Jo Oct 22, 2025
Environmental pollution and depletion of fossil energy have made the research for the exploitation and use of natural energy more and more intensive in the world, and wind power resources find wide application day by day because it is free of depletion and environmentally friendly.
Precedence has been given to the research on developing high-efficiency wind turbines, and as a result, various types of wind turbines have been developed to provide maximum wind energy.
As well known in the general momentum theory, the performance of wind turbines is characterized by the power coefficient, which is defined as the ratio of mechanical energy to kinetic energy of wind passing through the rotating blade face per unit time.
However, the total kinetic energy of wind mentioned above is not generated by the real wind flowing into the blade inlet because the nearer it gets to the face of blade, the lower the upstream velocity gets due to the pressure caused by the blade of wind turbine.
Kim Mun Hui, a researcher at the Faculty of Electrical Engineering, has presented the theoretical consideration results from the new concept on the rotor swept area.
She applied optimization theory of multivariate functions to describe the power characteristics of wind turbines by the relationship between the upstream area and the rotor swept area. She predicted that the upstream area is 1/1.125 times the rotor swept area and the value of the maximum power coefficient increases to 0.667.
In addition, she confirmed that the maximum value of the power coefficient is kept as 0.667 even in the case of rotors installed in several rows on one axis, and that the total power is not distributed to the rotors in each row, but depends on the rotor in the last row.
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Jo Oct 21, 2025
When a vehicle reenters the earth’s atmosphere at hypersonic speed, the surrounding air molecules are dissociated and ionized by the tremendous heat due to friction with atmosphere, and plasma sheath is formed around the hypersonic vehicle’s surface. The plasma sheath greatly attenuates the electromagnetic (EM) waves radiated from an onboard antenna through reflection and absorption effects, and causes intermittent communication outage. Therefore, the research on the interaction mechanism between the electromagnetic (EM) wave and the plasma sheath is of great significance.
Many studies have been done on the propagation characteristics of EM waves at the plasma sheath. However, only a few researches were focused on the propagations of obliquely incident EM waves on the reentry plasma sheath.
Han Yong Su, a section head at the Faculty of Physical Engineering, has investigated the propagation characteristics of obliquely incident S-polarization EM waves on the reentry plasma sheath by the scattering matrix method (SMM). Assuming the plasma sheath to be nonuniform, unmagnetized, cold, weakly ionized, collisional plasma in steady state, he examined the effects of incident angle, electron density profile and collision frequency on the reflection, transmission and absorption of obliquely incident S-polarization EM wave on plasma sheath.
The numerical results show that when the incident EM wave obliquely passes through the plasma sheath, the amplitudes of reflectance, transmittance and absorptivity are obviously modulated by the incident angle, electron density profile and collision frequency.
In addition, he has found that the transmittance and absorptivity peaks are shifted from the lower to the higher frequency with increasing incident angle, electron density profile and collision frequency.
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Jo Oct 19, 2025
LED is widely used in greenhouses as it is a non-pollution light source with high efficiency, long lifetime and small size and thermal radiation. Red light and blue light are efficiently absorbed by chlorophyll a and b, and spectra power distribution (SPD) of light source used in greenhouses has a great effect on the photosynthesis process and growth of plants.
Therefore, the effect of SPD and radiation of LED on the growth of plants is an important research focus.
The research group led by Yang Ki Won, a section head at the Faculty of Electronics, has manufactured a gravity injection vegetable-growing device (GI GROW) LED lamp by compounding red, green and blue using improved Gauss distribution to control the spectra power distribution (SPD) of LED.
This LED lamp consists of red, green and blue LEDs of 1W and its total output power is 1 152W, with 72 green LEDs, 864 red LEDs and 216 blue LEDs.
They have compared it with several other plans to evaluate its effectiveness. The results show that GI GROW (using this LED) could increase the fresh weight of lettuce by 1.5 times while reducing the cultivation period by 2.5 times, compared to the lettuce grown in a conventional vegetable greenhouse under the same conditions.
