Applications of inertial navigation and modern control theory to the all weather landing problem

Inertial navigation and automatic landing control theory applied to instrument landing proble

The distribution of shock waves in driven supersonic turbulence

Supersonic turbulence generates distributions of shock waves. Here, we analyse the shock waves in three-dimensional numerical simulations of uniformly driven supersonic turbulence, with and without magnetohydrodynamics and self-gravity. We can identify the nature of the turbulence by measuring the distribution of the shock strengths. We find that uniformly driven turbulence possesses a power law distribution of fast shocks with the number of shocks inversely proportional to the square root of the shock jump speed. A tail of high speed shocks steeper than Gaussian results from the random superposition of driving waves which decay rapidly. The energy is dissipated by a small range of fast shocks. These results contrast with the exponential distribution and slow shock dissipation associated with decaying turbulence. A strong magnetic field enhances the shock number transverse to the field direction at the expense of parallel shocks. A simulation with self-gravity demonstrates the development of a number of highly dissipative accretion shocks. Finally, we examine the dynamics to demonstrate how the power-law behaviour arises.Comment: accepted to Astron. & Astrophys.; ten page

Toxic Hazards Research Unit annual technical report, 1969 Final report, Jun. 1968 - May 1969

Apollo materials toxicity screening tests and effects of ethylene glycol, monomethylhydrazine, NF3, OF2, and ClF

Preliminary evaluation of infrared and radar imagery, Washington and Oregon coasts

Airborne infrared and radar photography of Oregon and Washington coastal region

Impacts of Reduced Water Availability on Lower Murray Irrigation, Australia

This article evaluates irrigated agriculture sector response and resultant economic impacts of climate change for a part of the Murray Darling Basin in Australia. A water balance model is used to predict reduced basin inflows for mild, moderate and severe climate change scenarios involving 10, 20, 40 Celcius warming, and predict 13%, 38% and 63% reduced inflows. Impact on irrigated agricultural production and profitability are estimated with a mathematical programming model using a two-stage approach that simultaneously estimates short and long-run adjustments. The model accounts for a range of adaptive responses including: deficit irrigation, temporarily fallowing some areas, and permanently reducing irrigated area and changing the mix of crops. The results suggest that relatively low cost adaptation strategies are available for moderate reduction in water availability and thus costs of such reduction are likely to be relatively small. In more severe climate change scenarios greater costs are estimated, adaptations predicted include a reduction in total area irrigated, investments in efficient irrigation, and a shift away from perennial to annual crops as the latter can be managed more profitably when water allocations in some years are very low.water availability, irrigation, Murray Darling Basin, climate change

Modification of Projected Velocity Power Spectra by Density Inhomogeneities in Compressible Supersonic Turbulence

(Modified) The scaling of velocity fluctuation, dv, as a function of spatial scale L in molecular clouds can be measured from size-linewidth relations, principal component analysis, or line centroid variation. Differing values of the power law index of the scaling relation dv = L^(g3D) in 3D are given by these different methods: the first two give g3D=0.5, while line centroid analysis gives g3D=0. This discrepancy has previously not been fully appreciated, as the variation of projected velocity line centroid fluctuations (dv_{lc} = L^(g2D)) is indeed described, in 2D, by g2D=0.5. However, if projection smoothing is accounted for, this implies that g3D=0. We suggest that a resolution of this discrepancy can be achieved by accounting for the effect of density inhomogeneity on the observed g2D obtained from velocity line centroid analysis. Numerical simulations of compressible turbulence are used to show that the effect of density inhomogeneity statistically reverses the effect of projection smoothing in the case of driven turbulence so that velocity line centroid analysis does indeed predict that g2D=g3D=0.5. Using our numerical results we can restore consistency between line centroid analysis, principal component analysis and size-linewidth relations, and we derive g3D=0.5, corresponding to shock-dominated (Burgers) turbulence. We find that this consistency requires that molecular clouds are continually driven on large scales or are only recently formed.Comment: 28 pages total, 20 figures, accepted for publication in Ap

Hierarchical Subquery Evaluation for Active Learning on a Graph

To train good supervised and semi-supervised object classifiers, it is critical that we not waste the time of the human experts who are providing the training labels. Existing active learning strategies can have uneven performance, being efficient on some datasets but wasteful on others, or inconsistent just between runs on the same dataset. We propose perplexity based graph construction and a new hierarchical subquery evaluation algorithm to combat this variability, and to release the potential of Expected Error Reduction. Under some specific circumstances, Expected Error Reduction has been one of the strongest-performing informativeness criteria for active learning. Until now, it has also been prohibitively costly to compute for sizeable datasets. We demonstrate our highly practical algorithm, comparing it to other active learning measures on classification datasets that vary in sparsity, dimensionality, and size. Our algorithm is consistent over multiple runs and achieves high accuracy, while querying the human expert for labels at a frequency that matches their desired time budget.Comment: CVPR 201

Economic assessment of acquiring water for environmental flows in the Murray Basin

This article is an economic analysis of reallocating River Murray Basin water from agriculture to the environment with and without the possibility of interregional water trade. Acquiring environmental flows as an equal percentage of water allocations from all irrigation regions in the Basin is estimated to reduce returns to irrigation. When the same volume of water is taken from selected low-value regions only, the net revenue reduction is less. In all scenarios considered, net revenue gains from freeing trade are estimated to outweigh the negative revenue effects of reallocating water for environmental flows. The model accounts for how stochastic weather affects market water demand, supply and requirements for environmental flows. Net irrigation revenue is estimated to be $75 million less than the baseline level for a scenario involving reallocating a constant volume of water for the environment in both wet and dry years. For a more realistic scenario involving more water for the environment in wet and less in dry years, estimated net revenue loss is reduced by 48 per cent to$39 million. Finally, the external salinity-related costs of water trading are estimated at around $1 million per annum, a quite modest amount compared to the direct irrigation benefits of trade.Resource /Energy Economics and Policy,