Jo Nov 25, 2022
Self-mixing (SM) technique has been a promising optical measurement technique for a few decades.
This technique is developing toward increasing the measurement distance and the limit of displacement measurement, enhancing the measurement accuracy and improving the real-time quality of the measurement. In addition, it is also important to drop the development cost of a sensor.
Estimation of the optical feedback factor C is the key to SM displacement measurement with a better resolution than half a wavelength. But this estimation is very complex and tricky, and it thus leads to its time-consuming nature, which is one of the important causes that increase the cost and labor for the development of a self-mixing sensor. There have been many methods reported for the C estimation, but they are very time-consuming, very sensitive to noise, or can only work in a certain feedback regime.
Kim Chol Hyon, a researcher at the Faculty of Physical Engineering, has proposed a method of the C estimation using the derivative of an SM signal. So to speak, he has solved a problem of fast estimation of the parameter of an SM interferometric system with the derivative in the jumping point of an SM signal. This method is very simple, and, what is more, it can work in all regimes including weak, moderate and strong feedback regimes.
The estimation precision of the proposed method is not only comparable to that of the data fitting technique but also much simpler than that. Therefore, it is effective in low-cost high-precision SM displacement measurement.
You can find the details of this in his paper “Fast estimation method of feedback factor based on the derivative of the self-mixing signal” presented to the SCI Journal “Applied optics”.
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Jo Nov 24, 2022
Water spraying itself is a dynamic course, and it is affected not only by the structure of an ultrasonic gas atomizer and the compressed air pressure but also by the movement of the compressed air flow in an atomizer.
The fundamental principle of formation of fine droplets in the ultrasonic gas atomizer is that a liquid sheet is disrupted into droplets by the energy of high-velocity air. If the ultrasonic energy is supplied, finer droplets with high sphericity and uniform size distribution can be achieved.
Kim Kang Dok, a section head at the Faculty of Mining Engineering, has observed water atomization of an ultrasonic gas atomizer by numerical simulation with CFD software ANSYS Fluent, and found out about the generation of ultrasound and water fog in the ultrasonic gas atomizer with a resonance chamber together with ultrasound characters (frequency, pressure level, power level).
Recently, experimental researches to improve the features of ultrasonic atomizers by air spray have been conducted, but only a little about numerical simulation was presented except for some experimental data.
Thus, he has simulated the characters of ultrasonic air atomization using the finite volume method based on the Roe solver in the structure similar to the Hartmann resonance chamber. Then, he has looked closely at the occurrence of oscillation and the factors affecting the oscillation, and investigated the distribution character of water droplets.
The experimental conditions for the simulation were compressed air pressure 3.5~4atm, air amount 0.1㎥/min, acoustic power in the cavity resonator 242dB, acoustic power at the outlet 172dB.
The range of frequency is 20~120 kHz, where 21~28 kHz has the highest density. The acoustic power decreases with the distance when the pressure of the compressed air is 0.3MPa.
The determination of the distribution characteristics of the atomizer indicated that condensation of water droplets decreased rapidly from the distance of 3m. Thus, it is clear that the rational spray distance of the atomizer is 3m. The results show that the number density of water particles is 1.52×1010 in the center, but it is 6×108 in the diffusion region.
You can find more information about this in his paper “Numerical simulation on the generation of ultrasound and Formation of Water fog in the Ultrasonic gas atomizer” presented to the SCI Journal “ULTRASONICS”.
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Jo Nov 23, 2022
“Chonsuguksujang” is a handicraft legacy which demonstrates the high level of our national culture in the period of the Three Kingdoms.
“Chonsuguksujang”, which was produced by some craftsmen in Koguryo, Paekje and Silla in the early seventh century, is the oldest of all existing embroideries in the world. It is a long piece of cloth embroidered with a paradise. At first, it was about 4.8 meters long by 1.2~1.5 meters wide. Later, it was torn into pieces and now several pieces are found in Junggung Temple, Popryung Temple, Jongchang Temple and other places in Japan.
About 100 turtlebacks and an excellent composition of 4 letters on each one, that is, 400 letters in all, were embroidered, but now only a few turtlebacks and letters can be seen.
When Japanese Crown prince Song Tok, who was active in introducing Korean culture from the end of the sixth century to the beginning of the seventh century, died in 622, his wife had it produced wishing his happiness in the other world, stricken with grief over his death.
The original picture was painted by Ka So Il from Koguryo and its embroidery and supervisory were all done by Koreans. On the purple and yellow silk cloth of “Chonsuguksujang” are embroidered a paradise made up of characters, palaces, Buddhist images, flowers, rabbits, the moon, a phoenix, lotus flowers, liana patterns, etc. and turtles with letters on their backs in coloured thread such as white, red, green, blue, light green, etc. Several elements ― jogori and skirts worn by the characters, the moon portrayed as rabbits pounding in a mortar, the shape of lotus flowers, liana patterns, gabled belfry buildings, etc. ― are in good accordance with a number of Koguryo mural paintings.
