129 research outputs found
A pan-Arctic assessment of the status of marine social-ecological systems
Marine social-ecological conditions in the Arctic are rapidly changing. With many transboundary issues, such as shifting ranges of fisheries, biodiversity loss, sea ice retreat, economic development and pollution, greater pan-Arctic assessment and co-management are necessary. We adapted the Ocean Health Index (OHI) to compile pan-Arctic data and evaluate ocean health for nine regions above the Arctic Circle to assess the extent to which pan-Arctic assessment is possible and identify broad social-ecological trends. While the quality and availability of data varied, we assessed and scored nine OHI goals, including the pressures and resilience measures acting upon them. Our results show the Arctic is sustainably delivering a range of benefits to people, but with room for improvement in all goals, particularly tourism, fisheries, and protected places. Successful management of biological resources and short-term positive impacts on biodiversity in response to climate change underlie these high goal scores. The OHI assesses the past and near-term future but does not account for medium- and long-term future risks associated with climate change, highlighting the need for ongoing monitoring, dynamic management, and strong action to mitigate its anticipated effects. A general increase in and standardisation of monitoring is urgently needed in the Arctic. Unified assessments, such as this one, can support national comparisons, data quality assessments, and discussions on the targeting of limited monitoring capabilities at the most pressing and urgent transboundary management challenges, which is a priority for achieving successful Arctic stewardship
A photoionization model of the compact HII region G29.96-0.02
We present a detailed photoionization model of G29.96-0.02 (hereafter
G29.96), one of the brightest Galactic Ultra Compact HII (UCHII) regions in the
Galaxy. This source has been observed extensively at radio and infrared
wavelengths. The most recent data include a complete ISO (SWS and LWS)
spectrum, which displays a remarkable richness in atomic fine-structure lines.
The number of observables is twice as much as the number available in previous
studies. In addition, most atomic species are now observed in two ionization
stages. The radio and infrared data on G29.96 are best reproduced using a
nebular model with two density components: a diffuse (n_e~680cm-3) extended (~1
pc) component surrounding a compact (~0.1 pc) dense (n_e~57000cm-3) core. The
properties of the ionizing star were derived using state-of-the-art stellar
atmosphere models. CoStar models yield an effective temperature of
\~30^{+2}_{-1} kK whereas more recent non-LTE line blanketed atmospheres with
stellar winds indicate somewhat higher values, Teff~32--38 kK. This range in
Teff is compatible with all observational constraints, including near-infrared
photometry and bolometric luminosity. The range 33-36 kK is also compatible
with the spectral type O5-O8 determined by Watson and Hanson (97) when recent
downward revisions of the effective temperature scale of O stars are taken into
account. The age of the ionizing star of G29.96 is found to be a few 10^6 yr,
much older than the expected lifetime of UCHII regions. Accurate gas phase
abundances are derived with the most robust results being Ne/S=7.5 and N/O=0.43
(1.3 and 3.5 times the solar values, respectively).Comment: Accepted in Astronomy and Astrophysic
Physical Conditions in Barnard's Loop, Components of the Orion-Eridanus Bubble, and Implications for the WIM Component of the ISM
We have supplemented existing spectra of Barnard's Loop with high accuracy
spectrophotometry of one new position. Cloudy photoionization models were
calculated for a variety of ionization parameters and stellar temperatures and
compared with the observations. After testing the procedure with recent
observations of M43, we establish that Barnard's Loop is photoionized by four
candidate ionizing stars, but agreement between the models and observations is
only possible if Barnard's Loop is enhanced in heavy elements by about a factor
of 1.4. Barnard's Loop is very similar in properties to the brightest
components of the Orion-Eridanus Bubble and the Warm Ionized Medium (WIM). We
are able to establish models that bound the range populated in low-ionization
color-color diagrams (I([SII])/I(H{\alpha}) versus I([NII])/I(H{\alpha})) using
only a limited range of ionization parameters and stellar temperatures.
Previously established variations in the relative abundance of heavy elements
render uncertain the most common method of determining electron temperatures
for components of the Orion-Eridanus Bubble and the WIM based on only the
I([NII])/I(H{\alpha}) ratio, although we confirm that the lowest surface
brightness components of the WIM are on average of higher electron temperature.
The electron temperatures for a few high surface brightness WIM components
determined by direct methods are comparable to those of classical bright H II
regions. In contrast, the low surface brightness HII regions studied by the
Wisconsin H{\alpha} Mapper are of lower temperatures than the classical bright
HII regions
Understanding the Spectral Energy Distributions of the Galactic Star Forming Regions IRAS 18314-0720, 18355-0532 & 18316-0602
Embedded Young Stellar Objects (YSO) in dense interstellar clouds is treated
self-consistently to understand their spectral energy distributions (SED).
