Numerical analysis for the free-boundary current reversal equilibrium in the AC plasma current operation in a tokamak

In recent decades, tokamak discharges with zero total toroidal current have been reported in tokamak experiments, and this is one of the key problems in alternating current(AC) operations.An efficient free-boundary equilibrium code is developed to investigate such advanced tokamak discharges with current reversal equilibrium configuration. The calculation results show that the reversal current equilibrium can maintain finite pressure and also has considerable effects on the position of the X-point and the magnetic separatrix shape, and hence also on the position of the strike point on the divertor plates, which is extremely useful for magnetic design, MHD stability analysis, and experimental data analysis etc. for the AC plasma current operation on tokamaks.

单级三相谐波电流注入可升降压AC/DC变换器

为适应电动车充电电压宽范围变化需求,本文针对传统充电桩前级整流器拓扑开展研究,提出一种新式单级三相AC/DC变换器。该变换器集成了三相桥式不控整流电路与Cuk模块,为降低输入侧电流谐波分量,选用双向开关管构建谐波电流回馈通路,整体构造成单级式拓扑结构。文章阐述了变换器的电路结构及工作模态,通过建立变换器的等效模型推导出电压增益。变换器通过简单的控制逻辑即可实现正弦输入电流并拥有高功率因数。最后通过搭建变换器数字控制实验平台验证了所提变换器的可行性。

基于ACFM的焊缝缺陷检测系统设计和试验

针对CNFC-3GS新燃料运输容器载荷试验前后吊耳角焊缝的非接触式(带涂层)表面检测需求,研发了一套交流电磁场(ACFM)检测系统和工艺,设计了高灵敏度的单阵列笔式探头,并编写了梯度算法软件,以提高对微小缺陷的检测能力。通过灵敏度试块、考试试块、模拟试块试验,验证了ACFM技术在表面和近表面缺陷检测方面的有效性,通过对不同试块的检测,结果表明该ACFM系统能够有效检出表面和近表面L≥1 mm的线形缺陷和D≥1 mm的圆形缺陷,打磨可以提高其检出能力。该ACFM检测系统稳定可靠,能够实现容器吊耳焊缝表面缺陷的快速有效检出,并初步判断缺陷的位置和大小,可以为铁磁性材料及焊缝的服役安全评价提供技术支撑。

Flow separation control over an airfoil using continuous alternating current plasma actuator

The flow separation control over an NACA 0015 airfoil using continuous alternating current(AC)dielectric barrier discharge(DBD)plasma actuator is investigated experimentally and numerically.This work is intended to report some observations made from our experiment,to which little attention is paid in the previous studies,but which is thought to be important to the understanding of control of complex flow separation with AC DBD.To this end,the response of separated flow to AC plasma actuation is visualized through the time-resolved particle image velocimetry(PIV)measurement,whereas numerical simulation is carried out to complement the experiment.The flow control process at chord-based Reynolds number(Re)of 3.31×105 is investigated.It is found that the response of external flow to plasma forcing is delayed for up to tens of milliseconds and the delay time increases with angle of attack increasing.Also observed is that at the intermediate angle of attack near stall,the forced flow features a well re-organized flow pattern.However,for airfoil at high post-stall angle of attack,the already well suppressed flow field can recover to the massively separated flow state and then reattach to airfoil surface with the flow pattern fluctuating between the two states in an irregular manner.This is contrary to one’s first thought that the forced flow at any angles of attack will become well organized and regular,and reflects the complexity of flow separation control.

Experimental design to measure the anchoring energy on substrate surface by using the alternating-current bridge

The anchoring property of the substrate surface of liquid crystal cells plays an important role in display and nondisplay fields. This property directly affects the deformation of liquid crystal molecules to change the phase difference through liquid crystal cells. In this paper, a test method based on the alternating-current bridge is proposed to determine the capacitance of liquid crystal cells and thus measure the anchoring energy of the substrate surface. The anchoring energy can be obtained by comparing the capacitance-voltage curves of twisted nematic liquid crystal cells with different anchoring properties in experimental and theoretical results simulated on the basis of Frank elastic theory. Compared with the other methods to determine the anchoring energy, our proposed method requires a simple treatment of liquid crystal cells and allows easy and high-accuracy measurements, thereby expanding the test ideas on the performance parameters of liquid crystal devices.

