Helical streamers guided by surface electromagnetic standing waves

The streamer that is driven by the specific pulse DC discharge parameters can stably form a three-dimensional helical plasma channel in a long dielectric tube in the low-temperature plasma experiment,in cases when there were neither external background magnetic field or other factors that destroyed the poloidal symmetry of the tube.The formation mechanism and chirality of helical streamers are discussed according to the surface electromagnetic standing wave theory.The shape of the helical streamers and the characteristics of helical branches are quantitatively analyzed to further expand the application of plasma and streamer theory in the helix problem and chiral catalytic synthesis.

基于Data Streamer开发的摩擦力可视化测量装置

在初中物理教材中通过弹簧测力计测量摩擦力,由于拉力变化不均匀,实验结果存在偏差.本文针对原实验的不足进行改进创新,用Data Streamer串口采集插件实时读取拉力传感器采集的摩擦力数据到Excel中进行数据分析,绘制出可视化的实时动态图像,让实验者直观感知摩擦力的实时变化过程,增强实验的趣味性和交互性.

Dynamic propagation velocity of a positive streamer in a 3 m air gap under lightning impulse voltage

Streamers represent an important stage in the initiation of gap discharge. In this work, we used an eight-frame intensified charge-coupled device camera to capture the streamer development process when a lightning impulse voltage of 95%–100% U50% was applied in a 3 m rod–plate gap and the streamer velocity was analyzed. Analysis of the observations shows that streamer velocity can be defined by three stages: rapid velocity decline(stage 1), rapid velocity rise(stage 2)and slow velocity decline(stage 3). The effects of electrode shape, applied voltage and gap breakdown or withstanding on streamer velocity were analyzed. The electrode with a larger radius of curvature will result in a higher initial velocity, and a higher voltage amplitude will cause the streamer to propagate faster at stage 3. Gap withstanding or breakdown has no obvious effect on streamer velocity. In addition, the experimental results are compared with previous results and the statistical characteristics of the primary streamer discharge are discussed.

Modification of streamer-to-leader transition model based on radial thermal expansion in the sphere-plane gap discharge at high altitude

Historically,streamer-to-leader transition studies mainly focused on the rod-plane gap and low altitude analysis,with limited attention paid to the sphere-plane gap at high altitude analysis.In this work,sphere-plane gap discharge tests were carried out under the gap distance of 5 m at the Qinghai Ultra High Voltage(UHV)test base at an altitude of 2200 m.The experiments measured the physical parameters such as the discharge current,electric field intensity and instantaneous optical power.The duration of the dark period and the critical charge of streamer-toleader transition were obtained at high altitude.Based on radial thermal expansion of the streamer stem,we established a modified streamer-to-leader transition model of the sphere-plane gap discharge at high altitude,and calculated the stem temperature,stem radii and the duration of streamer-to-leader transition.Compared with the measured duration of sphere-plane electrode discharge at an altitude of 2200 m,the error rate of the modified model was 0.94%,while the classical model was 6.97%,demonstrating the effectiveness of the modified model.From the comparisons and analysis,several suggestions are proposed to improve the numerical model for further quantitative investigations of the leader inception.

High-resolution frequency-domain Radon transform and variable-depth streamer data deghosting

Receiver ghost reflections adversely affect variable-depth streamer （VDS） data acquisition. In addition, the frequency notches caused by the interference between receiver ghosts and primary waves strongly affect seismic data processing and imaging. We developed a high-resolution Radon transform algorithm and used it to predict receiver ghosts from VDS data. The receiver ghost reflections are subtracted and removed from the raw data. We propose a forward Radon transform operator of VDS data in the frequency domain and, based on the ray paths of the receiver ghosts, we propose an inverse Radon transform operator. We apply the proposed methodology to model and field data with good results. We use matching and subtracting modules of commercially available seismic data processing software to remove the receiver ghosts. The frequency notches are compensated and the effective frequency bandwidth of the seismic data broadens.

Simultaneous prestack inversion of variable-depth streamer seismic data

Variable-depth streamer seismic data are characterized by low and high frequencies and can be used to obtain high-quality and resolution images of complex subsurface structures. Taking advantage of the frequency range in the variable-depth streamer data, we propose the simultaneous inversion of prestack data from variable-offset stack gathers to obtain the P-wave impedance, S-wave impedance, and density. Next, we validate the method by using model and actual variable-depth streamer data from the Huizhou block. The results suggest that the broadband data recorded by variable-depth streamers improve the signal-to-noise ratio and quality of the inversion results and outperform the constant-depth streamer data in delineating the underground stratigraphy.

