278 research outputs found
VLBI study of maser kinematics in high-mass SFRs. I. G16.59-0.05
The present paper focuses on the high-mass star-forming region G16.59-0.05.
Methods: Using the VLBA and the EVN arrays, we conducted phase-referenced
observations of the three most powerful maser species in G16.59-0.05: H2O at
22.2 GHz (4 epochs), CH3OH at 6.7 GHz (3 epochs), and OH at 1.665 GHz (1
epoch). In addition, we performed high-resolution (> 0".1), high-sensitivity (<
0.1 mJy) VLA observations of the radio continuum emission from the star-forming
region at 1.3 and 3.6 cm. Results: This is the first work to report accurate
measurements of the "relative" proper motions of the 6.7 GHz CH3OH masers. The
different spatial and 3-D velocity distribution clearly indicate that the 22
GHz water and 6.7 GHz methanol masers are tracing different kinematic
environments. The bipolar distribution of 6.7 GHz maser l.o.s. velocities and
the regular pattern of observed proper motions suggest that these masers are
tracing rotation around a central mass of about 35 solar masses. The flattened
spatial distribution of the 6.7 GHz masers, oriented NW-SE, suggests that they
can originate in a disk/toroid rotating around the massive YSO which drives the
12CO(2-1) outflow, oriented NE-SW, observed on arcsec scale. The extended,
radio continuum source observed close to the 6.7 GHz masers could be excited by
a wide-angle wind emitted from the YSO associated with the methanol masers, and
such a wind is proven to be sufficiently energetic to drive the NE-SW 12CO(2-1)
outflow. The H2O masers distribute across a region offset about 0".5 to the NW
of the CH3OH masers, in the same area where emission of high-density molecular
tracers, typical of HMCs, was detected. We postulate that a distinct YSO,
possibly in an earlier evolutionary phase than that exciting the methanol
masers, is responsible for the excitation of the water masers and the HMC
molecular lines. (Abridged)Comment: 20 pages, 8 figures, 3 tables, accepted by Astronomy and Astrophysic
Re-analysis of the radio luminosity function of Galactic HII regions
We have re-analyzed continuum and recombination lines radio data available in
the literature in order to derive the luminosity function (LF) of Galactic HII
regions. The study is performed by considering the first and fourth Galactic
quadrants independently. We estimate the completeness level of the sample in
the fourth quadrant at 5 Jy, and the one in the first quadrant at 2 Jy. We show
that the two samples (fourth or first quadrant) include, as well as giant and
super-giant HII regions, a significant number of sub-giant sources. The LF is
obtained, in each Galactic quadrant, with a generalized Schmidt's estimator
using an effective volume derived from the observed spatial distribution of the
considered HII regions. The re-analysis also takes advantage of recently
published ancillary absorption data allowing to solve the distance ambiguity
for several objects. A single power-law fit to the LFs retrieves a slope equal
to -2.23+/-0.07 (fourth quadrant) and to -1.85+/-0.11 (first quadrant). We also
find marginal evidence of a luminosity break at L_knee = 10^23.45 erg s^(-1)
Hz^(-1) for the LF in the fourth quadrant. We convert radio luminosities into
equivalent H_alpha and Lyman continuum luminosities to facilitate comparisons
with extra-galactic studies. We obtain an average total HII regions Lyman
continuum luminosity of 0.89 +/- 0.23 * 10^(53) sec^(-1), corresponding to 30%
of the total ionizing luminosity of the Galaxy.Comment: accepted for publication in Ap
Molecular line mapping of the giant molecular cloud associated with RCW 106 - II. Column density and dynamical state of the clumps
We present a fully sampled C^{18}O (1-0) map towards the southern giant
molecular cloud (GMC) associated with the HII region RCW 106, and use it in
combination with previous ^{13}CO (1-0) mapping to estimate the gas column
density as a function of position and velocity. We find localized regions of
significant ^{13}CO optical depth in the northern part of the cloud, with
several of the high-opacity clouds in this region likely associated with a
limb-brightened shell around the HII region G333.6-0.2. Optical depth
corrections broaden the distribution of column densities in the cloud, yielding
a log-normal distribution as predicted by simulations of turbulence.
