基于谱聚类的不平衡数据欠采样方法研究

不平衡数据的分类问题在数据挖掘和机器学习领域中,一直是备受关注的问题.论文从数据预处理方面出发,提出一种基于谱聚类的欠采样方法,以此来降低数据的不平衡程度.先对多类样本进行谱聚类,根据每个聚类簇的密集程度,以及到少类样本的平均距离,来计算每个聚类簇的采样数目和选取怎样的多类样本,此欠采样方法可以有效去除多数类的冗余数据.实验结果证明,该算法可以有效提升少类样本的分类效果.     

基于位置的稀疏群体查询

在基于位置的社交网络中,找到一个特殊的群体/社区是非常重要的.现在的研究都集中于寻找群体之间关系紧密的密集子图.相对于紧密的群体/子图,对于稀疏群的研究少之又少.虽然现有工作开始研究稀疏群体查询问题,但是还没有研究基于位置的稀疏群体查询问题,而基于位置的服务在现实生活中有很多需求.因此,研究基于位置的稀疏群查询的问题变得有研究价值.基于位置的稀疏群体查询是为了找到一群用户,不仅用户之间满足一定的稀疏性(即用户之间的社交距离大于k),且最小化用户到查询位置的距离和.针对这个问题,首先提出基于c-邻居的基本处理算法(简称baseline),其主要利用存储的c-邻居信息以及距离剪枝来帮助快速获得查询结果.但是baseline算法的空间消耗太大,且在稀疏阈值参数k>c时查询效率不高.为了解决这些问题,进一步提出基于c-邻居和反向c-邻居的查询优化算法(简称ICN),不仅利用存储的c-邻居且利用反向c-邻居信息来处理参数k>c的情况,从而快速获得查询结果.实验结果和理论表明,提出的两种查询处理方法是有效的和正确的.     

边界约束对弯曲-伸展元三轴波速试验的影响

利用弯曲-伸展元开展干砂小应变剪切波试验和除气水压缩波试验,研究了三轴试样的不同约束边界对弯曲-伸展元量测剪切波速和压缩波速的影响,并对波速试验结果进行分析。研究结果表明:以干砂为试验对象的剪切波速试验结果介于砂土中剪切波速与边界材料的剪切波速之间,受到约束边界的材质、长度和壁厚的显著影响;而以除气水为试验对象的压缩波速试验结果受样品约束边界的影响较小。在不同约束材质下,剪切波在干砂中的传播速度与约束材料的刚度有关,材料的刚度越小对干砂剪切波速测试结果影响越小。弯曲-伸展元激发频率的相关性与边界约束无关,只与测试材料有关。研究成果有助于获取准确的弯曲-伸展元波速试验结果。     

混有CACC车辆和ACC车辆的混合交通流驾驶舒适性

为了探索协同自适应巡航控制(cooperative adaptive cruise control,CACC)车辆对交通系统的潜在影响,分析了CACC车辆市场普及过程中存在的CACC车辆、自适应巡航控制(adaptive cruise control,ACC)车辆与人工驾驶车辆混合交通流驾驶舒适性.应用加州伯克利PATH实车验证的ACC模型和CACC模型进行数值仿真实验,采用国际ISO-2631-1标准评价混合交通流舒适性,并对ACC和CACC期望车间时距进行参数敏感性分析.最后,从交通流稳定性的角度,对舒适性仿真结果进行了讨论.结果表明:随着CACC市场率的增加,舒适性呈现先恶化、再逐渐提升的趋势.较大的ACC车间时距有利于抑制舒适性的恶化程度,CACC车辆对舒适性的提升作用不受其车间时距取值的影响.混合交通流稳定性定性地决定了舒适性的变化趋势,人工车辆安装车车通信设备,有助于舒适性的逐渐提升.     

大内跨小边跨框架结构预应力筋优化布置方法

预应力筋的优化布置是大内跨小边跨的多跨预应力混凝土框架结构合理设计计算的关键.为满足控制截面承载力最大的需要,以往常将大跨所需预应力筋布置为连续曲线,并按水平直线延伸通过其相邻的两小跨,按这种布置方式仅使大跨内产生竖向向上的预应力等效荷载,可较好平衡大跨的竖向外荷载;而若将大跨及相邻的两小跨统一考虑,预应力筋按连续曲线布置,张拉产生的预应力等效荷载不但可有效平衡大跨的竖向外荷载而且也可平衡小跨的竖向外荷载,可以使荷载平衡得到优化实现.以一典型工程为例,分析了在相同条件下两种预应力筋布置过程中张拉引起的综合弯矩、主弯矩和次弯矩的分布和量值上差异,比较了两类布筋形式对正截面承载力计算结果的影响,验证了对大内跨小边跨框架结构统一考虑后整体上按三段连续正反抛物线预应力筋布置的合理性.     

