Attitude control for spacecraft Patent

Attitude control device for space vehicle

Confined nanorods: jamming due to helical buckling

We investigate a longitudinally loaded elastic nanorod inside a cylindrical channel and show within the context of classical elasticity theory that the Euler buckling instability leads to a helical postbuckling form of the rod within the channel. The local pitch of the confined helix changes along the channel and so does the longitudinal force transmitted along the rod, diminishing away from the loaded end. This creates a possibility of jamming of the nanorod within the channel.Comment: 8 pages, 8 figure

OH(1720 MHz) Masers As Signposts of Molecular Shocks

We present observations of molecular gas made with the 15-m James Clark Maxwell Telescope toward the sites of OH(1720 MHz) masers in three supernova remnants: W28, W44 and 3C391. Maps made in the 12CO J=3-2 line reveal that the OH masers are preferentially located along the edges of thin filaments or clumps of molecular gas. There is a strong correlation between the morphology of the molecular gas and the relativistic gas traced by synchrotron emission at centimeter wavelengths. Broad CO line widths (dV=30-50 km/s) are seen along these gaseous ridges, while narrow lines are seen off the ridges. The ratio of H2CO line strengths is used to determine temperatures in the broad-line gas of 80 K, and the 13CO J=3-2 column density suggests densities of 10^4-10^5 cm{-3}. These observations support the hypothesis that the OH(1720 MHz) masers originate in post-shock gas, heated by the passage of a supernova remnant shock through dense molecular gas. From the observational constraints on the density, velocity and magnetic field we examine the physical properties of the shock and discuss the shock-production of OH. These OH(1720 MHz) masers are useful ``signposts'', which point to the most promising locations to study supernova remnant/molecular cloud interactions.Comment: ApJ (in press

Invariant manifolds and the geometry of front propagation in fluid flows

Recent theoretical and experimental work has demonstrated the existence of one-sided, invariant barriers to the propagation of reaction-diffusion fronts in quasi-two-dimensional periodically-driven fluid flows. These barriers were called burning invariant manifolds (BIMs). We provide a detailed theoretical analysis of BIMs, providing criteria for their existence, a classification of their stability, a formalization of their barrier property, and mechanisms by which the barriers can be circumvented. This analysis assumes the sharp front limit and negligible feedback of the front on the fluid velocity. A low-dimensional dynamical systems analysis provides the core of our results.Comment: 14 pages, 11 figures. To appear in Chaos Focus Issue: Chemo-Hydrodynamic Patterns and Instabilities (2012

High specific radioactivities of osmium from photonuclear reactions

The investigation described in this thesis has included a study of the activities in iridium, osmium, and rhenium which were produced by photonuclear reactions in osmium and iridium. Osmium activities produced by slow neutron bombardment on osmium metal have also been investigated. During the course of these experiments a method of concentrating osmium activities by the Szilard-Chaimers process was discovered and was further developed

A Decision Support System for Rangeland Management in Degrading Environments

The continued viability and productivity of commercial and emerging agriculture in KwaZulu-Natal Province, South Africa, depends on the accurate assessment and sustainable utilization of available natural resources. Sustainability implies that growth and development must take place, and be maintained over time, within the limits set by natural ecosystems. Utilizing an extensive GIS database, field surveys and remote sensing technology, a land assessment decision support system (LADSS) has been developed in an attempt to define these limits for the Province. This system has been developed to assess the appropriate use of existing resources as well as the suitability of current land use practices. LADSS includes a predictive tool which allows the impact of a proposed change in land use to be forecast within 590 agro-ecological zones of the Province