绝缘子污秽成分分析与清洗剂去污机理研究

为深入了解高压绝缘子污秽的组成和带电清洗剂对高压绝缘子表面污秽的去除机理,对高压绝缘子表面污秽进行了扫描电镜、红外光谱、x-射线衍射、x-射线荧光光谱和离子色谱分析,用接触角法研究了污秽粘附于绝缘子表面的作用力,测定了带电清洗剂和高压绝缘子的表面张力(γ);通过杨氏和表面能方程,分别计算出粘附功Wa、铺展系数Sw/s和浸湿功Wi。研究结果表明,污秽与绝缘子表面之间为van der Waals引力,无氢键形成。带电清洗剂表面张力较小,Wa>Wi>Sw/s≥0,表明带电清洗剂能在被污染的绝缘子表面自发浸湿和铺展。在带电清洗剂的作用下,减小了污秽与绝缘子表面的van der Waals结合力,使污秽从绝缘子表面脱附下来。该研究对开发新的绝缘子带电清洗剂提供了实验与理论依据。     

Attachment of inorganic nanoparticles onto carbon nanotubes

Carbon nanotubes have been the focus of intensive study due to their unique structure-dependent electronic and mechanical properties. They are thought to have potential applications as catalyst supports in heterogeneous catalysis, high engineering reinforcements, and molecular wires for the next generation of electronic devices. Good dispersion of carbon nanotubes in a matrix of composite materials, especially in inorganic materials, indeed is a significant problem due to the strong Van der Walls force between CNTs and the poor compatibility between the two phases. It is the intention of our research work to overcome the difficulties regarding incorporation of carbon nanotubes in structural and functional ceramics. The initial step toward this goal involves coating CNTs with materials that will eliminate the undesirable attractive interactions between the nanotubes and facilitate their incorporation into composites. In the present study, two new and simple methods named as heterogeneous coagulation and direct hydrolysis have been developed to attach various inorganic nano particles such as alumina, zirconia and titania to the surface of carbon nanotubes. These functionalization methods might be new strategies to altering the electronic properties of nanotubes. We expected that the attachment of metal oxides to nanotube surfaces will promote better ceramic or other inorganic matrix-CNT adhesion and may lead to the development of homogeneous composites, thereafter improving mechanical and/or electrical properties.     

基于第一性原理的表面氟化聚乙烯界面势垒特性研究

为了从分子层面解释表面氟化聚乙烯相比于聚乙烯空间电荷更少的原因,采用第一性原理对构建的表面氟化聚乙烯模型进行计算。探讨了分子模型的静电势能分布、范德华表面局部电子亲和能、态密度和核-壳模型的轨道分布及平面平均静电势能,从微观角度对聚乙烯表面氟化界面的电子结构进行了分析研究。结果表明:聚乙烯的最低未占轨道(LUMO)具有链间特性,而氟化层具有链中特性。随着轨道序号的上升,轨道分布在二者界面呈现出从氟化层的链上转移至聚乙烯链间的过渡特征。聚乙烯本体具有负的电子亲和能,而氟化层具有正的电子亲和能,聚乙烯和氟化层结构界面处会形成电子势垒,起到抑制电子注入的作用。     

基于风力机尾流排斥的平坦地形风电场微观选址优化

平坦地形风电场微观选址的优化研究中,常采用带有随机量的元启发式算法,这些算法难以达到全局最优,优化效率较低,且通常需要通过划分网格、增加约束才能得到稳定解。针对这些问题,文中提出了一种专门针对平坦地形风电场微观选址的高效且有稳定优化解的元启发式算法——风力机尾流排斥优化算法。参考范德华力原理,提出了风力机尾流排斥力的概念,用于描述风力机在尾流作用下的相互影响:2台风力机之间尾流作用越大,风力机尾流排斥力也越大。在算法优化过程中,风力机会在风力机尾流排斥力的作用下向使尾流减小的方向不断移动,直到达到最优解。仿真结果表明:风力机尾流排斥优化算法不需要网格约束,优化效率高,能得到确定的优质解,且优化结果符合实际工程要求。     

Impact of inelastic phonon scattering in the OFF state of Tunnel-field-effect transistors

We study the impact of electron–phonon interaction on the subthreshold operation region of Tunnel-FETs by means of full-quantum simulations. Our approach is based on the nonequilibrium Green’s function method, where acoustic and optical phonon scatterings are taken into account through the self-consistent Born approximation. Two device architectures are analyzed: InAs nanowire longitudinal Tunnel-FETs, and 2D vertical Tunnel-FETs based on either an GaSb/AlSb/InAs heterostructure or a MoS\(_2\)/WTe\(_2\) van der Waals heterojunction. In InAs nanowire Tunnel-FETs with interface traps, electron–phonon interaction deteriorates the subthreshold swing by allowing trap-assisted tunneling at energies higher than the valence-band edge in the source. In vertical heterojunction Tunnel-FETs, optical phonon scattering increases the OFF current by inducing inelastic transition in the overlap region even in the absence of traps.     

