ACTIVE CONTROL OF A FLEXIBLE CANTILEVER PLATE WITH MULTIPLE TIME DELAYS

Active control of a flexible cantilever plate with multiple time delays is investigated using the discrete optimal control method. A controller with multiple time delays is presented. In this controller, time delay effect is incorporated in the mathematical model of the dynamic system throughout the control design and no approximations and assumptions are made in the controller derivation, so the system stability is easily guaranteed. Furthermore, this controller is available for both small time delays and large time delays. The feasibility and efficiency of the proposed controller are verified through numerical simulations in the end of this paper.     

电子束激励KrF激光放大器稳定运行的重要技术问题

介绍了用于天光一号高功率氟化氪(KrF)准分子激光系统中的电子束双向激励主放大器稳定运行中必须解决的一些重要技术问题：水介质脉冲传输线中的绝缘支撑击穿问题;大面积电子束二极管阳极膜的安装;与压力膜接触处Hibachi筋的形状;二极管后脉冲的形成及其对阳极膜和阴极发射体造成的损害等问题。还着重描述了主开关导通时刻对二极管后脉冲的影响及最佳导通时刻的确定。     

余弦高斯光束在梯度折射率介质中的传输特性

为了研究光束在梯度折射率介质中的传输规律,利用广义惠更斯-菲涅耳衍射积分法,推导出余弦高斯光束在梯度折射率介质中传输的解析表达式,对余弦高斯光束在梯度折射率介质中的传输特性进行了分析,并进一步讨论了介质梯度折射率系数和调制参数对传输特性的影响。结果表明,余弦高斯光束在梯度折射率介质中传输时,轴上光强分布呈现周期性变化,横向光强分布受梯度折射率系数和调制参数影响较大。余弦高斯光束传输时具有不稳定性,通过适当调节参数,可在空间某位置实现余弦高斯光束的整形。     

测量行波管电子注的法拉第筒的热分析

利用ANSYS软件对测量行波管电子注截面的法拉第筒探头进行了热分析研究。分析了在单脉冲情况下,测量各种直径的不同脉冲功率密度的电子注、不同脉冲宽度对法拉第筒温度的影响,研究了测量不同功率密度的电子注可以使用的脉冲宽度。结果表明,仅法拉第筒上的注斑区域温度迅速上升,温度梯度较大,其它部分温度基本不变,为保证法拉第筒能够持续正常工作,在单脉冲情况下,对于功率密度大于5×106 W/cm2的电子注,需使用宽度小于0.5 μs的脉冲,最好是0.1 μs和0.2 μs的脉冲进行测量,与文献结果相符。测量一定功率密度的电子注,需选择合适的脉冲宽度。另外,考虑热量的累积效应,分析了脉冲重复频率对法拉第筒工作温度和散热情况的影响。结果表明,脉冲重复频率设为10~100 Hz是比较合适的。     

线性变压器源驱动相对论速调管放大器的初步实验

利用新研制的紧凑型线性变压器驱动源（LTD）脉冲功率源二极管产生的电子束源,开展了S波段长脉冲相对论速调管放大器（RKA）的初步实验研究。采用无箔空心阴极和0.9 T恒流源引导磁场从LTD二极管引出了电压600 kV、束流6 kA、脉宽150 ns的环形电子束,该电子束经过1个同轴输入腔和2个同轴调制腔的调制后,产生了幅度5 kA、脉宽110 ns的基波调制束流,采用该调制束流驱动同轴微波提取腔,辐射输出了峰值功率820 MW/110 ns的辐射微波,效率28％,增益36 dB。同时,开展了重复脉冲RKA和相位特性的实验研究,重复频率10 Hz运行时,辐射微波达到800 MW/100 ns,相位抖动小于 20°。     

双曲余弦高斯列阵光束通过湍流大气传输的角扩展及方向性

采用积分变换,推导出了双曲余弦高斯（ChG）列阵光束通过湍流大气传输的二阶矩束宽和角扩展的解析公式,给出了ChG列阵光束与一束高斯光束具有相同角扩展的条件。研究表明:相干合成的ChG列阵光束的角扩展比非相干合成的小,但是,非相干合成的ChG列阵光束的角扩展受湍流影响比相干合成ChG光束小;相干合成情况下,ChG列阵光束的角扩展随离心参数、束腰宽度和相对子光束间距的变化均出现振荡,但在湍流中的振荡减弱,非相干合成情况下,ChG列阵光束的角扩展与相对子光束间距和光束数无关。     

