Nonparallel stability of three-dimensional compressible boundary layers. Part 1: Stability analysis

A compressible linear stability theory is presented for nonparallel three-dimensional boundary-layer flows, taking into account the normal velocity component as well as the streamwise and spanwise variations of the basic flow. The method of multiple scales is used to account for the nonparallelism of the basic flow, and equations are derived for the spatial evolution of the disturbance amplitude and wavenumber. The numerical procedure for obtaining the solution of the nonparallel problem is outlined

Goertler instability in compressible boundary layers along curved surfaces with suction and cooling

The Goertler instability of the laminar compressible boundary layer flows along concave surfaces is investigated. The linearized disturbance equations for the three-dimensional, counter-rotating streamwise vortices in two-dimensional boundary layers are presented in an orthogonal curvilinear coordinate. The basic approximation of the disturbance equations, that includes the effect of the growth of the boundary layer, is considered and solved numerically. The effect of compressibility on critical stability limits, growth rates, and amplitude ratios of the vortices is evaluated for a range of Mach numbers for 0 to 5. The effect of wall cooling and suction of the boundary layer on the development of Goertler vortices is investigated for different Mach numbers

Nonparallel stability of two-dimensional nonuniformly heated boundary-layer flows

An analysis is presented for the linear stability of water boundary-layer flows over nonuniformly flat plates. Included in the analysis are disturbances due to velocity, pressure, temperatures, density, and transport properties as well as variations of the liquid properties with temperature. The method of multiple scales is used to account for the nonparallelism of the mean flow. In contrast with previous analyses, the nonsimilarity of the mean flow is taken into account. No analysis agrees, even qualitatively, with the experimental data when similar profiles are used. However, both the parallel and nonparallel results qualitatively agree with the experimental results of Strazisar and Reshotko when nonsimilar profiles are used

On the formulation of the dynamic mixed subgrid‐scale model

The dynamic mixed subgrid‐scale model of Zang et al. [Phys. Fluids A 5, 3186 (1993)] (DMM1) is modified with respect to the incorporation of the similarity model in order to remove a mathematical inconsistency. Compared to DMM1, the magnitude of the dynamic model coefficient of the modified model (DMM2) is increased considerably, while it is still significantly smaller than as occurs in the dynamic subgrid‐scale eddy‐viscosity model of Germano [J. Fluid Mech. 238, 325 (1992)] (DSM). Large eddy simulations(LES) for the weakly compressible mixing layer are conducted using these three models and results are compared with direct numerical simulation (DNS) data. LES based on DMM1 gives a significant improvement over LES using DSM, while even better agreement is achieved with DMM2

Effect of vitamin B17 on experimentally induced colon cancer in adult male albino rat

Background: Colon cancer is considered to be the third most common cancer worldwide. At diagnosis of colon cancer, 3.7–11% developed bone metastasis. Diet based strategies are important for prevention and treatment of colon cancer. This study investigated the effect of vitamin B17 on a DMH induced rat model of colon cancer. Materials and methods: Eighty young adult male albino rats were divided into five groups: group I (control group), group II (vitamin B17), group III (colon cancer), group IV (protected) and group V (treated). Distal colon sections were prepared for light and scanning electron microscopic examination. Lumbar vertebrae specimens were prepared for light microscopic study. Morphometric and statistical analysis were done. Results: In comparison with the control, both colon cancer and treated groups showed invasion of the colonic tissue by pleomorphic branching colonic glands of variable shapes and sizes lined with dysplastic elongated hyperchromatic nuclei with frequent mitotic figures or stratified multi-layered crowded nuclei with an extremely significant (p < 0.0001) reduction of goblet cell number when compared to the control together with major pathological bone changes were observed in colon cancer and the treated groups. Conclusions: While the protected group showed impressive improvement of all previously mentioned diameters

Molecular Identification, Antimicrobial and Antioxidant Activities of the Tropical Seagrass Halophila stipulacea Grown in El-Bardawil Lake, Egypt

Abstract: Halophila stipulacea a tropical seagrass entered the Mediterranean Sea from the Red Sea after the opening of the Suez Canal in 1869. Up to date, no genetic studies of Halophila stipulacea from El-Bardawil Lake are available. In order to verify the molecular identity of El-Bardawil lake isolates of Halophila stipulacea, employing Random Amplified Polymorphic analysis (RAPD) which carried out using six decamer primers, 26 amplified bands were produced, the highest number of amplified fragments (11 fragments) was produced by primer OP C04 and the OP B07 whereas OPC03 was the lowest primer (7 fragments). In this study, aqueous extract from Halophila stipulacea was assayed against some microorganisms using zone inhibition technique. The extract showed moderate activity against Gram-positive bacteria and high activity against filamentous Aspergillus niger fungus. In addition the antioxidant activity of the methanolic extract was studied and showed a moderate activity of the Halophila stipulacea seagrass reached 40%. The total phenolic content in the seagrass extract was 0.523 mg tannic acid equivalent /g

Decay constants, semi-leptonic and non-leptonic decays in a Bethe-Salpeter Model

We evaluate the decay constants for the B and $D$ mesons and the form factors for the semileptonic decays of the B meson to $D$ and $D^*$ mesons in a Bethe-Salpeter model. From data we extract $V_{cb}=0.039 \pm 0.002$ from ${\bar B} \to D^* l {\bar{\nu}}$ and $V_{cb}=0.037 \pm 0.004$ from ${\bar B} \to D l {\bar{\nu}}$ decays. The form factors are then used to obtain non-leptonic decay partial widths for $B\to D \pi (K)$ and $B \to D D (D_s)$ in the factorization approximation.Comment: 15 Pages, 3 Postscript figures (available also from [email protected]

Weak decays of the B_c meson to B_s and B mesons in the relativistic quark model

Semileptonic and nonleptonic decays of the B_c meson to B_s and B mesons, caused by the c\to s,d quark transitions, are studied in the framework of the relativistic quark model. The heavy quark expansion in inverse powers of the active c and spectator \bar b quark is used to simplify calculations while the final s and d quarks in the B_s and B mesons are treated relativistically. The decay form factors are explicitly expressed through the overlap integrals of the meson wave functions in the whole accessible kinematical range. The obtained results are compared with the predictions of other approaches.Comment: 24 pages, 12 figures, version to appear in Eur. Phys. J.

Characterization and Breakdown of South Gabal EL A’urf Polymineralized ore Material

The polymineralized ore material of south Gabal El-A’urf area hosts several economic minerals. These include tanteuxenite, monazite, bastanasite, anatase, as well as zircon. The corresponding interesting rare metals of these minerals include Nb, Ta, lanthanides (REE), Ti, and Zr. Different breakdown techniques have been investigated namely; agitation, pug and fusion. The latter technique is found to be preferred under the following conditions; potassium bisulphate ore/reagent weight ratio of 1/3 at 650 ºC for 3h. The realized dissolution efficiencies for all metal values were as follows 98.0% and 99.3% for Nb and Ta respectively as well as complete dissolution for lanthanides (REE) and 94% for Ti while Zr did not exceed 20% and concentrated in the residue left behind. This study of breakdown techniques aims to characterization of ore material of south Gabal El-A’urf area as well as preparing a proper leach liquor suitable for further recovery procedure and obtain pure remarket able products