Semi-similar solutions of the unsteady compressible second-order boundary layer flow at the stagnation point

Semi-similar solutions of the unsteady compressible laminar boundary layer flow over two-dimensional and axisymmetric bodies at the stagnation point with mass transfer are studied for all the second-order boundary layer effects when the free stream velocity varies arbitrarily with time. The set of partial differential equations governing the unsteady compressible second-order boundary layers representing all the effects are derived for the first time. These partial differential equations are solved numerically using an implicit finite-difference scheme. The results are obtained for two particular unsteady free stream velocity distributions: (a) an accelerating stream and (b) a fluctuating stream. It is observed that the total skin friction and heat transfer are strongly affected by the surface mass transfer and wall temperature. However, their variation with time is significant only for large times. The second-order boundary layer effects are found to be more pronounced in the case of no mass transfer or injection as compared to that for suction. Résumé Des solutions semi-similaires d'écoulement variable compressible de couche limite sur des corps bi-dimensionnels thermique, sont étudiées pour tous les effets de couche limite du second ordre, lorsque la vitesse de l'écoulement libre varie arbitrairement avec le temps. Le systéme d'équations aux dérivées partielles représentant tous les effets est écrit pour la premiére fois. On le résout numériquement á l'aide d'un schéma implicite aux différences finies. Les résultats sont obtenus pour deux cas de vitesse variable d'écoulement libre: (a) un écoulement accéléré et (b) un écoulement fluctuant. On observe que le frottement pariétal total et le transfert de chaleur sont fortement affectés par le transfert de masse et la température pariétaux. Néanmoins, leur variation avec le temps est sensible seulement pour des grandes durées. Les effets sont trouvés plus prononcés dans le cas de l'absence du transfert de masse ou de l'injection par rapport au cas de l'aspiration.

Unsteady mixed convection with double diffusion over a horizontal cylinder and a sphere within a porous medium

The combined effects of the permeability of the medium, magnetic field, buoyancy forces and dissipation on the unsteady mixed convection flow over a horizontal cylinder and a sphere embedded in a porous medium have been studied. The nonlinear coupled partial differential equations with three independent variables have been solved numerically using an implicit finite-difference scheme in combination with the quasilinearization technique. The skin friction, heat transfer and mass transfer increase with the permeability of the medium, magnetic field and buoyancy parameter. The heat and mass transfer continuously decrease with the stream-wise distance, whereas the skin friction increases from zero, attains a maximum and then decreases to zero. The skin friction, heat transfer and mass transfer are significantly affected by the free stream velocity distribution. The effect of dissipation parameter is found to be more pronounced on the heat transfer than on the skin friction and mass transfer

Antibodies raised against denatured DNA bind to double-stranded DNA

Antibodies raised against denatured DNA complexed with methylated bovine serum albumin have been reported to react with ssDNA but not with dsDNA. Using a highly sensitive avidin-biotin microELISA, we report that such antibodies also bind to dsDNA. Antibodies which reacted with ssDNA and dsDNA were found to be IgG type. The antibodies did not react with tRNA and rRNA. The binding of antibodies to dsDNA was partially inhibited dy individual deoxyribonucleotides. ssDNA as well as dsDNA inhibited the binding of antibodies to dsDNA. The binding of these antibodies to supercoiled and relaxed forms of pBR322 DNA was demonstrated by gel retardation assay. The cross-reaction with ssDNA was observed even after affinity purification on native DNA-cellulose. The antibodies were also shown to bind to poly(dA-dT)·poly(dA-dT)

Second-order boundary-layer effects for the unsteady laminar incompressible three-dimensional stagnation-point flow

