Surface hardening of metals by ultrasonically accelerated small metal balls

The influence of the technological parameters on the surface hardening of metals by ultrasonically accelerated small balls was evaluated. It was demonstrated that the impact force grows with the increase of the amplitude and frequency of ultrasonic vibrations, density of material and size of balls and decreases with the increase of the distance between irradiator and sample. The experimental results showed that the ultrasonic impact treatment of steel might be used in industrial scale. The general advantages of the ultrasonic treatment are very short treatment time and the ability to treat all shapes with a simple apparatus.     

Poisson-Fokker-Planck model for biomolecules translocation through nanopore driven by electroosmotic flow

A non-continuous electroosmotic flow model (PFP model) is built based on Poisson equation, Fokker-Planck equation and Navier-Stokse equation, and used to predict the DNA molecule translocation through nanopore. PFP model discards the continuum assumption of ion translocation and considers ions as discrete particles. In addition, this model includes the contributions of Coulomb electrostatic potential between ions, Brownian motion of ions and viscous friction to ion transportation. No ionic diffusion coefficient and other phenomenological parameters are needed in the PFP model. It is worth noting that the PFP model can describe non-equilibrium electroosmotic transportation of ions in a channel of a size comparable with the mean free path of ion. A modified clustering method is proposed for the numerical solution of PFP model, and ion current translocation through nanopore with a radius of 1 nm is simulated using the modified clustering method. The external electric field, wall charge density of nanopore, surface charge density of DNA, as well as ion average number density, influence the electroosmotic velocity profile of electrolyte solution, the velocity of DNA translocation through nanopore and ion current blockade. Results show that the ion average number density of electrolyte and surface charge density of nanopore have a significant effect on the translocation velocity of DNA and the ion current blockade. The translocation velocity of DNA is proportional to the surface charge density of nanopore, and is inversely proportional to ion average number density of electrolyte solution. Thus, the translocation velocity of DNAs can be controlled to improve the accuracy of sequencing by adjusting the external electric field, ion average number density of electrolyte and surface charge density of nanopore. Ion current decreases when the ion average number density is larger than the critical value and increases when the ion average number density is lower than the critical value. Our numerical simulation shows that the translocation velocity of DNA given by the PFP model agrees with the experimental, results better than that given by PNP model or PB model.     

Triboelectric charging and dielectric properties of pharmaceutically relevant mixtures

Binary mixtures of pharmaceutically relevant powders were investigated using dielectric spectroscopy over a frequency range of 10⁻³ to 300 kHz. Two different binary mixtures were studied as a function of concentration; pseudoephedrine hydrochloride in dicalcium phosphate dihydrate and acetaminophen in microcrystalline cellulose, respectively. Dielectric properties obtained from measurements of these systems are reported and found to follow a trend similar to the observed triboelectric behavior after low-shear tumble blending. Powder samples for charge measurement were mixed using a stainless steel blender and dispensed directly into a Faraday pail. For the two binary mixtures studied, low-frequency conductivity calculated from the imaginary part of the complex permittivity (or loss factor) was observed to be sensitive to water content. Furthermore, the unanticipated trends previously reported in the measured specific charge after blending were observed to correspond with the surface charge density calculated from the capacitance of the composite material. The implications of moisture and the physical and chemical properties of these dielectric mixtures are also discussed with supporting results.     

AlGaN/GaN HEMT器件电流坍塌和膝点电压漂移机理的研究

考虑了势垒层、缓冲层体陷阱及表面电荷的浓度变化对电流坍塌和膝点电压的影响,发现表面电荷和势垒层体陷阱浓度的变化对沟道电子的浓度影响较小,表面电荷浓度变化下的膝点电压的偏移和坍塌强度的大小与势垒层势阱能量的变化有着主要的关系.缓冲层有着比势垒层更强的局域作用,势垒层和缓冲层的体陷阱浓度在一定范围变化时的膝点电压偏移主要是由沟道电子浓度的变化而引起的,但偏移量却比表面电荷浓度变化的情况下小很多.势阱能量的变化是造成膝点电压偏移的重要原因,坍塌强度主要取决于势阱能量和沟道的电子浓度. 关键词： AlGaN/GaN高电子迁移率晶体管 电流坍塌 膝点电压 陷阱俘获     

表层氟化聚乙烯中的空间电荷

本文试图简要地汇集近年来与近期我们所取得的关于表面氟化对聚乙烯(PE) 空间电荷行为影响的研究结果, 总结与探讨PE中的空间电荷积累与其氟化层特性和特征间的关联. 这些结果显示在氟化反应气中没有氧存在时一个非常薄的氟化层能产生有效的电荷抑制, 而当氧存在时为达到有效的电荷阻挡、需要一个具有高氟化度的非常厚的氟化层. 在影响空间电荷的诸电学因素中, 氟化层的电荷传导特性比其电荷俘获特性和介电常数或极性对阻止电荷注入材料内部更为重要, 尽管氟化层的高介电常数和被俘获的电荷会降低界面电场、因此减少电荷的电极注入. 氟化层的电荷传导特性密切关联于其自由体积, 反应混合气中存在的氧对减小自由体积、因此对电荷的抑制具有强的负面影响.     

