Jo Oct 6, 2025
Electrospinning is widely used as a versatile and convenient method for producing nanofibers. However, the drawback of this method is its low productivity. To overcome this drawback, various kinds of electrospinning methods have been developed. They are divided into two broad sorts. One is multi-needle electrospinning, which uses a spinneret consisting of many needles, and the other is needleless electrospinning. Multi-needle electrospinning finds its wide application in the field of advanced materials as it enables controlling the properties of nanofibers as well as producing special kinds of nanofibers such as core-shell nanofibers.
In multi-needle electrospinning, strong electrical interaction between the spinneret needles caused by the increased number of nozzles breaks the uniformity of electric field at the spinneret needle tip, which consequently destabilizes the flow of polymer jet and degrades the quality of fibers. Therefore, keeping the electric field uniform at the spinneret needle tip is a key factor for obtaining good-quality nanofibers.
There have been many studies so far to improve the uniformity of electric field. However, few of them dealt with optimal structure parameters to maximize the uniformity of electric field at the spinneret needle tip. In addition, there are almost no reports on the investigation of uniformity of electric field while varying the parameters of a dielectric medium such as the length, the diameter and the relative permittivity when it is inserted between spinneret needles.
Jang Kum Chol, a researcher at the Institute of Nano Science and Technology, has investigated the effects of geometric parameters of a dielectric medium around the spinneret needle on electric field uniformity in order to obtain uniform electric field distribution at the spinneret needle tip.
He simulated the electric field distribution using COMSOL Multiphysics 5.4 and optimized the dielectric medium parameters to improve the electric field uniformity by using Taguchi method.
As a result, he has confirmed that the electric field uniformity is the best when the diameter, length, arrangement distance and relative permittivity of a dielectric medium are 1.5mm, 5mm, 4mm and 2.3, respectively.
After optimization, the uniformity was over 1.27 times higher than before optimization.
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Jo Oct 5, 2025
Yut-game is a folk game in which players compete with each other moving pieces on the board as indicated by the faces of sticks.
It is one of the typical folk games enjoyed by the Korean people from olden times.
The terms used in the game “to”, “kae”, “kol”, “yut” (“shyung”) and “mo” are said to have originated from the job titles of the Puyo dynasty or from the purposes of breeding five kinds of domestic animals―pig, dog, sheep, cow and horse―distributed to five villages.
The yut-game is played with four sticks.
The sticks were usually made of wood, and chestnuts and beans were also used instead of wood sticks.
Round straight wood sticks 2 centimeters in diameter and 10-15 centimeters long were split in two semi-circle sticks for the game.
Who moved pieces round more on the board than opponents as indicated by the faces of sticks was the winner.
The yut-game, which has been enjoyed by the Korean people from olden times, is still being widely played on public holidays including the Lunar New Year’s Day.
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Jo Oct 2, 2025
Research on temperature field is of great importance for hot-pressing processes of ceramic materials. It affects both the uniformity of materials and the properties of ceramic products. Additionally, non-uniformity causes formation of thermal residual stresses during sintering.
Previous works mostly focused on the sintering of traditional ceramics and very few of them aimed at the hot pressing of modern ceramic materials.
Mun Hyok Chol, a researcher at the Faculty of Chemical Engineering, has proposed a heat transfer model for a system comprised of the mixture of Al2O3 and TiB2 and a graphite mould. Then, he has established a new method of determining the coefficient of heat transmission of ceramic composite by taking into account the change of porosity with sintering temperature, and simulated the temperature field using the COMSOL Multiphysics software.
He set the most suitable heating rate as 0.5K/s by analyzing both material properties and manufacturing efficiency.
The simulation result has shown increased initial relative density of blanks and more uniform temperature distribution of the system during hot pressing, which leads to further improvement of the physical and mechanical properties of ceramic composite materials.
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Jo Oct 1, 2025
The Korean people have celebrated Chusok (Harvest Moon Day) as a great folk holiday from olden times.
The term Chusok, which literally means autumn evening, originated from the practice of celebrating the full moon day in autumn of abundant harvest.
