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기계적 합금법으로 제조된 Al-Nb 합금 및 Al-Al3Nb 복합재료 압출재의 인장 특성
김상식,박민우,정광철,안인섭,류영빈,이광민 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.12
Tensile behavior of mechanically alloyed(MA) Al-5 wt.%Nb alloy extrusion was examined at various temperatures and strain rates. The tensile ductility of MA Al-5wt.%Nb alloy extrusion was greatly reduced with increasing temperature and/or decreasing strain rate. The SEM observations of side and fracture surfaces of tensile fractured specimens demonstrated that the overall void density formed during deformation was considerably reduced, along with the sign of decreased plasticity around the dimples on the fracture surface. To understand the effect of grain size on the deformation behavior of submicron grain sized alloys, Al-5 vol. %Al₃Nb composite extrusions with different grain sizes were fabricated and tensile tested at different temperatures. The present study confirms that the reduction in tensile ductility of submicron grain sized alloys at elevated temperatures are undoubtedly related to the grain size. Fast dynamic recovery rates, due to the lack of dislocation substructures, in submicron grain sized alloys appears to be responsible for the elevated temperature reduction in tensile ductility.
김연수,한진석,이정상,김병국,이중건,정윤철,이진학,최영진,안규리,김성권,이현순 대한내과학회 1994 대한내과학회지 Vol.46 No.2
Castlemam's disease is an asymptomatic and benign lymph node hyperplasia which is frequently manifested as mediastinal mass in over 70% of cases. Amyloidosis is rarely associated with Castleman's disease. Recently we experienced a patient with nephrotic syndrome due to renal amyloidosis who had been previously diagnosed as Castleman's disease of retroperitoneal lymph node enlargement. A 47-year old woman was admitted because of generalized edema and chest tightness. Five months ago she diagnosed as Castlman's disease-plasma cell type, of retroperitoneal lymph node enlargement. The patient was followed up through outpatient department without any specific medication. Physical examination showed pale conjunctivae, palpable mass on epigastric area and pretibial pitting edema. The hemoglobin, leukocyte count and erythrocyte sedimentation rate were 96 g/L, 5.9×109/L and 127 mm/hour, respectively. The blood urea nitogen was 3.6 mmol/L and creatinine was 88 umol/L. The urinalysis showed 3 positive for albumin. Twentyfour hour urine contained 16.6 grams of protein. A computerized tomographic (CT) scan of the abdomen disclosed multiple lymph node enlargement at mesentery. Percutaneous needle biopsy of kidney showed massive infiltration of pale pinkish amorphous material in the glomerular tuft forming large nodules. Ultrastructural examination exhibited heavy deposition of amyloid fibrils in the mesangium and perpendicular to glomerular basement membrane. Polarizing microscopy with Congo-red stain revealed prominent yellow green birefringence in glomeruli, tubules and interstitium.
기계적합금화법으로 제조된 Al-Fe-V-Si 합금 합출재의 고온취성 현상에 관한 연구
김상식,김회곤,정광철,안인섭 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.9
Tensile behavior of mechanically alloyed Al-8.5Fe-1.3V-1.7Si alloy extrusions, with various grain sizes ranging from 0.1 to 0.6 ㎛, were examined within the temperature range between 25℃ and 250℃. It was found that both tensile strength and ductility gradually decreased with increasing temperature and/or decreasing strain rate. The SEM fractographic examination showed that MA/PM Al-Fe-V-Si alloy extrusions failed by dimpled rupture, regardless of test conditions. The size and depth of dimples, however, differed considerably with different testing temperatures and strain rates. TEM micrographs of deformed specimens showed that the formation of dislocation structures within the grain was extremely limited at each test temperatures, and was further restricted at elevated temperatures. The present observations suggest that the enhanced dynamic recovery is responsible for the nil work hardening and plastic instabilities between growing voids at elevated temperatures, leading to a reduced tensile ductility.
고온자전합성법에 의한 Ti/Al 복합판재의 미세조직 형성과정
박우진,안상호,정재영,김낙준,이원철 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.10
Microstructural evolution of Ti/Al layered structures annealed at various temperature has been investigated by using optical microscopy, scanning electron microscopy, and X-ray diffractometry. Ti/Al layered sheets have been produced by dipping two Ti sheets in Al melt. The Ti/Al interfaces showed good bonding characteristics in as-dipped sheet. Microstructure of the heat-treated Ti/Al sheet varies depending on the subsequent annealing temperature. In the Ti/Al layered composite annealed at temperature below Al melting point, thin TiAl₃ layer was formed by the diffusion process at the Ti/Al interfaces. In the case of composite exposed at temperature above Al melting point, the equiaxed TiAl₃particles protruded into Al matrix from the thin TiAl₃ layer as well as the formation of thin TiAl₃ layer. TiAl₃ particles become homogeneously distributed within the Al matrix away from the Ti/Al interface with increasing annealing time. The formation of TiAl₃ phase in Ti/Al sheet annealed at temperature above Al melting point is believed to be formed by the exothermic chemical reaction.
