| 1. |
- Bejger, M., et al.
(författare)
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Collisional Penrose Process near the Horizon of Extreme Kerr Black Holes
- 2012
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 109:12
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Tidskriftsartikel (refereegranskat)abstract
- Collisions of particles in black hole ergospheres may result in an arbitrarily large center-of-mass energy. This led recently to the suggestion [M. Banados, J. Silk, and S. M. West, Phys. Rev. Lett. 103, 111102 (2009)] that black holes can act as ultimate particle accelerators. If the energy of an outgoing particle is larger than the total energy of the infalling particles, the energy excess must come from the rotational energy of the black hole and hence, a Penrose process is involved. However, while the center-of-mass energy diverges, the position of the collision makes it impossible for energetic particles to escape to infinity. Following an earlier work on collisional Penrose processes [T. Piran and J. Shaham, Phys. Rev. D 16, 1615 (1977)], we show that even under the most favorable idealized conditions the maximal energy of an escaping particle is only a modest factor above the total initial energy of the colliding particles. This implies that one should not expect collisions around a black hole to act as spectacular cosmic accelerators.
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| 2. |
- Guermazi, Ali, et al.
(författare)
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Prevalence of abnormalities in knees detected by MRI in adults without knee osteoarthritis: population based observational study (Framingham Osteoarthritis Study)
- 2012
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Ingår i: BMJ: British Medical Journal. - : BMJ. - 1756-1833. ; 345, s. 5339-5339
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Tidskriftsartikel (refereegranskat)abstract
- Objective To examine use of magnetic resonance imaging (MRI) of knees with no radiographic evidence of osteoarthritis to determine the prevalence of structural lesions associated with osteoarthritis and their relation to age, sex, and obesity. Design Population based observational study. Setting Community cohort in Framingham, MA, United States (Framingham osteoarthritis study). Participants 710 people aged >50 who had no radiographic evidence of knee osteoarthritis (Kellgren-Lawrence grade 0) and who underwent MRI of the knee. Main outcome measures Prevalence of MRI findings that are suggestive of knee osteoarthritis (osteophytes, cartilage damage, bone marrow lesions, subchondral cysts, meniscal lesions, synovitis, attrition, and ligamentous lesions) in all participants and after stratification by age, sex, body mass index (BMI), and the presence or absence of knee pain. Pain was assessed by three different questions and also by WOMAC questionnaire. Results Of the 710 participants, 393 (55%) were women, 660 (93%) were white, and 206 (29%) had knee pain in the past month. The mean age was 62.3 years and mean BMI was 27.9. Prevalence of "any abnormality" was 89% (631/710) overall. Osteophytes were the most common abnormality among all participants (74%, 524/710), followed by cartilage damage (69%, 492/710) and bone marrow lesions (52%, 371/710). The higher the age, the higher the prevalence of all types of abnormalities detectable by MRI. There were no significant differences in the prevalence of any of the features between BMI groups. The prevalence of at least one type of pathology ("any abnormality") was high in both painful (90-97%, depending on pain definition) and painless (86-88%) knees. Conclusions MRI shows lesions in the tibiofemoral joint in most middle aged and elderly people in whom knee radiographs do not show any features of osteoarthritis, regardless of pain.
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| 3. |
- Haugen, Ida K., et al.
(författare)
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Prevalence, incidence and progression of hand osteoarthritis in the general population: the Framingham Osteoarthritis Study
- 2011
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Ingår i: Annals of the Rheumatic Diseases. - : BMJ. - 1468-2060 .- 0003-4967. ; 70:9, s. 1581-1586
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Tidskriftsartikel (refereegranskat)abstract
- Objectives To describe the prevalence and longitudinal course of radiographic, erosive and symptomatic hand osteoarthritis (HOA) in the general population. Methods Framingham osteoarthritis (OA) study participants obtained bilateral hand radiographs at baseline and 9-year follow-up. The authors defined radiographic HOA at joint level as Kellgren-Lawrence grade (KLG)>= 2, erosive HOA as KLG >= 2 plus erosion and symptomatic HOA as KLG >= 2 plus pain/aching/stiffness. Presence of HOA at individual level was defined as >= 1 affected joint. The prevalence was age-standardised (US 2000 Population 40-84 years). Results Mean (SD) baseline age was 58.9 (9.9) years (56.5% women). The age-standardised prevalence of HOA was only modestly higher in women (44.2%) than men (37.7%), whereas the age-standardised prevalence of erosive and symptomatic OA was much higher in women (9.9% vs 3.3%, and 15.9% vs 8.2%). The crude incidence of HOA over 9-year follow-up was similar in women (34.6%) and men (33.7%), whereas the majority of those women (96.4%) and men (91.4%) with HOA at baseline showed progression during follow-up. Incident metacarpophalangeal and wrist OA were rare, but occurred more frequently and from an earlier age in men than women. Development of erosive disease occurred mainly in those with non-erosive HOA at baseline (as opposed to those without HOA), and was more frequent in women (17.3%) than men (9.6%). Conclusions The usual female predominance of prevalent and incident HOA was less clear for radiographic HOA than for symptomatic and erosive HOA. With an ageing population, the impact of HOA will further increase.
