61 research outputs found

    Radial imbibition in paper under temperature differences

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    Spontaneous radial imbibition into thin circular samples of porous material when they have been subjected to radial temperature differences was analyzed theoretically and experimentally. The use of the Darcy equation allows us to take into account temperature variations in the dynamic viscosity and surface tension in order to found the one-dimensional equation for the imbibition fronts. Experiments in blotting paper show the good fit between the experimental data to theoretical profiles.Fil: Lopez Villa, Abel. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzados. Departamento de Investigaciones Educativas.; MéxicoFil: Medina, Abraham. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzados. Departamento de Investigaciones Educativas.; MéxicoFil: Higuera, F. J.. No especifíca;Fil: Mac Intyre, Jonatan Raúl. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física Arroyo Seco; ArgentinaFil: Perazzo, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Medicina Traslacional, Trasplante y Bioingeniería. Fundación Favaloro. Instituto de Medicina Traslacional, Trasplante y Bioingeniería; ArgentinaFil: Gomba, Juan Manuel. Universidad Favaloro; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Tandil. Centro de Investigaciones En Fisica E Ingenieria del Centro de la Provincia de Buenos Aires. Sede Olavarria del Centro de Investifaciones En Fisica E Ingenieria del Centro de la Provincia de Buenos Aires | Universidad Nacional del Centro de la Pcia.de Bs.as.. Centro de Investigaciones En Fisica E Ingenieria del Centro de la Provincia de Buenos Aires. Sede Olavarria del Centro de Investifaciones En Fisica E Ingenieria del Centro de la Provincia de Buenos Aires.; Argentin

    Migración de gotas por efecto termocapilar: dependencia cuadrática de la tensión superficial con la temperatura

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    Se estudia la migración de gotas depositadas sobre una superficie sólida a la cual se le aplica un gradiente uniforme de temperatura. El presente estudio está enfocado en líquidos parcialmente mojantes denominados “self-rewetting”, cuya característica distintiva es la dependencia cuadrática de la tensión superficial con la temperatura. A pesar de que estos líquidos presentan una dinámica compleja, aquí se mostrará como las soluciones obtenidas para líquidos con dependencia lineal en la temperatura pueden adaptarse y ser utilizadas para describir su flujo. A diferencia de los líquidos con tensión superficial lineal en la temperatura, el ancho de las gotas de líquido self-rewetting crece con el tiempo.We study the migration of droplets on a solid surface which is under a uniform temperature gradient. The present article focus on partial wetting fluids which surface tension depends on the squared temperature. These type of liquids, called self-rewetting, show a complex dynamics and here we will compare with those liquids of linear dependence in the temperature. Unlike to the latter ones, the droplet width increases with the time.Fil: Mac Intyre, J. R.. Aalto University; FinlandiaFil: Gomba, Juan Manuel. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Perazzo, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Medicina Traslacional, Trasplante y Bioingeniería. Fundación Favaloro. Instituto de Medicina Traslacional, Trasplante y Bioingeniería; Argentina. Universidad Favaloro; Argentin

    Droplet actuation induced by coalescence: experimental evidences and phenomenological modeling

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    This paper considers the interaction between two droplets placed on a substrate in immediate vicinity. We show here that when the two droplets are of different fluids and especially when one of the droplet is highly volatile, a wealth of fascinating phenomena can be observed. In particular, the interaction may result in the actuation of the droplet system, i.e. its displacement over a finite length. In order to control this displacement, we consider droplets confined on a hydrophilic stripe created by plasma-treating a PDMS substrate. This controlled actuation opens up unexplored opportunities in the field of microfluidics. In order to explain the observed actuation phenomenon, we propose a simple phenomenological model based on Newton's second law and a simple balance between the driving force arising from surface energy gradients and the viscous resistive force. This simple model is able to reproduce qualitatively and quantitatively the observed droplet dynamics

    Distribution épidémiologique de l’infection à VIH chez les femmes enceintes dans les dix régions du Cameroun et implications stratégiques pour les programmes de prévention

