USB数据传输中CRC校验码的并行算法实现

文章介绍了用于USB总线数据传输的CRC校验的原理和算法，并且采用并行电路实现USB2．0中的CRC产生和CRC校验，与传统的串行电路实现相比，并行电路实现方法虽然在芯片面积上大于串行电路实现，但由于降低了时钟频率，电路更容易综合实现，并且大大降低了功耗，有利于低功耗电路设计。     

重复压裂裂缝转向时油藏数值模拟研究

裂缝转向的实现及选井、选层、优化设计等的数值模拟和机理是转向重复压裂需进一步研究解决的问题,为此,采用黑油模型,研究了在反九点注采井网中,不同储集层渗透率下,转向重复压裂的裂缝穿透率和导流能力等对采油动态的影响。研究表明,不论是渗透率高的地层还是渗透率低的地层,不利裂缝方位的边井最适合实施转向重复压裂且需要比常规重复压裂更大的缝长,而有利裂缝方位的边井和角井只需要与常规重复压裂相当的缝长;同时,转向重复压裂需要比常规重复压裂更高的裂缝导流能力。     

贴片机脱机编程的快捷方法

SMT生产线中的大多数加工设备均为数控设备。它们编程所需要的大多数特征数据均可从CAD设计系统中得到。文章介绍了如何从CAD设计系统中导出X、Y坐标数据,并转换成贴片数据的方法和思路,以期引起更多的同行加入到这方面的研究中。     

贴片设备的选择

随着电子工业的飞速发展,贴片设备已被广泛应用于大规模电子组装生产上。文章就贴片机选型时应注意的几个关键技术问题作简单介绍,希望对企业选择贴装设备有一定的帮助。     

随机减量技术中周期激励的影响及消除方法

本文针对机械系统中通常存在确定性周期激励的事实 ,论证了周期干扰成分的存在对提取的随机减量特征信号的影响 ,基于数字滤波技术提出了一种从周期干扰环境中提取随机减量特征信号的简便方法。在回转机械稳定性监测中的应用实例表明本文提出的方法是有效的。     

连续油管技术与装备发展综述

自世界上第一台连续油管作业机问世至今,连续油管作业技术与装备已经过了40多年的发展历程,以其占地面积小、作业成本低、搬迁安装方便、保护油层、增加油井产量和使用范围广等诸多不可比拟的优势,得到迅速发展,并广泛应用于钻井、完井、试油、采油、修井和集输等各个作业领域。实践表明,连续油管作业技术与装备是一项具有巨大潜力和生命力的实用性技术。目前,该项技术的应用日趋活跃,备受关注。在总结连续油管作业技术与装备的发展现状和展示其发展趋势的基础上,客观地分析了国内连续油管技术与装备的应用与研究现状,提出相应的发展对策。     

Flash器件中氧化硅/氮化硅/氧化硅的特性

对普遍采用的氧化硅/氮化硅/氧化硅( ONO)三层复合结构介质层的制备工艺及特性进行了研究分析,研究了ONO的漏电特性以及顶氧( top oxide)和底氧( bottom oxide)的厚度对ONO层漏电的影响.结果表明,采用较薄的底氧和较厚的顶氧,既能保证较高的临界电场强度,又能获得较薄的等效氧化层厚度,提高耦合率,降低编程电压.     

Estimating crystallinity in high density polyethylene fibers using online Raman spectroscopy

Online Raman spectra, obtained at different points along the spin line during pilot‐scale nonisothermal melt spinning of high density polyethylene (HDPE) fibers, are presented for the first time. The fraction of the crystalline phase corresponding to each spectrum was determined from the normalized integrated intensity of the 1418 cm^?1 Raman band. It is well established that this band represents the orthorhombic crystalline phase in polyethylene. The estimates of percent crystallinity obtained from decomposition of the Raman spectrum were compared with the percent crystallinity from differential scanning calorimetry (DSC) measurements. It is concluded that online Raman spectroscopy can be successfully used to monitor the development of crystallinity in HDPE fibers as a function of distance from the spinneret. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 545–549, 2003     

Magnetic Properties of Fe-Doped Rutile

Ball-milling method was applied to dissolve Fe into titanium dioxide (TiO₂). X-ray diffraction indicated the starting anatase changed to a rutile-type structure with oxygen deficiency after ball milling. Transmission electron microscopy and X-ray absorption experiments were conducted to examine the possible existence of magnetic impurities in the ball-milled powders after they were leached in HCl solutions. Temperature dependence of the resistivity shows semiconducting behavior and the magnetic hysteresis loops at 5 and 300 K exhibit ferromagnetic characteristics. Fe-doped TiO₂ films were also prepared by pulsed laser deposition. The magnetic properties of the films are discussed.