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排序方式: 共有3919条查询结果,搜索用时 15 毫秒
31.
D. Dietrich ÖVE H. Reiter Th. Sauter H. -J. Schweinzer 《e & i Elektrotechnik und Informationstechnik》1997,114(5):225-230
The past decade may be regarded as the phase of the fundamental developments in fieldbus systems that were based on the OSI model. Today we are entering a second stage. It is the objective of this issue to present the current state and where the further developments will lead to. This introductory article is intended to give an overview on the subject. 相似文献
32.
M. Muhr ÖVE S. Pack ÖVE H. Haidvogl F. Kreyca 《e & i Elektrotechnik und Informationstechnik》1997,114(11):680-686
Recently appeared defects on high voltage cables have required an urgent evaluation of the impact of lightning strikes necessary. In some cases overvoltages between the copper wire screen of the cable and earth may appear which cause damages of the cablesheath. Field measurements with a classification of the voltage impulses at the copper wire screen have been made to evaluate the number of events. Additionally a numerical model was developed to study the effects of atmospheric discharges on underground cables with emphasis to the influence on the cablesheath. This numeric method was also applied to estimate the effectiveness of different protection arrangements. This contribution presents evaluation methods for overvoltages of cables and a model used firstly for calculating the stress caused by differential voltages and secondly to determinate the influence of protection measures. 相似文献
33.
M. Mayer ÖVE 《e & i Elektrotechnik und Informationstechnik》2000,117(11):728-735
For first try designs of microwave power amplifiers it is necessary to know the entire physical behaviour of the used components with high accuracy. The attention should be directed especially to the center component of these circuits, the power transistor, whose nonlinear characteristics have an essential impact on the behavior of the whole amplifier. This article gives an overview of current methods of measurement for microwave power transistor characterization. Furthermore a measurement system is presented, capable of characterizing microwave power transistors within a frequency range from 30 kHz to 8.7 GHz at bias current up to 7.5 A including self heating effects. 相似文献
34.
Ömer Kavaklıoğlu Baruch Schneider 《Journal of Infrared, Millimeter and Terahertz Waves》2008,29(4):329-352
A rigorous analytical representation for the multiple scattering coefficients of the fields radiated by an infinite grating of dielectric circular cylinders excited by an obliquely incident plane electromagnetic wave is derived in terms of the “well-known scattering coefficients of an isolated dielectric cylinder at oblique incidence” and “Schlömilch series”. In addition, a generalized sum-integral grating equation is acquired for the multiple scattered amplitude of a cylinder at oblique incidence in the grating in terms of the scattering coefficients of the insulating dielectric circular cylinder at oblique incidence. 相似文献
35.
E. BORIE G. GANTENBEIN B. JÖDICKE G. DAMMERTZ O. DUMBRAJS T. GEIST 《International Journal of Electronics》2013,100(5-6):687-720
The gyrotron is a powerful source of millimetre wave radiation. Fusion applications require more power per tube than is currently available This in turn means that the resonator must be highly overmoded, with a dense mode spectrum, which leads to mode competition. The influence of external parameters, such as the applied magnetic field, electron beam, and resonator geometry, on mode competition in tubes designed to operate at 150 and 140 GHz in the TE03 mode is investigated theoretically and experimentally. It can be shown that even when the mode spectrum is fairly dense, single mode operation of a gyrotron is possible. The influence of startup conditions on output power is investigated in the 150 GHz experiment. In some cases, modes with an axial index of 2 were excited. 相似文献
36.
