Effect of low processing rate on homogeneous microstructural evolution of polyacrylonitrile‑based carbon fibers

Doo‑Won Kim,Dae Ho Kim,Sung Ryong Kim,Bo‑Hye Kim,Yun Hyuk Bang,Duck Joo Yang,Go Bong Choi,Yoong Ahm Kim,Kap Seung Yang 한국탄소학회 2019 Carbon Letters Vol.29 No.5

This study demonstrates that low processing rate for producing polyacrylonitrile (PAN)-based carbon fiber is a critical to obtain a homogeneous radial microstructure with high resistance to oxidation, thereby resulting in their improved mechanical strength. The dry-jet wet spun PAN organic fibers were processed (e.g., stabilized and then carbonized) utilizing two different rates; one is 1.6 times longer than the other. The effect of processing rate on the microstructural evolutions of carbon fibers was analyzed by scanning electron microscopy after slow etching in air, as well as Raman mapping after graphitization. The rapidly processed fiber exhibited the multilayered radial structure, which is caused by the radial direction stretching of the extrusion in the spinning. In case of the slowly processed fiber, the layered radial structure formed in the spinning process was changed into a more homogeneous radial microstructure. The slowly processed fibers showed higher oxidation resistance, higher mechanical properties, and higher crystallinity than the rapidly processed one. Raman mapping confirmed that the microstructure developed during spinning was sustained even though fiber was thermally treated up to 2800 °C.

Solar Cells: Amorphous Zinc Stannate (Zn₂SnO₄) Nanofibers Networks as Photoelectrodes for Organic Dye‐Sensitized Solar Cells (Adv. Funct. Mater. 25/2013)

Choi, Seung‐,Hoon,Hwang, Daesub,Kim, Dong‐,Young,Kervella, Yann,Maldivi, Pascale,Jang, Sung‐,Yeon,Demadrille, Renaud,Kim, Il‐,Doo WILEY‐VCH Verlag 2013 Advanced Functional Materials Vol.23 No.25

<P>Highly porous amorphous Zn<SUB>2</SUB>SnO<SUB>4</SUB> electrodes are prepared using electrospinning techniques and combined with organic or ruthenium dyes to fabricate dye‐sensitized solar cells. As reported by Sung‐Yeon Jang, Renaud Demadrille, Il‐Doo Kim, and co‐workers on page 3146, the devices based on 3‐μm‐thick electrodes and the organic dyes demonstrate significantly improved performances compared to those using the ruthenium complex. Using this approach, solar cells with power conversion efficiencies up to 3.7% are obtained. </P>

ALGORITHM FOR FINDING 90/150 TRIDIAGONAL MATRICES

Sung Jin CHO,Un Sook CHOI,Han Doo KIM,Yoon Hee HWANG,Jin Gyoung KIM 한국산업응용수학회 2006 한국산업응용수학회 학술대회 논문집 Vol.1 No.2

In this paper, we propose a new method for finding 90/150 Linear Hybrid Group Cellular Automata(LHGCA) for CA-polynomials.

Preparation of Bipolar Plate for Fuel Cell Using CNT/Graphite Nano-Composite

Choi, Jong-Min,Kim, Tae-Jin,Hyun, Min-Soo,Peck, Dong-Hyun,Kim, Sang-Kyung,Lee, Byung-Rok,Park, Jong-Soo,Jung, Doo-Hwan 한국탄소학회 2005 Carbon Letters Vol.6 No.3

Bipolar plates require some specific properties such as electrical conductivity, mechanical strength, chemical stability, and low permeability for the fuel cell application. This study investigated the effects of carbon nanotube (CNT) contents and process conditions of hot press molding on the electrical and physical properties using CNT 3~7 wt% added graphite nano-composites in the curing temperatures range of 140~$200^{\circ}C$ and pressure of 200~300 kg/$cm^2$. Bulk density, hardness and flexural strength increased with increasing CNT contents, curing pressure and temperature. With the 7 wt% CNT added noncomposite, the electrical resistance improved by 30% and the flexural strength increased by 25% as compared to that without CNT at the temperature of $160^{\circ}C$ and pressure of 300 kg/$cm^2$. These properties were close to the DOE reference criteria as bulk resistance of 13 $m{\Omega}cm$ and tensile strength of 515 kg/$cm^2$.

