819 research outputs found
A numerical fit of analytical to simulated density profiles in dark matter haloes
Analytical and geometrical properties of generalized power-law (GPL) density
profiles are investigated in detail. In particular, a one-to-one correspondence
is found between mathematical parameters and geometrical parameters. Then GPL
density profiles are compared with simulated dark haloes (SDH) density
profiles, and nonlinear least-absolute values and least-squares fits involving
the above mentioned five parameters (RFSM5 method) are prescribed. More
specifically, the sum of absolute values or squares of absolute logarithmic
residuals is evaluated on a large number of points making a 5-dimension
hypergrid, through a few iterations. The size is progressively reduced around a
fiducial minimum, and superpositions on nodes of earlier hypergrids are
avoided. An application is made to a sample of 17 SDHs on the scale of cluster
of galaxies, within a flat CDM cosmological model (Rasia et al. 2004).
In dealing with the mean SDH density profile, a virial radius, averaged over
the whole sample, is assigned, which allows the calculation of the remaining
parameters. Using a RFSM5 method provides a better fit with respect to other
methods. No evident correlation is found between SDH dynamical state (relaxed
or merging) and asymptotic inner slope of the logarithmic density profile or
(for SDH comparable virial masses) scaled radius. Mean values and standard
deviations of some parameters are calculated, and a comparison with previous
results is made with regard to the scaled radius. A certain degree of
degeneracy is found in fitting GPL to SDH density profiles. If it is intrinsic
to the RFSM5 method or it could be reduced by the next generation of
high-resolution simulations, still remains an open question.Comment: 44 pages, 6 figures, updated version with recent results from
high-resolution simulations (Diemand et al. 2004; Reed et al. 2005) included
in the discussion; accepted for publication on SAJ (Serbian Astronomical
Journal
Relations Between Quantum Maps and Quantum States
The relation between completely positive maps and compound states is
investigated in terms of the notion of quantum conditional probability
Unital Positive Maps and Quantum States
We analyze the structure of the subset of states generated by unital
completely positive quantum maps, A witness that certifies that a state does
not belong to the subset generated by a given map is constructed. We analyse
the representations of positive maps and their relation to quantum
Perron-Frobenius theory.Comment: 14 page
Wigner's Problem and Alternative Commutation Relations for Quantum Mechanics
It is shown, that for quantum systems the vectorfield associated with the
equations of motion may admit alternative Hamiltonian descriptions, both in the
Schr\"odinger and Heisenberg pictures. We illustrate these ambiguities in terms
of simple examples.Comment: Latex,14 pages,accepted by Int. Jour.Mod.Phy
Dark matter haloes: an additional criterion for the choice of fitting density profiles
Simulated dark matter haloes are fitted by self-similar, universal density
profiles, where the scaled parameters depend only on a scaled (truncation)
radius which, in turn, is supposed to be independent on the mass and the
formation redshift. A criterion for the choice of the best fitting density
profile is proposed, with regard to a set of high-resolution simulations, where
some averaging procedure on scaled density profiles has been performed, in
connection with a number of fitting density profiles. An application is made to
a pair of sets each made of a dozen of high-resolution simulations, which are
available in literature, in connection with two currently used fitting density
profiles, where the dependence of the scaled radius on the mass and the
formation redshift, may be neglected to a first extent. Some features of the
early evolution of dark matter haloes represented by fitting density profiles,
are discussed in the limit of the spherical top-hat model.Comment: 62 pages, 9 figures, accepted for publication on SAJ (Serbian
Astronomical Journal), paragraph and reference added for section
Classical and Quantum Systems: Alternative Hamiltonian Descriptions
In complete analogy with the classical situation (which is briefly reviewed)
it is possible to define bi-Hamiltonian descriptions for Quantum systems. We
also analyze compatible Hermitian structures in full analogy with compatible
Poisson structures.Comment: To appear on Theor. Math. Phy
The low-mass population of the Rho Ophiuchi molecular cloud
Star formation theories are currently divergent regarding the fundamental
physical processes that dominate the substellar regime. Observations of nearby
young open clusters allow the brown dwarf (BD) population to be characterised
down to the planetary mass regime, which ultimately must be accommodated by a
successful theory. We hope to uncover the low-mass population of the Rho
Ophiuchi molecular cloud and investigate the properties of the newly found
brown dwarfs. We use near-IR deep images (reaching completeness limits of
approximately 20.5 mag in J, and 18.9 mag in H and Ks) taken with the Wide
Field IR Camera (WIRCam) at the Canada France Hawaii Telescope (CFHT) to
identify candidate members of Rho Oph in the substellar regime. A spectroscopic
follow-up of a small sample of the candidates allows us to assess their
spectral type, and subsequently their temperature and membership. We select 110
candidate members of the Rho Ophiuchi molecular cloud, from which 80 have not
previously been associated with the cloud. We observed a small sample of these
and spectroscopically confirm six new brown dwarfs with spectral types ranging
from M6.5 to M8.25
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