1,780 research outputs found
Identifying, Monitoring, and Assessing Promising Innovations: Using Evaluation to Support Rapid-Cycle Change
Examines the new Center for Medicare and Medicaid Innovation's mission, critical issues, and challenges in finding effective ways to raise healthcare quality and lower costs, documenting innovation, and providing evidence to support broad policy change
Chinaâs Closing Window of Opportunity
American civilian and military leaders must dismiss the fatally flawed theory that time is on Chinaâs side in the struggle over the fate of Taiwan. The real danger of a PRC attack is in this decade, when Taiwan is most vulnerable, not in the next. Closer military ties with Taiwan, more cautious dealings with China, a strengthened U.S. naval and air presence in the western Pacific, and complementary nonmilitary measures are needed
Accretion disks around binary black holes of unequal mass: GRMHD simulations near decoupling
We report on simulations in general relativity of magnetized disks onto black
hole binaries. We vary the binary mass ratio from 1:1 to 1:10 and evolve the
systems when they orbit near the binary-disk decoupling radius. We compare
(surface) density profiles, accretion rates (relative to a single, non-spinning
black hole), variability, effective -stress levels and luminosities as
functions of the mass ratio. We treat the disks in two limiting regimes: rapid
radiative cooling and no radiative cooling. The magnetic field lines clearly
reveal jets emerging from both black hole horizons and merging into one common
jet at large distances. The magnetic fields give rise to much stronger shock
heating than the pure hydrodynamic flows, completely alter the disk structure,
and boost accretion rates and luminosities. Accretion streams near the horizons
are among the densest structures; in fact, the 1:10 no-cooling evolution
results in a refilling of the cavity. The typical effective temperature in the
bulk of the disk is yielding characteristic thermal frequencies . These systems are
thus promising targets for many extragalactic optical surveys, such as LSST,
WFIRST, and PanSTARRS.Comment: 29 pages, 23 captioned figures, 3 tables, submitted to PR
Accretion disks around binary black holes of unequal mass: GRMHD simulations of postdecoupling and merger
We report results from simulations in general relativity of magnetized disks
accreting onto merging black hole binaries, starting from relaxed disk initial
data. The simulations feature an effective, rapid radiative cooling scheme as a
limiting case of future treatments with radiative transfer. Here we evolve the
systems after binary-disk decoupling through inspiral and merger, and analyze
the dependence on the binary mass ratio with and . We find that the luminosity associated with local
cooling is larger than the luminosity associated with matter kinetic outflows,
while the electromagnetic (Poynting) luminosity associated with bulk transport
of magnetic field energy is the smallest. The cooling luminosity around merger
is only marginally smaller than that of a single, non-spinning black hole.
Incipient jets are launched independently of the mass ratio, while the same
initial disk accreting on a single non-spinning black hole does not lead to a
jet, as expected. For all mass ratios we see a transient behavior in the
collimated, magnetized outflows lasting after
merger: the outflows become increasingly magnetically dominated and accelerated
to higher velocities, boosting the Poynting luminosity. These sudden changes
can alter the electromagnetic emission across the jet and potentially help
distinguish mergers of black holes in AGNs from single accreting black holes
based on jet morphology alone.Comment: 15 pages, 6 figures, matches published versio
Binary Black-Hole Mergers in Magnetized Disks: Simulations in Full General Relativity
We present results from the first fully general relativistic,
magnetohydrodynamic (GRMHD) simulations of an equal-mass black hole binary
(BHBH) in a magnetized, circumbinary accretion disk. We simulate both the pre
and post-decoupling phases of a BHBH-disk system and both "cooling" and
"no-cooling" gas flows. Prior to decoupling, the competition between the binary
tidal torques and the effective viscous torques due to MHD turbulence depletes
the disk interior to the binary orbit. However, it also induces a two-stream
accretion flow and mildly relativistic polar outflows from the BHs. Following
decoupling, but before gas fills the low-density "hollow" surrounding the
remnant, the accretion rate is reduced, while there is a prompt electromagnetic
(EM) luminosity enhancement following merger due to shock heating and accretion
onto the spinning BH remnant. This investigation, though preliminary, previews
more detailed GRMHD simulations we plan to perform in anticipation of future,
simultaneous detections of gravitational and EM radiation from a merging
BHBH-disk system.Comment: 5 pages, 5 figure
Accretion Disks Around Binary Black Holes Of Unequal Mass: General Relativistic Magnetohydrodynamic Simulations Near Decoupling
Perceptions, experiences and opportunities for occupational safety and health professionals arising out of the COVID-19 Pandemic
