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중성자 회절법에 의한 Ni-W 합금 소결체의 격자상수 측정
김찬중,김민우,박순동,전병혁,장석원,성백석,Kim, Chan-Joong,Kim, Min-Woon,Park, Soon-Dong,Jun, Byung-Hyuk,Jang, Serk-Won,Seong, Baek-Seok 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.3
Ni-W(1-5 at.%) alloy rods were made by powder metallurgy process including powder mixing, compacting and subsequent sintering. Ni and W powder of appropriate compositions were mixed by a ball milling and isostatically pressed in a rubber mold into a rod. The compacted rods were sintered at $1000^{\circ}C-1150^{\circ}C$ at a reduced atmosphere for densification. The lattice parameters of Ni-W alloys were estimated by a high resolution neutron powder diffractometer. All sintered rods were found to have a face centered cubic structure without any impurity phase, but the diffraction peak locations were linearly shifted with increasing W content. The lattice parameter of a pure Ni rod was $3.5238{\AA}$ which is consistent with the value reported in JCPDS data. The lattice parameter of N-W alloy rods increased by $0.004{\AA}$ for 1 atomic % of W, which indicates the formation of a Ni-W solid solution due to the substitution of nickel atoms by tungsten atoms of larger size.
대면적 단결정 Gd<sub>1.5</sub>Ba<sub>2</sub>Cu<sub>3</sub>O<sub>7-y</sub> 벌크 초전도체의 초전도 특성
김찬중,박승연,김광모,박순동,전병혁,Kim, Chan-Joong,Park, Seung Yeon,Kim, Kwang-Mo,Park, Soon-Dong,Jun, Byung-Hyuk 한국재료학회 2012 한국재료학회지 Vol.22 No.11
Large single grain $Gd_{1.5}Ba_2Cu_3O_{7-y}$ (Gd1.5) bulk superconductors were fabricated by a top-seeded melt growth (TSMG) process using an $NdBa_2Cu_3O_{7-y}$ seed. The seeded Gd1.5 powder compacts with a diameter of 50 mm were subjected to the heating cycles of a TSMG process. After the TSMG process, the diameter of the single grain Gd1.5 compact was reduced to 43 mm owing to the volume contraction during the heat treatment. The superconducting transition temperature ($T_c$) of the top surface of the single grain Gd1.5 sample was as high as 93.5 K. The critical current densities ($J_cs$) at 77 K and 1T and 1.5 T were in ranges of 25,200-43,900 $A/cm^2$ and 10,000-23,000 $A/cm^2$, respectively. The maximum attractive force at 77 K of the sample field-cooled using an Nd-B-Fe permanent magnet (surface magnetic field of 0. 527 T) was 108.3 N; the maximum repulsive force of the zero field-cooled sample was 262 N. The magnetic flux density of the sample field-cooled at 77 K was 0.311T, which is approximately 85% of the applied magnetic field of 0.375 T. Microstructure investigation showed that many $Gd_2BaCuO_5$ (Gd211) particles of a few ${\mu}m$ in size, which are flux pinning sites of Gd123, were trapped within the $GdBa_2Cu_3O_{7-y}$ (Gd123) grain; unreacted $Ba_3Cu_5O_8$ liquid and Gd211 particles were present near the edge regions of the single grain Gd1.5 bulk compact.
당뇨병 환자에서 백내장 수술 후 수정체유화술 시간에 따른 각막내피세포의 변화
김찬중,최상경,Chan Joong Kim,Sang Kyung Choi 대한안과학회 2007 대한안과학회지 Vol.48 No.11
Purpose: To investigate the difference in corneal endothelial cell loss between diabetic and non-diabetic patients who were divided by the degree of phacoemulsification time after phacoemulsification with intraocular lens implantation. Methods: Forty eyes of 30 patients with diabetes and 47 eyes of 36 patients without diabetes were divided by phacoemulsification time into 3 groups: less than 40 seconds, from 40 to 80 seconds and over 80 seconds. The corneal endothelial cell density was compared before and 1, 4 and 16 weeks after phacoemulsification by one-way ANOVA. Bivariate correlation analysis was used to identify the correlation between phacoemulsification time and the endothelial density before and 1, 4 and 16 weeks after phcoemulsification. Results: The endothelial cell densities in diabetic and non-diabetic patients with different phacoemulsification time were not significantly different when compared before and 1, 4 and 16 weeks after phacoemulsification (P>0.05). Phacoemulsificaiton time and endothelial cell loss at 1, 4 and 16 weeks also showed no significant correlation. Conclusions: Diabetes and differences in phacoemulsification time had no significant influence on corneal endothelial cell loss. This result suggests uncomplicated phacoemulsificaion is a safe method for cataract extraction in patients with or without diabetes.