Surface force induced by a point charge in multilayered dielectrics

Local surface force density and total force induced by a point charge embedded in a three-layered dielectric system are calculated. The two ratios between the dielectric constants of the three layers are found to play a primary role: they determine the direction of the surface force density and total force, as well as distribution of the surface force density, which can vary monotonically or non-monotonically with the radial position. The position of the charge, however, only affects the magnitude of the forces. The formulation can be extended to establish a theoretical framework for situations involving a distribution of charges.     

Influence of adsorbed sulfur on surface reaction kinetics and surface self-diffusion on iron

The nitrogenation of iron in N₂ and the carburization of iron in CH₄H₂ mixtures were studied in a flow apparatus by a resistance method in the presence of adsorbed sulfur. From these measurements the adsorption isotherm for sulfur on iron was obtained at 850°C and the change of the surface energy in dependence on the sulfur activity could be calculated. These results and measurements of the growth of grain boundary grooves were used to determine the influence of adsorbed sulfur on the surface self-diffusion of iron, which is enhanced by a factor of 3 to 5 in the presence of a saturated layer of adsorbed sulfur.     

Influence of dispersive long-range interactions on properties of vapour–liquid equilibria and interfaces of binary Lennard-Jones mixtures

The influence of dispersive long-range interactions on properties of vapour–liquid equilibria and interfaces of six binary Lennard-Jones (LJ) mixtures was studied by molecular dynamics (MD) simulations and density gradient theory (DGT). The mixtures were investigated at a constant temperature T, at which the low-boiling component, which is the same in all mixtures, is subcritical. Two different high-boiling components were considered: one is subcritical, the other is supercritical at T. Furthermore, the unlike dispersive interaction was varied such that mixtures with three different types of phase behaviour were obtained: ideal, low-boiling azeotrope, and high-boiling azeotrope. In a first series of simulations, the full LJ potential was used to describe these mixtures. To assess the influence of the long-range interactions, these results were compared with simulations carried out with the LJ truncated and shifted (LJTS) potential applying the corresponding states principle. The dispersive long-range interactions have a significant influence on the surface tension and the interfacial thickness of the studied mixtures, whereas the relative adsorption and the enrichment are hardly affected. Furthermore, the influence of the long-range interactions on Henry's law constants and the phase envelopes of the vapour–liquid equilibrium was investigated. The long-range interactions have practically no influence on the composition dependency of the investigated mixture properties.     

MIE experiments and simultaneous measurement of the transferred charge – A verification of the ignition threshold limits

Using the apparatus for the determination of the MIE a wide series of experiments have been carried out in hydrogen/air, ethene/air, propane/air and acetone/air mixtures. The transferred charge as a criterion to judge the ignition potential is determined to verify the thresholds of transferred charge given in the standards. The stored charge in the capacitance before the discharge is compared to the transferred charge in the spark. The correlation of ignition energy and transferred charge is examined and the thresholds of the transferred charge are discussed. The MIE of the above-mentioned mixtures are reviewed taking into account the measurement uncertainty.     

基于AFM的固液界面表面电荷密度测量方法

固液界面的表面电荷会影响微纳流体系统的流体阻力,因此如何测量固液界面的表面电荷密度以及分析表面电荷的产生机理对于研究表面电荷对流体阻力的影响具有较大的意义。提出了一种基于接触式AFM的固液界面表面电荷密度测量方法。基于该方法测量了浸在去离子水和0.01 mol/L的NaCl溶液中的高硼硅玻璃和二氧化硅样本的表面电荷密度,并研究了溶液pH值对表面电荷的影响。研究结果表明高硼硅玻璃和二氧化硅由于表面硅烷基的电离带负电。溶液pH值和离子浓度的增加都会增加浸在去离子水和0.01 mol/L的NaCl溶液中高硼硅玻璃和二氧化硅的表面电荷密度的绝对值。     

氢氧化铝/环氧树脂复合材料的电荷衰减特性北大核心CSCD

环氧树脂电气绝缘性能优良,但是其在脉冲功率设备中充当绝缘子时,表面容易带电且不易衰减,当表面电荷集聚到一定的程度会造成局部放电甚至发展为沿面闪络。为了提高环氧树脂的沿面闪络性能,用中心粒径为1μm的氢氧化铝(ATH)无机填料来改善环氧树脂复合材料的表面性能。分别制备了ATH填料质量分数为0%(纯环氧),20%,40%,60%,80%和100%的ATH/环氧树脂复合材料试样。用电声脉冲法研究了ATH填料对环氧树脂复合材料电荷衰减性能的影响,对比了试样直流极化场强为10kV/mm和30kV/mm的试验结果。结果表明:ATH/环氧树脂复合材料电荷的衰减常数不仅与填料的质量分数有关,而且与试样的带电量有关。     

Influence of hydrostatic pressure and gas content on continuous ultrasound emulsification.

