20,301 research outputs found
Heat transfer simulation of evacuated tube collectors (ETC): An application to a prototype
Since fossil fuels shortages are predicted for the forthcoming generations, the use of renewable energy sources is playing a key role and is strongly recommended worldwide by national and international regulations. In this scenario, solar collectors for hot water preparation, space heating and cooling are becoming an increasingly interesting alternative, especially in the building sector because of population growth. Thus, the present paper is addressed to numerically investigate the thermal behaviour of a prototypal evacuated tube by solving the heat transfer differential equations using the Finite Element Method. This is to reproduce the heat transfer process occurring within the real system, helping the industry improve the prototype
Interactions of the solar neutrinos with the deuterons
Starting from chiral Lagrangians, possessing the SU(2)_L x SU(2)_R local
chiral symmetry, we derive weak axial one-boson exchange currents in the
leading order in the 1/M expansion (M is the nucleon mass). We apply these
currents in calculations of the cross sections for the disintegration of the
deuterons by the low energy neutrinos. The nuclear wave functions are derived
from a variant of the OBEPQB potential and from the Nijmegen 93 and Nijmegen I
nucleon-nucleon interactions. The comparison of our cross sections with those
obtained within the pionless effective field theory and other potential model
calculations shows that the solar neutrino-deuteron cross sections can be
calculated within an accuracy of 3.3 %.Comment: 6 pages, 1 figure, 6 tables, conference tal
Model dependence of the neutrino-deuteron disintegration cross sections at low energies
Model dependence of the reaction rates for the weak breakup of deuterons by
low energy neutrinos is studied starting from the cross sections derived from
potential models and also from pionless effective field theory. Choosing the
spread of the reaction yields, caused basically by the different ways the
two-body currents are treated, as a measure of the model dependent uncertainty,
we conclude that the breakup reactions are 2 - 3 % uncertain, and that
even the ratio of the charged to neutral current reaction rates is also
2 % uncertain.Comment: 13 pages, 1 figure, 6 tables, version published in Phys. Rev. C 75,
044610 (2007
A hot bubble at the centre of M81
Context. Messier 81 has the nearest active nucleus with broad H
emission. A detailed study of this galaxy's centre is important for
understanding the innermost structure of the AGN phenomenon.
Aims. Our goal is to seek previously undetected structures using additional
techniques to reanalyse a data cube obtained with the GMOS-IFU installed on the
Gemini North telescope (Schnorr M\"uller et al. 2011).
Method. We analysed the data cube using techniques of noise reduction,
spatial deconvolution, starlight subtraction, PCA tomography, and comparison
with HST images.
Results. We identified a hot bubble with T 43500 K that is associated
with strong emission of [N II]5755\AA\ and a high [O
I]6300/H ratio; the bubble displays a bluish continuum,
surrounded by a thin shell of H + [N II] emission. We also reinterpret
the outflow found by Schnorr M\"uller et al. (2011) showing that the
blueshifted cone nearly coincides with the radio jet, as expected.
Conclusions. We interpret the hot bubble as having been caused by post
starburst events that left one or more clusters of young stars, similar to the
ones found at the centre of the Milky Way, such as the Arches and the IRS 16
clusters. Shocked structures from combined young stellar winds or supernova
remnants are probably the cause of this hot gas and the low ionization
emission.Comment: 5 pages, 4 figures, accepted for publication in A&
The role of the pion pair term in the theory of the weak axial meson exchange currents
The structure of the weak axial pion exchange current is discussed in various
models. It is shown how the interplay of the chiral invariance and the double
counting problem restricts uniquely the form of the pion potential term, in the
case when the nuclear dynamics is described by the Schroedinger equation with
the static nucleon-nucleon potential.Comment: 17 pages, 1 figure, 2 tables, stylistic changes of the tex
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