Jo Jul 28, 2026
Chaotic map which has excellent unpredictability and complexity is extensively used in various fields such as information security, information communication, system control, etc., and thus, there is an intensive research work to improve its chaotic characteristics.
Generally, digital images, compared to text data, have some characteristics different from ordinary data, such as 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 a fast and secure algorithm is needed for its encryption.
Jong Chol Min, a researcher at the Institute of Information Technology, studied the excellent chaotic performance of 2D-ICCM (2D Infinite Collapse Coupling Map) proposed by a researcher and proposed a simple-structured and fast-speed pixel-level image encryption algorithm using 2D-ICCM.
In image encryption algorithms using chaotic maps, it is common to repeat permutation and diffusion processes several times in order to increase the complexity of encryption and decryption processes. However, it results in degradation of the whole performance of encryption scheme, especially degradation of the ability to resist against cropping and noise attacks in the decryption process. Therefore, he bolstered the system complexity by using the chaotic output sequence used in each step interchangeably while repeating the permutation and diffusion process only twice.
He verified through various experiments that the pixel-level image encryption algorithm using 2D-ICCM has comparatively better chaotic performance than the previous 2D chaotic maps and algorithms.
His paper “A New Color Image Encryption Algorithm Using 2D Chaotic Map” was presented at “2025 10th International Conference on Intelligent Information Technology (ICIIT 2025)”.
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Jo Jul 27, 2026
In neural machine translation (NMT), BPE is usually used to limit vocabularies since a large number of vocabularies have a negative impact on training. Use of BPE could limit the number of vocabularies to some extent, but word alignment by attention mechanism cannot be done correctly since vocabularies are not properly segmented into word stems.
In neural machine translation, a huge number of vocabularies from the corpus have a negative impact on its training, and the longer the length of sentences which reflects the number of tokens is, the longer the training time gets. Therefore, it is important to perform good tokenization for minimizing the number of vocabularies and the length of sentences.
Kim Tong Gwon, a researcher at the Institute of Information Technology, proposed a stem and ending based tokenization (SEBT) method for improving the accuracy of word alignment by applying to tokenization a stem and ending dictionary which was made by segmenting BPE tokens into stems and endings.
This method has four advantages:
First, it is possible to reduce the number of vocabularies by correctly segmenting the stems and endings of Russian and Korean.
Second, it can improve learning efficiency by relieving the sparse word problem.
Third, it can improve the alignment accuracy between Russian and Korean tokens in the attention mechanism.
Fourth, it can reduce the training time since the sentence length is not increased after tokenization.
The experiments showed that this approach improves the performance of Russian-Korean NMT by improving the alignment between Russian and Korean tokens during the training of Russian-Korean neural machine translation and by reducing the number of Russian and Korean vocabularies.
You can find more information in his paper “SEBT: Word Stem and Ending based Tokenization in Russian-Korean Neural Machine Translation” in “2025 10th International Conference on Intelligent Information Technology (ICIIT 2025)”.
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Jo Jul 26, 2026
Since the impact performance of a drill is the main parameter for determining the drilling efficiency, study of the impact performance of a drill has a crucial influence on its productivity. As the impact energy of a rock drill is an important characteristic to evaluate its performance, many researchers have proposed various methods of measuring impact energy in order to evaluate it accurately.
Evaluating the impact performance of a rock drill by their methods requires a standardized rock sample in advance. Therefore, it is difficult to apply them to the performance test of a rock drill in batch production processes.
Yang Un Hyok, a section head at the Faculty of Mining Engineering, proposed a new structure of measuring device for estimating the impact energy of a percussive drill and analyzed its characteristics.
In the newly proposed measurement device, the maximum value of the pressure wave generated by the impact of 33-56J is approximately linear, with a range of 12-15MPa. It is shown that the error in the new proposed measurement device is less than 5% when the oil temperature is 10-70℃, air content is less than 2% and oil leakage is 10%.
The results of the study show that the proposed device ensures high measurement accuracy and significantly reduces damage to the sensor.
For more information, please refer to his paper “Influence of Oil Temperature, Air Content and Leakage in Hydraulic Measuring Device for Estimating Impact Energy of Rock Drill” in “Proceedings of KUTIC-2025”.