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    Introduction: le Cameroun se situe dans un contexte d'épidémie  généralisée du VIH. La sous-population des femmes enceintes, facilementaccessible au sein de la population générale, représente une cible  robante pour mener la surveillance du VIH et estimer l'évolution épidémiologique. L'objectif de notre étude était d'évaluer la distribution épidémiologique du VIH chez les femmes enceintes.Méthodes: étude transversale menée en 2012 chez 6521 femmes  enceintes (49,3% âgées de 15-24 ans) en première consultation prénatale (CPN1) dans 60 sites des 10 régions Camerounaises. L'algorithme en série a été utilisé pour le sérodiagnostic du VIH.Résultats: la prévalence du VIH était de 7,8% (508/6521), avec une  différence non significative (p=0,297) entre milieu rural (7,4%) et milieu urbain (8,1%). En zone rurale, cette prévalence variait de 0,7% à  l'Extrême-Nord à 11,8% au Sud. Cependant, en zone urbaine elle variait de 4% à l'Ouest à 11,1% au Sud-Ouest. Suivant l'âge, la prévalence était plus élevée (11,3%) chez les femmes de 35-39 ans. Suivant le niveau de scolarisation, la prévalence du VIH était plus faible (4,4%) chez celles non-scolarisées, et plus élevée (9,3%) chez celles ayant un niveau  primaire. Selon la profession, l'infection était plus élevée chez les  coiffeuses (15,5%), secrétaires (14,8%), commerçantes (12,9%) et  institutrices/enseignantes (10,8%). Conclusion: la prévalence du VIH reste élevée chez les femmes enceintes au Cameroun, sans distinction entre milieux rural et urbain. Les stratégies de prévention devraient s'orienter préférentiellement chez les femmes enceintes âgées, celles du niveau d'instruction primaire, et celles du  secteur des petites et moyennes entreprises

    Re-recruiting postpartum women living with HIV into a follow-up study in Cape Town, South Africa

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    Abstract Objective Recruitment and retention present major challenges to longitudinal research in maternal and child health, yet there are few insights into optimal strategies that can be employed in low-resource settings. Following prior participation in a longitudinal study following women living with HIV through pregnancy and breastfeeding in Cape Town, women were re-contacted at least 18 months after the last study contact and were invited to attend an additional follow-up visit. We describe lessons learnt and offer recommendations for a multiphase recruitment approach. Results Using telephone calls, home visits, clinic tracing and Facebook/WhatsApp messages, we located 387 of the 463 eligible women and successfully enrolled 353 (91% of those contacted). Phone calls were the most successful strategy, yielding 67% of enrolments. Over half of the women had changed their contact information since participation in the previous study. We recommend that researchers collect multiple contact details and use several recruitment strategies in parallel from the start of a study. Participants in longitudinal studies may require frequent contact to update contact information, particularly in settings where mobility is common

    Alteration of sarcoplasmic reticulum Ca<sup>2+</sup> ATPase expression in lower limb ischemia caused by atherosclerosis obliterans

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    Atherosclerosis is a disease caused by a build-up of fatty plaques and cholesterol in the arteries. The lumen of the vessels is obliterated resulting in restricted blood supply to tissues. In ischemic conditions, the cytosolic Ca2+ level of skeletal muscle may increase, indicating the alteration of Ca2+ removal mechanisms. Ca2+ is transported from cytosol into the sarcoplasmic reticulum by Ca2+ ATPase (SERCA), with its 1a isoform expressed in adult, while its 1b isoform in neonatal and regenerating fast-twitch skeletal muscle. To investigate the role of these isoforms in ischemic skeletal muscle, biopsies from musculus biceps femoris of patients who underwent amputation due to atherosclerosis were examined. Samples were removed from the visibly healthy and hypoxia-affected tissue. Significantly increased SERCA1a expression was detected under the ischemic conditions (246 ± 69%; p  0.05), whereas SERCA2a did not change. In addition, in primary cultures derived from hypoxia-affected tissue, the diameter and fusion index of myotubes were significantly increased (30 ± 1.6 µm vs. 41 ± 2.4 µm and 31 ± 4% vs. 45 ± 3%; p < 0.05). We propose that the increased SERCA1a expression indicates the existence and location of compensating mechanisms in ischemic muscle
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