基于ROS的无人机仿真开放性实验教学设计与实现

该文基于机器人操作系统(ROS)仿真环境提出一种开放性的无人机仿真实验教学方案,通过ROS集成的可视化功能,利用Kinect等设备获取环境信息、搭建无人机动力学模型和三维可视化模型,设计三维环境航迹规划算法,并通过动态演示技术,实现ROS环境下的无人机航迹规划动态演示,使学生能够从开放性试验中实现无人机的运动控制、航迹规划和可视化编程等技术。基于ROS的无人机仿真实验是运动控制、规划算法、可视化编程等技术的一种典型的综合性应用,有助于学生深入学习无人机的原理和航迹规划方法。教学实践证明开放性教学方案在教学实践中取得较满意的效果。     

基于改进蚁群算法的无人机航迹规划

针对无人机在指定地点执行侦察、 巡逻或攻击等任务, 将无人机执行任务的航迹代价模型转化为旅行商问题, 采用改进蚁群算法实现航迹规划。通过引入去交叉禁忌搜索策略, 对基本蚁群算法进行改进, 以解决在收敛后期易陷入局部最优的问题。同时, 利用数值仿真对所研究的基于改进蚁群算法的无人机航迹规划算法进行验证。仿真结果表明, 该算法能提高了无人机航迹优化能力。     

复杂动态环境下基于DMPC-PSO的多无人机在线航迹规划

本文采用"有限集中指挥-分布式自主协调"的控制结构,研究多无人机协同低空突防航迹规划,对战场环境信息部分已知的情况,提出了多无人机航迹"预规划-在线轨迹跟踪"的模式,采用分布式模型预测控制和粒子群优化(DMPC-PSO)算法对多无人机的航迹进行预测和优化.仿真结果表明:利用该方法规划的多无人机的航迹不仅要满足低空突防的要求,具有良好的地形跟随、地形回避、威胁回避性能,更具有高的实时性与环境适应性,能在复杂战场环境发生变化时,及时在线调整以满足无人机安全、航迹最优等性能的要求.     

基于MPC-PSO的无人机在线航迹规划

研究了无人机在战场环境部分已知突然出现动态威胁情况下的三维在线航迹规划问题.采用"预规划-在线轨迹跟踪"的模式,根据已知的环境信息,离线规划出UAV的参考航迹.然后UAV在飞行过程中,需要在跟踪参考航迹的基础上,对UAV未来一段航迹进行预测,然后利用粒子群算法优化出UAV的最优(或次优)的飞行航迹.与传统的在线规划方法粒子群和稀疏A*搜索算法相比,该方法有效地提高了规划航迹的可行性和实时性,降低了算法的复杂度.仿真表明该算法是一种有效的无人机路径规划算法.     

动态步长BI-RRT的无人机航迹规划算法

为解决传统RRT算法收敛速度慢、生成的航径距离过长等问题,提出动态步长BI-RRT算法。首先,采用引向目标的采样策略对空间进行探索以得到采样点,利用动态步长策略确定该采样点的增长步长以确定新节点;之后,通过树枝裁剪策略对新节点进行调整,当探索到目标节点时,算法返回初始航迹,对于初始航迹,应用贪心算法对航迹点进行筛选,以减少无人机(UAV)的无效节点与总航迹长度;最后,利用B样条进行平滑处理,得到一条可行航迹。搭建了二维和三维环境下的仿真地图模型,验证了该算法在保证无人机避障的基础上获得一条有效航迹。动态步长BI-RRT算法在无人机航迹规划方面不仅有实时性强、航迹光滑的优点,而且与分段优化RRT算法相比,在优化航迹节点个数的前提下,提高了收敛速度且降低了航迹距离。     

