碳纳米管薄膜传感器及其应变传感特性

碳纳米管薄膜可作为应变传感器用于结构损伤的健康监测。采用机械搅拌、超声处理和高速离心等分散工艺将多壁碳纳米管单分散后,通过真空吸滤法制备碳纳米管薄膜。对碳纳米管薄膜传感器进行了深入的研究,设计了一种高灵敏度的碳纳管薄膜应变传感器,与结构基体一体成型。弯曲应变传感实验表明碳纳米管薄膜传感器在不同的应变范围、不同的循环次数、不同的温度范围等条件下都具有良好的应变传感特性。结果表明碳纳米管薄膜传感器灵敏度较高,灵敏度系数为188.31(0~22 500 με),且具有较好的应变传感可逆性和可重复性。      

成形极限预测韧性断裂准则及屈服准则的影响

将韧性断裂准则用于预测板材成形极限,通过数值模拟HS钢、IF钢和6111-T4铝合金3种板材在单向拉伸、平面应变和双向等拉等不同应变路径下的变形过程,获得试件中心区域主应变最大单元的应变历史,结合成形极限实验数据计算韧性断裂准则的材料常数;通过对接近平面应变变形路径下的模拟结果与实验获得的网格应变相比较分析了Hill48,Hill90和Barlat89 3种各向异性屈服准则对模拟获得的应变路径的影响.结果表明,Barlat89屈服准则可以较好地描述单元的应变路径;在此基础上比较了几种韧性断裂准则用于预测板材断裂成形极限的计算结果, Cockcroft-Latham准则和总塑性功准则的计算结果比较理想,材料常数的确定也较为简单.      

ε-N曲线三参数幂函数公式

给出了一种描述ε-N曲线的三参数幂函数公式,与著名的Manson-Coffin公式相比,它能更好地拟合各种材料的应变-寿命试验数据,并且可以更方便地用于计算结构的损伤和寿命。     

含区间参数不确定结构的损伤识别方法

针对损伤识别中遇到的含统计信息不足的不确定参数的结构,以区间向量来描述其中的不确定参数。基于有限元理论给出了应变模态的测试方法,进一步将应变模态表示为区间参数的函数,结合一阶Taylor展开与区间分析,计算了参数不确定条件下应变模态的界限,给出了一种考虑参数不确定的结构损伤识别方法,并在理论上对比分析了与基于概率方法的区别与联系。为验证方法的合理性,对简支梁在不同位置损伤的情况进行了数值模拟,分析了不同损伤程度以及参数不同不确定程度下简支梁应变模态的变化规律,简要讨论了噪声对识别准确性的影响。为含不确定参数的结构的损伤识别提供了一种新的方法和思路。      

成形极限曲线（FLC）的新概念

失稳理论是FLC的理论基础。文章论述了FLC理论研究中存在的问题。指出:一般出厂板的表面状况不会影响板料的集中失稳;板内损伤平面应变时最严重。双拉时,板内损伤的积累、发展,导致应力状态向平面应变漂移;拉压时,载荷失稳后引起的双拉,也会导致平面应变。因此平面应变状态的出现是板料集中失稳的共同原因。在此基础上提出了建立FLC的统一的模型。     

材料非线性对复合材料层板损伤的影响

根据Hahn-Tsai非线性应力应变关系,用有限元方法对受拉伸载荷作用的含孔复合材料层板损伤演变进行了模拟计算,由非线性有限元方法得到的应力、应变以及最终载荷与以往线性分析方法得到的结果比较表明:考虑材料非线性可以提高计算精度;参数研究表明非线性系数的变化对正交各向异性板的影响较大,而对准各向同性板的影响较少.     

基于恒应变率控制的椭圆凹模胀形试验方法

为确定2A16-O铝合金板材在不同温度及应变率下的成形极限曲线(FLCs),应用改进Hollomon公式获取满足外插可靠度的拟合应力应变,通过有限元分析(FEA)不同椭圆度的椭圆凹模胀形破裂位置,优化工艺参数得到指定应变路径下的成形极限点,建立了液体压力与等效应变及应变率的公式,推导出压力变化率与应变率的定量关系。以应变率控制的椭圆凹模胀形与单拉试验相结合,获得2A16-O铝合金板材在不同温度及应变率下的FLCs,为定量分析应变率的影响规律和评判理论预测方法的准确性提供了依据。      

