| 1. |
- Ahumada, T., et al.
(författare)
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Discovery and confirmation of the shortest gamma-ray burst from a collapsar
- 2021
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Ingår i: Nature Astronomy. - : Springer Nature. - 2397-3366. ; 5:9, s. 917-927
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Tidskriftsartikel (refereegranskat)abstract
- Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the Universe. The duration and hardness distribution of GRBs has two clusters1, now understood to reflect (at least) two different progenitors2. Short-hard GRBs (SGRBs; T90 < 2 s) arise from compact binary mergers, and long-soft GRBs (LGRBs; T90 > 2 s) have been attributed to the collapse of peculiar massive stars (collapsars)3. The discovery of SN 1998bw/GRB 980425 (ref. 4) marked the first association of an LGRB with a collapsar, and AT 2017gfo (ref. 5)/GRB 170817A/GW170817 (ref. 6) marked the first association of an SGRB with a binary neutron star merger, which also produced a gravitational wave. Here, we present the discovery of ZTF20abwysqy (AT2020scz), a fast-fading optical transient in the Fermi satellite and the Interplanetary Network localization regions of GRB 200826A; X-ray and radio emission further confirm that this is the afterglow. Follow-up imaging (at rest-frame 16.5 days) reveals excess emission above the afterglow that cannot be explained as an underlying kilonova, but which is consistent with being the supernova. Although the GRB duration is short (rest-frame T90 of 0.65 s), our panchromatic follow-up data confirm a collapsar origin. GRB 200826A is the shortest LGRB found with an associated collapsar; it appears to sit on the brink between a successful and a failed collapsar. Our discovery is consistent with the hypothesis that most collapsars fail to produce ultra-relativistic jets.
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| 2. |
- Anand, S., et al.
(författare)
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Optical follow-up of the neutron star–black hole mergers S200105ae and S200115j
- 2020
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Ingår i: Nature Astronomy. - : Nature Research. - 2397-3366.
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Tidskriftsartikel (refereegranskat)abstract
- LIGO and Virgo’s third observing run revealed the first neutron star–black hole (NSBH) merger candidates in gravitational waves. These events are predicted to synthesize r-process elements1,2 creating optical/near-infrared ‘kilonova’ emission. The joint gravitational wave and electromagnetic detection of an NSBH merger could be used to constrain the equation of state of dense nuclear matter3, and independently measure the local expansion rate of the Universe4. Here, we present the optical follow-up and analysis of two of the only three high-significance NSBH merger candidates detected to date, S200105ae and S200115j, with the Zwicky Transient Facility5. The Zwicky Transient Facility observed ~48% of S200105ae and ~22% of S200115j’s localization probabilities, with observations sensitive to kilonovae brighter than −17.5 mag fading at 0.5 mag d−1 in the g- and r-bands; extensive searches and systematic follow-up of candidates did not yield a viable counterpart. We present state-of-the-art kilonova models tailored to NSBH systems that place constraints on the ejecta properties of these NSBH mergers. We show that with observed depths of apparent magnitude ~22 mag, attainable in metre-class, wide-field-of-view survey instruments, strong constraints on ejecta mass are possible, with the potential to rule out low mass ratios, high black hole spins and large neutron star radii.
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| 3. |
- Berndtsson, Ronny, et al.
