3,031 research outputs found
Nilpotentization of the kinematics of the n-trailer system at singular points and motion planning through the singular locus
We propose in this paper a constructive procedure that transforms locally,
even at singular configurations, the kinematics of a car towing trailers into
Kumpera-Ruiz normal form. This construction converts the nonholonomic motion
planning problem into an algebraic problem (the resolution of a system of
polynomial equations), which we illustrate by steering the two-trailer system
in a neighborhood of singular configurations. We show also that the n-trailer
system is a universal local model for all Goursat structures and that all
Goursat structures are locally nilpotentizable.Comment: LaTeX2e, 23 pages, 4 figures, submitted to International journal of
contro
Contact systems and corank one involutive subdistributions
We give necessary and sufficient geometric conditions for a distribution (or
a Pfaffian system) to be locally equivalent to the canonical contact system on
Jn(R,Rm), the space of n-jets of maps from R into Rm. We study the geometry of
that class of systems, in particular, the existence of corank one involutive
subdistributions. We also distinguish regular points, at which the system is
equivalent to the canonical contact system, and singular points, at which we
propose a new normal form that generalizes the canonical contact system on
Jn(R,Rm) in a way analogous to that how Kumpera-Ruiz normal form generalizes
the canonical contact system on Jn(R,R), which is also called Goursat normal
form.Comment: LaTeX2e, 29 pages, submitted to Acta applicandae mathematica
A Census of White Dwarfs Within 40 Parsecs of the Sun
Our aim is to compile a catalog of white dwarfs within 40 parsecs of the Sun,
in which newly discovered objects would significantly increase the completeness
of the current census. White dwarf candidates are identified from the
SUPERBLINK proper motion database (Lepine & Shara 2005), which allows us to
investigate stars down to a proper motion limit as low as 40 mas yr-1. The
selection criteria and distance estimates are based on a combination of
color-magnitude and reduced proper motion diagrams. Candidates with distances
less than 50 parsecs are selected for spectroscopic follow-up. We present our
preliminary sample of spectroscopically confirmed white dwarfs, as well as
their atmospheric parameters. These parameters are obtained using the
spectroscopic technique developed in Bergeron et al.(1992) for DA stars. DB,
DQ, and DZ stars are also analyzed spectroscopically. For featureless spectra
as well as those showing only Halpha, we perform a detailed photometric
analysis of their energy distribution.Comment: 4 pages, 3 figures, to appear in AIP Conference Proceedings for the
17th European White Dwarf Worksho
The Effect of Corotation on the Radial Gradient of Metallicity of Spiral Galaxies
The corotation radius in a spiral galaxy is the radius where the spiral
pattern speed has the same velocity of the rotation curve. By compiling results
from the literature for 20 spiral galaxies we verified a strong correlation
between the radius of the minima or inflections of the metallicity distribution
and the corotation radius.Comment: 3 pages, 1 figur
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