空间碎片云演变过程的阶段划分

根据碎片云从破碎点开始向空间扩散过程中碎片密度和形状的变化规律,以几何形状和起主要作用的因素为特征,定义了球形、椭球形、绳形、螺旋线形、全方位弥漫直至球壳形六个演变阶段.论述了在各个阶段的主要特征和对演变过程起主要作用的因素.总结了与演变过程相关的轨道运动理论和研究方法,分析了各个阶段演变的动力学原理.在球形阶段起主要作用的是分离速度;椭球形阶段可以利用线性化相对运动方程进行分析;绳形与螺旋线形在几何上有质变,但都有结点和结线,并可以利用速度增量理论分析和解释其存在的原因.轨道摄动力消除了结点和结线,导致碎片云的全方位弥漫,并最终使碎片云趋于球壳形.推导和罗列了各阶段转换标志点时刻的计算公式,利用计算机仿真的方法,给出了近地轨道各个阶段碎片云分布示意图,验证了演变过程阶段划分的合理性.     

基于小波的航空发动机叶片孔探损伤检测

发动机孔探技术是航空发动机内部故障检测的重要技术,而叶片损伤则是发动机内部的一种常见损伤.针对发动机叶片损伤的特点,通过对损伤模型的分析,应用SUSAN(Smallest Univalue Segment Assimilating Nucleus)边缘检测算法对叶片损伤进行定位,应用小波变换对孔探图像进行分解,得到不同位置处的不同频率分量.并根据损伤模型的分析通过已定位的损伤位置来确定损伤法线方向的频谱分量,计算出损伤处除直流分量之外的其它频率分量的频谱能量,从而依据损伤频谱能量检测并估计发动机叶片的损伤.实验结果表明,应用此方法可以定量检测并估计航空发动机叶片表面损伤情况,为检测并估计发动机叶片损伤提供了理论和实践依据.      

碳纤维增强树脂基层板应变率相关损伤数值研究

为了研究高应变率载荷对于碳纤维增强树脂基复合材料变形破坏行为的影响,通过应变率修正式对复合材料的刚度与强度进行修正,建立了可考虑应变率效应的复合材料损伤数值模型,采用该模型对不同应变率条件下层板结构的面内破坏行为进行了模拟并与文献实验进行了对比分析。计算结果表明:本文所构建的数值模型可以有效预测树脂基层板结构在不同应变率条件下的破坏特征,并在材料刚度与强度硬化现象的预测方面有着较高精度;对于0°、90°铺层主导的试件,由于其力学性能近似为线性,数值模型在强度预测方面获得了较高精度;而对于±45°铺层主导试件,其在不同应变率条件下表现出较强的非线性损伤特性,因此模型在其强度性能预测方面存在一定误差。     

Learning in an immersive digital theater

The Houston Museum of Natural Science, in collaboration with Rice University has an outreach program taking portable digital theaters to schools and community sites for over five years and has conducted research on student learning in this immersive environment. By using an external independent evaluator, the effectiveness of NASA-funded Education and Public Outreach (EPO) projects can be assessed. This paper documents interactive techniques and learning strategies in full-dome digital theaters. The presentation is divided into Evaluation Strategies and Results and Interactivity Strategies and Results. All learners from grades 3–12 showed statistically significant short-term increase in knowledge of basic Earth science concepts after a single 22-min show. Improvements were more significant on items that were taught using more than one modality of instruction: hearing, seeing, discussion, and immersion. Thus immersive theater can be an effective as well as engaging teaching method for Earth and Space science concepts, particularly those that are intrinsically three-dimensional and thus most effectively taught in an immersive environment. The portable system allows taking the educational experience to rural and tribal sites where the underserved students could not afford the time or expense to travel to museums.     

Stochastic particle acceleration by the forced interaction of relativistic current sheets

We address the problem of interacting relativistic current sheets in self-consistent kinetic plasma simulations within the framework of the Particle-In-Cell model. The interaction is enforced in head-on collisions of up to 10 current sheets at relativistic bulk speeds. The simulations are motivated by the general problem of Poynting flux dissipation in ‘striped wind’ configurations presumably governing the relativistic outflows pervasive in pulsar winds and gamma-ray bursts. We identify the generation of non-thermal particles and formation of a stable power-law shape in the particle energy distributions f(γ) dγ ∝ γ^−s dγ. In 1D, a spectral index s ∼ 2 is observed and attributed to a stochastic Fermi-type acceleration mechanism. In 2D, the generic index of s ∼ 3–4 is retained as in previous simulations of individual current sheets. Whereas in 2D the high energy cut-off is constrained by the limited dissipation of magnetic energy, in 1D the process converts the bulk motion of current sheets towards directed particle momentum of an exclusive class of non-thermal particles.     

