Humidity-insensitive water evaporation from molecular complex fluids

We investigated theoretically water evaporation from concentrated supramolecular mixtures, such as solutions of polymers or amphiphilic molecules, using numerical resolutions of a one dimensional model based on mass transport equations. Solvent evaporation leads to the formation of a concentrated solute layer at the drying interface, which slows down evaporation in a long-time scale regime. In this regime, often referred to as the falling rate period, evaporation is dominated by diffusive mass transport within the solution, as already known. However, we demonstrate that, in this regime, the rate of evaporation does not also depend on the ambient humidity for many molecular complex fluids. Using analytical solutions in some limiting cases, we first demonstrate that a sharp decrease of the water chemical activity at high solute concentration, leads to evaporation rates which depend weakly on the humidity, as the solute concentration at the drying interface slightly depends on the humidity. However, we also show that a strong decrease of the mutual diffusion coefficient of the solution enhances considerably this effect, leading to nearly independent evaporation rates over a wide range of humidity. The decrease of the mutual diffusion coefficient indeed induces strong concentration gradients at the drying interface, which shield the concentration profiles from humidity variations, except in a very thin region close to the drying interface.Comment: 13 pages, 10 figure

Transient Rayleigh-Benard-Marangoni Convection due to Evaporation : a Linear Non-normal Stability Analysis

The convective instability in a plane liquid layer with time-dependent temperature profile is investigated by means of a general method suitable for linear stability analysis of an unsteady basic flow. The method is based on a non-normal approach, and predicts the onset of instability, critical wave number and time. The method is applied to transient Rayleigh-Benard-Marangoni convection due to cooling by evaporation. Numerical results as well as theoretical scalings for the critical parameters as function of the Biot number are presented for the limiting cases of purely buoyancy-driven and purely surface-tension-driven convection. Critical parameters from calculations are in good agreement with those from experiments on drying polymer solutions, where the surface cooling is induced by solvent evaporation.Comment: 31 pages, 8 figure

Can hydrodynamic contact line paradox be solved by evaporation--condensation?

We investigate a possibility to regularize the hydrodynamic contact line singularity in the configuration of partial wetting (liquid wedge on a solid substrate) via evaporation-condensation, when an inert gas is present in the atmosphere above the liquid. The no-slip condition is imposed at the solid-liquid interface and the system is assumed to be isothermal. The mass exchange dynamics is controlled by vapor diffusion in the inert gas and interfacial kinetic resistance. The coupling between the liquid meniscus curvature and mass exchange is provided by the Kelvin effect. The atmosphere is saturated and the substrate moves at a steady velocity with respect to the liquid wedge. A multi-scale analysis is performed. The liquid dynamics description in the phase-change-controlled microregion and visco-capillary intermediate region is based on the lubrication equations. The vapor diffusion is considered in the gas phase. It is shown that from the mathematical point of view, the phase exchange relieves the contact line singularity. The liquid mass is conserved: evaporation existing on a part of the meniscus and condensation occurring over another part compensate exactly each other. However, numerical estimations carried out for three common fluids (ethanol, water and glycerol) at the ambient conditions show that the characteristic length scales are tiny

Estudios comparativo de protocolos de encaminamiento en redes VANET

Las redes inalámbricas han revolucionado los intercambios de datos y defi¬nido un nuevo paradigma, el del “Always On-Always Connected”. Dentro de este paradigma, las comunicaciones en entornos vehiculares abren un nuevo campo de investigación en la comunidad científica. La forma más común de considerar las redes inalámbricas es aquella en la cual los clientes móviles se conectan a una estación base (BS) que controla las comunicaciones. Esta BS cubre una cierta área de cobertura en la cual todos los clientes que controla pueden comunicarse entre sí. El alcance a clientes de otras redes se hace a través de un segmento generalmente fijo. Los clientes son capaces de desplazarse y de cambiar de BS sin corte de cobertura mediante un proceso llamado handover. Las comunicaciones ad-hoc, y más precisamente las comunicaciones VA-NETs (“Vehicular Ad-Hoc Network”) plantean nuevos retos. En este tipo de redes no existe infraestructura de red sino que se compone de los propios nodos móviles autónomos comunicándose entre sí por enlaces inalámbricos. En este entorno desaparece el control centralizado de la red que proporcionaba la BS. Los nodos deben asumir responsabilidades de encaminamiento y de mantenimiento de la red. El control de red está distribuido entre los mismos nodos. A esos nuevos retos de control de red se suman las características de topologías del entorno vehicular. Las características de las redes vehiculares son en general hostil al intercambio de tráfico. El proceso de encaminamiento no se puede asumir de la misma manera que en las redes clásicas. Es necesario que cada nodo por separado y todos en su conjuntos sean capaces de proporcionar un mecanismo dinámico de encaminamiento. Este encaminamiento mulito se basa en las capacidades de cada nodo. Los protocolos de encaminamiento clásicos no sirven en ese entorno ya que no están preparados para variaciones de topología, puede que no converjan. En tal entorno, el envío de paquetes entre nodos se vuelve todo un reto

Une sémantique d'ESTEREL par ensembles partiellement ordonnés de signaux

On décrit une nouvelle sémantique formelle du langage Esterel. Cette sémantique est donnée sous forme de signaux partiellement ordonnés entre eux. Cette sémantique est définie à partir d'un calcul de processus inhérent à Esterel et est ensuite étendue à Esterel tout entier. Cette sémantique est directe dans le sens où elle ne fait pas appel à la notion de critère d'observation, elle vérifie le déterminisme des programmes et admet la modularité

