38,657 research outputs found
Possible scenario for MaVaN's as the only neutrino flavor conversion mechanism in the Sun
Mass Varying neutrino mechanisms were proposed to link the neutrino mass
scale with dark energy, addressing the coincidence problem. In some scenarios
this mass can present a dependence on the baryonic density felt by neutrinos,
creating an effective neutrino mass that depends both on the neutrino and
baryonic densities. In this article we investigate the possibility that a
neutrino effective mass is the only flavour conversion mechanism acting in
neutrino oscillation experiments. We present a parameterization on the
environmental effects on neutrino mass that produces the right flavour
conversion probabilities for solar and terrestrial neutrinos experiments.Comment: 12 pages, 4 figure
Collision-Dependent Atom Tunnelling Rate in Bose-Einstein Condensates
We show that the interaction (cross-collision) between atoms trapped in
distinct sites of a double-well potential can significantly increase the atom
tunneling rate for special trap configurations leading to an effective linear
Rabi regime of population oscillation between the trap wells. The inclusion of
cross-collisional effects significantly extends the validity of the two-mode
model approach allowing it to be alternatively employed to explain the recently
observed increase of tunneling rates due to nonlinear interactions.Comment: 4 pages, 2 figures. Replaced with improved versio
Optimal Conditions for Atomic Homodyne Detection on Bose-Einstein Condensates
The dynamics of a two-mode Bose-Einstein condensate trapped in a double-well
potential results approximately in an effective Rabi oscillation regime of
exchange of population between both wells for sufficiently strong overlap
between the modes functions. Facing this system as a temporal atomic beam
splitter we show that this regime is optimal for a nondestructive atom-number
measurement allowing an atomic homodyne detection, thus yielding indirect
relative phase information about one of the two-mode condensates.Comment: 9 pages, 5 figure
The Origin of Fluorine: Abundances in AGB Carbon Stars Revisited
Revised spectroscopic parameters for the HF molecule and a new CN line list
in the 2.3 mu region have been recently available, allowing a revision of the F
content in AGB stars. AGB carbon stars are the only observationally confirmed
sources of fluorine. Nowadays there is not a consensus on the relevance of AGB
stars in its Galactic chemical evolution. The aim of this article is to better
constrain the contribution of these stars with a more accurate estimate of
their fluorine abundances. Using new spectroscopic tools and LTE spectral
synthesis, we redetermine fluorine abundances from several HF lines in the
K-band in a sample of Galactic and extragalactic AGB carbon stars of spectral
types N, J and SC spanning a wide range of metallicities. On average, the new
derived fluorine abundances are systematically lower by 0.33 dex with respect
to previous determinations. This may derive from a combination of the lower
excitation energies of the HF lines and the larger macroturbulence parameters
used here as well as from the new adopted CN line list. Yet, theoretical
nucleosynthesis models in AGB stars agree with the new fluorine determinations
at solar metallicities. At low metallicities, an agreement between theory and
observations can be found by handling in a different way the
radiative/convective interface at the base of the convective envelope. New
fluorine spectroscopic measurements agree with theoretical models at low and at
solar metallicity. Despite this, complementary sources are needed to explain
its observed abundance in the solar neighbourhood.Comment: 9 pages, 4 figures, accepted in A&
Influence of bed elevation discordance on flow patterns and head losses in an open-channel confluence
Confluences play a major role in the dynamics of networks of natural and man-made open channels, and field measurements on river confluences reveal that discordance in bed elevation is common. Studies of schematized confluences with a step at the interface between the tributary and the main channel bed reveal that bed elevation discordance is an important additional control for the confluence hydrodynamics. This study aimed to improve understanding of the influence of bed elevation discordance on the flow patterns and head losses in a right-angled confluence of an open channel with rectangular cross-sections. A large eddy simulation (LES)-based numerical model was set up and validated with experiments by others. Four configurations with different bed discordance ratios were investigated. The results confirm that, with increasing bed elevation discordance, the tributary streamlines at the confluence interface deviate less from the geometrical confluence angle, the extent of the recirculation zone (RZ) gets smaller, the ratio of the water depth upstream to that downstream of the confluence decreases, and the water level depression reduces. The bed elevation discordance also leads to the development of a large-scale structure in the lee of the step. Despite the appearance of the large-scale structure, the reduced extent of the RZ and associated changes in flow deflection/contraction reduce total head losses experienced by the main channel with an increase of the bed discordance ratio. It turns out that bed elevation discordance converts the lateral momentum from the tributary to streamwise momentum in the main channel more efficiently. (C) 2019 Hohai University. Production and hosting by Elsevier B.V
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