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Initial arc formation in high-current drawn vacuum arc was investigated experimentally and analyzed quantitatively in this paper. Experiments were conducted in a demountable vacuum chamber. Characteristics of molten metal bridges evolution and arc voltage indicated that initial arc formation could be divided into three stages. The correlation between the rupture of molten metal bridges and the fluctuation of arc voltage in stage 2 was analyzed. In addition, characteristics in stage 2 under different arc currents and opening speeds were analyzed quantitatively. [ABSTRACT FROM AUTHOR]

Bottom-up nanofabrication, organizing colloidal nanoparticles into ordered clusters with structural and functional complexity, provides an alternative to yield nanometric smart structures unachievable in traditional top-down approaches. Those remarkable structures assembled of colloidal nanoparticles possessing optical properties feature exotic optical responses under the illumination of incident light, showing highly dependent on the particle separation, composition, and arrangement. Here, the nanoscale electromagnetic coupling in magnetic–plasmonic nanoparticle clusters is analyzed by using a 3D full-wave computational model, and the mechanism of the resonances in a split-ring resonator out of magnetic–plasmonic nanoparticle building blocks is also illustrated. In particular, once assembling those artificial molecules (split-ring resonator) into secondary metamaterial superstructures, such as split-ring resonator dimer and Y-shaped structures, a series of exotic optical responses are presented due to the greatly enhanced near-field coupling of nanoparticles and the generation of antiparallel ring currents in the asymmetrical superstructure, exhibiting flexible sensitivity to the changes of the surrounding environment. Besides, the H-shaped arrangement exhibits high sensitivity with Q = 50.5 at λ = 2.02 μ m. Our finding provides a platform for yielding complex structures with flexible tunability of the optical response through arranging those assembled artificial molecules into complex secondary structures, allowing for the development of smart sensing devices. [ABSTRACT FROM AUTHOR]

Due to vacuum interrupter's excellent interruption performance, an increasing number of on-load tap-changers (OLTCs) have chosen it as a load changeover switch in recent years. The stability of the arcing process is crucial for the interruption since the vacuum interrupter in OLTC must break current frequently with the requirement of long electrical life. In this paper, experiments on butt contacts and axial magnetic field (AMF) contacts applied in OLTC were carried out in a demountable vacuum chamber, and the arcing process was investigated by a high-speed camera. Investigations were conducted on the effects of opening speed, opening phase, current amplitude, and AMF on arc characteristics, e.g., arc expansion and arc voltage. The experiment findings demonstrated that expansion and instability of arc increased with higher opening speed, number of cathode spots moving to the inclined surface decreased with shorter arcing time, and that cathode spots' propensity to form group cathode spots increased with higher current. AMF lessened the impact of high opening speed and high current on the arcing process. The investigation carried out in this paper helps to better understand the characteristics of arc evolution and the influence of some key factors, which may serve as a guide for improving the design and vacuum arc control of vacuum OLTCs. [ABSTRACT FROM AUTHOR]

Numerical investigation was carried out on the evolution of inhomogeneous energy deposition of polarity effects in negative polarity electrical explosion of aluminum wire in vacuum. First, radial electric field distribution of the aluminum wire was simulated. The results showed that the initial electric field near electrodes was much smaller than that in the middle of the wire. A model of electrical wire explosion based on ZEUS-EW with artificial limitation on breakdown time of the aluminum wire was used to simulate the behavior of inhomogeneous energy deposition of the polarity effect. The complete evolution process of electrical explosion of the aluminum wire with inhomogeneous energy deposition was further explored and qualitatively divided into three stages according to the simulation results. Finally, the influence of some factors on the inhomogeneous energy deposition simulation was investigated. This study provides some help for a better understanding of the polarity effect in the process of wire explosion. [ABSTRACT FROM AUTHOR]

In this paper, the evolution of vacuum arc under different conditions in the quench protection switch (QPS) based on forced current zero was investigated experimentally and analyzed quantitatively. Experiments were conducted with cup-shaped axial magnetic field (AMF) contacts in a demountable vacuum chamber. Images of the arc column were photographed through the observation window with a high-speed digital camera with exposure time of 2 μs. Arc appearance was analyzed quantitatively through digital image processing. Quantified arc appearance and arc voltage characteristics indicated that the high-current vacuum arc evolution in the QPS could be divided into four stages: arc formation stage, arc column merging stage, diffusing stage, and fast extinguishing stage. The influence of AMF on the evolution of high-current vacuum arc in the diffusing stage was also studied. Experiment results indicated that the vacuum arc at relatively low current had a simpler evolution process and the arc column merging had less correlation with voltage stability. It was found that the vacuum arc with a long gap distance developed faster and the time required to enter the stable burning state was shorter. In addition, the vacuum arc with long arcing time tended to constrict again, which is not beneficial to current interruption. [ABSTRACT FROM AUTHOR]

Patterning a wide range of colloidal plasmonic nanoparticles into prescribed spatial arrangements, analogous to the formation of natural materials, enables the fabrication of functionalized structures with novel optical properties, such as Fano resonance, magneto-optical Kerr effect, negative refraction, etc. Currently, capillarity-assisted particle assembly is always utilized to place colloidal particles at predetermined positions by exploiting the capillary forces resulting from the motion of an evaporating droplet. However, this technique requires specialized equipment and the assembly process is always carried out in an open system, thereby introducing the risk of contamination and limiting its applications. Here, we present a microfluidic and magnetic field-assisted self-assembly of colloidal magnetic-plasmonic nanoparticles by utilizing magnetic dipole–dipole interactions resulting from the localized magnetic gradient field produced by an array of soft-magnetic elements and external magnetic bias field. The magnetized magnetic-plasmonic nanoparticles are controlled to deposit at the predesigned traps microfabricated onto the soft-magnetic elements. After deposition, the inlet velocity of the microchannel is improved to clear away the particles out of the traps, forming arrays of patterns with consistent structures. Furthermore, a Lagrangian–Eulerian model is introduced for the first time to predict the processing of the microfluidic and magnetic field-assisted self-assembly of colloidal magnetic-plasmonic nanoparticles by taking the magnetic and hydrodynamic forces and particle–fluid interaction into account. Our analysis demonstrates that the particle–fluid interaction not only plays a significant role in determining the final self-assembled nanostructures, but provides an opportunity to improve the consistency of the assembled nanostructures. The microfluidic and magnetic field-assisted self-assembly protocol proposed here enables the patterning of colloidal magnetic-plasmonic nanoparticles to be carried out in a controlled environment and also opens up a new direction for assembling complex structures. [ABSTRACT FROM AUTHOR]

