浅析网络安全的技术-毕业设计(论文)外文翻译 (2)

引言概述：在现代高等教育中，毕业设计（或称为毕业论文、学士论文等）是学生完成学业的重要环节。

而对于一些特定的专业，例如翻译专业，有时候还需要完成外文翻译这一项任务。

本文将探讨毕设外文翻译的意义和目的，以及为什么对翻译专业的学生而言这一任务极其重要。

正文内容：1.提高翻译能力和技巧外文翻译是一项对翻译专业学生而言十分重要的任务，通过进行外文翻译，学生们可以通过实践提高自己的翻译能力和技巧。

在这个过程中，他们可以学习如何处理不同类型的外文文本，熟悉不同领域的专业术语，并掌握一些常用的翻译技巧和策略。

2.扩展语言和文化知识毕设外文翻译要求学生们对翻译语言的相关知识和背景有一定的了解。

在进行翻译时，学生们需要遵循目标语言的语法规则，并确保所翻译的内容准确、清晰地传达源语言的意义。

通过这一过程，学生们可以进一步扩展自己的语言和文化知识，提高自己的跨文化沟通能力。

3.提供实践机会毕设外文翻译为学生们提供了一个实践的机会，让他们能够将在课堂上所学到的理论知识应用于实际操作中。

通过实践，学生们可以对所学知识的理解更加深入，同时也可以发现并解决实际翻译过程中的问题和挑战。

这对于学生们将来从事翻译工作时具备更好的实践能力和经验具有重要意义。

4.培养翻译专业素养毕设外文翻译要求学生们具备良好的翻译专业素养。

在进行翻译过程中，学生们需要保持专业的态度和责任心，严谨地对待每一个翻译任务。

他们需要学会如何进行翻译质量的评估和控制，以确保最终翻译稿的准确性和流畅性。

这一系列的要求和实践，可以帮助学生们培养出色的翻译专业素养。

5.提升自我学习和研究能力毕设外文翻译要求学生们进行广泛的文献阅读和研究，以便更好地理解所翻译的内容，并找到适当的翻译方法和策略。

在这个过程中，学生们需要培养自己的自主学习和研究能力，提高对学术和专业领域的敏感性，并能够独立思考和解决问题。

这将对学生们未来的学术研究和进一步的职业发展产生积极的影响。

总结：引言概述:毕业设计外文翻译（Thesis Translation）是指在毕业设计过程中，对相关外文文献进行翻译，并将其应用于研究中，以提供理论支持和参考。

外文翻译原文及译文学院计算机学院专业计算机科学与技术班级学号姓名指导教师负责教师2011年6月Detecting ARP Spoofing: An Active TechniqueVivek Ramachandran and Sukumar NandiCisco Systems, Inc., Bangalore IndiaIndian Institute of Technology, Guwahati, Assam, IndiaAbstract. The Address Resolution Protocol (ARP) due to itsstatelessness and lack of an authentication mechanism for verifyingthe identity of the sender has a long history of being prone tospoofing attacks. ARP spoofing is sometimes the starting point formore sophisticated LAN attacks like denial of service, man in themiddle and session hijacking. The current methods of detection use apassive approach, monitoring the ARP traffic and looking forinconsistencies in the Ethernet to IP address mapping. The maindrawback of the passive approach is the time lag between learningand detecting spoofing. This sometimes leads to the attack beingdiscovered long after it has been orchestrated. In this paper, wepresent an active technique to detect ARP spoofing. We inject ARPrequest and TCP SYN packets into the network to probe forinconsistencies. This technique is faster, intelligent, scalable andmore reliable in detecting attacks than the passive methods. It canalso additionally detect the real mapping of MAC to IP addresses to afair degree of accuracy in the event of an actual attack.1. IntroductionThe ARP protocol is one of the most basic but essential protocols for LAN communication. The ARP protocol is used to resolve the MAC address of a host given its IP address. This is done by sending an ARP request packet (broadcasted) on the network. The concerned host now replies back with its MAC address in an ARP reply packet (unicast). In some situations a host might broadcast its own MAC address in a special Gratuitous ARP packet. All hosts maintain an ARP cache where all address mappingslearnt from the network (dynamic entries) or configured by the administrator (static entries) are kept. The dynamic entries age out after a fixed interval of time, which varies across operating systems. After the entry ages out it is deleted from the cache and if the host wants to communicate with the same peer, another ARP request is made. The static entries never age out.The ARP protocol is stateless. Hosts will cache all ARP replies sent to them even if they had not sent an explicit ARP request for it. Even if a previous unexpired dynamic ARP entry is there in the ARP cache it will be overwritten by a newer ARP reply packet on most operating systems. All hosts blindly cache the ARP replies they receive, as they have no mechanism to authenticate their peer. This is the root problem, which leads to ARP spoofing.ARP spoofing is the process of forging ARP packets to be able to impersonate another host on the network. In the most general form of ARP spoofing the attacker sends spoofed ARP responses to the victim periodically. The period between the spoofed responses is much lesser than the ARP cache entry timeout period for the operating system running on the victim host. This will ensure that the victim host would never make an ARP request for the host whose address the attacker is impersonating. Following subsection briefly discuss the current detection and mitigation techniques.1.1 Current Mitigation and Detection TechniquesExisting ARP spoofing detection techniques are discussed next sequentially.1.1.1 Secure ARP Protocol (S-ARP)This has been proposed as a replacement for the ARP protocol in S-ARP: a Secure Address Resolution Protocol. The S-ARP protocol is definitely a permanent solution to ARP spoofing but the biggest drawback is that we will have to make changes to the network stack of all the hosts. This is not very scalable as going for a stack upgrade across all available operating systems is something both vendors and customers will not be happy about. As S-ARP uses Digital Signature Algorithm (DSA) we have the additional overhead of cryptographic calculations though the authors of the paper have claimed that this overhead is not significant.1.1.2 Static MAC EntriesAdding static MAC addresses on every host for all other hosts will not allow spoofing but is not a scalable solution at all and managing all these entries is a full time job by itself. This can fail miserably if mobile hosts such as laptops are periodically introduced into the network. Also some operating systems are known to overwrite static ARP entries if they receive Gratuitous ARP packets (GARP).1.1.3 Kernel Based PatchesKernel based patches such as Anticap and Antidote have made an attempt to protect from ARP spoofing at a individual host level. Anticap does not allow updating of the host ARP cache by an ARP reply that carries a different MAC address then the one already in the cache. This unfortunately makes it drop legal gratuitous ARP replies as well, which is a violation to the ARP protocol specification. Antidote on receiving an ARP reply whose MAC address differs from the previously cached one tries to check if the previously learnt MAC is still alive. If the previously learnt MAC is still alive then the update is rejected and the offending MAC address is added to a list of banned addresses.Both the above techniques rely on the fact that the ARP entry in the cache is the legitimate one. This creates a race situation between the attacker and the victim. If the attacker gets his spoofed ARP entry into the host’s cache before the real host can, then the real MAC address is banned. This can only be undone by administrative intervention. Thus we can conclude that wrong learning may cause these tools to fail in detecting ARP spoofing.1.1.4 Passive DetectionIn Passive Detection we sniff the ARP requests/responses on the network and construct a MAC address to IP address mapping database. If we notice a change in any of these mappings in future ARP traffic then we raise an alarm and conclude that an ARP spoofing attack is underway. The most popular tool in this category is ARPWATCH.The main drawback of the passive method is a time lag between learning the address mappings and subsequent attack detection. In a situation where the ARP spoofing began before the detection tool was started for the first time, the tool will learn the forged replies in it’s IP to MAC address mapping database. Now only after the victim starts communicating with some other host the inconsistency will be detected and an alarm rose. The attacker may have made his getaway because of this delay. Also a spoofed entry learned as in the above scenario would have to be manually undone by the networkadministrator. The only solution to this problem is to manually feed the correct address mappings into the database before starting the tool or create an attack free learning traffic. Both of these are unreasonable due to scalability and mobility issues. An ideal example would be mobile hosts e.g. laptops brought in by customers or visitors to a company. This slow learning curve makes it impossible to install passive tools on a large network (1000+ hosts) and expect them to identify attacks instantaneously.The passive techniques do not have any intelligence and blindly look for a mismatch in the ARP traffic with their learnt database tables. If an ARP spoofing is detected than there is no way of ascertaining if the newly seen address mapping is because of a spoofing attempt or the previously learnt one was actually a spoofed one. Our technique will determine the real MAC to IP mapping during an actual attack to a fair degree of accuracy.The passive learning technique is also very unreliable. A new address mapping is learnt when ARP traffic is seen from them. Thus a switch ARP Cache table overflow attempt by the generation of random ARP reply packets per second with arbitrary MAC and IP addresses will just result in new stations being discovered instead of being reported as attack traffic. To overcome problems in earlier techniques, we present a new ARP spoofing detection technique. Our technique uses an active approach to detect ARP spoofing. We send out ARP request and TCP SYN packets to probe the authenticity of the ARP traffic we see in the network. The approach is faster, intelligent, scalable and more reliable in detecting attacks than the passive methods. It can also additionally detect the real mapping of MAC to IP addresses to a fair degree of accuracy in the event of an actual attack. A description of the technique in detail is reported in following sections.2 The Proposed Active Detection Technique for ARP spoofingThe proposed technique actively interacts with the network to gauge the presence of ARP spoofing attacks. We will henceforth assume the following about the network we desire to protect.2.1 Assumptions1. The attacker’s computer has a normal network stack. This assumption will hold for most of the attacks as “ready to use” ARP spoofing tools have always been the attacker’s most popular choice. If the attacker does use a customized stack then our technique willstill detect ARP spoofing but will not be able to predict the correct address mappings anymore. We will discuss performance in the presence of a customized stack in section 2.5.2. The individual hosts we desire to protect on the network may use a personal firewall but at least one TCP port should be allowed through the firewall. This is to allow our probe packets (TCP SYN packets) to go through. This is a reasonable assumption as even if a firewall is installed some LAN based services such as NETBIOS etc are normally allowed through it for LAN communication.3. We assume that all devices, which we protect, have a TCP/IP network stack up and running.2.2 TerminologyWe now introduce the terminology used in the rest of this paper.1. Threshold interval: ARP replies to an ARP request must be received within a specified time interval. After this time has elapsed we will consider the ARP request to have “expired”.We will call this interval as the “Threshold Interval”. This will be administratively configurable on any tool using our technique.2. Host Database: This is the mapping of all legitimate IP and MAC pairs on the network verified and learnt by our technique.The ARP packets consist of the MAC header and the ARP header. Based on the value of the source and destination MAC addresses in the MAC header and as advertised in the ARP header we can divide the all ARP packets into 2 categories.1. Inconsistent Header ARP packets: The MAC addresses in the MAC and ARP header differ i.e. Source MAC address in MAC header! = Source MAC address in ARP header (in ARP requests/responses) and/or Destination MAC address in MAC header! = Destination address in ARP header (only for ARP replies).2. Consistent Header ARP packets: These are the compliment of the Inconsistent Header ARP packets. The MAC addresses in the MAC and ARP headers match in these packets.Note that Inconsistent Header ARP packets are guaranteed spoofed packets as such an anomaly is only possible in attack traffic. Based on the above classification we can further bunch the Consistent Header ARP packets into three groups:1. Full ARP Cycle: An ARP request and its corresponding ARP replies seen within the threshold interval.2. Request Half Cycle: An ARP request for which no replies are sent as seen within the threshold time.3. Response Half Cycle: An ARP reply generated without an ARP request. These three categories form the basis of our input to the ARP spoofing detection mechanism. The following subsection discusses the Architecture of the proposed technique in detail.2.3 ArchitecturePlease refer to Figure 1 for the architecture discussion. We have adopted a modularized approach and have divided our spoof detection into the following modules:1. ARP Sniffer module: This sniffs all ARP traffic from the network.2. MAC - ARP header anomaly detector module: This module classifies the ARP traffic into Inconsistent Header ARP packets and Consistent Header ARP packets.3. Known Traffic Filter module: This filters all the traffic, which is already learnt. It will either drop the packet if the IP to MAC mapping is coherent with the learnt Host Database or raise an alarm if there are any contradictions. All the new ARP packets with unknown addresses are sent to the Spoof Detection Engine for verification.4. Spoof Detection Engine module: This is the main detection engine. We feed the Consistent Header ARP packets to it as input. The design of this module will be discussed in Section 2.4.5. Add to Database Module: Legitimate ARP entries verified by the Spoof Detection Engine are added to the Host Database by this module.6. Spoof Alarm Module: This module raises an alarm on detection of ARP spoofing by sending a mail, SMS etc to the administrator.Fig. 1. Inter-relation between various Modules used by the ARP Spoof Detection AlgorithmAs shown in Figure 1, the ARP Sniffer module sniffs all the ARP traffic in its LAN segment and passes it to the MAC – ARP Header Anomaly Detector. This module passes the entire Consistent Header ARP packets to the Known Traffic Filter module. The entireInconsistent Header ARP packets are sent to the Spoof Alarm. This is done because the Inconsistent Header ARP packets are all spoofed packets as discussed earlier. The Known Traffic Filter module will remove all traffic coherent with the already learnt addresses by consulting the Host Database. If there is a contradiction in the ARP traffic for already learnt addresses then it raises a Spoof Alarm. All new ARP traffic is passed to the Spoof Detection Engine.The Spoof Detection Engine applies our detection algorithm to detect ARP spoofing. The newly seen Consistent Header ARP packets are input to this module. The engine now internally bunches these packets into the three categories discussed in Section 2.2 namely Full ARP Cycle, Request and Response Half Cycle packets. The detection algorithm applied by the engine will be discussed in the section 2.4. After applying the detection algorithm the Spoof Detection engine either sends the ARP entry to the Add to Database module or the Spoof Alarm module. The Add to Database module will add these verified MAC and IP address mapping to the Host Database. The spoof detection engine is discussed in detail next.2.4 The Spoof Detection EngineThe Spoof Detection Engine is the heart of the whole system. The three different ARP Cycle packets as discussed in Section 2.2 are treated in slightly different ways by the Spoof Detection Engine to detect an attempted spoofing. The Spoof Detection Engine works based on the following Rules:Rule A: “The network interface card of a host will accept packets sent to its MAC address, Broadcast address and subscribed multicast addresses. It will pass on these packets to the IP layer. The IP layer will only accept IP packets addressed to its IP address(s) and will silently discard the rest of the packets. If the accepted packet is a TCP packet it is passed on to the TCP layer. If a TCP SYN packet is received then the host will either respond back with a TCP SYN/ACK packet if the destination port is open or with a TCP RST packet if the port is closed”.Rule B: “The attacker can spoof ARP packets imp ersonating a host but he can never stop the real host from replying to ARP requests (or any other packet) sent to it. The valid assumption here is that the r eal host is up on the network.”It should be noted that these rules have been derived from the correct behavior that a host’s network stack should exhibit when it receives a packet. To exemplify Rule A, let a host have MAC address = X and IP address = Y. If this host receives a packet with destination MAC address = X and destination IP address = Z then even though the network interface card would accept the packet as the destination MAC address matches, the host’s network stack will silently discard this packet as the destination IP address does not match, without sending any error messages back to the source of the packet.Based on Rule A, we can conceive of two types of probe packets from a host’s network stack point of view which we will use to detect ARP spoofing.a. Right MAC – Wrong IP packet: The destination MAC address in the packet is of the hos t but the IP address is invalid and does not correspond to any of the host’s addresses. The destination host will silently drop this packet.b. Right MAC – Right IP packet: The destination MAC address and IP addresses pairs are of the host’s and its networ k stack accepts it.We will henceforth assume that the attacker is using an unmodified network stack. The performance of our technique in the presence of a modified network stack will be evaluated in Section 2.5. Based on the above observation we will construct our own packets based on Rule A and send them on the network. We will use the address information in the ARP response packet sent by the host whose authenticity is to be verified. We will use the MAC and IP addresses used in the ARP response packet to construct a TCP SYN packet i.e. the destination MAC and IP in the TCP SYN packet will be the source MAC and IP address advertised in the ARP response packet and the source MAC and IP in the TCP SYN packet would be of the host running the Spoof Detection Engine. The TCP destination port will be chosen based on the presence/absence of packet filtering firewalls on the network hosts. If there is a firewall installed on the hosts we will choose the “allowed TCP port” (as in section 2.1) and if no firewalls ar e there then we can choose any TCP port. The rest of the header values in the TCP SYN packet will be set as usual.When a TCP SYN packet as constructed above is sent to the source of the ARP reply packet, the host’s response will be based on Rule A. If the ARP response was from the real host its IP stack will respond back with either a TCP RST packet (If the destination port is closed) or a TCP SYN/ACK packet (if the destination port is open).If the ARP response had been from a malicious host then its network stack would silently discard the TCP SYN packet in accordance with Rule A. Thus based on the fact that the Spoof Detection Engine does/does not receive any TCP packets in return to the SYN packet it sent, it can judge the authenticity of the received ARP response packet.APR欺骗检测：一种主动技术手段维克拉玛苍兰和舒库玛南迪思科系统公司班加罗尔印度印度理工学院，古瓦哈蒂，阿萨姆，印度摘要.地址解析协议（ARP）由于其无状态性和缺乏对发送者身份进行验证的机制，因而长久以来常被用于欺骗攻击。

