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  • 1
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    The star formation history of galaxies: the role of galaxy mass, morphology and environment (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-10
    Description: We analyse the star formation history (SFH) of galaxies as a function of present-day environment, galaxy stellar mass and morphology. The SFH is derived by means of a non-parametric spectrophotometric model applied to individual galaxies at z  ~ 0.04–0.1 in the WIde-field Nearby Galaxy-cluster Survey (WINGS) clusters and the Padova Millennium Galaxy and Group Catalogue (PM2GC) field. The field reconstructed evolution of the star formation rate density (SFRD) follows the values observed at each redshift, except at z  〉 2, where our estimate is ~1.7 higher than the high- z observed value. The slope of the SFRD decline with time gets progressively steeper going from low-mass to high-mass haloes. The decrease of the SFRD since z  = 2 is due to (1) quenching – 50 per cent of the SFRD in the field and 75 per cent in clusters at z  〉 2 originated in galaxies that are passive today – and (2) the fact that the average SFR of today's star-forming galaxies has decreased with time. We quantify the contribution to the SFRD( z ) of galaxies of today's different masses and morphologies. The current morphology correlates with the current star formation activity but is irrelevant for the past stellar history. The average SFH depends on galaxy mass, but galaxies of a given mass have different histories depending on their environment. We conclude that the variation of the SFRD( z ) with environment is not driven by different distributions of galaxy masses and morphologies in clusters and field, and must be due to an accelerated formation in high-mass haloes compared to low-mass ones even for galaxies that will end up having the same galaxy mass today.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    A New Technique for Estimating The Lifetime of Bursts of Electron Precipitation From Sounding Rocket Measurements (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract At 0735 UT on December 13 2015,the Rocket Experiment for Neutral Upwelling‐2 (RENU2) experiment launched north towards the auroral cusp region from Andoya, Norway. The instrumented rocket included an electron spectrometer, photometers that measured the auroral redline and greenline, and an instrument that measured ionospheric thermal electron temperature. On the down leg, just south of Svalbard, the rocket entered a region of poleward moving auroral forms (PMAFs) that were characterized by narrow structures due to a combination of spatial and temporal variations. A noticeable feature was that the redline to greenline brightness ratio was much smaller than expected. A model is developed that shows that these emissions can be used to estimate the lifetimes of bursty electron precipitation. This model is shown to be consistent with some PMAF lifetimes being on the order of 100 ms. The correlation between the precipitation and temperature bursts suggest that some transport occurred.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    RENU2 UV PMT observations of the cusp (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The Rocket Experiment for Neutral Upwelling 2 (RENU2) sounding rocket launched from the Andøya Space Center on 13 December 2015 into the dayside polar cusp. An ultraviolet photomultiplier tube (UV PMT) on the RENU2 payload was oriented to look up along the spin axis for emissions of neutral atomic oxygen above the payload. Data from the UV PMT has been compared to predicted auroral emissions calculated by the Global Airglow (GLOW) model. The comparison between GLOW calculations driven by RENU2 electron precipitation measurements and UV PMT data suggest enhanced neutral density in the cusp at altitudes above the RENU2 trajectory.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Contamination in electron observations of the silicon detector onboard Cluster/RAPID/IES instrument in Earth's radiation belts and ring current (2016)
    Wiley
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    Publication Date: 2016-06-11
    Description: Since more than 15 years, the Cluster mission passes through Earth's radiation belts at least once every two days for several hours, measuring the electron intensity at energies from 30 to 400 keV. This data has previously been considered not usable due to contamination caused by penetrating energetic particles (protons at 〉100 keV and electrons at 〉400 keV). In this study, we assess the level of distortion of energetic electron spectra from the RAPID/IES detector, determining the efficiency of its shielding. We base our assessment on the analysis of experimental data and a radiation transport code (Geant4). In simulations, we use the incident particle energy distribution of the AE9/AP9 radiation belt models. We identify the Roederer L-values, L ⋆ , and energy channels that should be used with caution: at 3≤L ⋆ ≤4, all energy channels (40 – 400 keV) are contaminated by protons (≃230 to 630 keV and 〉600 MeV); at L ⋆ ≃1 and 4–6, the energy channels at 95 – 400 keV are contaminated by high energy electrons (〉400 keV). Comparison of the data with electron and proton observations from RBSP/MagEIS indicates that the subtraction of proton fluxes at energies ≃ 230–630 keV from the IES electron data adequately removes the proton contamination. We demonstrate the usefulness of the corrected data for scientific applications.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Dust energy balance study of two edge-on spiral galaxies in the Herschel-ATLAS survey (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-10
