超顺磁性Fe2O3较Fe3O4用于磁共振胃肠造影剂的优劣研究     

桂维玲 《实验室研究与探索》2008,27(11)

用超顺磁性氧化铁制备磁共振造影剂的报道较多,其中的磁粒均为Fe3O4。本文提出了用Fe2O3的可行性,并根据超顺磁性理论推导出两种微粒显示超顺磁现象的临界尺寸理论值分别为24.8nm、31.6 nm,在1.5T磁共振磁场中的临界值为7.1 nm、11.1 nm;根据磁学理论,分析了磁共振造影剂稳定的机理;推导出在磁共振磁场中,两者在造影剂中稳定悬浮的极限尺寸为13.3 nm、14 nm。得出在造影剂中,两者既能稳定悬浮又具有超顺磁性的临界尺寸为7.1 nm、11.1 nm的结论。同时分析了两者用做磁共振胃肠造影剂的优劣点。  相似文献   

悬挑式外脚手架应用分析     

陈庆 《嘉应学院学报》2005,23(6):110-112

当施工条件不允许搭设落地式外脚手架时,经过计算采用悬挑式外脚手架,缩短了工期,满足了业主的要求.  相似文献   

“I Didn't Do Nothin'”: The Discursive Construction of School Suspension   总被引：1，自引：0，他引：1  

Vavrus  Frances  Cole  KimMarie 《The Urban Review》2002,34(2):87-111

This article examines the issue of school suspension by looking at the sociocultural factors that influence a teacher's decision to remove a student from the classroom. The authors use ethnographic and discourse analytic approaches to study how disciplinary moments are constructed by teachers and students in an urban high school in the Midwest. The analysis of classroom observations, videotaped lessons, and interviews from a longitudinal study at this multiethnic high school shows that suspensions frequently occur in the absence of any physical violence or blatant verbal abuse. Rather, suspensions are often preceded by a complex series of nonviolent events when one disruptive act among many is singled out for action by the teacher. This study has implications for current debates about zero-tolerance policies that disproportionately affect students of color for their misbehavior in school. Our analysis suggests that removing a student from class is a highly contextualized decision based on subtle race and gender relations that cannot be adequately addressed in school discipline policies.  相似文献   

Do sports help students stay away from misbehavior,suspension, or dropout?     

《Studies in Educational Evaluation》2021

This paper explores whether high-school sports are functional and accessible activities to keep students from school disciplinary behaviors. For this purpose, we included students racial and linguistic status, socioeconomic status, sex, and prior academic performance with the school’s proportion of free-lunch recipients and minorities, to understand how sport participation affects students of diverse groups. Additionally, the study implemented a multilevel mediation modeling to the Education Longitudinal Study (ELS) data and assessed student dropouts with sequential mediators of sport participation, school misbehavior, and suspension. The findings of the study largely revealed that White students participated in sports more than Black, Hispanic, and Asian. Likewise, students who speak English as the primary language and male students participated in sports more than their counterparts. White sport participants displayed fewer incidents of suspension than White non-sport participants. Black, Hispanic, and White sport participants had lower dropout incidents than their non-sport-participating counterparts.  相似文献   

液固两相槽道流中柱状粒子取向的数值研究   总被引：1，自引：0，他引：1  

周强  林建忠  王叶龙 《科技通报》2004,20(5):375-380

对柱状粒子在槽道流场内的运动进行数值模拟，然后用统计方法得出大量柱状粒子的取向分布；给出了粒子长径比、粒子密度和流场区域对粒子取向分布的影响．计算结果表明，柱状粒子长径比的变化对粒子取向分布的影响不明显，粒子密度对粒子取向分布有一定影响，而流场区域所造成的流场横向速度梯度对粒子取向分布有重要影响．随着流场横向速度梯度增大，粒子取向趋势愈加明显，且当流场横向速度梯度增大到一定程度时，粒子取向都趋向于流动方向．文中部分结果与相关实验进行了比较，两者定性吻合较好。  相似文献   

