123 research outputs found
The Dark Matter Distribution in Galaxy Cluster Cores
Determining the structure of galaxy clusters is essential for an
understanding of large scale structure in the universe, and may hold important
clues to the identity and nature of dark matter particles. Moreover, the core
dark matter distribution may offer insight into the structure formation
process. Unfortunately, cluster cores also tend to be the site of complicated
astrophysics. X-ray imaging spectroscopy of relaxed clusters, a standard
technique for mapping their dark matter distributions, is often complicated by
the presence of their putative ``cooling flow'' gas, and the dark matter
profile one derives for a cluster is sensitive to assumptions made about the
distribution of this gas. Here we present a statistical analysis of these
assumptions and their effect on our understanding of dark matter in galaxy
clusters.Comment: Poster contribution to the 13th Annual Astrophysics Conference in
Maryland, The Emergence of Cosmic Structure; 4 page
Optimization in Differentiable Manifolds in Order to Determine the Method of Construction of Prehistoric Wall-Paintings
In this paper a general methodology is introduced for the determination of
potential prototype curves used for the drawing of prehistoric wall-paintings.
The approach includes a) preprocessing of the wall-paintings contours to
properly partition them, according to their curvature, b) choice of prototype
curves families, c) analysis and optimization in 4-manifold for a first
estimation of the form of these prototypes, d) clustering of the contour parts
and the prototypes, to determine a minimal number of potential guides, e)
further optimization in 4-manifold, applied to each cluster separately, in
order to determine the exact functional form of the potential guides, together
with the corresponding drawn contour parts. The introduced methodology
simultaneously deals with two problems: a) the arbitrariness in data-points
orientation and b) the determination of one proper form for a prototype curve
that optimally fits the corresponding contour data. Arbitrariness in
orientation has been dealt with a novel curvature based error, while the proper
forms of curve prototypes have been exhaustively determined by embedding
curvature deformations of the prototypes into 4-manifolds. Application of this
methodology to celebrated wall-paintings excavated at Tyrins, Greece and the
Greek island of Thera, manifests it is highly probable that these
wall-paintings had been drawn by means of geometric guides that correspond to
linear spirals and hyperbolae. These geometric forms fit the drawings' lines
with an exceptionally low average error, less than 0.39mm. Hence, the approach
suggests the existence of accurate realizations of complicated geometric
entities, more than 1000 years before their axiomatic formulation in Classical
Ages
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