Radiative transfer calculations in spherical geometry involving the dust as
well as the gas component, have been carried out to explain observations
covering a wide spectral range encompassing near-infrared to radio continuum
wavelengths. Various geometric and physical details of the YSOs are determined
from this modelling scheme. In order to assess the effectiveness of this
self-consistent scheme, three young Galactic star forming regions associated
with IRAS 18314-0720, 18355-0532 and 18316-0602 have been modelled as test
cases. They cover a large range of luminosity ( 40). The modelling of
their SEDs has led to information about various details of these sources, e.g.
embedded energy source, cloud structure & size, density distribution,
composition & abundance of dust grains etc. In all three cases, the best fit
model corresponds to the uniform density distribution.Comment: AAMS style manuscript with 3 tables (in a separate file) and 4
figures. To appear in Journal of Astronophysics & Astronom
Distant Voices: Learners' Stories About the Affective Side of Learning a Language at a Distance
Learning a language at a distance has its own special challenges. The remoteness of the learning context can mean isolation for the learner, communication difficulties for the teacher and problems of access for the researcher. Yet distance language learners are likely to be no more skilled in self-regulation than classroom learners, and to require high levels of support. Research tools are needed, therefore, which allow them to talk freely about their learning in order to help distance educators target support appropriately. This paper draws on data from two pilot ethnographic studies of distance language learners using think-aloud protocols to access their thought processes as they tackled two designated language tasks. They were carried out as part of a wider study in each case to investigate aspects of affect including beliefs, motivation and anxiety. The audio-taped voices provided rich insights into the advantages and disadvantages, pleasures and frustrations, comforts and anxieties of learning a language at a distance, and the strategies learners use to manage in a distance environment. The studies underlined the importance of listening to students and using their voices as a basis for discussion on improving aspects of the design and delivery of distance language courses
Toward a Multifaceted Heuristic of Digital Reading to Inform Assessment, Research, Practice, and Policy
In this commentary, the author explores the tension between almost 30 years of work that has embraced increasingly complex conceptions of digital reading and recent studies that risk oversimplifying digital reading as a singular entity analogous with reading text on a screen. The author begins by tracing a line of theoretical and empirical work that both informs and complicates our understanding of digital literacy and, more specifically, digital reading. Then, a heuristic is proposed to systematically organize, label, and define a multifaceted set of increasingly complex terms, concepts, and practices that characterize the spectrum of digital reading experiences. Research that informs this heuristic is used to illustrate how more precision in defining digital reading can promote greater clarity across research methods and advance a more systematic study of promising digital reading practices. Finally, the author discusses implications for assessment, research, practice, and policy
Planetary nebulae: abundances and abundance gradients
In this work, a review is given of some recent results and problems involved in the determination of chemical abundances of galactic planetary nebulae, particularly regarding disk and bulge objects
Origin of the Metallicity Distribution in the Thick Disc
Aims. Using a suite of cosmological chemodynamical disc galaxy simulations, we assess how (a) radial metallicity
gradients evolve with scaleheight; (b) the vertical metallicity gradients change through the thick disc; and (c) the
vertical gradient of the stellar rotation velocity varies through the disc. We compare with the Milky Way to search for
analogous trends. Methods. We analyse five simulated spiral galaxies with masses comparable to the Milky Way. The simulations span a range of star formation and energy feedback strengths and prescriptions, particle- and grid-based hydrodynamical implementations, as well as initial conditions/assembly history. Disc stars are identified initially via kinematic decomposition, with a posteriori spatial cuts providing the final sample from which radial and vertical gradients are inferred.
Results. Consistently, we find that the steeper, negative, radial metallicity gradients seen in the mid-plane flatten with
increasing height away from the plane. In simulations with stronger (and/or more spatially-extended) feedback, the
negative radial gradients invert, becoming positive for heights in excess of !1 kpc. Such behaviour is consistent with
that inferred from recent observations. Our measurements of the vertical metallicity gradients show no clear correlation
with galactocentric radius, and are in good agreement with those observed in the Milky Way’s thick disc (locally).
Each of the simulations presents a decline in rotational velocity with increasing height from the mid-plane, albeit the
majority have shallower kinematic gradients than that of the Milky Way.
Conclusions. Simulations employing stronger/more extended feedback prescriptions possess radial and vertical metallicity
and kinematic gradients more in line with recent observations. The inverted, positive, radial metallicity gradients seen in the simulated thick stellar discs originate from a population of younger, more metal-rich, stars formed in-situ, superimposed upon a background population of older migrators from the inner disc; the contrast provided by the former increases radially, due to the inside-out growth of the disc. A similar behaviour may be responsible for the same
flattening seen in the radial gradients with scaleheight in the Milky Way
A Project Portfolio Management Approach to Tacklingthe Exploration/Exploitation Trade-off
Organizational ambidexterity (OA) is an essen-tial capability for surviving in dynamic business environ-ments that advocates the simultaneous engagement inexploration and exploitation. Over the last decades,knowledge on OA has substantially matured, coveringinsights into antecedents, outcomes, and moderators of OA.However, there is little prescriptive knowledge that offersguidance on how to put OA into practice and to tackle thetrade-off between exploration and exploitation. To addressthis gap, the authors adopt the design science researchparadigm and propose an economic decision model asartifact. The decision model assists organizations inselecting and scheduling exploration and exploitation pro-jects to become ambidextrous in an economically reason-able manner. As for justificatory knowledge, the decisionmodel draws from prescriptive knowledge on projectportfolio management and value-based management, andfrom descriptive knowledge related to OA to structure thefield of action. To evaluate the decision model, its designspecification is discussed against theory-backed designobjectives and with industry experts. The paper alsoinstantiates the decision model as a software prototype andapplies the prototype to a case based on real-world data
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