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        검색결과 5

        1.
        2003.03 KCI 등재 구독 인증기관 무료, 개인회원 유료
        In this study, densified 4D carbon/carbon composites were made from carbon fiber and coal tar pitch through the process of pressure impregnation and carbonization and then followed by carbonization and graphitization. To improve the oxidative resistance of the prepared carbon/carbon composites, the surface of carbon/carbon composites was coated on SiC by the pack cementation method. The SiC coated layer was created by depending on the constitution of pack powder, and reaction time of pack-cementation. The morpology of crystalline and texture of these SiC coated carbon/carbon composites were investigated by XRD, SEM/EDS observation. So the coating mechanism of pack-cementation process was proposed. The oxidative res istance were observed through the air oxidation test, and then the optimal condition of pack cementation was found by them. Besides, the oxidative mechanism of SiC formed was proposed through the observation of SiC coated surface, which was undergone by oxidation test.
        4,000원
        2.
        2001.12 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The Carbon/Carbon composite was prepared from 3D carbon fiber preform and coal tar pitch as matrix precursor. In order to evaluate of ablative characteristics of the composite, liquid rocket system was employed Kerosene and liquid oxygen was used as propellants, operating at a nominal chamber pressure of 330 psi and a nominal mixture ratio (O/F) of 2.0. The results of an experimental evaluation were that high density composite exhibited high, while low density composites showed low erosion resistance. The erosion rate against heat flux was highly depended on the density of the materials. The morphology of eroded fiber showed differently according to collision angle with heat flux on the composite. The granular matrix which derived from carbonization pressure of 900 bar was more resistance to heat flux than well-developed flow type matrix.
        4,000원
        3.
        2017.03 KCI 등재 서비스 종료(열람 제한)
        이 연구는 외국인노동자 부모를 따라 한국에 입국한 러시아와 중앙아시아 출신 고려인 중도입국청소년의 한국 학교생활 경험을 심층적으로 탐색하여 그들이 경험을 이해하고 시 사점을 찾는데 목적이 있다. 연구를 위해 1년 이상 한국에서 학교생활을 경험한 3명의 고 려인 중도입국청소년을 연구 참여자로 선정하였다. 연구자는 내러티브 탐구방법을 사용해 그들의 학교생활 경험을 탐색하였고, 그 경험을 또래관계, 교사와의 관계, 학업성취 영역으 로 나누어 살펴보았다. 그 결과 첫째, 한국어 구사 한계로 인한 의사소통의 문제가 학교생 활 전반에 걸쳐 나타났다. 둘째, 또래와의 관계에서 한국어 부족과 문화적 차이는 상호 친 밀감 형성에 어려움을 갖게 하였다. 욕설을 듣고 왕따를 경험하였으며, 이러한 경험은 곧 학교부적응으로 이어졌다. 셋째, 교사와의 관계에서 교사들은 친절히 대해주는 편이었으나, 중도입국 청소년의 한국어 이해 부족과 부진한 학습 활동으로 인해 교내 활동에서 제외될 때에는 배려라기보다는 교사의 무관심과 무시로 여기고 있었다. 넷째, 학업성취면에서 출신 국의 우수한 학교성적과 한국에서의 낮은 학업성취 결과는 이들로 하여금 어려움을 겪게 했는데, 특히 교과과정, 진도수준 차이가 수업적응에 어려움을 겪게 하였다.
        4.
        2009.09 KCI 등재 서비스 종료(열람 제한)
        The purpose of the present study is to analyze pollutant runoff characteristics from non-point sources in Joman River basin. The present study contains analyzed results of rainfall and SS, BOD, COD, TN, TP runoff from Joman River basin. This study contains a sensitivity analysis of parameters that affect the simulation results of rainfall and pollutants runoff. Result of the sensitivity analysis shows that proportion of watershed and impervious areas is the most sensitive to peak discharge and total flowrate for rainfall runoff and that WASHPO is the most sensitive parameter for pollutants runoff. For parameter estimation and verification, flowrate and water quality is measured at the Kangdong Bridge in Haeban stream. A single rainfall event is use to perform parameter estimation and verification. Results of the present study show that total pollutant loads of Joman River basin is 11,600 ton of SS, 452 ton of BOD, 1,084 ton of COD, 515 ton of TN, and 49 ton of TP, respectively. In addition, it is found that contribution ratio of non‐point source and total source is 89% of SS, 63% of BOD, 61% of COD, 21% of TN, and 32% of TP, respectively.
        5.
        2009.09 KCI 등재 서비스 종료(열람 제한)
        An objective of this study is as follows: 1) performing sensitivity analysis and parameter estimation of RMA2 and RMA4 models for the West-Nakdong River, 2) drawing up alternatives of gates-operation for water-quality enhancement, and 3) quantitative evaluation of methodology of 'flow-restoration by gates-operation' among 'Comprehensive Plan Improving Water-Quality in the West-Nakdong River(WNR)' with the target water-quality(BOD at Nakbon-N point: below 4.3 mg/L). The parameters for the RMA2 (depth-averaged two-dimensional flow model) and RMA4 (depth-averaged two-dimensional water-quality model) were determined by sensitivity analysis. Result of parameter estimation for RMA2 and RMA4 models is 1,000 Pa․s of the eddy viscosity, 20 of the Peclet number, 0.025 of the Manning coefficient, and 1.0 m2/s of the diffusion coefficient. We have evaluated the effects of water-quality enhancement of the selected alternatives by numerical simulation technique with the models under the steady-state flow condition and the time-variant transport condition. Because of no-resuspension from river bottom and considering BOD as conservative matter, these simulation results slightly differ from real phenomena. In the case of 50 m3/s of Daejeo-gate inflow, two-dimensional flow pn results result represents that small velocity occurs in the Pyungkang Stream and no flow in the Maekdo River. In the WNR, there occurs the most rapid flow near timhae-bridge. In the WNR, changes of water-quality for the four selected simulation cases(6, 10, 30, 50 m3/s of the Daejeo-gate inflow) were predicted. Since the Daejeo-Gate and the Noksan-Gate can be opened up to 7 days, it would be found that sustainable inflow of 30 m3/s at the Daejeo-gate makes BOD in the WNR to be under the target of water-quality.