Complex dynamics in double-diffusive convection

The dynamics of a small Prandtl number binary mixture in a laterally heated cavity is studied numerically. By combining temporal integration, steady state solving and linear stability analysis of the full PDE equations, we have been able to locate and characterize a codimension-three degenerate Takens-Bogdanov point whose unfolding describes the dynamics of the system for a certain range of Rayleigh numbers and separation ratios near S=-1.Comment: 8 pages, 5 figure

Reflections on the Need for More Training in Neuroethics for Future Physicians: An Interdisciplinary Approach

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Time-dependent patterns in quasivertical cylindrical binary convection

This paper reports on numerical investigations of the effect of a slight inclination a on pattern formation in a shallow vertical cylindrical cell heated from below for binary mixtures with a positive value of the Soret coefficient. By using direct numerical simulation of the three-dimensional Boussinesq equations with Soret effect in cylindrical geometry, we show that a slight inclination of the cell in the range a˜0.036rad=2° strongly influences pattern selection. The large-scale shear flow (LSSF) induced by the small tilt of gravity overcomes the squarelike arrangements observed in noninclined cylinders in the Soret regime, stratifies the fluid along the direction of inclination, and produces an enhanced separation of the two components of the mixture. The competition between shear effects and horizontal and vertical buoyancy alters significantly the dynamics observed in noninclined convection. Additional unexpected time-dependent patterns coexist with the basic LSSF. We focus on an unsual periodic state recently discovered in an experiment, the so-called superhighway convection state (SHC), in which ascending and descending regions of fluid move in opposite directions. We provide numerical confirmation that Boussinesq Navier-Stokes equations with standard boundary conditions contain the essential ingredients that allow for the existence of such a state. Also, we obtain a persistent heteroclinic structure where regular oscillations between a SHC pattern and a state of nearly stationary longitudinal rolls take place. We characterize numerically these time-dependent patterns and investigate the dynamics around the threshold of convection.Postprint (author's final draft

Experiència d'aprenentatge d'avaluació del medi natural per a estudiants de ciències ambientals. L'ús i l'estat de conservació dels sòls

En aquesta comunicació es presenta una activitat docent dissenyada pels professors de l'assignatura de Gestió i Conservació de Sòls de la UAB (tercer curs de Ciències Ambientals) que pretén desenvolupar la capacitat d'observació dels estudiants perquè siguin capaços de reconèixer en el camp processos que comporten la degradació dels sòls d'una determinada zona i, analitzar-ne les causes

Secondary flows in a laterally heated horizontal cylinder

In this paper we study the problem of thermal convection in a laterally heated, finite, horizontal cylinder. We consider cylinders of moderate aspect ratio (height/diameter approximate to 2) containing a small Prandtl number fluid (sigma < 0.026) typical of molten metals and molten semiconductors. We use the Navier-Stokes and energy equations in the Boussinesq approximation to calculate numerically the basic steady states, analyze their linear stability, and compute some nonlinear secondary flows originated from the instabilities. All the calculated flows and the stability analysis are characterized by their symmetry properties. Due to the confined cylindrical geometry, -presence of lateral walls and lids-, all the flows are completely three dimensional even for the basic steady states. In the range of Prandtl numbers studied, we have identified four different types of instabilities, either oscillatory or stationary. The physical mechanisms, shear or buoyancy, of the corresponding flow transitions have been analyzed. As the value of the Prandtl number approaches sigma = 0.026 the scenario of bifurcations becomes more complicated due to the existence of two different stable basic states originated in a saddle-node bifurcation; a fact that had been overlooked in previous works. (C) 2014 AIP Publishing LLC.Postprint (published version

Pattern selection near the onset of convection in binary mixtures in cylindrical cells

