| 1. |
- Akiyama, Kazunori, et al.
(författare)
-
First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multiwavelength Observations, Data Processing, and Calibration
- 2022
-
Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
-
Tidskriftsartikel (refereegranskat)abstract
- We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at the position of the supermassive black hole Sagittarius A* (Sgr A*), collected during the 2017 April 5-11 campaign. The observations were carried out with eight facilities at six locations across the globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. The majority of the 1.3 mm emission arises from horizon scales, where intrinsic structural source variability is detected on timescales of minutes to hours. The effects of interstellar scattering on the image and its variability are found to be subdominant to intrinsic source structure. The calibrated visibility amplitudes, particularly the locations of the visibility minima, are broadly consistent with a blurred ring with a diameter of similar to 50 mu as, as determined in later works in this series. Contemporaneous multiwavelength monitoring of Sgr A* was performed at 22, 43, and 86 GHz and at near-infrared and X-ray wavelengths. Several X-ray flares from Sgr A* are detected by Chandra, one at low significance jointly with Swift on 2017 April 7 and the other at higher significance jointly with NuSTAR on 2017 April 11. The brighter April 11 flare is not observed simultaneously by the EHT but is followed by a significant increase in millimeter flux variability immediately after the X-ray outburst, indicating a likely connection in the emission physics near the event horizon. We compare Sgr A*'s broadband flux during the EHT campaign to its historical spectral energy distribution and find that both the quiescent emission and flare emission are consistent with its long-term behavior.
|
|
| 2. |
- Clark, Andrew G., et al.
(författare)
-
Evolution of genes and genomes on the Drosophila phylogeny
- 2007
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 450:7167, s. 203-218
-
Tidskriftsartikel (refereegranskat)abstract
- Comparative analysis of multiple genomes in a phylogenetic framework dramatically improves the precision and sensitivity of evolutionary inference, producing more robust results than single-genome analyses can provide. The genomes of 12 Drosophila species, ten of which are presented here for the first time (sechellia, simulans, yakuba, erecta, ananassae, persimilis, willistoni, mojavensis, virilis and grimshawi), illustrate how rates and patterns of sequence divergence across taxa can illuminate evolutionary processes on a genomic scale. These genome sequences augment the formidable genetic tools that have made Drosophila melanogaster a pre-eminent model for animal genetics, and will further catalyse fundamental research on mechanisms of development, cell biology, genetics, disease, neurobiology, behaviour, physiology and evolution. Despite remarkable similarities among these Drosophila species, we identified many putatively non-neutral changes in protein-coding genes, non-coding RNA genes, and cis-regulatory regions. These may prove to underlie differences in the ecology and behaviour of these diverse species.
|
|
| 3. |
- Kim, Jae-Young, et al.
(författare)
-
Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution
- 2020
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 640
-
Tidskriftsartikel (refereegranskat)abstract
- 3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique - global Very Long Baseline Interferometry (VLBI) at 1.3mm (230 GHz) - to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array, at an angular resolution of ∼20 μas (at a redshift of z = 0:536 this corresponds to ∼0:13 pc ∼ 1700 Schwarzschild radii with a black hole mass MBH = 8 × 108 M⊙). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation.We find a multicomponent inner jet morphology with the northernmost component elongated perpendicular to the direction of the jet, as imaged at longer wavelengths. The elongated nuclear structure is consistent on all four observing days and across diffierent imaging methods and model-fitting techniques, and therefore appears robust. Owing to its compactness and brightness, we associate the northern nuclear structure as the VLBI "core". This morphology can be interpreted as either a broad resolved jet base or a spatially bent jet.We also find significant day-to-day variations in the closure phases, which appear most pronounced on the triangles with the longest baselines. Our analysis shows that this variation is related to a systematic change of the source structure. Two inner jet components move non-radially at apparent speeds of ∼15 c and ∼20 c (∼1:3 and ∼1:7 μas day-1, respectively), which more strongly supports the scenario of traveling shocks or instabilities in a bent, possibly rotating jet. The observed apparent speeds are also coincident with the 3C 279 large-scale jet kinematics observed at longer (cm) wavelengths, suggesting no significant jet acceleration between the 1.3mm core and the outer jet. The intrinsic brightness temperature of the jet components are ≤1010 K, a magnitude or more lower than typical values seen at ≥7mm wavelengths. The low brightness temperature and morphological complexity suggest that the core region of 3C 279 becomes optically thin at short (mm) wavelengths.
|
|
| 4. |
- White, Rehema, et al.