The splitting and threshold currents of vacuum arc cathode spots in axial magnetic fields (AMFs) up to 220 mT are investigated experimentally. Measurements are made on electrodes of Cu and CuCr25 with electrode separations of 2 and 6 mm. The electrode diameter is 30 mm. All the experiments are conducted in a demountable vacuum chamber evacuated continuously by a turbo-molecular pump to a pressure of the order of 10−3 Pa. The spots are photographed using a high-speed digital camera with an exposure time of 2 μs. The AMF is applied by means of two permanent magnets placed symmetrically inside the chamber. The experimental results indicate that the splitting and threshold current decrease in the presence of AMF and tend to certain constant values when the field gets stronger. The splitting and threshold currents are considerably larger than Cu electrodes than those with CuCr25 electrodes. With increasing electrode separation, the splitting current decreases while the threshold current increases. Possible explanations are proposed to account for the experimental observations. [ABSTRACT FROM AUTHOR]

The dielectric recovery process has decisive effects on the current interruption process in vacuum circuit breakers, which has attracted the special attention of researchers. In commercial vacuum interrupters, ions and electrons of the residual plasma between the contact gap are separated and then fly to the electrodes under the effect of the transient recovery voltage after current zero. During this period, the post-arc current forms. During the formation of the post-arc current, ions also enter the post-arc anode due to their thermal motion. Therefore, the number of net electrons, which form the post-arc current, is only part of the total electrons between the contact gap at current zero. During the post-arc sheath expansion process, almost all electrons in the contact gap will enter the post-arc anode under the effects of the transient recovery voltage. If the proportion of ions and electrons, which enter the post-arc anode, can be obtained, the total number of electrons and consequently the residual plasma density between the contact gap could be estimated from the integration of the post-arc current. In this paper, the influences on the absorption of charged particles by the post-arc anode of some factors, e.g., rising rate of transient recovery voltage and metal vapor, have been simulated and discussed with a one-dimensional particle in cell-Monte Carlo collision model. [ABSTRACT FROM AUTHOR]

Focusing and separation of particles and cells by magnetophoresis are important steps in many applications. In simple terms, the magnetophoresis can be classified into a positive one and a negative one. The most important characteristic of negative magnetophoresis is that particles and cells can be manipulated in a label-free manner. In this paper, continuous separation based on negative magnetophoresis is studied numerically using a three-dimensional model considering the interaction between particles and the ferrofluid. Firstly, the separation of two sized particles is investigated with a straight microchannel with two opposite permanent magnets for focusing particles before their separation by another bias magnet. Then the influence of size and position of permanent magnets and geometry of microchannel are investigated to achieve a better particle separation. Moreover, the effects of the concentration of the ferrofluid, the size difference of the particles, the magnet-channel distance and the flow velocity on the particle separation are analyzed. [ABSTRACT FROM AUTHOR]

The dielectric recovery process is a crucial stage of current interruption in a vacuum circuit breaker (VCB). The postarc current is an important macroscopic electric characteristic of the dielectric recovery process, which has caused many concerns in the past few decades. In this paper, the postarc currents of VCBs with different types of contacts, such as butt contacts, axial magnetic field contacts, and transverse magnetic field contacts with different materials are measured with a high-resolution current-zero diagnostic system. Besides, the appearance of vacuum arcs is recorded using a high-speed camera in the experiments. The relationship between the arc memory effect and the postarc current is analyzed. What is more, the influence of the instability of the vacuum arc shape on the dispersion of postarc current is also studied. [ABSTRACT FROM AUTHOR]

A quench protection switch (QPS) is indispensable to protect the magnet coils from the damage of quench in a superconducting Tokamak. In this paper, a QPS based on artificial current zero is involved. The vacuum circuit breaker (VCB), which is driven by a high-speed electromagnetic repulsion mechanism, is used as the main circuit breaker (MCB). Two kinds of commercial vacuum interrupters (VIs), which have contacts generating axial magnetic field (AMF) and transverse magnetic field (TMF), respectively, are applied. The breaking current with an amplitude of 10~25 kA is generated by an LC oscillating circuit. The countercurrent with frequency in the range of 500–3000 Hz is provided by a commutation branch. The interruption performance of the two kinds of VIs under different breaking current and countercurrent frequencies is investigated. The experimental results indicate that the differences in interruption performance under the two types of contacts are increasing with larger frequencies of countercurrents. [ABSTRACT FROM AUTHOR]

The Robson drift phenomenon is a macroscopic reflection of the movement of a cathode spot (CS) in oblique magnetic field (OMF). Although it was discovered many years ago, its physical mechanism remains unclear. In this paper, the influence of OMF on the Robson drift of CS motion is simulated. A 2-D stepwise model of the movement of a single CS in OMF is established. It is assumed that the probability of generating a new spot in directions of Amperian force, anti-Amperian force, and directions perpendicular to Amperian force, is proportional to the magnetic pressure around the old spot. The drift angle and velocity of the CS in OMF are simulated. The simulation results show that the drift angle of the CS in OMF has liner relationship with the inclination angle of magnetic field, and it has no obvious relationship with the strength of the applied magnetic field and the amplitude of the arc current, which are in a good agreement with the experimental results. Besides, under the same angle of magnetic field, the velocity of spot motion increases linearly with the strength of OMF. Moreover, the simulation results show that the transverse magnetic field component has a much more predominant influence on the CS velocity than the axial magnetic field component, which are also in agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Fast interruption is vitally important in high-voltage direct current (HVDC) system to suppress the rapid increase of short current. In this paper, a multi-physics coupling simulation model of a high-speed electromagnetic repulsion mechanism (ERM) which is a part of HVDC breaker is proposed. The opening process with an electromagnetic buffer of ERM is investigated. The simulation results including forces, currents, displacements, and velocities are analyzed. Furthermore, a prototype of ERM is designed and developed. Results show that the efficacy of the proposed simulation methodologies is verified by the experimental results. The opening process of ERM could be divided into six stages. During an opening action, the impact of collision on the motion of ERM cannot be ignored. A good buffering effect can be achieved by reasonably setting the related parameters of the electromagnetic buffer. [ABSTRACT FROM AUTHOR]