Laparoscopy vs. laparotomy for embryo transfer to produce transgenic goats (Capra hircus)

Sang Tae Shin,Sung Keun Jang,Hong Suk Yang,Ok Keun Lee,Yhong Hee Shim,Won Il Choi,Doo Soo Lee,Gwan Sun Lee,Jong Ki Cho,Young Won Lee 대한수의학회 2008 JOURNAL OF VETERINARY SCIENCE Vol.9 No.1

This study was performed to produce transgenic Korean native goat (Capra hircus) by laparoscopic embryo transfer (ET) to overcome the limitations of ET performed by laparotomy. Transgenic embryos were produced by DNA pronuclear microinjection of in vivo zygotes. The recipient goats were synchronized for estrus by using an introvaginal progesterone devices as a controlled internal drugreleasing insert (CIDR) for 13 days and injection of 400 IU PMSG 48 h before removal of the insert. Embryos were transferred on day 3 and 4 after removal of the insert. Recipient goats were deprived of feed for 48 h, then suspended in a laparotomy cradle at an angle of 45o. After obtaining a sufficient pneumoperitoneum, the laparoscope and forceps were inserted abdominally through 5 mm trocar sleeves. Examination of the ovaries and uterus was performed and then 213 embryos were transferred into the oviducts via the infundibula of 76 recipient goats. To compare pregnancy rates, ET was also performed by laparotomy in 82 recipient goats. The pregnancies in the recipient goats were diagnosed by ultrasound on day 30 after embryo transfer. The pregnancy rate with laparoscopic ET was significantly higher than with ET performed by laparotomy (46.1% vs. 28.6%, p < 0.05). In addition, the pregnancy rates were compared between ovulated and non-ovulated ovaries of the recipient goats in the laparoscopic ET group. No significant difference was observed between the pregnancy rates of ovulated and non-ovulated ovaries (41.3% vs. 33.3%, p < 0.05) suggesting that ET may also be possible in non-ovulated recipients through artificial rupture of Graafian follicles. These results suggest that laparoscopic ET is a highly efficient method for the transfer of goat embryos. This study was performed to produce transgenic Korean native goat (Capra hircus) by laparoscopic embryo transfer (ET) to overcome the limitations of ET performed by laparotomy. Transgenic embryos were produced by DNA pronuclear microinjection of in vivo zygotes. The recipient goats were synchronized for estrus by using an introvaginal progesterone devices as a controlled internal drugreleasing insert (CIDR) for 13 days and injection of 400 IU PMSG 48 h before removal of the insert. Embryos were transferred on day 3 and 4 after removal of the insert. Recipient goats were deprived of feed for 48 h, then suspended in a laparotomy cradle at an angle of 45o. After obtaining a sufficient pneumoperitoneum, the laparoscope and forceps were inserted abdominally through 5 mm trocar sleeves. Examination of the ovaries and uterus was performed and then 213 embryos were transferred into the oviducts via the infundibula of 76 recipient goats. To compare pregnancy rates, ET was also performed by laparotomy in 82 recipient goats. The pregnancies in the recipient goats were diagnosed by ultrasound on day 30 after embryo transfer. The pregnancy rate with laparoscopic ET was significantly higher than with ET performed by laparotomy (46.1% vs. 28.6%, p < 0.05). In addition, the pregnancy rates were compared between ovulated and non-ovulated ovaries of the recipient goats in the laparoscopic ET group. No significant difference was observed between the pregnancy rates of ovulated and non-ovulated ovaries (41.3% vs. 33.3%, p < 0.05) suggesting that ET may also be possible in non-ovulated recipients through artificial rupture of Graafian follicles. These results suggest that laparoscopic ET is a highly efficient method for the transfer of goat embryos.

