基于自聚焦BP的圆周SAR运动补偿方法

圆周SAR由于平台运动轨迹的复杂性,导致沿航迹向和切航迹向回波信号存在严重耦合,因此成像处理运动补偿问题尤为复杂。本文针对圆周SAR成像运动补偿问题,首先分析运动误差对成像质量的影响;然后利用自聚焦BP算法对运动误差进行补偿,并与传统BP算法性能进行对比,验证了自聚焦BP算法对圆周SAR运动补偿的有效性;最后利用自回归思想将自聚焦BP算法进行改进并扩展到圆周SAR三维成像中,通过仿真实验,对比传统BP算法结果,验证了该算法在三维成像中的优势。     

GPS定位中电离层折射的影响与消除

电离层是GPS测量的主要误差源,文中论述GPS测量中电离层的特征,电离层的折射系数以及电离层的影响.最后介绍了对GPS观测量进行电离层改正和消除的几种方法.     

小波分解层数对电离层预报的影响

针对电离层总电子含量(TEC)所具有的非线性、非平稳的特性,本文将小波分析理论引入到时间序列分析方法中,对IGS中心提供的不同纬度前8 d电离层格网点观测数据进行不同层数的分解,而后采用ARIMA模型预报后4d TEC数据。将预报结果与观测数据对比并统计精度,实验结果表明对电离层格网点数据进行1层~3层分解能够取得较好的预报效果,并且采用1层分解所得预报效果最佳。     

基于线性补偿函数的机载双基SAR二维频谱研究

简洁的二维频谱解析式模型是研究任意构型的机载双基SAR成像算法的基础。本文提出一种适用于任意构型的机载双基SAR二维频谱解析表达式,它是通过利用曲线拟合和驻定相位定理得到的。首先,采用泰勒级数定理将机载双基SAR的斜距史函数等效为双曲线和线性误差补偿函数的复合函数。接下来,利用驻定相位定理得到最终的二维频谱表达式。对于机载双基SAR,上述二维频谱模型是精确且简洁的。最后,通过大量的仿真结果验证了上述二维频谱模型的有效性。     

浅析电离层对基于南宁CORS站的网络RTK定位精度的影响

在低纬度地区,电离层活动较为活跃,对基于CORS站的网络RTK定位精度影响较大,为加强南宁CORS站的应用和服务,本文通过电离层电子密度处理分析软件分析了南宁地区的电离层活动水平情况,并分析了电离层延迟情况及与RTK定位精度之间的关系,得出了一些对基于南宁CORS站的网络RTK定位测量有指导意义的结论。     

基于CORS的区域电离层建模及其在PPP中的应用

利用CORS观测数据计算电离层延迟,采用低阶球谐函数建立实时区域电离层模型。对非差非组合PPP进行电离层约束,加快PPP收敛速度。与传统消电离层组合PPP相比,初始历元误差小于0.5 m,E、N方向收敛速度提升显著,U方向有一定改善,定位精度提升了12.2%。     

补偿最小二乘估计精化AR(p)的变形建模与预测

以AR(p)模型为例,考虑模型误差对变形预测的影响,将模型误差看做非参数信号,采用半参数补偿最小二乘方法来处理,即利用半参数中的非参数分量表达模型误差;为更好地控制残差部分VTPV和光滑部分STRS之间的平衡,提出一种求解平滑参数α的Xu函数;最后,通过实例将精化后的AR(p)模型与灰色模型、灰神经网络模型、常规AR模型的结果进行了比较。结果表明,补偿最小二乘方法能有效地处理变形建模中存在的模型误差,具有较好的预测效果。     

电离层、对流层对GPS伪距单点定位精度影响的效果分析

讨论了GPS单历元伪距单点定位中的电离层、对流层的改正模型,在此基础上,基于GPSTk库,首先利用随机选择的12个IGS站提供的观测和导航数据进行了只改正电离层模型、只改正对流层模型、两者均改正模型、两者均不改正模型4种模式的单历元解算,然后采用高频率(20 Hz)动态数据同样进行了4种模式的解算.最后实验数据解算结果表明:无论是静态单点定位还是动态单点定位,电离层改正模型和对流层模型对提高定位精度都起着重要的作用.     

非线性最小二乘估计的蚁群遗传融合算法

基于对遗传算法和蚁群算法的分析,提出把蚁群算法和遗传算法相结合的混合算法,有效避免了两种算法的不足之处,并将该混合遗传算法用于非线性最小二乘参数估计中,算例验证了该算法的可行性和有效,性。     

M估计的权函数选取及其抗差性比较

对几种不同的估计方法的权函数选取进行了详述,并将参数稳健估计的思想应用到半参数模型估计中,提出了半参数模型抗差广义补偿最小二乘估计,通过算例对其稳健性进行了比较,得出了结论。     

两种典型电离层延迟改正模型的效果研究

针对单频GPS接收机受电离层影响较大的特点,分析讨论了Klobuchar模型和IONEX模型的使用特点及其改正精度,讨论了两种不同的电离层延迟改正模型的改正效果,研究结果可以为单频GPS用户有效修正电离层延迟影响提供好的建议。     

上海世博会交通管控措施效果评价

针对世博期间上海交通部门制定的一系列交通管控措施,立足于实际状况的定量分析及客观描述,对其管控效果进行了后评估,以期为今后大型活动的交通组织方案提供指导。     

微穿孔板几何参数估算及其对吸声性能的影响

不规则孔微穿孔板几何参数无法直接获知,造成吸声性能计算困难,故提出一种微穿孔板几何参数估算方法。将不规则孔等效处理为圆孔,利用马氏理论关于圆孔微穿孔板的基本理论,建立了微穿孔板几何参数估算模型;将参数估算结果用于吸声性能预测,理论计算与实验结果吻合。根据微穿孔板几何参数对高吸声性能区域的影响,探讨了马氏理论适用极限与微穿孔板几何参数的关系,以及微穿孔板受粉尘污染后吸声性能演变规律。将微穿孔板参数点取在面积较大的高吸声性能区域中间部位,可获得较大的马氏理论适用极限;微穿孔板参数点位于高吸声性能区域右上部位时,一定程度的粉尘污染不会降低吸声性能.     

