727 research outputs found
Disentangling Scaling Properties in Anisotropic and Inhomogeneous Turbulence
We address scaling in inhomogeneous and anisotropic turbulent flows by
decomposing structure functions into their irreducible representation of the
SO(3) symmetry group which are designated by indices. Employing
simulations of channel flows with Re we demonstrate that
different components characterized by different display different scaling
exponents, but for a given these remain the same at different distances
from the wall. The exponent agrees extremely well with high Re
measurements of the scaling exponents, demonstrating the vitality of the SO(3)
decomposition.Comment: 4 page
El desafío de las drogas, el crimen organizado y el terrorismo en África Occidental y Central
África Occidental se ha convertido en un destino atractivo para las redes de delincuencia internacional. En asociación con redes locales, está surgiendo progresivamente un nuevo modelo específico de criminalidad que está comenzando a exportarse.
Existen numerosos factores que explican la creciente importancia de África Occidental y Central en el mapa mundial del crimen organizado y las organizaciones criminales transnacionales. La concurrencia de factores externos como el rápido crecimiento demográfico, el urbanismo descontrolado, gobiernos ineficaces y dinámicas diásporas regionales y mundiales amplifican los efectos de las dificultades políticas, económicas y sociales. Ante esta situación, las redes extranjeras de delincuencia transnacional bien asentadas y en busca de bases operativas seguras para llevar a cabo sus operaciones ilícitas (tráfico de narcóticos, trata de seres humanos, mercancías pirateadas, migración ilegal y recursos naturales) cooperan y cohabitan con las recientes y exitosas redes de delincuencia propias de África Occidental. Los esfuerzos realizados por los gobiernos nacionales para atajar la situación se han limitado hasta ahora a la redacción de marcos legales. Si no se ataja esta situación de forma oportuna y enérgica, cualquier progreso encaminado hacia la consecución de sociedades democráticas liberales quedará ralentizado, por no decir secuestrado
Hartree approximation in curved spacetimes revisited II: The semiclassical Einstein equations and de Sitter self-consistent solutions
We consider the semiclassical Einstein equations (SEE) in the presence of a
quantum scalar field with self-interaction . Working in the
Hartree truncation of the two-particle irreducible (2PI) effective action, we
compute the vacuum expectation value of the energy-momentum tensor of the
scalar field, which act as a source of the SEE. We obtain the renormalized SEE
by implementing a consistent renormalization procedure. We apply our results to
find self-consistent de Sitter solutions to the SEE in situations with or
without spontaneous breaking of the -symmetry.Comment: 32 pages, 4 figure
Quantum dissipative effects in graphene-like mirrors
We study quantum dissipative effects due to the accelerated motion of a
single, imperfect, zero-width mirror. It is assumed that the microscopic
degrees of freedom on the mirror are confined to it, like in plasma or graphene
sheets. Therefore, the mirror is described by a vacuum polarization tensor
concentrated on a time-dependent surface. Under certain
assumptions about the microscopic model for the mirror, we obtain a rather
general expression for the Euclidean effective action, a functional of the
time-dependent mirror's position, in terms of two invariants that characterize
the tensor . The final result can be written in terms of the
TE and TM reflection coefficients of the mirror, with qualitatively different
contributions coming from them. We apply that general expression to derive the
imaginary part of the `in-out' effective action, which measures dissipative
effects induced by the mirror's motion, in different models, in particular for
an accelerated graphene sheet.Comment: 8 pages, 2 figures. Minor changes, version to be published in Phys.
Rev.
Casimir interaction between two concentric cylinders at nonzero temperature
We study the finite temperature Casimir interaction between two concentric
cylinders. When the separation between the cylinders is much smaller than the
radii of the cylinders, the asymptotic expansions of the Casimir interaction
are derived. Both the low temperature and the high temperature regions are
considered. The leading terms are found to agree with the proximity force
approximations. The low temperature leading term of the temperature correction
is also computed and it is found to be independent of the boundary conditions
imposed on the larger cylinder.Comment: 6 pages, 1 figur
Quantum dissipative effects in moving mirrors: a functional approach
We use a functional approach to study various aspects of the quantum
effective dynamics of moving, planar, dispersive mirrors, coupled to scalar or
Dirac fields, in different numbers of dimensions. We first compute the
Euclidean effective action, and use it to derive the imaginary part of the
`in-out' effective action. We also obtain, for the case of the real scalar
field in 1+1 dimensions, the Schwinger-Keldysh effective action and a
semiclassical Langevin equation that describes the motion of the mirror
including noise and dissipative effects due to its coupling to the quantum
fields.Comment: References added. Version to appear in Phys. Rev.
The New Transatlantic Bonanza: Cocaine on Highway 10.
The 10th Parallel marine and aerial routes linking South America and West Africa harbor a long history of trade between the two continents. More recently, these routes have become one of the preferred routes used by Latin American traffickers for shipping multi-tons of cocaine destined for the growing European market. The Parallel’s growing importance in cocaine trafficking has made it known as cocaine “Highway 10” among law enforcement.
Latin American cocaine trafficking organizations, particularly the Colombian ones, have established stable bases in West Africa, controlling and developing the route. West African facilitators, Nigerians as well as an increasing number of nationals from all countries where shipments are stocked, have developed a stronger capacity for taking over more ambitious and lucrative role in the business as transporters, partners, and final buyers. In one case (Guinea), the West African partner had already started developing his own trafficking and manufacturing capacity, reproducing the patterns that made Colombia the business model of the drug industry. In this reshaped context, of particular concern is the role played by the Colombian FARC (Fuerzas Armadas Revolucionarias de Colombia) as provider of cocaine shipments to West African cocaine entrepreneurs, as well as the impact of drug trafficking money on the financing of terrorist and rebel groups operating in the Sahel-Saharan belt
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