This study explored perceptions, experiences and opportunities for the occupational safety and health professional (OSHP) as a result of COVID-19. Using qualitative methods, interviews took place with OSHPs in two organisations to understand how their role developed during the pandemic. Additionally, seven focus groups were organised and met virtually, using the Zoom platform, each addressing a different topic identified by the researchers. Participants (n = 45) from 10 different countries were distributed among the focus groups. Topics were separated into four themes: impact on the workplace; the psychosocial dynamic; medical and health issues and occupational safety and health (OSH) issues. Results were subsequently divided into seven action categories and compared with the findings from the organisational interviews. Comparison pointed to an expanded role for the OSHP including business continuity, resilience and wellbeing in addition to assessing and controlling risks emerging during the pandemic. There is also the need for a means to adequately disseminate trustworthy information. Results indicated that there was no single âaverageâ role of the OSHP, demonstrating essential contributions as a member of the management team. Results also stressed that the pandemic carried three health-related co-morbidities, stress, Post-Traumatic Stress Disorder and burnout. Directions for future research included: the education of the OSHP to support a move away from compliance towards risk management; determining how mental health issues in organisations should be managed; expanded roles for OSHPs within business; and implications for professional bodies, membership institutions and academia in supporting the above-mentioned emerging roles
Accretion Disks Around Binary Black Holes Of Unequal Mass: General Relativistic Mhd Simulations Of Postdecoupling And Merger
We report results from simulations in general relativity of magnetized disks accreting onto merging black hole binaries, starting from relaxed disk initial data. The simulations feature an effective, rapid radiative cooling scheme as a limiting case of future treatments with radiative transfer. Here we evolve the systems after binary-disk decoupling through inspiral and merger, and analyze the dependence on the binary mass ratio with and . We find that the luminosity associated with local cooling is larger than the luminosity associated with matter kinetic outflows, while the electromagnetic (Poynting) luminosity associated with bulk transport of magnetic field energy is the smallest. The cooling luminosity around merger is only marginally smaller than that of a single, non-spinning black hole. Incipient jets are launched independently of the mass ratio, while the same initial disk accreting on a single non-spinning black hole does not lead to a jet, as expected. For all mass ratios we see a transient behavior in the collimated, magnetized outflows lasting after merger: the outflows become increasingly magnetically dominated and accelerated to higher velocities, boosting the Poynting luminosity. These sudden changes can alter the electromagnetic emission across the jet and potentially help distinguish mergers of black holes in AGNs from single accreting black holes based on jet morphology alone
Norden, reframed
This paper calls for Norden to be understood as a metaframe. Related formulations like âNordic artâ or âNordic welfareâ function as mesoframes. These trigger multiple framing devices. A cache of related framing devices constitutes a framing archive. Framing devices work best when operating unobtrusively such that inclusions, exclusions and inconsistencies are condoned or naturalised. Their artifice, however, becomes apparent whenever a frame is questioned. Questioning or criticising a frame gives rise to a framing dispute. The theoretical justification for these typologies is provided at the outset. This schema is then applied to a select range of empirical examples drawn largely from the disciplinary frames (Ernst 1996) of art history and museum studies. Despite this specificity it is envisaged that the general principles set out below can and will be used to address a variety of devices, disputes and archives in Norden and beyond
Growth variations and scattering mechanisms in metamorphic In0.75Ga0.25As/In-0.75 Al0.25As quantum wells grown by molecular beam epitaxy
Modulation doped metamorphic In0.75Ga0.25As/In0.75Al0.25As quantum wells (QW) were grown on GaAs substrates by molecular beam epitaxy (MBE) with step-graded buffer layers. The electron mobility of the QWs has been improved by varying the MBE growth conditions, including substrate temperature, arsenic over pressure and modulation doping level. By applying a bias voltage to SiO2 insulated gates, the electron density in the QW can be tuned from 1Ă1011 to 5.3Ă1011 cmâ2. A peak mobility of 4.3Ă105 cm2Vâ1sâ1 is obtained at 3.7Ă1011 cmâ2 at 1.5 K before the onset of second subband population. To understand the evolution of mobility, transport data is fitted to a model that takes into account scattering from background impurities, modulation doping, alloy disorder and interface roughness. According to the fits, scattering from background impurities is dominant while that from alloy disorder becomes more significant at high carrier density
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