| 1. |
- Ames, E., et al.
(författare)
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Dynamics of gravitational collapse in the axisymmetric Einstein-Vlasov system
- 2021
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Ingår i: Classical and Quantum Gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 38:10
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Tidskriftsartikel (refereegranskat)abstract
- We numerically investigate the dynamics near black hole formation of solutions to the Einstein-Vlasov system in axisymmetry. Our results are obtained using a particle-in-cell and finite difference code based on the (2 + 1) + 1 formulation of the Einstein field equations in axisymmetry. Solutions are launched from non-stationary initial data and exhibit type I critical behaviour. In particular, we find lifetime scaling in solutions containing black holes, and support that the critical solutions are stationary. Our results contain examples of solutions that form black holes, perform damped oscillations, and appear to disperse. We prove that complete dispersal of the solution implies that it has nonpositive binding energy.
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| 2. |
- Ames, Ellery, et al.
(författare)
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Hoop and weak cosmic censorship conjectures for the axisymmetric Einstein-Vlasov system
- 2023
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 108:6
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Tidskriftsartikel (refereegranskat)abstract
- We consider gravitational collapse for the axially symmetric Einstein-Vlasov system. We investigate the weak cosmic censorship conjecture in the case of highly prolate initial data and we investigate the "only if"part of the Hoop conjecture. Shapiro and Teukolsky initiated a similar study in 1991 [Formation of Naked Singularities: The Violation of Cosmic Censorship, Phys. Rev. Lett. 66, 994 (1991)PRLTAO0031-900710.1103/PhysRevLett.66.994] where they found support that the weak cosmic censorship conjecture was violated for sufficiently prolate spheroidal initial data. More recently, independent studies of this problem have been carried out by Yoo et al. [3D simulation of spindle gravitational collapse of a collisionless particle system, Classical Quantum Gravity 34, 105010 (2017)CQGRDG0264-938110.1088/1361-6382/aa6ad5] and by East [Cosmic Censorship Upheld in Spheroidal Collapse of Collisionless Matter, Phys. Rev. Lett. 122, 231103 (2019)PRLTAO0031-900710.1103/PhysRevLett.122.231103]. A common feature in these works is that the initial data are dustlike. Dust can be considered as a singular case of matter described by the Einstein-Vlasov system. The original motivation by Shapiro and Teukolsky to study this problem is based on the Lin-Mestel-Shu instability for gravitational collapse of uniform spheroids in the case of dust in Newtonian gravity. We argue that the Lin-Mestel-Shu solution is not relevant for studying the weak cosmic censorship conjecture of the Einstein-Vlasov system and we argue that dustlike initial data is also not relevant. To investigate collapse of highly prolate spheroidal configurations for the Einstein-Vlasov system is nevertheless interesting in view of the Hoop conjecture. By choosing highly prolate initial data the weak cosmic censorship conjecture is seriously tested. We carry out such a study for initial data which are not dustlike. We find formation of an apparent horizon in all cases we consider, which provides support for the weak cosmic censorship conjecture. In our tests of the Hoop conjecture we compute the polar circumference CH,p at the time when the apparent horizon forms and find that it is less than 12% above 4πM, where M is the irreducible mass of the apparent horizon, which agrees with the spirit of the Hoop conjecture.
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| 3. |
- Ames, Ellery, et al.
(författare)
-
Hoop and weak cosmic censorship conjectures for the axisymmetric Einstein-Vlasov system
- 2023
-
Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 108:6
-
Tidskriftsartikel (refereegranskat)abstract
- We consider gravitational collapse for the axially symmetric Einstein-Vlasov system. We investigate the weak cosmic censorship conjecture in the case of highly prolate initial data and we investigate the "only if"part of the Hoop conjecture. Shapiro and Teukolsky initiated a similar study in 1991 [Formation of Naked Singularities: The Violation of Cosmic Censorship, Phys. Rev. Lett. 66, 994 (1991)PRLTAO0031-900710.1103/PhysRevLett.66.994] where they found support that the weak cosmic censorship conjecture was violated for sufficiently prolate spheroidal initial data. More recently, independent studies of this problem have been carried out by Yoo et al. [3D simulation of spindle gravitational collapse of a collisionless particle system, Classical Quantum Gravity 34, 105010 (2017)CQGRDG0264-938110.1088/1361-6382/aa6ad5] and by East [Cosmic Censorship Upheld in Spheroidal Collapse of Collisionless Matter, Phys. Rev. Lett. 122, 231103 (2019)PRLTAO0031-900710.1103/PhysRevLett.122.231103]. A common feature in these works is that the initial data are dustlike. Dust can be considered as a singular case of matter described by the Einstein-Vlasov system. The original motivation by Shapiro and Teukolsky to study this problem is based on the Lin-Mestel-Shu instability for gravitational collapse of uniform spheroids in the case of dust in Newtonian gravity. We argue that the Lin-Mestel-Shu solution is not relevant for studying the weak cosmic censorship conjecture of the Einstein-Vlasov system and we argue that dustlike initial data is also not relevant. To investigate collapse of highly prolate spheroidal configurations for the Einstein-Vlasov system is nevertheless interesting in view of the Hoop conjecture. By choosing highly prolate initial data the weak cosmic censorship conjecture is seriously tested. We carry out such a study for initial data which are not dustlike. We find formation of an apparent horizon in all cases we consider, which provides support for the weak cosmic censorship conjecture. In our tests of the Hoop conjecture we compute the polar circumference CH,p at the time when the apparent horizon forms and find that it is less than 12% above 4πM, where M is the irreducible mass of the apparent horizon, which agrees with the spirit of the Hoop conjecture.