Prognostic implications of CD14 positivity in acute myeloid leukemia arising from myelodysplastic syndrome.

Choi, Yunsuk,Lee, Je-Hwan,Kim, Sung-Doo,Kim, Dae-Young,Lee, Jung-Hee,Seol, Miee,Kang, Young-Ah,Jeon, Mijin,Jung, Ah Rang,Lee, Kyoo-Hyung Elsevier Science Publishers 2013 International journal of hematology Vol.97 No.2

<P>Secondary acute myeloid leukemia (s-AML) arising from myelodysplastic syndrome (MDS) shows different clinical features from de novo AML. We assessed the prognostic significance of immunophenotypic markers in patients with s-AML arising from MDS. Sixty-five adults diagnosed with AML arising from MDS between 1996 and 2010 were retrospectively analyzed. Immunophenotyping was performed for markers including CD3, CD7, CD10, CD13, CD14, CD19, CD33, CD34, CD41, CD45, CD56, CD65, CD117, HLA-DR, and TdT. Of these immunophenotypic markers, only CD14 positivity was significantly associated with lower complete remission rate (P = 0.034) and significantly shorter overall survival (OS, P < 0.001) and event-free survival (EFS, P < 0.001) on univariate analysis. On multivariate analysis, these differences remained significant in terms of OS [hazard ratio (HR) 4.49; P < 0.001] and EFS (HR 4.06; P < 0.001). Other significant prognostic variables included age 60 years [shorter OS (P = 0.003) and EFS (P = 0.020)], higher WBC count (>60,000/μL) [shorter OS (P < 0.001) and EFS (P = 0.001)], and poor cytogenetic risk group [shorter OS (P = 0.005)]. CD14 expression on leukemic blasts is an independent prognostic factor for survival outcomes in patients with AML arising from MDS.</P>

The deposition behavior of SiC:H films deposited using a remote PECVD system with an HMDS precursor and C2H2 dilution gas

Doo Jin Choi,Sung Hyuk Cho,Young Jin Lee,김태송 한양대학교 세라믹연구소 2007 Journal of Ceramic Processing Research Vol.8 No.6

Silicon carbide (SiC) is a very attractive material in terms of its mechanical strength, chemical inertness, and other properties for applications in microsystems. SiC:H films were deposited on (100) silicon wafers by a remote plasma enhanced chemical vapor deposition (RPE-CVD) system in the temperature range of 300 oC-450 oC. Hexamethyldisilane (HMDS) and H2 gas were used as a precursor and a carrier gas, respectively. C2H2 dilution gas was used in order to increase the carbon content in the films. The plasma power was varied from 200W to 300W. The stoichiometric and bonding properties of deposited films were investigated by an Fourier transform infrared (FTIR) spectrometer and X-ray photoelectron spectroscopy (XPS). The thickness of deposited films was measured by ellipsometry. The growth rate of SiC:H films decreased with an increase of temperature from 300 oC to 400 oC, however, it increased again at 450 oC. The growth rate of films increased with the plasma power for all deposition conditions. As the deposition temperature was increased, the sp3/(sp2+sp3) ratio increased from 0.32 to 0.64, which affected the growth behavior and properties of the films. A higher activation energy and lower potential energy of the sp3 reaction make the sp3 reaction dominant consuming more energy as the deposition temperature was increased. This caused a thickness decrease with an increase of deposition temperature.

