S-matrices for spinor particles on Reissner-Nordstr\"{o}m black holes

The scattering problems arising when considering the contribution of the topologically inequivalent configurations of the spinors on Reissner-Nordstr\"{o}m black holes to the Hawking radiation are correctly stated. The corresponding $S$-matrices are described and presented in the form convenient to numerical computations.Comment: 11 pages, LaTe

First make something – principled, creative design as a tool for multi-disciplinary research in clinical engineering

Design provides a set of tools for exploring our world and these can give very different insights from the tools of the natural scientist or social scientist. The Art and Design Research Centre at Sheffield Hallam University is developing the use of creative practice at the centre of multi-disciplinary research and has demonstrated that this approach can bring significant results in areas of research which are more usually thought of thought of as science or engineering. This paper describes a 3-year project which has provided completely new ideas for the design of artificial limbs based on close analogies with human anatomy. The project was intended to look at very long-term developments but has also resulted in ideas for today's products and has changed the thinking of both clinicians and manufacturers. Investigative methods included iterative cycles of creative development and reflection; work with users including the production of video material to stimulate their thinking beyond the state of the art; and both qualitative and quantitative evaluation of design outcomes with scientific and clinical specialists.</p

High-frequency high-voltage high-power DC-to-DC converters

The current and voltage waveshapes associated with the power transitor and the power diode in an example current-or-voltage step-up (buck-boost) converter were analyzed to highlight the problems and possible tradeoffs involved in the design of high voltage high power converters operating at switching frequencies in the range of 100 Khz. Although the fast switching speeds of currently available power diodes and transistors permit converter operation at high switching frequencies, the resulting time rates of changes of current coupled with parasitic inductances in series with the semiconductor switches, produce large repetitive voltage transients across the semiconductor switches, potentially far in excess of the device voltage ratings. The need is established for semiconductor switch protection circuitry to control the peak voltages appearing across the semiconductor switches, as well as to provide the waveshaping action require for a given semiconductor device. The possible tradeoffs, as well as the factors affecting the tradeoffs that must be considered in order to maximize the efficiency of the converters are enumerated

Analysis of transistor and snubber turn-off dynamics in high-frequency high-voltage high-power converters

Dc to dc converters which operate reliably and efficiently at switching frequencies high enough to effect substantial reductions in the size and weight of converter energy storage elements are studied. A two winding current or voltage stepup (buck boost) dc-to-dc converter power stage submodule designed to operate in the 2.5-kW range, with an input voltage range of 110 to 180 V dc, and an output voltage of 250 V dc is emphasized. In order to assess the limitations of present day component and circuit technologies, a design goal switching frequency of 10 kHz was maintained. The converter design requirements represent a unique combination of high frequency, high voltage, and high power operation. The turn off dynamics of the primary circuit power switching transistor and its associated turn off snubber circuitry are investigated

Vacuum thermal conductivity measurements of NASA E4A1 elastomeric heat shield material

Line source vacuum thermal conductivity measures for elastomeric heat shield materia

Agricultural land use mapping

The author has identified the following significant results. Agricultural areas were selected or analysis in southeastern Pennsylvania, north central Montana, and southern Texas. These three sites represent a broad range of soils, soil parent materials, climate, modes of agricultural operation, crops, and field sizes. In each of these three sites, ERTS-1 digital data were processed to determine the feasibility of automatically mapping agricultural land use. In Pennsylvania, forest land, cultivated land, and water were separable within a 25,000 acre area. Four classes of water were also classified and identified, using ground truth. A less complex land use pattern was analyzed in Hill County, Montana. A land use map was prepared shown alternating patterns of summer fallow and stubble fields. The location of farmsteads could be inferred, along with that of a railroad line. A river and a creek flowing into the river were discernible. Six categories of water, related to sediment content and depth, were defined in the reservoir held by the Fresno dam. These classifications were completed on a 150 square mile area. Analysis of the data from Texas is in its formative stages. A test site has been selected and a brightness map has been produced