5,186 research outputs found
Enhanced OH in C-type shock waves in molecular clouds
Cosmic-ray and X-ray ionisations in molecular gas produce a weak
far-ultraviolet flux through the radiative decay of H2 molecules that have been
excited by collisions with energetic electrons (the Prasad-Tarafdar mechanism).
I consider the effect of this dissociating flux on the oxygen chemistry in
C-type shocks.
Typically a few percent of the water molecules produced within the shock
front are dissociated before the gas has cooled to 50K. The resulting column
density of warm OH rises from 10^15 to 10^16 cm^-2 as the ionisation rate is
increased from 10^-17 (typical of dark clouds) to 10^-15 s^-1 (adjacent to
supernova remnants). These column densities produce substantial emission in the
far-infrared rotational transitions of OH, and are consistent with the OH/H2O
ratios inferred from ISO observations of emission from molecular shocks. For
high ionisation rates the column of warm OH is sufficient to explain the
OH(1720 MHz) masers that occur where molecular clouds are being shocked by
supernova remnants.
The predicted abundance of OH throughout the shock front will enable C-type
shocks to be examined with high spectral resolution through radio observations
of the four hyperfine ground state transitions of OH at 18cm and heterodyne
measurements of emission in the FIR (e.g. from SOFIA)Comment: 5 pp incl 3 figs, LaTeX, uses emulateapj.sty; ApJ Letters in press.
Revised 2nd paragraph of discussio
Enhancing the decision-making process of project managers in the built environment: An integrated approach
A study of the project manager’s (PM) function must be to examine: what their role is, their skills, and training needed. The project manager needs wide perspective regarding the classic management functions of control, coordination, communication, and the settling of performance standards. If the PM is a professional, their performance must be of the highest standard, and must be accountable for a high level of productivity. This is the project manager’s Achilles heel.
Another problem is the absence of feedback during the early stages through to completion of the project. During the project’s life the relative importance of their responsibilities may change several times, including the constant changing of the dynamic environment. The PM will aim for a balanced emphasis; they will try to be flexible so they can adapt to new circumstances as they occur. The PM needs tried and tested methods to aid his decision making. This paper posits an integrated development and use of methods such as; scenario planning, effectuation, and reflective thinking to enhance decision making. The paper concludes with potential benefits that this method brings to the PM when fully understood and tested in the application domain
Thermal OH (1667/65 MHz) Absorption and Nonthermal OH (1720 MHz) Emission Towards the W28 Supernova Remnant
The W28 supernova remnant is an excellent prototype for observing shocked gas
resulting from the interaction of supernova remnants (SNRs) and adjacent
molecular clouds (MCs). We present two new signatures of shocked molecular gas
in this remnant. One is the detection of main-line extended OH (1667 MHz)
absorption with broad linewidths. The column density of OH estimated from the
optical depth profiles is consistent with a theoretical model in which
OH is formed behind a C-type shock front. The second is the detection of
extended, weak OH (1720 MHz) line emission with narrow linewidth distributed
throughout the shocked region of W28. These give observational support to the
idea that compact maser sources delineate the brightest component of a much
larger region of main line OH absorption and nonthermal OH (1720 MHz) emission
tracing the global structure of shocked molecular gas. Main line OH (1665/67)
absorption and extended OH (1720 MHz) emission line studies can serve as
powerful tools to detect SNR-MC interaction even when bright OH (1720 MHz)
masers are absent.Comment: 14 pages, 3 figures, one table, to appear in ApJ (Jan 10, 2003
Patient-reported outcomes following flexible sigmoidoscopy screening for colorectal cancer in a demonstration screening programme in the UK
<p>OBJECTIVES: Flexible sigmoidoscopy (FS) screening for colorectal cancer will be introduced into the National Cancer Screening Programmes in England in 2013. Patient-reported outcome measures (PROMs) from trial participants indicate high acceptability and no adverse physical or psychological consequences, but this may not generalize to routine screening in the community. This study examined PROMs in a community-based FS screening programme.</p>
<p>METHODS: Eligible adults aged 58-59 (n = 2016) registered at 34 London general practices were mailed a National Health Service-endorsed invitation to attend FS screening. Pain and side-effects were assessed in a 'morning-after' questionnaire, and satisfaction was assessed in a three-month follow-up questionnaire. Anxiety, self-rated health and colorectal symptoms were assessed at prescreening and follow-up.</p>
<p>RESULTS: In total, 1020 people attended screening and were included in the current analyses, of whom 913 (90%) returned the morning-after questionnaire, and 674 (66%) the follow-up questionnaire. The prescreening questionnaire had been completed by 751 (74%) of those who attended. The majority (87%) of respondents reported no pain or mild pain, and the most frequent side-effect (wind) was only experienced more than mildly by 16%. Satisfaction was extremely high, with 98% glad they had the test; 97% would encourage a friend to have it. From prescreening to follow-up there were no changes in anxiety or self-rated health, and the number of colorectal symptoms declined. Satisfaction and changes in wellbeing were not moderated by gender, deprivation, ethnicity or screening outcome.</p>
