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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.
Choi,Yong-Ho,Lee,Won-Yun,Lim,Kwang-Muk,Park,Doo-Won,Lee,Myung-Ho,Lee,Chang-Woo,Lee,Hyun-Duk,Lee,Jung-Ho 대한방사선 방어학회 1997 방사선방어학회지 Vol.22 No.3
고추의 이식 2일전 및 이식후 세 차례에 걸쳐 54Mn, 60Co, 85Sr , 137Cs의 혼합용액을 온실내 재배상자의 토양에 처리하고 고추의 청과와 적과에 대한 전이계수(㎡/㎏-dry)를 조사하였다. 전이계수는 핵종, 처리시기 및 수확시기에 따라 20∼100배 정도의 변이를 보였다. 핵종간에 전이계수는 대체로 85Sr>54Mn> 60C> 137Cs의 순이었으나 처리에서 수확까지의 기간이 짧을 경우 54Mn와 60Co 전이계수가 85Sr보다 높았다. 85Sr와 137Cs 전이계수는 가장 늦은 처리에서 그 전처리에 비해 수확시기에 따라 3∼20배 정도 감소하였다. 54Mn와 60Co 전이계수는 이식후 처리시기에 따른 변이가 비교적 적었다. 이식전 토양과의 혼합처리시 전이계수는 이식 2일후 토양 표면 처리에 비해 54Mn, 60Co , 85Sr 의 경우 최고 3∼9배 정도 높았으나 137Cs 의 경우 차이가 없었다. 본 연구 결과는 고추의 재배기간중 사고발생시 고추 열매내 방사성 핵종의 뿌리흡수 농도를 예측하고 고추의 수확 및 이용대책을 수립하는 데 활용될 수 있다. A mixed solution of 54Mn, 60Co, 85Sr and 137Cs was applied to the soil of culture boxes in a greenhouse 2 days before transplanting red pepper and at 3 different times during its growth for investigating transfer factors (㎡/㎏-dry) for its green and red fruits. Transfer factors varied with radionuclide, application time and harvest time by factors of about 20∼100. They decreased mostly in the order of 85Sr>54Mn> 60C> 137Cs while 54Mn and 60Co was higher than 85Sr when time lapse between application and harvest was short. Transfer factors of 85Sr and 137Cs at the last applocation were lower than those at the previous one by factors of 3∼20 depending on harvest time. Variations in 54Mn and 60Co transfer factors with application time after transplanting were comparatively low. Transfer factors of 54Mn, 60Co and 85Sr mixed with topsoil before transplanting were up to 3∼9 times higher than those for the application onto soil surface 2 days after transplanting while there was no difference in 137Cs. The present results can be referred to in estimating root-uptake concentrations of the radionuclides in red pepper fruit and taking proper measures for its harvest and consumption at the event of an accidental release during the growing season of red pepper.
Doo Jin Choi,Ji Won Choi,Jisun Lee,Chang Won Lee,Seul Lee,Andriy Synytsya,Yong Il Park 한국당과학회 2013 한국당과학회 학술대회 Vol.2013 No.1
A water-soluble polysaccharide (SPS-CF) was isolated and purified from Korean green alga Maesaengi Capsosiphon fulvescens mainly by dilute acid extraction, ethanol precipitation, and DEAE-cellulose ion exchange chromatography. The results of present study performed for monosaccharide composition of this polysaccharide using HPLC of PMP labelled sugars, HPAEC-PAD, GC-FID and TLC, clearly demonstrated that the most prominent neutral monosaccharides of SPS-CF are xylose (44–52 mol %) and rhamnose (34–45 mol %), while mannose and galactose are present at much lesser extent or in negligible amount. These extensive monosaccharide analyses and correlation NMR measurements confirmed that it is a sulphated glucuronorhamnoxylan (ulvan) type polysaccharide, whose backbone is composed of alternating sequence of 4-linked L-rhamnose-3-sulphate and D-xylose residues (ulvobiose) carrying monomeric D-glucuronic acid or D-glucuronic acid-3-sulphate on O-2 of some L-rhamnose-3-sulphate units as the side chains. The SPS-CF exhibited significant invitro anticoagulant activity by which the activated partial thromboplastin time (aPTT) and thrombin time (TT) were significantly prolonged. Also, Enzyme Linked Immunosorbent Assay showed that the SPS-CF significantly stimulates the release of the pro-inflammatory cytokines, TNF-α and IL-6, in a dose-dependent manner. RT-PCR analysis demonstrated that the SPS-CF also induced a more than two-fold increase in the expression of iNOS and COX-2, responsible for the induction of NO and PGE2, respectively, at 5 μg/ml in RAW264.7 murine macrophages. The results of this study demonstrated that the SPS-CF isolated from Korean C. fulvescens Maesaengi is an ulvan type polysaccharide and can be considered as potential anticoagulant and immunostimulating agent.
