Forecasting space weather: Can new econometric methods improve accuracy?

Space weather forecasts are currently used in areas ranging from navigation and communication to electric power system operations. The relevant forecast horizons can range from as little as 24 h to several days. This paper analyzes the predictability of two major space weather measures using new time series methods, many of them derived from econometrics. The data sets are the A_p geomagnetic index and the solar radio flux at 10.7 cm. The methods tested include nonlinear regressions, neural networks, frequency domain algorithms, GARCH models (which utilize the residual variance), state transition models, and models that combine elements of several techniques. While combined models are complex, they can be programmed using modern statistical software. The data frequency is daily, and forecasting experiments are run over horizons ranging from 1 to 7 days. Two major conclusions stand out. First, the frequency domain method forecasts the A_p index more accurately than any time domain model, including both regressions and neural networks. This finding is very robust, and holds for all forecast horizons. Combining the frequency domain method with other techniques yields a further small improvement in accuracy. Second, the neural network forecasts the solar flux more accurately than any other method, although at short horizons (2 days or less) the regression and net yield similar results. The neural net does best when it includes measures of the long-term component in the data.     

初探民用飞机EWIS安全评估

结合EWIS自身的特征,提供安全评估的基本思路,着重对EWIS安全性适航条款§25.1709进行分析与理解,介绍了目前常用的五种安全评估分析方法,并简要介绍了EWIS安全分析中输入数据常用的获取途径。     

软件逆向工程分析技术研究及应用

软件逆向工程对软件维护、复用和创新提供了可靠保证,但一直未见成熟的软件逆向工程理论和方法。介绍了软件逆向工程的基本概念,主要研究了软件逆向分析中常用的静态分析方法和动态分析方法,以汽车实时嵌入式控制系统软件为例介绍了两种分析方法的应用,并对两种分析方法进行比较,可为软件逆向工程的发展和深入研究提供借鉴。     

基于名义极限因子和降维方法的涡轮盘结构可靠性优化

结合名义极限因子方法完全实现了可靠性分析与优化过程的解耦,使可靠性分析成为进行优化之前的预分析过程,而在预分析中采用的基于降维的可靠性分析技术,在一阶可靠度方法(FORM)获得的计算结果的基础上进行适晕的数值计算就能够提高可靠性分析的结果.最后,以某涡轮盘结构优化为例对提出的方法可行性和效率进行了验证,结果表明:该方法...     

浅谈理工类专业教师的教书育人工作

在新的历史时期，面对新世纪复杂多变的国际形势和我们面临的艰巨的历史任务，高等教育如何全面实现培养高素质人才的崇高目标，这是关系到建设有中国特色社会主义事业的命运和前途的历史性课题，教师作为人类灵魂的工程师，不失时机地寻找合适的途径做好教书育人工作，这是对教师的基本要求，也是教师的职业道德和责任。     

High order optimal feedback control of space trajectories with bounded control

Optimal feedback control is classically based on linear approximations, whose accuracy drops off rapidly in highly nonlinear dynamics. Several nonlinear optimal feedback control strategies have appeared in recent years. Among them, differential algebraic techniques have been used to tackle nonlinearities by expanding the solution of the optimal control problem about a reference trajectory and reducing the computation of optimal feedback control laws to the evaluation of high order polynomials. However, the resulting high order method could not handle control saturation constraints, which remain a critical facet of nonlinear optimal feedback control. This work introduces the management of saturating actuators in the differential algebraic method. More specifically, the constraints are included in the optimal control problem formulation and differential algebra is used to expand the associated optimal bang–bang solution with respect to the initial and terminal conditions. Optimal feedback control laws for thrust direction and switching times are again computed by evaluating the resulting polynomials. Illustrative applications are presented in the frame of the optimal low-thrust transfer to asteroid 1996 FG₃.     

Large-eddy simulation:Past,present and the future

Large-eddy simulation(LES) was originally proposed for simulating atmospheric flows in the 1960 s and has become one of the most promising and successful methodology for simulating turbulent flows with the improvement of computing power. It is now feasible to simulate complex engineering flows using LES. However, apart from the computing power, significant challenges still remain for LES to reach a level of maturity that brings this approach to the mainstream of engineering and industrial computations. This paper will describe briefly LES formalism first, present a quick glance at its history, review its current state focusing mainly on its applications in transitional flows and gas turbine combustor flows, discuss some major modelling and numerical challenges/issues that we are facing now and in the near future, and finish with the concluding remarks.     

普通高校开展瑜伽课程教学方法初探

随着瑜伽课程逐渐走入高校体育课堂,通过教师自身对学生瑜伽课程的讲授,认为瑜伽课程教学方法中的面对面教学法、语言引导教学法、鼓励学习教学法等值得推广,对学生进行终身瑜伽锻炼产生良好的促进作用。     

访问AutoCAD 图形方法综述

当前AutoCAD的图形输出存在着很多对外不公开文件格式,为实现加工信息的集成及数控加工,必须对AutoCAD的图形文件进行访问、读取、转化成我们所需要的格式,所以对访问AutoCAD图形文件的方法必须进行深入分析,详细地论述访问AutoCAD的图形文件的LISP、VBA、DXF、Ob jectX ARX等各种方法的优缺点,从而可根据不同的开发环境,选择合适的开发方法,以提高工作效率。     

用张量分量混合插值的复合材料壳元公式

将张量分量混合插值壳体理论推广至复合材料壳元，并集成入大型有限元分析软件ＡＰＯＬＡＮＳ。该复合材料壳元具有线性、几何非线性及热弹性分析功能。可用于非对称、非均衡复合材料结构分析。与常规８节点复合材料壳元比较有精度好、效率高，且避免了单元“锁定”