Coefficients d'échange thermique superficiel : détermination par méthodes inverses en conduction bidimensionnelle transitoire

This work concerns the cooling by compressed air flow of the plungers used in the glass forming processes. The bad control of the plunger temperature leads to an increase of the fabrication default. Thus the objective of the study is to develop a thermal model which will allow the calculation of the plunger temperature field and which-will be used to optimize the cooling system configuration. In a first stage, the temperature field in the plunger/glass/mold system is determined with a on dimensional model. The radiation in the glass is treated with the discrete ordinate method and the model takes into account the different steps of forming cycle. This simplified model is used tio better understand the dehavior of the heat transfer in the plunger/glass/mold system and to determine the parameter that must be known accurately. The boundary conditions at the plunger/glass interface and at the inner surface cooled by air must be known accuraltely ti determine the plunger temperature. Two experimental set-up have been realized to determine by inverse heat conduction methods thes unknown boundary condition. The heat transfer coefficient between the plunger and the galss and between the plunger and the air are shown and examined for different experimental situations. The two dimensional thermal model solved with the finite elements technique is then described. Based on the boundary conditions determined experimentally, an example of the plunger temperature field during a glass forming cycle is given.Ce travail traite du refroidissement par air comprimé des poinçons utilisés pour le formage d'ébauches en verre. Une mauvaise maîtrise de la température de ces poinçons entraînant une augmentation des défauts de fabrication, le but est de développer un modèle thermique permettant de prédire leur température, afin d'améliorer la conception du système de refroidissement.Dans une première étape, le champ de température dans le système poinçon/verre/moule est calculé grâce à un modèle monodimensionnel, reproduisant les différentes étapes d'un cycle de formage. Ce modèle est utilisé dans le but de mieux comprendre la nature des transferts de chaleur dans le système poinçon/verre/moule, et pour préciser les hypothèses du modèle destiné à l'optimisation du système de refroidissement du poinçon.La modélisation fine du poinçon nécessitant la connaissance des conditions aux limites aux surfaces soumises au contact avec le verre d'une part, et à l'action de la ventilation d'autre part, ces dernières sont obtenues expérimentalement, en utilisant les méthodes inverses en conduction. Les valeurs du coefficient d'échange entre le poinçon et le verre, et entre le poinçon et l'air comprimé sont présentées et discutées, pour différentes conditions expérimentales.Pour finir, le modèle bidimensionnel de simulation du poinçon, basé sur la résolution de l'équation de la conduction en éléments finis, et utilisant les conditions aux limites déterminées expérimentalement est décrit, et un exemple de simulation est détaillé

Helminthofaune des caprins en Saone-et-Loire. Influence du pâturage mixte avec les bovins

Les caprins sont particulièrement concernés par la forte prévalence de la résistance des nématodes aux traitements anthelminthiques classiques. Il devient donc urgent de développer des méthodes alternatives de contrôle du parasitisme, afin de réduire le nombre de traitements, préservant ainsi leur efficacité à long terme. L'auteur a étudié une méthode de contrôle basée sur la gestion du pâturage en comparant des infestations naturelles de caprins en pâturage homologue avec celles de caprins en pâturage alterné ou continu avec des bovins. Cette étude a permis de recenser les différentes espèces parasitaires rencontrées chez les caprins de Saône et Loire. Lors de pâturage mixte, les caprins ne sont pas pénalisés par l'acquisition massive de parasites de bovins. Nous avons montré également une diminution du parasitisme des caprins lors de pâturage continu avec les bovins. Cette diminution semble s'expliquer par une dilution du risque parasitaire grâce à des surfaces pâturables plus importantes

Efeitos do taping em atletas overhead com tendinopatia da coifa dos rotadores: uma revisão bibliográfica

Projeto de Graduação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Licenciado em FisioterapiaIntrodução: A tendinopatia da coifa dos rotadores é uma das principais causas de dor em atletas overhead. O taping tem sido proposto como uma das técnicas possíveis no tratamento da tendinopatia da coifa dos rotadores. Objetivo: Estudar os efeitos do taping no tratamento da tendinopatia da coifa dos rotadores em atletas overhead. Metodologia: A pesquisa computorizada foi feita através das bases de dados PubMed, PEDro e do motor de pesquisa Google Scholar. Resultados: Foram selecionados cinco artigos com técnicas de taping rígido e elástico, analisando os efeitos na reposição articular, dor, amplitude de movimento, atividade muscular, cinemática e dinâmica do espaço subacromial. Conclusão: O taping apresentou resultados significativos relativamente à cinemática, dinâmica do espaço subacromial, atividade muscular e reposição articular. Não houve efeitos significativos sobre o aumento da amplitude de movimento e a diminuição da dor.Introduction: Rotator cuff tendinopathy is one of the main causes of pain in overhead athletes. Taping has been proposed as one of the possible techniques in the treatment of rotator cuff tendinopathy. Objective: To study the effects of taping in the treatment of rotator cuff tendinopathy in overhead athletes. Methodology: A computerized search was performed using Pubmed, PEDro and Google Scholar databases. Results: Five studies were selected with rigid and elastic taping techniques, analyzing the effects on joint reposition, pain, range of motion, muscle activity, kinematic and dynamics of the subacromial space. Conclusion: Taping showed significant results on kinematic, muscle activity, subacromial space dynamics and joint reposition. There were no significant effects on increasing range of motion and decreasing pain.N/