The effect of boron,oxygen, and fluorine in ion implanted GaAs

Effects of boron, fluorine, and oxygen in GaAs have been investigated by electrical characterization using current-voltage, capacitance-voltage and deep level transient spectroscopy techniques. Ion implantation at 100 keV energy was conducted with doses of 10¹¹ and 10¹²/cm². Carrier compensation was observed in each implanted sample. The compensation effect strongly depended on ion implantation condition and ion species. More free carriers were compensated for higher dose and heavier species; however, severe surface damage would also be induced that degrade electrical performance. Rapid thermal annealing treatment showed the heavier ion implanted samples to be more thermally stable. Defect levels for each implanted species were compared and identified. A native shallow defect E4 was easily removed by ion implantation. In higher dose and heavier ion implantation, both electron and hole traps were induced. However, in some cases, heavier ion implantation also removed native defects. Acceptor-type surface states were created by implantation that degrade material electrical characteristics and also reduce the effect of compensation. The damage induced traps were mostly point-defects or point-defect/impurity complexes as evidenced by sensitivity to heat treatment.     

Solidification Behavior of Undercooled Liquid Aluminum Oxide

Solidification of aluminum oxide from undercooled melts was investigated in containerless experiments. Specimens were levitated in a gas jet, stabilized with an acoustic positioning device, and melted with cw CO₂ laser beams. Cooling curves were obtained by optical pyrometry when the laser intensity was reduced. The materials examined were high-purity Verneuil sapphire, 99.5% polycrystalline alumina, and oxide materials recovered from the effluent of an aluminum-fueled rocket motor. The degree of undercooling, the apparent temperature behavior during the thermal arrest on solidification, and the structure of the materials formed were different in argon and oxygen atmospheres. Undercooling of the sapphire and alumina materials was 360 ± 10 K in an oxygen atmosphere and approximately 450 K in argon. Melting and solidification of high-purity sapphire resulted in a dendritic and porous polycrystalline material in oxygen. Dense, larger crystals were obtained in argon. Products formed from 99.5% alumina were discolored and the cores were white, indicating impurity segregation effects. More reproducible behavior was observed for the sapphire and 99.5% alumina than for the tungstencontaminated rocket motor effluent materials.     

Evaluation of iron–epoxy metal nanocomposite in glass fibre and Kevlar

This paper deals with the enrichment of the both mechanical and electrical properties of Kevlar and glass fibres, not including mounting the weight of the structure by adding the iron (Fe) nanocomposites with the epoxy resin. The Fe is mixed well with the epoxy to increase the mechanical constancy and the electrical property of the fibre by a non-covalent approach. The synthesis of metal nanocomposite with epoxy is done by the direct mixing method. The Kevlar and the glass fibre were taken as the samples for this study. The zinc oxide and epoxy were mixed simultaneously using a mechanical stirrer to give appropriate dispersion and adhesion without disturbing the hydrophobic performance of the epoxy, and the Fe powder and epoxy are added with a hardener in the ratio of 1:1:0.1. The results show that the mechanical property of the fibre increased with the decrease in the weight of the laminate when they are treated with the metal nanocomposite.     

Cell cycle behavior and MyoD expression in response to T3 differ in normal and mdx dystrophic primary muscle cell cultures

Since mdx limb muscle regeneration in vivo is accompanied by rapid myoblast proliferation and differentiation compared to normal, we tested the possibility that proliferation and differentiation were differentially regulated in normal and mdx dystrophic muscle cells. Cell cycle behavior, MyoD expression, and the effects of thyroid hormone (T3) treatment were examined in primary cultures. Using a 4-hour pulse time for bromodeoxyuridine (BrdU) incorporation during S-phase, the phases of the cell cycle (early S, late S, G(2)/M, and G(0)/G(1)) were separated by 2-colour fluorescence (BrdU/PI) analysis using flow cytometry. The G(0)/G(1)-early S and the late S-G(2)/M transitions were examined under the influence of T3 in cycling normal and mdx muscle cell cultures over a 20-hour time period. Myogenesis and differentiation were assessed morphologically and by immunostaining for MyoD protein. Mdx cultures had fewer cells in G(0)/G(1) at 20 hours and more cells in early and late S-phase compared to normal cultures. T3 significantly increased the proportion of normal cells in early S-phase by 20 hours, and reduced the proportions in G(2)/M phase. Over the same time interval in parallel cultures, the proportion of MyoD+ normal cells decreased significantly. In the absence of T3, mdx cell cultures showed greater proportions of cells in S-phase than normal cultures, and similar increases in S-phase and loss of MyoD expression over time. However, mdx cultures had no change in the proportion that were MyoD+ during T3 treatment. The results confirm that T3 in primary cultures increased proliferation and prevented the de-differentiation of mdx cells to a greater degree than was typical of normal cells. The different susceptibilities to T3-related shifts between proliferation and differentiation observed in vitro support the idea that committed mdx myoblasts may be more activated and proliferative than normal myoblasts during regeneration in vivo.     