Electrical Characteristics of an Alternating Current Plasma Igniter in Airflow

The electrical characteristics of an alternating current （AC） plasma igniter were investigated for a working gas of air at atmospheric pressure. The discharge voltage and current were measured in air in both breakdown and stable combustion processes, respectively, and the current-zero phenomena, voltage-current （V-I） characteristics were studied for different working gas flow rates. The results indicated that the working gas between anode and cathode could be ionized to generate gas discharge when the voltage reached 8 kV, and the maximum current was 33.36 A. When the current came to zero, current-zero phenomena appeared with duration of 2 #s. At the current-zero moment, dynamic resistance between electrodes became extremely high, and the maximum value could reach 445 kf~, which was the main factor to restrain the current. With increasing working gas flow rates, the gradient of V-I characteristic curves was increased, as was the dynamic resistance. At a constant driven power, the discharge voltage increased.

Characterization of alternating current impedance properties of biomedical electrodes

To study the alternating current (AC) impedance properties of Ag/AgCl electrocardiograph (ECG) electrodes, the electrode pair was gel-to-gel connected, and then the electrical potential was recorded after a safe stimulating current passes through the electrode pair, so the AC impedance data of ECG electrodes were obtained. Varying the frequency and value of stimulating current, the detailed comparison and analysis of AC impedance properties of the electrodes were performed, and the stability was further characterized by using the continuous measurement within 24 h. The experimental results show that the AC impedance values of electrodes decreased, and then slightly increased with the increase of frequency of stimulating current. The minimum AC impedance value was obtained when the frequency was changed to 10 kHz. When the stimulating current increased, the AC impedance values of electrodes showed a slight decrease, but did not change significantly. Besides, the continuous measurement results show that the impedance value presented a significant increase in the initial 30 min, and then was stabilized in the following measuring process.

Research on the electrical characteristics of an organic thin-film field-effect transistor based on alternating-current resistance

In this article, an organic thin-film field-effect transistor （OTFFET） with top-gate and bottom-contact geometry based on pentacene as the active layer is fabricated. The experimental data of the I-V are obtained from the OTFFET device. The alternating-current （AC） resistance value of the OTFFET device is calculated using the derivation method from the experimental data, and the AC resistance trend curves of the OTFFET device are obtained with the region fitting method. We analyse the characteristics of the OTFFET device with an AC resistance trend curve. To discover whether it has a high resistance, it is proposed to judge the region of the source/drain voltage （VDs） less than the transition voltage, thereby determining whether the contact between the metal electrode and the organic semiconductor layer of the OTFFET device is Ohmic or non-Ohmic. The theoretical analysis shows that the field-effect mobility and the AC resistance are in reverse proportion. Therefore, we point out that reducing AC resistance is necessary if field-effect mobility is to be improved.

基于Hexverter的AC/AC系统交流不对称故障控制策略研究

六边形模块化多电平换流器(hexagonal modular multilevel converter,Hexverter)作为一种新型的AC/AC功率变换器,在未来海上风电场并网及低频输电技术中有着广阔的应用前景。为了解决Hexverter在电力系统不对称故障工况的稳定运行,文章首先对Hexverter的拓扑结构和工作原理简要介绍,并对其支路电流、支路功率进行分析。然后,研究其AC/AC系统交流侧不对称故障工况下的控制策略,基于理论推导部分得出的Hexverter六个支路间功率分布的规律(即不相邻的三个支路功率分别相等的特征),设计了子模块电容电压均衡控制方法,共包含两部分控制,分别为六个支路间子模块电容电压均衡控制和每个支路内部n个子模块电容电压之间的均衡控制。考虑到支路电流含有两侧交流系统不同频率成分,基于比例谐振控制器,提出了一种对支路电流直接进行控制的方法。最后,通过算例中稳态工况与故障工况研究分别对其工作原理和文中所提出的控制策略有效性进行验证。结果表明,在二次侧交流系统发生BC相短路故障期间,整个系统保持稳定运行,各个子模块电压始终保持均衡,仿真结果验证了文中所提控制策略的有效性。

广州地铁18号线和22号线AC 25 kV同相牵引供电方案研究

广州地铁18和22号线属于市域铁路,速度高、运量大,牵引供电系统采用AC 25 kV供电制式。针对AC 25 kV牵引供电系统存在的电分相问题,在牵引变电所采用单相组合式同相供电方案,取消牵引变电所出口电分相;牵引变电所供电臂间采用电子开关过分相,消除所间无电区。该供电系统解决了电能质量问题,实现全线不断电同相供电,列车无感知断电运行,安全高效地实现了运量提升、再生制动能量利用提高等目标,是AC 25 kV智能同相牵引供电技术在城市轨道交通中的成功应用。

