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Three-dimensional (3D) YBO3:Tb3+ flower-like and dense flower-like hierarchitecture constituted of nanoflakes are solvothermally synthesized in the presence of polyborate precursors in the mixture of ethanol and water. The growth process of the YBO3:Tb3+ flowers and dense flowers was explored based on the time-dependent experiment and the results showed that the growth mechanism follows an in situ growth rather than self-assembly process as reported previously. YBO3:Tb3+ morphologies composed of nanoflakes are achieved by controlling the concentration of ethanol and dependence of photoluminescence on morphology was studied. Remarkable photoluminescence enhancement was observed for YBO3:Tb3+ with flower-like morphology demonstrating the potential of the microstructure in future applications as a green phosphor. Such a synthetic method and growth mechanism may be applied to fabricate complex 3D architectures of other materials. 相似文献
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Anirban Chakraborty James C. Earthman 《Metallurgical and Materials Transactions A》1997,28(4):979-989
Finite element simulations of the high-temperature behavior of single-phase γ, dual-phase α2+γ, and fully lamellar (FL) α2+γTiAl intermetallic alloy microstructures have been performed. Nonlinear viscous primary creep deformation is modeled in
each phase based on published creep data. Models were also developed that incorporate grain boundary and lath boundary sliding
in addition to the dislocation creep flow within each phase. Overall strain rates are compared to gain an understanding of
the relative influence each of these localized deformation mechanisms has on the creep strength of the microstructures considered.
Facet stress enhancement factors were also determined for the transverse grain facets in each model to examine the relative
susceptibility to creep damage. The results indicate that a mechanism for unrestricted sliding of γ lath boundaries theorized
by Hazzledine and co-workers leads to unrealistically high strain rates. However, the results also suggest that the greater
creep strength observed experimentally for the lamellar microstructure is primarily due to inhibited former grain boundary
sliding (GBS) in this microstructure compared to relatively unimpeded GBS in the equiaxed microstructures. The serrated nature
of the former grain boundaries generally observed for lamellar TiAl alloys is consistent with this finding. 相似文献
5.
A hitherto unavailable analytical solution to the free vibration problem of general cross-ply laminated rigidly clamped rectangular plates, incorporating first-order shear deformation, and rotatory and in-plane inertias into the formulation, is presented. A recently developed boundary continuous displacement-based generalized Navier solution technique is used to solve the five highly coupled linear second-order partial differential equations with constant coefficients, and the associated geometric boundary conditions. The assumed solution functions are in the form of double Fourier series, which satisfy the rigidly clamped boundary conditions a priori in a manner similar to the conventional Navier method. Convergence characteristics of the natural frequencies of both symmetric and antisymmetric cross-ply plates are numerically established. Other numerical results presented herein include (i) comparison with the corresponding available first-order shear deformation theory-based Galerkin and classical lamination theory-based boundary-discontinuous analytical solutions, and (ii) study of the effects of thickness and aspect ratio on the natural frequencies. 相似文献
6.
Yousefi M. Chaudhuri S.K. Safavi-Naeini S. 《Antennas and Propagation, IEEE Transactions on》1994,42(1):38-46
Dielectric resonators (DR's) are widely used in telecommunication systems. A method is proposed here to find the resonant frequency and field distribution in a substrate-mounted DR structure. The field of a dielectric rod has been decomposed into a combination of guided modes with unknown coefficients and an unknown continuous spectrum of radiation field. The unknowns are then obtained by applying two generalized impedance boundary conditions (GIBC's) representing the substrate and air layers at the top and bottom of the DR. This leads to the calculation of the total (guided+radiation) field as well as the resonant frequency of the structure 相似文献
7.
Poor-grade fireclay products contain substantial amount of glass. A glass of similar composition was synthesized, nucleated
and heat-treated for crystallization of mullite. The size and size-distribution of mullite crystals, the rate of change of
size and the aspect ratio of the crystals were investigated in relation to the nucleating agents and temperature. 相似文献
8.
Ying Wang Chaudhuri S.K. Safavi-Naeini S. 《Antennas and Propagation, IEEE Transactions on》2002,50(11):1598-1604
A novel method of studying wave penetration through inhomogeneous walls using the hybrid technique based on combining finite-difference time-domain (FDTD) and ray tracing methods is presented . The FDTD method is used to analyze the transmission characteristics of inhomogeneous walls. Using the knowledge of the tangential electric and magnetic field distributions along the borders of the FDTD computation domain, rays are sent out to cover the rest of the environment so that prediction of signal coverage can be made more efficiently without compromising the accuracy. Numerical results of the method have been compared and shown to agree very well with those of measurement and those of full wave analysis. Examples have shown the inadequacy of the traditional ray tracing method in the presence of walls made of concrete blocks. However, the proposed method can accurately predict signal coverage by taking into account the scattered fields by the inhomogeneity inside the walls. The method does not add much to computational complexity. Reduction in computation time is even more significant when the incident waves can be approximated to be plane waves and the wall structure is periodic. 相似文献
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Several studies have reported a lower prevalence of Parkinson's disease (PD) in populations of African origin than in populations of European origin, raising the possibility that the former are protected against PD. However, the confounding effects of low case ascertainment and high selective mortality on PD prevalence estimates in populations of African origin cannot be ruled out at this time. One hypothesis consistent with available data is that populations of African origin are vulnerable to vascular parkinsonism, which is associated with high mortality. 相似文献