4,238 research outputs found
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
Local water markets for irrigation in southern Spain: A multicriteria approach
Spanish authorities have recently approved a new legislative framework for the creation of local water markets to improve allocative efficiency for this scarce resource. This paper analyses the potential impacts of the policy. A utility function for three groups of farmers was elicited, using a method that does not require interaction with the decision‐makers. Utility was measured as a function of the first two moments of the distribution of total gross margin. The utility functions were then used to simulate farmers' responses to changes in the price of water.Resource /Energy Economics and Policy,
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
What are the prospects for privatizing infrastructure? Lessons from U. S. roads and solid waste
Infrastructure (Economics) ; Roads
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