Decomposing the ^{13}CO and C^{18}O data cubes into clumps, we find relatively
weak correlations between size and linewidth, and a more sensitive dependence
of luminosity on size than would be predicted by a constant average column
density. The clump mass spectrum has a slope near -1.7, consistent with
previous studies. The most massive clumps appear to have gravitational binding
energies well in excess of virial equilibrium; we discuss possible
explanations, which include magnetic support and neglect of time-varying
surface terms in the virial theorem. Unlike molecular clouds as a whole, the
clumps within the RCW 106 GMC, while elongated, appear to show random
orientations with respect to the Galactic plane.Comment: 17 pages, to appear in MNRA
2018 Top Trends in Academic Libraries
Every other year, the ACRL Research Planning and Review Committee produces a document on top trends in higher education as they relate to academic librarianship. Topics in this edition of ACRL Top Trends will be familiar to some readers who will hopefully learn of new materials to expand their knowledge. Other readers will be made aware of trends that are outside of their experience. This is the nature of trends in our current technological and educational environments: change is continual, but it affects different libraries at different rates. The 2018 top trends share several overarching themes, including the impact of market forces, technology, and the political environment on libraries
2022 Top Trends in Academic Libraries
This article summarizes trending topics in academic librarianship from the past two yearsâa time of tremendous upheaval and change, including a global pandemic, difficult reflections concerning racial justice, and war between nation states. Rapid changes and uncertainty from these events have created a significant amount of shifts to academic libraries, higher education, and society in general. Such shifts have yielded new perspectives and innovations in how librarians approach delivering services, supporting student success, managing staff and physical spaces, embracing new technology, and managing data. This report attempts to provide a snapshot of developments worth noting
Modelling the population size and dynamics of the British grey seal
Funding: part-funded by the UK Natural Environment Research Council to SMRU (Grant no. SMRU1001).1. Grey seals (Halichoerus grypus) were the first mammals to be protected by an Act of Parliament in the UK and are currently protected under UK, Scottish, and EU conservation legislation. Reporting requirements under each of these statutes requires accurate and timely population estimates. Monitoring is principally conducted by aerial surveys of the breeding colonies; these are used to produce estimates of annual pup production. Translating these data to estimates of adult population size requires information about demographic parameters such as fecundity and sex ratio. 2. An ageâstructured population dynamics model is presented, which includes density dependence in pup survival, with separate carrying capacities in each of the four breeding regions considered (North Sea, Inner Hebrides, Outer Hebrides, and Orkney). This model is embedded within a Bayesian stateâspace modelling framework, allowing the population model to be linked to available data and the use of informative prior distributions on demographic parameters. A computerâintensive fitting algorithm is presented based on particle filtering methods. 3. The model is fitted to regionâlevel pup production estimates from 1984 to 2010 and an independent estimate of adult population size, derived from aerial surveys of hauledâout seals in 2008. The fitted model is used to estimate total population size from 1984 to 2010. 4. The population in the North Sea region has increased at a nearâconstant rate; growth in the other three regions began to slow in the midâ1990s and these populations appear to have reached carrying capacity. The total population size of seals aged 1 year or older in 2010 was estimated to be 116 100 (95% CI 98 400â138 600), an increase of <1% on the previous year. 5. The modelling and fitting methods are widely applicable to other wildlife populations where diverse sources of information are available and inference is required for the underlying population dynamics.PostprintPeer reviewe
Enhancement in the rate of nitrate degradation on Au- and Ag-decorated TiO2 photocatalysts
The solar-driven reduction of nitrate to nitrogen has been studied in the presence of a formate hole scavenger, over a series of Au- and Ag-decorated TiO2 catalysts. In this study, the catalyst preparation protocol was found to influence the nitrate transformation in the order: incipient wetness impregnation > stabilizer-free sol immobilization > sol immobilization. However, the sequence of performing specific treatment steps such as drying, calcination and sieving had a less pronounced effect. Low-conversion conditions were utilized to study the photo-degradation of nitrate over a range of monometallic and bimetallic catalysts with metal concentrations in the range M = 0â1 wt% (M: Au, Ag, Pd, AuAg). Our findings demonstrate that selectively degrading nitrate to N2 over these co-catalysts is non-trivial and is metal content dependent. For Au-doped TiO2 catalysts, the highest activity was measured over 0.2 wt% Au/TiO2 while a higher metal loading of 0.4 wt% was required for the Ag/TiO2 photocatalyst. Product selectivity was also demonstrated to be dependent on metal and metal loading: approximately 22% nitrite selectivity was determined over a 0.1 wt% Ag-doped catalysts, however this product was not detected when utilising Au-doped catalysts. Total selectivity to dinitrogen was shown to be possible on both Au and Ag doped catalysts, and again this was dependent on the concentration of the metal (Ag > 0.3 wt%; 0.2 < Au â„ 0.4 wt%)
Self-driving Multimodal Studies at User Facilities
Multimodal characterization is commonly required for understanding materials.
User facilities possess the infrastructure to perform these measurements,
albeit in serial over days to months. In this paper, we describe a unified
multimodal measurement of a single sample library at distant instruments,
driven by a concert of distributed agents that use analysis from each modality
to inform the direction of the other in real time. Powered by the Bluesky
project at the National Synchrotron Light Source II, this experiment is a
world's first for beamline science, and provides a blueprint for future
approaches to multimodal and multifidelity experiments at user facilities.Comment: 36th Conference on Neural Information Processing Systems (NeurIPS
2022). AI4Mat Worksho
Foreground simulations for the LOFAR - Epoch of Reionization Experiment
Future high redshift 21-cm experiments will suffer from a high degree of
contamination, due both to astrophysical foregrounds and to non-astrophysical
and instrumental effects. In order to reliably extract the cosmological signal
from the observed data, it is essential to understand very well all data
components and their influence on the extracted signal. Here we present
simulated astrophysical foregrounds datacubes and discuss their possible
statistical effects on the data. The foreground maps are produced assuming 5
deg x 5 deg windows that match those expected to be observed by the LOFAR
Epoch-of-Reionization (EoR) key science project. We show that with the expected
LOFAR-EoR sky and receiver noise levels, which amount to ~52 mK at 150 MHz
after 300 hours of total observing time, a simple polynomial fit allows a
statistical reconstruction of the signal. We also show that the polynomial
fitting will work for maps with realistic yet idealised instrument response,
i.e., a response that includes only a uniform uv coverage as a function of
frequency and ignores many other uncertainties. Polarized galactic synchrotron
maps that include internal polarization and a number of Faraday screens along
the line of sight are also simulated. The importance of these stems from the
fact that the LOFAR instrument, in common with all current interferometric EoR
experiments has an instrumentally polarized response.Comment: 18 figures, 3 tables, accepted to be published in MNRA
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