共查询到20条相似文献，搜索用时 62 毫秒
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主动声呐自导系统发出的回波信号表现为一种频域展宽信号,对频域展宽信号的准确检测是实现声呐精确探测的技术难题。传统方法中采用分数阶傅立叶变换方法设计检测算法,声呐自导系统径向运动过程中的回波与样本之间的失配导致检测性能下降。利用自然对数变换对线性调频信号的能量聚焦特性,提出一种基于自然对数似然分解的频域展宽信号能量聚集方法,构建主动自导系统回波频域展宽信号模型构建,进行算法改进设计,实现对主动声呐自导系统回波信号的准确检测。仿真实验结果表明,算法能使回波信号在自然对数频域产生明显的能量聚集,提高检测性能,检测概率较传统方法提高明显。 相似文献
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提出一种改进的飞控雷达系统雷达波模糊度函数控制距离估计算法,并将算法有效进行移植进行软件设计,应用于飞机飞行控制智能距离估计系统中。采用对数调频信号的调频形式构建飞控距离估计信号模型,分析了该信号的模糊度函数及对距离的分辨力。提取攻击和地面目标检测性能曲线,设计了飞控智能距离估计软件系统并进行安装调试。算法仿真实验和软件系统测试性能表明,相比传统的线性调频波信号雷达距离估计,改进的飞控距离估计算法能在信噪比极低环境下,随着飞机姿态速度的快速变换,距离估计结果精确。软件设计平台具有较好友好性和人际交互性,能有效移植到飞机控制平台中。 相似文献
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对高速运动目标的基带回波扩散参数的准确估计和挖掘是实现目标信号检测和参量估计的重要内容。高速运动目标在发射脉冲是产生多普勒扩散,导致在速度模糊的情况下对基带回波参数估计困难。提出一种基于AT-Tree模式挖掘模式的运动目标的基带回波扩散参数估计算法。构建高速运动目标信号模型和目标多普勒扩散模型,基于AT-Tree模式进行基带回波随机过程分析,建立项的平均概率值得到AT-Tree树型结构,将有序的项集添加到AT-Tree上,实现对基带回波扩散参数的挖掘和估计,在分辨力足够的前提下,对参数实现高分辨搜索,提高挖掘性能。仿真结果表明,该算法能使高速运动目标的基带回波调频信号在分数域上能形成明显的能量积聚,形成一个冲激函数,基带回波扩散参数的数据挖掘的精确度较高,精度较好,在制导参数估计和目标检测等领域应用价值较高。 相似文献
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在分组交换网络通信系统中,由于带宽频移键控产生谐振干扰,导致信号传输不稳定,甚至产生误码和丢包。提出一种基于连续小波变换与带宽时延-尺度耦合特性构建的复杂网络带宽频间谐振抗干扰算法。对抗干扰模型进行时间-尺度分析,把干扰信号模型分解成一组带宽双曲调频信号,并分析信号时间平移与尺度伸缩等同效应,有效抑制谐振干扰。仿真验证了算法的有效性,时间-尺度建模分析结果准确,有效抑制了网络带宽频间谐振干扰,大幅降低了复杂分组交换网络通信的误码率,对提高网络安全性能具有积极意义。 相似文献
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航行器随着下潜深度增加受到的压力也随之增加,当下潜到一定深度压力出现异常会影响到航行器的稳定运行。传统的水下航行器压力检测系统存在不能动态组网以及不能对异常压力进行准确检测等弊端。为此,设计出一种新的水下航行器异常压力检测网络系统,对检测系统的通信协议、硬件设计方案和数据采集方法分别进行了详细的阐述。检测系统改进了路由协议,提高了对异常压力信号检测的准确性。实验结果证明,该系统具有较强的稳定性,能够提高对航行器异常压力信号的检测的准确性。 相似文献
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提出基于dbN小波算子小波变换分解行星齿轮故障特征的故障检测算法,算法可以在轻微损坏时就较好地判断出齿轮故障。通过分析行星齿轮的故障成型,以及故障的冲击振动传播路径,建立其故障模型,在利用小波变换方法对其故障信号进行分析,检测方法可以较好地进行故障识别与检测,对比传统的傅里叶变换,新算法可以对微弱信号识别,能同时判断缺陷轮齿的频率和出现的时间,在排除故障时能准确分析故障位置,以及故障类型。仿真实验表明改进算法小波变换,具有弱信号检测能力强,准确判断故障出现时间,为尽早发现故障与解决故障问题提供了保障,故障检测概率提高了15%。具有较好的工程实用性。 相似文献
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《科技通报》2015,(10)
ipsweep攻击信号广泛存在于复杂进化网络系统中,对其实现自校正分离,进行攻击信号准确检测。传统算法采用PSO辨别树算法进行复杂进化网络的ipsweep攻击自校正分离算法设计,存在自适应差和检测性能不好的问题。提出一种基于Dopplerlet变换匹配投影ipsweep攻击自校正分离算法。提取攻击信号传播路径的随机概率密度特征,计算自校正分离属性的信息熵的预测值,提取信号在Dopplerle空间中相干点积功率累积尺度坐标,得到ipsweep攻击信号的自校正分离模型改进设计。仿真结果表明,该算法能有效提高对ipsweep攻击信号检测性能,传统算法的检测概率为63%,而该算法的检测概率为92%,检测性能提升明显,且能有效实现对ipsweep攻击信号Dopplerle空间谱检测。 相似文献
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A research 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 in red wine-can improve the sensitivity of mice to the hormone insulin according to a report in the October issue of Cell Metabolism.…… 《中国科学院院刊(英文版)》2008,22(1):14-15
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. 相似文献
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《中国科学院院刊(英文版)》2008,22(1):2-3
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. 相似文献
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Marjorie Armstrong-Stassen Margaret Landstrom Ramona Lumpkin 《The Information Society》1998,14(2):153-164
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. 相似文献
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《中国科学院院刊(英文版)》2008,22(1)
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." 相似文献
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Active biological molecules 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 therapy new nanodevice construction.…… 《中国科学院院刊(英文版)》2008,22(1):22-22
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. 相似文献
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A joint study by Prof. ZHANG Zhibin from the CAS Institute of Zoology his co-workers from Norway US 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 the National Academy of Sciences on September .…… 《中国科学院院刊(英文版)》2008,22(1):6-7
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. 相似文献
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Caroline Haythornthwaite 《The Information Society》2001,17(3):211-226
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. 相似文献
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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. 相似文献
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Leah A. Lievrouw 《The Information Society》2000,16(2):155-159
This essay focuses on universal service and the Internet as means to support social and political participation. The emphasis on access to telecommunications systems in conventional approaches to universal service is contrasted with access to content. A model of the information environment is described that accounts for the roles of content and conduit, both of which are necessary conditions to achieve true access. A method is outlined for employing information indicators to observe or measure the information environment. 相似文献
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Puay Tang 《The Information Society》1998,14(1):19-31
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. 相似文献