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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Jo May 15, 2025
Synchronization system and digital scanning conversion system of an ultrasonic diagnostic device plays an important role in improving its operation stability, runtime processing velocity and image quality based on the electrical characteristic parameters of a selected probe.
As most of the existing synchronization systems of an ultrasonic diagnostic device have circuits composed of 74/54 series standard TTL ICs, the circuit design is complex and the operation is not stable.
Kye Pong Sang, an institute head at the Faculty of Electronics, has composed a synchronization system and a digital scanning conversion system for ultrasonic diagnostic devices based on the domestic convex array probe widely introduced in our country, and built a device using EPGA.
First, he combined dynamic focus scanning system and cross scanning system in order to improve the directivity of ultrasonic sound and to increase scanning lines for high quality image. Second, he designed a synchronization system for an ultrasonic diagnostic device composed of circular sector scanning systems using the convex array probe by defining the input clock frequency in consideration of the parameters of probe and by counting it with the clock frequency as a reference clock. Third, he precisely calculated the delay time of transmit driver impulse applied to each vibrate chip of convex array probe, and achieved it with inner phase-locking loop (PLL) of Cyclone series FPGA. Then, he designed a digital scanning conversion system in a small image memory mode and realized a high speed coordinate transformation. Finally, he performed two-dimensional plane interpolation for ultrasonic sampling data, and designed a processing circuit.
As a result, he significantly improved the run-time processing speed and the image quality of an ultrasonic diagnostic device, and enhanced the accuracy, stability and reliability of its operation.
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Jo May 14, 2025
In information security systems, the Broadcast Encryption (BE) scheme is important for guaranteeing secure multi-users communication in insecure channels, so it is widely studied in the world. Especially, BE scheme is a cryptographic primitive to achieve group communication such as video services.
Identity-based Encryption (IBE) technology is a new public key cryptographic primitive completely different from traditional ones. Extensively studied worldwide, it is expanding its application scope for its high utility.
A comprehensive survey of all the research results presents the main concerns in constructing (anonymous) Identity-Based Broadcast Encryption (IBBE) scheme as follows.
First, in the aspect of security requirement, it is preferable to achieve adaptive CCA security.
Second, in the aspect of performance evaluation, it is more desirable to obtain constant-size system public parameters, user secret key, ciphertext and decryption cost for IBBE schemes.
Third, in terms of computation efficiency, it is better to construct IBBE schemes based on prime order bilinear mapping and to have a small number of paring operation.
Forth, IBBE must satisfy anonymity.
Myong Kwang Min, a researcher at the Faculty of Information Science and Technology, based on the analysis of the characteristics of IBBE, has proposed an effective IBBE scheme with adaptive CCA security and anonymity and a small amount of paring operation by combining unforgeable digital signature scheme and IBE, and proved its security.
Through the performance comparison and computation evaluation, he has proved that the proposed scheme is superior to the previous one in terms of parameter size and computational amount while satisfying the adaptive CCA security and anonymity.
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