Reality and causality in quantum gravity modified electrodynamics

We present a general description of the propagation properties of quantum gravity modified electrodynamics characterized by constitutive relations up to second order in the correction parameter. The effective description corresponds to an electrodynamics in a dispersive and absorptive non-local medium, where the Green functions and the refraction indices can be explicitly calculated. The reality of the electromagnetic field together with the requirement of causal propagation in a given referrence frame leads to restrictions in the form of such refraction indices. In particular, absorption must be present in all cases and, contrary to the usual assumption, it is the dominant aspect in those effective models which exhibit linear effects in the correction parameter not related to birefringence. In such a situation absorption is linear while propagation is quadratical in the correction parameter.Comment: 15 pages, LaTex, minor changes to clarify some points, version accepted for publicatio

Lorentz violating electrodynamics

After summarizing the most interesting results in the calculation of synchrotron radiation in the Myers-Pospelov effective model for Lorentz invariance violating (LIV) electrodynamics, we present a general unified way of describing the radiation regime of LIV electrodynamics which include the following three different models : Gambini-Pullin, Ellis et al. and Myers-Pospelov. Such unification reduces to the standard approach of radiation in a dispersive and absortive (in general) medium with a given index of refraction. The formulation is presented up to second order in the LIV parameter and it is explicitly applied to the synchrotron radiation case.Comment: 11 pages, extended version of the talk given by L.F. Urrutia in the VI Mexican School: Approaches to Quantum Gravity, Playa del Carmen, Mexico, Nov. 2004. Minor chages in the text and added reference

Phenomenological description of quantum gravity inspired modified classical electrodynamics

We discuss a large class of phenomenological models incorporating quantum gravity motivated corrections to electrodynamics. The framework is that of electrodynamics in a birefringent and dispersive medium with non-local constitutive relations, which are considered up to second order in the inverse of the energy characterizing the quantum gravity scale. The energy-momentum tensor, Green functions and frequency dependent refraction indices are obtained, leading to departures from standard physics. The effective character of the theory is also emphasized by introducing a frequency cutoff. The analysis of its effects upon the standard notion of causality is performed, showing that in the radiation regime the expected corrections get further suppressed by highly oscillating terms, thus forbiding causality violations to show up in the corresponding observational effects.Comment: 14 pages, to be published in Obregon Festschrift 2006, Gen. Rel. and Gra

Radiation in Lorentz violating electrodynamics

Synchrotron radiation is analyzed in the classical effective Lorentz invariance violating model of Myers-Pospelov. Within the full far-field approximation we compute the electric and magnetic fields, the angular distribution of the power spectrum and the total emitted power in the m-th harmonic, as well as the polarization. We find the appearance of rather unexpected and large amplifying factors, which go together with the otherwise negligible naive expansion parameter. This opens up the possibility of further exploring Lorentz invariance violations by synchrotron radiation measurements in astrophysical sources where these amplifying factors are important.Comment: Presented at the Second Mexican Meeting on Theoretical and Experimental Physics, El Colegio Nacional, Mexico City, 6-10 September 200

Enhancement of the bioproduction potential of an amylaceous effluent

9 páginas, 12 figuras, 4 tablasThe treatment of starchy effluents could provide the basis for a series of simultaneous or alternative bioproductions easily integrable into a system of greater economic attraction that the simple production of SCP. In order to define some of the possible options, this study uses an amylaceous effluent for simultaneous production of SCP and an amylolytic preparation which is partially consumed in the saccharification of a parallel flow of the same effluent concentrated by ultrafiltration with cutoff at 100 kD. With regard to the development of the above system, this paper describes the problems associated with ultrafiltration, the conditions that optimize saccharification of the concentrate and the requirements of various possible bioproductions that couM be obtained from the saccharified concentrate.CICYT (project ALl 789- 9O).Peer reviewe

Perturbative Hamiltonian constraints for higher order theories

We present a method for constructing a consistent low energy canonical formalism for higher order time-derivative theories, extending the Dirac method to include perturbative Hamiltonian constraints. We apply it to two paradigmatic examples: the Pais-Uhlenbeck oscillator and the Bernard-Duncan scalar field. We also compare the results, both at the classical and quantum level, with the ones corresponding to a direct perturbative construction applied to the exact higher order theory. This comparison highligths the soundness of the present formalism.Comment: 26 pages, 4 figures; review section shortened and appendices change

Intervención para promover hábitos saludables y reducir obesidad en adolescentes de preparatoria

Enero-Junio 2014 219 Resumen / Abstract El objetivo del trabajo fue determinar cambios en la prevalencia de sobrepeso/ obesidad, hábitos alimenticios y ejercicio físico al inicio y fi nal del primer año de preparatoria posterior a una intervención para promover hábitos saludables. Se rea- lizó antropometría y cuestionario sobre alimentación y ejercicio físico al inicio y fi nal del año escolar a 304 alumnos de ca- torce a diecisiete años. Se implementó un programa anual de conferencias, supercla- ses deportivas y redes sociales como Face- book y Twitter. Se logró incrementar el consumo de raciones/día de frutas y ver- duras y reducir la ingestión en días/sema- na de refrescos y papas fritas. No hubo cambios signifi cativos en la prevalencia de sobrepeso/obesidad. La intervención co- lectiva a través de clases y redes sociales mejoró los hábitos alimenticios pero no lo- gró disminuir el sobrepeso/obesidad. Se requiere probar otro tipo de estrategia en adolescentes