Influence of aging on phosphorus sorption to alum floc in lake water

Alum is often added to eutrophic lakes to limit the release of phosphorus from sediments. This study quantified the effect of age and extent of crystallization on the phosphate (PO4-P) sorption capacity of alum floc. Aluminum hydroxide flocs were formed from alum addition at a dose of 25 mg/L of Al3+ to Big Bear Lake waters returned to the laboratory; flocs were then aged for 4, 20, 50, 120, and 180 days in the treated lake waters. The physical and mineralogical properties of the alum floc were characterized using surface area and thermal analyses. Phosphate sorption to the floc was evaluated using filtered lake water and NaCl/NaHCO3 solutions spiked with PO4-P concentrations ranging from 0 to 100 mg/L. The Langmuir model provided reasonable fits to data (r2 = 0.97-1.00), from which sorption constants and sorption maxima were determined. Phosphate sorption decreased with increased floc age and crystallinity and decreased surface area. Phosphate sorption maximum of the alum floc aged for 6 months was about 50% lower than freshly precipitated floc, while the binding constant, Kads, decreased approximately 65% over this same time period.     

Cadmium deposition and hepatic microsomal activity in mice fed Swiss chard grown on municipal incinerator refuse ash

Incineration of municipal solid waste results in the production of millions of tons of ash that may be typically high in heavy metals such as cadmium. Disposal of such ash in landfills capped with soil could lead to absorption of such metals by plants and deposition in foraging animal tissues. In this study, weanling, male mice were fed swiss chard that was grown on soil amended with 10% w/w municipal incinerator refuse ash. Cadmium was taken up by the swiss chard (8.15 ppm, dry wt). The mice fed diets containing 25% of ash-grown chard showed mean kidney and liver concentrations of cadmium (ppm, dry wt), respectively, of 2.80 +/- 0.30 and 0.45 +/- 0.03. Control mice fed soil-grown chard showed significantly lower kidney and liver concentrations of cadmium, i.e. 0.39 +/- 0.02 and 0.05 +/- 0.00 ppm. Since refuse incinerator ashes may contain various organic toxicants that can be hepatic microsomal inducers, the relative liver weights and hepatic microsomal aminopyrine N-demethylase and p-nitroanisole O-demethylase activities of mice fed control or ash-grown chard were measured. No consistent increases in these latter parameters were found in the ash-grown chard fed mice as compared with the control animals.     

An improved analysis of experimental data from 125 I hot-line autoradiographs: allowing for the effects of background grains

In this paper we suggest a new statistical method of correcting the results of hot-line experiments for the effects of background sources and we use the new method to reassess the adequacy of three probability distributions proposed in the literature for image spread from line sources. The data are from sources labelled with ¹²⁵I in semi-thin resin sections 0·4-0·8 μm in thickness. The new method reveals that two of the models describe the empirical distributions more closely than earlier analysis had suggested, and it confirms an increasing relationship between half distance of image spread and the thickness of the source. However, it also confirms that considerable ‘inter hot-line’ experimental variation remains, even after background correction. This suggests that multiple experiments are needed to produce reliable estimates of half distance.     

