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排序方式: 共有1964条查询结果,搜索用时 15 毫秒
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Lamya Benamar Christine Balagué Mohamad Ghassany 《Journal of Computer-Mediated Communication》2017,22(6):337-362
This research focuses on the identification of social roles and an investigation of their influence in online context. Relying on a systemic approach for role conceptualization, we investigate member's activity, shared content and position in the network within a consumer to consumer social media‐based community (SMC) around a product. This investigation led to the identification of ten core roles, based on three key elements: object of interest (product, practice, and community), main contribution type (sharing information and seeking information), individual orientation (factual, emotional). We propose an explanation about how these roles, through their positioning, participate in the community dynamics and how they contribute to the creation and diffusion of cookery as a social practice, shaping the periphery around this practice. 相似文献
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Pasquale Avella 《Computers & Operations Research》2012,39(7):1625-1632
The p-median problem (PMP) consists of locating p facilities (medians) in order to minimize the sum of distances from each client to the nearest facility. The interest in the large-scale PMP arises from applications in cluster analysis, where a set of patterns has to be partitioned into subsets (clusters) on the base of similarity.In this paper we introduce a new heuristic for large-scale PMP instances, based on Lagrangean relaxation. It consists of three main components: subgradient column generation, combining subgradient optimization with column generation; a “core” heuristic, which computes an upper bound by solving a reduced problem defined by a subset of the original variables chosen on a base of Lagrangean reduced costs; and an aggregation procedure that defines reduced size instances by aggregating together clients with the facilities. Computational results show that the proposed heuristic is able to compute good quality lower and upper bounds for instances up to 90,000 clients and potential facilities. 相似文献
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基于简化的二进制差别矩阵的快速属性约简算法 总被引:8,自引:0,他引:8
目前,基于二进制差别矩阵的属性约简算法有如下不足:算法的时间和空间复杂度不理想;所得到的属性约简与由基于正区域的属性约简的定义得到的属性约简不一致。本文给出一个简化的二进制差别矩阵和相应的属性约简的定义,证明了该定义与基于正区域的属性约简的定义是一致的。由于在简化的二进制的差别矩阵中,要先求出IND(C),故设计了一个较好的求IND(C)的算法,其复杂度被降低为O(|U‖U|)。在此基础上设计了一个快速属性约简算法,其时间复杂度和空间复杂度分别被降为max{O(|C|^2(|U'pos‖U/C|)),O(|C‖U|)}和max{O|U|},O(|C|(|U'pos‖U/C|))}。 相似文献
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Formation of Gold and Silver Nanoparticle Arrays and Thin Shells on Mesostructured Silica Nanofibers
S. Zhang W. Ni X. Kou M. H. Yeung L. Sun J. Wang C. Yan 《Advanced functional materials》2007,17(16):3258-3266
Mesostructured silica nanofibers synthesized in high yields with cetyltrimethylammonium bromide as the structure‐directing agent in HBr solutions are used as templates for the assembly of Au and Ag nanoparticles and the formation of thin Au shells along the fiber axis. Presynthesized spherical Au and Ag nanoparticles are adsorbed in varying amounts onto the silica nanofibers through bifunctional linking molecules. Nonspherical Au nanoparticles with sharp tips are synthesized on the nanofibers through a seed‐mediated growth approach. The number density of nonspherical Au nanoparticles is controlled by varying the amount of seeded nanofibers relative to the amount of supplied Au precursor. This seed‐mediated growth is further used to form continuous Au shells around the silica nanofibers. Both the Au‐ and Ag‐nanoparticle/silica‐nanofiber hybrid nanostructures and silica/Au core/shell fibers exhibit extinction spectra that are distinct from the spectra of Au and Ag nanoparticles in solution, indicating the presence of new surface plasmon resonance modes in the silica/Au core/shell fibers and surface plasmon coupling between closely spaced metal nanoparticles assembled on silica nanofibers. Spherical Au‐ and Ag‐nanoparticle/silica‐nanofiber hybrid nanostructures are further used as substrates for surface‐enhanced Raman spectroscopy, and the enhancement factors of the Raman signals obtained on the Ag‐nanoparticle/silica‐nanofiber hybrid nanostructures are 2 × 105 for 4‐mercaptobenzoic acid and 4‐mercaptophenol and 7 × 107 for rhodamine B isothiocyanate. These hybrid nanostructures are therefore potentially useful for ultrasensitive chemical and biological sensing by using molecular vibrational signatures. 相似文献
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�������¸�ѹ�뾮���嶯̬������ϵͳ������ 总被引:3,自引:0,他引:3
智能型高温高压入井流体动态损害评价系统是石油勘探开发中评价油气层损害程度的新型实验仪器,它可以测量岩心受入井流体损害前各分段的原始渗透率值,然后不需取出岩心,就可以直接在模拟储层温度、压力及流速条件下,用泥浆泵驱替高压液体罐中的入井流体,在岩心端面进行动态剪切损害。损害过程完成后,也不需取出岩心,而是通过换向阀门改变流体的流动方向,再由平流泵驱替液体,测量储层岩心受损害后各段的渗透率值。通过对比岩心各分段的渗透率变化情况,即可确定岩心受入井流体损害的深度和程度,从而优选出满足保护油气层需要的钻井液与完井液。此外,还可以进行岩心的各种敏感性实验。该评价系统体积小、造价低、适用范围广、功能强、自动化程度高,克服了因重复装卸岩心所造成的实验误差较大的缺点,与同类实验仪器相比具有明显的先进性和优越性。 相似文献
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