工作距离可调的激光显微操纵器光学系统设计

考虑传统激光显微操纵器的缺点,采用反射式结构设计了新的激光显微操纵器,以提高激光显微操纵器输出光斑的质量。用He-Ne激光作为指示光束,CO2激光作为工作光束,对两种光斑的重合性、光斑大小进行了优化设计;利用ZEMAX软件中多重结构的功能使系统设计满足200～400 mm工作距离可调的要求。对设计的系统进行了实验,给出了光学系统图、能量图及点列图表。实验结果表明,在规定的工作距离内,系统的光斑重合性,光束均匀性、稳定性及可靠性等方面均有了很大提高。该激光显微操纵器与手术显微镜结合,有术野清晰,操作安全的特点,可满足医疗的长期使用要求。     

Spot size diagnostics for flash radiographic X-ray sources at LAPA

Spot size is one of the parameters to characterize the performance of a radiographic X-ray source. It determines the degree of blurring due to magnification directly. In recent years, a variety of measurement methods have been used to diagnose X-ray spot size at Laboratory of Accelerator Physics and Application (LAPA). Computer simulations and experiments showed that using a rolled-edge to measure the spot size are more accurate, and the intensity distribution of X-ray source was obtained by a device with a square aperture. Experimental and simulation results on a flash X-ray source at our laboratory are presented and discussed in this paper. In addition, a new method for time resolved diagnostics of X-ray spot size is introduced too.     

合肥光源单束团下束团长度和能散的测量

根据同步光与储存环中的束流信号具有相同的时间结构的原理,测量同步光脉冲的半高全宽值可以计算出束团的长度。根据合肥光源的特点和实际需要,选择快速光电接收器搭配高速高带宽示波器作为在线测量束团长度和纵向分布等的主要手段。对单束团模式下束团长度随流强和高频腔腔压的变化趋势进行了测量。测量结果表明:束团长度与腔压的0.3次方成反比,比理论值0.5小;而束团长度随流强的增长率为2.0 ps/mA。通过测量纵向量子寿命进行了能散随流强变化的间接测量,结果表明,束团的拉伸是能散变化和势阱效应共同作用的结果。     

星敏感器光学系统弥散斑测试方法

提出了一种星敏感器光学系统弥散斑尺寸的测试方法,主要是利用平行光管、转台和CCD显微摄像系统组成弥散斑测量系统,采集图像后,采用双三次插值像元细分,提取图像中灰度值,依据瑞利判据计算弥散斑尺寸。通过实际测量和试验验证,光学系统0.8视场弥散斑测量精度可以达到0.5μm,重复测量精度可达0.2μm。     

激光束受限衍射对扫描系统分辨本领的影响

基于菲涅耳衍射积分公式推导出激光束经扫描元件衍射后场分布表达式,数值分析了激光束经扫描元件后衍射场振幅分布、激光束在扫描面上的光斑半径和激光扫描系统光学分辨本领的大小.结果表明,改变入射光束的束腰半径对激光扫描系统线分辨率、可分辨光点数和分辨容积产生不同的衍射影响.采用近似和拟合方法,分段给出不同衍射情况下激光扫描系统的线分辨率的函数表达式,并通过误差分析证明了近似和拟合函数表达式的精确性.     

大气湍流中部分相干聚焦涡旋光束的传输特性

基于广义惠更斯-菲涅耳原理和相位结构函数的平方近似,研究了部分相干高斯-谢尔模型涡旋光束被聚焦后在大气湍流中的传输特性,得到了焦平面上光强解析表达式.利用该表达式,详细研究了该类光束在大气湍流中传输焦平面上的光强分布特性.结果表明：在大气湍流中,随着传输距离的增加,涡旋光束的奇异性逐渐降低.对于拓扑荷大的以及空间相干长度较长的涡旋光束,光束奇异性的保持相对要好.在一定的焦距长度和湍流大气条件下,我们可以通过调整光源的拓扑荷和相干长度控制焦面光强分布和焦斑大小.另外,有一定拓扑荷的涡旋光束可以在一定程度上降低大气湍流对传输光束焦面光强分布的影响.     

