变压器油流动带电度的微静电测量方法及其影响因素

为推动我国变压器油流动带电度测量技术的标准化,在实验室建立了一套微静电测量系统,制定了详细的测量规程,并对影响测量结果的关键因素(温度、流速、滤纸和油流次数)进行了试验研究和讨论.研究结果表明:变压器油流动带电度的测量值随温度(10～50℃)的升高显著增加,据此推导出带电度随温度变化的校正公式;新油的带电度基本不受流速的影响,老化油的带电度随流速增长下降明显;滤纸和油流次数同样是影响测量结果的重要因素.该研究对于推动我国变压器油流动带电度测量技术的标准化工作具有积极意义.

变压器油的带电度测试方法及试验研究

介绍了“过滤式”变压器油静电带电测试系统，包括测试装置及试验方法，以及采用该系统对国产变压器油进行试验的最新成果。在此基础上，初步试验研究并分析了苯并三唑（ＢＴＡ）对油中静电的抑制作用及影响。

大型变压器油带电度检测方法的研究

本项目依据国家发改委发改办工业[2006]1093号文将制定"大型变压器油带电倾向性检测方法"的任务由安徽省电力科学研究院负责完成的要求进行,重点对变压器油带电度检测方法进行研究,采用"

大型变压器油带电度检测仪和检测方法的研究

在强迫油循环的大型变压器中,油流带电引发的静电放电是威胁大型变压器安全运行的重要因素之一。对变压器油进行带电度测量,以便对带电度超标的变压器油采取措施并及时改善运行条件,以防止变压器因油流放电故障而造成变压器损坏。文章介绍了采用过滤法进行大型变压器油带电度检测仪器的原理和结构,制作过程中的改进以及国产油和进口油的带电度测试结果,实际大型变压器油的带电度测试结果。

模拟实际运行工况的变压器油流带电特性

变压器油纸绝缘系统内普遍存在着油流带电现象。随着变压器油老化程度加剧,不断上升的油流带电度容易引发变压器油放电甚至击穿现象,极大地威胁着变压器绝缘系统运行寿命。该研究以人工加速热老化油样(5种老化时间)与实际运行变压器老化油样(5种运行时间)为对象,首先研究人工加速老化油流带电度随油流速的变化规律,然后对比研究不同老化程度下2种变压器油样的油流带电度、介质损耗、体电阻率等理化参数,建立2种老化方法之间关系。研究发现:利用人工加速热老化方法可以模拟实现变压器运行工况,为实际运行变压器老化评估技术提供了必要的理论与实验基础。

IC Implementation of a Programmable CMOS Voltage Reference

A new approach for the design and implementation of a programmable voltage reference based on an improved current mode bandgap voltage reference is presented. The circuit is simulated and fabricated with Chartered 0. 35μm mixed-signal technology. Measurements demonstrate that the temperature coefficient is ± 36. 3ppm/℃ from 0 to 100℃ when the VID inputs are 11110.As the supply voltage is varied from 2.7 to 5V, the voltage reference varies by about 5mV. The maximum glitch of the transient response is about 20mV at 125kHz. Depending on the state of the five VID inputs,an output voltage between 1.1 and 1.85V is programmed in increments of 25mV.

Measurable surface d charge of Pd as a descriptor for the selective hydrogenation activity of quinoline

Au Pd nanoalloys with tunable Pd concentrations have been synthesized and used as model catalysts. They have been directly imaged by high-angle annular dark-field scanning transmission electron microscopy and investigated by thorough analyses of their extended X-ray absorption fine structure, X-ray absorption near-edge structure, X-ray diffraction and X-ray photoelectron spectroscopy measurements. The bimetallic nanoparticles are embedded in a carbonaceous matrix and have almost an identical structure at the atomic level and the same electronic properties as Au Pd bulk alloys with the same compositions. The d-electron increase at surface Pd sites is determined by the Pd concentration of the alloy. Similarly, their activation entropy and catalytic activity for the hydrogenation of quinoline is related to the Pd concentration, with Au50 Pd50 the most active of the alloys investigated. An almost 11 times higher activity was achieved compared to a pure Pd catalyst. The experimentally measurable surface d charge at the Pd sites in the Au Pd was found to linearly correlate with the activation entropy and catalytic activity for the hydrogenation of quinoline. The alloy structure is stable, showing negligible metal segregation, dissolution-redeposition and aggregation during the hydrogenation process which involves strong adsorption.

