光学窗口凹腔流场的光学传输效应研究

当带有光学成像探测制导系统的高速飞行器在大气层内飞行时,光学窗口与来流之间会形成复杂的凹腔绕流流场,产生气动光学效应。建立了求解超声速流场的高精度LES/RANS混合算法模型,研究了超声速流动条件下的Settles三维凹腔流动;在计算得到精确流场数据的基础上,研究了凹腔剪切层区域的光学传输效应。结果表明,凹腔流动的剪切层结构将引起光线抖动,导致严重的波面畸变,明显降低光强斯特雷尔(Strehl)比,严重影响光学传输性能,进而大大降低光学制导精度。     

Study on the luminescence and energy level of lanthanide ions in Lu(0.8)Sc(0.2)BO3 host

Emission and excitation spectra of undoped and Ln(3+) (Ln = Ce, Pr, Nd, Yb)-doped Lu(0.8)Sc(0.2)BO(3) were studied by vacuum ultraviolet spectroscopy, and the X-ray excited luminescence spectra were measured as well at room temperature. The undoped specimen presented two different emissions upon excitation at energies in the vicinity of the band gap or with X-ray. The emission at the highest energy side, located at 4.77 eV, was ascribed to self-trapped exciton, which is anchored by electron capture around the Sc site. We also observed three broad emission bands at 4.43, 3.02, and 2.10 eV, which might be attributed to the trapped exciton, defect -related emissions, or both. Energy transfer processes to the doped lanthanide ions in Lu(0.8)Sc(0.2)BO(3) via exciton state or sequential electron-hole capture are discussed. Finally, the energy level diagram for divalent and trivalent lanthanides in Lu(0.8)Sc(0.2)BO(3) was constructed using the obtained spectroscopic parameters and the three parameters method (Dorenbos, P. J. Phys.: Condens. Matter 2003, 15, 8417).     

X‐ray fluorescence computed tomography with absorption correction for biomedical samples

To obtain accurate distributions of trace elements in biomedical samples nondestructively, the problems on absorption correction and radiation dose are confronted in X‐ray fluorescence computed tomography. In this paper, the absorption‐corrected ordered subsets expectation maximization (AC‐OSEM) algorithm is developed to solve these problems. Simulation results show that the AC‐OSEM‐based X‐ray fluorescence computed tomography is accurate when only the incident X‐ray attenuation map is known and relatively fewer projections are provided. In addition, for the biomedical samples, the simplified approximate expression of the fluorescence attenuation map is practicable. Experiments on the biomedical samples were also carried out to evaluate the applicability of the AC‐OSEM algorithm to soft tissues, which demonstrates that the distribution of the trace element Fe in the pathological liver could be clearly revealed. Copyright © 2014 John Wiley & Sons, Ltd.     

Three-dimensional structure of polystyrene colloidal crystal by synchrotron radiation X-ray phase-contrast computed tomography

Colloidal crystal with long-range ordered structure has attracted great attention for their applications in various fields. Although perfect colloidal crystals have been achieved by some fabrications for utilization, little is known about their exact structures and internal defects. In this study, we use synchrotron radiation (SR) phase-contrast computed tomography (CT) to noninvasively access the internal structure of polystyrene (PS) colloidal crystals in three dimensions (3D). The phase-attenuation duality Paganin algorithm phase retrieval was employed to achieve a satisfactory contrast and outline of the spheres. After CT reconstruction, the positions of individual PS particles and structural defects are identified in three dimensions, and the local crystal structure is revealed. Further quantitative analysis of the void system in colloidal crystal illustrates that single voids can be mostly attributed to tetrahedron void of sphere close packing, but the interconnected voids with large volume induce a sphere volume fraction of 59.39 % that reflects a metastable glass behavior of colloidal crystal arrangement. The void orientation result reveals that the 3D close-packing difficulty mainly lies in the stacking of interlayer.     

One‐step polymerization of hydrophilic ionic liquid imprinted polymer in water for selective separation and detection of levofloxacin from environmental matrices

A novel green hydrophilic levofloxacin imprinted polymer was presented via one‐step polymerization in water using ionic liquid 1,6‐hexa‐3,3′‐bis‐1‐vinylimidazolium bromine with multiple hydrophilic groups and 2‐hydroxyethyl methacrylate as a co‐functional monomer. Adsorption experiment revealed that the ionic liquid significantly improved the water compatible of imprinted polymer, and the excellent recognition of molecularly imprinted polymer for levofloxacin in water corresponds to the synergetic effect of H‐bonding and the electrostatic and π–π interactions between the levofloxacin and co‐functional monomer. Furthermore, the adsorption process of the imprinted material towards levofloxacin fitted the Langmuir model, and the maximum binding amount of levofloxacin onto the imprinted and corresponding non‐imprinted polymer were 16.45 and 6.82 mg/g at 25°C, respectively. After optimizing the parameters affecting solid phase extraction performance, an enrichment and determination system was achieved to separate and detect levofloxacin from water and sediment samples with recoveries that ranged from 83.67 to 101.33% and relative standard deviation of less than 5.59%.     

Crystal growth of PbFCl by modified Bridgman method

Lead fluoride chloride (PbFCl) crystal was grown by modified Bridgman method. The result of X-ray powder diffraction pattern (XRD) was well accordant with the data of JCPDS card. The transmittance spectrum was first reported without absorption band from 270 to 800 nm. Three emission bands were first observed at room temperature when excited by ultraviolet light.     

标度理论及其分形几何

 本文利用量纲分析的方法，对分形中周长-面积关系与一般分形曲线的长度公式的量纲进行了分析；给出了普通标度理论与分形中标度变换间的定量关系。我们给出了描述随机耗散系统中分形的一种数学理论与分形结构上的输运过程，并讨论了某些预言性的结果，有待实验上加以证明。     

钇掺杂量对LuxY1-xAlO3:Ce晶体结构和发光性能的影响

研究了Y掺杂量对LuxY1-xAlO3：Ce晶体结构和发光性能的影响，结果表明：固溶体晶体LuxY1-xAlO3：Ce（x=0～0．3）仍为正交晶系赝钙钛矿型结构。随着Y掺杂量的减少，晶胞体积减小、晶体密度增大、本征吸收降低、光输出增大，衰减时间由YAlO3：Ce的29．7ns降低至Lu0.3Y0.7Al03：Ce的24．2ns。随着Y掺杂量的减少，发射谱的峰位由YAlO3：Ce的390nm逐步紫移至Lu0.3Y0.7AlO3：Ce的384nm，这表明尽管LuxY1-xAlO3：Ce晶体的光激发一发射机制并未发生明显的变化，但掺杂还是引起了稀土格位晶体场的变化，激活离子Ce^3＋的激发态与基态能级之间的能级差随Y掺杂量的减少逐步加大。Y掺杂含量的降低在改善晶体闪烁性能的同时也降低了晶体的热稳定性，增强了晶体的放射性本底。     

金属粉末爆炸烧结界面能量沉积机制

本文用绝热摩擦机制和微爆炸焊接模型讨论了爆炸烧结过程中金属粉末颗粒边界局部升温以至熔融的机理。指出这种升温时间大致和激波前沿的上升时间相当,约10-8秒量级 升温率高达1011度/秒。其界面温度可超过常压下的金属熔点。并与McQueen等人建立的多孔隙材料的绝热压缩理论进行了比较。