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| 4. |
- Ames, Ellery, 1984, et al.
(författare)
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Stationary solutions of the axially symmetric Einstein-Vlasov system: present status and open problems
- 2024
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Ingår i: Classical and Quantum Gravity. - 0264-9381 .- 1361-6382. ; 41:7
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Forskningsöversikt (refereegranskat)abstract
- The purpose of this work is to review the status about stationary solutions of the axially symmetric Einstein-Vlasov system with a focus on open problems of both analytical and numerical nature. For the latter we emphasize that the code used to construct stationary solutions in Ames et al (2016 Class. Quantum Grav. 33 155008; 2019 Phys. Rev. D 99 024012) is open source, see Ames and Logg (2023 J. Open Source Softw. 8 5979). In the analytical setting the open problems include establishing methods for proving existence of axisymmetric stationary solutions which are far from spherically symmetric, both in the general case and for certain special classes of solutions pointed out in the text. In the numerical setting there are intriguing properties of highly relativistic solutions that demand further attention, such as whether a sequence of such stationary solutions can approach a Kerr black hole, or if they necessarily approach the thin ring limit reminiscent of cosmic strings. The question of whether stationary solutions include states with thin-disk like morphologies as seen in many galaxies is also open. Finally, there are opportunities to extend this research to new settings such as the case of massless particles and coupled black hole-matter systems. We believe that some of the open problems highlighted here are of central importance for the understanding of nature.
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| 5. |
- Andreasson, Håkan, 1966, et al.
(författare)
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Comments on the paper ‘Static solutions of the Vlasov–Einstein system’ by G. Wolansky
- 2020
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Ingår i: Archive for Rational Mechanics and Analysis. - : Springer Science and Business Media LLC. - 1432-0673 .- 0003-9527. ; 235:1, s. 783-791
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Tidskriftsartikel (refereegranskat)abstract
- In this note we address the attempted proof of the existence of static solutions to the Einstein–Vlasov system as given in Wolansky (Arch Ration Mech Anal 156:205–230, 2001). We focus on a specific and central part of the proof which concerns a variational problem with an obstacle. We show that two important claims in Wolansky (2001) are incorrect and we question the validity of a third claim. We also discuss the variational problem and its difficulties with the aim of stimulating further investigation of this intriguing problem in particular answering the question of whether or not static solutions of the Einstein–Vlasov system can be found as local minimizers of an energy-Casimir functional.
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| 6. |
- Andreasson, Håkan, 1966
(författare)
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Existence of Steady States of the Massless Einstein-Vlasov System Surrounding a Schwarzschild Black Hole
- 2021
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Ingår i: Annales Henri Poincare. - : Springer Science and Business Media LLC. - 1424-0637 .- 1424-0661. ; 22, s. 4271-4297
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Tidskriftsartikel (refereegranskat)abstract
- We show that there exist steady states of the spherically symmetric massless Einstein-Vlasov system which surround a Schwarzschild black hole. The steady states are (thick) shells with finite mass and compact support. Furthermore we prove that an arbitrary number of shells, necessarily well separated, can surround the black hole. To our knowledge this is the first result of static self-gravitating solutions to any massless Einstein-matter system which surround a black hole. We also include a numerical investigation about the properties of the shells.
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| 7. |
- Andreasson, Håkan, 1966, et al.
