Electrochemical behavior of Pb-Ag-Nd alloy during pulse current polarization in H_2SO_4 solution

The anodic layer and oxygen evolution behavior of Pb-Ag-Nd alloy during pulse current polarization and constant current polarization in 160 g/L H2SO4 solution was comparatively investigated by chronopotentiometry, SEM, XRD, EIS and Tafel techniques. The results show that the anodic layer on Pb-Ag-Nd alloy formed through pulse current polarization is more intact and presents fewer micro-holes than that formed through constant current polarization. This could be attributed to the low current density period, which works as a ‘recovery period＇. During this period, the oxygen evolution reaction is less intense, which benefits the recovery of porous anodic layer. Pb-Ag-Nd anode also shows a lower anodic potential during pulse current polarization, which is in accordance with its smaller charge transfer resistance and smaller Tafel slope coefficient at high over-potential region. The lower anodic potential could be ascribed to the higher concentration of Pb O2 in the anodic layer, which promotes the formation of more reactive sites for the oxygen evolution reaction.

The effects of electric and magnetic fields on the current spin polarization and magnetoresistance in a ferromagnetic/organic semiconductor/ferromagnetic（FM/OSC/FM） system

From experimental results of spin polarized injection and transport in organic semiconductors（OSCs）,we theoretically study the current spin polarization and magnetoresistance under an electric and a magnetic field in a ferromagnetic/organic semiconductor/ferromagnetic（FM/OSC/FM） sandwich structure according to the spin drift-diffusion theory and Ohm＇s law.From the calculations,it is found that the interfacial current spin polarization is enhanced by several orders of magnitude through tuning the magnetic and electric fields by taking into account the specific characteristics of OSC.Furthermore,the effects of the electric and magnetic fields on the magnetoresistance are also discussed in the sandwich structure.

Strong Current-Polarization and Negative Differential Resistance in FeN3-Embedded Armchair Graphene Nanoribbons

Motivated by the recent advances of transition-metal-nitrogen-carbon (TM-N-C) materials in catalysis, we investigate the electronic structure and transport properties of FeN3-embedded armchair and zigzag graphene nanoribbons (FeN3@AGNRs, FeN3@ZGNRs) with different widths. The first-principles results indicate that the FeN3 induces significant changes on the band structures of both ZGNRs and AGNRs, making the resultant systems quite different from the pristine ones and own room-temperature stable ferromagnetic (FM) ground states. While only FeN3@AGNRs possess a significant spin-dependent negative differential resistance (NDR) and a striking current polarization (nearly 100%) behaviors, due to that FeN3 introduces two isolated spin-down states, which contribute current with different performances when they couple with different frontier orbits. It is suggested that by embedding FeN3 complexes, AGNRs can be used to build spin devices in spintronics.

The effects of electric and magnetic fields on the current spin polarization and magnetoresistance in a ferromagnetic/organic semiconductor/ferromagnetic(FM/OSC/FM) system

From experimental results of spin polarized injection and transport in organic semiconductors(OSCs),we theoretically study the current spin polarization and magnetoresistance under an electric and a magnetic field in a ferromagnetic/organic semiconductor/ferromagnetic(FM/OSC/FM) sandwich structure according to the spin drift-diffusion theory and Ohm’s law.From the calculations,it is found that the interfacial current spin polarization is enhanced by several orders of magnitude through tuning the magnetic and electric fields by taking into account the specific characteristics of OSC.Furthermore,the effects of the electric and magnetic fields on the magnetoresistance are also discussed in the sandwich structure.

Effect of Finite-Ion-Banana-Width on the Polarization Contribution to the Neoclassical Tearing Modes Evolution

In the previous analytical description of the neoclassical polarization current effect on the neoclassical tearing modes （NTMs）, it is usually assumed that the magnetic island is much larger than the finite-ion-banana-width （FBW）. This assumption is questionable when the experimentally observed seed island width of the NTMs is comparable to the FBW. We introduce a simple and direct theoretical method to investigate the FBW effect on the neoclassical polarization contribution to the NTM evolution in collisional plasmas. The results show that, the FBW effect can strongly modify the neoclassical polarization current profile near the island separatrix, and thus weaken its probably stabilizing effect on the NTMs.

Current Polarity Detection and Current Compensation Strategy for PAC Based Three-Phase ZVS PWM Converter

A novel software implementation for current polarity detection and current compensation is presented. For a three-phase zero-voltage soft-switching （ZVS） PWM converter based on phase and amplitude control （PAC）, when saw-tooth carriers with alternate positive and negative slopes are adopted, the positive or negative slopes are chosen according to the phase current polarity. Since polarity reversal causes current distortion, current at the instant of reversal should be compensated for. Based on the characteristic of unity power factor converter in rectification and regeneration modes, a software implementation for current polarity detection is proposed. Distortion of current zero-crossing caused by using saw-tooth carriers with alternate positive and negative slopes is analyzed, and the relevant compensation method is proposed. Experimental study with a 1.5 kW device shows that phase current has a small harmonic content and power factor is high both in rectification and regeneration modes.

