Browsing by Author "Xu, Yang"

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    Social Capital, Cognitions, and Firm Innovation: Theoretical Model and Empirical Studies
    Xu, Yang (Virginia Tech, 2006-06-01)
    Innovation is the central value of economic behavior. In this dissertation research, I attempt to explore the social and cognitive origins of firm innovation through three interrelated studies, by merging several research streams — managerial cognitions, social networks, and innovation, and collecting data through multiple methods — archives and surveys. First, I proposed a social-cognitive view to study the sources of firm innovation. In the context of firm innovation, top management teams' cognitions or an entrepreneur's cognitions shape the way they use the social structure available to them, while the social structures influence the embedded actors' cognitions and ultimately strategic actions. Managers and entrepreneurs form collaborative partnerships aimed at innovation and competitiveness. During this dynamic social learning process, cognitive differences influence the formation of social capital and its realized benefits. The impact of social capital on innovation cannot be evaluated without understanding the individual cognitive characteristic first. Next, I tested this theoretical model in two contexts. In the first empirical study, I derived firm-level hypotheses that link the top management team's cognitions, the firm's social capital, and the technological innovations. These hypotheses are tested on a sample of U.S. semiconductor firms in the years 1991-1998. In the second empirical study, I derived similar hypotheses that link entrepreneur's cognitions, social capital and startup's technological innovations. A survey was conducted in both Pennsylvania and Virginia, targeting the entrepreneurial firms in technology industries. The hypotheses were empirically tested on a final sample of 70 U.S. small and medium-sized manufacturers. Two empirical studies supported some of the derived hypotheses and the findings have significant theoretical, empirical, and practical implications. In a diverse social network, actors' knowledge structure tends to be more complex, and more centralized. In addition, these studies indicate that both social capital and cognitive structure play important roles in technological innovation. By distinguishing between cognitive structures, as well as social capital characteristics, and by investigating their effects on firm innovations, this dissertation extends the literature on organization theory, innovation research, entrepreneurship, and research methodologies. This dissertation research deepens our understanding of firm innovation, and opens a whole line of further research.
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    Synthesis and Characterization of Silica Coated CdSe/CdS Core/Shell Quantum Dots
    Xu, Yang (Virginia Tech, 2005-12-02)
    A great deal of interest has been dawn on the colloidal chemistry based semiconductor nanocrysallites, also known as quantum dots (QDs). Because of the strong quantum confinement, quantum dots have unique size-dependent optical properties, which are much more superior to the conventional organic fluorescence materials. In addition, strong chemical resistant makes inorganic semiconductor QDs ideal candidate for next-generation of bio-labels and drug delivery vehicles. This report presents a user friendly approach to synthesize high quality biocompatible CdSe QDs in aqueous solution. Size of the dots can be controlled by adjusting the temperature, pH of the solution, and ratio of the precursors. A thin CdS layer was grown on CdSe QDs, forming a CdSe/CdS core/shell structure, to improve the photoluminescence. In order to use these QDs in-vivo, a more chemically robust coating, silica, was grown on the core/shell structure QD. The optical properties of the QDs were characterized by absorption and photoluminescence spectra. X-ray diffraction and transmission electron microscopy were conducted to verify the QDs composition and structure.