Turning waves and breakdown for incompressible flows

We consider the evolution of an interface generated between two immiscible incompressible and irrotational fluids. Specifically we study the Muskat and water wave problems. We show that starting with a family of initial data given by (\al,f_0(\al)), the interface reaches a regime in finite time in which is no longer a graph. Therefore there exists a time $t^*$ where the solution of the free boundary problem parameterized as (\al,f(\al,t)) blows-up: \|\da f\|_{L^\infty}(t^*)=\infty. In particular, for the Muskat problem, this result allows us to reach an unstable regime, for which the Rayleigh-Taylor condition changes sign and the solution breaks down.Comment: 15 page

Absence of splash singularities for surface quasi-geostrophic sharp fronts and the Muskat problem

In this paper, for both the sharp front surface quasi-geostrophic equation and the Muskat problem, we rule out the “splash singularity” blow-up scenario; in other words, we prove that the contours evolving from either of these systems cannot intersect at a single point while the free boundary remains smooth. Splash singularities have been shown to hold for the free boundary incompressible Euler equation in the form of the water waves contour evolution problem. Our result confirms the numerical simulations in earlier work, in which it was shown that the curvature blows up because the contours collapse at a point. Here, we prove that maintaining control of the curvature will remove the possibility of pointwise interphase collapse. Another conclusion that we provide is a better understanding of earlier work in which squirt singularities are ruled out; in this case, a positive volume of fluid between the contours cannot be ejected in finite time.Ministerio de Ciencia e InnovaciónNational Science FoundationAlfred P. Sloan Foundatio

Cloreto de potássio na linha de semeadura pode causar danos à soja.

bitstream/item/24735/1/COT200264.pdfDocumento on-line

Numerical flow analysis of a centrifugal compressor with ported and without ported shroud

Turbochargers are commonly used in automotive engines to increase the internal combustion engine performance during off design operation conditions. When used, a most wide operation range for the turbocharger is desired, which is limited on the compressor side by the choke condition and the surge phenomenon. The ported shroud technology is used to extend the operable working range of the compressor, which permits flow disturbances that block the blade passage to escape and stream back through the shroud cavity to the compressor inlet. The impact of this technology on a speed-line at near optimal operation condition and near surge operation condition is investigated. A numerical study investigating the flow-field in a centrifugal compressor of an automotive turbocharger has been performed using Large Eddy Simulation. The wheel rotation is handled by the numerically expensive sliding mesh technique. In this analysis, the full compressor geometry (360 deg) is considered. Numerical solutions with and without ported shroud for a near optimal operation condition and near-surge operation condition. The flow-field of the different cases is analyzed to elucidate the functionality of the ported shroud. In agreement with previous observations, it was found that the ported shroud reduces the flow disturbances in the blade passage for all operating conditions. However, the compressor efficiency for the off-design operation condition was found to be higher without the ported shroud, supporting the findings reported recently by an experimental investigation. The computational results are validated with experimental measurements in terms of the performance parameters and available Particle Image Velocimetry data. Copyright © 2014 SAE International

A 27 kDa protein binds to a positive and a negative regulatory sequence in the promoter of the ICL1 gene from Saccharomyces cerevisiae

6 pages, 6 figures, 1 table.IsocitrateICL1, is one of the key enzymes of the glyoxylate pathway, which operates as an anaplerotic route for replenishing the tricarboxylic acid cycle; it is required for growth of Saccharomyces cerevisiae on carbon sources such as ethanol, but is dispensable when fermentable carbon sources are available. The positive regulation of the ICL1 gene by an upstream activating sequence (UAS) element located between -397 and -388 has been previously reported. In this paper we show that the ICL1 promoter sequence 5'-AGTCCGGACTAGCATCCCAG-3' located between -261 and -242 contains an upstream repressing sequence (URS) element. We have identified and partially purified a 27 kDa protein that binds specifically to both the UAS and URS sequences of the ICL1 promoter. For both UAS and URS, binding requires the protein Snf1 (Cat1), a protein kinase essential for the derepression of genes repressed by glucose. Binding does not take place with extracts from glucose-grown strains, unless they lack Mig1, a negative regulatory protein involved in glucose repression.This work was supported by grants PB94-0091-C02-01 and PB94-0091-C02-02 from the DGICYT.Peer reviewe

On the global existence for the Muskat problem

The Muskat problem models the dynamics of the interface between two incompressible immiscible fluids with different constant densities. In this work we prove three results. First we prove an $L^2(\R)$ maximum principle, in the form of a new ``log'' conservation law (???) which is satisfied by the equation (???) for the interface. Our second result is a proof of global existence of Lipschitz continuous solutions for initial data that satisfy ∥f0∥L∞<∞ and ∥∂xf0∥L∞<1. We take advantage of the fact that the bound ∥∂xf0∥L∞<1 is propagated by solutions, which grants strong compactness properties in comparison to the log conservation law. Lastly, we prove a global existence result for unique strong solutions if the initial data is smaller than an explicitly computable constant, for instance ∥f∥1≤1/5. Previous results of this sort used a small constant ϵ≪1 which was not explicit.National Science FoundationMinisterio de Ciencia e InnovaciónEuropean Research Counci

Alterações na biomassa microbiana do solo em cultivos de mandioca sob diferentes coberturas vegetais.

O presente estudo teve como objetivo avaliar o efeito do cultivo da mandioca em plantio direto sob diferentes coberturas vegetais na biomassa microbiana do solo e índices derivados. Tais parâmetros foram avaliados também em sistema sob preparo convencional (aração e gradagem) e sistema natural (mata nativa), para comparação. Os estudos foram conduzidos no Município de Glória de Dourados, MS,num Argissolo vermelho distrófico, de textura arenosabitstream/item/65168/1/BP200421.pd