共查询到20条相似文献,搜索用时 125 毫秒
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简单介绍了毫米波的基本概念及相关背景,分析了毫米波的四个传播特性,并由此引出毫米米波通信具有通信容量大,安全保密好,传输质量高及全天候通信四大优点.阐述了毫米波地面通信及毫米波卫星通信的发展情况,以毫米波通信技术在电子对抗中的军事应用为例进行重点探讨,最后展望毫米波通信技术将会开创未来新型应用领域并拥有广阔的发展前景。 相似文献
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由于毫米波在技术上的优势,使得工作在毫米波频段的接收机具有体积小、重量轻、携带信息容量大和抗干扰能力强等特点,受到越来越广泛的应用。论述了毫米波接收机主要工作原理、研制过程及研制结果。该毫米波接收机主要包括毫米波功和器、电调衰减器、开关、毫米波LNA以及毫米波混频器等多个单元。通过电路优化设计,研制出的毫米波接收机增益为23.2 dB;噪声系数为11 dB;开关隔离度为42 dB;开关速度为3 ns。 相似文献
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The authors present a survey of modern nonlinear CAD (computer-aided design) techniques as applied to the specific field of microwave circuits. A number of fundamental aspects of the nonlinear CAD problem, including simulation, optimization, intermodulation, frequency conversion, stability, and noise, are addressed and developed. For each one it is shown that either well-established CAD solutions are available, or at least a solution approach suitable for implementation in a general-purpose CAD environment can be outlined. Also, the discussion shows that the various subjects are not just separate items, but rather can be chained in a strictly logical sequence. Finally, an elementary treatment of vector processing is given, to show that supercomputers can handle the involved large-size numerical problems efficiently 相似文献
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The first-order nonlinear analysis of IMPATT diodes is performed and a model is obtained in which the nonlinear effects due to avalanche are separated from the activity and transit-time effects. Such a mildly nonlinear model is suitable for CAD applications. The determination of the model parameters by means of small signal measurements is outlined, and the applicability of the proposed model is demonstrated on real devices. 相似文献
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Use of sample entropy approach to study heart rate variability in obstructive sleep apnea syndrome 总被引:6,自引:0,他引:6
Sample entropy, a nonlinear signal processing approach, was used as a measure of signal complexity to evaluate the cyclic behavior of heart rate variability (HRV) in obstructive sleep apnea syndrome (OSAS). In a group of 10 normal and 25 OSA subjects, the sample entropy measure showed that normal subjects have significantly more complex HRV pattern than the OSA subjects (p < 0.005). When compared with spectral analysis in a minute-by-minute classification, sample entropy had an accuracy of 70.3% (69.5% sensitivity, 70.8% specificity) while the spectral analysis had an accuracy of 70.4% (71.3% sensitivity, 69.9% specificity). The combination of the two methods improved the accuracy to 72.9% (72.2% sensitivity, 73.3% specificity). The sample entropy approach does not show major improvement over the existing methods. In fact, its accuracy in detecting sleep apnea is relatively low in the well classified data of the physionet. Its main achievement however, is the simplicity of computation. Sample entropy and other nonlinear methods might be useful tools to detect apnea episodes during sleep. 相似文献
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The diagnosis of coronary artery disease (CAD) is an important task in the management of cardiology patients. Recently, the use of pharmacological stress testing has become available as an alternative to exercise stress testing (ETT). A new system (device-drug combination) was developed specifically for the diagnosis of coronary artery disease. The system uses a novel catecholamine, arbutamine, which is infused intravenously to increase heart rate (HR) and cardiac contractility in order to evoke signs of ischemia. The development of a closed-loop control algorithm for the delivery of this drug and a pharmacodynamic (PD) model representing the HR response to arbutamine infusions are presented. Model parameters are estimated from clinical data on normal volunteers and patients. Based on this mathematical model, a rule-based control algorithm is designed. The structure of the control algorithm is discussed and testing of the algorithm based on simulations and animal and human trials are summarized. Results from clinical trials shows that the algorithm controls the HR increase according to a selected trajectory. The automated delivery of the drug can provide the cardiologist with an efficient, effective, and safe method for administering a pharmacological stress test 相似文献
