共查询到17条相似文献，搜索用时 656 毫秒
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利用调和序列和活动标架研究了复格拉斯曼流形G(2,5)中线性满的全纯2球.利用SU(2)的不可约酉表示构造了G(2,5)中的一些齐性全纯2球.在U(5)等价意义下确定常高斯曲率为2/3和4/3的所有线性满的退化全纯2球.最后证明在某一特定条件下常高斯曲率为4/3的非退化的全纯2球一定是U(5)等价的. 相似文献
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研究了微分几何中的几个不等式 ,提出了几个相关的不等式 .( 1 )对平面上的Schur定理 ,给出了一种解析的证法 ,它比已知的一些 (几何的 )证法显得简洁、明快 ,进而还用积分几何方法作了些讨论 .( 2 )对欧氏空间中闭曲线的F偄ｒｙ不等式 ,用活动标架法 ,将其推广到了球面 (正常高斯曲率曲面 )中 .( 3)对三维欧氏空间中闭曲面的F偄ｒｙ不等式 ,用活动标架法 ,将其中积分式前的常系数 4 π进一步改进为 1 ;此外 ,还将其推广到四维的欧氏空间中 .这一不等式可能推广于更高维或一般的欧氏空间中 ,有待进一步研究 . 相似文献
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在酸性盐NH4Cl中证实简单方便的制得了多元取代呋喃化合物2,5-二甲基-3-甲酸乙酯呋喃(1b)和2,5-二甲基-3,4-二甲酸呋喃(1c). 相似文献
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从齐性曲面的等距群出发,讨论CPn中的齐性曲面,得到了CPn中等距群为2维的齐性曲面的分类,并且用李群与活动标架相结合的方法给出了CP2中齐性曲面的分类定理的证明. 相似文献
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摘 要 用密度泛函理论B3LYP方法,结合6-31G(d,p)和6-311 +G(d,p)基组,研究苯基取代的六元碳链双烯酮阴离子自由基的分子内环加成反应.探讨反应物分别通过[4+2]和[2+2]环加成反应生成六元环产物(i)和四元环产物(ii)的反应机理.结果表明,2个反应都是分步进行的,都先经过第1个过渡态得到中间体.然后从该中间体出发,反应(i)经过第2个过渡态得到六元环产物;反应(ii)经过另外一个过渡态得到四元环产物.计算表明反应(i)是主反应通道. 相似文献
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通过李群、活动标架，以及调和映射来研究从S2到CPn的共形极小浸入．首先，用一种新方法证明Bolton的一个定理，从S2到的全纯曲线在差一个刚动的情况下由度量唯一决定；其次，利用从 S2到CPn的共形极小浸入来构造从S2到G2,n+1的共形极小浸入；最后，如果φ 是从S2到CPn 的全实共形极小浸入，且φ 是常曲率的，则可以找出具体的等距变换ｇ，使得ｇφ 包含在RPnCPn中． 相似文献
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利用标准的SU(2)不可约酉表示,构造了SU(2)到G2的实不可约表示.同时,研究了S6中不同的SU(2)-轨道类型,特别是3维CR-轨道. 相似文献
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从齐性曲面的等距群出发，讨论CPn中的齐性曲面，得到了CPn中等距群为2维的齐性曲面的分类，并且用李群与活动标价相结合的方法给出了CP2中齐性曲面的分类定理的证明。 相似文献
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Market creation is moving to the centre of mission-oriented innovation policy. This is particularly visible in the space sector. Agencies such as the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) are developing market-creating innovation policies in response to (a) the increasing emphasis on societal grand challenges, (b) the rise of a new wave of space companies (often referred to as “New Space”) and (c) the global trend towards interconnecting and interlinking of industries (a trend referred to as Industry 4.0). In this paper we explore the changing nature of mission-oriented innovation policies for market creation for two agencies, NASA and ESA. For these agencies, earlier mission-oriented policies focused on clear challenges with identifiable concrete problems and directed by a strong centralized agency. Contrast this with today, with broadly defined grand challenges, decentralized innovation systems with mixed top-down and bottom-up problem definition. We describe the current drivers and pressures that are creating a window for policy change, and we present examples of how NASA and ESA are responding to these pressures and use this exploration to dig deeper into the evolving frames of market-creating innovation policy in the space sector to identify the challenges for such policies and to further articulate a research agenda. 相似文献
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In this paper, laser beam resonant interaction with pendant microdroplets that are seeded with a laser dye (Rhodamine 6G (Rh6G)) water solution or oily Vitamin A emulsion with Rhodamine 6G solution in water is investigated through fluorescence spectra analysis. The excitation is made with the second harmonic generated beam emitted by a pulsed Nd:YAG laser system at 532 nm. The pendant microdroplets containing emulsion exhibit an enhanced fluorescence signal. This effect can be explained as being due to the scattering of light by the sub-micrometric drops of oily Vitamin A in emulsion and by the spherical geometry of the pendant droplet. The droplet acts as an optical resonator amplifying the fluorescence signal with the possibility of producing lasing effect. Here, we also investigate how Rhodamine 6G concentration, pumping laser beam energies and number of pumping laser pulses influence the fluorescence behavior. The results can be useful in optical imaging, since they can lead to the use of smaller quantities of fluorescent dyes to obtain results with the same quality. 相似文献
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Hellsten I Dawson J Leydesdorff L 《Public understanding of science (Bristol, England)》2010,19(5):590-608
The framing of issues in the mass media plays a crucial role in the public understanding of science and technology. This article contributes to research concerned with the analysis of media frames over time by making an analytical distinction between implicit and explicit media frames, and by introducing an automated method for the analysis of implicit frames. In particular, we apply a semantic maps method to a case study on the newspaper debate about artificial sweeteners, published in the New York Times between 1980 and 2006. Our results show that the analysis of semantic changes enables us to filter out the dynamics of implicit frames, and to detect emerging metaphors in public debates. Theoretically, we discuss the relation between implicit frames in public debates and the codification of meaning and information in scientific discourses, and suggest further avenues for research interested in the automated analysis of frame changes and trends in public debates. 相似文献
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采用构建线性同胚以影响框架结构的方法对Hilbert空间框架的稳定性进行了讨论，给出了框架扰动的一个比较简洁的结果，此外对于Riesz基也得到了类似的扰动结果。 相似文献
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The U.S.-China dispute surrounding 5G motivates further examination on China’s approach to international standardization. While China’s challenges with various standard initiatives to the global standards regime peaked in the 5G dispute have attracted public interests, scholarly approach to the dispute is still limited. We place the dispute in the context of China’s long-standing attempts for international standardization in ICT sectors. With enhanced economic power, China has pursued for pushing indigenous technologies into international standards, which has been a core part of its national science and technology (S&T) policy. This paper examines China’s international standard initiatives from the perspective of techno-nationalism. Our literature review identifies three pillars of techno-nationalism: state empowerment, growth orientation, and global connection. Then we investigate three cases of WAPI, TD-SCDMA and 5G and discuss how the patterns of developing international standards have varied in the framework of techno-nationalism. Over time, China’s international standard initiatives based on techno-nationalism have strengthened global connection and growth orientation, with increasing proximity to techno-nationalism of the Western style. In particular, China’s aspiration for growth orientation was much enhanced with the 5G standard initiative, compared to WAPI or TD-SCDMA, as it aims to be the first mover in the 5G race. Overall, our study suggests that China’s national S&T policy has been moving from the ‘catch-up’ to the ‘first-mover’ strategy, but the transformation continues to take place in the framework of techno-nationalism. 相似文献