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.
...
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.
...
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.
...
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.
...
Jo Jun 29, 2023
Most of the existing routing protocols designed for EH-WSNs (energy harvesting wireless sensor network) are competition-based so they use multiple criteria for CH selection.
To provide balanced energy utilization, factors such as residual energy, distance to BS, adjacency degree, energy harvesting rate were considered and in some protocols even link statistics were included because they help us use a better link to reduce the link loss and ensure the reliability of data transmission.
Especially, in data transmission phase, a transmission power adjustment scheme was introduced to use harvested energy more efficiently. However, in overall operation stages including CH selection, next-hop CH selection and joining CMs to CH, multiple criteria that reflect the property of each node were not used. This resulted in unbalanced utilization of harvested energy.
Also, transmission power adjustment for lengthening the transmission distance was applied only when the rechargeable battery is nearly charged, so it left the possibility to further increase the utilization of the harvested energy.
Especially, energy consumed for sensing was ignored in designing routing protocols under the consideration that it is much less than that consumed for transmission and reception.
To solve the problems above, Ri Man Gun, an institute head at the Faculty of Communications, has proposed a novel improved equal hierarchical cluster-based routing protocol to enhance balanced utilization of the harvested energy as well as to ensure the reliability of communication and the network connectivity.
You can find more information about this in his paper “An Improved Equal Hierarchical Cluster-based Routing Protocol for EH-WSNs to Enhance Balanced Utilization of Harvested Energy” in “IEEE Access” (SCI).
...
Jo Jun 27, 2023
A research team led by Kim Myong Hui, a researcher at the Nano Physics Engineering Institute, has developed a dielectric barrier discharge (DBD) ozone generator power supply, and analyzed the discharge characteristics of load through a simulation on the ozone generator power supply circuit by MATLAB 7.0 to increase ozone production and improve the efficiency of the ozone generation supply.
The DBD ozone generator is largely composed of an ozone generating tube and an inverter power supply. In order to increase ozone production, it is necessary to improve the efficiency of the power supply by matching the power supply and the ozone generating tube.
The DBD ozone generator power supply consists of a rectifier, a filter, an inverter and a booster.
For matching, they connected the compensation inductor for constructing the resonant circuit in series with the circuit.
Then, they carried out a simulation analysis of a voltage-type load series resonant DBD ozone generator power supply by MATLAB Simulink. The main parameters of the simulated DBD ozone generator power supply are input voltage 220V/50 Hz, power 600W, frequency 4kHz, transformer primary voltage 250V, secondary voltage 3 000V, discharge gap capacitance 1nF and dielectric capacitance 5nF.
The simulation result demonstrates that if a resonant circuit is constructed by series connection of the compensation inductor to the transformer primary or secondary side, the load current and discharge voltage phases are almost identical, i.e., the matching of the power supply and the ozone generating tube can be ensured and the efficiency of the power supply can be raised.
...
© 2021 KumChaek University of Technology