Precipitation of equilibrium phases in vapour-quenched Al-Ni. Al-Cu and Al-Fe alloys

In situ annealing experiments in the transmission electron microscope have been used to investigate the thermal stability and precipitation behaviour of non-equilibrium phases in vapour-quenched Al-Ni, Al-Cu and Al-Fe alloys prepared by co-sputtering. The non-equilibrium phases exhibit surprisingly high thermal stability and the general nature of precipitation is different from that in liquid-quenched or conventional alloys. These phenomena are caused by the very small as-quenched grain size.     

Diffusion in metallic glasses

Rutherfordα-particles backscattering technique was employed for measurements of diffusion rates in metallic glasses. Effects of relaxation, crystallization and plastic deformation on diffusion rates were also investigated. It has been observed that the diffusion rates of a metallic solute are of the same orders of magnitude in both metal-metal and metal-metalloid glasses. A higher diffusivity is likely if there is a large difference between melting points of the solute and matrix. Relaxation has no effect on diffusion, however, diffusivity increases on crystallization. An increase in diffusivity is also observed on plastic deformation of metallic glass.     

Electrochemical performance, biocompatibility, and adhesion of new polymer matrices for solid-state ion sensors.

Ammonium and potassium ion-selective membranes formulated with PVC/hydroxylated PVC, polyurethane/hydroxylated PVC, and moisture-curable silicone rubber matrices are studied in an effort to extend the lifetime of solid-state ion sensors through improved membrane adhesion. The PVC/membranes exhibit electrochemical performance equivalent to that of conventional PVC membranes in terms of slope, detection limit, and selectivity. The polyurethane- and silicone-rubber-based membranes have better adhesion to silicon nitride than do PVC or hydroxylated PVC matrices. Incorporating a silanizing reagent (silicon tetrachloride) significantly improves the adhesion of the polyurethane matrix. The use of silicon tetrachloride in membrane matrices also enhances the electrochemical stability of the interfacial potential between ion-selective polymer-matrix membranes and silver epoxy inner reference electrodes of solid-state sensors. The biocompatibility of the polymer matrices is examined via radiotracer protein adsorption studies and whole blood clotting time measurements. The polyurethane- and silicone-rubber-based membranes exhibit less overall nonspecific protein adsorption than the PVC or hydroxylated PVC matrices.     

A Test of the Equality of Survival Distributions Based on Paired Observations from Conditionally Independent Exponential Distributions

A model describes the joint distribution of paired survival times based on certain reasonable assumptions appropriate for biological data generated in a clinical trial setting or for certain failure data. An exact parametric test for equality of mean survival times for data following this distribution is developed. The power of the exact test is investigated by a computer simulation study for various sample sizes and values of the model parameters and compared to that of alternative tests. Heretofore, researchers desiring to analyze paired survival data have resorted to paired t tests or nonparametric procedures such as the sign test or signed ranks test. The t-test is invalid for non-normally distributed data although the robustness of the test might minimize the difficulty. The nonparametric tests, by their nature, fail to use the data completely. This paper presents an exact parametric test based on a distribution whose justification requires rather modest and reasonable assumptions. Critical values for the test can be obtained from a table of the chi-square distribution. This exact test appears to be a viable alternative to non-parametric approaches to the analysis of paired survival data. It is extremely easy to calculate on a hand calculator. In fact, since no data storage is required (unlike the signed ranks test), the calculations can be readily programmed on a programmable calculator. The modeling of bivariate and multivariate survival data we believe has not been adequately addressed in the statistical and engineering literature. We hope that this paper will spark additional work.     

Life tasks, self-concept ideals, and cognitive strategies in a life transition.

This paper reports on data from a longitudinal study in which normative life tasks and individuals' personal versions of those tasks are investigated in the context of students making the transition from home and high school to college life. Analyses focus both on common patterns of life-task appraisal in interpersonal and achievement domains and on differences in the self-concepts and cognitive strategies that individual students bring to bear as they confront these normative pressures (Cantor & Kihlstrom, 1987). In particular, we investigate the impact of students' actual-ideal self-discrepancies (Higgins, Klein, & Strauman, 1985) on subjective stress and satisfaction in achievement and interpersonal life-task domains and suggest that self-concept discrepancy negatively affects adjustment in the achievement domain and positively affects social outcomes. Students using a defensive-pessimism strategy motivated themselves by confronting their anxieties in advance of stressful tasks, whereas those using an optimistic strategy assumed the best until proved otherwise—protecting self-esteem after the fact in the event of disappointment (Norem & Cantor, 1986a, 1986b). This analysis, thus, begins at the level of normative "readings" of life tasks in a shared transition period and gradually moves toward consideration of how individuals navigate those tasks in personally meaningful ways. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The asquenched microstructure and tempering behavior of rapidly solidified tungsten steels

Transmission electron microscopy, and microhardness testing were used to examine the as-quenched structure and mechanical properties of a series of rapidly solidified (RS) iron-tungsten-carbon-alloys ranging from 6 to 23 pct tungsten with a constant W:C atomic ratio of 2:1, and Tl high speed tool steel. The RS iron-tungsten-carbon alloys were found to exhibit a significant change in microstructure and hardness as the tungsten and carbon content was increased. The change in morphology was from lath martensite in the lower tungsten alloys to a solidification structure of δ-ferrite cells surrounded by austenite and M₆C carbide, in the higher tungsten alloys. A model is proposed to explain the morphologicl change. In addition, the tempering behaviors of RS Fe-6.2 wt pct W-0.21 wt pct C, Fe-23 wt pct W-0.75 wt pct C and Tl high speed tool steel were examined and compared to those observed for the conventional solution-treated and quenched alloys. A discussion is also included on the microstructural dependence upon cooling rate of RS high speed tool steels. formerly of School of Engineering and Applied Sciences, University of Sussex, Falmer, Brighton, England.