Scaling analysis and model estimation of solar corona index

A monthly average solar green coronal index time series for the period from January 1939 to December 2008 collected from NOAA (The National Oceanic and Atmospheric Administration) has been analysed in this paper in perspective of scaling analysis and modelling. Smoothed and de-noising have been done using suitable mother wavelet as a pre-requisite. The Finite Variance Scaling Method (FVSM), Higuchi method, rescaled range (R/S) and a generalized method have been applied to calculate the scaling exponents and fractal dimensions of the time series. Autocorrelation function (ACF) is used to find autoregressive (AR) process and Partial autocorrelation function (PACF) has been used to get the order of AR model. Finally a best fit model has been proposed using Yule-Walker Method with supporting results of goodness of fit and wavelet spectrum. The results reveal an anti-persistent, Short Range Dependent (SRD), self-similar property with signatures of non-causality, non-stationarity and nonlinearity in the data series. The model shows the best fit to the data under observation.     

Development of a gas chromatography compatible Sample Processing System (SPS) for the in-situ analysis of refractory organic matter in martian soil: preliminary results

In the frame of the 2009 Mars Science Laboratory (MSL) mission a new sample preparation system (SPS) compatible with gas chromatography–mass spectrometry (GC–MS) has been developed for the in situ analysis of complex organic molecules in the Martian soil. The goal is to detect, if they exist, some of the key compounds that play an important role in life on Earth including carboxylic acids, amino acids and nucleobases.     

基于LuGre模型的电液加载系统摩擦补偿

为了提高电液加载系统控制精度,针对摩擦问题提出了基于LuGre摩擦模型的前馈补偿方法.建立了用于摩擦仿真分析和补偿器设计的电液加载系统数学模型;通过实验获取并分析了相关的摩擦数据;基于实验数据进行LuGre模型参数辨识,把LuGre模型和辨识结果引入电液加载系统数学模型,并进行仿真结果与实际摩擦数据的对照,证明了LuGre摩擦模型的准确性.设计前馈补偿器,进行了实验对比,实验结果表明前馈补偿器可将摩擦产生的控制误差有效地降至未补偿时的30%左右.      

CoRoT and Kepler results: Solar-like oscillators

The space-borne observatories CoRoT (Convection Rotation and planetary Transits) and Kepler have provided photometric time series data of unprecedented precision for large numbers of stars. These data have revolutionized the fields of transiting exoplanets and asteroseismology. In this review some important asteroseismic results obtained using data from the CoRoT and Kepler space missions concerning stars that show solar-like oscillations are discussed. These results comprise, among others, measurements of the location of the base of the convection zone and helium second-ionization zone in main-sequence stars, the presence (or not) of core-helium burning in red-giant stars, as well as differential rotation in these stars.     

Radioactivity of the Moon and planets

In this report the main results of the study of radioactivity of the solar sistem bodies are considered. The radioactivity of the Moon and planets was measured by means of vehicles in situ. The radioactivity of the lunar samples, brought to the Earth was studied with laboratory equipment.     

Return to Europa: Overview of the Jupiter Europa orbiter mission

Missions to explore Europa have been imagined ever since the Voyager mission first suggested that Europa was geologically very young. Subsequently, the Galileo spacecraft supplied fascinating new insights into this satellite of Jupiter. Now, an international team is proposing a return to the Jupiter system and Europa with the Europa Jupiter System Mission (EJSM). Currently, NASA and ESA are designing two orbiters that would explore the Jovian system and then each would settle into orbit around one of Jupiter’s icy satellites, Europa and Ganymede. In addition, the Japanese Aerospace eXploration Agency (JAXA) is considering a Jupiter magnetospheric orbiter and the Russian Space Agency is investigating a Europa lander.     

基于最小值原理的冗余度机器人动力学控制

为了解冗余度机器人全局法优化中数值求解的困难,本文讨论了动力学方程的建立,无约束和有约束最优控制问题之间的内在联系,重点分析了求解最优控制问题的数值方法,文中提出了双向异步积分迭代的求解正则方程组的直接迭代法,较好解决了状态方程和协态方程稳定相逆给求解两点这值问题带来的困难。     

基于GPS载波相位的微卫星姿态算法研究

GPS姿态系统是利用GPS载波相位测量来确定载体的航向和姿态角。本文对微卫星的GPS姿态系统进行了研究。重点解决短基线的GPS状态算法，讨论了姿态价格函数的了小化方法。测试结果表明，所提的算法对小于1m的基线是有效的。