具有消像差和光程补偿功能的新型取样光栅

 在惯性约束聚变(ICF)终端光学聚焦系统中,采用取样光栅将透射的高功率三倍频光按约0.5%的效率进行聚焦采样,送入能量计中进行诊断。提出了用取样光栅对结构取代单取样光栅,通过合理选择系统参数,包括两块光栅的距离、光栅倾斜角度等,设计出的消像差取样光栅可同时进行能量诊断、光脉冲响应测量、以及远场光斑质量的检测。计算结果显示：光程差从8.3 cm降低到8.7 mm,像点的均方根半径为0.777 μm,达到衍射极限和使用要求。这为ICF系统中激光能量、波前畸变的诊断提供了一种可供选择的新诊断装置。     

基于人眼视觉非均匀特性的实时Mean Shift跟踪方法

由于在成像制导过程中需要实时处理大量的信息,为了在尽可能保留有效信息情况下降低计算量,采用了一种人眼视觉非均匀采样模型——对数极坐标模型,来压缩信息量以提高计算速度;另外,由于对数极坐标变换对目标形状具有旋转和缩放不变性,在跟踪非刚性变形目标时该模型能表现出很好的稳健性;考虑到在成像跟踪末段,质心、角点之类的跟踪方法会产生匹配点漂移,为了抑制匹配点漂移,采用基于目标强度特征的Mean Shift跟踪方法,并对采用Gauss核函数的Mean Shift方法进行了优化来加快计算速度;实验结果表明,该方法能够有效抑制匹配点漂移,是一个稳健的目标跟踪方法.     

Dustiness test of nanopowders using a standard rotating drum with a modified sampling train

The standard rotating drum tester was used to determine the dustiness of two nanopowders, nano-TiO₂ and fine ZnO, in standard 1-min tests. Then, the sampling train was modified to determine the number and mass distributions of the generated particles in the respirable size range using a Scanning Mobility Particle Sizer (SMPS), an Aerodynamic Particle Sizer (APS) and a Multi-orifice Uniform Deposit Impactor (MOUDI) in the 30-min tests. It was found that very few particles below 100 nm were generated and the released rate of particles decreased with increasing rotation time for both nanopowders in the 30-min tests. Due to the fluffy structure of the released TiO₂ agglomerated particles, the mass distributions measured by the MOUDI showed large differences with those determined by the APS assuming the apparent bulk densities of the powders. The differences were small for the ZnO agglomerates, which were more compact than the TiO₂ agglomerates.     

Phase-shift, refraction and focusing based on the metamaterial technologies

We address the problem of positive phase-shifting, negative refraction and focusing via a flat lens on the basis of the metamaterial technologies. With this aim, three examples are considered which differ by the technology employed and the operating frequency. The first one concerns negative-zero-positive refraction by using a prism-shaped electromagnetic metamaterial which consists of omega-type inclusion arrays operating at microwaves. The experimental verification was done in this case by angle-resolved transmission measurements. Second, we report on the phase-shift properties of a negative index transmission line which operates at Terahertz frequencies. In order to experimentally demonstrate the left-handed character of the propagation along the line, resulting in a phase advance, we used time domain experiments. At last, focusing by double refraction in a flat negative index lens was demonstrated by the theoretical and experimental mapping of the intensity of the electric field. Such a mapping of the E-field was carried out at near infrared (1.5 μm) by analysis in the time domain and scanning by near field optical microscopy. To cite this article: D. Lippens, C. R. Physique 10 (2009).     