The Korean people have long regarded visiting their ancestral graves on the day of Chusok as a natural duty and a traditional custom.
When they visited their ancestral graves, they carried dishes cooked of new cereals to hold a memorial service, dressed in festive clothing.
For successful celebration of Chusok, they made all dishes the day before.
The special festival dishes of Chusok are half-moon-shaped new rice cake, steamed rice cake, chestnut dumpling, liquor, etc., among which half-moon-shaped rice cake has been accepted to be indispensable as a symbolic dish of Chusok.
Nochi made of glutinous rice powder, malty powder, etc. was also famous as a special dish of Pyongyang
People enjoyed the day playing several folk games including ssirum, swinging, tug of war, etc.
Enjoying the full moon was another custom of the day.
They either gathered in their house yards or climbed high mountains around them to see the rising moon.
This custom reflects the inner world of the sentimental and emotional Korean nation.
The Korean people still celebrate Chusok significantly as a traditional folk holiday and as an occasion of recollecting the unforgettable revolutionary forerunners, comrades, family members, relatives and friends who passed away.
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Jo Sep 30, 2025
On-demand charging schemes have been recently proposed to make efficient charging schedules of mobile chargers by introducing MCDM methods in wireless rechargeable sensor networks (WRSNs). However, most of the existing schemes use paired ratio scale (PRS) for weight assignment of multiple criteria to exaggerate the actual paired difference between them, and in the case of using FCNP of paired interval scale (PIS) for weight assignment of multiple criteria, weight compensation is not considered.
What is more, it is still unknown which is the best method for integrating FCNP with several MCDM approaches.
Rim Ju Song, a student at the Faculty of Communications, with the help of Ri Man Gun, an institute head of the same faculty, has proposed novel CS methods by integrated FCNP-VWA-MCDM(i) called FCVM(i) for solving all these problems.
The proposed methods first assign the weights to multiple criteria discriminating charging request node (cRNs) using FCNP and make compensation of them to be relatively exact weights with VWA. Then, on the basis of these weights, MCDM(i) is used to select the most proper next charging position. Recharging schedule is drawn up in this way and, at the same time, reasonable partial charging time at the selected charging locations are determined using the assigned weights with FCNP-VWA.
The extended experimental results prove that the FCVM(1) using TOPSIS gives the best performance among FCVM(i) methods.
You can find the details in his paper “FCVM(i): Integrated FCNP-VWA-MCDM(i) Methods for On-Demand Charging Scheduling in WRSNs” in “Journal of Data Science and Intelligent Systems” (SCI).
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Jo Sep 29, 2025
Fractal interpolation function (FIF) is a function which interpolates a given data set and whose graph is a fractal set. In 1986, M. F. Barnsley introduced the FIF using an iterated function system (IFS). Ever since, many researchers have studied the FIFs and applied them to a lot of scientific fields such as computer graphics, function approximation, signal processing, metallurgy, earth science, surface physics, geography, geology, medical science, chemistry, etc.
Rakotch contraction is the generalization of Banach contraction, which implies that the use of Rakotch’s fixed point theorem enables modeling of more objects than the use of Banach’s fixed point theorem. Moreover, hidden variable recurrent fractal interpolation functions (HVRFIFs) with Hölder function factors are more general than fractal interpolation functions (FIFs), recurrent FIFs and hidden variable FIFs with Lipschitz function factors.
Ro Chung Il, a researcher at the Faculty of Applied Mathematics, has demonstrated that HVRFIFs can be constructed using the Rakotch’s fixed point theorem, and investigated the analytical and geometric properties of those HVRFIFs.
Firstly, he constructed nonlinear hidden variable recurrent fractal interpolation functions with Hölder function factors on the basis of a given data set using Rakotch contractions. Next, he analyzed the smoothness of the HVRFIFs and showed that they are stable for the small perturbations of the given data. Finally, he obtained the lower and upper bounds for their box-counting dimensions.
If further information is needed, please refer to his paper “Analytical properties and the box-counting dimension of nonlinear hidden variable recurrent fractal interpolation functions constructed by using Rakotch’s fixed point theorem” in “Applied Mathematics and Computation” (SCI).
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