Experimental Study on Branch and Diffuse Type of Streamers in Leader Restrike of Long Air Gap Discharge

One of the main problems in the Ultra High Voltage （UHV） transmission project is to choose the external insulation distance, which requires a deep understanding of the long air gap discharge mechanism. The leader-streamer propagation is one of most important stages in long air gap discharge. In the conductor-tower lattice configuration, we have measured the voltage, the current on the high voltage side and the electric field in the gap. While the streamer in the leader-streamer system presented a conical or hyperboloid diffuse shape, the clear branch structure streamer in front of the leader was firstly observed by a high speed camera in： the experiment. Besides, it is found that the leader velocity, width and injected charge for the branch type streamer are greater than those of a diffuse type. We propose that the phenomenon results from the high humidity, which was 15.5-16.5 g/m3 in our experiment.

Dynamical Tropopause Variability and Potential Vorticity Streamers in the Northern Hemisphere——A Climatological Analysis

This study presents a 44-year climatology of potential vorticity （PV） streamers in the Northern Hemisphere based upon analyses of the ERA-40 reanalysis data set. A comparison to an existing 15-year climatology yields very good agreement in the locations of PV streamer frequency maxima, but some differences are found in the amplitude of frequencies. The climatology is assessed with the focus on links between PV streamer frequencies and the synoptic- and planetary-scale variability of the dynamical tropopause. A comprehensive overview is provided on where （zonally） and when （seasonally） short-term variability throughout the extra-tropical and sub-tropical tropopause is enhanced or reduced. Several key processes that influence this variability are discussed. Baroclinic processes, for example, determine the variability in the storm-track areas in winter, whereas the Asian summer monsoon significantly influences the variability over Asia. The paper also describes links between the frequency of PV streamers in the extra-tropical and subtropical tropopause and three major northern hemisphere teleconnection patterns. The observed changes in the PV streamer frequencies are closely related to concomitant variations of PV and its gradient within the tropopause region. During opposite phases of the North Atlantic Oscillation the location of the streamer frequency maxima shifts significantly in the Atlantic and European region in both the extra-tropics and subtropics. The influence of ENSO on the streamer frequencies is most pronounced in the subtropical Pacific.

Corona with Streamers in Atmospheric Pressure Air in a Highly Inhomogeneous Electric Field

The paper presents research data on positive and negative coronas inatmospheric pressure air in a highly inhomogeneous electric field. Thedata show that irrespective of the polarity of pointed electrodes placed ina high electric field (200 kV/cm), this type of discharge develops via ballstreamers even if the gap voltage rises slowly (0.2 kV/ms). The start voltageof first positive streamers, compared to negative ones, is higher andthe amplitude and the frequency of their current pulses are much lower:about two times and more than two orders of magnitude, respectively.The higher frequency of current pulses from negative streamers provideshigher average currents and larger luminous areas of negative coronascompared to positive ones. Positive and negative cylindrical streamersfrom a pointed to a plane electrode are detected and successive dischargetransitions at both polarities are identified.

Study of Formation and Propagation of Streamers in SF_6 and Its Gas Mixtures with Low Content of SF_6 Using a One-Dimensional Fluid Model

Using a hybrid Monte Carlo Collision/Fluid model, the formation and propagation of streamers in SF6 and its gas mixtures are simulated. The simulation is based on an accurate numerical solution of Poisson＇s equation in conjunction with the continuity fluid equation for electrons, negative ions, and positive ions. The factors that influence the formation and propagation of streamers are investigated. The electron density, positive and negative ion density, and electric field in the discharge channel are also presented, which are very important in understanding the phenomena of streamers and in assessing the insulation strength of the gas mixture.

