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关于侵彻问题研究现状的综述 总被引：4，自引：0，他引：4
在军事工程上研究弹丸对岩石或混凝土等介质的侵彻问题,具有十分重要的理论和现实意义.本文详细介绍了经验法、近似解析法和数值分析法三种方法研究侵彻问题的进展情况,并对比分析了各种方法研究侵彻问题的优缺点. 相似文献
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《科学中国人》2016,(29)
伴随着社会的发展,世界上重要目标建设越来越多,防护等级也越来越高。各国高价值的目标都实现了地下化/半地下化,防护的强度也有很大的提高,具体表现在防护的厚度和防护结构的复杂程度。使用反深层硬目标战斗部即钻地弹可以对地下/半地下目标实施有效的打击,钻地弹亦成为重要的战略战术武器。因此,钻地弹对地下/半地下目标打击的规律成为武器开发和军事研究的重点之一。当前,关于侵彻的研究一般将钢筋混凝土看作一个均质靶体,很少考虑钢筋对弹体运动的影响。为了加深对侵彻问题的深入研究,得到更加准确的侵彻规律。算法建立基于弹体与钢筋作用的等效单自由度模型,并进行编程实现,通过商业软件计算初步验证了弹筋接触程序计算的合理性。开展钻地弹深/斜侵彻混凝土靶过程中弹体同钢筋作用规律的研究,无论是对于推进侵彻理论的发展,还是提高武器装备的打击能力都具有重要的意义。 相似文献
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利用聚能效应原理,研究药型罩产生聚能杆式侵彻体的特性,设计了一种采用大隔板、大锥角药型罩装药结构。通过实验验证,可有效提高对钢筋混凝土目标靶的穿深及开孔孔径。 相似文献
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本文在投资者非理性、管理者理性框架下探讨投资者情绪能否通过理性迎合渠道对企业研发投资产生影响,以及资本市场业绩预期压力能否对这种迎合效应起到抑制作用,并进一步比较不同规模、盈利能力和管理层持股企业间迎合效应的差异。研究结果显示:总体而言,投资者情绪对企业研发投资的影响支持了迎合假说;资本市场业绩预期压力能够抑制企业研发投资对投资者情绪的迎合程度;而以上效应只存在于小规模、低盈利能力以及管理层高持股的企业,说明企业规模、盈利能力和管理层持股是管理层迎合投资者情绪和维护资本市场形象动机的重要影响因素。本文研究结论对于上市公司、投资者、证券分析师以及市场监管部门都具有重要的政策涵义。 相似文献
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本文通过LS-DYNA非线性动力学分析软件对三种不同头部形状的弹体垂直侵彻土壤的过程进行了数值仿真,在初速度为500m/s时获取了弹体侵彻靶板的深度、速度、加速度及能量变化曲线,仿真结果表明:三种不同头部形状的弹性弹体在500m/s的初速度下侵彻泡沫土壤的深度差别不大,平头弹体的速度损失最快,剩余速度最小,动能的损失最多。 相似文献
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运用空间自回归模型和空间杜宾模型,针对2005—2015年中国30个省级的面板数据研究环境规制对制造业绩效的影响以及地方政府竞争对两者关系的调节作用。研究发现:环境规制对制造业绩效具有负向直接效应和正向空间溢出效应;在地方政府竞争的作用下,环境规制对制造业绩效的负向直接效应和正向空间溢出效应均被缩小;环境规制负向影响制造业绩效的总效应,引入地方政府竞争后,总效应的负向影响将被缩小;环境规制对制造业绩效的直接效应、空间溢出效应、总效应以及地方政府竞争对这3种效应的调节作用具有区域差异性。 相似文献
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异地并购是一种打破市场分割现象,实现资源高效配置的重要形式。针对前期文献中学者们对异地并购中地理距离和技术资源跨区域流动之间影响关系的研究存在较大差异,本文基于经济地理理论和信息不对称理论,以2009-2019年间我国高新技术上市企业发生的异地并购交易为研究样本,研究了地理距离对技术资源跨区域流动的影响效应以及并购双方技术重叠的调节作用。研究结果表明,地理距离对技术资源跨区域流动有显著的负向影响,在分组回归中,这种负向影响在制造业和新创企业分组中更显著；技术资源重叠对地理距离和技术资源跨区域流动间负向关系有显著的缓解效应。进一步研究发现,并购方董事长和总经理两职分离、独董地理临近性以及高管团队规模能显著削弱地理距离的负面影响效应。研究结论从并购前标的方选择和并购后资源整合的双视角为如何缓解异地并购中地理距离的束缚效应提供了理论依据,深化了我们对跨区域资源流动中地理距离影响效应的认知。 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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《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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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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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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《中国科学院院刊(英文版)》2014,(3)
<正>In Xishuangbanna,one of China’s most biodiverse regions,landscape has changed dramatically during the past three decades due to the conversion of tropical rainforest to rubber plantations.In steep areas,terraces are often constructed before planting rubber trees,which causes two important changes in the soil:the destabilization of soil in the bench terraces and the increased vulnerability of unvegetated riser faces to erosion.Few studies have documented the nature and intensity of erosion on bench terraces.Prof.LIU Wenjie and his colleagues from the Xishuangbanna Tropical Botanical Garden(XTBG)conducted a study in Menglun County(21°5′39″N,101°15′55″E),Xishuangbanna to evaluate the influence 相似文献