The investigation of vertical transport in semiconductor heterojunction systems has recently undergone a renaissance due to improved epitaxial techniques in a number of material systems. By usin resonant tunneling, we can perform electronic spectroscopy not only o f the double barrier structure itself, but of any system (with quantized well states) suitably coupled to a resonant tunneling spect...

Measurements have been made of the sputtering yields, the mass spectra of ejected molecules, and ejection rates for various kiloelectronvolt ions incident on sodium sulfide (Na2S). The sputtering yields were small compared to those measured earlier for the more volatile sulfur ($8) and SO2 due to the strong ionic bonding in the solid. The mechanism of sputtering for the corotating sulfur and ox...

A yeast-derived phosphomannan mixture was chemically sulfonated and the composition and structure of the product mixture was studied. This phosphosulfomannan mixture, PI-88, is currently under clinical evaluation as an anti-cancer agent. Analysis using capillary electrophoresis demonstrated that PI-88 was a multi-component mixture. Gel permeation chromatography provided four fractions of PI-88 ...

1Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA 2Laboratório de Ictiologia Sistemática e Evolutiva, Departamento de Botânica e Zoologia, Universidade Federal do Rio Grande do Norte, Av. Senador Salgado Filho 3000, 56078-970 Natal, RN, Brazil 3Department of Biological Sciences, University of Alabama, Tuscaloosa, AL 35487, USA 4Department of BioSci...

Abstract--The wake flow behind a normal or an inclined plate is predicted by a discrete-vortex method. The vortex shedding phenomenon at the leading and the trailing edges is simulated by a vorticity creation technique according to the Kutta condition. This approach required that the strengths and locations of discrete vortices just shed from the edges be determined such that their presence in ...

About 93.1 million workers were covered under workers' compensation laws in 1988--an increase of 11 percent from the 1984 total. Benefit amounts totaled $30.7 billion--an increase of about 56 percent since 1984. Of the total payments made under the workers' compensation program, $17.6 billion went to disabled workers, $1.6 billion to their survivors, and $11.5 billion for medical care. The Soci...

Iterative schemes have provided a new way to devise complex sequences of RF pulses. In broadband spin decoupling they offer a significant reduction in RF power deposition for a given operating bandwidth (I, 2) and much better tolerance of instrumental imperfections (3, 4). New composite pulses for broadband, narrowband, or band-pass inversion (5-8) or excitation (9, IO) have also been discovere...