We report numerical investigations of three-dimensional pattern formation of binary mixtures in a vertical cylindrical container heated from below. Negative separation ratio mixtures, for which the onset of convection occurs via a subcritical Hopf bifurcation, are considered. We focus on the dynamics in the neighbourhood of the initial oscillatory instability and analyze the spatio-temporal properties of the patterns for different values of the aspect ratio of the cell, 0.25 less than or similar to Gamma less than or similar to 11 (Gamma equivalent to R/d, where R is the radius of the cell and d its height). Despite the oscillatory nature of the primary instability, for highly constrained geometries, Gamma less than or similar to 2.5, only pure thermal stationary modes are selected after long transients. As the aspect ratio of the cell increases, for intermediate aspect ratio cells such as Gamma = 3, multistability and coexistence of stationary and time-dependent patterns is observed. In highly extended cylinders, Gamma approximate to 11, the dynamics near the onset is completely different from the pure fluid case, and a startling diversity of confined patterns is observed. Many of these patterns are consistent with experimental observations. Remarkably, though, we have obtained persistent large amplitude highly localized states not reported previously.Postprint (published version

A revision of the revaluation index of Spanish pensions [WP]

This article reviews the methodological aspects of the revaluation index of Spanish pensions developed following Law 23/2013 which regulates the sustainability factor and revaluation index of the Social Security pension system. From a gradual breakdown of the elements that make up the revaluation index, an exposition is given of the formal and implementation problems it involves. Finally, its use is illustrated with numerical results

A blue sky catastrophe in double-diffusive convection

A global bifurcation of the blue sky catastrophe type has been found in a small Prandtl number binary mixture contained in a laterally heated cavity. The system has been studied numerically applying the tools of bifurcation theory. The catastrophe corresponds to the destruction of an orbit which, for a large range of Rayleigh numbers, is the only stable solution. This orbit is born in a global saddle-loop bifurcation and becomes chaotic in a period doubling cascade just before its disappearance at the blue sky catastrophe.Comment: 4 pages, 6 figures, REVTeX, To be published in Physical Review Letter

Stationary localized solutions in binary convection in slightly inclined rectangular cells

We analyze numerically the effect of a slight inclination in the lowest part of the snaking branches of convectons that are present in negative separation ratio binary mixtures in two-dimensional elongated rectangular cells. The exploration reveals the existence of novel stationary localized solutions with striking spatial features different from those of convectons. The numerical continuation of these solutions with respect to the inclination of the cell unveils the existence of even further families of localized structures that can organize in closed branches. A variety of localized solutions coexist for the same heating and inclination, depicting a highly complex scenario for solutions in the lowest part of the snaking diagrams for moderate to high heating. The different localized solutions obtained in the horizontal cell are discussed in detail.Postprint (author's final draft

A novel ‘sea-thermal’, synergistic co-valorisation approach for biofuels production from unavoidable food waste (almond hulls) and plastic residues (disposable face masks)

This work first-time addresses the synergetic hydrothermal co-valorisation of almond hulls (an unavoidable food waste) and FFP2 face masks (a common plastic material) using seawater (a sustainable reaction medium). The effects of the feedstock composition (each material alone and all possible binary combinations) and the reaction medium (deionised water, seawater and all possible binary mixtures) have been evaluated at 350 °C and 170 bar over a wide range of reaction times (20–180 min). Bilateral biomass-plastic synergistic and antagonistic interactions between both feedstocks, combined with several promoting and inhibiting effects displayed by seawater, ruled the distribution of the reaction products and their most important physicochemical and fuel properties. Process optimisation revealed that the formation of an energy-dense (32 MJ/kg) liquid biofuel was maximised (26% biocrude yield) by conducting the process with almond hulls in deionised water for 115 min. At the same time, face masks promoted solid biofuel formation (83% hydrochar yield, 46 MJ/kg) by coprocessing an almond hulls/disposable face masks mixture (8:92 wt%) in salted (seawater/deionised water mixture with 37471 ppm salinity) water for 180 min. Conducting the process with seawater (44608 ppm salinity) for 180 min allowed coprocessing of both materials (22/78 wt% almond hulls/face masks) efficiently to maximise biofuels production (13% biocrude yield, HHV = 33 MJ/kg and 67% hydrochar yield, HHV = 49 MJ/kg). These results are a breakthrough in developing season-free and flexible biorefineries, which contribute to reducing pollution and bringing out the hidden value of human activity common residues