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高国东 《内蒙古科技与经济》2018,(18)
本文中高聚物微裂纹指的是长度在几个um到几百个um的裂纹,本文尤其是对著名的微损伤判据进行了理论解说,对微裂纹孔洞纤维质发展机制、微裂纹发展动态过程、表面能及微裂纹发展的模型等进行了系统分析,概括了当前最为前沿的高聚物微裂纹的研究进展,阐述了高聚物微损伤理论的工程应用。 相似文献
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本文利用边界元的数值计算方法(BEM),计算了在不同外部应力作用下材料内部具有不同形态的微裂纹尖端区域的应力场情况和应力集中因子,得出了在不同应力作用条件下微裂纹尖端区域的最大主应力场分布和应力集中因子,并给出了不同应力条件和裂纹形态与应力集中因子的关系。在裂纹尖端这些高应力区内一些与结构畸变有关的效应如原子外层电子能量增加与逃逸现象等是能够发生的。 相似文献
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低强度岩体在荷载影响下的蠕变损伤发展过程是一个复杂的裂隙发生扩展过程,通过采用实时成像技术得到当轴向荷载达到极限强度附近时,岩石微破裂聚集形成裂隙,蠕变率在短时间增加,产生更大的塑性变形,当轴向荷载达到极限强度附近时,在相对小的荷载作用下微损伤发生蠕变。当荷载比较大的时候,岩石直接进入加速蠕变阶段,立即发生破坏。通过实时成像技术对低强度岩体的蠕变微分析得到一些对荷载影响下低强度岩体稳定性分析有益的结果。 相似文献
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吊车引起的循环荷载受外界影响较为明显,且循环幅值比较大。论文通过室内模型试验分析了静力和循环荷载条件下桩身应力应变的传递特性,研究了当桩周填土分别为黄土和饱和黄土时不同循环荷载幅值对单桩承载性特性影响。最后得出了循环荷载作用下单桩沉降的变化规律,饱和黄土中单桩承载力特性。 相似文献
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花岗岩薄片不同矿物成分在图像中可能存在相同灰度分布甚至相似纹理。通过结合正交偏光镜镜下图片干涉色信息和单偏光镜图片信息分析,提高了花岗岩薄片石英分割的准确率。方法是从单偏光镜和正交偏光镜下图片中提取图像块的特征信息,运用支持向量机分类方法对图像块进行分类,在分类为石英的图像块中选取种子,再根据两张图片信息,用区域生长方法完成石英分割。该方法实现了自动化分割,分割准确率高,实验证明该方法切实可行。 相似文献
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Ti基准晶由于其特殊的晶体结构而成为具有前途的新型贮氢材料。Ti45Zr38Ni17准晶最大吸氢量时,氢原子与金属原子比约等于2,明显高于普通金属间化合物贮氢材料,但其平台压力低,氢很难放出。为了改善准晶的气态放氢性能,Takasaki等采用机械合金化及热处理的方法制备了Ti45Zr38Ni17准晶粉末。该粉末达到最大贮氢量时,氢原子与金属原子比等于1.5,这可能是由于准晶中含有少量的Ti2Ni型晶体相的原因。同时,在充放氢过程中,准晶相不稳定。Majzoub等采用电化学方法氢化Ti45Zr38Ni17准晶,贮氢量最大时氢原子与金属原子比为1.9,并且在充氢过程中无晶体相生成。到目前为止,准晶作为镍氢电池负极材料的电化学贮氢性能的研究未见报道。在本章中,将研究Ti45Zr38Ni17Cu3准晶作为镍氢电池负极时的最大放电容量和循环稳定性。为了对比,也研究了非晶合金的相关电化学性能。 相似文献
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首先通过24块事先已经经过冻融循环的混凝土试件,外加循环荷载条件,考察循环荷载和冻融循环次数两个参数对CFRP-混凝土界面的极限荷载的影响。结果表明:复合荷载作用下,界面极限荷载下降很快,总体呈现线性下降趋势,界面极限荷载减少为原来的1/8,界面承载能力大为削弱。影响界面极限荷载中的因素中,循环荷载其主要作用。 相似文献
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Marjorie Armstrong-Stassen Margaret Landstrom Ramona Lumpkin 《The Information Society》1998,14(2):153-164
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. 相似文献
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A joint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology his co-workers from Norway US 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 the National Academy of Sciences on September .…… 《中国科学院院刊(英文版)》2008,22(1):6-7
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. 相似文献
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Caroline Haythornthwaite 《The Information Society》2001,17(3):211-226
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. 相似文献
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《中国科学院院刊(英文版)》2008,22(1):2-3
CAS should stick to the principle of rendering service to, and giving impetus for, the development of China＇s science enterprise by making S＆T innovations, said CAS President LU Yongxiang. The CAS president made the remarks in a recent talk to communicate the gist of the winter session of the Party＇s Leading-member Group at CAS, which was held from 7 to 11 January in Beijing. 相似文献
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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. 相似文献
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《中国科学院院刊(英文版)》2008,22(1)
With great care, Dr. ZHOU Zhonghe takes out a package wrapped by cotton tissue from a drawer and says: "This is the gem of our collections: the fossil of a bird that lived 125 million years ago!" Then, pointing at a tiny mound, he explains: "Look, this is the claw and that is the head. It was in the egg shell and ready to hatch ... The species fell into a family of waterside inhabitants." 相似文献
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Puay Tang 《The Information Society》1998,14(1):19-31
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. 相似文献
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Milton Mueller 《The Information Society》2001,17(3):151-163
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. 相似文献
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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.…… 《中国科学院院刊(英文版)》2008,22(1):15-15
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. 相似文献
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Leah A. Lievrouw 《The Information Society》1998,14(2):83-96
The main premise of this article is that in information societies generally, and in virtual social contexts particularly, a distinctive style of interaction to facilitate the communication of difference, heterotopic communication , has emerged. It rests on two cultural foundations: an ideological belief in the positive, socially integrating power of communication, and a prevailing ethic of instrumental rationality, subjective individualism, and strategically practiced self-interest. The former is demonstrated by the use of simulation and spectacle as sources of information; exhibitionism/voyeurism as a communicative style; and the awareness of surveillance. The latter is seen in the competitive use of knowledge as a commodity; a surface globalism masking deep parochialism; lateral as well as vertical information inequity; and the use of public versus private as strategies for engagement rather than as spaces. Those who engage in heterotopic communication resort to their 'own devices' both in the sense of personal agendas, strategies, interests, and interpretations, and in the form of the telecommunication tools that help realize them. These personal and technological devices allow individuals with the right educational and technical resources to avoid exposure to disagreement, difference, or other information that does not serve their direct purposes or reflect their particular views of the world; yet they also help convey the appearance of openness, availability, and cooperation. This style of interaction is used strategically in combination with information and communication technologies to gain social or economic advantages, but it may encourage social separatism and parochialism, inhibit the negotiation of disputes, and emphasize competing interests. 相似文献