1,256 research outputs found
Bisous model - detecting filamentary patterns in point processes
The cosmic web is a highly complex geometrical pattern, with galaxy clusters
at the intersection of filaments and filaments at the intersection of walls.
Identifying and describing the filamentary network is not a trivial task due to
the overwhelming complexity of the structure, its connectivity and the
intrinsic hierarchical nature. To detect and quantify galactic filaments we use
the Bisous model, which is a marked point process built to model
multi-dimensional patterns. The Bisous filament finder works directly with the
galaxy distribution data and the model intrinsically takes into account the
connectivity of the filamentary network. The Bisous model generates the visit
map (the probability to find a filament at a given point) together with the
filament orientation field. Using these two fields, we can extract filament
spines from the data. Together with this paper we publish the computer code for
the Bisous model that is made available in GitHub. The Bisous filament finder
has been successfully used in several cosmological applications and further
development of the model will allow to detect the filamentary network also in
photometric redshift surveys, using the full redshift posterior. We also want
to encourage the astro-statistical community to use the model and to connect it
with all other existing methods for filamentary pattern detection and
characterisation.Comment: 12 pages, 6 figures, accepted by Astronomy and Computin
Gauge and Lorentz transformation placed on the same foundation
In this note we show that a "dynamical" interaction for arbitrary spin can be
constructed in a straightforward way if gauge and Lorentz transformations are
placed on the same foundation. As Lorentz transformations act on space-time
coordinates, gauge transformations are applied to the gauge field. Placing
these two transformations on the same ground means that all quantized field
like spin-1/2 and spin-3/2 spinors are functions not only of the coordinates
but also of the gauge field components. This change of perspective solves a
couple of problems occuring for higher spin fields like the loss of causality,
bad high-energy properties and the deviation of the gyromagnetic ratio from its
constant value g=2 for any spin, as caused by applying the minimal coupling.
Starting with a "dynamical" interaction, a non-minimal coupling can be derived
which is consistent with causality, the expectation for the gyromagnetic ratio,
and well-behaved for high energies. As a consequence, on this stage the
(elektromagnetic) gauge field has to be considered as classical field.
Therefore, standard quantum field theory cannot be applied. Despite this
inconvenience, such a common ground is consistent with an old dream of
physicists almost a century ago. Our approach, therefore, indicates a
straightforward way to realize this dream.Comment: 12 pages, no figures, published version. arXiv admin note:
substantial text overlap with arXiv:0908.376
Galaxy filaments as pearl necklaces
Context. Galaxies in the Universe form chains (filaments) that connect groups
and clusters of galaxies. The filamentary network includes nearly half of the
galaxies and is visually the most striking feature in cosmological maps.
Aims. We study the distribution of galaxies along the filamentary network,
trying to find specific patterns and regularities.
Methods. Galaxy filaments are defined by the Bisous model, a marked point
process with interactions. We use the two-point correlation function and the
Rayleigh Z-squared statistic to study how galaxies and galaxy groups are
distributed along the filaments.
Results. We show that galaxies and groups are not uniformly distributed along
filaments, but tend to form a regular pattern. The characteristic length of the
pattern is around 7 Mpc/h. A slightly smaller characteristic length 4 Mpc/h can
also be found, using the Z-squared statistic.
Conclusions. We find that galaxy filaments in the Universe are like pearl
necklaces, where the pearls are galaxy groups distributed more or less
regularly along the filaments. We propose that this well defined characteristic
scale could be used to test various cosmological models and to probe
environmental effects on the formation and evolution of galaxies.Comment: 8 pages, 9 figures, 1 table, accepted for publication in A&
The Lymph Nodes and the Lymph Vessels of the Abdominal Wall, Pelvic Wall and the Pelvic Limb of Swine
This article is the continuation of previously published papers regarding the lymph nodes of swine and their drainage areas. The details of the material and methods have been described and discussed previously
The Lymph Vessels of the Thoracic Limb of Swine
This article is the continuation of previously published papers regarding the lymph nodes of swine and their afferent and efferent lymph vessels (drainage areas). The details of the materials and methods have been described and discussed previously
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