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 5, 2025
Maktae Rock is about 700 meters away in the direction of Pangung-ri from the seat of Namap-ri, Yomju County, North Phyongan Province.
There is a low hill in the east and a vast paddy field in the west of the rock, and several kilometers away from the field is the West Sea of Korea.
It is a mysterious standing rock whose covering layer was washed and cut by rain and wind during the long geological period to expose the red felsic dyke in its interior by abrasion and weathering.
The rock is ten meters tall and sixteen meters round at the bottom.
Although it looks as if it was going to fall down, it is well balanced. This old rock has many cracks.
It is well known from long ago as it is seen even several kilometers away.
It is a natural monument of great significance in studying the weathering of red felsite, and abrasion and coastal sedimentation constantly happening at the boundary between the sea and the land.
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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 Apr 1, 2025
From olden times, the Korean ancestors have created and carried forward several customs suited to the warm seasonal features of April.
The seasonal divisions of April include chongmyong and kogu.
Chongmyong literally means the beginning of clear bright spring weather.
When chongmyong was approaching, our people cleared out all the traces of winter, and sowed various kinds of flower seeds in the garden and planted fruit trees around the house. In the countryside, they soaked rice seeds in water to sow them in the seedbed before chongmyong. They usually started spring sowing that day.
On the occasion of chongmyong, our people visited or moved the tombs of their ancestors.
Typical dishes for the day are steamed wheat flour cake, shredded green gram paste and seasoned edible herbs such as bracken, fern, aralia shoots and anise.
Chongmyong usually falls between April 4 and 6.
Kogu means the time when the rain useful for the growth of crops falls.
Our people were busy with farming at this time since it was an important period governing the successful farming of the year. On the day of kogu they sowed seeds of rice, foxtail millet, sweet potato, sesame, etc.
In the period around chongmyong and kogu, our people played several folk games and did fishing in rivers and seas.
Kogu falls around April 20 according to the solar calendar.
As mentioned above, the Korean people have created and carried forward several customs suited to the seasonal features of April from long ago.
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