Effects of pulse parameters on arc characteristics and weld penetration in hybrid pulse VP-GTAW of aluminum alloy

A novel ultrafast-convert hybrid pulse variable polarity gas tungsten arc welding process （HPVP-GTAW） is developed. High frequency pulse square-wave current which has a frequency of more than 20 kHz is exactly integrated in the positive polarity current duration. The effects of pulse current parameters on arc characteristics and weld penetration have been studied during the HPVP-GTAW process using Al-5. 8 Mg alloy plates. The arc characteristics studied by arc voltage and its profile, weld penetration noted by the ratio of weld depth to width have been found to be influenced significantly by the pulse current. The experimental results show that the HPVP-GTA W process can improve the arc profile predominantly and obtain the higher weld penetration with lower heat input. The observation may help in understanding the weld characteristics with respect to variation in the pulse current parameters which may be beneficial in using the novel HPVP-GTAW process to produce the better weld quality of aluminum alloy plates.

Effects of Silica Fume and Steel Fiber on Chloride Ion Penetration and Corrosion Behavior of Cement-based Composites

This project was aimed to evaluate the chloride permeability and corrosion behavior of cement-based composites which comprised fibers and silica fume in the mixes~ Resistivity, polarization resistance, ponding and rapid chloride penetration results of specimens were obtained through tests. Test results indicate that resistivity, open circuit potentials and direct current polarization of specimens with w/b ratio of 0.35 are higher than those of specimens with w/b ratio of 0.55. For length-diameter ratio of 65, resistivity and direct current polarization of specimens with fiber length of 35 mm were similar to those of 60 mm. In addition the open circuit potentials of specimens with fiber length of 60 mm were slightly higher that those of 35 mm. The resistivity decreased with increasing steel fiber content, and the open circuit potential and direct current polarization increased with increasing steel fiber content. The specimens containing silica fume were found to provide higher resistivity, open circuit potentials and direct current polarization than the control specimens. The incorporation of steel fiber and silica fume in composites achieved more significantly decreases in resistivity and increases in direct current polarization than steel fiber composites or silica fume composites. The penetration depth and six-hour total charge passed of specimens for w/b ratio of 0.35 were lower than those for w/b ratio of 0.55. For length-diameter ratio of 65, the penetration depth of specimens for fiber length of 35 mm was similar to that of 60 mm. The penetration depth decreased with increased steel fiber content in the composites. By regression analysis, a good correlation between open circuit potential and direct current polarization, and chloride penetration depth and direct current polarization.

Effect of current polarity on electrical sliding wear behavior of Cu-WS_2-graphite-WS_2 nanotube composites in air and vacuum conditions

In this paper Cu-WS2-graphite-WS2nanotube composites were fabricated by powder metallurgy hot pressing method.The effect of current polarity on the wear rates and contact voltage drops of the composites were investigated using a brush-on-slip ring tribometer rubbing against Cu-5 wt.%Ag alloy ring in air and vacuum,respectively.The worn surfaces of the composites were analyzed by scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy(XPS).Surface profile curves of the worn tracks were measured using the surface profiler.The results demonstrated that the current polarity has a significant effect on the wear rates and contact voltage drops of the composites in both air and vacuum conditions.Positive brush possesses a higher wear rate compared with the negative brush in the air atmosphere since the electrical field direction activates oxidation at the positive brush surface while inhibits oxidation at the negative brush surface.Except for the regular wear losses,the combined effect of molten metal bridge erosion and arc erosion cause the positive brush to lose extra material and the negative brush to gain extra material,so the positive brush shows a higher wear rate in the vacuum condition.The contact voltage drop of the positive brush is lower than that of the negative brush in the air atmosphere,but contrarily,the positive brush shows a higher contact voltage drop in the vacuum condition.

Spin polarized current injection and transportation in a double T-shaped organic spintronic device

A double T-shaped device model is constructed to investigate the spin polarized current injection and transportation properties in organic semiconductors.Based on the spin diffusion theory and Ohm’s law and considering the different charge-spin relationship of the special carriers in organic semiconductors,the current spin polarization has been obtained.Effects of the branch current ratio and the polaron proportion on the spin polarized current injection efficiency are studied.From the calculation,it is found that the improvement of the spin polarized current injection efficiency can be obtained by adjusting the branch current ratio;moreover,high polaron proportion in organic semiconductors is beneficial for obtaining high current spin polarization.