Jo Oct 26, 2026
The 3rd generation high-strength Al-Li alloy, AA2099 alloy has high specific strength and hardness, strong corrosion resistance, favorable service characteristics at ultra-low temperatures and good damage tolerance. Especially, its fine-grained compact fiber structure which does not have any internal defects provides high thermal creep strength and good surface quality after hot working. These advantages make AA2099 alloys an alternative to the traditional high-strength aluminum alloys in aerospace fields.
Like other high-strength Al-Li alloys, AA2099 alloys have such weak plasticity at room temperature that the cold plastic working methods are not applicable to making machine parts or workpieces which require complicated or large deformation. Therefore, hot working is the main choice. Accurate prediction of the flow stress of AA2099 alloys in hot working process is of primary importance in economizing Al-Li alloys widely used in aerospace industry, designing rational hot working processes such as hot rolling and forging, and increasing the processing efficiency.
During hot working process, the plastic deformation exerted on the material causes changes in the microstructure and mechanical properties, which are shown as the change in flow stress. Therefore, the development of constitutive material models is of major theoretical and practical significance in predicting the flow stress at different deformation temperatures, strain rates and strains to provide important theoretical basis for the selection of hot working equipment and engineering design.
The constitutive models developed so far include phenomenological models, physical models and ANN models. Phenomenological constitutive models include Johnson-Cook (J-C), Arrhenius (AH) models, etc. which are simple to develop, but have low prediction accuracy. In contrast, physical models such as microstructure-based models (MS-B) have very high prediction accuracy, but they are complex to express and difficult to develop. On the other hand, ANN constitutive models require a large number of experimental data to train the neural network, so it costs a lot to develop them. In a word, each model has its own advantages and disadvantages.
Han Yun Hyok, a student at the Faculty of Material Science and Technology, has developed phenomenological models (modified J-C and strain compensated Arrhenius (SC-AH) model) and a physical model (MS-B model) for predicting the hot flow stress behavior in AA2099 alloy, and identified a constitutive model that can predict the flow stress of this alloy most accurately by comparing their predictability.
He estimated the prediction accuracy by means of the average absolute relative error and correlation coefficient. The accuracy was 5.09% and 0.992 8 for the modified Johnson-Cook model, 6.12% and 0.9820 for the strain compensated Arrhenius model, and, 1.58% and 0.9994 for the microstructure-based model.
The accuracy of the proposed MS-B model was the highest with 1.58% and 0.9994 and the flow stress predicted by the proposed microstructure-based model was in good consistent with the experimental results. This indicates that the proposed microstructure-based model can accurately describe the hot deformation behavior of AA2099 Al-Li alloy.
You can find the details in his paper “Constitutive Analysis on Hot Deformation Behavior of AA2099 Alloy for Modeling of Flow Stress” in “Mechanics of Solids” (SCI).
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Jo Oct 25, 2026
Studies on infectious viruses have been conducted over a long period of time to understand their transmission and characteristics of variation, to gain a lot of knowledge such as testing methods and treatment measures, and to develop various vaccines.
The world’s danger of contagion still continues to spread, and the reality implies that viruses need to be more deeply studied.
One of the problems is the prediction of virus transmission by mathematical modeling. This research based on mathematical modeling has been widely conducted in the world, running up to thousands of pieces.
Mathematical modeling makes it possible to predict future transmission situations and to predict the number of medical personnel, beds, medical equipment, medical drug supplies, etc. that hospitals need to prepare. It can also simulate and find a rational approach for health care.
Kim Ju Hyong, a researcher at the Faculty of Biomedical Engineering, proposed a genetic algorithm method to determine the unknown parameters involved in the mathematical model that describes the transmission of virus infection, one of the global optimization calculation methods.
To test the validity of this method, he built a SEIHRD model and compared the accuracy of the simulation with the determination results of unknown parameters when the underlying data were prepared in various forms.
For further details, please refer to his paper “A Method to Determine the Unknown Parameters of Mathematical Model of Epidemic Transmission by Genetic Algorithm” in “Proceedings of KUTIC-2025”.
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Jo Oct 23, 2026
In several fields such as space engineering, it is very important to evaluate the performance degradation of electronic components by high-energy protons.
Charged particles such as protons cause excitation or ionization in semiconductor crystals. However, a very small fraction of the energy loss is then used to displace atoms from their equilibrium positions to create primary displacement atoms (non-ionizing processes). The generated primary displacement atoms cause cascade processes by displacing many atoms, which proceed until the transferred energy becomes smaller than the threshold required to displace the atoms. In the space environment, the defects created by incident particles create new energy levels within the band gap, and the levels change the electrical and optical properties of the electronic device and material. In other words, the protons in space environment cause single-event effects (SEE), total ionization dose (TID) effects, and displacement damage dose (DDD) effects in the electronic device.