(författare)
-
Golf and Sustainable Development: Opportunities from Theory to Practice
- 2016
-
Ingår i: International Journal of Golf Science. - : Human Kinetics. - 2168-7595 .- 2168-7609. ; 5 (suppl.), s. S75-S76
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: Sustainable development (SD) has been an internationally supported concept since the Brundtland report defined it as ‘development that meets the needs of the present without compromising the ability of future generations to meet their own needs’ (WCED,1987). Since then, many definitions of SD have been explored (e.g. Kates et al 2005; Redclift, 2005) and a range of theoretical models has been applied. The three pillars model of sustainable development, balancing environmental, economic and social aspects of sustainable development, has been widely used in practice but more recently critiqued as a ‘weak model’ of sustainability (Dresner, 2002). Alternative models include strong sustainability, in which natural capital cannot always be exchanged for financial or other forms (Dietz and Neumayer, 2007), or wider framings such as “action into the meaning, making and maintenance of Life in the long term” (Ferraro et al., 2010). In this paper we ask what these theoretical models could bring to the concept and practice of golf.Method: Three theoretical models for sustainable development were applied to assess understandings of golf and practices of golf: ‘three pillars’, ‘strong sustainability’ and ‘integration of humans and nature’. Firstly, a literature search for peer reviewed literature on ‘golf and sustainable development / sustainability’ was undertaken using JSTOR and Web of Science. Secondly, a review of websites of major organizations and significant golf sector reports (including R&A, USGA, PGA, GEO, WGF) captured grey literature and practice recommendations. Thirdly, we engaged with the golf sector through attending and speaking at conferences, discussions with key informants and working with practitioners throughout a three year period. Finally, values and indicators of the theoretical models were mapped across ways in which golf was framed and practised and some practical recommendations derived.Analysis/Results: The peer reviewed literature identified focused primarily on golf and economic development or environmental management. Whilst the ‘three pillars’ model was explicitly mentioned in some golf sector mainstream sites, sustainability was often confined to golf course management. Some cases maintained a holistic focus on sustainable development, others embedded sustainability within areas of practice. There was little evidence of ‘strong sustainability’ in discourse or practice, and regional differences. Some excellent projects going beyond environmental management were identified. Engagement within the golf sector demonstrated wider framings of sustainability, with willingness to explore access, participation and management norms for financial, reputational and value based reasons.Conclusions: Advances in theoretical models of sustainable development have not yet had a significant impact on concepts and practices in the golf sector, although there are some encouraging examples such as supporting local deprived communities, enhancing access, diversification and event carbon accounting and procurement. Golf could benefit from a wider conceptual analysis, potentially leading to an improved role of golf in biodiversity conservation, resource (including carbon) management, physical activity and health, community development and economic outcomes. Practices to promote include local community support, multi-functionality and diversity of golf courses, access programs and rigorous sustainable golf course design and management across all world regions.Keywords: Sustainability, Sustainable Development, Theory and practiceReferencesDietz, S. & Neumayer, E. 2007. Weak and strong sustainability in the SEEA: Concepts and measurement. Ecological Economics, 61, 617-626.Dresner, S. 2002. The principles of sustainability, London, Earthscan Ltd.Ferraro, E., White, R. M., Cox, E., Bebbington, K. J. & Wilson, S. 2010. Craft and sustainable development: reflections on Scottish craft and pathways to sustainability. Craft + Design Enquiry, 3, 1-26.Kates W. Robert , Thomas M. Parris & Anthony A. Leiserowitz, 2005. What is Sustainable Development? Goals, Indicators, Values, and Practice, Environment: Science and Policy for Sustainable Development, 47:3, 8-21, DOI: 10.1080/00139157.2005.10524444Redclift, M. 2005. Sustainable development (1987-2005): An oxymoron comes of age. Sustainable Development, 13, 212-227.
|
|