进一步改善ACS抗血小板治疗效果:CURRENT OASIS 7浅析

急性冠脉综合征(acute coronary syndromes,ACS)的病生理机制决定了抗血小板治疗是ACS药物治疗的基石,对于接受经皮冠状动脉介入治疗(percutaneous transluminal coronary intervention,PCD的患者尤其如此。

Effects of alternating current interference on corrosion of X60 pipeline steel

With rapid economic development in China, demand for energy and transportation is growing. Due to the limitations of factors such as terrain and traffic, a large number of buried oil and gas pipelines are parallel to high- voltage transmission lines and electrified railways over long distances. Alternating pipelines is very serious in laboratory experiments were current （AC） corrosion of such cases. In this work, carried out with an electrochemical method in a simulated soil solution at various AC current densities from 0 to 200 A]m2 and AC frequencies from 10 to 200 Hz. Experimental results indicated that with an increase in the AC current density, the corrosion po- tential of an X60 steel electrode shifted negatively, the anodic current density increased significantly, and the corrosion rate increased. Moreover, with an increase in the AC frequency, the corrosion potential of the X60 electrode shifted positively and the anodic current density decreased, which led to a decrease in the corrosion rate. Furthermore, the morphology of X60 electrodes indicated that uniform corrosion occurred at a low AC current density; while corrosion pits were found on the X60 electrode surface at a high AC current density, and deep corrosion pits seriously damaged the pipelines and might lead to leakage.

Reversibility of visual field defects through induction of brain plasticity: vision restoration, recovery and rehabilitation using alternating current stimulation

For decades visual field defects were considered irreversible because it was thought that in the visual system the regeneration potential of the neuronal tissues is low.Nevertheless,there is always some potential for partial recovery of the visual field defect that can be achieved through induction of neuroplasticity.Neuroplasticity refers to the ability of the brain to change its own functional architecture by modulating synaptic efficacy.It is maintained throughout life and just as neurological rehabilitation can improve motor coordination,visual field defects in glaucoma,diabetic retinopathy or optic neuropathy can be improved by inducing neuroplasticity.In ophthalmology many new treatment paradigms have been tested that can induce neuroplastic changes,including non-invasive alternating current stimulation.Treatment with alternating current stimulation(e.g.,30 minutes,daily for 10 days using transorbital electrodes and^10 Hz)activates the entire retina and parts of the brain.Electroencephalography and functional magnetic resonance imaging studies revealed local activation of the visual cortex,global reorganization of functional brain networks,and enhanced blood flow,which together activate neurons and their networks.The future of low vision is optimistic because vision loss is indeed,partially reversible.

隔离型AC-DC矩阵变换器最小电流应力控制方法

针对隔离型AC-DC矩阵变换器降低功率器件成本、提高效率和抑制电磁干扰等需求,提出了一种基于零矢量嵌入的移相策略的最小电流应力控制方法。基于移相策略深入研究了影响变换器电流应力的关键因素。建立了三维(3D)功率模型,从中求取等功率分布线,通过引入功率约束条件以及移相角范围,对电流应力在限定条件下采用序列二次寻优方法进行最小化寻优,得到使电流应力最小的最优移相比。仿真和实验结果表明,基于零矢量调制的移相调制策略可以实现前后级电路的协调控制,功率因数在0.96左右,直流侧输出电压和电流稳定且纹波小。因此,采用所提控制方法,在保证网侧和直流侧的基本性能的同时,实现了对变换器电流应力的最小化。

Alternating Pulse Current in Eiectrocoagulation for Wastewater Treatment to Prevent the Passivation of Al Electrode

A novel current feed style, alternating pulse current, was proposed in electrocoagulation aiming at preventing the passivation of electrode materials. The open circuit potential （OCP） measurements after anodic and cathodic potentiodynamic polarization showed that cathodic polarization could activate Al electrode. The surface of Al electrode after alternating pulse current electrocoagulation was investigated by scanning electron microscope （SEM） and X-ray photoelectron spectroscopy （XPS）, and the results indicate that passivation of Al is not observed. Furthermore, the simulated wastewater treatment tests show that alternating pulse current electrocoagulation has a visible energy saving effect and is worthy of generalization.

