圆柱振荡绕流中涡旋运动模式(pattern)的数值模拟

提出并发展的一种基于区域分解思想,综合了解N-S方程的有限差分法及涡法各自优点的新数值方法,计算了各种 Keulegan-Carpenter数下(Kc=2~24)振荡流绕圆柱的流动。系统地研究了振荡流中涡旋运动模式随Kc数变化的规律,模拟了不对称区、单对涡区(或模向区)、双对涡区(或对角区)和三对涡区四种不同的涡旋运动模式。将计算所得的阻力系数C_D、惯性系数C_M与国外近期发表的计算结果进行了比较。     

Refractive index sensing by using Fano resonance enhanced two‐photon luminescence

Utilizing three‐dimensional vectorial electromagnetic simulation, we propose a new refractive index sensing mechanism based on Fano resonance enhanced two‐photon‐absorption induced luminescence (TPL). The TPL from gold nanodisk heptamer (GNDH), which is affected by the refractive index of surrounding material, is used as an example to demonstrate the sensing mechanism facilitated by Fano resonance. The sensitivity of our method is about one order of magnitude better than the conventional refractive index sensing strategy employing plasmonic Fano resonance, while the size of the sensing probe can be further reduced at the same time.

     

An unconventional method for measuring the Tc L3‐edge of technetium compounds

Tc L₃‐edge XANES spectra have been collected on powder samples of SrTcO₃ (octahedral Tc⁴⁺) and NH₄TcO₄ (tetrahedral Tc⁷⁺) immobilized in an epoxy resin. Features in the Tc L₃‐edge XANES spectra are compared with the pre‐edge feature of the Tc K‐edge as well as other 4d transition metal L₃‐edges. Evidence of crystal field splitting is obvious in the Tc L₃‐edge, which is sensitive to the coordination number and oxidation state of the Tc cation. The Tc L₃ absorption edge energy difference between SrTcO₃ (Tc⁴⁺) and NH₄TcO₄ (Tc⁷⁺) shows that the energy shift at the Tc L₃‐edge is an effective tool for studying changes in the oxidation states of technetium compounds. The Tc L₃‐edge spectra are compared with those obtained from Mo and Ru oxide standards with various oxidation states and coordination environments. Most importantly, fitting the Tc L₃‐edge to component peaks can provide direct evidence of crystal field splitting that cannot be obtained from the Tc K‐edge.     

装备使用与保障研究数据的生成方法研究

装备使用与保障数据是开展装备科学研究的重要依据,而由于管理不善、保密、样本过少等原因常常导致相关数据缺少应有的积累,无法满足实际研究的需要。为了克服这一困难,文章提出通过算法生成数据予以解决。首先根据数据的应用特性,将装备使用与保障数据看作简单数据、规律已知数据和规律未知数据三类,分别制定生成策略。对于简单数据和规律已知数据,通过已有的商用软件或简单的自定义方法生成;对于规律未知数据,采用模式注入或特性继承的方法生成。在某大型装备管理综合信息系统的设计开发中,对这些生成方法进行了工程实践,结果表明了方法的正确性和可行性。     

壁面材质和温度场对熔融硅润湿角的影响

本文建立了毛细模型, 采用微流动两相流水平集法计算了熔融态硅液与壁面的润湿角, 以人造金刚石作为壁面材料的计算结果与实验结果进行比较, 验证了该模型和计算方法的正确性. 在此基础上, 分别选用碳化硅、石墨和人造金刚石作为壁面材料, 探讨了不同壁面材料表面张力和壁面黏附力对润湿角的影响规律. 结果发现, 相同温度下的毛细力作用使得熔融硅液出现起伏上升现象; 润湿角均有不同程度的减小然后增大, 最终趋于稳定; 初始阶段, 由于气/熔融硅液表面张力与气/壁面表面张力之差变化较大, 液面起伏波动较大; 随后趋于稳定上升. 同时发现石墨作为壁面材料时, 以上变化更易趋于稳定. 该研究为熔体中生长晶体硅获得更稳定的生长环境提供了理论依据.     

基于O2-O2吸收的非相干宽带腔增强吸收光谱浓度反演方法研究

针对传统非相干宽带腔增强吸收光谱浓度反演方法的定量结果易受镜片反射率标定误差的影响问题, 提出了一种基于测量大气O₂-O₂吸收的浓度反演方法. 该方法是将非相干宽带腔增强吸收光谱技术的光学增强腔等效成吸收光程不随波长变化的多次反射池, 首先根据测得的宽带腔增强大气吸收谱和参考谱计算出光学厚度, 并应用差分光学吸收光谱算法拟合修正后的气体吸收截面到光学厚度, 反演得到大气中O₂-O₂以及被测气体的柱浓度, 然后根据O₂-O₂在大气中的含量已知且相对稳定这一特性, 确定出等效多次反射池的吸收光程, 最后从被测气体的柱浓度中扣除吸收光程信息得到被测气体的浓度值. 以监测大气中NO₂实验为例, 应用该方法在454-487 nm波段反演得到了大气NO₂的浓度(1-30 ppbv范围内), 并将反演结果与传统浓度反演方法的结果进行了对比, 发现两者的不一致性在7%以内. 实验结果表明, 非相干宽带腔增强吸收光谱技术可以利用大气O₂-O₂的吸收来定量其他被测气体的浓度, 而且定量结果对镜片反射率的标定误差不敏感.     

氮烃混合工质中氖的作用机理

氮烃混合工质由于有较大的制冷量,在节流制冷器中已广泛应用,然而它的制冷温度却较高,在使用中受到一定的限制。文中通过对在氮烃混合工质中加入氖的分析,揭示了氖降低混合工质制冷温度的机理     

两束脉冲激光在级联的三能级系统中的传播

利用密度矩阵方程和麦克斯韦传播方程的耦合考虑激光脉冲的横向效应,在柱对称的条件下,研究了两束脉冲在级联系统中的共振传播,考察了脉冲在光学厚介质中的时空演化过程。数值计算中考虑了两个能级的自发辐射速度,给出了脉能量的空间演化及电熟粒子在空间的分布。     

非费米液体层间隧道作用下的Tc与零温能隙

本文在自旋电荷相统一的非费米液体前提下,同时考虑相一作用Ｖ及层间随着作用ＴＪ,推导出非费米液体层间隧道的超导转变温度Ｔｃ的解析式,给出了临界耦合因子λＴＪｃ,λｃ与α关系式,并且数值计算了零温能隙随ＴＪ及α的变化趋势。     

Measuring the power-law exponent of an atmospheric turbulence phase power spectrum with a Shack Hartmann wave-front sensor

For non-Kolmogorov turbulence we develop a differential angle-of-arrival fluctuation coefficient, which is the ratio between the transverse and longitudinal differential angle-of-arrival variances, and a slope structure-correlation coefficient, which is the ratio between the transverse and longitudinal differences of the slope correlation function and the slope structure function, to measure the power-law exponent of a phase power spectrum with a Shack-Hartmann wave-front sensor: The differential arrival-of-angle fluctuation coefficient and the slope structure-correlation coefficient are both related to power-law exponent beta and are independent of strength parameter rho(0) of the turbulence. We compare the methods developed and use them to evaluate beta in recently completed horizontal atmospheric experiments for 1000-m laser beam propagation.