Jo Sep 12, 2025
Polyester fibers currently represent more than half of fibers in global use, and the most commonly-used of them is polyethylene terephthalate (PET), which has continued to increase in its production. In addition, with the improvement in the people’s living standard, the use cycle of textiles is getting much shorter, which leads to the production of textile waste, reaching 90% of global fiber production. On the other hand, resource depletion and environmental pollution have become a serious problem, and people have been better aware of the environmental system, which has encouraged positive efforts to recycle textile waste.
There are three main ways to reuse waste textiles, namely, mechanical, physical and chemical methods. In the chemical method, polyester is decomposed into monomers or oligomers before being separated and purified to obtain desired chemical products. This is a complete fiber-fiber cycle technique that can produce new textile fibers from waste textiles. In the 2010s, some countries synthesized PET for textile fibers by applying the chemical method to PET waste plastics to produce clothing such as suits, shirts, etc. Chemical recycling methods of post-consumer PET include glycolysis, hydrolysis and others. In glycolysis, in particular, Bis(2-hydroxyethyl terephthalate) monomer (BHET) and oligomer are obtained by trans-esterification between diol and ester groups of PET.
Since BHET is used as a PET synthetic feedstock, many studies have been carried out on glycolysis of PET. However, previous studies addressed glycolysis of relatively clean PET waste, and little attention has been paid to PET waste fibers containing various impurities such as dyes.
Ri Myong Chol, a researcher at the Faculty of Materials Science and Technology, has investigated the preparation of BHET by glycolysis of PET textile waste under microwave irradiation.
The experimental results show that high purity BHET used as a precursor for PET synthesis can be prepared by pre-decolorization of PET textile and glycolysis of PET before recrystallization of BHET.
When PET textile and PET plastics are glycolyzed under the same reaction conditions, the conversion of PET and the yield of BHET are higher in the fiber than in the plastics. The reason lies in the fact that the depolymerization reaction rate gets faster in the PET fiber because the specific surface area of fiber is much larger than that of plastics and the molecular weight of PET fiber is lighter than that of PET plastics.
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Jo Sep 10, 2025
Kwangbop Temple, situated in Taesong-dong, Taesong District, is one of the typical Buddhist temples in Pyongyang and the surrounding area. It was built during the period ruled by King Kwanggaetho of Koguryo and rebuilt in 1727. In July, 1952, during the Fatherland Liberation War, it was completely destroyed by the US imperialists’ bombing and it was restored to its original state in 1990.
Kwangbop Temple is comprised of Taeung Hall, eastern and western monasteries, five-storied octagonal pagoda, etc. The buildings are distributed symmetrically with the pagoda in the center. The way of siting buildings on the four sides of a pagoda was frequently found in the period of Koguryo.
Taeung Hall, the main building of the temple, is a magnificent two-storied gabled house. In the hall are placed three Buddhist statues including Shakyamuni Tathagata and some Buddhist images. The hall is painted colorfully in glittering gold.
The lotus pond transmitted from olden times and the monument to Kwangbop Temple erected in 1727 still remain around the temple. The legend about the nine dragons and ninety-nine ponds of Mt. Taesong, namely, Mt. Kuryong is recorded on the monument.
Kwangbop Temple on the picturesque Mt. Taesong is in good preservation and care as a national treasure and a precious cultural legacy demonstrating the advanced architectural skills of Korean ancestors in those times.
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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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