Statistical models for shear strength of RC beam‐column joints using machine‐learning techniques

This paper proposes a new set of probabilistic joint shear strength models using the conventional multiple linear regression method, and advanced machine‐learning methods of multivariate adaptive regression splines (MARS) and symbolic regression (SR). In order to achieve high‐fidelity regression models with reduced model errors and bias, this study constructs extensive experimental databases for reinforced and unreinforced concrete joints by collecting existing beam‐column joint subassemblage tests from multiple sources. Various influential parameters that affect joint shear strength such as material properties, design parameters, and joint configuration are investigated through tests of statistical significance. After performing a set of regression analyses, the comparison of simulation results indicates that MARS approach is the best estimation method. Moreover, the accuracy of analytical predictions of the derived MARS model is compared with that of existing joint shear strength relationships. The comparison results show that the proposed model is more accurate compared to existing relationships. This joint shear strength prediction model can be readily implemented into joint response models for evaluation of earthquake performance and inelastic responses of building frames. Copyright © 2014 John Wiley & Sons, Ltd.     

基于空间曲面拟合的自适应阈值选取方法

提出了一种基于空间多项式曲面拟合的自适应阈值选取方法,该方法初步考虑了图像上空间目标、背景及像素的空间分布特征,拟合了图像及其空间分布结构。     

基于环形扫面测量的三维直流电阻率法任意各向异性模型响应特征

高精度地下任意各向异性介质电性分布特征识别是当前的热门研究课题。本文以国内外前人工作为基础,基于非结构化网格,利用基于梯度恢复的后验误差估计指导网格自适应细化过程,实现了直流电阻率法三维有限元数值模拟。通过与一维模型半解析解的对比,验证了本文算法的有效性。考虑到电各向异性介质在观测中存在视电阻率反常现象,本文采用了环形扫面测量方法。通过对几种典型各向异性模型的模拟分析,得到了相应的各向异性影响规律和识别特征,各向异性主轴电阻率之间的比值大小决定了椭圆型视电阻率极性曲线长轴与短轴的比值大小,主轴电阻率的旋转方向会改变视电阻率极性曲线的形状。本文的算法研究及数值模拟技术可为直流电法数据精细处理和解释提供技术支撑。     

EST Adaptive optics performance estimations

We give a short overview of the Adaptive Optics (AO) and Multi‐conjugate Adaptive Optics (MCAO) system of the planned 4 m European Solar Telescope (EST). The optimization process of the AO / MCAO parameters is shown, including the parameters and layout of the Shack‐Hartmann wavefront sensor setup and the DMs. We show the expected performance of the AO and MCAO system (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Prediction of weather parameters on a very short time scale by an Auto Regressive process for aviation flight planning

Forecasting weather parameters such as temperature and pressure with a reasonable degree of accuracy three hours ahead of the scheduled departure of an aircraft helps economic and efficient planning of aircraft operations. However, these two parameters exhibit a high degree of persistency and have nonstationary mean and variance at sub-periods (i.e. at 0000, 0300, 0600,…, 2100UTC). Hence these series have been standardised (to have mean 0 and variance 1) and thereafter seasonal differenced (lag 8) to achieve almost near stationarity. An attempt has been made to fit the standardised and seasonal differenced series of Chennai (a coastal station) and Trichy (an inland station) airport into an Auto Regressive (AR) process. The model coefficients have been estimated based on adaptive filter algorithm which uses the method of convergence by the steepest descent. The models were tested with an independent data set and diagnostic checks were made on the residual error series. An independent estimation of fractal dimension has also been made in this study to conform the number parameters used in the AR processes. The models contemplated in this study are parsimonious and can be used to forecast surface temperature and pressure.     

作为复杂适应系统的农业文化遗产：复杂性的挑战

本文首先阐述了农业系统的复杂性,并对农业系统所面对不确定性,以及外部系统的冲击和压力而形成的动态性进行了分析,提出“复杂适应性系统理论”为研究活态的农业系统,尤其为研究中国的全球重要农业文化遗产（GIAHS）提供了可能,而这些农业文化遗产系统（或其中某些部分）对于研究抵抗力和自我良性管理具有重要的意义.本文认为当前研究中的相关方法将会对整个系统的认识产生新的见解,同时避免把系统分解为各组分进行微观研究再重新还原成整体的研究思路.本文通过综述与GIAHS相关的方法并将旅游引入农村系统（作为一种扰动）,认为可以创造新的方法来认识农村发展干预措施对古老景观的影响,特别是分布在中国农村的许多景观.     

基于分层自适应部分模型的遥感图像飞机目标检测

提出一种基于分层自适应部分模型(HAPM,hierarchical adaptive part-based model)的目标检测方法,用于遥感图像的飞机目标检测。针对目前目标检测方法在子类型数目确定、模型多分辨率结构关系方面存在的不足,构造如下算法:首先构建一个扩展的Part-based Model模型;其次,分别从子类型的自适应选择、子类型的多层次建模和检测阶段加权距离变换的形变优化等方面对其进行改进;最后,HAPM算法充分考虑了模型的形变,同时结合多层次的建模思想使得目标的检测精度和算法适用性大大增强。用收集的10大国际机场的真实遥感图像数据进行实验验证,证明了算法的有效性。     

Improvement in the performance of solar adaptive optics

Adaptive optics （AO）, which provides diffraction limited imaging over a field-of-view （FOV）, is a powerful technique for solar observation. In the tomographic approach, each wavefront sensor （WFS） is looking at a single reference that acts as a guide star. This allows a 3D reconstruction of the distorted wavefront to be made. The correction is applied by one or more deformable mirrors （DMs）. This technique benefits from information about atmospheric turbulence at different layers, which can be used to reconstruct the wavefront extremely well. With the assistance of the MAOS software package, we consider the tomography errors and WFS aliasing errors, and focus on how the performance of a solar telescope （pointing toward zenith） is related to atmospheric anisoplanatism. We theoretically quantify the performance of the to- mographic solar AO system. The results indicate that the tomographic AO system can improve the average Strehl ratio of a solar telescope in a 10＂ - 80＂ diameter FOV by only employing one DM conjugated to the telescope pupil. Furthermore, we discuss the effects of DM conjugate altitude on the correction achievable by the AO system by selecting two atmospheric models that differ mainly in terms of atmospheric prop- erties at ground level, and present the optimum DM conjugate altitudes for different observation sites.     

信息分配系数的自适应滤波在GPS/DR组合导航中的应用

在组合导航中常采用联合滤波器进行多源传感器的信息融合,其中信息分配系数的取值直接影响着联合滤波器的性能。在详细分析子滤波器状态变量估计协方差阵特点的基础上,文中提出了采用两组信息分配系数的自适应联合滤波模型,并将设计的自适应联合滤波模型应用于车载GPS/DR组合导航中。仿真实验表明,导航的位置精度提高约为40%;速度精度提高约为10%。同时也提高了组合系统的容错性和可靠性。