10,470 research outputs found
Astrophysical Configurations with Background Cosmology: Probing Dark Energy at Astrophysical Scales
We explore the effects of a positive cosmological constant on astrophysical
and cosmological configurations described by a polytropic equation of state. We
derive the conditions for equilibrium and stability of such configurations and
consider some astrophysical examples where our analysis may be relevant. We
show that in the presence of the cosmological constant the isothermal sphere is
not a viable astrophysical model since the density in this model does not go
asymptotically to zero. The cosmological constant implies that, for polytropic
index smaller than five, the central density has to exceed a certain minimal
value in terms of the vacuum density in order to guarantee the existence of a
finite size object. We examine such configurations together with effects of
in other exotic possibilities, such as neutrino and boson stars, and
we compare our results to N-body simulations. The astrophysical properties and
configurations found in this article are specific features resulting from the
existence of a dark energy component. Hence, if found in nature would be an
independent probe of a cosmological constant, complementary to other
observations.Comment: 23 pages, 11 figures, 2 tables. Reference added. Mon. Not. Roy.
Astro. Soc in prin
Extended Definition of Capacity in Airport Systems
Nowadays the main airports throughout the world are suffering because their capacity are getting close to saturation
due to the air traffic which is still increasing besides the economic crisis and oil prices. In addition, the forecasts
predict an increase in air traffic of at least 3.6% until 2020. This situation makes very important to come up with
solutions to alleviate capacity congestions in the main airports throughout the world. Capacity has been perceived
traditionally as the factor to be addressed in airport systems and it is faced through a technical perspective. In this
paper we propose to change the mind-set and view capacity of airport systems taking other factors than pure
technical ones. The discussion is illustrated with the example of Schiphol Airport
Spinodal instability growth in new stochastic approaches
Are spinodal instabilities the leading mechanism in the fragmentation of a
fermionic system? Numerous experimental indications suggest such a scenario and
stimulated much effort in giving a suitable description, without being
finalised in a dedicated transport model.
On the one hand, the bulk character of spinodal behaviour requires an
accurate treatment of the one-body dynamics, in presence of mechanical
instabilities. On the other hand, pure mean-field implementations do not apply
to situations where instabilities, bifurcations and chaos are present. The
evolution of instabilities should be treated in a large-amplitude framework
requiring fluctuations of Langevin type.
We present new stochastic approaches constructed by requiring a thorough
description of the mean-field response in presence of instabilities. Their
particular relevance is an improved description of the spinodal fragmentation
mechanism at the threshold, where the instability growth is frustrated by the
mean-field resilience.Comment: Conf. proc. IWM2014-EC, Catania, 6-9 May 201
Symmetron with a non-minimal kinetic term
We investigate the compatibility of the Symmetron with dark energy by
introducing a non-minimal kinetic term associated with the Symmetron. In this
new model, the effect of the friction term appearing in the equation of motion
of the Symmetron field becomes more pronounced due to the non-minimal kinetic
term appearing in the action and, under specific conditions after symmetry
breaking, the universe experiences an accelerating phase which, in spite of the
large effective mass of the scalar field, lasts as long as the Hubble time
.Comment: 12 pages, 4 figures, to appear in JCA
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