Evaluation of Phase-Commutated Converters for Slip-Power Control in Induction Drives

Three different phase-commutation thyristor bridges are applied to slip-power control of an induction motor. The performance of the drive is experimentally evaluated for each thyristor bridge with respect to input power factor, efficiency, total. input current, size of the dc-link inductor, and regulation. The best results are obtained with the eight-thyristor bridge while the conventional six-thyristor converter offers the worst overall performance.     

Determination of power absorption in man exposed to high frequency electromagnetic fields by thermographic measurements on scale models

Ultrafiltrable serum uric acid (u.a.) was determined by ultrafiltration under in vivo conditions in humans using a reliable technique described in detail. It could be demonstrated that u.a. binding to macromolecules occurs in healthy humans (controls) and in patients with renal calcium stones. The percentage of free u.a. in controls (n=60) averages 86.2 +/- 0.9 SEM. With increasing age, bound u.a. rises slightly. On the other hand, younger (less than 40 years) stone patients have significantly more bound u.a. than matched controls (80.7 +/- 1.0 SEM; p less than 0.001), whereas this is not found in elderly patients. The degree of binding is not related to concentration of plasma proteins but inversely related to free fatty acid concentration in healthy controls (r= -0.52; p less than 0.01). It is suggested that no augmentation of tubular u.a. filtered by the glomeruli could have occurred. The origin of fasting hyperuricosuria shown earlier to be a prominent feature of young renal calcium stone formers is yet unknown.     

Approximate method for calculations using concentration-dependent diffusion coefficients

Standard methods are available for calculating the results of diffusion processes providing the diffusion coefficient is a constant. In fact, the diffusion coefficient changes radically with composition in most alloy systems and therefore the standard methods are not quantitatively applicable. It is shown that a correction can be made for the variation of the diffusion coefficient with concentration by employing a special coordinate transformation. Illustrative calculations for two types of variation of the diffusion coefficient with concentration show that the accuracy of this approximate method is of the order of 20 pct for large changes in the diffusion coefficient. The relation of the present method to that of Wagner is discussed.     

An Experimental Test of Five Process Models for Subtraction.

This study is concerned with processes used by second- and fourth-grade children in solving single-digit subtraction problems. Five possible models of the solution process were evaluated by fitting observed reaction times to the linear regression predicted by each model. Most second graders and all fourth graders were best fit by a model in which the child either counted down from the larger number or counted up from the smaller, depending on which procedure required the fewest steps. In addition, there was a decrease between Grades 1 and 2 in the time taken for each step in the procedure. The results suggest a developmental trend in which children moved from a fixed algorithmic model to a more heuristic one involving judgment and estimation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The application of the foam fractionation process to the removal of viruses process to the removal of viruses: Part II. The prediction of the residual surfuctant concentration

Variations in the initial concentration of the surfuctant. Arquad T50 (a blend of alkyl quaternary ammonium chlorides), and the gas to liquid flow ratio were assessed for their effect upon the residual surfactant level. This concentration was found to be dependent upon these variables as well as upon the bubble diameter in the liquid phase as determined by the gas rate. An equation was derived which represented the removal of surfactant as a power function of (i) its initial concentration, (ii) the gas to liquid flow rate ratio and (iii) the gas flow rate. The error of this equation established that this empirical approach accurately represented the removal of the surface-active agent.     

Elastic plastic buckling of internally pressurized torispherical vessel heads

Comparisons of test and theory are presented for the nonaxisymmetric bifurcation buckling of ten aluminium vessel heads fabricated and tested by Patel and Gill at the University of Manchester in 1976. In the test specimens, the sphere radius was equal to the cylinder diameter and only the torus radius was varied. All specimens were of constant internal cylinder diameter to nominal thickness ratio of 531.5. Meridional variation of thickness was accounted for in the analysis, which was carried out with the BOSOR5 computer program. The analysis includes both material and geometrical nonlinear prebuckling behavior. The results indicate that incipient nonsymmetric buckling can be predicted with reasonable accuracy by means of an eigenvalue formulation.     

Sur de nouveaux conducteurs ioniques du lithium de structure boracite

The electrical study of lithium boracites, which are electronic insulators, shows a high mobility of the Li⁺ cation. They are the first high isotropically conducting Li compounds.