组件感知的高分辨率三维物体重建方法

基于体素表示的三维物体重建计算代价会随着体素分辨率的增加呈立方增长.为了缓解这一问题,提出组件感知的三维物体重建方法,将三维物体分解成多个组件,通过预测组件几何结构和组装组件的方式重建三维物体,从而将高分辨率三维物体的重建问题分解成一系列低分辨率组件的重建问题.组件感知的三维物体重建方法使用组件位置预测模块预测所有组件的位置;使用组件特征提取模块融合组件表观特征与组件几何特征生成组件联合特征;使用组件几何结构重建模块根据组件联合特征重建组件的几何形状;最后将所有组件按其位置信息组装成高分辨率的三维物体.实验使用ShapeNet数据集在一个拥有12 GB内存的NVIDIA 1080 Maxwell GPU上进行.对比方法包括一个基于八叉树的高分辨率重建方法、一个基于LSTM的低分辨率重建方法和一个使用编码器-解码器架构的Baseline方法.高分辨率重建结果显示,组件感知的三维物体重建方法能够以较小的计算代价取得满意的高分辨率三维物体重建精度.在低分辨率重建实验上,该方法也取得了更高的重建精度,在13个类别上的平均精度达到了0.618.     

Guaranteeing performance for uncertain nonlinear systems with bounded state constraint and mismatching condition

The control design problem for the uncertain nonlinear system with bounded state constraint and mismatching condition is considered in this paper. The uncertainty in the system, which may be due to unknown system parameters and external disturbance, is nonlinear and time‐varying. The state of the system is constrained to be bounded. The system does not satisfy the (global) matching condition. A creative one‐to‐one state transformation is proposed by converting the bounded states into the unbounded ones. A step‐by‐step state transformation is proposed to convert the mismatched system into a matched system. The robust control is then proposed based on the transformed system. The control is demonstrated to be able to guarantee the uniform boundedness and uniform ultimate boundedness of the system in the presence of uncertainty, while the state constraint can be always guaranteed.     

Hierarchical inversion‐based output tracking control for uncertain autonomous underwater vehicles using extended Kalman filter

In this study, a hierarchical inversion‐based output tracking controller (HIOTC) is developed for an autonomous underwater vehicle (AUV) subject to random uncertainties (e.g., current disturbances, unmodeled dynamics, and parameter variations) and noises (e.g., process and measurement noises). The proposed HIOTC respectively utilizes a combination of feedforward and feedback controls in a hierarchical structure based on the kinematic and dynamic models of the system. Moreover, to obtain uncontaminated or unavailable states for implementing the proposed control law, the extended Kalman filter (EKF) is employed to estimate the system states. Then, the position outputs, orientation, and velocity of the AUV are reached with guaranteed asymptotic stability. The robustness of the proposed HIOTC is verified through injection of random uncertainties into the system model. The closed‐loop stability of the proposed individual subsystems is respectively guaranteed to have uniformly ultimately bounded (UUB) performance based on the Lyapunov stability criteria. In addition, the asymptotic tracking of the overall system is demonstrated using Barbalat's lemma. Finally, the feasibility and effectiveness of the proposed control scheme are evaluated through computer simulations and it is shown that the overall system achieves good asymptotic tracking performance.     

Performance‐based near‐optimal vibration control for nonlinear offshore platforms with delayed input

This paper investigates the vibration control problem for offshore platform, where the nonlinear characteristics, delayed input and external wave force are considered in time domain. By introducing a delay‐free reconstructional vector and applying the maximum principle, the original vibration problem for offshore platform is formulated as a nonlinear two‐point‐boundary‐value (TPBV) problem with delayed items. The major contribution of this paper is that a performance‐based near‐optimal vibration control strategy is proposed by solving this nonlinear TPBV problem, which includes a feedback item with offshore platform system state, a feedforward item with wave force state, and a compensator for nonlinear and delayed items with infinite supersensitive component. In particular, the designed compensator is calculated from two group series of linear differential equations by introducing a parameter for expending the Maclaurin series of nonlinear and delay items. Meanwhile, an iterative algorithm is designed to make the proposed vibration control scheme computable based on the control performance in each iterative procedure. Finally, experimental results show that the displacement, velocity and performance index of an employed offshore platform achieved small values under the proposed control strategy and designed algorithm.     

