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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Jo May 13, 2025
Mesocellular silica foam (MCF) is a kind of new mesoporous silica material found in 1999, with the largest pore size (up to 50nm) of all mesoporous materials synthesized to date, which has the three dimensional cubic mesopore structure of a typical foam phase. The specific surface area reaches 1 000m2/g, and the pore size and pore volume are large. Relatively large spherical pores are interconnected by small pores.
Compared to the mesoporous materials of MCM and SBA series with relatively small pore size, MCF has large specific surface area and pore size and it is scalable. Its specific 3D foam structure characteristics have a great theoretical research significance and wide application prospect in various fields. For example, as a catalyst support, it is beneficial to the mass transfer and diffusion of reactants and products by increasing the metal loading. Recently, several studies have applied it to the esterification solidification of alcohol, hydrogenation, dehydrogenation, CO2 adsorption, hydrogen peroxide synthesis, etc., which has shown its excellent performance.
Plasma treatment, a gas phase treatment technique combined with a kind of physical and chemical method, has several advantages like no pollution, low energy consumption, no water consumption and no use of chemical reagents. In particular, low temperature plasma treatment causes physical and chemical changes near the surface of materials to be treated, while maintaining their own properties. Therefore, low temperature plasma treatment is of great importance in the functionalization of materials surface.
Mun Se Hyon, a researcher at the Institute of Nano Science and Technology, has carried out a surface modification treatment in the mesoporous material pore channel using dielectric barrier discharge (DBD) with 3D mesocellular silica foam (MCF) as a support, and investigated the effect of plasma treatment conditions on the reaction on MCF surface.
First, he synthesized mesocellular silica foam (MCF) by sol-gel method and treated the surface of MCF by DBD to enhance its surface activity. After plasma treatment, he modified amine groups on the MCF pore channel surface.
To investigate the effect of plasma treatment on the mesoporous material MCF support, he modified amine groups on both treated and untreated MCF surfaces. Then, he compared the specific surface area of catalyst support MCF-NH2 synthesized by the two methods and the amount of -OH in the pore channel via nitrogen adsorption and desorption analysis (BET), infrared spectroscopy (IR) and thermo gravimetric (TG) analysis.
The results showed that plasma treatment greatly influences the pore structure of the mesoporous material MCF, and even the activity of the MCF surface obtained.
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Jo May 11, 2025
Chongbaek Juniper growing in Chongbaek-ri, Kumya County, South Hamgyong Province was planted around 1550. It is 10 meters tall, with the root collar of 5.4 meters round and the canopy of 18 meters from east to west and 21 meters from north to south.
At the height of 50 centimeters, it spreads in three big branches that are 2.6 meters, 2.1 meters and 2.2 meters round, respectively.
It looks like a collection of small clouds from a short distance and like a large furled umbrella from a long distance.
The oldest and largest tree on the eastern coast is a natural monument that is significant for studying the size and age of juniper trees and adds beauty to this area.
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Jo May 9, 2025
Plasma technology has been widely used in various forms in the fields of functional materials, new materials synthesis, metal cutting, ozone generation, air purification, food, environmental, chemical, mechanical industries, etc. In particular, surface treatment of objects based on plasma has been studied by many researchers because it can improve several properties of the surface and broaden its application.
Dielectric barrier discharge is a very effective non-equilibrium plasma generation method that prevents the transition into spark and arc discharge that occurs in the discharge gap by inserting dielectric into the discharge space. Corona discharge is also an effective method of non-equilibrium plasma generation at atmospheric pressure. However, its discharge area is small and the power density is not high. Hence, if corona discharge and dielectric barrier discharge are properly combined, the discharge is more uniform and stable due to the corona effect at the corona electrode in the discharge space and high power density atmospheric pressure discharge can be realized.
The discharge formed by high frequency and high pressure after the insertion of dielectric into the corona discharge space is called dielectric barrier corona discharge (DBCD). Treatment of the surface of resin or cloth by DBCD can improve the surface properties by changing the adhesion, resistance, dyeing, painting, gloss, wear resistance, hydrophobicity, etc.
Kim Jin Hyok, a researcher at the Institute of Nano Science and Technology, has generated dielectric barrier corona discharge using quartz glass as dielectric in the atmosphere, treated the surface of Tetron fabric by passing it through the discharge space, and considered the change of its characteristics. At high frequency, high pressure power supply of 15 kHz and 18kV, he treated the Tetron fabric with varying discharge power, treatment speed and number of treatments, and measured the change of water penetration time to compare its surface characteristics.
As a result, he has found the following.
First, the higher the discharge power is, the shorter the water penetration time gets and the better the hydrophobicity becomes. When the slower the treatment speed is, i.e., the longer the treatment time for the unit area of the Tetron fabric is, the higher the treatment efficiency is, which leads to the shorter water penetration time. The more the number of treatment is, the better the surface properties become and the shorter the water penetration time gets.
From these characteristics, he determined the optimal surface treatment parameters by the Taguchi method. They are 900W of discharge power, 7cm/s of treatment migration rate and 4 rounds of treatment. Under these conditions, water penetration time is 9.2s.
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