The enhancement of weakly exothermic polymerization fronts

Abstract The propagation of one-dimensional waves resulting from chemical reactions in a sandwich-type two-layer setting is considered. One layer, termed the polymerization layer, contains the monomer and initiator molecules needed for the initiation of a self-propagating polymer front. The other layer will be referred to as the enhancement layer, and it contains the necessary reactants to support a highly exothermic self-propagating reaction wave. Heat exchange occurs between the layers, and as a result, there is a net diffusion of heat away from the region undergoing the more exothermic reaction. As frontal polymerization (FP) reactions are known not to be very exothermic, an overall transfer of heat from the enhancement layer into the polymerization layer takes place. An analysis of the basic state of the system is carried out to investigate the effect of heat transfer on the polymerization reaction. An enhancement layer is shown to promote FP. This analysis is applicable to the manufacture of thin polymer films by FP

Numerical experiments for segmenting medical images using level sets

Image segmentation is the process by which objects are separated from background information. Structural segmentation from 2D and 3D images is an important step in the analysis of medical image data. In this technical report, we utilize level set algorithms and active contours without edges to segment two and three-dimensional image data. Besides synthetical data, we also use magnetic resonance images of the human brain provided by the Institute of Biomedical Research in Light and Images of the University of Coimbra (IBILI

A phenomenological model for desorption in polymers

A phenomenological formulation is adopted to investigate desorption in polymers. The speed of the front is studied and the well-posedeness of the general model is analyzed. Numerical simulations illustrating the dynamics of the desorption process described by the proposed model are includedCenter for Mathematics of University of Coimbr

Solitary waves on a free surface of a heated Maxwell fluid

International audienceThe existence of an oscillatory instability in the Bénard?Marangoni phenomenon for a viscoelastic Maxwell's fluid is explored. We consider a fluid that is bounded above by a free deformable surface and below by an impermeable bottom. The fluid is subject to a temperature gradient, inducing instabilities. We show that due to balance between viscous dissipation and energy injection from thermal gradients, a long-wave oscillatory instability develops. In the weak nonlinear regime, it is governed by the Korteweg?de Vries equation. Stable nonlinear structures such as solitons are thus predicted. The specific influence of viscoelasticity on the dynamics is discussed and shown to affect the amplitude of the soliton, pointing out the possible existence of depression waves in this case. Experimental feasibility is examined leading to the conclusion that for realistic fluids, depression waves should be more easily seen in the Bénard?Marangoni system

Solitary waves on a free surface of a heated Maxwell fluid

The existence of an oscillatory instability in the Benard Marangoni phenomenon for a viscoelastic Maxwell's fluid is explored. We consider a fluid that is bounded above by a free deformable surface and below by an impermeable bottom. The fluid is subject to a temperature gradient, inducing instabilities. We show that due to balance between viscous dissipation and energy injection from thermal gradients, a long-wave oscillatory instability develops. In the weak nonlinear regime, it is governed by the Korteweg-de Vries equation. Stable nonlinear structures such as solitons are thus predicted. The specific influence of viscoelasticity on the dynamics is discussed and shown to affect the amplitude of the soliton, pointing out the possible existence of depression waves in this case. Experimental feasibility is examined leading to the conclusion that for realistic fluids, depression waves should be more easily seen in the Benard Marangoni system.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Investigating journal bearing characteristics incorporating variable viscosity, couple-stress lubricant, slip-velocity, magnetic fluid, and sinusoidal surface-texturing

This study contributes to the practical understanding of journal bearings by comprehensively exploring the impact of variable viscosity, sinusoidal surface texturing, slip velocity, magnetic fluid, and couple-stress lubricants on the pressure distribution. Utilising the Barus variable viscosity formula, incorporating ferrofluid as a magnetic lubricant, and employing the Finite Difference Method for numerical analysis, this research reveals insights such as increased load-carrying capacity and pressure distribution in textured bearings. The results indicate that a small distance ratio and high magnetic parameters increase magnetic pressure. Textured bearings increased the load-carrying capacity and pressure distribution by approximately 246 % and 165 %, respectively. In addition, the magnetic, couple-stress, piezo-viscosity, and maximal slip parameters increase the load. Reducing the bearing attitude angle improves the load-carrying capacity. The magnetic parameter increases the attitude angle, as does the slip parameter. High values of the couple-stress parameter reduce friction, particularly in the presence of a textured surface, and the presence of a textured surface amplifies this effect. The study highlights the influence of magnetic, couple-stress, piezo-viscosity, and slip parameters on the bearing's performance, offering valuable insights for optimising journal bearing designs and operations in various engineering applications