The Hertz contact in chain elastic collisions

A theoretical analysis about the influence of the Hertz elastic contact on a three body chain collision is presented. In spite of the elastic character of the collision, the final velocity of each particle depends on the particular interaction between them. A system involving two elastic spheres falling together one in top of the other under the action of gravity, and colliding with an horizontal hard wall is studied in detail. The effect of the Hertz contact interaction can be easily put in evidence for some particular situations.Comment: 5 pages, 6 figure

Lorentz Violating Julia-Toulouse Mechanism

We propose a new Lorentz invariant violating extension for the pure photonic sector of the Standard Model due to the condensation of topological defects in the context of the Julia-Toulouse mechanism. Possible physical consequences leading to direct measurable effects over the confining properties of the elementary particles are explored.Comment: 4 page

On sign-changeable interaction in FLRW cosmology

We investigate an interacting two-fluid model in a spatially flat Friedmann-Lema\^itre-Robertson-Walker (FLRW) Universe, when the energy transfer between these two dark components is produced by a factorisable nonlinear sign-changeable interaction depending linearly on the energy density and quadratically on the deceleration parameter. We solve the source equation and obtain the effective energy densities of the dark sector and their components. We show that the effective equation of state of the dark sector includes some of the several kind of Chaplygin gas equations of state as well as a generalization of the polytropic equation of state. We use bayesian statistics methods to constrain free parameters in the models during its most recent evolution considering supernovae type Ia and measurements of the Hubble expansion rate. The resulting constraints provide new information on sign-changeable interactions, its equivalences and compatibility with previous models and novel late time universe dynamics.Comment: 8 figure

La neutralidad como forma de encuadre en una campaña electoral

Analiza los aspectos teóricos del framing presentando la neutralidad como una de las múltiples o ilimitadas formas en que este se puede manifestar. Sostiene que el encuadre o enfoque que los medios de comunicación den a la cobertura de una campaña electoral, y especialmente a los atributos o rasgos personales de un candidato, tendrá incidencia en la opinión pública, incluso cuando se opte por mecanismos de framing que beneficien o faciliten que el público reciba el mensaje encuadrado por los mismos candidatos, como puede suceder con la neutralidad. Concluye que en la campaña presidencial chilena de 1999 se facilitó que se impusiera el encuadre del mensaje de los candidatos por sobre el framing de los medios

Coulomb's law modification driven by a logarithmic electrodynamics

We examine physical aspects for the electric version of a recently proposed logarithmic electrodynamics, for which the electric field of a point-like charge is finite at the origin. It is shown that this electrodynamics displays the vacuum birefringence phenomenon in the presence of external magnetic field. Afterwards we compute the lowest-order modification to the interaction energy by means of the gauge-invariant but path-dependent variables formalism. These are shown to result in a long-range ($1/r^3$-type) correction, in addition to a linear and another logarithmic correction, to the Coulomb potential.Comment: 4 pages. arXiv admin note: text overlap with arXiv:1709.0386