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排序方式: 共有637条查询结果,搜索用时 15 毫秒
1.
主要研究了CDMA蜂窝通信系统的工作原理,且以基于IS-95标准的前向链路为主。利用MATLAB软件建立了前向链路中各器件的模块,实现了CDMA基带信号发生器,并在时域及频内进行了测量。 相似文献
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A network of powerful personal computers, linked by a high-speed local area network, is being seen increasingly as an alternative to a traditional centralized time-sharing operating system. The PULSE project is investigating how such a system may be constructed to give the benefits of a self-sufficient personal computer to each user without losing the facilities for communication and sharing of data inherent in centralized systems. In particular, a distributed file system has been built which provides a single global UNIX 1 UNIX is a trademark of Bell Laboratories. -like hierarchy, with a consistent appearance when accessed from any machine. Replicated copies of files are maintained to improve reliability, increase performance, and enable each machine to run stand-alone, albeit with reduced facilities. 相似文献
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研究了在250℃、不同挤压比下挤压变形对Mg95 Zn4.3 Y0.7合金组织及性能的影响。结果表明,Mg95 Zn4.3 Y0.7经过挤压变形后,合金中晶界处的共晶相破碎,弥散分布至晶粒内部,并且晶粒显著细化。同时,随着挤压比的增大,晶粒细化程度增加,合金的力学性能单调增加。当挤压比为16时,合金晶粒尺寸为5-8μm,抗拉强度为288.9MPa,显微硬度HV值为117.8。 相似文献
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Epilepsy is a neurological disorder which is characterized by transient and unexpected electrical disturbance of the brain. The electroencephalogram (EEG) is a commonly used signal for detection of epileptic seizures. This paper presents a new method for classification of ictal and seizure-free EEG signals. The proposed method is based on the empirical mode decomposition (EMD) and the second-order difference plot (SODP). The EMD method decomposes an EEG signal into a set of symmetric and band-limited signals termed as intrinsic mode functions (IMFs). The SODP of IMFs provides elliptical structure. The 95% confidence ellipse area measured from the SODP of IMFs has been used as a feature in order to discriminate seizure-free EEG signals from the epileptic seizure EEG signals. The feature space obtained from the ellipse area parameters of two IMFs has been used for classification of ictal and seizure-free EEG signals using the artificial neural network (ANN) classifier. It has been shown that the feature space formed using ellipse area parameters of first and second IMFs has given good classification performance. Experimental results on EEG database available by the University of Bonn, Germany, are included to illustrate the effectiveness of the proposed method. 相似文献
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针对目前读卡器主频低、速度慢、便携性差等不足,提出了一种基于S3C6410的RFID读卡系统设计方案。本文以高性能的S3C6410嵌入式微处理器为核心,选用新型的CR95HF射频芯片,开发设计了一款高主频的搭载Android嵌入式系统的新型手持式RFID读卡器。该读卡器工作在高频13.56MHz,支持ISO14443、ISO15693等多种协议。实验证明,该读卡器能对符合协议的标签进行读写操作,读写距离能够满足需要,具有便携、稳定性高、处理速度快等特点。 相似文献
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Simon Piché 《Chemical engineering science》2005,60(22):6452-6461
The oxidative absorption of hydrogen sulfide (H2S) into a solution of ferric chelate of trans-1,2- diaminocyclohexanetetraacetate (CDTA) was studied in a counter-current laboratory column randomly packed with 15 mm plastic Ralu rings. The present investigation takes concern about the Kraft pulping situation where dilute H2S concentrations are omnipresent in large-volume gas effluents. A fractional two-level factorial approach was instigated to determine the significance of six operating variables, namely the solution's alkalinity (pH; 8.5-10.5), the liquid mass flow rate (L;1.73-), the solution's ionic strength (IC;0.01-), the gas mass flow rate (G;0.19-), the inlet H2S concentration (CH2S,0;70-430 ppm) and the initial ferric CDTA concentration (CFe,0;100 -). Initially, a Plackett-Burman design matrix of seven duplicated experiments revealed that pH is the leading factor controlling the H2S conversion rate while the ionic strength and ferric CDTA concentration effects remained negligible within the factorial domain. Surface response analysis based on 11 duplicated factorial experiments plus 10 central composite trials revealed that the H2S conversion significantly increases with liquid flow rate but decreases with growing H2S load up. Further examination about the influence of ferric CDTA on H2S absorption rate was set up over a broader concentration range (CFe,0;0- at pH of 9.5 and 10.5. It showed good potential at as H2S conversion increased by a significant 25% for both pH values in comparison to pure alkaline solutions containing no ferric CDTA. 相似文献
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C90油管钢的氢损伤 总被引:4,自引:0,他引:4
对比研究了三种油管钢(宝钢的C90和日本的SM90及SM95)的氢致开裂性能.SM90,SM95和C90产生氢损伤的临界扩散氢质量分数(×10~(-6))分别为1.76,4.3和8.38;临界全氢质量分数(×10~(-6))分别为4.24,6.35和10.22三种钢在H_2S中的门槛应力σ_(th)/σ_s分别为0.64,0.80和0.85.三种油管钢抗氢损伤能力和抗氢致滞后断裂的能力是一致的,以C90为最好,它和氢的扩散系数无关.C90钢缺口试样氢致滞后断裂门槛值K_(IH)与可扩散的氢质量分数w_0有关,实验获得K_(IH)=46-12.51ln_(w0).理论分析和实验结果完全一致.对C90钢,当w_0≤4.8×10-6时,在任何K_I/K_C下均将获得韧窝断口;w_0≥7.6×10~(-6),K_I/K_C≥0.5时,则氢致韧断;K_I/K_C≤0.4时,则氢致脆断. 相似文献
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