Jo May 8, 2023
Pak Yong Ho, a researcher at the Nano Physics Engineering Institute, by using a polymer jet fluid model by CFD, has calculated the velocity field distribution in it to determine a uniform velocity profile and determined a new curved profile of the collector to obtain uniform fiber in an arched multi-nozzle electrospinning device.
Electrospinning is a method of producing micro fibres by injecting polymer solutions in electrostatic fields. Microfibers obtained by electrospinning have widely been applied in various fields, due to their superior properties such as very small diameter, high porosity, large specific surface area, etc.
Recently, highly productive electrospinning methods such as multi-nozzle electrospinning and nozzle-free electrospinning have been proposed. Multi-nozzle electrospinning is a method of overlapping many nozzles, so it is difficult to realize stable and continuous spinning as nonuniform distribution of electric fields at the nozzle tip creates corona discharge by strong electrical interaction between the nozzles.
Based on the calculation of the flow rate in angular jet flow through a CFD simulation of the jet flow in an electrostatic field, he determined the contour shape of the collector plate obtained by the uniform velocity plane. Then, he drew the curve equation of the curved collector which can obtain uniform diameter electrospun fiber in the multi-nozzle electrospinning system where an arched multi-nozzle and a curved collector are combined. After that, he found the curve equation of the curved collector to obtain uniform electrospun nanofiber with the diameter of 131.3nm, which is suitable for preparing a nanofiber ionexchange membrane for electrodialysis.
The curve equation of the collector profile for obtaining the electrospun nanofiber (131.3nm in diameter) in an arched multi-nozzle electrospining device is y=-2-12x3+0.002x2-2-8x-91.991.
It means that a new methodology to obtain uniform electrospun fibers with arbitrary diameters in a multi-nozzle electrospinning device without additional means was developed.
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Jo May 7, 2023
“Rimwonsipryukji” compiled by a realist scholar So Yu Gu (1764―1845) in 1825, is a national classic where documentary records concerning economy and culture are arranged in categories.
Rimwonsipryukji, which is left incomplete, is a huge work, running to 113 volumes and 62 books. This enables us to guess what an enormous book he mapped out.
Divided into 16 parts, Rimwonsipryukji contains valuable information extracted from as many as 500-odd kinds of domestic and foreign records that was considered indispensable for developing the national economy and daily life. All the information is organized in categories and followed by the origins of the data and the author’s opinion of each item.
The front parts Ponriji and Kwangyuji are about agriculture. Here, general knowledge of agriculture and methods of cultivating and processing 33 kinds of vegetables and over 20 kinds of medicinal herbs are introduced. The author wrote that success or failure of agriculture depends on the skills and efforts of humans, not on natural conditions.
The horticultural parts Yewonji and Manhakji deal with methods of growing more than 50 kinds of flowers, over 30 kinds of ornamental grasses, 30 kinds of fruit trees, several kinds of trees, tea plants, tobacco plants, etc. and even those of changing the colours of flowers artificially.
Poyangji and Injeji give a detailed description of rules of diet for good health and longevity, exercise, massage, taking medicine, taking care of the elderly and children, and other things concerned with branches of medicine like gynaecology, paediatrics, surgery, etc.
Rimwonsipryukji serves as one of the invaluable national classics since it not only reflects the author’s aspiration to make a positive contribution to the development of the national economy and culture but also contains copious amount of all-round knowledge about the socio-economic situations, medicine, food culture, life style, etc. in the latter half of the feudal Joson dynasty.
Ri Won Chol, researcher at the Academy of Social Sciences
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Jo May 5, 2023
Ro Myong Gum, a researcher at the Nano Physics Engineering Institute, has investigated the effects of laser power on the reduction of graphene oxide by 355nm UV impulse laser.
Graphene oxide, which is chemically exfoliated from graphite, a precursor of graphene, is a suitable material for producing graphene in large quantities. However, reduction is necessary because graphene oxide is an insulator.
In the past, a chemical method, heating treatment, microwave and plasma, etc. were applied to the reduction of graphene oxide, but nowadays graphene oxide reduction by laser is under study.
She performed some experiments on the thermodynamic change of a graphene oxide film when graphene oxide is irradiated by 355nm UV impulse laser, and confirmed the impact factors of laser on the reduction.
