复合材料散斑检测中的小波降噪技术

电子剪切散斑干涉检测技术非常适宜复合材料的无损检测。但散斑图像往往含有较大的噪声,如何对散斑图像进行降噪处理是一个非常重要的问题。小波变换是变分辨率的分析方法,可以有效地降低噪声,而同时又较好地保存了图像细节,本文应用小波降噪技术来对散斑图像进行降噪处理,取得了较好的效果。     

Deramp range migration processing for space-borne spotlight synthetic aperture radar

The deramp range migration algorithm (DRMA) for space-borne spotlight synthetic aperture radar (SAR) is presented, which is based on the two-step algorithm and range migration algorithm. The presented algorithm combines the advantages of SPECAN algorithm and range migration algorithm. Firstly, the presented algorithm performs a bulk azimuth raw data compression to achieve a pixel spacing no larger than the expected azimuth resolution of the fully focused image. Therefore, the azimuth spectral folding phenomenon is overcome. Secondly, the residual and precise focusing of the synthetic aperture radar data is achieved by applying the range migration algorithm. The space-borne SAR focusing parameters’ computation is also described in the paper. At the end of this paper, results are presented which confirm the validity of the presented algorithm.     

基于量子傅里叶变换的模式特征提取算法

量子算法由于具有量子态的叠加性、相干性和纠缠性使得它可以解决一些经典NP问题,并且它具有许多传统算法所没有的优点.本文利用量子傅里叶变换提出了一个模式特征提取算法,它借助量子并行特性只需进行一次量子傅里叶变换就可以提取模式特征,所以它提取模式特征的速度比传统特征提取算法有了指数级的提高.利用该算法提取出来的特征可以进行模式识别或图像识别.本文通过理论推导证明了该算法的可行性,通过简单的模式图验证了该模式特征提取算法的有用性.     

A fast satellite selection algorithm with floating high cut-off elevation angle based on ADOP for instantaneous multi-GNSS single-frequency relative positioning

With the Global Navigation Satellite System (GNSS) developing, the single-frequency single-epoch multiple GNSSs (multi-GNSS) relative positioning has become feasible. Since a larger number of the observed satellites make the instantaneous (single-epoch) positioning time-consuming, a proper satellite selection is necessary. Among the present methods, the satellite selection with a fixed high cut-off elevation angle (CEA) is least time-consuming. However, there is no criterion how large a fixed high CEA should be to achieve a high success rate and less time consumption. Besides, a fixed high CEA makes the number of visible satellites largely variable, which affects the success rate. Hence, a satellite selection strategy based on ambiguity dilution of precision (ADOP) is proposed. Firstly, the theoretical proof that the ADOP increases the least when removing satellites are all low-elevation-angle satellites is given, which is important to achieve the fast positioning with a high success rate. Then, the threshold $\beta$ is calculated for a different number of satellites and a given ADOP. The satellites are selected based on their elevation angles from high to low until $\beta$ of the selected satellites becomes smaller than the corresponding threshold; this method is called the extended floating CEA multi-GNSS (EF-multi-GNSS). The comparison of the single-frequency single-epoch positioning performance of the EF-multi-GNSS with the satellite selections based on a fixed low CEA (L-multi-GNSS) and a fixed high CEA (H-multi-GNSS) via the relative positioning experiments shows that: (1) the EF-multi-GNSS with a minimal number of satellites can achieve the fast positioning and a high success rate close to 100%. It can greatly reduce the time consumption of the L-multi-GNSS, by about 64.0%, by selecting 12.6 satellites of 23.4 satellites; (2) the floating CEA of EF-multi-GNSS eliminates the consideration how large a fixed high CEA should be, and a CEA larger than the fixed high CEA of the H-multi-GNSS makes it more suitable for different conditions.     

