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Lim, JeongHoon,Shin, Hyeyoung,Kim, MinJoong,Lee, Hoin,Lee, Kug-Seung,Kwon, YongKeun,Song, DongHoon,Oh, SeKwon,Kim, Hyungjun,Cho, EunAe American Chemical Society 2018 NANO LETTERS Vol.18 No.4
<P>Bimetallic PtNi nanoparticles have been considered as a promising electrocatalyst for oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs) owing to their high catalytic activity. However, under typical fuel cell operating conditions, Ni atoms easily dissolve into the electrolyte, resulting in degradation of the catalyst and the membrane-electrode assembly (MEA). Here, we report gallium-doped PtNi octahedral nanoparticles on a carbon support (Ga-PtNi/C). The Ga-PtNi/C shows high ORR activity, marking an 11.7-fold improvement in the mass activity (1.24 A mg<SUB>Pt</SUB><SUP>-1</SUP>) and a 17.3-fold improvement in the specific activity (2.53 mA cm<SUP>-2</SUP>) compared to the commercial Pt/C (0.106 A mg<SUB>Pt</SUB><SUP>-1</SUP> and 0.146 mA cm<SUP>-2</SUP>). Density functional theory calculations demonstrate that addition of Ga to octahedral PtNi can cause an increase in the oxygen intermediate binding energy, leading to the enhanced catalytic activity toward ORR. In a voltage-cycling test, the Ga-PtNi/C exhibits superior stability to PtNi/C and the commercial Pt/C, maintaining the initial Ni concentration and octahedral shape of the nanoparticles. Single cell using the Ga-PtNi/C exhibits higher initial performance and durability than those using the PtNi/C and the commercial Pt/C. The majority of the Ga-PtNi nanoparticles well maintain the octahedral shape without agglomeration after the single cell durability test (30,000 cycles). This work demonstrates that the octahedral Ga-PtNi/C can be utilized as a highly active and durable ORR catalyst in practical fuel cell applications.</P> [FIG OMISSION]</BR>
DECAY OF TURBULENCE IN FLUIDS WITH POLYTROPIC EQUATIONS OF STATE
Lim, Jeonghoon,Cho, Jungyeon The Korean Astronomical Society 2020 Journal of The Korean Astronomical Society Vol.53 No.2
We present numerical simulations of decaying hydrodynamic turbulence initially driven by solenoidal (divergence-free) and compressive (curl-free) drivings. Most previous numerical studies for decaying turbulence assume an isothermal equation of state (EOS). Here we use a polytropic EOS, P ∝ ρ<sup>γ</sup>, with polytropic exponent γ ranging from 0.7 to 5/3. We mainly aim at determining the effects of γ and driving schemes on the decay law of turbulence energy, E ∝ t<sup>-α</sup>. We additionally study probability density function (PDF) of gas density and skewness of the distribution in polytropic turbulence driven by compressive driving. Our findings are as follows. First of all, we find that even if γ does not strongly change the decay law, the driving schemes weakly change the relation; in our all simulations, turbulence decays with α ≈ 1, but compressive driving yields smaller α than solenoidal driving at the same sonic Mach number. Second, we calculate compressive and solenoidal velocity components separately and compare their decay rates in turbulence initially driven by compressive driving. We find that the former decays much faster so that it ends up having a smaller fraction than the latter. Third, the density PDF of compressively driven turbulence with γ > 1 deviates from log-normal distribution: it has a power-law tail at low density as in the case of solenoidally driven turbulence. However, as it decays, the density PDF becomes approximately log-normal. We discuss why decay rates of compressive and solenoidal velocity components are different in compressively driven turbulence and astrophysical implication of our findings.
Development of Golf Shaft with Carbon Nanotubes and Marketing Strategy
Youngsam Lim,Jeonghoon Jang,Yongho Choi 보안공학연구지원센터 2014 International Journal of Software Engineering and Vol.8 No.12
It was reported that golf equipment market is expected to increase continuously and quickly. However, Korean golf organizations could not produce high-end technology products through scientific research and development; despite they have a high technical competence and good infrastructure. In order to solve the problem, direction and goal of researches and developments should be clear. The domestic golf industry organizations have focused on the short-term profits and did not pursue in-depth scientific researches. Therefore, it is needed to make long-term plans which are comprehensive and systematic to strengthen the competitiveness. In this study, authors incorporate nanomaterials to golf shafts as high-end technology and suggest strategies to promote competitiveness through the nano-technology, effective planning and management.