In terms of the proton-induced DDD effect, the most sensitive electronic component is bipolar devices. Generally, proton accelerators, 1 MeV neutron source, and 1 MeV electron source are used to estimate the DDD effect in bipolar devices.
Considering the high cost for testing these methods, Kang Myong Chol, a section head at the Faculty of Electronics, proposed a method of evaluating the proton-induced DDD effect on the bipolar devices by using the existing Pu-Be isotope neutron source. Then, he verified the accuracy of the proton-induced DDD effect estimation using the Pu-Be isotope neutron source by using the optocouplers, TLP521-1GB and PC817C.
The proposed method can be used to evaluate the durability of electronic devices operating in proton environments.
You can find more information in his paper “Proton Induced Damage Estimation in Bipolar Device” in “Proceedings of KUTIC-2025”.
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Jo Oct 22, 2026
Direct methanol fuel cells (DMFCs) exhibit some advantages such as easy storage and transportation of fuel, and high specific energy density, compared to lithium batteries. However, there are still many problems in the widespread use of passive DMFC as lithium batteries.
One of the problems is the rapid removal of carbon dioxide at the anode to enhance the performance of passive DMFC. Carbon dioxide removal depends on the structure of the anode flow field (AFF), MEA and even operating conditions. Most of the efforts to effectively remove carbon dioxide have focused on reducing the bubble resistance of CO2 by improving the structure and shape of AFF.
However, efforts to reduce the negative impact of CO2 gas in MEA have not reached complete separation of two-phase flow in the anode gas diffusion layer (AGDL).
Jon Song Hyok, a researcher at the Faculty of Chemical Engineering, has proposed a new anode gas diffusion layer (AGDL) structure that can overcome the effects of two-phase flow in the MEA, the core of passive DMFC.
Using the anode carbon paper hydrophobically treated with 50wt.% PTFE loading, carbon dioxide is released to the lateral venting channels and methanol is allowed to be fed through a hole in the middle of the carbon paper.
Compared to the conventional DMFC, this improved AGDL provided a stable operating environment by separating the two-phase flow inside the cell and showed good performance with the maximum power density 17.3mW/cm2 at 12.0M methanol concentration.
If more information is needed, please refer to his paper “Efficient CO2 Removal by Improving Diffusion Layer Structure in Methanol Fuel Cells” in “Proceedings of KUTIC-2025”.
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Jo Oct 21, 2026
When a vehicle reenters the earth’s atmosphere at a hypersonic speed, the surrounding air molecules are dissociated and ionized by the tremendous heat due to atmospheric friction, and a plasma sheath surrounding the hypersonic vehicle’s surface will be formed. The plasma sheath greatly attenuates the electromagnetic (EM) waves radiated from an onboard antenna through reflection and absorption effects, and intermittent communication outage and blackout are frequently caused by the plasma sheath. Therefore, research on the interaction mechanism between EM waves and plasma sheath is of great significance.
Many studies have been conducted on the propagation characteristics of EM waves at the plasma sheath. However, the propagations of obliquely incident EM waves in the reentry plasma sheath have not been actively studied, and only a few studies dealt with it.
Han Yong Su, a researcher at the Faculty of Physics, has investigated the propagation properties of obliquely incident S-polarization electromagnetic waves into reentry plasma with bi-Gaussian electron density profile.
Based on the continuous boundary condition of electromagnetic (EM) waves in multilayer plasma, he deduced a scattering matrix equation of the obliquely incident S-polarization EM wave, and investigated the properties of reflection, transmission and absorption in terms of incident angle, plasma electron density distribution, and collision frequency, respectively.
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 confirmed that the transmittance peak and absorptivity peak are shifted from a lower frequency to a higher frequency with the increase in the incident angle, electron density profile and collision frequency.
You can find more information in his paper “Numerical Investigation for Propagation Characteristics of Obliquely Incident EM Waves in Plasma Sheath” in “Proceedings of KUTIC-2025”.
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Jo Oct 20, 2026
Dynamic time-warping is a method of matching by computing similarity using the elastic distance between two time series. This method was developed for speech recognition and it has been applied to many areas.
This matching method makes one time series to be compressed and stretched nonlinearly in the time axis direction based on the dynamic programming to minimize the elastic distance between two time series of different lengths.
In the literature, matching is implemented by changing the scale of time axis in the time series.
Jong Sung Il, a lecturer at the Faculty of Applied Mathematics, has proposed a time-phase scale varying DTW method of implementing matching by varying the scale of phase as well as that of time axis. Then, he applied it to a sine function with varying amplitude to verify its effectiveness.
For further details, please refer to his paper “Pattern Detection Method using Phase Varying Dynamic Time Warping in Time Series” in “Proceedings of KUTIC-2025”.
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