Exposure of biological cells to high-voltage, short-duration electric pulses causes a transient increase in their plasma membrane permeability, allowing transmembrane transport of otherwise impermeant molecules. In recent years, large steps were made in the understanding of underlying events. Formation of aqueous pores in the lipid bilayer is now a widely recognized mechanism, but evidence is growing that changes to individual membrane lipids and proteins also contribute, substantiating the need for terminological distinction between electroporation and electropermeabilization. We first revisit experimental evidence for electrically induced membrane permeability, its correlation with transmembrane voltage, and continuum models of electropermeabilization that disregard the molecular-level structure and events. We then present insights from molecular-level modeling, particularly atomistic simulations that enhance understanding of pore formation, and evidence of chemical modifications of membrane lipids and functional modulation of membrane proteins affecting membrane permeability. Finally, we discuss the remaining challenges to our full understanding of electroporation and electropermeabilization.

Membrane Electroporation and Electropermeabilization: Mechanisms and Models

Background
Therapeutic irreversible electroporation (IRE) is an emerging technology for the non-thermal ablation of tumors. The technique involves delivering a series of unipolar electric pulses to permanently destabilize the plasma membrane of cancer cells through an increase in transmembrane potential, which leads to the development of a tissue lesion. Clinically, IRE requires the administration of paralytic agents to prevent muscle contractions during treatment that are associated with the delivery of electric pulses. This study shows that by applying high-frequency, bipolar bursts, muscle contractions can be eliminated during IRE without compromising the non-thermal mechanism of cell death.

https://link.springer.com/content/pdf/10.1186%2F1475-925X-10-102.pdf

High-frequency irreversible electroporation (H-FIRE) for non-thermal ablation without muscle contraction

Ferrofluids are suspensions of magnetic nanoparticles that have the attractive feature of being controlled by applied magnetic fields. Ferrofluids have been studied for decades in an ever growing number of applications that take advantage of their response to applied magnetic fields. Here, we provide a summary of recent advances in established and emerging applications of ferrofluids, including applications in optics, sensors, actuators, seals, lubrication, and static/dynamic magnetically driven assembly of structures.

Recent progress in ferrofluids research: novel applications of magnetically controllable and tunable fluids

Plasma catalysis holds great promise for environmental applications, provided that the process viability can be maximized in terms of energy efficiency and product selectivity. This requires a fundamental understanding of the various processes taking place and especially the mutual interactions between plasma and catalyst. In this review, we therefore first examine the various effects of the plasma on the catalyst and of the catalyst on the plasma that have been described in the literature. Most of these studies are purely experimental. The urgently needed fundamental understanding of the mechanisms underpinning plasma catalysis, however, may also be obtained through modelling and simulation. Therefore, we also provide here an overview of the modelling efforts that have been developed already, on both the atomistic and the macroscale, and we identify the data that can be obtained with these models to illustrate how modelling and simulation may contribute to this field. Last but not least, we also identify future modelling opportunities to obtain a more complete understanding of the various underlying plasma catalytic effects, which is needed to provide a comprehensive picture of plasma catalysis.

Understanding plasma catalysis through modelling and simulation—a review

Plasma N2-fixation : 1900-2014

Artificial pollution tests have been carried out to study AC flashover performances of various types of porcelain, glass, and polymeric insulators in this paper. The experimental results show that the polluted flashover voltage Uf is affected by equivalent salt deposit density rhoESDD and nonsoluble deposit density rhoNSDD, the influences of which are independent of each other. Based on the analyses of the flashover voltages, the correction formulas of the flashover voltages Uf of various insulators at various rhoESDD and rhoNSDD levels are pointed out. The experimental results also show that there is a distinct difference among the flashover voltages of various types of polluted insulators. At the same pollution degree, the antipollution performance of the fog-type glass insulator is better than those of the outer-rib porcelain insulators. In terms of the effectiveness of creepage distance of insulators, the antipollution performance of polymeric insulators is superior to those of porcelain and glass insulators.

Study on AC Artificial-Contaminated Flashover Performance of Various Types of Insulators

In order to improve the reliability of power transmission lines, one of the key issues is to reduce the hazard of contamination flashovers. Presently, the most efficient way is to clean (or replace) the heavily polluted insulators. The leakage current is the critical online quantity that can be detected. A number of laboratory experiments on 35 kV voltage class ceramic and glass insulators show that the leakage current fully reflects the entire process of contamination flashover development. The test results reveal that the process can be classified into three stages, i.e., security stage, forecast stage and danger stage. The results, that were duplicated several times, are based on three characteristics of the leakage current, i.e., the root-mean-square value, waveforms, and power spectrum estimation. In addition, the boundaries of the three stages in both time domain and power spectrum domain are also determined. All these can be used for the stage pre-warning of contamination flashovers. The security stage is most important since it precedes the contamination flashover sufficiently. The three characteristics of the leakage current in the security stage are proposed as the inputs of a neural network model together with the operating voltage, and the relative humidity in order to determine the equivalent salt deposit density (ESDD) of the insulators. The comparison of the simulated and actual (measured) results demonstrates that the ESDD prediction model has a very low relative error if the training data and the testing data both come from the security stage. The application of this research results in (1) optimal ESDD prediction inputs and (2) sufficient pre-warning time before the ultimate contamination flashover.

