Unsteady mixed convection flow in stagnation region adjacent to a vertical surface

The unsteady two-dimensional laminar mixed convection flow in the stagnation region of a vertical surface has been studied where the buoyancy forces are due to both the temperature and concentration gradients. The unsteadiness in the flow and temperature fields is caused by the time-dependent free stream velocity. Both arbitrary wall temperature and concentration, and arbitrary surface heat and mass flux variations have been considered. The Navier-Stokes equations, the energy equation and the concentration equation, which are coupled nonlinear partial differential equations with three independent variables, have been reduced to a set of nonlinear ordinary differential equations. The analysis has also been done using boundary layer approximations and the difference between the solutions has been discussed. The governing ordinary differential equations for buoyancy assisting and buoyancy opposing regions have been solved numerically using a shooting method. The skin friction, heat transfer and mass transfer coefficients increase with the buoyancy parameter. However, the skin friction coefficient increases with the parameter lambda, which represents the unsteadiness in the free stream velocity, but the heat and mass transfer coefficients decrease. In the case of buoyancy opposed flow, the solution does not exist beyond a certain critical value of the buoyancy parameter. Also, for a certain range of the buoyancy parameter dual solutions exist.

Interaction of rhodium(III) with DNA

The nature of interaction of Rh(III) with DNA was studied using viscometry and ultraviolet, visible and infrared spectroscopy. The rate of interaction was found to be very slow at room temperature taking several days for completion. The time needed to attain equilibrium is dependent on the concentrations of metal ion, higher the concentration shorter the period required for equilibration. Visible spectra of Rh(III) were found to alter considerably in the presence of DNA. An increase in absorbance and a red shift were observed in the ultraviolet spectra of DNA in the presence of Rh(III). The specific viscosity of DNA solution was found to decrease asymptotically with time and concentrations of metal ion. The melting temperature of DNA was found to increase at lower metal ion concentrations, whereas at higher values a decrease was obtained. At still higher metal ion concentrations (Image ) a ‘nonmeltable state’ of DNA was observed. These results seem to indicate that Rh(III) binds both with the phosphate and the bases of the DNA.

Heat conduction with a phase change in a cylindrical mould

Analytical short time solution of moving boundary in heat conduction in a cylindrical mould under prescribed flux boundary condition has been studied in this paper. Partial differential equations are converted to integro-differential equations. These integro-differential equations which are coupled have been solved analytically for short time by choosing suitable series expansions for the unknown quantitities.

Exact solution for the unsteady motion of a viscous-fluid in a porous annulus

An exact solution to the problem of time-dependent motion of a viscous fluid in an annulus with porous walls is obtained under the assumption that the rate of suction at one wall is equal to the rate of injection at the other. Finite Hankel transform is used to obtain a closed-form solution for the axial velocity. The average axial velocity profiles are depicted graphically.

Dilute solution properties of methyl methacrylate—acrylonitrile copolymer (MA2)

This article deals with studies of the dilute solution properties of methyl methacrylate-acrylonitrile (MMA-AN) copolymer of 0.415 mole fraction (mf) of acrylonitrile composition. Mark—Houwink parameters for this copolymer have been evaluated in acetonitrile (MeCN), 2-butanone (MEK), dimethyl formamide (DMF), and γ-butyrolactone (γ-BL). The Mark-Houwink exponent a in all four solvents at all temperatures is larger than the corresponding values of the parent homopolymers. The solvent power is in the order of DMF < γ–BL < MEK < MeCN; [η] decreases with an increase in temperature, which is behavior characteristic of polymers in good solvent. The unperturbed dimensions (K0) values, obtained by the Stockmayer–Fixman method, are lower than those for the parent homopolymers and depend on solvent as well as temperature. The solute—solvent interaction parameter X1 values are close to 0.5; X1 is independent of temperature. The excess interaction parameter XABvalues are negative. The results for this copolymer system in regard to low second virial coefficient A2, large X1, and high a values suggest that the large extension of these copolymer chains is due to the unusual short-range interactions.

Comparative study of different formulations and solution methods for two phase flow in saturated porous media

Six models (Simulators) are formulated and developed with all possible combinations of pressure and saturation of the phases as primary variables. A comparative study between six simulators with two numerical methods, conventional simultaneous and modified sequential methods are carried out. The results of the numerical models are compared with the laboratory experimental results to study the accuracy of the model especially in heterogeneous porous media. From the study it is observed that the simulator using pressure and saturation of the wetting fluid (PW, SW formulation) is the best among the models tested. Many simulators with nonwetting phase as one of the primary variables did not converge when used along with simultaneous method. Based on simulator 1 (PW, SW formulation), a comparison of different solution methods such as simultaneous method, modified sequential and adaptive solution modified sequential method are carried out on 4 test problems including heterogeneous and randomly heterogeneous problems. It is found that the modified sequential and adaptive solution modified sequential methods could save the memory by half and as also the CPU time required by these methods is very less when compared with that using simultaneous method. It is also found that the simulator with PNW and PW as the primary variable which had problem of convergence using the simultaneous method, converged using both the modified sequential method and also using adaptive solution modified sequential method. The present study indicates that pressure and saturation formulation along with adaptive solution modified sequential method is the best among the different simulators and methods tested.

