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91.
Journal of the Operational Research Society - 相似文献
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Sharon P. Hudson 《School science and mathematics》1996,96(3):133-139
The purpose of this study was to describe the supply and potential shortages of science teachers in the United States. Ninety-six percent of the State Science Consultants of the 50 State Boards of Education responded to a 1992 survey to assess the supply of science teachers. This survey was modeled after Howe and Gerlovich's 1982 study to provide an assessment of changes in science teacher supply over the last 10 years. Although there were improvements in the supply of science teachers, shortages were reported in all science subjects and were particularly critical in physics, chemistry, and earth science. In addition to providing a needed update on science teacher supply, this study analyzed 45 previous studies of science teacher supply and found convincing evidence to support the hypothesis that there is a persistent but fluctuating long term shortage of science teachers. This shortage is attributed to competition with business and industry. To alleviate critical shortages of science teachers, it is recommended that salaries be raised to be more competitive with industry and a national database be established to facilitate monitoring the supply of science teachers. 相似文献
95.
THE ANTI-HIV ACTIVITIES OF PHOTOACTIVE TERTHIOPHENES 总被引:1,自引:0,他引:1
J. B. Hudson L. Harris R. J. Marles J. T. Arnason 《Photochemistry and photobiology》1993,58(2):246-250
Abstract— Various synthetic analogues of the naturally occurring terthiophene, α-terthienyl (αT), were evaluated for anti-human immunodeficiency virus (HIV) activity. The compounds were incubated individually with a known amount of the virus, with or without UVA radiation (long-wavelength ultraviolet) and residual virus was monitored for its ability to produce cytopathic effects in cell culture and the production of virus-specific protein (p24). The basic terthiophene structure was essential for good anti-HIV activity, although various side chains, such as alcohols, bromo, methyl, thiomethyl and trimethylsilyl groups, permitted retention of maximum activity. Under optimum conditions, as little as 12 ng/mL of these compounds ( i.e approximately 3 × 10−8 M ) could inactivate 103 infectious virions. None of the compounds however were more active than αT itself. In all cases, UVA radiation was essential. Several side chains decreased the antiviral efficacy, and some side chains abrogated the activity. 相似文献
96.
Ping-pong balls form convenient reference targets for underwater sonars. Theoretical and experimental studies have confirmed that the acoustic target strength of such a ball can be predicted to within about ±·58 dB over a wide range of frequencies, even down to frequencies at which the wavelength in water exceeds the radius of the ball. Computed and experimental results are compared. 相似文献
97.
Probability Theory and Related Fields - 相似文献
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Molar extinction coefficients of some carbohydrates viz. l-arabinose (C5H10O5), d-glucose (C6H12O6), d-mannose (C6H12O6), d-galactose (C6H12O6), d(-) fructose (C6H12O6) and maltose (C12H24O12) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a
narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter
polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying
within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well. 相似文献
100.