Use of leakage currents of insulators to determine the stage characteristics of the flashover process and contamination level prediction

Aging of two kinds of transformer insulation paper in natural ester is compared to that in conventional transformer oil (mineral oil). Sealed aging vessels containing copper, insulation paper (Kraft paper and thermally upgraded paper), and dielectric fluid (mineral oil and natural ester) were aged at 90, 110, and 130°C for 399, 371, and 329 days. Under the same aging condition, both the degree of polymerization (DP) and the leveling-off degree of polymerization (LODP) for natural ester aged paper were higher than the ones for mineral oil aged paper, and the micro surface of natural ester aged paper was destroyed less seriously than that of the mineral oil aged paper. The aging time to reach LODP for natural ester aged paper was only 1/4 to 2/3 of that for mineral oil aged paper. When water content in natural ester for natural ester aged Kraft paper samples reached the maximum, acids concentration in natural ester increased abruptly. Water content in natural ester decreased in the whole aging process for natural ester aged thermally upgraded paper samples. Six physical and chemical mechanisms for the slower aging rate of natural ester aged paper are proposed. Evidence for transesterification between natural ester and paper was presented with infrared spectra instrument. Although the acids in natural ester were far more than in mineral oil, the natural ester can significantly slow the thermal aging of the paper. Three mechanisms of this abnormal phenomenon were presented. Copyright © 2009 John Wiley & Sons, Ltd.

A comparative study of thermal aging of transformer insulation paper impregnated in natural ester and in mineral oil

A method is introduced for testing insulators under icing conditions. The method is based on and developed from those described in the standard of IEC60-1, IEC 60507 and IEEE Task Force on Insulator Icing Test Methods, which give instructions to test insulators under pollution. Then, the paper explores the effects of various factors, including ice thickness, pollution severity on the surface of insulators before ice accretion, atmospheric pressure, and shed profiles, on the flashover performance of short samples of two different types of silicone rubber (SIR) composite long rod insulators intended for ultra high voltage (UHV) ac transmission lines. The experiments were carried out in the multi-function artificial climate chamber in the High Voltage and Insulation Technological Laboratory of Chongqing University, China. The experimental results reveal the regularity of the effects of ice thickness, pollution severity and atmospheric pressure on the average flashover voltage of two types of composite insulators. Those can provide reference for the outdoor insulation design for UHV ac transmission lines.

Flashover Performance of Pre-contaminated and Ice-covered Composite Insulators to be Used in 1000 kV UHV AC Transmission Lines

In order to assess how severe the contamination level of the surface of power line insulators and to prevent unpredictable contamination flashovers, it is important to seek optimal prediction characteristics. That leads to the increase of the warning time and to the improvement of the reliability of the pre-warning system. Nearly 30 insulator strings at five pollution levels were tested in an artificial fog chamber, where their leakage currents were continuously recorded at the same operation conditions. The three characteristics of the leakage current, namely the mean value, maximum value, and the standard deviation of the root-mean-square (RMS) value of the leakage current, have been extracted. They describe jointly the current contamination levels of an insulator surface. In addition, regression equations between the three characteristics and various contamination levels have been established. The same three characteristics have been selected and used as the inputs of a neural network model together with two more parameters, the relative humidity and operating voltage. Also, the influence of each characteristic on the contamination prediction results has been investigated. The model is appropriate to predict the equivalent salt deposit densities (ESDD) with a difference of less than 0.035 mg/cm2 if the training data and the testing data are selected at the security stage. This research results in the optimal prediction input parameters and sufficient pre-warning time before a contamination flashover.

Caixin Sun

Papers

Study on AC Artificial-Contaminated Flashover Performance of Various Types of Insulators

Use of leakage currents of insulators to determine the stage characteristics of the flashover process and contamination level prediction

A comparative study of thermal aging of transformer insulation paper impregnated in natural ester and in mineral oil

Flashover Performance of Pre-contaminated and Ice-covered Composite Insulators to be Used in 1000 kV UHV AC Transmission Lines

Contamination Level Prediction of Insulators Based on the Characteristics of Leakage Current