Jo Mar 30, 2023
A research team led by Kye Myong Ho, an institute head at the Faculty of Metal Engineering, has developed an energy dispersive X-ray fluorescence (EDXRF) analyzer.
The analyzer has several advantages: nondestructive analysis without any chemical reagents, simultaneous analysis of several elements in a short time, very simple structure, wide range of concentration standardless analysis and convenience in use.
It is made up of a high voltage power unit, an x-ray tube, a semiconductor detector, a multi-channel pulse height analyzer, a control circuit, a vacuum pump and analysis software.
The maximum power of the x-ray tube is 50W and the energy resolution of the semiconductor detector is 149eV. The analyzer enables measurement in the vacuum and its measuring time is below 5 minutes.
The analytical software is used for instrument control, qualitative analysis, semi-quantitative analysis, calibration curve drawing and quantitative analysis.
In the software, the voltage and current of the x-ray tube are set according to elements, and fluorescence spectrum is collected. Semi-quantitative analysis is available by standardless analysis. For semi-quantitative analysis, the kind of sample must be selected before measuring. You can also make a quantitative analysis by a standard curve. First, you should select the standard curve for a sample, and then quantitative analysis result is presented.
EDXRF analyzer can be widely used for analysing element concentration of substances such as alloy, mineral, cement, precious metals and catalyzers in the fields like metal, chemical, building materials, mining industries, prospecting and archaeology.
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Jo Mar 29, 2023
A research team led by Kim Hyong Chol, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has developed a dredging vessel for building tideland banks with the soil on the ocean floor.
The dredging vessel can remarkably increase the construction speed of tideland banks in the absence or shortage of mountainous soil, and carry out continuous work without being affected by rising tide and falling tide.
The dredger consists of a hull, two back side shovel excavators, a bunker, a main belt conveyor, an intermediate belt conveyor, a ground tackle, etc.
The two back side shovel excavators, separated from the front of the hull to the left and right sides, perform the function of digging the soil on the ocean floor up into the bunker.
The excavation width of the ocean floor is set to be larger than the hull width and the excavation depth is set to form a section larger than the section of a bank.
The main belt conveyor lays the excavated soil on the bank. The main belt conveyor is installed vertically to one side so that the dredging vessel can move along the bank to dig up soil onto the bank. To ensure the safety of the bank, the dredging vessel works 30m away from the bank, so the main belt conveyor is longer than 30m.
In order to keep a balance with the two excavators, the main belt conveyor is set up on the stern, and the intermediate belt carrying the soil in the bunker to the main belt conveyor is placed on the central longitudinal section of the hull.
This dredging vessel is characterized by its structure in which excavation and transport are carried out by one boat, and by its operation whereby at the time of high tide, it works on the tidal water, and at the time of low tide it floats on the water left in the pool excavated by itself, regardless of tidal current.
This dredging vessel can be efficiently used to build tideland banks, tidal power stations and other dams on the water areas whose floors are exposed during low tides.
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Jo Mar 28, 2023
A research team led by Cha Pong Il, a section head at the Faculty of Mechanical Science and Technology, has developed a multi-rotor UAV that could enjoy wide use in agriculture.
The agricultural multi-rotor UAV is a piece of battery-powered up-to-date mechanical equipment for scattering various agricultural chemicals and fertilizers, and taking and transmitting the photographs of crops.
Iron-shell construction is used for its safe operation under 15-kilogram effective load.
Its specification is as follows.
Flight velocity: 5-10m/s
Flight altitude: 3-10m
Endurance: 15-20 minute
Effective mass : 15㎏
Take-off mass: 40㎏
Working area (1 time): 1 hectare
Temperature condition: -10~40℃
The effectiveness of the agricultural multi-rotor UAV is as follows.
Scattering of agricultural chemicals, fertilizer and seeds by a multi-rotor UAV enhances working efficiency remarkably, about 100 times higher than by human. It will do all kinds of harmful work like agricultural chemical spray, which leads to the improvement of working conditions for farmers. It consumes no fuel, so it is environmentally-friendly.
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Jo Mar 26, 2023
Although it appears that enough researches have been made as regards the estimation of the optical feedback factor C of a self-mixing interferometer, no method of the C estimation can ensure its reliability if the operation of the self-mixing displacement sensor covers the strong feedback regime with fringe loss due to large displacement of a target.
