Numerical simulation of an uncharged droplet in a uniform electric field

The deformations of a real dielectric droplet subjected to a uniform alternating electric field and immersed in an insulating fluid are numerically studied by the Boundary Element Method. The alternating electric field time scale is taken much smaller than the hydrodynamic time scale of the droplet shape deformation. The influence of the frequency and the conductivity of the droplet upon the critical electric field, beyond which instabilities develop, are compared with the experimental measurements. Numerical results well account for experimental data while an unexpected good correspondence with Taylor's theory is found.     

Electrohydrodynamic behaviors of droplet under a uniform direct current electric field

The electrohydrodynamic behaviors and evolution processes of silicone oil droplet in castor oil under uniform direct current(DC)electric field are visually observed based on a high-speed microscopic platform.Subsequently,the effects of different working conditions,such as electric field strength,droplet size,etc.,on droplet behaviors are roundly discussed.It can be found that there are four droplet behavior modes,including Taylor deformation,typical oblique rotation,periodic oscillation,and fracture,which change with the increase of electric field strength.It is also demonstrated that the degree of flat ellipse deformation gets larger under a stronger electric field.Moreover,both of the stronger electric field and smaller droplet size lead to an increase in the rotation angle of the droplet.     

Dynamics of the microstructure of current channels and the generation of high-energy electrons in nanosecond discharges in air

The results of the three-dimensional numerical simulation of the dynamics of the microstructure of high-voltage nanosecond discharges in air at atmospheric pressure are presented. It is established that the fast (at a time of ≈10 ns) broadening and significant decrease in the gas concentration in the microchannels occur as a result of the ohmic heating of microchannels with the diameter of 1–30 μm. It was shown that the broadening of microchannels in a nanosecond diffusive discharge provides an increase in the ratio of the electric field strength to the gas concentration in microchannels to values sufficient for the generation highenergy electron beams and X-ray bremsstrahlung in them. Features of the dynamics of the system of microchannels and its effect on the efficiency of the generation of high-energy electrons in discharges developing in the microstructuring regime of the current channels are considered.     

Investigation on dynamics of double emulsion droplet in a uniform electric field

Phase field method based on Cahn–Hilliard free energy formulation is adopted for predicting the behavior of double emulsion droplet suspended in a continuous phase under the influence of a uniform electric field. The role played by the inner droplet on the electric-field-driven fluid flow, and also on deformation of the outer droplet is predicted by present numerical simulation. Three different kind of deformation type of outer and inner droplet (prolate–oblate, prolate–prolate and oblate–prolate) has been observed. With increase in the volume fraction of inner drop, transition in the deformation of outer drop from prolate to oblate occurs at lower value of fluid permittivity ratio.     

Microstructure of the current channels in a nanosecond spark discharge in atmospheric-pressure air in uniform and highly nonuniform electric fields

The microstructure of a nanosecond spark discharge in atmospheric-pressure air in uniform and highly nonuniform electric fields is investigated. It is found that an 0.1-to 0.4-mm spark channel consists of a large number (from 100 to 1000) of 5-to 10-μm-diameter microchannels distributed nearly uniformly over the channel cross section. The current amplitude in the spark is 1.5–3 kA, and the current density in a microchannel is 10⁷ A/cm². It is shown that the formation of the microstructure cannot be attributed to ionization-heating instability. The instability of the ionization wave front is suggested as a mechanism for the microstructure formation.     

Numerical simulation of a direct current glow discharge in atmospheric pressure helium

Characteristics of a direct current(DC) discharge in atmospheric pressure helium are numerically investigated based on a one-dimensional fluid model. The results indicate that the discharge does not reach its steady state till it takes a period of time. Moreover, the required time increases and the current density of the steady state decreases with increasing the gap width. Through analyzing the spatial distributions of the electron density, the ion density and the electric field at different discharge moments, it is found that the DC discharge starts with a Townsend regime, then transits to a glow regime. In addition, the discharge operates in a normal glow mode or an abnormal glow one under different parameters, such as the gap width, the ballast resistors, and the secondary electron emission coefficients, judged by its voltage–current characteristics.     

Decay in presence of a uniform electric field

The decay-rate of an eigenstate into the continuum is calculated in a simple 1-dimensional model, when a small uniform electric field is switched on. It is shown that this rate is very sensitive to changes in the field strength, in conformity with experimental observations.Supported by the Fonds National Suisse.     

Two-dimensional Wannier-Mott exciton in a uniform electric field

A new treatment of the problem of a two-dimensional Wannier-Mott exciton in a uniform electric field, based on the parabolic coordinates, is presented. The quasi-stationary Hamiltonian is regularized, and the efficient numerical methods are applied. The dependence of the exciton binding energy on the electric field is computed. The results are very close to those obtained by the perturbation theory calculations.     

