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The Ho3+/Pr3+ co-doped NaYF4 single crystals with various Pr3+ concentrations and constant Ho3+ molar percentage of ~1% were grown by an improved Bridgman method. Compared with the Ho3+ single-doped NaYF4 crystal, an obviously enhanced emission band at 2.85 μm is observed under 640 nm excitation. The Judd-Ofelt strength parameters (Ω 2, Ω 4 and Ω 6) are calculated, the radiative transition probabilities (A), the fluorescence branching ratios (β) and the radiative lifetime (τ rad) are obtained in the meantime. The energy transfer from Pr3+ to Ho3+ and the optimum fluorescence emission of Ho3+ ions around 2.85 μm are investigated. Moreover, the maximum emission cross section of above samples at 2.85 μm is calculated to be 0.72×10-20 cm2 for the NaYF4 single crystal with Ho3+ molar percentage of 1% and Pr3+ molar percentage of 0.5% according to the measured absorption spectrum. All results suggest that the Ho3+/Pr3+ co-doped NaYF4 single crystal may have potential applications in mid-infrared lasers. 相似文献
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由于出山店水库下游河床水位低且水深变幅较大,能量较为集中,对下游冲刷严重,传统消能方式很难满足工程需求。本文结合出山店混凝土坝下消能防冲实验研究成果,对宽尾墩的水流特点、掺气特征、消能效果等进行了探讨,再通过数值模拟得出的水面线计算成果与实验结果吻合良好。最后,经过模型试验、数值模拟的结果进行比选,得出溢流表孔采用底流消能同时联合T型墩、非完全宽尾墩等辅助消能方式的消能率有所提高,消能效果提升明显。本研究可为类似的低水头、大单宽流量、低佛劳德数水库消能设计与试验研究提供参考。 相似文献
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大多数学者对于高拱坝的稳定安全余度的研究都是讲有一定的安全余度或安全度。董玉文、任青文总结目前拱坝安全度的分析方法主要有:柔度系数法、安全系数法、可靠度方法和模型试验法;王仁坤应用AAA-90程序、TFINE程序和HS2程序进行了二滩拱坝的超载分析,对二滩拱坝的安全富裕度给出了量化结果。根据拱坝的结构形态及受力特点,拱坝稳定与否主要取决于坝肩,国内外大多数拱坝失事都是由拱坝的坝肩失稳引起,因此研究拱坝稳定安全余度主要是研究坝肩的稳定安全余度。 相似文献
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