830 research outputs found
Mid-Infrared diagnostics of metal-rich HII regions from VLT and Spitzer Spectroscopy of Young Massive Stars in W31
We present near-IR VLT/ISAAC and mid-IR Spitzer/IRS spectroscopy of the young
massive cluster in the W31 star-forming region. H-band spectroscopy provides
refined classifications for four cluster members O stars with respect to Blum
et al. In addition, photospheric features are detected in the massive Young
Stellar Object (mYSO) #26. Spectroscopy permits estimates of stellar
temperatures and masses, from which a cluster age of ~0.6 Myr and distance of
3.3 kpc are obtained, in excellent agreement with Blum et al. IRS spectroscopy
reveals mid-infrared fine structure line fluxes of [Ne II-III] and [S III-IV]
for four O stars and five mYSOs. In common with previous studies, stellar
temperatures of individual stars are severely underestimated from the observed
ratios of fine-structure lines, despite the use of contemporary stellar
atmosphere and photoionization models. We construct empirical temperature
calibrations based upon the W31 cluster stars of known spectral type,
supplemented by two inner Milky Way ultracompact (UC) HII regions whose
ionizing star properties are established. Calibrations involving [NeIII]
15.5um/[NeII] 12.8um, [SIV] 10.5um/[NeII] 12.8um or [ArIII] 9.0um/[NeII] 12.8um
have application in deducing the spectral types of early- to mid- O stars for
other inner Milky Way compact and UCHII regions. Finally, evolutionary phases
and timescales for the massive stellar content in W31 are discussed, due to the
presence of numerous young massive stars at different formation phases in a
`coeval' cluster.Comment: 16 pages, 13 figures, accepted for MNRA
One-micron spectroscopy of normal OB stars
We have obtained spectra of 70 normal OB stars in the near-IR I (1-Όm) band. The strongest features are those due to lines of the hydrogen Paschen series and neutral and ionized helium, which are, for the most part, in absorption. The information content in this spectral range is sufficient for only a rough classification of hot stars into `early O', `late O' and `B' types. Curiously, the leading He i triplet line, He i λ1.0830 Όm, is usually not detectable, although in a few stars it is in emission; its behaviour generally correlates with the leading helium singlet line, He i λ 2.058 Ό m. These two features appear to be present in emission only in stars with extremes of mass loss or wind extension
High-mass X-ray binaries and OB-runaway stars
High-mass X-ray binaries (HMXBs) represent an important phase in the
evolution of massive binary systems. HMXBs provide unique diagnostics to test
massive-star evolution, to probe the physics of radiation-driven winds, to
study the process of mass accretion, and to measure fundamental parameters of
compact objects. As a consequence of the supernova explosion that produced the
neutron star (or black hole) in these systems, HMXBs have high space velocities
and thus are runaways. Alternatively, OB-runaway stars can be ejected from a
cluster through dynamical interactions. Observations obtained with the
Hipparcos satellite indicate that both scenarios are at work. Only for a
minority of the OB runaways (and HMXBs) a wind bow shock has been detected.
This might be explained by the varying local conditions of the interstellar
medium.Comment: 15 pages, latex (sty file included) with 5 embedded figures (one in
jpg format), to appear in Proc. "Influence of binaries on stellar population
studies", Eds. Vanbeveren, Van Rensberge
The role of input noise in transcriptional regulation
Even under constant external conditions, the expression levels of genes
fluctuate. Much emphasis has been placed on the components of this noise that
are due to randomness in transcription and translation; here we analyze the
role of noise associated with the inputs to transcriptional regulation, the
random arrival and binding of transcription factors to their target sites along
the genome. This noise sets a fundamental physical limit to the reliability of
genetic control, and has clear signatures, but we show that these are easily
obscured by experimental limitations and even by conventional methods for
plotting the variance vs. mean expression level. We argue that simple, global
models of noise dominated by transcription and translation are inconsistent
with the embedding of gene expression in a network of regulatory interactions.
