The energy method analysis of the Darcy–Bénard problem with viscous dissipation

A nonlinear analysis of the effect of viscous dissipation on the Rayleigh–Bénard instability in a fluid saturated porous layer is performed. The saturated medium is modelled through Darcy’s law, with the layer bounded by two parallel impermeable walls kept at different uniform temperatures, so that heating from below is supplied. While it is well known that viscous dissipation does not influence the linear threshold to instability, a rigorous nonlinear analysis of the instability when viscous dissipation is taken into account is still lacking. This paper aims to fill this gap. The energy method is employed to prove the nonlinear conditional stability of the basic conduction state. In other words, it is shown that a finite initial perturbation exponentially decays in time provided that its initial amplitude is smaller than a given finite value

Regular solutions for nonlinear elliptic equations, with convective terms, in Orlicz spaces

We establish some existence and regularity results to the Dirichlet problem, for a class of quasilinear elliptic equations involving a partial differential operator, depending on the gradient of the solution. Our results are formulated in the Orlicz-Sobolev spaces and under general growth conditions on the convection term. The sub- and supersolutions method is a key tool in the proof of the existence results

Elliptic problems with convection terms in Orlicz spaces

The existence of a solution to a Dirichlet problem, for a class of nonlinear elliptic equations, with a convection term, is established. The main novelties of the paper stand on general growth conditions on the gradient variable, and on minimal assumptions on Ω. The approach is based on the method of sub and supersolutions. The solution is a zero of an auxiliary pseudomonotone operator build via truncation techniques. We present also some examples in which we highlight the generality of our growth conditions

Method for identification of Virulence Determinants

Disclosed are methods for the determination of virulence determinants in bacteria and in particular bacteria of the genus Mycobacterium. Also disclosed are compositions and methods for stimulating an immune response in an animal using bacteria and virulence determinants identified by the methods of the present invention

Investigation of degradation mechanisms in low-voltage p-channel power MOSFETs under High Temperature Gate Bias stress

In this work we investigate the degradation mechanisms occurring in a p-channel trench-gate power MOSFET under High Temperature Gate Bias (HTGB) stress. The impact of negative bias temperature stress is analysed by evaluating relevant figures of merit for the considered device: threshold voltage, transconductance and on-resistance. Temperatures and gate voltages as large as 175 \ub0C and 1224 V, respectively, are adopted to accelerate the degradation in the device. Moreover, in order to investigate the origin of degradation mechanisms we analyse the interface states generation and the charge trapping processes, the impact of a switching gate voltage during the stress phase and the recovery phase after HTGB stress

Development of matte finishes in electrostatic (EFB) and conventional hot dipping (CHDFB) fluidized bed coating process

This study focuses on the correlation between the thermo-rheological properties of a thermosetting powder coating system with its surface structure build-up. Epoxy powder coating systems, which displayed surface matting and surface wrinkling, were examined. Firstly, the evolution of the complex viscosity was correlated with the cure kinetic. Secondly, the structure build-up on the surface of the coatings was investigated with a combined SEM-CLA profilometry analysis at different stages of curing process for both EFB and CHDFB coating processes. Different finishes were found to characterize the films applied by using EFB and CHDFB coating processes as a result of the different way the film is heated by. Finally, a strict relationship of film morphology to the degree of conversion and to the evolution of the complex viscosity was found out for both EFB and CHDFB coating processes. The surface structure is built up after gelation point and continues to evolve after gelation with a full development of the film fine structure. Differences were observed in the surface structure build-up when different curing temperature was used, thereby indicating an influence of minimum viscosity on achievable finishing. These experimental results lead to further advances in a better understanding of the formation of surface topography and morphology of polymeric films. They also provide important indications for the settings of curing parameters in both EFB and CHDFB coating processes as well as for the development of new powder coating formulations. © 2007 Elsevier B.V. All rights reserved

Development of smooth finishes in electrostatic fluidized bed (EFB) coating process of high-performance thermoplastic powders (PPA 571 H)