A preliminary approach of dynamic identification of slender buildings by neuronal networks

The study of the dynamic behavior of slender masonry structures is usually related to the preservation of the historic heritage. This study, for bell towers and industrial masonry chimneys, is particularly relevant in areas with an important seismic hazard. The analysis of the dynamic behavior of masonry structures is particularly complex due to the multiple effects that can affect the variation of its main frequencies along the seasons of the year: temperature and humidity. Moreover, these dynamic properties also vary considerably in structures built in areas where land subsidence due to the variation of the phreatic level along the year is particularly evident: the stiffness of the soil–structure interaction also varies. This paper presents a study to evaluate the possibility of detecting the variation of groundwater level based on the readings obtained using accelerometers in different positions on the structure. To do this a general case study was considered: a 3D numerical model of a bellower. The variation of the phreatic level was evaluated between 0 and −20 m, and 81 cases studies were developed modifying the rigidity of the soil–structure interaction associated to a position of the phreatic level. To simulate the dispositions of accelerometers on a real construction, 16 points of the numerical model were selected along the structure to obtain modal displacements in two orthogonal directions. Through an adjustment by using neural networks, a good correlation has been observed between the predicted position of the water table and acceleration readings obtained from the numerical model. It is possible to conclude that with a discrete register of accelerations on the tower it is possible to predict the water table depth.     

Relaxation Dynamics and Magnetic Anisotropy in a Low‐Symmetry DyIII Complex

The magnetic behaviour of a Dy(LH)₃ complex (LH^? is the anion of 2‐hydroxy‐N′‐[(E)‐(2‐hydroxy‐3‐methoxyphenyl)methylidene]benzhydrazide) was analysed in depth from both theoretical and experimental points of view. Cantilever torque magnetometry indicated that the complex has Ising‐type anisotropy, and provided two possible directions for the easy axis of anisotropy due to the presence of two magnetically non‐equivalent molecules in the crystal. Ab initio calculations confirmed the strong Ising‐type anisotropy and disentangled the two possible orientations. The computed results obtained by using ab initio calculations were then used to rationalise the composite dynamic behaviour observed for both pure Dy^III phase and Y^III diluted phase, which showed two different relaxation channels in zero and non‐zero static magnetic fields. In particular, we showed that the relaxation behaviour at the higher temperature range can be correctly reproduced by using a master matrix approach, which suggests that Orbach relaxation is occurring through a second excited doublet.     

部分相干光束经过湍流大气传输研究进展

相较于相干光束,部分相干光束经过湍流大气传输能够有效地抑制湍流引起的光束展宽、光斑漂移及光强闪烁等扰动效应,在自由空间光通信、激光雷达和激光遥感等方面有重要的应用前景.近年来,部分相干光束湍流大气传输研究受到越来越多学者的关注.本文回顾了部分相干光束在湍流大气中传输特性研究的发展历程、理论基础及常用的理论方法,介绍了处理光束经过湍流大气传输的相位屏数值模拟方法,以及如何把该方法运用到处理部分相干光束传输.     

用四台阶相位板产生涡旋光束

涡旋光束的产生与应用是当前光学领域的研究热点. 利用傅里叶级数展开法分析了四台阶相位板的相位结构, 发现四台阶相位板可看作是由一系列不同拓扑荷数的螺旋相位板所组成, 用线偏振光直接照射相位板时, 将产生多级衍射光波, 各级衍射光均为不同拓扑荷数的涡旋光波, 由于多级衍射光波间的干涉导致光强分布偏离轴对称分布, 因而与涡旋光波有一定差距. 在此基础上, 提出了用四台阶相位板产生涡旋光束的新方案, 借助于Mach-Zehnder 干涉仪光路, 两块四台阶相位板产生的衍射光干涉叠加, 通过调节干涉仪光路的相位差, 使一部分衍射级干涉相消, 另一部分衍射级干涉相长, 相互加强, 从而把线偏振光转换为涡旋光束. 数值模拟计算了几种周期数不同的四台阶相位板衍射光强和角动量分布, 并与螺旋相位板进行比较, 证明用简单的四台阶相位板不仅能够获得与用螺旋相位板相同的涡旋光束, 而且可以用周期数较小的四台阶相位板产生具有大拓扑荷数的涡旋光束, 降低了制作相位板的难度.