Browsing by Author "Wang, Z. G."
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- Controlled growth of epitaxial BiFeO3 films using self-assembled BiFeO3-CoFe2O4 multiferroic heterostructures as a templateLi, Yanxi; Yang, Yaodong; Yao, Jianjun; Viswan, Ravindranath; Wang, Z. G.; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2012-07-01)The growth mechanism of a BiFeO3 layer deposited on self assembled (0.65) BiFeO3-(0.35) CoFe2O4 (BFO-CFO) composite thin films was studied. Epitaxial and self-assembled BFO-CFO thin films were deposited on SrTiO3 (111) substrates by pulsed laser deposition and were subsequently used as a seed layer for the deposition of an additional BFO layer. x-ray line scans showed the heterostructures were highly epitaxial. Cross-sectional scanning electron microscopy and focused ion beam images revealed the top BFO layer grew preferentially from BFO nanopillars in the BFO-CFO thin films, thus, demonstrating controlled growth. The multiferroic properties of this new nanostructure were then studied. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4734508]
- Direct measurement of magnetoelectric exchange in self-assembled epitaxial BiFeO3-CoFe2O4 nanocomposite thin filmsYan, Li; Xing, Zengping; Wang, Z. G.; Wang, T.; Lei, G. Y.; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2009-05-01)We report the direct measurement of a magnetoelectric (ME) exchange between magnetostrictive CoFe2O4 nanopillars in a piezoelectric BiFeO3 matrix for single-layer nanocomposite epitaxial thin films grown on (001) SrTiO3 substrates with SrRuO3 bottom electrodes. The ME coefficient was measured by a magnetic cantilever method and had a maximum value of similar to 20 mV/cm Oe. The films possessed saturation polarization (60 mu C/cm(2)) and magnetization (410 emu/cc) properties equivalent to bulk values, with typical hysteresis loops.
- Elastography Method for Reconstruction of Nonlinear Breast Tissue PropertiesWang, Z. G.; Liu, Y.; Wang, G.; Sun, L. Z. (Hindawi, 2009-07-09)Elastography is developed as a quantitative approach to imaging linear elastic properties of tissues to detect suspicious tumors. In this paper a nonlinear elastography method is introduced for reconstruction of complex breast tissue properties. The elastic parameters are estimated by optimally minimizing the difference between the computed forces and experimental measures. A nonlinear adjoint method is derived to calculate the gradient of the objective function, which significantly enhances the numerical efficiency and stability. Simulations are conducted on a three-dimensional heterogeneous breast phantom extracting from real imaging including fatty tissue, glandular tissue, and tumors. Anexponential-form of nonlinear material model is applied. The effect of noise is taken into account.Results demonstrate that the proposed nonlinear method opens the door toward nonlinear elastographyand provides guidelines for future development and clinical application in breast cancer study.
- Nonlinear Elasto-Mammography for Characterization of Breast Tissue PropertiesWang, Z. G.; Liu, Y.; Wang, G.; Sun, L. Z. (Hindawi, 2011-12-22)Quantification of the mechanical behavior of normal and cancerous tissues has important implication in the diagnosis of breast tumor. The present work extends the authors' nonlinear elastography framework to incorporate the conventional X-ray mammography, where the projection of displacement information is acquired instead of full three-dimensional (3D) vector. The elastic parameters of normal and cancerous breast tissues are identified by minimizing the difference between the measurement and the corresponding computational prediction. An adjoint method is derived to calculate the gradient of the objective function. Simulations are conducted on a 3D breast phantom consisting of the fatty tissue, glandular tissue, and cancerous tumor, whose mechanical responses are hyperelastic in nature. The material parameters are identified with consideration of measurement error. The results demonstrate that the projective displacements acquired in X-ray mammography provide sufficient constitutive information of the tumor and prove the usability and robustness of the proposed method and algorithm.