Infrared small target tracking based on sample constrained particle filtering and sparse representation

Infrared search and track technology for small target plays an important role in infrared warning and guidance. In view of the tacking randomness and uncertainty caused by background clutter and noise interference, a robust tracking method for infrared small target based on sample constrained particle filtering and sparse representation is proposed in this paper. Firstly, to distinguish the normal region and interference region in target sub-blocks, we introduce a binary support vector, and combine it with the target sparse representation model, after which a particle filtering observation model based on sparse reconstruction error differences between sample targets is developed. Secondly, we utilize saliency extraction to obtain the high frequency area in infrared image, and make it as a priori knowledge of the transition probability model to limit the particle filtering sampling process. Lastly, the tracking result is brought about via target state estimation and the Bayesian posteriori probability calculation. Theoretical analyses and experimental results show that our method can enhance the state estimation ability of stochastic particles, improve the sparse representation adaptabilities for infrared small targets, and optimize the tracking accuracy for infrared small moving targets.     

基于光脉冲诱导快相与弛豫荧光的光合作用参数测量技术

为了更准确获取反映植物生理状态的荧光动力学曲线,基于光合作用电子传递过程研究了植物光合作用参数测量技术.采用可变光脉冲技术将植物光合作用过程分段为快相与弛豫过程,并测量激发光诱导产生的荧光动力学曲线.对激发光带宽与响应时间进行了定量分析;对I-V转换单元与MFB滤波器进行了设计与仿真分析,获取快相荧光动力学信息;采用同步脉冲采样积分技术,对微弱弛豫荧光进行积分,实现了快相与弛豫荧光动力学曲线的完整测量,并结合非线性拟合算法获取光合作用参数.测试结果表明,系统信噪比达到23.8 dB;暗适应与光适应下,本系统所测Fv/Fm与Water-PAM测量结果的线性相关系数分别达到0.980和0.997.该研究结果为植物光合作用研究及过程参数测量提供了一种测量手段.     

EAST共振磁扰动线圈电源响应延迟分析及优化

为了提高EAST装置中共振磁扰动(RMP)线圈电源的输出电压、电流响应速度和输出特性,对共振磁扰动线圈电源的响应时间延迟进行了分析和优化处理。详细分析了对称规则采样和单极性倍频PWM调制过程所产生的时间延迟,针对该部分时间延迟提出了多次采样延时数据更新方法,对逆变电源控制器进行优化和改进。实验结果表明,采用该方法后电源输出响应时间延迟从206μs减小为70μs,可以满足EAST实验的需求。     

室内环境下基于图优化的视觉惯性SLAM方法

基于图优化的即时定位与同步构图(SLAM)方法是在视觉里程计运动估计的基础上通过增加一个回环检测,从而对非线性多约束进行优化来提高定位精度。在视觉运动估计中,针对视觉特征点匹配错误率高的问题,提出了一种ORB特征点聚类抽样匹配跟踪的方法。在位姿图优化上,提出了一种改进型的回环检测方法,减少了两种错误匹配的可能性。最后将视觉SLAM与惯性导航进行组合,提高了系统的稳定性和定位精度。使用公开的室内SLAM测试数据集进行仿真,结果表明,该方法的定位均方根误差在厘米级,生成的点云地图清晰可见。     

High-speed non-intrusive measurements of fuel velocity fields at high-pressure injectors

Using a single high-speed camera and a frequency modulated laser, a novel approach is presented for fast velocity field measurements in unsteady spray flows. The velocity range is from zero up to several 100 m/s, which requires a high measurement rate and a large dynamic. Typically, flow measurements require to seed tracer particles to the fluid. A paradigm shift to seeding-free measurements is presented. The light scattered at the phase boundaries of the fluid droplets is evaluated. In order to validate the high-speed measurement system, a detailed uncertainty analysis is performed by means of measurements as well as simulations. Thereby, variations of the scattered light intensity, which are based on the high temporal velocity gradients, are found to be the main contribution to the uncertainty. The eventually measurement results, obtained at a measurement rate of 500 kHz, exhibit spray velocities ranging from 0 m/s up to 400 m/s in less than 1 ms, and the detection of unsteady and irregular flow phenomena with a characteristic time of several μs is achieved. This demonstrates the high measurement rate, the high temporal resolution and the large measurement range of the proposed high-speed measurement system.