Development of all-solid coherent Doppler wind lidar

A 1 064-nm pulsed coherent Doppler lidar (CDL) prototype is developed to measure short range wind speed in the lower altitude troposphere layer. The CDL system adopts an injection-seeded Nd:YAG laser with the pulse duration of 80 ns, single pulse energy of 0.5 mJ, and pulse repetition rate of 200 Hz. Speed calibration experiments are implemented to obtain a speed accuracy of 0.3 m/s using a hard target. Data analysis results show that the CDL system can obtain a line-of-sight wind velocity at a range of 30 to 500 m with the range resolution of 40 m and 38 pulses accumulation.     

Multi-wavelength pulse generation using flattop optical frequency comb and arrayed waveguide grating

A scheme of multi-wavelength pulse generator using optical frequency comb and arrayed waveguide grating (AWG) is proposed and experimentally demonstrated. A flattop optical frequency comb is shaped into multiple narrowband Gaussian spectra by using an AWG which contains a number of Gaussian channels, and then multi-wavelength optical pulses are achieved. In the experiment, six wavelength pulses with full width at half-maximum (FWHM) of 14.6 ps at 10 GHz are obtained, and two wavelength-interleaved pulse trains at 20 GHz and four wavelength-interleaved pulse trains at 40 GHz are demonstrated by using the multi-wavelength optical pulses. This scheme has flexibility because the pulse width, the repetition rate, and time-interval can be readily controlled.     

手持红外热像仪自动对焦电路的设计与实现

自动对焦可以快速、准确地将镜头调节到最佳位置,但目前该方式在算法和电路设计上还不够成熟,制约了它的应用。通过优化电路设计,选用TMS320VC5509A、FIFO和串口FLASH等低功耗、小尺寸封装芯片组成低功耗自动对焦电路,并基于Sobel算子的Tenengrad的改进图像边缘能量评价函数,采用可变窗口、合适的阈值,配合粗调（定步长）和精调（可变步长）搜索算法,设计实现了一种手持红外热像仪快速、准确地自动对焦的电路。实验结果表明,该方法高效可行,不仅能实现手持红外热像仪对目标的快速捕获,并能降低操作强度。     

机动平台光电跟踪系统的自抗扰控制研究

针对机动平台光电跟踪系统跟踪目标需具备较强动态抗扰能力的问题,提出了一种将包含了非线性跟踪微分器、扩张状态观测器、非线性状态误差反馈三个环节的结构完整的自抗扰控制器用于光电跟踪伺服系统的速度环的思路。针对某单轴稳定转台设计了二阶自抗扰控制器,并进行了仿真研究。结果表明,该控制器对外扰变化及系统模型不确定性具有良好的鲁棒性和适应性,且能有效抑制系统中存在的非线性因素的影响。     

神光Ⅱ终端光学组件的频率变换逆问题研究

在激光惯性约束核聚变(ICF)精确打靶中,对激光束变换、整形和控制要求苛刻,通过数字在线操控技术能够在线实现激光系统的自动校准,而频率变换是数字在线操控技术中的关键一环。在不进行逼近迭代计算的情况下,基于可逆的傅里叶变换和龙格-库塔算法,对神光II终端靶场系统中负单轴晶体KDP的"I+II"类频率变换的逆问题进行了探讨和相应的算法研究,并给出了对应的模拟计算结果。最后,与神光装置运行的实验数据进行比对,验证了频率变换逆问题算法的正确性和稳定性。     

双带频率选择表面设计

为了实现频率选择表面(FSS)的双带特性,设计了由矩形栅格和三圆环组合单元FSS。对FSS的谱域求解方法进行了详细的描述。采用谱域法分析了不同角度和极化入射波下FSS的频率响应性能。结果表明,所设计的FSS对于不同入射角度和极化电磁波具有稳定的双带、平顶传输及陡峭下降边缘特性。双带特性大致表现为1.8～5.4GHz的阻带和5.4～20.0GHz的通带。阻带谐振频率稳定在3.1GHz左右,而通带在-4dB的平顶传输带宽达14.3GHz以上。其陡峭下降边缘特性表现为S波段信号强烈反射,而其他波段信号通过,从而实现多波段通讯。该结构FSS可应用于卫星通信、雷达罩及其他相关领域。     

组合调整频率会影响投资者的回报率么?——基于分析师股票推荐的投资策略研究

利用巨灵数据库的分析师评级数据,从投资者角度建立动态组合,检验了按每日、每周、每两周、每月、每季度头寸调整频率后的超额收益,研究发现:"买入"评级组合在各种头寸调整频率策略下都获得了超越市场指数的超额回报率,其中按每周频率进行头寸调整策略获得的市场调整后平均超额回报率最高,按三个月频率进行头寸调整策略获得的市场调整后平均超额回报率最低。投资者在面对分析师一致认为"买入"评级股票时,可按照每周更新的频率构建组合,以获取较高的超额回报率。投资者如果按季度调整频率来卖出股票可能会错失投资机会,卖掉的股票很可能会跑赢市场,投资者可按每两周或每四周的频率调整投资组合中的股票,卖出负面推荐评级"减持/卖出"股票,降低投资亏损。     

弹性需求下城市公交网络服务的优化

对具有弹性需求的城市公交网络系统进行了票价结构与发车频率组合的优化。考虑到公交定价和发车频率会影响乘客需求以及乘客对路径的选择行为,将这一问题描述为一个双层规划问题,上层是寻求社会福利最大的优化问题;下层考虑了乘客的出行选择行为,为弹性需求下乘客在城市公交网络上流量分布的随机用户平衡分配模型。鉴于双层规划问题的非凸性,运用模拟退火算法对模型进行求解,并给出一个仿真算例说明提出的模型和算法的合理性。     

Calculations of the vibrational frequency and isotopic shift of UF6 and U2F6

Molecular structure, vibrational frequency and infrared intensity of UF6 are investigated by using the revised Perdew Burke-Enzerhof function with the triple-zeta polarized basis set. The calculation results are in good agreement with the experimental values and indicate the existence of a stable U2F6 molecule with a multiple bonded U2 unit. The calculation results also predict that the D3d symmetry of U2F6 is more stable than D3h. The optimized geometries, vibrational frequencies, and infrared intensities are also reported for U2F6 molecules in D3d symmetry. In addition, the isotopic shift of vibrational frequencies of the two molecules under isotopic substitution of uranium atom are also investigated with the same method. The U2F6 molecule is predicted to be better than UF6 for laser uranic isotope separation.     

Dynamic control of retrieval contrast in a ∧-type atomic system

We propose an efficient scheme for optimizing the optical memory of a sequence of signal light pulses in a system of ultracold atoms in ∧ configuration.The memory procedure consists of write-in,storage,and retrieval phases.By applying a weak microwave field in the storage stage,additional phase-dependent terms are included,and the contrast of the output signal pulses can be dynamically controlled（enhanced or suppressed） through manipulating the relative phase φ between optical and microwave fields.Our numerical analysis shows that the contrast is enhanced to the most extent when φ = 1.5π.In addition,the contrast is in proportion to the Rabi frequency of the microwave field with a certain relative phase.