水声通信网络媒介访问控制协议的研究

媒介访问控制协议是数据链路层协议中最重要的部分,对信道的分配起着决定性的作用。本文设计了一种普通访问模式和MACAW访问模式相结合的媒介访问控制协议,分别对信道和水下通信设备进行建模,对普通访问模式和MACAW访问模式在吞吐量、误码率和传输延迟进行了仿真。     

基于0-1游程频数检测的链路层加密数据识别

链路层加密数据的识别是进一步开展网络安全防护和协议识别的前提,当前方法主要是对流量所属的上层协议类型进行加密数据识别,采用混合多级的加密流量识别方法,对链路层加密数据的识别性能欠佳。提出一种基于0-1游程频数检测的链路层加密数据识别算法,采用随机性检测理论,进行链路层数据加密解密方案设计,构建标准正态分布函数的统计量对比特序列进行码元频数检测,实现0-1游程频数检测算法。实验表明,该算法能有效解决链路层块内频数检测过程中的分块长度选择及对加密数据识别率低的问题,链路层加密数据准确识别率提高显著,在网络保密数据传输等领域具有很好应用价值。     

TCP/IP数据链路层的研究

数据链路层的基本功能是向该层用户提供透明的和可靠的数据传送基本服务,数据链层所使用的停止等待协议、ARQ是其基本功能得以实现的保证。在简要介绍数据链路层的基本概念和协议的基础上重点介绍了ARQ协议的原理、工作过程及其应用。     

基本数据链路层协议的Petri网模型分析与优化

数据链路层位于网络体系结构第二层,向网络层提供统一界面。因此数据链路层协议的设计分析有着比较重要的意义。本文对一个基本的数据链路层协议原有Petri网模型进行了改进及分析,使得模型对协议的验证更加具有合理性。     

外语教育重在培养兴趣

在传统的外语课堂中,教师是教学过程的主体,是课堂上唯一的信息来源,而学生则是教学过程的客体,是被动的信息接受器。传统的教学理论没有充分认识到语言作为一种交际工具的实践性特点,只一味地把外语作为纯知识讲授,从而歪曲了语言习得的自然规律,致使学生兴趣全无,外语教学的课堂效果不甚理想。本文针对这一问题,从分析学习者的需要、转变教育理念以学习者为中心,调控学习者情感因素等三个方面探讨了如何做到在外语教学中真正做到以培养学生的英语学习兴趣为目标。     

ARP欺骗攻击原理及安全防范策略

ARP(Address Resolution Protocol)即地址解析协议,该协议将网络层的IP地址转换为数据链路层地址。TCP/IP协议中规定,IP地址为32位,由网络号和网络内的主机号构成,每一台接入局域网或者Internet的主机都要配置一个IP地址。在以太网中,源主机和目的主机通信时,源主机不仅要知道目的主机的IP地址,还要知道目的主机的数据链路层地址,即网卡的MAC地址,同时规定MAC地址为48位。ARP协议所做的工作就是查询目的主机的IP地址所对应的MAC地址,并实现双方通信。本文介绍了ARP在TCP/IP协议中的作用,描述了它的工作原理,详细分析了ARP欺骗攻击过程,并提出了安全防范策略     

IP与ATM结合的信息传送技术

IP是面向无连接的协议,有自己的寻径和路由选择。而ATM是面向连接的技术,有自己的信令、选路和地址结构,要结合这两种技术是很复杂的。目前结合ATM与IP的策略主要有两种:重叠模型和集成模型。重叠模型是指IP数据包在ATM上传送,把ATM看成数据链路层协议,在它上面运行IP协议,这种模型需要定义两套地址结构、路由协议及维护管理功能。重叠模型主要有三种实现方法:即传统的IPOA、局域网仿真LANE和     

大数据环境下电力行业信息生态模型构建及应用研究

【目的/意义】随着我国电力行业的快速发展,大数据技术在电力行业中的应用也得到了进一步提升,掌握大数据技术对于我国电力行业的建设具有十分重要意义。【方法/过程】本文首先阐述了电力行业大数据的含义和特征,然后构建了在大数据环境下基于信息生态理论的电力行业信息生态模型,最后在电力行业信息生态模型基础上构建了电力行业大数据应用框架模型。【结果/结论】为了解决电力行业中信息生态失衡的现象,避免电力行业在大数据应用过程中出现复杂性、无序性、不稳定性等问题。     