Explosions of aluminum wires driven by a negative fast rising current (∼80 A/ns) are numerically investigated by using a magnetohydrodynamic code with cold start conditions. A wide range of semi-empirical equations of state based on the Thomas–Fermi–Kirzhnits model and a modified Lee–More–Desjarlais conductivity model are used to model the behavior of the exploding product. The formation and the evolution of the core–corona structure are presented. The corona reaches a maximum temperature of ∼100 eV after the voltage breakdown and expands at a constant speed of 39 km/s. The influence of the wire diameter on the characteristics of the explosion is studied, which shows the maximum energy deposition of 2.6 eV/atom at a wire diameter of 18.4 μm. The simulation is compared with the previous experimental result and shows good agreement. [ABSTRACT FROM AUTHOR]

Highlights • Closed-form magnetic moment and magnetic force analysis. • The influence of magnetic dipole interaction force on the self-assembly of MNPs. • 3D self-assembly process of MNPs. Abstract The self-assembly of magnetic core-shell nanoparticles in the presence of a magnetic template, which consists of an array of soft-magnetic elements embedded in non-magnetic substrate, is analyzed by using discrete element method. An external bias magnetic field is used to magnetize the soft-magnetic elements to saturate state. The high-gradient field produced by elements combined with biased uniform magnetic field provides a flexible way to control the behavior of particles. An equivalent source method is adopted to obtain the closed-form magnetic field analysis, which not only improves the calculation efficiency but also enables accurate prediction of the Kelvin force. In the presence of magnetic field, the behavior of the magnetic nanoparticles is dependent on the magnetic and hydrodynamic forces. Therefore, the assembled structures of magnetic nanoparticles are firstly investigated without considering the magnetic dipole interaction force, in which an unordered nanostructure is formed. As a contrast, the self-assembly of particles is also simulated by taking all forces into account. In this case, the magnetic nanoparticles assemble into an ordered 3D structure, which presents a hexagonal close packed structure. A comparison between the results of the mentioned two cases denotes that the magnetic dipole interaction force plays an important role in controlling the self-assembly of magnetic nanoparticles. [ABSTRACT FROM AUTHOR]

Highlights • The dye-tracing and concentration-measuring experiments provide a means of observing the behavior of particle and fluid. • A closed-form magnetic field analysis is performed to obtain an accurate prediction of magnetic force. • Three-dimensional distribution of particle concentration is investigated by using Fluent, Ansys. • A comparison between the uncoupled model and coupled model is provided. • A comparison between experimental and numerical results is provided. Abstract Dye-tracing and concentration-measuring experiments are carried out to investigate the magnetophoresis of magnetic nanoparticles (MNP) in the presence of an external cylindrical permanent magnet. The magnetophoresis of MNP, inducing an obvious forced-convective flowing of the carrier fluid, which can be observed by visualizing flowing of carrier fluid, results in a temporal and spatial variation of particle concentration. Moreover, in order to get insight into the physical mechanisms of magnetophoresis of MNP, a coupled particle-fluid analysis, in which the non-linear drift-diffusion differential equation is incorporated into the Navier-Stokes equation, is adopted to discuss the influence of particle-fluid interaction on the variation of particle concentration and the kinetics of carrier fluid. It is worth noting that the equivalent current source (ECS) method is adopted to obtain a closed-form field analysis, which provides exactly prediction of the Kelvin force and enables magnetophoretic analysis more efficient. In dye-tracing experiments, an obvious vortex can be observed as the methylene blue moves with the convection of carrier fluid. Furthermore, this phenomenon is also predicted by using the coupled particle-fluid model. A comparison between the experimental and numerical results shows that the hydrodynamic interactions between MNP and carrier fluid plays an important role in inducing forced-convective flowing of carrier fluid and enhancing the magnetophoresis of MNP. Furthermore, these results also denote that the coupled particle-fluid model provides a more efficient and accurate method in investigating the magnetophoresis of MNP. [ABSTRACT FROM AUTHOR]

The quench protection switch (QPS) is an indispensable component ensuring the safety of the magnet coils of a superconducting Tokamak when a quench happens. In this paper, the second commutation process of a QPS based on artificial current zero is investigated. In this process, the current, which has already transferred from the bypass switch to the main circuit breaker, is forced to commutate from the vacuum circuit breaker (VCB) to the discharge resistor by the countercurrent. An LC oscillating circuit is applied to generate oscillating current to simulate the direct current near its peak which is about 20 kA. The countercurrent with frequencies of 500 and 1000 Hz is provided by a commutation branch. The equivalence of the experimental interrupting process compared with the practical situation is analyzed. Two kinds of vacuum interrupters of the VCB are used in experiments. One kind is equipped with contacts generating transverse magnetic field, and axial magnetic field contacts are used in another one. The experimental results indicate that the initial process of the vacuum arc before injecting the countercurrent has crucial impacts on the interruption performance. The countercurrent with the frequency of 500 Hz is easier to interrupt the current than the case of 1000 Hz. [ABSTRACT FROM AUTHOR]

The quench protection switch (QPS) is very important for ensuring the safety of the magnet coils of a superconducting Tokamak. The main function of a QPS is to protect the magnet as the coil quench occurs. Besides, a QPS has to withstand almost all of the coil current of some tens of kA flowing through it in the normal operation condition. This task is undertaken by the by-pass switch (BPS), which is an indispensable component of a QPS, no matter what principle the QPS is based on. Therefore, the study of the temperature rise is very important for optimal design of a BPS. In this paper, a scheme of a high-current BPS is proposed. The steady temperature rise of the BPS is simulated in the condition of natural convection with the approach of Computational Fluid Dynamics (CFD). Furthermore, the influence of the space between each individual switch unit is investigated. Simulation results indicate that there exists an appropriate space, beyond which the mutual influence of adjacent contacts can be accepted. This space can be regarded as a reference in designing a BPS with the trade-off between the dimension of the BPS (and the QPS) and its current-carrying capacity. [ABSTRACT FROM AUTHOR]

