The generation of two-dimensional thermal convection induced simultaneously by gravity and high-frequency vibration in a bounded rectangular enclosure or in a layer is investigated theoretically and numerically. The horizontal walls of the container are maintained at constant temperatures while the vertical boundaries are thermally insulated, impermeable and adiabatic. General equations for the description of the time-averaged convective flow and, within this framework, the generalized Boussinesq approximation are formulated. These equations are solved using a spectral collocation method to study the influence of vibrations (angle and intensity). Hence, a theoretical study shows that mechanical quasi-equilibrium (i.e., state in which the averaged velocity is zero but the oscillatory component is in general non-zero) is impossible when the direction of vibration is not parallel to the temperature gradient. In the other case, it is proved that the mechanical equilibrium is linearly stable up to a critical value of the unique stability parameter, which depends on the vibrational field. In this paper, it is shown that high-frequency vertical oscillations can delay convective instabilities and, in this way, reduce the convective flow. The isotherms are oriented perpendicular to the axis of vibration. In the case where the direction of vibration is perpendicular to the temperature gradient, small values of the Grashof number, the stability parameter, induce the generation of an average convective flow. When the aspect ratio is large enough, the character of the bifurcation is practically the same as in the limiting case of an infinitely long layer.

Introduction les traumatismes de la face constituent un problème de santé publique physiquement et psychologiquement, caractérisé par la variété des lésions et parfois par la gravité des séquelles esthétiques ou fonctionnelle. Le but de ce travail était de décrire le profil épidémiologique et tomodensitométrique des fractures maxillo-faciales à Mopti. Méthodes étude descriptive transversale de janvier 2019 à décembre 2019 au Service de Radiologie de l´Hôpital de Mopti. Étaient inclus tous les patients ayant bénéficié une tomodensitométrie maxillo-faciale pour traumatisme avec fracture au scanner pendant cette période. Les variables analysées étaient l´âge, le sexe, l´étiologie et les types de fractures observées à la tomodensitométrie. L´enregistrement et l´analyse des données étaient faits avec les logiciels SPSS version 20 et Excel 2013. Résultats sur un total de 120 patients, l´âge moyen était de 26,43 ans avec un écart-type de 14,547. Les hommes ont prédominé avec 75% (n= 90). Les accidents de la voie publique étaient l´étiologie fréquente avec 50% (n= 60). Les fractures occlus-faciales représentaient 38,33% (n= 46) avec une prédominance des fractures Lefort II soit 22,50% (n= 27). Conclusion cette étude nous a permis d´identifier les couches de la population les plus touchées par les fractures maxillo-faciales dans la région de Mopti tels que les adolescents et les adultes jeunes. Le profil tomodensitométrique était dominé par les fractures occlusofaciales notamment celles de Lefort type II.

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Sirenomelia is a rare fetal malformation with more or less complete fusion of both lower limbs consistently associated with bilateral renal abnormalities. The positive diagnosis can be made antenatally by ultrasound during the first trimester of pregnancy but often before the 22 weeks of amenorrhea. The objective was to think about the possible diagnosis by ultrasound in front of the urinary anomalies and the ologiamnios during the morphological study of the second trimester of pregnancy. We report a case of sirenomelia in a 25-year-old lady as part of the routine prenatal assessment suspected and confirmed during the morphological ultrasound of the second trimester of pregnancy and confirmed after the termination of pregnancy in Mali in the Health Center of Reference of commune III of the district of Bamako. The morphological ultrasound made it possible to diagnose the malformation of the urinary tract, the amniotic fluid and to make the therapeutic decision of medical termination of pregnancy at the end of confirming the siren syndrome.

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