Precursor Dependent Microstructure Evolution and Nonstoichiometry in Nanostructured Cerium Oxide Coatings Using the Solution Precursor Plasma Spray Technique

A solution precursor plasma spray (SPPS) technique has been used for direct deposition of cerium oxide nanoparticles (CNPs) from various cerium salt solutions as precursors. Solution precursors were injected into the hot zone of a plasma plume to deposit CNP coatings. A numerical study of the droplet injection model has been employed for microstructure development during SPPS. The decomposition of each precursor to cerium oxide was analyzed by thermogravimetric-differential thermal analysis and validated by thermodynamic calculations. The presence of the cerium oxide phase in the coatings was confirmed by X-ray diffraction studies. Transmission electron microscopy studies confirmed nanocrystalline (grain size <14 nm) characteristic of the coatings. X-ray photoelectron spectroscopy studies indicated the presence of a high concentration of Ce3+ (up to 0.32) in the coating prepared by SPPS. The processing and microstructure evolution of cerium oxide coatings with high nonstoichiometry are reported.

Direct Growth of Gold Nanorods on Gold and Indium Tin Oxide Surfaces: Spectral, Electrochemical, and Electrocatalytic Studies

The surfactant-assisted seed-mediated growth method was used for the formation of gold nanorods (GNRs) directly on gold (Au) and indium tin oxide (ITO) surfaces. Citrate-stabilized similar to 2.6 nm spherical gold nanoparticles (AuNPs) were first self-assembled on ITO or Au surfaces modified with (3-mercaptopropyl)-trimethoxysilane (MPTS) sol-gel film and then immersed in a cationic surfactant growth solution to form GNRs. The growth of GNRs on the MPTS sol gel film modified ITO surface was monitored by UV-visible spectroscopy. The ITO surface with the attached spherical AuNPs shows a surface plasmon resonance band at 550 nm. The intensity of this absorption band increases while increasing the immersion time of the AuNP-modified ITO surface into the growth solution, and after 5 h, an additional shoulder band around 680 nm was observed. The intensity of this shoulder band increases, and it was shifted to longer wavelength as the immersion time of the AuNP-modified ITO surface into the growth solution increases. After 20 h, a predominant wave at 720 nm was observed along with a band at 550 nm. Further immersion of the modified ITO surface into the growth solution did not change the absorption characteristics. The bands observed at 550 and 720 nm were characteristics of GNRs, corresponding to transverse and longitudinal waves, respectively. The AFM images showed the presence of GNRs on the surface of the MPTS sol gel modified ITO surface with a typical length of similar to 100-120 nm and a width of similar to 20-22 nm in addition to a few spherical AuNPs, indicating that seeded spherical AuNPs were not completely involved in the GNRs' formation. Finally, the electrocatalytic activity of the surface-grown GNRs on the MPTS sol gel film modified Au electrode toward the oxidation of ascorbic acid (AA) was studied. Unlike a polycrystalline Au electrode, the surface-grown GNR-modified electrode shows two well-defined voltammetric peaks for AA at 0.01 and 0.35 V in alkaline, neutral, and acidic pHs. The cause for the observed two oxidation peaks for AA was due to the presence of both nanorods and spherical nanoparticles on the electrode surface. The presence of spherical AuNPs on the MPTS sol gel film oxidized AA at more positive potential, whereas the GNRs oxidized AA at less positive potential. The observed 340 mV less positive potential shift in the oxidation of AA suggested that GNRs are better electrocatalysts for the oxidation of AA than the spherical AuNPs.

Nonnegative integral solution of linear equations

A method to obtain a nonnegative integral solution of a system of linear equations, if such a solution exists is given. The method writes linear equations as an integer programming problem and then solves the problem using a combination of artificial basis technique and a method of integer forms.

An improved iterative finite element solution for pin joints

Accurate, reliable and economical methods of determining stress distributions are important for fastener joints. In the past the contact stress problems in these mechanically fastened joints using interference or push or clearance fit pins were solved using both inverse and iterative techniques. Inverse techniques were found to be most efficient, but at times inadequate in the presence of asymmetries. Iterative techniques based on the finite element method of analysis have wider applications, but they have the major drawbacks of being expensive and time-consuming. In this paper an improved finite element technique for iteration is presented to overcome these drawbacks. The improved iterative technique employs a frontal solver for elimination of variables not requiring iteration, by creation of a dummy element. This automatically results in a large reduction in computer time and in the size of the problem to be handled during iteration. Numerical results are compared with those available in the literature. The method is used to study an eccentrically located pin in a quasi-isotropic laminated plate under uniform tension.

