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91.
92.
张曙辉 《水利与建筑工程学报》2002,8(3):15-20
使用进口或国产核子密度仪测定土坝及土堤压实干密度具有操作简便、快速之优点。通过对不同的土质进行了现场核子密度仪与环刀法测定干密度的对比试验后 ,证明核子密度仪在测定土的干密度时 ,用环刀法测定并进行校核是必要和重要的 相似文献
93.
Ran-Rong Lee 《Journal of the American Ceramic Society》1991,74(9):2242-2249
AIN ceramics with densities varying from 3.18 to 3.30 g/cm3 and room-temperature thermal conductivities varying from 88 to 193 W/m K were produced. Different sintering conditions, packing powders, AIN powder sources, carbon additive, and sintering times were evaluated, and the key processing parameters which cause the differences in density and thermal conductivity were identified. SEM, TEM, and EDS were used to characterize the correlation between thermal conductivity, microstructure, and processing parameters. The important parameters which control the thermal conductivity of AIN ceramics are discussed. 相似文献
94.
热释电系数的测量方法 总被引:2,自引:0,他引:2
描述热释电系数的两种测量方法。其一为电荷积分法,测试系统简单,测量数据准确,且能满足零电场条件下的测量。其二为动态电流法,采用调制热源技术,研究在特定温度条件下热释电材料的动态热释电响应。 相似文献
95.
电流模式n阶传输函数的OA-OTA实现 总被引:1,自引:0,他引:1
马云辉 《固体电子学研究与进展》2002,22(3):294-296,360
提出了一种新的实现任意 n阶电流模式传输函数的网络结构。该电路仅含运算放大器 (OA)和运算跨导放大器 (OTA)有源器件 ,因而适于全集成。适当设置 OTA的跨导值能实现任意高阶传输函数 ,且传输函数的系数可独立调整。文中推导了滤波器的设计公式 ,并给出了截止频率为 1 0 0 k Hz的三阶巴特沃斯低通滤波器实例 ,PSPICE仿真结果表明所提电路及设计公式是正确的 相似文献
96.
Hiroaki Yamada Toshihiko Tanaka Shigeyuki Funabiki 《Electrical Engineering in Japan》2006,157(4):56-65
This paper proposes a novel method of suppressing the inrush current of transformers. A small‐rated voltage‐source PWM converter is connected in series to the transformers through a matching transformer. As the connected PWM converter serves as a resistor for the source current, no inrush phenomena occurs. The required rating of the PWM converter, which serves as the damping resistor for the inrush phenomena, is 1/400 that of the main transformers in single‐phase circuits. In three‐phase circuits, it is 1/900. The basic principle of the proposed method is discussed. Digital computer simulation is implemented to confirm the validity and excellent practicability of the proposed method using the PSCAD/EMTDC. A prototype experimental model is constructed and tested. The experimental results demonstrate that the proposed method can perfectly suppress the inrush phenomena. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(4): 56–65, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20174 相似文献
97.
An effective system control method is presented for applying a three‐phase current‐source PWM converter with a deadbeat controller to active power filters (APFs). In the shunt‐type configuration, the APF is controlled such that the current drawn by the APF from the utility is equal to the current harmonics and reactive current required for the load. To attain the time‐optimal response of the APF supply current, a two‐dimensional deadbeat control scheme is applied to APF current control. Furthermore, in order to cancel both the delay in the two‐dimensional deadbeat control scheme and the delay in DSP control strategy, an Adaptive Line Enhancer (ALE) is introduced in order to predict the desired value three sampling periods ahead. ALE has another function of bringing robustness to the deadbeat control system. Due to the ALE, settling time is made short in a transient state. On the other hand, total harmonic distortion (THD) of source currents can be minimized compared to the case where ideal identification of the controlled system can be made. The experimental results obtained from the DSP‐based APF are also reported. The compensating ability of this APF is very high in accuracy and responsiveness although the modulation frequency is rather low. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 50–61, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20014 相似文献
98.
Thermodynamic analysis of solar photovoltaic cell systems 总被引:1,自引:0,他引:1
Ahmet Duran Sahin Ibrahim Dincer Marc A. Rosen 《Solar Energy Materials & Solar Cells》2007,91(2-3):153-159
The thermodynamic characteristics of solar photovoltaic (PV) cells are investigated from a perspective based on exergy. A new efficiency is developed that is useful in studying PV performance and possible improvements. Exergy analysis is applied to a PV system and its components, and exergy flows, losses and efficiencies are evaluated. Energy efficiency is seen to vary between 7% and 12% during the day. In contrast, exergy efficiencies, which incorporate the second law of thermodynamics and account for solar irradiation exergy values, are lower for electricity generation using the considered PV system, ranging from 2% to 8%. Values of “fill factors” are determined for the system and observed to be similar to values of exergy efficiency. 相似文献
99.
加强农村广播电视的发展,提高其覆盖率是关键,针对这一问题,阐述了解决农村广播电视覆盖的手段,对农村广播电视覆盖现状做了详细的分析,并提出建议和措施。 相似文献
100.
JUJUN JULIANTY† PANFILO BELO‡ ELVEDA SMITH‡ LUCY McPROUD‡ 《International Journal of Food Science & Technology》1994,29(3):315-320
Four levels of egg white powder (EWP), 0, 1.5, 3.0 and 4.5%, were added to fisfc cracker formulation consisting of tapioca starch, fish paste, and water. the mixture was extruded through a single screw extruder, and the extrudate was cut, dried, heated in a microwave, and the degrees of expansion, bulk density, colour and protein content were measured.
The addition of 1.5 and 3.0% EWP had no significant effect ( P < 0.01) on diametral and longitudinal expansion, however, 4.5% EWP significantly ( P < 0.01) reduced them. Bulk density and protein content of the final product increased as the percentage of EWP increased in the formulation. the total colour difference measurement showed a significant increase ( P < 0.01) in brown colouration at 4.5% EWP. 相似文献
The addition of 1.5 and 3.0% EWP had no significant effect ( P < 0.01) on diametral and longitudinal expansion, however, 4.5% EWP significantly ( P < 0.01) reduced them. Bulk density and protein content of the final product increased as the percentage of EWP increased in the formulation. the total colour difference measurement showed a significant increase ( P < 0.01) in brown colouration at 4.5% EWP. 相似文献