认知任务驱动的fMRI脑功能网络构建方法

针对脑功能网络的构建受到特定大脑图谱对兴趣点描述准确度及覆盖度的限制,提出了基于认知任务信息和神经影像数据的脑功能网络构建方法。首先计算fMRI体素对于认知任务的敏感度,然后在此基础上选取兼顾分布均衡和去中心化的大脑兴趣点,从而构建任务驱动的脑功能网络。实验通过在人脸情绪识别认知任务相关的梭状回构造任务驱动的脑功能网络,其度中心性、聚类系数、全局效率、局部效率这四个复杂网络指标均优于典型大脑图谱梭状回中兴趣点构成的网络。结果表明,计算得到的大脑兴趣点具有更强的整合性,更适合用于表征特定认知任务下的脑功能网络。     

运载火箭测发控技术未来发展与展望

工业电子、测试、测控、仪表、大数据、云平台等技术的发展,为运载火箭测发控技术的发展提供了先进的技术途径;运载火箭箭上电气系统一体化设计,火箭快速测发、健康管理、子级独立测试、异地远程测试发射支持等需求,给测发控系统研制及更新换代提出更高的要求;通过对运载火箭地面测控系统供配电、有线测控、无线测控、数传通信、测发控软件5个组成部分的演变及发展方向进行了论证分析,并提出了后续测发控系统技术发展的规划路线;同时结合未来运载火箭的发展需求和目前测发控系统现状提出了测发控系统后续发展的可实施途径;最后提出顶层规范技术路径;从型号牵引转变为装备化研制;规范型谱产品研制、箭上地面同步发展的测发控系统设计新思路;为未来运载火箭测发控系统研制提供方向。     

Effect of deposition time on microstructures and growth behavior of ZrC coatings prepared by low pressure chemical vapor deposition with the Br<Subscript>2</Subscript>-Zr-C<Subscript>3</Subscript>H<Subscript>6</Subscript>-H<Subscript>2</Subscript>-Ar System

ZrC coatings were deposited on graphite substrates by low pressure chemical vapor deposition (LPCVD) with the Br₂-Zr-C₃H₆-H₂-Ar system. The effects of deposition time on the microstructures and growth behavior of ZrC coatings were investigated. ZrC coating grew in an island-layer mode. The formation of coating was dominated by the nucleation of ZrC in the initial 20 minutes, and the rapid nucleation generated a fine-grained structure of ZrC coating. When the deposition time was over 30 min, the growth of coating was dominated by that of crystals, giving a column-arranged structure. Energy dispersive X-ray spectroscopy showed that the molar ratio of carbon to zirconium was near 1:1 in ZrC coating, and X-ray photoelectron spectroscopy showed that ZrC was the main phase in coatings, accompanied by about 2.5mol% ZrO₂ minor phase.     

冲角对车轮与道岔尖轨弹塑性接触的影响

在机车运行中轮轨间存在冲角,改变轮轨接触关系.针对冲角对车轮与尖轨接触的影响问题,建立了车轮—尖轨接触三维有限元模型,通过弹塑性接触计算,分析不同冲角工况下的接触情况.结果表明:轮轨间冲角的存在,导致车轮与钢轨接触位置发生改变,基本轨和尖轨接触斑中心不在同一钢轨横断面上,冲角越大,超前或滞后的数值越大;车轮与尖轨接触法向力随冲角的增大而增大;不同冲角工况下车轮与尖轨的接触等效应力变化规律基本一致,最大等效应力均出现在2 m位置处;冲角的增大会造成尖轨前端等效应力增大,导致车轮轮缘与尖轨的磨耗增加,降低车轮和尖轨的使用寿命.     

Sealing of Ejection Hole at the Bottom of Projectile for Wired Transmission System of Penetration Data

It is difficult to find the projectile when people want to get the penetration data in a hard recovery method, so a recovery system of penetration data is designed based on an ejection mode from the projectile base and a method of wired transmission, at the same time, the system was sealed with a designed sealing device, the working principle of which was introduced. Using Fluent as the simulation platform, the transient pressure of seal cavity was simulated based on the change of chamber pressure, and steady-state pressure of seal clearance and seal cavity were simulated based on the maximum chamber pressure. The sealing performance was tested by a pressure test system. The results of simulation and experiment show that the maximum pressure of seal cavity is 139.4.kPa when the maximum chamber pressure is 242.9.MPa and the maximum temperature of gunpowder explosive gas is 2.166.5.K, so the sealing performance can be assured. The sealing device can be taken as a reference in sealing research on gunpowder gas at the bottom of projection.     

混凝法去除水中TiO2纳米颗粒

为了探讨混凝法去除水中纳米颗粒的可行性及最佳条件,研究了无机混凝剂（PAC、PFS、PAFC）和有机絮凝剂（CPAM、APAM、NPAM）对TiO₂纳米颗粒的去除效果,并考察了投加量、pH、沉淀时间、水力条件及有机无机复配对TiO₂纳米颗粒去除效率的影响。单独投加PAC、PFS和PAFC时,三者对应的最高去除率分别为92.51%、84.43%、95.66%。单独投加CPAM、APAM、NPAM时三者对应的去除率仅为61.72%、29.06%、55.37%。复配最佳混凝条件为：投加40 mg/LPAC和3 mg/LCPAM,pH值为9,G值143.5/s,沉淀时间15 min,此时,TiO₂纳米颗粒去除率为99.6%。