本科生毕业设计 (论文)
外文翻译
原文标题
Worlds Collide:
Exploring the Use of Social Media Technologies for
Online Learning
译文标题
世界的碰撞：
探索社交媒体技术在在线学习的应用
作者所在系别计算机科学与工程系作者所在专业计算机科学与技术作者所在班级
作者姓名
作者学号
指导教师姓名
指导教师职称讲师
完成时间2013年2月
北华航天工业学院教务处制
注：1. 指导教师对译文进行评阅时应注意以下几个方面：①翻译的外文文献与毕业设计（论文）的主题是否高度相关，并作为外文参考文献列入毕业设计（论文）的参考文献；②翻译的外文文献字数是否达到规定数量（3 000字以上）；③译文语言是否准确、通顺、具有参考价值。

2. 外文原文应以附件的方式置于译文之后。

网络安全外文翻译附件1：外文资料翻译译文网络安全1 简介在计算机网络最初出现的几十年里，它主要用于在各大学的研究人员之间传送电子邮件，以及共同合作的职员间共享打印机。

在这种条件下，安全性未能引起足够的注意，但是现在，众多的普通市民使用网络来处理银行事务、购物和纳税，网络安全逐渐成为一个潜在的巨大问题。

安全性是一个涉及面很广的问题，其中也涉及到是否构成犯罪行为的问题。

大多数安全性问题的出现都是由于有恶意的人试图获得某种好处或损害某些人而故意引起的。

网络安全性可以被粗略地分为4个相互交织的部分：保密、鉴别、反拒认以及完整性控制。

保密是指保护信息不被未授权者访问，这是人们在谈到网络安全性时最常想到的问题。

鉴别主要指在揭示敏感信息或进行事务处理之前先确认对方身份。

反拒认主要与鉴别有关：当你的客户下了一份要采购1000万双手套的订单，后来他宣称每双的价格是69美分，如何证明他原先答应的价格是89美分呢？最后，如何确定自己收到的消息是最初发送的那条消息，而不是被有恶意的敌人篡改或伪造过的呢？所有这些问题（保密、鉴别、反拒认和完整性控制）也发生在传统的系统中，但却有很大的差别。

在讨论解决方法之前，值得花些时间考虑网络安全性属于协议组的哪一部分的内容。

可能无法确定一个单独的位置，因为安全性与每一层都有关。

以下将从不同的角度来介绍网络安全性。

2 计算机病毒在我们这个富有健康意识的社会中，任何形式的病毒都是敌人。

计算机病毒则尤其是个祸害。

这类病毒可以、也的确侵袭过没有防范的计算机系统，轻者可能仅仅是惹人心烦，重者可能造成灾难性的软件及数据损失，导致时间及财力的浪费。

各家公司越来越多地使用计算机进行企业管理，这对于企业来说是至关重要的。

然而，随着计算机病毒威胁的出现，病毒引发的系统瘫痪屡有发生，其代价正不断增长。

我们应当关注这一问题，但恐慌是没有必要的。

正如良好的饮食、运动及医疗保健可以延年益寿一样，谨慎高效的防病毒策略也可以最大限度地减少病毒入侵的机会。

中英文资料外文翻译计算机网络计算机网络，通常简单的被称作是一种网络，是一家集电脑和设备为一体的沟通渠道，便于用户之间的沟通交流和资源共享。

网络可以根据其多种特点来分类。

计算机网络允许资源和信息在互联设备中共享。

一．历史早期的计算机网络通信始于20世纪50年代末，包括军事雷达系统、半自动地面防空系统及其相关的商业航空订票系统、半自动商业研究环境。

1957年俄罗斯向太空发射人造卫星。

十八个月后，美国开始设立高级研究计划局(ARPA)并第一次发射人造卫星。

然后用阿帕网上的另外一台计算机分享了这个信息。

这一切的负责者是美国博士莱德里尔克。

阿帕网于来于自印度，1969年印度将其名字改为因特网。

上世纪60年代，高级研究计划局(ARPA)开始为美国国防部资助并设计高级研究计划局网(阿帕网)。

因特网的发展始于1969年，20世纪60年代起开始在此基础上设计开发，由此，阿帕网演变成现代互联网。

二．目的计算机网络可以被用于各种用途:为通信提供便利:使用网络，人们很容易通过电子邮件、即时信息、聊天室、电话、视频电话和视频会议来进行沟通和交流。

共享硬件:在网络环境下，每台计算机可以获取和使用网络硬件资源，例如打印一份文件可以通过网络打印机。

共享文件：数据和信息: 在网络环境中，授权用户可以访问存储在其他计算机上的网络数据和信息。

提供进入数据和信息共享存储设备的能力是许多网络的一个重要特征。

共享软件:用户可以连接到远程计算机的网络应用程序。

信息保存。

安全保证。

三．网络分类下面的列表显示用于网络分类：3．1连接方式计算机网络可以据硬件和软件技术分为用来连接个人设备的网络，如：光纤、局域网、无线局域网、家用网络设备、电缆通讯和G.hn（有线家庭网络标准）等等。

以太网的定义，它是由IEEE 802标准，并利用各种媒介，使设备之间进行通信的网络。

经常部署的设备包括网络集线器、交换机、网桥、路由器。

无线局域网技术是使用无线设备进行连接的。

网络设计与规划中英文对照外文翻译文献现代企业面临的挑战尽管企业进行了大量的IT资本投资，但许多公司发现，大部分关键网络资源和信息资产仍处于自由状态。

实际上，许多"孤立"的应用程序和数据库无法相互通信，这是一种常见的商业现象。

2.The n: Service-Oriented ork Architecture (SONA)___'___(SONA) ___ is based on a service-oriented architecture (SOA) approach。

___.解决方案：面向服务的网络架构（SONA）___的面向服务的网络架构（SONA）是一个全面的框架，帮助企业克服网络设计和规划的挑战。

SONA基于面向服务的架构（SOA）方法，使企业能够将不同的应用程序和数据库集成到一个统一的网络中。

3.___ SONABy implementing SONA。

businesses ___ of benefits。

___。

increased security。

___。

___ security features。

such as identity and access management。

to protect critical n assets。

Finally。

___.SONA的好处通过实施SONA，企业可以获得许多好处，包括提高网络敏捷性、增加安全性和降低成本。

SONA通过提供灵活和可扩展的网络架构，使企业能够快速适应不断变化的业务需求。

此外，SONA提供了增强的安全功能，如身份和访问管理，以保护关键信息资产。

最后，SONA通过简化网络管理和减少对额外硬件和软件的需求，帮助企业降低成本。

4.nIn today's fast-paced business environment。

it is essential for ___。

secure。

and cost-effective ork architecture.结论在今天快节奏的商业环境中，企业必须拥有一个可以快速适应不断变化的业务需求的网络基础设施。

论文外文文献翻译以下是一篇700字左右的论文外文文献翻译：原文题目：The Role of Artificial Intelligence in Medical Diagnostics: A Review原文摘要：In recent years, there has been a growing interest in the use of artificial intelligence (AI) in the field of medical diagnostics. AI has the potential to improve the accuracy and efficiency of medical diagnoses, and can assist clinicians in making treatment decisions. This review aims to examine the current state of AI in medical diagnostics, and discuss its advantages and limitations. Several AI techniques, including machine learning, deep learning, and natural language processing, are discussed. The review also examines the ethical and legal considerations associated with the use of AI in medical diagnostics. Overall, AI has shown great promise in improving medical diagnostics, but further research is needed to fully understand its potential benefits and limitations.AI在医学诊断中发挥的作用：一项综述近年来，人工智能（AI）在医学诊断领域的应用引起了越来越多的关注。

