536 research outputs found
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
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"
Gamma-ray emission from novae related to positron annihilation: constraints on its observability posed by new experimental nuclear data
Classical novae emit gamma-ray radiation at 511 keV and below, with a cut-off
at around (20-30) keV, related to positron annihilation and its Comptonization
in the expanding envelope. This emission has been elusive up to now, because it
occurs at epochs well before the maximum in optical luminosity, but it could be
detected by some sensitive intrument on board a satellite, provided that the
nova is close enough and that it is observed at the right moment. The detection
of this emission, which is a challenge for the now available and for the future
gamma-ray instruments, would shed light into the physical processes occurring
in the early phases of the explosion, which are invisible in other lower energy
ranges. A good prediction of the emitted fluxes and of the corresponding
detectability distances with different instruments relies critically on a good
knowledge of reaction rates relevant to f18 destruction, which have been
subject to a strong revision after recent nuclear spectroscopy measurements.
With respect to previous results, smaller ejected masses of f18 are predicted,
leading to smaller emitted fluxes in the (20-511) keV range and shorter
detectability distances.Comment: 9 pages, 2 figures, accepted for publication in Astrophys. J. Letter
Gamma-ray emission of classical novae and its detectability by INTEGRAL
A lot of information concerning the mechanism of nova explosions will be
extracted from the possible future observations with INTEGRAL. In order to be
prepared for this task, we are performing detailed models of the gamma-ray
emission of classical novae, for a wide range of possible initial conditions.
Spectra at different epochs after the explosion and light curves for the
different lines (511, 478 and 1275 keV) and the continuum are presented, as
well as the detectability distances with INTEGRAL spectrometer SPI. New results
related to 18F synthesis related to very recent data of nuclear physics are
advanced as preliminary.Comment: 4 pages, 2 figures, to appear in "3rd INTEGRAL Workshop: The Extreme
Universe", Taormina (Italy
Unitary evolution and uniqueness of the Fock quantization in flat cosmologies with compact spatial sections
We study the Fock quantization of scalar fields with a time dependent mass in
cosmological scenarios with flat compact spatial sections. This framework
describes physically interesting situations like, e.g., cosmological
perturbations in flat Friedmann-Robertson-Walker spacetimes, generally
including a suitable scaling of them by a background function. We prove that
the requirements of vacuum invariance under the spatial isometries and of a
unitary quantum dynamics select (a) a unique canonical pair of field variables
among all those related by time dependent canonical transformations which scale
the field configurations, and (b) a unique Fock representation for the
canonical commutation relations of this pair of variables. Though the proof is
generalizable to other compact spatial topologies in three or less dimensions,
we focus on the case of the three-torus owing to its relevance in cosmology,
paying a especial attention to the role played by the spatial isometries in the
determination of the representation.Comment: 23 pages. New section 4.2. Added references. Published in EJT
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