times lower in the control digester compared to the spiked digesters, whereas hydrogen sulfide was 2 times lower in the ENPs spiked digester indicating inhibitory effect on sulfate reducing microorganisms. Based on the ether-linked isoprenoids concentration, the total abundance of methanogens was 1.4 times lower in the ENPs spiked digester than in the control and metal salt spiked digesters. Pyrosequencing indicated 80% decrease in abundance and diversity of methanogens in ENPs spiked digester compared to the control digester. Methanosarcina acetivorans and Methanosarcina barkeri were identified as nano-tolerant as their relative abundance increased by a factor of 6 and 11, respectively, compared to the other digesters. The results further provide compelling evidence on the resilience of Fusobacteria, Actinobacteria and the Trojan horse-like effect of ENPs which offered a competitive advantage to some organisms while reducing microbial abundance and diversity
Creation of a type IIS restriction endonuclease with a long recognition sequence
Type IIS restriction endonucleases cleave DNA outside their recognition sequences, and are therefore particularly useful in the assembly of DNA from smaller fragments. A limitation of type IIS restriction endonucleases in assembly of long DNA sequences is the relative abundance of their target sites. To facilitate ligation-based assembly of extremely long pieces of DNA, we have engineered a new type IIS restriction endonuclease that combines the specificity of the homing endonuclease I-SceI with the type IIS cleavage pattern of FokI. We linked a non-cleaving mutant of I-SceI, which conveys to the chimeric enzyme its specificity for an 18-bp DNA sequence, to the catalytic domain of FokI, which cuts DNA at a defined site outside the target site. Whereas previously described chimeric endonucleases do not produce type IIS-like precise DNA overhangs suitable for ligation, our chimeric endonuclease cleaves double-stranded DNA exactly 2 and 6 nt from the target site to generate homogeneous, 5′, four-base overhangs, which can be ligated with 90% fidelity. We anticipate that these enzymes will be particularly useful in manipulation of DNA fragments larger than a thousand bases, which are very likely to contain target sites for all natural type IIS restriction endonucleases
Occupational Radiation Protection in Interventional Radiology: A Joint Guideline of the Cardiovascular and Interventional Radiology Society of Europe and the Society of Interventional Radiology
No Abstract
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