Jo Sep 9, 2025
A converter that changes one AC power to another is called an AC/AC converter. The AC/AC converter has become a research topic in the field of power electronics because of its applications converting one AC voltage to another, including lighting control, soft start of induction motors, blowers and pumps.
An AC/AC converter has several conversion modes, among which the method of directly changing the input AC voltage to another AC voltage based on the operating principle of a direct buck-type DC/DC converter can implement PWM (Pulse Width Modulation) control to smoothly control the amplitude value of the output voltage.
O Yong Hun, a researcher at the Robotics Institute, has proposed a circuit planning for a buck-type direct AC/AC converter that can directly change AC voltage to lower AC voltage without the help of a transformer, based on the operation principle of a buck-type DC/DC converter. In addition, he has investigated the correlation between the several factors affecting the input and output waveforms under constant load conditions by means of MATLAB simulations.
The theoretical study and simulations of a buck-type direct AC/AC converter can be concluded as follows: The buck-type direct AC/AC converter is theoretically possible and is applicable at small-scale yield power levels (500W), but in order to achieve high power, efforts should be directed to circuitry and space isolation problems to prevent harmonic production rather than enlarging the capacitance of the output device.
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Jo Sep 8, 2025
Hwajang Hermitage, belonging to Pohyon Temple of Mt Myohyang, was first built in the period of Koryo and was rebuilt several times after 1654. The present building was rebuilt in 1818. The hermitage is four kans (11.95m) long and two kans (5.55m) wide. The foundation stones are natural ones and the ceiling is coffered. The front wall is painted with fairies flying in the sky and there is a corridor along it.
Unlike other hermitages for sitting in religious meditation, Hwajang Hermitage was a place for teaching the Buddhist Scripture and even Confucianism-related things. Therefore, it is said to have been much frequented by those who worshipped Buddhism and Confucianism.
The priests decorated this hermitage colorfully to implant Buddhism into them. Hwajang Hermitage, one of the Buddhist temple buildings of the feudal Joson dynasty, is a precious historical relic visited by a lot of people as one of the sightseeing beauties of Manphok Valley on Mt Myohyang.
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Jo Sep 5, 2025
Wind or solar power generation systems are at an early stage of equipment or technical cycle life, but hydroelectric facilities are typically older and operate with a mismatched assortment of hardware and controls, which are not optimized to work as a unified system.
The changes of many parameters that affect the efficiency of a plant make it difficult for operators to fully optimize it. Thus, if hydropower plants are operated and maintained by operators, they may affect the efficiency of the generating equipment.
This is the reason why the operation and maintenance management system of hydroelectric power plants should have high control performance, be reliable and inexpensive, and minimize personal intervention.
Ri Kyong Hyok, a researcher at the Faculty of Electrical Engineering, has built a fieldbus control system by CAN and an SCADA system by Ethernet using the CAN interface function, Ethernet interface function and 485 interface function of a microcomputer, and integrated these systems to realize an automation system for hydroelectric power plants.
To improve real-time control, he installed two CAN networks, and further enhanced the reliability of the field bus system by checking the measurement accuracy of control parameters and monitoring the communication status of CAN bus in real time.
His research results have laid a foundation for implementing an integrated automation system using CAN bus in various fields of industry as well as in hydropower plants.
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Jo Sep 1, 2025
Jongum Gate is the southern gate of the northern castle of the Walled City of Pyongyang in the period of Koguryo. It is on Moran Hill in Pyongyang City.
First built in the mid-sixth century, it was repaired and reconstructed several times.
The present gatehouse, which was rebuilt in 1714 and burnt down during the past Fatherland Liberation War, was restored to the original state in 1959.
The embankment piled up with smoothly faced granite has a beautiful stable arched gateway, which is about 3 meters wide, 3.4 meters high and 6.35 meters long.
On the embankment is a gate house, which is three kans (7.36 meters) long and two kans (4.35 meters) wide.
Jongum Gate is a precious cultural relic that demonstrates the excellent architecture of the Korean ancestors and their patriotic spirit of bravely fighting against foreign aggressors.
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Jo Aug 29, 2025
Cutting tools have a decisive influence on the quality of machined parts and the efficiency of machining. Especially, the precision of cutting tools often leads to the precision of the gear class components.
There are two gear cutting methods; by forming and by generation. Because the gear cutting by forming has low machining accuracy and productivity, the gear cutting by generation is in common use. For gear generating, cutting tools such as a hob and a gear shaper cutter should be designed and manufactured precisely enough to increase the machining accuracy of gears.
The profile of a gear cutter is determined by the envelope equation of the instantaneous trajectory of the gear tooth profile. Therefore, the profile of the cutter can be determined only on the condition that the profile equation of the gear tooth to be machined is known. If the gear tooth profile is given as the measurement data or is a complex transcendental function, it is impossible to determine the profile of the cutter.
Choe Myong Chol, an institute head at the Faculty of Mechanical Science and Technology, has proposed a new method for 3D design of the toothed tool profile from the measurement data of a sample gear without any complex calculations in the way of reverse engineering.
This method can be applied to all generating cutters ranging from 2D to 3D tools.
For further details, please refer to his paper “3-D Design Method of the Gear Cutting Tool Profile Based on Reverse Engineering” in “Transactions of the Indian National Academy of Engineering” (SCI).
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Jo Aug 28, 2025
Silicoaluminophosphate (SAPO) molecular sieves have opened new perspectives in the conversion process of dimethyl ether to olefins (DTO) and recently, SAPO-18 catalysts with enhanced stability have been reported as catalysts for DTO reactions.
SAPO-18 is a microporous crystal of the AEI-type framework, in which only dimethyl ether (DME), light olefins and linear hydrocarbons can pass through the pores, while aromatic intermediates formed inside the pores cannot. This leads to coke deposition by the growth of aromatic intermediates during reactions, and the deposited coke blocks the pore entrance of the catalyst, leading to deactivation.
Therefore, it is necessary to improve the performance of catalysts that can delay their deactivation in the DTO reaction using the SAPO-18 catalyst.
Ho Yu Gyong, a researcher at the Institute of Nano Science and Technology, has steam-treated the hydrothermally synthesized SAPO-18 catalyst to investigate the catalytic performance in dimethyl ether to olefins (DTO) reactions.
After steam treatment, micropores and mesopores were created on the SAPO-18 catalyst.
To evaluate the catalytic activity of steamed SAPO-18, she carried out a DTO reaction at 673K with weight hourly space velocity (WHSV) of 3.546h-1. The result showed that the steamed SAPO-18 (S-773) steamed at 773K exhibited excellent DTO conversion performance.
You can find the details in her paper “Steam-treated SAPO-18 with well-regulated acidity and excellent DTO performance” in “Journal of the Indian Chemical Society” (SCI).
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