Laminar dust flames in a reduced-gravity environment

The propagation of laminar dust flames in suspensions of iron in gaseous oxidizers was studied in a low-gravity environment onboard a parabolic flight aircraft. The reduction of buoyancy-induced convective flows and particle settling permitted the measurement of fundamental combustion parameters, such as the burning velocity and the flame quenching distance over a wide range of particle sizes and in different gaseous mixtures. Experimentally measured flame speeds and quenching distances were found in good agreement with theoretical predictions of a simplified analytical model that assumes particles burning in a diffusive mode. However, the comparison of flame speeds in oxygen–argon and oxygen–helium iron suspensions indicates the possibility that fine micron-sized particles burn in the kinetic mode. Furthermore, when the particle spacing is large compared to the scale of the reaction zone, a theoretical analysis suggests the existence of a new so-called discrete flame propagation regime. Discrete flames are strongly dependent on particle density fluctuations and demonstrate directed percolation behavior near flame propagation limits. The experimental observation of discrete flames in particle suspensions will require low levels of gravity over extended periods available only on orbital platforms.     

Phytochromes play a role in phototropism and gravitropism in Arabidopsis roots.

Phototropism as well as gravitropism plays a role in the oriented growth of roots in flowering plants. In blue or white light, roots exhibit negative phototropism, but red light induces positive phototropism in Arabidopsis roots. Phytochrome A (phyA) and phyB mediate the positive red-light-based photoresponse in roots since single mutants (and the double phyAB mutant) were severely impaired in this response. In blue-light-based negative phototropism, phyA and phyAB (but not phyB) were inhibited in the response relative to the WT. In root gravitropism, phyB and phyAB (but not phyA) were inhibited in the response compared to the WT. The differences observed in tropistic responses were not due to growth limitations since the growth rates among all the mutants tested were not significantly different from that of the WT. Thus, our study shows that the blue-light and red-light systems interact in roots and that phytochrome plays a key role in plant development by integrating multiple environmental stimuli.     

Radio emission from EA eclipsing binaries: Evidence for kilogauss early- and late-type stars

Space Science Reviews -     

Canadian space policy

Canada's geography made it an early leader in the development of space technology, and generated a civilian-oriented, terrestrially focused space programme with a strong focus on communications and an increasing emphasis on transferring space technology and activity from the government to the private sector. During the 1980s Canada's space programme has strengthened and broadened measurably; its now contains major projects in Earth observation and robotics as well as communications, and has diversified its international partnerships from the USA to Europe. However, persisting weaknesses in launch capability, space science and military space programmes, and the dependence of all three current major projects (Msat, Radarsat, and the International Space Station's Mobile Servicing System) on the USA represent potential vulnerabilities which require national investments and expanded international affiliations if they are to be offset.     

Integrated Avionics: Watershed in Systems Development

For aeronautical weapon systems now entering development, avionics will equal or surpass airframe, propulsion, and weapons in establishing system effectiveness, both in terms of mission accomplishment and in terms of reliability, availability, supportability, and life cycle cost. Emerging technologies created the opportunity to satisfy demanding operational needs and to provide the means to upgrade systems against an evolving threat. This requires, however, basic changes in the skills, design methods, and constraints applied to avionics development. This paper highlights trends in avionics technology and systems and suggests some of the new ground rules which must be imposed to realize their full potential. Avionics considerations must be a central element of system development from the very outset, and the process of conceptual planning and program estimation must take the new realities of avionics into account.     

Solar neutrinos: Theory versus observation

The current state of the solar neutrino problem is described. The predictions of solar models (standard and nonstandard) are reviewed. The neutrino absorption cross sections for all detectors of current interest are reviewed with special emphasis on the uncertainties that exist in the calculations for each target. A long-term program for neutrino spectroscopy of the solar interior is outlined. It is shown, in addition, that stellar collapses can be detected within the galaxy by the proposed solar neutrino detectors.     

Planetary science with space telescope

A discussion is given of the various capabilities and advantages of the Space Telescope observatory, scheduled for launch into Earth-orbit in 1984. The first generation instruments are described, and a detailed example for one specific observing program, an intercomparison of Uranus and Neptune, is made. The importance of an extra-solar planet search is emphasized.