Linear temporal and spatio-temporal stability analysis of a binary liquid film flowing down an inclined uniformly heated plate

Temporal and spatio-temporal instabilities of binary liquid films flowing down an inclined uniformly heated plate with Soret effect are investigated by using the Chebyshev collocation method to solve the full system of linear stability equations. Seven dimensionless parameters, i.e. the Kapitza, Galileo, Prandtl, Lewis, Soret, Marangoni, and Biot numbers (Ka, G, Pr, L, X, M, B), as well as the inclination angle (beta) are used to control the flow system. In the case of pure spanwise perturbations, thermocapillary S- and P-modes are obtained. It is found that the most dangerous modes are stationary for positive Soret numbers (chi >= 0), and oscillatory for chi 0 and even merges with the long-wave S-mode. In the case of streamwise perturbations, a long-wave surface mode (H-mode) is also obtained. From the neutral curves, it is found that larger Soret numbers make the film flow more unstable as do larger Marangoni numbers. The increase of these parameters leads to the merging of the long-wave H- and S-modes, making the situation long-wave unstable for any Galileo number. It also strongly influences the short-wave P-mode which becomes the most critical for large enough Galileo numbers. Furthermore, from the boundary curves between absolute and convective instabilities (AI/CI) calculated for both the long-wave instability (S- and H-modes) and the short-wave instability (P-mode), it is shown that for small Galileo numbers the AI/CI boundary curves are determined by the long-wave instability, while for large Galileo numbers they are determined by the short-wave instability

On the effect of thermodiffusion on solute segregation during the growth of semiconductor materials by the vertical Bridgman method

The effect of thermodiffusion on dopant distribution in the melt and in the grown crystal is investigated numerically for a vertical Bridgman configuration for situations of pure thermal convection corresponding to dilute alloys. The dopant distribution is shown to be significantly affected by the Soret parameter value. The sensitivity of the system to a variety of parameters, including the Grashof number and the so-called furnace residence time, i.e. the time during which the crucible is maintained in the furnace before initiating the solidification process, is assessed by means of parametric simulations. Moreover, the results indicate that variations in the sign of the Soret parameter can lead to diametrically opposite behaviours, while an increase in the intensity of the thermal convection generally leads to a mitigation of the effects induced by thermodiffusion. On the basis of the numerical results some useful criteria are drawn which could help crystal growers to discern the complex interrelations among the various parameters under one’s control (that are not independent of one another) and to elaborate rational guidelines relating to strategies to be used to improve the quality of the resulting crystals

Effet d'un champ magnétique uniforme sur les instabilités de Rayleigh–Bénard avec effet Soret. Influence of a magnetic field on the stability of a binary fluid with Soret effect

L’effet de l’intensité et de l’orientation d’un champ magnétique uniforme sur la transition critique au sein d’une couche fluide binaire, électriquement conductrice, stratifiée en température et en concentration, en prenant en considération l’effet Soret, est étudié numériquement. Pour une telle configuration, les résultats ont mis en évidence que les seuils critiques correspondant à un champ magnétique de direction quelconque peuvent se déduire de ceux obtenus pour un champ magnétique vertical et que les axes des rouleaux marginaux des modes instables sont désormais alignés avec la composante horizontale du champ magnétique. Par ailleurs, une étude analytique est menée pour étudier l’impact du champ magnétique sur les instabilités monocellulaires. L’effet du champ magnétique sur de telles instabilités a mis en évidence un phénomène inédit consistant à modifier profondément la nature des modes instables, qui perdent leur caractère monocellulaire pour retrouver leur aspect à plusieurs rouleaux qui les caractérisaient sans champ magnétique pour ψψ0, la valeur du nombre de Hartmann Ha(ψ, Le)correspondant à cette transition responsable d’une modification significative des transferts de masse et de chaleur peut être déterminée à partir des relations analytiques établies dans le cadre de ce travail

Intracardiac thrombus in Behçet's disease: Two case reports

Intracardiac thrombus in Behçet's disease is an extremely rare manifestation. We report two such cases. A 20-year-old man presented with dyspnoea, cough and haemoptysis. Right heart thrombus associated with pulmonary artery aneurysm and thromboembolism was identified by helical CT and transoesophageal echocardiography. The second case was a 29-year-old male admitted for fever and chest pain. A diagnosis of right atrial thrombosis associated with pulmonary embolism and hyperhomocysteinemia was made. Due to the absence of haemodynamic compromise, medical management consisting of immunosupressive and anticoagulation therapy was adopted which resulted in complete dissolution of the thrombus with dramatic clinical improvement in both cases of clinical status. Conclusion: intracardiac thrombus is a rare complication of Behçet's disease. As shown in our patients, medical treatment should be considered as the first line

