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《科技通报》2017,(1)
海洋工程深水基桩下段埋置于土中,基桩上段暴露于水中和空气中,基于一维杆理论建立了饱和土中深水基桩的竖向振动简化计算模型。利用阻抗传递法,获得了深水基桩的桩顶竖向振动频域解析解和时域半解析解。计算结果表明,桩土接触相对滑移模型在接触刚度很大时与完全黏结条件下的深水基桩竖向振动响应基本一致,当接触刚度减小时,基桩动力响应增大,说明完全黏结条件过高地估计了土层的阻抗,造成桩顶响应减弱;频率相关的阻尼系数可以抑制导纳的发散效应,能够更好地模拟桩土动力相互作用。分层模型计算表明,暴露段对基桩振动产生明显影响,时域反射信号在泥面处会产生同向反射,此外,上、下土层的模量比也会对桩的振动响应产生一定的影响,这些不加以甄别会引起基桩检测误判。 相似文献
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CFG桩全名为碎石粉煤灰混凝土桩，是由房建基础工程的沉管灌注桩演变而来，属于复合地基处理形式。该桩是通过锤击力、振动力、振动冲击力或静压力将暂时堵住下端开口的无缝钢管（即套管）沉入到地基预定，然后向套管内（下入钢筋笼）灌注混凝土，再用动力将套管拔出地面．钢筋笼和混凝土留在地下形成的桩。本文结合CFG桩在某一工程实例的成功应用，阐述了不同施工工艺对CFG桩施工质量的影响以及施工质量的控制要点。 相似文献
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在软土地基修建高等级公路中,"桥头跳车问题"是一个技术难题。低强度桩是一种新型处理桥头深厚软基工法,采用变桩长的思想,使沉降逐渐过渡。某大桥桥头段深厚软基采用该工法处理,对桩顶及桩间土沉降、土工格栅上沉降、深层土体水平位移、孔隙水压力、土压力等进行了现场监测,并进行了静载荷试验,对测试结果进行了分析。结果表明,该工法能大幅度减小沉降,形成沉降过渡,减小对桥台基础的水平推力,具有显著的经济效益。 相似文献
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回顾和总结桩土接触界面无厚度Goodman单元法的主导思想，针对竖向受力承载群桩的P-S曲线数值分析模型给出了三维无厚度界面单元，以模拟桩土相互接触界面，利用所建立的桩土数值模型对群桩的P-S曲线进行了数值模拟分析和预测，探讨群桩工作机理及群桩效应。 相似文献
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针对深层搅拌桩复合桩复合地基设计与施工中关于桩型选择、桩顶与桩端的处理等特殊土加固几个问题从技术和经济角度提出见解。 相似文献
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挤密碎石桩是采用振动沉桩法先用桩管振动成孔,填入足够数量的碎石,并振动密实而形成桩体。通过对桩身用重型Ⅱ动力触探,桩间土用标准贯入和静力触探进行检测,测试结果达到设计要求。 相似文献
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《科技通报》2017,(1)
对水平与轴向荷载作用下单桩内力变形的求解提出了一种状态空间法。首先,根据线弹性地基反力理论、Euler-Bernoulli梁理论和桩单元平衡条件,建立了地面以上及以下桩身响应的状态方程,其中桩周土体对桩的反力采用三参数模型来模拟。其次,为了使上述状态方程线性化,将地面以上和以下桩身等分为若干桩段,并设各桩段上的地基反力系数、轴力与自由段上水平分布荷载都为常数,建立了地面以上及以下各桩段响应的线性化状态方程。第三,利用桩顶、桩底条件以及各桩段之间的位移内力连续光滑条件,得到了水平轴向荷载共同作用下桩变形内力的状态空间解,编制了计算程序。最后研究了轴向荷载对桩顶水平位移和桩身最大弯矩的影响。计算结果表明:本方法和程序是易于使用且可靠的;当轴向荷载或者水平位移较大时,轴向荷载对桩身弯曲响应的影响很大。 相似文献
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A research group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol-a chemical found in the skins of red grapes in red wine-can improve the sensitivity of mice to the hormone insulin according to a report in the October issue of Cell Metabolism.…… 《中国科学院院刊(英文版)》2008,22(1):14-15
Aresearch group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol--a chemical found in the skins of red grapes and in red wine--can improve the sensitivity of mice to the hormone insulin, according to a report in the October,2007 issue of Cell Metabolism. As insulin resistance is often characterized as the most critical factor contributing to the development of Type 2 diabetes, the findings“provide a potential new therapeutic approach for preventing or treating” both conditions, the researchers said. 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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Active biological molecules functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery disease diagnosis therapy new nanodevice construction.…… 《中国科学院院刊(英文版)》2008,22(1):22-22
Active biological molecules and functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery, disease diagnosis and therapy, and new nanodevice construction. 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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Leah A. Lievrouw 《The Information Society》2000,16(2):155-159
This essay focuses on universal service and the Internet as means to support social and political participation. The emphasis on access to telecommunications systems in conventional approaches to universal service is contrasted with access to content. A model of the information environment is described that accounts for the roles of content and conduit, both of which are necessary conditions to achieve true access. A method is outlined for employing information indicators to observe or measure the information environment. 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