Instability of dilute bidisperse suspensions resulting from particle interactions

Experimental evidence shows that initially homogeneous bidisperse suspensions become unstable due to initial perturbations in particle concentrations. As a result of this instability, the particles segregate and form vertical streams (so-called fingering phenomena) during their sedimentation process.In this thesis we deal with modelling the macroscopic behaviour and studying the stability of the suspension. A continuum model is developed and used in order to model the formation of vertical streams and study the instability of dilute bidisperse suspensions. The macroscopic behaviour of the suspension is closely related to and depends on the microstructure and the relative motion of particles in the suspension. Thus the calculation of the trajectories of the particles is an essential step in the mathematical modelling of the behaviour of the suspension. Classical low Reynolds number hydrodynamics predicts that sedimenting solid spherical particles approach one another typically to within 10$sp{-3}$ of a radius, indicating that the surface roughness of the particles can become significant and takes part in the interaction process. The trajectories of two solid spheres sedimenting in either a quiescent fluid or a shear flow are calculated. It is shown that as a result of physical contact between the particles, a horizontal flux of each species of particles is generated. These results are used to calculate the detailed macroscopic equations for the concentrations. Finally the macroscopic equations are solved for two specific suspensions using a linear stability analysis and also numerically using a Control-Volume-Finite-Difference technique. The obtained results predict the instability of these specific suspensions and the formation of vertical streams which have been observed experimentally

Evaluation of disinfecting effect of 5% sodium hypochlorite solution diluted to 2:100 along with the use of disposable covers on HBV contaminated dental office surfaces and equipments

Background and Aim: The efficiency of disinfecting materials and procedures in removal of contamination from dental surfaces and equipments is essential. In authors' previous study, daily use of 2:100 dilution of 5% sodium hypochlorite in water and disposable covers were recommended since HBV contamination was found on semi-critical parts of the operative dentistry department. The aim of this study was to evaluate the HBV contamination following application of the recommended procedures.Materials and Methods: The study was conducted in two parts. In the first cross-sectional part, samples were collected from 17 sites of dental surfaces. In the second interventional part samples were collected from 10 sites of 9 dental and 3 sites of 2 light cure units, before and after disinfection with 5% sodium hypochlorite solution diluted to 2:100. Sterile cotton swabs moistened with sterile BSAS (Bovine Serum Albumin in Sodium Chloride) solution were used for sampling. Samples were tested by PCR technique in Pasteur Institute, Iran.Results: None of the samples collected in the first part of the study showed contamination. In the second part of the study, from 96 samples taken from various parts of dental and light cure units, before and after disinfection, there was only one HBV contaminated site before disinfection which showed no contamination after disinfection.Conclusion: Based on the results of this study, disinfecting procedure with 5% sodium hypochlorite solution diluted to 2:100 along with using disposable covers is effective in preventing HBV contamination

Dynamic and Static Properties of Double-Layered Compound Acoustic Black Hole Structures

2017-2018 > Academic research: refereed > Publication in refereed journal201805 bcrcAccepted ManuscriptRGCOthersNational Science Foundation of China; NUAA State Key Laboratory ProgramPublishe

Clinical factors affecting the translucency of monolithic Y-TZP ceramics

The use of monolithic yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics in aesthetically critical regions is questionable because of the insufficient translucency and opacity of the restorations. Intrinsic (manufacturing process) and extrinsic factors (laboratory procedures and clinical factors) can affect the translucency of monolithic zirconia. In this narrative review, the clinical factors (thickness, cementation type, colour of the monolithic zirconia, surface finishing methods and wear, dental background, cement colour, low temperature degradation) affecting the translucency of monolithic Y-TZP ceramics were reported

South African medicinal plant extracts active against influenza A virus

Abstract Background Influenza infection remains a major health threat for animals and humans which crucially requires effective antiviral remedies. The usage of herbal medications as readily available alternatives for their compatibility with the body and fewer side effects compared to synthetic chemical treatments has become popular globally. The aim of this study was to investigate and screen in vitro anti-influenza activity of extracts of five South African medicinal plants, namely Tabernaemontana ventricosa, Cussonia spicata, Rapanea melanophloeos, Pittosporum viridiflorum and Clerodendrum glabrum, species which are used traditionally for the treatment of several diseases such as inflammatory and respiratory diseases. Methods Methanol, ethanol (100% and 30%), acetone, hot and cold water extracts of the powdered plants leaves were obtained by standard methods. The cytotoxicity was determined by the MTT colorimetric assay on MDCK cells. The concentrations below CC50 values were tested for antiviral activity against influenza A virus (IAV) in different combination treatments. The effect of extracts on viral surface glycoproteins and viral titer were tested by HI and HA virological assays, respectively. Results Based on the applied methods, the most effective results against IAV were obtained from Rapanea melanophloeos methanol leaf extract (EC50 = 113.3 μg/ml) and Pittosporum viridiflorum methanol, 100% and 30% ethanol and acetone leaf extracts (EC50 values = 3.6, 3.4, 19.2, 82.3 μg/ml, respectively) in all types of combined treatments especially in pre- and post-penetration combined treatments with highly significant effects against viral titer (P ≤ 0.01). Conclusion The outcomes offer for the first time a scientific basis for the use of extracts of Rapanea melanophloeos and Pittosporum viridiflorum against IAV. It is worth focusing on the isolation and identification of effective active compounds and elucidating the mechanism of action from these species. However, Tabernaemontana ventricosa, Cussonia spicata and Clerodendrum glabrum leaf extracts were ineffective in vitro in this study