CAN总线协议分析器的设计

CAN总线是一种应用广泛的实时性现场总线,本文提出了采用独立CAN控制器SJA1000和高速单片机Atmega64进行CAN总线数据侦听,再经过USB通信芯片FT245BM传输到计算机,在PC机上采用CAN总线协议分析软件显示与存储各帧信息的CAN总线协议分析器系统的设计。本文阐述了CAN总线协议分析器的硬件结构及实现方案并对软件编程进行了介绍。     

运用建构主义教学理论提高计算机程序设计算法教学实效

计算机程序设计算法在高中信息科技教学过程中是重点,也是难点。程序设计算法的相关概念比较枯燥,理论过于抽象,对学生的逻辑思维能力要求较高,所以在教学过程中往往难以把握,也不易调动学生的兴趣。在传统的教学过程中,学生对这部分知识的掌握比较困难。本文结合课堂教学实践,从三个方面探究运用建构主义教学理论构建计算机程序设计算法教学过程,促进学生对知识的理解和掌握,与传统的教学方法比较,运用构建主义理论教学方法取得更好的教学效果。     

Students' Reactions to the Introduction of Videoconferencing for Classroom Instruction

This study examined how students who had no prior experience with videoconferencing would react to the use of videoconferencing as an instructional medium. Students enrolled in seven different courses completed a questionnaire at the beginning of the semester and again at the end of the semester. Students at the origination and remote sites did not differ in their reactions toward videoconferencing but there was a significant difference for gender. Women reacted less favorably to videoconferencing. Compared to the beginning of the semester, students reported significantly less positive attitudes toward taking a course through videoconferencing at the end of the semester. There were no significant differences in students' attitudes toward videoconferencing across courses at the beginning of the semester but there were significant differences across the courses at the end of the semester. The results suggest the need for better preparation for both students and instructors.     

Cooler temperatures inductive to locust outbreaks

Ajoint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology and his co-workers from Norway, US and Swiss have indicated that historical outbreaks of migratory locusts in China were associated with cold spells, suggesting that China＇s projected climate warming could decrease the pest＇s numbers. The study was published in Proceedings of theNational Academy of Sciences on 17 September, 2007.     

Exploring Multiplexity: Social Network Structures in a Computer-Supported Distance Learning Class

A computer-mediated group is a complex entity whose members exchange many types of information via multiple means of communication in pursuit of goals specific to their environment. Over time, they coordinate technical features of media with locally enacted use to achieve a viable working arrangement. To explore this complex interaction, a case study is presented of the social networks of interactions and media use among members of a class of computer-supported distance learners. Results show how group structures associated with project teams dominated who communicated with whom, about what, and via which media over the term, and how media came to occupy their own communication niches: Webboard for diffuse class-wide communication; Internet Relay Chat more to named others but still for general communication across the class; and e-mail primarily for intrateam communication. Face-to-face interaction, occurring only during a short on-campus session, appears to have had a catalytic effect on social and emotional exchanges. Results suggest the need to structure exchanges to balance class-wide sharing of ideas with subgroup interactions that facilitate project completion, and to provide media that support these two modes of interaction.     

Low doses of a red wine ingredient figh diabetes in mice

Aresearch group led by Prof. ZHAI Qiwei from the Institute for Nutritional Sciences under the CAS Shanghai Institutes for Biological Sciences has discovered that even relatively low doses of resveratrol--a chemical found in the skins of red grapes and in red wine--can improve the sensitivity of mice to the hormone insulin, according to a report in the October,2007 issue of Cell Metabolism. As insulin resistance is often characterized as the most critical factor contributing to the development of Type 2 diabetes, the findings“provide a potential new therapeutic approach for preventing or treating” both conditions, the researchers said.     

