| 1. |
- Dornelas, M., et al.
(författare)
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BioTIME: A database of biodiversity time series for the Anthropocene
- 2018
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Ingår i: Global Ecology and Biogeography. - : Wiley. - 1466-822X .- 1466-8238. ; 27:7, s. 760-786
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Tidskriftsartikel (refereegranskat)abstract
- Motivation: The BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community-led open-source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene. Main types of variables included: The database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record. Spatial location and grain: BioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km(2) (158 cm(2)) to 100 km(2) (1,000,000,000,000 cm(2)). Time period and grainBio: TIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year. Major taxa and level of measurement: BioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates.
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| 2. |
- Barnes, Ashley T., et al.
(författare)
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Young massive star cluster formation in the Galactic Centre is driven by global gravitational collapse of high-mass molecular clouds
- 2019
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 486:1, s. 283-303
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Tidskriftsartikel (refereegranskat)abstract
- Young massive clusters (YMCs) are the most compact, high-mass stellar systems still forming at the present day. The precursor clouds to such systems are, however, rare due to their large initial gas mass reservoirs and rapid dispersal time-scales due to stellar feedback. None the less, unlike their high-z counterparts, these precursors are resolvable down to the sites of individually forming stars, and hence represent the ideal environments in which to test the current theories of star and cluster formation. Using high angular resolution (1 arcsec / 0.05 pc) and sensitivity ALMA observations of two YMC progenitor clouds in the Galactic Centre, we have identified a suite of molecular line transitions - e.g. c-C3H2 (7 - 6) - that are believed to be optically thin, and reliably trace the gas structure in the highest density gas on star-forming core scales. We conduct a virial analysis of the identified core and proto-cluster regions, and show that half of the cores (5/10) and both proto-clusters are unstable to gravitational collapse. This is the first kinematic evidence of global gravitational collapse in YMC precursor clouds at such an early evolutionary stage. The implications are that if these clouds are to form YMCs, then they likely do so via the 'conveyor-belt' mode, whereby stars continually form within dispersed dense gas cores as the cloud undergoes global gravitational collapse. The concurrent contraction of both the cluster-scale gas and embedded (proto-)stars ultimately leads to the high (proto-)stellar density in YMCs.
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| 3. |
- Feldman, G., et al.
(författare)
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New results for Compton scattering on deuterium : A better determination of the neutron electromagnetic polarizabilities
- 2015
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Ingår i: Proceedings of Science. - 1824-8039.
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Tidskriftsartikel (refereegranskat)abstract
- The electric and magnetic polarizabilities of the proton are now well known, owing to Compton scattering measurements on hydrogen targets; however, the neutron polarizabilities are still relatively uncertain, compared to the proton values. To address this problem, a multiinstitutional collaboration has conducted a program of elastic Compton scattering experiments on deuterium at the MAX IV Laboratory in Lund, Sweden using tagged photons in the energy range Eγ= 65-115 MeV. We assembled at one laboratory, for the first time, three of the world's largest NaI detectors, each having better than ΔE/E ∼ 2% photon energy resolution. We have measured elastic Compton scattering cross sections at lab angles of θγ= 60°, 120° and 150° over this energy range in 8 MeV steps. This effectively doubles the world's set of elastic Compton scattering data from deuterium and provides valuable input for chiral effective field theory (χEFT) calculations. These new deuterium data overlap previous measurements and extend them by 20 MeV to higher energies. Based on χEFT fits to the expanded world data set, new values for the neutron electric and magnetic polarizabilities have been obtained with greater accuracy than previously achieved, decreasing the statistical error by more than 30%.
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| 4. |
- Sokolov, V., et al.
(författare)
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Temperature structure and kinematics of the IRDC G035.39-00.33
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 606
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Tidskriftsartikel (refereegranskat)abstract
- © ESO, 2017. Aims. Infrared dark clouds represent the earliest stages of high-mass star formation. Detailed observations of their physical conditions on all physical scales are required to improve our understanding of their role in fueling star formation. Methods. We investigate the large-scale structure of the IRDC G035.39-00.33, probing the dense gas with the classical ammonia thermometer. This allows us to put reliable constraints on the temperature of the extended, pc-scale dense gas reservoir and to probe the magnitude of its non-Thermal motions. Available far-infrared observations can be used in tandem with the observed ammonia emission to estimate the total gas mass contained in G035.39-00.33. Results. We identify a main velocity component as a prominent filament, manifested as an ammonia emission intensity ridge spanning more than 6 pc, consistent with the previous studies on the Northern part of the cloud. A number of additional line-of-sight components are found, and a large-scale linear velocity gradient of ~ 0.2km s -1 pc -1 is found along the ridge of the IRDC. In contrast to the dust temperature map, an ammonia-derived kinetic temperature map, presented for the entirety of the cloud, reveals local temperature enhancements towards the massive protostellar cores. We show that without properly accounting for the line of sight contamination, the dust temperature is 2-3 K larger than the gas temperature measured with NH 3 . Conclusions. While both the large-scale kinematics and temperature structure are consistent with that of starless dark filaments, the kinetic gas temperature profile on smaller scales is suggestive of tracing the heating mechanism coincident with the locations of massive protostellar cores.
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| 5. |
- Myers, L. S., et al.
(författare)
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Compton scattering from the deuteron below pion-production threshold
- 2015
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 92:2
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Tidskriftsartikel (refereegranskat)abstract
- Differential cross sections for elastic scattering of photons from the deuteron have recently been measured at the Tagged-Photon Facility at the MAX IV Laboratory in Lund, Sweden. These first new measurements in more than a decade further constrain the isoscalar electromagnetic polarizabilities of the nucleon and provide the first-ever results above 100 MeV, where the sensitivity to the polarizabilities is increased. We add 23 points between 70 and 112 MeV, at angles 60 degrees, 120 degrees, and 150 degrees. Analysis of these data using a chiral effective field theory indicates that the cross sections are both self-consistent and consistent with previous measurements. Extracted values of alpha(s) = [12.1 +/- 0.8(stat) +/- 0.2(BSR) +/- 0.8(th)] x 10(-4) fm(3) and beta(s) = [2.4 +/- 0.8(stat) +/- 0.2(BSR) +/- 0.8(th)] x 10(-4) fm(3) are obtained from a fit to these 23 new data points. This paper presents in detail the experimental conditions and the data analysis used to extract the cross sections.
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| 6. |
- Riener, M., et al.
(författare)
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GAUSSPY+: A fully automated Gaussian decomposition package for emission line spectra
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 628
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Tidskriftsartikel (refereegranskat)abstract
- Our understanding of the dynamics of the interstellar medium is informed by the study of the detailed velocity structure of emission line observations. One approach to study the velocity structure is to decompose the spectra into individual velocity components; this leads to a description of the data set that is significantly reduced in complexity. However, this decomposition requires full automation lest it become prohibitive for large data sets, such as Galactic plane surveys. We developed GAUSSPY+, a fully automated Gaussian decomposition package that can be applied to emission line data sets, especially large surveys of HI and isotopologues of CO. We built our package upon the existing GAUSSPY algorithm and significantly improved its performance for noisy data. New functionalities of GAUSSPY+ include: (i) automated preparatory steps, such as an accurate noise estimation, which can also be used as stand-alone applications; (ii) an improved fitting routine; (iii) an automated spatial refitting routine that can add spatial coherence to the decomposition results by refitting spectra based on neighbouring fit solutions. We thoroughly tested the performance of GAUSSPY+ on synthetic spectra and a test field from the Galactic Ring Survey. We found that GAUSSPY+ can deal with cases of complex emission and even low to moderate signal-to-noise values.
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