Method for denoising and reconstructing radar HRRP using modified sparse auto-encoder

A high resolution range profile (HRRP) is a summation vector of the sub-echoes of the target scattering points acquired by a wide-band radar. Generally, HRRPs obtained in a non-cooperative complex electromagnetic environment are contaminated by strong noise. Effective pre-processing of the HRRP data can greatly improve the accuracy of target recognition. In this paper, a denoising and reconstruction method for HRRP is proposed based on a Modified Sparse Auto-Encoder, which is a representative non-linear model. To better reconstruct the HRRP, a sparse constraint is added to the proposed model and the sparse coefficient is calculated based on the intrinsic dimension of HRRP. The denoising of the HRRP is performed by adding random noise to the input HRRP data during the training process and fine-tuning the weight matrix through singular-value decomposition. The results of simulations showed that the proposed method can both reconstruct the signal with fidelity and suppress noise effectively, significantly outperforming other methods, especially in low Signal-to-Noise Ratio conditions.     

Testing Modified Newtonian Dynamics with LISA Pathfinder

We suggest that LISA Pathfinder, a technology demonstrator for the future gravitational wave observatory LISA, could be used to carry out a direct experimental test of Modified Newtonian Dynamics (MOND). The LISA Pathfinder spacecraft is currently being built and the launch date is just a few years away. No modifications of the spacecraft are required, nor any interference with its nominal mission. The basic concept is to fly LISA Pathfinder through the region around the Sun-Earth saddle point, in an extended mission phase, once the original mission goals are achieved. We examine various strategies to reach the saddle point, and find that the preferred strategy, yielding relatively short transfer times of just over 1 year, probably involves a lunar fly-by. LISA Pathfinder will be able to probe the intermediate MOND regime, i.e. the transition between deep MOND and Newtonian gravity. We present robust estimates of the anomalous gravity gradients that LISA Pathfinder should be exposed to, based on MONDian effects as derived from the Tensor-Vector-Scalar (TeVeS) theory. The spacecraft speed and spatial scale of the MOND signal combine in a way that the spectral signature of the signal falls precisely into LISA Pathfinder’s measurement bandwidth. We find that if the gravity gradiometer on-board the spacecraft achieves its currently predicted sensitivity, these anomalous gradients could not just be detected, but measured in some detail.     

嵌入中空纤维的树脂基复合阻尼材料设计

文章对一种耦合了中空纤维原材料阻尼特性和中空结构缓冲作用的嵌入中空纤维的树脂基复合阻尼新材料进行了研究.分析了各影响因素对三层中空纤维层合(3-HL)、带约束层的单层中空纤维夹心(2-CSLH)、带约束层的中空纤维蜂窝夹心结构(2-CSHC)这三种结构复合材料阻尼性能的主次影响规律,且前两者中阻尼最优试样与2-CSHC试样阻尼值大于0.54的阻尼平台区较宽,△Hz分别为5Hz-112Hz,7Hz-200Hz;阻尼峰值分别可达0.56和0.59;结构设计优越性为2-CSHC>2-CSLH>3-HL.     

Interface flux reconstruction method based on optimized weight essentially non-oscillatory scheme

Aimed at the computational aeroacoustics multi-scale problem of complex configurations discretized with multi-size mesh, the flux reconstruction method based on modified Weight Essentially Non-Oscillatory (WENO) scheme is proposed at the interfaces of multi-block grids. With the idea of Dispersion-Relation-Preserving (DRP) scheme, different weight coefficients are obtained by optimization, so that it is in WENO schemes with various characteristics of dispersion and dissipation. On the basis, hybrid flux vector splitting method is utilized to intelligently judge the amplitude of the gap between grid interfaces. After the simulation and analysis of 1D convection equation with different initial conditions, modified WENO scheme is proved to be able to independently distinguish the gap amplitude and generate corresponding dissipation according to the grid resolution. Using the idea of flux reconstruction at grid interfaces, modified WENO scheme with increasing dissipation is applied at grid points, while DRP scheme with low dispersion and dissipation is applied at the inner part of grids. Moreover, Gauss impulse spread and periodic point sound source flow among three cylinders with multi-scale grids are carried out. The results show that the flux reconstruction method at grid interfaces is capable of dealing with Computational AeroAcoustics (CAA) multi-scale problems.     

大尺寸CFRP固体火箭发动机壳体湿法缠绕用树脂配方研制

针对大尺寸炭纤维增强复合材料（CFRP）固体火箭发动机壳体的制备要求,研制了一种具 有良好粘度－温度及粘度－时间特性的炭纤维复合材料湿法缠绕成型树脂配方A。采用差示 扫描量热法（DSC）、傅立叶红外光谱（FT-IR）等分析技术对树脂基体的固化反应进行了系 统地研究,并测试了配方的粘度、力学性能及容器爆破强度。结果表明,该树脂配方A的反应 表观活化能为41.71 kJ／moL,室温下粘度低（≤0.5390 Pa·s）,适用期较长 （＞48 h ） ,不仅完全满足大尺寸CFRP固体火箭发动机壳体的湿法缠绕成型工艺要求,而且其树脂基体 及其炭纤维复合材料表现出优良的力学性能。炭纤维复合材料界面粘接良好,缠绕的
Φ150 mm容器的PV／W均大于48 km,纤维强度转化率达到89.0％以上。
     

A study on the resistance performance of epoxy nano-composites under the vacuum ultraviolet irradiation

Irradiation damage effects of the epoxy resin 648 and epoxy nano-composites are studied by means of simulating the vacuum ultraviolet (VUV) irradiation whose wavelength ranges from 5 to 200 nm. Experimental results of the mass loss, SEM and XPS show that nano-TiO₂ particles exhibit better resistance performance under VUV. Comparing with epoxy resin, the epoxy nano-composite brings significantly less mass loss, slighter flexural strength variation and decreasing gas extraction with less gas component varieties after irradiation. What is more, no new carbon peak-value has been found and principle components of O_ls peak-value remain unchanged on the surface.     

基于FIP WA的RCS快速计算

为改善基于矩量法(MOM)快速多极子(FMM)的稳定性,介绍了快速非均匀平面波算法(FIPWA).根据入射波及电场积分方程(EFIE),采用修正最陡下降路径(MSDP)进行数值积分和内插外推转换,建立了二雏FIPWA模型.该法基于格林函数谱域积分,其转移因子不含特殊函数而仅有初等函数,便于数值实现和稳定性控制,其多层形式复杂度与多层快速多极子(MLFMA)相当.算例表明:该算法与MOM吻合较好,且大幅节省计算时间及计算机内存.     

高强高模聚酰亚胺纤维增强环氧复合材料研究进展

本文综述了当前高强高模聚酰亚胺（PI）纤维增强环氧（EP）复合材料的制备及应用研究进展,较全面地介绍了PI/EP复合材料的成型工艺性能、界面性能、力学性能及破坏机制、电性能、耐损伤性能、防弹性能等,对其应用研究方向进行了展望。     

航天器相对姿态跟踪的非线性前馈控制

针对航天器相对姿态跟踪过程中严重的非线性及控制器设计的复杂性,建立了基于修正罗德里格斯参数的航天器相对姿态运动学和动力学方程并根据Lyapunov直接法设计了非线性前馈控制律.设计的控制律不仅保证闭环系统稳定,还使得航天器相对姿态跟踪误差快速收敛到零点邻域内.通过在Matlab/Simulink环境下对航天器相对姿态跟踪进行数值仿真,验证了建立模型和设计控制律的有效性.