一种基于小波分解和压缩感知的冲击声学无损检测方法

压缩感知理论对稀疏信号的采样与重构十分有效,该文将对携带信息量少的冲击声信号利用压缩感知理论进行采样,提出一种基于小波分解和压缩感知的冲击声学无损检测方法。首先,对冲击声信号进行小波分解构建观测矩阵,求解l1最优化问题,完成类别的稀疏表示,然后对表示误差进行分类,得到检测结果。仿真及实验结果表明,该方法实用有效,其检测系统性能稳定,在信噪比3 dB时可达到90%以上的正确率。     

宽测绘带SAR成像的一种侧摆模式及其压缩感知处理方法

宽测绘带合成孔径雷达(SAR)采用了不同的信号录取方式及成像算法,但现有的ScanSAR和循序扫描体制(TOPSAR)往往会造成场景分辨率的整体下降。针对这一问题,该文采用一种新的侧摆模式进行宽幅场景成像。该模式通过距离向波束角度的变化,以损失部分积累时间为代价,得到宽幅场景的回波信号,继而采用稀疏算法在方位向实现降采样成像。仿真结果表明,在波束变化轨迹确定后,星载雷达侧摆模式下稀疏SAR成像可有效增加场景幅宽,同时确保场景中心区域的高分辨成像。     

压缩采样技术及其应用

如何降低宽带模拟信号数字化过程中的采样率,以及如何有效的对大量数据进行压缩存储一直是学者们关心的问题。该文综述了最近出现的一种新型信号处理方法压缩采样(Compressive Sampling, CS),也称压缩传感(Compressive Sensing)。该方法通过对稀疏信号进行观测而非采样,只需少量观测点就能精确的重构原始信号。结果表明新方法的观测频率可以远远低于奈奎斯特采样频率。该文除介绍其基本原理和主要实现方法外,同时列举了多种应用,并指出若干待研究的问题。     

基于最优索引广义正交匹配追踪的非正交多址系统多用户检测

作为5G的关键技术之一,非正交多址(NOMA)通过非正交方式访问无线通信资源,以实现提高频谱利用率、增加用户连接数的目的。该文提出将压缩感知(CS)及广义正交匹配追踪(gOMP)算法引入上行免调度NOMA系统,从而增强NOMA系统活跃用户检测及数据接收的性能。通过每次迭代识别多个索引,gOMP算法实际上是传统的正交匹配追踪(OMP)算法的扩展。为了获得最优性能,研究分析了在gOMP算法信号重构的每次迭代中所应选择的最优索引数目。仿真结果表明：与其它的贪婪追踪算法及梯度投影稀疏重构(GPSR)算法相比,最优索引gOMP算法具有更优异的信号重构性能;并且,对于不同的活跃用户数或过载率等参数配置的NOMA系统,均表现出最优的多用户检测性能。

     

Syntheses and evaluation of biodegradable multifunctional polymer networks

The biodegradable, injectable and in situ crosslinkable polymer networks based upon di(propylene fumarate)-dimethacrylate (DPFDMA) and polycaprolactone trimethacrylate (PCLTMA), were prepared and characterized. The polymer networks were initiated by photopolymerization. The initial compressive (CS) and diametral tensile strengths (DTS) of the networks materials were determined and used to evaluate the effects of PCLTMA/DPFDMA ratios on the degradation behavior. The networks exhibited initial DTS values ranging from 2.5 to 9.3 MPa and CS values ranging from 1.8 to 146.0 MPa. The increase of PCLTMA in the formulation led to an increase in viscosity and DTS. The degree of conversions and polymerization shrinkage of the resins ranged from 60% to 72% and 5.1% to 6.4%, respectively. After 6 month, PCL300TMA/DPFDMA resins at a ratio of 100/0, 75/25 and 25/75 lost 70%, 87% and 46% of their initial CS, respectively, while PCL900TMA/DPFDMA and PCL300TMA/PCL900TMA resins at 75/25 lost 100% and 83% of their initial CS, respectively.     

