45,784 research outputs found
On the stability of circular orbits in galactic dynamics: Newtonian thin disks
The study of off-equatorial orbits in razor-thin disks is still in its
beginnings. Contrary to what was presented in the literature in recent
publications, the vertical stability criterion for equatorial circular orbits
cannot be based on the vertical epicyclic frequency, because of the
discontinuity in the gravitational field on the equatorial plane. We present a
rigorous criterion for the vertical stability of circular orbits in systems
composed by a razor-thin disk surrounded by a smooth axially symmetric
distribution of matter, the latter representing additional structures such as
thick disk, bulge and (dark matter) halo. This criterion is satisfied once the
mass surface density of the thin disk is positive. Qualitative and quantitative
analyses of nearly equatorial orbits are presented. In particular, the analysis
of nearly equatorial orbits allows us to construct an approximate analytical
third integral of motion in this region of phase-space, which describes the
shape of these orbits in the meridional plane.Comment: 3 pages, 1 figure. In Proceedings of the MG13 Meeting on General
Relativity, Stockholm University, Sweden, 1-7 July 2012. World Scientific,
Singapore. Based on arXiv:1206.6501. in The Thirteenth Marcel Grossmann
Meeting: On Recent Developments in Theoretical and Experimental General
Relativity, Astrophysics, and Relativistic Field Theories (In 3 Volumes),
chap. 438, pages 2346-2348 (2015
Production of thermal photons in viscous fluid dynamics with temperature-dependent shear viscosity
We compute the spectrum of thermal photons created in Au+Au collisions at
GeV, taking into account dissipative corrections in
production processes corresponding to the quark--gluon plasma and hadronic
phases. To describe the evolution of the fireball we use a viscous fluid
dynamic model with different parametrizations for the temperature--dependence
of . We find that the spectrum significantly depends on the values of
in the QGP phase, and is almost insensitive to the values in the
hadronic phase. We also compare the influence of the temperature--dependence of
on the spectrum of thermal photons to that of using different
equations of state in the fluid dynamic simulations, finding that both effects
are of the same order of magnitude.Comment: 16 pages, 4 figures. Accepted for publication in Mod. Phys. Lett.
Triangle singularities in and
We study the appearance of structures in the decay of the into and final states by forming
invariant mass distributions of and pairs,
respectively. The structure in the distribution is associated to the
kinematical triangle singularity that appears when the () decay process is followed by the decay
of the into and the subsequent rescattering of the () pair forming the ()
resonance. We find this type of non-resonant peaks at 2850 MeV in the invariant
mass of pairs from decays and
around 3000 MeV in the invariant mass of pairs from decays. By employing the measured branching ratios of
the and decays, we
predict the branching ratios for the processes into and , in the vicinity of the
triangle singularity peak, to be about and ,
respectively. The observation of this reaction would also give extra support to
the molecular picture of the and .Comment: 18 pages, 15 figures, accepted version for publication in Eur. Phys.
J.
Chaotic behavior of the Compound Nucleus, open Quantum Dots and other nanostructures
It is well established that physical systems exhibit both ordered and chaotic
behavior. The chaotic behavior of nanostructure such as open quantum dots has
been confirmed experimentally and discussed exhaustively theoretically. This is
manifested through random fluctuations in the electronic conductance. What
useful information can be extracted from this noise in the conductance? In this
contribution we shall address this question. In particular, we will show that
the average maxima density in the conductance is directly related to the
correlation function whose characteristic width is a measure of energy- or
applied magnetic field- correlation length. The idea behind the above has been
originally discovered in the context of the atomic nucleus, a mesoscopic
system. Our findings are directly applicable to graphene.Comment: 10 pages, 5 figures. Contribution to: "4th International Workshop on
Compound-Nuclear Reactions and Related Topics (CNR*13)", October 7-11, 2013,
Maresias, Brazil. To appear in the proceeding
Water Funds: Conserving Green Infrastructure
This manual is an effort by TNC to compile, analyze and synthesize its own experience, together with that of the water funds already in existence and under creation, in order to provide operational guidelines to people and organizations interested in establishing a water fund or similar mechanism. Each location has different ecological, social, economic, legal and institutional features and, therefore, each water fund will have its own characteristics, phases and projections. This manual presents general guidelines and logical steps that must be followed to boost the opportunities and benefits of a water fund and to minimize possible obstacles for its creation. It is not intended to be an in-depth look at every aspect of water funds. Although TNC participates in several other initiatives and similar approaches to watershed management, such as the water producers program in Brazil, this document will not address those initiatives and will only focus on the water funds scheme, placing greater emphasis on experiences in the Andean region
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