Formation of a small ‘bead lightning’ in a half-microsecond discharge in air

The formation of periodic plasma clots which form a discharge channel similar to bead lightning has been studied with a four-channel intensified charge-coupled device (ICCD) camera simultaneously with the recording of voltage and current waveforms. It was found that a diffuse discharge was formed at the initial stage due to the development of a wide streamer. Runaway electrons were registered. Beads were formed as a result of the development of the spark leader after the diffuse stage. It was assumed that the diameter of the spark leader periodically changes in accordance with the change in the electric field strength in the spark leader head. As a result, narrow sections of the channel heat up more and glow brighter.     

Leader discharge over a water surface in a Lichtenberg figure geometry

A multichannel leader discharge over a water surface is investigated in a Lichtenberg figure geometry. It is established that the Ohmic conductivity of water causes nonlinearity of the R(t)C discharge circuit. A mutual one-to-one correspondence between the channel lengths and the currents flowing in them is established during the discharge, and the discharge has a selfconsistent character. A mechanism is proposed for the initiation of initial channels by maxima which arise in the charge structure of the planar double layer on the water surface during the development of Rayleigh-Bénard instability in the layer after the pulsed corona from the anode reaches the water. Zh. Tekh. Fiz. 68, 63–66 (November 1998)     

Self-consistent development and fractal structure of leader discharges along a water surface

Ideas regarding the development of single-and multichannel leader discharges over water surfaces are generalized on the basis of experimental data. The Ohmic conductivity of water is found to be manifested in the self consistency of their dynamics and fractal structure. The fractal dimensionality of a single-channel leader discharge is found to be 0.96±0.05 and that of a multichannel discharge to be 1.85±0.05. Mechanisms are proposed for the branching of leader discharge channels and for the development of bifurcations from branches and channels. Zh. Tekh. Fiz. 69, 35–40 (April 1999)     

Effect of the initial plasma parameters on the structure of the current sheets developing in two-dimensional magnetic fields with a null line

The effect of the initial plasma parameters on the structure of the plasma of the current sheets that form in two-dimensional magnetic fields with a null line is studied by holographic interferometry. The evolution of the plasma sheets that develop in an initial low-density plasma, where a gas is mainly ionized by a pulse current passing through the plasma and initiating the formation of a current sheet, has been comprehensively studied for the first time. At the early stage of evolution, the spatial structure of such a plasma sheet differs substantially from the classic current sheets forming in a dense plasma. Nevertheless, extended plasma sheets with similar parameters form eventually irrespective of the initial plasma density.     

Technique for calculating the vulnerability of explosive surface objects by lightning

A probabilistic technique for estimating the vulnerability of explosive surface objects by lightning has been proposed. It uses a combined criterion for initiation of upward streamer and leader discharges form the elements of the object and lightning diverters. This criterion takes into account the probabilistic nature of avalanche–streamer and streamer–leader transitions and also the trajectories of the lightning’s downward stepped leader and lightning current. It has been shown that, if the formation of the downward leader of incomplete streamer discharges from the elements of the object in an electric field is neglected (these discharges may set fire on explosive emissions), the probability of lightning-induced failure of the object is underestimated by several times compared with the calculated value.     

Enhancement of Cooling Rate for a Hot Steel Plate using Air-Atomized Spray with Surfactant-Added Water

The objective of the current research deals with the experimental study of an air-atomized spray with surfactant-added water, cooling a 12-mm-thick AISI-1020 stationary steel plate at three different initial surface temperatures (400°C, 600°C, and 900°C). Furthermore, the effects of surfactant concentration and airflow rate on the cooling rate have been investigated. The surface heat flux and surface temperature show a significant improvement in cooling for all three cases of initial surface temperatures when the air-atomized spray was used with surfactant-added water.     

Specifics of operation of a cold-cathode thyratron with a backward voltage half-wave

The specifics of operating a metal-ceramic TPI1-10k/50 thyratron in electric circuits with capacitance, inductance, and active resistance have been examined under circuit parameters that establish oscillatory current. Experiments have been performed at an anode voltage as high as 30 kV, a forward current of up to 7.6 kA, and a length of the first current half-period that varies from 0.38 to 1.9 μs. The data on operating modes in which this thyratron may handle a backward current wave and when current interruption is observed in the second half-period have been obtained. It has been demonstrated that a certain current flows through the thyratron in the backward direction during the interruption process. The amplitude of this current and the maximum backward voltage at the thyratron define whether the current is interrupted or repeat back-voltage device breakdown occurs. If the maximum backward current is on the level of several hundred amperes, complete current interruption occurs at backward voltages of up to 12 kV. The physical mechanisms of current interruption have been discussed.     

