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排序方式: 共有243条查询结果,搜索用时 15 毫秒
81.
William Paneral Brent Leslie Derek Lovingood Robert Stapleton Mike Anderson Anna McRae Leri Atwater Thomas Manning Dennis Phillips 《The Chemical Educator》2002,7(3):149-154
A discharge is arced to different solutions containing the simple molecular species water, methanol, and ammonia. We show that the impact of the discharge at the discharge-solution interface produces a range of organic molecules, including amino acids and polymers containing carboxylate, amine, imine, and cyano groups. The classic Miller-Urey experiment, of which there are hundreds of variations, changing parameters such as gas composition, pressures, and voltage have been tested, involves the production of simple amino acids and other species in the gas phase in an arc discharge. This works emphasis is the production of various chemical species at a discharge-liquid interface. The analysis of the product is conducted by IR, UV–VIS, LC–MS and MALDI–MS. As a laboratory exercise or a demonstration, this simple derivation of the Miller-Urey experiment can be used in a variety of teaching settings, from high school through advanced undergraduate research classes to demonstrate the basic hypothesis of how life on Earth may have started. 相似文献
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Abstract Treatment of readily available monomethyl maleic acid (1) with three equivalents of methyl magnesium iodide followed by an excess of 2-methyl-1-propenyl magnesium bromide and a catalytic amount of CuBr produces d?-pyrocin (3) in a high yield. 相似文献
85.
Md. Imam Uddin Jason R. Buck Michael L. Schulte Dewei Tang Samir A. Saleh Yiu-Yin Cheung Joel Harp H. Charles Manning 《Tetrahedron letters》2014
A novel and highly efficient synthetic method leveraging microwave-assisted organic synthesis (MAOS) to yield di-7-azaindolylmethanes (DAIMs) is reported. Under MAOS conditions, reaction of 7-azaindole with aldehydes resulted predominantly in DAIMs, as opposed to the expected 7-azaindole addition products that form at ambient temperature. Based upon studies of different indoles and azaindoles with various aromatic and aliphatic aldehydes, we herein propose a mechanism where rapid and efficient microwave heating promotes nucleophilicity of 7-azaindoles toward the corresponding alkylidene–azaindolene intermediate to form the DAIM. This sequence provides a versatile approach to efficiently synthesize novel DAIMs that may be useful pharmaceuticals. 相似文献
86.
Stack DW Peter N Manning RE Fristrup KM 《The Journal of the Acoustical Society of America》2011,129(3):1375-1380
Noise impacts resources and visitor experience in many protected natural areas, and visitors can be the dominant source of noise. This experimental study tested the efficacy and acceptability of signs asking visitors to be quiet at Muir Woods National Monument, California. Signs declaring a "quiet zone" (at the park's Cathedral Grove) or a "quiet day" (throughout the park) were posted on a randomized schedule that included control days (no signs). Visitor surveys were conducted to measure the cognitive and behavioral responses of visitors to the signs and test the acceptability of these management practices to visitors. Visitors were highly supportive of these management practices and reported that they consciously limited the amount of noise they produced. Sound level measurements showed substantial decreases on days when signs were posted. 相似文献
87.
Dr. J. E. Warren C. G. Perkins Dr. K. E. Jelfs Dr. P. Boldrin Dr. P. A. Chater Dr. G. J. Miller Dr. T. D. Manning Dr. M. E. Briggs Dr. K. C. Stylianou Dr. J. B. Claridge Prof. M. J. Rosseinsky 《Angewandte Chemie (International ed. in English)》2014,53(18):4592-4596
A flexible metal‐organic framework selectively sorbs para‐ (pX) over meta‐xylene (mX) by synergic restructuring around pX coupled with generation of unused void space upon mX loading. The nature of the structural change suggests more generally that flexible structures which are initially mismatched in terms of fit and capacity to the preferred guest are strong candidates for effective molecular separations. 相似文献
88.
M. Dobrowolny E. Melchioni U. Guidoni L. Iess M. Maggi R. Orfei Y. de Conchy C. C. Harvey R. M. Manning F. Wouters et al. 《Il Nuovo Cimento C》1994,17(1):101-121
Summary This paper describes the RETE (Research on Electrodynamic Tether Effects) experiment mounted on board the TSS (Tethered-Satellite
System) satellite which was deployed on a cable from the space Shuttle Atlantis during the TSS mission flown in August 1992.
The experiment layout and its modes of operation are described in detail. To give an idea of RETE capabilities and actual
performance during the mission, samples of measurements are also presented. 相似文献
89.
Anthony Manning 《Proceedings of the American Mathematical Society》2005,133(4):995-997
We relate the growth rate of volume in the universal cover of a compact Riemannian manifold to the growth in the fundamental group in terms of word length in a given set of generators and the length of geodesics representing these generators.
90.
Thomas F. Lytle Charles S. Manning William W. Walker Julia S. Lytle David S. Page 《应用有机金属化学》2003,17(9):653-661
Dibutyltin (DBT) is used in the plastics polymerization process as a catalyst in polyvinyl chloride (PVC) products and is the primary degradation product of tributyltin (TBT), an antifoulant in marine paint. DBT and other organotin compounds make their way into the environment through antifoulants, PVC processing plants, and PVC products maintained in water and water‐handling systems. A flow‐through saltwater life‐cycle toxicity test was conducted to determine the chronic effect of DBT to the sheepshead minnow (Cyprinodon variegatus Lacepede), an estuarine species. Embryos were monitored through hatch, maturation, growth, and reproduction in DBT concentrations of 158, 286, 453, 887, and 1510 µg l?1. Progeny were monitored for survival as embryos and fry/juveniles, and growth for 30 days post‐isolation. Mean length of parental generation fish was significantly reduced on day 30 at DBT concentrations ≥887 µg l?1, setting the lowest observable effect concentration (LOEC) at 887 µg l?1 and the no observable effect concentration (NOEC) at 453 µg l?1. Fecundity, as egg viability, was significantly reduced at the LOEC. Survival of parental and progeny generation embryos and mean length, wet weight and dry weight of progeny generation juveniles were not significantly affected at concentrations ≤LOEC. TBT, a toxic impurity in DBT reversibly produced in DBT by the process of comproportionation, was also monitored throughout this study. Comparing measured levels of TBT in this study with levels exerting toxic effects in an earlier TBT life‐cycle study with C. variegatus suggests biological responses in this study were likely due to the TBT impurity and not to DBT alone. Results indicate that TBT impurity as low as 0.1% may have a significant influence on the perceived toxicity of DBT and that spontaneous production of TBT in DBT may be the major source of biological toxicity of DBT. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献