516 research outputs found
Catchment management agencies as crucibles in which to develop responsible leaders in South Africa
During the past 17 years in South Africa, far-reaching policy, legislation and institutional changes in water-related governance have occurred. Responsible leaders have ensured that a paradigm of integrated water resource management (IWRM) is firmly entrenched in the above policy, legislation and institutional arrangements. IWRM in turn demands a level of interaction between individuals, disciplines and organisations such that multi-sector, multi-level stakeholders can collectively, timeously, wisely and cost-effectively visit the consequences of their proposed, present and past actions. Such social learning processes demand leadership and the ongoing development of leaders at all levels. This paper is structured around the propositions for leadership development in the field outlined by Scharmer (2009a). The principal aim of the paper is to reveal the extent to which the multi-sector catchment management agency (CMA) phenomenon is an ideal crucible for leadership development in the field. It is argued that the complex adaptive system that embodies the water realm needs to be engaged by developing complex adaptive systems of governance and that the CMAs have the potential to meet this requirement. Furthermore, it is argued that processes to achieve this required leadership are also ideal for developing leadership. At a time when worldwide developments in communication and computer technology have spawned an exponential growth in successful endeavours related to self-organising around common challenges, the CMA provides a unique and nourishing context for self-organising that simultaneously connects to South Africa’s water governance mainstream of policies, laws, institutions and administrative procedures
Probing the formation of intermediate- to high-mass stars in protoclusters II. Comparison between millimeter interferometric observations of NGC 2264-C and SPH simulations of a collapsing clump
The earliest phases of massive star formation in clusters are still poorly
understood. Here, we test the hypothesis for high-mass star formation proposed
in our earlier paper (Peretto et al. 2006). In order to confirm the physical
validity of this hypothesis, we carried out IRAM Plateau de Bure interferometer
observations of NGC 2264-C and performed SPH numerical simulations of the
collapse of a Jeans-unstable, prolate dense clump. Our Plateau de Bure
observations reveal the presence of a new compact source (C-MM13) located only
\~ 10000 AU away, but separated by ~ 1.1 km/s in (projected) velocity, from the
most massive Class 0 object (C-MM3) lying at the very center of NGC 2264-C.
Detailed comparison with our numerical SPH simulations supports the view that
NGC 2264-C is an elongated cluster-forming clump in the process of collapsing
and fragmenting along its long axis, leading to a strong dynamical interaction
and possible protostar merger in the central region of the clump. The present
study also sets several quantitative constraints on the initial conditions of
large-scale collapse in NGC 2264-C. Our hydrodynamic simulations indicate that
the observed velocity pattern characterizes an early phase of protocluster
collapse which survives for an only short period of time (i.e., < 10^5 yr). To
provide a good match to the observations the simulations require an initial
ratio of turbulent to gravitational energy of only ~ 5 %, which strongly
suggests that the NGC 2264-C clump is structured primarily by gravity rather
than turbulence. The required "cold'' initial conditions may result from rapid
compression by an external trigger.Comment: 15 pages, 8 figures, accepted for publication in A&
Debris Disks: Probing Planet Formation
Debris disks are the dust disks found around ~20% of nearby main sequence
stars in far-IR surveys. They can be considered as descendants of
protoplanetary disks or components of planetary systems, providing valuable
information on circumstellar disk evolution and the outcome of planet
formation. The debris disk population can be explained by the steady
collisional erosion of planetesimal belts; population models constrain where
(10-100au) and in what quantity (>1Mearth) planetesimals (>10km in size)
typically form in protoplanetary disks. Gas is now seen long into the debris
disk phase. Some of this is secondary implying planetesimals have a Solar
System comet-like composition, but some systems may retain primordial gas.
Ongoing planet formation processes are invoked for some debris disks, such as
the continued growth of dwarf planets in an unstirred disk, or the growth of
terrestrial planets through giant impacts. Planets imprint structure on debris
disks in many ways; images of gaps, clumps, warps, eccentricities and other
disk asymmetries, are readily explained by planets at >>5au. Hot dust in the
region planets are commonly found (<5au) is seen for a growing number of stars.
