基于码元频数检测的比特序列加密算法

采用随机性码元频数检测的方法实现对链路层加密数据的识别,提高随机性码元频数检测识别率。传统方法采用随机抽样的比特序列加密方法,加密与未加密链路层出现混同,加密性能不好。提出一种基于随机性码元频数检测的比特序列加密算法。构建随机性码元频数检测保密通信系统,建立随机性码元频数比特序列模型,选择分块长度作为分块长度目标值,求解发送端随机性码元频数比特序列加密的时延,进行码元频数检测,实现比特序列加密算法改进。获得足够泛化性能的控制密钥,提高承载信息信号所引起的随机性码元频数比特序列的抗噪性能。仿真结果表明,采用该算法,能有效提高对未加密数据的识别率,提高识别结果的可信度,展示了较好的应用价值。     

基于Chirp导频的DS-CDMA信道多径时延估计

直接序列扩频(DS-CDMA)通信系统存在的多径衰落特性使通信系统的性能急剧恶化,必须精确的估计出多径信道时延以便更好的设计通信系统。Chirp导频信号包含丰富的时域和频域信息,通过发射单分量Chirp信号作为直接序列扩频(DS-CDMA)的导频信号,在接收端采用用分数阶傅立叶变换(FRFT)进行多径时延估计。仿真结果表明该算法有良好的估计性能。     

超短波无线通信保密技术的应用分析

本文讨论GOLD序列等不同跳频序列的性能,基于队列理论,通过增大跳频序列线性复杂度,提出了混合混沌映射跳频序列方法,仿真证明该方法可增加系统的抗预测能力,且跳频序列的平衡性等性能良好,容易实现,适用于超短波通信系统,基于对无线信道分析,利用训练系列判决反馈均衡快速信道估算方法,运用混沌序列实现保密通信功能。串联结构的混沌扩频序列容易实现,保密性能优异。     

基于蜂窝网传输的文本混沌保密通信

针对局域网中进行保密通信在空间上和距离上的局限性,提出了以Android移动终端为基础,蜂窝网为传输载体结合混沌保密算法进行文本数据加密传输的设计;介绍了Android客户端程序及服务器上服务端程序的设计流程,给出了混沌保密算法的整个设计详情,最终实现了加密文本通过蜂窝网的传输保密性;实验结果也证实了该设计具有极好的保密性能和数据传输性能。     

基于频带划分关键帧编码的信息隐藏算法

信息隐藏技术是保证网络数据传输安全性和保密性的关键技术,设计信息隐藏算法提高数据保密通信性能。传统方法采用全监督学习加密算法,无法获得足够泛化性能的控制密钥,抗噪性能差,信息隐藏效果不好。提出一种基于频带划分关键帧编码的信息隐藏算法。对簇内的成员进行管理,对WZ帧进行DCT变换,得到DCT系数带,每个系数带进行均匀量化,构造节点数据并查集把Wyner-Ziv编码思想应用到关键帧中,DCT变换后的关键帧进行频带划分,设计低频带编解码方法,提高信息隐藏性能。实验结果表明,该算法能有效实现信息隐藏,数据的编码和解码性能较好,信噪比提高,性能优于传统算法。     

水声跳频通信系统的设计与实现

本文以工程需求开展水声跳频通信的研究,针对复杂信道特点提出一套适合于多途环境下的水声跳频通信方法,并构建了通信系统。开发数字信号处理算法,在水池实验条件下,实现了跳频编码信号的解调,恢复出基带通信信息。     

高安全低成本保密电话设计与实现

针对基于传统的密码算法保密电话数据加密存在的缺陷,提出一种基于成对载波和混沌加密技术的保密电话解决方案。该方案用成对载波和回波抵消的体制保证语音信号的安全,用密码的方法保证整个数字传输通信系统的安全性,因此,电话系统保密性更高,实用性更强。     

复杂光传感器网络通信的非线性失真抑制算法

光传感器网络通信应用环境中,受到发射功率高、电磁干扰强等复杂背景影响,导致通信信号非线性失真,需要进行非线性失真抑制处理,改善传感器网络通信性能。提出一种基于单周信道正负信号特征配准的复杂光传感器网络通信的非线性失真抑制算法。将传感器网络通信系统的通信实信号分解为正信号和负信号,采用分段拟合的方式,构建复杂光传感器信号解析模型,进行特征配准实现非线性失真抑制。仿真实验以峰值平均功率比为评价指标,进行性能验证,结果分析表明,采用该算法进行复杂光传感器网络通信,稳定性和精确度优于传统算法,抗噪性能较好,提高峰值平均功率,能有效实现非线性失真抑制。     

应用双重滤波去噪的混合加密图像认证算法

为了避免图像压缩与恶意篡改对图像认证的影响,提出一种以图像自适应中值滤波和Haar小波滤波为基础,通过混合加密处理来实现的图像认证算法。在图像双重滤波去噪的基础上,算法通过DCT和DWT混合变换域提取图像的特征信息,并且结合幻方算法和Arnold算法对图像进行混合加密,接收方通过密钥与hash值进行认证。实验结果表明,算法提高了抗图像压缩和图像篡改的性能,并且能够快速检测并精确定位篡改位置,为图像在网络中传输提供了较好的安全性。     

OFDM通信系统设计与分析

正交频分复用(OFDM)作为4G中的关键技术,不但有很高的频带利用率,而且它的抗多径干扰能力也十分优秀。本文设计了一个基于FFT算法的OFDM通信系统,在计算机上进行了仿真。从仿真的结果可以看出,经过高斯白噪声信道前后的信号产生了失真。为了初步验证本系统的正确性,输入不同的信噪比并计算信号通过本系统的误码率,并最终得到验证。     

To serve and promote science development via innovation

CAS should stick to the principle of rendering service to, and giving impetus for, the development of China＇s science enterprise by making S＆T innovations, said CAS President LU Yongxiang. The CAS president made the remarks in a recent talk to communicate the gist of the winter session of the Party＇s Leading-member Group at CAS, which was held from 7 to 11 January in Beijing.     

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.     

Tracing the origin and early radiation of birds——Paleornithologist ZHOU Zhonghe

With great care, Dr. ZHOU Zhonghe takes out a package wrapped by cotton tissue from a drawer and says: "This is the gem of our collections: the fossil of a bird that lived 125 million years ago!" Then, pointing at a tiny mound, he explains: "Look, this is the claw and that is the head. It was in the egg shell and ready to hatch ... The species fell into a family of waterside inhabitants."     

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.     

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.     

Stern-Gerlach effect goes chiral

Prof. SUN Changpu from the CAS Institute of Theoretical Physics and coworkers from University of Basel in Switzerland have worked out a way --at least in theory --to split a beam of molecules according to their chirality. The technique involves passing the molecules through three different laser beams and is similar to the famous Stern-Gerlach effect, whereby a beam of atoms passing through a magnetic field is split in two according to the atoms＇ spin states （Phys. Rev. Lett. 99 130403）.