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| 9. |
- Akiyama, Kazunori, et al.
(författare)
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First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multiwavelength Observations, Data Processing, and Calibration
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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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.
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| 10. |
- Garrard, S. L., et al.
(författare)
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Biological impacts of ocean acidification: a postgraduate perspective on research priorities
- 2013
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Ingår i: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 160:8, s. 1789-1805
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Tidskriftsartikel (refereegranskat)abstract
- Research into the effects of ocean acidification (OA) on marine organisms has greatly increased during the past decade, as realization of the potential dramatic impacts has grown. Studies have revealed the multifarious responses of organisms to OA conditions, indicating a high level of intra- and interspecific variation in species' ability to accommodate these alterations. If we are to provide policy makers with sound, scientific input regarding the expected consequences of OA, we need a broader understanding of these predicted changes. As a group of 20 multi-disciplinary postgraduate students from around the globe, with a study focus on OA, we are a strong representation of 'next generation' scientists in this field. In this unique cumulative paper, we review knowledge gaps in terms of assessing the biological impacts of OA, outlining directions for future research.
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| 11. |
- Angelopoulus, M., et al.
(författare)
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Physical properties of sea ice cores from site MCS_FYI measured on legs 1 to 3 of the MOSAiC expedition.
- 2022
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Ingår i: PANGAEA.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present sea ice temperature and salinity data from first-year ice (FYI) and second-year ice (SYI) relevant to the temporal development of sea ice permeability and brine drainage efficiency from the early growth phase in October 2019 to the onset of spring warming in May 2020. Our dataset was collected in the central Arctic Ocean during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) Expedition in 2019 to 2020. MOSAiC was an international transpolar drift expedition in which the German icebreaker RV Polarstern anchored into an ice floe to gain new insights into Arctic climate over a full annual cycle. In October 2019, RV Polarstern moored to an ice floe in the Siberian sector of the Arctic at 85 degrees north and 137 degrees east to begin the drift towards the North Pole and the Fram Strait via the Transpolar Drift Stream. The data presented here were collected during the first three legs of the expedition, so all the coring activities took place on the same floe. The end dates of legs 1, 2, and 3 were 13 December, 24 February, and 4 June, respectively. The dataset contributed to a baseline study entitled, Deciphering the properties of different Arctic ice types during the growth phase of the MOSAiC floes: Implications for future studies. The study highlights downward directed gas pathways in FYI and SYI by inferring sea ice permeability and potential brine release from several time series of temperature and salinity measurements. The physical properties presented in this paper lay the foundation for subsequent analyses on actual gas contents measured in the ice cores, as well as air-ice and ice-ocean gas fluxes. Sea ice cores were collected with a Kovacs Mark II 9 cm diameter corer. To measure ice temperatures, about 4.5 cm deep holes were drilled into the core (intervals varied by site and leg) . The temperatures were measured by a digital thermometer within minutes after the cores were retrieved. The ice cores were placed into pre-labelled plastic sleeves sealed at the bottom end. The ice cores were transported to RV Polarstern and stored in a -20 degrees Celsius freezer. Each of the cores was sub-sampled, melted at room temperature, and processed for salinity within one or two days. The practical salinity was estimated by measuring the electrical conductivity and temperature of the melted samples using a WTW Cond 3151 salinometer equipped with a Tetra-Con 325 four-electrode conductivity cell. The practical salinity represents the the salinity estimated from the electrical conductivity of the solution. The dataset also contains derived variables, including sea ice density, brine volume fraction, and the Rayleigh number.
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| 12. |
- Angelopoulus, M., et al.
