门禁系统的RS422/RS485总线解决方案

目前各种工业场合诸如门禁考勤系统、自动收费系统、数据远传系统（如三表的数据采集传输）等中,远距离串行数据通信的可靠性显得非常重要。RS232串行总线的接口电平比TTL电平大,使得抗干扰能力增强;但RS232规定了其最大负载为2500pF的电容,通信距离也被限制,通常适合于20m以内的数据通信,且是单端通信,必然存在不可消除的共地噪声和共模干扰问题。     

Multipole shimming of permanent magnets using harmonic corrector rings

Shimming systems are required to provide sufficient field homogeneity for high resolution nuclear magnetic resonance (NMR). In certain specialized applications, such as rotating-field NMR and mobile ex situ NMR, permanent magnet-based shimming systems can provide considerable advantages. We present a simple two-dimensional shimming method based on harmonic corrector rings which can provide arbitrary multipole order shimming corrections. Results demonstrate, for example, that quadrupolar order shimming improves the linewidth by up to an order of magnitude. An additional order of magnitude reduction is in principle achievable by utilizing this shimming method for z-gradient correction and higher order xy gradients.     

A simple Hebbian/anti-Hebbian network learns the sparse, independent components of natural images

Slightly modified versions of an early Hebbian/anti-Hebbian neural network are shown to be capable of extracting the sparse, independent linear components of a prefiltered natural image set. An explanation for this capability in terms of a coupling between two hypothetical networks is presented. The simple networks presented here provide alternative, biologically plausible mechanisms for sparse, factorial coding in early primate vision.     

一种基于小波变换的图像自适应盲水印算法*

根据人类视觉系统（HVS）特征和小波变换的多分辨分解特性,提出了一种基于小波变换的图像数字水印算法。该算法在原始图像的LL域自适应地嵌入盲水印,提取或检测时无需参考原始图像或原始水印,实现了全盲检测,与其他许多算法相比,提高了水印的强度,且兼顾了水印的容量,计算简单,易于实现。实验结果表明,该方法具有较强的鲁棒性和安全性,适用于数字图像的版权保护。     

数据仓库地图化的LMRA模型

本文研究数据仓库地地图化解决方案,利用ＯＬＡＰ技术,提出关系型数据地图化的空间ＬＭＲ模型及其运算。     

Ni-Zn-Cu/AC催化剂上甲醇气相低压羰基化反应

采用BET，XRD和TPR手段对甲醇低压气相羰化合成醋酸的镍基催化剂进行了表征。考察了不同负载配比下，三金属负载催化剂(Ni—Zn—Cu／AC)对羰化活性的影响。结果表明，三金属负载具有协同作用，Cu、Zn的添加改善了催化刺的羰基化性能；在适宜的工艺条件下，(5％Ni-5％Zn-5％Cu)，AC的配比组合活性最好，甲醇的转化率为94．58％，醋酸的单程选择性为16，58％，羰基类化合物的总收率为51．26％；进一步工艺条件考察表明，羰化产物的选择性和醋酸收率既取决于进料摩尔配比CH，OH／CH3I和CO／CH3OH的变化，也与羰化温度的高低和接触时间的长短有关系．