本科毕业设计(论文) 外文翻译（附外文原文）系 ( 院 )：信息科学与工程学院课题名称：学生信息管理系统专业(方向)：计算机科学与技术（应用）7.1 Enter ActionMappingsThe Model 2 architecture (see chapter 1) encourages us to use servlets and Java- Server Pages in the same application. Under Model 2, we start by calling a servlet.The servlet handles the business logic and directs control to the appropriate pageto complete the response.The web application deployment descriptor (web.xml) lets us map a URL patternto a servlet. This can be a general pattern, like *.do, or a specific path, like saveRecord.do.Some applications implement Model 2 by mapping a servlet to each business operation. This approach works, but many applications involve dozens or hundredsof business operations. Since servlets are multithreaded, instantiating so manyservlets is not the best use of server resources. Servlets are designed to handle anynumber of parallel requests. There is no performance benefit in simply creatingmore and more servlets.The servlet’s primary job is to interact with the container and HTTP. Handlinga business operation is something that a servlet could delegate to another component. Struts does this by having the ActionServlet delegate the business operationto an object. Using a servlet to receive a request and route it to a handler is knownas the Front Controller pattern [Go3].Of course, simply delegating the business operation to another componentdoes not solve the problem of mapping URIs [W3C, URI] to business operations.Our only way of communicating with a web browser is through HTTP requests and URIs. Arranging for a URI to trigger a business operation is an essential part of developing a web application.Meanwhile, in practice many business operations are handled in similar ways.Since Java is multithreaded, we could get better use of our server resources if wecould use the same Action object to handle similar operations. But for this towork, we might need to pass the object a set of configuration parameters to usewith each operation.So what’s the bottom line? To implement Model 2 in an efficient and flexibleway, we need to:Enter ActionMappings 195♉ Route requests for our business operations to a single servlet♉ Determine which business operation is related to the request♉ Load a multithreaded helper object to handle the business operation♉ Pass the helper object the specifics of each request along with any configuration detail used by this operationThis is where ActionMappings come in.7.1.1 The ActionMapping beanAn ActionMapping (org.apache.struts.action.ActionMapping) describes howthe framework handles each discrete business operation (or action). In Struts,each ActionMapping is associated with a specific URI through its path property. When a request comes in, the ActionServlet uses the path property to select the corresponding ActionMapping. The set of ActionMapping objects is kept in an ActionMappings collection (org.apache.struts.action.ActionMappings). Originally, the ActionMapping object was used to extend the Action objectrather than the Action class. When used with an Action, a mapping gives a specific Action object additional responsibilities and new functionality. So, it was essentiallyan Action decorator [Go4]. Along the way, the ActionMapping evolved into anobject in its own right and can be used with or without an Action.DEFINITION The intent of the decorator pattern is to attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassingfor extending functionality [Go4].The ActionMappings are usually created through the Struts configuration file.For more about this file, see chapter 4.7.1.2 The ActionMappings catalogThe ActionMappings catalog the business logic available to a Struts application.When a request comes in, the servlet finds its entry in the ActionMappings catalogand pulls the corresponding bean.The ActionServlet uses the ActionMapping bean to decide what to do next. Itmay need to forward control off to another resource. Or it may need to populateand validate an ActionForm bean. At some point, it may have to pass control to an Action object, and when the Action returns, it may have to look up an Action-Forward associated with this mapping.196 CHAPTER 7Designing with ActionMappingsThe ActionMapping works like a routing slip for the servlet. Depending onhow the mapping is filled out, the request could go just about anywhere.The ActionMappings represent the core design of a Struts application. If youwant to figure out how a Struts application works, start with the ActionMappings. Ifyou want to figure out how to write a new Struts application, start with the Action- Mappings. The mappings are at the absolute center of every Struts application.In this chapter, we take a close look at the ActionMapping properties andexplore how they help you design the flow of a Struts application.1.0 vs 1.1 In Struts 1.1, ActionMapping subclasses ActionConfig (org.apache. struts.config.ActionConfig) and adds API methods required forbackward compatibility. ActionMapping is not deprecated, and how thehierarchy will be handled in future releases has not been determined.For now, we refer to the ActionMapping class, but you should note thatin Struts 1.1 all of the action properties are actually defined by the ActionConfigsuper class. The ActionMapping class otherwise works thesame way in both versions.7.2 ActionMapping propertiesTable 7.1 describes the base ActionMapping properties. As with other configuration components, developers may extend ActionMapping to provide additionalproperties.Table 7.1 The base ActionMapping propertiesProperty Descriptionpath The URI path from the request used to select this mapping. (API command) forward The context-relative path of the resource that should serve this request via a forward.Exactly one of the forward, include, or type properties must be specified.orinclude The context-relative path of the resource that should serve this request via aninclude. Exactly one of the forward, include, or type properties must be specified.ortype Optionally specifies a subclass oforg.apache.struts.action.ActionMappingthat should be used when instantiating this mapping.className The fully qualified name of the Action class used by this mapping. SinceStruts 1.1ActionMapping properties 197In the sections that follow, we take a look at each of these properties.7.2.1 The path propertyThe ActionMapping URI, or path, will look to the user like just another file onthe web server. But it does not represent a file. It is a virtual reference to our ActionMapping.Because it is exposed to other systems, the path is not really a logical name, likethose we use with ActionForward. The path can include slashes and an extension—as if it referred to a file system—but they are all just part of a single name.The ActionMappings themselves are a “flat” namespace with no type of internalhierarchy whatsoever. They just happen to use the same characters that we areused to seeing in hierarchical file systems.name The name of the form bean, if any, associated with this action. This is not the classname. It is the logical name used in the form bean configuration.roles The list of security roles that may access this mapping.scope The identifier of the scope (request or session) within which the form bean, if any,associated with this mapping will be created.validate Set to true if the validate method of the form bean (if any) associated with thismapping should be called.input Context-relative path of the input form to which control should be returned ifa validationerror is encountered. This can be any URI: HTML, JSP, VM, or another Action- Mapping.parameter General-purpose configuration parameter that can be used to pass extra informationto the Action selected by this ActionMapping.attribute Name of the request-scope or session-scope attribute under which our form bean isaccessed, if it is other than the bean's specified name.prefix Prefix used to match request parameter names to form bean property names, if any.suffix Suffix used to match request parameter names when populating the properties ofour ActionForm bean, if any.unknown Can be set to true if this mapping should be configured as the default for this application(to handle all requests not handled by another mapping). Only one mappingcan be defined as the default unknown mapping within an application.forwards(s) Block of ActionForwards for this mapping to use, if any.exception(s) Block of ExceptionHandlers for this mapping to use, if any.Table 7.1 The base ActionMapping properties (continued)Property DescriptionSinceStruts 1.1SinceStruts 1.1198 CHAPTER 7Designing with ActionMappingsOf course, it can still be useful to treat your ActionMappings as if they werepart of a hierarchy and group related commands under the same "folder." Theonly restriction is that the names must match whatever pattern is used in the application’s deployment description (web.xml) for the ActionServlet. This is usuallyeither /do/* or *.do, but any similar pattern can be used.If you are working in a team environment, different team members can begiven different ActionMapping namespaces to use. Some people may be workingwith the /customer ActionMappings, others may be working with the /vendor ActionMappings. This may also relate to the Java package hierarchy the team isusing. Since the ActionMapping URIs are logical constructs, they can be organizedin any way that suits your project.With Struts 1.1, these types of namespaces can be promoted to applicationmodules. Each team can work independently on its own module, with its own setof configuration files and presentation pages. Configuring your application to use multiple modules is covered in chapter 4.DEFINITION The web runs on URIs, and most URIs map to physical files. If you want to change the resource, you change the corresponding file. Some URIs, likeStruts actions, are virtual references. They do not have a correspondingfile but are handled by a programming component. To change the resource,we change how the component is programmed. But since thepath is a URI and interacts with other systems outside our control, thepath is not a true logical reference—the name of an ActionForward, forinstance. We can change the name of an ActionForward without consultingother systems. It’s an internal, logical reference. If we change thepath to an ActionMapping, we might need to update other systems thatrefer to the ActionMapping through its public URI.7.2.2 The forward propertyWhen the forward property is specified, the servlet will not pass the request to an Action class but will make a call to RequestDispatcher.forward. Since the operationdoes not use an Action class, it can be used to integrate Struts with otherresources and to prototype systems. The forward, include, and type propertiesare mutually exclusive. (See chapter 6 for more information.)7.2.3 The include propertyWhen the include property is specified, the servlet will not pass the request to an Action class but will make a call to RequestDispatcher.include. The operationActionMapping properties 199does not use an Action class and can be used to integrate Struts with other components. The forward, include, and type properties are mutually exclusive. (Seechapter 6 for more information.)7.2.4 The type propertyMost mappings will specify an Action class type rather than a forward or include.An Action class may be used by more than one mapping. The mappings may specifyform beans, parameters, forwards, or exceptions. The forward, include, andtype properties are mutually exclusive.7.2.5 The className propertyWhen specified, className is the fully qualified Java classname of the ActionMapping subclass that should be used for this object. This allows you to use your own ActionMapping subclass with specialized methods and properties. See alsosection 7.4.7.2.6 The name propertyThis property specifies the logical name for the form bean, as given in the formbean segment of the Struts configuration file. By default, this is also the name tobe used when placing the form bean in the request or session context. Use theattribute property of this class to specify a different attribute key.7.2.7 The roles propertyThis property is a comma-delimited list of the security role names that are allowed access to this ActionMapping object. By default, the same system that is used with standard container-based security is applied to the list of roles given here. Thismeans you can use action-based security in lieu of specifying URL patterns in the deployment descriptor, or you can use both together.The security check is handled by the processRoles method of the Request- Processor (org.apache.struts.action.RequestProcessor). By subclassing RequestProcessor, you can also use the roles property with application-based security. See chapter 9 for more about subclassing RequestProcessor.7.2.8 The scope propertyThe ActionForm bean can be stored in the current request or in the session scope (where it will be available to additional requests). While most developers userequest scope for the ActionForm, the framework default is session scope. Tomake request the default, see section 7.4.SinceStruts 1.1SinceStruts 1.1200 CHAPTER 7Designing with ActionMappings7.2.9 The validate propertyAn important step in the lifecycle of an ActionForm is to validate its data before offering it to the business layer. When the validate property for a mapping is true, the ActionServlet will call the ActionForm’s validate method. If validate returns false, the request is forwarded to the resource given by the input property.Often, developers will create a pair of mappings for each data entry form. Onemapping will have validate set to false, so you can create an empty form. Theother has validate set to true and is used to submit the completed form.NOTE Whether or not the ActionForm validate method is called does not relateto the ActionServlet’s validating property. That switch controlshow the Struts configuration file is processed.7.2.10 The input propertyWhen validate is set to true, it is important that a valid path for input be provided. This is where control will pass should the ActionForm validate methodreturn false. Often, this is the address for a presentation page. Sometimes it willbe another Action path (with validate set to false) that is required to generatedata objects needed by the page.NOTE The input path often leads back to the page that submitted the request.While it seems natural for the framework to return the request to whereit originated, this is not a simple task in a web application. A request is oftenpassed from component to component before a response is sent backto the browser. The browser only knows the path it used to retrieve theinput page, which may or may not also be the correct path to use for theinput property. While it may be possible to try and generate a default inputpage based on the HTTP referrer attribute, the Struts designersdeemed that approach unreliable.inputForwardIn Struts 1.0, the ActionMapping input property is always a literal URI. InStruts 1.1, it may optionally be the name of an ActionForward instead. The ActionForward is retrieved and its path property is used as the input property.This can be a global or local ActionForward.To use ActionForwards here instead of literal paths, set the inputForwardattribute on the <controller> element for this module to true:SinceStruts 1.1ActionMapping properties 201<controller inputForward="true">For more about configuring Struts, see chapter 4. For more about ActionForwards,see chapter 6.7.2.11 The parameter propertyThe generic parameter property allows Actions to be configured at runtime. Severalof the standard Struts Actions make use of this property, and the standardScaffold Actions often use it, too. The parameter property may contain a URI, the name of a method, the name of a class, or any other bit of information an Actionmay need at runtime. This flexibility allows some Actions to do double and tripleduty, slashing the number of distinct Action classes an application needs on hand.Within an Action class, the parameter property is retrieved from the mappingpassed to perform:parameter = mapping.getParameter();Multiple parametersWhile multiple parameters are not supported by the standard ActionMappingsclass, there are some easy ways to implement this, including using HttpUtils, a StringTokenizer, or a Properties file (java.util.Properties).HttpUtils. Although deprecated as of the Servlet API 2.3 specification, theHttpUtils package (javax.servlet.http.HttpUtils) provides a static method that parses any string as if it were a query string and returns a Hashtable(java.util.Hashtable):Hashtable parameters = parseQueryString(parameter);The parameter property for your mapping then becomes just another query string, because you might use it elsewhere in the Struts configuration. stringTokenizer. Another simple approach is to delimit the parameters using the token of your choice—such as a comma, colon, or semicolon—and use the StringTokenizer to read them back:StringTokenizer incoming =new StringTokenizer(mapping.getParameter(),";");int i = 0;String[] parameters = new String[incoming.countTokens()]; while (incoming.hasMoreTokens()) {parameters[i++] = incoming.nextToken().trim();}202 CHAPTER 7Designing with ActionMappingsProperties file. While slightly more complicated than the others, another popular approach to providing multiple parameters to an ActionMapping is with a standard Properties files (java.util.Properties). Depending on your needs, the Properties file could be stored in an absolute location in your file system or anywhere on your application’s CLASSPATH.The Commons Scaffold package [ASF, Commons] provides a ResourceUtils package (mons.scaffold.util.ResourceUtils) with methods forloading a Properties file from an absolute location or from your application’s CLASSPATH.7.2.12 The attribute propertyFrom time to time, you may need to store two copies of the same ActionForm inthe same context at the same time. This most often happens when ActionFormsare being stored in the session context as part of a workflow. To keep their names from conflicting, you can use the attribute property to give one ActionForm bean a different name.An alternative approach is to define another ActionForm bean in the configuration, using the same type but under a different name.7.2.13 The prefix and suffix propertiesLike attribute, the prefix and suffix properties can be used to help avoid naming conflicts in your application. When specified, these switches enable aprefix or suffix for the property name, forming an alias when it is populatedfrom the request.If the prefix this was specified, thenthisName=McClanahanbecomes equivalent toname=McClanahanfor the purpose of populating the ActionForm. Either or both parameters would call getName("McClanahan");This does not affect how the properties are written by the tag extensions. It affects how the autopopulation mechanism perceives them in the request.Nested components 2037.2.14 The unknown ActionMappingWhile surfing the Web, most of us have encountered the dreaded 404— page not found message. Most web servers provide some special features for processing requests for unknown pages, so webmasters can steer users in the right direction. Struts offers a similar service for ActionMapping 404s—the unknown ActionMapping. In the Struts configuration file, you can specify one ActionMapping toreceive any requests for an ActionMapping that would not otherwise be matched:<actionname="/debug"forward="/pages/debug.jsp"/>When this option is not set, a request for an ActionMapping that cannot bematched throws400 Invalid path /notHere was requestedNote that by a request for an ActionMapping, we mean a URI that matches the prefix or suffix specified for the servlet (usually /do/* or *.do). Requests for other URI patterns, good or bad, will be handled by other servlets or by the container:/do/notHere (goes to the unknown ActionMapping)/notHere.txt (goes to the container)7.3 Nested componentsThe ActionMapping properties are helpful when it comes to getting an Action torun a business operation. But they tell only part of the story. There is still much todo when the Action returns.An Action may have more than one outcome. We may need to register several ActionForwards so that the Action can take its pick.7.3.1 Local forwardsIn the normal course, an ActionMapping is used to select an Action object to handle the request. The Action returns an ActionForward that indicates which pageshould complete the response.The reason we use ActionForwards is that, in practice, presentation pages areeither often reused or often changed, or both. In either case, it is good practice to encapsulate the page’s location behind a logical name, like “success” or “failure.”The ActionForward object lets us assign a logical name to any given URI.204 CHAPTER 7Designing with ActionMappingsOf course, logical concepts like success or failure are often relative. What represents success to one Action may represent failure to another. Each Action-Mapping can have its own set of local ActionForwards. When the Action asks for a forward (by name), the local set is checked before trying the global forwards. See chapter 6 for more about ActionForwards.Local forwards are usually specified in the Struts configuration file. See chapter4 for details.7.3.2 Local exceptionsMost often, an application’s exception handlers (org.apache.struts.action. ExceptionHandler) can be declared globally. However, if a given ActionMapping needs to handle an exception differently, it can have its own set of local exception handlers that are checked before the global set.Local exceptions are usually specified in the Struts configuration file. Seechapter 4 for details.7.4 Rolling your own ActionMappingWhile ActionMapping provides an impressive array of properties, developers may also provide their own subclass with additional properties or methods. InStruts 1.0, this is configured in the deployment descriptor (web.xml) for the ActionServlet:<init-param><param-name>mapping</param-name><param-value>app.MyActionMapping</param-value></init-param>In Struts 1.1, this is configured in the Struts configuration file as an attribute to the <action-mappings> element:<action-mappings type="app.MyActionMapping">Individual mappings may also be set to use another type through the className attribute:<action className="app.MyActionMapping">For more about configuring Struts, see chapter 4.SinceStruts 1.1Summary 205The framework provides two base ActionMapping classes, shown in table 7.2. They can be selected as the default or used as a base for your own subclasses.The framework default is SessionActionMapping, so scope defaults to session. Subclasses that provide new properties may set them in the Struts configuration using a standard mechanism:<set-property property="myProperty" value="myValue" /> Using this standard mechanism helps developers avoid subclassing the Action- Servlet just to recognize the new properties when it digests the configuration file. This is actually a feature of the Digester that Struts simply inherits.7.5 SummarySun’s Model 2 architecture teaches that servlets and JavaServer Pages should be used together in the same application. The servlets can handle flow control and data acquisition, and the JavaServer Pages can handle the HTML.Struts takes this one step further and delegates much of the flow control anddata acquisition to Action objects. The application then needs only a single servletto act as a traffic cop. All the real work is parceled out to the Actions and theStruts configuration objects.Like servlets, Actions are efficient, multithreaded singletons. A single Actionobject can be handling any number of requests at the same time, optimizing your server’s resources.To get the most use out of your Actions, the ActionMapping object is used as a decorator for the Action object. It gives the Action a URI, or several URIs, and away to pass different configuration settings to an Action depending on which URIis called.In this chapter, we took a close look at the ActionMapping properties andexplained each property’s role in the scheme of things. We also looked at extendingthe standard ActionMapping object with custom properties—just in case yourscheme needs even more things.Table 7.2 The default ActionMapping classesActionMapping Descriptionorg.apache.struts.action.SessionActionMapping Defaults the scope property to sessionorg.apache.struts.action.RequestActionMapping Defaults the scope property to request206 CHAPTER 7Designing with ActionMappingsIn chapter 8, the real fun begins. The configuration objects covered so far aremainly a support system. They help the controller match an incoming requestwith a server-side operation. Now that we have the supporting players, let’s meet the Struts diva: the Action object.7.1 进入ActionMappingModel 2 架构(第1章)鼓励在同一个应用中使用servlet和JSP页面。

