Jo Aug 9, 2026
The working principle of electron microscopes is to form an image by using electron beams and electron lenses instead of light beams and optical lenses in optical microscopes. The design and focusing characteristics of magnetic lenses determine the main parameters of electron microscopes. The electro-optical (EO) system of transmission electron microscopy can be classified into illumination and imaging systems. The former consists of an electron gun and a focusing lens while the latter is made up of a sample chamber, an objective lens and intermediate and projective lenses. In an EO system, lenses are the most important components and the one that plays a crucial role among lenses is an objective lens.
There are many studies in the literature on the method of calculating the focal length of magnetic lenses in transmission electron microscopes, but these calculations are empirical, based on only pole-piece diameter, gap and the number of excitation turns in a magnetic lens. The effect of the change of various factors such as other structural dimensions, magnetic lens material and magnetic circuit configuration on the focal length is not mentioned, .
In magnetic lenses, the pole-piece diameter and the gap are of primary importance, but the magnetic circuit constituting the lens, the position of the magnetic flux-making coil, and other structural dimensions will influence the magnetic field distribution and the focal length. Therefore, the conventional focal length calculation method presents many problems in the design of real magnetic lenses.
Kim Hak Chol, a researcher at the Faculty of Electronics, proposed a new method of calculating the focal length by simulating the magnetic field distribution and trajectory of a magnetic lens.
Using a simulation tool, he set the structure dimensions, excitation conditions and material settings just like real ones and calculated the magnetic field distribution based on them. Then, he determined the focal length from the trajectory data by means of the method of calculating the focal length based on the electro-optical theory.
Unlike conventional focal length calculations, the proposed method can improve the accuracy of magnetic lens design, with all the factors affecting the focal length in consideration.
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Jo Aug 7, 2026
Accurate quantitative evaluation of the performance of pneumatic rock drills is important to improve the performance and put the design on a scientific basis.
A rock drill receives energy from a compressor or a hydraulic system and transfers impact energy through the drill and bit to crush rocks. Impact energy, the main performance index of rock drills, was estimated by many researchers in an indirect way because direct measurement is difficult.
Those measurement methods are difficult to apply to the performance tests of mass-produced drills as they require modification of the structure of percussion drills or preparation of standardized rock samples.
In view of these practical requirements, Pak Chol Hyok, a researcher at the Faculty of Mining Engineering, proposed a new structure of impact energy measurement device and analyzed its performance through simulation.
The analysis results show that the stress wave transmitted through the drill rod is converted into the pressure wave of oil filled inside the cylinder. Its maximum value is 15-28MPa, varying with position. Therefore, suitable location of measurement points can raise measurement accuracy while extending the service life of the sensor.
The newly proposed measuring device is more reliable and more convenient to operate than the method of determining the impact energy by stress wave measurement.
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Jo Aug 6, 2026
Generally, the design of small acoustic devices for mobile phones uses acoustic analysis techniques involving equivalent circuits. This acoustic analysis technique is an approach to find acoustic parameter values on acoustic equivalent circuits from the size values of angular acoustic device by the classical acoustic theory-based acoustic theory equation, and to predict acoustic properties electronically based on their acoustic parameters. Thus, it provides simple modeling and it does not take a long time to interpret. However, this acoustic analysis technique cannot predict exact acoustic characteristics because it cannot represent the variation of acoustic parameters due to the change of the “position relationship” or “geometry” in acoustic devices.
Han Myong U, a researcher at the Faculty of Communication, proposed an acoustic parameter estimation method which verifies, by finite element method, the structure of resonance frequency response due to the acoustic porthole position that could not be explained by the original equivalent circuit analysis method, and explains acoustic weight and acoustic capacity.
A genetic algorithm has been used for traditional acoustic parameter estimation, but it requires a very long time to estimate the correct factor because it depends on the search by mutations around the optimal solution. The proposed estimation method uses a hybrid genetic algorithm that switches to simulated annealing that performs well local retrieval after convergence to some extent around the optimal solution by a genetic algorithm.
He compared the measured results with the simulation results by the proposed method to validate its effectiveness. The results showed that the proposed estimation approach can accurately estimate acoustic capacity with respect to resonant frequency, and acoustic mass parameters, and it is possible to estimate acoustic parameters with respect to the position or shape of a compact acoustic device.
