基于拟连续高阶滑模的高超声速飞行器再入姿态控制

考虑模型参数不确定和外界干扰对再入制导控制性能的影响,基于拟连续高阶滑模控制策略对高超声速飞行器的再入制导控制问题进行了研究.首先,给出再入制导指令的设计过程.其次,基于再入飞行特性对模型进行简化,获得面向控制的姿态模型,在此基础上,通过引入新的控制变量,设计解耦滑模面,实现姿态间的解耦.再次,为了削弱控制抖振,通过引入虚拟控制,对系统进行增广,基于齐次性理论设计拟连续三阶滑模再入姿态控制器,确保系统在有限时间实现对制导指令的稳定跟踪.最后,六自由度再入飞行器的制导控制一体化仿真结果表明,本研究给出的控制策略在不影响系统鲁棒性的同时,能够实现对标称轨迹和再入姿态的综合控制.     

Adaptive model-following control of a certain class of non-linear process unit. Application to a continuous periodic reactor

An adaptive model-following control (AMFC) technique is developed which considers: (a) non-linear process unit models of the class

= g(x_p) + P(x_p)u_p with dim (x_p) = dim (u_p) and P(x_p) invertible for all x_p; and (b) non-linear reference models of the class

= m(x_m, r). The basic control consists of a type of model-following scheme, and the adaptation mechanism is obtained through an approach which is equivalent to that utilized for the linear case. In order to apply the proposed control algorithm, the unknown (or slowly time-varying) process unit model (PUM) parameters must be “extracted” from the non-linear terms of g(x_p) and P(x_p). This is performed through an appropriate PUM transformation which requires the unknown parameters to appear linearly in each of the original PUM terms. If this is not the case, then series expansions are necessary prior to the transformation. The proposed technique is applied to a simulated example investigated previously by Liaw and Bailey (1974, A.I.Ch.E. J.17, 924–932), which consists of a chemical reactor operated under periodic control. Although the present method requires a relatively higher control effort, an improved performance is obtained.     

一种用于常识空间信息处理的定性空间关系模型

在空间信息处理中,一些常识空间信息通常结合多方面空间关系,而且这些空间关系是动态变化的.为了有效地表示这些复杂的空间关系,并对其进行推理,提出了一种结合拓扑、方向和大小关系的空间信息处理模型TDSC (topology-direction-size calculus),并基于TDSC模型提出了处理动态空间关系变化的表示推理框架.首先,利用同对象多属性的方法建立了融合大小、拓扑和方向关系的完备至斥基本关系表示;然后提出了复合表生成算法和推理算法,使得原有模型的表示和推理结果可以直接在新模型中使用.同时提出处理动态空间关系的邻域划分图,给出了邻域划分图的自动生成算法,以及TDSC模型的邻域划分图.最后给出基于TDSC模型邻域划分图的表示和推理框架,并结合实例说明框架的正确性和有效性.     

基于多层次空间注意力的图文评论情感分析方法

随着社交网络的不断普及,相对于传统的文字描述,人们更倾向于发布图文结合的评论来表达自己的情感与意见。针对图文情感分析方法中仅考虑图文间的高级语义联系,而较少注意图片的低层次情感特征以及中层美学特征与文本情感之间关联性的问题,提出了一种基于多层次空间注意力（MLSA）的图文评论情感分析方法。所提方法以文本内容为驱动,使用MLSA设计图像与文本之间的特征融合方法,该特征融合方法不仅关注与文本相关的图像实体特征,而且充分利用图像的中层美学特征和低层视觉特征,从而从多个不同角度挖掘图文之间的情感共现。在两个公开的图文情感数据集MVSA_Single和MVSA_Multi上,该方法的分类效果相对于对比方法中最优的方法的分类效果在准确率上分别提高了0.96和1.06个百分点,在F1值上分别提高了0.96和0.62个百分点。实验结果表明,综合分析文本特征和图像特征之间的层次化联系能有效地增强神经网络捕捉图文情感语义的能力,从而更准确地预测图文整体的情感。     

Petri网及ExSpect在任务可靠性仿真中的应用

任务可靠性的仿真方法有多种,这些方法由于系统的复杂性均存在某些方面的局限。本文首先介绍了任务可靠性的基本概念和一种新的用于任务可靠性仿真的方法-基本Petri网理论。并详细分析和比较了Petri网理论与其他仿真方法的优点和不足之处。随后介绍以Petri网理论为基础的仿真软件-ExSpect的发展、组成及其语言特点。最后,列举当前已成功应用的五个仿真实例来验证ExSpect仿真软件在任务可靠性仿真方面的适用性。     

增益控制策略下的梯度域路径追踪算法

针对梯度域路径追踪算法在像素平面均匀采样的策略会使渲染图像在不同频率区域的渲染质量差别较大的问题,提出增益控制策略下的梯度域路径追踪算法.引入平均梯度计算局部平均梯度值,筛选并标记出高频区域和低频区域,将低频区域的样本用于对高频区域增强采样;随着每轮渲染高低频区域的不断更新,自适应地对样本进行分配,实现像素平面采样的增益控制.一方面,在不同材质和光照的场景下,将改进算法和梯度域路径追踪算法进行实验对比,结果表明,文中算法使人眼敏感的高频区域渲染更加细腻;另一方面,使用均方误差、峰值信噪比和结构相似度3种图像质量评价指标评价渲染图像,并对比采样过程中3个指标的变化情况,结果表明,在保证样本数量相同的条件下,文中算法可以加快渲染的收敛速度,提高渲染效率.     

A multi-institutional, multinational study of programming concepts using card sort data

Abstract: This paper presents a case study of the use of a repeated single‐criterion card sort with an unusually large, diverse participant group. The study, whose goal was to elicit novice programmers' knowledge of programming concepts, involved over 20 researchers from four continents and 276 participants drawn from 20 different institutions. In this paper we present the design of the study and the unexpected result that there were few discernible systematic differences in the population. The study was one of the activities of the National Science Foundation funded Bootstrapping Research in Computer Science Education project (2003).     

Adaptive finite element methods for the analysis of inviscid compressible flow: Part I. Fast refinement/unrefinement and moving mesh methods for unstructured meshes

New adaptive finite element methods are presented for the analysis of unsteady inviscid compressible flow in arbitrary two-dimensional domains. The procedures described herein are used in conjunction with a semi-explicit two-step algorithm for solving the time-dependent Euler equations in two space dimensions. Two schemes are presented for monitoring the evolution of error, and error estimates are used as a basis for a mesh refinement strategy. The capability of unrefinement (adaptively coarsening the mesh) is also included. The methods do not require a structured mesh and are applicable to quite general geometries.     

基于免疫否定选择算法的机场航班延误状态检测与实现

把免疫算法中的否定选择算法运用到航班延误状态的诊断检测与预测中,将生物免疫系统机制与机场航班运行机制联系起来,建立了相应的自体集合、检测细胞、抗原信息及它们之间的匹配模型,给出了检测方法。首先根据机场航班运行数据生成航班检测的成熟检测器和记忆检测器,然后用否定选择算法和航班数据对检测器进行训练和改进,最后利用检测器中的信息对机场航班状态分段进行预测,获得每个时段的航班延误状况,为机场有关部门对航班延误应急处理提供决策支持。仿真实验表明,该方法能较准确地预测航班的延误状态,且实时性好。