Mitochondria-Targeted Vitamin E Protects Skin from UVB-Irradiation
( Won Serk Kim ),( Ikyon Kim ),( Wang Kyun Kim ),( Ju Yeon Choi ),( Doo Yeong Kim ),( Sung Guk Moon ),( Hyung Keun Min ),( Min Kyu Song ),( Jong Hyuk Sung ) 한국응용약물학회 2016 Biomolecules & Therapeutics(구 응용약물학회지) Vol.24 No.3
Mitochondria-targeted vitamin E (MVE) is designed to accumulate within mitochondria and is applied to decrease mitochondrial oxidative damage. However, the protective effects of MVE in skin cells have not been identified. We investigated the protective effect of MVE against UVB in dermal fibroblasts and immortalized human keratinocyte cell line (HaCaT). In addition, we studied the wound-healing effect of MVE in animal models. We found that MVE increased the proliferation and survival of fibroblasts at low concentration (i.e., nM ranges). In addition, MVE increased collagen production and downregulated matrix metalloproteinase1. MVE also increased the proliferation and survival of HaCaT cells. UVB increased reactive oxygen species (ROS) production in fibroblasts and HaCaT cells, while MVE decreased ROS production at low concentration. In an animal experiment, MVE accelerated wound healing from laser-induced skin damage. These results collectively suggest that low dose MVE protects skin from UVB irradiation. Therefore, MVE can be developed as a cosmetic raw material.
Choi, Hyuk,Lee, Heung‐,Man,Nam, Kyoung Won,Choi, Jaesoon,Lee, Jung‐,Joo,Kim, Ho Chul,Song, Seung Joon,Ahn, Chi Bum,Son, Ho Sung,Lim, Choon Hak,Son, Kuk Hui,Park, Yong Doo,Jeong, Gi Seok,Su Blackwell Publishing Inc 2011 Artificial Organs Vol.35 No.6
<P><B>Abstract</B></P><P>In 2002, the paracorporeal pulsatile electro‐mechanical pneumatic ventricular assist device (VAD) began to be developed by the Korea Artificial Organ Center at Korea University under a Health & Medical Technology Research and Development program which finished in 2008. In vitro durability testing was conducted on the paracorporeal pulsatile pneumatic VAD to determine device durability and to evaluate device failures. The 1‐ and 2‐year reliability of the paracorporeal pulsatile pneumatic VAD was shown to be 91.2% and 54.9%, respectively, with an 80% confidence level. Failure modes were analyzed using fault tree analysis, with customized software continuously acquiring data during the test period. After this period, 21 in vivo animal tests were done, with 14 cases of left atrium to left ventricle (LV) inflow cannulation (36Fr)/outflow grafting to descending aorta, and seven cases of apex cannulation of LV to descending aorta (12 mm). The longest postoperative day (182 days) in Korea was recently recorded in in vivo animal testing (bovine, 90 kg, male, 3.5–4.0 L/min flow rate, and 55 bpm).</P>
Nanoscale Pillar-Enhanced Tribological Surfaces as Antifouling Membranes
Choi, Wansuk,Chan, Edwin P.,Park, Jong-Hyun,Ahn, Won-Gi,Jung, Hyun Wook,Hong, Seungkwan,Lee, Jong Suk,Han, Ji-Young,Park, Sangpil,Ko, Doo-Hyun,Lee, Jung-Hyun American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.45
<P>We present a nonconventional membrane surface modification approach that utilizes surface topography to manipulate the tribology of foulant accumulation on water desalination membranes via imprinting of submicron titanium dioxide (TiO2) pillar patterns onto the molecularly structured, flat membrane surface. This versatile approach overcomes the constraint of the conventional approach relying on interfacial polymerization that inevitably leads to the formation of ill-defined surface topography. Compared to the nonpatterned membranes, the patterned membranes showed significantly improved fouling resistance for both organic protein and bacterial foulants. The use of hydrophilic TiO2 as a pattern material increases the membrane hydrophilicity, imparting improved chemical antifouling resistance to the membrane. Fouling behavior was also interpreted in terms of the topographical effect depending on the relative size of foulants to the pattern dimension. In addition, computational fluid dynamics simulation suggests that the enhanced antifouling of the patterned membrane is attributed to the enhancement in overall and local shear stress at the fluid TiO2 pattern interface.</P>
Resistivity Increase in 6H-SiC Crystal Grown with Simple Modification in PVT Process
Choi, Jung Woo,Park, Jong Hwi,Seo, Jung Doo,Kim, Jung Gyu,Kyun, Myung Ok,Ku, Kap Ryeol,Kim, Young Gon,Choi, Su Hun,Lee, Won Jae Trans Tech Publications, Ltd. 2018 Materials science forum Vol.924 No.-
<P>6H-SiC single crystal was grown with simple modification in PVT process to investigate the aspect of resistivity change in crystal. The modified process consisted of a new initial step to get rid of impurities in the growth cell before the main growth of SiC crystal. The new step in the modified process was designed to consist of higher temperature than the growth temperature for sublimation of impurities. SiC crystal grown with using 2 times of impurities sublimation process (ISP) step exhibited lower variation of resistivity value on whole wafer than SiC grown using with 1 time. With implementation of new modified step in growth process, SiC single crystal with resistivity value above 10<SUP>3</SUP>Ωcm could be obtained by simple PVT process and conventional low-purity SiC source material.</P>