Band structures of TiO_2 doped with N, C and B

This study on the band structures and charge densities of nitrogen (N)-, carbon (C)- and boron (B)-doped titanium dioxide (TiO2) by first-principles simulation with the CASTEP code (Segall et al., 2002) showed that the three 2p bands of im-purity atom are located above the valence-band maximum and below the Ti 3d bands, and that along with the decreasing of im-purity atomic number, the fluctuations become more intensive. We cannot observe obvious band-gap narrowing in our result. Therefore, the cause of absorption in visible light might be the isolated impurity atom 2p states in band-gap rather than the band-gap narrowing.

Dielectric Confinement Effect on Calculating the Band Gap of PbSe Quantum Dots

Considering the dielectric confinement effect on excitonics of PbSe quantum dots （QDs）, a correction factor in the wave function was introduced to propose a new band gap calculation model for QDs. The modified model showed great consistency with the experimental data, especially in small size range. According to the variation of confined barrier, the band gap calculation model of PbSe QDs was analyzed in different solvents. The calculating results showed that the modified model was almost solvent-independent, which was consistent with our experimental results and related reports.

Research of the electrical anisotropic characteristics of water-conducting fractured zones in coal seams

Water flooding disasters are one of the five natural coal-mining disasters that threaten the lives of coal miners. The main causes of this flooding are water-conducting fractured zones within coal seams. However, when resistivity methods are used to detect water-conducting fractured zones in coal seams, incorrect conclusions can be drawn because of electrical anisotropy within the water-conducting fractured zones. We present, in this paper, a new geo-electrical model based on the geology of water-conducting fractured zones in coal seams. Factors that influence electrical anisotropy were analyzed, including formation water resistivity, porosity, fracture density, and fracture surface roughness, pressure, and dip angle. Numerical simulation was used to evaluate the proposed electrical method. The results demonstrate a closed relationship between the shape of apparent resistivity and the strike and dip of a fracture. Hence, the findings of this paper provide a practical resistivity method for coal-mining production.

Electronic and Optical Properties of Rock-Salt A1N under High Pressure via First-Principles Analysis

Electronic and optical properties of rock-salt AIN under high pressure are investigated by first-principlesmethod based on the plane-wave basis set.Analysis of band structures suggests that the rock-salt AIN has an indirectgap of 4.53 eV,which is in good agreement with other results.By investigating the effects of pressure on the energygap,the different movement of conduction band at X point below and above 22.5 GPa is predicted.The opticalproperties including dielectric function,absorption,reflectivity,and refractive index are also calculated and analyzed.Itis found that the rock-salt AIN is transparent from the partially ultra-violet to the visible light area and hardly does thetransparence affected by the pressure.Furthermore,the curve of optical spectrum will shift to high energy area (blueshift) with increasing pressure.

Optimization Design of Silicon Micro - capacitive Accelerometer with PWM Technique

The property of silicon micro-capacitive accelerometer is analyzed and discussed by establishing the model of the sensor,to lay a basis for optimization design of sensor system structure. Discussed issues include the static modeling and dynamic behavior of the two commonly used structures,i.e., double-cantilever supported and four-beam supported structures, and also the measurement range of these devices.

Electronic and Optical Properties of Cubic SrHfO_3

In order to clarify the mechanism of optical transitions for cubic SrHfO_3, we have investigated the electronicstructure and optical properties of cubic SrHfO_3 using the plane-wave ultrasoft pseudopotential technique based on thefirst-principles density-functional theory (DFT).The ground-state properties, obtained by minimizing the total energy,are in favorable agreement with the previous work.From the band structure and charge densities as well as the theoryof crystal-field and molecular-orbital bonding, we have systematically studied how the optical transitions are affected bythe electronic structure and molecular orbitals.Our calculated complex dielectric function is in good agreement withthe experimental data and the optical transitions are in accord with the electronic structure.

Holographic Duals of Quark Gluon Plasmas with Unquenched Flavors

We review the construction of gravitational solutions holographically dual to N=1 quiver gauge theories with dynamical flavor multiplets.We focus on the D3-D7 construction and consider the finite temperature,finite quark chemical potential case where there is a charged black hole in the dual solution.Discussed physical outputs of the model include its thermodynamics (with susceptibilities) and general hydrodynamic properties.

