8,036 research outputs found
Self Similar Spherical Collapse Revisited: a Comparison between Gas and Dark Matter Dynamics
We reconsider the collapse of cosmic structures in an Einstein-de Sitter
Universe, using the self similar initial conditions of Fillmore & Goldreich
(1984). We first derive a new approximation to describe the dark matter
dynamics in spherical geometry, that we refer to the "fluid approach". This
method enables us to recover the self-similarity solutions of Fillmore &
Goldreich for dark matter. We derive also new self-similarity solutions for the
gas. We thus compare directly gas and dark matter dynamics, focusing on the
differences due to their different dimensionalities in velocity space. This
work may have interesting consequences for gas and dark matter distributions in
large galaxy clusters, allowing to explain why the total mass profile is always
steeper than the X-ray gas profile. We discuss also the shape of the dark
matter density profile found in N-body simulations in terms of a change of
dimensionality in the dark matter velocity space. The stable clustering
hypothesis has been finally considered in the light of this analytical
approach.Comment: 14 pages, 2 figures, accepted for publication in The Astrophysical
Journa
A Generalization of Haldane state-counting procedure and -deformations of statistics
We consider the generalization of Haldane's state-counting procedure to
describe all possible types of exclusion statistics which are linear in the
deformation parameter . The statistics are parametrized by elements of the
symmetric group of the particles in question. For several specific cases we
determine the form of the distribution functions which generalizes results
obtained by Wu. Using them we analyze the low-temperature behavior and
thermodynamic properties of these systems and compare our results with previous
studies of the thermodynamics of a gas of -ons. Various possible physical
applications of these constructions are discussed.Comment: 17 pages, latex, 6 figures small corrections were made, reference and
acknowledgments are adde
Alkali-activated cements for ground improvement
The paper studies alkali-activated (AA) slag cements for soil stabilisation, as alternatives to traditional binders such as Portland cement or lime. A number of alkali activators were considered, containing also a range of salts and a material retrieved from waste (Paper Sludge Ash, PSA). The results are discussed in terms of unconfined compressive strength (UCS) at two different curing times. In general alkali-activated cements based on the use of alkali salts only had a modest performance in terms of strength improvement; a material that showed promise however as slag activator was the PSA. Further analysis is recommended in order to gain a better understanding of the complex mechanisms involved towards engineering uses for soil stabilisation
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