Jo Jul 11, 2023
A research team led by Kim Yong Chol, a researcher at the Faculty of Chemical Engineering, has established a method for preparing nano-cuprous oxide by mechanochemical method.
Mechanochemical method, an effective one for obtaining a desired product by simply ball milling reactants in solid phase with mechanical energy required for chemical reactions, has been widely applied recently.
Mechanochemical method is convenient to run and environmentally friendly. In addition, as mechanochemical actions, which increase the driving force of a reaction and the reaction speed, it enables chemical reactions that are impossible or difficult to perform at room temperature.
Therefore, mechanochemical reactions have some characteristics different from ordinary chemical reactions, and reaction mechanisms and thermodynamic and kinetic characteristics are also significantly different from ordinary thermochemical reactions.
Taking into account the factors influencing the preparation of copper oxide from copper sulfate, glucose and sodium hydroxide, they prepared nano cuprous oxide by mechanochemical method.
To prepare nano-cuprous oxide, copper sulphate was chosen as a precursor, glucose as a reductant, and sodium dodecyl sulphate (SDS) as a dispersant for the experiment.
First, required amount of copper sulphate and glucose were pulverized, respectively, and mixed uniformly. Then, pulverized sodium hydroxide and SDS were added to the mixture, respectively, and then ground in a ball mill.
As the milling time increased, the mixture turned from pale blue to orange, and the reaction continued for 50 minutes.
The milled product was taken out, dissolved in distilled water and left to separate the layers. After filtering and washing several times with distilled water and ethanol, they finally obtained nano-cuprous oxide powder by drying it at 60℃ for 4 hours.
The characteristics of the nano-cuprous oxide prepared in the experiments were analyzed by XRD and SEM.
Nano-cuprous oxide prepared in this way can be utilized as a disinfectant at fruit farms, as a photocatalyst in chemical industry and as a colourant in ceramic industry.
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Jo Jul 9, 2023
Sokgakchonmundo is an astronomical chart (constellation drawing) carved on a stone, true to the meaning of the term.
The chart was made between the late fifth century and the early sixth century.
Although the chart does not exist at present, Chonsangryolchabunyajido made at the end of the fourteenth century convincingly demonstrates how profound astronomical knowledge the chart involved.
Chonsangryolchabunyajido was made with a slight adjustment to the rubbed copy of Sokgakchonmundo, which had been lost during a war (invasion of the Tang dynasty) in the Koguryo age as the constellation on the copy was a little different from that in those days.
Sokgakchonmundo shows 1 475 stars grouped on 307 constellations on a large stone about 2 metres long and 1.2 metres wide, drawn with the universe with the Arctic in the centre.
The chart also shows the equator circle, the ecliptic circle, the Arctic Circle, the longitude line and even the Galaxy.
Koguryo’s Sokgakchonmundo is one of the world’s oldest stellar charts and it contains a larger number of stars than an astronomical chart made in China in the middle of the third century.
Sokgakchonmundo is one of the precious cultural legacies that intensively show the high level of astronomical development of Koguryo.
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Jo Jul 7, 2023
Hyon Song Chol, a section head at the Faculty of Electrical Engineering, has developed an 800A electrolytic power unit where polarity can be reversed.
Polarity reversion technology can prevent resistance from getting larger and speed of electrolysis from getting slower, due to the silver oxide film formed on the anode during gold refining.
A periodic negative bath voltage makes a silver oxide film separate from the anode. As a result, the fineness of gold and the speed of electrolysis increase with less power consumed.
The polarity reversible electrolytic power unit consists of a full-wave rectifier, a high frequency transformer and a bridge drive unit, a rectifier and filter, and a polarity reversing unit.
The bridge drive unit of the high frequency transformer drives it at 20kHz using phase shift and a soft switching mode.
The voltage at the secondary side of high frequency transformer is then full-wave rectified and filtered, becoming two DC power sources with separated ground.
From these two DC power sources, a negative and a positive voltage are alternatively output periodically by changing the channel with two thyristors at the polarity reversing unit. The polarity reversing unit is constructed in the way of minimizing voltage drop on the current routine, as well as befitting the feature of the thyrister that costs less per unit current but is free from self-closing.
Compared with previous control rectifiers, the voltage distortiong rate is decreased by 5%, the cost by 60% and the weight by 30%.
This device can be used not only as an electrolytic power source unit for non-ferrous metal refining but also as a plating power source unit.
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Jo Jul 6, 2023
“Nongsajiksol” is a book on agriculture where farming methods and experiences suitable for the climatic and soil conditions of our country are comprehensively systematized. It was written by a feudal bureaucrat and scholar Jong Cho (? – 1434) in 1429, hundreds of years from now.
The book has a small amount of information with farming experiences limited to certain areas, but it has a lot of valuable information necessary for farming ranging from preparation of seeds, ploughing and preparation of compost and manure to methods of growing several kinds of grain crops.
In addition, written in the book are use of various kinds of farming tools, methods of manuring, and how to cultivate cereals like millet, foxtail millet, wheat, barley, etc. and legumes such as beans, adzuki beans, mung beans, etc., sesame and buckwheat.
Therefore, the book was republished several times until the later period of the feudal Joson dynasty in order to be widely used in agriculture and consulted for other agricultural books.
Although it has some defects due to the purpose of compilation and the class limitation of the author, “Nongsajiksol”, the oldest of all agricultural books from the middle ages of our country still found, serves as an important historical record for research into the development of farming methods and skills of that time.
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Jo Jul 3, 2023
May Circuits ’23 was held on HackerEarth from 20 to 27.
The contest, which drew over 1 700 contestants from different countries in the world, set forth 8 problems including one challenge problem.
A student from Kim Chaek University of Technology (KUT) took the first place with a perfect score of 800. Three other KUT students ranked within the top 10 places including the 3rd and the 4th.
Not resting on their laurels, they are making redoubled efforts to make greater achievements next time.
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Jo Jul 1, 2023
A thungso (a Korean bamboo flute) is one of the musical instruments peculiar to our nation which have been widely played by the folk from olden times.
This typical national pipe instrument is played held sidewards. It has been loved by our people in a long course of history.
It originated from a kinjo (jangjok) that Koguryo people had invented.
According to historical records including “History of Koryo”, Koguryo’s kinjo was improved into a thungso during the Koryo dynasty, but it was also called kinjo until then.
In “Akhakgwebom” compiled at the end of the fifteenth century, the name was fixed as thungso, which means a wooden pipe instrument whose ends are perforated through.
With soft, stirring, appealing and melodious timbre, it can fully express exciting thoughts and feelings.
Widely used for a solo and accompaniment to folk songs and folk games, it has been a popular national instrument.
A thungso is making a contribution to the cultural and emotional life of people and the development of Juche-oriented music blooming day after day under the wise leadership of the Workers' Party of Korea.
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