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991.
用于危险场所的电气设备和保护系统按指令94/9/EC要求,必须设计为防爆型。按防爆要求,设备或保护系统,无论是在正常运行时或故障状态下,不能成为点燃源。在防爆技术发展的进程中,研究出了各种各样的保护方式,这些保护方式在欧洲协调标准中都有相应的规定。在一些保护方式中,如浇封型“m”,充砂型“q”,正压型“p”和油浸型“o”,采用适当的设计方法(保护措施)可以阻止可能产生点燃源的电气装置的部件与爆炸性环境接触;在增安型“e”和本安型“i”中, 相似文献
992.
该文提出一种适用于模块并联工作的高效率的同步整流驱动电路。采用这种驱动电路,同步整流的波形和驱动损耗可以做到和自驱动一样的效果,同时又解决了多个模块并联时会产生短路的问题。此外,采用这种驱动电路还可以调节驱动电压幅度的高低。文中从时域和频域两个角度对此电路进行了详细的原理分析。采用所推荐驱动电路的36~75V输入,1.8V/60A输出,四分之一砖标准的模块电源效率高达90%以上。最后,仿真结果验证了该电路调节同步整流驱动电压幅度的功能。 相似文献
993.
Montanari G.C. Laurent C. Teyssedre G. Campus A. Nilsson U.H. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2005,12(3):438-446
This paper discusses the results of space charge, conduction current and electrical lifetime measurements performed on widely-used materials for electrical insulation, that is, low density polyethylene (LDPE) and cross-linked polyethylene (XLPE). Space charge accumulation profiles were compared in LDPE, low density polyethylene plus antioxidant (LDPE+AO) and XLPE, with consideration of thermal treatment effects in LDPE and XLPE. Significant variation (decrease) of accumulated space charge and apparent mobility, as well as slight decrease of conduction current, can be seen going from LDPE to LDPE+AO and XLPE, which may be associated with formation of deeper trap levels (or an increase of their density). On the contrary, electrical life under AC voltage does not show significant differences from LDPE to XLPE. This latter result underlines that life under high AC electrical stress is mostly determined by defects (weak points) rather than material characteristics associated with charge injection and transport. 相似文献
994.
This paper addresses the problem of simultaneous localization and mapping (SLAM) by a mobile robot. An incremental SLAM algorithm is introduced that is derived from multigrid methods used for solving partial differential equations. The approach improves on the performance of previous relaxation methods for robot mapping, because it optimizes the map at multiple levels of resolution. The resulting algorithm has an update time that is linear in the number of estimated features for typical indoor environments, even when closing very large loops, and offers advantages in handling nonlinearities compared with other SLAM algorithms. Experimental comparisons with alternative algorithms using two well-known data sets and mapping results on a real robot are also presented. 相似文献
995.
This paper presents, in detail, the implementation of a new control strategy, Kalman-based active observer controller (AOB), for the path following of wheeled mobile robots (WMRs) subject to nonholonomic constraints. This control strategy presents some particularities as being used in discrete mode, and being robust against uncertainties and disturbances such as the ones due to the use of the input-output feedback-linearization method in discrete mode, while it was developed to be used in continuous mode. The performance of the proposed control algorithm is verified via computer simulation, and is compared with other control strategies, such as pole placement controller (PPC) and PPC with a Kalman filter observer (CKF). 相似文献
996.
The European Institute Center for Anti-Virus Research (EICAR; www.eicar.org) held its 14th annual conference and attracted about 100 researchers, vendors, users, and government representatives interested in discussing the fields latest developments. This report presents a brief overview of what went on at the invited talks, paper presentations, and industry sessions. 相似文献
997.
998.
Hiroyasu Hotokezaka Noboru Aoyagi Yasuhiro Kawahara Noriko U. Yamaguchi Shinya Nagasaki Ken Sasaki Satoru Tanaka 《Microsystem Technologies》2005,11(8-10):974-979
Laser-induced breakdown spectroscopy (LIBS) has been applied for quantitative analysis of Al2O3, CaCO3 and MgO particles suspended in water. In the single elemental system, the plasma emission intensities of Al, Ca and Mg were linearly increased with concentration of elements in the range of 1.0×10?5–1.0×10?3 M, 1.0×10?4–2.0×10?3 M and 8.0×10?5 –4.0×10?3 M, respectively. We also investigated the concentration dependence of breakdown spectra for suspended mixtures of Al2O3, CaCO3 and MgO particles. The emission lines, such as Al I, Ca I, Ca II and Mg I, were appeared in the LIBS spectrum simultaneously, and each emission peak could be deconvoluted. The plasma emission intensities of Al, Ca and Mg in the multielemental system were also linearly increased with their concentrations in the range of 1.0×10?5–1.0×10?3 M, 1.0×10?4–2.0×10?3 M and 4.0×10?4–2.0×10?3 M, respectively. LIBS was found to be available for quantitative and qualitative measurement of the concentrations of Al2O3, CaCO3 and MgO particles suspended in water. The present results suggest that LIBS is a potentially useful tool for in-situ analysis on particles composition and concentrations for environmental monitoring by the wearable information equipments. 相似文献
999.
Yichuan Yu S. Karlsson C.P. Liu R. Schatz U. Westergren O. Kjebon C.H. Chuang Sailing He L. Thylen A.B. Krysa J.S. Roberts A.J. Seeds 《Photonics Technology Letters, IEEE》2006,18(6):770-772
An InGaAsP multiple-quantum-well asymmetric Fabry-Pe/spl acute/rot modulator/detector has been developed for radio-over-fiber systems. The measured bandwidth is more than 6 GHz and the total insertion loss is 7.1 dB. The property of nonlinearity and spurious-free dynamic range (SFDR) has been studied theoretically. By optimizing the operation optical wavelength and bias voltage based on the numerical simulation, fifth-order nonlinearity dominates the intermodulation distortion and an SFDR of 101 dB/spl middot/Hz/sup 4/5/ has been achieved experimentally. 相似文献
1000.
Optimal space-frequency Group codes for MIMO-OFDM system 总被引:2,自引:0,他引:2
Space-frequency (SF) group codes are designed for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. A rather general channel model is assumed, where the channel is frequency-selective Rayleigh fading with arbitrary power-delay profile. It is shown that the SF group code has a symmetric distance structure like the space-time group code, if the group consists of diagonal matrices. A scenario where the multiple codewords are loaded onto the subcarriers of the OFDM system in parallel is considered. The optimality condition on the choice of subcarrier allocation is found, and an optimal subcarrier-allocation scheme is proposed. A transmit scheme where rotated versions of the same signal are transmitted from different transmit antennas is proposed, and it is shown that it satisfies the optimality condition. Then matrix groups are designed which guarantee that the resulting SF codes are full rank. Numerical comparisons with recently published techniques in the literature verify our improved performance. 相似文献