That is the main reason why the precision of the sensor degenerates for measurement of large displacement.
Kim Chol Hyon, a researcher at the Faculty of Physical Engineering, has proposed a novel C estimation method called region tracking for C value, which is indispensable for measurement of long-range displacement, and demonstrated its fidelity experimentally.
He classified the fringe loss which arises in moderate and strong feedback regimes into an individual fringe loss and a collective fringe loss. Then, he clarified that the individual fringe loss is induced due to the hysteresis of the self-mixing effect and the collective fringe loss due to the minimum line width mode competition principle.
The displacement reconstruction based on the proposed region tracking method ensures better precision than a half wavelength, depending on the method of displacement retrieval. The approach presented will make a great contribution to further improvement of the accuracy of the self-mixing displacement sensor for large displacement.
For more information about this, please refer to his paper “Improvement of precision of self-mixing displacement sensor based on region tracking for large displacement” published in “Optics Communications” (SCI).
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Jo Mar 25, 2023
Sodium hypochlorite antiseptic solution (NaOCl) has been widely used all over the world to prevent the spread of epidemic diseases. However, due to its low sterilizing power, it needs high concentration of activated chlorine, which is harmful to the human body and environment and results in the corrosion of metal products.
Scientists found that disinfection is caused by hypochloric acid(HOCl), not sodium hypochlorite (NaOCl) and recommended using hypochloric acid with pH 6~7.2, ORP≧900mV for disinfection. Accordingly, hypochloric acid is being produced by electrolysing admixed solution of NaCl, HCl and H2O in electrolytic baths without diaphragms, but this method is restricted in its output.
A research team led by Choe Hyon Ho, a section head at the Faculty of Electronics, has succeeded in preparing neutral electrolytic water with hypochloric acid by mixing sodium hypochlorite (NaOCl), chlorhydric acid (HCl) and water (H2O) sodium hypochlorite antiseptic solution at the sodium hypochlorite antiseptic solution production sites existing in the DPRK.
They determined the ratio of additional amount of chlorhydric acid to the mixing amount of water for preparing neutral electrolytic water through some basic experiments.
The preparation method can satisfy the demand for neutral electrolytic water with hypochloric acid for several uses with less consumption of salt, electrolytic plates and electric power than before.
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Jo Mar 23, 2023
When silicon is anisotropically etched, the etch rate of individual crystal planes of silicon is different from one another. Therefore, corner undercutting in KOH solution is critical and it is difficult to form full convex corners without compensation. Consequently, an abnormal square structure can be generated, which affects the operation characteristics of elements.
In the fabrication of diaphragms for a pressure sensing unit with square-shaped convex corners, compensation patterns should be arranged in each corner so that the beam part, where resistances are set up, is not changed by etching.
Several compensation methods have been used to solve this problem. Triangular, square and banded compensation patterns have been widely used to protect rectangular edges and these are now recognized to be classic compensation methods.
However, general principles to design individual compensation structures and compensation patterns, especially formulae to determine the dimension of compensation patterns do not seem to be introduced in detail.
Jon Chung Hyok, a researcher at the Faculty of Semiconductor Institute, has proposed a method to determine the shape and dimension of reasonable compensation patterns to make very thin diaphragms from 10~15㎛ to 250~300㎛ in thickness with square mass.
First, for fabrication of V-grooves structures with mass by corner compensation, he showed the compensation mechanism by several compensation patterns. The experiments on different types of compensation patterns showed that a diagonal-type compensation pattern is the best in performance. However, when etching depth should be ranged from 150㎛ to 200㎛, this compensation pattern is not suitable for compensation because the dimension of the mass and diaphragm should be restricted along their edges.
Next, on the analysis of the experimental results, he determined conditions for V-grooves structure from the given compensation pattern.
He concluded that when two types of compensation patterns are combined, the dimension of a square compensation pattern should be calculated before compensated corners with band compensation patterns are used to satisfy the insufficient etching depth, in order to increase the compensation effect.
Subsequently, he has made a diaphragm with the mass where a/h is less than 3.72 and b/h is less than 3.33 by applying corner compensation patterns.
More information about this is found in his paper “V-grooves Structures of Semiconductor Pressure Sensors with mass by Convex Corner Compensation” published in “Journal of Analog and Digital Devices” (EI).
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