Superconductivity of Ce$O_2$-added Y-Ba-Cu-0 Superconductors Prepared by Partial Melt Process
김찬중,김기백,이규원,원동연,Kim, Chan-Joong,Kim, Ki-Baik,Lee, Kyu-Won,Won, Dong-Yeon Materials Research Society of Korea 1992 한국재료학회지 Vol.2 No.3
$CeO_2$를 첨가한 Y-Ba-Cu-0 초전도체를 포정반응을 포함한 준용용법으로 제조하여 미세조직과 초전도성을 관찰하였다. 첨가한 $CeO_2$는 포정반응중에 $BaCeO_3$로 변화하였으며, 이 $BaCeO_3$는 방향성 성장한 1-2-3 초전도상의 기지에 미세하게 분산된다. 초전도체의 $T_{c}$는 첨가된 $CeO_2$함량에 관계없이 90K 이상으로 매우 높았다. 이는 준용융공정을 적용함으로서 제2상물질을 초전도상으로부터 분리할 수 있었기 때문으로 사료된다. The $CeO_2$-added Y-Ba-Cu-O oxides were prepared by the partial melt process involving the peritectic reaction, liquid + 2-1-1 phase ${\rightarrow}$ 1-2-3 phase, to investigate the effect of the dopant on microstructure and superconductivity. During the peritec reaction, all the added $CeO_2$ was converted to $BaCeO_3$ particles which were finely dispersed in large 1-2-3 grains. Superconducting transition temperature($T_{c}R=0$ point) of the partial-melted samples was as high as 90K regardless of $CeO_2$ content up to 5wt%, which is owing to the separation of the second phase from the 1-2-3 superconducting phase.
저 순도 BaCO<sub>3</sub> 분말을 사용한 Yba<sub>2</sub>Cu<sub>3</sub>O<sub>7-y</sub> 초전도체의 합성
김찬중,박순동,최정숙,전병혁,문종백,이상헌,성태현,Kim, Chan-Joong,Park, Soon-Dong,Choi, Jung-Suk,Jun, Byung-Hyuk,Moon, Jong-Baik,Lee, Sang-Heon,Sung, Tae-Hyun 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.1
[ $YBa_2Cu_3O_{7-y}$ ](123) powders were synthesized by the solid state reaction method using two different purity $BaCO_3$ powders (99.75% and 99.7% purity) and $Y_2O_3$ (99.9%) and CuO (99.9%) powders. The effect of $BaCO_3$ purity on the formation of a 123 phase and the superconducting properties were investigated. The mixtures of raw powders were calcined at temperature ranges of $800^{\circ}C-880^{\circ}C$ in air and finally made into a single grain samples by a melt processing with top seeding. It was found that a 123 phase was well formed at temperature above $870^{\circ}C$, but the purity effect on the 123 formation was negligible. The single-grain 123 samples prepared from the different $BaCO_3$ powders showed the same $T_c$ value of 90.5 K and similar $J_c$ values about $10^4\;A/cm^2$ at 0 T and 77 K, and $10^3\;A/cm^2$ at 2 T and 77 K. This result indicates that the low purity, cheap price $BaCO_3$ powder can be used as a raw material for the fabrication of single-grain, high-$J_c$ superconducting levitator.
이산 코사인 변환 기법을 이용한 선택적인 홍채영상 알고리즘
김찬중 ( Chan Joong Kim ),김재훈 ( Jai-hoon Kim ),최복천 ( Bok Chun Choi ) 한국정보처리학회 2010 한국정보처리학회 학술대회논문집 Vol.17 No.2
대부분의 홍채인식 시스템의 전반부를 살펴보면 카메라를 통한 이미지를 획득 후 전처리 과정에서 동공의 경계를 잡는 과정이 수행된다. 카메라를 통한 이미지 획득 시 초점이 좋은 이미지와 나쁜 이미지가 같이 획득이 된다. 초점이 나쁜 이미지는 동공의 경계를 잡는 과정에 있어서 좋은 이미지보다 시간이 오래 걸리기 마련이다. 이에 본 논문에서는 영상획득 후 동공의 경계를 잡는 과정 전에 DCT(Discrete Cosine Transform)를 이용한 선명도 측정하는 방법을 제안한다. 카메라를 통한 영상을 획득한 후 초점이 좋은 영상과 나쁜 영상을 구분하게 되고 초점이 좋은 영상만을 선택하여 다음 과정인 동공의 경계를 잡는 작업을 수행하게 된다. 제안하는 방법은 DCT를 이용한 이미지의 선별 작업에 시간이 소비 되지만 나쁜 영상을 이용하여 동공의 경계를 잡느라 걸리는 시간을 줄일 수 있는 장점을 기대할 수 있다. 우선적으로 수학적 분석을 통하여 23%의 속도 절감을 통한 성능 개선의 가능성을 보였고, 실제 구현을 통하여 속도 향상이 기대된다.