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排序方式: 共有4818条查询结果,搜索用时 15 毫秒
1.
2.
Koichi Itagaki Md. Mortuza Ali Hiroshi Kitamura Takeo Maruyama 《Electrical Engineering in Japan》1992,112(2):1-10
Several sealed-off triggered vacuum gaps are connected in series to improve hold-off voltage. The characteristics of impulse breakdown voltage of these series-connected gaps are investigated experimentally. The sum hold-off voltage of series-connected gaps decreases to a unit hold-off voltage when the maximum value of voltage division ratio across the gaps increases to unity. Self-breakdown probability of the series-connected gaps is always higher than that of a single gap under the same conditions. Hence, stage efficiency of the multistage gap decreases with increasing number of stages. Its value is 90 percent with 2-stage gap and 75 percent with 5-stage gap, respectively, under the same voltage division ratio and the same gap length (2.0 mm) in each stage. Triggered breakdown voltage of 2- or 3- stage gap is several hundred volts when all gaps are triggered simultaneously at the peak of the main impulse wave and a working voltage range is nearly 100 percent in this case. The working voltage range decreases with number of stages. Its value is 45 percent with 3-stage gap and 15 percent with 5-stage gap, respectively, when one triggered gap is fired for switching. 相似文献
3.
Goni O. Hossain F. Yusuf S.U. Rahman M. Kaneko E. Takahashi H. 《Power Delivery, IEEE Transactions on》2006,21(4):1778-1786
Simulation of very fast surge phenomena in a three-dimensional (3-D) structure requires a method based on Maxwell's equations, such as the finite-difference time-domain (FDTD) method or the method of moments, because circuit-equation-based methods cannot handle the phenomena. This paper uses a method of thin-wire representation of the vertical conductor system for the FDTD method which is suitable for the 3-D surge simulation. The thin-wire representation is indispensable to simulate electromagnetic surges on wires or steel frames in which the radius is smaller than a discretized space step used in the FDTD simulation. In this paper, a general surge analysis program named the virtual surge test lab based on the Maxwell's equations formulated by the FDTD method, is used to simulate the surge phenomena of a vertical conductor, including the effects of horizontal wave incidence and vertical wave incidence. Experimental results on the reduced scale model have been presented in order to compare among the simulation results by the FDTD method and the results using numerical electromagnetic code based on the MoM. 相似文献
4.
An experimental study of heat transfer to boiling liquids under natural convective flow has been carried out in a single tube vertical thermosiphon reboiler to investigate the effect of heat flux and submergence on circulation rates. The test liquids used were distilled water, various concentrations of propan-2-ol in water and their azeotrope. The test section was an electrically heated stainless steel tube of 25.56 mm i.d., 28.85 mm o.d. and 1900 mm long with twenty-one spot welded copper constantan thermocouples to measure the variations in wall temperature along its axis. The uniform heat fluxes in the range of 3.5–42.4 kW/m2 were employed while inlet liquid sub-cooling varied from 0.2 to 30.7 °C. The liquid submergence levels were maintained in the range 30–100%. The typical experimental data has been graphically presented and discussed. An empirical correlation has been developed from the experimental data of the present study through regression analysis. 相似文献
5.
Sanghyun Ju Jianye Li Pimparkar N. Alam M.A. Chang R.P.H. Janes D.B. 《Nanotechnology, IEEE Transactions on》2007,6(3):390-395
Nanorod field-effect transistors (FETs) that use multiple Mg-doped ZnO nanorods and a SiO2 gate insulator were fabricated and characterized. The use of multiple nanorods provides higher on-currents without significant degradation in threshold voltage shift and subthreshold slopes. It has been observed that the on-currents of the multiple ZnO nanorod FETs increase approximately linearly with the number of nanorods, with on-currents of ~1 muA per nanorod and little change in off-current (~4times10-12). The subthreshold slopes and on-off ratios typically improve as the number of nanorods within the device channel is increased, reflecting good uniformity of properties from nanorod to nanorod. It is expected that Mg dopants contribute to high n-type semiconductor characteristics during ZnO nanorod growth. For comparison, nonintentionally doped ZnO nanorod FETs are fabricated, and show low conductivity to compare with Mg-doped ZnO nanorods. In addition, temperature-dependent current-voltage characteristics of single ZnO nanorod FETs indicate that the activation energy of the drain current is very low (0.05-0.16 eV) at gate voltages both above and below threshold 相似文献
6.
7.
The authors present a multiserver, first-come first-served queuing system that alternates between two modes of system operation. In one mode, all s servers are available, and in the other mode, only s -1 servers are available for serving the customers. This is due to breakdown of one of the servers. The random variables representing the system with s servers and s -1 servers have exponential distributions. In such a system, the steady-state birth/death equations are coupled because of the two modes of operation. A recursive solution is presented for computing the steady-state probabilities of such a system. Once these probabilities are known, the performance measures of interest can be easily obtained. Two practical examples validate the results and show the utility of this method. A distinct advantage of the recursive technique is that it is much faster and requires much less memory than the existing nonrecursive techniques. In a bilevel situation, the system performance measures are always bounded by two independent queuing systems with s and s -1 servers. A procedure has been outlined for extension to multiple modes of system operation 相似文献
8.
Michael E. Prudich M. Khairul Alam Noor-Un Nahar 《Particulate Science and Technology》1994,12(2):127-137
The objective of the present study was to generate submicrometer calcium hydroxide aerosols and to investigate the effectiveness of such aerosols in sulfur capture. The effectiveness of SO2 removal by Ca(OH)2 aerosol has been investigated in an isothermal reactor. Ca(OH) 2 aerosol was generated by a novel fluidizer system in which submicrometer-sized powders were entrained in gases. SO2 was added to this aerosol to a concentration of 2000 ppm. The aerosol-SO2 mixture was heated to 550°C-750°C in an isothermal tube reactor. The SO2 removal efficiency, which varied from 20% to 70%, was determined to be a function of the aerosol concentration, reactor temperature and residence time. The fraction of aerosol reacted was not affected strongly by the aerosol concentration. The reaction kinetics were determined from the experimental data using a simple analytical model in which the rate is first order in both SO2 and calcium hydroxide aerosol concentrations. 相似文献
9.
The deformation behavior of several single- and two-phase coarse microstructures has been examined using microhardness measurements.
It has been found that the strength response of a coarse phase in isolation is distinctly different from its response when
it exists in a two-phase system. The second phase alters the mechanical state of the first one andvice versa even in the plastically undeformed condition. This phenomenon is explained in terms of the existence of an appreciable amount
of residual stresses in two-phase coarse microstructures. These stresses primarily arise due to the difference in thermal
expansion coefficients of the phases. The in- fluence of elastic stress field on microhardness response is shown with a new
type of experiment to support the proposed explanation. The present results question the existing expressions for deformation
modeling of multiphase materials because of the uncertainties in the estimation of the average strength of the phases in a
two-phase system. 相似文献
10.