The residual axial magnetic field (AMF) at current zero, which is caused by large \mathrmdi/\mathrmdt during the forced current-zero stage of DC interruption based on the technique of artificial current zero, has a significant influence on the interruption performance of the vacuum circuit breaker. In this paper, a model of AMF contacts system is developed by finite-element-analysis software Ansys. The eddy current induced in the contacts system is also analyzed by an equivalent circuit. The influence of the frequency of countercurrent and the characteristics of saturable reactor, which results in the change of \mathrmdi/\mathrmdt before current zero, are investigated. The results demonstrate that the frequency of countercurrent has a significant influence on the residual AMF at current zero. The residual AMF decays exponentially after current zero with a time constant independent of the countercurrent frequency. The residual AMF can be reduced by using a saturable reactor. The effect of a saturable reactor depends mainly on the duration of the low \mathrmdi/\mathrmdt stage before current zero. [ABSTRACT FROM AUTHOR]

Due to the peculiar magnetic properties and the ability to function in cell-level biological interaction, superparamagnetic nanoparticles (SMNP) have been being the attractive carrier for gene delivery. The superparamagnetic nanoparticles with surface-bound gene vector can be attracted to the surface of cells by the Kelvin force provided by external magnetic field. In this article, the influence of the oscillating magnetic field on the characteristics of magnetofection is studied in terms of the magnetophoretic velocity. The magnetic field of a cylindrical permanent magnet is calculated by equivalent current source (ECS) method, and the Kelvin force is derived by using the effective moment method. The results show that the static magnetic field accelerates the sedimentation of the particles, and drives the particles inward towards the axis of the magnet. Based on the investigation of the magnetophoretic velocity of the particle under horizontally oscillating magnetic field, an oscillating velocity within the amplitude of the magnet oscillation is observed. Furthermore, simulation results indicate that the oscillating amplitude plays an important role in regulating the active region, where the particles may present oscillating motion. The analysis of the magnetophoretic velocity gives us an insight into the physical mechanism of the magnetofection. It's also helpful to the optimal design of the magnetofection system. [ABSTRACT FROM AUTHOR]

The motion of cathode spots plays a crucial important role in removing oxide layer on a metal surface by vacuum arc. In this paper, the characteristics of the motion of a single cathode spot on metal surface with oxide layer are investigated experimentally. Experiments are conducted in a detachable vacuum chamber. A hollow copper anode with a hole of 10~\text mm \times 10 mm is used in order to observe the 2-D motion of the cathode spot. The motion of the cathode spot during the descaling process is photographed by a high-speed digital camera with an exposure time of 2~\mu \texts . Experimental results indicate that there are slow motion and fast motion of the cathode spot during descaling process, and the slow motion is the basic characteristic in most of the descaling time. The probability distribution of the cathode spot’s displacement and resident time, the average velocity, and the movement parameter S^2/t are analyzed quantitatively. The results indicate that with the increase of gap distance or the decrease of oxide layer thickness, the cathode spot becomes more active. [ABSTRACT FROM PUBLISHER]

• The combination of Ω- and straight-shaped obstacles enhance the mixing performance. • Well mixing is achieved as the obstacles are in contact with the walls of Tesla chambers. • Increasing the radius of Ω-shaped obstacles can improve the performance of micromixer. • The hexagonal chambers are better than triangle and Tesla chambers. An efficient fluid mixing performance is achieved by a Tesla/hexagon-shaped passive micromixer in a wide range of Reynolds numbers with short mixing length (4.2 mm/1.15 mm from the origin). The passive micromixers are composed of Tesla/hexagonal chambers and Ω-shaped obstacles or combined with straight-shaped obstacles that induce the generation of vortex, contraction and expansion process, the changes of the flow direction, and even the split and recombination of streams. The mixing process of two fluids (water and ferrofluid) is numerically investigated using computational fluid dynamics. For the Tesla-shaped micromixer embedded with Ω-shaped obstacles, a sufficient mixing is obtained as the obstacles are in contact with the internal walls of Tesla chambers. In the hexagon-shaped micromixer, the combination of straight- and omega-shaped obstacles greatly enhance the performance of micromixer in particular at moderate flow rate (1< Re <10). Moreover, reasonable increasing the curvature radius of the omega-shaped obstacles can further improve its mixing performance. The designed passive micromixers were also fabricated, tested and compared with the numerical results through the soft-lithography processes, and the good agreement between the experimental and numerical results identifies our predictions. The good performance of the designed micromixers provides a new direction in designing micromixer with high-throughput and short mixing length. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, the influence of an external transverse magnetic field, in parallel with the cathode surface, on the ignition probabilities of a cathode spot (CS) in the Amperian and retrograde directions is developed assuming that the ignition probability of a new CS is proportional to the magnetic pressure around the old one. Furthermore, both stepwise and statistical models are established to simulate the random and retrograde motions of a single CS of vacuum arc, assuming that the 2-D motion of the CS in the $xy$ plane is equivalent to the synthesis of two independent 1-D movements along the $x$ - and $y$ -axis, respectively. With both models, the random and retrograde motions of a single Cu CS are simulated step by step and statistically, respectively. It was found that stepwise simulation results agree well with the statistical results, and they are also consistent with the relevant experimental results. The difference in retrograde motion velocity between the present stepwise model and that assuming that a new CS can be ignited in any direction around the old one is discussed. [ABSTRACT FROM PUBLISHER]

• A hybrid magnetic field produced by microwires and Halbach magnets is proposed to enhance the mixing between ferrofluid and water. • We numerically and experimentally analyze the effects of the arrangement and the number of microwires on the mixing efficiency. • By adjusting the direction and the magnetite of uniform magnetic field, we receive optimal mixing efficiency 99.06%. With the development in biomedical and biotechnological areas, novel and efficient microfluidic devices integrated with sufficient and rapid mixing function have been attracting enormous scientific attention as versatile and robust platform for low cost and non-contact biological analysis and diagnose. Here, we design and fabricate a magnetic micromixer integrated with special designed microwires, a Y-shaped microchannel and uniform magnetic field for realizing rapid mixing between ferrofluid and deionized water. A comprehensive analysis on the dynamic behavior of ferrofluid is performed by using 3D Eulerian-Eulerian model. Good consistency between experiment and numerical results demonstrates that the enhanced mixing in the presence of longitudinally arranged microwires is due to the introduction of eddies, whose impacts are strengthened with the increase of the number of microwires (n w). However, increasing n w requires a long microchannel and long time to complete mixing. In order to further improve the mixing performance of our micromixer, a horizontally arranged microwire combined with a particular uniform magnetic field is proposed to provide enough magnetic force for enhancing the mixing of ferrofluid and deionized water, receiving optimal mixing efficiency 99.06%. The flexible tunability of external uniform magnetic field enables desired performance of our designed system. [ABSTRACT FROM AUTHOR]