This dust usually originates in an outer belt (e.g., from exocomets), although
an asteroid belt or recent collision is sometimes inferred.Comment: Invited review, accepted for publication in the 'Handbook of
Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018
Exocometary gas structure, origin and physical properties around β Pictoris through ALMA CO multitransition observations
Recent ALMA observations unveiled the structure of CO gas in the 23 Myr-old
Pictoris planetary system, a component that has been discovered in many
similarly young debris disks. We here present ALMA CO J=2-1 observations, at an
improved spectro-spatial resolution and sensitivity compared to previous CO
J=3-2 observations. We find that 1) the CO clump is radially broad, favouring
the resonant migration over the giant impact scenario for its dynamical origin,
2) the CO disk is vertically tilted compared to the main dust disk, at an angle
consistent with the scattered light warp. We then use position-velocity
diagrams to trace Keplerian radii in the orbital plane of the disk. Assuming a
perfectly edge-on geometry, this shows a CO scale height increasing with radius
as , and an electron density (derived from CO line ratios through
NLTE analysis) in agreement with thermodynamical models. Furthermore, we show
how observations of optically thin line ratios can solve the primordial versus
secondary origin dichotomy in gas-bearing debris disks. As shown for
Pictoris, subthermal (NLTE) CO excitation is symptomatic of H densities
that are insufficient to shield CO from photodissociation over the system's
lifetime. This means that replenishment from exocometary volatiles must be
taking place, proving the secondary origin of the disk. In this scenario,
assuming steady state production/destruction of CO gas, we derive the CO+CO
ice abundance by mass in Pic's exocomets to be at most 6%,
consistent with comets in our own Solar System and in the coeval HD181327
system.LM acknowledges support by STFC and ESO through graduate studentships and, together with MCW and QK, by the European Union through ERC grant number 279973. Work of OP is funded by the Royal Society Dorothy Hodgkin Fellowship, and AMH gratefully acknowledges support from NSF grant AST-1412647.This is the final version of the article. It first appeared from Oxford University Press via https://doi.org/10.1093/mnras/stw241
On the gas temperature in circumstellar disks around A stars
In circumstellar disks or shells it is often assumed that gas and dust
temperatures are equal where the latter is determined by radiative equilibrium.
This paper deals with the question whether this assumption is applicable for
tenous circumstellar disks around young A stars. In this paper the thin
hydrostatic equilibrium models described by Kamp & Bertoldi (2000) are combined
with a detailed heating/cooling balance for the gas. The most important heating
and cooling processes are heating through infrared pumping, heating due to the
drift velocity of dust grains, and fine structure and molecular line cooling.
Throughout the whole disk gas and dust are not efficiently coupled by
collisions and hence their temperatures are quite different. Most of the gas in
the disk models considered here stays well below 300 K. In the temperature
range below 300 K the gas chemistry is not much affected by T_gas and therefore
the simplifying approximation T_gas = T_dust can be used for calculating the
chemical structure of the disk. Nevertheless the gas temperature is important
for the quantitative interpretation of observations, like fine structure and
molecular lines.Comment: 16 pages, 31 figures, A&A accepted May 4, 200
Impact of gastroesophageal reflux disease on work absenteeism, presenteeism and productivity in daily life: a European observational study
<p>Abstract</p> <p>Background</p> <p>The RANGE (<it>R</it>etrospective <it>AN</it>alysis of <it>G</it>astro<it>E</it>sophageal reflux disease [GERD]) study assessed differences among patients consulting a primary care physician due to GERD-related reasons in terms of: symptoms, diagnosis and management, response to treatment, and effects on productivity, costs and health-related quality of life. This subanalysis of RANGE determined the impact of GERD on productivity in work and daily life.</p> <p>Methods</p> <p>RANGE was conducted at 134 primary care sites across six European countries (Germany, Greece, Norway, Spain, Sweden and the UK). All subjects (aged ≥18 years) who consulted with their primary care physician over a 4-month identification period were screened retrospectively, and those consulting at least once for GERD-related reasons were identified (index visit). From this population, a random sample was selected to enter the study and attended a follow-up appointment, during which the impact of GERD on productivity while working (absenteeism and presenteeism) and in daily life was evaluated using the self-reported Work Productivity and Activity Impairment Questionnaire for patients with GERD (WPAI-GERD).</p> <p>Results</p> <p>Overall, 373,610 subjects consulted with their primary care physician over the 4-month identification period, 12,815 for GERD-related reasons (3.4%); 2678 randomly selected patients attended the follow-up appointment. Average absenteeism due to GERD was highest in Germany (3.2 hours/week) and lowest in the UK (0.4 hours/week), with an average of up to 6.7 additional hours/week lost due to presenteeism in Norway. The average monetary impact of GERD-related work absenteeism and presenteeism were substantial in all countries (from €55/week per employed patient in the UK to €273/patient in Sweden). Reductions in productivity in daily life of up to 26% were observed across the European countries.</p> <p>Conclusion</p> <p>GERD places a significant burden on primary care patients, in terms of work absenteeism and presenteeism and in daily life. The resulting costs to the local economy may be substantial. Improved management of GERD could be expected to lessen the impact of GERD on productivity and reduce costs.</p
