| 1. |
- Fathi, Kambiz, et al.
(författare)
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Streaming Motions toward the Supermassive Black Hole in NGC 1097
- 2006
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Ingår i: AstrophysicalJournal Letters. - : American Astronomical Society. ; 641:L25
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- We have used GMOS-IFU and high-resolution HST-ACS observations to map, in unprecedented detail, the gas velocity field and structure within the 0.7 kpc circumnuclear ring of the SBb LINER/Seyfert 1 galaxy NGC 1097. We find clear evidence of radial streaming motions associated with spiral structures leading to the unresolved (<3.5 pc) nucleus, which we interpret as part of the fueling chain by which gas is transported to the nuclear starburst and supermassive black hole.
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| 2. |
- Storchi-Bergmann, Thaisa, et al.
(författare)
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{Nuclear spirals as feeding channels to the Supermassive Black Hole: the case of the galaxy NGC6951
- 2007
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Ingår i: Astropjysical Journals. - : American Astronomical Society. ; 670:959
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- We report the discovery of gas streaming motions along nuclear spiral arms toward the LINER nucleus of the galaxy NGC 6951. The observations, obtained using the GMOS integral field spectrograph on the Gemini North telescope, yielded maps of the flux distributions and gas kinematics in the Hα, [N ii] λ6584, and [S ii] λλ6717, 6731 emission lines of the inner 7x15 arcsec of the galaxy. This region includes a circumnuclear star‐forming ring with a radius of 500 pc, a nuclear spiral inside the ring, and the LINER nucleus. The kinematics of the ionized gas is dominated by rotation, but subtraction of a kinematic model of a rotating exponential disk reveals deviations from circular rotation within the nuclear ring that can be attributed to (1) streaming motions along the nuclear spiral arms and (2) a bipolar outflow that seems to be associated with a nuclear jet. On the basis of the observed streaming velocities and geometry of the spiral arms, we estimate a mass inflow rate of ionized gas of ≈ 3x10^-4 M yr−1, which is on the order of the accretion rate necessary to power the LINER nucleus of NGC 6951. Similar streaming motions toward the nucleus of another galaxy with a LINER nucleus, NGC 1097, have been reported by our group in a previous paper. Taken together, these results support a scenario in which nuclear spirals are channels through which matter is transferred from galactic scales to the nuclear region to feed the supermassive black hole.
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| 3. |
- Åström, Karl Johan, et al.
(författare)
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Event Based Control
- 2008
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Ingår i: Analysis and Design of Nonlinear Control Systems : In Honor of Alberto Isidori - In Honor of Alberto Isidori. - 9783540743576 ; , s. 127-147
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Bokkapitel (refereegranskat)abstract
- In spite of the success of traditional sampled-data theory in computer control it has some disadvantages particularly for distributed, asynchronous, and multi-rate system. Event based sampling is an alternative which is explored in this paper. A simple example illustrates the differences between periodic and event based sampling. The architecture of a general structure for event based control is presented. The key elements are an event detector, an observer, and a control signal generator, which can be regarded as a generalized data-hold. Relations to nonlinear systems are discussed. Design of an event based controller is illustrated for a simple model of a micro-mechanical accelerometer.
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