In this paper, the relationship between the external transverse magnetic field (TMF) and the ignition probability of new cathode spot in different directions is developed assuming that the ignition probability of a new cathode spot is proportional to the magnetic pressure around the old one. Furthermore, a method is established to simulate the 2-D motion of a cathode spot step-by-step. With this approach, stepwise simulations of the 2-D retrograde motion of a single Cu cathode spot are carried out in a large range of flux density of TMF ( Bem ). Simulation results indicate that, if the self-generated magnetic field Bsm exceeds the applied magnetic field Bem , i.e., B\textrm {em}\le B{sm} , there is a linear relationship between the velocity of the retrograde motion and Bem , in certain range of Bem , after which the velocity of the retrograde motion increases slowly and nonlinearly with further increase of B\textrm {em} . This phenomenon agrees well with relevant experiment results. In the linear stage, the dependence of velocity constant on the spatial step and the temporal step of the motion of cathode spot is investigated as well. Moreover, when Bem>Bsm , the velocity of cathode spot decreases with the increase of B\textrm {em} , even the macroscopic motion is still in the retrograde direction. This effect might also contribute to the reversal of cathode spot motion from the retrograde direction to the Amperian direction at strong TMF besides the predominant effect of the deflection of arc column toward the Amperian direction. [ABSTRACT FROM PUBLISHER]

Cathode spots (CSs) dynamics in the initial expansion stage of high-current triggered vacuum arc and the influence of axial magnetic field (AMF) was investigated experimentally. Experiments were conducted with butt contacts in a demountable vacuum chamber. Images of CSs were photographed with a high-speed digital camera with exposure time of 2 \(\mu \) s. The uniform and constant AMF in the intercontacts region was supplied by external magnetic field coil. In high-current triggered vacuum arc, CSs expanded across the cathode surface in basically a ring-shaped pattern. Experimental results showed that the expansion ring consisted of group CSs (GCSs) and individual CSs at the beginning of the expansion process. The GCS moved outward faster than individual CS. Research results indicated that an AMF could reduce the tendency of formation of GCS. The effect of local plasma and global plasma, which could be significantly influenced by AMF, on the motion pattern and distribution of CSs in the initial expansion stage was investigated. [ABSTRACT FROM PUBLISHER]

The expansion speed of cathode spots (CSs) in the initial expansion stage of high-current triggered vacuum arc was investigated experimentally. Experiments were conducted with butt contacts in a demountable vacuum chamber. Images of CSs were photographed with a high-speed digital camera with exposure time of 2 \mus. The uniform constant axial magnetic field (AMF) was supplied by an external magnetic field coil. The combined influence of contact gap of 2–10 mm and AMF of 0–70 mT on CSs expansion speed in the initial expansion stage was mainly investigated. Investigation results indicated that the variation of contact gap could influence the CSs expansion speed by changing the plasma density inside the cathode arc root in two ways: loss of arc plasma and constriction of arc column. AMF could weaken these two effects caused by the variation of contact gap. In addition, experimental results indicated that there existed a critical current for a given AMF. If the arc current peak was less than the critical current, the given AMF could inhibit the arc column constriction effectively both at contact gap of 8 and 10 mm, which could maintain the dependence that CSs expansion speed increased with contact gap; otherwise, the constriction of arc column played a major role in the influence on CSs expansion speed. In this case, the CSs expansion speed was lower at contact gap of 10 mm than that at 8 mm. [ABSTRACT FROM AUTHOR]

In this paper, the influence of an axial magnetic field (AMF) on the expansion speed of cathode spots (CSs) in the initial expansion stage of high-current triggered vacuum arc is investigated experimentally in a demountable vacuum chamber. Butt contacts with contact plate material of oxygen-free high-thermal-conductivity Cu and CuCr25 were used in experiments. Images of CSs are photographed with a high-speed digital camera with an exposure time of 2 \mus. The uniform constant AMF in the intercontact region is supplied by external magnetic field coil. Experimental results indicate that, in an arc stabilized by AMF, CS expansion speed also increases with the increase of di/dt, which is the same as that in arc burning freely. In addition, quasi-quantitative analysis of the experimental results show that the bending and lengthening of CS motion trajectory in AMF are not sufficient to explain the decrease of CS expansion speed with AMF. Another reason might be related to the inhibitory effect of AMF on the loss of arc plasma, which could also contribute to the decrease of CS expansion speed. [ABSTRACT FROM AUTHOR]

This paper analyzes how removing oxide layer on metal surface by vacuum arc could be a green substitute for the traditional acid-washing and mechanical cleaning technique widely used in the metallurgical industry, which is harmful to the environment. In this paper, the effects of vacuum arc on removing oxide layer on the surface of carbon-steel tubes, which were used as the cathode, is investigated experimentally. External coils are used to generate transverse magnetic field (TMF) driving cathode spots to rotate on tube surface. Experiments are conducted in a vacuum chamber with Ar as the protection gas under different TMF flux densities. Arc images are captured by a high-speed digital camera with an exposure time of 2 \mus. The influence of transverse magnetic flux density on the characteristics of arc and descaling effect is mainly investigated. [ABSTRACT FROM AUTHOR]

The initial expansion process in a drawn vacuum arc and the influence of axial magnetic field (AMF) were investigated experimentally in a demountable vacuum chamber. Arc characteristics were investigated with the aid of a high-speed digital camera with an exposure time of 2 \mu\s . In a drawn vacuum arc, the arc sequence begins with the bridge column arc formed after the rupture of the molten metal bridge. This column evolves into the transition mode, which consisted of a central column with few or no cathode spots (CSs) outside the column, and then into the fully diffuse mode. Experimental results indicated that in transition mode arc, the expansion process could be characterized by the appearance of CSs outside the central column, and could be classified into two patterns, “slow” expansion and “quick” expansion according to the characteristics of the formation and motion of new CSs (conducting channels) outside the central column of arc. The influence of AMF and its distribution on the expansion process was also investigated. Investigation results indicated that AMF had two contrary effects, i.e., inhibiting effect and prompting effect, on the initial expansion stage of drawn vacuum arc. Furthermore, saddle-shaped AMF could encourage the arc transition into diffuse mode more effectively than bell-shaped AMF. [ABSTRACT FROM PUBLISHER]

