Jo Apr 8, 2025
Diesel engines are widely used in various fields of national economy due to their low specific fuel consumption, high torque and high power density at low speed. Valve timing is one of the main characteristics that has a great influence on the fuel economy and exhaust gas emission characteristics of internal combustion (IC) engines. At present, supercharging of internal combustion engine, common rail fuel system and variable valve timing are the key technologies for improving the performance of IC engines by reducing specific fuel consumption and harmful components in the exhaust gas.
In order to analyze the effect of valve timing on the engine performance, a one-dimensional simulation analysis model is required to analyze the working process of the engine. GT-Power, Ricardo-Wave and AVL/BOOST are widely used for analyzing the working process of IC engines.
Many researchers have developed models and optimized their properties for different internal combustion engines using these programs and various analytical methods.
Jang Song Ho, a researcher at the Faculty of Mechanical Science and Technology, has established a one-dimensional working process analysis model of the 4D4-12.5/11 engine with the bore of 110mm, the stroke of 115mm and the engine displacement of 4.75L by using GT-Power, and determined the most suitable valve timing using the experimental design, the artificial neural network and the genetic algorithm of the GT-Power program.
Applying the optimal valve timing (variable distribution phase) for the engine speed to the 4D4-12.5/11 engine, the engine power increases by 1.37% at 1 400r/min and 2.75% at 2 200 r/min, respectively, compared to the initial valve timing. The effect of the intake opening angle (IVO) and exhaust closing angle (EVC) on the engine power is not so significant, but the intake closing angle (IVC) and exhaust opening angle (EVO) have a great influence on it. In addition, the effect of valve timing on the engine power is greater at the nominal state (2 200r/min) compared to the maximum torque state (1 400r/min).
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Jo Apr 7, 2025
Generally, the communication system requires transmit-and-receive using one antenna. A duplexer is an important component in a wireless transceiver because it allows simultaneous transmission and reception of signals by means of a single antenna. With a single antenna, a duplexer is normally used for a microwave transceiver to isolate a transmitter from a receiver electrically. Therefore, a duplexer is generally composed of two individual band-pass filters with different center frequencies. Conventionally, the band-pass filter of a duplexer is a coaxial cavity filter with high quality factor.
Filter tuning in coaxial cavity filters can be realized by tuning screws. In this case, the tuning screws are adjusted from the lid towards the resonator inside the cavity. The goal of filter tuning is to find the optimum locations of tuning screws that satisfy the required filter response.
The optimization design of microwave filters may be achieved by using the optimization tools supported by CST Studio. These optimization tools change all the filter geometries to obtain the geometric parameters when the error function between the current frequency response and the desired frequency response is less than the threshold. However, use of these tools provides no guarantee that each step of optimization always goes in the right direction and optimization process is very time-consuming. Furthermore, the required frequency response may not be obtained accurately. Hence, recently, optimization routines using space mapping technique have been widely exploited.
Kim Myong Sik, a section head at the Faculty of Communications, has found a new optimization method to determine the location of tuning screws of the coaxial cavity filter for mobile base stations by using the space mapping technique, and verified the band-pass characteristics of the duplexer.
Unlike the optimization algorithms supported by CST Studio, the proposed method guarantees much faster optimization and can always produce the expected results.
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Jo Apr 3, 2025
Since blasting always carries a great risk of accidents, it is of vital importance to ensure the maximum initiation reliability, precision and safety of blasting devices.
The present initiation systems include an electric initiation system and an electronic initiation system using electric wires as a blasting device, and a detonating cord system and a non-electric “Nonel” initiation system without using wires.
The detonating cord system and the non-electric “Nonel” system account for more than 80-90% of the currently used blasting devices. The detonating cord system is still widely used in open-cut bench blasting and underground mining blasting due to its high detonation reliability by the bidirectional initiation of the circuit despite its high-cost and emission of a large quantity of blasting gas.
In the meanwhile, the “Nonel” initiation system has the advantage of low cost, but its reliability is lower than the bidirectional initiation system because the circuits are connected in a unidirectional (indirect) initiation mode. Therefore, there is a continuous research to increase the initiation reliability of these unidirectional connectors.
Ryu In Mu, a researcher at the Faculty of Mining Engineering, has completed an initiation system available for all blasting operations including mine blasting by adding the components of the non-electric "pulkkot" initiation system, a direct-initiation bidirectional blasting device, and by improving its characteristics.
This initiating system provides tensile strength of more than 1N ensuring 100% initiation of shock tubes in the connector and it is safe in blasting, and storage and handling of system elements because the connector has no detonators.
