单摆周期公式的应用

在教学中单摆周期公式T=2π√L/g中L为等效摆长,g为等效重力加速度,由单摆所在的空间位置决定,由g=GM/R2知,g随地球表面不同位置、不同高度而变化,在不同星球上也不尽相同,因此应求出单摆所在处的等效值g'代入公式,即g不一定等于9.8m/s2.     

某型机操纵摇臂裂纹故障分析与改进

正对某型机航向操纵摇臂贯穿性裂纹故障进行了故障树梳理,并通过理论分析、仿真计算及试验数据对故障原因进行了排查和定位。在此基础上提出了针对性的改进方案,最终通过试验对改进方案有效性进行了验证。故障概述外场某型机换季大检查时,发现某型机航向操纵摇臂有一贯穿性裂纹,如图1所示。裂纹位置及断口宏观形貌如图2所示,裂纹位于图2箭头所指处,侧壁外表面及R1倒角转接位置,侧壁两端R1倒角处均有裂纹向内扩展。     

纳米塑料粒子在不同温度工况条件下的性能分析

近年来,计算材料科学发展突飞猛进,利用计算机进行分子动力学模拟,进行新材料的设计也成为探索复合材料的主要方式。在本文中,提出利用纳米二氧化硅作为PMMA基体的增强体,从而克服PMMA力学性能不良的缺点;对纳米二氧化硅粒子进行表面改性,增强与PMMA基体的相容性,增大分子间作用力,进一步提高力学性能。本文主要使用分子动力学模拟的研究方法,对纯PMMA、PMMA/Si O2复合材料和PMMA/改性Si O2复合材料体系进行分子动力学模拟和力学模拟。     

氧化钐/丁基乳胶防辐射复合材料的制备

文章采用湿法球磨表面改性工艺,以硬脂酸为表面改性剂制备了改性氧化钐浆料,并直接添加到丁基胶乳中分散均匀得到氧化钐/丁基乳胶防辐射复合材料。实验考察了硬脂酸用量、球磨转速及球磨时间对氧化钐表面改性程度的影响,对复合材料进行了DSC、力学性能及X射线屏蔽性能测试。实验结果表明,氧化钐表面改性程度对复合胶乳分散稳定性有较大影响,表面改性程度过低和过高都不利于氧化钐在丁基胶乳中的分散,当改性氧化钐活化指数达到96%,水接触角为102°时,复合胶乳分散稳定性最优,力学性能降低程度最低;当改性氧化钐添加量为20phr时,复合材料X射线屏蔽性能较优,其铅当量达到0.17mm Pb。     

复合半导体石墨烯与氮化镓界面结构的性质

正本文采用基于密度泛函理论的第一性原理对单层石墨烯(2×2)/氮化镓(3~1/2×3~1/2)的异质结构进行了研究。重点讨论了界面处的几何结构,电子结构,表面的功函数以及石墨烯诱导的电荷密度的变化。计算表明,当单层石墨烯附在氮化镓表面时,其结合力为范德瓦尔斯力,体系表现出半导体特性,石墨烯在K点附近的狄拉克锥结构不再存在,并形成大小为0.12eV的带隙。表面的功函数为5.26eV,电子不容易脱离体系表面。计算结果为石墨烯作为氮化镓材料的吸附层的设计和应用提供了理论依据。     

黄土地区重力式U型桥台尺寸效应对其力学性能的影响研究

为研究黄土地区高大宽重力式U型桥台开裂病害与其自身结构尺寸之间的关系,本文利用有限元软件ANSYS建立三维实体模型,考虑桥台与土体接触的状态非线性问题,通过设置不同工况和和控制变量的方法分别模拟不同阶段桥台尺寸效应对其力学性能的影响。结果表明,重力式U型桥台前墙与侧墙交接部位高度约2/3处为其薄弱环节,该处拉应力随桥台高度、宽度及侧墙长度的增加呈线性增长规律。     

基于h指数及其扩展指数的科研评价

通过《中国引文库》,利用2001-2010年我国"985工程"第一期34所高校所发表的论文及其被引数据,根据相关指数的定义,分别统计计算出各院校的h指数及其G指数、W指数、A指数、H(2)指数、R指数、标准化指数 (h,G,W,H(2),R,A)_i 和年代增长速率h_y,从不同角度全面综合评价高校学术水平,结果表明,h指数、G指数、W指数和H(2)指数区分度小、灵敏度低,因此应该结合A指数、R指数与标准化指数和h_y进一步区分开,为综合评价高校科研能力提供理论参考和借鉴意义。     