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| 4. |
- Haugen, Ida Kristin, et al.
(författare)
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The association between erosive hand osteoarthritis and subchondral bone attrition of the knee: the Framingham Osteoarthritis Study
- 2012
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Ingår i: Annals of the Rheumatic Diseases. - : BMJ. - 1468-2060 .- 0003-4967. ; 71:10, s. 1698-1701
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Tidskriftsartikel (refereegranskat)abstract
- Objective To examine whether erosive hand osteoarthritis (OA) is associated with knee subchondral bone attrition (SBA) and systemic bone mineral density (BMD). Methods Associations of MRI-defined knee SBA with radiographic erosive hand OA were evaluated in 1253 Framingham participants using logistic regression with generalised estimating equations. We also examined the association between the number of erosive OA finger joints and SBA adjusted for the number of non-erosive OA finger joints. Associations between erosive hand OA and femoral neck BMD were explored in 2236 participants with linear regression. Analyses were adjusted for age, sex and body mass index. Results Participants with erosive hand OA had increased odds of knee SBA (OR = 1.60, 95% CI 1.07 to 2.38). The relation between the number of erosive OA finger joints and SBA became non-significant when adjusted for the number of non-erosive OA joints as a proxy for the burden of disease. There was a non-significant trend towards higher BMD in erosive hand OA compared with participants without hand OA. Conclusions Erosive hand OA was associated with knee SBA, but the relation might be best explained by a heightened burden of disease. No significant relation of erosive hand OA with BMD was found.
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| 5. |
- Haugen, Ida K., et al.
(författare)
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The Associations Between Finger Length Pattern, Osteoarthritis, and Knee Injury: Data From the Framingham Community Cohort
- 2011
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Ingår i: Arthritis and Rheumatism. - : Wiley. - 1529-0131 .- 0004-3591. ; 63:8, s. 2284-2288
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Tidskriftsartikel (refereegranskat)abstract
- Objective. To investigate the associations of index finger-to-ring finger (2D:4D) length ratio with radiographic knee and hand osteoarthritis (OA), previous knee injury, and meniscal lesions in the general population. Methods. We measured the length of the right second and fourth phalangeal and metacarpal bones on hand radiographs from 1,020 randomly recruited subjects (ages 51-92 years). Knee radiography and magnetic resonance imaging (MRI) were performed on subjects. Women and men were divided into tertiles according to their 2D: 4D phalangeal and metacarpal ratios. We assessed the odds ratios (ORs) and 95% confidence intervals (95% CIs) for radiographic knee OA, severe symptomatic knee OA, radiographic hand OA, previous knee injury, and MRI-defined meniscal lesion, using logistic regression with adjustment for age and body mass index. Because hand OA may affect the 2D: 4D phalangeal ratio, we performed sensitivity analyses in subjects without joint space narrowing in the second and fourth interphalangeal joints. Results. We found no significant associations between 2D: 4D length ratio and radiographic knee OA, severe symptomatic knee OA, or meniscal lesions. Low 2D: 4D phalangeal ratio was associated with hand OA in women (OR 1.80, 95% CI 1.11-2.93), but in the sensitivity analysis, the association was attenuated (OR 1.35, 95% CI 0.79-2.32). Low 2D: 4D phalangeal ratios were associated with knee injury in men (OR 1.78, 95% CI 1.02-3.10). We found no significant associations for 2D:4D metacarpal ratios. Conclusion. Low 2D:4D phalangeal ratios in men are associated with knee injury, but we did not find any significant association with knee OA. Low 2D:4D length ratio may be a consequence, rather than a cause, of hand OA in women.
