Jo Oct 16, 2025
Chaotic mapping has been widely used in cryptography for its dynamic nature, but it has some unsuitable security characteristics due to its limited precision. Therefore, improving the characteristics of chaotic mapping is essential for improving chaos-based encryption algorithms.
Choe Song Bom, a researcher at the Faculty of Information Science and Technology, has presented a plan to improve one-dimensional logistic mapping by parameter variation with delay coupling method and feedback control, proposed a new two-dimensional chaotic mapping, and further enhanced its randomness by selectively shifting the position of generated chaotic sequences. In addition, he has proposed a new image encryption algorithm based on the improved chaotic mapping.
The results of various simulation experiments showed that the proposed image encryption algorithm provides high-level security and is superior to the previous chaos-based encryption algorithms.
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Jo Oct 14, 2025
Concentration of some heavy metals such as As, Hg, Pb, Cd and Sn in food is a very important hygienic index. Because several of these elements are highly toxic, determining them at low concentration levels is of great importance for food factories.
In recent years, hydride generation atomic fluorescence spectrometers useful for determining the elements that form hydrides such as Pb, Hg, Cd, Zn, As, Sb, Bi, Ge, Sn and Se have been developed. Hydride generation technique provided a method for concentrating analytes and led to enhancing the detection limits for these elements by a factor of 10 to 100. This single-channel hydride generation atomic fluorescence spectrometer (HG-AFS) has some shortages like impossible simultaneous determination of several elements and long analysis time.
The advent of atomic fluorescence spectrometers equipped with a non-dispersive system led to the development of a multichannel atomic fluorescence spectrometer for simultaneous determination of several elements. The non-dispersive atomic fluorescence spectrometry (NDAFS) has several advantages of simple and low-cost instrumentation, adaptability to multi-element analysis, and highly-sensitive and simultaneous collection of energy from multiple lines.
There have been many reports on simultaneous determination by this spectrometer, but most of them are for two elements, and the only three-element simultaneous determination is As-Sb-Se simultaneous determination.
Ri Un Hui, a researcher at the Faculty of Metal Engineering, has studied the optimal conditions and method for simultaneous determination of As, Sn and Cd, and successfully introduced them into the analysis of several kinds of food.
This method can be widely used for analyzing not only food but also soil, water, biological samples, the environment, etc.
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Jo Oct 13, 2025
Welding has been widely used in many fields of industry. Its advantages include high efficiency of joining, simple operation, good flexibility and low cost. However, uneven temperature distribution inevitably exists during welding. Such uneven temperature distribution causes rapid thermal expansion, which leads to heterogeneous plastic deformation by thermal constriction in and near the welding joint. Thus, residual stress appears in welding structure after cooling.
In order to accurately predict welding residual stress and deformation, welding temperature distribution should be simulated properly. What is important in welding simulation is to apply suitable heat source models according to the welding methods. The models include spot heat source model, line heat source model (HSM), surface heat source model and volume heat source model. As heat is transferred to workpieces in the form of volume in most welding methods, volume HSM is most widely used. Volume HSM is classified into semi-sphere HSM, elliptical heat source model and double-elliptical heat source model. At present, double-elliptical model is accepted as the most appropriate heat source model for gas metal arc welding (GMAW) with steep temperature slope at the front section of the welding pool and smooth slope at the rear section.
Cha Kwang Jin, a researcher at the Faculty of Materials Science and Technology, has performed a welding temperature simulation by FEM and predicted temperature distribution while varying welding parameters such as welding current.
For the simulation, he employed ANSYS software widely used for welding simulations across the world that offers the most approximate parameters to the desired result by varying several parameters of its own optimization module.
The FEM analysis results and experiment results of welding show that the analysis result is accurate when Gauss-distributed double-elliptical heat source for GMAW process simulation is used.
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Jo Oct 9, 2025
Recently, attempts have been made to use fiber-reinforced plastic composites as aircraft structural materials, but aluminum alloys still have 70% utilization as airborne fuselage materials. In particular, high-alloy duralumin Du16 has been used as the main material for manufacturing aircraft fuselage surfaces and blades.