Glutaraldehyde 와 자동 세척기를 이용한 내시경 소독방법의 임상에서의 유용성
김영호,손희정,윤성원,최규완,이남용,백승운,이준행,고광철,이풍렬,이종철,송재훈,안병훈,김재준,최원혁,홍일철 대한소화기내시경학회 2001 Clinical Endoscopy Vol.22 No.6
Background/Aims: Safety of endoscopic procedures has been a major issue over the last 10 years. Most endoscopy units use 2% glutaraldehyde and automated endoscope reprocessors (AERs) for disinfecting gastrointestinal endoscopes. We attempted an in-use evaluation of the current reprocessing procedures. Methods: Thirty flexible endoscopes were randomly collected just after upper endoscopic examinations and were disinfected using 2% glutaraldehyde in an AER. Cultures were taken from biopsy channels (S-l), tip of the insertion tubes (S-2), umbilical cords (S-3), and angulation knobs (S-4). Results: In 63,3% (19/30) of endoscopes, there was no microbial contamination after disinfection procedures. The culture positive rates of S-l, S-2, S-3, and S-4 samples were 20,0%, 0.0%, 3.3%, and 20.0%, respectively. Microorganisms of 13 species were identified, but there was no pathogen related with reported infectious complications after endoscopic procedures. Conclusions: Current disinfection procedure using 2% glutaraldehyde and an AER appears to be very effective in decontaminating patient-used endoscopes. Low level microbial contamination of endoscopes after conventional reprocessing methods may not impose great risk on patients.
Ahn, Jae-Il,Lee, Doo-Hoon,Ryu, Yang-Hwan,Jang, In-Keun,Yoon, Mun-Young,Shin, Youn Ho,Seo, Young-Kwon,Yoon, Hee-Hoon,Kim, Jae-Chan,Song, Kye-Yong,Yang, Eun-Kyung,Kim, Ki-Ho,Park, Jung-Keug Blackwell Publishing Inc 2007 Artificial Organs Vol.31 No.9
<P>Abstract: </P><P>Rabbit corneal epithelium was reconstructed using tilting dynamic culture with a self-manufactured, amniotic membrane (AM) supporter and a lyophilized amniotic membrane (LAM). Rabbit corneal epithelial (RCE) cells were cultured and cryopreserved after isolation from the limbus. The second- and third-passage RCE cells were plated onto the epithelial side of the LAM of Ahn's AM supporter. Two days later, the air–liquid interface culture was maintained with third-passage RCE cells for 6 days and second-passage corneal epithelial cells for 9 days. The average viability of thawed RCE cells, assessed using trypan blue dye exclusion, was 77.42%. The reconstructed corneal epithelium was characterized by histological (hematoxylin and eosin) and immunohistochemical staining (proliferating cell nuclear antigen) for light microscopy, and by reverse transcriptase-polymerase chain reaction, glucose assay, and transmission electron microscopy. The basal layer of the reconstructed corneal epithelium was well formed, and the epithelium was tightly constructed due to the increase in cell proliferation and differentiation caused by the tilting dynamic culture, as opposed to static culture. Tilting dynamic culture was useful for the reconstruction of the epithelium using easily damaged epithelial cells and resulted in more stratum cell layers. Moreover, cytokeratin (CK3) mRNA expression in tilting dynamic cultured third-passage RCE cells seeded onto AM was greater than in static cultured third-passage RCE cells. The morphology of the reconstructed corneal epithelium on LAM by tilting dynamic culture for 9 days resembled that of the skin epidermis. This was thought to be because the tilting dynamic culture not only accelerated the proliferation and differentiation of cells by physical or mechanical stimulation, but also ensured that the supply of medium was delivered to the basal cells more efficiently. Thus, the reconstruction of the corneal epithelium using LAM and tilting dynamic culture was considered to be a good in vitro model for autologous or allogeneic transplantation of corneal epithelium and skin epidermis in patients with damaged epithelia. </P>
Jung‑Hun Lee,Min‑Su Park,Hong‑Seon Ahn,Kyung‑Won Park,Jun‑Seok Oh,Seung‑Gyu Jeon,Dong‑Kyu Kim,Jae‑Eon Kim 대한전기학회 2020 Journal of Electrical Engineering & Technology Vol.15 No.4
When large scales DG are connected to the distribution system of unidirectional power currents, bi-directional power currents are formed, making it impossible to use conventional overcurrent protection methods alone to detect and isolate fault sections for ground and short-circuit faults. To solve these problems, this study proposed the method of protection against single-line-ground fault of common neutral line multi-contact local power distribution system using distance relay and directional relay. The proposed protection method was applied to the common neutral multi-ground distribution system to validate the protection against single-line-ground fault through the PSCAD/EMTDC software package and efectively detect and isolate only the zone of single-line-ground fault without malfunctions.
Ahn Jae-Il,Jang In-Keun,Lee Doo-Hoon,Seo Young-Kwon,Yoon Hee-Hoon,Shin Youn-Ho,Kim Jae-Chan,Song Kye-Yong,Lee Hee-Gu,Yang Eun-Kyung,Kim Ki-Ho,Park Jung-Keung The Korean Society for Biotechnology and Bioengine 2005 Biotechnology and Bioprocess Engineering Vol.10 No.3
Many researchers have employed cryopreserved amniotic membrane (CAM) in the treatment of a severely damaged cornea, using corneal epithelial cells cultured on an amniotic membrane (AM). In this study, two Teflon rings were made for culturing the cells on the LAM and CAM, and were then used to support the AM, which is referred to in this paper as an Ahn's AM supporter. The primary corneal epithelial cells were obtained from the limbus, using an ex-plantation method. The corneal epithelium could be reconstructed by culturing the thirdpassage corneal epithelial cells on the AM. A lyophilized amniotic membrane (LAM) has a higher rate of graft take, a longer shelf life, is easier to store, and safer, due to gamma irradiation, than a (AM. The corneal epithelium reconstructed on the LAM and (AM, supported by the twoTeflon rings, was similar to normal corneal epithelium. However, the advantages of the LAM over that of the (AM make the former more useful. The reconstruction model of the corneal epithelium, using AM, is considered as a good in vitro model for transplantation of cornel epithelium into patients with a severely damaged cornea.