(Quasi 3D) Numerical simulation of operation of a capacitive type nanoparticle counter

Operation of a nanoparticle counter is based on condensation of water on nanoparticles forming water droplets which are fed to a capacitive type detector. Impaction of a water droplet onto the water filled detector causes formation of a crater resulting in change of capacitance that is measured by associated electronics. Numerical simulation of electric field distribution during droplet impaction has been performed in order to analyze the suitability of the approach and to estimate the magnitude of change of detector capacitance during droplet impaction. A single impinging droplet is able to cause capacitance change in the femtofarad range.     

On the nature of bipolar flashes that share the same channel to ground

The paper examines the relationship between sequential events in bipolar flashes of two groups sharing the same channel to ground: one initiated by an upward positive leader, the other by a natural flash. Two quite different mechanisms are involved in the occurrence of the bipolar flashes of each group: The bipolar events that start as a natural flash are results of recoil leaders sharing parts of the initial branching structure; the bipolar events that start as upward positive leaders are the result of the interaction between these leaders' initial branching structures and the branches of the intracloud flashes they triggered.     

Passivation of n-GaAs (100) surface by a Langmuir-Blodgett film

We report the results of passivation of n-GaAs surface by Langmuir-Blodgett films. The capacitance-voltage and current-voltage characteristics in a metal-insulator-semiconductor configuration fabricated using films as insulators, show that the frequency dispersion of the accumulation capacitance is small, indicating that the high frequency capacitance under accumulation is due to the LB film. It has been shown that it reduces the surface barrier characteristic of GaAs surfaces, and may offer hope for unpinning the surface Fermi level. We offer a possible explanation for these findings in terms of the advanced unified defect and the effective work function models.     

电极/水溶液界面的SERS研究Ⅰ.Cu/1.0M的Na_2SO_4和NaCl溶液体系

电极／水溶液界面的ＳＥＲＳ研究Ⅰ．Ｃｕ／１．０Ｍ的Ｎａ２ＳＯ４和ＮａＣｌ溶液体系陈燕霞黄开启田中群（厦门大学化学系固体表面物理化学国家重点实验室物理化学研究所厦门３６１００５）ＳＥＲＳＳｔｕｄｉｅｓｏｆＥｌｅｃｔｒｏｄｅ／ＥｌｅｃｔｒｏｌｙｔｅＳｏ...     

Local capacitance analysis using a modified deep level spectrometer

A bimorph-based xz scanner and an amplifier, increasing the capacitance and current measurement sensitivities 250-times and 1000-times, respectively, have been built into the cryostat of a deep level transient spectrometer. The setup renders point by point local capacitance-voltage (C?CV) at 1 MHz and dc currentvoltage (I?CV) measurements using a sharp tip placed into tunnelling distance from the surface of analysed semiconductor sample. The C?CV measurements revealed a strong dependence on the probe/sample separation, ranging from MOS-type at small tunnelling currents to Schottky-type at currents exceeding approximately 10 pA. Marked hysteresis was observed, indicating changes of surface state occupancy. These slow states are otherwise hardly detected, since they are absent in semiconductor/metal contacts and in MOS structures they would become mostly passivated interface states. The setup enables calibrated, fixed zero level capacitance measurement. The stray capacitance is the dominant component of the measured capacitance but it can be easily discarded.     

Effect of substrate morphology on the roughness evolution of ultra thin DLC films

The effect of substrate roughness on growth of ultra thin diamond-like carbon (DLC) films has been studied. The ultra thin DLC films have been deposited on silicon substrates with initial surface roughness of 0.15, 0.46 and 1.08 nm using a filted cathodic vacuum arc (FCVA) system. The films were characterized by Raman spectroscope, transmission electron microscope (TEM) and atomic force microscopy (AFM) to investigate the evolution of the surface roughness as a function of the film thickness. The experimental results show that the evolution of the surface morphology in an atomic scale depends on the initial surface morphology of the silicon substrate. For smooth silicon substrate (initial surface roughness of 0.15 nm), the surface roughness decreased with DLC thickness. However, for silicon substrate with initial surface roughness of 0.46 and 1.08 nm, the film surface roughness decreased first and then increased to a maximum and subsequently decreased again. The preferred growth of the valley and the island growth of DLC were employed to interpret the influence of substrate morphology on the evolution of DLC film roughness.     

Two-dimensional residual charge density distribution measurement of surface leader

The charge density distribution of the surface leader has never been measured before. Because the surface leader usually covers a long distance, and the surface potential caused by leader discharge is usually very high, this creates difficulties in measuring the potential distribution of the surface leader. In this paper, with a feedback type electrostatic probe based on a field-nullify technique, a charge density distribution scanning system is developed. A two-layer structure pipe is designed to lower the surface potential after discharge. In this way, the surface potential distribution caused by the residual charge of the leader discharge under the application voltage as high as to 40 kV can be measured. The surface charge density distribution including the leader and streamer is perfectly measured, which is in good agreement with the photograph.     