This paper deals with the analysis of the evolution of the surface morphology of metal substrates coated with high-performance thermoplastic powders, namely PPA 571 H, by using electrostatic fluidized bed (EFB) process. Attention has been particularly focused on the relationship between baking time and temperature of EFB coated substrates and the morphological characteristics of the resulting polymeric films. First, thermal behaviour of PPA 571 H polymeric powders was characterized by using standard calorimetric techniques. Accordingly, PPA 571 H melting kinetic was experimentally deduced. Based upon experimental findings, predictive analytical model was also developed and employed to trace 'iso-conversion' curves out. Second, metal substrates, made from low carbon steel (AISI 1040), were EFB coated and baked at several baking time and temperatures. Combined analyses of scanning electron and confocal microscopes were led to measure the evolution of the films surface morphology under different baking conditions. Accordingly, a relationship between film morphologies and melting degree was sought. Consistent trends of roughness parameters versus baking parameters were found, with smoother finishes of the polymeric films being achieved for higher degrees of melting, that is, for higher baking temperature and time. Full maps and related analytical models of the finishing levels according to baking parameters were also built up, hence providing first useful indications to powder coaters on how to best deal with their settings. © 2006 Elsevier B.V. All rights reserved

ATP Release by Infected Bovine Monocytes Increases the Intracellular Survival of \u3ci\u3eMycobacterium avium\u3c/i\u3e Subsp. \u3ci\u3eparatuberculosis\u3c/i\u3e

Mycobacterium avium subsp. paratuberculosis is the etiologic agent of Johne’s disease, a chronic intestinal infection in ruminants. Adenosine 5′-Triphosphate (ATP) has been reported to induce killing of several Mycobacterium species in human and murine macrophages. We investigated whether ATP secreted from M. avium subsp. paratuberculosis-infected bovine monocytes affects intracellular survival of the bacilli. Bovine monocytes constitutively secreted ATP during an 8-day incubation period in vitro; however, M. avium subsp. paratuberculosis infection did not enhance ATP release. Removal of extracellular ATP by the addition of apyrase increased the viability of infected monocytes, but surprisingly decreased the number of viable intracellular bacilli. In contrast to previous reports, addition of extracellular ATP (1 mM) increased intracellular survival of M. avium subsp. paratuberculosis in bovine monocytes. Neither apyrase nor ATP altered production of reactive oxygen intermediates (ROI) or reactive nitrogen intermediates (RNI) by bovine monocytes. These results suggest that ATP release from infected bovine monocytes improves, rather than decreases, the intracellular survival of M. avium subsp. paratuberculosis

A rheological model for the flowability of aerated fine powders

A mechanically stirred fluid-bed rheometer (msFBR) was used to study the rheology of powders aerated below the fluidisation threshold. Glass ballotini (group B) and silica powders (group A) with different fine contents were tested. The torque necessary to rotate an impeller immersed in a bed of aerated powders was measured for different impeller depths and aeration rates. A model was developed: (a) to estimate the state of stress at the impeller depth, following Janssen’s approach for the evaluation of stresses in silos, and (b) to evaluate the torque, with the hypothesis that it is determined by the powder shear on a flat cylinder surface around the impeller. The model uses some powder properties, such as the dynamic and the wall yield loci of the powder used, which were estimated with a Peschl shear cell modified for small loads. The reasonable prediction of the torque at impeller depth larger than 3 cm provided by the model supports the hypothesis that the torque is defined by the plastic deformation of powders and can be explained within a simple Mohr–Coulomb approach to powder flow. The passive stress distribution that appears to set up during the shearing experiments leaves open some fundamental questions regarding the limiting conditions determining such behaviour. As in previous experiments found in the literature, aeration does not affect the rheology of powders but modifies the stress distribution within the bed. The content of fines turns out to be a key factor in the determination of powder rheology as measured both with the shear cell and with the fluid-bed rheometer