Gas and dust around A-type stars at tens of Myr: signatures of cometary breakup
Discs of dusty debris around main-sequence stars indicate fragmentation of orbiting planetesimals, and for a few A-type stars, a gas component is also seen that may come from collisionally released volatiles. Here we find the sixth example of a CO-hosting disc, around the ∼30 Myr-old A0-star HD 32997. Two more of these CO-hosting stars, HD 21997 and 49 Cet, have also been imaged in dust with SCUBA-2 within the SCUBA-2 Survey of Nearby Stars project. A census of 27 A-type debris hosts within 125 pc now shows 7/16 detections of carbon-bearing gas within the 5–50 Myr epoch, with no detections in 11 older systems. Such a prolonged period of high fragmentation rates corresponds quite well to the epoch when most of the Earth was assembled from planetesimal collisions. Recent models propose that collisional products can be spatially asymmetric if they originate at one location in the disc, with CO particularly exhibiting this behaviour as it can photodissociate in less than an orbital period. Of the six CO-hosting systems, only β Pic is in clear support of this hypothesis. However, radiative transfer modelling with the ProDiMo code shows that the CO is also hard to explain in a proto-planetary disc context.JSG and PW thank the ERC for funding for project DiscAnalysis, under the grant FP7-SPACE-2011 collaborative project 284405. JPM is supported by a UNSW Vice-Chancellor's postdoctoral fellowship. MCW and LM acknowledge the support of the European Union through ERC grant 279973. The JCMT is operated by the East Asian Observatory on behalf of The National Astronomical Observatory of Japan, Academia Sinica Institute of Astronomy and Astrophysics, the Korea Astronomy and Space Science Institute, the National Astronomical Observatories of China and the Chinese Academy of Sciences (Grant No. XDB09000000), with additional funding support from the Science and Technology Facilities Council of the United Kingdom and participating universities in the United Kingdom and Canada. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ
Priority water research questions for South Africa developed through participatory processes
This paper describes a collaborative process of identifying and prioritising current and future water research questions from a wide range of water specialists within South Africa. Over 1 600 questions were collected, reduced in number and prioritised by specialists working in water research and practice. A total of 59 questions were finally proposed as an outcome of the study and are categorised under the themes of change, data, ecosystems, governance, innovation and resources. The questions range in scale, challenge and urgency, and are also aligned with prevailing paradigms in water research. The majority of the questions dealt with relatively short- to medium-term research requirements and most focused on immediate issues such as water supply, service delivery and technical solutions. Formulations of long-term research questions were sparse, partly because some of the principles and methods used in this study were difficult to apply in the South African context, and also because researchers are influenced by addressing what are believed to be the more immediate, short-term water-related challenges in South Africa. This is the first initiative of its kind to produce a comprehensive and inclusive list of research priorities for water in South Africa.Keywords: research, questions, collaboration, prioritisation, South Afric
Circumstellar discs: What will be next?
This prospective chapter gives our view on the evolution of the study of
circumstellar discs within the next 20 years from both observational and
theoretical sides. We first present the expected improvements in our knowledge
of protoplanetary discs as for their masses, sizes, chemistry, the presence of
planets as well as the evolutionary processes shaping these discs. We then
explore the older debris disc stage and explain what will be learnt concerning
their birth, the intrinsic links between these discs and planets, the hot dust
and the gas detected around main sequence stars as well as discs around white
dwarfs.Comment: invited review; comments welcome (32 pages
A planetary system as the origin of structure in Fomalhaut's dust belt
The Sun and >15 percent of nearby stars are surrounded by dusty debris disks
that must be collisionally replenished by asteroids and comets, as the dust
would otherwise be depleted on <10 Myr timescales (ref. 1). Theoretical studies
show that disk structure can be modified by the gravitational influence of
planets (ref. 2-4), but the observational evidence is incomplete, at least in
part because maps of the thermal infrared emission from disks have low linear
resolution (35 AU in the best case; ref. 5). Optical images provide higher
resolution, but the closest examples (AU Mic and Beta Pic) are edge-on (ref.
6,7), preventing the direct measurement of azimuthal and radial disk structure
that is required for fitting theoretical models of planetary perturbations.
Here we report the detection of optical light reflected from the dust grains
orbiting Fomalhaut (HD 216956). The system is inclined 24 degrees away from
edge-on, enabling the measurement of disk structure around its entire
circumference, at a linear resolution of 0.5 AU. The dust is distributed in a
belt 25 AU wide, with a very sharp inner edge at a radial distance of 133 AU,
and we measure an offset of 15 AU between the belt's geometric centre and
Fomalhaut. Taken together, the sharp inner edge and offset demonstrate the
presence of planet-mass objects orbiting Fomalhaut.Comment: 8 pages, 3 figures, 1 tabl
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