Generalised relativistic Ohm's laws, extended gauge transformations and magnetic linking

Generalisations of the relativistic ideal Ohm's law are presented that include specific dynamical features of the current carrying particles in a plasma. Cases of interest for space and laboratory plasmas are identified where these generalisations allow for the definition of generalised electromagnetic fields that transform under a Lorentz boost in the same way as the real electromagnetic fields and that obey the same set of homogeneous Maxwell's equations

Pressure anisotropy generation in a magnetized plasma configuration with a shear flow velocity

The nonlinear evolution of the Kelvin Helmholtz instability in a magnetized plasma with a perpendicular flow close to, or in, the supermagnetosonic regime can produce a significant parallel-to-perpendicular pressure anisotropy. This anisotropy, localized inside the flow shear region, can make the configuration unstable either to the mirror or to the firehose instability and, in general, can affect the development of the KHI. The interface between the solar wind and the Earth's magnetospheric plasma at the magnetospheric equatorial flanks provides a relevant setting for the development of this complex nonlinear dynamics.Comment: 11 pages, 7 figures, submitted to Plasma Phys. Control. Fusio

Expansion of a finite size plasma in vacuum

The expansion dynamics of a finite size plasma is examined from an analytical perspective. Results regarding the charge distribution as well as the electrostatic potential are presented. The acceleration of the ions and the associated cooling of the electrons that takes place during the plasma expansion is described. An extensive analysis of the transition between the semi infinite and the finite size plasma behaviour is carried out. Finally, a test of the analytical results, performed through numerical simulations, is presented.Comment: 4 pages with 5 figure

Covariant form of the ideal magnetohydrodynamic "connection theorem" in a relativistic plasma

The magnetic connection theorem of ideal Magnetohydrodynamics by Newcomb [Newcomb W.A., Ann. Phys., 3, 347 (1958)] and its covariant formulation are rederived and reinterpreted in terms of a "time resetting" projection that accounts for the loss of simultaneity in different reference frames between spatially separated events.Comment: 3 pages- 0 figures EPL, accepted in pres

La inseguridad ciudadana : los años del miedo

Fil: Pegoraro, Juan S. Universidad de Buenos Aires. Facultad de Ciencias Sociales. Instituto de Investigaciones Gino Germani; Argentina.En muchos aspectos, la herencia autoritaria, ilegal y corrupta de la última dictadura parece cercar a la\ndemocracia tanto como en sus endebles comienzos, hace ya 20 años. A la originaria debilidad\ninstitucional del alfonsinismo y la permanente amenaza golpista por parte de los militares, se sumó el\ndescontrol económico del '89. Con la anticipada asunción de Carlos Menem, el desguace económico\nestatal e industrial y el trasvasamiento de riqueza hacia el 20% más favorecido de la población fue\nacompañado por un clima de flagrante impunidad. Como consecuencia, en la última década se\nobserva un fuerte crecimiento de los delitos interpersonales violentos. Los excluidos del modelo\nparecen rebelarse así contra el genocidio social que les impuso la versión vernácula del\nneoliberalismo

Towards interactive global illumination effects via sequential Monte Carlo adaptation

Journal ArticleThis paper presents a novel method that effectively combines both control variates and importance sampling in a sequential Monte Carlo context while handling general single-bounce global illumination effects. The radiance estimates computed during the rendering process are cached in an adaptive per-pixel structure that defines dynamic predicate functions for both variance reduction techniques and guarantees well-behaved PDFs, yielding continually increasing efficiencies thanks to a marginal computational overhead

Enhancing proton acceleration by using composite targets

Efficient laser ion acceleration requires high laser intensities, which can only be obtained by tightly focusing laser radiation. In the radiation pressure acceleration regime, where the tightly focused laser driver leads to the appearance of the fundamental limit for the maximum attainable ion energy, this limit corresponds to the laser pulse group velocity as well as to another limit connected with the transverse expansion of the accelerated foil and consequent onset of the foil transparency. These limits can be relaxed by using composite targets, consisting of a thin foil followed by a near critical density slab. Such targets provide guiding of a laser pulse inside a self-generated channel and background electrons, being snowplowed by the pulse, compensate for the transverse expansion. The use of composite targets results in a significant increase in maximum ion energy, compared to a single foil target case.Comment: 16 pages, 9 figure

Radiation Pressure Acceleration: the factors limiting maximum attainable ion energy

Radiation pressure acceleration (RPA) is a highly efficient mechanism of laser-driven ion acceleration, with with near complete transfer of the laser energy to the ions in the relativistic regime. However, there is a fundamental limit on the maximum attainable ion energy, which is determined by the group velocity of the laser. The tightly focused laser pulses have group velocities smaller than the vacuum light speed, and, since they offer the high intensity needed for the RPA regime, it is plausible that group velocity effects would manifest themselves in the experiments involving tightly focused pulses and thin foils. However, in this case, finite spot size effects are important, and another limiting factor, the transverse expansion of the target, may dominate over the group velocity effect. As the laser pulse diffracts after passing the focus, the target expands accordingly due to the transverse intensity profile of the laser. Due to this expansion, the areal density of the target decreases, making it transparent for radiation and effectively terminating the acceleration. The off-normal incidence of the laser on the target, due either to the experimental setup, or to the deformation of the target, will also lead to establishing a limit on maximum ion energy.Comment: 17 pages, 6 figure