3,093 research outputs found
Algebraic density property of Danilov-Gizatullin surfaces
A Danilov-Gizatullin surface is an affine surface which is the complement
of an ample section of a Hirzebruch surface. The remarkable theorem of
Danilov and Gizatullin states that the isomorphism class of depends only on
the self-intersection number . In this paper we apply their theorem to
present as the quotient of an affine threefold by a torus action, and to
prove that the Lie algebra generated by the complete algebraic vector fields on
coincides with the set of all algebraic vector fields.Comment: 12 page
Applications of expert systems for satellite autonomy
Some aspects of the on-board application of expert systems in artificial satellites are discussed. The activities of the study, which include the implementation of two prototypes on a dedicated artificial intelligence machine, are described. The general implications of the experience are then discussed. These concern the interrelationship between the expert system and the architecture of the satellite and the expert system's impact on the mission definition phase of the satellite lifecycle. The main obstacles that need to be overcome before operational use of onboard expert systems can take place are discussed
The Abell 85 BCG: a nucleated, core-less galaxy
New high-resolution r band imaging of the brightest cluster galaxy (BCG) in
Abell 85 (Holm 15A) was obtained using the Gemini Multi Object Spectrograph.
These data were taken with the aim of deriving an accurate surface brightness
profile of the BCG of Abell 85, in particular its central region. The new
Gemini data show clear evidence of a previously unreported nuclear emission
that is evident as a distinct light excess in the central kiloparsec of the
surface brightness profile. We find that the light profile is never flat nor
does it present a downward trend towards the center of the galaxy. That is, the
new Gemini data show a different physical reality from the featureless,
"evacuated core" recently claimed for the Abell 85 BCG. After trying different
models, we find that the surface brightness profile of the BCG of Abell 85 is
best fit by a double Sersic model.Comment: Gemini web feature: Supermassive black hole that wasn't -
http://gemini.edu/node/1247
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