基于截断加权基追踪模型的迭代支撑探测算法

迭代支撑探测算法是基于截断的基追踪(Basis Pursuit,BP)模型的一种l_1最小化信号重构算法,它可以实现信号的快速重构并且所需要的观测值比经典的L1算法以及迭代加权L1算法更少.本文针对非零元具有快速退化分布性质的稀疏信号,提出了一种改进算法一一基于截断的加权BP模型的迭代支撑探测算法.在迭代的过程中,改进的算法探测原信号支撑集中元素的同时调整重构模型的权值,使得重构模型更有利于实现信号的精确重构.根据所考虑的信号的非零元具有快速退化分布性质这样的先验信息,利用阈值法则探测原信号支撑集中的元素.最后通过Matlab数值实验实现了算法,验证了基于截断的加权BP模型的迭代支撑探测算法比迭代加权L1算法需要的观测值更少,并且比迭代加权L1算法以及传统的迭代支撑探测算法需要更少的重构时间就可以实现信号的精确重构.     

Online semi-supervised compressive coding for robust visual tracking

In this paper we propose an online semi-supervised compressive coding algorithm, termed SCC, for robust visual tracking. The first contribution of this work is a novel adaptive compressive sensing based appearance model, which adopts the weighted random projection to exploit both local and discriminative information of the object. The second contribution is a semi-supervised coding technique for online sample labeling, which iteratively updates the distributions of positive and negative samples during tracking. Under such a circumstance, the pseudo-labels of unlabeled samples from the current frame are predicted according to the local smoothness regularizer and the similarity between the prior and the current model. To effectively track the object, a discriminative classifier is online updated by using the unlabeled samples with pseudo-labels in the weighted compressed domain. Experimental results demonstrate that our proposed algorithm outperforms the state-of-the-art tracking methods on challenging video sequences.     

Numerical assessment of the analytical models used to determine flexural and shear moduli in I-Beams when the tensile and compressive moduli are different

The different compressive and tensile moduli of fibre reinforced composites have been considered in the analysis of the flexural and shear moduli of I-beams. Firstly, the neutral axis has been determined analytically and then, assuming that location of the neutral axis, the analytical flexural modulus of I-beams has also been obtained. In order to assess the proposed procedure, virtual pure bending and three-point bending tests at different spans have been carried out using the finite element method. The compressive and tensile moduli have been taken into account by defining two parts in the numerical models. The numerical flexural and shear moduli have been determined by reducing the data obtained in the virtual tests. Analytical and numerical results are in good agreement. Therefore, the flexural modulus determined by the proposed analytical approach can be introduced as a material property in the finite element method.     

Compressive response of composite ceramic particle-reinforced polyurethane foam

Quasi-static and dynamic compressive tests are undertaken on the polyurethane (PU) foam and fumed silica reinforced polyurethane (PU/SiO₂) foam experimentally. The ceramic microspheres with varying mass fractions are adopted to mix with the PU/SiO₂ foam to fabricate the composite particle-reinforced foams. The effects of strain rate and particle mass fraction are discussed to identify and quantify the compressive response, energy-absorbing characteristic, and the associated mechanisms of the composite foams. The results show the initial collapse strength and plateau stress of the foams are improved significantly by reinforcing with the ceramic microsphere within 60 wt% at quasi-static compression. The rate sensitivity is observed on all the foams, but in different patterns due to the influence of ceramic microsphere. The compressive response affected by ceramic microsphere can be attributed to the particle cluster effect and stress wave propagation. Together with the deformation, the compressive characteristic experiences non-monotonic change from the low to high strain rates. The specific energy absorption (SEA) of the foam with 41 wt% ceramic microsphere show the largest magnitude at quasi-static compression. With the increasing strain rate, the ceramic reinforced foam exhibits superior energy absorption efficiency at high strain rates to that of the pure foams.     

HDPE/CB高分子导电复合体系的单轴形变与压阻行为

根据基体形变及其与渗流网络结构之间的关系,研究了高密度聚乙烯(HDPE)/炭黑(CB)复合材料压阻行为的发生机制及其影响稳定性的力学因素.结果表明,单轴压阻行为的产生源于材料受外力变形而导致的渗流网络微结构变化,且这种变化强烈依赖于填料含量.当填料含量较低时(渗流阈值附近),体系电阻率随压力升高而表现为电阻正压力系数行为;当填料含量较高时,体系电阻率随压力升高显现电阻负压力系数效应.完全卸载的零压力下,电阻基线随压缩循环随循环次数增大而发生漂移,这种漂移与轴向残余压缩应变有关,可以通过增加循环次数来加以稳定.交联可以减小残余压缩应变,并抑制高填充复合体系电阻基线的漂移.