Genesis and preservation of a uranium-rich paleozoic epithermal system with a surface expression (Northern Flinders Ranges, South Australia): radiogenic heat driving regional hydrothermal circulation over geological timescales

The surface expressions of hydrothermal systems are prime targets for astrobiological exploration, and fossil systems on Earth provide an analogue to guide this endeavor. The Paleozoic Mt. Gee-Mt. Painter system (MGPS) in the Northern Flinders Ranges of South Australia is exceptionally well preserved and displays both a subsurface quartz sinter (boiling horizon) and remnants of aerial sinter pools that lie in near-original position. The energy source for the MGPS is not related to volcanism but to radiogenic heat produced by U-Th-K-rich host rocks. This radiogenic heat source drove hydrothermal circulation over a long period of time (hundreds of millions of years, from Permian to present), with peaks in hydrothermal activity during periods of uplift and high water supply. This process is reflected by ongoing hot spring activity along a nearby fault. The exceptional preservation of the MGPS resulted from the lack of proximal volcanism, coupled with tectonics driven by an oscillating far-field stress that resulted in episodic basement uplift. Hydrothermal activity caused the remobilization of U and rare earth elements (REE) in host rocks into (sub)economic concentrations. Radiogenic-heat-driven systems are attractive analogues for environments that can sustain life over geological times; the MGPS preserves evidence of episodic fluid flow for the past ～300 million years. During periods of reduced hydrothermal activity (e.g., limited water supply, quiet tectonics), radiolytic H(2) production has the potential to support an ecosystem indefinitely. Remote exploration for deposits similar to those at the MGPS systems can be achieved by combining hyperspectral and gamma-ray spectroscopy.     

A Digital Map Set for the Night Attack Aircraft

There has been much interest recently in applying cartographic digital data bases to advanced avionics systems as a solution to specific problems associated with night attack aircraft missions. The tremendous computer horsepower required to accomplish this task in real-time in an airborne environment is well documented. Hardware implementation of complex algorithms traditionally has produced custom devices which accomplish a specific function on a specific data structure. Historically, this has resulted in powerful but inflexible systems incapable of adapting to the changing requirements of military missions. In an age of evolving technology, these pitfalls must be avoided by incorporating expected changes into the design of digital map systems. If they are made to accommodate a variety of cartographic data bases and allow for programmable manipulation of those bases, this new class of digital map sets can be reconfigured at the software level to meet the changing requirements of aircraft missions. This paper addresses current design concepts for such a map system on a Night Attack aircraft. The focus is on issues concerning the development and handling of existing map data products to meet current system requirements. This system, called the Digital Map Set (DMS), is being designed to accomplish the classical manipulations of Defense Mapping Agency Digital Land Mass System data. Additionally, aeronautical charts, aerial reconnaissance photos, flight plan data, and other two-dimensional bit mapped graphics also are accommodated. Mission requirements relating to the cartographic data bases shall be discussed along with ground support station and airborne system design issues.     

The Phoenix signal detection system

The Phoenix system is based on that developed for the Targeted Search element of the former NASA High Resolution Microwave Survey (HRMS). The Phoenix system was used at the Parkes 64 m and Mopra 22 m antennas of the Australian Telescope National Facility in the first part of 1995. The system consists of: (1) an RF/IF subsystem providing 1–3 GHz coverage; (2) a search subsystem with a 20 MHz, dual-polarization search bandwidth; (3) a two-site, pseudo-interferometric follow-up subsystem that reobserves interesting signals found by the search subsystem; and (4) a control subsystem capable of automatic searching.     

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 -     

The future of Earth observations in the USA

Earth observations is a controversial subject because of the diversity of interests involved, but one that should not be ignored, as is currently the case, by the US government. This article describes the changing character of Earth observations and the opportunities it provides for economic benefit and national and international economies of scale. Such opportunities can best be met by the formation of an international Earth observations body, in which the USA, represented by an expanded EOSAT, should play a leading role.     

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.