Aerodynamic Drag Reduction for Satellites in Low Earth Orbit

Stalker (AIAA Paper 87-0403) has suggested that, by ejecting molecules directly upstream from the entire face of a satellite, it is possible to reduce the drag on a satellite in low-Earth orbit and hence maintain orbit with a total fuel mass (for forward ejection and conventional reaction rockets) less than the typical mass requirements of conventional rockets. An analytical analysis is presented here, as well as Monte Carlo simulations. These indicate that to reduce the overall drag on the satellite significantly, collisions between the freestream and ejected molecules must occur at least two satellite diameters upstream. This can be achieved if the molecules are ejected far upstream from the satellite’s surface through a sting that projects forward from the satellite. Using some estimates of what would be feasible sting arrangements, we find that the drag on the satellite can be reduced to such an extent that the satellite’s orbit can be maintained with a total fuel mass of less than 60% of that required for reaction rockets alone. Upstream ejection is effective in reducing the drag for freestream Knudsen numbers less than approximately 250, but not otherwise.

Houses near Cotton Tree Housing Estate, Maroochydore

This pilot project at Cotton Tree, Maroochydore, on two adjacent, linear parcels of land has one of the properties privately owned while the other is owned by the public housing authority. Both owners commissioned Lindsay and Kerry Clare to design housing for their separate needs which enabled the two projects to be governed by a single planning and design strategy. This entailed the realignment of the dividing boundary to form two approximately square blocks which made possible the retention of an important stand of mature paperbark trees and gave each block a more useful street frontage. The scheme provides seven two-bedroom units and one single-bedroom unit as the private component, with six single-bedroom units, three two-bedroom units and two three-bedroom units forming the public housing. The dwellings are deployed as an interlaced mat of freestanding blocks, car courts, courtyard gardens, patios and decks. The key distinction between the public and private parts of the scheme is the pooling of the car parking spaces in the public housing to create a shared courtyard. The housing climbs to three storeys on its southern edge and falls to a single storey on the north-western corner. This enables all units and the principal private outdoor spaces to have a northern orientation. The interiors of both the public and private units are skilfully arranged to take full advantage of views, light and breeze.

Holiday houses, Judge House, Camp Island

As seen from hill behind.

'Tetol': a stereo-rigid four-strand motif for alkali and alkaline earth metal ion coordination

The tetraalcohol 2,3,5,6-endo,endo,endo,endo-tetrakis(hydroxymethyl]bicyclo[2.2.1]heptane (tetol, 1) has been prepared and crystallises readily as the lithium(I) complex [Li(1)(2)]Cl, forming an oligomeric multi-chain structure in which pairs of alcohols from two crystallographically independent tetol molecules bind lithium ions tetrahedrally. However, formation of monomeric structures in solution is inferred from electrospray mass spectroscopy, which has also shown evidence of exchange of lithium ion in the complexed species by added alkaline earth ions. (C) 2000 Elsevier Science S.A. All rights reserved.

Anisotropic convection model for the earth's mantle

The paper presents a theory for modeling flow in anisotropic, viscous rock. This theory has originally been developed for the simulation of large deformation processes including the folding and kinking of multi-layered visco-elastic rock (Muhlhaus et al. [1,2]). The orientation of slip planes in the context of crystallographic slip is determined by the normal vector - the director - of these surfaces. The model is applied to simulate anisotropic mantle convection. We compare the evolution of flow patterns, Nusselt number and director orientations for isotropic and anisotropic rheologies. In the simulations we utilize two different finite element methodologies: The Lagrangian Integration Point Method Moresi et al [8] and an Eulerian formulation, which we implemented into the finite element based pde solver Fastflo (www.cmis.csiro.au/Fastflo/). The reason for utilizing two different finite element codes was firstly to study the influence of an anisotropic power law rheology which currently is not implemented into the Lagrangian Integration point scheme [8] and secondly to study the numerical performance of Eulerian (Fastflo)- and Lagrangian integration schemes [8]. It turned out that whereas in the Lagrangian method the Nusselt number vs time plot reached only a quasi steady state where the Nusselt number oscillates around a steady state value the Eulerian scheme reaches exact steady states and produces a high degree of alignment (director orientation locally orthogonal to velocity vector almost everywhere in the computational domain). In the simulations emergent anisotropy was strongest in terms of modulus contrast in the up and down-welling plumes. Mechanisms for anisotropic material behavior in the mantle dynamics context are discussed by Christensen [3]. The dominant mineral phases in the mantle generally do not exhibit strong elastic anisotropy but they still may be oriented by the convective flow. Thus viscous anisotropy (the main focus of this paper) may or may not correlate with elastic or seismic anisotropy.

The strain-driven pyrochlore to "defect fluorite" phase transition in rare earth sesquioxide stabilized cubic zirconias

The relationship between the ordering characteristic of the pyrochlore structure type and that characteristic of the defect fluorite structure type (immediately on either side of two phase regions separating the two structure types) in a range of rare eath sesquioxide stabilized cubic zirconias is investigated via electron diffraction and imaging. Systematic structural change as a function of composition and relative size of the constituent metal ions is highlighted and a multi-q to single-q = 1/2 [111]* model proposed for the observed pyrochlore to defect fluorite phase transition. Strain introduced into the close-packed {111} metal ion planes of the defect fluorite average structure by the local cation and oxygen vacancy distribution is pointed to as the likely origin of the observed behavior. (C) 2001 Academic Press

Earth pressure on cantilever walls at design retained heights

There are many methods for the analysis and design of embedded cantilever retaining walls. They involve various different simplifications of the pressure distribution to allow calculation of the limiting equilibrium retained height and the bending moment when the retained height is less than the limiting equilibrium value, i.e. the serviceability case. Recently, a new method for determining the serviceability earth pressure and bending moment has been proposed. This method makes an assumption defining the point of zero net pressure. This assumption implies that the passive pressure is not fully mobilised immediately below the excavation level. The finite element analyses presented in this paper examine the net pressure distribution on walls in which the retained height is less, than the limiting equilibrium value. The study shows that for all practical walls, the earth pressure distributions on the front and back of the wall are at their limit values, Kp and K-a respectively, when the lumped factor of safety F-r is less than or equal to2.0. A rectilinear net pressure distribution is proposed that is intuitively logical. It produces good predictions of the complete bending moment diagram for walls in the service configuration and the proposed method gives results that have excellent agreement with centrifuge model tests. The study shows that the method for determining the serviceability bending moment suggested by Padfield and Mair(1) in the CIRIA Report 104 gives excellent predictions of the maximum bending moment in practical cantilever walls. It provides the missing data that have been needed to verify and justify the CIRIA 104 method.

Tungsten isotope evidence from similar to 3.8-Gyr metamorphosed sediments for early meteorite bombardment of the Earth

The 'Late Heavy Bombardment' was a phase in the impact history of the Moon that occurred 3.8-4.0 Gyr ago, when the lunar basins with known dates were formed(1,2). But no record of this event has yet been reported from the few surviving rocks of this age on the Earth. Here we report tungsten isotope anomalies, based on the Hf-182-W-182 system (half-life of 9 Myr), in metamorphosed sedimentary rocks from the 3.7-3.8-Gyr-old Isua greenstone belt of West Greenland and closely related rocks from northern Labrador, Canada. As it is difficult to conceive of a mechanism by which tungsten isotope heterogeneities could have been preserved in the Earth's dynamic crust-mantle environment from a time when short-lived Hf-182 was still present, we conclude that the metamorphosed sediments contain a component derived from meteorites.