Waveguide Design at Infrared Wavelength With Asymmetric Dielectric Surface Gratings
Dongyeal Lim,Heeseung Lim,Jae Seok Choi,Jeonghoon Yoo IEEE 2014 IEEE transactions on magnetics Vol.50 No.2
<P>In this paper, we propose waveguide design at infrared wavelength with asymmetric dielectric surface gratings. Surface gratings are able to generate the surface plasmon polariton effect at the outlet of radiated light through an aperture. The property and the shape of gratings are key factors behind generating collimated beams from subwavelength slits or holes surrounded by corrugated surfaces. Grating design is conducted by structural optimization based on the phase field method. The design objective is set to maximize the Poynting vector in the measuring area, and it is focused on finding a clear shape of grating structure for the manufacturing feasibility to be taken into account. The simulation and optimization process is performed by using the commercial package COMSOL associated with the MATLAB programming.</P>
JeongHoon Park,Jae Young, Cho,Jung Sook Yeom,Jin Su Jun,Ji Sook Park,Eun Sil Park,Ji Hyun Seo,Jae Young Lim,Chan-Hoo Park,Hyang-Ok Woo The Korean Society of Pediatric Gastroenterology 2023 Pediatric gastroenterology, hepatology & nutrition Vol.26 No.3
Purpose: The starting time for probiotic supplementation in preterm infants after birth varies widely. This study aimed to investigate the optimal time for initiating probiotics to reduce adverse outcomes in preterm or very low birth weight (VLBW) infants. Methods: Medical records of preterm infants born at a gestational age (GA) of <32 weeks or VLBW infants in 2011-2020 were reviewed respectively. The infants who received Saccharomyces boulardii probiotics within 7 days of birth were grouped into an early introduction (EI) group, and those who received supplemented probiotics after 7 days of birth were part of the late introduction (LI) group. Clinical characteristics were compared between the two groups and analyzed statistically. Results: A total of 370 infants were included. The mean GA (29.1 weeks vs. 31.2 weeks, p<0.001) and birth weight (1,235.9 g vs. 1491.4 g, p<0.001) were lower in the LI group (n=223) than in the EI group. The multivariate analysis indicated that factors affecting the LI of probiotics were GA at birth (odds ratio [OR], 1.52; p<0.001) and the enteral nutrition start day (OR, 1.47; p<0.001). The late probiotic introduction was associated with a risk of late-onset sepsis (OR, 2.85; p=0.020), delayed full enteral nutrition (OR, 5.44; p<0.001), and extrauterine growth restriction (OR, 1.67; p=0.033) on multivariate analyses after adjusting for GA. Conclusion: Early supplementation of probiotics within a week after birth may reduce adverse outcomes among preterm or VLBW infants.
Lim, Eun Jin,Yoon, Yu Jeong,Heo, Jeonghoon,Lee, Tae Hwa,Kim, Young-Ho MDPI 2018 INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES Vol.19 No.10
<P>Ciprofloxacin (CIP) is a potent antimicrobial agent with multiple effects on host cells and tissues. Previous studies have highlighted their proapoptotic effect on human cancer cells. The current study showed that subtoxic doses of CIP effectively sensitized multiple cancer cells to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Although TRAIL alone mediated the partial proteolytic processing of procaspase-3 in lung cancer cells, co-treatment with CIP and TRAIL efficiently restored the complete activation of caspases. We found that treatment of lung cancer with CIP significantly upregulated the expression and protein stability of death receptor (DR) 5. These effects were mediated through the regulation of transcription factor CCAT enhancer-binding protein homologous protein (CHOP) since the silencing of these signaling molecules abrogated the effect of CIP. Taken together, these results indicated that the upregulation of death receptor expression and protein stability by CIP contributed to the restoration of TRAIL-sensitivity in lung cancer cells.</P>