All the second-order boundary-layer effects on the unsteady laminar incompressible flow at the stagnation-point of a three-dimensional body for both nodal and saddle point regions have been studied. It has been assumed that the free-stream velocity, wall temperature and mass transfer vary arbitrarily with time. The effect of the Prandtl number has been taken into account. The partial differential equations governing the flow have been derived for the first time and then solved numerically unsteady free-stream velocity distributions, the nature of the using an implicit finite-difference scheme. It is found that the stagnation point and the mass transfer strongly affect the skin friction and heat transfer whereas the effects of the Prandtl number and the variation of the wall temperature with time are only on the heat transfer. The skin friction due to the combined effects of first- and second-order boundary layers is less than the skin friction due to, the first-order boundary layers whereas the heat transfer has the opposite behaviour. Suction increases the skin friction and heat transfer but injection does the opposite

Effect of various factors influencing the delamination behavior of surfactant intercalated layered double hydroxides

The delamination-restacking behavior of a number of layered double hydroxides (LDHs) differing in [M-II]/[M-III] ratio, constituent metal ions and intercalated surfactant anions in different organic solvents has been studied. Colloidal dispersion due to delamination and the stability of the colloid obtained have been found to be not affected much by the nature of the constituent metal ions but increase with increase in the size of the surfactant anion. LDHs with low [M-II]/[M-III] ratio delaminate better than the ones with high [M-II]/[M-III] ratio. Delamination is best in alcohols such as 1-butanol, 1-hexanol, 1-octanol and I-decanol, while a little delamination occurs in nonpolar solvents such as hexane. In all the cases, the original layered solid could be obtained through restacking of layers from the colloidal dispersion.

Structural, dielectric and ferroelectric properties of four-layer Aurivillius phase Na0.5La0.5Bi4Ti4O15

Monophasic Na0.5La0.5Bi4Ti4O15 powders were synthesized via the conventional solid-state reaction route. The X-ray powder diffraction (XRD), selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) studies carried out on the as synthesized powdered samples confirmed the phase to be a four-layer Aurivillius that crystallizes in an orthorhombic A2(1)am space group. The microstructure and the chemical composition of the sintered sample were examined by scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDX). The dielectric properties of the ceramics have been studied in the 27-700 degrees C temperature range at various frequencies (100 Hz to 1 MHz). A sharp dielectric anomaly was observed at 580 degrees C for all the frequencies corresponding to the ferroelectric to paraelectric phase transition. Saturated ferroelectric hysteresis loops were observed at 200 degrees C and the associated remnant polarization (P-r) and coercive field (E-c) were found to be 7.4 mu C/cm(2) and 34.8 kV/cm, respectively. AC conductivity analysis confirmed the existence of two different conduction mechanisms in the ferroelectric region. Activation energies calculated from the Arrhenius plots were similar to 0.24 eV and similar to 0.84 eV in the 300-450 degrees C and 450-580 degrees C temperature ranges, respectively. (C) 2010 Elsevier B.V. All rights reserved.

Binding of deoxyadenylate and deoxycytidylate antibodies to double-stranded DNA

Antibodies raised against deoxyadenylate and deoxycytidylate were found to react with double stranded DNA as assessed by highly sensitive avidin-biotin microELISA. The binding was specific as it was completely inhibited by the homologous hapten. The antibodies did not react with tRNA and rRNA. These antibodies were also shown to react with supercoiled and relaxed forms of pBR322 DNA as demonstrated by gel retardation assay. ssDNA, single-stranded DNA; dsDNA, double-stranded DNA; CT DNA, calf thymus DNA; AB microELISA, avidin-biotin microELISA; dpA, deoxyadenylate; dpC, deoxycytidylate; avidin-HRP, avidin-horseradish peroxidase

Evidence for double valence fluctuation in metallic oxides of lead

The possible role of double valence fluctuation in both lead and oxide ions with reference to metallization in oxides of lead is examined by x-ray-photoemission spectroscopy, ultraviolet-photoemission spectroscopy (UPS), and 207Pb NMR studies. The double valence fluctuations may be viewed as Pb4++2O2-⇄Pb2+O22-. While the insulating oxides PbO, Pb3O4, and Sr2PbO4 show a single oxide ion, O2- characterized by O(1s) at 529.7 eV, the insulating peroxide BaO2 is characterized by the ion O22- with a single O(1s) at 533 eV. The metallic PbO2, BaPbO3, BaBiPbO3, and SrPbO3 showed the occurrence of both O2- and O22- ions. The valence band in these compounds has also been studied by UPS, and clear evidence for the coexistence of O2- and O22- is seen in PbO2. A simultaneous study of 207Pb NMR suggests that the Pb ion could also exist in mixed-valence states. Qualitative arguments are presented to rationalize the existence of such mixed valences of the anion in metal oxides in general and their role in superconductivity.

