Study of Superconducting Fault Current Limiter Using Vacuum Interrupter Driven by Electromagnetic Repulsion Force for Commutating Switch

Using a high-temperature superconductor, we constructed and tested a model superconducting fault current limiter (SFCL). The superconductor and the vacuum interrupter as the commutation switch were connected in parallel using a bypass coil. When the fault current flows in this equipment, the superconductor is quenched and the current is transferred to the parallel coil because of the voltage drop in the superconductor. This large current in the parallel coil actuates the magnetic repulsion mechanism of the vacuum interrupter. Due to the opening of the vacuum interrupter, the current in the superconductor is broken. By using this equipment, the current flow time in the superconductor can be easily minimized. On the other hand, the fault current is also easily limited by large reactance of the parallel coil     

A control law for vehicle merging inspired by dragonfly behavior

Autonomous control of vehicles has recently attracted considerable attention. In this sense, vehicle merging has become an important topic in this field of research. However, in conventional studies, the controlled vehicle must calculate the movement of other surrounding vehicles to complete the merge, requiring high computational costs. In this paper, we focus on dragonfly behavior to solve this issue. Indeed, insects can behave adaptively in the complex real world in spite of the limited size of their brains. They reduce the computational requirements of their brain by relying on different properties of their surroundings, basing their intelligent behaviors on simple strategies. The behavior of a dragonfly when chasing a prey is an example of these strategies. In this study, we address the vehicle merging maneuver by applying dragonfly’s strategies to control the movement of the merging vehicle. We propose a simple control method inspired by the aforementioned strategies and, finally, we present simulation results that were conducted to demonstrate the effectiveness of this method.     

Solar energy powered Rankine cycle using supercritical CO2

A solar energy powered Rankine cycle using supercritical CO₂ for combined production of electricity and thermal energy is proposed. The proposed system consists of evacuated solar collectors, power generating turbine, high-temperature heat recovery system, low-temperature heat recovery system, and feed pump. The system utilizes evacuated solar collectors to convert CO₂ into high-temperature supercritical state, used to drive a turbine and thereby produce mechanical energy and hence electricity. The system also recovers heat (high-temperature heat and low-temperature heat), which could be used for refrigeration, air conditioning, hot water supply, etc. in domestic or commercial buildings. An experimental prototype has been designed and constructed. The prototype system has been tested under typical summer conditions in Kyoto, Japan; It was found that CO₂ is efficiently converted into high-temperature supercritical state, of while electricity and hot water can be generated. The experimental results show that the solar energy powered Rankine cycle using CO₂ works stably in a trans-critical region. The estimated power generation efficiency is 0.25 and heat recovery efficiency is 0.65. This study shows the potential of the application of the solar-powered Rankine cycle using supercritical CO₂.     

Optical properties of C60/a-C superlattice structures for solar cell applications

C₆₀/amorphous carbon superlattice structures were fabricated by shutter-controlled molecular beam deposition. The periodic structure of resulted films was confirmed by X-ray diffraction measurements. From the UV–vis reflectance/transmittance measurements, the energy shift of absorption edge was observed in the superlattice structures as a function of their well width. The carbon-based superlattice structure is the useful technique to control the band gap energy of carbon materials.     

Corrosion resistance of structural materials in high-temperature aqueous sulfuric acids in thermochemical water-splitting iodine–sulfur process

Very harsh environments exist in the iodine–sulfur process for hydrogen production. Structural materials for sulfuric acid vaporizers and concentrators are exposed to high-temperature corrosive environments. Immersion tests were carried out to evaluate the corrosion resistance of ceramics and to evaluate corrosion-resistant metals exposed to environments of aqueous sulfuric acids at temperatures of 320, 380, and 460 °C, and pressure of 2 MPa. The aqueous sulfuric acid concentrations for the temperatures were 75, 85, and 95 wt%, respectively. Ceramic specimens of silicon carbides (SiC), silicon-impregnated silicon carbides (Si–SiC), and silicon nitrides (Si₃N₄) showed excellent corrosion resistance from weight loss measurements after exposure to 75, 85, and 95 wt% sulfuric acid. High-silicon irons with silicon content of 20 wt% showed a fair measure of corrosion resistance. However, evidence of crack formation was detected via microscopy. Silicon enriched steels severely suffered from uniform corrosion with a corrosion rate in 95 wt% sulfuric acid of approximately 1 g m⁻² h⁻¹. Among the tested materials, the ceramics SiC, Si–SiC, and Si₃N₄ were found to be suitable candidates for structural materials in direct contact with the considered environments.     

Effective thermal conductivity of compressed woods

Compression is one solution to improve the strength of softwoods. The effective thermal conductivities of compressed Japanese cedars (cryptomeria japonica), which were compressed in the radial direction of the wood, were measured. Both the effective thermal conductivities in the tangential and fiber directions increase proportionally to the density increment due to the compression. However, the thermal conductivity in the radial direction (compression direction) increases slightly with the density increment. Numerical computations were conducted to explain the characteristics of thermal conductivity in the radial direction by using a microscopic heat conduction model for the compressed wood. The numerical results were compared with the measured values. And the physical mechanism of the heat conduction in the compressed woods is discussed.     

High-performance carbon counter electrode for dye-sensitized solar cells

Here, we reported that a new carbon electrode prepared with an activated carbon was superior to a Pt sputtered electrode as the counter electrode of dye-sensitized solar cells. The photovoltaic performance was largely influenced by the roughness factor of carbon electrode. The open-circuit voltage increased by about 60 mV using the carbon counter electrode compared to the Pt counter electrode because of positive shift of the formal potential for I₃⁻/I⁻ couple.     

Simulation study of electrical dynamic characteristics of lithium-ion battery

The electrical dynamic characteristics of a lithium-ion battery have been simulated by an equivalent circuit, which is derived from the measured impedance. The transient voltage response to the various kinds of applied current waves such as single pulse, single rectangular, triangle, and sawtooth waves is experimentally examined and calculated by using the numerical Laplace transform with the equivalent circuit. The experimental and calculated results are compared and discussed, focusing on the range of current where the linear relationship is valid. Changing the time range, the state of charge (SOC) and the battery temperature as parameters, their influence on the linear range of the applied current has been investigated.     

Growth features of crystals in laser‐welded aluminium and aluminium alloys

In the present work, the increase in the basicity index of the slag system of the flux, represented by the ternary system of MnO–SiO₂–CaO oxides, is evaluated. The increment of the basicity index is performed by the addition of CaO, keeping the MnO/SiO₂ percentage relation of the system constant, in order to evaluate the behaviour of the chemical composition resulting from the metal deposited by SAW. As a result, it is possible to intensify the Mn transfer to the deposited metal and at the same time attenuate that of the Si, S, P and the carbon remains basically unalterable. All this makes it possible, in combination with low-manganese wire, to obtain similar results to those obtained with fluxes of lower basicity in combination with medium manganese wires.