ABSTRACTWind turbine control is an important task to make the electricity generation secure in terms of energy demand and machine safety. It also yields to control the desired power level and optimized energy because of the assignment of turbine speed. The contactless piezoelectric wind energy harvester (CPWEH) used in this study has three piezoelectric layers located around the shaft with 120 degrees apart and they are buckled by the magnetic force without any physical contact. The superiority of this device is to generate energy for low wind speeds such as 1.5 m/s. However, for high speeds, high total harmonic distortions (THDs) govern the waveforms, thus controlling the turbine speed becomes necessary for optimizing the output power. Encouraged by this, a small low inertia dc generator is coupled with the wind turbine, and the generator terminals are connected to a resistor through a power switch to generate a braking torque that opposes to wind speed direction. By controlling the switch properly, turbine speed is ensured to remain within a certain band, which accordingly prevents the turbine from rotating very fast at damaging wind speeds. Several experiments are performed on the developed CPWEH with/without the presented control scheme which prove the existence of promising performance of our proposal. 相似文献
37.
Ü. Özgür X. Gu S. Chevtchenko J. Spradlin S. -J. Cho H. Morkoç F. H. Pollak H. O. Everitt B. Nemeth J. E. Nause 《Journal of Electronic Materials》2006,35(4):550-555
Thermal conductivities (κ) of melt-grown bulk ZnO samples thermally treated under different conditions were measured using
scanning thermal microscopy. Samples annealed in air at 1050°C for 3 h and treated with N-plasma at 750°C for 1 min. exhibited
κ=1.35±0.08 W/cm-K and κ=1.47±0.08 W/cm-K, respectively. These are the highest values reported for ZnO. Atomic force microscopy
(AFM) and conductive-AFM measurements revealed that surface carrier concentration as well as surface morphology affected the
thermal conductivity. 相似文献
38.
Stefan Thiemann Swetlana J. Sachnov Fredrik Pettersson Roger Bollström Ronald Österbacka Peter Wasserscheid Jana Zaumseil 《Advanced functional materials》2014,24(5):625-634
A new class of biofriendly ionogels produced by gelation of microcellulose thin films with tailored 1‐ethyl‐3‐methylimidazolium methylphosphonate ionic liquids are demonstrated. The cellulose ionogels show promising properties for application in flexible electronics, such as transparency, flexibility, transferability, and high specific capacitances of 5 to 15 μF cm?2. They can be laminated onto any substrate such as multilayer‐coated paper and act as high capacitance dielectrics for inorganic (spray‐coated ZnO and colloidal ZnO nanorods) and organic (poly[3‐hexylthiophene], P3HT) electrolyte‐gated field‐effect transistors (FETs), that operate at very low voltages (<2 V). Field‐effect mobilities in ionogel‐gated spray‐coated ZnO FETs reach 75 cm2 V?1 s?1 and a typical increase of mobility with decreasing specific capacitance of the ionogel is observed. Solution‐processed, colloidal ZnO nanorods and laminated cellulose ionogels enable the fabrication of the first electrolyte‐gated, flexible circuits on paper, which operate at bending radii down to 1.1 mm. 相似文献
39.
T. Mayer ÖVE 《e & i Elektrotechnik und Informationstechnik》1999,116(7-8):421-427
Wind power stations in windfarms connected to the power system can disturb the power quality. Effects like pole-reconnections, shadowing-effects as well as wind squalls will result in power fluctuations. So voltage fluctuations and flicker effects will occur. We present results of field measurements, carried out on windfarms in Germany in April 1998. 相似文献
40.
Uğur Güdükbay Serkan Bayraktar Çetin Koca Bülent Özgüç 《Signal, Image and Video Processing》2014,8(3):415-422
We present a particle-based method to simulate and visualize the interaction of knitwear with fluids. The knitwear is modeled using spring-mass systems and the fluid is modeled using the smoothed particle hydrodynamics method. Two-way coupling is achieved by considering surface tension, capillary, and interparticle forces between the fluid and knitwear. The simulation of fluid and knitwear particles is performed on the graphics processing unit. Photorealistic rendering of knitwear and fluid is achieved by using a hardware-accelerated rasterization-based rendering technique. Our method is able to simulate and visualize the macro- and microstructure of free-form knitwear and reflective and refractive characteristics of the fluid surface. 相似文献