<p>CONCLUSIONS: PROMs indicate high acceptability of FS screening in 58-59 year olds, with no adverse effects on colorectal symptoms, health status or psychological wellbeing.</p>
Flaring Activity of Sgr A* at 43 and 22 GHz: Evidence for Expanding Hot Plasma
We have carried out Very Large Array (VLA) continuum observations to study
the variability of Sgr A* at 43 GHz (=7mm) and 22 GHz
(=13mm). A low level of flare activity has been detected with a
duration of 2 hours at these frequencies, showing the peak flare
emission at 43 GHz leading the 22 GHz peak flare by to 40 minutes. The
overall characteristics of the flare emission are interpreted in terms of the
plasmon model of Van der Laan (1966) by considering the ejection and
adiabatically expansion of a uniform, spherical plasma blob due to flare
activity. The observed peak of the flare emission with a spectral index
of =1.6 is consistent with the prediction that the peak
emission shifts toward lower frequencies in an adiabatically-expanding
self-absorbed source. We present the expected synchrotron light curves for an
expanding blob as well as the peak frequency emission as a function of the
energy spectral index constrained by the available flaring measurements in
near-IR, sub-millimeter, millimeter and radio wavelengths. We note that the
blob model is consistent with the available measurements, however, we can not
rule out the jet of Sgr A*. If expanding material leaves the gravitational
potential of Sgr A*, the total mass-loss rate of nonthermal and thermal
particles is estimated to be M yr. We
discuss the implication of the mass-loss rate since this value matches closely
with the estimated accretion rate based on polarization measurements.Comment: Revised with new Figures 1 and 2, 17 pages, 4 figures, ApJ (in press
Downward shortwave surface irradiance from 17 sites for the FIRE/SRB Wisconsin experiment
A field experiment was conducted in Wisconsin during Oct. to Nov. 1986 for purposes of both intensive cirrus cloud measurments and SRB algorithm validation activities. The cirrus cloud measurements were part of the FIRE. Tables are presented which show data from 17 sites in the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment/Surface Radiation Budget (FIRE/SRB) Wisconsin experiment region. A discussion of intercomparison results and calibration inconsistencies is also included
The Population of the Galactic Center Filaments: Position Angle Distribution Reveal a Degree-scale Collimated Outflow from Sgr A* along the Galactic Plane
We have examined the distribution of the position angle (PA) of the Galactic
center filaments with lengths and as well as their length
distribution as a function of PA. We find bimodal PA distributions of the
filaments, long and short populations of radio filaments. Our PA study shows
the evidence for a distinct population of short filaments with PA close to the
Galactic plane. Mainly thermal short radio filaments () have PAs
concentrated close to the Galactic plane within .
Remarkably, the short filament PAs are radial with respect to the Galactic
center at , and extend in the direction toward Sgr A*. On a smaller
scale, the prominent Sgr E HII complex G358.7-0.0 provides a vivid example of
the nearly radial distribution of short filaments. The bimodal PA distribution
suggests different origin for two distinct filament populations. We argue that
alignment of the short filament population results from the ram pressure of a
degree-scale outflow from Sgr A* that exceeds the internal filament pressure,
and aligns them along the Galactic plane. The ram pressure is estimated to be
2 cm K at a distance of 300pc, requiring biconical mass
outflow rate \msol\, yr with an opening angle of
. This outflow aligns not only the magnetized filaments along the
Galactic plane but also accelerates thermal material associated with embedded
or partially embedded clouds. This places an estimate of 6 Myr as the age
of the outflow.Comment: 19 pages, 8 figures, ApJL (June 2nd, 2023
Nonlinear Development and Observational Consequences of Wardle C-Shock Instabilities
We compute the nonlinear development of the instabilities in C-shocks first
described by Wardle, using a version of the ZEUS code modified to include a
semi-implicit treatment of ambipolar diffusion. We find that, in three
dimensions, thin sheets parallel to the shock velocity and perpendicular to the
magnetic field lines form. High resolution, two-dimensional models show that
the sheets are confined by the Brandenburg & Zweibel ambipolar diffusion
singularity, forcing them to numerically unresolvable thinness. Hot and cold
regions form around these filaments, disrupting the uniform temperature
structure characteristic of a steady-state C-shock. This filamentary region
steadily grows as the shock progresses. We compare steady-state to unstable
C-shocks, showing excitation diagrams, line ratios, and line profiles for
molecular hydrogen lines visible in the K-band, with the Infrared Space
Observatory, and with NICMOS on the Hubble Space Telescope.Comment: 24 pages, 18 figures, uses aaspp4.sty, submitted to ApJ, 26 March
1997 Larger figures are jpegs; original postscript is available from
http://www.mpia-hd.mpg.de/MPIA/Projects/THEORY/maclow/papers/cshk/p2.htm
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