基于改进MOGOA的无人机群航迹规划研究

针对电子侦察系统中反辐射无人机群进行辐射源无源定位时机群的编队形式会对定位精度产生影响的问题,将克拉美-罗界(Cramer-Rao lower bound,CRLB)作为定位精度方面的优化目标,与其他优化目标、约束一起引入机群的航迹规划中,使无人机群运动过程中保持良好编队,确保无源定位精度.文中针对多优化目标复杂环境中航迹规划算法寻优能力不高的问题,提出了一种基于改进多目标蝗虫算法(IMOGOA)的无人机群3维航迹规划方法,通过对MOGOA的选择方式、收敛参数进行改进从而提高算法的收敛性能以及全局搜索性能.首先,建立无人机群航迹规划的运动学模型,并引入距离约束,除定位精度以外还引入了路程、威胁代价等作为航迹规划的优化目标函数,然后,对改进多目标蝗虫算法进行详细说明,最后设计基于IMOGOA的无人机群航迹规划方案的算法流程,并在设定场景中对该算法的性能进行了仿真分析.结果表明,所提出的IMOGOA能够成功地规划出无人机群从初始位置到辐射源位置处的3维航迹,同时使无人机群在运动过程中保持良好的定位精度,经IMOGOA规划的机群编队定位精度最高可达1.2%,性能明显优于正方形编队和随机编队,并通过将IMOGOA与原始蝗虫算法(GOA)、原始多目标蝗虫算法进行对比,结果表明IMOGOA的收敛速度比MOGOA快11.1%,搜索性能相较GOA提升13.8%.     

船舶航迹保持的神经网络控制器研究

提出一种船舶航迹保持在线神经网络控制器。该控制器能解决精确的船舶动态模型难以建立的问题,能用舵角同时控制航迹偏差和航向偏差,能通过对控制精度的直接计算来自动地在线训练学习而不需离线训练学习过程。计算机仿真结果表明了该控制器训练方法的有效性和控制的鲁棒性。     

无侧滑角传感器的飞翼无人机抗侧风控制方法

飞翼布局无人机(UAV)由于缺少垂直尾翼的安定作用,航向通道不稳定或具有弱稳定性,侧风条件下容易引起侧滑,影响航迹跟踪精度。针对一种没有安装侧滑角传感器的小型飞翼无人机,根据惯性器件测量数据和无人机气动参数,使用扩展Kalman滤波方法估计无人机的侧滑角大小并控制消除侧滑。在抑制侧滑的条件下,推导建立了无人机航迹跟踪侧向运动的非线性模型,利用反馈线性化方法,将运动模型转化为带有扰动的线性模型,进而引入虚拟控制变量,使用保性能H∞鲁棒控制器设计方法,优化得到航迹跟踪反馈控制参数。仿真结果表明:该方法能够估计并有效抑制侧风条件下飞翼无人机侧滑等干扰,实现航迹的精确跟踪。     

基于动态加权A*算法的无人机航迹规划

随着无人机航迹规划高维空间的扩展,无人机的飞行环境变得异常复杂,其外部威胁不再是简单的二维静态威胁,传统的蚁群算法和人工势场算法已经不能满足实时性和高复杂环境的要求。为解决上述问题,提出新的基于动态加权A^*算法的无人机航迹规划。首先对无人机的飞行环境进行建模,通过研究航迹规划的转弯半径、航迹段长度和最大航程限制等约束条件,用于保证无人机的安全飞行,从而降低坠机率和威胁概率;其次,通过研究无人机的航迹和外部威胁参数,设计出新的航行方式,降低航行危险和减少损失;然后,通过扩展顶点势能定位和网格图整体变化的动态权重,获得动态环境下的代价函数,增加避障搜索速度、精度和加深回避程度。最后,通过仿真结果表明,在同一应用环境下,所提算法与蚁群算法和人工势场算法相比,航迹路径最优、威胁代价最小和算法执行的时间最短。综上,基于动态加权A^*算法很好地应用于无人机航迹规划,降低了无人机航迹代价,缩短了算法完成时间,提高了复杂环境下无人机航迹规划的搜索速度和精度。     

基于Q学习的无人机三维航迹规划算法

针对现有的基于强化学习的无人机航迹规划方法因无法充分考虑无人机的航迹约束而使规划获得的航迹可用性较差的问题,提出一种更有效的无人机三维航迹规划算法.该算法利用无人机的航迹约束条件指导规划空间离散化,不仅降低了最终的离散规划问题的规模,而且也在一定程度上提高了规划获得的航迹的可用性,通过在回报函数中引入回报成型技术,使算法具有满意的收敛速度.无人机三维航迹规划的典型仿真结果表明了所提出算法的有效性.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

《Chinese Science Bulletin》SUBJECT INDEX TO VOLUME 59(2014)

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Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with