PhD

dissertationA multicompartment model of MRI signal intensity that is a function of perfusion is developed based upon the assumption that biological tissue can be represented by blood, tissue and immobile water compartments and that excited endogenous protons can be used as a tracer. The principle is analogues to tracer kinetic techniques used in many fields of biological science. First, the longitudinal magnetization for a two-compartment model, representing blood and tissue, is derived from the modified Bloch equations as a function of the following physiological parameters: blood flow velocity, tissue to blood volume fraction, diffusion, and rate of exchange between the blood and extravascular tissue compartments. Simulations of slice profiles excited by a repetitive sequence of 90° slice-selective pulses show that the signal intensity in the compartments are modulated by these physiological parameters. Second, the longitudinal and transverse magnetization for both a two-compartment model and a three-compartment model are derived and studied using chromatography column phantoms containing Sephadex gels, which were used to simulate tissue perfusion and the exchange of protons between extravascular and intravascular tissue compartments. Computer simulations were compared in experiments that used two chromatography columns. Slice-selective spin-echo experiments were performed. The results of the experiments agreed with computer simulations, which showed that the MRI signal intensity in the perfused columns is a function of the rate of exchange between extrabead and intrabead compartments. The exchange process modifies the transit time of protons passing through an excited region. Simulations and experiments also showed that both two-compartment and three-compartment models could be used to fit experimental data. Finally, an experiment was performed on a human brain using arterially tagged endogenous protons as a tracer combined with magnetization transfer techniques to eliminate the immobile water compartment. Our simulations and experimental results show that the accuracy of kinetic parameter estimates will rely on the signal contrast that depends upon the flow velocity of the labeled spins. The arterial spin labeling technique has significant potential to be used for quantitatively measuring tissue perfusion in vivo using clinical MRI

BBR-induced Stark shifts and level broadening in helium atom

The precise calculations of blackbody radiation (BBR)-induced Stark shifts and depopulation rates for low-lying states of helium atom with the use of variational approach are presented. An effect of the BBR-induced induced Stark-mixing of energy levels is considered. It is shown that this effect leads to a significant reduction of lifetimes of helium excited states. As a consequence the influence of Stark-mixing effect on the decay rates of metastable states in helium is discussed in context of formation processes of the cosmic microwave background

Research on the Application of Computational Materials Science in Undergraduate Teaching

In this paper, by taking first-principles software as examples, we apply computational materials science to the teaching process of undergraduates majoring in physics, chemistry and materials. We pay attention to the connection between theoretical research and experimental models, makes the abstract principle intuitive and dynamic, and facilitates students’ understanding of knowledge, a deep understanding of the structure of materials and the relationship between theoretical properties and macro properties, which can greatly enhance students’ initiative and creativity in participating in teaching activities. To a great extent, this has played a role of computational simulation as a bridge between theoretical teaching and experimental teaching to continue to explore the complementary relationship between computational simulation, theoretical teaching and experimental teaching, build a teaching model for the application and design ability training of materials and chemistry talents

Concern for Information Privacy and Online Consumer Purchasing in China

Individuals’ concern for information privacy (CFIP) impacts beliefs, intentions, and behaviors in a variety of contexts, including consumer electronic commerce. Most empirical studies on the impact of CFIP on electronic commerce have been conducted using consumers in the United States. Despite China’s growing economy and increasing importance in the global economy, to date, there has been no empirical study of CFIP’s impact on Chinese consumers’ willingness to engage in transactions online. The purpose of this study is to test a widely-referenced model of CFIP’s role in consumer e-commerce in the context of China. We conducted surveys of Chinese consumers’ willingness to engage in transactions with two online merchants, a familiar merchant (Taobao) and a less-familiar merchant (Amazon). For both merchants, CFIP had only mediated impacts on consumers’ willingness to transact with online merchants. While there were similarities between our results and those reported in the original study, there were also differences. Our findings provide a number of contributions for research and practice