Book reviews

RESOURCE TRENDS AND POPULATION POLICY: A TIME FOR REASSESSMENT, by Lester R. Brown. Worldwatch Institute, Washington, D.C., May 1979; Worldwatch Paper 29. (Paperback $2.00)

THE NEXT SEVENTY YEARS: POPULATION, FOOD AND RESOURCES, by B. Gil‐land. Abacus Press, London, 1979. 133 pp. (£9.50)

POPULATION POLICY ANALYSIS, edited by M. E. Kraft and M. Schneider. D. C. Heath, London, 1979. (£0.00)

ENVIRONMENTAL IMPACT ASSESSMENT, by Brian B. Clark, Ronald Bisset and Peter Wath‐ern. Manssell, London and Bowker, New York, 1980. 516 pp. (£0.00)

ADVANCES IN ECOLOGICAL RESEARCH, Vol. 11, edited by Amyan MacFadyen. Academic Press, London, 1980. 428 pp. (£25.00)

MICROBIAL GROWTH AND SURVIVAL IN EXTREMES OF ENVIRONMENT, edited by G. W. Gould and Janet E. Cory. Academic Press, London, 1980. 244 pp. (£16.00)

UNDER NEW MANAGEMENT: Port Growth and Emerging Coastal Management Programs, by Marc Hershman, Robert Goodwin, Andrew Ruot‐sala, Maureen McCrea and Yehuda Hayuth. A Washington Sea Grant Publication, 1978. 212 pp. ($12.50)

HANDBOOK OF INDUSTRIAL ENERGY ANALYSIS, by J. Boustead and G. F. Hancock. Ellis‐Harwood, Chichester, U.K., 1979. (£25.00)

TREE GROWTH AND ENVIRONMENTAL STRESSES, by T. T. Kozlowski. University of Washington Press, Seattle and London, 1979. vii + 192 pp. (£12.50)

ALL GOOD THINGS AROUND US, by Pamela Michael. Illustrated by Christabel King. Ernest Benn Ltd., London, 1980. 240 pp. (£12.95)

HUMAN GEOGRAPHY (2nd Edition), by A. V. Perpillou. Longman Group, London, U.K., 1977. xviii + 570 pp. 37 pls., 27 maps and diagrams, Index. (Paperback £5.50)

INDUSTRIAL AND HAZARDOUS WASTES IMPOUNDMENT, by N. P. Cheremisinoff, P. N. Cheremisinoff, F. Ellerbeck and A. J. Perna. Ann Arbor Science, Michigan, 1979. ix + 475 pp. Index. (£16.25)

PHOSPHORUS IN THE ENVIRONMENT: ITS CHEMISTRY AND BIOCHEMISTRY. (Ciba Foundation No. 57, New Series), by Ruth Porter and David W. Fitzsimons. Elsevier, 1978. (£18.15)

TOXIC AND HAZARDOUS WASTE DISPOSAL. Vol. II, edited by R. B. Pojasek (Options for Sterilization Solidifications). Ann Arbor Science, Michigan, U.S.A., 1979, 259 pp. (£19.80)

SON OF THE WILDERNESS (The Life of John Muir), by Linnie Marsh Wolfe. The University of Wisconsin Press, Madison, 1978. 364 pp. (Paperback £4.90)

NATURE'S PRICE, by W. van Dieren and M. G. W. Hummelinck. Marion Boyars, London, Boston, 1979. (Paperback £3.50)

PERMACULTURE ONE, by Bill (B. C.) Molli‐son and David Holmgren. Corgi Books, Trans‐world Publishers Ltd., Melbourne, Australia. 128 pp. (A $4.95)

ENVIRONMENTAL AERODYNAMICS, by R. S. Scorer. Ellis Horwood, Chichester, U.K., 1978. 488 pp. (Hardback £20.00; paperback £7.50)     

Artificial neural networks for machining processes surface roughness modeling

In recent years, several papers on machining processes have focused on the use of artificial neural networks for modeling surface roughness. Even in such a specific niche of engineering literature, the papers differ considerably in terms of how they define network architectures and validate results, as well as in their training algorithms, error measures, and the like. Furthermore, a perusal of the individual papers leaves a researcher without a clear, sweeping view of what the field’s cutting edge is. Hence, this work reviews a number of these papers, providing a summary and analysis of the findings. Based on recommendations made by scholars of neurocomputing and statistics, the review includes a set of comparison criteria as well as assesses how the research findings were validated. This work also identifies trends in the literature and highlights their main differences. Ultimately, this work points to underexplored issues for future research and shows ways to improve how the results are validated.