(författare)
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Climate variability and its effects on regional hydrology: a case study for the Baltic Sea drainage basin
- 2009
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Ingår i: 18th World Imacs Congress and Modsim09 International Congress on Modelling and Simulation - Interfacing Modelling and Simulation With Mathematical and Computational Sciences. ; , s. 3893-3899
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Konferensbidrag (refereegranskat)abstract
- As climate models can be used to reproduce historical climates, the outcomes can be used to put climate extremes in to a proper historical perspective. This also allows investigation of nonlinear properties of hydrologic processes (e. g. precipitation, runoff) to better understand regional hydrologic dynamics. To this end, the present study uses results from a so-called 'paleosimulation' (i.e. simulation of climate during periods prior to the development of measuring instruments, including historic and geologic time, for which only proxy climate records are available) covering the Baltic Sea drainage basin and the surrounding areas. Time series of annual temperature, precipitation, and runoff are simulated to study their dynamic characteristics. Three different simulation periods between years 1000 and 1929 are considered: 1000-1199, 1551-1749, and 1751-1929; these three periods represent a warm, a cool, and an intermediate climate episode, respectively. Both linear (autocorrelation function) and nonlinear (phase space reconstruction) methods are employed. The autocorrelation function is a normalized measure of the linear correlation among successive values in a time series, while the basic idea behind the phase space reconstruction is that the past history of a single variable contains important information about the dynamics of the multivariable system. The 30-year average for all the three variables seems to follow a quasi-periodic behavior. An increasing trend is noted for temperature and precipitation during the later periods, but no such pronounced trend is evident for runoff. There is a general linear correlation between annual temperature and precipitation equal to 0.53, and between precipitation and runoff equal to 0.77; however, the correlation between temperature and runoff is as low as 0.30. The annual temperature series has one significant autocorrelation coefficient (lag 1 year), but precipitation and runoff series have no significant coefficients. Significant and slowly decreasing autocorrelation may be an indication of chaotic dynamics and temporal persistence that could be related to fractals. Due to the small autocorrelation, further analyses are carried out using serial time series (i.e. the simulated data are assumed continuous in time). The 30-year moving average for these serial time series reveals linear correlations between the variables; the cross-correlation between temperature and precipitation is 0.88, between precipitation and runoff is 0.83, and between temperature and runoff is 0.52. For these serial time series, phase space reconstruction is carried out to investigate the possible presence of attractors. Univariate (temperature, precipitation and runoff, independently) as well as multivariate (temperature-precipitation, temperature-runoff, precipitation-runoff) reconstructions are performed. For reconstruction, a delay time value of 5 years is considered for the univariate cases, while two delay time values (0 and 5 years) are considered for the multivariate cases. The results generally indicate clear attractors for all the variables and combinations, suggesting nonlinear relationships between temperature, precipitation, and runoff. These relationships could be exploited in prediction schemes, in both univariate and multivariate senses. Such an analysis would contribute to a better understanding of regional runoff dynamics due to climate effects. This is especially important for the Baltic Basin, since transport of nutrients, for example, are strongly correlated to the runoff conditions.
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| 4. |
- Berndtsson, R., et al.
(författare)
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Climate variability and its effects on regional hydrology : A case study for the Baltic Sea drainage basin
- 2020
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Ingår i: 18th World IMACS Congress and MODSIM 2009 - International Congress on Modelling and Simulation : Interfacing Modelling and Simulation with Mathematical and Computational Sciences, Proceedings - Interfacing Modelling and Simulation with Mathematical and Computational Sciences, Proceedings. - 9780975840078 ; , s. 3893-3899
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Konferensbidrag (refereegranskat)abstract