A study of symbolic processing and computational aspects in helicopter dynamics

Even research models of helicopter dynamics often lead to a large number of equations of motion with periodic coefficients; and Floquet theory is a widely used mathematical tool for dynamic analysis. Presently, three approaches are used in generating the equations of motion. These are (1) general-purpose symbolic processors such as REDUCE and MACSYMA, (2) a special-purpose symbolic processor, DEHIM (Dynamic Equations for Helicopter Interpretive Models), and (3) completely numerical approaches. In this paper, comparative aspects of the first two purely algebraic approaches are studied by applying REDUCE and DEHIM to the same set of problems. These problems range from a linear model with one degree of freedom to a mildly non-linear multi-bladed rotor model with several degrees of freedom. Further, computational issues in applying Floquet theory are also studied, which refer to (1) the equilibrium solution for periodic forced response together with the transition matrix for perturbations about that response and (2) a small number of eigenvalues and eigenvectors of the unsymmetric transition matrix. The study showed the following: (1) compared to REDUCE, DEHIM is far more portable and economical, but it is also less user-friendly, particularly during learning phases; (2) the problems of finding the periodic response and eigenvalues are well conditioned.

Synthesis and electrical properties of the (PVA)(0.7)(Kl)(0.3)center dot xH(2)SO(4) (0 <= x <= 5) polymer electrolytes and their performance in a primary Zn/MnO2 battery

Solid acid polymer electrolytes (SAPE) were synthesised using polyvinyl alcohol, potassium iodide and sulphuric acid in different molar ratios by solution cast technique. The temperature dependent nature of electrical conductivity and the impedance of the polymer electrolytes were determined along with the associated activation energy. The electrical conductivity at room temperature was found to be strongly depended on the amorphous nature of the polymers and H2SO4 concentration. The ac (100 Hz to 10 MHz) and dc conductivities of the polymer electrolytes with different H2SO4 concentrations were analyzed. A maximum dc conductivity of 1.05 x 10(-3) S cm(-1) has been achieved at ambient temperature for electrolytes containing 5 M H2SO4. The frequency and temperature dependent dielectric and electrical modulus properties of the SAPE were studied. The charge transport in the present polymer electrolyte was obtained using Wagner's polarization technique, which demonstrated the charge transport to be mainly due to ions. Using these solid acid polymer electrolytes novel Zn/SAPE/MnO2 solid state batteries were fabricated and their discharge capacity was calculated. An open circuit voltage of 1.758V was obtained for 5 M H2SO4 based Zn/SAPE/MnO2 battery. (C) 2010 Elsevier Ltd. All rights reserved.

Nonsimilar boundary layers for non-Darcy mixed convection flow about a horizontal surface in a saturated porous medium

The nonsimilar non-Darcy mixed convection flow about a heated horizontal surface in a saturated porous medium has been studied when the surface temperature is a power function of distance (Tw = T∞ ± Axλ). The analysis is performed for the cases of parallel and stagnation flows with favourable induced pressure gradient. The partial differential equations governing the flow have been solved numerically using the Keller box method. The heat transfer is enhanced due to the buoyancy parameter and wall temperature, but the non-Darcy parameter reduces it. For non-Darcy flow, the similarity solution exists only for the case of parallel flow.

Analytical and numerical solutions of inward spherical solidification of a superheated melt with radiative-convective heat transfer and density jump at freezing front

Analytical and numerical solutions of a general problem related to the radially symmetric inward spherical solidification of a superheated melt have been studied in this paper. In the radiation-convection type boundary conditions, the heat transfer coefficient has been taken as time dependent which could be infinite, at time,t=0. This is necessary, for the initiation of instantaneous solidification of superheated melt, over its surface. The analytical solution consists of employing suitable fictitious initial temperatures and fictitious extensions of the original region occupied by the melt. The numerical solution consists of finite difference scheme in which the grid points move with the freezing front. The numerical scheme can handle with ease the density changes in the solid and liquid states and the shrinkage or expansions of volumes due to density changes. In the numerical results, obtained for the moving boundary and temperatures, the effects of several parameters such as latent heat, Boltzmann constant, density ratios, heat transfer coefficients, etc. have been shown. The correctness of numerical results has also been checked by satisfying the integral heat balance at every timestep.

A photoelastic approach to framed structure-foundation beam-soil interaction

The interaction of a framed structure with a foundation beam resting on an elastic medium, representing the soil, has been studied using the photoelastic method. The contact pressure distribution, the fibre stress in the foundation beam and frame structure, as well as the stresses in the elastic medium, have been obtained. These have been compared with theoretical results obtained by idealizing the soil as (a) elastic half plane, and (b) elastic half space. It is shown that the photoelastic method can provide an easy solution to this type of problem if the soil can be idealized as an elastic continuum.