1,125 research outputs found
Formation of episodic jets and associated flares from black hole accretion systems
Episodic ejections of blobs (episodic jets) are widely observed in black hole
sources and usually associated with flares. In this paper, by performing and
analyzing three dimensional general relativity magnetohydrodynamical numerical
simulations of accretion flows, we investigate their physical mechanisms. We
find that magnetic reconnection occurs in the accretion flow, likely due to the
turbulent motion and differential rotation of the accretion flow, resulting in
flares and formation of flux ropes. Flux ropes formed inside of 10-15
gravitational radii are found to mainly stay within the accretion flow, while
flux ropes formed beyond this radius are ejected outward by magnetic forces and
form the episodic jets. These results confirm the basic scenario proposed in
Yuan et al.(2009). Moreover, our simulations find that the predicted velocity
of the ejected blobs is in good consistency with observations of Sgr A*, M81,
and M87. The whole processes are found to occur quasi-periodically, with the
period being the orbital time at the radius where the flux rope is formed. The
predicted period of flares and ejections is consistent with those found from
the light curves or image of Sgr A*, M87, and PKS 1510-089. The possible
applications to protostellar accretion systems are discussed.Comment: 16 pages, 13 figures; accepted for publication in Ap
The properties of wind and jet from a super-Eddington accretion flow around a supermassive black hole
Wind and jet are important medium of AGN feedback thus it is crucial to
obtain their properties for the feedback study. In this paper we investigate
the properties of wind and jet launched from a super-Eddington accretion flow
around a supermassive black hole. For this aim, we have performed radiation
magnetohydrodynamical simulation of a magnetically arrested super-Eddington
accretion flows. We then have analyzed the simulation data by the ``virtual
particle trajectory'' approach and obtained the mass flux, poloidal and
toroidal velocities, and mass-flux-weighted momentum and energy fluxes of wind
and jet. The mass flux is found to be 2-6 times higher than that obtained based
on the time-averaged streamline method widely used in literature. Depending on
the black hole spin, the momentum flux of wind is found to be at least 2 times
larger than that of jet, while the total energy flux of jet is at most 3 times
larger than that of wind. These results are similar to the case of hot
accretion flows and imply that winds likely play a more important role than jet
in AGN feedback. The acceleration mechanism of wind and jet is analyzed and
found to be dominated by Lorentz force rather than radiation force.Comment: 13 pages, 13 figures; submitted to MNRA
Two distinct strategies of cotton and soybean differing in leaf movement to perform photosynthesis under drought in the field
This paper reports an experimental test of the hypothesis that cotton and soybean differing in leaf movement
have distinct strategies to perform photosynthesis under drought. Cotton and soybean were exposed to two water regimes:
drought stressed and well watered. Drought-stressed cotton and soybean had lower maximum CO2 assimilation rates than
well-watered (control) plants. Drought reduced the light saturation point and photorespiration of both species – especially
in soybean. Area-based leaf nitrogen decreased in drought-stressed soybean but increased in drought-stressed cotton.
Drought decreased PSII quantum yield (FPSII) in soybean leaves, but increased FPSII in cotton leaves. Drought induced an
increase in light absorbed by the PSII antennae that is dissipated thermally via DpH- and xanthophylls-regulated processes in
soybean leaves, but a decrease in cotton leaves. Soybean leaves appeared to have greater cyclic electron flow (CEF) around
PSI than cotton leaves and drought further increased CEF in soybean leaves. In contrast, CEF slightly decreased in cotton
under drought. These results suggest that the difference in leaf movement between cotton and soybean leaves gives rise to
different strategies to perform photosynthesis and to contrasting photoprotective mechanisms for utilisation or dissipation
of excess light energy. We suggest that soybean preferentially uses light-regulated non-photochemical energy dissipation,
which may have been enhanced by the higher CEF in drought-stressed leaves. In contrast, cotton appears to rely on enhanced
electron transport flux for light energy utilisation under drought, for example, in enhanced nitrogen assimilation
Damage Effects of Fluid filled Submunitions by High Velocity Projectile Impact
A series of tests investigating the damage effects of fluid-filled submunitions by high velocity projectile impact were conducted. An analytical model is presented, in which the yaw angle of the projectile was taken into account. Based on the analytical model, the influence of the strike angle, hit-point offset distance and projectile length to diameter ratio on submunition damage ratio were predicted. The analytical results showed a good agreement with the experiments. The submunition damage ratio strongly depends on the hit-point offset distance, showing a significant decrease with increasing hit-point offset distance. For large hit-point offset distance, increasing the length to diameter ratio of the projectile will effectively improve the submunition damage ratio. There is an appropriate yaw angle of the projectile in which the submunition damage ratio will be maximal
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