Compressible Boundary-Layer Swirling Flow in a Nozzle and a Diffuser With Highly Cooled Wall

The steady laminar compressible boundary-layer swirling flow with variable gas properties and mass transfer through a conical nozzle, and a diffuser with a highly cooled wall has been studied. The partial differential equations governing the nonsimilar flow have been transformed to a system of coordinates using modified Lees transformation. The resulting equations are transformed into coordinates having finite ranges by means of a transformation which maps an infinite region into a finite region. The ensuing equations are then solved numerically using an implicit finite-difference scheme. The results indicate that the variation of the density-viscosity product across the boundary layer and mass transfer have strong effect on the skin friction and heat transfer. Separationless flow along the entire length of the diffuser can be obtained by applying suction. The results are found to be in good agreement with those of the local nonsimilarity method but they differ appreciably from those of the local similarity method.

Flow and heat transfer in steady laminar compressible boundary layer swirling flow in a nozzle

The axisymmetric steady laminar compressible boundary layer swirling flow of a gas with variable properties in a nozzle has been investigated. The partial differential equations governing the non-similar flow have been transformed into new co-ordinates having finite ranges by means of a transformation which maps an infinite range into a finite one. The resulting equations have been solved numerically using an implicit finite-difference scheme. The computations have been carried out for compressible swirling flow through a convergent conical nozzle. The results indicate that the swirl exerts a strong influence on the longitudinal skin friction, but its effect on the tangential skin friction and heat transfer is comparatively small. The effect of the variation of the density-viscosity product across the boundary layer is appreciable only at low-wall temperature. The results are in good agreement with those of the local-similarity method for small values of the longitudinal distance.

Laminar compressible boundary layer flow at a three-dimensional stagnation point with vectored mass transfer

The effect of surface mass transfer velocities having normal, principal and transverse direction components (�vectored� suction and injection) on the steady, laminar, compressible boundary layer at a three-dimensional stagnation point has been investigated both for nodal and saddle points of attachment. The similarity solutions of the boundary layer equations were obtained numerically by the method of parametric differentiation. The principal and transverse direction surface mass transfer velocities significantly affect the skin friction (both in the principal and transverse directions) and the heat transfer. Also the inadequacy of assuming a linear viscosity-temperature relation at low-wall temperatures is shown.

System effects in double‐channel gated‐integrator‐based deep‐level transient spectroscopy

The effects of the two sampling gate positions, and their widths and the integrator response times on the position, height, and shape of the peaks obtained in a double‐channel gated‐integrator‐based deep‐level transient spectroscopy (DLTS) system are evaluated. The best compromise between the sensitivity and the resolution of the DLTS system is shown to be obtained when the ratio of the two sampling gate positions is about 20. An integrator response time of about 100 ms is shown to be suitable for practical values of emission time constants and heating rates generally used.

Unsteady three-dimensional boundary layer flow over a flat plate with attached cylinder

The unsteady laminar incompressible three-dimensional boundary layer flow and heat transfer on a flat plate with an attached cylinder have been studied when the free stream velocity components and wall temperature vary inversely as linear and quadratic functions of time, respectively. The governing semisimilar partial differential equations with three independent variables have been solved numerically using a quasilinear finite-difference scheme. The results indicate that the skin friction increases with parameter ? which characterizes the unsteadiness in the free stream velocity and the streamwise distance Image , but the heat transfer decreases. However, the skin friction and heat transfer are found to change little along Image . The effect of the Prandtl number on the heat transfer is found to be more pronounced when ? is small, whereas the effect of the dissipation parameter is more pronounced when ? is comparatively large.