- As climate models can be used to reproduce historical climates, the outcomes can be used to put climate extremes in to a proper historical perspective. This also allows investigation of nonlinear properties of hydrologic processes (e.g. precipitation, runoff) to better understand regional hydrologic dynamics. To this end, the present study uses results from a so-called 'paleosimulation' (i.e. simulation of climate during periods prior to the development of measuring instruments, including historic and geologic time, for which only proxy climate records are available) covering the Baltic Sea drainage basin and the surrounding areas. Time series of annual temperature, precipitation, and runoff are simulated to study their dynamic characteristics. Three different simulation periods between years 1000 and 1929 are considered: 1000-1199, 1551-1749, and 1751-1929; these three periods represent a warm, a cool, and an intermediate climate episode, respectively. Both linear (autocorrelation function) and nonlinear (phase space reconstruction) methods are employed. The autocorrelation function is a normalized measure of the linear correlation among successive values in a time series, while the basic idea behind the phase space reconstruction is that the past history of a single variable contains important information about the dynamics of the multivariable system. The 30-year average for all the three variables seems to follow a quasi-periodic behavior. An increasing trend is noted for temperature and precipitation during the later periods, but no such pronounced trend is evident for runoff. There is a general linear correlation between annual temperature and precipitation equal to 0.53, and between precipitation and runoff equal to 0.77; however, the correlation between temperature and runoff is as low as 0.30. The annual temperature series has one significant autocorrelation coefficient (lag 1 year), but precipitation and runoff series have no significant coefficients. Significant and slowly decreasing autocorrelation may be an indication of chaotic dynamics and temporal persistence that could be related to fractals. Due to the small autocorrelation, further analyses are carried out using serial time series (i.e. the simulated data are assumed continuous in time). The 30-year moving average for these serial time series reveals linear correlations between the variables; the cross-correlation between temperature and precipitation is 0.88, between precipitation and runoff is 0.83, and between temperature and runoff is 0.52. For these serial time series, phase space reconstruction is carried out to investigate the possible presence of attractors. Univariate (temperature, precipitation and runoff, independently) as well as multivariate (temperature-precipitation, temperature-runoff, precipitation-runoff) reconstructions are performed. For reconstruction, a delay time value of 5 years is considered for the univariate cases, while two delay time values (0 and 5 years) are considered for the multivariate cases. The results generally indicate clear attractors for all the variables and combinations, suggesting nonlinear relationships between temperature, precipitation, and runoff. These relationships could be exploited in prediction schemes, in both univariate and multivariate senses. Such an analysis would contribute to a better understanding of regional runoff dynamics due to climate effects. This is especially important for the Baltic Basin, since transport of nutrients, for example, are strongly correlated to the runoff conditions.
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| 5. |
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| 6. |
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| 7. |
- Libwea, J. N., et al.
(författare)
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Antimicrobial stewardship in the era of the COVID-19 pandemic: A systematic review protocol on the opportunities and challenges for Sub-Saharan Africa
- 2023
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Ingår i: Medicine. - 0025-7974. ; 102:19
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Forskningsöversikt (refereegranskat)abstract
- Background: Antimicrobial resistance (AMR) remains one of the leading threats to global public health and this may increase following COVID-19 pandemic. This is particularly the case in Africa where regulations on antimicrobial usage are weak. This protocol outlines the steps to undertake a systematic review to synthesize evidence on drivers of AMR and evaluate existing approaches to strengthening antimicrobial stewardship (AMS) programs in Sub-Saharan Africa (SSA). On the basis of the evidence generated from the evidence synthesis, the overarching goal of this work is to provide recommendations to support best practices in AMS implementation in SSA. Methods:A systematic search will be conducted using the following databases: Global Health Library, PubMed, Cumulative Index to Nursing and Allied Health Literature, Scopus, Google Scholar, Global Health, Embase, African Journals Online Library, Web of Science, antimicrobial databases (WHO COVID-19, TrACSS, NDARO, and JPIAMR), and the Cochrane databases for systematic reviews. Studies will be included if they assess AMR and AMS in SSA from January 2000 to January 31, 2023. Results:The primary outcomes will include the drivers of AMR and approaches to AMS implementation in SSA. The Preferred Reporting Items for Systematic Reviews and Meta-analyses will guide the reporting of this systematic review. Conclusions:The findings are expected to provide evidence on best practices and resource sharing for policy consideration to healthcare providers and other stakeholders both at the local and international levels. Additionally, the study seeks to establish drivers specific to AMR during the COVID-19 era in the SSA, for example, with the observed increasing trend of antimicrobial misuse during the first or second year of the pandemic may provide valuable insights for policy recommendation in preparedness and response measures to future pandemics. PROSPERO registration number:CRD42022368853.
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| 8. |
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| 9. |
- Ramdas, S., et al.
