477 research outputs found
Inspecting school social quality:Assessing and improving school effectiveness in the social domain
Sensitive Limits on the Water Abundance in Cold Low Mass Molecular Cores
We present SWAS observations of water vapor in two cold star-less clouds, B68
and Core D in rho Ophiuchus. Sensitive non-detections of the 1(10)-1(01)
transition of o-H2O are reported for each source. Both molecular cores have
been previously examined by detailed observations that have characterized the
physical structure. Using these rather well defined physical properties and a
Monte-Carlo radiation transfer model we have removed one of the largest
uncertainties from the abundance calculation and set the lowest water abundance
limit to date in cold low-mass molecular cores. These limits are < 3 x 10^{-8}
(relative to H2) and < 8 x 10^{-9} in B68 and rho Oph D, respectively. Such low
abundances confirm the general lack of ortho-water vapor in cold (T < 20 K)
cores. Provided that the ortho/para ratio of water is not near zero, these
limits are well below theoretical predictions and appear to support the
suggestion that most of the water in dense low-mass cores is frozen onto the
surfaces of cold dust grains.Comment: 12 pages, 3 figures, accepted by Astrophysical Journal Letter
Envelope structure of deeply embedded young stellar objects in the Serpens Molecular Cloud
Aperture synthesis and single-dish (sub) millimeter molecular lines and
continuum observations reveal in great detail the envelope structure of deeply
embedded young stellar objects (SMM1, SMM2, SMM3, SMM4) in the densely
star-forming Serpens Molecular Cloud. Resolved millimeter continuum emission
constrains the density structure to a radial power law with index -2.0 +/- 0.5,
and envelope masses of 8.7, 3.0, and 5.3 M_sol for SMM1, SMM3, and SMM4. The
core SMM2 does not seem to have a central condensation and may not have formed
a star yet. The molecular line observations can be described by the same
envelope model, if an additional, small amount of warm (100 K) material is
included. This probably corresponds to the inner few hundred AU of the envelope
were the temperature is high. In the interferometer beam, the molecular lines
reveal the inner regions of the envelopes, as well as interaction of the
outflow with the surrounding envelope. Bright HCO+ and HCN emission outlines
the cavities, while SiO and SO trace the direct impact of the outflow on
ambient gas. Taken together, these observations provide a first comprehensive
view of the physical and chemical structure of the envelopes of deeply embedded
young stellar objects in a clustered environment on scales between 1000 and
10,000 AU.Comment: 46 pages, incl. 12 postscript figures, uses ApJ latex and psfig
macro
Longitudinal study on nerve ultrasound and corneal confocal microscopy in NF155 paranodopathy
We report the case of a 27-year-old patient with subacute anti-neurofascin-155 neuropathy with bifacial palsy, who showed excellent response to rituximab. We provide longitudinal data of established clinical scores, nerve conduction studies, antibody titers, and novel imaging methods (nerve ultrasonography and corneal confocal microscopy). Clinical and electrophysiological improvement followed the reduction of serum antibody titer and correlated with a reduction of corneal inflammatory cellular infiltrates whereas the increase in the cross-sectional area of the peripheral nerves remained 12 months after first manifestation. Our findings suggest that novel techniques provide useful follow-up parameters in paranodopathies
Quiescent Dense Gas in Protostellar Clusters: the Ophiuchus A Core
We present combined BIMA interferometer and IRAM 30 m Telescope data of N2H+
1-0 line emission across the nearby dense, star forming core Ophiuchus A (Oph
A) at high linear resolution (e.g., ~1000 AU). Six maxima of integrated line
intensity are detected which we designate Oph A-N1 through N6. The N4 and N5
maxima are coincident with the starless continuum objects SM1 and SM2
respectively but the other maxima are not coincident with previously-identified
objects. In contrast, relatively little N2H+ 1-0 emission is coincident with
the starless object SM2 and the Class 0 protostar VLA 1623. The FWHM of the
N2H+ 1-0 line, Delta V, varies by a factor of ~5 across Oph A. Values of Delta
V < 0.3 km/s are found in 14 locations in Oph A, but only that associated with
N6 is both well-defined spatially and larger than the beam size. Centroid
velocities of the line, V_LSR, vary relatively little, having an rms of only
\~0.17 km/s. Small-scale V_LSR gradients of <0.5 km/s over ~0.01 pc are found
near SM1, SM1N, and SM2, but not N6. The low N2H+ abundances of SM2 or VLA 1623
relative to SM1, SM1N, or N6 may reflect relatively greater amounts of N2
adsorption onto dust grains in their colder and probably denser interiors. The
low Delta V of N6, i.e., 0.193 km/s FWHM, is only marginally larger than the
FWHM expected from thermal motions alone, suggesting turbulent motions in the
Oph A core have been reduced dramatically at this location. The non-detection
of N6 in previous thermal continuum maps suggests that interesting sites
possibly related to star formation may be overlooked in such data.Comment: LaTex with 7 figures, produces 36 pages. Accepted for publication in
ApJ. Typo related to Equation 3 fixed, caused derived values of N(N2H+) and
X(N2H+) to be low by factors of ~40%. Conclusions of paper are unchange
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Multiple needs: meeting the challenge. Opportunity Nottingham year four (midway) report 2014-2022
This report is an account of the work of Opportunity Nottingham (ON) as it reaches the midway point of its eight-year programme. It builds on the 2016 report Changing lives, changing systems, moving beyond the initial concern with basic effectiveness, and towards an exploration of the ways in which ON has gone further in the pursuit of its goals, and has met some of the challenges it has encountered on the way. The report is therefore divided into three parts:
The beneficiary challenge
The system challenge
The legacy challeng
In situ SR-XRD study of FeCO₃ precipitation kinetics onto carbon steel in CO₂-containing environments: The influence of brine pH
