Jo Mar 26, 2025
Rapid development of computer network increases the applications of e-learning, which provides teachers and students with convenience and flexibility.
In the environment of distance education, interaction is a very important factor for raising the efficiency of teaching and self-study. Especially, in distance education of design project which deals with the designing of circuits or machinery, ensuring the interaction becomes more important since explicit and implicit knowledge hold large portion at the same time.
To raise the interaction in the distance learning, Jong Kum Sil, a lecturer at the Faculty of Distance Education, has proposed an e-learning system where a virtual board is introduced.
The main system consists of a teacher’s computer equipped with various exam and plagiarism-prevention tools, and client computers connected with the teacher’s by network. It also includes various tools for assessing the students’ design projects and the virtual board which is connected with teacher’s computer, so the students can ask questions online through the virtual board for teacher’s guidance. By inserting authentication to the students’ multi-media, she raised the fairness and objectiveness in assessing the students’ tasks.
For further details, please refer to her paper “An interactive e-learning system equipped with plagiarism detection tool for the distance education of the design course” in “INFORMATICA” (SCI).
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Jo Mar 25, 2025
Hydrogen sulfide is a polluting gas that is produced in various industrial fields including oil processing and fertilizer production. It is also generated in the course of people’s living. Hydrogen sulfide is very toxic to human health. Hydrogen sulfide can cause blood poisoning and its high concentrations (higher than 250ppm) may lead to death.
Therefore, detection of toxic gases has been a major focus of sensor research in recent years. Accurate measurement of hydrogen sulfide gas concentration is very important for protecting human life and health. So far, various sensors for detecting hydrogen sulfide gas have been developed.
Chemoresistive sensors based on conductive polymer are cheap and operable and responsive at room temperature. In particular, nanocomposites based on conductive polymer and metal oxide nanoparticles have excellent nanostructural properties and high sensitivity and their responses to gases are fast.
Cha Ho San, a student at the Faculty of Chemical Engineering, has prepared a chemoresistive H2S gas sensor based on PANI/TiO2/CuCl2 nanocomposite (PTCN) impregnated fabric by in situ synthesis method (ISM).
For more information, please refer to his paper “Chemoresistive H2S sensor based on PANI/TiO2/CuCl2 nanocomposite impregnated conductive fabric using TOPSIS and Taguchi method” in “Engineering Research Express” (SCI).
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Jo Mar 23, 2025
Elimination of parasitic vibration presents itself as a nuisance for the industrial application of self-mixing sensors. The parasitic vibration is the vibration of the self-mixing sensor itself, which has an evil effect on the measurement accuracy. Although the elimination of the parasitic vibration is very important, there have not been enough studies on it.
A solid-state accelerometer (SSA) is often used for the removal of parasitic vibration. The SSA coupled with the SM sensor measures the acceleration of the parasitic vibration and it is double integrated to obtain the displacement, which is subtracted from the displacement reconstructed from the SM sensor to extract true target motion. The fatal shortcoming of the elimination of parasitic vibration based on SSAs is that the error of the SSA has a direct effect on the measurement. The error of the SSA keeps on being accumulated with time in a real-time displacement measurement in particular.
Kim Chol Hyon, a section head at the Faculty of Physical Engineering, has proposed a method of eliminating the hand-induced parasitic vibration based on FFT.
His method can provide the displacement reconstruction error less than 30nm by taking a proper cutoff frequency and data length and it can be applied to the measurement of mechanic vibration of 10 to 1 000Hz. Besides, this method can be applied to all cases where there is some difference between the main frequency of parasitic vibration and the frequency of the measured object.
For more information, please refer to his paper “Elimination of hand-induced parasitic vibration in self-mixing displacement measurement based on FFT” in “Applied Optics” (SCI).
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Jo Mar 21, 2025
Self-mixing interferometry (SMI) is well known as a very effective technology for the measurement of displacement, vibration, velocity, etc. due to its unique advantages. Hence, many achievements have been made in the research of the SMI theory and its application.
Unfortunately, however, few studies on the stability of self-mixing signals (SMSs) can be found. In fact, stable SMSs are not readily obtained because many factors have an effect on their stability. The injection current of the semiconductor laser (SL) in particular has a vital effect on the stability.
