Ionic conductivity in samarium-doped NaCl

A study of ionic conductivity as a function of temperature has been carried out in NaCl and NaCl doped with 0.5 and 1.0 mol% samarium. The conductivity-temperature plot of NaCl exhibits a well-known three-stage conductivity in the temperature range 100 to 650° C. The knee separating intrinsic and extrinsic regions is at a temperature of about 525° C. The conductivity-temperature plots of samarium-doped NaCl exhibit three-stage extrinsic (II, III and IV) conductivity in the temperature range 100 to 525° C. The intrinsic region I, was not observed in these plots, as the conductivity measurements were taken up to 525° C. From the analysis of these plots activation energies for the migration of cation vacancy, the formation of Schottky pairs, the association of the samarium ion with a cation vacancy and the dilution of samarium ions in the lattice of NaCl are calculated. These values are compared with previously reported ones.     

A nonlinear theory of wake development

Summary A simple new series, using an expansion of the velocity profile in parabolic cylinder functions, has been developed to describe the nonlinear evolution of a steady, laminar, incompressible wake from a given arbitrary initial profile. The first term in this series is itself found to provide a very satisfactory prediction of the decay of the maximum velocity defect in the wake behind a flat plate or aft of the recirculation zone behind a symmetric blunt body. A detailed analysis, including higher order terms, has been made of the flat plate wake with a Blasius profile at the trailing edge. The same method yields, as a special case, complete results for the development of linearized wakes with arbitrary initial profile under the influence of arbitrary pressure gradients. Finally, for purposes of comparison, a simple approximate solution is obtained using momentum integral methods, and found to predict satisfactorily the decay of the maximum velocity defect.     

Pattern Recognition of Canine Duodenal Contractile Activity

An application of statistical pattern recognition technique to the classification of canine duodenal contractile activity resulting from the ingestion of three different test meals, viz. water, acid, and solid, is described. Feature vectors were extracted from the contractile activities recorded by means of strain gauges, and were based on average duration, number, and intensities of contractions, as well as their frequency and propagational characteristics. Pattern training and classification were performed via the Bayes decision rule. The resuits indicate that the three different meals give rise to three different kinds of contractile activities. An improvement in the classifier's performance was observed when it was updated with correctly classified patterns. The results appear to suggest that pattern analysis techniques add a new dimension to the study of gastrointestinal motility in health and disease. For example, pattern recognition techniques can also be extended to identify contractile patterns altered due to such pathological conditions as irritable bowel syndrome and postoperative diarrhea and, hence, elucidate the underlying relationship between contractile activity and distal propulsion of contents.     

The effect of austenitizing temperature upon the microstructure and mechanical properties of experimental Fe/Cr/C steels

The present study investigates the as-quenched mechanical propertiesviz, strength, ductility and sharp notch (K _Ic ) as well as blunt notch (Charpy) toughness, of simple Fe/Cr/C alloys with and without titanium as a function of austenitizing temperature. For the ternary Fe/Cr/C alloys the results are consistent with earlier investigations, but the fracture toughness does not change with increasing austenitizing temperatures after 0.2 wt pct Ti is added. The titanium forms carbides (TiC) that did not dissolve, providing a roughly constant number of crack nucleation sites, and preventing austenite grain growth up to 1100°C. The differences in mechanical behavior, particularly the rounded notch toughness, are discussed and explained in terms of the microstructural characteristics of the alloys, as determined by detailed electron microscopy analysis.     

DC electrical conduction in solution-grown pure and iodine-doped poly(butylene terephthalate) films

DC electrical conduction in poly(butylene terephthalate) films sandwiched between planar aluminium electrodes was investigated. The films were grown by the isothermal immersion technique. The conduction process was studied in the temperature range 300–450K, with an applied electric field of 0.22 × 10⁷?6.66 × 10⁷ Vm^?1. It was found that the Richardson-Schottky type of conduction mechanism was dominant throughout the temperature range of study. The values of the Schottky field lowering constant β, the effective metalinsulator potential barrier and the activation energy were evaluated. The value of the activation energy (U = 0.7 eV) indicates the predominance of electronic conduction. The effect of impurities like iodine on electrical conduction was also investigated.     

Monte Carlo simulation of low density flows

The necessity for adopting a kinetic-theoretical approach to obtain aerodynamic characteristics in low density flow past space vehicles is highlighted in this paper; it is shown how long-standing difficulties in theoretically handling such flows can be circumvented by adopting a Monte Carlo technique. The principles underlying the technique are briefly described, and are first illustrated by applying the technique to the evaluation of the drag of cylinders and cones in collisionless flow. The Markoff process underlying the Monte Carlo simulation of the full Boltzmann equation with collisions is then described in detail. Instead of the time-counter strategy of Bird, a theoretically sounder ‘Random Collision Number’ (RCN) strategy has been adopted in the present simulation. In this strategy the number of collisions in each time-step in the computation is a random number drawn from an appropriate distribution. Computer programs using this strategy have been developed for calculating aerodynamic characteristics like drag and heat transfer for a cone in the transition regime between free molecule and continuum flow. The results obtained from these programs show that both time-counter and RCN strategies require almost the same computer time.