电弧特性及其对熔池形貌影响的数值模拟

通过电弧模型与熔池模型耦合数值模拟,研究了氩弧和氦弧特性及其对SUS304不锈钢钨极惰性气体保护（TIG）焊熔池形貌的影响.通过比较氩弧和氦弧的温度轮廓线以及阳极表面电流密度和热流密度分布发现,氦弧的径向距离比氩弧收缩明显,导致更多热量传递给阳极.模拟了氩弧和氦弧下浮力、电磁力、表面张力和气体剪切力分别对熔池形貌的影响.结果表明：不论是在氩弧还是在氦弧下熔池中表面张力是影响熔池形貌的最主要驱动力.在氩弧下,影响熔池形貌的另一个重要的驱动力是气体剪切力,而氦弧下则是电磁力.由于电磁力引起的内对流运动增加了熔深,从而导致相同氧含量时氦弧下的熔深和焊缝深宽比要高于氩弧下的熔深和焊缝深宽比.随着氧含量的增加,氩弧和氦弧下的焊缝深宽比均先增加而后保持不变.焊缝深宽比的模拟结果与实验结果符合较好. 关键词： 氩弧 氦弧 电弧特性 熔池形貌     

A force-based failure criterion for spot weld design

This paper suggests a very simple, force-based formula that combines four failure modes into one dimensionless equation to govern spot weld failure under general static loading conditions. The four failure modes are shear, rotation, normal and peel. The normal separation mode and the peel mode are corresponding to mode I (opening mode). The tensile/shear mode is mode II (sliding mode), and the in-plane rotation mode is mode III (tearing mode). Test coupons and test fixtures are designed and tested to establish and verify this equation. To further verify this equation, a long difficult to understand automotive spot weld failure problem was studied. Applying finite element-calculated resultant loads to the proposed formula resulted in analytical values that correlated very well with the long time field observed spot weld failures. This analytical prediction reasonably explained the spot weld failure mechanism and provided good design directions to improve the durability of the auto structure.     

Failure of spot welds under in-plane static loading

Under in-plane loading conditions, two independent modes contribute to the failure of a spot weld: the in-plane shear mode and the in-plane rotational mode. In this work, the failures of both modes under large static load are examined individually. To study the combined failure of these two modes, two special test coupons are designed. The first coupon contains one spot weld. The second coupon contains five spot welds. Tests conducted in this work show that a very simple force-based failure criterion can be used to predict the failure of a spot weld under large in-plane combined static loads. Current multiaxial failure theory cannot explain this combined failure. This force-based spot weld failure criterion fits current automotive industry needs for body shell finite element application very well.     

Fluctuations in airport arrival and departure traffic: A network analysis

Air traffic is a typical complex system,in which movements of traffic components(pilots,controllers,equipment,and environment),especially airport arrival and departure traffic,form complicated spatial and temporal dynamics.The fluctuations of airport arrival and departure traffic are studied from the point of view of networks as the special correlation between different airports.Our collected flow volume data on the time-dependent activity of US airport arrival and departure traffic indicate that the coupling between the average flux and the fluctuation of an individual airport obeys a certain scaling law with a wide variety of scaling exponents between 1/2 and 1.These scaling phenomena can explain the interaction between the airport internal dynamics(e.g.queuing at airports,a ground delay program and following flying traffic) and a change in the external(network-wide) traffic demand(e.g.an increase in traffic during peak hours every day),allowing us to further understand the mechanisms governing the collective behaviour of the transportation system.We separate internal dynamics from external fluctuations using a scaling law which is helpful for us to systematically determine the origin of fluctuations in airport arrival and departure traffic,uncovering the collective dynamics.Hot spot features are observed in airport traffic data as the dynamical inhomogeneity in the fluxes of individual airports.The intrinsic characteristics of airport arrival and departure traffic under severe weather is discussed as well.