    Description: Interstellar dust in galaxies can be traced either through its extinction effects on the star light or through its thermal emission at infrared wavelengths. Recent radiative transfer studies of several nearby edge-on galaxies have found an apparent inconsistency in the dust energy balance: the radiative transfer models that successfully explain the optical extinction underestimate the observed fluxes by an average factor of 3. We investigate the dust energy balance for IC 4225 and NGC 5166, two edge-on spiral galaxies observed by the Herschel Space Observatory in the frame of the H-ATLAS survey. We start from models which were constrained from optical data and extend them to construct the entire spectral energy distribution of our galaxies. These predicted values are subsequently compared to the observed far-infrared fluxes. We find that including a young stellar population in the modelling is necessary as it plays a non-negligible part in the heating of the dust grains. While the modelling approach for both galaxies is nearly identical, we find two very different results. As is often seen in other edge-on spiral galaxies, the far-infrared emission of our radiative transfer model of IC 4225 underestimates the observed fluxes by a factor of about 3. For NGC 5166 on the other hand, we find that both the predicted spectral energy distribution as well as the simulated images match the observations particularly well. We explore possible reasons for this difference and conclude that it is unlikely that one single mechanism is the cause of the dust energy balance problem in spiral galaxies. We discuss the different approaches that can be considered in order to get a conclusive answer on the origin this discrepancy.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Dust energy balance study of two edge-on spiral galaxies in the Herschel-ATLAS survey (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-12
    Description: Interstellar dust in galaxies can be traced either through its extinction effects on the star light or through its thermal emission at infrared wavelengths. Recent radiative transfer studies of several nearby edge-on galaxies have found an apparent inconsistency in the dust energy balance: the radiative transfer models that successfully explain the optical extinction underestimate the observed fluxes by an average factor of 3. We investigate the dust energy balance for IC 4225 and NGC 5166, two edge-on spiral galaxies observed by the Herschel Space Observatory in the frame of the H-ATLAS survey. We start from models which were constrained from optical data and extend them to construct the entire spectral energy distribution of our galaxies. These predicted values are subsequently compared to the observed far-infrared fluxes. We find that including a young stellar population in the modelling is necessary as it plays a non-negligible part in the heating of the dust grains. While the modelling approach for both galaxies is nearly identical, we find two very different results. As is often seen in other edge-on spiral galaxies, the far-infrared emission of our radiative transfer model of IC 4225 underestimates the observed fluxes by a factor of about 3. For NGC 5166 on the other hand, we find that both the predicted spectral energy distribution as well as the simulated images match the observations particularly well. We explore possible reasons for this difference and conclude that it is unlikely that one single mechanism is the cause of the dust energy balance problem in spiral galaxies. We discuss the different approaches that can be considered in order to get a conclusive answer on the origin this discrepancy.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Density variations in the Earth's magnetospheric cusps (2016)
    Wiley
    Details
    Publication Date: 2016-02-21
    Description: Seven years of measurements from the Polar spacecraft are surveyed to monitor the variations of plasma density within the magnetospheric cusps. The spacecraft's orbital precession from 1998 through 2005 allows for coverage of both the northern and southern cusps from low altitude out to the magnetopause. In the mid- and high- altitude cusp, plasma density scales well with the solar wind density ( n c u s p / n s w ∼0.8). This trend is fairly steady for radial distances greater then 4 R E . At low altitudes ( r 〈4 R E ) the density increases with decreasing altitude and even exceeds the solar wind density due to contributions from the ionosphere. The density of high charge-state Oxygen (O 〉+2 ) also displays a positive trend with solar wind density within the cusp. A multifluid simulation with the BATSRUS MHD model was run to monitor the relative contributions of the ionosphere and solar wind plasma within the cusp. The simulation provides similar results to the statistical measurements from Polar and confirms the presence of ionospheric plasma at low altitudes.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Control of mucin-type O-glycosylation: A classification of the polypeptide GalNAc-transferase gene family (2012)
