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| 2. |
- Battarbee, Markus, et al.
(författare)
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Helium in the Earth's foreshock : a global Vlasiator survey
- 2020
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 38:5, s. 1081-1099
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Tidskriftsartikel (refereegranskat)abstract
- The foreshock is a region of space upstream of the Earth's bow shock extending along the interplanetary magnetic field (IMF). It is permeated by shock-reflected ions and electrons, low-frequency waves, and various plasma transients. We investigate the extent of the He2+ foreshock using Vlasiator, a global hybrid-Vlasov simulation. We perform the first numerical global survey of the helium foreshock and interpret some historical foreshock observations in a global context. The foreshock edge is populated by both proton and helium field-aligned beams, with the proton foreshock extending slightly further into the solar wind than the helium foreshock and both extending well beyond the ultra-low frequency (ULF) wave foreshock. We compare our simulation results with Magnetosphere Multiscale (MMS) Hot Plasma Composition Analyzer (HPCA) measurements, showing how the gradient of suprathermal ion densities at the foreshock crossing can vary between events. Our analysis suggests that the IMF cone angle and the associated shock obliquity gradient can play a role in explaining this differing behaviour. We also investigate wave-ion interactions with wavelet analysis and show that the dynamics and heating of He2+ must result from proton-driven ULF waves. Enhancements in ion agyrotropy are found in relation to, for example, the ion foreshock boundary, the ULF foreshock boundary, and specular reflection of ions at the bow shock. We show that specular reflection can describe many of the foreshock ion velocity distribution function (VDF) enhancements. Wave-wave interactions deep in the foreshock cause de-coherence of wavefronts, allowing He2+ to be scattered less than protons.
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| 3. |
- Carlsson, Lena E, et al.
(författare)
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Platelet receptor and clotting factor polymorphisms as genetic risk factors for thromboembolic complications in heparin-induced thrombocytopenia.
- 2003
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Ingår i: Pharmacogenetics. - 0960-314X .- 1473-561X. ; 13:5, s. 253-8
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Tidskriftsartikel (refereegranskat)abstract
- Heparin-induced thrombocytopenia (HIT) is an immune mediated adverse reaction to heparin treatment often associated with limb- and/or life-threatening thromboembolic complications (TECs). Presently, no prognostic marker has been identified that allows differentiation between mildly (isolated thrombocytopenia) and severely (TECs) affected patients. This study assesses the impact of platelet glycoprotein- and clotting factor polymorphisms in HIT-patients with isolated thrombocytopenia compared to HIT-patients with TECs. Sixty-three HIT-patients with isolated thrombocytopenia and 79 HIT-patients with HIT-related TECs were genotyped for GPIIb-IIIa polymorphisms (HPA-1, HPA-3), GPIa-IIa polymorphisms (HPA-5, GPIaC807T), GPIb-IX-V polymorphisms (HPA-2, Kozak-5, VNTR), and clotting factor polymorphisms (FV-Leiden R506Q, prothrombin PT-G20210A and MTHFR C677T). Women more often presented with TECs than men (P = 0.04). No differences in genotype frequencies could be seen on comparing HIT-patients with and without TECs. Analysing men and women separately, the C allele of the Kozak polymorphism was overrepresented in men who developed TECs (P = 0.034). The enhanced risk of women to develop HIT-associated TECs remains unexplained but it is potentially important in view of recent data on sex-hormone related changes of haemostasis. There was no correlation between platelet glycoprotein- and clotting factor polymorphisms and the risk to develop HIT-associated TECs. An association between the development of TECs and the Kozak-5C allele could be seen among male patients. However, this would need to be assessed in further larger studies. Most likely, the high levels of thrombin generation during acute HIT are so procoagulant that less pronounced risk factors such as polymorphisms are overshadowed.
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| 5. |
- Clark, M. S., et al.
(författare)
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Multi-omics for studying and understanding polar life
- 2023
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Ingår i: Nature Communications. - : NATURE PORTFOLIO. - 2041-1723. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- Polar ecosystems are experiencing amongst the most rapid rates of regional warming on Earth. Here, we discuss ‘omics’ approaches to investigate polar biodiversity, including the current state of the art, future perspectives and recommendations. We propose a community road map to generate and more fully exploit multi-omics data from polar organisms. These data are needed for the comprehensive evaluation of polar biodiversity and to reveal how life evolved and adapted to permanently cold environments with extreme seasonality. We argue that concerted action is required to mitigate the impact of warming on polar ecosystems via conservation efforts, to sustainably manage these unique habitats and their ecosystem services, and for the sustainable bioprospecting of novel genes and compounds for societal gain.
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| 6. |
- Dragisic, Zlatan, et al.
(författare)
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Results of the Ontology Alignment Evaluation Initiative 2014
- 2014
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Ingår i: International Workshop on Ontology Matching. ; , s. 61-104
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Konferensbidrag (refereegranskat)abstract
- Ontology matching consists of finding correspondences between se-mantically related entities of two ontologies. OAEI campaigns aim at comparingontology matching systems on precisely defined test cases. These test cases canuse ontologies of different nature (from simple thesauri to expressive OWL on-tologies) and use different modalities, e.g., blind evaluation, open evaluation andconsensus. OAEI 2014 offered 7 tracks with 9 test cases followed by 14 partici-pants. Since 2010, the campaign has been using a new evaluation modality which provides more automation to the evaluation. This paper is an overall presentationof the OAEI 2014 campaign.
