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崔慶圭(Kyung-Kyu Choi),張太因(Tae-In Jang),尹亨羲(Hyung-Hee Yoon),鄭彩均(Chae-Kyun Jung) 대한전기학회 2007 전기학회논문지 Vol.56 No.12
The conventional CCPU(Cable Covering Protective Unit) modeling methods which are used by Type 99 and Type 92 in EMTP simulation are firstly discussed in this paper, and then some problems of them are also investigated. Modeling method using Type 99 causes unstable characteristic at initial transient of CCPU operation. Time delay has also effect on the output of CCPU modeling. So, in this paper, a new modeling method for CCPU is designed by DBM(Data Base Module) of EMTP. The characteristic of Type 92 is used for the new modeling method. The reliability of this one is proved by comparing simulation with measured data. Specially, at initial transient, the waveform of the new method shows more stable result than that of conventional method using Type 99. Also, the peak value is similar to measured data.
최경규(Kyung-Kyu Choi),김동훈(Dong-Hoon Kim),박홍근(Hong-Gun Park) 한국구조물진단유지관리학회 2010 한국구조물진단학회 학술발표회논문집 Vol.2010 No.2
In the present study, a unified design method applicable to slab-column connections and column footings was developed. For verification, the proposed method was applied to existing test results with wide ranges of design parameters. In the comparison, it was found that the proposed method shows better strength prediction compared to current design method.
최하진(Choi, Ha-Jin),최경규(Choi, Kyung-Kyu),최완철(Choi, Oan-Chul),황용재(Hwang, Yong-Jae) 대한건축학회 2012 大韓建築學會論文集 : 構造系 Vol.28 No.6
On the basis of dry shrinkage tests of fiber reinforced concrete performed in the previous study, an analytical model was developed to predict the cracking time of concrete in ring test. Due to the geometrical characteristics of the ring type restrained shrinkage test, differential shrinkage causes complex tensile stress in concrete ring. For simplicity in application, the ring test specimens were idealized as linear specimens and the degree of restraint was defined considering displacement compatibility between steel and concrete rings. The tensile stress in ring test specimens was also defined using elastic modulus of concrete and free dry shrinkage strain. The tensile strength of concrete was derived from CEB-FIP model based on flexural test results. In the proposed model, cracking development tine is determined at the intersection between tensile stress and tensile strength curves of concrete ring. Compared with existing test results the proposed model shows reliable prediction of the crack development time.
개방 근첨 치아의 근관 충전방법에 따른 치근단 폐쇄효과에 관한 연구
소현,최호영,최경규,최기운,So, Hyun,Choi, Ho-Young,Choi, Kyung-Kyu,Choi, Gi-Woon 대한치과보존학회 2000 Restorative Dentistry & Endodontics Vol.25 No.3
The purpose of this study was to compare the leakage of four different obturation techniques in conjunction with immediate apical barrier of ${\beta}$-tricalcium phosphate(TCP) in teeth with open apex. Eighty single-rooted human premolar teeth were prepared and sectioned horizontally, so maximum diameter in apex was 4mm. Apical defects that were similar to open apex, were created with #1/2 round bur and SF104R bur. The apical foramen were opened to a size 80 file extended 3mm beyond the apex. The teeth were placed into the oasis block soaked saline to simulate periapical tissue often associated with pulpless teeth and received apical barriers consisting of TCP followed by obturation using lateral condensation technique, vertical condensation technique, continuous wave technique and thermoplasticized gutta-percha injection technique. Two unobturated teeth served as positive and negative controls. Teeth were immersed in resorcinol-formaldehyde resin for S days at $4^{\circ}C$, and the resin was allowed to polymerize completely for 4 days at room temperature. Teeth were then sectioned horizontally at 1.5mm(level 1), 2.5mm(level 2) and 3.5mm(level 3) from the apex, and examined under a stereomicroscope at ${\times}40$ magnification. The photographs were taken at ${\times}40$ magnification of the filling in each level and scanned. The leakage length in tooth/resin interface was measured at each of the three levels. Each ratio of leakage was obtained by calculating the ratio of the leakage length of canal wall infiltrated with resin to the total length of the canal and was analyzed statistically(One-way ANOVA and Scheffe test). The result were as follows : 1. At the level 1, there was the least leakage in the thermoplasticized gutta-percha injection technique group(group 4), but there was statistically significant(p<0.05). 2. At the level 2, there was the least leakage in the thermoplasticized gutta-percha injection technique group(group 4), and the most leakage in the continuous wave technique group(group 3). There was statistically significant difference between the thermoplasticized gutta-percha injection technique group and the continuous wave technique group(p<0.05). 3. At the level 3, there was the least leakage in the thermoplasticized gutta-percha injection technique group(group 4), but there were no statistically significant differences between other groups(p>0.05). These results suggest that thermoplasticized gutta-percha injection technique which had 1mm apical gutta-percha matrix after the formation of TCP apical barrier, can demonstrate favorable apical sealing.