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Jo Oct 17, 2025
Commonly-used ore of Mn is pyrolusite whose main composition is MnO2. With rapidly growing demand for Mn products, low grade Mn ores and secondary Mn sources impossible to be processed by conventional metallurgical methods have become important Mn sources.
In recent years, various hydrometallurgical methods based on various reductants have been developed for the recovery of Mn from these sources. In other words, the reductive acid leaching of low-grade Mn ores in sulfuric or hydrochloric acid solutions with reductants such as hydrogen peroxide, oxalic acid, glucose, corncob, aqueous methanol, ferrous sulfate, pyrite and sulphur was the main focus. However, these leaching techniques have some drawbacks. For example, oxidants and reductants are expensive and sulfur dioxide may be harmful to the environment, and organic reductants are effective but expensive, and their consumption is too much.
Pak Yong Song, a section head at the Faculty of Metal Engineering, has conducted an experiment to enhance the leaching rate of Mn in the preparation of Mn sulfate by the direct reductive leaching method using sawdust as a reductant and spent electrolyte as leaching solution, and confirmed its effectiveness.
He has examined the effects of experimental parameters such as the amount of concentrated sulfuric acid (95%), the amount of reductant, leaching temperature and leaching time.
The results show the following.
First, in order to enhance the leaching rate of Mn, the amount of concentrated sulfuric acid (95%) has to be 2.5mL, the amount of reductant 0.75g, the leaching temperature 85℃ and the leaching time 6h for 10g of pyrolusite powder. In this case, the leaching rate of Mn reaches 98.25%. Second, suitable solid/liquid ratio by spent electrolyte is needed to reduce the viscosity of the solution and provide suitable conditions for filtration.
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Jo Oct 16, 2025
Chaotic mapping has been widely used in cryptography for its dynamic nature, but it has some unsuitable security characteristics due to its limited precision. Therefore, improving the characteristics of chaotic mapping is essential for improving chaos-based encryption algorithms.
Choe Song Bom, a researcher at the Faculty of Information Science and Technology, has presented a plan to improve one-dimensional logistic mapping by parameter variation with delay coupling method and feedback control, proposed a new two-dimensional chaotic mapping, and further enhanced its randomness by selectively shifting the position of generated chaotic sequences. In addition, he has proposed a new image encryption algorithm based on the improved chaotic mapping.
The results of various simulation experiments showed that the proposed image encryption algorithm provides high-level security and is superior to the previous chaos-based encryption algorithms.
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Jo Oct 14, 2025
Concentration of some heavy metals such as As, Hg, Pb, Cd and Sn in food is a very important hygienic index. Because several of these elements are highly toxic, determining them at low concentration levels is of great importance for food factories.
In recent years, hydride generation atomic fluorescence spectrometers useful for determining the elements that form hydrides such as Pb, Hg, Cd, Zn, As, Sb, Bi, Ge, Sn and Se have been developed. Hydride generation technique provided a method for concentrating analytes and led to enhancing the detection limits for these elements by a factor of 10 to 100. This single-channel hydride generation atomic fluorescence spectrometer (HG-AFS) has some shortages like impossible simultaneous determination of several elements and long analysis time.
The advent of atomic fluorescence spectrometers equipped with a non-dispersive system led to the development of a multichannel atomic fluorescence spectrometer for simultaneous determination of several elements. The non-dispersive atomic fluorescence spectrometry (NDAFS) has several advantages of simple and low-cost instrumentation, adaptability to multi-element analysis, and highly-sensitive and simultaneous collection of energy from multiple lines.
There have been many reports on simultaneous determination by this spectrometer, but most of them are for two elements, and the only three-element simultaneous determination is As-Sb-Se simultaneous determination.
Ri Un Hui, a researcher at the Faculty of Metal Engineering, has studied the optimal conditions and method for simultaneous determination of As, Sn and Cd, and successfully introduced them into the analysis of several kinds of food.
This method can be widely used for analyzing not only food but also soil, water, biological samples, the environment, etc.
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