毕业设计外文文献翻译专业交通运输姓名张有节同组成员赖思琪杨鹏指导老师刘习华Campus Network planning and Construction At present, China's rapid development of the cause of the campus network, to early 2003, almost all colleges have set up their own campus network, and carry out a variety of its services and applications. Campus Network build a rich learning resources to enhance the efficiency of education. But as the number of users increased dramatically increased and the pattern of operations, campus network security is increasingly conspicuous, and the ever threat to the healthy development of the campus network, as an education development of the information industry should not be neglected problem. This paper focuses on the campus network design and the process of building the campus network established the goal of building, campus network technology programme design, information resources construction, application software development, network management and security, the five key issues. The campus network is the infrastructure of importance of school, taking the school teaching, research, managing and outward communicate many roles of etc..The safe condition of the campus net affects the teaching activity of the school directly.Set up in the network of initial stage, the safe problem may still be not outstanding, but along with applied thorough, various data of the campus net would nasty play increment, the safe problem beginning of various each kind perplexes us.The Internet flies to develop soon, to the campus network the teachers and the students' life and studies have already produced the profound influence, the network have already not have no place in our life at. But at enjoy the convenience that high technology bring at the same time, we need to be awake of know, the safe problem of network also become the network application more and more increasingly and seriously huge bar, the situation that the campus network safety hazes already arrived and must unify the management and resolve thoroughly, only good resolve the safe problem of network, the application of the campus network then can be healthy, high speed of development. We should consider the comprehensive usage fire wall and encrypt several measures, such as technique and the anti-virus software...etc. completely, work in coordination, strengthening the management, looking for thebalance point of insure the network safety and the network efficiency from it, the safety of the comprehensive exaltation campus network, thus build up rise a set of real in keeping with safe system of the calculator network of the school.The time today's knowledge-based economy and information technology have the development and popularization of Internet in the world have decided the time the network will become the main tool for information. With the development of computer network technology, network has become an important platform for the exchange of information. Internet-based e-learning with time-sensitive, shared, interactive and many of the characteristics of the individual, so it has a traditional teaching model of unmatched advantages. It created a new teaching model, breaking the traditional teaching model at the time and space limitations, the use of advanced teaching methods and teaching methods, greatly improve the teaching efficiency and teaching effectiveness, teaching and learning activities to enable a new level. Do a good job in the design of the campus network, are among the schools, both internal and external communication between the key and convenient.21st century the size of the campus network and application level are reflected in schools and science teaching and learning environment an important component of the force, so we should make use of existing campus conditions, design a secure, unified campus network.Large Campus Network DesignBusinesses operating large campus networks are increasingly looking for infrastructure upgrades to:(1) Handle high bandwidth applications such as voice, video, and IP multicast Improve backbone capacity for shared Ethernet or FDDI campus backbones(2) Support applications based on Novell IPX, DECNET, AppleTalk, and SNA(3) Offer high availability, performance, & manageability for your company's intranet.Use Layer 2, Layer 3, or ATM backbone solutions to expand your large campus network. In typical designs, the buildings or different parts of the campus connect together across a high performance, switched backbone. Network redundancy andhigh availability is provided at each layer. A high capacity, centralized server farm provides resources to the campus, and when combined with Cisco IOS, network management strategies support QoS, security, troubleshooting, and other common management features from end to end.Medium Campus Network Design A medium campus consists of one large building or several buildings. Networking for a medium campus is designed for high availability, performance, and manageability. This is also called a 'collapsed backbone' design for medium campus networks. Additional requirements of these designs typically include:(1) High performance and availability for bandwidth applications such as voice, video, and IP multicast(2) Shared Ethernet or FDDI building backbone which is running out of capacity(3)Support for applications based on Novell IPX, DECNET, AppleTalk, and SNA Based on the Cisco A VVID architecture, these intelligent network platforms and products provide the basis for a complete network solution.Small campus networks DesignIn most cases, network redundancy is not the top priority, but cost effectiveness is. Additional requirements of these designs typically include:(1) High performance and availability for bandwidth applications such as voice, video, and IP multicast(2) Shared Ethernet or FDDI building backbone which is running out of capacity(3) Support for applications based on Novell IPX, DECNET, AppleTalk, and SNA校园网的规划与构建目前，我国校园网事业飞速发展，至2003年初，几乎所有的大中专院校都建立了自己的校园网，并在其上开展了多种服务和应用。

南京理工大学毕业设计(论文)外文资料翻译学院（系）：电子工程与光电技术学院专业：电子科学与技术姓名：高航学号： 0704240113外文出处: ZTE COMMUNICATIONS 2009, 7 (4)(用外文写)附件： 1.外文资料译文；2.外文原文。

附件1：外文资料翻译译文一种用于移动终端视频图像色彩增强的实时方法作者:金辉摘要:智能手机在可视通话的过程中，由于摄像头和液晶显示器等硬件性能上的一些局限性，使其在某些条件或环境下采集的视频图像光线昏暗，或者视频图像表现的颜色不够鲜艳、靓丽甚至发生偏色。

文章提出一种在硬件具体的特性和性能参数下，对视频图像的明亮可视度以及颜色进行增强的实时方法。

在智能手机上的应用和验证显示，该方法不需要额外的芯片就能够改善移动可视电话中视频图像的主观视觉效果，提高亮度、清晰度，并使颜色的表现更丰富、艳丽。

关键字:移动可视终端；色彩增强；明亮可视度增强目前，对于移动智能手机来讲，传统的话音业务已经无法满足广大消费者个性化、差异化需求，所以各项增值业务被视为新的黄金增长点。

