5,358 research outputs found
The effect of temperature-dependent solubility on the onset of thermosolutal convection in a horizontal porous layer
We consider the onset of thermosolutal (double-diffusive) convection of a binary fluid in a horizontal porous layer subject to fixed temperatures and chemical equilibrium on the bounding surfaces, in the case when the solubility of the dissolved component depends on temperature. We use a linear stability analysis to investigate how the dissolution or precipitation of this component affects the onset of convection and the selection of an unstable wavenumber; we extend this analysis using a Galerkin method to predict the structure of the initial bifurcation and compare our analytical results with numerical integration of the full nonlinear equations. We find that the reactive term may be stabilizing or destabilizing, with subtle effects particularly when the thermal gradient is destabilizing but the solutal gradient is stabilizing. The preferred spatial wavelength of convective cells at onset may also be substantially increased or reduced, and strongly reactive systems tend to prefer direct to subcritical bifurcation. These results have implications for geothermal-reservoir management and ore prospecting
Astrophysical and cosmological constraints to neutrino properties
The astrophysical and cosmological constraints on neutrino properties (masses, lifetimes, numbers of flavors, etc.) are reviewed. The freeze out of neutrinos in the early Universe are discussed and then the cosmological limits on masses for stable neutrinos are derived. The freeze out argument coupled with observational limits is then used to constrain decaying neutrinos as well. The limits to neutrino properties which follow from SN1987A are then reviewed. The constraint from the big bang nucleosynthesis on the number of neutrino flavors is also considered. Astrophysical constraints on neutrino-mixing as well as future observations of relevance to neutrino physics are briefly discussed
The Onset of Chaos in Pulsating Variable Stars
Random changes in pulsation period occur in cool pulsating Mira variables,
Type A, B, and C semiregular variables, RV Tauri variables, and in most
classical Cepheids. The physical processes responsible for such fluctuations
are uncertain, but presumably originate in temporal modifications of the
envelope convection in such stars. Such fluctuations are seemingly random over
a few pulsation cycles of the stars, but are dominated by the regularity of the
primary pulsation over the long term. The magnitude of stochasticity in
pulsating stars appears to be linked directly to their dimensions, although not
in simple fashion. It is relatively larger in M supergiants, for example, than
in short-period Cepheids, but is common enough that it can be detected in
visual observations for many types of pulsating stars. Although chaos was
discovered in such stars 80 years ago, detection of its general presence in the
group has only been possible in recent studies.Comment: To appear in the proceedings of the Odessa Variable Stars 2010
Conference (see http://uavso.org.ua/?page=vs2010&lang=en), edited by I.
Andronov and V. Kovtyuk
Call-by-name, Call-by-value, Call-by-need, and the Linear Lambda Calculus
Girard described two translations of intuitionistic logic into linear logic, one where A -> B maps to (!A) -o B, and another where it maps to !(A -o B). We detail the action of these translations on terms, and show that the first corresponds to a call-by-name calculus, while the second corresponds to call-by-value. We further show that if the target of the translation is taken to be an affine calculus, where ! controls contraction but weakening is allowed everywhere, then the second translation corresponds to a call-by-need calculus, as recently defined by Ariola, Felleisen, Maraist, Odersky, and Wadler. Thus the different calling mechanisms can be explained in terms of logical translations, bringing them into the scope of the Curry-Howard isomorphism
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