Analysis of recent experiments on transcriptional control in the early
Drosophila embryo shows that these results are quantitatively consistent with
the predicted signatures of input noise, and we discuss the experiments needed
to test the importance of input noise more generally.Comment: 11 pages, 5 figures minor correction
Astronomical Spectroscopy
Spectroscopy is one of the most important tools that an astronomer has for
studying the universe. This chapter begins by discussing the basics, including
the different types of optical spectrographs, with extension to the ultraviolet
and the near-infrared. Emphasis is given to the fundamentals of how
spectrographs are used, and the trade-offs involved in designing an
observational experiment. It then covers observing and reduction techniques,
noting that some of the standard practices of flat-fielding often actually
degrade the quality of the data rather than improve it. Although the focus is
on point sources, spatially resolved spectroscopy of extended sources is also
briefly discussed. Discussion of differential extinction, the impact of
crowding, multi-object techniques, optimal extractions, flat-fielding
considerations, and determining radial velocities and velocity dispersions
provide the spectroscopist with the fundamentals needed to obtain the best
data. Finally the chapter combines the previous material by providing some
examples of real-life observing experiences with several typical instruments.Comment: An abridged version of a chapter to appear in Planets, Stars and
Stellar Systems, to be published in 2011 by Springer. Slightly revise
FDGâPET. A possible prognostic factor in head and neck cancer
Previous studies have shown that high uptake of 18F-fluoro-2-deoxy-glucose in head and neck cancer, as determined by the standardized uptake value on positron emission tomography scan, was associated with poor survival. The aim of this study was to confirm the association and to establish whether a high standardized uptake value had prognostic significance. Seventy-three consecutive patients with newly diagnosed squamous cell carcinoma of the head and neck underwent a positron emission tomography study before treatment. Age, gender, performance status tumour grade, stage, maximal tumour diameter and standardized uptake value were analyzed for their possible association with survival. The median standardized uptake value for all primary tumours was 7.16 (90% range 2.30 to 18.60). In univariate survival analysis the cumulative survival was decreased as the stage, tumour diameter and standardized uptake value increased. An standardized uptake value of 10 was taken as a cut-off for high and low uptake tumours. When these two groups were compared, an standardized uptake value >10 predicted for significantly worse outcome (P=0.003). Multivariate analysis demonstrated that an standardized uptake value >10 provided prognostic information independent of the tumour stage and diameter (P=0.002). We conclude that high FDG uptake (standardized uptake value>10) on positron emission tomography is an important marker for poor outcome in primary squamous cell carcinoma of the head and neck. Standardized uptake value may be useful in distinguishing those tumours with a more aggressive biological nature and hence identifying patients that require intensive treatment protocols including hyperfractionated radiotherapy and/or chemotherapy
MHC-class-II are expressed in a subpopulation of human neural stem cells in vitro in an IFN gamma-independent fashion and during development
This work was supported by grants from Great Ormond Street Hospital Childrenâs Charity, Newlife Foundation,
the Antony Nolan Trust, a studentship to CAG from Consejo Nacional de Ciencia y Tecnologia (CONACyT)
and Instituto Jaliscience de la Juventud (IJJ), Mexico and GOSH NIHR Biomedical Research Centre. The human
embryonic and fetal material was provided by the Human Developmental Biology Resource (http://hdbr.org)
jointly funded by the Medical Research Council (grant G070089) and The Wellcome Trust (grant GR082557)
Observation of associated near-side and away-side long-range correlations in âsNN=5.02ââTeV proton-lead collisions with the ATLAS detector
Two-particle correlations in relative azimuthal angle (ÎÏ) and pseudorapidity (Îη) are measured in âsNN=5.02ââTeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1ââÎŒb-1 of data as a function of transverse momentum (pT) and the transverse energy (ÎŁETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Îη|<5) ânear-sideâ (ÎÏâŒ0) correlation that grows rapidly with increasing ÎŁETPb. A long-range âaway-sideâ (ÎÏâŒÏ) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ÎŁETPb, is found to match the near-side correlation in magnitude, shape (in Îη and ÎÏ) and ÎŁETPb dependence. The resultant ÎÏ correlation is approximately symmetric about Ï/2, and is consistent with a dominant cosâĄ2ÎÏ modulation for all ÎŁETPb ranges and particle pT
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