Jo Jun 23, 2025
A superconducting magnetic bearing (SMB) composed of a high-temperature superconductor (HTS) and permanent magnets (PMs) is simple and easy in use since it is not necessary to supply a source of electricity for excitation windings. However, the SMB is restricted in the load capacity because of the limitation of the magnetization strength of the PM. Thus, it is a very important problem to improve the load capacity of the SMB.
Jo Ju Hak, a post-graduate student of the Faculty of Physical Engineering, has determined a suitable direction of the magnetization of ring-type PMs that brings about the maximum levitation force in a four-surface levitation superconducting magnetic bearing (FSL-SMB) composed of a ring-type HTS bulk and six ring-type PMs.
The simulation results show that the maximum levitation force is generated only when the upper part of PMs is combined with opposite polarity. In this case, the outer radius of inner PMs at the top and bottom sides of the ring-type HTS bulk is about 32.5mm.
The FSL-SMB with opposite polarity will contribute to the improvement of the performance of SMBs consisting of HTS bulk and superconducting magnetic bearings.
You can find the details in his paper “Analysis on magnetization arrangements of ring-type permanent magnets in four surface levitation superconducting magnetic bearing” in “Engineering Research Express” (SCI).
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Jo Jun 21, 2025
Flotation, which is a major physicochemical technology for separating and enriching desired components according to their differences in surface wettability and floatability, is a cost-effective process with low water and reagent consumption, convenient industrial adaptation and high metal recovery.
Because of this advantage, flotation technology can be actively applied to valuable mineral separation from raw ore as well as metal recovery from secondary resources, such as mine tailings, waste slag, dust, and scrap metal. Over the past few decades, there has been considerable interest in research efforts to recover heavy metals from secondary resources, resulting in the development of various separation and enrichment techniques to recover metals from waste.
In particular, various secondary resource recycling reviews have also been reported over the last ten years. However, the reagent regimes and the separation mechanisms have not been investigated comprehensively when flotation technology is applied to recover metals from secondary resources.
Ri Kyong Hun, a researcher at the Faculty of Mining Engineering, has put forward some views on the actual situation of metal recovery/removal from several solid wastes and wastewater by flotation technology.
His study was focused on the reagent regimes and physicochemical & electrochemical mechanism of flotation.
For more information, please refer to his paper “Application of flotation to recovery/removal of heavy metals in secondary resources: A comprehensive review” in “Minerals Engineering” (SCI).
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Jo Jun 20, 2025
The basic function of shock absorbers used in vehicle suspension systems is to prevent vehicles from prolonged oscillation resulted by the inhomogeneity on the surface of roads.
There are several types of dampers used in suspension systems. The most common one is a hydraulic or telescopic shock absorber. The telescopic twin-tube shock absorber is widely used for vehicles, due its simple structure and reliable security. The hydraulic shock absorber is mounted concentrically with a coil spring between the lower suspension arm and the vehicle body. In order to provide damping to the suspension system, the shock absorber dissipates energy in the compression stroke (jounce) and extension stroke (bounce) whenever a vehicle moves in shock on the road. The shock absorber is the key element of suspension systems. It is used to dissipate energy and therefore, it reduces vertical oscillation of vehicles caused by the unevenness of road surfaces.
The hydraulic shock absorber is made up of a piston rod, three chambers (compression, rebound and reserve chambers) and four valves (rebound, rebound intake, compression and compression intake-valves). The rebound and compression chambers are completely filled with viscous fluid, whereas the reservoir has only a partial filling. The rest space of the reservoir is filled with high-pressure atmospheric air or nitrogen gas.
Friction exists in all mechanical systems that have parts with relative movement. In the hydraulic shock absorber, the frictional force is caused by the contacted parts.
Previous studies have explained that the property of friction force between piston and cylinder, excessively high viscous oil property inside the shock absorber and the stiffness of the piston valve have a negative effect on the behavior of hydraulic shock absorbers.
Kwak Yong Song, a researcher at the Robotics Institute, has considered the damping characteristics of shock absorbers by the effect of friction in the guide bearing, and then investigated the damping characteristics of suspension systems.
He used the simulation program MATLAB Simulink for the dynamic response (time-displacement characteristic) to the impulse loading of an automobile suspension system.
