The Influence of Network Effect on the Valuation of Online Networking Companies

Online networks are having an enormous economic impact, both at the micro and the macro level. The growth of the online networks involves the participation of users, advertisers, and platform providers. This paper argues that the optimal revenue is directly proportional to user population, which is a key factor driving the online networking firms forward. Also, different companies are able to generate different value from each individual user. These arguments are supported by our empirical tests analyzing the current online networking giants. Empirical models further suggest that our theoretical model performs best when we look at the relationship between growth rate of revenue and that of user population. In addition, higher speed of user population growth and larger initial user population have positive influences in a network\u27s valuation

Control of CaCO3 crystal growth on PDAC/PSS self-assembled multilayers

Fabrication of biomimetic larminated composite by mimicking the cyclical matrix control process to form the highly structured Mollusca nacre was presented in this paper. (PDAC/PSS)(n) self-assembled multilayers were built-up through alternative adsorption of polycation and polyanion to a substrate as matrices and their chemical structure was characterized by UV-vis absorption spectra. And then the deposition of CaCO3 took place on the multilayers by dipping them into a supersaturated CaCO3 solution. The crystals regulated by (PDAC/PSS)(15)PDAC exhibited hexahedral shape and had a size of about 30 similar to 40 mu m after 10 h deposition. Hexagonal CaCO3 platelet crystals could be observed on (PDAC/PSS)15 with a relative small size of 10 similar to 20 mu m, which is very similar to the crystals existing in natural nacre. Therefore, CaCO3 crystals with remarkable morphology similarity to natural biornineralization products were obtained in the presence of artificial polyanion. However, X-ray diffraction results indicated that crystal lattice of both the samples was different from any kind of natural nacre. Consequently, it might be supposed that electrostatic effect is one of the key factors in morphology control while the crystal lattice was determined by other factors. Furthermore, end surface SEM image of (PDAC/PSS)(15)-CaCO3 composite elucidated that alternation of multilayer growth and deposition of inorganic crystals coupled with morphology regulation could form laminated material

聚电解质膜PDAC/PSS诱导CaCO_3结晶的研究

以模拟软体动物珍珠层的周期性基质控制形成过程制备仿生层状复合材料.将聚苯乙烯磺酸钠(PSS)与聚二烯二甲基氯化铵(PDAC)用逐层浸渍的方法使其组装成多层膜,用于诱导过饱和溶液中CaCO3的结晶,详细研究了膜紫外吸收随组装层数增加的线性变化.扫描电镜和X射线衍射表征了晶体的形貌和结构.(PDAC/PSS)15PDAC膜诱导获得的CaCO3晶体为六面体结构,晶体尺寸为30～40μm;(PDAC/PSS)15膜诱导CaCO3结晶,可以在膜表面获得形貌与珍珠层非常相似的CaCO3晶体,结晶10h获得的晶片结构呈规则的六边形,片尺寸约为10～20μm.X射线衍射结果表明两种晶体的晶格结构与天然珍珠层差异明显,说明静电作用为晶体形貌的主控因素之一,但不是晶格结构的决定因素.复合材料断面电镜照片表明其为层状结构

Control of CaCO3 crystal growth on PDAC/PSS self-assembled multilayers

Fabrication of biomimetic larminated composite by mimicking the cyclical matrix control process to form the highly structured Mollusca nacre was presented in this paper. (PDAC/PSS)(n) self-assembled multilayers were built-up through alternative adsorption of polycation and polyanion to a substrate as matrices and their chemical structure was characterized by UV-vis absorption spectra. And then the deposition of CaCO3 took place on the multilayers by dipping them into a supersaturated CaCO3 solution. The crystals regulated by (PDAC/PSS)(15)PDAC exhibited hexahedral shape and had a size of about 30 similar to 40 mu m after 10 h deposition. Hexagonal CaCO3 platelet crystals could be observed on (PDAC/PSS)15 with a relative small size of 10 similar to 20 mu m, which is very similar to the crystals existing in natural nacre. Therefore, CaCO3 crystals with remarkable morphology similarity to natural biornineralization products were obtained in the presence of artificial polyanion. However, X-ray diffraction results indicated that crystal lattice of both the samples was different from any kind of natural nacre. Consequently, it might be supposed that electrostatic effect is one of the key factors in morphology control while the crystal lattice was determined by other factors. Furthermore, end surface SEM image of (PDAC/PSS)(15)-CaCO3 composite elucidated that alternation of multilayer growth and deposition of inorganic crystals coupled with morphology regulation could form laminated material

利用自组装膜在模拟体液中诱导结晶的研究

研究了聚电解质自组装膜的制备,及该膜在模拟体液中诱导羟基磷灰石(HA)结晶的实验。利用紫外 吸收仪检测到自组装膜膜厚的增长,扫描电镜显示了在普通洁净玻璃表面与装有薄膜的玻璃表面上诱导结 晶时所形成的晶体形貌之不同

利用新型一次性激流灌注式生物反应器培养动物细胞

利用新型一次性培养袋在5～10L激流灌注式生物反应器中培养3种贴壁和3种悬浮细胞,通过在线控制培养温度、pH值和溶氧等工艺参数,监测并分析培养过程中细胞密度、活率、糖耗等的变化情况.结果表明,贴壁培养细胞MDCK,VERO和DF-1培养6d后消化计数,密度分别达4.8×106,1.0×107和1.5×107mL-1,细胞状态良好,活率在90%以上.悬浮细胞CHO,BHK-21和Sf9经无血清悬浮驯化后,经种子链扩增,在激流式反应器中悬浮培养的初始接种密度分别为2.0×106,2.1×106和2.15×106mL-1时,培养一段时间后其最高培养密度分别可达2.0×107,2.1×107和1.8×107mL-1,维持培养时间分别为13,12和10d