Jo May 22, 2025
Magnetic resonance imaging (MRI) finds wide application in various studies and clinical practice related to the quantitative and intuitive assessment of cerebral nerve system because of its good contrast and high resolution for brain structures. Most of them require an image processing step called brain extraction by which only the brain part is segmented from cranial magnetic resonance (MR) images.
Though a number of brain extraction algorithms have been presented, brain extraction tool (BET) is still regarded as a favorable tool in the neuroimaging community, and most of the brain extraction algorithms proposed up to date have used the BET as an important competing method to compare their performance.
BET based on the deformable surface initializes the surface as a spherical mesh, and then evolves the surface toward the brain border with small movements applying iteratively a set of forces depending on local parameters to the vertices on the surface. Adopting the local parameters, in general, doesn’t guarantee the balanced evolution all over the surface to generate self-intersections because some vertices may move more quickly while others move slowly depending on the local conditions. This is why BET should have small movements for evolution. Because BET adopts local parameters and small movements, the evolution of deformable surface may not only require more iteration but also tend to easily fall into local optimum resulting in falsely negative regions. Though the computing efficiency of BET is acceptable for clinical applications at present, the computation time is still an important issue when taking the increasing resolution of MRI or large-scale studies into account.
Son Chang Il, a researcher at the Faculty of Biology and Medicine Engineering, has proposed a modified BET (BETWP) consisting of two steps of surface evolution for fast and accurate brain extraction.
He introduced a new fast model using a global parameter, the global mean inter-vertex distance of evolution surface. This fast model is adopted in the preprocessing step and then the original BET model completes the evolution of surface in the second step.
The experiments for evaluating the computation efficiency and segmentation quality have shown that the proposed scheme has a couple of advantages over BET. First, it can improve the evolution speed at least twice for brain extraction without any failure due to self-intersection. Second, it can significantly improve the segmentation quality on JC, TE and NE including the false negative ratio for both MRI modalities (T1-weighted image and DW image).
For more information, please refer to his paper “Fast BET Based on Pre-Processing Evolution Using Global Mean Inter-Vertex Distance of Deformable Surface for MRI Brain Extraction” in “International Journal of Image and Graphics” (SCI).
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Jo May 21, 2025
Banach’s contraction principle, which holds an important position in the fixed point theory, has been extended in two directions; one is the generalization of metric spaces (MS), and the other is the change of contraction conditions.
Recently, a new generalization of MS called DCMS has been introduced. The concept of F-contraction, first proposed by a researcher in 2012, has become an important generalization of Banach’s contraction mapping. Since then, many authors have further investigated his result, suggesting various extensions and modifications. They first presented results that underwent change or omission of some of the three conditions for the mapping F.
Kil Chol Jin, a researcher at the Faculty of Applied Mathematics, has investigated the generalization of DCMS using a previous researcher’s idea.
First, he defined a new space, namely, triplecomposed metric space (TCMS), by combining the properties of RMS and DCMS. He formed TCMS by using the composition of three functions in a quadrilateral inequality. Second, he presented fixed point results for nonlinear FT-contractions using only (F1) in TCMS. Finally, he led the obtained results to the application of nonlinear integral equations.
You can find details in his paper “Triple-Composed Metric Spaces and Related Fixed Point Results With Application” in “Journal of Function Spaces” (SCI).
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Jo May 20, 2025
Weightlifting is one of the Olympic sports, which is divided into two lifts: snatch and jerk. In the clean and jerk, the barbell is first lifted above the chest and then jerked overhead. Barbell’s trajectory and kinematic characteristics such as velocity are important factors for evaluating weightlifting technique.
Previous studies revealed some drawbacks in the research into the jerk in clean and jerk. They paid little attention to the elasticity of the weightlifting bar, which is not a rigid body. Therefore, effective use of the elasticity enables lifting more weight.
Jon Min Hyok, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has investigated the kinematic analysis and optimization of jerk considering the elasticity of weightlifting bar and the damping effect of the body, to help weightlifters to achieve good technical skills for clean and jerk.
First of all, in order to derive the barbell’s velocity and acceleration over time, he tracked the barbell’s trajectory from the video clip of lifter’s performance by using image processing technologies such as pattern recognition. Since the pulling action of jerk is similar to that of snatch, he set focus only on jerking. To evaluate jerk technique, he newly introduced five kinematic characteristics “Jerk-Preparing-Time, ” “Jerk-Drive-Velocity, ” “Jerk-Time, ” “Jerk-Offset, ” and “Jerk-Drop”. Then, he proposed a kinematic model comprised of springs and dashpots in order to simulate and optimize the jerk using the elasticity of weightlifting bar. He estimated the spring constant and damping coefficient of the model by analyzing the barbell’s oscillation on the shoulders. He also calculated the spring constant by the theory of bending of beam. Finally, he formulated an optimal control problem based on the proposed kinematic model to optimize jerk.
The advantages of the proposed method are its simplicity, flexibility and no need for any equipment except a camera. It will help coaches or weightlifters improve their jerk technique based on correct numerical evaluation.