移动可视电话作为3G的标志性核心业务，逐渐受到各方的广泛关注。

视频通话过程中视频图像的质量直接影响到业务的普及与扩展，将来也会在市场上掀起一场完美的视频应用风暴。

在对TD-SCDMA的3G终端性能测试中，视频通话是测试的关键环节之一。

大部分3G手机终端视频通话质量都有不尽如人意的地方，如延迟、拖影、马赛克等现象。

这些主要是由于网络原因造成的视频质量问题。

除此之外还有视频图像本身的质量问题，如在暗的环境下，采集的图像昏暗不清，打可视电话时色彩不够丰富亮丽等。

这些问题已受到各通信设备供应商和技术研究者的关注。

在视频处理领域中，主观视觉质量的改善是视频增强的一个主要内容。

在消费电子领域中，视频增强技术令产品对于消费者更具有吸引力和魅力。

如今许多厂商都需要拥有自主的色彩增强技术，“颜色再现增强技术”已成为一个重要的话题。

计算机外⽂翻译（完整）毕业设计(论⽂)外⽂资料翻译专业：计算机科学与技术姓名：王成明学号：06120186外⽂出处：The History of the Internet附件： 1.外⽂原⽂ 2.外⽂资料翻译译⽂；附件1：外⽂原⽂The History of the InternetThe Beginning - ARPAnetThe Internet started as a project by the US government. The object of the project was to create a means of communications between long distance points, in the event of a nation wide emergency or, more specifically, nuclear war. The project was called ARPAnet, and it is what the Internet started as. Funded specifically for military communication, the engineers responsible for ARPANet had no idea of the possibilities of an "Internet."By definition, an 'Internet' is four or more computers connected by a network.ARPAnet achieved its network by using a protocol called TCP/IP. The basics around this protocol was that if information sent over a network failed to get through on one route, it would find another route to work with, as well as establishing a means for one computer to "talk" to another computer, regardless of whether it was a PC or a Macintosh.By the 80's ARPAnet, just years away from becoming the more well known Internet, had 200 computers. The Defense Department, satisfied with ARPAnets results, decided to fully adopt it into service, and connected many military computers and resources into the network. ARPAnet then had 562 computers on its network. By the year 1984, it had over 1000 computers on its network.In 1986 ARPAnet (supposedly) shut down, but only the organization shut down, and the existing networks still existed between the more than 1000 computers. It shut down due to a failied link up with NSF, who wanted to connect its 5 countywide super computers into ARPAnet.With the funding of NSF, new high speed lines were successfully installed at line speeds of 56k (a normal modem nowadays) through telephone lines in 1988. By that time, there were 28,174 computers on the (by then decided) Internet. In 1989 there were 80,000 computers on it. By 1989, there were290,000.Another network was built to support the incredible number of people joining. It was constructed in 1992.Today - The InternetToday, the Internet has become one of the most important technological advancements in the history of humanity. Everyone wants to get 'on line' to experience the wealth of information of the Internet. Millions of people now use the Internet, and it's predicted that by the year 2003 every single person on the planet will have Internet access. The Internet has truly become a way of life in our time and era, and is evolving so quickly its hard to determine where it will go next, as computer and network technology improve every day.HOW IT WORKS:It's a standard thing. People using the Internet. Shopping, playing games,conversing in virtual Internet environments.The Internet is not a 'thing' itself. The Internet cannot just "crash." It functions the same way as the telephone system, only there is no Internet company that runs the Internet.The Internet is a collection of millioins of computers that are all connected to each other, or have the means to connect to each other. The Internet is just like an office network, only it has millions of computers connected to it.The main thing about how the Internet works is communication. How does a computer in Houston know how to access data on a computer in Tokyo to view a webpage?Internet communication, communication among computers connected to the Internet, is based on a language. This language is called TCP/IP. TCP/IP establishes a language for a computer to access and transmit data over the Internet system.But TCP/IP assumes that there is a physical connecetion between onecomputer and another. This is not usually the case. There would have to be a network wire that went to every computer connected to the Internet, but that would make the Internet impossible to access.The physical connection that is requireed is established by way of modems,phonelines, and other modem cable connections (like cable modems or DSL). Modems on computers read and transmit data over established lines,which could be phonelines or data lines. The actual hard core connections are established among computers called routers.A router is a computer that serves as a traffic controller for information.To explain this better, let's look at how a standard computer might viewa webpage.1. The user's computer dials into an Internet Service Provider (ISP). The ISP might in turn be connected to another ISP, or a straight connection into the Internet backbone.2. The user launches a web browser like Netscape or Internet Explorer and types in an internet location to go to.3. Here's where the tricky part comes in. First, the computer sends data about it's data request to a router. A router is a very high speed powerful computer running special software. The collection of routers in the world make what is called a "backbone," on which all the data on the Internet is transferred. The backbone presently operates at a speed of several gigabytes per-second. Such a speed compared to a normal modem is like comparing the heat of the sun to the heat of an ice-cube.Routers handle data that is going back and forth. A router puts small chunks of data into packages called packets, which function similarly to envelopes. So, when the request for the webpage goes through, it uses TCP/IP protocols to tell the router what to do with the data, where it's going, and overall where the user wants to go.4. The router sends these packets to other routers, eventually leadingto the target computer. It's like whisper down the lane (only the information remains intact).5. When the information reaches the target web server, the webserver then begins to send the web page back. A webserver is the computer where the webpage is stored that is running a program that handles requests for the webpage and sends the webpage to whoever wants to see it.6. The webpage is put in packets, sent through routers, and arrive at the users computer where the user can view the webpage once it is assembled.The packets which contain the data also contain special information that lets routers and other computers know how to reassemble the data in the right order.With millions of web pages, and millions of users, using the Internet is not always easy for a beginning user, especially for someone who is not entirely comfortale with using computers. Below you can find tips tricks and help on how to use main services of the Internet.Before you access webpages, you must have a web browser to actually be able to view the webpages. Most Internet Access Providers provide you with a web browser in the software they usually give to customers; you. The fact that you are viewing this page means that you have a web browser. The top two use browsers are Netscape Communicator and Microsoft Internet Explorer. Netscape can be found at /doc/bedc387343323968011c9268.html and MSIE can be found at /doc/bedc387343323968011c9268.html /ie.The fact that you're reading this right now means that you have a web browser.Next you must be familiar with actually using webpages. A webpage is a collection of hyperlinks, images, text, forms, menus, and multimedia. To "navigate" a webpage, simply click the links it provides or follow it's own instructions (like if it has a form you need to use, it will probably instruct you how to use it). Basically, everything about a webpage is made to be self-explanetory. That is the nature of a webpage, to be easily navigatable."Oh no! a 404 error! 'Cannot find web page?'" is a common remark made by new web-users.Sometimes websites have errors. But an error on a website is not the user's fault, of course.A 404 error means that the page you tried to go to does not exist. This could be because the site is still being constructed and the page hasn't been created yet, or because the site author made a typo in the page. There's nothing much to do about a 404 error except for e-mailing the site administrator (of the page you wanted to go to) an telling him/her about the error.A Javascript error is the result of a programming error in the Javascript code of a website. Not all websites utilize Javascript, but many do. Javascript is different from Java, and most browsers now support Javascript. If you are using an old version of a web browser (Netscape 3.0 for example), you might get Javascript errors because sites utilize Javascript versions that your browser does not support. So, you can try getting a newer version of your web browser.E-mail stands for Electronic Mail, and that's what it is. E-mail enables people to send letters, and even files and pictures to each other.To use e-mail, you must have an e-mail client, which is just like a personal post office, since it retrieves and stores e-mail. Secondly, you must have an e-mail account. Most Internet Service Providers provide free e-mail account(s) for free. Some services offer free e-mail, like Hotmail, and Geocities.After configuring your e-mail client with your POP3 and SMTP server address (your e-mail provider will give you that information), you are ready to receive mail.An attachment is a file sent in a letter. If someone sends you an attachment and you don't know who it is, don't run the file, ever. It could be a virus or some other kind of nasty programs. You can't get a virus justby reading e-mail, you'll have to physically execute some form of program for a virus to strike.A signature is a feature of many e-mail programs. A signature is added to the end of every e-mail you send out. You can put a text graphic, your business information, anything you want.Imagine that a computer on the Internet is an island in the sea. The sea is filled with millions of islands. This is the Internet. Imagine an island communicates with other island by sending ships to other islands and receiving ships. The island has ports to accept and send out ships.A computer on the Internet has access nodes called ports. A port is just a symbolic object that allows the computer to operate on a network (or the Internet). This method is similar to the island/ocean symbolism above.Telnet refers to accessing ports on a server directly with a text connection. Almost every kind of Internet function, like accessing web pages,"chatting," and e-mailing is done over a Telnet connection.Telnetting requires a Telnet client. A telnet program comes with the Windows system, so Windows users can access telnet by typing in "telnet" (without the "'s) in the run dialog. Linux has it built into the command line; telnet. A popular telnet program for Macintosh is NCSA telnet.Any server software (web page daemon, chat daemon) can be accessed via telnet, although they are not usually meant to be accessed in such a manner. For instance, it is possible to connect directly to a mail server and check your mail by interfacing with the e-mail server software, but it's easier to use an e-mail client (of course).There are millions of WebPages that come from all over the world, yet how will you know what the address of a page you want is?Search engines save the day. A search engine is a very large website that allows you to search it's own database of websites. For instance, if you wanted to find a website on dogs, you'd search for "dog" or "dogs" or "dog information." Here are a few search-engines.1. Altavista (/doc/bedc387343323968011c9268.html ) - Web spider & Indexed2. Yahoo (/doc/bedc387343323968011c9268.html ) - Web spider & Indexed Collection3. Excite (/doc/bedc387343323968011c9268.html ) - Web spider & Indexed4. Lycos (/doc/bedc387343323968011c9268.html ) - Web spider & Indexed5. Metasearch (/doc/bedc387343323968011c9268.html ) - Multiple searchA web spider is a program used by search engines that goes from page to page, following any link it can possibly find. This means that a search engine can literally map out as much of the Internet as it's own time and speed allows for.An indexed collection uses hand-added links. For instance, on Yahoo's site. You can click on Computers & the Internet. Then you can click on Hardware. Then you can click on Modems, etc., and along the way through sections, there are sites available which relate to what section you're in.Metasearch searches many search engines at the same time, finding the top choices from about 10 search engines, making searching a lot more effective.Once you are able to use search engines, you can effectively find the pages you want.With the arrival of networking and multi user systems, security has always been on the mind of system developers and system operators. Since the dawn of AT&T and its phone network, hackers have been known by many, hackers who find ways all the time of breaking into systems. It used to not be that big of a problem, since networking was limited to big corporate companies or government computers who could afford the necessary computer security.The biggest problem now-a-days is personal information. Why should you be careful while making purchases via a website? Let's look at how the internet works, quickly.The user is transferring credit card information to a webpage. Looks safe, right? Not necessarily. As the user submits the information, it is being streamed through a series of computers that make up the Internet backbone.The information is in little chunks, in packages called packets. Here's the problem: While the information is being transferred through this big backbone, what is preventing a "hacker" from intercepting this data stream at one of the backbone points?Big-brother is not watching you if you access a web site, but users should be aware of potential threats while transmitting private information. There are methods of enforcing security, like password protection, an most importantly, encryption.Encryption means scrambling data into a code that can only be unscrambled on the "other end." Browser's like Netscape Communicator and Internet Explorer feature encryption support for making on-line transfers. Some encryptions work better than others. The most advanced encryption system is called DES (Data Encryption Standard), and it was adopted by the US Defense Department because it was deemed so difficult to 'crack' that they considered it a security risk if it would fall into another countries hands.A DES uses a single key of information to unlock an entire document. The problem is, there are 75 trillion possible keys to use, so it is a highly difficult system to break. One document was cracked and decoded, but it was a combined effort of14,000 computers networked over the Internet that took a while to do it, so most hackers don't have that many resources available.附件2：外⽂资料翻译译⽂Internet的历史起源——ARPAnetInternet是被美国政府作为⼀项⼯程进⾏开发的。

附件1（毕业设计一）材料科学与工程学院毕业实习环节外文翻译要求一、翻译论文的选择：1、与自己毕业设计相关的外文参考文献2、该译文可以作为设计论文中文献综述中的部分内容；3、原则上选取的英语原文不超过5页。

二、译文结构内容1、作者，英文原文题目，期刊名称，卷期号，年份，起止页码，2、文章题目，作者（保持英文，不需翻译），作者单位（英文不变）3、摘要，关键词4、正文部分：引言，试验过程，结果与讨论，结论，参考文献（保持原文状态）5、译文中的图标需要翻译，图可以复印后粘贴或扫描插入三、译文和原文统一装订在一起，独立与毕业论文一起上交四、几点附属说明1 文章所在期刊的期刊名及相关信息不要翻译。

2 文章的作者，作者的单位，地址，下注的通讯作者的情况，参考文献不要翻译。

3文章的题目，摘要，关键词，及正文都要按照原文的顺序来翻译。

4文章中图表翻译示例如下：此为翻译前的表格：此为翻译后的表格：表1 微波和常规方法加工的粉体金属样品的性能Table 1 Properties of microwave and conventionally processedpowdered metal samplesMW 代表微波烧结；conv代表常规方法。

大部分微波烧结的样品的断裂模量比常规方法烧结的要高。

许多微波烧结的样品的密度也是高于常规方法烧成的样品。

MW, microwave processed; conv., conventionally processed. Themodulus of rupture(MOR) of most microwave-processed samples ishigher than that of the conventional samples. The densities of manymicrowave-processed samples are also higher than those ofconventional samples.即表头和注释中英文都要。

