Jo Feb 25, 2022
Ri In Sik, a researcher at the Semi-conductor Institute, made an analysis of reverse voltage distribution of high-voltage diode stack considering the effect of temperature.
First, he presented an equivalent circuit of a high–voltage silicon diode taking into account the effects of temperature and reverse voltage, and obtained an analytical expression for impedance of a diode. Then, he proposed the most generalized equivalent circuit of a high–voltage diode stack consisting of a serial connection of several diodes, and obtained an analytical expression for the reverse voltage applied to each diode. As a result, he offered an easy estimation of the reverse voltage distribution of a high–voltage diode stack by an analytical method, not in an experimental way.
High–voltage diode stacks (HVDS) are now widely used in extracorporeal shock wave lithotriptors, diagnostic X–ray equipment, sound detectors, night glasses, high–voltage magnetic compression modulators, high–voltage pulse generators, dust collectors and electrostatic fly–ash separators at thermal power plants.
The most important characteristic of an HVDS is reverse voltage distribution between chips or diodes. If the non–uniformity of reverse voltage distribution is severe, twice the breakdown voltage of P–N junction or more can be applied to the chips or diodes placed on high–voltage terminal and ground terminal, leading to their destructions. The reverse voltage distribution of an HVDS is mainly affected by the characteristics of chips or diodes, such as the dependence of the temperature and the reverse voltage on the impedance of them. The dependence of impedances of chips or diodes on temperature and reverse voltage strongly affect the reverse voltage distribution of an HVDS. Also, according to an HVDS consisting of stacked chips or a serial connection of individual diodes, the leakage impedances connected to the high–voltage terminal and the ground terminal are varied and they strongly affect the reverse voltage distribution. The stacking of chips and a serial connection of the individual diodes are the technologies that have been widely used to manufacture HVDS.
The reverse current of the diode increases and its barrier resistance decreases with increasing temperature and reverse voltage. In addition, when the reverse voltage of the diode increases, the width of the space–charge layer increases, thus the barrier resistance decreases. Consequently, the impedance of the diode decreases with increasing temperature and reverse voltage. Hence, the equivalent circuit of an HVDS consisting of a serial connection of the individual diodes is needed in order to analyze the reverse voltage distribution of it, considering the effects of the temperature and the reverse voltage of the diodes.
That is why, he proposed and analyzed a new equivalent circuit of an HVDS, including not only the impedance and the uniform voltage impedance of each device, but also the leakage impedance connected to the high–voltage terminal and the ground terminal.
The calculated values of the reverse voltage distribution of a high–voltage diode stack were shown to be in good agreement with the measured values.
His essay “Analysis of Reverse Voltage Distribution of High–Voltage Diode Stack Considering Effect of Temperature” is carried in SCI Journal “Solid-State Electronics”.
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Jo Feb 24, 2022
The research group led by Ma Min Gon, vice dean of the Faculty of Information Science and Technology, has developed a Korean braille character reader which converts raised letters read by an image input device into a character code readable by ordinary people.
When books published in raised type for the blind to read by groping are read by an image input device like a scanner, the raised parts are shown in dim dots.
In order to extract these dim dots more precisely, they proposed and realized several new basic methods: binarization by wavelet difference image, tilt estimation by Hough conversion, dot extraction by dot database and Maharanobis distance for precise extraction without being affected by the scanning direction, charline extraction from dots capable of strongly overcoming noises, substitution of braille code for unicode by bidirection scanning, postprocess based on geometrical position of dots, etc.
Thus, they were able to raise the extraction precision up to 96% and the recognition speed up to 1 second per page.
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Jo Feb 22, 2022
A research group led by Ri Yong Min, a researcher at the Faculty of Materials Science and Technology, has developed a screw rolling mill with individually driven rollers and established a rolling process which can produce bars of more than 20mm in diameter through one pass without a roller change from round steel of 50mm in diameter, consuming less power. They will no longer need an ordinary light section rolling mill in machine factories and repair bases that have a great demand for bars in various diameters.
In this rolling process, round steel of 50mm in diameter is heated to 850~950℃ in a heating furnace and is rolled into bars of 20mm in diameter through one pass in a cantilevered 3-helical rolling mill with individually driven rollers that has a large feed angle and an elongation angle before they are cut into necessary lengths.
Thus, they can produce bars of different diameters from short scrap iron by changing no rolls but adjusting the roll gap, and ensure the metal yield of more than 99% and the roundness of ±0.1.
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Jo Feb 21, 2022
Kim Won Ok, a researcher at the Faculty of Information Science and Technology, has developed a C/C++ programming evaluation system to raise practical programming skills of students who are learning C/C++ programming including those who are receiving distance education, and to make an accurate evaluation of the programming assignments performed by them.
What she has done includes the combination of web and other applications by TCP socket communication, the implementation of a C/C++ programming environment by C++ compiler and I/O stream pipeline, accurate evaluation of assignment performance, and the security of learning-related data including assignments by user certification, copy paste protection and encryption.
She herself tried making and running a program so as to make a programming tool and a system for evaluating programming accuracy. This helped raise students’ programming skills and enthusiasm for study, and evaluate their assignment performance rapidly and accurately.
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Jo Feb 19, 2022
Pak Il Chol, a researcher at Faculty of Information Science and Technology, has developed a Java API compound retrieval program on the basis of the collection of code snippets and feature extraction. In this program it is possible to realize ranking of code snippets suitable for user intention from their application degree and brevity degree.
He increased the rate of indexing by 0.3GB per hour and the precision and recall by 6% and 9% respectively, which resulted in the improvement of the development speed and quality of programs. Thus, he ensured the guarantee for reducing the labour and time needed for program development to one tenth.
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Jo Feb 17, 2022
Ri Sok Chol, a section head at the Faculty of Metal Engineering employed genetic programming (GP) to derive a CaO-SiO2-Al2O3 slag viscosity equation and presented an algorithm for it.
Slag viscosity is a key property that determines the stability and productivity in the metallurgical furnace operation, and it is of great importance in understanding the fluid dynamic of molten slags and slag-metal reaction kinetics during the pyrometallurgy process.
Up to now, there have been many experiments to measure, and models to estimate slag viscosity. Viscosity models can be classified into explicit models, structural models, and miscellaneous models according to the way in which they are connected to the description of slag structure.
A slag viscosity equation described with only slag composition and temperature was successfully derived by genetic programming (GP).
The viscosities of CaO-SiO2-Al2O3 system slag can be simply and expediently calculated in a wide range of compositions and temperatures by using the derived viscosity equation.
The average relative error between the values obtained by the equation and the experimental data used for its derivation is as low as 17.1%. To evaluate the accuracy of the viscosity equation of CaO-SiO2-Al2O3 system slag, experimental data and results calculated by many researchers and not used for the derivation of the viscosity equation were compared, and a reasonably good agreement was demonstrated between the results calculated by viscosity equation and other researchers’ experimental and calculated data. The calculation of viscosity showed higher accuracy than previous models.
His essay “Derivation of CaO-SiO2-Al2O3 System Slag Viscosity Equation by GP” was carried in SCI Journal “Journal of Mining and Metallurgy, Section B: Metallurgy”.
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