Team development and performance in construction design teams: an assessment of a hierarchical model with mediating effect of compensation

A high-performance construction workplace invests in its human resources and facilitates their technical and innovation skills through team development. Though team development has been explored in many studies, to date, little research has disentangled how team development and compensation methods enhance team performance in construction companies. Accordingly, team development as a hierarchical, reflective construct, incorporating six associated components was extended and the variables of the model in a nomological network analysed using partial least squares (PLS). As a result, with the help of PLS path modelling, a hierarchical team development construct with the mediating effects of compensation on the relationship between team development and team performance was developed. The research analysis was completed on a sample population of 128 construction design teams and the results lead to the development of a model that shows team development has a significant direct and indirect impact on team performance. The results also confirm the mediating role of group compensation on the relationship between team development and team performance. In general, it is suggested that the design teams achieved better performance when the leaders adapted team compensation methods consistent with the team development practices.     

抵偿坐标换算程序的设计与实现

由于投影存在着投影变形,当变形达到一定数值时,必须采取措施限制投影变形,通常采用的方法是选取抵偿面对坐标进行抵偿变换,但采用抵偿椭球变换的方法来建立抵偿坐标系的方法意义明确直接,便于理解,因此,为了实现抵偿坐标换算,采用抵偿椭球变换的方法使用Visual C++开发了抵偿坐标换算程序,从而提高了抵偿坐标换算的效率和计算的可靠性,具有很好的实用意义。     

造价控制中的索赔案例

通过对具体索赔事件的描述,从索赔事件分析、索赔意向通知、证据资料准备、索赔报告的编写与送达、双方协调、工程师审核及索赔事件的解决方面介绍了索赔事件的处理要点,以期积累索赔经验。     

全补偿型混凝土膨胀剂及其对高强混凝土干缩的补偿

介绍了全补偿型混凝土膨胀剂FEA100的组成原理及主要性能,通过混凝土试验,认为FEA100用于C50~C90高强混凝土时,可使其干缩得到80%~100%的补偿;可以制取自应力值达1.5 MPa或更高水平的钢管混凝土及大配筋率抗裂混凝土。     

超声导波的频散补偿与模式分离算法研究

超声导波已被广泛应用于无损检测与评价,针对超声导波应用中普遍存在的模式混叠与频散问题,本文在采用频谱相位与信号时延函数建模导波频散信号传递系统的基础上,提出了一种单一模式的频散补偿算法。进一步地,通过将选择性频散补偿技术与导波模式分离相结合,本文算法克服了传统补偿算法所不能解决的多模式导波频散问题。板中的Lamb波A_0,A_1和S_0混合模式仿真分析表明,本算法不仅可用于单一导波模式信号合成与频散补偿,而且可在实现多模式混合导波信号选择性频散补偿基础上,解决多模式导波信号中单一模式提取与分离。本文研究有助于超声导波多模式频散信号的分析与处理.     

供热管道的热伸长及其补偿

通过对供热管道受热伸长及增设各种补偿器的分析和研究,指出了供热管道的安装缺陷,并针对性地论述了各类补偿器的技术规范要求,达到了供热管网安全运行的目的和效果。     

Estimation of the smoke produced in fires

Some of the major difficulties that confront the estimation of smoke that may be produced at fires are considered. They include the confusion over the units in which smoke is expressed, reliability of laboratory test methods for smoke production developed so far, and the factors which may cause a difference between laboratory tests on the one hand and fire tests in general, and fire ground conditions on the other. Information on some of the latter factors is reported in the experimental results on the smoke produced by samples of materials of different height, burning freely, both singly and as combinations of two materials comprising the sides of a small, square chimney. It was found that within the range of heights of chimney of 3.2 – 15 cm the smoke potential of materials, D_o (smoke produced per unit weight of volatiles), reduced as the height increased by a factor of 1.5 – 2. In general, also, the contribution of different materials was additive unless one of them did not burn well by itself, in which case less smoke was produced than expected.In addition, a number of approximate working formulae have been developed to estimate D_o of materials burned in fire tests, from measurements of smokiness, D_L, obtained in the test, together with other data, such as gas analyses or temperature, that may be available. D_o is expressed in units of ob m³/g, which is based on a new unit for smokiness, the obscura (ob), used to express D_L. On the whole, values of D_o obtained in this way did not differ radically from values obtained under flaming conditions using bench tests, but there is evidence that under ventilation-controlled conditions with vertical vents, substantially higher values of D_o may be obtained than under fuel-controlled conditions. From information on D_o thus obtained, combined with information on D_o available from bench tests, a tentative list of values of D_o is given, for different materials burning under different conditions, which may be used as a first step towards predicting smoke output and smokiness in fire situations.