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Kim, Yun Hyeok,Choi, Gwang-Mun,Shin, Dahye,Kim, Yong Ho,Jang, Dongchan,Bae, Byeong-Soo American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.49
<P>Any transition toward an era of flexible electronics will have to overcome the mechanical limitations of materials. Specifically, the attainment of both strength and flexibility, which are generally mutually exclusive, is required including glass-like wear resistance, plastic-like compliance, and a high level of strain. Here, we fabricate a urethane-methacrylate-siloxane hybrid (UMSH) material. It is found that UMSH, with molecule-level hybridization of urethane linkage and methacrylate-siloxane conetworks, demonstrates ceramic-like high strength (574 MPa), yet polymer-like low modulus (8.42 GPa), and even high strain (6.3%) at fracture with excellent optical transparency. This combination of high strength, flexibility, and optical transparency indicates that this is a suitable material for glass substitution and can be used as a transparent flexible cover window for foldable display.</P> [FIG OMISSION]</BR>
Effect of Rutile/Anatase TiO2 on surface properties of ZnO-Al2O3-CaO-SiO2 glass system
Dongchan Kim,Seunggu Kang,Kangduk Kim 한양대학교 청정에너지연구소 2023 Journal of Ceramic Processing Research Vol.24 No.5
In this study, we investigated the effects of dimorphous nucleating agentsrutile TiO2 and anatase TiO2, on the crystallizationand surface properties of ZnO-Al2O3-CaO-SiO2-based glass. Glass specimens were prepared by substituting rutile TiO2 andanatase TiO2 at 1, 3, and 5 wt.% and subsequently heat treating at 1050 °C for 90 min to induce crystallization. Thecrystallization characteristics and surface properties of the crystallized glass were analyzed using X-ray diffraction (XRD),scanning electron microscopy (SEM), gloss, Fourier-transform infrared (FTIR) spectroscopy, hardness, and colorimetricanalyses. The XRD and SEM analyses revealed the presence of a titanite crystalline phase in the glass matrix. However, theaddition of anatase TiO2 as a nucleating agent resulted in a significant decrease in glossiness. FTIR deconvolution in the rangeof 800-1300 cm−1 showed an increase in the degree of [SiO4] tetrahedral polymerization with higher levels of crystallization. micro-Vickers hardness of the glass specimens increased from the original value of 6.32 GPa to a maximum of 7.05 GPa,indicating enhanced hardness due to crystallization. Colorimetric analysis indicated that the inclusion of rutile TiO2 as anucleating agent increased the Yellow Index of anatase TiO2.
Dongchan Kim,Sungkyun Cho 국제무예학회 2020 International Journal of Martial Arts Vol.6 No.-
Objective: This study was conducted to determine the capacity of taekwondo as a leisure activity to reduce the acculturative stress of U.S. soldiers stationed in the Republic of Korea (ROK; South Korea) and to improve their working efficiency. An additional, goal was to determine whether taekwondo was an appropriate activity for the Korean head-start program by investigating its effectiveness in minimizing U.S. soldiers’ acculturative stress and maximizing their life satisfaction in South Korea. Methods: To achieve those goals, the researchers surveyed 200 U.S. soldiers while they were stationed in South Korea, using convenience sampling. Among the collected questionnaires, the researchers discarded 23 with unusable or corrupted responses, leaving 177 questionnaires for data analysis. To acquire the results, frequency analysis, confirmatory factor analysis, correlation analysis, and multi-regression analyses were performed using SPSS ver. 23 and AMOS 21.0. Results: The results indicate that taekwondo training satisfaction is a negative predictor of acculturative stress and a positive predictor of life satisfaction, and that acculturative stress is a negative predictor of life satisfaction. Conclusion: The findings are discussed in light of previous works, along with ways to improve the taekwondo program as a leisure activity to reduce acculturative stress.
