Jo Apr 29, 2025
The exhaustion of fossil fuel resources and constant evil effect of the global warming due to greenhouse gas emission needs the introduction of new kinds of energy system. Now, hydrogen energy system is attracting a great deal of attention as a reasonable energy system that can solve almost all kinds of environmental problems.
Proton exchange membrane (PEM) water electrolysis is considered as a main option to integrate and to miniaturize hydrogen energy systems. An advantage of PEM water electrolysis is short start-up time, high current density, high pressurized hydrogen production possibility and no use of corrosive solutions like alkali.
The kinds and properties of an anodic porous transport layer (PTL) play an important role in water management and ohmic resistance reduction. Some materials such as porous carbon materials (carbon fiber or carbon paper) and metals (Ti or Ni) can be used as the PTLs of PEM water electrolyzers.
Jang Tae Il, a researcher at the Institute of Nano Science and Technology, has concluded that the hot-pressed carbon paper is a superior PTL for improving the conductivity of the catalyst coated layer (CCL), and intensified his research to use carbon paper as an anodic PTL.
First, he found that anti-oxidized and hydrophilically treated carbon paper could be used as anodic PTL. Then, during the formation of a micro protective layer (MPL) by protective agents, he conducted plasma treatment of the hydrophobized carbon paper followed by impregnation with the hydrophilic polymer Nafion solution before repeating immersion-drying processes several times and heat treatment at 140℃ for 30 min to use carbon paper as anodic PTL.
PEM water electrolyzer prepared with the hydrophilic anodic PTL displayed desirable performance; initial voltage at 1.2A·cm-2 of current density at 80℃ was 1.76±0.02V, and finally measured voltage 1.84±0.02V after 6 270h of testing.
For more information, please refer to his paper “Hydrophilic treatment of carbon paper for anodic porous transport layer in proton exchange membrane water electrolyzer” in “Reaction Kinetics, Mechanisms and Catalysis” (SCI).
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Jo Apr 28, 2025
Commercial pure titanium (Cp Ti) and Ti alloys have good mechanical properties, excellent biocompatibility, corrosion resistance and specific strength, and most suitable characteristics required for biomedical applications. So, they have been widely used in many biomedical applications including hip joints, dental implants, etc. Especially, the alloys with lower modulus are desired because the moduli of alloys are required to be much more similar to bone.
There are many kinds of Ti alloys applicable to biomedical applications. To evaluate the performance of Ti alloys, it is necessary to consider the multiple biomedical and mechanical properties comprehensively, not individually. Therefore, Ti alloy selection becomes a multi-attribute decision-making (MADM) problem for evaluating the multiple candidate Ti alloys in consideration of their multiple conflicting attributes and selecting the best one among them, and it could be solved using the MADM methods.
Many works have applied the multiple MADMs to solve the biomaterials selection problems. However, the previous works have the following shortcomings: (1) they do not reflect the preference-weights of each MADM in the integrated ranks, and (2) they determine only the integrated evaluation ranks of candidates, and do not determine the integrated evaluation values of candidates.
Yang Won Chol, a researcher at the Faculty of Materials Science and Technology, has proposed a new integrated MADM methodology based on the integrated comprehensive evaluation index (ICEI) of candidates: ICEI-MADM.
The ICEIs are the preference-weighted averages of comprehensive evaluation indices (CEIs) of candidates obtained from individual MADMs, and the preference-weights are calculated by the normalized average correlation coefficients between rankings from the individual MADMs.
To demonstrate the effectiveness of the proposed method, he applied the method to the comprehensive evaluation of the performance of biomedical Ti alloys and the selection of the best of them.
For more information, please refer to his paper “Integrated multi-attribute decision-making methodology based on integrated comprehensive evaluation index: application to titanium alloy selection” in “Applied Physics A” (SCI).
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Jo Apr 26, 2025
The Interior Permanent-Magnet Brushless DC Motor (IPMBLDCM) without exciting winding and exciting source is widely used to replace traditional DC motors for subway locomotives. IPMBLDCM is gaining a great deal of interest for subway locomotive applications due to its high efficiency, simple control mode and small size.
PMBLDCM has a wide speed regulation range and its start current, start torque and starting time are small. Also, PMBLDCM generates enough torque and speed by the combination mode of motor/generator. From zero to base speed, it is dependent on applied voltage, and above the base speed, it is dependent on flux weakening by torque angle.
Cha Myong Song, a section head at the Faculty of Electrical Engineering, has proposed a winding design and lead angle control method for the maximum speed of an IPMBLDCM for subway locomotives.
The maximum speed of the IPMBLDCM is regulated by the linkage flux and armature reaction by lead angle control because permanent magnet magnetomotive force (mmf) cannot be regulated directly. The maximum speed of IPMBLDCM for the subway locomotive is 2.34 times the rated speed. As the speed regulation ratio is larger than 2, the maximum speed of motor must be ensured by lead angle and conductors per slot. If the lead angle is regulated, no-load speed is increased by changing linkage flux at no-load state and the rated speed is increased by armature reaction.
He simulated the relation between the speed, torque, output power and efficiency for the lead-angle and conductors per slot by means of Ansoft Maxwell/RMxprt. The simulation results verified that the speed, torque, output power and efficiency are constant in the range of 47°-68° and the maximum speed is 1948r/min. The experimental results indicated that the operation of the IPMBLDCM is stable at the maximum speed.