单摆周期公式的应用

在教学中单摆周期公式T=2π√L/g中L为等效摆长，g为等效重力加速度，由单摆所在的空间位置决定，由g=GM/R^2知,g随地球表面不同位置、不同高度而变化，在不同星球上也不尽相同，因此应求出单摆所在处的等效值g代入公式，即g不一定等于9．8m／s^2。     

M型磷脂酶A2受体与特发性膜性肾病及中医证型的研究

目的:检测肾组织中磷脂酶A2受体(M-type phospholipase A2 receptor,PLA2R)的表达,探究肾组织中PLA2R与特发性膜性肾病及中医证型的联系。方法:回顾性分析2016年4月至2019年6月广西中医药大学附属瑞康医院经肾活检证实的70例肾病综合征(nephrotic syndrome,NS)患者作为研究对象,其中包括30例特发性膜性肾病、1例乙型肝炎病毒相关性膜性肾病、2例V型狼疮肾炎、6例Ig A肾病、6例微小病变性肾病、4例系膜增生性肾小球肾炎和1例局灶节段性肾小球硬化及20例非膜性肾小球疾病。结果:(1)IMN组、SMN组、对照组PLA2R在肾脏组织表达的阳性率分别为22/30(73.33%)、6/20(30%)、3/20(15%),三组间肾组织PLA2R的表达有显著统计学差异(P0.05);(2)三组患者实验室指标相比较,血肌酐、血清白蛋白、尿β2微球蛋白、24 h尿蛋白定量、总胆固醇均无统计学差异(P0.05);(3)中医证型与肾组织PLA2R的表达之间差异无统计学意义(P0.05)。结论:(1)肾组织PLA2R的表达可用于MN,可用于IMN和SMN的鉴别诊断;(2)中医证型与相关指标有一定的相关性,与肾组织PLA2R的表达不存在相关性。     

纳米SiO2改性道路拆除再生集料力学性能研究

为研究纳米SiO₂对道路拆除再生集料力学性能的改良效果,采用无侧限抗压试验和三轴试验分别对再生集料和掺入4‰纳米SiO₂的再生集料进行研究。试验结果表明：掺入4‰纳米SiO₂可以有效提升再生集料的无侧限抗压强度、抗剪强度和抵抗变形的能力;纳米SiO₂主要通过提升内摩擦角来达到增强再生集料抗剪强度的作用。研究结果表明掺入4‰的纳米SiO₂可以有效增强再生集料的力学性能。     

压裂泵阀箱失效研究

压裂泵是油气田上产增存的主要设备,但其液力端阀箱却经常早期失效。通过对现场使用的各型压裂泵阀箱的综合对比分析,对阀箱基体常见失效准则进行了归纳,开展了阀箱失效模式的研究。综合现场失效数据分析,认为疲劳开裂是阀箱最主要和最危险的失效模式。     

某型安装支架的疲劳寿命分析

某设备通过安装支架固定在飞机座舱中,在飞机大幅度、长时间的剧烈振动下,支架结构在薄弱点处发生断裂。采用Catia和UG对该设备及其安装支架建立三维模型,对设备装配的振动模态、安装支架的应力分布及安装支架尺寸对疲劳寿命的影响进行了分析和计算。计算结果表明,侧壁厚度对支架寿命影响很小,Z向振动是导致安装支架断裂的主要原因,断裂发生在Z向应力集中处。计算结果与故障现象一致。     

大型民用飞机框与长桁、蒙皮的连接结构分析

文章主要分析了目前几种主流大型民用飞机A320,波音737,波音747飞机机身框与长桁、蒙皮连接的不同结构形式的优缺点。     

Students' Reactions to the Introduction of Videoconferencing for Classroom Instruction

This study examined how students who had no prior experience with videoconferencing would react to the use of videoconferencing as an instructional medium. Students enrolled in seven different courses completed a questionnaire at the beginning of the semester and again at the end of the semester. Students at the origination and remote sites did not differ in their reactions toward videoconferencing but there was a significant difference for gender. Women reacted less favorably to videoconferencing. Compared to the beginning of the semester, students reported significantly less positive attitudes toward taking a course through videoconferencing at the end of the semester. There were no significant differences in students' attitudes toward videoconferencing across courses at the beginning of the semester but there were significant differences across the courses at the end of the semester. The results suggest the need for better preparation for both students and instructors.     

Cooler temperatures inductive to locust outbreaks

Ajoint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology and his co-workers from Norway, US and Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells, suggesting that China＇s projected climate warming could decrease the pest＇s numbers. The study was published in Proceedings of theNational Academy of Sciences on 17 September, 2007.     