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Evaluation of respiratory muscles activity by means of cross mutual information function at different levels of ventilatory effort 总被引:1,自引:0,他引:1
Alonso JF Mañanas MA Hoyer D Topor ZL Bruce EN 《IEEE transactions on bio-medical engineering》2007,54(9):1573-1582
Analysis of respiratory muscles activity is an effective technique for the study of pulmonary diseases such as obstructive sleep apnea syndrome (OSAS). Respiratory diseases, especially those associated with changes in the mechanical properties of the respiratory apparatus, are often associated with disruptions of the normally highly coordinated contractions of respiratory muscles. Due to the complexity of the respiratory control, the assessment of OSAS related dysfunctions by linear methods are not sufficient. Therefore, the objective of this study was the detection of diagnostically relevant nonlinear complex respiratory mechanisms. Two aims of this work were: (1) to assess coordination of respiratory muscles contractions through evaluation of interactions between respiratory signals and myographic signals through nonlinear analysis by means of cross mutual information function (CMIF); (2) to differentiate between functioning of respiratory muscles in patients with OSAS and in normal subjects. Electromyographic (EMG) and mechanomyographic (MMG) signals were recorded from three respiratory muscles: genioglossus, sternomastoid and diaphragm. Inspiratory pressure and flow were also acquired. All signals were measured in eight patients with OSAS and eight healthy subjects during an increased respiratory effort while awake. Several variables were defined and calculated from CMIF in order to describe correlation between signals. The results indicate different nonlinear couplings of respiratory muscles in both populations. This effect is progressively more evident at higher levels of respiratory effort. 相似文献
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Pouladian M Golpayegani MR Tehrani-Fard AA Bubvay-Nejad M 《IEEE transactions on bio-medical engineering》2005,52(4):743-747
Coronary artery disease (CAD) causes oscillations in peripheral arteries. Oscillations of the walls of the brachial arteries of 51 patients were recorded [together with the electrocardiogram (ECG)] by an accelerometer at different cuff pressures. By analyzing the energy of the oscillations in the 30-250 Hz band, 16 of 22 patients with CAD and 26 of 29 non-CAD subjects were classified correctly, independent of the ECG, and with no effect of heart murmurs. 相似文献
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目的了解急性冠脉综合征患者冠脉CTA、冠脉造影、OCT的表现。方法急性冠脉综合征患者3例,在行冠脉造影前均行64排CT(Somatom Definition)冠脉CTA检查,明确罪犯病变;常规冠状动脉造影后行OCT检查(Lightlab),分别分析冠脉CT、冠脉造影和OCT影像学结果。结果冠脉CTA均提示为软斑块,斑块最低CT值均小于100Hu,1例伴有轻度钙化,斑块负荷较重,均呈正性重构;OCT示2例有极薄的纤维帽(分别为50μm和40μm),纤维帽后有大的脂核。结论冠脉CTA对于血管壁较宏观的观察较有优势,冠脉造影可以动态观察血管的情况,OCT可细致观察血管壁、斑块和血栓。 相似文献
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《Microwave Theory and Techniques》2009,57(6):1425-1432
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A CAD-oriented nonlinear model of SiC MESFET based on pulsed I(V),pulsed S-parameter measurements 总被引:1,自引:0,他引:1
Siriex D. Noblanc O. Barataud D. Chartier E. Brylinski C. Quere R. 《Electron Devices, IEEE Transactions on》1999,46(3):580-584
In order to use SiC devices in CAD nonlinear circuits, a nonlinear model of 4H-SiC MESFET has been obtained using a technique based on pulsed I(V) characteristics and pulsed S-parameter measurements. The nonlinear I-V drain-source current was represented using a table-based model which was implemented in a harmonic balance simulator. Its accuracy is shown by a comparison with active load-pull measurements 相似文献