The body material of an airplane varies in its nature with the speed of flight, so it is very important to determine whether a given alloy can be used as a body material for subsonic and supersonic aircrafts.
Previous studies show that the grain growth of duralumin alloy at annealing temperatures above 300 °C leads to poor mechanical properties, but they failed to deal with annealing at temperatures below that. What is more, they did not cover the changes in the texture and property with temperature when the body of an airplane is heated during the flight.
Therefore, Ri Hyon Song, a researcher at the Faculty of Materials Science and Technology, has measured the fuselage heating temperature range by means of simulation analysis and investigated the changes in the texture and property with annealing temperature.
First, he designed a model of a supersonic aircraft and conducted a simulation analysis of the temperature distribution of the body surface according to flight speed. Then, he performed hardness and microstructure observation experiments.
The results showed that Du16 alloy does not degrade its hardness at 100℃ for 8 hours of annealing, and above 300℃, the hardness is gradually degraded with time.
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Jo Oct 6, 2025
Electrospinning is widely used as a versatile and convenient method for producing nanofibers. However, the drawback of this method is its low productivity. To overcome this drawback, various kinds of electrospinning methods have been developed. They are divided into two broad sorts. One is multi-needle electrospinning, which uses a spinneret consisting of many needles, and the other is needleless electrospinning. Multi-needle electrospinning finds its wide application in the field of advanced materials as it enables controlling the properties of nanofibers as well as producing special kinds of nanofibers such as core-shell nanofibers.
In multi-needle electrospinning, strong electrical interaction between the spinneret needles caused by the increased number of nozzles breaks the uniformity of electric field at the spinneret needle tip, which consequently destabilizes the flow of polymer jet and degrades the quality of fibers. Therefore, keeping the electric field uniform at the spinneret needle tip is a key factor for obtaining good-quality nanofibers.
There have been many studies so far to improve the uniformity of electric field. However, few of them dealt with optimal structure parameters to maximize the uniformity of electric field at the spinneret needle tip. In addition, there are almost no reports on the investigation of uniformity of electric field while varying the parameters of a dielectric medium such as the length, the diameter and the relative permittivity when it is inserted between spinneret needles.
Jang Kum Chol, a researcher at the Institute of Nano Science and Technology, has investigated the effects of geometric parameters of a dielectric medium around the spinneret needle on electric field uniformity in order to obtain uniform electric field distribution at the spinneret needle tip.
He simulated the electric field distribution using COMSOL Multiphysics 5.4 and optimized the dielectric medium parameters to improve the electric field uniformity by using Taguchi method.
As a result, he has confirmed that the electric field uniformity is the best when the diameter, length, arrangement distance and relative permittivity of a dielectric medium are 1.5mm, 5mm, 4mm and 2.3, respectively.
After optimization, the uniformity was over 1.27 times higher than before optimization.
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Jo Oct 2, 2025
Research on temperature field is of great importance for hot-pressing processes of ceramic materials. It affects both the uniformity of materials and the properties of ceramic products. Additionally, non-uniformity causes formation of thermal residual stresses during sintering.
Previous works mostly focused on the sintering of traditional ceramics and very few of them aimed at the hot pressing of modern ceramic materials.
Mun Hyok Chol, a researcher at the Faculty of Chemical Engineering, has proposed a heat transfer model for a system comprised of the mixture of Al2O3 and TiB2 and a graphite mould. Then, he has established a new method of determining the coefficient of heat transmission of ceramic composite by taking into account the change of porosity with sintering temperature, and simulated the temperature field using the COMSOL Multiphysics software.
He set the most suitable heating rate as 0.5K/s by analyzing both material properties and manufacturing efficiency.
The simulation result has shown increased initial relative density of blanks and more uniform temperature distribution of the system during hot pressing, which leads to further improvement of the physical and mechanical properties of ceramic composite materials.
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