On the interpretation of some electrical aging and relaxation phenomena in solid dielectrics

Electrical aging and relaxation in solid dielectrics are phenomena studied for decades but still largely poorly understood. The lack of understanding, or sometimes the misunderstanding, are partly due to inadequate or deficient theories and partly due to wrong interpretation of theories or concepts developed for other materials than dielectrics. In addition, a serious analysis of some of the empirical and approximate relationships often used to interpret polymer relaxations reveals that they are not only limited and restrictive but also that they are based on very dubious assumptions. Dry or wet electrical aging is much more complex and often includes many phenomena with synergetic effects such as thermal aging, electrochemical reactions, space charge effects, etc. In this lecture, we intend to show that some of the theories often cited in the literature are wrong or inappropriate. We show why they cannot describe the phenomena at play and we present some alternatives for future work in the domains of relaxation and electrical aging. The relations between aging, space charges and polarization of polyethylene (PE) under the influence of high electrical fields (above 20 kV/mm) are discussed in light of our electrical aging model. It is our contention that strong charge injection occurs only after nanocavity formation, i.e. above the critical field. The amorphous phase is then significantly deformed and weak van der Waals attraction bonds are broken, leading to another faster aging regime. The possible relation between the nanocavity formation at moderate fields and bonds breaking at higher fields proposed in our aging model and various polarization measurements is discussed. One objective of this paper is to encourage the development of more complex and complete theories specific to dielectrics. Some experimental work needed to achieve this goal is pointed out.     

Adhesion of charged powders to a metal surface in the powdercoating process

Substrate-particle adhesion of electrostatically charged, nonconducting particles deposited on electrically grounded substrates is discussed. Glass microspheres of diameters ranging from 25.5-74.1 μm, charged by corona and tribe-charging, were deposited in a monolayer on conducting stannic-oxide coated surfaces of glass plates (NESA). The total force of adhesion due to electrostatic, van der Waals, and gravitational forces was measured by observing the removal of particles by applying a known electric field between the particle coated surface and a clean surface of a second NESA glass, placed parallel to it at a distance of 0.013 m. The adhesive force was measured as a function of particle size and charge. The net average charge on the particles was measured using a Faraday cup. The experimental values agree well with the calculated force of adhesion for a single layer deposition. The charge decay of the particles was studied using a noncontact electrostatic voltmeter. The charge relaxation time of the deposited powder was found to increase with time. A physical model of the adhesion of charged powder paints deposited on a grounded metal substrate is presented. The role of the forces acting on a spherical polymer particle deposited on the surface of a uniform coating of powder paint is investigated as a function of particle diameter and charge. The particles are assumed to be unipolarly charged and deposited uniformly on the substrate. The relative magnitudes of the electrostatic attractive and repulsive forces are analyzed as functions of powder film thickness and particle size     

Aging and polarization phenomena in PE under high electric fields

The influence of high electrical DC fields (>20 kV/mm) on aging, polarization and on the morphology of polyethylene (PE) is discussed. Infrared and positron annihilation spectroscopy measurements as well as capacitance measurements tend to suggest that the polymer morphology is modified by high fields. The author shows that the accelerated electrical aging characteristics of PE are linked directly to the morphology changes induced by the field. Below a so-called critical field, the activation volume of the aging process is dependent on the field-induced strain. Above the critical field, the amorphous phase is deformed significantly, and weak van der Waals bonds are broken, leading to another, faster, aging regime. There is an excellent agreement between the proposed model and experimental data obtained with various PE samples. The possible relation between the submicrocavity formation proposed in his aging model and various polarization measurements is discussed. It is his contention that strong charge injection occurs only after submicrocavity formation, i.e. after weak bond breakage. As is well known, the polarization currents obtained under high fields are controlled by space charges. It seems that the wave packets and the negative resistance observed at >100 kV/mm in PE are associated with a steady state in field-induced defect formation. This suggests that space charges are related to the formation of submicrocavities and, therefore, are a consequence, not a cause, of high field aging.     

Interlayer exciton formation,relaxation, and transport in TMD van der Waals heterostructures

Van der Waals (vdW) heterostructures based on transition metal dichalcogenides (TMDs) generally possess a type-Ⅱ band alignment that facilitates the formation o...     

