3,962 research outputs found
Brownian motion of black holes in stellar systems with non-Maxwellian distribution for the stars field
A massive black hole at the center of a dense stellar system, such as a
globular cluster or a galactic nucleus, is subject to a random walk due
gravitational encounters with nearby stars. It behaves as a Brownian particle,
since it is much more massive than the surrounding stars and moves much more
slowly than they do. If the distribution function for the stellar velocities is
Maxwellian, there is a exact equipartition of kinetic energy between the black
hole and the stars in the stationary state. However, if the distribution
function deviates from a Maxwellian form, the strict equipartition cannot be
achieved. The deviation from equipartition is quantified in this work by
applying the Tsallis q-distribution for the stellar velocities in a
q-isothermal stellar system and in a generalized King model.Comment: Presented at XXVI Int. Astronomical Union General Assembly, Symp.
238, Prague, Czech Republic, Aug 21-25 200
Gravity with extra dimensions and dark matter interpretation: A straightforward approach
Any connection between dark matter and extra dimensions can be cognizably
evinced from the associated effective energy-momentum tensor. In order to
investigate and test such relationship, a higher dimensional spacetime endowed
with a factorizable general metric is regarded to derive a general expression
for the stress tensor -- from the Einstein-Hilbert action -- and to elicit the
effective gravitational potential. A particular construction for the case of
six dimensions is provided, and it is forthwith revealed that the missing mass
phenomenon may be explained, irrespective of the dark matter existence.
Moreover, the existence of extra dimensions in the universe accrues the
possibility of a straightforward mechanism for such explanation. A
configuration which density profile coincides with the Newtonian potential for
spiral galaxies is constructed, from a 4-dimensional isotropic metric plus
extra-dimensional components. A Miyamoto-Nagai \emph{ansatz} is used to solve
Einstein equations. The stable rotation curves associated to such system are
computed, in full compliance to the observational data, without fitting
techniques. The density profiles are reconstructed and compared to that ones
obtained from the Newtonian potential.Comment: 13 pages, 6 figure
On the localization properties of an RPWELL gas-avalanche detector
A study of the localization properties of a single-element Resistive Plate
WELL (RPWELL) detector is presented. The detector comprises of a single-sided
THick Gaseous Electron Multiplier (THGEM) coupled to a segmented readout anode
through a doped silicate-glass plate of 10 cm bulk
resistivity. Operated in ambient Ne/(5CH) gas, the detector has been
investigated with 150 GeV muons at CERN-SPS. Signals induced through the
resistive plate on anode readout strips were recorded with APV25/SRS
electronics. The experimental results are compared with that of Monte Carlo
simulations. The effects of various physics phenomena on the position
resolution are discussed. The measured position resolution in the present
configuration is 0.28 mm RMS - compatible with the holes-pattern of the
multiplier. Possible ways for improving the detector position resolution are
suggested
New species of Xestoleberididae (Crustacea, Ostracoda) from Archipelago of SĂŁo Pedro and SĂŁo Paulo, Equatorial Atlantic
Two new species of Xestoleberididae: Xestoleberis brasilinsularis sp. nov. and Xestoleberis machadoae sp. nov., both endemic to Archipelago of SĂŁo Pedro and SĂŁo Paulo, are described. The record of these shallow marine waters species from Brazilian oceanic islands represents an important contribution to the knowledge of the evolutionary history the species inhabit areas
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