Parametric Quintic-Spline Approach to the Solution of a System of Fourth-Order Boundary-Value Problems

In this paper, we use parametric quintic splines to derive some consistency relations which are then used to develop a numerical method for computing the solution of a system of fourth-order boundary-value problems associated with obstacle, unilateral, and contact problems. It is known that a class of variational inequalities related to contact problems in elastostatics can be characterized by a sequence of variational inequations, which are solved using some numerical method. Numerical evidence is presented to show the applicability and superiority of the new method over other collocation, finite difference, and spline methods.     

Furtivity and Masking Problems in Time-Dependent Electromagnetic Obstacle Scattering

In this paper, we consider furtivity and masking problems in time-dependent three-dimensional electromagnetic obstacle scattering. That is, we propose a criterion based on a merit function to minimize or to mask the electromagnetic field scattered by a bounded obstacle when hit by an incoming electromagnetic field and, with respect to this criterion, we drive the optimal strategy. These problems are natural generalizations to the context of electromagnetic scattering of the furtivity problem in time-dependent acoustic obstacle scattering presented in Ref. 1. We propose mathematical models of the furtivity and masking time-dependent three-dimensional electromagnetic scattering problems that consist in optimal control problems for systems of partial differential equations derived from the Maxwell equations. These control problems are approached using the Pontryagin maximum principle. We formulate the first-order optimality conditions for the control problems considered as exterior problems defined outside the obstacle for systems of partial differential equations. Moreover, the first-order optimality conditions derived are solved numerically with a highly parallelizable numerical method based on a perturbative series of the type considered in Refs. 2–3. Finally, we assess and validate the mathematical models and the numerical method proposed analyzing the numerical results obtained with a parallel implementation of the numerical method in several experiments on test problems. Impressive speedup factors are obtained executing the algorithms on a parallel machine when the number of processors used in the computation ranges between 1 and 100. Some virtual reality applications and some animations relative to the numerical experiments can be found in the website http://www.econ.unian.it/recchioni/w10/.     

数控机床伺服系统故障的维修

列举了数据机床故障实例,介绍了数控机床伺服系统故障的维修。     

A new oxamato-bridged heterotrinuclear NiCuNi complex with irregular spin state structure: Synthesis, spectroscopy, crystal structure and magnetism

A new oxamato-bridged Ni^IICu^IINi^II species, [Ni(tacn)(H₂O)]₂[μ-Cu(pba)](ClO₄)₂·6H₂O 1, (tacn=1,4,7-triazacyclononane; pba=1,3-propylenebis(oxamato)) has been synthesized and structurally as well as magnetically characterized. Complex 1 has a discrete trinuclear Ni^IICu^IINi^II structure: Two nickel(II) ions are bridged by [Cu(pba)]²⁻ anion, macrocyclic ligand tacn works as terminal ligand of the nickel(II) center. The magnetic data of compound 1 was analyzed by means of

leading to g_Cu=2.19, g_Ni=2.18, J=−112.8 cm⁻¹, D=±4.31 cm⁻¹. The parameters are compared with the similar complexes and the irregular spin state structure of complex 1 is also described here.     

一种DSM模型下飞行障碍物尺度的研究

在一种数字表面模型(DSM)建模方法的基础上,对威胁飞行器低空飞行安全的独立障碍物的尺度与DSM纵横断面采样间距的关系进行了分析,给出了独立障碍物的定义、分类和确定独立障碍物的方法。通过对7.2km2一典型城市地域的仿真试验表明,DSM纵横断面间距在3～25m之间,威胁飞行器地形跟踪制导安全的孤立障碍物较少,同时装订并实时处理的DSM模型数据量也较小,并在纵横断面间距12.5m处达到两者最优。     

移动通信中多重建筑物的遮挡损耗

用Uniform Geometrical Theory of Diffraction（UTD)分析了等高度等间距的建筑物对移动通信中移动台接收信号的影响，给出了易于计算的UTD拟合表达式，计算表明，此时Hata模型、COST231模型的计算结果和UTD的计算结果是较为接近的，但要精确地比较各场点的传播损耗只能用UTD按照实际的不等高度，不等间距的建筑物分布来计算，结果表明，当移动台前一幢建筑物的直接路径被阻挡时，UTD方法能较确定的反映此时的传播损耗。     

基于激光雷达的移动机器人环境建模与避障

为了提高自主移动机器人运行的安全性和可靠性 ,提出了一种基于激光雷达的距离信息进行环境建模和避障的方法。首先简要描述了激光雷达的工作原理 ,比较了几类常用的激光雷达 ,并介绍了激光测量系统 ( laser measure-ment system,LMS)。然后给出了一种用于移动机器人环境建模和避障的算法 -时变势场法 ,在此基础上提出了改进算法 -多分辨率势场法 ,实验表明其性能优于原算法。最后讨论激光雷达在实际应用中的一些问题。目前 ,该方法已成功地应用于清华室外移动机器人 THMR- V     

多车环境下智能货车的紧急转向决策及轨迹规划

决策与规划是实现自动驾驶的关键技术,针对自动驾驶货车在紧急转向避障时需要考虑换道时目标车道的安全性和规划出最优避障轨迹的问题,采用将换道时左右车道上的车辆与自车的相对距离和换道的最小安全距离的差值分别建立模糊关系的方法,通过比较模糊规则推理设计的安全值,选择更安全的车道进行转向避障,为了迅速规划出最优避障轨迹,采用三阶贝塞尔曲线,通过设计4个控制点坐标形成避障曲线,为了防止转向时横向加速度过大导致货车发生侧翻和速度过快与前车发生碰撞,设计车辆的稳定性边界和碰撞边界对控制点进行约束,使用MATLAB中的函数求解出不同车速下的最优换道轨迹,最后使用仿真软件进行仿真验证,结果表明设计出的避障决策和轨迹规划可以安全、有效地避开障碍。     

基于单目视觉的横穿障碍物检测

提出一种基于单目视觉的横穿障碍物检测方法.首先,基于道路平面假设,根据特征点的位置约束以及逆透视投影变换下的性质,提取地面特征点对.其次,采用迭代加权最小二乘法估计自车平移和旋转运动参数.然后,利用估计的运动参数对图像光流进行旋转补偿,并基于道路C 速度空间生成障碍物的候选标记点.最后,对候选标记点进行分组聚类和验证,确定横穿障碍物区域.不同交通场景下的实验结果表明,上述方法能够适用于各种自车运动,有效检测横穿障碍物.