Browsing by Author "Zhang, Zhenyu"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Institutional Investor Cliques Information Dissemination, and the Value of Information: Evidence from Insider Trading
    Zhang, Zhenyu (Virginia Tech, 2023-04-19)
    I analyze the relationship between insider trading outcomes and insiders' information environment within a network. While most existing studies rely on one dimension of commonality (e.g., personal ties, professional ties, geographic proximity) to construct the social network, I document the formation of the institutional investor groups (cliques) that exogenously connect firm-level insiders within the social network. Using difference-in-differences designs examining changes in clique size, I provide empirical evidence on the information dissemination channels within a network in which its members are quasi-randomly selected. Insider transactions in larger cliques exhibit lower abnormal trading profits, higher level of trading frequency, and larger amount of trade size, suggesting information dissemination is increasing in clique size. Then, I provide empirical evidence that the association between the value of information and the information dissemination rate is monotonic, consistent with prior theoretical studies.
  • Thumbnail Image
    Thermo-Mechanical Behavior of Polymer Composites Exposed to Fire
    Zhang, Zhenyu (Virginia Tech, 2010-06-29)
    One of the most critical issues for Polymer Matrix Composites (PMCs) in naval applications is the structural performance of composites at high temperature such as that experienced in a fire. A three-dimensional model including the effect of orthotropic viscoelasticity and decomposition is developed to predict the thermo-mechanical behavior and compressive failure of polymer matrix composites (PMCs) subjected to heat and compressive load. An overlaid element technique is proposed for incorporating the model into commercial finite element software ABAQUS. The technique is employed with the user subroutines to provide practicing engineers a convenient tool to perform analysis and design studies on composite materials subjected to combined fire exposure and mechanical loading. The resulting code is verified and validated by comparing its results with other numerical results and experimentally measured data from the one-sided heating of composites at small (coupon) scale and intermediate scale. The good agreement obtained indicates the capability of the model to predict material behavior for different composite material systems with different fiber stacking sequences, different sample sizes, and different combined thermo-mechanical loadings. In addition, an experimental technique utilizing Vacuum Assisted Resin Transfer Molding (VARTM) is developed to manufacture PMCs with a hypodermic needle inserted for internal pressure measurement. One-sided heating tests are conducted on the glass/vinyl ester composites to measure the pressure at different locations through thickness during the decomposition process. The model is employed to simulate the heating process and predict the internal pressure due to the matrix decomposition. Both predicted and measured results indicate that the range of the internal pressure peak in the designed test is around 1.1-1.3 atmosphere pressure.