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排序方式: 共有640条查询结果,搜索用时 15 毫秒
1.
A 3-wave longitudinal design was used to examine the relationships among emotional restraint, peer drug associations, and gateway drug use in a sample of 1,256 middle school students. Structural equation modeling was used to compare 3 models: (1) One model viewed drug use as a consequence of emotional restraint and peer variables; (2) 1 viewed drug use as a cause of restraint and peer variables; and (3) 1 included reciprocal effects. All 3 models fit the data fairly well. However, the reciprocal model fit the data significantly better than either of the others. Within this model, low emotional restraint was significantly related to subsequent increases in gateway drug use among boys. In contrast, peer drug models and peer pressure were not related to subsequent changes in gateway drug use. Changes in peer drug models were, however, predicted by previous levels of gateway drug use. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
2.
Tan J.C. Crossley P.A. McLaren P.G. Hall I. Farrell J. Gale P. 《Power Delivery, IEEE Transactions on》2002,17(1):68-74
This paper describes a sequential tripping strategy used in a wide area back-up protection expert system (BPES) to combat situations in which protection relays have maloperated or information is missing. The BPES is an innovative back-up protection scheme designed to prevent the occurrence of widespread blackouts. The BPES evaluates the certainty that transmission lines are likely to be affected by the fault and uses a sequential tripping strategy to isolate the fault if a firm decision is not available due to maloperated relays and/or missing information. The mode of analysis and the sequential tripping strategy ensures that the BPES will clear a fault at minimum risk to the network. An example is included to demonstrate how the certainty factor based sequential tripping strategy is employed by the BPES to clear a fault which occurred on the South Western part of the UK National Grid System 相似文献
3.
This paper presents an investigation on a single-mode-multimode-single-mode fiber structure. A one-way guided-mode propagation analysis for the circular symmetry waveguide is employed to model the light propagation and the approximated formulations are derived and evaluated concerning the accuracy. Phase conjunction of the multimode interference within the fiber structure is revealed. A simple way to predict and analyze the spectral response of the structure is presented through the space to wavelength mapping with the derived approximated formulations. The prediction of spectral response is verified numerically and experimentally. 相似文献
4.
We formulate a class of difference schemes for stiff initial-value problems, with a small parameter ε multiplying the first derivative. We derive necessary conditions for uniform convergence with respect to the small parameter ε, that is the solution of the difference scheme uih satisfies |uih−u(xi)| Ch, where C is independent of h and ε. We also derive sufficient conditions for uniform convergence and show that a subclass of schemes is also optimal in the sense that |uih−u(xi)| C min (h, ε). Finally, we show that this class contains higher-order schemes. 相似文献
5.
WE Farrell DJ Simpson JE Bicknell AJ Talbot AS Bates RN Clayton 《Canadian Metallurgical Quarterly》1997,57(13):2703-2709
We have screened 57 cases of primary, nonfunctional, pituitary adenomas for loss of heterozygosity of markers on chromosome 9p. Using a panel of 11 microsatellite markers, we found hemizygous deletion with at least one of the markers in 18 tumors (31.5%). The frequency of loss was similar in both noninvasive (8 of 26; 31%) and invasive tumors (10 of 31; 32%), suggesting that loss on this chromosome might be an early event in pituitary tumorigenesis. Two discrete areas of loss were punctuated by a region of retention of heterozygosity between the markers D9S171 and IFNA, indicative of homozygous deletion. However, multiplex PCR analysis (MTS1 and MTS2) and the presence of a 3' untranslated region polymorphism in MTS1 suggested that neither of these tumor suppressor genes was homozygously deleted. In 6 of the 18 tumors showing LOH, sufficient DNA was also available for Southern blot analysis and, in all cases, showed retention of MTS1. Cell mixing experiments of tumor cell DNA homozygously deleted for MTS1 with DNA in which neither copy of the gene was deleted only gave rise to a signal at contamination levels greater than 30% and could discriminate homozygous and hemizygous loss. These studies support the recent findings that mechanisms other than hemi- and homozygous deletion are most likely responsible for the loss of MTS1 gene product in pituitary tumors (M. Woloschak et al., Cancer Res., 56: 2493-2486, 1996.). These data show that losses on either side of 9p21-22, both or either of which may be deleted, are involved in pituitary tumorigenesis and provide evidence for distinct suppressor gene loci, in addition to MTS1, on chromosome 9p. 相似文献
6.
Since pneumotachograph masks are commonly used in studies of speech breathing, the purpose of this study was to measure the differences in respiratory volumetric and frequency measures during speech under two conditions: with and without a circumferentially vented pneumotachograph mask coupled to the face. Thus we sought to identify whether changes in breathing patterns occur with the use of a specific face mask, because these patterns are accepted as representative of normal speech breathing. Subjects were 10 normal-speaking women, each of whom produced a syllable train and a connected speech task, both at comfortable intensity levels. Respiratory measures were made using linearized magnetometers during speech production. The measurements included lung volume, rib cage volume, and abdominal volume at utterance initiation and termination, volume excursions during the utterance, and the number of breath groups during the speech task. There were no significant differences between the mask-on and mask-off conditions in volumetric and frequency measures. A significant task difference for abdominal initiation was found. It was concluded that the use of a circumferentially vented pneumotachograph mask does not alter the reliability of respiratory volume and frequency measures for studies of voice. 相似文献
7.
Comparative study of the molecular species of chloropropanediol diesters and triacylglycerols in milk fat 总被引:1,自引:0,他引:1
In an effort to establish the origin of the fatty acid esters of 3-chloropropanediol, which recently have been isolated in
small amounts from goat milk, we compared the molecular species composition of the chlorohydrin diesters and of goat milk
triacylglycerols. The chloropropanediol diesters were found to be composed of molecular species containing C10−C18 fatty acids and corresponded closely in carbon number to those calculated for the long chain sn-1,2-diacyl-glycerol moieties
of goat milk triacylglycerols. The molecular species of goat milk total triacylglycerols contained C4−C18 fatty acids. It is suggested that triacylglycerols and chloropropanediol diesters are derived from the same pool of long
chain fatty acids. A molecular distillate of bovine milk fat did not contain chloropropanediol diesters, while the available
samples of human milk fat were shown to contain alkyldiacylglycerols as the major components of a neutral lipid fraction corresponding
in polarity to the chloropropanediol diesters. 相似文献
8.
Silicic acid column chromatography was used to separate the polar lipids of goats' milk into glycolipid, phosphatidylethanolamine,
phosphatidylserine plus phosphatidylinositol, phosphatidylcholine, and sphingomyelin fractions. Each fraction was purified
by column chromatography and its fatty acid profile determined by gas liquid chromatography and mass spectrometry. The glycerophospholipids
each contained 18∶1 as the predominant fatty acid (∼45%). The sphingolipids contained a high percentage of long-chain saturated
fatty acids (C22 to C24>45%); the glycolipid fraction also contained ca. 2% 2-hydroxy fatty acids. The data represent a comprehensive cross-sectional
study of the major polar lipids found in goats' milks. 相似文献
9.
Delay- and Disruption-Tolerant Networking 总被引:3,自引:0,他引:3
Delay- and disruption-tolerant networking (DTN) grew out of attempts to develop an Interplanetary Internet but has evolved into an active area of networking research, with applications in space networking, military tactical networking, and networking for various challenged communities. The DTN Research Group provides an open forum in which DTN researchers and developers can collaborate to further develop this experimental technology. 相似文献
10.