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| 7. |
- Dubart, M., et al.
(författare)
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Sub-grid modeling of pitch-angle diffusion for ion-scale waves in hybrid-Vlasov simulations with Cartesian velocity space
- 2022
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 29:10
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Tidskriftsartikel (refereegranskat)abstract
- Numerical simulations have grown to play a central role in modern sciences over the years. The ever-improving technology of supercomputers has made large and precise models available. However, this accuracy is often limited by the cost of computational resources. Lowering the simulation's spatial resolution in order to conserve resources can lead to key processes being unresolved. We have shown in a previous study how insufficient spatial resolution of the proton cyclotron instability leads to a misrepresentation of ion dynamics in hybrid-Vlasov simulations. This leads to larger than expected temperature anisotropy and loss-cone shaped velocity distribution functions. In this study, we present a sub-grid numerical model to introduce pitch-angle diffusion in a 3D Cartesian velocity space, at a spatial resolution where the relevant wave-particle interactions were previously not correctly resolved. We show that the method is successfully able to isotropize loss-cone shaped velocity distribution functions, and that this method could be applied to simulations in order to save computational resources and still correctly model wave-particle interactions.
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| 8. |
- George, H., et al.
(författare)
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Estimating Inner Magnetospheric Radial Diffusion Using a Hybrid-Vlasov Simulation
- 2022
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Ingår i: Frontiers in Astronomy and Space Sciences. - : Frontiers Media S.A.. - 2296-987X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Radial diffusion coefficients quantify non-adiabatic transport of energetic particles by electromagnetic field fluctuations in planetary radiation belts. Theoretically, radial diffusion occurs for an ensemble of particles that experience irreversible violation of their third adiabatic invariant, which is equivalent to a change in their Roederer L* parameter. Thus, the Roederer L* coordinate is the fundamental quantity from which radial diffusion coefficients can be computed. In this study, we present a methodology to calculate the Lagrangian derivative of L* from global magnetospheric simulations, and test it with an application to Vlasiator, a hybrid-Vlasov model of near-Earth space. We use a Hamiltonian formalism for particles confined to closed drift shells with conserved first and second adiabatic invariants to compute changes in the guiding center drift paths due to electric and magnetic field fluctuations. We investigate the feasibility of this methodology by computing the time derivative of L* for an equatorial ultrarelativistic electron population travelling along four guiding center drift paths in the outer radiation belt during a 5 minute portion of a Vlasiator simulation. Radial diffusion in this simulation is primarily driven by ultralow frequency waves in the Pc3 range (10-45 s period range) that are generated in the foreshock and transmitted through the magnetopause to the outer radiation belt environment. Our results show that an alternative methodology to compute detailed radial diffusion transport is now available and could form the basis for comparison studies between numerical and observational measurements of radial transport in the Earth's radiation belts.
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| 9. |
- Johlander, Andreas, 1990-, et al.
(författare)
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Ion Acceleration Efficiency at the Earth's Bow Shock : Observations and Simulation Results
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 914:2
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Tidskriftsartikel (refereegranskat)abstract
- Collisionless shocks are some of the most efficient particle accelerators in heliospheric and astrophysical plasmas. Here we study and quantify ion acceleration at Earth's bow shock with observations from NASA's Magnetospheric Multiscale (MMS) satellites and in a global hybrid-Vlasov simulation. From the MMS observations, we find that quasiparallel shocks are more efficient at accelerating ions. There, up to 15% of the available energy goes into accelerating ions above 10 times their initial energy. Above a shock-normal angle of similar to 50 degrees, essentially no energetic ions are observed downstream of the shock. We find that ion acceleration efficiency is significantly lower when the shock has a low Mach number (M ( A ) < 6) while there is little Mach number dependence for higher values. We also find that ion acceleration is lower on the flanks of the bow shock than at the subsolar point regardless of the Mach number. The observations show that a higher connection time of an upstream field line leads to somewhat higher acceleration efficiency. To complement the observations, we perform a global hybrid-Vlasov simulation with realistic solar-wind parameters with the shape and size of the bow shock. We find that the ion acceleration efficiency in the simulation shows good quantitative agreement with the MMS observations. With the combined approach of direct spacecraft observations, we quantify ion acceleration in a wide range of shock angles and Mach numbers.
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| 10. |
- Johlander, Andreas, 1990-, et al.
(författare)
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Quasi-Parallel Shock Reformation Seen by Magnetospheric Multiscale and Ion-Kinetic Simulations
- 2022
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 49:2
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Tidskriftsartikel (refereegranskat)abstract
- Shock waves in collisionless plasmas are among the most efficient particle accelerators in space. Shock reformation is a process important to plasma heating and acceleration, but direct observations of reformation at quasi-parallel shocks have been lacking. Here, we investigate Earth's quasi-parallel bow shock with observations by the four Magnetospheric Multiscale spacecraft. The multi-spacecraft observations provide evidence of short large-amplitude magnetic structures (SLAMS) causing reformation of the quasi-parallel shock. We perform an ion-kinetic Vlasiator simulation of the bow shock and show that SLAMS reforming the bow shock recreates the multi-spacecraft measurements. This provides a method for identifying shock reformation in the future.
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