Heat transfer in boundary layer flow of a micropolar fluid past a curved surface with suction and injection

Van Dyke's singular perturbation technique has been used to study the heat transfer in the flow of a micropolar fluid past a curved surface with suction and injection. The conditions for similar solutions of the thermal boundary layer equations have been obtained. In addition to the usual “no slip” condition for velocity, the two types of boundary conditions used for microrotation are: (i) no relative spin on the boundary; (ii) the anti-symmetric part of the stress tensor vanishes at the boundary. The effect of suction or injection on velocity, microrotation, temperature, skin friction coefficient, wall couple stress coefficient, displacement and momentum thicknesses, rate of heat transfer and adiabatic wall temperature have been studied. It is observed that with the increase of injection velocity, the thickness of the boundary layer is increased and the local drag is reduced. A comparison with the results obtained for a Newtonian fluid reveals that the microelements present in the fluid reduce the velocity and frictional drag, and cool the boundary.     

Evaluation of performance criteria of the CSI-IM drive system

The stability, sensitivity, and static velocity error coefficient of an induction motor (IM) drive fed by a current-source inverter (CSI) are analyzed to obtain the necessary information for the design of a practical system. These analyses are considered useful for determining an appropriate subsystem to compensate for performance deficiencies     

Effect of pretreatment on the anodic behaviour of lead alloys for use in electrowinning operations. I

Lead alloys are widely used as anodes in electrowinning operations, for the recovery of metals such as zinc, copper and chromium. When lead alloys are used as such it takes a long time for the build up of a compact, adherent and protective lead dioxide film. During the initial period prior to the build up of the compact layer of lead dioxide, the rate of anodic dissolution is very high, leading to a decrease in the purity of the cathode deposit. In order to minimize the duration of the conditioning of the anode, it is customary to build up a compact lead dioxide layer by pretreating the anodes in suitable electrolytes. An attempt is made to evaluate the performance of the pretreated electrodes by potentiodynamic methods.     

Convulsions with meningiomas: incidence and significance

In a study of a consecutive series of 127 surgically treated meningiomas, it was found that 29% of the patients had reported with convulsions as their initial symptom. In this group, surgical excision of the meningioma stopped the convulsions in about half of the patients, but the others continued to have seizures after their operations. Among those patients with meningiomas who did not have preoperative convulsions, about one-sixth (15 patients) developed postoperative seizures. Patients in both groups required prolonged anticonvulsant medication. Factors predisposing to the occurrence of postoperative seizures were the site of the tumor, faulty surgical technique, and a preoperative history of seizures.     

Thermal and optical properties of Cd1-x Zn x S thin films by photoacoustics

Ternary compounds Cd_1-x Zn _x S for various Zn concentration in thin films are synthesized by spray pyrolysis and studied by photoacoustics technique for thermal and optical properties. The thermal diffusivity as a function of the alloy composition measured by photoacoustics shows a maximum at x = 0.6. The optical band gap increases with zinc concentration and the continuous change indicates the formation of solid solution.     

A mixed integer programme for optimal static capacitor allocation in power systems

A method is presented for the determination of optimal size and location of static capacitor installations in a power system network for maintenance of the bus voltage magnitudes within prescribed limits under highly loaded or outage conditions. The problem is formulated as an optimization problem with the objective function representing the cost of capacitor installations and the constraints represent the reactive power flow equation of the system and the limits on the variations of the tap settings of the tap changing transformers and the generator bus voltages. The generator bus voltage magnitudes are continuously variable and the capacitor units to be installed and the tap settings are treated as discrete or integer variables. By partioning the variables into control and controlled quantities, a number of variables are eliminated from the problem. The problem is then decomposed into two smaller subproblems with integer or continuous variables. These result in the reduction of the computer memory and time requirements.     

Asymptotic behavior of a hierarchical system of learning automata

Learning automata arranged in a two-level hierarchy are considered. The automata operate in a stationary random environment and update their action probabilities according to the linear-reward-ε-penalty algorithm at each level. Unlike some hierarchical systems previously proposed, no information transfer exists from one level to another, and yet the hierarchy possesses good convergence properties. Using weak-convergence concepts it is shown that for large time and small values of parameters in the algorithm, the evolution of the optimal path probability can be represented by a diffusion whose parameters can be computed explicitly.     

Predicting diffusivity and rate constant for vapour-phase diffusion coupled solid—solid reactions

There have been only few studies yielding information about kinetics and diffusion in solid—solid systems, largely due to the intricate relationship between diffusion and reaction processes. Delineating between these processes is beset with many difficulties.Unsteady-state vapour-phase diffusion and reaction in solid—solid systems is treated mathematically. A method is presented here to predict the diffusivity and the rate constant from concentration profiles that could be obtained from experiments between cylindrical pellets in contact with each other in solid—solid systems.