Four contact electrical measurements on the anisotropic high-Tc superconductors: voltage reversals

We describe three mechanisms for the anomalous voltage reversals which are occasionally observed during four contact current-voltage measurements on the high temperature superconductors. Voltage reversals have been frequently observed for whiskers of the bismuth strontium calcium copper oxide (BSSCO) compounds, and we describe measurements made on high quality whiskers of the 2:2:1:2 and 2:2:2:3 phases. A simple model based on extreme anisotropy plus offset contacts can explain the gross features of four contact measurements in the ohmic flux-flow regime, but not the wealth of reversal phenomena found for the IVVI configuration in the lower temperature irreversibility region.     

Calculations of the reflection and transmission of ultrasound by cracks in steel filled with liquid sodium

The ultrasonic reflection and transmission amplitudes of idealized cracks in steel filled with liquid sodium are calculated as a function of the angle of incidence and crack width for an incident compression wave of frequency 2.25 MHz. It is concluded that it should be no more difficult to detect a liquid-sodium filled crack than an air filled crack for widths greater than 0.01 mm, which is typical of fatigue crack widths.     

Isolation and structure of rebeccamycin - a new antitumor antibiotic from nocardia aerocoligenes

The isolation and structure elucidation of rebeccamycin 1, a new antitumor agent from $\text{Nocardia}$$\text{Aerocoligenes}$, is described. The NMR spectra of 1 and its peracetate 2 are discussed.     

Photoelastic analysis of contact stresses in the presence of machining irregularities

Three-dimensional stress-freezing photoelasticity is used to analyze the stress distributions in a shaft with a shrink-fit ring. Of particular concern is the stress redistribution when machining irregularities are present at the contact surface. Details of the model manufacture, data reduction, and analysis are given.     

X-Ray diffraction at high temperatures

Experimental equipment for X-ray diffraction at high temperatures is introduced and the possibility to directly observe the evolution of the atomic (geometric) structure as a function of temperature is discussed. Recent results on crystallization investigations of amorphous iron-based alloys and on the structural development in thin molybdenum sulphide films are given. The kinetics of the process was followed by means of time resolved experiments in both cases.