The method of magnetic field calculation and its influence on simulating the motion of cathode spots (CSs) in a vacuum arc were investigated in this paper. A method based on coordinate transformation and magnetic field superposition principle was proposed. In this method, the influence of current passing through an electrode rod and a contact plate was taken into account. Comparison was made between the proposed method and two simplified methods which were on the basis of the Biot–Savart law. Moreover, simulation results of CS motion with magnetic field calculated by different methods were shown and compared. Investigation results indicated that current passing through the contact plate and electrode rod could significantly influence the magnetic field and thus influence the simulation results of CS motion. Furthermore, it was shown that the proposed magnetic field calculation method had higher calculation accuracy with acceptable consumption of calculation time. [ABSTRACT FROM AUTHOR]

Removing an oxide layer on a metal surface by vacuum arc has been preliminarily used in the metallurgical industry as an environment-friendly substitutor for the traditional acid-washing technique. In this paper, the influence of protection gas pressure on descaling process is investigated experimentally. Arc images taken by a high-speed digital camera indicated that the descaling rate was closely related to the motion pattern of cathode spots in different gas pressures. The decrease of descaling rate with the increase of gas pressure could be partly attributed to the formation of cathode-spot group and its less mobility at high gas pressure. The influence of gas pressure on the power density of cathode spot was also analyzed. It seemed that higher gas pressure would lead to the decrease of the ratio of power input into the cathode spot to the total arc power, which could also contribute to the decrease of the descaling rate. [ABSTRACT FROM PUBLISHER]

Experiments on a drawn vacuum arc with forced current zero, which was formed by injection of a countercurrent with a frequency of 1 kHz, were conducted in a detachable vacuum chamber. The prospective peak main current was 3.5 kA. Arc characteristics were investigated with the aid of a high-speed digital camera with an exposure time of 2 \mu\s. In this paper, the influence of axial magnetic field (AMF) distribution and anode material on the evolution of vacuum arc in the initial expanding stage is mainly investigated. Three types of electrodes were used in the experiments. One of them was simple electrodes with butt contact plates, and the other two types were specially designed electrodes generating a conventional bell-shaped AMF profile and a saddle-shaped AMF distribution, respectively. OFHC copper and WCu10 were used as anodes for the electrodes with bell-shaped AMF. The appearance of vacuum arc in the forced current-zero stage is also investigated. [ABSTRACT FROM AUTHOR]

In the Special Issue, we are very pleased to present the expanded versions of selected papers from the 27th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV). It was held at the Xi’an Jiaotong-Liverpool International Conference, Suzhou, China, from September 18–23, 2016. [ABSTRACT FROM PUBLISHER]

To void breakdown between busbars, the dissociation unit is applied in the arc chamber of an air circuit breaker (ACB) to cool down the hot gas exhausted from the vent of the arc chamber in the interrupting process. Cooling efficiency and flow resistance of the dissociation unit have important roles, which can greatly affect the safety of the low voltage switcher and interrupting performance of the arc chamber. The most common structure style of the dissociation unit is a multilayer metal wire mesh, and it has a complex microstructure. Then, it is unreasonable to directly simulate the dissociation unit due to the huge cost of calculation. In this study, the porous medium model is introduced and a combination of two different porous materials is applied to simplify the simulation model of the dissociation unit. Based on the porous model and simplified arc chamber model, the ACB with the dissociation unit is analyzed. The cooling effect and flow resistance of the dissociation unit are evaluated in the breaking process. By comparing experimental and simulated pressures in the arc chamber, this simulation approach is verified. [ABSTRACT FROM AUTHOR]

In this paper, a bidirectional fluid–solid interaction method is established to investigate the influence of the outlet elastic baffle on the pressure in the arc chamber in the breaking process of a low-voltage circuit breaker. Based on the computational fluid dynamic method, the flow model in the arc chamber is established. The model of the outlet baffle, with consideration of the nonlinear behavior, is established by the finite element method. By introducing dynamic grid technology, the interaction process of deformation of the outlet baffle and arc chamber pressure can be analyzed. A simple arc extinguishing chamber with an outlet baffle is designed, and experiments with a LC oscillating circuit are carried out. By using a high-speed camera and a pressure sensor, the deformation of the baffle and the pressure of the arc chamber are measured in the breaking process. The simulation model is verified by experimental results. It is worth noting that the flutter behavior of the elastic baffle was observed in the experiments and in the numerical simulation. Through simulation analysis, it is found that the flutter behavior is caused by the first-order mode of the elastic baffle under the excitation of arc chamber pressure. [ABSTRACT FROM AUTHOR]

Vacuum circuit breakers (VCB) are commonly used in active mechanical direct current circuit breakers (DC CBs) to accomplish the interruption of the fault current. The post-arc current phenomenon of a VCB is related to the dielectric recovery process of the VCB. Thus, we performed experiments to investigate the influence on the post-arc current by taking the electrode separation, breaking current, and interruption of the bi-directional current with the injecting high frequency current in a fixed direction into account. To be in accordance with the practical interruption duty, the breaking current in the experiment ranges from 500 A to 20 kA. At the same time, the di/dt at current zero (CZ) varies between 200 and 1100 A/μs. The experiment results reveal that the peak value of the post-arc current in an active DC circuit breaker can reach more than 100 A with high di/dt at CZ. It is found that with a longer electrode separation, not only the residual charge increases but also the post-arc current increases. The arcing current before CZ can influence the post-arc current but the effective duration before CZ is short. This duration is the memory time and it is derived from the experiment results. The influence of the breaking current and interruption of the bi-directional current with the injecting current in a fixed direction are dependent on the relation of the current commutation time with the memory time. [ABSTRACT FROM AUTHOR]

Based on a magnetohydrodynamic model, a numerical simulation of high-current vacuum arc (HCVA) is carried out. In this model, the kinetic energy terms and ion viscosity terms in energy conservation equations are considered. Compared with the supersonic constricted vacuum arc, the ion flow in HCVA is in the subsonic status. Therefore, boundary conditions of cathode and anode sides have to be adjusted for HCVA. According to the simulation results of HCVA, we can find that the maximal plasma pressure appears near the cathode side. The characteristics of HCVA are significantly different from those of supersonic vacuum arc. Then, we make the comparisons between simulation results and experimental results (such as electron number density, electron temperature, ion temperature, high speed charge-coupled device photographs, and so on). The simulation results are in agreement with the experimental results. In addition, we also analyze the influence of different arc models on the distribution of current density in the anode side. [ABSTRACT FROM AUTHOR]