网络安全与防火墙技术外文翻译文献(文档含中英文对照即英文原文和中文翻译)原文：Research of Network Security and Firewalls TechniquesAbstract:As the key facility that maintains the network security , firewalls take the purpose of establishing an obstacle between trust and trustless network, and put corresponding safety strategy into practice. In this paper , the computer network security and the techniques of firewalls were mainly discussed, the concept and classification of the firewalls were introduced. It also introduced three kind's of basic implement techniques of the firewalls: Packet filtering , Application Proxy and Monitor model indetail. Finally described the trend of development of the firewalls techniques in Internet briefly.Key words: network security, firewalls, Packet filtering, monitor1. IntroductionNow with the computer network and e-commerce used widely, network security has become an important problem that we must consider and resolve. More and more professions. enterprises and individuals surfer from the security problem in different degree. they are looking for the more reliable safety solution . In the defense system adopted by network security at present, the firewalls stand the very important position.As the key facility that maintains the network security. firewalls take the purpose of establishing an obstacle between trust and trustless network, and put corresponding safety strategy into practice.All the firewalls have the function to filter the IP address. This task checks the IP packet, makes the decision whether to release or to abandon it according to the source address and destination address of the IP. Shown in Fig.I, there is a firewall between two network sections, an UNIX computer is on one side of the firewall, and the other side is a PC client. While the PC client asks a telnet request for the UNIX computer, the client procedure of telnet in the PC produces a TCP packet and passes the packet to the local protocol stack to prepare to send. The protocol stack fills it in one IP packet. then, sends it to UNIX computer through the path defined by the TCP/IP stack of PC. The IP packet can't reach the UNIX computer until it passes the firewall between the PC and the UNIX computer.Fig. I Ip Address FilteringThe application firewall is a very efficient means of network security on Internet, it is installed between the trust and trustless network, can isolate the connection between the trust and trustless network, and doesn't hamper people's access to the trustless network at the same time. It can isolate the connection between the risk area (namely there may be a certain risk on Internet) and the safe area (LAN), and doesn't hamper people's access to the risk area at the same time. Firewall can monitor the traffic flowing in and out from the network to finish the task seemingly impossible;it only allows the safe and checked information to enter into, and meanwhile resists on the data that may bring about the threat to enterprise. As the fault and defect of the security problem become more and more general, the invasion to the network not only comes from the super attack means, but also may be from the lower-level mistakes or improper password selections on the configuration. So, the function of the firewalls is preventing the communication that not hoped and authorized passes in and out of the network protected. forcing the companies to strengthen their own network security policy. The general firewalls can achieve the following purposes: First, restraining others from entering the inside network, filtering the unsafe service and illegal user; Second, preventing the invaders from closing to your defense installation; Third,limiting the user to access the special site; Fourth,providing convenience for monitoring the Internet security.2. The classification and implement technology of firewallsAn integrated firewalls system usually consists of screening router and proxy server. The screening router is a multi-port IP router. it check the each coming IP packet according to the group regular to judge whether to transmit it. The screening router gets information from the packet. fot example the protocol number. the IP address and port number that receiving and sending massages. the flag of link even some other IP selections. filtering IP packet. The proxy server are server process in the firewall. it can replace the network user to finish the specific TCP/IP function. A proxy server is naturally a gateway of application layer. a gateway of two networks joined specific network application. Users contact with proxy server by one of the TCP/IP application such as Telnet or FTP. the proxy server ask the users for the name of the remote host. which users want to access. After the users have answered and offered the correct users' identities and authentication information, the proxy server communicates the remote host, act as the relay between two communication sites. The whole course can be totally transparent to users.There are mainly three types in the firewalls: packet filtering. application gateways and state detection.Packet filtering firewall works on the network layer.it can filter the source address. destination address. source port and destination port of TCP/IP data packet. It has advantages such as the higher efficiency.transparent to user. and users might not feel the existence of the packer filtering firewall, unless he is the illegal user and has been refused. The shortcomings are that it can't ensure the security to most services and protocols, unable to distinguish thedifferent users of the same IP address effectively,and it is difficult to be configured, monitored and managed. can't offer enough daily records and warning.The application gateways firewall performs its function on the application layer, it connects with specific middle-joint (firewall) by a client procedure, and then the middle-joint connects with the server actually. Unlike the packet filtering firewall. when using the firewall of this kind. there is no direct connection between the outside networks. so even if the matter has happened in the firewall. the outside networks can't connect with networks protected. The application gateway firewall offers the detailed daily records and auditing function, it improved the security of the network greatly. and provides the possibility to improve the security performance of the existing software too. The application gateways firewall solves the safety problem based on the specific application program. the products based on Proxy will be improved to configure the service in common use and non-standard port. However. so long as the application program needs upgrading. the users based on Proxy will find that they must buy new Proxy server. As a technique of network safety. Firewall combined with proxy server has simple and practical characteristics, can reach a certain security request in case of not revising the original network application system. However. if the firewall system is broken through. the network protected is in having no state of protecting. And if an enterprise hopes to launch the business activity on Internet and carry on communication with numerous customers. it can't meet the demands. In addition, the firewall based on Proxy Service will often makes the performance of the network obviously drop.The third generation of firewall takes the detection technique of state as the core,combines the packet filtering firewall and application gateways firewall. The state detection firewall accesses and analyzes the data achieved from the communication layer through the module of state detection to perform its function. The state monitor act as firewall technique. it is best in security perfonnance, it adopts a software engine.which executes the tactics of network security on the gateways, called the detection module. On the premise of not influencing the network to work normally, detection module collects the relevant data to monitor each of the network communication layers, collects a part of data, namely status information, and stores the data up dynamically for the reference in making security decision afterward. Detection modulesupports many kinds of protocols and application program, and can implement the expansion of application and service very easily. Different from other safety schemes, before the user's access reaches the operating system of network gateways, the state monitor should collect the relevant data to analyze, combine network configuration and safety regulation to make the decisions of acceptance, refutation, appraisal or encrypting to the communication etc Once a certain access violates the security regulation, the safety alarm will refuse it and write down to report the state of the network to the system management device. This technology has defects too, namely the configuration of the state monitor is very complicated, and will decelerate the network.3. New generation technique of firewallsAccording to the present firewalls market, the domestic and internationalmanufacturers of firewall can all support the basic function of the firewall well,including access control, the network address transform, proxy, authentication, daily records audit etc. However, as stated before, with the attack to the network increasing, and user's requisition for network security improving day by day, the firewall must get further development. Combine the present experience of research and development and the achievement,some relevant studies point out, according to the development trend of application and technology, how to strengthen the security of firewall, improve the performance of firewall, enrich the function of firewall, will become the problem that the manufacturer of firewalls must face and solve next.The purpose of the new generation firewall is mainly combining the packet filtering and proxy technology, overcoming the defects in the safety respect of two; being able to exert the omnidirectional control from the layer of data chain to the application layer; implementing the micro-kernel of TCP/IP protocol to perform all the security control on the layer of TCP/IP protocol; based on the micro-kernel above, making the speed to exceed thetraditional packet filtering firewall; Offering the transparent mode of proxy. lightening the configuration work on the client; Supporting the data encryption and decryption (DES and RSA ), offering the strong support to the Virtual Private Network VPN; hiding the Inside information totally; producing a new firewall theory.The new techniqe of firewalls has not only covered all the functions of traditional packet filtering firewalls, but also has remarkable advantages in opposing overall the attack means of IP deception, SYN Flood, ICMP. ARP, etc. strengthening proxy service, merging it with packet filtering, then adding the intelligence filteringtechnology to make the security of the firewall rising to another height.4. ConclusionNow the firewall has already been widely used on Internet, and because of its characteristic of not limited to the TCP/IP protocol, it has more vitality outside Internet progressively too. To be subjective, the firewall is not the omnipotent prescription of solving the problem of network security, but only a component of the network security policy and tactics. However, understanding the technology of firewall and learning to use it in actual operation, believing that every net friend may be benefited a lot from the network life in the new century.翻译：网络安全与防火墙技术研究摘要：作为关键设施，维护网络的安全性，防火墙采取建立信任与不可靠的网络障碍的目的，并落实相应的安全策略。

附录一翻译Computer network security and to guard againstAbstract: When mankind entered the 21st century information society, the network society of the time, China will establish a complete set of network security system, especially from the policy and law to establish China's own characteristics, network security system.Key words: computer; network; security; preventIn the information age, information can help groups or individuals so that they benefit from, the same information can also be used to pose a threat to them, caused damage. Therefore network security, including the composition of network hardware, software and network transmission of information security, so that they do not because of accidental or malicious destruction of the attacks, network security not only the technical aspects, but also management issues, both complement each other, are indispensable.First, the concept of computer network securityInternational Organization for Standardization of "computer security" is defined as: "To establish a data processing system and the adoption of technology and management of security protection, the protection of computer hardware, software, data is not due to accidental and malicious destruction of reasons, change and leakage." The above definition of computer security includes physical security and logical security of both the contents of the contents of the logic of security could be understood as we often say that the information security, information refers to the confidentiality, integrity and availability of protection, and network security Information security is the meaning of the extension, that network security is a network of information confidentiality, integrity and availability protection. Computer network security as the specific meaning of the user changes, the user isdifferent on the network security awareness and requirements will be different. From the ordinary user's point of view, could only hope that personal privacy or confidential information transmission on the network be protected against eavesdropping, tampering and forgery; and network provider in addition to care about these network information security, we must also consider how to deal with sudden natural disasters, such as military strikes against the destruction of network hardware, as well as unusual in the network how to restore network communications, and maintain the continuity of network communications.In essence, the network security, including the composition of network hardware, software and network transmission of information security, so that they do not because of accidental or malicious attacks on the destruction of both the technical aspects of network security issues, there are management issues, the two sides complement each other, are indispensable. Man-made network intrusion and attacks makes network security is facing new challenges.Second, computer network security status quoComputer network security is the network hardware, software and data systems are protected from accidental or malicious destruction of reasons, alteration, disclosure, the system continuous, reliable, normal operation of network services without disruption. Computer and network technology has the complexity and diversity, makes computer and network security has become a need to continue to update and improve the area. At present, hackers method has been more than the type of computer virus, and many attacks are fatal. In the Internet network, because the Internet does not have the time and geographical constraints, whenever there is a means to generate new attacks, we can in a week around the world, these attacks means the use of network and system vulnerabilities to attack computer systems and resulting in network paralysis. Worms, backdoor (Back-doors), Rootkits, DOS (DenialofServices) and Sniffer (network monitor) is a familiar means of several hacker attacks. However, none of these attacks means they reflect the astonishing power of today become worse. These types of attacks means the new variant, with previousattacks appeared methods, more intelligent, targeted against Internet-based protocols and operating system level. From the Web process control procedures to the kernel-level Rootlets. Hackers practices escalating renovation, to the user's ability to guard against information security challenge.Third, computer network security precautions1, to strengthen the internal network management and the use of safety awareness among staff, many computer systems commonly used passwords to control access to system resources, which is anti-virus process, the most vulnerable and the most economical methods. Network administrator and terminal operator privileges in accordance with their responsibilities, choose a different password for the application data legitimate operation, to prevent unauthorized users to access the data and the use of network resources.On the network, software installation and management is crucial, it is not only related to network maintenance and management efficiency and quality, but also to the network security. A good antivirus software can be easily installed within minutes to the organization each NT server can also be downloaded and spread to all the purpose of the machine by the network administrator set up and manage to focus, it will work with the operating system and other security is closely linked to become a part of network security management, and automatically provide the best network virus defensive measures. When the computer virus on-line resources applications attack, such as the virus exists in the information-sharing network of media, it is necessary to the security at the gateway, on the network front-end for antivirus.2, network firewall technologyIs a kind of used to strengthen the network access control to prevent the external network users to illegal means to enter the external network through the internal network, access internal network resources and protect the internal network operating environment special for Network Interconnection Devices. It is between two or more networks such as packet transmission link in accordance with a certain degree of security strategy to implement the inspection, to determine whether thenetwork communication between are allowed to, and monitor the network running. Although the firewall is to protect the network from an effective means of hacking, but there are obviously inadequate: through the firewall can not protect against outside attack other means, can not prevent defectors from the inside and inadvertent threats posed by users, but also can not completely prevent the transmission of the virus have been infected with the software or documents, and can not protect against data-driven attacks.3, security encryption technologyEncryption technology for the global e-commerce to provide a guarantee, so that Internet-based electronic trading system has become possible, thus improving the symmetric encryption and asymmetric encryption technology is still the mainstream of the 21st century. Symmetric encryption to the conventional password-based technology, computing encryption and decryption operations use the same key. Asymmetric encryption, encryption key that is different from the decryption key, encryption keys are made public, anyone can use, only the decryption key to decrypt people know.4, the network host operating system security and physical security measures Network firewall as the first line of defense and can not fully protect the internal network, must be combined with other measures to improve the safety of the system level. After the firewall is based on the network host operating system security and physical security measures. In accordance with the level from low to high, namely, the physical security of the host system, the core operating system security, system security, application services security and file system security; At the same time, host security checks and bug fixes, as well as a backup safety system as a supplementary safety measures. These constitute the entire network system, the second line of defense, the main part of a breakthrough to prevent the firewall as well as attacks from within. System backup is the last line of defense network system, used to attack after the System Restore. The firewall and host security measures is the overall system security by auditing, intrusion detection and response processor constitute the overall safety inspection and response measures. It from the networksystem firewall, network host or even directly from the network link layer on the extraction of network status information, as input to the intrusion detection subsystem. Intrusion Detection System in accordance with certain rules to determine whether there is any invasion of the incident, if the invasion occurred, the emergency treatment measures, and generate a warning message. Moreover, the system's security audit also can be used as the future consequences of aggressive behavior and to deal with security policy on the system to improve sources of information.In short, network security is a comprehensive issue, involving technology, management, use and many other aspects, including both its own information system security issues, there are physical and logical technical measures, a kind of technology can only solve the problem on the one hand, rather than a panacea. To this end the establishment of a network with Chinese characteristics, security system, the need for national policies and regulations to support and joint research and development group. Security and anti-security like two sides of contradictions, always pick-up, so the security industry is a future with the development of new technologies and the continuous development of industry.计算机网络安全和防范摘要：当人类跨入21世纪的信息社会，网络社会的时候，我国将建立一套完整的网络安全系统，特别是从政策和法律，建立我国自己的特点，网络安全系统。