Wear behavior of <Emphasis Type="Italic">in-situ</Emphasis> TiC particles reinforced aluminum matrix composite

The microstructure, tensile property and wear resistance of 7075 aluminum matrix composite reinforced with TiC particles prepared by in-situ reaction casting were investigated. The effect of TiC reinforcement on wear behavior was analyzed. The wear mechanism was also discussed. A micro-mechanism model of reaction kinetics for synthesis of TiC was acquired. Results show that TiC could increase the tensile and yield strength, but decrease the elongation. Besides, TiC particles improve the property of wear resistance of 7075 aluminum alloy. The wear mechanisms include abrasive wear and adhesive wear in wear test process.     

Preparation and performance research of cement-based grouting materials with high early strength and expansion

Main performance of the cement grouting materials made up by Portland cement(PC) and sulphoaluminate cement(SAC) was investigated in this program, a kind of expanding agent(EA) which was mainly constituted by metakaolin and alunite was utilized for the compensation of the shrinkage, the hydration products and micro structure of the grouting materials were researched by X-ray diffraction(XRD) and scanning electron microscopy (SEM). The results showed that a high expansion rate of the grouting materials could be reached as the expanding agent mixed in 6% of PC mass; the addition of SAC in the S2(PC:SAC:EA=34:6:2.25) brought a further improvement of the expansion rate of the grouting materials, the analysis of XRD and SEM showed that due to the reaction of expanding agent and SAC in the grouting materials, more ettringite crystal was generated, which resulted in a higher early strength, the addition of SAC played an expansion and strength reinforcement role in the grouting materials.     

Synthesis of HTPB based PU-PS IPN membrane for pervaporation recovery of butanol

Hydroxyl terminated polybutadiene(HTPB) based polyurethane(PU)-polystyrene(PS) interpenetrating polymer network(IPN) was prepared and characterized by FTIR, TGA, WCA, swelling experiments, and SEM. The IPN was used for pervaporation(PV) recovery of butanol. Both the permeation flux and separation factor increased with feed temperature, and both water and butanol fluxes increased with feed concentration while no obvious effect of concentration on separation factor was found. Through the formation of IPN structure, the total flux of HTPB based PU increased greatly with the decrease of separation factor. At the feed temperature of 60 °C, the IPN membrane obtained a total flux of 613.3 g/m~2 h with a separation factor of 6.15.     

High precision frequency measurement based on the characteristic of the fuzzy area

The phase difference change is random in the discrete fuzzy area by considering the limit of device resolution, which the device can not stably capture, and the precision of the measured value only reaches the level of ns, but the phase difference change in the concentrated fuzzy area is step by step, and the device can stably capture the change of ps. By using the fuzzy area conversion technology, a high precision frequency measurement is designed. Through computer control and frequency synthesis,the discrete fuzzy area is converted to the concentrated fuzzy area, the ps stability properties of phase difference change on the border of the concentrated fuzzy area is used, the precision can be improved two or three orders of magnitude, and the high precision measurement in a wide range is achieved.     

MIMO radar waveform design in the presence of clutter and colored noise

The existing MIMO radar waveform design methods only deal with the optimization of radar waveform with the presence of clutter or colored noise, and unfortunately can not get the optimal waveform with the scenario when the clutter and colored noise coexist, which is more realistic in practical applications. To address this problem, a novel MIMO radar waveform design method based on mutual information in the presence of clutter and colored noise is proposed. The proposed scheme considers the influence of the target's response, clutter and colored noise on the optimization of the radar waveform. The mathematical expression for the transmit waveform matrix is achieved by theoretical derivation. What is more important, an optimal pairing of the eigenvectors of the target, clutter and colored noise is given and the power allocation for each antenna is optimized by the water-filling method. Simulation results show that when the total transmit power is 10dB, the proposed method's MI is 8bit and 4bit more than that of the general water-filling method and the method which only considers the pairing of the target's response and noise, respectively.