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Ethereal, evanescent, elusive?these are adjectives a poet might use to describe the fragile stuff of clouds. They are accurate, and evocative, but still another adjective?electrified?may prove to be more important in the years immediately ahead. Workers in the fields of atmospheric electricity and cloud physics have accumulated sufficient evidence to suggest that electric fields, forces, and charges in the earth's lower atmosphere play a critical role?perhaps the critical role?in the development and behavior of clouds that produce precipitation. This in turn suggests that manipulation of the electrical properties of clouds may someday provide the long-sought key to modification of the weather by man. 相似文献
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Besides the vascular changes caused by arteriosclerosis the compression stenosis is the most frequent form of the isolated restriction of the arteria coeliaca. The compression of the arteria coeliaca, caused by the ligamentum arcuatum medianum or a fribromatous ganglion tissue, can cause complaints similar to the symptoms of angina abdominalis: pains in the epigastrium, postprandial pains, loss of weight, nausea/vomiting, diarrhea, 93% of the patients with severe vascular compression have an abdominal vascular murmur. Of 31 patients with angiographically proved compression stenosis, 11 patients suffering from occlusion or intense stenosis had to be operated because of heavy complaints. The angiographic and intraoperative findings allow the conclusion that there is a connection between the extent of the stenosis and the clinical appearance. The decompression of the arteria coeliaca, in other words the detachment of the compressing tissue leads to total complaintlessness in 83% of the patients. If the arteria coeliaca is hypoplastic a vessel widening or a bypass operation is necessary to establish normal blood circulation in the epigastric organs. 相似文献
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Plaque samples were obtained from 13 children receiving long-term therapy with benzathine penicillin for the prevention of rheumatic fever recurrences, 31 children receiving oral sulfadiazine for the same purpose, and 29 untreated siblings. The therapies were found to have no effect upon the proportions of Streptococcus mutans or lactobacilli in dental plaque, upon the percentage of children harboring the organisms, nor upon the susceptibility of the organisms to penicillin and sulfadiazine. Of the S. mutans strains tested, 97% had a minimal inhibitory concentration of penicillin G of less than 48 ng/ml and, of the lactobacillus strains tested, 96.8% had a minimal inhibitory concentration of less than 1,600 ng/ml. All strains of both organisms were profoundly resistant to sulfadiazine. 相似文献
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HG Nurnberg 《Canadian Metallurgical Quarterly》1976,37(9):521-523
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The dynamic-mechanical and thermal scanning behaviour of a series of specially synthesized linear segmented polyurethanes is presented. These materials possess a well defined segment molecular weight and molecular weight distribution and no possibility of intermolecular hydrogen bonding. The dynamic-mechanical transitions observed are assigned to specific molecular motions and the effect of segment size and molecular weight distribution is described. The results are explained in terms of hard segment domain perfection. Differential scanning calorimetry (d.s.c.) curves of annealed samples indicate that domain morphology may be affected by thermal treatment. A comparison of dynamic mechanical and d.s.c. results to hydrogen-bonded polyurethanes is made. 相似文献