热解法合成P（AM-co-MAA）/SnO_2有机-无机复合微球的研究     

杨菊香  龙旭  杨晓慧 《西安文理学院学报》2011,(4):33-37

采用反相悬浮聚合法合成了聚丙烯酰胺-甲基丙烯酸（P（AM-co-MAA））微凝胶,并以其作为模板,通过热解法制备了一系列微米级、表面具有特异结构的P（AM-co-MAA）/SnO2有机-无机复合微球材料.详细考察了反应时间、SnCl4的浓度和热解温度等因素对复合微球的形貌结构的影响.通过SEM,XRD,FT-IR,TG等手段来表征复合微球的结构、形貌、含量.微球上沉积的SnO2层随着SnCl4的浓度增大而加厚.采用模板法制备复合材料具有操作过程简单、反应条件温和等特点,因此,可将此方法可进一步拓展到其他有机-无机复合材料的制备中.  相似文献   

追诉时效与刑事诉讼程序之关系的反思——浅析创设追诉时效中止制度的必要性     

苏承涛  李俭彬 《重庆师专学报》2011,(6):106-109

我国刑法在规定司法机关对犯罪人追究刑事责任有效期限的同时,用时效中断、时效延长对追诉时效进行补充,建立了比较完善的体系。由于理论和实践对追诉时效与刑事诉讼程序之间的关系缺乏必要的关注．极少反思案件进入刑事诉讼程序后追诉时效是否继续发挥作用。本文在比较法的视野下,对追诉时效与刑事诉讼程序的关系进行尝试性的厘定,得出我国刑法追诉时效存在的缺陷,为了填补该缺陷而建议在刑法中创设追诉时效中止制度。  相似文献   

从“这个歌星很白”看颜色词的对外汉语教学   总被引：1，自引：0，他引：1  

辛亚宁 《郧阳师范高等专科学校学报》2005,25(2):126-128

文章阐释和界定汉语颜色词的文化附加义的角度,探讨了留学生在学习汉语颜色词的偏误原因,并在颜色词的对外汉语教学方面作了初步的尝试性探讨。  相似文献   

谈悬吊训练在篮球运动员体能训练中的应用     

黎伟军  曹洁 《湖北体育科技》2010,29(5):543-544

核心力量训练作为篮球运动中较新的体能训练观念正在逐渐被重视。通过探索悬吊训练手段方法在篮球运动员的体能训练中的应用,帮助运动员提高体能素质和竞技水平。  相似文献   

The Role of the School District in Student Discipline: Building Consensus in Cincinnati     

Lionel H. Brown  Kelvin S. Beckett 《The Urban Review》2006,38(3):235-256

The problem of student discipline disproportionately affects urban schools with large numbers of low income and ethnic minority students. Research over the past 35 years however has consistently shown that discipline policies that are understood and accepted by teachers, students, and parents and consistently enforced by school officials, correlate with lower levels of student disruption. The important role that urban school districts can play in building consensus in support of student discipline policies has not been well documented. But increased levels of student mobility in large urban areas, and increased diversity among the families served by urban districts, highlight the need for district-wide codes of behavior that provide schools with a range of discipline programs that serve the needs of their particular communities. The purpose of this article is to demonstrate how the process of developing and implementing a district-wide code of student behavior in Cincinnati played an important role in reducing disruptive behaviors leading to student suspension and expulsion. By involving all stakeholders in the development of its policies, and by responding to the concerns of all stakeholders in the range of programs it offered, the Cincinnati Public Schools was able to build consensus across socioeconomic and ethnic lines and make its code of behavior effective. On the basis of the evidence presented, it is argued that urban school districts can play a more active role in the area of student discipline. By developing and implementing district-wide codes of behavior that are understood and accepted by teachers, students, and parents, and consistently enforced by school officials, urban districts can lay the foundation on which schools can build healthy learning communities. Dr. Lionel H. Brown holds Bachelors, Masters, and Doctoral degrees from the University of Cincinnati. Dr. Brown is retired from the Cincinnati Public Schools (CPS) where he served as a teacher, vice-principal, principal, and Deputy Superintendent. His responsibilities in the role of CPS Deputy Superintendent included the Department of Curriculum and Instruction, the Office of Student Discipline, and the Office of Student Affairs. Dr. Brown is currently an Assistant Professor in the Division of Educational Studies, College of Education, Criminal Justice, and Human Services, University of Cincinnati, Cincinnati, Ohio. His research and teaching interests include urban education, alternative education, and programs for Black males.Dr. Kelvin S. Beckett holds Bachelors and Masters degrees from the University of British Columbia, Canada and a Doctoral degree from the University of London, United Kingdom. He is an Adjunct Lecturer in the Division of Educational Studies, College of Education, Criminal Justice, and Human Services, University of Cincinnati, Cincinnati, Ohio. His teaching and research interests include urban education and alternative education.  相似文献