Topological flat bands in twisted trilayer graphene

Twisted trilayer graphene(TLG)may be the simplest realistic system so far,which has flat bands with nontrivial topology.Here,we give a comprehensive calculation about its band structures and the band topology,i.e.,valley Chern number of the nearly flat bands,with the continuum model.With realistic parameters,the magic angle of twisted TLG is about 1.12°,at which two nearly flat bands appears.Unlike the twisted bilayer graphene,a small twist angle can induce a tiny gap at all the Dirac points,which can be enlarged further by a perpendicular electric field.The valley Chern numbers of the two nearly flat bands in the twisted TLG depends on the twist angleθand the perpendicular electric field E⊥.Considering its topological flat bands,the twisted TLG should be an ideal experimental platform to study the strongly correlated physics in topologically nontrivial flat band systems.And,due to its reduced symmetry,the correlated states in twisted TLG should be quite different from that in twisted bilayer graphene and twisted double bilayer graphene.

Variability features of the width of the tropical belt from COSMIC radio occultation data

In this work, we analyzed time-series and trends of the tropical belt edges and widths with three methods based on the tropopause using new global positioning system radio occultation(GPS RO) data from the Constellation Observing System for Meteorology, Ionosphere, and Climate(COSMIC) mission for September 2006–February 2014. The results from the three methods agreed well with previous studies and new features were found. To avoid the El Ni?o Southern Oscillation(ENSO) and Quasi-Biennial Oscillation(QBO) influence, we applied a simple multiple linear regression model to the monthly anomalies to obtain the tropical belt edges and width trends. During the study, we found equatorward movements of the tropical belt edges on both hemispheres. The narrowing of the tropical belt mainly occurred in the Pacific Ocean. We also found that the deseasonalized monthly anomalies of the tropical belt width were closely related with the ENSO and QBO. The tropical belt at a height of 15 km was mostly closely related with the ENSO. The correlations between the QBO and the tropical belt were consistent for the three methods.

GaN-based LEDs for light communication

Rapid improvement in the efficiency of GaN-based LEDs not only speed up its applications for general illumination, but offer the possibilities for data transmission. This review is to provide an overview of current progresses of GaN-based LEDs for light communications. The modulation bandwidth of GaN-based LEDs has been first improved by optimizing the LED epilayer structures and the modulation bandwidth of 73 MHz was achieved at the driving current density of 40 A/cm2 by changing the multi-quantum well structures. After that, in order to increase the current density tolerance, different parallel flip-chip micro-LED arrays were fabricated. With a high injected current density of ~7900 A/cm2, a maximum modulation bandwidth of ~227 MHz was obtained with optical power greater than 30 mW. Besides the increase of carrier concentrations, the radiative recombination coefficient B was also enhanced by modifying the photon surrounding environment based on some novel nanostructures such as resonant cavity, surface plasmon, and photonic crystals. The optical 3 dB modulation bandwidth of GaN-based nanostructure LEDs with Ag nanoparticles was enhanced by 2 times compared with GaN-based nanostructure LEDs without Ag nanoparticles.Our results demonstrate that using the QW-SP coupling can effectively help to enhance the carrier spontaneous emission rate and also increase the modulation bandwidth for LEDs, especially for LEDs with high intrinsic IQE. In addition, we discuss the progress of the faster color conversion stimulated by GaN-based LEDs.

High temperature property studies of the 6H-SiC MOS capacitor

N-type and p-type 6H-SiC metal oxide semiconductor (MOS) capacitor samples are fabricated with a typical method,and the high frequency capacitor voltage (C-V) curves of these samples are measured at temperatures ranging from 293 to 533 K.There exists huge difference between the n-type and p-type samples.Flat-band voltage shift of the n-type sample becomes larger with temperature rising,but that of the p-type sample have very little change.This may be caused by the residual Al in the p-type oxide.Both types of the SiC samples follow the same rule of flat-band voltage changing with temperature.But their mechanisms are different as temperature is above 453 K.Of both types the p-type SiC is more suitable for high temperature applications.

Determination of bandgaps of photoactive materials in perovskite solar cells at high temperatures by in-situ temperature-dependent resistance measurement

Normally, it is difficult to directly measure the bandgaps of perovskite based on methylammonium(MA) or formamidinium(FA) at high temperatures due to material decomposition. We prevent the decomposition by keeping the synthesized perovskite films(MAPbI_3 and MAPbI_3) in organic iodide vapors, then measure the in-situ resistance of the films at varied temperatures, and further evaluate the bandgaps of these two materials. The evaluated bandgaps are consistent with the results from ultraviolet-visible(UV-vis) absorption spectrum. The bandgap of MAPbI_3 decreases with temperature above 95 ℃, whereas that of FAPbI_3 first increases with temperature from 95 ℃ to 107 ℃ and then decreases with temperature above 107 ℃.