Jo Mar 6, 2026
The microwave cavity filter, which is operated by coaxial resonators with high Q-factors above 4 000, has high power and high performance.
Coupling matrix synthesis is the most important step in the design of microwave filters. This is because coupling matrix is the most critical in mapping the theoretical filter characteristic polynomial to the parameters of a physical filter model.
The coupling matrix of a microwave cavity filter is not a feasible topology, so it must be reconstructed by performing a similarity transformation. The reconstruction of coupling matrix using the rotation matrix is not suitable for lossy filter design and there are several problems in reconstructing the coupling matrix, which necessitates different approaches.
Kim Chol Jin, a researcher at the Faculty of Communication, proposed using hyperbolic reflection matrix in the coupling matrix synthesis to design a microwave cavity filter for use in mobile station remote radio units.
First, he synthesized an orthogonal matrix that can simplify the complex coupling matrix obtained in the design of a microwave filter with loss considerations. Then, he solved the problem of code control of cross-coupling arising in reconstructing a general coupling matrix.
The experimental results show that a coupling matrix is reconstructed to have desired topology and that a hyperbolic reflection matrix can reconstruct a complex coupling matrix.
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Jo Mar 5, 2026
Although many serious problems are being caused due to the air pollution and rapid fossil fuel depletion, coal combustion is still a major method for energy generation. Therefore, most heat power plants use pulverized coal as the fuel for steam boilers. Even in this case, however, there are still many problems such as expensive cost of oil, difficulty in its storage and supply, stabilization of ignition and/or burning caused by hot corrosion of surface and heavy metals pollution. These problems require new ways of ignition and burning stabilization.
Due to additional pulverization of coal granules, excitation and dissociation of molecules, and production of free radicals, plasma-assisted combustion technique has drawn considerable attention as a promising method for enhancing combustion.
Plasma-assisted combustion can be classified into equilibrium plasma-assisted combustion (EPAC) and non-equilibrium plasma-assisted combustion (NEPAC). Most equilibrium plasma burners use a plasma torch of arc jet, which has some disadvantages such as fast consumption and frequent replacement of electrodes, complexity of cooling system and low energy efficiency. NEPAC produces incomparably higher vibrational temperature and electron temperature than the translational temperature in non-equilibrium plasmas. Therefore, the non-equilibrium plasma is of particular interest as far as combustion is concerned. The plasma generated by gliding arc discharge that includes both thermal effect and non-equilibrium characteristics is quasi non-equilibrium plasma suitable for fuel combustion.
Ri Thae Nam, a researcher at the Faculty of Physics, built a pulverized coal burner and conducted some experiments, on the basis of the understanding of the characteristics of non-equilibrium plasma generated by gliding arc discharge.
First, he performed a test on the experimental set-up composed of a plasmatron and a burner using gliding arc discharge with two electrodes. He drew distinctive temperature distribution curves at four measuring points of the set-up and confirmed the combustion possibility of low-grade coal. Then, he constructed a combustion system of pulverized coal for boiler ignition and obtained stabilized pulverized coal flame through the secondary burner. Finally, he analyzed the possibility and advantage of boiler ignition by the proposed combustion system in contrast to that of heavy oil or natural gas.
The analysis results showed that the introduction of the proposed combustion system could bring major economical effects by reducing the energy needed for ignition and combustion of coal.
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Jo Mar 4, 2026
The 39th Science and Technology Festival of Kim Chaek University of Technology took place from Feb. 24 to 27 on the theme “Steady Development of Sci-tech Capability”.
The festival was divided into 7 panels including metal and chemistry, machine and transport, etc. Presented there were more than 260-odd sci-tech achievements including “Robotization and streamlining of precision mold production process” and “Establishment of active lime production process”.
During the festival, there were presentation and examination of sci-tech proposals and technical exchange among visitors. Trophies, certificates and prizes were awarded to the highly-praised units and individuals.
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Jo Mar 2, 2026
Yakbap is a national dish peculiar to the Korean people and a typical dish for First Full Moon Day (lunar January 15).
It is of high nutritive value and delicious with good harmony of honey, sesame oil, chestnuts, dates, etc.
Here is the recipe for yakbap.
First, glutinous rice is washed, cleaned and soaked in water for about three hours. Second, chestnuts are thoroughly peeled off and cut into two pieces. Third, dates are cleaned before the seeds are removed. The half is smashed and the other half is cut into two. Fourth, glutinous rice is steamed or boiled and it is placed on a big vessel. Then, sugar is mixed evenly with the rice to prevent the rice grains from sticking to one another. Fifth, chestnuts and dates are added after seasoning with soy. Then, sesame oil and honey are evenly mixed with it before putting it in a pot with a lid. Sixth, the yakbap pot is put into a cauldron with water and fixed before putting the lid and boiling it. Finally, it is boiled for eight to ten hours while regulating the fire for continuous boiling of water after boiling it over intense fire for half an hour. After 20-24 hours, yakbap looks more delicious. The finished yakbap is put in a container with a lid and served with pine nut seeds and cinnamon powder on it.
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Jo Mar 1, 2026
On the day of First Full Moon Day (lunar January 15), people used to enjoy rice wrapped in edible herbs such as laver, dried vegetable leaves, aster, etc. It was called pokssam. Tongguksesigi wrote that pokssam was the rice wrapped in vegetable leaves or laver, and eating the soup cooked of dried cucumber stalks, eggplant skin, radish leaves, cabbage leaves, etc. on the day helped bear the heat.
In the past, our country had a custom of drying wild edible herbs like aster, bracken and roots of broad bellflowers and vegetables such as eggplant, pumpkin, radish, cabbage, etc. in autumn for frying them or cooking soup of them and wrapping rice in them in winter. In some areas including Kaesong, perilla leaves were used for pokssam. Our people’s custom of drying and storing various kinds of edible herbs to make special dishes shows not only their meticulous and frugal way of life but also the development of their diverse dietary life.
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Jo Feb 28, 2026
NOMA (Non-Orthogonal Multiple Access) is the main technology of 5th generation communication system for controlling the throughputs of users by using power allocation corresponding to information transmission time.
In the previous researches, they assumed that all users have the same channel weights in the aspects of power allocation and sum rate.
However, their assumption makes it difficult to simultaneously satisfy the sum rate and user fairness.
Kim Tong Jin, a researcher at the Faculty of Communication, proposed an improved energy harvesting scheme to achieve the maximum sum rate by using weighted users.
The proposed scheme is based on an energy harvesting model and the sum rate is expressed by the throughput of the Nth user.
He set the channel weight of the Nth user to be a certain value and calculated the weights of other users by using the weight of the Nth user so that all users have the same rate and the scheme has the maximum sum rate. Then, he assumed that the sum rate does not depend on the number of users and the channel weight of the Nth user. Under this assumption, he calculated the optimal information transfer time to maximize the sum rate.
He compared the new scheme with the previous one in terms of the channel weight for the Nth user and information transfer time. The results showed that when the number of users in one source block is increased, the sum rate and user fairness are improved significantly.
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