(författare)
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Physical properties of sea ice cores from site MCS-SYI measured on legs 1 to 3 of the MOSAiC expedition
- 2022
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Ingår i: PANGAEA.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present sea ice temperature and salinity data from first-year ice (FYI) and second-year ice (SYI) relevant to the temporal development of sea ice permeability and brine drainage efficiency from the early growth phase in October 2019 to the onset of spring warming in May 2020. Our dataset was collected in the central Arctic Ocean during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) Expedition in 2019 to 2020. MOSAiC was an international transpolar drift expedition in which the German icebreaker RV Polarstern anchored into an ice floe to gain new insights into Arctic climate over a full annual cycle. In October 2019, RV Polarstern moored to an ice floe in the Siberian sector of the Arctic at 85 degrees north and 137 degrees east to begin the drift towards the North Pole and the Fram Strait via the Transpolar Drift Stream. The data presented here were collected during the first three legs of the expedition, so all the coring activities took place on the same floe. The end dates of legs 1, 2, and 3 were 13 December, 24 February, and 4 June, respectively. The dataset contributed to a baseline study entitled, Deciphering the properties of different Arctic ice types during the growth phase of the MOSAiC floes: Implications for future studies. The study highlights downward directed gas pathways in FYI and SYI by inferring sea ice permeability and potential brine release from several time series of temperature and salinity measurements. The physical properties presented in this paper lay the foundation for subsequent analyses on actual gas contents measured in the ice cores, as well as air-ice and ice-ocean gas fluxes. Sea ice cores were collected with a Kovacs Mark II 9 cm diameter corer. To measure ice temperatures, about 4.5 cm deep holes were drilled into the core (intervals varied by site and leg) . The temperatures were measured by a digital thermometer within minutes after the cores were retrieved. The ice cores were placed into pre-labelled plastic sleeves sealed at the bottom end. The ice cores were transported to RV Polarstern and stored in a -20 degrees Celsius freezer. Each of the cores was sub-sampled, melted at room temperature, and processed for salinity within one or two days. The practical salinity was estimated by measuring the electrical conductivity and temperature of the melted samples using a WTW Cond 3151 salinometer equipped with a Tetra-Con 325 four-electrode conductivity cell. The practical salinity represents the the salinity estimated from the electrical conductivity of the solution. The dataset also contains derived variables, including sea ice density, brine volume fraction, and the Rayleigh number.
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| 13. |
- Benesch, Henric, 1972, et al.
(författare)
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Ingreppsfestival
- 2010
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Ingår i: Kanaltorgsgatan, Heurlins plats, Stenpiren, Verkstadsgatan (Göteborg).
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- I samband med det forskningsprojektet Ingrepp genomfördes en Ingreppfestival med avseende på att i ett öppet publikt sammanhang diskutera utgångspunkterna forskningsgruppen formulerat i tabloiden Ingrepp – en tidning om städer, planering och konst, vilket delades ut gratis en vecka innan festivalen. I tidningen hittade man läsning kring städer, stadsutveckling, konst och konstnärlig forskning vilken hade bäring på den utvecklingsprocess som pågick och pågår på Södra Älvstranden i Göteborg. Både tabloiden och festivalen var ett direkt uttryck för gruppen vilja att ta ut diskussionen på gatan och i sitt sammanhang, men också ett sätt att pröva konstens och akademins möjligheter att gripa in och delta i samhälleliga skeenden. Festivalen vilken turnerade runt på fyra platser under fyra dagar längs Södra Älvstranden innefattade allt ifrån inbjudna samtal/debatter/seminarier till workshops kring Södra Älvstrandens framtid till tipspromenader, picnics och olika former av performativa iscensättningar under bar himmel.
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| 15. |
- Feldt, Robert, et al.
(författare)
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Analyzing the cost of complying to the ECSS standards for software development
- 2010
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Ingår i: European Space Agency, (Special Publication) ESA SP. Conference on DAta Systems in Aerospace, DASIA 2010; Budapest; 1-4 June 2010. - Budapest : European Space Agency. - 0379-6566. - 9789290922469 ; 682, s. 303-307
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Konferensbidrag (refereegranskat)abstract
- Software for space applications has special requirements in terms of reliability and dependability. Standards are one of the primary mechanisms to ensure a sufficient quality level, with the European Cooperation on Space Standardization (ECSS) standards being the main ones. The use of standards is not only a benefit since they can incur considerable costs in terms of, for example, additional documentation and activities. For making the right decisions on which development and quality assurance activities to focus on it is important to know not only their added value but also their costs. Here we present a method for analyzing the cost of standard compliance (CoSC) in software development. It is based on a model which divides the costs into four different types based on their primary value: development, quality-adding, confidence-adding and adherence. The adherence costs are those costs that are incurred by or follows from the use of a standard but does not add any immediate value to either the functionality, quality or quality assurance of the software. Initial results from applying the method in an industrial company adhering to ECSS is presented.