Ultrasound is one means among others of producing emulsions mechanically. Droplet disruption in sonicated liquid-liquid systems is considered to be controlled by cavitation. Both hydrostatic pressure and gas content of the liquids influence the probability and intensity of cavitation. Continuous ultrasound emulsification experiments were carried out to elucidate the effect of these parameters on the result of droplet disruption. Maximum energy density in the apparatus decreases with increasing hydrostatic pressure, probably due to partial suppression of cavitation which is the main mechanism of power dissipation. At constant energy density there is no significant influence of hydrostatic pressure on the emulsification result, however. Corresponding results were obtained for the influence of the gas content. Gas saturation or partial degassing prior to emulsification lead to a shift in maximum energy density. But, again, at constant energy density no clear effect on the droplet size of the emulsion is observed.     

Modeling of ionization–recombination processes in the atmospheric surface layer

The electrical structure of non-stationary horizontally-homogenous surface layer with multi-charged aerosol particles was mathematically modeled in the approximation of turbulent electrode effect. The profiles of positive and negative small ions and nuclei, electric field, polar air conductivity, current density and space charge density were computed in different time periods and various physical conditions. The mathematical model of non-stationary horizontally homogenous surface layer with aerosol particles was made regarding turbulent mixing and convective transport. The space-time distributions of positive and negative small ions and nuclei, electric field, electrical conductivity, current density and space charge density for various physical conditions (aerosol concentrations, turbulent mixing, convective transport, air ionization rate, electric field strength near surface, aerosol particles size) were received. Experimental data of electrical and meteorological parameters were measured and analyzed. It was received that theoretical results are in a good agreement with experimental data.     

电解质浓度对胶体粒子表面有效电荷的影响

胶体粒子的表面有效电荷是决定胶体性质的重要物理量,但溶液环境(如电解质溶液浓度)是否影响其数值至今尚无统一认识,近年来的一些研究工作给出了存在争议的不同结果和假设.在直接实验测量方面,由于电解质离子和胶体表面吸附离子的置换,粒子表面基团的不完全电离和胶体粒子对离子吸附的共同作用,使得对这类粒子在不同溶液环境下的表面有效电荷的测量和变化机理的认识极为困难.针对该问题,本文测定了羧基和磺酸基修饰的聚苯乙烯胶体颗粒在不同粒子浓度和HCl浓度下的电导率,由于两种粒子与HCl电离产生的阳离子相同(均为H+),可根据电导率-数密度法(迁移法)得到胶体颗粒表面有效电荷数.通过实验结果分析,明确了HCl浓度以及粒子数密度对胶体粒子表面电荷的影响规律以及表面电荷随HCl浓度增大的原因.除此之外,羧基修饰颗粒比磺酸基修饰颗粒的表面电荷随HCl浓度变化更快;对于同一HCl浓度,磺酸基修饰胶体表面电荷不受粒子数密度影响,而羧基修饰胶体颗粒却与之相关.基于粒子表面电荷的理论模型,对这些问题都给出了相应的解释.     

Estimation of Plasma Density by Surface Plasmons for Surface-Wave Plasmas

An estimation method of plasma density based on surface plasmons theory for surface-wave plasmas is proposed. The number of standing-wave is obtained directly from the discharge image, and the propagation constant is calculated with the trim size of the apparatus in this method, then plasma density can be determined with the value of 9.1 × 10^17m^-3. Plasma density is measured using a Langmuir probe, the value is 8.1 × 10^17m^-3 which is very close to the predicted value of surface plasmons theory. Numerical simulation is used to check the number of standing-wave by the finite-difference time-domain （FDTD） method also. All results are compatible both of theoretical analysis and experimental measurement.     

Effective method for measuring the energy of propagating brush discharges

Due to their very high energy propagating brush discharges are the most dangerous electrostatic discharges. As it is known, they usually occur on thick insulating layers on which significant charge can be accumulated. Discharge energy is a function of several parameters, like the surface charge density (influenced by the thickness of the layer and its relative permittivity), the size of the charged surface, etc. This paper represents a laboratory model to examine the energy of propagating brush discharges. Based on these measurements list of results were evaluated to estimate the energy of the generated propagating brush discharges. This energy is especially important to determine how incentive these discharges are. By the help of the model the effect of the polarity of the original charging, the surface charge density of the sample and the geometry of the sample have been examined.     