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Jo Aug 4, 2026
Lithium has been used as molten salt in aluminum electrolytic baths, as an additive in glass and ceramic manufacturing, and for lubricant production. With the development of science and technology, the application range of lithium has been further extended—it is particularly widely used in the fields of battery, rubber, refining, refrigeration, welding, medicine, aviation and nuclear power. Lithium isotope 6Li has become the main material of thermonuclear reactions, and lithium is an important energy source for the development of human society, with its wide use in thermonuclear reactions and high-energy lithium batteries. Among more than 130 lithium minerals known so far, the most industrially-valued mineral is spodumene.
Spodumene is being separated by various methods, among which flotation is dominant for lithium ore.
Previous studies on the flotation of spodumene mainly focused on cleaning using anion collectors, which indicates that reagent systems are different depending on the type and amount of gangue minerals present in the ore.
Kim Song Chol, a researcher at the Faculty of Mining Engineering, investigated the effects of several reagents on the flotation performance of spodumene via flotation experiments, and evaluated the mechanism of various components in fatty acid soap on spodumene surface via quantitative mechanical simulations.
The results of an individual experiment and an optimization experiment showed that a concentrate with Li2O grade of 2.55% can be obtained with recovery of 76.89% in roughing flotation.
The simulation results of the interaction energy between spodumene {110} surface and several kinds of fatty acid soap showed the following order of adsorption strength; sodium linoleic acid > sodium linolic acid > sodium oleic acid > sodium palmitin acid > sodium stearic acid.
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Jo Jul 31, 2026
The displacement ventilation system (DVS) is one of the mechanical ventilation systems which blow the air with lower temperature than indoor air from the lower part of a room and cause upward moving of indoor air by buoyant force to exhaust it at the ceiling.
As DVS is aimed at meeting only the requirements of workplaces, the thermal and concentration stratification is formed between lower and upper parts. DVS makes the quality of the air better and exhausts the polluted air effectively, and therefore the saving efficiency of energy is remarkable. In the designing of DVS, the height of thermodynamic stratification has to be controlled to be higher than that of the workplace for people, but it should not be too high. This is because being too high might cause an increment in the amount of air blast, which results in waste. Thus, the determination of the height of thermodynamic stratification is one of the vital problems in the application of DVS.
Paek Myong Chol, a section head at the Faculty of Thermal Engineering, analyzed the characteristics of indoor airflow and temperature distribution in the hybrid displacement ventilation system (HDVS) where a vertical supply duct was installed at the middle height of a building by computational fluid dynamics (CFD). Then, he investigated the specific influence of the velocity of air inflow and the length of the supply duct on the air temperature.
The results show that the proposed system saves 35kw of energy compared to the mixing ventilation system, which leads to the annual energy saving of about 80 000kW·h.
If more information is needed, you can refer to his paper “Energy Saving Characteristics of Hybrid Displacement Ventilation System with Vertical Supply Duct” in “GAS Journal of Engineering and Technology” (SCI).
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Jo Jul 30, 2026
All the digital data stored, copied and distributed on the network have their own specific information, and digital images, as one of the fastest multimedia formats that can deliver their information in a visual way, particularly have a great amount of information. Most of the digital images transmitted through network are private, and especially, those with sensitive information such as medical diagnostic images can lead to irrevocable disaster when they are disclosed to be abused. Therefore, it is very important for digital images to be secured.
In general, digital images, when compared to text data, are characterized by very large capacity, high overlap, and strong correlation between adjacent pixels. On the other hand, digital image data requires strong real-time property in communication, storage and distribution, and hence, it requires a prompt and secure image encryption algorithm. From this necessity, many precedent researchers have proposed some improved chaotic maps and applied them to various image encryption algorithms.
Song Ok Chol, an institute head at the Institute of Information Technology, configured a novel 3D-ICCM (3D Infinite Collapse Coupling Map) with better chaotic performance by combining three 1D infinite collapse maps that has the best chaotic characteristics among the existing 1D chaotic maps, and analyzed its chaotic characteristics through a comparison with the previous 3D-ICM. Then, he proposed a new simple-structured pixel-level image encryption algorithm and evaluated its performance by applying the proposed 3D-ICCM.
The experimental simulation and analysis show that the proposed 3D-ICCM and image encryption algorithms have excellent performance.
For more information, please refer to his paper “Robust pixel-level image encryption algorithm using 3D infinite collapse coupling map” in “Multimedia Tools and Applications” (SCI).
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