Kim Chol Hyon, a section head at the Faculty of Physical Engineering, has investigated the effect of the injection current on the stability of SMSs in SMI theoretically and experimentally while varying the injection current, and consequently found the law of stable injection current.
This law demonstrates that there exist stable injection current points suppressing bifurcations, and their positions depend only on the external cavity length. The law advises driving the SL at an injection current corresponding to a non-bifurcation range in order to acquire clear SMSs favorable for displacement reconstruction.
For further details, please refer to his paper “Regularity of bifurcation in a self-mixing laser diode” in “Applied Optics” (SCI).
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Jo Mar 19, 2025
The deck, bottom, side shell, bulkhead structures and superstructures consist of stiffened panels and grillages, which serve as the most important components in ship structures. The ship grillage structure consisting of several girders crossing each other and a plate is a complex structural system. In a structural system consisting of several structural components with several possible failure modes, system failure generally occurs as a complex combination of failure modes.
However, as the stiffeners and transverse girders are related to each other in the ship grillage structure which consists of several stiffeners, transverse girders and plates, it is incorrect that the grillage will fail if any of the stiffeners or transverse girders fail. Therefore, the system reliability of the ship grillage should be estimated by taking account of all possible failure modes and paths of the stiffeners and transverse girders. In addition, if some stiffeners fail, the remaining (unbroken) stiffeners will be subjected to the external load, which leads to the stress redistribution for them.
Ri Yong Ho, an institute head at the Faculty of Shipbuilding and Ocean Engineering, has proposed a method for estimating the system reliability of ship grillage under combined axial compression and lateral pressure load, and estimated the structural system reliability on the buckling collapse of the bottom structure of an oil tanker.
First, he modeled the grillage into a structural system consisting of several longitudinal stiffeners and transverse girders with attached plating in parallel, respectively, and considered how the external load is distributed and transferred to the longitudinal stiffeners and transverse girders. On this basis, he estimated the reliability of each stiffener on the buckling collapse. Then, he performed an analysis of the system reliability of the ship grillage, considering the stress redistribution in the remaining unbroken stiffeners after any one of the stiffeners failed.
The results of the comparison with the literature show that the proposed method can more realistically and accurately evaluate the reliability of the structural system.
You can find the details in his paper “A method for estimating the system reliability of ship grillage structure” in “Marine Systems & Ocean Technology” (SCI).
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Jo Mar 18, 2025
PEF, a novel non-thermal processing technology, which started to be applied to liquid food processing, has the potential to be used effectively in extracting useful ingredients from microorganisms, plant cells and animal cells. Unlike heat treatment, PEF treatment can preserve the natural favor, nutrients and functions of liquid foods such as fruit juice, vegetable juice and milk. Thus, it is regarded as a technology that corresponds to the increasing demand for fresh food.
During PEF treatment, high electric field (of 10~50kV/cm with a pulse duration of 1~100㎲) is applied to the target liquid. Then, the biological cells under the PEF undergo electroporation, which makes holes in the cell membrane. As a result, the intracellular contents leak and therefore the cells die off. This is the very principle of pasteurization or extraction methods.
PEF chambers have three main kinds―parallel-plate, co-axial, and co-linear―and other kinds derived from them. Most continuous PEF systems use co-linear chamber. Its drawback, however, is the non-uniformity of processing parameters in the chamber. The non-uniformity of the electric field in the treatment chamber remarkably increases the temperature in the regions with electric field strength peaks, and the liquid food passing through this region is overheated, which produces undesirable results like quality degradation due to contamination and composition modification. On the other hand, the lower electric field could rather be responsible for under-processing and therefore increases energy consumption alone due to Joule heat.
Based on the analysis of the previous studies, Kim Jin Hak, a researcher at the Faculty of Physical Engineering, has proposed a co-linear treatment chamber with sub-electrodes to increase the uniformity of the electric field intensity distribution inside the treatment chamber and to increase the volume of the treatment chamber, and investigated the effect of the sub-electrodes on the uniformity of electric field, the average electric field strength and the throughput of chamber.
The simulations and experiments have shown that the improved treatment chamber with sub-electrodes can produce more uniform fields in the treatment space, not only to ensure the uniformity of treatment but also to increase the throughput and reduce power consumption.
For more information, please refer to his paper “Improvement in uniformity of co-linear pulsed electric field treatment chamber by sub-electrodes and its optimization” in “Journal of Food Process Engineering” (SCI).
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