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| 2. |
- Akiyama, Kazunori, et al.
(författare)
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First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
- 2019
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 875:1
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Tidskriftsartikel (refereegranskat)abstract
- We present the first Event Horizon Telescope (EHT) images of M87, using observations from April 2017 at 1.3 mm wavelength. These images show a prominent ring with a diameter of similar to 40 mu as, consistent with the size and shape of the lensed photon orbit encircling the "shadow" of a supermassive black hole. The ring is persistent across four observing nights and shows enhanced brightness in the south. To assess the reliability of these results, we implemented a two-stage imaging procedure. In the first stage, four teams, each blind to the others' work, produced images of M87 using both an established method (CLEAN) and a newer technique (regularized maximum likelihood). This stage allowed us to avoid shared human bias and to assess common features among independent reconstructions. In the second stage, we reconstructed synthetic data from a large survey of imaging parameters and then compared the results with the corresponding ground truth images. This stage allowed us to select parameters objectively to use when reconstructing images of M87. Across all tests in both stages, the ring diameter and asymmetry remained stable, insensitive to the choice of imaging technique. We describe the EHT imaging procedures, the primary image features in M87, and the dependence of these features on imaging assumptions.
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| 3. |
- Akiyama, Kazunori, et al.
(författare)
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First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
- 2019
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 875:1
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Tidskriftsartikel (refereegranskat)abstract
- The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider the physical implications of the asymmetric ring seen in the 2017 EHT data. To this end, we construct a large library of models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by general relativistic ray tracing. We compare the observed visibilities with this library and confirm that the asymmetric ring is consistent with earlier predictions of strong gravitational lensing of synchrotron emission from a hot plasma orbiting near the black hole event horizon. The ring radius and ring asymmetry depend on black hole mass and spin, respectively, and both are therefore expected to be stable when observed in future EHT campaigns. Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity. If the black hole spin and M87's large scale jet are aligned, then the black hole spin vector is pointed away from Earth. Models in our library of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets. At the same time, in those models that produce a sufficiently powerful jet, the latter is powered by extraction of black hole spin energy through mechanisms akin to the Blandford-Znajek process. We briefly consider alternatives to a black hole for the central compact object. Analysis of existing EHT polarization data and data taken simultaneously at other wavelengths will soon enable new tests of the GRMHD models, as will future EHT campaigns at 230 and 345 GHz.
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| 4. |
- Akiyama, Kazunori, et al.
(författare)
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First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
- 2019
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 875:1
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements of the properties of the central radio source in M87 using Event Horizon Telescope data obtained during the 2017 campaign. We develop and fit geometric crescent models (asymmetric rings with interior brightness depressions) using two independent sampling algorithms that consider distinct representations of the visibility data. We show that the crescent family of models is statistically preferred over other comparably complex geometric models that we explore. We calibrate the geometric model parameters using general relativistic magnetohydrodynamic (GRMHD) models of the emission region and estimate physical properties of the source. We further fit images generated from GRMHD models directly to the data. We compare the derived emission region and black hole parameters from these analyses with those recovered from reconstructed images. There is a remarkable consistency among all methods and data sets. We find that >50% of the total flux at arcsecond scales comes from near the horizon, and that the emission is dramatically suppressed interior to this region by a factor >10, providing direct evidence of the predicted shadow of a black hole. Across all methods, we measure a crescent diameter of 42 +/- 3 mu as and constrain its fractional width to be
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| 5. |
- Gold, Judith E., et al.
(författare)
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Knee pain in nursing home workers after implementation of a safe resident handling program
- 2018
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Ingår i: American Journal of Industrial Medicine. - : Wiley. - 0271-3586 .- 1097-0274. ; 61:10, s. 849-860
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Approximately 25-30% of nursing personnel experience knee pain (KP). We sought to identify physical and psychosocial work exposures, and personal factors related to prevalent, incident, and persistent KP 5-8 years after safe resident handing program (SRHP) implementation in nursing homes.Methods: Health and exposure information was obtained from worker surveys 5-6 years (“F5”) and 7-8 years (“F6”) post-SRHP implementation. Prevalent KP correlates were examined at F5; persistent and incident KP predictors were analyzed at F6, utilizing robust Poisson multivariable regression.Results: F5 KP prevalence (19.7%) was associated with combined physical exposures, and with either high job strain or low social support, in separate models. Two-year persistent KP was similarly associated with these psychosocial exposures. Being overweight was associated with KP in all analyses.Conclusions: The SRHP program did not eliminate knee physical loading, which should be reduced to prevent nursing home worker KP. Workplace psychosocial exposures (high job strain, low social support) also appeared germane.
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| 6. |
- Gold, Judith, et al.
(författare)
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Predictors of low back pain in nursing home workers after implementation of a safe resident handling programme
- 2017
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Ingår i: Occupational and Environmental Medicine. - : BMJ. - 1351-0711 .- 1470-7926. ; 74:6, s. 389-395
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Tidskriftsartikel (refereegranskat)abstract
- Objectives. Healthcare workers have high rates of low back pain (LBP) related to handling patients. A large chain of nursing homes experienced reduced biomechanical load, compensation claims and costs following implementation of a safe resident handling programme (SRHP). The aim of this study was to examine whether LBP similarly declined and whether it was associated with relevant self-reported occupational exposures or personal health factors.Methods. Worker surveys were conducted on multiple occasions beginning with the week of first SRHP introduction (baseline). In each survey, the outcome was LBP during the prior 3 months with at least mild severity during the past week. Robust Poisson multivariable regression models were constructed to examine correlates of LBP cross-sectionally at 2 years (F3) and longitudinally at 5–6 years (F5) post-SRHP implementation among workers also in at least one prior survey.Results. LBP prevalence declined minimally between baseline and F3. The prevalence was 37% at F3 and cumulative incidence to F5 was 22%. LBP prevalence at F3 was positively associated with combined physical exposures, psychological job demands and prior back injury, while frequent lift device usage and ‘intense’ aerobic exercise frequency were protective. At F5, the multivariable model included frequent lift usage at F3 (relative risk (RR) 0.39 (0.18 to 0.84)) and F5 work– family imbalance (RR=1.82 (1.12 to 2.98)).Conclusions. In this observational study, resident lifting device usage predicted reduced LBP in nursing home workers. Other physical and psychosocial demands of nursing home work also contributed, while frequent intense aerobic exercise appeared to reduce LBP risk.
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| 7. |
- Sagrén, Cecilia, 1959-, et al.
(författare)
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Framtidsfrågor Restaureringskonst 2016-2017 Kungl Konsthögskolan
- 2017
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Rapport (populärvet., debatt m.m.)abstract
- Restaureringskonst vid Kungl Konsthögskolan i Stockholm har läsåret 2016-2017 haft temat Framtidsfrågor. Utöver professionskunskap och teori har fronten och framtidsfrågor inom ämnet studerats. Publikationen visar en del av årets arbete i form av artiklar. Praktisk träning i dokumentation och värdering avspeglas liksom gemensamma studieresor, föreläsningar och milstolpar inom restaurering. Framtidsfrågor har inga enkla svar med för att kunskapsuppbyggnaden ska ligga i fronten är Restaureringskonst en aktiv deltagare i diskussionen.
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