Relaxation Effect of Synthetic Ceramide Analogues in Cat Esophageal Smooth Muscle Cells

Doo Won Lee,Sun Young Park,Jung Su Ryu,Sung Hyo Kim,Chae Uk Im,Su Hang Choi,Se Eun Lee,Sung Kwon Ko,Uy Dong Sohn 대한생리학회-대한약리학회 2008 The Korean Journal of Physiology & Pharmacology Vol.12 No.4

Ceramide has emerged as a novel second messenger for intracellular signalling. It is produced from sphingomyelin and is involved in the control of cell differntiation, proliferation, and apoptosis. C₂- ceramide, short chain ceramide, plays a role in mediating contraction of cat esophageal smooth muscle cells. We examined the effect of synthesized ceramide analogues on the C₂-ceramide and ACh-induced contraction in esophageal smooth muscle cells isolated with collagenase. CY3523, CY3525, or CY3723 inhibited C₂-ceramide induced contraction, in a time dependent manne. Each analogue also inhibited the contraction in concentration dependent manners. CY 3523, CY 3525, and CY 3723 had no effect to the contraction induced by PMA. The inhibition with CY3523, CY3525 and CY3723 on the C₂- ceramide induced contraction was recovered by PMA. These analogues decreased the density of MAPK bands (p44/42 or p38) in the western blot. These results suggest that ceramide analogues can inhibit C₂-ceramide induced contraction via PKC and MAPK dependent pathway.

The impact of Model for End-Stage Liver Disease score on deceased donor liver transplant outcomes in low volume liver transplantation center: a retrospective and singlecenter study

Doo-Ho Lee,Yeon Ho Park,Seok Won Choi,Kug Hyun Nam,Sang Tae Choi,Doojin Kim 대한외과학회 2021 Annals of Surgical Treatment and Research(ASRT) Vol.101 No.6

Purpose: In June 2016, the Model for End-Stage Liver Disease (MELD) score was employed in South Korea instead of the Child-Turcotte-Pugh (CTP) score. This study compared the outcomes of deceased donor liver transplantation (DDLT) before and after the MELD system application. Methods: This retrospective study reviewed 48 patients who underwent DDLT for end-stage liver disease at a single tertiary referral center between January 2014 and December 2018. The patients were categorized into the pre-MELD (22 patients) and post-MELD (26 patients) groups. The demographics, postoperative outcomes, and overall survival time were evaluated between the 2 groups. Results: The 2 groups had no differences in age, sex, ABO type, etiology for liver transplantation, CTP-score, operation time, cold ischemic time, and amount of red blood cell transfusion, although their MELD score differed significantly (post-MELD group, 36.2 ± 4.9; pre-MELD group, 27.7 ± 11.8; P < 0.001). The post-MELD group has longer intensive care unit stay (11.2 ± 9.5 days vs. 5.7 ± 4.5 days, P = 0.018) and hospital stay than the pre-MELD group (36.8 ± 26 days vs. 22.8 ± 9.3 days, P = 0.016). The 1-year survival rate was lower in the post-MELD group (61.5% vs. 86.4%, P = 0.029). Conclusion: After MELD allocation, patients with high MELD scores had increased DDLT and consequently required a longer recovery time, which could negatively affect survival. According to the experience of a small-volume center, these problems were related to both severe organ shortages in South Korea and MELD allocation.

Influence of C₂F₆ Addition to Cl₂/Ar Gas on Nanometer-Scale Etch Characteristics of TiN Thin Films Using Inductively Coupled Plasma

Choi, Jae Sang,Cho, Doo Hyeon,Lim, Eun Taek,Chung, Chee Won The Electrochemical Society 2018 ECS journal of solid state science and technology Vol.7 No.6

<P>Micro- and nano-scale patterned TiN thin films were etched in Cl-2/Ar and Cl-2/C2F6/Ar gases by inductively coupled plasma reactive ion etching. As C2F6 gas was added to the Cl-2/Ar gas mixture, the etch profile of the TiN films was improved and the etch selectivity of the TiN film to the E-beam resist was increased. X-ray photoelectron spectroscopy revealed various etch by-products and polymer layers on the etched film surface. Overall, the addition of C2F6 to Cl-2/Ar gas was quite effective in improving the etch profile and could contribute to the higher anisotropic etch profile of nano-scale patterned TiN thin films. (C) 2018 The Electrochemical Society.</P>