15,862 research outputs found
A family of Prym-Tyurin varieties of exponent 3
We investigate a family of correspondences associated to \'etale coverings of
degree 3 of hyperelliptic curves. They lead to Prym-Tyurin varieties of
exponent 3. We identify these varieties and derive some consequences.Comment: names of authors correcte
Proper motions in the VVV Survey: Results for more than 15 million stars across NGC 6544
Context: In the last six years, the VVV survey mapped 562 sq. deg. across the
bulge and southern disk of the Galaxy. However, a detailed study of these
regions, which includes globular clusters (GCs) and thousands of open
clusters is by no means an easy challenge. High differential reddening and
severe crowding along the line of sight makes highly hamper to reliably
distinguish stars belonging to different populations and/or systems. Aims: The
aim of this study is to separate stars that likely belong to the Galactic GC
NGC 6544 from its surrounding field by means of proper motion (PM) techniques.
Methods: This work was based upon a new astrometric reduction method optimized
for images of the VVV survey. Results: Photometry over the six years baseline
of the survey allowed us to obtain a mean precision of mas/yr, in
each PM coordinate, for stars with Ks < 15 mag. In the area studied here,
cluster stars separate very well from field stars, down to the main sequence
turnoff and below, allowing us to derive for the first time the absolute PM of
NGC 6544. Isochrone fitting on the clean and differential reddening corrected
cluster color magnitude diagram yields an age of 11-13 Gyr, and
metallicity [Fe/H] = -1.5 dex, in agreement with previous studies restricted to
the cluster core. We were able to derive the cluster orbit assuming an
axisymmetric model of the Galaxy and conclude that NGC 6544 is likely a halo
GC. We have not detected tidal tail signatures associated to the cluster, but a
remarkable elongation in the galactic center direction has been found. The
precision achieved in the PM determination also allows us to separate bulge
stars from foreground disk stars, enabling the kinematical selection of bona
fide bulge stars across the whole survey area. Our results show that VVV data
is perfectly suitable for this kind of analysis.Comment: 13 pages, 12 figures, accepted in A&
Chemical potential as a source of stability for gravitating Skyrmions
A discussion of the stability of self gravitating Skyrmions, with a large
winding number N, in a Schwarzschild type of metric, is presented for the case
where an isospin chemical potential is introduced. It turns out that the
chemical potential stabilizes the behavior of the Skyrmion discussed previously
in the literature. This analysis is carried on in the framework of a
variational approach using different ansaetze for the radial profile of the
Skyrmion. We found a divergent behavior for the size of the Skyrmion,
associated to a certain critical value of the chemical potential. At
this point, the mass of the Skyrmion vanishes. is essentialy
independent of gravitating effects. The stability of a large N skyrmion against
decays into single particles is also discussed.Comment: 10 pages, 4 figures Small changes to the previous version and a new
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A benchmark study on identification of inelastic parameters based on deep drawing processes using pso – nelder mead hybrid approach
Optimization techniques have been increasingly used to identification of inelastic material parameters owing to their generality. Development of robust techniques to solving this class of inverse problems has been a challenge to researchers mainly due to the nonlinear character of the problem and behaviour of the objective function. Within this framework, this work discusses application of Particle Swarm Optimization (PSO) and a PSO – Nelder Mead hybrid approach to identification of inelastic parameters based on a benchmark solution of the deep drawing process
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