Density functional theory （DFT） plays a significant role in the development of visible light responsive photocatalysts. Based on the first-principles plane-wave ultrasoft pseudopotential （USPP） method, the crystal...Density functional theory （DFT） plays a significant role in the development of visible light responsive photocatalysts. Based on the first-principles plane-wave ultrasoft pseudopotential （USPP） method, the crystal structures of α,β,γ, and 5-Bi2O3 were optimally calculated for the total density of states （TDOS） and the partial density of states （PDOS） of Bi, O atoms. The calculation for Ti（IV） doped Bi2O3 supercell was carried out. The effects of Ti（IV）-doping on the electron structures and light absorption properties of various Bi2O3 were analyzed. The results showed that Ti 3d orbital appeared in the forbidden band of Bi2O3 and hybridized with O 2p, Bi 6p orbitals. The narrowed band gap （Eg） and red-shift of light absorption edge are responsible for the enhanced photoeatalytic activity of Bi2O3. The Ⅱ-Bi2O3 and Ti-doped β-Bi2O3 were prepared by a hydrotherrnal synthesis method. The improvement of the photoeatalytic activity of Bi2O3 has also been verified by the characteristics of the UV-vis diffuse reflection spectrum and the experimental evaluation of the photocatalytic degradation of crystal violet in aqueous solution.展开更多
掺铋光纤放大器有助于将光纤通信系统拓展至新的传输波段。然而,其增益和噪声性能存在相互制约的关系,提升增益往往会导致噪声性能的恶化,反之亦然。因此,提出一种结合反向传播神经网络(BPNN)和带精英保留策略的快速非支配排序遗传算法(...掺铋光纤放大器有助于将光纤通信系统拓展至新的传输波段。然而,其增益和噪声性能存在相互制约的关系,提升增益往往会导致噪声性能的恶化,反之亦然。因此,提出一种结合反向传播神经网络(BPNN)和带精英保留策略的快速非支配排序遗传算法(NSGA-Ⅱ)的多目标优化方法,通过对两级掺铋光纤放大器结构进行设计,实现了增益和噪声性能的同时优化。使用经过训练的BPNN对增益和噪声系数预测的均方根误差分别为0.191和0.084,具有较高预测精度。以高增益和低噪声系数为目标,使用NSGA-Ⅱ算法进行优化,得到包含500个解的Pareto最优解集。优化后,放大器所能实现的平均增益范围为15~37 d B,相应的平均噪声系数范围为4.95~5.31 d B。利用BPNN代替求解耦合微分方程来评价个体适应度,使得优化时间较传统方法由106s左右降低为80 s左右,大幅提升了优化效率。所提方法也为其他掺杂光纤放大器的高效率、多目标结构优化设计提供了一种新的思路。展开更多
基金supported by the National High Technology Research and Development Program (863 program, 2006AA06Z323)National Key Technology R&D Program (2008BAC32B06-3) of Chinaspecial fund of State Key Laboratory of Water Environment Simulation (08ESPCT-Z)
文摘Density functional theory （DFT） plays a significant role in the development of visible light responsive photocatalysts. Based on the first-principles plane-wave ultrasoft pseudopotential （USPP） method, the crystal structures of α,β,γ, and 5-Bi2O3 were optimally calculated for the total density of states （TDOS） and the partial density of states （PDOS） of Bi, O atoms. The calculation for Ti（IV） doped Bi2O3 supercell was carried out. The effects of Ti（IV）-doping on the electron structures and light absorption properties of various Bi2O3 were analyzed. The results showed that Ti 3d orbital appeared in the forbidden band of Bi2O3 and hybridized with O 2p, Bi 6p orbitals. The narrowed band gap （Eg） and red-shift of light absorption edge are responsible for the enhanced photoeatalytic activity of Bi2O3. The Ⅱ-Bi2O3 and Ti-doped β-Bi2O3 were prepared by a hydrotherrnal synthesis method. The improvement of the photoeatalytic activity of Bi2O3 has also been verified by the characteristics of the UV-vis diffuse reflection spectrum and the experimental evaluation of the photocatalytic degradation of crystal violet in aqueous solution.
文摘掺铋光纤放大器有助于将光纤通信系统拓展至新的传输波段。然而,其增益和噪声性能存在相互制约的关系,提升增益往往会导致噪声性能的恶化,反之亦然。因此,提出一种结合反向传播神经网络(BPNN)和带精英保留策略的快速非支配排序遗传算法(NSGA-Ⅱ)的多目标优化方法,通过对两级掺铋光纤放大器结构进行设计,实现了增益和噪声性能的同时优化。使用经过训练的BPNN对增益和噪声系数预测的均方根误差分别为0.191和0.084,具有较高预测精度。以高增益和低噪声系数为目标,使用NSGA-Ⅱ算法进行优化,得到包含500个解的Pareto最优解集。优化后,放大器所能实现的平均增益范围为15~37 d B,相应的平均噪声系数范围为4.95~5.31 d B。利用BPNN代替求解耦合微分方程来评价个体适应度,使得优化时间较传统方法由106s左右降低为80 s左右,大幅提升了优化效率。所提方法也为其他掺杂光纤放大器的高效率、多目标结构优化设计提供了一种新的思路。
