酰胺基改性聚酯的研究及发展

介绍了酰胺基改性聚酯（聚酰胺酯）的制备方法及其研究发展的成果。酰胺基的加入提高了聚酯的吸湿性和染色能力,对拓宽聚酯在工业及民用品中的应用都有着重大的意义和积极的作用,本文还对聚酰胺酯的发展前景作了初步的展望。     

硼酸-柠檬酸比色法测银杏枝叶中黄酮苷含量

用硼酸-柠檬酸比色法测定了银杏枝叶不同季节黄酮苷的含量,结果表明:硼酸-柠檬酸比色法测定银杏枝叶中的黄酮苷含量稳定性好,精度高,标准差为0.06,黄酮苷测定回收率为98.3%～101.1%,测定结果不受脂溶性杂质的干扰;银杏枝叶中的黄酮苷含量随季节的变化而变化,8月黄酮苷含量最高。     

新型多线切割机张力控制系统研究

分析了多线切割机的工作原理、组成结构及其工作过程。介绍了多线切割机的总体控制方案,并对多线切割机的张力控制系统进行深入地理论研究,建立了控制系统的运动学和动力学模型。在此基础上,提出了一种PID速度同步跟随控制方案。试验结果表明,该方案可靠、稳定、控制精度高、调整方便。     

An L-shaped array for estimating 2-D directions of wave arrival

A simple structured 2-D array, the L-shaped array, is presented. The L-shaped array consists of two uniform linear arrays (ULA) connected orthogonally at one end of each ULA. It is shown that the Cramer-Rao bounds (CRB) of the estimated wave directions based on the L-shaped array are about 37% smaller than those for the cross array. The CRB indicates the accuracy potential because it is the (reachable) lower bound on the variance of any unbiased estimate. An efficient maximum likelihood algorithm is developed utilizing the ULA structure inherent in the L-shaped array     

一种基于低轨卫星通信的定时同步研究

定时恢复是数字接收机中的关键技术,基于某特定LEO低轨卫星通信系统应用,重点研究了异步时钟采样恢复法的工作原理,提出了一种改进的Gardner定时误差检测算法,给出了整个定时环路的具体实现方案,并针对其性能进行了分析。仿真结果表明,在大多普勒加速度的卫星信道环境下,该方案能够满足系统设计的要求,且实现结构简单、优化,可大幅降低算法复杂度,在较高信噪比的情况下,具有更加优化的性能。     

一类参数空间利用率最优的直线检测方法

针对Hough变换过程中参数空间利用率低的问题,提出了一类直线检测方法,该方法极大地提高了参数空间的利用率.首先提出了基于仿射变换的Hough变换的实现方法,然后提出了实现完全空间Hough变换的充分必要条件并给予证明,从而建立了能够实现完全空间Hough变换的仿射变换形式,最后提出了一种典型的完全Hough变换形式并给出了算法的详细计算过程.对图像进行特定的仿射变换以改变其定义域,对仿射变换后图像进行Hough变换并计算直线参数.仿真结果表明:该方法对参数累加数组的利用率可以达到100%;同时,与其他方法相比,检测精度得到了提高.     

认知无线电对通信对抗装备建设的启示

认知无线电(Cognitive Radio,CR)技术的提出,为解决不断增长的无线通信应用需求与日益紧张的无线频谱资源之间的矛盾提供了一种有效的解决途径。在较详细地阐述了认知无线电基本原理的基础上,分析了认知无线通信系统的技术特点、关键技术、应用前景,以及对抗难点和思路,探讨并给出了认知无线电通信系统对抗装备的设计、验证、试验等方面的技术支持和启示。     

Timing and hamming weight attacks on minimal cost encryption scheme

The timing and Hamming weight attacks on the data encryption standard (DES) cryptosystem for minimal cost encryption scheme is presented in this article. In the attack, timing information on encryption processing is used to select and collect effective plaintexts for attack. Then the collected plaintexts are utilized to infer the expanded key differences of the secret key, from which most bits of the expanded secret key are recovered. The remaining bits of the expanded secret key are deduced by the correlations between Hamming weight values of the input of the S-boxes in the first-round. Finally, from the linear relation of the encryption time and the secret key's Hamming weight, the entire 56 bits of the secret key are thoroughly recovered. Using the attack, the minimal cost encryption scheme can be broken with 223 known plaintexts and about 221 calculations at a success rate a＞99%. The attack has lower computing complexity, and the method is more effective than other previous methods.     

用EPON技术建设有线电视宽带接入示范小区

EPON技术是一种新型的光纤接入网技术,对EPON的网络结构和技术本质作了详细的介绍,分析和比较EPON在住宅小区的组网方式,选择EPON＋LAN和兀TH两种组网方式在示范小区进行建设。     

Comments and Further Results on ‘Performance Evaluation of a New BPSK-OFDM Timing Estimation Algorithm’

This comment first points out some inaccurate formulae and irrelevant comparisons between Wen’s algorithm and Beek’s one. Then, the correct formulae are provided, the limitations of these two estimators are discussed and some investigations on the local maximum in timing estimation are also presented. Both the simulation and the analysis demonstrate that the timing precision of Wen’s algorithm highly depends on the length of cyclic prefix (CP) and the channel fading rate. On the other hand, Beek’s algorithm will work better under a large CP length and in fast fading channels.