Metastability of superconducting compounds in the y-ba-cu-o system.

Precision isothermal solution calorimetry was used to determine the standard-state enthalpy of formation of a number of phases in the Y-Ba-Cu-O system. An analysis of the data indicates that YBa(2)Cu(4)O(8) is thermodynamically metastable under ambient conditions. Taken together with the results from previous investigations, these data show that all of the superconducting compounds in the Y-Ba-Cu-O system are thermodynamically metastable at low temperatures.

High Tc ceramic superconductors: introduction, background, and challenges to the electron microscopist.

This introductory article reviews the recent developments in high Tc superconducting ceramics. Particular emphasis is given to the structural and chemical aspects of these compounds that may be of interest to the electron microscopist. Included are some of the contributions made by electron microscopy techniques over the last 10 months. The applications of electron microscopy to solving practical problems associated with these exciting new materials are also discussed.

US evaluation of the rotator cuff.

Ultrasonographic (US) evaluation of the moving shoulder is a new method for evaluating the integrity of the rotator cuff. In the past, contrast arthrography has provided the only nonoperative technique for demonstrating defects in the rotator cuff. We present the details of this new technique and describe 79 patients whose US results were correlated with the findings at arthrography and/or surgery. US allows evaluation of both shoulders at once, an advantage over arthrography, where usually only one side is evaluated at a single sitting. Improvements in US instrumentation, especially the introduction of high-resolution linear-array devices and the use of experienced ultrasonographers, have improved the accuracy of US. Because US is rapid, safe, noninvasive, and inexpensive, we advocate its use instead of arthrography as the routine test of rotator cuff integrity.