Advanced propulsion concepts

The topics presented are covered in viewgraph form. The programmatic objective is to establish the feasibility of propulsion technologies for vastly expanded space activity. The technical objective is a revolutionary performance sought, such as: (1) about 1 kg/kW specific mass; (2) specific impulse tailored to mission requirements; (3) ability to use in-situ resources; (4) round-trips to Mars in months; (5) round-trips to outer planets in 1 to 2 years; and (6) the capability for robotic mission beyond the solar system

Industrializing the near-earth asteroids: Speculations on human activities in space in the latter half of the 21st century

The use of solar system resources for human industry can be viewed as a natural extension of the continual growth of our species' habitat. Motivations for human activities in space can be discussed in terms of five distinct areas: (1) information processing and collection; (2) materials processing; (3) energy production to meet terrestrial power needs; (4) the use of extraterrestrial materials; and (5) disaster avoidance. When considering 21st-Century activities in space, each of these basic motivations must be treated in light of issues likely to be relevant to the 21st-Century earth. Many of the problems facing 21st-Century earth may stem from the need to maintain the world population of 8 to 10 billion people as is projected from expected growth rates. These problems are likely to include managing the impact of industrial processes on the terrestrial biosphere while providing adequate energy production and material goods for the growing population. The most important human activities in space in the latter half of the 21st Century may be associated with harnessing the resources of the near-earth asteroids for industrial processes. These above topics are discussed with an emphasis on space industrialization

Analytical technique for determining the polarization dependence of optical matrix elements in quantum wires with band-coupling effects

We present an analytical technique for determining polarization-dependent optical transition matrix elements in quantum wires which rigorously incorporates the effects of band coupling. Using this technique, we examine the polarization anisotropy of the two lowest energy optical transitions in a GaAs quantum wire. Contrary to assumptions employed in previous studies, we show that the valence states involved in these transitions are a strong admixture of light and heavy hole character. The lowest energy transition is found to be four times stronger for electric fields oriented parallel to the wire than for the perpendicular orientation. In contrast, the next highest transition does not interact with optical waves polarized along the wire axis. We discuss sources of error which arise in simpler one-band models of this phenomenon in addition to the neglect of band coupling and show that the coupled band model presented here is essential for predicting these effects

Materials for Spring Fabrication

Tato práce se zabývá přehledem materiálů pro výrobu pružin, jejich charakteristikou a použitím pro jednotlivé průmyslové aplikace. Dále pak shrnuje možnosti tepelného a mechanického zpracování jednotlivých materiálů a dopad tohoto zpracování na strukturu a vlastnosti. Informace jsem čerpal z dostupných publikací a zpracoval do této rešerše.This work deals with an overview of materials for the manufacture of springs, their characteristics and use for various industrial applications. Then summarizes the thermal and mechanical processing of different materials and the impact of treatment on structure and properties. I gathered information from available publications and worked in this research.

Quantitative measurement of the composition of Al_xGa_(1−x)As heterostructures using a simple backscattered electron detector

We describe a technique for the quantitative measurement of composition in Al_xGa_(1−x)As heterostructures using a simple solid‐state backscattered electron detector in a scanning electron microscope. Calibration data are presented and are shown to be consistent with the Castaing [Adv. Electron. Electron Phys. 13, 317 (1960)] theory. The technique is applied to image representative Al_xGa_(1−x)As heterostructures including a graded index separate confinement heterostructure (GRINSCH) laser structure

Nanometer scale wire structures fabricated by diffusion-induced selective disordering of a GaAs(AlGaAs) quantum well

A shallow zinc diffusion technique is used to selectively disorder a GaAs quantum well creating nanometer scale wire structures. Spectrally resolved cathodoluminescence images of the structures are presented as well as local spectra of cathodoluminescence emission from the structures. Blue shifting of the luminescence from the wire structures is observed