Influence of Different Surface Treatments of H13 Hot Work Die Steel on Its Thermal Fatigue Behaviors   总被引：1，自引：0，他引：1  

MINYong－an  WUXiao－chun 《上海大学学报(英文版)》2001,5(4):326-330

Thermal fatigue checking is general failure of hot work die steels,which is relative with the structures and properties of the steels and the stress alternated during the employment.The Uddeholm test method on thermal fatigue is used to compare the behaviors of different samples,which are treated with plasma nitriding 、plasma sulfur-carbon-nitriding、boronizing or not treated.The results show that the nitriding improves the thermal fatigue property of the tool steel,while the plasma sulfur-carbon-nitriding and the boronizing impair the property.The mechanisms are induced as follows .By increasing the hardness and changing the stress distribution in the surface layer,surface treatment can decrease the plastic deformation and the temsile stress during the cycling.Therefore,the generation and growth of the cracks are restrained.On the other hand,as results of surface treating,in the surface layer the toughness declines and the expanding coefficient ascendes;the latter change caused the strengthening of the tensile and compressive stress during the cycling.Thus the resistance to thermal fatigue is weakened.Whether or not the surface treatment is favor to thermal fatigue of tool steels relies on which factor is dominant.  相似文献   

现代远程教育与数字图书馆     

胡根桥  彭国柱 《中国教育技术装备》2007,(8):51-52

本文从现代远程教育的特点出发,讨论了现代远程教育需要数字图书馆的参与。数字图书馆适合现代远程教育的发展,为远程教育提供网络信息资源,它能够干预远程教育的教学过程,能够为远程学习提供网络平台。  相似文献   

哈贝马斯的现代性概念探析     

胡辉华 《首都师范大学学报(社会科学版)》2006,(1):44-49

现代性是哈贝马斯包罗万象的思想体系中的核心概念之一。在哈贝马斯看来,现代性根源于现时代的自我意识和自我理解,在形式上由文化现代性构想及其自我确证构成,其实质内涵规定并塑造现代社会和生活世界的现实状况。对现代性的不同理解是哈贝马斯和后现代主义者思想分歧的根本原因。  相似文献   

试论农村和谐社会的构建——农村民主政治建设面临的问题及对策     

杨飞  梁闻菁  尹文涛  郗泽宁 《齐齐哈尔师范高等专科学校学报》2007,(2):16-18

农村民主政治建设，是构建和谐农村社会的关键因素之一。当前。我国农村的民主政治建设进程中出现了村党支部与村委会、乡政与村治、村治机关与村民等一系列的矛盾。村民自治的家族化倾向也开始出现。这些不和谐因素的出现，有其深刻的体制原因、历史原因。也有村治机关自身的原因。从法律上界定村委会与村党支部、乡政与村治的权力界限，大力发展市场经济，健全村民自治制度等是消除这些矛盾，实现农村民主政治和经济社会和谐发展的重要措施。  相似文献   

Bullying, violence, and risk behavior in South African school students     

Liang H  Flisher AJ  Lombard CJ 《Child abuse & neglect》2007,31(2):161-171

OBJECTIVES: To examine the prevalence of bullying behavior in adolescents from Cape Town and Durban, South Africa, and the association of these behaviors with levels of violence and risk behavior. METHOD: Five thousand and seventy-four adolescent schoolchildren in grade 8 (mean age 14.2 years) and grade 11 (mean age 17.4 years) at 72 Government schools in Cape Town and Durban, South Africa completed self-report questionnaires on participation in bullying, violent, anti-social and risk behaviors. RESULTS: Over a third (36.3%) of students were involved in bullying behavior, 8.2% as bullies, 19.3% as victims and 8.7% as bully-victims (those that are both bullied and bully others). Male students were most at risk of both perpetration and victimization, with younger boys more vulnerable to victimization. Violent and anti-social behaviors were increased in bullies, victims and bully-victims compared to controls not involved in any bullying behavior (p<.01 in all cases). Risk taking behavior was elevated for bullies and bully-victims, but for victims was largely comparable to controls. Victims were less likely to smoke than controls (odds ratio .83, p<.05). Bully-victims showed largely comparable violent, anti-social and risk taking behavior profiles to bullies. Bully-victims showed comparable suicidal ideation and smoking profiles to victims. CONCLUSIONS: Results were in keeping with Western findings. Involvement in bullying is a common problem for young South Africans. Bullying behavior can act as an indicator of violent, anti-social and risk-taking behaviors.  相似文献   