The result has shown that the friction at the shock absorber guide bearing has a practically negligible effect on the suspension system input amplitudes of more than 40mm, but has a significant effect on the input amplitudes of less than 30mm.
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Jo Jun 18, 2025
In the research papers on uncertain linear complementarity problems, stochastic versions have been applied and attracted much attention, and the stochastic linear complementarity problem was established. In the study of the stochastic linear complementarity problems, three types of appropriate deterministic formulations have been proposed. According to these formulations, several methods and techniques have been proposed and studied.
However, if probabilistic methods are adopted to deal with uncertain linear complementarity problems, there arise the following problems. First, the probability distributions of random matrix and random vector are known in advance, which may not be appropriate in many real situations. Next, the solutions to the three formulations may not satisfy some conditions of the problem, and thus, there is no guarantee that the solutions to satisfy some “hard” conditions, i.e., those which must be satisfied in some practical problems. Moreover, the difficulty with quick computation due to the growing size of the problem is another challenge.
Ri Won Ju, a researcher at the Faculty of Management of Industrial Economy, has investigated uncertain linear complementarity problems by adopting the robust optimization technique. He focused on the solutions to Uncertain Linear Complementarity Problems (ULCP) different from the best well-known technique based on stochastic linear complementarity problems.
He proposed the notion of the ρ-robust counterpart and the ρ-robust solutions of ULCP. For three important examples of uncertainty set, namely, the unknown-but-bounded uncertainty set, the simple ellipsoidal uncertainty set and the intersection-of-ellipsoids uncertainty set, he obtained some necessary and sufficient conditions, and sufficient conditions which the ρ-robust solutions of ULCP satisfy, respectively, and discussed some special cases.
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Jo Jun 17, 2025
Compared to traditional education, online learning environments present some problems along with advantages in data collection, independence from time and space, etc. One of the problems is plagiarism in examinations and assignments. Plagiarism is a serious problem that arises in many aspects of education. If plagiarism is not handled adequately, plagiarists will benefit more with less effort.
Various methods have been proposed to prevent plagiarism. For online task execution, technical solutions such as plagiarism detection tools or various task types (e.g., face-to-face queries, task personalization) have been proposed. In some educational institutions, for example, the assignments sent by students need to be analyzed by means of plagiarism detection software. However, students tend to be more versatile and subtle in their plagiarism.
Kim Hyok, a researcher at the Faculty of Distance Education, has worked to accurately detect plagiarized drawings and reduce learners’ plagiarism behavior in online assignments by analyzing the plagiarism characteristics of machine drawings.
First, he compared the drawing images sent by students in the past three years to find plagiarism characteristics and provided feedback on the plagiarized ones to ensure that the plagiarism features were fully studied. Then, he provided feedback on the drawings presented in the last one year to confirm whether plagiarized drawings were fully detected and whether it affects the reduction of plagiarism performance of students.
He found that after feedback was provided, the detection ratio of plagiarized drawings was 89.2% and plagiarism behavior was reduced to 37.03%.
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Jo Jun 16, 2025
Deep Neural Network (DNN) is the core area of Artificial Intelligence (AI), which deals with algorithms that mechanically mimic the biological structure and function of brains. The deep learning model consists of a number of neurons, activation functions, optimization algorithms, data addition tools, etc.
Deep learning based on artificial neural networks is well suited for modeling, classifying and recognizing complex data such as images, speeches, texts, language translation, etc. However, the use of deep neural networks requires a large amount of training data. In order to identify personal information, for example, you need to record a large number of pictures and voices of each person for training. The large amount of training data leads to a huge amount of computation, and therefore, they are distributed to the computers connected to the Internet worldwide, or high-performance computers equipped with GPUs are used.
Kim Sun Il, a researcher at the Faculty of Metal Engineering, has established a detection system to increase the detection speed and rate of amorphous body detection, using deep neural network that is widely used worldwide, and evaluated its performance. He configured the deep neural network suitably for amorphous body detection based on YOLOv4 that provides high speed and detection rate for object detection.
First, he modified the K-means clustering method used in the standard YOLOv4 to fit the database used to increase the detection rate. Then, he modified the structure of the model to increase the detection speed by reducing the number of overlapping layers to 16 and the number of parameters to 17 059 472.
With the proposed deep neural network, the detection rate is 98% and the time of processing the image of a frame is 0.04s, which demonstrates its high detection accuracy and real-time performance.
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