(författare)
-
STATIC SOLUTIONS TO THE SPHERICALLY SYMMETRIC EINSTEIN-VLASOV SYSTEM: A PARTICLE NUMBER-CASIMIR APPROACH
- 2023
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Ingår i: SIAM Journal on Mathematical Analysis. - 1095-7154 .- 0036-1410. ; 55:5, s. 4843-4879
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Tidskriftsartikel (refereegranskat)abstract
- The existence of nontrivial static spherically symmetric solutions to the Einstein- Vlasov system is well-known. However, it is an open problem whether or not static solutions arise as minimizers of a variational problem. Apart from being of interest in its own right, it is the connection to nonlinear stability that gives this topic its importance. This problem was considered in [G. Wolansky, Arch. Ration. Mech. Anal., 156 (2001), pp. 205-230], but as has been pointed out in [H. Andr\'easson and M. Kunze, Arch. Ration. Mech. Anal., 235 (2020), pp. 783-791], that paper contained serious flaws. In this work we construct static solutions by solving the Euler- Lagrange equation for the energy density ρ as a fixed point problem. The Euler-Lagrange equation originates from the particle number-Casimir functional introduced in Wolansky (2001). We then define a density function f on phase space which induces the energy density \rho and we show that it constitutes a static solution of the Einstein-Vlasov system. Hence we settle rigorously parts of what Wolansky (2001) attempted to prove.
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| 8. |
- Berggren, Robert, et al.
(författare)
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Hamnen
- 2021
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Ingår i: Göteborg - 400 år genom kartor. - : A-Script Förlag. - 9789187171314 ; , s. 105-119
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 9. |
- From, Malin, et al.
(författare)
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Tuning the properties of regenerated cellulose : Effects of polarity and water solubility of the coagulation medium
- 2020
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Ingår i: Carbohydrate Polymers. - : Elsevier Ltd. - 0144-8617 .- 1879-1344. ; 236
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the effect of different alcohols and esters as a coagulation medium in the regeneration of cellulose dissolved in an aqueous LiOH-urea-based solvent was thoroughly investigated using various methods such as solid state NMR, X-ray diffraction, water contact angle, oxygen gas permeability, mechanical testing, and scanning electron microscopy. It was observed that several material properties of the regenerated cellulose films follow trends that correlate to the degree of cellulose II crystallinity, which is determined to be set by the miscibility of the coagulant medium (nonsolvent) and the aqueous alkali cellulose solvent rather than the nonsolvents’ polarity. This article provides an insight, thus creating a possibility to carefully tune and control the cellulose material properties when tailor-made for different applications.
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| 10. |
- Holmberg, Lina
(författare)
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Trauma Care - Implementation, Evaluation and Validation
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Trauma is a major cause of death and morbidity in all ages, which makes continuous improvement of trauma care a high priority. During the last decades, Sweden’s trauma system has evolved with initiation of a national trauma registry (SweTrau) in 2011 and the Swedish National Trauma Triage criteria (SNTTC) in 2017. However, the Swedish trauma panorama has evolved as well, something this thesis aimed to explore, alongside with evaluating the safety and accuracy of the SNTTC and performing the first validation of SweTrau. Paper I is a prospective stepped-wedge cohort study, showing unchanged 30-day mortality, over- and undertriage after the implementation of the SNTTC, as well as a reduction of the lowest level of trauma call by almost 50%, proving that the SNTTC are safe to use. In Paper II, a retrospective multicentre cohort study, the SNTTC are further investigated, displaying a sensitivity of almost 85% while also assessing specificity, positive predictive value (PPV) and positive likelihood ratio (LR+). With no additional enhancing criteria found, the SNTTC are concluded to efficiently identify severely injured patients. Paper III reports the first validation of SweTrau; an on-site re-registration compared with the original registration in SweTrau. It demonstrates that the data in SweTrau is reliable, with high accuracy (85.8%), correctness (89.7%), data completeness (88.5%) and correlation (87.5%), while being comparable to international trauma registries using the Utstein template of trauma. Case completeness and timeliness are identified as areas of improvement. In Paper IV, nine-year trauma trends in two major trauma centres are analysed in a retrospective cohort study. A sharp reduction in intensive care unit admissions is seen, as well as a worrying increase in penetrating trauma (>50%) and mortality for patients with a low injury severity score (1.3%-2.7%, p=0.005), all of which require further investigation. In conclusion; this thesis has confirmed that the SNTTC are safe and efficient, as well as pin-pointed important trauma areas to focus on in the future. Finally, it has established the validity of the data in SweTrau - a major source of Swedish trauma research.
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