As compared with conventional reduction methods, the proposed method is simple in process and enables reduction and mask at the same time, so it will prove the most suitable for manufacturing micro-electronic devices.
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Jo May 4, 2023
Fort on Mt. Taesong is the largest and oldest of all the fortresses on mountains of Koguryo.
Located in Taesong-dong, Taesong District, Pyongyang City, it was built to defend Anhak Palace, the royal palace of Koguryo from the 3rd to 5th century.
The fort is surrounded by wide and narrow rivers on three sides ― east, west and south ― and the north is linked to a mountain range, so it is very advantageous in terms of military affairs, economy and transportation.
It is 7 076 metres round and the total length of the walls runs to 9 284 metres. It could hold a huge number of people, combat equipment and supplies as it had two vast deep valleys between the six mountain peaks linked to one another. It had food storages, armouries, quarters, general’s terraces, gates, etc.
Pyramid-shaped stones were laid in single-sided piles on the peaks and in double-sided piles across the valleys. Double and treble walls were built on important spots. On the top of the walls were parapets, low zigzag walls, and on important points were bastions to strengthen the defense of the fort.
Abundant in water resource, the fort had as many as 170 ponds including a carp pond and Jangsu Pond. It had two gates ― Somunbong Gate and South Gate, which was 5 kan × 2 kan ( 1 kan = 5.965 feet) in size and 19.5 metres in height.
In the fort, a lot of relics and remains like Koguryo roofing tiles, gilt-bronze images of Buddha, stone boxes for keeping Buddhist scriptures, etc. were discovered, and many legends including the story of a Rok tribe lady associated with the fort have been handed down.
Many relics including some parts of the wall, Jangsu Pavilion, South Gate and Jangsu Pond are now restored to the original state to play an important part in the study of Koguryo’s fortress system.
Fort on Mt. Taesong with strong defences, which served as a reliable one in the fights against foreign invaders, was an impregnable fortress that had hardly been found in the world history of fortress construction.
Ko Ju Il, researcher at the Academy of Social Sciences
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Jo May 2, 2023
U Yong Nam, a section head at the Robotics Institute, has made a study of the mobile properties of an omnidirectional AGV with Mecanum wheels.
A Mecanum wheel, which is designed to move a vehicle in any direction, consists of a series of rollers attached to its circumference.
ADAMS was used for the simulation, where he analyzed the motion in X and Y directions, turning round on the position and oblique.
The simulation result showed that the velocity error in the X-direction movement and turning round on the position of the AGV is small and stabilization is fast, and vice-versa in the Y-direction movement and oblique.
The results verified that an AGV with four Mecanum wheels can operate in a static state.
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Jo Apr 30, 2023
“Koryosajolyo” is a book where the history of Koryo, the first unified state of our nation, is recorded in order of year, month and date.
“Koryosa” (History of Koryo), which was written in 1451, touches a huge amount of materials divided into categories, so it was inconvenient to learn the contemporary history chronologically at a glance.
That is why after the completion of “Koryosa”, a more concise one “Koryosajolyo” was compiled.
“Koryosajolyo” was completed in 1452 by Kim Jong So, Jong Rin Ji et al. who had worked at “Koryosa”, and published in the following year 1453.
The title “Koryosajolyo” means “the main parts of Koryo history” and it consists of 35 volumes, which is about a quarter of “Koryosa” in 139 volumes.
In the book is recorded the history of the feudal Koryo dynasty in order of reign of the 34 kings from the founder king to King Kongyang, and the events and facts during their reigns are arranged in yearly, monthly and daily order.
It gives a large amount of information about the feudal Koryo State ― politics including the state machinery, ranks of government posts, punitive system, anti-aggression and anti-feudal struggle; economy including the land system and tax system; culture including education and art; military affairs including the military system, national defense, etc.; nature including astronomy, geography, natural disaster, etc.; information about individuals that made contributions to the development of science and culture.
Although it reveals some shortcomings due to the class restrictions of the compilers, “Koryosajolyo” serves as an important national classic legacy that shows the history of the Koryo since “Koryosajolyo” and “Koryosa” constitute key documents to the research into the history of the Koryo dynasty by compensating each other’s defects.
Ri Won Chol, researcher at the Academy of Social Sciences
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