Exceptionally pure epitaxial diamond layers have been grown by microwave plasma chemical vapour deposition, which have low boron doping, from 5 × 10 14 to 1 × 10 16 cm −3 , and the compensating n-type impurities are the lowest reported for any semiconducting diamond, <3 × 10 13 cm −3 . The hydrogen impurities that bind with the boron making them electrically inactive can be significantly reduced by baking the diamond to >700 • C for ∼1 s in air. Schottky diodes made on these epitaxial diamond films have breakdown voltages >6 kV, twelve times the highest breakdown voltage reported for any diamond diode and higher than any other semiconductor Schottky diode.
This study uses novel approaches to estimate the fall characteristics of hail, covering a size range from about 0.5 to 7 cm, and the drag coefficients of lump and conical graupel. Three-dimensional (3D) volume scans of 60 hailstones of sizes from 2.5 to 6.7 cm were printed in three dimensions using acrylonitrile butadiene styrene (ABS) plastic, and their terminal velocities were measured in the Mainz, Germany, vertical wind tunnel. To simulate lump graupel, 40 of the hailstones were printed with maximum dimensions of about 0.2, 0.3, and 0.5 cm, and their terminal velocities were measured. Conical graupel, whose three dimensions (maximum dimension 0.1–1 cm) were estimated from an analytical representation and printed, and the terminal velocities of seven groups of particles were measured in the tunnel. From these experiments, with printed particle densities from 0.2 to 0.9 g cm−3, together with earlier observations, relationships between the drag coefficient and the Reynolds number and between the Reynolds number and the Best number were derived for a wide range of particle sizes and heights (pressures) in the atmosphere. This information, together with the combined total of more than 2800 hailstones for which the mass and the cross-sectional area were measured, has been used to develop size-dependent relationships for the terminal velocity, the mass flux, and the kinetic energy of realistic hailstones.
The odorous compound 2-acetyl-1-pyrroline (2AP) was the cause of an undesirable "mousy" odor that developed when raw pearl millet grits were wetted and slowly dried. The 2AP in millet was identified by comparing gas chromatography (GC) retention times, odor at the GC sniffing port, mass spectra, and vapor-phase infrared spectra with those of 2AP from Jasmine and Indian Basmati aromatic rices. Identification of 2AP in aromatic rices had been reported previously. The odor of 2AP at the sniffing port was similar to the undesirable odor in bulk samples of wetted millet grits and was the key factor in identifying 2AP as the odorous component. Both blue and yellow raw millet grits produced 2AP and the mousy odor.
The physical properties of 2295 hailstones that developed in Great Plains (US) storms were measured, including their maximum dimension, mass, and cross-sectional area. Using these data, size-dependent relationships for their terminal velocities and kinetic energies are developed. These relationships can be used in weather forecast modeling and hail damage prediction and assessment. When hailstones are assumed to be spherical, their terminal velocities and kinetic energies are in agreement with what has been reported in previous studies. When non-sphericity is considered, which is the case for natural hail, the terminal velocities and kinetic energies are, on average, lower than those of spheres of the same maximum diameter, but can be larger.
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