In conclusion, “Chonsuguksujang” is a piece of handiwork that demonstrates the standard of cultural development of our country of that time.
Pak Sin Jong, researcher at the Academy of Social Sciences
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Jo Nov 22, 2022
Leather shoes called katsin in Korean were worn from long ago in our country.
Our nation did a lot of hunting, so they made shoes of animal skins from ancient times. Such shoes were called “hyoktap” in historical records.
In the period of the Three Kingdoms, shoes with very low or no ankles were called “ri” or “hye” and high boots “hwa”.
Later through the Koryo and feudal Joson dynasties, leather shoes were made better in line with the aesthetic sense of the time and the taste of the people, and subsequently their names became diverse.
Shoes and boots equivalent to the previous “ri” were also found during the feudal Joson dynasty. They were named “hye”. “Hye” was sorted into hukphihye, punthuhye, thuhye, phichohye, thaesahye, palmaksin, jinsin, etc. while “hwa” was classified into hukphihwa, mokhwa, hyopgumhwa, kijahwa, jonphihwa, tanhwa, tonghwa, etc. All these were made mainly of leather, so they were called katsin (leather shoes). Leather shoes except jinsin were also called “marunsin” (dry shoes) as they were usually worn on dry land in good weather. Jinsin (wet shoes), true to the meaning of its name, was for muddy ground when it was snowing or raining, so it was made of oil-treated leather to stop water infiltrating inside. For durability and to keep leather shoes from moth, people used to hang them on the wall above the fireplace to expose them to smoke or put hog grease on the surface of leather.
Pak Sin Jong, researcher at the Academy of Social Sciences
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Jo Nov 21, 2022
Chlorination leaching, one of non-cyanidation processes, which was in use until the end of 19th century after its development in the middle of the 19th century, was deprecated after the cyanidation process was born. However, in the eighties of the 20th century it was found that chlorination leaching had a good effect on fine grains of gold ores, and researchers’ interest in it revived, leading to some successes.
Compared to cyanidation leaching, chlorination leaching of gold by chlorine or hypochlorite has faster gold leaching rate and less pollution. What is more, it is cheaper and simpler.
Kim Chang Sok, a researcher at the Science Engineering Institute, has conducted thermodynamic and experimental research on chlorination leaching of refractory gold concentrates. Then, he has observed the influence of the redox potential on gold leaching and confirmed reasonable conditions for the potential.
The results demonstrate that for a higher leaching rate of gold, leaching time should be more than two hours and redox potential should be controlled at 1.0V or more. Under the conditions of the initial concentration of active chlorine 0.5%, the value of pH 4.0, the leaching time at least two hours and the redox potential more than 1.0V, the leaching rate of gold could reach over 96%.
You can find more information about this in his paper “Research on Chlorination Leaching of Pressure Oxidized Refractory Gold Concentrate” presented to the SCI Journal “Hydrometallurgy”.
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Jo Nov 20, 2022
An apron is one of the things that show well a good living habit of Korean women, who have always loved smartness.
An apron is a piece of clothing that women wear over the front of the body and tie around the waist when cooking.
The custom of wearing an apron in our country has a very long history. Maids wearing semi-oval aprons are painted on the mural paintings in Kamsin Tomb and Anak Tomb No. 2 of Koguryo, which tells us that aprons started to be used already in our country before the period of the Three Kingdoms. As shown in the murals, aprons of that time were similar in shape to present-day aprons. They were made in different colours including white and light pink, and red or pink strips of cloth were sewn around them. The custom was inherited down to the feudal Joson dynasty, when aprons made of four pieces of cotton cloth in pleats were almost similar to skirts in length, and they were worn over skirts to cover the front as well as the sides of the body. Among the aprons that had been passed down from olden times was “Haengju Apron” named after the patriotic deeds of the women in the fortress on Mt. Haengju, who carried stones in their aprons to assist the warriors in the battle against Japanese invaders during the Japanese invasion of Korea in 1592.
Aprons were made of thin white cotton cloth such as cotton or calico and they were always washed, starched and ironed before use.
It is a fine custom of our women to wear smart aprons whenever working ― cooking in particular. It was a normal practice for our women to wear aprons when serving food to guests as well as preparing meals for the family in the mornings and evenings, and it was regarded as common courtesy to take them off when they need to enter rooms or answer the door in the middle of cooking. In a word, aprons served as an important symbol of the aesthetic feelings of our women, who have loved neatness and cleanliness from early days.
Today our women enjoy wearing aprons when they do the housework. Present-day aprons that are made of white cloth in semi-oval or rectangular shape to cover front parts only are decorated with simple flower embroidery, applique, lace or small pockets.
Pak Sin Jong, researcher at the Academy of Social Sciences
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