学习建构主义理论改善初中物理教学     

丁长亮 《当代教育论坛》2006,(22):110-111

建构主义的学习理论认为:学习过程不是学习者被动地接受知识,而是积极地建构知识的过程;在学校里,学习不是教师向学生传递知识的过程,而是学生建构自己的知识和能力的过程.在初中物理教学中,可从以下四个方面来理解建构主义理论的观点.  相似文献   

锰对大豆膜脂过氧化及POD和CAT活性的影响研究   总被引：11，自引：0，他引：11  

胡蕾  施益华  刘鹏  徐根娣  王芳  章丹丹  李奇勇 《金华职业技术学院学报》2003,3(1):29-32

利用水培方法,研究了不同锰浓度(0、0.003、0.03、3、3.0、30mg/kg)对浙春2号和浙春3号大豆膜脂过氧化和POD(过氧化物酶)和CAT(过氧化氢酶)活性的影响。结果表明：高锰(30mg/kg)和缺锰胁迫将显著增加了质膜透性,大大降低了POD和CAT的活性;而适量的锰(0．03—3mg/kg)对于提高POD和CAT的活性,降低质膜透性都有积极的作用。2个大豆品种对锰的反应存在一定的基因型差异,浙春2号对缺锰和高锰胁迫的抵御能力大于浙春3号。  相似文献   

对影响我国大学公共体育课程改革因素的调查   总被引：5，自引：0，他引：5  

吴燕丹  陈亮 《闽江学院学报》2004,25(5):113-116

随着社会的进步和教育事业的发展，高校公共体育课程出现了不能完全适应时代发展和人才培养要求的问题，通过对我国普通高校公共体育课程改革中出现的较为普遍的问题进行归纳分析，根据时代与社会的需要进行创新，建立课程的新框架、新体系。  相似文献   

祁术的组织培养及快速繁殖技术研究     

胡长玉  叶玉娟  郝祥霞  胡跃 《黄山学院学报》2006,8(5):57-60

为研究祁术的组织培养及快速繁殖技术,选用祁术的叶片和下胚轴为外植体材料,接种于附加植物生长调节剂NAA,6-BA及其组合的MS固体培养基上.结果表明:下胚轴为外植体明显好于叶片,对于愈伤组织形成,叶片采用MS NAA(0.5mg/L) 6-BA(2mg/L);下胚轴MS NAA(0.5mg/L) 6-BA(2mg/L);MS NAA(0.5mg/L) 6-BA(1mg/L)为宜.对于叶片丛生芽愈伤组织培养基用MS NAA(0.2mg/L) 6-BA(2.8mg/L),下胚轴丛生芽愈伤组织培养基用MS NAA(0.01mg/L) 6-BA(0.1mg/L);MS NAA(0.05mg/L) 6-BA(0.1mg/L)为宜,诱导生根以1/2MS NAA0.3mg/L最佳,生根率达95%以上.  相似文献   

学习不良儿童言语交际策略的理解与运用     

俞国良  闫嵘 《华东师范大学学报(教育科学版)》2006,24(1):43-48

言语交际策略是个体根据特定社会习俗,通过语言表达和理解意图,从而实现交际目标并获得良好社交效果的一种能力。它是言语、社交习俗和元认知三种知识成分的有机结合。以往研究表明,与一般儿童相比,学习不良儿童在言语交际策略的理解与运用上均存在一定程度的缺陷。言语交际策略研究,将为进一步探索学习不良儿童社会技能缺失的原因,以及社会认知发展的内部规律提供新的视角,因而具有理论价值与实践意义。  相似文献