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Ki-Kang Kim,Soo-Min Kim,Yan Cui,Mun-Seok Jeong,Jong-Hun Han,Young-Chul Choi,Kay-Hyeok An,Kyung-Hui Oh,Young-Hee Lee 한국탄소학회 2009 Carbon Letters Vol.10 No.1
We measured the degree of macrodispersion of the various single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) using UV-VIS-NIR absorption spectroscopy. CNTs were dispersed with SDS of 2 wt % in deionized water using the homogenizer and then were further centrifugated at 6000 g for 10 min. The degree of macrodispersion, expressed by Dm(λ)=Aa(λ)/Ab(λ)*100 (%), where λ is the wavelength and Aa(λ) and Ab(λ) are the absorbance of the sample after and before centrifugation, respectively. In the case of MWCNTs, we evaluated the degree of macrodispersion by the average degree of macrodispersion (Dm(λ)) between 1000 and 1200 nm. The degree of macrodispersion of SWCNTs was evaluated at the wavelength in which van Hove singularity-related transition regions were excluded, i.e., the range was chosen between E11S and E22S peaks. We have estimated six samples with the same method. The standard deviation of each sample was lower than 5. Therefore, we presented a reliable evaluation method for the macrodispersion of CNTs for standardization.
Current Adjusting Auto Zeroing Multipath Operational Amplifier
Min-Hyeok Son(손민혁),Moo-Kyoung Yoo(유무경),Hyeok-Tae Son(손혁태),Kyoung-Hwan Kim(김경환),Ji-Hyang Wi(위지향),Gi-Bae Nam(남기배),Man-Hyeok Choi(최만혁),In-Ju Yu(유인주),Hyung-Ho Ko(고형호) 대한전자공학회 2024 대한전자공학회 학술대회 Vol.2024 No.6
This paper proposes a circuit for reducing lowfrequency noise and offset by applying a ping-pong structure and multipath structure based on current adjusting auto zeroing (CAAZ). CAAZ differs from two prominent auto zeroing techniques by not having an auto zeroing cap in the signal path but existing in the folded cascode stage. This distinction addresses issues such as increased thermal noise due to input signal division and insufficient gain leading to residual offset components in conventional input auto zeroing. Moreover, it can resolve the limited gain issue of output auto zeroing. By applying a multipath structure, the paper suggests using CAAZ ping-pong and integrator in the low-frequency path, while using single-ended differential difference amplifier with a class AB output stage in the high-frequency path for power savings, proposing a low-frequency noise reduction amplifier with a wider bandwidth. A CAAZ multipath amplifier was fabricated using a 0.18 μm TSMC complementary metal-oxide-semiconductor (CMOS) process. The proposed amplifier consumes 0.263 mW with a 1.8 V supply and has an active area of 0.493 mm2. It achieves a unit gain bandwidth (UGBW) of 4.155 MHz, an input referred noise of 29.36 nV/√Hz, and a noise efficiency factor (NEF) of 12.3.
Transient effects of jumping lunge on sand on balance ability in healthy adults: a preliminary study
Min-hyeok Choi,Ho-jin Shin,함석찬,이민구,조휘영 물리치료재활과학회 2018 Physical therapy rehabilitation science Vol.7 No.4
Objective: The purpose of this study was to show the temporary effects of performing jumping lunges on a sand surface on static balance and dynamic balance. Design: Randomized controlled trial. Methods: Twenty healthy subjects volunteered in the study and was randomly assigned into either the sand group (n=10) or the control group (n=10). The subjects in the sand group performed jumping lunges on a sand surface and the subjects in the control group performed jumping lunges on a firm surface. The intervention was performed for 3 sets of 8 repetitions by both groups. To measure static balance, the force plate was employed to measure the center of pressure (CoP) area, and the CoP velocity during one-legged standing. Anterior, postero-medial, postero-lateral movements was assessed using the Star Excursion Balance Test (SEBT) to measure dynamic balance. Results: After the intervention, the sand group showed statistically significant improvements on all variables (CoP area, CoP velocity) in static balance (p<0.05). There were statistically significant changes in CoP area and CoP velocities between the two groups (p<0.05). In the sand group, there were significant improvements in the postero-medial and postero-lateral directions (p<0.05) except for anterior direction on dynamic balance. In the control group, there was a significant improvement in the postero- lateral and anterior directions (p<0.05). In comparison of the two groups, there was no statistically significant improvement in all variables. Conclusions: This study demonstrated that performing jumping lunges on a sand surface was effective in improving static and dynamic balance temporarily.
Choi, Yun-Hyeok,Yoo, Hee-Jung,Noh, Ill Chan,Lee, Jeong-Min,Park, Jae Won,Choi, Wahn Soo,Choi, Jung Ho 대한약학회 2012 Archives of Pharmacal Research Vol.35 No.5
The inhibition of Interleukin-1beta (IL-$1{\beta}$) is of substantial interest for the treatment of rheumatoid arthritis. Using an in vitro assay with RAW 264.7 cells, oxo-acetic acid 2-ethoxy-4-(3-hydroxy-2-oxopropyl) phenyl ester (1) was isolated from the roots of Paeonia suffruticosa Andrews as an inhibitor of IL-$1{\beta}$ with an $IC_{50}$ value of 56 ${\mu}M$. Compound 1 is a novel phenylesteric compound from P. suffruticosa Andrews. Compound 1 was shown to inhibit the production of pro-inflammatory cytokines in RAW 264.7 cells. Thus, a possible new action of novel compound is provided explaining the anti-rheumatoid arthritic properties of P. suffruticosa Andrews.
3.3 kW bidirectional charger design based on active‑clamp flyback circuits
Hyeok‑Min Kwon,Seung‑Min Nam,Jae‑Hyuck Choi,Chang‑Gyeo Jung,Jun‑Young Lee,Young‑Joo Kim 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.3
A 3.3 kW bidirectional charger using an active-clamp flyback circuit with a symmetrical structure is proposed in this paper. Unlike the currently used bidirectional resonant converter, the proposed charger has a simple structure. By adopting a symmetrical design for the proposed charger, it can achieve the same bidirectional gain and efficiency in forward and reverse operation. In addition, it has the advantage of being able to respond to a wide output voltage range through simple pulse-width modulation (PWM) control. Thus, it can be applied to multi-purpose charger designs for a variety of batteries. An elementary flyback converter has the disadvantage of having electrical stress of the switch. An active-clamp circuit is applied to solve this disadvantage and to implement zero-voltage switching (ZVS) on all of the switches. Thus, high efficiency can be achieved at a high frequency using four 1200 V class silicon-carbide field-effect transistors (SiC-FETs). The feasibility of the proposed charger was verified using a prototype converter with input and battery voltages of 400 and 100–450 V, respectively.