High-pressure runaway-electron-preionized diffuse discharges in a nonuniform electric field

High-pressure nanosecond diffuse (volume) discharges in a nonuniform electric field are studied experimentally using a recording system with a ?100-ps time resolution. As the voltage pulse shrinks to a width of ≈100 ps, the initiation of a diffuse discharge without a source of additional ionization is facilitated; specifically, a runaway-electron-preionized diffuse discharge is ignited in atmospheric-pressure air in the case of short interelectrode gaps. It is found that a major energy deposit into the plasma of this discharge is from an abnormal glow discharge following a maximum of the gap voltage.     

接地条形导体板对均匀电场的影响及其数值模拟

利用保角变换法和复位函数法,研究接地条形导体板对均匀电场的影响,给出其电势和场强分布,并利用软件MATLAB对场分布进行数值模拟.     

Molecular dynamics simulation of continuous current flow through a model biological membrane channel

The conductance of sodium ions through a simplified channel-membrane system immersed in a reservoir of 1M NaCl in SPC/E water is examined by molecular dynamics simulation. An applied external potential of 1.1 V drives the ions and water through a channel of length 25 A producing a current of 19.6 pA, in reasonable agreement with experimental findings. The stream of ions and water molecules flows continuously because of the constant applied field and periodic boundary conditions. We also examine the potential profile across the simulation cell, the average density distributions of the various species in the reservoir and radially in the channel, and the ion velocity in the channel.     

阴极金属微凸起电场增强因子数值模拟

 利用有限元方法对无穷大平板二极管中阴极表面金属微凸起的微观电场增强因子进行了计算研究,给出了微凸起微观电场增强因子随凸起参数的变化规律,拟合得到了微观电场增强因子的简单实用的经验表达式,并与文献中的近似公式进行了比较。模拟的结果表明,对锥状球头微凸起的电场增强因子,文献给出的近似公式误差较大,应避免使用。     

阴极金属微凸起电场增强因子数值模拟

利用有限元方法对无穷大平板二极管中阴极表面金属微凸起的微观电场增强因子进行了计算研究,给出了微凸起微观电场增强因子随凸起参数的变化规律,拟合得到了微观电场增强因子的简单实用的经验表达式,并与文献中的近似公式进行了比较。模拟的结果表明,对锥状球头微凸起的电场增强因子,文献给出的近似公式误差较大,应避免使用。     

Neutron emission during a nanosecond discharge in deuterium in a nonuniform electric field

Neutron emission during a nanosecond deuterium discharge formed at the nonuniform electric field is investigated. A stable neutron yield is observed when the cathode is made of metallic plates covered by a layer of deuterated zirconium and the anode is made of stainless steel in the form of a tube. It is shown that, when the deuterium pressure equals several Torr, neutrons are emitted from both deuterated and deuterium-free cathodes. The influence of the anode design on the neutron yield is studied.     

Structure of the glow of a nanosecond diffuse discharge in a strongly nonuniform electric field

The structure of the glow of a diffuse discharge in air under atmospheric pressure is studied in detail in the “rod (cathode)-plane” geometry for an electrode gap of 10 cm and a cathode tip radius from 3 cm to 2.4 μm. The amplitude of voltage across the gap was ～ 220 kV for voltage growth rate of ～10¹³ V/s and a pulse duration of 180 ns. It is found that the shape of the discharge glow strongly depends on the radius of the cathode tip. For large values of the radius, the multichannel form of the glow prevails, which is statistically transformed into a volume glow as the radius decreases from 5 mm to 60 μm. This transition is accompanied by a decrease in the amplitude of the discharge current from 440 to 140 A on the average. For ultrasmall radii of the cathode (2.4–7.7 μm), the multichannel form of the glow prevails again and the amplitude of the discharge current increases up to ～300 A.     

Numerical simulation of the magnetoresistance effect controlled by electric field in p–n junction

The magnetoresistance effect of a p–n junction under an electric field which is introduced by the gate voltage at room temperature is investigated by simulation. As auxiliary models, the Lombardi CVT model and carrier generationrecombination model are introduced into a drift-diffusion transport model and carrier continuity equations. All the equations are discretized by the finite-difference method and the box integration method and then solved by Newton iteration.Taking advantage of those models and methods, an abrupt junction with uniform doping is studied systematically, and the magnetoresistance as a function of doping concentration, SiO_2 thickness and geometrical size is also investigated. The simulation results show that the magnetoresistance(MR) can be controlled substantially by the gate and is dependent on the polarity of the magnetic field.