Development towards HVDC grids is drawing intense development of HVDC circuit‐breakers (CBs). The increasing rated voltage and capacity requires HVDC CBs with excellent performance to be installed and comprehensive tests on HVDC CBs are indispensable. This paper contributes to clarifying clearer test requirements on the current interruption test, which is the most challenging one and proposing a novel applicable test method. It is the toughest test because when an HVDC CB interrupts fault current, a high transient interruption voltage (TIV) is produced by the operation of metal oxide surge arrester (MOSA), and a large current continues flowing through MOSA simultaneously, which means considerable energy is demanded for the test. To verify an HVDC CB's current interruption ability, voltage withstand ability and energy dissipation ability in single test can be costly and even impractical in extra high voltage classes. Alternatively, a multi‐part test method is reasonable and valuable, in which the HVDC CB can be tested with large current and high voltage one after another, while the energy dissipation ability will be verified separately. At last, a proposed synthetic test circuit is validated by a simulation and a low voltage experiment, creating high equivalence between the simulation and the validation test. [ABSTRACT FROM AUTHOR]

This work investigates the dynamic characteristics of vacuum arc in the initial expansion process of a direct current (dc) circuit breaker. Based on the commercial cup-type axial magnetic field (AMF) contact, a 3-D transient magnetohydrodynamic (MHD) model is established. In the model, transient equations are used to study the transient characteristics of the vacuum arc. The effect of magnetic field hysteresis is also considered in the method. The dynamic mesh technique is adopted to simulate the electrode separation, which can make the simulation results more accurate. The simulation results show that, during the initial expansion process, with the increase in the current, the arc gradually expands in the electrode gap. The ion pressure, ion number density, axial current density, and energy flux density to the anode gradually decrease. Ion rotation can be observed under the influence of the magnetic field, and the rotation speed will increase with the increase in the current. Two different arc ignition positions are also compared. The result shows that igniting the arc at the contact center is more helpful to the success of the interruption of the dc circuit breaker. The appearance of the arc predicted by the model is consistent with the experimental results. [ABSTRACT FROM AUTHOR]

The preparation and storage of aluminum nanoparticles pose significant challenges due to their high chemical reactivity. This paper proposes a one-step method for the production of carbon-coated aluminum nanoparticles using an argon protective arc in a liquid nitrogen environment. The emission spectra of the arc validate that the method proposed in this paper can effectively mitigate the adverse impact of impurity gases such as oxygen and water on the product without the need for expensive vacuum equipment. The obtained nanoparticles underwent characterization through high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman analysis, thermogravimetric analysis, and dynamic light scattering. The characterization results demonstrate the successful synthesis of carbon-coated aluminum nanoparticles with nitrogen-doped fullerene shells. With an increase in arc current, the nanoparticles exhibit a corresponding enlargement in diameter, accompanied by a broader distribution. The characterization of the electrode erosion suggests that the aluminum droplet ejection plays a more important role in the nanoparticle generation process as the arc current increases. Optimized strategies are proposed to increase the percentage of successfully-formed carbon-coated aluminum nanoparticles. • One-step preparation of carbon-coated aluminum nanoparticles. • Arc discharge in liquid environment without vacuum and sealing equipment. • Core-shell structure: Al core wrapped in N-doped fullerenes. • The arc current impacts electrode erosion pattern and product characteristics. [ABSTRACT FROM AUTHOR]

Much research has been done on the motion of low-current vacuum-arc cathode spots (CSs). The relationship between the motion velocity of CSs and the magnetic field, particularly the relationship between the direction of CS motion and the ratio of Bz/Bt, has been revealed. However, little investigation on the motion of CSs in high-current vacuum arcs has been conducted before. In this paper, the motion of CSs of high-current vacuum arcs under different axial magnetic fields was experimentally investigated. Simultaneously, calculation of the motion of CSs based on the empirical formula has been done, and comparison with experiments and analysis were given. Experiments were conducted in a detachable vacuum chamber with an arc current of 10 kA (root mean square). Images of CSs were photographed with a high-speed digital camera with an exposure time of 2 \mu\s. With computer-aided numerical processing, the spatial distribution of the CSs was obtained, based on which the magnitude and direction of the CS motion velocity were calculated, and the CS motion trajectories around the current peak were plotted. Results indicated that the properties of the CS motion in high-current vacuum arcs are similar to those in low-current vacuum arcs. [ABSTRACT FROM AUTHOR]

Abstract: To change the structures and yields of carbon nano-products, transverse magnetic field (TMF) was introduced to arc discharge in liquid (de-ionized water, liquid nitrogen). Direct current was used to sustain the arc discharge between two graphite electrodes and cobalt powder was filled in drilled anodes as catalyst sometimes. Scanning electron microscopy and high-resolution transmission electron microscopy were used to investigate the nano-products. Some novel carbon nano-structures were obtained with the effect of TMF. For arc discharge in water, curled multi-walled carbon nanotubes and nano-structures with few layers were found in cathode depositions and floating products, respectively. For arc discharge in liquid nitrogen, twists of single-walled carbon nanotubes appeared in cathode depositions and the yields of spherical nano-particles in floating products increased. [Copyright &y& Elsevier]

Abstract: Based on two-temperature magnetic hydrodynamic (MHD) model, the influence of saddle-shaped distributed axial magnetic field (AMF, linearly increases along radial position) and bell-shaped distributed AMF (linearly decreases along radial position) on plasma loss and heat flux density to anode in subsonic high-current vacuum arc (HCVA) is simulated and analyzed. According to the simulation results, the saddle-shaped AMF can more effectively inhibit plasma loss from arc column than that of bell-shaped AMF. Comparisons between simulation results and experimental results further verify the correctness of model and simulation. [Copyright &y& Elsevier]