The Role of Intermediating Institutions in the Diffusion of Electronic Data Interchange (EDI): How Industry Associations Intervened in Denmark, Finland, and Hong Kong

Electronic data interchange (EDI) provides means for interorganizational communication, creates network externalities, requires an advanced information technology (IT) infrastructure, and relies on standards. In the diffusion of such innovations, institutional involvement is imperative. Such institutions contain governmental agencies, national and global standardization organizations, local government, and nonprofit private organizations like industry associations. The last type of organizations we call intermediating institutions. They intermediate or coordinate ("inscribe") the activities of a group of would-be adopters. Unfortunately, little is known of how these organizations shape the EDI diffusion trajectory. In this article we examine one specific type of intermediating organizations?industry associations?and how they advanced the EDI diffusion process in the grocery sectors of Hong Kong, Denmark and Finland. We identify six institutional measures, placed into a matrix formed by the mode of involvement (influence vs. regulation) and the type of diffusion force (supply push vs. demand pull), that can be mobilized to further the EDI diffusion. Industry associations were found to be active users of all these measures to varying degrees. Their role was critical especially in knowledge building, knowledge deployment, and standard setting. Furthermore, institutional involvement varied due to policy and cultural contingencies and power dependencies.     

How Electronic Publishers are Protecting Against Piracy: Doubts About Technical Systems of Protection

The increasing prospects of digital piracy has prompted the perceived need by electronic publishers to adopt technical systems of protection, and governments to reform their copyright laws. This article is a preliminary study of the management of intellectual property by electronic publishers, defined as those involved in the production of online databases, and CD-ROMs. It focuses on three main issues: (1) how electronic publishers view the increasing threat of piracy; (2) the methods of protection employed to protect intellectual property in digital format; and (3) the importance of technological protection of intellectual property in electronic publications. The analysis is based on a sample of 23 UK electronic publishers. The interviews revealed an interesting assortment of protection methods and did not show that technological protection was a preferred way. Instead, the means of protection, in addition to copyright law, comprised niche markets, pricing, trust, bad publicity, and nontechnical and technical means.     

Rough Justice: A Statistical Assessment of ICANN's Uniform Dispute Resolution Policy

Long-standing conflict between domain name registrants and trademark holders prompted the Internet Corporation for Assigned Names and Numbers (ICANN) to create a global, mandatory arbitration procedure known as the Uniform Dispute Resolution Policy (UDRP). The UDRP has been used in 2166 cases involving 3938 domain names as of 1 November 2000. The policy gives the initiator of a complaint, generally a trademark holder, the right to choose which ICANN-accredited dispute resolution service provider (RSP) will handle the case. During the preparation of the UDRP,some feared that complainant selection would lead to "forum shopping" that might bias the results. This article performs a statistical assessment of the forum-shopping thesis and finds support for it. There are statistically significant differences in the various RSPs' propensity to take away names from defendants; there are also major differences in the number of cases brought to each RSP. RSPs who take away names have the larger share of cases. The study examines other variables that might explain differences in market share, such as price, the plaintiff's nationality, or the time taken to decide a case. It finds that nationality and time also are correlated with market share. The study concludes that shopping for a favorable outcome is an important factor in the UDRP.     

Prevalence of soft neurological signs in Chinese people

Prof. Raymond C.K. Chen, a neuropsychologist with the CAS Institute of Psychology, has made novel progress in his studies of schizophrenia. His work has been reported by a recent issue of Behavioural Neurology.     

Molecular motor assembly of a biomimetic system

Active biological molecules and functional structures can be fabricated into a bio-mimetic system by using molecular assembly method. Such materials can be used for the drug delivery, disease diagnosis and therapy, and new nanodevice construction.     

Monoculture Rubber Plantations Have Negative Ef ects on Controlling Splash Erosion

<正>In Xishuangbanna,one of China’s most biodiverse regions,landscape has changed dramatically during the past three decades due to the conversion of tropical rainforest to rubber plantations.In steep areas,terraces are often constructed before planting rubber trees,which causes two important changes in the soil:the destabilization of soil in the bench terraces and the increased vulnerability of unvegetated riser faces to erosion.Few studies have documented the nature and intensity of erosion on bench terraces.Prof.LIU Wenjie and his colleagues from the Xishuangbanna Tropical Botanical Garden(XTBG)conducted a study in Menglun County(21°5′39″N,101°15′55″E),Xishuangbanna to evaluate the influence