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| 20. |
- Torstensson, Anders, et al.
(författare)
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Chemical and biological vertical distributions within central Arctic (>82 degrees N) sea ice during late summer
- 2023
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Publisher. - 0171-8630 .- 1616-1599. ; 703, s. 17-30
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Tidskriftsartikel (refereegranskat)abstract
- We assessed the distribution of biota (autotrophs and heterotrophs) and associated carbonate chemistry variables in Arctic sea ice at latitudes >82 degrees N during late summer and early autumn 2018. The sampled sea ice was relatively thick (average 1.4 m) with variable snow cover (mean 7 cm) and low bulk salinities throughout. Most measured variables, including carbonate chemistry parameters, were low in the upper half of the ice cores, but increased with depth. Measurements of particulate organic carbon (POC), chlorophyll a (chl a), bacterial abundance, and particulate extracellular polysaccharide (pEPS) in the cores strongly suggested that detrital carbon was the major particulate organic pool. Near the ice-water interface, autotrophic material comprised ca. 50% of the total POC, whereas pEPS and bacterial carbon accounted for ca. 8 and 1% of the total POC, respectively. Under-ice water was nutrient poor, providing only a small input of nutrients to support autotrophic growth, at least during the time of our sampling. While the Arctic Ocean has substantial interannual variability in sea-ice concentration and thickness, these measurements enrich the available database and suggest that during years when autumn sea ice is >1 m thick, sea-ice biota are limited in activity and biomass.
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| 21. |
- Torstensson, Peter, 1981, et al.
(författare)
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Hybrid model for prediction of impact noise generated at railway crossings
- 2018
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Ingår i: Notes on Numerical Fluid Mechanics and Multidisciplinary Design. - Cham : Springer International Publishing. - 1612-2909 .- 1860-0824. ; 139, s. 759-769, s. 759-769
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- A hybrid model for the prediction of impact noise at railway crossings is presented. The hybrid model combines the simulation of vertical wheel‒rail contact force in the time domain and the prediction of sound pressure level using a linear frequency-domain model. The time-domain model uses moving Green’s functions for the vehicle and track models (accounting for wheel flexibility and a discretely supported rail with space-variant beam properties) and a non-Hertzian wheel‒rail contact model. The time-domain and frequency-domain models are coupled based on the concept of an equivalent roughness spectrum. The model is demonstrated by investigating the influence of axle load, vehicle speed and wheel profile on generated impact noise levels. A negligible influence on impact noise is observed for axle loads in the interval 15–25 tonnes. On the other hand, increasing vehicle speed from 80 to 150 km/h, or comparing a nominal S1002 wheel profile with a severely hollow worn profile, result in substantially higher levels of impact noise; for the given wheel and track conditions the differences are in the order of 10 dB(A).
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| 22. |
- Wittgren, Hans B, et al.
(författare)
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An actor game on implementation of environmental quality standards for nitrogen in a Swedish agricultural catchment
- 2005
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Ingår i: Ambio. - : Royal Swedish Academy of Sciences. - 0044-7447 .- 1654-7209. ; 34:3, s. 237-247
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Tidskriftsartikel (refereegranskat)abstract
- Despite political efforts, diffuse pollution from agriculture continues to be the single largest source of nitrogen (N) emissions into the aquatic environment in many countries and regions. This fact, and the recent enactment of a new Swedish environmental code, led to the design of a study targeted at the evaluation of new N pollution abatement strategies. An actor game was chosen as the key component of the study, with a focus on four major goals: to test the implementability of legally binding environmental quality standards for nitrate concentration in groundwater and N transport to the sea, to find sets of agriculturally feasible and cost-effective measures to decrease N loads, to investigate the possibilities for collective action through negotiated and institutionalized actor cooperation, and to investigate the role of mathematical modeling in environmental N management. Characteristics from the agriculturally dominated catchment of Genevadsan (224 km(2)) on the southwest coast of Sweden served as the playing field for the actor game. The most noteworthy result from the study was that it appeared to be possible to meet ambitious environmental N standards with less economically drastic measures than anticipated by most of the participants. The actor game was shown to be a good method for learning about the new Swedish environmental code and its application and for gaining deeper insight into the issues of N management. In addition, the actor game functioned as an arena for gaining a more thorough understanding of the views of different stakeholders.
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