Improved high-rate performance and cycling stability of 1D LiFePO4 nanorods by a facile annealing process

To alleviate the main limitations of lithium ion diffusion rate and poor electronic conductivity for LiFePO4 cathode material, it is desirable to synthesize nano-size LiFePO4 material due to its enhanced electronic and lithium ion transport rates and thus an improved high-rate performance. However, our previous synthesized LiFePO4 nanorods only exhibited low high-rate and slightly unstable cycle performance. Possible reasons are the poor crystallization and Fe2+ oxidation of LiFePO4 nanorods prepared by hydrothermal method. In this paper, LiFePO4 nanorods were simply dealt with at 700 ℃ for 4 h under the protection of Ar and H2 mixture gas. The electrochemical properties of LiFePO4/Li cells were investigated by galvanostatic test and cyclic voltammetry(CV). The experimental results indicated that the annealed LiFePO4 nanorods delivered an excellent cycling stability and obviously improved capacity of 150 mA·h·g-1 at 1C, and even 122 mA·h·g-1 at 5C.     

Hot deformation behavior of low carbon steel during compression at elevated temperature

Hot compression tests of low carbon steel were carried out on Gleeble-3500 system in the temperature range from 750 to 900 ℃ and in the strain rate range from 0.001 to 1.0 s-1, and the associated microstructural evolution was studied by observations with a metallographic microscope. The results show that the stress-strain curves exhibit a peak stress at critical strain, after which the fl ow stresses decrease monotonically until reaching high strains, showing a dynamic fl ow softening. The peak stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by the Zener-Hollomon parameter Z in the hyperbolic sine equation. The fl ow stress increases with increasing strain rate and decreasing deforming temperature. The fl ow stress can be described by constitutive equation in hyperbolic sine function and can also be described by a Zener–Hollomon parameter Z. With increasing deformation temperature and decreasing strain rate, the grain size as well as the volume fraction of the recrystallized grains increase. The safe region for hot working of the alloy has been determined according to the processing map and microstructure at the true strain of 0.5, which is the deformation temperature of 840-940 ℃ and the strain rate of 0.001-1.0 s-1.     

基于OFDM信号的自适应水声信道估计算法

建立适用于OFDM水声通信信号的信道估计模型, 对MP算法进行改进, 引入路径门限调整机制克服虚假路径造成的不良影响, 通过重要路径权系数的迭代修正降低非正交性引入的估计误差, 以较小计算量取得了与OMP算法相当的估计精度; 针对传统信道估计算法对信道长度信息的依赖问题, 提出了一种信道长度自适应信道估计算法, 该算法能够对信道估计质量进行实时评价, 并根据评价结果实现信道估计算法预估信道长度的自适应调整, 满足未知水声信道精确估计及通信应用的需要; 基于OFDM导频元素个数与信道估计效果的关系研究, 提出了OFDM导频序列自调整的通信方案, 以较小的带宽损失保证了可靠的水声通信. 通过仿真和实地试验, 验证了该文研究内容的有效性.     

支持向量机与哈夫曼树实现多分类的研究

基于支持向量机和决策树的多分类方法存在错误累积问题,累积的错误往往使分类准确率下降,分类效果变差.在仔细分析了其产生错误累积原因的基础上,提出了基于哈夫曼树的支持向量机多分类方法.该方法首先将一个多分类问题分解为多个二分类问题,针对每个二分类问题使用支持向量机二分类方法解决;然后根据相异度来决策分类的优先顺序,构建基于哈夫曼树的支持向量机多分类模型;最后使用勒卡斯开源数据集进行验证,并将它与传统的支持向量机多分类方法进行实验比较.实验结果表明,新的方法在分类速度和分类精度上较传统的支持向量机多分类方法优越.     

改良型腰果酚醛树脂废气治理的研究

改良型腰果酚醛树脂应用到铸件等浸渍、粘合、烘干等过程中会产生恶臭,排放前需要降解处理。研究采用低温等离子体技术结合吸收方法处理改良型腰果酚醛树脂废气,考察了处理工程中峰值电压、停留时间、吸收液pH值对废气去除率的影响。实验室小试改良型腰果酚醛树脂废气进口浓度85 ppm,停留时间1.2 s时,去除率可达92%;工业扩大示范工程去除率最高可达80%,排气口出气平均恶臭浓度1 239.5(无量纲),满足《恶臭污染物排放标准》(GB14554-93)中相关规定。     

一类修正的q-Baskakov算子的逼近性质

Baskakov型算子是研究函数逼近问题的一种很重要的工具。该文基于Gupta所提出的q-Baskakov算子,介绍了一类修正的q-Baskakov算子,给出了该类算子的一些基本性质,并且得到了该类算子的一致收敛定理,从而进一步推广了q-Baskakov算子的一些结论。     

超高频RFID标签命令头解析模块设计

该文针对超高频RFIDISO 18000-6C标准,分析了移位寄存器解析方案的冗余状态,提出了采用有限状态机优化超高频RFID标签命令头解析面积的方法。采用Verilog HDL,通过设置6组命令,进行了常用方案和新提出方案逻辑门数量的对比,从而反应出标签芯片电路面积的变化。实验结果表明,当指令数量在12 32条之间时,用有限状态机解析命令头的电路面积比用移位寄存器解析的面积小15%33%。     

网络协议电视频道快速切换研究

网络协议电视（Internet Protocol Television,IPTV）已经成为新一代网络（Next Generation Net-work,NGN）中最具潜力的应用,主要由于其具有随时随地都能发送电视节目的特性。随着IEEE 802.16d/e的规格制订,它具有高带宽及低延迟的能力,因此适合作为发送多媒体串流的服务。此外,它也提供讯号高涵盖率、行动性支持以及非视线功能。我们可以利用IEEE 802.16d/e提供发送IPTV串流的媒介,并提出一个简单但却有效的IPTV频道切换算法以维持频道切换的时间在一个可容许的范围内。提出的算法根据热门频道及个人化频道的预载,以减少因为网络传输所造成的延迟,达到快速切换频道的目的。最后,通过实验结果证实算法的效能。     

基于医学院校移动图书馆智能服务模式的研究

本文总结了当前医学院校移动图书馆服务开展的现状,分析了当前服务过程中存在的问题与需求,提出了目前我国医学院校移动图书馆服务的优化与发展方向。     

基于单片机控制的燃气灶自动开关设计

本文以AT89C51单片机为核心,与传统电子燃气灶结合,设计出可以自动点火的燃气灶。该燃气灶通过感受压力来控制燃气的通断和点火,并通过温度传感器检测燃气灶是否已经点燃了。