毕业设计（论文）外文资料翻译系别：计算机系专业：计算机科学与技术班级：姓名：学号：外文出处：Web-Based Network education System1. IntroductionComputers and web applications bring a significant revolution in our social life and especially to our traditional mechanism of education. The era of education enable us to access mass of information whose remarkable character is digital so that computers can recognize and deal with this kind of expression of information. Digital campus construction is already on going in order to catch the new trend in quality education. The main functions of digital campus cover with distance such as web classroom, courseware on demand, distance examination. The digital campus information management system includes information management system, office automation system, administration examination system and virtual community such as online tutoring, bulletin board system etc. With the intensification of distance web education, how to estimate learning effect locally is an important issue. A comprehensive education system which utilizes information technology of the network to carry on college course to educate, it offers from the network classroom, essential study links discussing, answering questions, and processing homework to examination to teachers and students. This system should also support management activity of the educational administration, such as online course project, roll management, follow-up of quality. The self-adapted examination system is a sub-system of the Networking Institute's demonstration project. In Internet Universal, distance learning is by telephone, television, video and communications, asynchronous transmission mode of teaching information. In recent years, based on the introduction Internet Distance learning, World Wide Web Recognized as the most powerful curriculum information dissemination media, the Internet has hundreds of courses, there are more schools and teachers are being considered for Web Teaching. For Web Teaching, and that is using the World Wide Web as a teaching medium, transmission teaching in the implementation of online teaching, teaching management, and online testing and online exchanges. Realistic and complete implementation based on Web Teaching requires a user-friendly and efficient support online teaching platform support. Currently there are some in the international market such products, such as Lotus Company Learning Space , the British Columbia University computer science department development Web CT ,WBT System Company Top Class And Canada Simon Fraser University development Virtual. Many companies and schools are also being developed or is ready to develop similar software, such as the key institutions in preparation for the development of modern distancelearning and teaching support system. Online teaching platform should be aware of the support functions, which can or should provide the ancillary support, all of which feature current products, for effective online teaching is very important.2.The main characteristicTeachers can keep a student's screens' voice display and send information to all students or a group of broadcast; teachers can watch and listen to a student 's information, and control the student's keyboard and mouse , and do "hand in hand" type of guidance, and arbitrary switching among students ; and remote window control guidance, the window of multimedia network classroom software can control the intelligent rolling and teachers teaching in various other functions at the same time, the teacher can remote control machine on a number of students at the same time and also can let all (a group or a) student screens arranged in "the black screen", and lock the keyboard and mouse, reminding the attention of students; intelligent rolling screen: the screen broadcast and remote control operation uses the original smart scroll, free rolling technology, which need not undertake screen scaling, receiving students in the broadcast in the process of watching the operation; the mouse capture: it supports soft cursor, animated mouse cursor, mouse cursor broadcasting, even in windowed mode which can reflect the real-time changes in morphology and mouse; multi-point monitoring: multimedia network classroom software support multiple windows simultaneously with the same When the watch, which can also watch window distributed across multiple machines, real-time monitoring of all the other students in the state machine; broadcast: multimedia network classroom software support more audio and video file formats, support for VCD, MP3, W AV and other documents play online ; automatic login: students on the machine automatically log in the teacher machine; multimedia network classroom software has strong system stability, ensure the teaching process smoothly; perfect functions, beautiful interface which is easy to use the direct and concise operation, using the unified mode of operation; software, multimedia network classroom software does not need a server, simple installation, convenient upgrade and maintenance; hardware compatibility: multimedia network classroom software contents all the card, sound card, display card and can demonstrate good performance, and won't appear any unstable phenomenon.3. Design multimedia network classroom of thoughtIn the multimedia network classroom design, it focuses on solving the user pays as the following issues: (1)the multimedia network classroom is easy to use and individualized demand. Because each teacher for computer to different extent, teachers need to multimedia network classroom is simple and easy to use, one will see, will soon be able to undertake informatizal teaching. The computer master degree higher teacher needs according to computer and information understanding, personalized teaching.(2) multimedia network classroom and practicalteaching function. Information teaching is a means of teaching, its purpose is to improve the effect of teaching. This means whether the teaching habits, whether there is a wealth of practical teaching function, really help teachers for teaching, improve the effect of teaching has become the most concern of the teacher.(3)multimedia network classroom teaching management function. If a student who attends class does not listen to the teacher carefully, has nothing to do with the classroom things, such as playing games, or simply add or remove programs are headaches in teachers teaching; and in order to guarantee the teaching effection carrying smoothly, it also requires a corresponding teaching management function to assist.4.The multimedia network classroom program advantagesMultimedia network classroom solution has the following advantages.（1）Simple and easy to use, multimedia network classroom software use a graphical interface, whoes each function has a corresponding button, operating on a stick out a mile, so that teachers can see use it easily. （2）Flexible customized, which meets the demand of personal teaching. The teacher can customize multimedia network classroom software interface, icon, toolbar and also can customize the class model at the same time by using multimedia network classroom run concurrent design, each function of teaching can manage any combination and arbitrary. （3）Multimedia network classroom original thumbnail display mode which can make the whole class of the students computer screen contents show to teachers at the same time and let teachers watch easily in global.（4）practical teaching function of multimedia network classroom software offers practical and rich pedagogical features, including screen broadcasting, video broadcasting, voice broadcasting, issued procedures, and collection operations.（5）Supporting a variety of teaching strategies, which can use the broadcast function to broadcast the teacher's own screen to everyone.（6）teaching management function in the multimedia network classroom, which is subject to the control of the teacher, students can be remotely set machine, and the multimedia network classroom is also enhanced by many teachers and students interaction, such as "remote control", which fully ensured between student and teacher interaction.（7）In order to guarantee the teaching carrying out smoothly, the teacher wants multimedia network classroom software to help manage the students' situation. Multimedia network classroom software is provided for locking the computer black screen and hush functions（8) Multimedia network classroom daily maintenance workload is very big, the teacher does not have too much time to manage multimedia network classroom maintenance, hoping multimedia network classroom software can provide very good maintenance function. Multimedia network classroom with remote settings, document publishing, charge, delete, remote command, remote control and other functions.（9）multimedia network classroom software has strong system stability, high soft, hardware environment compatibility, regardless of level of computer configuration, graphics cards, sound card type, which can guarantee the normal operation of multimedia network classroom.（10）because of the multimedia network classroom is a pure software implementation, simple installation,upgrade and maintenance which is very convenient.5. The main functions of software in multimedia network teaching(1)Teaching function, including screen broadcasting, screen monitoring, voice broadcast, audio monitor, video broadcasting, electronic drawing board, news release, issued a document, collect documents, documents and other functions which the teacher in the class is the most commonly used functions.(2)Teaching management, multimedia network Teaching management function can ensure the teaching be carried out smoothly, including the class model, group management, call sign, lock computer, silent, black screen log. (3)Maintenance, for the convenience of teachers to multimedia classroom network maintenance, multimedia network teaching provides remote settings and other functions.6. Multimedia network teaching system buildingMultimedia network classroom is a small LAN environment, generally uses the 100M switching to the desktop, you can ensure that the audio and video files well transmission. Computer selection of good effects and economic benefits principle, selection of the computer multimedia network classroom should let the minimum guarantee the smooth operation of multimedia courseware, and commonly used methods of software, such as Word, Powerpoint, teacher's machine configuration is higher than the students machine configuration , and the best buying support WOL function computer.Finally the teacher machine, student machine, switching with twisted pair link, which sets the TCP / IP protocol, transfering through network, should instals on the multimedia network classroom software and a complete multimedia network classroom building.基于网络的教学系统1导言计算机和网络应用带来了重大变革，我们的社会生活，特别是我们的传统机制的教育得到了重大变革。

南京邮电大学毕业设计(论文)外文资料翻译学院专业学生姓名班级学号外文出处附件：1.外文资料翻译译文；2.外文原文指导教师评价：1．翻译内容与课题的结合度：□优□良□中□差2．翻译内容的准确、流畅：□优□良□中□差3．专业词汇翻译的准确性：□优□良□中□差4．翻译字符数是否符合规定要求：□符合□不符合指导教师签名：年月日附件1：外文资料翻译译文非常1.1Web 部署项目当ASP 第一次发布时，Web 编程还比较困难，因为需要 IIS 来处理 ASP 页。

后来， 2.0 和Visual Studio® 2005 通过引入网站开发模型使一切工作都变得容易了。

借助该网站模型，您不必在 Visual Studio 中创建新项目，而是可以指向一个目录并开始编写网页和代码。

此外，您还可以使用内置的 Development Server 快速测试站点， Development Server 将 寄宿在一个本地进程中，并消除了必须安装 IIS 才能进行开发这一先决条件。

该网站模型的魅力在于您在开发 Web 应用程序时无需考虑打包和部署。

需要其他类时怎么办？向 App_Code 目录添加一个 .cs 文件即可开始编写。

希望将可本地化的字符串存储在资源文件中时怎么办？向App_GlobalResources 目录添加一个 .resx 文件并键入字符串。

一切都顺顺当当；您根本就不必考虑编译和部署方面的事情。

在准备进行部署时，您有多种可选方案。

最简单的方案是将文件复制到主运行服务器并按要求编译每一个文件（和在测试环境中一样）。

第二种方案是使用aspnet_compiler.exe 实用工具将应用程序预编译为二进制版本，之后将只剩下要放到服务器上的一组程序集、静态内容和配置文件。

第三种方案也使用 aspnet_compiler.exe，但要创建一个可更新的二进制部署，其中 .as*x 文件保持不变（并且可修改），而所有代码文件都编译为二进制程序集。

本科毕业设计（论文）外文翻译译文学生姓名：院（系）：油气资源学院专业班级：物探0502指导教师：完成日期：年月日地震驱动评价与发展：以玻利维亚冲积盆地的研究为例起止页码：1099——1108出版日期：NOVEMBER 2005THE LEADING EDGE出版单位：PanYAmericanYEnergyvBuenosYAiresvYArgentinaJPYBLANGYvYBPYExplorationvYHoustonvYUSAJ.C.YCORDOVAandYE.YMARTINEZvYChacoYS.A.vYSantaYCruzvYBolivia 通过整合多种地球物理地质技术，在玻利维亚冲积盆地，我们可以减少许多与白垩纪储集层勘探有关的地质技术风险。

通过对这些远景区进行成功钻探我们可以验证我们的解释。

这些方法包括盆地模拟，联井及地震叠前同时反演，岩石性质及地震属性解释，A VO/A V A,水平地震同相轴，光谱分解。

联合解释能够得到构造和沉积模式的微笑校正。

迄今为止，在新区有七口井已经进行了成功钻探。

基质和区域地质。

Tarija/Chaco盆地的subandean 褶皱和冲断带山麓的中部和南部，部分扩展到玻利维亚的Boomerange地区经历了集中的成功的开采。

许多深大的泥盆纪气田已经被发现，目前正在生产。

另外在山麓发现的规模较小较浅的天然气和凝析气田和大的油田进行价格竞争，如果他们能产出较快的油流而且成本低。

最近发现气田就是这种情况。

接下来，我们赋予Aguja的虚假名字就是为了讲述这些油田的成功例子。

图1 Aguja油田位于玻利维亚中部Chaco盆地的西北角。

基底构造图显示了Isarzama背斜的相对位置。

地层柱状图显示了主要的储集层和源岩。

该油田在Trija和冲积盆地附近的益背斜基底上，该背斜将油田和Ben i盆地分开（图1），圈闭类型是上盘背斜，它存在于连续冲断层上，Aguja有两个主要结构：Aguja中部和Aguja Norte,通过重要的转换压缩断层将较早开发的“Sur”油田分开Yantata Centro结构是一个三路闭合对低角度逆冲断层并伴随有小的摆幅。