For the details, please refer to his paper “Kinematic Analysis and Optimization of Jerk Considering Elasticity of Weightlifting Bar and Damping Effect of Body in Clean and Jerk” in “Engineering Reports” (EI).
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Jo May 19, 2025
Impellers with two-dimensional blades are mainly employed in a centrifugal fan. The blade profile can be defined according to the distribution of flow parameters such as specified loading (velocity) and circulation. Here, velocity distribution is closely related with the increase of the boundary layers on the blade, flow separation, secondary flows and pressure pulsation, etc. So, it directly determines and controls the internal flow through the impeller. Thus, what is the most important in the blade design is to determine proper velocity distribution.
According to the literature, it is impossible to avoid secondary flow because of turning and curvature inside blade passage. However, there are several ways of decreasing the influence of secondary flow. Those are increasing the curvature radius of inlet vane and meridian surface, prevention of overlapping of the position of maximum vane curvature and the position of maximum meridian curvature, and controlling the enlargement of boundary layers inside flow passage.
A number of researches on the relative velocity distribution law of a centrifugal impeller have been conducted, but practical applications in the impeller design have not been reported. Instead, most impeller design methods considered average velocity distribution only. Velocity distribution on the lower surface, however, has an important influence on the flow pattern of impeller passage.
Kim Won Il, a section head at the Faculty of Aerospace Engineering, has proposed a calculation method for improving the impeller performance with flow control parameters such as reduction ratio of inlet area and maximum reduction ratio of mean relative flow velocity, and inlet gradient of rear relative flow velocity, and verified its effectiveness through CFD simulations.
The simulation result shows the following.
First, it is better to reduce the decrease in average flow relative velocity of gas flow, since it decreases the attack loss in the blade inlet. On the other hand, it is better to slightly increase the average relative velocity, since it suppresses the flow separation in the blade outlet. In addition, appropriate inlet gradient on the lower surface and position of maximum loading guarantees small change in the relative velocity of a real gas throughout the whole flow passage from the blade inlet to the outlet, and minimization of the thickness of the boundary layers.
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Jo May 18, 2025
Lung cancer is one of the major causes of non-accidental death. Because the lung is in touch with the external environment, it is affected most of all human viscera. According to a recent WHO report, due to the environmental pollution by overurbanization and industrialization, lung cancer is the leading cause of cancer-related deaths worldwide.
Now, the common and basis tool for early diagnosis of lung cancer is a chest CT machine. Modern CT imaging has made much progress in terms of resolution, speed and clarity compared to previous CT imaging with the advent of technology including information technology, but it still reveals some limitations in the perfect diagnosis of lung-related diseases from chest CT images. The diagnosis of lung cancer in the early stage requires biopsy and analysis of CT images taken at intervals of 6 to 18 months, which is dangerous and uncertain. However, many researchers have reported that it is possible to detect early stage lung cancer from CT images for timely treatment.
In particular, many studies have been carried out to develop a computer-aided detection/diagnosis system (CADe/CAD) that can help physicians with diagnosis by automatically detecting areas of suspected pulmonary nodules from the resulting large number of CT images, but there are still challenges to directly apply CADe/CAD for early detection of lung cancer due to the complexity of the lung and the resolution of CT images.
Based on the growth characteristics of cancer tissue cells, Pak Chun Hyok, a section head at the Faculty of Electronics, has proposed a method of detecting malignant pulmonary nodules with high ambiguity and high probability of developing into lung cancer.
The proposed scheme consists of four major stages: extraction of lung region from CT images, extraction of the region of interest (ROI), detection of candidate early lung cancer regions among extracted ROIs, and detection of early lung cancer regions.
The details are as follows.
First, lung segmentation using superpixels is performed to detect the correct lung region.
Second, based on the merging between superpixels within the obtained lung region, ROI is obtained.
Third, image segmentation based on level set algorithm and superpixel segmentation is performed to evaluate the ambiguity of candidate lesion regions.
Finally, malignant nodule is extracted by 3D continuity of lung cancer.
The evaluation result shows that the proposed method is feasible and effective for detection of malignant nodules.
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Jo May 16, 2025
Conjugate cam is a solid combination of two cams, which can be considered as one segment. Its structure is of great variety. There are two types of conjugate cam mechanism ―with/without self-locking. The former has one follower, while the latter consists of two followers. In self-locking conjugate cam, the follower is rotational or translational.
Self-locking conjugate cam mechanism is widely used in many modern machines such as high-speed textile machines, printers, cutters and machine tools for accurate kinematic transmission under high-speed and heavy loading.
Many researchers proposed synthesis methods of self-locking conjugate cam with a translational follower.
Kang Chol Su, a section head at the Faculty of Mechanical Science and Technology, has investigated a self-locking conjugate cam mechanism with a rational follower.
First, he conducted a structural analysis to calculate the minimum limit of permanent segment. Second, he proved that the ratio of the length of permanent segment to the lever with two arms depends on the feasible pressure angle, maximum displacement, movement rule and working angle.
On this basis, he built a mathematical model for the rotation center of the cam to satisfy the minimum-size condition, and gave an application example to determine the minimum radius of the cam, the initial location of the follower and the angle between levers with two arms.
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