155 research outputs found
Regime variance testing - a quantile approach
This paper is devoted to testing time series that exhibit behavior related to
two or more regimes with different statistical properties. Motivation of our
study are two real data sets from plasma physics with observable two-regimes
structure. In this paper we develop estimation procedure for critical point of
division the structure change of a time series. Moreover we propose three tests
for recognition such specific behavior. The presented methodology is based on
the empirical second moment and its main advantage is lack of the distribution
assumption. Moreover, the examined statistical properties we express in the
language of empirical quantiles of the squared data therefore the methodology
is an extension of the approach known from the literature. The theoretical
results we confirm by simulations and analysis of real data of turbulent
laboratory plasma
Detecting linear dependence by reduction maps
We consider the local to global principle for detecting linear dependence of
points in groups of the Mordell-Weil type. As applications of our general
setting we obtain corresponding statements for Mordell-Weil groups of non{-}CM
elliptic curves and some higher dimensional abelian varieties defined over
number fields, and also for odd dimensional K-groups of number fields.Comment: This is a revised version of the MPI preprint no. 14 from March 200
A support problem for the intermediate Jacobians of l-adic representations
This is a revised version of ANT-0332: "A support problem for the
intermediate Jacobians of l-adic representations", by G. Banaszak, W. Gajda &
P. Krason, which was placed on these archives on the 29th of January 2002.
Following a suggestion of the referee we have subdivided the paper into two
separate parts: "Support problem for the intermediate Jacobians of l-adic
representations", and "On Galois representations for abelian varieties with
complex and real multiplications".
Our results on the image of Galois and the Mumford-Tate conjecture for some
RM abelian varieties are contained in the second paper. Both papers were
accepted for publication
The orbital structure of a tidally induced bar
Orbits are the key building blocks of any density distribution and their
study helps us understand the kinematical structure and the evolution of
galaxies. Here we investigate orbits in a tidally induced bar of a dwarf
galaxy, using an -body simulation of an initially disky dwarf galaxy
orbiting a Milky Way-like host. After the first pericenter passage, a tidally
induced bar forms in the stellar component of the dwarf. The bar evolution is
different than in isolated galaxies and our analysis focuses on the period
before it buckles. We study the orbits in terms of their dominant frequencies,
which we calculate in a Cartesian coordinate frame rotating with the bar. Apart
from the well-known x orbits we find many other types, mostly with boxy
shapes of various degree of elongation. Some of them are also near-periodic,
admitting frequency ratios of 4/3, 3/2 and 5/3. The box orbits have various
degrees of vertical thickness but only a relatively small fraction of those
have banana (i.e. smile/frown) or infinity-symbol shapes in the edge-on view.
In the very center we also find orbits known from the potential of triaxial
ellipsoids. The elongation of the orbits grows with distance from the center of
the bar in agreement with the variation of the shape of the density
distribution. Our classification of orbits leads to the conclusion that more
than of them have boxy shapes, while only have shapes of
classical x orbits.Comment: 15 pages, 15 figures, accepted for publication in Ap
Tidally induced bars in dwarf galaxies on different orbits around a Milky Way-like host
Bars in galaxies may develop through a global instability or due to an
interaction with another system. We study bar formation in disky dwarf galaxies
orbiting a Milky Way-like galaxy. We employ -body simulations to study the
impact of initial orbital parameters: the size of the dwarf galaxy orbit and
the inclination of its disc with respect to the orbital plane. In all cases a
bar develops in the center of the dwarf during the first pericenter on its
orbit around the host. Between subsequent pericenter passages the bars are
stable, but at the pericenters they are usually weakened and shortened. The
initial properties and details of the further evolution of the bars depend
heavily on the orbital configuration. We find that for the exactly prograde
orientation, the strongest bar is formed for the intermediate-size orbit. On
the tighter orbit, the disc is too disturbed and stripped to form a strong bar.
On the wider orbit, the tidal interaction is too weak. The dependence on the
disc inclination is such that weaker bars form in more inclined discs. The bars
experience either a very weak buckling or none at all. We do not observe any
secular evolution, possibly because the dwarfs are perturbed at each pericenter
passage. The rotation speed of the bars can be classified as slow
(). We attribute this to the loss of a
significant fraction of the disc's rotation during the encounter with the host
galaxy.Comment: 17 pages, 14 figures, accepted to Ap
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