On the Moyal deformation of Nahm Equations in seven dimensions

We show how the reduced (anti-)self-dual Yang-Mills equations in seven dimensions described by the Nahm equations can be carried over to the Weyl-Wigner-Moyal formalism. In the process some new solutions for the cases of gauge groups SU(2) and SL(2,R) are explicitly obtained.Comment: 16+1 pages, LaTeX, no figure

Ground-state Wigner functional of linearized gravitational field

The deformation quantization formalism is applied to the linearized gravitational field. Standard aspects of this formalism are worked out before the ground state Wigner functional is obtained. Finally, the propagator for the graviton is also discussed within the context of this formalism.Comment: 18 pages, no figure

On the origin of white dwarfs with carbon-dominated atmospheres: The case of H1504+65

Aims. We explore different evolutionary scenarios to explain the helium, deficiency observed, in H1504+65, the most massive known PG1159 star. Methods. We concentrate mainly on the possibility that this star could be the result of mass loss shortly after its born-again and during its subsequent evolution through the [WCL] stage. This possibility is consistent with observational evidence of extensive mass-loss events in Sakurai's object and is in line with the finding that these mass losses give rise to PG1159 models with thin heliumrich envelopes and high rates of period change, as demanded by the pulsating star PG1159-035. We compute the post-born-again evolution of massive sequences by taking into account different mass-loss rate histories. Results. Our results show that stationary winds during the post-born-again evolution fail to remove completely the helium-rich envelope and are therefore unable to explain the helium deficiency observed, in H1504+65. Stationary winds during the Sakurai and [WCL] stages remove at most half of the envelope that survives the violent hydrogen burning during the born-again phase. Conclusions. In view of our results, the proposed evolutionary sequence of born-again stars to H.1504+65 and then to white dwarfs with carbon-rich atmospheres is difficult to reproduce unless the entire helium-rich envelope is ejected by non-stationary mass-loss episodes during the Sakurai stage.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Praxis de la interculturalidad: los retos del multiculturalismo y el ethos del mestizaje

En este documento se postula un itinerario que va del análisis crítico del multiculturalismo a la identificación de las condiciones que posibilitan el mestizaje cultural, y por tanto la práctica de la interculturalidad, la cual se basa en el reconocimiento de que aquello a conservar y proteger no son sólo las culturas en sí mismas, sino los espacios de comunicación e intercambio entre ellas.This paper posits an itinerary from a critical analysis of multiculturalism to the identification of those conditions that enable cultural miscegenation and intercultural praxis, which is based on the recognition that not only cultures in se have to be preserved and protected but the places for communication and exchange among them

An Alternative Interpretation for the Moduli Fields of the Cosmology Associated to Type IIB Supergravity with Fluxes

We start with a particular cosmological model derived from type IIB supergravity theory with fluxes, where usually the dilaton is interpreted as a Quintessence field. Instead of that, in this letter we interpret the dilaton as the dark matter of the universe. With this alternative interpretation we find that in this supergravity model gives a similar evolution and structure formation of the universe compared with the $\Lambda$CDM model in the linear regime of fluctuations of the structure formation. Some free parameters of the theory are fixed using the present cosmological observations. In the non-linear regimen there are some differences between the type IIB supergravity theory with the traditional CDM paradigm. The supergravity theory predicts the formation of galaxies earlier than the CDM and there is no density cusp in the center of galaxies. These differences can distinguish both models and can give a distinctive feature to the phenomenology of the cosmology coming from superstring theory with fluxes.Comment: 7 pages, 5 figures, references added, minor modifications, typos corrected. Version accepted for publication in IJMP

A consistency test of white dwarf and main sequence ages: NGC 6791

NGC 6791 is an open cluster that it is so close to us that can be imaged down to very faint luminosities. The main sequence turn-off age (∼8 Gyr) and the age derived from the cut-off of the white dwarf luminosity function (∼6 Gyr) were found to be significantly different. Here we demonstrate that the origin of this age discrepancy lies in an incorrect evaluation of the white dwarf cooling ages, and we show that when the relevant physical separation processes are included in the calculation of white dwarf sequences both ages are coincident.Facultad de Ciencias Astronómicas y Geofísica

A consistency test of white dwarf and main sequence ages: NGC 6791

NGC 6791 is an open cluster that it is so close to us that can be imaged down to very faint luminosities. The main sequence turn-off age (∼8 Gyr) and the age derived from the cut-off of the white dwarf luminosity function (∼6 Gyr) were found to be significantly different. Here we demonstrate that the origin of this age discrepancy lies in an incorrect evaluation of the white dwarf cooling ages, and we show that when the relevant physical separation processes are included in the calculation of white dwarf sequences both ages are coincident.Facultad de Ciencias Astronómicas y Geofísica

Estudio del efecto de la maduración acelerada y la refrigeración sobre la fisiología de la papaya maradol (Carica papaya L)

El término Daño por frío (DF) se ha empleado para describir el daño fisiológico que muchas plantas y sus frutos sufren como consecuencia del almacenamiento de las mismas a temperaturas bajas pero no de congelación. El DF es una preocupación para horticultores, industriales y científicos, debido a que los síntomas con los que se manifiesta afectan la calidad del producto hasta el punto en que no es comercializable. El presente estudio se realizó con el objetivo de determinar el tiempo máximo de vida útil de la papaya maradol fresca (Carica papaya L.) con y sin maduración acelerada utilizando etileno (500 μL/L/24 horas, 25ºC) y bajo almacenamiento refrigerado empleando un pre-acondicionamiento del fruto (0, 24, 48, 72, 96, 120, y144 horas de maduración previo a la refrigeración). Los frutos con tratamiento de etileno con 24 horas de maduración a 25ºC, previo a ser refrigeradas a 12ºC, fueron almacenados hasta por 17 días a dicha temperatura, sin que se presentara alguna alteración en las variables analizadas (firmeza de cáscara y pulpa, sólidos solubles, pH, acidez titulable y los síntomas del DF), siendo este el mejor de los tratamientos, con la ventaja de tener una maduración rápida y homogénea. Los frutos con tratamiento de etileno con 48 y más horas de maduración a 25ºC, previo a ser refrigeradas a 12ºC, presentan en menor tiempo, alteraciones como ablandamiento anormal, oscurecimiento en cáscara y pulpa (DF). No se encontraron diferencias en base a % de acidez titulable, pH y sólidos solubles entre los 2 tratamientos (con y sin aplicación de etileno) almacenados a las 24 horas o más a 12ºC. En conclusión, la aplicación del etileno resulta benéfico al lograr una maduración homogénea, atractiva para el consumidor, sin que la refrigeración constituya un elemento negativo ya que se logra mayor vida de anaquel y mejor cobertura de comercialización