Large-diameter astromast development

The 15-m-long by 0.75-diameter deployable supermast was delivered. The performance characteristics, design parameters, and developmental work associated with this mast are described. The main differences, besides the length of these two mast sections, are a change in the longeron material (the principal structural member) to a circular cross section and the incorporation of a lanyard-bridle system which makes unaided deployment and retraction possible in zero gravity

The geometry of the 37-tile microwave antenna support structure

The geometry of the support structure for a proposed parabolic shaped microwave antenna is examined. The surface of the antenna is comprised of 37 hexagonal shaped tiles, each connected to a truss module. The units are joined together to form a rigidized, faceted, concave parabolic surface. The geometry specifications are described through an explanation of the structural components which make up the antenna, a description of the coordinate system devised to identify the structure, and a presentation of the nondimensional results

Constraining the Angular Momentum-loss Rates of the Sun and Other Sun-like Stars

Stellar rotation, convection, and magnetism are intricately linked in low-mass stars like the Sun. In their outer convective envelopes, the interplay of rotation and convection form a magnetic dynamo capable of sustaining both large and small scale magnetic fields. The strength of these magnetic fields are observed to grow with increasing rotation rate. The coronae of low-mass stars are heated by these magnetic fields (the exact mechanism of which remains under debate), such that the thermal pressure drives a quasi-steady outflow of plasma, referred to as a stellar wind. Due to the interaction of the large-scale magnetic field with the outflowing plasma, stellar winds are able to efficiently remove angular momentum from these stars. Therefore, the evolution of rotation for low-mass stars (on the the main sequence) is governed by their stellar winds, and by interrelation, the evolution of their magnetic activity and stellar wind output. In this thesis I attempt to better constrain the angular momentum-loss rates of the Sun and other Sun-like stars through the use of magnetohydrodynamic simulations combined with a broad range of observations. Though I do not find a concrete value for the solar case, I reduce the uncertainty in its value to within a factor of a few by locating key factors/quantities which limit our predictions, and further highlight the importance of understanding the solar angular momentum-loss rate in an astrophysical context. For the other Sun-like stars, I find the simulation results largely under-predict the angular momentum-loss rates implied by current rotation-evolution models. The reason(s) for this are uncertain, but likely involve uncertainties in both the observed magnetic field strengths and mass-loss rates of these stars, along with the under-prediction of how much of the surface magnetic field is ``opened'' by the stellar wind.European Commissio

Large diameter astromast development, phase 1

Coilable-longeron lattice columns called Astromasts (trademark) were manufactured for a variety of spacecraft missions. These flight structures varied in diameter from 0.2 to 0.5 meter (9 to 19 in.), and the longest Astromast of this type deploys to a length of 30 meters (100 feet). A double-laced diagonal Astromast design referred to as the Supermast (trademark) which, because it has shorter baylengths than an Astromast, is approximately four times as strong. The longeron cross section and composite material selection for these structures are limited by the maximum strain associated with stowage and deployment. As a result, future requirements for deployable columns with high stiffness and strength require the development of both structures in larger diameters. The design, development, and manufacture of a 6.1-m-long (20-ft), 0.75-m-diameter (30-in.), double-laced diagonal version of the Astromast is described

Numerical simulation of intense multi-scale vortices generated by supercell thunderstorms

December 19, 1997.Bibliography: pages 276-287.Sponsored by National Science Foundation ATM-9306754.Sponsored by National Science Foundation ATM-9420045

Anomalous Stark Shifts in Single Vertically Coupled Pairs of InGaAs Quantum Dots

Vertically coupled Stranski Krastanow QDs are predicted to exhibit strong tunnelling interactions that lead to the formation of hybridised states. We report the results of investigations into single pairs of coupled QDs in the presence of an electric field that is able to bring individual carrier levels into resonance and to investigate the Stark shift properties of the excitons present. Pronounced changes in the Stark shift behaviour of exciton features are identified and attributed to the significant redistribution of the carrier wavefunctions as resonance between two QDs is achieved. At low electric fields coherent tunnelling between the two QD ground states is identified from the change in sign of the permanent dipole moment and dramatic increase of the electron polarisability, and at higher electric fields a distortion of the Stark shift is attributed to a coherent tunnelling effect between the ground state of the upper QD and the excited state of the lower QD.Comment: Conference paper for QD2004 3 figure

Development and application of operational techniques for the inventory and monitoring of resources and uses for the Texas coastal zone. Volume 1: Text

The author has identified the following significant results. Image interpretation and computer-assisted techniques were developed to analyze LANDSAT scenes in support of resource inventory and monitoring requirements for the Texas coastal region. Land cover and land use maps, at a scale of 1:125,000 for the image interpretation product and 1:24,000 for the computer-assisted product, were generated covering four Texas coastal test sites. Classification schemes which parallel national systems were developed for each procedure, including 23 classes for image interpretation technique and 13 classes for the computer-assisted technique. Results indicate that LANDSAT-derived land cover and land use maps can be successfully applied to a variety of planning and management activities on the Texas coast. Computer-derived land/water maps can be used with tide gage data to assess shoreline boundaries for management purposes

Development and application of operational techniques for the inventory and monitoring of resources and uses for the Texas coastal zone. Volume 2: Appendices

There are no author-identified significant results in this report