Electric-potential-measurement-based methodology for estimation of electric charge density at the surface of tribocharged insulating slabs

The auto-compensated electrostatic induction probe (ACEIP) is widely used for measuring the electric potential at the surface of conductive or insulating bodies. The aim of this paper is to elaborate a methodology for using this probe in view of performing the estimation of electric charge density at the surface of tribocharged insulating slabs. In such cases, the electric potential is not uniformly distributed on the surface under investigation. Metallic plates trimmed with different shapes were used to characterize the probe. Thus, a first series of experiments enabled a crude evaluation of the shape and size of the area “seen by the probe”: a 10-mm-diameter circle. Other experiments served to determine the transfer function that relates the value measured by the probe to the potential of a small area of constant electric potential located at a well-defined distance from it. By dividing the surface under investigation into a large number of small elementary areas, it was possible to use this transfer function to express the potential measured by the ACEIP as the sum of the contributions of each such element. An inverse matrix computation method enabled the estimation of the actual surface electric potential. Based on the results of a final set of experiments, the distribution of the electric charge density was estimated for slabs charged by corona-respectively triboelectric-effect.     

Double layers of H2 adsorption on an AlN sheet induced by electric field

In this paper, we propose an original functional method that makes it easy to determine the effect of any deviation in the shape of a nano-object from the well-studied shape (e.g., spherical) on the quantum characteristics of charge localized inside the nano-object. The maximum dimension of the object is determined by the magnitude of influence of quantum-size effects on quantum states of charge, and is limited by 100?nm. This method is ideologically similar to the perturbation theory, but the perturbation of the surface shape, rather than the potential, is used. Unlike the well-known variational methods of theoretical physics, this method is based on the assumption that the physical quantity is a functional of surface shape. Using the method developed, we present the quantum-size state of charges for two different complex shapes of nano-objects. The results from analyzing the quantum-size states of charge in the nano-objects with a deformed spherical shape indicated that the shape perturbations have a larger effect on the probability density of locating a particle inside the nano-object than on the surface energy spectrum and quantum density of the states.     

Charge density determination in icosahedral AlPdMn quasicrystal using quantitative convergent beam electron diffraction

Charge density distribution in icosahedral AlPdMn quasicrystal has been studied on a single-crystal specimen by using quantitative convergent beam electron diffraction (QCBED) technique. The QCBED systematic row method was used in the refinement of structure factors. To refine the low-order structure factors, the wave-mechanical formulation of electron diffraction dynamical theory was used in the calculation of electron diffraction intensities for the quasicrystal in fitting the experimental intensity line scan profiles. The shapes of atomic surfaces (occupation domains) were described with symmetry-adapted series of surface harmonics. An iterative procedure was used in determination of structure factors of the quasicrystal. The structure factors of nine strongest symmetry inequivalent reflections according to X-ray diffraction experiment were refined with QCBED technique. The average of refinement results for a given reflection performed on several CBED patterns, which were slightly different in orientation and sample thickness, and on different line scans, was taken as the value of structure factor for the reflection. The obtained structure factors for electrons were transformed into X-ray structure factors with Mott formula. The bonding charge density map for the quasicrystal was constructed with the obtained nine structure factors. Assuming that the atoms are spheres, the gain or loss of electrons for different atoms were calculated. It shows that identical atoms can have different valences at different kinds of positions. The bonding charge is localized along certain directions.     

Effect of ionic size on the structure of spherical double layers: a Monte Carlo simulation and density functional theory study

The effect of ionic size on the diffuse layer characteristics of a spherical double layer is studied using Monte Carlo simulation and density functional theory within the restricted primitive model. The macroion is modelled as an impenetrable charged hard sphere carrying a uniform surface charge density, surrounded by the small ions represented as charged hard spheres and the solvent is taken as a dielectric continuum. The density functional theory uses a partially perturbative scheme, where the hard sphere contribution to the one particle correlation function is evaluated using weighted density approximation and the ionic interactions are calculated using a second-order functional Taylor expansion with respect to a bulk electrolyte. The Monte Carlo simulations have been performed in the canonical ensemble. The detailed comparison is made in terms of zeta potentials for a wide range of physical conditions including different ionic diameters. The zeta potentials show a maximum or a minimum with respect to the polyion surface charge density for a divalent counterion. The ionic distribution profiles show considerable variations with the concentration of the electrolyte, the valency of the ions constituting the electrolyte, and the ionic size. This model study shows clear manipulations of ionic size and charge correlations in dictating the overall structure of the diffuse layer.