    Oxford University Press
    Details
    Publication Date: 2012-04-26
    Description: Glycosylation of proteins is an essential process in all eukaryotes and a great diversity in types of protein glycosylation exists in animals, plants and microorganisms. Mucin-type O-glycosylation, consisting of glycans attached via O -linked N -acetylgalactosamine (GalNAc) to serine and threonine residues, is one of the most abundant forms of protein glycosylation in animals. Although most protein glycosylation is controlled by one or two genes encoding the enzymes responsible for the initiation of glycosylation, i.e. the step where the first glycan is attached to the relevant amino acid residue in the protein, mucin-type O-glycosylation is controlled by a large family of up to 20 homologous genes encoding UDP-GalNAc:polypeptide GalNAc-transferases (GalNAc-Ts) (EC 2.4.1.41). Therefore, mucin-type O-glycosylation has the greatest potential for differential regulation in cells and tissues. The GalNAc-T family is the largest glycosyltransferase enzyme family covering a single known glycosidic linkage and it is highly conserved throughout animal evolution, although absent in bacteria, yeast and plants. Emerging studies have shown that the large number of genes ( GALNT s) in the GalNAc-T family do not provide full functional redundancy and single GalNAc-T genes have been shown to be important in both animals and human. Here, we present an overview of the GalNAc-T gene family in animals and propose a classification of the genes into subfamilies, which appear to be conserved in evolution structurally as well as functionally.
    Print ISSN: 0959-6658
    Electronic ISSN: 1460-2423
    Topics: Biology , Medicine
    Published by Oxford University Press
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  • 9
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    Macroecology in the age of Big Data – Where to go from here? (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Recent years have seen an exponential increase in the amount of data available in all sciences and application domains. Macroecology is part of this “Big Data” trend, with a strong rise in the volume of data that we are using for our research. Here, we summarize the most recent developments in macroecology in the age of Big Data that were presented at the 2018 annual meeting of the Specialist Group Macroecology of the Ecological Society of Germany, Austria and Switzerland (GfÖ). Supported by computational advances, macroecology has been a rapidly developing field over recent years. Our meeting highlighted important avenues for further progress in terms of standardized data collection, data integration, method development and process integration. In particular, we focus on (a) important data gaps and new initiatives to close them, for example through space‐ and airborne sensors, (b) how various data sources and types can be integrated, (c) how uncertainty can be assessed in data‐driven analyses and (d) how Big Data and machine learning approaches have opened new ways of investigating processes rather than simply describing patterns. We discuss how Big Data opens up new opportunities, but also poses new challenges to macroecological research. In the future, it will be essential to carefully assess data quality, the reproducibility of data compilation and analytical methods, and the communication of uncertainties. Major progress in the field will depend on the definition of data standards and workflows for macroecology, such that scientific quality and integrity are guaranteed, and collaboration in research projects is made easier.
    Print ISSN: 0305-0270
    Electronic ISSN: 1365-2699
    Topics: Biology , Geography
    Published by Wiley
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  • 10
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    Cluster energetic electron survey of the high-altitude cusp and adjacent regions (2011)
    Wiley
    Details
    Publication Date: 2011-12-14
    Description: A statistical study of the energetic electron population (E 〉 37 keV) in the high-altitude cusp and surrounding regions is conducted with 7 years of data from the Cluster spacecraft. The progression of Cluster's orbit during this period allows for a wide range of latitude on the dayside magnetosphere to be surveyed. Locations of the spacecraft are adjusted to account for changes in the solar wind and geomagnetic activity measurements. The survey shows (1) frequent presence of energetic electrons within the high latitude trapping region and exterior cusp, (2) energetic electron flux dropping off rapidly with distance from the magnetosphere into the magnetosheath, (3) a similar spectral power law for the electrons in the outer high latitude trapping region as the exterior cusp, and (4) a pitch angle distribution in the cusp peaking at 90°. These findings indicate the energetic electron population on potentially open field lines in the exterior cusp likely is fed by both the high latitude trapping region as well as local acceleration.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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