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排序方式: 共有2533条查询结果,搜索用时 15 毫秒
961.
Zekun Zhou Yue Shi Peisheng Zhu Yingqian Ma Huiying Wang Xin Ming 《International Journal of Electronics》2013,100(4):519-530
Various emission instabilities in oxide cathodes are discussed and interpreted by means of a model of dynamic surface emission centres. According to this model, barium atoms adsorbed on BaO, SrO or CaO on the surface of both the coating and the base metal can form effective emission centres. As bulk conduction through the grains is poor, the number of emitted electrons is larger than the number of electrons injected from the base metal under the high-current condition. Hence some grains are charged up to a high potential across the coating. This uneven potential distribution on the grain surface leads to a repeated bombardment of the grain by porous conducting electrons, which may produce dissociation of the oxide, secondary electron emission and heating of the grain. Since these processes alter the surface composition, which is a dominant factor in thermionic emission, instability of thermionic emission results. In extreme cases this instability may lead to local sparking. 相似文献
962.
Zekun Zhou Luping Feng Yingqian Ma Yue Shi Xin Ming Bo Zhang 《International Journal of Electronics》2013,100(10):1427-1438
A novel bandgap reference (BGR) with low temperature and supply voltage sensitivity without any resistor, which is compatible with standard CMOS process, is presented in this article. The proposed BGR utilises a differential amplifier with an offset voltage proportional to absolute temperature to compensate the temperature drift of emitter–base voltage. Besides, a self-biased current source with feedback is used to provide the bias current of the BGR core for reducing current mirror errors dependent on supply voltage and temperature further. Verification results of the proposed BGR implemented with 0.35?µm CMOS process demonstrate that a temperature coefficient of 10.2?ppm/°C is realised with temperature ranging from ?40°C to 140°C, and a power supply rejection ratio of 58?dB is achieved with a maximum supply current of 27?µA. The active area of the presented BGR is 160?×?140?µm2. 相似文献
963.
针对纠错输出编码分解框架的自身特点、从降低误判风险出发,研究了带拒绝域的ECOC多类分类方法.首先在二类划分过程中引入拒绝域,对不属于正负子类的待识别样本进行拒识;其次,在基分类器内部引入拒绝域,以最小化风险贝叶斯决策为目标,利用后验概率输出和代价矩阵寻找拒绝域阈值,对样本输出值落入拒绝域中的样本进行拒识;最后,研究了不同拒绝域输出的解码方法,并讨论了拒识码字个数和矩阵最小Hamming距离之间的关系.实验结果表明基于二类划分构造的拒绝域能够提高分类正确率,而基于基分类器构造的拒绝域能够减小分类代价. 相似文献
964.
为解决超外差接收机中镜像干扰的问题,采用了一种有源陷波滤波器(active notch-filter)来实现镜像抑制功能。并在此基础上设计了用于数字音频广播(Digital Audio Broadcast,DAB)系统的低噪声放大器。该LNA电路工作在L-band1.472GHz,,经过第一次变频到165MHz,其镜像频率为1.142GHz,有源陷波滤波器可提供超过55dB的镜像抑制度。整个LNA电路采用1.8V电源,消耗5mA电流,S11和S22分别为-22dB和-16dB,功率增益为21dB。噪声指数为1.45dB,输入P1db点为-25dBm。 相似文献
965.
Can Haimolu Murat Ciniviz brahim
zsert Yakup ingür Adnan Parlak M. Sahir Salman 《Renewable Energy》2008,33(7):1709-1715
Vegetable oils are a promising alternative among the different diesel fuel alternatives. However, the high viscosity, poor volatility and cold flow characteristics of vegetable oils can cause some problems such as injector coking, severe engine deposits, filter gumming, piston ring sticking and thickening of lubrication oil from long-term use in diesel engines. These problems can be eliminated or minimized by transesterification of the vegetable oils to form monoesters. These monoesters are known as biodiesel. The important advantages of biodiesel are lower exhaust gas emissions and its biodegradability and renewability compared with petroleum-based diesel fuel. Although the transesterification improves the fuel properties of vegetable oil, the viscosity and volatility of biodiesel are still worse than that of petroleum diesel fuel. The energy of the biodiesel can be released more efficiently with the concept of low heat rejection (LHR) engine. The aim of this study is to apply LHR engine for improving engine performance when biodiesel is used as an alternative fuel. For this purpose, a turbocharged direct injection (DI) diesel engine was converted to a LHR engine and the effects of biodiesel (produced from sunflower oil) usage in the LHR engine on its performance characteristics have been investigated experimentally. The results showed that specific fuel consumption and the brake thermal efficiency were improved and exhaust gas temperature before the turbine inlet was increased for both fuels in the LHR engine. 相似文献
966.
967.
为保证自主水下航行器在进行地形跟踪任务时,可以更好地抵抗外界环境及自身信号传输的干扰作用,提出一种基于自抗扰控制技术的地形跟踪控制方法,可以将地形跟踪转化为水下机器人的纵倾控制,并设计有运动保护机制。在仿真实验中,利用所设计方法,进行了三维运动仿真,模拟了机器人从水面到水下完成地形跟踪任务的全过程,并与基于PID控制方法的控制器进行比较。结果表明,基于自抗扰控制技术的地形跟踪控制方法能够准确完成预定任务,同时,相比于基于PID的跟踪方法,能够更有效地抑制干扰所造成的超调和震颤等现象,具有更优的控制效果。 相似文献
968.
This paper presents a new Ultra-WideBand (UWB) BandPass Filter (BPF) using half-wavelength (??/2) Stepped-Impedance Stub-Loaded Resonator (SISLR). Analytical equations derived by the even-odd mode analysis show the new filter has two tunable transmission zeros at both sides of the passband to provide a sharp rejection and seven transmission poles inside the passband to achieve U.S. UWB performance. For verification, a UWB BPF is designed, fabricated and measured. The measured results show that the fabricated filter has a -3 dB fractional bandwidth from 3.0 GHz to 10.9 GHz and its insertion loss less than 0.9 dB over the whole passband. Furthermore, the new filter exhibits a simple topology, sharp rejection, and deep stopband suppression. 相似文献
969.
高电源电压抑制比基准电压源的设计 总被引:1,自引:0,他引:1
在此通过对带隙基准电压源电路进行建模分析,针对逆变电路的中低频使用环境,设计了一个应用于高压逆变器电路中的高电源电压抑制比,低温度系数的带隙基准电压源。该电路采用1μm,700 V高压CMOS工艺,在5 V供电电压的基础上,采用一阶温度补偿,并通过设计高开环增益共源共栅两级放大器来提高电源电压抑制比,同时使用宽幅镜像电流偏置解决因共源共栅引起的输出摆幅变小的问题。基准电压源正常输出电压为2.394 V,温度系数为8 ppm/℃,中低频电压抑制比均可达到-112 dB。 相似文献
970.