Effects of rod radius and voltage on streamer discharge in a short air gap

Streamer discharge is the inaugural stage of gas discharge,and the average electron energy directly determines the electron collision reaction rate,which is a key parameter for studying streamer discharge.Therefore,taking into account the average electron energy,this work establishes a fluid chemical reaction model to simulate and study the course of evolution of a streamer discharge in a 5 mm rod–plate gap,considering 12 particles and 27 chemical reactions.It introduces the electron energy drift diffusion equation into the control equation,and analyzes the temporal and spatial changes of average electron energy,electric field intensity and electron density with change in rod radius and voltage.The effects of voltage and rod radius on the course of streamer discharge can be reflected more comprehensively by combining the average electron energies.Three different values of 0.3 mm,0.4 mm and 0.5 mm are set for the rod radius,and three different values of 5 k V,6 k V and 7 k V are set for the voltage.The influence of an excitation reaction on the streamer discharge is studied.The findings indicate that,as voltage raises,the streamer head’s electron density,electric field and average electron energy all rise,and the streamer develops more quickly.When the rod radius increases,the electron density,electric field and average electron energy of the streamer head all decrease,and the streamer’s evolution slows down.When an excitation reaction is added to the model,the average electron energy,the magnitude of the electric field and the density of electrons decrease,and the evolution of the streamer slows down.An increase in average electron energy will lead to an increase in electric field strength and electron density,and the development of the streamer will be faster.

Characteristic studies on positive and negative streamers of double-sided pulsed surface dielectric barrier discharge

The mechanisms of streamer generation and propagation in double-sided pulsed surface dielectric barrier discharge(SDBD)on both sides have been analyzed and investigated by experiment and numerical simulation.The fully exposed asymmetric SDBD has two discharge processes located on the high voltage electrode(HVE)side and the ground electrode(GE)side.Discharge images of the HVE side and GE side are taken by a digital camera under continuous pulse and ICCD(Intensified Charge Coupled Device)is utilized to diagnose the generation and propagation of streamers in single pulse discharge.In order to understand the physical mechanisms of streamer evolution more deeply,we establish a 2D simulation model and analyze it from the aspects of electron density,ion density,reduced electric field and electron impact ionization source term.The results show that the primary and secondary discharges on the HVE side and the GE side of the double-sided SDBD are composed of positive streamer and negative streamer,respectively.On the HVE side,the accumulation of positive charges on the dielectric surface causes the direction of the electric field to reverse,which is the principal factor for the polarity reversal of the streamer.On the GE side,both the negative charges accumulated on the dielectric surface and the falling voltage are the key factors for the streamer polarity switch.

Comparative Study of Streamers＇ Characteristics in Different Seed Based Insulating Oils under Lightning Impulse Voltages

This paper is aimed at the streamers in natural esters （vegetable oils） in point--plane electrode arrangement under lightning impulse voltage. The shape, stopping length, velocity and current of streamers are investigated. Six untreated commercial oils extracted from grape seeds, sunflower and rape seeds, corn, rice and sesame that could constitute potential liquids for high voltage applications are tested. A naphthenic mineral oil is also tested for comparison. It＇s shown that the streamers are filamentary for both polarities. For a given voltage, the stopping lengths （Lf） of streamers are longer when the point is positive than when it is negative; also, except mineral oil when the point is negative, the values of Lf-are very close in all tested oils. The streamers＇ velocities are in the same range for all vegetable oils and they vary between 0.4 km/s and 1.2 km/s for positive polarity and 0.2 km/s and 0.8 km/s for negative polarity.

天然酯绝缘油-纸界面的多分支流注放电仿真

油-纸界面的局部放电是油浸式变压器中油-纸绝缘失效的主要原因之一。文中在多分支流注放电数值模型的基础上进一步考虑油-纸界面的电荷输运特性,构建油-纸绝缘系统中的多分支流注放电模型,并利用有限元法分别对天然酯绝缘油和绝缘纸介电常数配比、针电极与纸板的间距影响下的沿面放电特性进行研究。结果表明,针电极与纸板的间距及绝缘油与绝缘纸的介电常数配比均会显著影响流注分支;针电极与纸板的间距越小,油-纸界面处的流注分支间的抑制越明显,油-纸界面的流注对z-轴流注的影响更显著;当绝缘油介电常数比纸板大时,流注在油中的发展和分支更为显著,反之则流注更易沿纸板表面发展及在油-纸界面聚集电荷。