Numerical investigation on the evolution of stratification instability seeded by resistive inclusions in electrically exploding aluminum wires is reported. The resistive inclusions at the submicrometer scale create hot spots with enhanced Joule heating during the first phase of electrical explosion in the wires, amplifying the peripheral current density. The temperature rise of a hot spot first increases and then decreases with resistivity. The hot spot reaches its maximum temperature rise at 70-times the aluminum resistivity. Exploding products ejected from localized hot spots pile up on both sides of the seeding regions. Perturbations in the front edge of the dense core emerge after several tens of nanoseconds. Bright stripes are formed inside out, providing a possible explanation for the absence of stratified structures at the very beginning of discharge. A numerical shadowgram is reconstructed using a flow visualization technique. The matching of the numerical shadowgram and experimental shadowgram indicates that the resistive inclusions characterized by increased resistivity comprise an important seed in stratification instability. This study helps in understanding the seeding mechanism of electrothermal instability in pulsed-power-driven plasma systems. [ABSTRACT FROM AUTHOR]

In this paper, computational results characterizing the formation and merging of counter-streaming interpenetrating plasma flows formed in exploding double parallel aluminum wires are presented. A radial magnetohydrodynamic computation is carried out first to obtain the parameters of core-corona structure in individual wires, providing an initial condition for the planar magnetohydrodynamic model in a multi-species fluids scheme with two-temperature treatment of plasma. In the XY plane, two aluminum plasma clouds are surrounded by extremely thin air, which represents a vacuum environment. A long-lasting compressed layer of extremely thin air in the central region of the inter-wire gap is formed before the merger of aluminum plasma flows. The accordance between the increasing mass fraction of aluminum plasma species in the central slit and the enhancement in self-emission light demonstrates that the real physical characteristics of extremely low-density vacuum environment plays an important role in merger of aluminum plasma flows. Current density is concentrated in the central column during the merging process of counter-streaming interpenetrating aluminum plasma flows, evolving from a structure of bifurcated current sheets into a single narrow sheet. Efficient numerical investigation on the interaction between counter-streaming plasma flows requires the incorporation of surrounding fluid species of extremely thin air. [ABSTRACT FROM AUTHOR]

Abstract: A magnetic field parallel to the carbon arc in water was used to increase the directionality of moving carbon particles and generate carbon nano-materials. The products were analyzed and compared with those obtained without a magnetic field. The study shows that the purity and quality of multi-walled carbon nanotubes in the cathode deposition formed by an arc in water with a magnetic field were both improved, and cylinder-like carbon structures were also found in the deposition. The influence of the magnetic field on the formation of the products was analyzed. [Copyright &y& Elsevier]

The anode activities are critical for high-current vacuum arc characteristics, especially the interruption performance of vacuum interrupters. The serious anode melting and sputter of liquid droplets into arc column often lead to interruption failure. In our previous work, the obvious anode melting and swirl flow of melted anode metal were detected at the center of anode surface when arc current exceeded a critical value under axial magnetic field (AMF). It is found that the AMF has great influence on the anode swirl flow, no swirl flow is found on the butt plate anode without AMF, but obvious swirl flow can be found when a moderate AMF is applied. Meanwhile, the swirl flow direction reversed if the AMF direction also reversed. The electromagnetic forcej×Bin anode melting pool and the impact force of ions coming from cathode plasma jets which are inclined to the arc axis on anode surface were thought to be two main possible reasons. In order to discover the physics behind the anode swirl flow phenomenon, special experiments have been conducted in this paper. Both the theoretical analysis and experimental results indicate that it is not the electromagnetic force but the interaction between ions from cathode plasma jets and anode melting pool that leads to the observed anode swirl flow. The inclination direction of cathode plasma jets, which is consistent with the direction of magnetic field vector, determines the direction of swirl flow. [ABSTRACT FROM AUTHOR]

A mid-infrared perfect metamaterial absorber (PMA) consisting of well-engineered unit cells, composed of metallic backed layer (Cu), dielectric layer (Al 2 O 3), matts-shaped meta cell (Cu), and an anti-oxidation layer from bottom to top, is proposed in this paper. The electromagnetic response of the designed PMA is analyzed using 3D full-wave computational model. Our analysis demonstrates that the maximum absorption is enhanced to 99.9% at the resonance wavelength of 7.35 µm, which is caused by magnetic polaritons (MPs) resonance between the incident beam and magnetic polaritons formed by three fluxing currents. Specially, a three-circulation equivalent circuit model is proposed to predict the resonant wavelength of the designed PMA, which comprehensively considers the influence of coupling capacitance not only between neighboring unit cells, but also between the metal lines inside the top metal pattern for the first time. The influence of geometrical parameters on resonant wavelength is predicted by the equivalent circuit model proposed in this paper, and the prediction error is less than 5% as compared with that of computational analysis. With well-engineered plasmonic meta-atoms, the designed PMA presents the characteristics of angle and polarization- independent with a smaller relative size (0.245λ) and a thinner relative thickness (0.053λ). Besides, an obvious red-shift of the resonance frequency of PMA is observed as the permittivity of dielectric layers is increased. The approach of establishing equivalent circuit model will provide methods for the analysis of PMA based on MPs with complex electromagnetic behavior. [ABSTRACT FROM AUTHOR]

In real power system, when the three-phase short-circuit fault occurs, the vacuum arc in one phase will be influenced by the transverse magnetic field generated by neighbor phases and bus bars. This kind of effect is the main cause of the unstable arc and deflected erosion of contact plates, which leads to the failure of vacuum circuit breakers interruption. The objective of this paper is to get more insight into the influence of external transverse magnetic field (ETMF) on vacuum arc’s behavior. The experiments were conducted in a demountable vacuum chamber with pressure about 10^-4 Pa. The cup-type axial magnetic field contacts were used, whose material was pure copper and the diameter is 35 mm. The uniform ETMF in the arc region was generated by two parallel bulk permanent magnets. The experiments were conducted under different ETMFs (0, 15, and 25 mT) and current levels (1-, 2.5-, and 4-kA rms) with different gap distances (6, 8.5, and 11 mm). The videos of arc column were recorded by a high-speed charge-coupled device camera. Under the action of ETMF, the vacuum arc got deflected. Due to the retrograde motion of cathode spots and Ampere force acting on arc column, the deflection behaviors during three typical periods (that is, initial, peak value, and close-to-current-zero period) were different. Moreover, the deflection level of vacuum arc at current peak value moment was greatly impacted by ETMF and gap distance. Larger the ETMF and gap distance were, higher the deflection level at current peak value moment was. The simulation results of arc deflection based on magnetic-hydrodynamic model were in agreement with experimental results in trends. [ABSTRACT FROM AUTHOR]