6,259 research outputs found
Magnetic Coupling of a Rotating Black Hole with Advection-Dominated Accretion Flows
A model of magnetic coupling (MC) of a rotating black hole (BH) with
advection- dominated accretion flow (MCADAF) is proposed. It turns out that
MCADAF providers a natural explanation for the transition radius between ADAF
and SSD, and could be used to interpret the highest luminosity of GX 339-4 in
hard-state. A very steep emissivity index can be produced in the innermost part
of the MCADAF,which is consistent with the recent XMM-Newton observations of
the nearby bright Seyfert 1 galaxy MCG-6-30-15 and with two X-ray binaries
(XRBs): XTE J1655-500 and GX 339-4. In addition, we estimate the BH spins in
Seyfert 1 galaxy MCG-6-30-15 and in the two XRBs based on this model.Comment: 18 pages, 9 figures,acceptted by New Astronom
A Physical Link Between Jet Formation and Hot Plasma in Active Galactic Nuclei
Recent observations suggest that in black hole X-ray binaries jet/outflow
formation is related to the hot plasma in the vicinity of the black hole,
either in the form of an advection-dominated accretion flow at low accretion
rates or in a disk corona at high accretion rates. We test the viability of
this scenario for supermassive black holes using two samples of active galactic
nuclei distinguished by the presence (radio-strong) and absence (radio-weak) of
well-collimated, relativistic jets. Each is centered on a narrow range of black
hole mass but spans a very broad range of Eddington ratios, effectively
simulating, in a statistical manner, the behavior of a single black hole
evolving across a wide spread in accretion states. Unlike the relationship
between the radio and optical luminosity, which shows an abruptly break between
high- and low-luminosity sources at an Eddington ratio of ~1, the radio
emission-a measure of the jet power-varies continuously with the hard X-ray
(2-10 keV) luminosity, roughly as L_R \propto L_X^(0.6-0.75). This relation,
which holds for both radio-weak and radio-strong active galaxies, is similar to
the one seen in X-ray binaries. Jet/outflow formation appears to be closely
linked to the conditions that give rise to the hot, optically thin coronal
emission associated with accretion flows, both in the regime of low and high
accretion rates.Comment: Accepted by ApJ, 8 pages, 3 figure
LocNet: Global localization in 3D point clouds for mobile vehicles
Global localization in 3D point clouds is a challenging problem of estimating
the pose of vehicles without any prior knowledge. In this paper, a solution to
this problem is presented by achieving place recognition and metric pose
estimation in the global prior map. Specifically, we present a semi-handcrafted
representation learning method for LiDAR point clouds using siamese LocNets,
which states the place recognition problem to a similarity modeling problem.
With the final learned representations by LocNet, a global localization
framework with range-only observations is proposed. To demonstrate the
performance and effectiveness of our global localization system, KITTI dataset
is employed for comparison with other algorithms, and also on our long-time
multi-session datasets for evaluation. The result shows that our system can
achieve high accuracy.Comment: 6 pages, IV 2018 accepte
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