Dynamics of the forced negative conductance series LCR circuit

In this paper, we make a revisit of a simple LCR circuit introduced earlier in 2005 by Thamilmaran et. al., and present the circuit simulation studies of its dynamics using the PSpice circuit simulator package. This is a simple sinusoidally forced series LCR circuit, employing an ordinary single PN junction diode in conjunction with a negative conductance as its nonlinearity. In circuit theoretic terms, this circuit is a modified form of the forced van der Pol type oscillator and is interesting because it exhibits a dual nature, namely, a forced van der Pol type circuit behaviour and an MLC circuit type behaviour for different parametric ranges. In addition, statistical studies have shown the circuit to possess strong chaoticity. Subsequent works on this circuit have shown the birth of strange nonchaos through four different routes, namely, the Heagy-Hammel route, gradual fractalization route, intermittency route, and Bubbling route. In lieu of these, we look at the circuit afresh and study its dynamics in an exhaustive manner. These studies reveal many new bifurcations and routes to chaos. These results have been verified using hardware experiments in addition to numerical computations.     

Synchronous and asynchronous operation in dual‐band VCOs

We present a comprehensive analysis of the asynchronous and synchronous operations of fourth‐order oscillators underlying dual‐band voltage‐controlled oscillators. We analyze the occurrence of the self‐synchronization phenomenon (internal resonance) if the ratio of normal frequencies is nearly a ratio of integers, which is 1:3 in the cubic approximation of the nonlinear oscillator characteristic. In this case, we have the simultaneous presence of 2 oscillations with a frequency ratio 1:3, which was demonstrated to be very effective in generating high‐frequency signals in mm‐wave range. The analysis is carried out by developing an analytical approach relying on the averaging principle, as it follows the van der Pol method. The averaging equations, derived simply by a quadrature, allow us to analyze easily the stationary and transient oscillations, and their stability, both in asynchronous and synchronous operations. Expressions for the amplitudes and phases were derived for a cubic nonlinearity and verified by Spice simulations.     

Locking and Noise in a Model of a Negative-Resistance Oscillator

Measurements of the locking voltage and frequency range for a simple negative-resistance oscillator are shown to be in excellent agreement with a theory which assumes a van der Pol nonlinearity. When the noise generated in the nonlinear element is taken into account, the measurements of output noise produced by a noise driving current are also in agreement with theory.     

Multiscale modeling of screening effects on conductivity of graphene in weakly bonded graphene-dielectric heterostructures

Graphene is often surrounded by different dielectric materials when integrated into realistic devices. The absence of dangling bonds allows graphene to bond weakly via the van der Waals interaction with the adjacent material surfaces and to retain its peculiar linear band structure. In such weakly bonded systems, however, the electronic properties of graphene are affected by the dielectric screening due to the long-range Coulomb interaction with the surrounding materials. Including the surrounding materials in the first principles density functional theory (DFT) calculations is computationally very demanding due to the large supercell size required to model heterogeneous interfaces. Here, we employ a multiscale approach combining DFT and the classical image-potential model to investigate the effects of screening from the surrounding materials (hBN, SiC, SiO₂, Al₂O₃, and HfO₂) on the dielectric function and charged impurity scattering limited conductivity of graphene. In this approach, the graphene layer is modeled using DFT and the screening from the surrounding materials is incorporated by introducing an effective dielectric function. The dielectric function and conductivity of graphene calculated using the simplified two-band Dirac model are compared with DFT calculations. The two-band Dirac model is found to significantly overestimate the dielectric screening and charged impurity scattering limited conductivity of graphene. The multiscale approach presented here can also be used to study screening effects in weakly bonded heterostructures of other emerging two-dimensional materials such as metal dichalcogenides.     

Concealed conduction effects in the atrium

A one-dimensional (1-D) model of the atrium together with the sinoatrial (SA) and atrioventricular (AV) nodes is presented in this article. The two nodes are each modeled by 15-element, diffusively coupled, modified van der Pol oscillator chains, while the atrium tissue is represented by a 90-element chain of diffusively coupled FitzHugh-Nagumo (FHN) equations. The modified van der Pol oscillators are able to reproduce physiologically important properties, such as the refraction period, phase-sensitivity properties, and modes of change of the action potential frequency. The activity of both branches of the autonomous nervous system may be introduced into the model in a simplified way. The model enables the study of the effect of the magnitude of the action potential conduction rate in the nodes on interspike intervals (ISIs; equivalent of RR intervals) and explains the occurrence of RR-interval alternans in certain patients. The effect of breathing modulation of heart rate and of a single deep breath can also be modeled. Finally, concealed conduction effects in the atrium are studied, yielding results comparable with recorded heart rate variability data.     