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Jo Jul 24, 2026
The mixture formation process in diesel engines consists of injection by which fuel is divided into small droplets, heating and evaporation of fuel, and mixing of fuel droplets and air in the combustion chamber. In other words, the shape and position of combustion chamber, fuel injection and air motion play a crucial role in the formation of mixture. Thus, many studies have been carried out in order to improve the mixing performance of fuel and air in the cylinder and improve combustion efficiency.
However, it was not fully taken into account that mass flow rate of intake air could be reduced when air swirl intensity was increased, while changing the inlet channel profile and the helical spiral shroud (HSS) shape of the intake valve. In addition, some attempts have been made to increase the air swirl and turbulent kinetic energy (TKE) by changing the shape of combustion chamber, but little study has been focused on improving the in-cylinder airflow characteristics by changing the eccentricity of combustion chamber.
Sin Mun Hak, a researcher at the Faculty of Mechanical Science and Technology, investigated the variation of in-cylinder swirl intensity and TKE depending on the eccentricity of combustion chamber. To this end, he conducted simulations of six series of eccentric combustion chambers.
The results showed that the air swirl intensity and turbulent kinetic energy in the combustion chamber increases as the y-axis eccentricity of combustion chamber is placed on the eccentric direction of injector and the x-axis eccentricity increases gradually from the centre of cylinder to the direction of injector. It was also shown that when the eccentricity is too large, there will be a drop in the fuel spray jet velocity or airflow separation in the region of mixture formation, resulting in a gradual increase in power and torque and then a decrease over a certain limit.
For more information, please refer to his paper “Effect of Combustion Chamber Eccentricity on In-Cylinder Air Flow and Combustion Process in Direct Injection Diesel Engine” in “Proceedings of KUTIC-2025”.
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Jo Jul 23, 2026
Nowadays, most spacecraft use solar array continuously facing the sun by solar array drive assembly (SADA) to increase the energy efficiency. However, in spacecraft with rotating flexible appendages, system dynamics and control are very difficult.
There has been an extensive study on suppressing the vibration caused by flexible appendages in such spacecraft across the world. What is attracting a great deal of attention is a method by the robust controller design. However, almost all robust control systems considered only fixed flexible appendages and neglected their rotation dynamics.
Sonu Kwang, a post-graduate student at the Faculty of Aerospace Engineering, proposed an attitude control method to suppress the vibration of flexible spacecraft with rotating solar array.
First, he simplified the singular dynamic model of spacecraft with rotation of flexible appendages by introducing extended state and modal identities into a non-singular state space-formed dynamic model. Based on this simplified dynamic model, he developed a PD-type static output feedback controller that essentially guarantees asymptotic stability and disturbance rejection. Then, he designed a compensator for the extended system including a static output feedback controller in order to ensure the stability of the control system under the influence of rotations of solar array, variation of natural frequency and damping coefficients, high-order flexible modes and measurement noises.
Through computer simulations, he found that the proposed attitude control system with and without compensators stabilized the attitude within 60s and suppressed flexible vibration.
You can find the details in his paper “Vibration Suppression for Flexible Spacecraft with Rotating Solar Array” in “Proceedings of KUTIC-2025”.
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Jo Jul 22, 2026
High accuracy and machining capability are the main requirements for metal cutting operations, and high cutting speed and feed rate increase the quality of machining parts, machining accuracy and metal removal per unit time. However, tool life and material removal rates are contradictory because of higher tool temperature, accelerated wear, shorter tool life, and lower machining efficiency with increasing tool replacement time and replacement rate.
Since both material removal rate and tool life are related to cutting conditions, it is necessary to choose appropriate cutting conditions.
Ham Kum Chol, a section head at the Faculty of Mechanical Science and Technology, developed an optimization model with maximum tool wear life at constant metal removal rate (efficiency) per unit time and proposed a method of optimizing the cutting conditions affecting tool life.
The tool wear model was constructed as a polynomial regression model from the simulation data using Deform3D finite element software, and the optimization solution was performed by MATLAB’s fmincon function.
The proposed method was applied to the cutting of high-temperature alloy Ti6A14V as a machining objective, which showed improved machining accuracy and machining time of center machine.
The proposed method can be applied to the selection of cutting conditions for maximizing tool life when machining various hard-working materials.
If more information is needed, please refer to his paper “Optimization of Cutting Parameters in Milling Based on Model of Tool Wear” in “Proceedings of KUTIC-2025”.
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