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| 6. |
- Rosswog, Stephan, et al.
(författare)
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The long-term evolution of neutron star merger remnants - I. The impact of r-process nucleosynthesis
- 2014
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 439:1, s. 744-756
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Tidskriftsartikel (refereegranskat)abstract
- We follow the long-term evolution of the dynamic ejecta of neutron star mergers for up to 100 years and over a density range of roughly 40 orders of magnitude. We include the nuclear energy input from the freshly synthesized, radioactively decaying nuclei in our simulations and study its effects on the remnant dynamics. Although the nuclear heating substantially alters the long-term evolution, we find that running nuclear networks over purely hydrodynamic simulations (i.e. without heating) yields actually acceptable nucleosynthesis results. The main dynamic effect of the radioactive heating is to quickly smooth out inhomogeneities in the initial mass distribution, subsequently the evolution proceeds self-similarly and after 100 years the remnant still carries the memory of the initial binary mass ratio. We also explore the nucleosynthetic yields for two mass ejection channels. The dynamic ejecta very robustly produce 'strong' r-process elements with A > 130 with a pattern that is essentially independent of the details of the merging system. From a simple model we find that neutrino-driven winds yield 'weak' r-process contributions with 50 < A < 130 whose abundance patterns vary substantially between different merger cases. This is because their electron fraction, set by the ratio of neutrino luminosities, varies considerably from case to case. Such winds do not produce any Ni-56, but a range of radioactive isotopes that are long-lived enough to produce a second, radioactively powered electromagnetic transient in addition to the 'macronova' from the dynamic ejecta. While our wind model is very simple, it nevertheless demonstrates the potential of such neutrino-driven winds for electromagnetic transients and it motivates further, more detailed neutrino-hydrodynamic studies. The properties of the mentioned transients are discussed in more detail in a companion paper.
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| 7. |
- Rosswog, Stephan, et al.
(författare)
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The multimessenger picture of compact object encounters : binary mergers versus dynamical collisions
- 2013
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 430:4, s. 2585-2604
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Tidskriftsartikel (refereegranskat)abstract
- We explore the multimessenger signatures of encounters between two neutron stars (ns(2)) and between a neutron star and a stellar mass black hole (nsbh). We focus on the differences between gravitational-wave-driven binary mergers and dynamical collisions that occur, for example, in globular clusters. Our discussion is based on Newtonian hydrodynamics simulations that incorporate a nuclear equation of state and a multiflavour neutrino treatment. For both types of encounters we compare the gravitational wave and neutrino emission properties. We also calculate the rates at which nearly unbound mass is delivered back to the central remnant in a ballistic-fallback-plus-viscous-disc model and we analyse the properties of the dynamically ejected matter. Last but not least we address the electromagnetic transients that accompany each type of encounter. We find that dynamical collisions are at least as promising as binary mergers for producing (short) gamma-ray bursts, but they also share the same possible caveats in terms of baryonic pollution. All encounter remnants produce peak neutrino luminosities of at least similar to 10(53) erg s(-1), some of the collision cases exceed this value by more than an order of magnitude. The canonical ns(2) merger case ejects more than 1 per cent of a solar mass of extremely neutron-rich (Y-e similar to 0.03) material, an amount that is consistent with double neutron star mergers being a major source of r-process in the galaxy. nsbh collisions eject very large amounts of matter (similar to 0.15 M-circle dot) which seriously constrains their admissible occurrence rates. The compact object collision rate (sum of ns(2) and nsbh) must therefore be less, likely much less, than 10 per cent of the ns(2) merger rate. The radioactively decaying ejecta produce optical-ultraviolet 'macronova' which, for the canonical merger case, peak after similar to 0.4 d with a luminosity of similar to 5 x 10(41) erg s(-1). ns(2) (nsbh) collisions reach up to two (four) times larger peak luminosities. The dynamic ejecta deposit a kinetic energy comparable to a supernova in the ambient medium. The canonical merger case releases approximately 2 x 10(50) erg, the most extreme (but likely rare) cases deposit kinetic energies of up to 10(52) erg. The deceleration of this mildly relativistic material by the ambient medium produces long lasting radio flares. A canonical ns(2) merger at the detection horizon of advanced LIGO/Virgo produces a radio flare that peaks on a time-scale of 1 yr with a flux of similar to 0.1 mJy at 1.4 GHz. Collisions eject more material at higher velocities and therefore produce brighter and longer lasting flares.
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