基于场致二次谐波的大气压脉冲流注放电时变非均匀电场测量研究

诊断大气压脉冲流注放电空间电场是实现流注放电精准调控和揭示等离子体不稳定性机制的重要基础。基于场致二次谐波的空间电场测量方法具有非侵入式、时空分辨率高等优点。然而,流注放电时变非均匀电场对二次谐波信号产生过程的影响规律尚不完善,真实电场标定系数随流注放电不同阶段的变化规律尚不清晰。该文首先计算二次谐波信号产生规律和电场空间分布的影响;然后,基于等离子体流体模拟,分析二次谐波信号对流注放电不同阶段时变非均匀电场的敏感程度;最后,基于纳秒脉冲激光场致二次谐波电场测量平台,实验获得了重频脉冲作用下组合电极结构产生的单根负流注轴向电场演变规律,分析脉冲重复频率对空间电场的影响机制,并针对流注放电时变非均匀电场特点提出电场致二次谐波测量优化若干建议。

主播-品牌关联度对消费者购买意愿的影响

主播作为品牌直播间的“前沿”代言人,在品牌建设中扮演着重要角色,但主播的代言效果并不总是尽如人意,这取决于主播与品牌之间的关联度。目前对于主播-品牌关联度是否会对消费者购买意愿产生影响尚不明晰。文章基于Hovland说服模型,通过问卷调查法探讨主播-品牌关联度对消费者购买意愿的影响以及这一影响发生的内在机制和边界条件。研究结果表明:主播-品牌关联度对消费者购买意愿具有显著正向影响;在此过程中,消费者自我-品牌联结发挥着部分中介作用。此外,由品牌知识的调节效应分析发现,其能够正向调节主播-品牌关联度与消费者自我-品牌联结的关系。这将丰富直播营销对消费者购买意愿影响的相关研究,为商家有针对性地选择主播,提升品牌代言效果提供重要参考。

主播群体规模对品牌直播销售绩效的倒U型影响研究——来自化妆品行业的实证?

直播电商活动中,主播群体是促进产品销售的核心人群。本研究重点关注品牌网络直播活动中主播群体规模、产品线宽度和品牌类型的匹配对品牌直播销售绩效的影响。本研究收集了2020年8月-12月共18周内化妆品行业中具有代表性的17个奢侈品牌和27个非奢侈品牌的抖音直播销售数据,其中包含261个主播、1,658个产品和3,119场直播。通过采用STATA的双向固定效应模型分析,本研究发现主播群体规模对品牌直播销量有显著的倒U型影响,直播产品线宽度对品牌直播销量有显著的直接正向影响。同时,直播产品线宽度和品牌类型调节了主播群体规模对品牌直播销量的倒U型影响。

考虑电压上升影响的“针-板”空气间隙直流负流注放电特性研究

负流注放电过程是一个高度非线性动力学过程,且发展过程复杂。该文针对“针–板”电极结构、1cm空气间隙,建立短空气间隙负流注放电模型并通过仿真试验验证模型合理性,分析外加上升时间及电压幅值对负流注放电发展过程空间电场强度、带电粒子浓度、流注发展速度、放电电流变化特性的影响。随负流注由“针”电极向“板”电极发展,放电区域内的轴线电场强度、电子浓度在短暂升高后呈现先降低后升高的变化趋势;随外加电压上升时间增大,流注头部的电场强度和电子浓度呈非线性上升趋势,外加电压上升时间T=0.01ns上升到T=2ns时,流注发展平均速度降低3.38mm/ns;随外加电压幅值增大,负流注头部的电场强度及电子浓度呈非线性上升趋势,外加电压幅值U_(0)=-20kV上升到U_(0)=-25kV时,流注发展平均速度上升2.7mm/ns。

纳秒脉冲下SF_(6)中的气固界面流注特性

在电磁脉冲模拟装置中,绝缘子的沿面闪络问题制约着装置的安全运行。为此通过将放电过程中正负离子和电子的连续性方程和泊松方程耦合,建立了脉冲电压下气-固界面流注放电的仿真模型,对不同电压极性、不同气压下的沿面放电流注的机理和特性进行了研究,并通过与实验结果进行对比,分析了电压极性及气压对沿面流注放电发展与介质表面电荷的影响。结果表明,正负流注在发展过程中存在差异,正流注头部电离剧烈,以步进方式向前发展,而负流注更容易产生阴极导向的正流注。负极性流注介质表面电荷积累要大于正极性表面,介质表面电荷累积造成的局部电场是负极性流注产生阴极导向正流注的主要原因。同时,随着外界气压的上升,流注发展半径减小,表面电荷累积量增加。