Y-shaped jets driven by an ultrasonic beam reflecting on a wall

International audienceThis paper presents an original experimental and numerical investigation of acoustic streaming driven by an acoustic beam reflecting on a wall. The water experiment features a 2 MHz acoustic beam totally reflecting on one of the tank glass walls. The velocity field in the plane containing the incident and reflected beam axes is investigated using Particle Image Velocimetry (PIV). It exhibits an original y-shaped structure: the impinging jet driven by the incident beam is continued by a wall jet, and a second jet is driven by the reflected beam, making an angle with the impinging jet. The flow is also numerically modeled as that of an incompressible fluid undergoing a volumetric acoustic force. This is a classical approach, but the complexity of the acoustic field in the reflection zone, however, makes it difficult to derive an exact force field in this area. Several approximations are thus tested; we show that the observed velocity field only weakly depends on the approximation used in this small region. The numerical model results are in good agreement with the experimental results. The spreading of the jets around their impingement points and the creeping of the wall jets along the walls are observed to allow the interaction of the flow with a large wall surface, which can even extend to the corners of the tank; this could be an interesting feature for applications requiring efficient heat and mass transfer at the wall. More fundamentally, the velocity field is shown to have both similarities and differences with the velocity field in a classical centered acoustic streaming jet. In particular its magnitude exhibits a fairly good agreement with a formerly derived scaling law based on the balance of the acoustic forcing with the inertia due to the flow acceleration along the beam axis

Action des ondes acoustiques sur la stabilité des écoulements en cavité 3D chauffée latéralement

Nous nous intéressons à l'influence des ondes acoustiques sur les transitions d'écoulement dans une cavité parallélépipédique chauffée latéralement et contenant un fluide de nombre de Prandtl Pr=0.01. Nous avons tout d'abord déterminé les diagrammes de bifurcation relatifs à l'écoulement généré par le chauffage latéral de la cavité, d'une part sans l'influence d'ondes acoustiques et d'autre part lorsque la cavité est soumise à un faisceau acoustique de section carrée et de taille adimensionnée Hb=0.62. Les solutions sont déterminées à l'aide d'une méthode de continuation et l'étude de leur stabilité, obtenue par une méthode d'Arnoldi, permet de cerner l'existence de points de bifurcation. Le tracé de ces diagrammes a montré une forte influence des ondes acoustiques sur les seuils de transition stationnaire et oscillatoire qui caractérisent cette situation. Nous avons ensuite suivi la variation de ces points de bifurcation stationnaire et oscillatoire. Les résultats ont montré que ces seuils de transition augmentent assez fortement avec l'intensité des ondes acoustiques, indiquant une bonne stabilisation de l'écoulement convectif par les ondes acoustiques

Apolipoprotein gene polymorphisms and plasma levels in healthy Tunisians and patients with coronary artery disease

<p>Abstract</p> <p>Aim</p> <p>To analyze apolipoprotein gene polymorphisms in the Tunisian population and to check the relation of these polymorphisms and homocysteine, lipid and apolipoprotein levels to the coronary artery disease (CAD).</p> <p>Methods</p> <p>In healthy blood donors and in patients with CAD complicated by myocardial infarction (MI) four apolipoprotein gene polymorphisms [APO (a) PNR, APO E, APO CI and APO CII] were determined and plasma levels of total homocysteine, total cholesterol (TC), triglycerides (TG), HDL-cholesterol (HLD-C) and apolipoproteins (apo A-I, Apo B, Apo E) were measured.</p> <p>Results</p> <p>Analysis of the four apolipoprotein gene polymorphisms shows a relative genetic homogeneity between Tunisian population and those on the other side of Mediterranean basin. Compared to controls, CAD patients have significantly higher main concentrations of TC, TG, LDL-C, apo B and homocysteine, and significantly lower ones of HDL-C, apo A-I and apo E. The four apolipoprotein gene polymorphisms have not showed any significant differences between patients and controls. However, the APO E4 allele appears to be associated to the severity of CAD and to high levels of atherogenic parameters and low level of apo E, which has very likely an anti-atherogenic role.</p> <p>Conclusion</p> <p>Although APO (a) PNR, APO CI and APO CII genes are analyzed in only few populations, they show a frequency distribution, which is not at variance with that of APO E gene and other widely studied genetic markers. In the Tunisian population the APO E 4 appears to be only indirectly involved in the severity of CAD. In the routine practice, in addition of classic parameters, it will be useful to measure the concentration of apo E and that of Homocysteine and if possible to determine the APO E gene polymorphism.</p

