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1.
针对磷酸酯/Al3+ 交联的油基压裂液交联速度慢,交联剂溶解性慢、稳定性差和价格高等缺点,首次对磷酸酯/Fe3+ 交联的油基压裂液体系进行了研究。通过对铁交联剂体系的优化,筛选一种磷酸酯/Fe3+ 交联的新型交联剂体系,并对磷酸酯/Fe3+ 油基冻胶压裂液性能进行了评价。结果表明:采用30%Fe2(SO4)3+15% 二乙醇胺+55% 水制备的新型交联剂体系,直接与磷酸酯混合即可形成油基冻胶,其性能不受放置时间的影响,交联速度快,成胶性能好,10 min 就可达到最大黏度;压裂液的抗温抗剪切性能高,与常规铝交联剂体系比较,压裂液成胶速度提高了20 倍,压裂液的抗温能力由原来100 ℃提高到135 ℃,并且压裂液的破胶性和滤失性等性能均能达到压裂施工的要求。 相似文献
2.
This study demonstrates the analytical leverage gained from considering the entire college pipeline—including the application, admission and graduation stages—in examining the economic position of various groups upon labor market entry. The findings, based on data from three elite universities in Israel, reveal that the process that shapes economic inequality between different ethnic and immigrant groups is not necessarily cumulative. Field of study stratification does not expand systematically from stage to stage and the position of groups on the field of study hierarchy at each stage is not entirely explained by academic preparation. Differential selection and attrition processes, as well as ambition and aspirations, also shape the position of ethnic groups in the earnings hierarchy and generate a non-cumulative pattern. These findings suggest that a cross-sectional assessment of field of study inequality at the graduation stage can generate misleading conclusions about group-based economic inequality among workers with a bachelor’s degree. 相似文献
3.
A. M. Abd El-Raheem 《Journal of Statistical Computation and Simulation》2019,89(16):3075-3104
The generalized half-normal (GHN) distribution and progressive type-II censoring are considered in this article for studying some statistical inferences of constant-stress accelerated life testing. The EM algorithm is considered to calculate the maximum likelihood estimates. Fisher information matrix is formed depending on the missing information law and it is utilized for structuring the asymptomatic confidence intervals. Further, interval estimation is discussed through bootstrap intervals. The Tierney and Kadane method, importance sampling procedure and Metropolis-Hastings algorithm are utilized to compute Bayesian estimates. Furthermore, predictive estimates for censored data and the related prediction intervals are obtained. We consider three optimality criteria to find out the optimal stress level. A real data set is used to illustrate the importance of GHN distribution as an alternative lifetime model for well-known distributions. Finally, a simulation study is provided with discussion. 相似文献
4.
Simulation results are reported on methods that allow both within group and between group heteroscedasticity when testing the hypothesis that independent groups have identical regression parameters. The methods are based on a combination of extant techniques, but their finite-sample properties have not been studied. Included are results on the impact of removing all leverage points or just bad leverage points. The method used to identify leverage points can be important and can improve control over the Type I error probability. Results are illustrated using data from the Well Elderly II study. 相似文献
5.
孙敬良 《中国农业大学学报(社会科学版)》2015,32(5):55-60
21世纪以来,中国农村治理研究陷入了本土化与主体性双重困境,中国农村社会基础的深度转型,农村研究方法的缺陷以及大规模村庄研究的局限,要求中国农村研究回归深度的村庄研究,尊重农民主体性。在回归村庄研究的方法论上,文章认为要突破国家政权建设理论等研究视角的局限,把市场化这一变量纳入分析视野中。村庄主位、农民主体、市场化过程同国家宏观治理体系的互动逻辑,应该构成后中国农村治理研究时代的主要内容。 相似文献
6.
Increased juvenile delinquency can be seen as an indicator for a deteriorating social fabric under conditions of rapid social change. Criminological theories suggest, however, that such conditions do not per se produce delinquency: They force youth into prodelinquent leisure activities with peers, leading to an endorsement of delinquent behavior and offering the infrastructure for it. Resources acquired in family and public life, however, may prevent youth from drifting into such prodelinquent leisure activities and indirectly from delinquent behavior. Empirical tests of these hypotheses have to employ simultaneous analyses of societal-level and individual-level data. On the basis of an international youth study, the paper undertakes such an analysis: In the years 1992–95, data from 42 independent samples of seventh graders from East and West Germany, Poland, Russia, Bulgaria, Slovakia, Hungary, Czechia, and Greece were surveyed. Data on deviant school behavior, delinquent drift, nurturant parenting, and subjective feelings of justice in public were obtained from 7282 thirteen- to fourteen-year-olds. Processes of rapid social change were incorporated as data on changes in GNP in the years proceeding the surveys. Analyses show that delinquent drift is a valid predictor of deviant school behavior only on the individual level. The extent to which adolescents engage in prodelinquent peer activities depends more on the cultural context in which adolescents live than on their personal experience in the family and in public. Nurturant parenting does, however, covary negatively with deviant school behavior irrespective of level of analysis. 相似文献
7.
烟毒影响近代中国社会至深且巨 ,南京国民政府自成立之日起便展开对这一社会问题的治理工作。抗战前十年其禁烟政策历经“寓禁于征”、断禁和渐禁三个阶段的演变 ,在禁烟领域作出了自己的努力 ,并取得阶段性成果 ,北洋军阀时期烟毒大泛滥的局面得到基本扼制。 相似文献
8.
非专业大学英语开设背诵课探讨 总被引:1,自引:0,他引:1
陈岭 《郑州航空工业管理学院学报(社会科学版)》2002,21(4):40-42
从3个方面分析阐述了背诵在外语学习中的重要性,并结合有关教学实践,提出在大学公共英语教学中增开背诵课的设想,并对如何开好背诵课提出一些建议。 相似文献
9.
从比较优势学说看我国就业增长 总被引:1,自引:0,他引:1
潘海红 《安徽农业大学学报(社会科学版)》2002,11(5):30-31
从比较优势学说理论来看,我国应该大力发展劳动密集型产业,以获取比较优势,但从我国出口产品的现状及存在问题来看,我国似乎更应该大力发展高新技术产业以提高出口产品的附加值.本文对这一矛盾形成的原因和对策进行探讨分析,并提出相应对策. 相似文献
10.
歌唱学习者成长的道路问题是一个认知能力的把握问题,这种认知能力把握水平的高低决定了他们的定位。在歌唱学习过程中合理把握自我知觉与群体评价的和谐关系,全面参照现实形象与角色形象,保持同一性,度衡自尊性,是自我意象在当前的歌唱学习大潮中所衍生的重要要求,更是歌唱学习健康发展的必要保障。 相似文献