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Lagrangian analysis of the formation and mass transport of compressible vortex rings generated by a shock tube 下载免费PDF全文
In order to understand the mass transport and the dynamic genesis associated with a compressible vortex formation,a dynamic analysis of compressible vortex rings (CVRs) generated by shock tubes by using the framework of Lagrangiancoherent structures (LCSs) and finite-time Lyapunov exponents field (FTLE) is performed. Numerical calculation is performed to simulate the evolution of CVRs generated by shock tubes with 70 mm, 100 mm, and 165 mm of the driver sectionat the circumstances of pressure ratio = 3. The formation of CVRs is studied according to FTLE fields. The mass transportduring the formation is obviously seen by the material manifold reveled by FTLE fields. A non-universal formation numberfor the three CVRs is obtained. Then the elliptic LCSs is implemented on three CVRs. Fluid particles separated by ellipticLCSs and ridges of FTLE are traced back to t = 0 to identify the fluid that eventually forms the CVRs. The elliptic LCSsencompass around 60% fluid material of the advected bulk but contain the majority of the circulation of the ring. The otherparts of the ring carrying almost zero circulation advect along with the ring. Combining the ridges of FTLE and the ellipticLCS, the whole CVR can be divided into three distinct dynamic parts: vortex part, entrainment part, and advected part. Inaddition, a criterion based on the vortex part formation is suggested to identify the formation number of CVRs. 相似文献
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共掺杂的二氧化锆纳米材料中Yb3+和Tm3+上转换发光 总被引:4,自引:0,他引:4
用共沉淀法制备了二氧化锆掺Yb3 和 0 2 (0 4 ,1)mol%Tm3 的纳米材料 ;用发射波长为 980nm的激光激发样品 ,测量了掺 0 2mol%Tm3 的纳米材料在不同退火温度下的上转换光谱 ;测量了在相同退火温度、不同泵浦电流下的上转换发射光谱 ;并研究了蓝色上转换发射的过程。 相似文献
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罗丹明6G/MCM-41纳米复合物的发光蓝移 总被引:3,自引:0,他引:3
介孔分子筛MCM-41具有规则排列的纳米量级的孔道,可以作为宿主封装其他材料。利用这一性质,将激光染料罗丹明6G分子封装在介孔分子筛MCM-41中形成了纳米复合物。用透射电镜、小角度X射线衍射和荧光光谱等方法对纳米复合物的性质进行了分析。用波长为480nm的光对纳米复合物进行激发,得到的发光峰为531nm。与无限稀罗丹明6G乙醇溶液的发光峰相比,这一发光峰有15nm的蓝移和明显的宽化。我们认为当罗丹明6G分子封装在MCM-41的介孔中时,罗丹明6G分子与介孔分子筛孔道表面分子之间存在较强的相互作用(包括氢键、静电吸引等),导致电子云被局域在具有较强吸引力的分子筛表面原子周围。引起激发态能量升高,发光峰蓝移。 相似文献
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二氧化锆纳米材料中三价铒离子的上转换发光 总被引:3,自引:0,他引:3
固态蓝绿光源非常适合于高强度光存储、色平板、光电和医疗诊断,迄今为止,对各种晶体中上转换发光进行了广泛的研究。三价铒离子由于其相当高的上转换发光速率被作为一种激活离子而受到研究者的表睐。我们用共沉淀法制备了掺铒离子的二氧化锆纳米材料,并对纳米的结构,颗粒大小,声子能量进行了表征;用980nmLD和F-4500荧光分析仪测量了两种样品的上转换发射光谱,并观察到强的绿色发射和弱的红色发射,出现这种发射现象的原因是由于低的掺杂浓度和低的声子能量,通过发光强度和泵浦电流关系的实验。我们得到:蓝色和红色上转换发射分别来自三光子,双光子和双光子过程。 相似文献
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