The growth of iron carbonate (FeCO₃) on the internal walls of carbon steel pipelines used for oil and gas transportation can reduce internal corrosion significantly. Solution pH can be considered as one of the most influential factors with regards to the kinetics, morphology and protection afforded by FeCO₃ films. This paper presents results from a recently developed in situ Synchrotron Radiation-X-ray Diffraction (SR-XRD) flow cell integrated with electrochemistry for corrosion measurements. The cell was used to follow the nucleation and growth kinetics of corrosion products on X65 carbon steel surfaces in a carbon dioxide (CO₂)-saturated 3.5 wt.% NaCl brine at 80 °C and a flow rate of 0.1 m/s over a range of solution pH values (6.3, 6.8 and 7). In all conditions, FeCO₃ was identified as the only crystalline phase to form. Electrochemical results coupled with post-test surface analysis indicate that at higher pH, larger portions of the surface become covered faster with thinner, more protective films consisting of smaller, denser and more compact crystals. The comparison between XRD main peak area intensities and FeCO₃ surface coverage, mass and volume indicates a qualitative relationship between these parameters at each pH, providing valuable information on the kinetics of film growth
Squeezed between shells? On the origin of the Lupus I molecular cloud. - II. APEX CO and GASS HI observations
Accepted for publication in a future issue of Astronomy & Astrophysics. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.Context. The Lupus I cloud is found between the Upper-Scorpius (USco) and the Upper-Centaurus-Lupus (UCL) sub-groups of the Scorpius-Centaurus OB-association, where the expanding USco H I shell appears to interact with a bubble currently driven by the winds of the remaining B-stars of UCL. Aims. We investigate if the Lupus I molecular could have formed in a colliding flow, and in particular, how the kinematics of the cloud might have been influenced by the larger scale gas dynamics. Methods. We performed APEX 13CO(2–1) and C 18O(2–1) line observations of three distinct parts of Lupus I that provide kinematic information on the cloud at high angular and spectral resolution. We compare those results to the atomic hydrogen data from the GASS H i survey and our dust emission results presented in the previous paper. Based on the velocity information, we present a geometric model for the interaction zone between the USco shell and the UCL wind bubble. Results. We present evidence that the molecular gas of Lupus I is tightly linked to the atomic material of the USco shell. The CO emission in Lupus I is found mainly at velocities between vLSR = 3–6 km s−1 which is in the same range as the H i velocities. Thus, the molecular cloud is co-moving with the expanding USco atomic H i shell. The gas in the cloud shows a complex kinematic structure with several line-of-sight components that overlay each other. The non-thermal velocity dispersion is in the transonic regime in all parts of the cloud and could be injected by external compression. Our observations and the derived geometric model agree with a scenario where Lupus I is located in the interaction zone between the USco shell and the UCL wind bubble. Conclusions. The kinematics observations are consistent with a scenario where the Lupus I cloud formed via shell instabilities. The particular location of Lupus I between USco and UCL suggests that counter-pressure from the UCL wind bubble and pre-existing density enhancements, perhaps left over from the gas stream that formed the stellar subgroups, may have played a role in its formation.Peer reviewedFinal Accepted Versio
Star Formation from Galaxies to Globules
The empirical laws of star formation suggest that galactic-scale gravity is
involved, but they do not identify the actual triggering mechanisms for
clusters in the final stages. Many other triggering processes satisfy the
empirical laws too, including turbulence compression and expanding shell
collapse. The self-similar nature of the gas and associated young stars
suggests that turbulence is more directly involved, but the small scale
morphology of gas around most embedded clusters does not look like a random
turbulent flow. Most clusters look triggered by other nearby stars. Such a
prominent local influence makes it difficult to understand the universality of
the Kennicutt and Schmidt laws on galactic scales. A unified view of
multi-scale star formation avoids most of these problems. Ambient self-gravity
produces spiral arms and drives much of the turbulence that leads to
self-similar structures, while localized energy input from existing clusters
and field supernovae triggers new clusters in pre-existing clouds. The
hierarchical structure in the gas made by turbulence ensures that the
triggering time scales with size, giving the Schmidt law over a wide range of
scales and the size-duration correlation for young star fields. The efficiency
of star formation is determined by the fraction of the gas above a critical
density of around 10^5 m(H2)/cc. Star formation is saturated to its largest
possible value given the fractal nature of the interstellar medium.Comment: accepted for ApJ, 42 pages, Dannie Heineman prize lecture, January
200
A Submillimeter View of Circumstellar Dust Disks in Ophiuchus
We present new multiwavelength submillimeter continuum measurements of the
circumstellar dust around 48 young stars in the Ophiuchus dark clouds.
Supplemented with previous 1.3 mm observations of an additional 99 objects from
the literature, the statistical distributions of disk masses and submillimeter
colors are calculated and compared to those in the Taurus-Auriga region. These
basic submillimeter properties of young stellar objects in both environments
are shown to be essentially identical. As with their Taurus counterparts, the
Oph circumstellar dust properties are shown to evolve along an empirical
evolution sequence based on the infrared spectral energy distribution. The
combined Oph and Taurus Class II samples (173 sources) are used to set
benchmark values for basic outer disk characteristics: M_disk ~ 0.005 solar
masses, M_disk/M_star ~ 1%, and ~ 2 (where between 350 microns and 1.3 mm). The precision of these numbers
are addressed in the context of substantial solid particle growth in the
earliest stages of the planet formation process. There is some circumstantial
evidence that disk masses inferred from submillimeter emission may be
under-estimated by up to an order of magnitude.Comment: accepted in ApJ; 38 pages, 11 figure
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