For more information, please refer to his paper “Winding Design and Lead-Angle Control for the Maximum Speed of an Interior Permanent-Magnet Brushless DC Motor” in “Journal of Electrical Power & Energy Systems” (SCI).
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Jo Apr 25, 2025
Low-pressure glow discharges (LPGD) are of topical interest for many applications such as lasers, plasma treatments and illuminators.
Simulations of LPGD have been reported in many works. Most of the numerical models for LPGDs used the monoatomic gases (especially argon) as background gases and failed to consider the excited species, which is essential for energy transport and chemical reaction mechanisms in plasma simulations and provides a more comprehensive understanding of the plasma dynamics.
Lattice Boltzmann Method (LBM) has several advantages such as simple calculation procedure, easy handling of complex geometries and simple implementation of parallel computation. In the last decades, the LBM has been utilized as an attractive method for fluid dynamics simulations such as multi-phase flows, multi-component flows and reactive flows.
In the applications of the LBM for plasma simulations, the coupling scheme of electrons and heavy species is important for the accuracy and stability of numerical simulations because of the huge difference between their parameters. For this combination, some interpolations and assumptions, which were used in previous studies, might lead to numerical errors.
Kim Yong Jun, a researcher at the Faculty of Physical Engineering, has proposed a mathematical model that uses the LBM to simulate the DC argon glow discharge.
He obtained the DC glow discharge through one- and two-dimension analyses, and compared them with the previous results.
The proposed model can be used as a mathematical model for simulating the nonequilibrium atomic (or molecular) plasmas with not only multi-components and multi-reactions, but also several electrode structures.
You can find more information in his paper “Lattice Boltzmann Simulation of Direct-current Glow Discharge at Low Pressure” in “International Journal of Modeling, Simulation, and Scientific Computing” (SCI).
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Jo Apr 24, 2025
Birds damage not only farms, orchards, fish farms, airports but also industrial and urban environments. Common methods for preventing bird damage include the use of scarecrows, the use of chemicals, and the use of nets. The method of scarecrows is not effective because of the fast adaptation of birds, the method of chemicals is effective only in small areas, and the method of nets is expensive.
In recent years, there have been many studies using sound waves, ultrasound and laser for bird repelling. The sonic method is difficult to prevent the adaption of birds, and the ultrasonic method has a small prevention area. Since the automatic laser bird repeller repeats illuminating the laser beam along a certain trajectory at regular intervals regardless of the presence or absence of birds, it is difficult to repel birds as soon as they appear in a certain position.
Pyon Su Bong, a section head at the Faculty of Metal Engineering, has developed a laser bird repellent system for scaring birds away as soon as they settle in the area under observation by a camera.
The object classification technique using the Caffe framework detects the bird in real-time captured images of a PTZ camera over a large area, and when a bird settles on an object in the area, the PTZ camera equipped with the laser beam generator is steered to the target bird, thereby scaring the bird away by attacking it by the laser beam.
For more information, please refer to his paper “Development and Efficacy of Laser Bird Repeller with PTZ Camera and Caffe Framework” in “Earth Sciences and Human Constructions” (SCI).
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Jo Apr 23, 2025
Water is one of the most important natural resources for all living organisms such as humans, animals, plants and other organisms. Providing high-quality water is a fundamental factor for human health, environmental protection and sustainable development. Water quality (WQ) is closely linked with human life and health, preservation of ecosystems, economic growth and social development.
The rapid growth and development of industry seriously affect the quality of surface and ground waters in the world. Most river systems are seriously suffering from metal pollution caused by industrial activities. In the iron and steel industry, a large amount of water is used for cooling, gas cleaning, washing operations and scale breaking, and it results in a huge quantity of wastewater. Common pollutants from wastewater include trace metals, dissolved metals, oils, suspended solids, organic compounds and inorganic pollutants. The water pollution caused by industrial activities such as iron and steel industry is one of the most critical problems that seriously threaten the ecosystem. A huge amount of industrial wastewater makes water pollution extremely serious.
Therefore, water quality evaluation (WQE) is very important in decision making for environmental protection and management. As there are different multiple WQ quality parameters, it is difficult to identify the WQ level.
Many WQE techniques have been developed and applied to WQ evaluation. Water quality index (WQI) is one of the most widely used methods for WQE.
Many works have tried to develop different WQIs by modifying the previous WQIs. By considering the previous WQE methods, the WQE problem can be considered as a multi-criteria decision making (MCDM) problem. Namely, it is a MCDM problem for evaluating and ranking the WQ levels of one or multiple monitoring sites in consideration of multiple WQ parameters.
The existing WQE methods have non-negligible disadvantages―lack of visualization and intuitivity of WQE results.
Yang Won Chol, a researcher at the Faculty of Materials Science and Technology, has developed a new effective approach to evaluate the WQ level not only quantitatively but also intuitively without requiring additional complicated graphical technique.
To this end, he proposed a new quadrant constellation graph-based water quality index (QCG-WQI) and map (QCG-WQM). The QCG-WQI evaluates the WQ level quantitatively, and QCG-WQM evaluates the WQ level intuitively.
The results of comparisons with the results obtained from the conventional multiattribute decision-making methods showed that the new method is a very effective, intuitive and quantitative water quality assessment tool.
You can find the details in his paper “A new quadrant constellation graph-based water quality index and map” in “Desalination and Water Treatment” (SCI).
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