Monitoring the spontaneous wetting process of hydrophobic microporous membrane assisted by alternating current impedance spectroscopy

In the process of membrane absorption,spontaneous wetting of hydrophobic microporous membrane causes membrane modification and increases membrane phase mass transfer resistance,which have attracted wide interest.However,due to the limitations of previous testing methods,the study of the spontaneous membrane wetting process is limited.Herein,we present a method for monitoring spontaneous membrane wetting by measuring its alternating current(AC)impedance.The impedance tests of the PVDF flat membranes and hollow fiber membranes were conducted in a two-electrode system.The results of equivalent circuit fitting indicate that the impedance value of the unwetted membrane is about 1.02×10^(10)Ω,which is close to the theoretical value of 1.4×10^(10)Ω,and this method can quantify the electrochemical impedance value of membranes with different degrees of spontaneous wetting.In addition,a method of impedance test for real-time monitoring of spontaneous wetting was designed.During the experiment,the timeliness and continuity of this method are confirmed with exact judgment under different conditions.In future work,the impedance data will be used to build model to predict the percentage of membrane wetting degree.

Determination of aniline in environmental water samples by alternating-current oscillopolarographic titration

A new method for the determination of aniline in environmental water based on oscillopolarographic titration was presented in this paper. Several factors including the kind, concentration, and volume of acid, the dosage of potassium bromide, the temperature and concentration of concomitant substances were investigated in detail. The experimental results indicated that this method was simple, rapid, and sensitive. The linear range was 8.367 × 10(?4) to 2.789 × 10(?2) mol L(?1), the relative standard deviation (R.S.D.) was lower than 0.96%, and the spiked recoveries of aniline in environmental water samples were in the range of 99.4–106.9% under the optimal conditions. The results indicated that the present method could be used as an alternative method for aniline determination in realworld water samples.

Effects of alternating current imposition and alkaline earth elements on modification of primary Mg_2Si crystals in hypereutectic Mg-Si alloy

The effects of alternating current imposition and/or alkaline earth elements on modification of the primary Mg2Si crystals in the hypereutectic Mg-Si alloy were investigated.An alternating current of 60 A with frequency of 1 kHz was applied into the hypereutectic Mg-Si melt which was alloyed with alkaline earth elements or not in the fixed temperature range from 700 to 630℃. The results show that the primary Mg2Si crystals could be refined by imposing alternating current or adding alkaline elements. Compared with the samples treated by adding 0.4%Ca or 0.4%Sr,higher modification efficiency could be obtained for the samples treated by imposing alternating current.No further modification efficiency could be obtained for the samples treated by imposing alternating current combined with 0.4%Ca or 0.4%Sr addition.

Continuous electromagnetic separation of inclusion from aluminum melt using alternating current

A novel scheme about the continuous electromagnetic purification of aluminum melt was put forward based on the utilization of a square separation pipe and a 50 Hz alternating current to produce electromagnetic force. It is experimentally found that with electrical current of 400 A/cm2, it takes only 10 s to remove 95% inclusion from aluminum melt. Comprehensive numerical simulations were carried out to investigate the dynamics mechanisms behind the process. The results show that the removal of inclusion is attributed to the cooperative effects of electromagnetic buoyancy and the secondary flow induced by the rotational electromagnetic force, and the removal efficient increases with the size of inclusion and the electrical current imposed. Theoretical predictions on the distribution and removal efficiency of inclusion were supported by the experiments.

前额叶Gamma频段t ACS对工作记忆影响的研究

基于行为学与脑电(electroencephalogram,EEG)特征评估40 Hz经颅交流电刺激(transcranial alternating current stimulation,tACS)对工作记忆的影响,进一步探究40 Hz经颅交流电刺激对脑电与认知功能的调节作用。选取34名被试,并在伪刺激或真刺激后参与工作记忆任务,同时采集被试的行为学数据与脑电数据,最终通过MATLAB与SPSS-26.0进行数据分析,得出40 Hz经颅交流电刺激对脑电、行为学数据指标的影响。通过数据分析发现,事件相关电位中P3a成分与P3b成分的幅值在不同刺激、不同任务量下表现出显著性,且被试在真刺激后顶叶区的theta-gamma相位幅值耦合显著提升。因此可以得出40 Hz经颅交流电刺激使得事件相关电位(event-related potential,ERP)相关成分幅值有显著变化,且能显著提升被试脑内的相位幅值耦合程度,从而提升了专注度,进而显著提升工作记忆的能力,使得相关行为学数据显著提高。