编号：毕业设计(论文)外文翻译（原文）院（系）：桂林电子科技大学专业：电子信息工程学生姓名： xx学号： xxxxxxxxxxxxx 指导教师单位：桂林电子科技大学姓名： xxxx职称： xx2014年x月xx日Timing on and off power supplyusesThe switching power supply products are widely used in industrial automation and control, military equipment, scientific equipment, LED lighting, industrial equipment,communications equipment,electrical equipment,instrumentation, medical equipment, semiconductor cooling and heating, air purifiers, electronic refrigerator, LCD monitor, LED lighting, communications equipment, audio-visual products, security, computer chassis, digital products and equipment and other fields.IntroductionWith the rapid development of power electronics technology, power electronics equipment and people's work, the relationship of life become increasingly close, and electronic equipment without reliable power, into the 1980s, computer power and the full realization of the switching power supply, the first to complete the computer Power new generation to enter the switching power supply in the 1990s have entered into a variety of electronic, electrical devices, program-controlled switchboards, communications, electronic testing equipment power control equipment, power supply, etc. have been widely used in switching power supply, but also to promote the rapid development of the switching power supply technology .Switching power supply is the use of modern power electronics technology to control the ratio of the switching transistor to turn on and off to maintain a stable output voltage power supply, switching power supply is generally controlled by pulse width modulation (PWM) ICs and switching devices (MOSFET, BJT) composition. Switching power supply and linear power compared to both the cost and growth with the increase of output power, but the two different growth rates. A power point, linear power supply costs, but higher than the switching power supply. With the development of power electronics technology and innovation, making the switching power supply technology to continue to innovate, the turning points of this cost is increasingly move to the low output power side, the switching power supply provides a broad space for development.The direction of its development is the high-frequency switching power supply, high frequency switching power supply miniaturization, and switching power supply into a wider range of application areas, especially in high-tech fields, and promote the miniaturization of high-tech products, light of. In addition, the development and application of the switching power supply in terms of energy conservation, resource conservation and environmental protection are of great significance.classificationModern switching power supply, there are two: one is the DC switching power supply; the other is the AC switching power supply. Introduces only DC switching power supply and its function is poor power quality of the original eco-power (coarse) - such as mains power or battery power, converted to meet the equipment requirements of high-quality DC voltage (Varitronix) . The core of the DC switching power supply DC / DC converter. DC switching power supply classification is dependent on the classification of DC / DC converter. In other words, the classification of the classification of the DC switching power supply and DC/DC converter is the classification of essentially the same, the DC / DC converter is basically a classification of the DC switching power supply.DC /DC converter between the input and output electrical isolation can be divided into two categories: one is isolated called isolated DC/DC converter; the other is not isolated as non-isolated DC / DC converter.Isolated DC / DC converter can also be classified by the number of active power devices. The single tube of DC / DC converter Forward (Forward), Feedback (Feedback) two. The double-barreled double-barreled DC/ DC converter Forward (Double Transistor Forward Converter), twin-tube feedback (Double Transistor Feedback Converter), Push-Pull (Push the Pull Converter) and half-bridge (Half-Bridge Converter) four. Four DC / DC converter is the full-bridge DC / DC converter (Full-Bridge Converter).Non-isolated DC / DC converter, according to the number of active power devices can be divided into single-tube, double pipe, and four three categories. Single tube to a total of six of the DC / DC converter, step-down (Buck) DC / DC converter, step-up (Boost) DC / DC converters, DC / DC converter, boost buck (Buck Boost) device of Cuk the DC / DC converter, the Zeta DC / DC converter and SEPIC, the DC / DC converter. DC / DC converters, the Buck and Boost type DC / DC converter is the basic buck-boost of Cuk, Zeta, SEPIC, type DC / DC converter is derived from a single tube in this six. The twin-tube cascaded double-barreled boost (buck-boost) DC / DC converter DC / DC converter. Four DC / DC converter is used, the full-bridge DC / DC converter (Full-Bridge Converter).Isolated DC / DC converter input and output electrical isolation is usually transformer to achieve the function of the transformer has a transformer, so conducive to the expansion of the converter output range of applications, but also easy to achieve different voltage output , or a variety of the same voltage output.Power switch voltage and current rating, the converter's output power is usually proportional to the number of switch. The more the number of switch, the greater the output power of the DC / DC converter, four type than the two output power is twice as large,single-tube output power of only four 1/4.A combination of non-isolated converters and isolated converters can be a single converter does not have their own characteristics. Energy transmission points, one-way transmission and two-way transmission of two DC / DC converter. DC / DC converter with bi-directional transmission function, either side of the transmission power from the power of lateral load power from the load-lateral side of the transmission power.DC / DC converter can be divided into self-excited and separately controlled. With the positive feedback signal converter to switch to self-sustaining periodic switching converter, called self-excited converter, such as the the Luo Yeer (Royer,) converter is a typical push-pull self-oscillating converter. Controlled DC / DC converter switching device control signal is generated by specialized external control circuit.the switching power supply.People in the field of switching power supply technology side of the development of power electronic devices, while the development of the switching inverter technology, the two promote each other to promote the switching power supply annual growth rate of more than two digits toward the light, small, thin, low-noise, high reliability, the direction of development of anti-jamming. Switching power supply can be divided into AC / DC and DC / DC two categories, AC / AC DC / AC, such as inverters, DC / DC converter is now modular design technology and production processes at home and abroad have already matured and standardization, and has been recognized by the user, but AC / DC modular, its own characteristics make the modular process, encounter more complex technology and manufacturing process. Hereinafter to illustrate the structure and characteristics of the two types of switching power supply.Self-excited: no external signal source can be self-oscillation, completely self-excited to see it as feedback oscillation circuit of a transformer.Separate excitation: entirely dependent on external sustain oscillations, excited used widely in practical applications. According to the excitation signal structure classification; can be divided into pulse-width-modulated and pulse amplitude modulated two pulse width modulated control the width of the signal is frequency, pulse amplitude modulation control signal amplitude between the same effect are the oscillation frequency to maintain within a certain range to achieve the effect of voltage stability. The winding of the transformer can generally be divided into three types, one group is involved in the oscillation of the primary winding, a group of sustained oscillations in the feedback winding, there is a group of load winding. Such as Shanghai is used in household appliances art technological production of switching power supply, 220V AC bridge rectifier, changing to about 300V DC filter added tothe collector of the switch into the transformer for high frequency oscillation, the feedback winding feedback to the base to maintain the circuit oscillating load winding induction signal, the DC voltage by the rectifier, filter, regulator to provide power to the load. Load winding to provide power at the same time, take up the ability to voltage stability, the principle is the voltage output circuit connected to a voltage sampling device to monitor the output voltage changes, and timely feedback to the oscillator circuit to adjust the oscillation frequency, so as to achieve stable voltage purposes, in order to avoid the interference of the circuit, the feedback voltage back to the oscillator circuit with optocoupler isolation.technology developmentsThe high-frequency switching power supply is the direction of its development, high-frequency switching power supply miniaturization, and switching power supply into the broader field of application, especially in high-tech fields, and promote the development and advancement of the switching power supply, an annual more than two-digit growth rate toward the light, small, thin, low noise, high reliability, the direction of the anti-jamming. Switching power supply can be divided into AC / DC and DC / DC two categories, the DC / DC converter is now modular design technology and production processes at home and abroad have already matured and standardized, and has been recognized by the user, but modular AC / DC, because of its own characteristics makes the modular process, encounter more complex technology and manufacturing process. In addition, the development and application of the switching power supply in terms of energy conservation, resource conservation and environmental protection are of great significance.The switching power supply applications in power electronic devices as diodes, IGBT and MOSFET.SCR switching power supply input rectifier circuit and soft start circuit, a small amount of applications, the GTR drive difficult, low switching frequency, gradually replace the IGBT and MOSFET.Direction of development of the switching power supply is a high-frequency, high reliability, low power, low noise, jamming and modular. Small, thin, and the key technology is the high frequency switching power supply light, so foreign major switching power supply manufacturers have committed to synchronize the development of new intelligent components, in particular, is to improve the secondary rectifier loss, and the power of iron Oxygen materials to increase scientific and technological innovation in order to improve the magnetic properties of high frequency and large magnetic flux density (Bs), and capacitor miniaturization is a key technology. SMT technology allows the switching power supply has made considerable progress, the arrangement of the components in the circuit board on bothsides, to ensure that the light of the switching power supply, a small, thin. High-frequency switching power supply is bound to the traditional PWM switching technology innovation, realization of ZVS, ZCS soft-switching technology has become the mainstream technology of the switching power supply, and a substantial increase in the efficiency of the switching power supply. Indicators for high reliability, switching power supply manufacturers in the United States by reducing the operating current, reducing the junction temperature and other measures to reduce the stress of the device, greatly improve the reliability of products.Modularity is the overall trend of switching power supply, distributed power systems can be composed of modular power supply, can be designed to N +1 redundant power system, and the parallel capacity expansion. For this shortcoming of the switching power supply running noise, separate the pursuit of high frequency noise will also increase, while the use of part of the resonant converter circuit technology to achieve high frequency, in theory, but also reduce noise, but some The practical application of the resonant converter technology, there are still technical problems, it is still a lot of work in this field, so that the technology to be practical.Power electronics technology innovation, switching power supply industry has broad prospects for development. To accelerate the pace of development of the switching power supply industry in China, it must take the road of technological innovation, out of joint production and research development path with Chinese characteristics and contribute to the rapid development of China's national economy.Developments and trends of the switching power supply1955 U.S. Royer (Roger) invented the self-oscillating push-pull transistor single-transformer DC-DC converter is the beginning of the high-frequency conversion control circuit 1957 check race Jen, Sen, invented a self-oscillating push-pull dual transformers, 1964, U.S. scientists canceled frequency transformer in series the idea of switching power supply, the power supply to the size and weight of the decline in a fundamental way. 1969 increased due to the pressure of the high-power silicon transistor, diode reverse recovery time shortened and other components to improve, and finally made a 25-kHz switching power supply.At present, the switching power supply to the small, lightweight and high efficiency characteristics are widely used in a variety of computer-oriented terminal equipment, communications equipment, etc. Almost all electronic equipment is indispensable for a rapid development of today's electronic information industry power mode. Bipolar transistor made of 100kHz, 500kHz power MOS-FET made, though already the practical switching power supply is currently available on the market, but its frequency to be further improved. Toimprove the switching frequency, it is necessary to reduce the switching losses, and to reduce the switching losses, the need for high-speed switch components. However, the switching speed will be affected by the distribution of the charge stored in the inductance and capacitance, or diode circuit to produce a surge or noise. This will not only affect the surrounding electronic equipment, but also greatly reduce the reliability of the power supply itself. Which, in order to prevent the switching Kai - closed the voltage surge, RC or LC buffers can be used, and the current surge can be caused by the diode stored charge of amorphous and other core made of magnetic buffer . However, the high frequency more than 1MHz, the resonant circuit to make the switch on the voltage or current through the switch was a sine wave, which can reduce switching losses, but also to control the occurrence of surges. This switch is called the resonant switch. Of this switching power supply is active, you can, in theory, because in this way do not need to greatly improve the switching speed of the switching losses reduced to zero, and the noise is expected to become one of the high-frequency switching power supply The main ways. At present, many countries in the world are committed to several trillion Hz converter utility.the principle of IntroductionThe switching power supply of the process is quite easy to understand, linear power supplies, power transistors operating in the linear mode and linear power, the PWM switching power supply to the power transistor turns on and off state, in both states, on the power transistor V - security product is very small (conduction, low voltage, large current; shutdown, voltage, current) V oltammetric product / power device is power semiconductor devices on the loss.Compared with the linear power supply, the PWM switching power supply more efficient process is achieved by "chopping", that is cut into the amplitude of the input DC voltage equal to the input voltage amplitude of the pulse voltage. The pulse duty cycle is adjusted by the switching power supply controller. Once the input voltage is cut into the AC square wave, its amplitude through the transformer to raise or lower. Number of groups of output voltage can be increased by increasing the number of primary and secondary windings of the transformer. After the last AC waveform after the rectifier filter the DC output voltage.The main purpose of the controller is to maintain the stability of the output voltage, the course of their work is very similar to the linear form of the controller. That is the function blocks of the controller, the voltage reference and error amplifier can be designed the same as the linear regulator. Their difference lies in the error amplifier output (error voltage) in the drive before the power tube to go through a voltage / pulse-width conversion unit.Switching power supply There are two main ways of working: Forward transformand boost transformation. Although they are all part of the layout difference is small, but the course of their work vary greatly, have advantages in specific applications.the circuit schematicThe so-called switching power supply, as the name implies, is a door, a door power through a closed power to stop by, then what is the door, the switching power supply using SCR, some switch, these two component performance is similar, are relying on the base switch control pole (SCR), coupled with the pulse signal to complete the on and off, the pulse signal is half attentive to control the pole voltage increases, the switch or transistor conduction, the filter output voltage of 300V, 220V rectifier conduction, transmitted through the switching transformer secondary through the transformer to the voltage increase or decrease for each circuit work. Oscillation pulse of negative semi-attentive to the power regulator, base, or SCR control voltage lower than the original set voltage power regulator cut-off, 300V power is off, switch the transformer secondary no voltage, then each circuit The required operating voltage, depends on this secondary road rectifier filter capacitor discharge to maintain. Repeat the process until the next pulse cycle is a half weeks when the signal arrival. This switch transformer is called the high-frequency transformer, because the operating frequency is higher than the 50HZ low frequency. Then promote the pulse of the switch or SCR, which requires the oscillator circuit, we know, the transistor has a characteristic, is the base-emitter voltage is 0.65-0.7V is the zoom state, 0.7V These are the saturated hydraulic conductivity state-0.1V-0.3V in the oscillatory state, then the operating point after a good tune, to rely on the deep negative feedback to generate a negative pressure, so that the oscillating tube onset, the frequency of the oscillating tube capacitor charging and discharging of the length of time from the base to determine the oscillation frequency of the output pulse amplitude, and vice versa on the small, which determines the size of the output voltage of the power regulator. Transformer secondary output voltage regulator, usually switching transformer, single around a set of coils, the voltage at its upper end, as the reference voltage after the rectifier filter, then through the optocoupler, this benchmark voltage return to the base of the oscillating tube pole to adjust the level of the oscillation frequency, if the transformer secondary voltage is increased, the sampling coil output voltage increases, the positive feedback voltage obtained through the optocoupler is also increased, this voltage is applied oscillating tube base, so that oscillation frequency is reduced, played a stable secondary output voltage stability, too small do not have to go into detail, nor it is necessary to understand the fine, such a high-power voltage transformer by switching transmission, separated and after the class returned by sampling the voltage from the opto-coupler pass separated after class, so before the mains voltage, and after the classseparation, which is called cold plate, it is safe, transformers before power is independent, which is called switching power supply.the DC / DC conversionDC / DC converter is a fixed DC voltage transformation into a variable DC voltage, also known as the DC chopper. There are two ways of working chopper, one Ts constant pulse width modulation mode, change the ton (General), the second is the frequency modulation, the same ton to change the Ts, (easy to produce interference). Circuit by the following categories:Buck circuit - the step-down chopper, the average output voltage U0 is less than the input voltage Ui, the same polarity.Boost Circuit - step-up chopper, the average output voltage switching power supply schematic U0 is greater than the input voltage Ui, the same polarity.Buck-Boost circuit - buck or boost chopper, the output average voltage U0 is greater than or less than the input voltage Ui, the opposite polarity, the inductance transmission.Cuk circuit - a buck or boost chopper, the output average voltage U0 is greater than or less than the input voltage Ui, the opposite polarity, capacitance transmission.The above-mentioned non-isolated circuit, the isolation circuit forward circuits, feedback circuit, the half-bridge circuit, the full bridge circuit, push-pull circuit. Today's soft-switching technology makes a qualitative leap in the DC / DC the U.S. VICOR company design and manufacture a variety of ECI soft-switching DC / DC converter, the maximum output power 300W, 600W, 800W, etc., the corresponding power density (6.2 , 10,17) W/cm3 efficiency (80-90)%. A the Japanese Nemic Lambda latest using soft-switching technology, high frequency switching power supply module RM Series, its switching frequency (200 to 300) kHz, power density has reached 27W/cm3 with synchronous rectifier (MOSFETs instead of Schottky diodes ), so that the whole circuit efficiency by up to 90%.AC / DC conversionAC / DC conversion will transform AC to DC, the power flow can be bi-directional power flow by the power flow to load known as the "rectification", referred to as "active inverter power flow returned by the load power. AC / DC converter input 50/60Hz AC due must be rectified, filtered, so the volume is relatively large filter capacitor is essential, while experiencing safety standards (such as UL, CCEE, etc.) and EMC Directive restrictions (such as IEC, FCC, CSA) in the AC input side must be added to the EMC filter and use meets the safety standards of the components, thus limiting the miniaturization of the volume of AC / DC power, In addition, due to internal frequency, high voltage, current switching, making the problem difficult to solve EMC also high demands on the internal high-density mountingcircuit design, for the same reason, the high voltage, high current switch makes power supply loss increases, limiting the AC / DC converter modular process, and therefore must be used to power system optimal design method to make it work efficiency to reach a certain level of satisfaction.AC / DC conversion circuit wiring can be divided into half-wave circuit, full-wave circuit. Press the power phase can be divided into single-phase three-phase, multiphase. Can be divided into a quadrant, two quadrant, three quadrants, four-quadrant circuit work quadrant.he selection of the switching power supplySwitching power supply input on the anti-jamming performance, compared to its circuit structure characteristics (multi-level series), the input disturbances, such as surge voltage is difficult to pass on the stability of the output voltage of the technical indicators and linear power have greater advantages, the output voltage stability up to (0.5)%. Switching power supply module as an integrated power electronic devices should be selected。

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教务处
2006年2月27日杭州电子科技大学
毕业设计(论文)外文文献翻译
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杭州电子科技大学
毕业设计（论文）外文文献翻译毕业设计（论文）题目
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