Pair-field susceptibility of superconducting Al-Er films

Measurements of the imaginary part of the pair-field susceptibility have been carried out on dirty-limit superconducting Al films doped with Er impurities at temperatures within 20% of the critical temperature T _c. These studies are the first measurements of (, k) as a function of the pair-breaking parameter . Samples exhibiting values of up to 0.1 were studied. At temperatures above T _c the diffusive time-dependent Ginzburg-Landau equation for order-parameter fluctuations was found to be valid in the presence of pair-breaking, with the Ginzburg-Landau time an increasing function of the pair-breaking, in quantitative agreement with theory. The characteristic frequencies of the transverse and longitudinal modes of the order parameter disequilibrium were determined from the measurements of (, k) below T _c by fitting to a functional form which exhibits the essential features of the most detailed theories, in particular those of Orbach and Entin-Wohlman, Dinter, and Schön and Ambegaokar, The propagating charge-imbalance wave was found to be overdamped for large values of , consistent with the theory of the transverse mode in the presence of finite pair-breaking. The peak in the excess current found near the gap voltage appears to be due to a resonance in the longitudinal mode pair-field susceptibility and not the result of single-particle tunneling as previously suggested by imanek and Hayward. The width of this resonance as derived by Schön and Ambegaokar for the gap regime is equal to the reciprocal of the spin-flip scattering time. The other characteristic feature of the pair-field susceptibility is the peak associated with the longitudinal mode, which occurs at a frequency which is a measure of the relaxation of the amplitude of the order parameter. Dinter's theory, in particular, describes the dependence of the width of this peak on the pair-breaking parameter .Support for this research was initially provided by the Department of Energy and later by the NSF under Grant DMR-8006959. The Office of Naval Research provided He gas used in these experiments.     

Pattern Recognition via Observation Correlations

In some pattern recognition tasks multiple observations of an observation vector Y = {Y1, Y2, ..., YM} are available for each object and the covariances of the Yi are characteristic of the object. With the assistance of a model of the generating process for Y a theoretical basis for the comparison of the covariance matrices is developed. Measurements based on synthetic data support the theory, and an application to some speaker verification is given as an example.     

An electron spin resonance investigation of carbon black-filled polybutadiene

This paper describes an ESR investigation complemented with X-ray measurements, ofcis-polybutadiene filled with a range of carbon blacks. The aim was to derive further insight into the rubber-carbon black interaction. There are two distinguishable free spin species in the carbon blacks; free spin carriers and localized free spins. There appears to be a correlation between the localized free spin concentration and defects concentrations in the carbon blacks as determined by X-ray measurements. The interpretation of experimental data emphasizes the importance of considerations of the structure parameter of the carbon blacks.     

Localization of vitamin A in the small intestine of mouse. An electron microscope radioautographic study

Localization of vitamin A in the small intestine of mice was studied with electron microscope radioautography after administration of tritiated vitamin A. The label was concentrated over lipid droplets in cells distributed in the lamina propria and the submucous layer. The cells were similar both to fibroblasts and to fat-storing cells in their morphological features. The name "Vitamin A-Storing Cell" is proposed for these labeled cells, including the fat-storing cell in the liver.     

The theory of grain boundary segregation in terms of surface adsorption analogues

The theory of equilibrium solute segregation at solid/solid interfaces can be approached usefully from classical surface/gas adsorption isotherms of varying complexity and encompassing both chemisorption and physisorption behavior. Thus, the McLean segregation theory, the simplest type of behavior, is the counterpart of the Langmuir theory for solid/gas adsorption. Assuming strong pair interactions between segregate neighbors, the McLean theory can be adapted to a more complex form, the analogue of the Fowler isotherm, in which adsorbate clustering or protoprecipitation occurs. Again, multilayer segregation is possible, which can be rationalized by " BET " adsorption analogue behavior. Recent developments show how isotherms may be extended to multicomponent systems, assuming interactions between elements and segregants, with important implications in the behavior of embrittlement-prone engineering steels. The mass action equilibrium approach for surface adsorptive reactions is extended here to grain boundaries and tested on the limited number of isotherms available. This may prove to be a useful analytical procedure, giving a rapid insight into the nature of the segregation process, such as adsorbate interactions and variations in adsorption potential among the various sites. This paper is based on a presentation made at a symposium on “Fundamentals of Grain Boundary Segregation” held at the Niagara Falls Meeting of The Metallurgical Society of AIME, September 21, 1976, under the sponsorship of the Physical Metallurgy Committee.