On the characteristic time for the realization of instability on a flat charged liquid surface

A nonlinear integral equation that describes the time evolution of the amplitude of a nonlinear unstable wave on the flat uniform charged surface of an ideal incompressible liquid has been derived and solved. The characteristic time for the realization of instability is found to be determined by the initial amplitude of a virtual wave initiating the instability and the supercritical increment in the Tonks-Frenkel parameter. At a zero supercritical increment, the characteristic time for the realization of instability is only determined by the initial amplitude and can be rather long (up to eight hours). This effect is characteristic of a flat charged liquid surface and does not occur in charged drops.     

放电参数对同轴枪中等离子体团的分离的影响

同轴枪中的等离子体团的分离现象主要是由同轴枪内磁场的梯度造成的电流层倾斜而引起的一个增强反馈过程导致的, 这种分离现象越来越成为限制同轴枪有效使用的一个不利因素. 在实验上研究放电参数对等离子体团的分离的影响, 对理论研究和实际应用都具有重要意义. 在实验中发现, 利用光电倍增管可以直接观察到等离子体团的分离程度, 由此可以研究放电参数对等离子体团的分离的影响. 本实验主要研究电容充电电压、电容、放电气压这三个参数对分层现象的影响. 实验发现, 分离程度随着电容以及其充电电压的增大而增强, 随着气压的增大而减弱. 实验结果基于雪犁模型进行分析, 电容以及电容充电电压的增大使放电电流增强使磁场梯度增大而导致电流层的倾斜程度增加, 而使等离子体团的分离程度变严重, 相反, 气压的增加使需要加速更多粒子而导致电流层的倾斜程度减弱, 而使等离子体团分离程度减弱. 分析认为, 通过控制在加速过程中影响电流层倾斜程度的因素可控制共轴枪中等离子体团的分离程度.     

Capacitance of a Surface to a Point and Variational Inequalities

Based on variational principles, a new concept of the capacitance of a surface to a point, which has a clear physical meaning, is introduced. It is demonstrated that this concept can be used to derive the variational inequalities for the capacitance coefficients of a system of conductors. Examples of calculations of the capacitance of a surface to a point and the variational inequalities are given.     

Determination of the curie temperature of a single Ni nanowire from the analysis of current-voltage characteristics

A new method of measuring the Curie temperature of a single nanowire located on the surface of an insulating substrate has been proposed. The method is based on the analysis of the current-voltage characteristics of the nanowire obtained at different initial temperatures of the sample. A maximum is observed on the dependence of the first derivative of the resistance on the applied power, the position of which is shifted to lower powers with increasing initial temperature. The Curie temperature is determined graphically as the temperature at zero power. The Curie temperature of a nickel nanowire formed on a SiO₂/Si surface by the scanning probe lithography method has been measured. The critical current density at which the transition from the ferromagnetic to the paramagnetic state occurs has been determined.     

针-板空气间隙流注放电起始过程的三维PIC/MCC仿真研究

流注放电作为自然界中闪电传播的预电离机制、高压输变线路间长空间间隙放电的重要初始阶段,在工业领域存在诸多潜在应用,近年来引起人们越来越多的关注.流注放电具有典型的多尺度、非线性的放电特征,实验观测中多呈现出分叉等不规则结构.为了研究其微观结构特性和行为特征,本文采用三维粒子仿真模型(PIC/MCC),着重研究了流注从针型正电极的起始和发展过程.模型采用了可变自适应网格、可变粒子权重以及并行计算等技术,有效地降低了三维粒子仿真的计算时间.通过调节针型电极上的施加电压幅值、改变气体组分及调整电极形状尺寸等,研究了放电参数变化对流注放电的分叉结构、半径等行为的影响.模拟结果表明:随着电压的升高,流注的半径及分叉数目增加;对比不同气体组分(纯氧以及不同比例氮氧混合气体),发现其对流注的分叉数目影响较为显著;针型电极结构直接影响了流注的起始时间和形貌.     

大气中Pd-H(D)系中H(D)的释放及其表面附近H的分布

将经过950℃热处理后缓慢冷却及淬火处理的Pd样品,分别作为阴极在重水(D₂O)和轻水(H₂O)中进行150h电解,以引入H和D。用X射线衍射方法测量Pd-H(D)系存放于大气中经过不同时间后的衍射图及β相晶格常数的变化,并用¹H(¹⁹F,αγ)¹⁶O核反应测量H在各Pd-H(D)系表面层中的分布。淬火Pd与退火Pd相对比,在电解吸H(D)后,前者初始含H(D)百分比较高而H(D)的释放速度较快。H的浓度在Pd-H合金的表面处达到极大值而在离表面深度为数百埃处达到极小值。 关键词：