复合绝缘子伞套间粘接结构及性能的分析

为了确保伞套间粘接性能，选用特配的粘合剂，采取半自机械化套粘伞裙装置，把自动化打磨好内口表面的、与护套采用过盈配合的、内绝缘强度高于外绝缘强度1倍所确定的内口长度的伞裙套粘在护套上。保证伞套间粘接部位实现硅氧烷分子交链完全、补强剂颗粒表面羟基及分子间范德华力利用充分、没有大直径填充剂颗粒存在的界面，使界面具有较高的机械强度和良好的绝缘性能。伞间套的过盈配合在相应部位处所出现的弹性变形，因其网状分子结构中的硅氧烷分子螺旋状态的存在，而使其蠕变性能极为缓慢，应力松弛现象几乎不存在．伞套间粘接性能是可靠的。     

Electronic properties of single-wall carbon nanotubes and their dependence on synthetic methods

Since their discovery in 1991, carbon nanotubes have been intensively studied, and a number of new applications have been identified. Applications range from nanoelectronics to hydrogen absorption for battery electrodes and fuel cells. Because of their high electrical conductivity and strength, high sensitivity atomic force microscopes already use carbon nanotubes for their tips, and carbon nanostructures are also used as electron beam emitters for medical and scientific equipment. Electron emission is directly correlated with the work function and the ionization potential of carbon nanotubes. Gaussian 98 software was used to perform theoretical quantum calculations on a limited set of HyperChem 5.01 simulated metallic single-wall carbon nanotubes. These initial sets of calculations show that bandgaps and work functions of these small carbon nanostructures are dependent upon the diameter of the tubes, and to a lesser degree so is the ionization potential. In addition, we demonstrate how the manufacturing methods can directly affect the diameter of the nanotubes produced, and therefore directly influence the electrical properties of the nanotubes.     

关于层状化合物氧基氯化铁(FeOCl)结构与物理化学特性的研究

讨论了氧基氯化铁FeOCl的晶体结构.FeOCl的晶格参数:a=0.378nm、b=0.792nm、c=0.330nm.在a、b面上每个氧原子与三个铁原于相部,每个铁原子与三个气原子及一个氯原子相邻.Cl-Cl间的最近距离为0.368nm,由范德华力相结合.在充放电时Li与溶剂分子易沿着这个由范德华力相键合的面进入FeOCl的晶体中,但是FeOCl自身的结构欠稳定,当大分子的有机溶剂嵌入FeOCl层间后,将导致结构的崩溃,因此FeOCl只能作为锂一次电池的阴极材料,作为二次电池阴极材料时必需对其进行改性处理.     

交联愈合剂/环氧树脂界面相容性分子动力学研究

为从分子水平分析紫外光固化过程中愈合剂修复环氧树脂基复合材料断裂面的微观机制,采用分子动力学方法研究了交联愈合剂/环氧树脂界面相的微观结构、相互作用能、力学性能和分子间径向分布函数.结果说明:交联愈合剂/环氧树脂的界面相厚度、相互作用能、拉伸模量z分量分别约为环氧树脂/环氧树脂的88.5％、85％和80％,表明交联愈合...     

Time evolution of current density in conducting single-walled carbon nanotubes

In the present work, we study the trembling motion known as Zitterbewegung in a conducting single-walled carbon nanotube by using the long-wave approximation. The Heisenberg representation is used to derive an analytical expression for the current density operator along the axial and spiral direction, which describes the current induced by the motion of the electronic wave packet in the carbon nanotubes. We have considered a number of parameters to describe the Gaussian wave packet, such as: the values of the initial pseudo-spin polarization, the initial carrier wave vector and the width of the localized packet along the axial and spiral coordinates. As a result, we show that the oscillation in current density can be controlled not only by the initial parameters of the wave packet, but mainly by choosing the up and low components of the localized quantum state. The analysis of the interference between the conduction and valence bands of quantum states is emphasized as the possibility of the emergence of the transient or aperiodic temporal oscillations in the average value for the current density in the conducting single-walled carbon nanotubes.     

On the electronic and transport properties of semiconducting carbon nanotubes: the role of $$\hbox {sp}^3$$-defects

The effect of \(\hbox {sp}^3\)-defects on the electronic and transport properties of semiconducting carbon nanotubes has been systematically studied on the basis of a quantum mechanical tight-binding model. We have calculated the band structure for carbon nanotubes with ordered defect patterns showing a large impact on the bandgap energy whereas for randomly distributed defects the band structure remains relatively robust. The transport behavior has been studied on the basis of the Green’s function method. The results indicate that the conductance of defective carbon nanotubes strongly depends on the number of defects and the tube diameter. We further show that the transport properties can be classified, depending on the number of defects, into two regimes which are either characterized by the mean-free path or the localization length. For both, analytical equations describing the impact of the tube diameter as well as the number of defects are derived. Comparing these values with the channel length indicates the dominant transport regime.