042: Real life dual antiplatelet therapy after NSTE-ACS in a Tunisian population: is there a need for 12 months of treatment?

AimEven if the recommended duration for dual antiplatelet therapy (DAT) after non ST elevation acute coronary syndromes (NSTE-ACS) is 12 months, evidence concerning the benefit of clopidogrel adjunction especially beyond 3 months remains poor. The aim of the study was to assess the effective clopidogrel intake and the incidence of a composite endpoint including all causes death and non fatal myocardial infarction in a Tunisian population after NSTE-ACS.MethodsWe included patients admitted for NSTE-ACS in our department between January 2010 and August 2011 for whom long term evaluation was possible. In-hospital deaths were excluded (including post operative deaths). By telephone follow up, we evaluated the effective DAT duration and the occurrence of all causes death and non-fatal myocardial infarction.ResultsOne hundred thirty patients were included. Mean (SD) follow up was 261 (99) days. DAT was effectively observed during 94(103 days (extremes ranging from 0 to 360 days). Angioplasty was performed in 51.5%, coronary artery bypass graft in 8.4% and medical therapy was considered in 40.1%. In 35 (26.9%) patients, aspirin was the only antiplatelet therapy taken after discharge although DAT was prescribed; 46.9% of the patients took the DAT for more than 3 months, and 23.1% for more than 6 months. The composite endpoint occurred in 6 (4.6%) patients: 2 deaths (both of cardiac causes) and 4 myocardial infarctions. Three of them were under DAT, and the 3 others remained event free during 7, 240 and 270 days after clopidogrel withdrawal. These findings suggest that DAT does not protect against death or myocardial infarction. The rebound phenomenon after clopidogrel withdrawal isn’t patent in our population.ConclusionIn the Tunisian context, DAT observance is poor after NSTE-ACS. Death and non fatal myocardial infarction don’t seem to be reduced by DAT and the rebound phenomenon after clopidogrel withdrawal isn’t patent. This may be in part attributed to the small sample of population and the predominantly low risk (as assessed by TIMI risk score), but larger studies are needed to strengthen the evidence for DAT after NSTE-ACS

Etude de stabilité linéaire de l'écoulement multicouche de films non-Newtoniens sur un plan incliné

Il s'agit d'une analyse temporelle de stabilité linéaire de l'écoulement stratifié de films sur un plan incliné. Nous nous sommes intéressés au cas de deux couches non miscibles de fluides non-newtoniens. La rhéologie des fluides étudiés est décrite par la loi de Carreau, selon laquelle une augmentation du taux de cisaillement dans l'écoulement génère une diminution locale de la viscosité du fluide. Une méthode spectrale de collocation basée sur les polynômes de Chebyshev a été employée pour la discrétisation de l'équation d'Orr-Sommerfeld généralisée, résolue sous forme d'un problème aux valeurs propres. Les effets de la stratification en densité ont été étudiés dans le cas où la couche inférieure est la moins visqueuse. Cette situation est favorable à l'apparition des instabilités interfaciales. Nous avons pu mettre en évidence l'existence d'un rapport de densité seuil à partir duquel on observe un basculement d'une instabilité de grande longueur d'onde à une instabilité de longueur d'onde modérée. L'influence des propriétés rhéofluidifiantes des fluides sur la position de ce seuil a été également étudiée

Structures convectives dans les écoulements à surface libre

Notre travail vise à évaluer le rôle de phénomènes perturbateurs dans la dynamique d'un système fluide chauffé avec surface libre. La variation des seuils primaires de déclenchement de la convection a d'abord été calculée en fonction de la taille de la cellule, l'influence de la tension de surface et du transfert de chaleur sur ces seuils de déclenchement (et au-delà) a également été traité