The non-electric "pulkkot" initiation system was fully introduced into all blasting operations including open and underground mine blasting, thus reducing the cost of fragmentation significantly by increasing the explosive energy more than twice without explosion and blasting gas exhaust with a reliability of 99.99% without misfire.
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Jo Apr 2, 2025
The 38th Science and Technology Festival of Kim Chaek University of Technology (KUT) took place from Feb. 4 to 7 in the university gymnasium, on the theme “Science and technology is the locomotive of the overall national prosperity”.
The festival was divided into a machine and transport panel, an IT and communications panel and an electron and automation panel. Presented there were more than 270 sci-tech achievements from 30-odd units of KUT.
Highly appreciated were 80-odd research achievements among which two proposals including “Heavy rail steel productivity enhancement and quality improvement by the combined steel making method and CO gas stirring method” by Ra Ju Hyon, an institute head of the Faculty of Metal Engineering got special grade, twelve took the first place and twenty-five took the second.
In the ranking of units, the Faculty of Heat Engineering, the Faculty of Electronics and the Faculty of Electrical Engineering took the lead.
During the festival, successes and experience were widely shared and transferred through the presentation and examination of valuable sci-tech proposals and technical exchange among visitors.
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Jo Mar 28, 2025
Nitrite is one of the toxic substances existing in foods such as fish, meat products and vegetables, which has a great impact on human life and health. When nitrite ions enter the body, they bind with blood hemoglobin to form metahemoglobin, causing it to lose its oxygen-carrying capacity. It also combines with amines and amides of the digestive organ to produce carcinogenic nitrosamine compound. Therefore, an accurate measurement of nitrite concentration is very important for protecting human life and health.
So far, various methods of detecting nitrite, such as chromatography, spectrophotometry, and electrochemical analysis, have been developed. Among these methods, the detection of nitrite ions by electrochemical sensing electrodes is a major candidate for nitrite detection due to its high sensitivity, selectivity and fast response. In particular, modified electrodes based on conducting polymers including polyaniline, polypyrrole and polyphenylene have received great attention in the development of sensing electrodes using them because of their ability to prevent surface contamination and improve the electrochemical properties of the electrodes.
Pak Jong Sung, a section head at the Faculty of Chemical Engineering, has developed a novel electrochemically modified carbon paste electrode based on PANI-TiO2/Pt nanocomposites.
The experimental results demonstrate that the PANI-TiO2/Pt electrode has pretty excellent electrocatalytic ability for oxidation of nitrite.
For more information, please refer to his paper “Electrochemical Detection of Nitrite on PANI-TiO2/Pt Nanocomposite−Modified Carbon Paste Electrodes Using TOPSIS and Taguchi Methods” in “ACS Omega” (SCI).
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Jo Mar 27, 2025
Commonly, arsenic-bearing gold ore is very refractory. Therefore, it is necessary to break these ores up to the gold particle size or decompose them to make gold exposed before leaching. The process such as decomposition and crushing prior to leaching is called pretreatment of refractory gold ore. Recently, many researchers have studied the pretreatment of gold bearing arsenopyrite to expose gold and remove arsenic by changing the mineral composition, electrochemical and physicochemical properties of gold ore.
There are many pretreatment methods of refractory gold ores including roasting oxidation, bacterial oxidation, pressure oxidation and chemical pretreatment. Particularly, the chemical treatment methods are widely used due to its low cost. Among them, alkaline pretreatment is considered to be the most economical and eco-friendly. However, this method is not widely used due to the dependence of alkaline concentration, temperature and pressure.
Recently, ultrasound has been widely used to accelerate the speed of chemical reaction. Many researchers have already studied the effects of ultrasound on gold and zinc extraction, on copper extraction from copper ore, on leaching of phosphate using hydrochloric acid, and on sulfuric acid leaching of colemanite. However, the effects of ultrasonic power and intensity of mechanical agitation on leaching of minerals are rarely involved.
Hong Won Chol, a researcher at the Faculty of Mining Engineering, has investigated the effect of the ultrasonic power and mechanical agitation intensity of pulp on alkaline pretreatment of gold-bearing arsenopyrite.
He studied the effect of the pulp temperature on the leaching efficiency in alkaline pretreatment of arsenopyrite under both ultrasonic and non-ultrasonic conditions. Compared with the non-ultrasound condition at the temperature of 60℃, arsenic extraction and gold extraction increased by 20 % and 14.4 %, respectively, in the presence of ultrasound at ambient temperature.
You can find more information in his paper “Effects of Ultrasonic Power and Intensity of Mechanical Agitation on Pretreatment of a Gold-Bearing Arsenopyrite” in “Archives of Acoustics” (SCI).
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