水对ＰＡＮ／ＤＭＳＯ／Ｈ２Ｏ的流变行为和原丝性能的影响

研究了水对PAN/DMSO/H2O纺丝液的流变行为和可纺性能的影响.结果表明,在较高的剪切速率下,PAN溶液表现出"切力变稀".而在较低的剪切速率下,随着温度的增加,溶液黏度逐渐变低.水含量对溶液的黏度有较大影响.随着体系中水含量的不同,H2O-PAN之间的水和作用于水的脱溶剂作用之间形成竞争,从而决定黏度的变化.适量水的加入可以提高纤维的力学性能.随着纤维拉伸倍数的增加,聚丙烯腈纤维的断裂强度增加,断裂伸长率下降.在一定的纺丝条件下,随着含水量的增加,纺丝原液的可纺性会降低.而适量的水有利于获得具有弥散状微孔的均一结构的原丝.     

动量轮失效物理模型试验方案研究

论述了动量轮失效物理模型及其试验方法, 其目的是提高动量轮产品的研制水平和进行动量轮寿命预计. 文章主要内容包括失效物理模型、试验环境模拟、试验模型技术状态的认可、失效影响因素分析、试验过程中数据采集方法及建立失效物理的数学评判表达式.      

软件定义的GNSS反射信号接收机设计

分析了导航卫星反射信号的特点,给出了反射信号软件接收机的总体结构及其主要模块,主要包括接收直射和反射信号的天线、射频前端和高速A/D变换器,以及数据处理用的计算机.重点介绍了反射信号处理的基本过程,其中主要讨论了本地反射信号C/A码的生成模式,在此基础上分析了反射信号相关功率的计算方法,并给出了具体的仿真计算实例.设计了反射信号处理的具体实现软件,包括详细的流程图,关键参数和主要函数的定义及用户界面,利用实际采集的数据进行了验证,结果表明所设计的反射信号接收机运行稳定,能根据用户输入的不同参数提供导航卫星反射信号的相关功率输出.     

汽车DYC模糊PID控制方法

直接横摆力矩控制DYC(Direct Yaw-Moment Control)是提高汽车操纵稳定性特性的重要方法,其研究对于提高汽车的主动安全性具有重要意义.在深入研究汽车操纵动力学和先进控制理论的基础上,设计了具有智能积分模块的模糊PID(Proportion-Integral-Differential)控制器,将该控制方法应用于DYC控制.建立了能够反映车辆转向工况基本动力学性质的车辆动力学模型,在Simulink环境下对开发的智能积分模糊PID控制器进行了仿真测试与分析.仿真结果验证了算法的可行性和有效性,表明智能积分模糊PID控制方法可以实现较为理想的DYC控制效果,在该领域具有良好的应用前景.     

碳纤维复合材料高速开槽铣削试验研究

针对碳纤维复合材料加工常用的开槽切削进行了高速铣削试验,对切削力进行了检测并在此基础上进行了经验公式回归分析,分析了转速、进给速度、切深对切削力的影响及正反螺旋对切削棱边毛刺的影响。     

The Lunar Reconnaissance Orbiter Laser Ranging Investigation

The objective of the Lunar Reconnaissance Orbiter (LRO) Laser Ranging (LR) system is to collect precise measurements of range that allow the spacecraft to achieve its requirement for precision orbit determination. The LR will make one-way range measurements via laser pulse time-of-flight from Earth to LRO, and will determine the position of the spacecraft at a sub-meter level with respect to ground stations on Earth and the center of mass of the Moon. Ranging will occur whenever LRO is visible in the line of sight from participating Earth ground tracking stations. The LR consists of two primary components, a flight system and ground system. The flight system consists of a small receiver telescope mounted on the LRO high-gain antenna that captures the uplinked laser signal, and a fiber optic cable that routes the signal to the Lunar Orbiter Laser Altimeter (LOLA) instrument on LRO. The LOLA instrument receiver records the time of the laser signal based on an ultrastable crystal oscillator, and provides the information to the onboard LRO data system for storage and/or transmittal to the ground through the spacecraft radio frequency link. The LR ground system consists of a network of satellite laser ranging stations, a data reception and distribution facility, and the LOLA Science Operations Center. LR measurements will enable the determination of a three-dimensional geodetic grid for the Moon based on the precise seleno-location of ground spots from LOLA.