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介绍一套低成本的PLC冗余系统——西门子PLC软冗余在氮气连续供应中的实现,对系统的构成、PLC的软冗余组态及其软冗余的编程等进行详细的介绍和说明。实际应用说明本控制系统能够达到期望的控制要求。 相似文献
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在许多重要工业应用场合,需要长期、连续、安全可靠的控制保障。冗余控制是一种解决方案,在SIEMENS,S7系列PLC中,有S7—300的软冗余和S7的硬冗余两种解决方案。通过对两种冗余的概念、工作原理、硬件配置以及整体性能等方面的研究,阐述了PLC软冗余及硬冗余控制系统在工业生产中所适用的场合。 相似文献
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本文介绍了基于美国罗克韦尔公司ControlLogix控制器的玻壳成型冗余自控系统,应用基于PROFIBUS—DP、MPI及Ethemet的网络通信手段,通过软冗余的方式实现对生产线设备的控制。作者阐述了该冗余控制系统的基本工作原理、软硬件构成与通信网络配置、功能特点及程序设计等方面的内容。 相似文献
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张建成 《自动化与仪器仪表》2003,(4):30-32
介绍了PLC在汽化冷却系统中的应用。整个系统实现了双PLC冗余、通讯冗余、电源冗余,三个汽包并联调节,有效地提高了系统的安全性和可靠性,实际应用效果非常好。 相似文献
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介绍基于美国AB公司PLC的玻壳成型冗余自控系统。控制技术通过软冗余方式实现,网络通信采用Profibus-DP、MPI及Ethernet方式。 相似文献
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垃圾短信问题越来越严重,为了识别中文垃圾短信,将人工免疫系统的方法引入中文垃圾短信识别领域。针对中文短信息系统本身的一些特点,提出了适应这些特点的人工免疫算法,并在实验中得到验证。实验结果表明,基于人工免疫的中文垃圾短信识别方法具有较低的错误否定率和错误肯定率。 相似文献
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花指令模糊变换是代码模糊变换策略中的一种有效方法.在分析现有花指令加密方法的基础上,提出一种子程序花指令模糊变换方案,并利用形式化方法对其进行描述.通过研究子程序花指令模糊变换各种形式化的定义,推导出若干引理,从"XOR及CMP扩展"、"伪分支构造"、"JNE后加花指令"等3个方面加以形式化的证明,使得经上述子程序花指令模糊变换的程序具有与原程序相同的逻辑性.最后,以代码模糊变换评测标准对该算法的效果进行了详细分析. 相似文献
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Junk computing, the use of information systems in a way that does not directly advance organizational goals, can both diminish productivity and add value to a work environment. Results of a year-long study of the types and causes of junk computing can help managers reduce performance losses without stifling employee creativity. 相似文献
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Junk computing, the use of information systems in a way that does not directly advance organizational goals, can both diminish productivity and add value to a work environment. Results of a year-long study of the types and causes of junk computing can help managers reduce performance losses without stifling employee creativity. 相似文献
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Martin Rheinländer 《Computers & Mathematics with Applications》2010,59(7):2150-2167
The stability structure for lattice Boltzmann schemes has been introduced in Banda et al. (2006) [16], Junk and Yong (2007) [14] to analyze the stability of numerical algorithms. The first purpose of this paper is to discuss the stability structure from the perspective of matrix analysis. Its second goal is to illustrate and apply the results to different classes of lattice Boltzmann collision operators. In particular we formulate an equivalence condition–just recently also reported in Yong (2008) [18]–that guarantees the existence of a pre-stability structure. It is then illustrated by several examples, how this equivalence condition can be effectively employed for the systematic verification and construction of stable collision operators. Finally, we point out some shortcomings of the stability structure approach arising in certain cases. 相似文献
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电子邮件作为一种重要的信息交互手段,引发了诸如垃圾邮件、恶意邮件、隐私泄露等一系列严重的问题。
垃圾邮件检测是近年来出现的一个研究领域,其目的在于判定一封邮件是否为垃圾邮件。提出了一种基于邮件行为
的垃圾邮件检测技术I3JMD,介绍了邮件行为检测的主要思想和算法过程。通过在实际邮件集上的实验和分析,给出
了新方法的一些性能评判。 相似文献
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Should marketers providing e-mail advertising to sellers of weight loss, phone sex, and get-rich-quick-scheme services have a right to send unsolicited e-mail via online services such as AOL? Does the First Amendment of the US Constitution guarantee such access as a form of free speech? Do the antitrust laws prohibit AOL and other servers from denying these marketers access to an essential facility of competition? Cyber Promotions Inc. thinks so, but the federal district court in Philadelphia did not agree. Cyber sends e-mail advertising via the Internet and AOL to AOL subscribers and to subscribers of other services linked to AOL on the Net. During the period from November 4 to November 11, 1996, Cyber sent approximately 2 million unsolicited e-mail messages through AOL to AOL subscribers. AOL tried to block Cyber's e-mail by implementing a program that AOL termed “Preferred Mail The Guard Against Junk E-Mail”. Under this system, AOL subscribers could click on a preference box captioned “I want junk e-mail!” If subscribers clicked on the box, they would get unsolicited advertising, but not otherwise. The author looks at the issues in this case 相似文献
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当今大型企业应用系统的特点是规模大、数量多、功能复杂,应用系统的安全对整个网络的安全至关重要。阐述了应用系统安全性要求,分析了Domino系统安全的特点,设计了应用层安全的解决方案和系统数据传输加密措施,最后分析了实现硬件身份验证的三种措施,并给出了相应的建议,为大型企业应用系统安全建设提供了借鉴。 相似文献