Gamma-ray signatures of classical novae

The role of classical novae as potential gamma-ray emitters is reviewed, on the basis of theoretical models of the gamma-ray emission from different nova types. The interpretation of the up to now negative results of the gamma-ray observations of novae, as well as the prospects for detectability with future instruments (specially onboard INTEGRAL) are also discussed.Comment: 10 pages, 7 figures. Invited talk at the "Gamma 2001" Symposium, April 4-6, 2001, Baltimore, Maryland. To be published by AI

Uniqueness of the Fock quantization of scalar fields and processes with signature change in cosmology

We study scalar fields subject to an equation of the Klein-Gordon type in nonstationary spacetimes, such as those found in cosmology, assuming that all the relevant spatial dependence is contained in the Laplacian. We show that the field description ---with a specific canonical pair--- and the Fock representation for the quantization of the field are fixed indeed in a unique way (except for unitary transformations that do not affect the physical predictions) if we adopt the combined criterion of (a) imposing the invariance of the vacuum under the group of spatial symmetries of the field equations and (b) requiring a unitary implementation of the dynamics in the quantum theory. Besides, we provide a spacetime interpretation of the field equations as those corresponding to a scalar field in a cosmological spacetime that is conformally ultrastatic. In addition, in the privileged Fock quantization, we investigate the generalization of the evolution of physical states from the hyperbolic dynamical regime to an elliptic regime. In order to do this, we contemplate the possibility of processes with signature change in the spacetime where the field propagates and discuss the behavior of the background geometry when the change happens, proving that the spacetime metric degenerates. Finally, we argue that this kind of signature change leads naturally to a phenomenon of particle creation, with exponential production.Comment: 11 pages, version accepted for publication in Physical Review

Ameliorating the effect of Zingiber officinale (ginger) hydroethanolic extract on scopolamine-induced memory impairment in adult male rats

Background and aims: The spice Zingiber officinale or ginger possesses antioxidant and neuroprotective effects. In this study we hypothesized that treatment with hydroethanolic extract of ginger (50, 100 and 200 mg/kg, p.o) would have an effect on the scopolamine-induced memory impairment in rats. Methods: In this experimental study, 64 male Wistar rats were divided into eight groups (8 rats in each group): normal saline, scopolamine (1 mg/kg), ginger extract (50, 100 and 200 mg/kg), or scopolamine (1 mg/kg) plus ginger extract (50, 100 and 200 mg/kg). Memory impairment was induced with a single injection of scopolamine (1 mg/kg, i.p). Cognitive functions were evaluated using passive avoidance learning (PAL) task. Retention test was carried out 24 hours after training, and the latency of entering the dark compartment step-through latency (STL) and the total time in the dark compartment (TDC) were recorded. All statistical analysis was carried out at 5% level of significance using SPSS version 21. The data were analyzed by ANOVA followed by Tukey’s test. Results: The time latency in scopolamine-treated group was lower than control (p<0.001). Treatment of the animals by 100 and 200 mg/kg of ginger extract before the training trial increased the time latency at 24 h after the training trial (p<0.01). Also, administration of extract at doses of 100 and 200 mg/kg in scopolamine received groups before retention trials, increased the time latency than the scopolamine only treated groups (p<0.001). Conclusion: The results revealed that the ginger hydroethanolic extract attenuated scopolamine-induced memory impairment

Prospects for detectability of classical novae with INTEGRAL

Classical novae are potential gamma-ray emitters, both in lines and in a continuum. Continuum emission (at energies between 20-30 and 511 keV) and line emission at 511 keV are related to positron annihilation and its Comptonization in the expanding shell; 18F is the main responsible of positron production. The lines at 478 and 1275 keV have their origin in the decay of the radioactive nuclei 7Be and 22Na. Updated models of nova explosions have been adopted for the computation of the gamma-ray emission. New yields of some radioactive isotopes directly translate into new detectability distances of classical novae with INTEGRAL.Comment: Contributed paper at the 4th INTEGRAL Workshop, 4-8 September 2000, Alicante (Spain). To be published in the ESA-SP series: 4 pages, 4 figure

The prompt gamma-ray emission of novae

Classical novae are potential gamma-ray emitters, because of the disintegration of some radioactive nuclei synthesized during the explosion. Some short-lived isotopes (such as 13N and 18F), as well as the medium-lived 22Na, decay emitting positrons, which annihilate with electrons and thus are responsible for the prompt emission of gamma-rays from novae. This emission consists of a 511 keV line plus a continuum between 20 and 511 keV, and is released before the maximum in visual luminosity, i.e., before the discovery of the nova. The main characteristics of this prompt emission, together with the related uncertainties (both of nuclear and hydrodynamical origin, with a particular emphasis on the influence of the envelope properties) and prospects for detectability are analyzed in this paper.Comment: 6 pages, 3 figures (6 PS files), to appear in New Astronomy Reviews (Proceedings of the Ringberg Workshop "Astronomy with Radioactivities III"

Tendiendo puentes : como acortar la cadena de los productos cárnicos

La máxima «del campo a la mesa» encuentra en la ganadería un agujero de complicada solución. Los animales deben ser sacrificados en un matadero para después poder ser comercializados, es decir, hay un intermediario obligado. Cada vez cierran más mataderos y cada vez menos manos controlan más ganado; así pues, las granjas pequeñas difícilmente pueden comercializar su producto en su mercado más próximo y las personas que compramos en las carnicerías cercanas no podemos acceder a él. A pesar de esta complicación, encontramos iniciativas y soluciones que acercan y conectan consumo y producto