Exploring Multiplexity: Social Network Structures in a Computer-Supported Distance Learning Class

A computer-mediated group is a complex entity whose members exchange many types of information via multiple means of communication in pursuit of goals specific to their environment. Over time, they coordinate technical features of media with locally enacted use to achieve a viable working arrangement. To explore this complex interaction, a case study is presented of the social networks of interactions and media use among members of a class of computer-supported distance learners. Results show how group structures associated with project teams dominated who communicated with whom, about what, and via which media over the term, and how media came to occupy their own communication niches: Webboard for diffuse class-wide communication; Internet Relay Chat more to named others but still for general communication across the class; and e-mail primarily for intrateam communication. Face-to-face interaction, occurring only during a short on-campus session, appears to have had a catalytic effect on social and emotional exchanges. Results suggest the need to structure exchanges to balance class-wide sharing of ideas with subgroup interactions that facilitate project completion, and to provide media that support these two modes of interaction.     

The Role of Intermediating Institutions in the Diffusion of Electronic Data Interchange (EDI): How Industry Associations Intervened in Denmark, Finland, and Hong Kong

Electronic data interchange (EDI) provides means for interorganizational communication, creates network externalities, requires an advanced information technology (IT) infrastructure, and relies on standards. In the diffusion of such innovations, institutional involvement is imperative. Such institutions contain governmental agencies, national and global standardization organizations, local government, and nonprofit private organizations like industry associations. The last type of organizations we call intermediating institutions. They intermediate or coordinate ("inscribe") the activities of a group of would-be adopters. Unfortunately, little is known of how these organizations shape the EDI diffusion trajectory. In this article we examine one specific type of intermediating organizations?industry associations?and how they advanced the EDI diffusion process in the grocery sectors of Hong Kong, Denmark and Finland. We identify six institutional measures, placed into a matrix formed by the mode of involvement (influence vs. regulation) and the type of diffusion force (supply push vs. demand pull), that can be mobilized to further the EDI diffusion. Industry associations were found to be active users of all these measures to varying degrees. Their role was critical especially in knowledge building, knowledge deployment, and standard setting. Furthermore, institutional involvement varied due to policy and cultural contingencies and power dependencies.     

How Electronic Publishers are Protecting Against Piracy: Doubts About Technical Systems of Protection

The increasing prospects of digital piracy has prompted the perceived need by electronic publishers to adopt technical systems of protection, and governments to reform their copyright laws. This article is a preliminary study of the management of intellectual property by electronic publishers, defined as those involved in the production of online databases, and CD-ROMs. It focuses on three main issues: (1) how electronic publishers view the increasing threat of piracy; (2) the methods of protection employed to protect intellectual property in digital format; and (3) the importance of technological protection of intellectual property in electronic publications. The analysis is based on a sample of 23 UK electronic publishers. The interviews revealed an interesting assortment of protection methods and did not show that technological protection was a preferred way. Instead, the means of protection, in addition to copyright law, comprised niche markets, pricing, trust, bad publicity, and nontechnical and technical means.     

Rough Justice: A Statistical Assessment of ICANN's Uniform Dispute Resolution Policy

Long-standing conflict between domain name registrants and trademark holders prompted the Internet Corporation for Assigned Names and Numbers (ICANN) to create a global, mandatory arbitration procedure known as the Uniform Dispute Resolution Policy (UDRP). The UDRP has been used in 2166 cases involving 3938 domain names as of 1 November 2000. The policy gives the initiator of a complaint, generally a trademark holder, the right to choose which ICANN-accredited dispute resolution service provider (RSP) will handle the case. During the preparation of the UDRP,some feared that complainant selection would lead to "forum shopping" that might bias the results. This article performs a statistical assessment of the forum-shopping thesis and finds support for it. There are statistically significant differences in the various RSPs' propensity to take away names from defendants; there are also major differences in the number of cases brought to each RSP. RSPs who take away names have the larger share of cases. The study examines other variables that might explain differences in market share, such as price, the plaintiff's nationality, or the time taken to decide a case. It finds that nationality and time also are correlated with market share. The study concludes that shopping for a favorable outcome is an important factor in the UDRP.     

Prevalence of soft neurological signs in Chinese people

Prof. Raymond C.K. Chen, a neuropsychologist with the CAS Institute of Psychology, has made novel progress in his studies of schizophrenia. His work has been reported by a recent issue of Behavioural Neurology.