2,253 research outputs found
Uniformizing surfaces via discrete harmonic maps
We show that for any closed surface of genus greater than one and for any
finite weighted graph filling the surface, there exists a hyperbolic metric
which realizes the least Dirichlet energy harmonic embedding of the graph among
a fixed homotopy class and all hyperbolic metrics on the surface. We give
explicit examples of such hyperbolic surfaces through a new interpretation of
the Nielsen realization problem for the mapping class groups.Comment: 31 pages, 5 figure
A massive disk galaxy at z>3 along the sightline of QSO 1508+5714
We have obtained deep images in the BVRIJHKs bands of the field centered on
QSO 1508+5714 (z_{em} =4.28) with the Suprime camera, FOCAS and MOIRCS cameras
on Subaru telescope. We report here the detection of a B-dropout galaxy, which
is 3\secpoint 5 north-west of the QSO sightline. A photometric redshift
analysis is presented to complement the color selection. Given the photometric
properties of this object (, making , if
placed at its photometric redshift ), as well as the
Srsic index () derived from a 2-D imaging decomposition
of the HST WFPC2 image taken in the filter, the identified system is
consistent with a massive disk galaxy at z>3. If confirmed, it would be one of
the most distant massive disk galaxies known so far.Comment: 12 pages, 6 figures, accepted by PASJ, Vol.61/No.5, 200
Head-Trajectory-Tracking Control of a Snake Robot and Its Robustness Under Actuator Failure
This brief considers the problem of trajectory tracking of a planar snake robot without a lateral constraint. The reference trajectory of the head position and the orientation of link 1 are given, and torque control is determined to reduce tracking errors. The performance of the controller was tested in a number of simulations. The robustness during actuator failure was also studied. We assumed that one of the actuators was broken and the corresponding joint became passive. Furthermore, as a more realistic situation, we considered an instance when some of the states were not readily accessible from the sensor readings and needed to be estimated by an observer. The extended Kalman filter was employed for this purpose, and the performance of the closed-loop system with the observer was also tested in simulations
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