| 1. |
- Veres, P., et al.
(författare)
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Observation of inverse Compton emission from a long gamma-ray burst
- 2019
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Ingår i: Nature. - : NATURE PUBLISHING GROUP. - 0028-0836 .- 1476-4687. ; 575:7783, s. 459-
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Tidskriftsartikel (refereegranskat)abstract
- Long-duration gamma-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterized by an initial phase of bright and highly variable radiation in the kiloelectron volt-to-mega electronvoltband, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission(1,2). Subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands(1-6). The afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock(7-9). Recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from GRB 190114C(10,11). Here we report multifrequency observations of GRB 190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from 5 x 10(-6) to 10(12) electronvolts. We find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. This component is associated with the afterglow and is satisfactorily explained by inverse Compton up-scattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed teraelectronvolt component are typical for GRBs, supporting the possibility that inverse Compton emission is commonly produced in GRBs.
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| 2. |
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| 3. |
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| 4. |
- Kehoe, Laura, et al.
(författare)
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Make EU trade with Brazil sustainable
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6438, s. 341-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 5. |
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| 6. |
- Helmstetter, A. J., et al.
(författare)
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Unraveling the Phylogenomic Relationships of the Most Diverse African Palm Genus Raphia (Calamoideae, Arecaceae)
- 2020
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Ingår i: Plants-Basel. - : MDPI AG. - 2223-7747. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- Palms are conspicuous floristic elements across the tropics. In continental Africa, even though there are less than 70 documented species, they are omnipresent across the tropical landscape. The genus Raphia has 20 accepted species in Africa and one species endemic to the Neotropics. It is the most economically important genus of African palms with most of its species producing food and construction material. Raphia is divided into five sections based on inflorescence morphology. Nevertheless, the taxonomy of Raphia is problematic with no intra-generic phylogenetic study available. We present a phylogenetic study of the genus using a targeted exon capture approach sequencing of 56 individuals representing 18 out of the 21 species. Our results recovered five well supported clades within the genus. Three sections correspond to those based on inflorescence morphology. R. regalis is strongly supported as sister to all other Raphia species and is placed into a newly described section: Erectae. Overall, morphological based identifications agreed well with our phylogenetic analyses, with 12 species recovered as monophyletic based on our sampling. Species delimitation analyses recovered 17 or 23 species depending on the confidence level used. Species delimitation is especially problematic in the Raphiate and Temulentae sections. In addition, our clustering analysis using SNP data suggested that individual clusters matched geographic distribution. The Neotropical species R. taedigera is supported as a distinct species, rejecting the hypothesis of a recent introduction into South America. Our analyses support the hypothesis that the Raphia individuals from Madagascar are potentially a distinct species different from the widely distributed R. farinifera. In conclusion, our results support the infra generic classification of Raphia based on inflorescence morphology, which is shown to be phylogenetically useful. Classification and species delimitation within sections remains problematic even with our phylogenomic approach. Certain widely distributed species could potentially contain cryptic species. More in-depth studies should be undertaken using morphometrics, increased sampling, and more variable markers. Our study provides a robust phylogenomic framework that enables further investigation on the biogeographic history, morphological evolution, and other eco-evolutionary aspects of this charismatic, socially, and economically important palm genus.
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| 7. |
- Rocchetti, Giulia Albani, et al.
(författare)
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Selecting the best candidates for resurrecting extinct-in-the-wild plants from herbaria
- 2022
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Ingår i: Nature Plants. - : Springer Science and Business Media LLC. - 2055-0278. ; 8:12, s. 1385-1393
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Tidskriftsartikel (refereegranskat)abstract
- Resurrecting extinct species is a fascinating and challenging idea for scientists and the general public. Whereas some theoretical progress has been made for animals, the resurrection of extinct plants (de-extinction sensu lato) is a relatively recently discussed topic. In this context, the term ‘de-extinction’ is used sensu lato to refer to the resurrection of ‘extinct in the wild’ species from seeds or tissues preserved in herbaria, as we acknowledge the current impossibility of knowing a priori whether a herbarium seed is alive and can germinate. In plants, this could be achieved by germinating or in vitro tissue-culturing old diaspores such as seeds or spores available in herbarium specimens. This paper reports the first list of plant de-extinction candidates based on the actual availability of seeds in herbarium specimens of globally extinct plants. We reviewed globally extinct seed plants using online resources and additional literature on national red lists, resulting in a list of 361 extinct taxa. We then proposed a method of prioritizing candidates for seed-plant de-extinction from diaspores found in herbarium specimens and complemented this with a phylogenetic approach to identify species that may maximize evolutionarily distinct features. Finally, combining data on seed storage behaviour and longevity, as well as specimen age in the novel ‘best de-extinction candidate’ score (DEXSCO), we identified 556 herbarium specimens belonging to 161 extinct species with available seeds. We expect that this list of de-extinction candidates and the novel approach to rank them will boost research efforts towards the first-ever plant de-extinction.
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| 8. |
- Schmidt, M., et al.
(författare)
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Diversity, distribution and preliminary conservation status of the flora of Burkina Faso
- 2017
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Ingår i: Phytotaxa. - : Magnolia Press. - 1179-3155 .- 1179-3163. ; 304:1, s. 1-215
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Tidskriftsartikel (refereegranskat)abstract
- West Africa is a floristically understudied region that is facing severe environmental changes in the 21 st century. Basic distribution data and information on the conservation status for most plant species of the region are scarce, and good information only exists for small areas of interest or for key species. This lack of knowledge seriously hampers urgently needed regional conservation efforts. Here we present comprehensive distribution information and preliminary, automated species conservation assessments for the flora of Burkina Faso, a country in tropical West Africa with a flora and vegetation typical for the savanna belt of the region. We documented and analysed the distribution of 1,568 species or 80% of the flora of Burkina Faso based on an expert curated dataset comprising ca. 150,000 occurrence records from herbarium specimens and vegetation surveys. We used this dataset and environmental niche models to calculate three indicator variables for a preliminary, automated conservation assessment. We classified 350 species (18% of the flora, excluding introduced species) as potentially "Critically Endangered", "Endangered", "Vulnerable" or "Near-Threatened" on the national level. The analyses confirmed species-rich areas in the south-west and south-east of the country, and showed a particular concentration of potentially Endangered species in the south. Furthermore, the proportion of potentially Endangered species differed between plant families, growth forms and habitats. Our results set the base for further plant geographical and ecological studies and are a data-driven baseline for further conservation assessments and large scale conservation strategies of the West African flora.
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| 9. |
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