(författare)
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A multi-layer functional genomic analysis to understand noncoding genetic variation in lipids
- 2022
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Ingår i: American Journal of Human Genetics. - : Elsevier BV. - 0002-9297 .- 1537-6605. ; 109:8, s. 1366-1387
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Tidskriftsartikel (refereegranskat)abstract
- A major challenge of genome-wide association studies (GWASs) is to translate phenotypic associations into biological insights. Here, we integrate a large GWAS on blood lipids involving 1.6 million individuals from five ancestries with a wide array of functional genomic datasets to discover regulatory mechanisms underlying lipid associations. We first prioritize lipid-associated genes with expression quantitative trait locus (eQTL) colocalizations and then add chromatin interaction data to narrow the search for functional genes. Polygenic enrichment analysis across 697 annotations from a host of tissues and cell types confirms the central role of the liver in lipid levels and highlights the selective enrichment of adipose-specific chromatin marks in high-density lipoprotein cholesterol and triglycerides. Overlapping transcription factor (TF) binding sites with lipid-associated loci identifies TFs relevant in lipid biology. In addition, we present an integrative framework to prioritize causal variants at GWAS loci, producing a comprehensive list of candidate causal genes and variants with multiple layers of functional evidence. We highlight two of the prioritized genes, CREBRF and RRBP1, which show convergent evidence across functional datasets supporting their roles in lipid biology.
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| 10. |
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| 11. |
- Wilk, Julie, et al.
(författare)
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From forecasts to action - What is needed to make seasonal forecasts useful for South African smallholder farmers?
- 2017
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Ingår i: International Journal of Disaster Risk Reduction. - : ELSEVIER SCIENCE BV. - 2212-4209. ; 25, s. 202-211
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Tidskriftsartikel (refereegranskat)abstract
- This paper explores the barriers that limit the use of SFs by smallholder farmers and policy-makers and practical, political and personal changes in the Limpopo Department of Agriculture and Rural Development (LDARD) that could enhance greater usage of SFs in risk management. Interviews and workshops were performed with LDARD staff at province, district municipality and service center level within the Extension and Advisory Services and Disaster Management Services divisions. Many extension officers repeatedly pointed out the need to move from reactive to proactive policies. This could entail creating effective channels for bottom-up communication of emerging ground conditions coupled with relief and support efforts distributed even during hazardous events, not only after greater losses have been felt. Different perceptions and understandings of if and how SFs inform national subsidies and site-specific recommendations distributed in the province to extension staff that departmental communication could be improved to increase trust and reliability of the forecasts and accompanying recommendations for farmers.
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| 12. |
- Zouganelis, I., et al.
(författare)
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The Solar Orbiter Science Activity Plan : Translating solar and heliospheric physics questions into action
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 642
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Tidskriftsartikel (refereegranskat)abstract
- Solar Orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. The ultimate goal is to understand how the Sun produces and controls the heliosphere, filling the Solar System and driving the planetary environments. With six remote-sensing and four in-situ instrument suites, the coordination and planning of the operations are essential to address the following four top-level science questions: (1) What drives the solar wind and where does the coronal magnetic field originate?; (2) How do solar transients drive heliospheric variability?; (3) How do solar eruptions produce energetic particle radiation that fills the heliosphere?; (4) How does the solar dynamo work and drive connections between the Sun and the heliosphere? Maximising the mission's science return requires considering the characteristics of each orbit, including the relative position of the spacecraft to Earth (affecting downlink rates), trajectory events (such as gravitational assist manoeuvres), and the phase of the solar activity cycle. Furthermore, since each orbit's science telemetry will be downloaded over the course of the following orbit, science operations must be planned at mission level, rather than at the level of individual orbits. It is important to explore the way in which those science questions are translated into an actual plan of observations that fits into the mission, thus ensuring that no opportunities are missed. First, the overarching goals are broken down into specific, answerable questions along with the required observations and the so-called Science Activity Plan (SAP) is developed to achieve this. The SAP groups objectives that require similar observations into Solar Orbiter Observing Plans, resulting in a strategic, top-level view of the optimal opportunities for science observations during the mission lifetime. This allows for all four mission goals to be addressed. In this paper, we introduce Solar Orbiter's SAP through a series of examples and the strategy being followed.
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