An algorithm and observability research of autonomous navigation and joint attitude determination in asteroid exploration descent stage

In this paper, an autonomous relative navigation and joint attitude determination algorithm in asteroid exploration descent stage is researched based on feature point information of perpendicular asteroid surface image observed by optical navigation camera, distance vectors from spacecraft to asteroid measured by three angled installed lidars and relative velocity increment measured by accelerometer when the relative distance vector to the centroid of asteroid can not be obtained. The inertial attitude of spacecraft is determined by sun vector, star vectors and inertial angular velocity respectively measured by sun sensor, star trackers and inertial reference unit. Also, in order to obtain measurement error model transferred from sensor noise, a covariance matrix solver considering error correlation is presented via the error model of normalized vector to first order. Numerical simulation and improved observability evaluation of filtering are undertaken to discuss the results of complete sensor observation and weak observation of lidars, and verify the effectiveness of the presented relative navigation and attitude determination algorithm.     

Lattice-based key exchange on small integer solution problem

In this paper, we propose a new hard problem, called bilateral inhomogeneous small integer solution （Bi-ISIS）, which can be seen as an extension of the small integer solution problem on lattices. The main idea is that, instead of choosing a rectangle matrix, we choose a square matrix with small rank to generate Bi-ISIS problem without affecting the hardness of the underlying SIS problem. Based on this new problem, we present two new hardness problems： computational Bi-ISIS and decisional problems. As a direct application of these problems, we construct a new lattice-based key exchange （KE） protocol, which is analogous to the classic Diffie- Hellman KE protocol. We prove the security of this protocol and show that it provides better security in case of worst-case hardness of lattice problems, relatively efficient implementations, and great simplicity.     

基于网络学堂辅助高等数学教学的应用性研究简

本文针对网络学堂如何辅助高等数学课堂教学进行了研究,介绍了建设高等数学网络学堂的必要性,提出了建设高等数学网络学堂的途径,最后探讨了如何利用网络学堂提高高等数学教学质量。     

组合KdV方程的Hamilton系统

本文根据KdV方程的Hamilton系统,构造并证明了组合KdV方程的Hamilton系统。     

Crystallization behavior,mechanical properties,and environmental biodegradability of poly(β‐hydroxybutyrate)/cellulose acetate butyrate blends

The miscibility, crystallization behavior, tensile properties, and environmental biodegradability of poly(β‐hydroxybutyrate) (PHB)/cellulose acetate butyrate (CAB) blends were studied with differential scanning calorimetry, scanning electron microscopy, wide‐angle X‐ray diffraction, and polarizing optical microscopy. The results indicated that PHB and CAB were miscible in the melt state. With an increase in the CAB content, the degree of crystallinity and melting temperature of the PHB phase decreased, and this broadened the narrow processability window of PHB. As the elongation at break increased from 2.2 to 7.3%, the toughness and ductility of PHB improved. From the degradation test, it could be concluded that degradation occurred gradually from the surface to the inside and that the degradation rate could be adjusted by the addition of the CAB content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2116–2122, 2003     

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.     

基于局部45°原则的折线图坐标轴网格生成

坐标轴网格是辅助人们观察统计折线图的重要参考结构.文中研究了有利人们感知直线斜率的坐标轴标签.首先通过一系列用户实验探索折线图中网格局部长宽比对于估计线段斜率这一任务的影响,通过用户估计的倾斜角度与直线真实的倾斜角度的误差大小反映不同实验条件的影响程度.实验得出的结论是适当的网格密度、接近正方形的网格格子局部长宽比有利于准确的斜率估计.基于该实验结论,提出了新的为折线图数据自动生成坐标轴的算法,考虑最大标签、最小标签和间隔步长3个变量,参考前人关于标签简洁性、覆盖性、重叠程度的定义,将正方化的局部长宽比这一因素加入水平和垂直2条坐标轴的标签联合优化之中,该算法能够生成既美观又提高图形感知准确性的坐标轴网格.     

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。     

Performance evaluation of anti-radiation based on the gamma degradation process

In the environment of space radiation, the high-energy charged particles or high-energy photons acting on a spacecraft can cause either temporary device degradation or permanent failure. The traditional probability model is difficult to obtain reliable estimation of unit radiation resistance performance with small samples. Considering that different products will change differently after high-energy particle radiation, we construct a model based on the gamma degradation process. This model can efficiently describe the law of unit radiation resistance variation with the total radiation dose levels under the effect of the total dose and displacement damage. Finally, the proposed model is used to assess the anti-radiation performance of the N-channel power MOSFET device STRH60N20FSY3 produced by STM to obtain average unit radiation resistance, survival probability, survival function, etc.     

Theoretical Investigation of the Viscous Damping Coefficient of Hydraulic Actuators

The viscous damping coefficient(VDC) of hydraulic actuators is crucial for system modeling,control and dynamic characteristic analysis.Currently,the researches on hydraulic actuators focus on behavior assessment,promotion of control performance and efficiency.However,the estimation of the VDC is difficult due to a lack of study.Firstly,using two types of hydraulic cylinders,behaviors of the VDC are experimentally examined with velocities and pressure variations.For the tested plunger type hydraulic cylinder,the exponential model B=αυ~(-β),(α0,β0)or B=α_1e~(-β_1υ)+α_2e~(-β_2υ)(α_1,α_20,β_1,β_20),fits the relation between the VDC and velocities for a given pressure of chamber with high precision.The magnitude of the VDC decreases almost linearly under certain velocities when increasing the chamber pressure from 0.6 MPa to 6.0 MPa.Furthermore,the effects of the chamber pressures on the VDC of piston and plunge type hydraulic cylinders are different due to different sealing types.In order to investigate the VDC of a plunger type hydraulic actuator drastically,a steady-state numerical model has been developed to describe the mechanism incorporating tandem seal lubrication,back-up ring related friction behaviors and shear stress of fluid.It is shown that the simulated results of VDC agree with the measured results with a good accuracy.The proposed method provides an instruction to predict the VDC in system modeling and analysis.