588,689 research outputs found
Line Polar Grassmann Codes of Orthogonal Type
Polar Grassmann codes of orthogonal type have been introduced in I. Cardinali
and L. Giuzzi, \emph{Codes and caps from orthogonal Grassmannians}, {Finite
Fields Appl.} {\bf 24} (2013), 148-169. They are subcodes of the Grassmann code
arising from the projective system defined by the Pl\"ucker embedding of a
polar Grassmannian of orthogonal type. In the present paper we fully determine
the minimum distance of line polar Grassmann Codes of orthogonal type for
odd
Tits Geometry and Positive Curvature
There is a well known link between (maximal) polar representations and
isotropy representations of symmetric spaces provided by Dadok. Moreover, the
theory by Tits and Burns-Spatzier provides a link between irreducible symmetric
spaces of non-compact type of rank at least three and irreducible topological
spherical buildings of rank at least three.
We discover and exploit a rich structure of a (connected) chamber system of
finite (Coxeter) type M associated with any polar action of cohomogeneity at
least two on any simply connected closed positively curved manifold. Although
this chamber system is typically not a Tits geometry of type M, we prove that
in all cases but two that its universal Tits cover indeed is a building. We
construct a topology on this universal cover making it into a compact spherical
building in the sense of Burns and Spatzier. Using this structure we classify
up to equivariant diffeomorphism all polar actions on (simply connected)
positively curved manifolds of cohomogeneity at least two.Comment: 43 pages, to appear in Acta Mathematic
Radiation-detector optical-imaging device is of simplified construction
A simplified radiation detector was designed which employs an activated continuous front surface consisting of either the diffused or barrier type of semiconducting material with a grid structure on the nonactivated side of the detector. Its form may be either a rectangular coordinate or a polar coordinate system
The Anisotropic Distribution of M 31 Satellite Galaxies: A Polar Great Plane of Early-Type Companions
The highly anisotropic distribution and apparent alignment of the Galactic
satellites in polar great planes begs the question how common such
distributions are. The satellite system of M31 is the only nearby system for
which we currently have sufficiently accurate distances to study the
three-dimensional satellite distribution. We present the spatial distribution
of the 15 presently known M31 companions in a coordinate system centered on M31
and aligned with its disk. Through a detailed statistical analysis we show that
the full satellite sample describes a plane that is inclined by -56 deg with
respect to the poles of M31 and that has an r.m.s. height of 100 kpc. With 88%
the statistical significance of this plane is low and it is unlikely to have a
physical meaning. The great stellar stream found near Andromeda is inclined to
this plane by 7 deg. There is little evidence for a Holmberg effect. If we
confine our analysis to early-type dwarfs, we find a best-fit polar plane
within 5 deg to 7 deg from the pole of M31. This polar great plane has a
statistical significance of 99.3% and includes all dSphs (except for And II),
M32, NGC 147, and PegDIG. The r.m.s. distance of these galaxies from the polar
plane is 16 kpc. The nearby spiral M33 has a distance of only about 3 kpc from
this plane, which points toward the M81 group. We discuss the anisotropic
distribution of M31's early-type companions in the framework of three
scenarios, namely as remnants of the break-up of a larger progenitor, as tracer
of a prolate dark matter halo, and as tracer of collapse along large-scale
filaments. (Abridged)Comment: 14 pages, 5 figures, accepted for publication in the Astronomical
Journa
d-Wave Superfluidity in Optical Lattices of Ultracold Polar Molecules
Recent work on ultracold polar molecules, governed by a generalization of the
t-J Hamiltonian, suggests that molecules may be better suited than atoms for
studying d-wave superfluidity due to stronger interactions and larger
tunability of the system. We compute the phase diagram for polar molecules in a
checkerboard lattice consisting of weakly coupled square plaquettes. In the
simplest experimentally realizable case where there is only tunneling and an
XX-type spin-spin interaction, we identify the parameter regime where d-wave
superfluidity occurs. We also find that the inclusion of a density-density
interaction destroys the superfluid phase and that the inclusion of a
spin-density or an Ising-type spin-spin interaction can enhance the superfluid
phase. We also propose schemes for experimentally realizing the perturbative
calculations exhibiting enhanced d-wave superfluidity.Comment: 22 pages, 12 figures; v2: revised discussion
Photometric structure of the peculiar galaxy ESO 235-G58
We present the near-infrared and optical properties of the peculiar galaxy
ESO 235-G58, which resembles a late-type ringed barred spiral seen close to
face-on. However, the apparent bar of ESO 235-G58 is in reality an edge-on disk
galaxy of relatively low luminosity. We have analyzed the light and color
distributions of ESO 235-G58 in the NIR and optical bands and compared them
with the typical properties observed for other morphological galaxy types,
including polar ring galaxies. Similar properties are observed for ESO 235-G58,
polar ring galaxies, and spiral galaxies, which leads us to conclude that this
peculiar system is a polar-ring-related galaxy, characterized by a low inclined
ring/disk structure, as pointed out by Buta & Crocker in an earlier study,
rather than a barred galaxy.Comment: 16 pages, 15 figures, accepted for publication in Astronomy &
Astrophysic
Prediction of thickness limits of ideal polar ultrathin films
Competition between electronic and atomic reconstruction is a constantly
recurring theme in transition-metal oxides. We use density functional theory
calculations to study this competition for a model system consisting of a thin
film of the polar, infinite-layer structure ACuO2 (A=Ca, Sr, Ba) grown on a
nonpolar, perovskite SrTiO3 substrate. A transition from the bulk planar
structure to a chain-type thin film accompanied by substantial changes to the
electronic structure is predicted for a SrCuO2 film fewer than five unit cells
thick. An analytical model explains why atomic reconstruction becomes more
favorable than electronic reconstruction as the film becomes thinner, and
suggests that similar considerations should be valid for other polar films
Line polar Grassmann codes of orthogonal type
Polar Grassmann codes of orthogonal type have been introduced in I. Cardinali and L. Giuzzi, \emph{Codes and caps from orthogonal Grassmannians}, {Finite Fields Appl.} {\bf 24} (2013), 148-169. They are subcodes of the Grassmann code arising from the projective system defined by the Pl\"ucker embedding of a polar Grassmannian of orthogonal type. In the present paper we fully determine the minimum distance of line polar Grassmann Codes of orthogonal type for q odd
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