Real-time volume imaging using a crossed electrode array

This paper describes a unique crossed electrode array for real-time volume ultrasound imaging. By placing orthogonal linear array electrode patterns on the opposite sides of a hemispherically shaped composite transducer substrate, a 2D array can be fabricated using a small fraction of the elements required for a traditional 2D array. The performance of the array is investigated using a computer simulation of the radiation pattern. We show that by using a 288-element crossed electrode pattern it is possible to collect large field of view volume images (60deg times 60degsector) at real-time frame rates (>20 volume images/s), with image contrast and resolution comparable to what can be obtained using a conventional 128-element linear phased array.     

Soil, water, and pasture enrichment of antimony and arsenic within a coastal floodplain system

Moderate levels of enrichment with environmental contaminants, such as arsenic (As) and antimony (Sb), have received less attention than gross contamination related to obvious point sources of pollution. Within the Macleay floodplain of north-eastern NSW it was found that approximately 90% of the floodplain is enriched in As and Sb, and 6-8% of the floodplain contains As and Sb levels greater than current Australian soil environmental investigation levels. Variation in surface and depth distributions indicated flood deposition of As and Sb across major environmental floodplain environments, with highest accumulation in modern swamp depositional environments. The soil enrichment was reflected by pasture uptake (up to 6.4 and 2.2 mg kg(-1) for As and Sb, respectively) and elevated surface water concentrations (up to 10 and 21 times drinking guideline values and 2.9 and 6.9 times freshwater trigger values for protection of 95% of species for As and Sb, respectively) of these metalloids. Significant relationships between pasture and total soil levels imply higher relative availability than is typical at grossly contaminated sites. Implications for metalloid mobility and availability in acid sulfate soil environments in the floodplain are discussed.     

Effect of edges on the reliability of GaAs and (AlGa) as heterojunction leds

The effect of various diode geometries on the degradation rate of heterojunction diodes with either GaAs or (AlGa)As in the recombination region has been studied. It is shown that GaAs diodes are particularly sensitive to edge-related degradation which varies with the current density J as J^3/2. The addition of Al to the recombination region considerably reduces the degradation rate of diodes both with and without exposed edges, and data are reported for Al_0.1Ga_0.9As stripe-contact edge-emitting structures operating for over 20,000 hours with no change in output at 1000 A/cm².     

Computer assisted teaching of fluid mechanics and heat transfer

A computer-assisted course in fluid mechanics and heat transfer was offered in the sessions 1974/5 and 1975/6 to final-year B.Sc. students in Mechanical Engineering at Imperial College, London. This paper describes the course, the use made of the computer, and the results of the evaluation of the course.     

Photoluminescence efficiency and size distribution of self assembled ge dots on porous TiO2

For Ge nanodots approximately 20 nm in diameter grown by annealing a thin amorphous Ge layer deposited by molecular beam epitaxy on a mesoporous TiO2 layer on Si(001), photoluminescence (PL) was observed as a wide near-infrared band near 800 meV. Using a tight binding theoretical model, the energy-dependent PL spectrum was transformed into a dependence on dot size. The average dot size determined the peak energy of the PL band and its shape depended on the size distribution, including bandgap enlargement due to quantum confinement. Combining the dot sample PL with an established dependence of emission efficiency on dot diameter, it was possible to derive a dot size distribution and compare it with results obtained independently from atomic force microscopy.