Kim, Dongwoo,Lee, DongChan,Jang, Dong Soo,Jeon, Yongseok,Kim, Yongchan Elsevier 2018 Applied thermal engineering Vol.132 No.-
<P><B>Abstract</B></P> <P>In this study, the flow boiling heat transfer characteristics of R-1234ze(E) and R-134a in plate heat exchangers with different Chevron angles are measured and analyzed as a function of the mass flux, saturation temperature, vapor quality, and heat flux. The effect of the mass flux on the heat transfer and pressure drop of R-1234ze(E) is substantial. The heat transfer coefficient of R-1234ze(E) for a Chevron angle of 60° is approximately 3.7 times higher than that for a Chevron angle of 30° at high vapor qualities owing to the intensified turbulent flow. Moreover, for a Chevron angle of 60°, the average heat transfer coefficient of R-1234ze(E) is on average 4.7% higher than that of R-134a due to its higher equivalent Reynolds number. However, the average pressure drop of R-1234ze(E) is higher than that of R-134a owing to the lower vapor density of R-1234ze(E). Finally, the correlations for the heat transfer and pressure drop of R-1234ze(E) are developed in the plate heat exchangers with different Chevron angles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The flow boiling heat transfer characteristics of R-1234ze(E) and R-134a in plate heat exchangers are measured and analyzed. </LI> <LI> The heat transfer coefficients of R-1234ze(E) and R-134a are quite similar at the same mass flux. </LI> <LI> R-1234ze(E) shows higher pressure drop than R-134a owing to the lower vapor density. </LI> <LI> The correlations for the heat transfer and pressure drop of R-1234ze(E) are developed considering different Chevron angles. </LI> </UL> </P>
A panoramic study of K-factors for 111 processes at the 14 TeV LHC
Kim Dongjoo,Lee Soojin,Jung Hanseok,Kim Dongchan,Kim Jinheung,Song Jeonghyeon 한국물리학회 2024 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.84 No.12
In this comprehensive study, we investigate K-factors (K = 휎NLO∕휎LO ≡ 1 + 훿K) for a broad array of Standard Model processes at the 14 TeV LHC, which are pivotal for background assessments in Beyond the Standard Model (BSM) searches. Using MadGraph5_aMC@NLO, we calculate the leading-order and next-to-leading-order (NLO) cross-sections and compute the corresponding K-factors for 111 processes. Our analysis reveals K-factors ranging from 1.005 for pp → jjj to 4.221 for pp → W±훾훾훾. Key fndings include: (i) processes involving photons display signifcantly high K-factors, attributed to gluon-initiated processes at NLO; (ii) processes with multiple particle productions, particularly those involving vector bosons, exhibit elevated K-factors due to multiple real emission processes; (iii) there exists an inverse correlation between the number of jets and 훿K, indicating that the addition of jets generally leads to a decrease in 훿K. In addition, our investigation into diferential K-factors relative to transverse momentum and invariant mass shows notable increases with higher pT , but minimal changes with invariant mass. This study highlights the indispensable role of precise K-factor evaluations for accurate interpretations of BSM search outcomes.
Multi-slice imAGe generation using intra-slice paraLLel imaging and Inter-slice shifting (MAGGULLI)
Kim, Dongchan,Seo, Hyunseok,Oh, Changheun,Han, Yeji,Park, HyunWook IOP 2016 Physics in medicine & biology Vol.61 No.4
<P>For acceleration of imaging time, multi-band imaging techniques (e.g. CAIPIRINHA) use the sensitivity differences of the multi-channel RF coils in the slice selection direction. To more effectively utilize the RF coil characteristics than the conventional multi-band imaging techniques, we propose a new imaging technique, called multi-slice image generation using intra-slice parallel imaging and inter-slice shifting (MAGGULLI). The proposed technique used an inter-slice shifting gradient in slice selection direction to make multi-slice images shift in the frequency encoding direction. Thus, aliasing caused by sub-sampling in the phase encoding direction is orthogonal to that by multi-band imaging with the inter-slice shifting, both of which are resolved by using the sensitivity information of the RF coil. Phantom and <I>in vivo</I> imaging experiments for the acceleration factors up to 10 demonstrate that the quality of the images reconstructed by MAGGULLI are better than that of CAIPIRINHA for high acceleration factors in the qualitative and quantitative analysis.</P>