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김지환,지승묵,윤영식,여종석 한국진공학회 2018 Applied Science and Convergence Technology Vol.27 No.6
Selective laser melting (SLM) is a promising additive manufacturing technique applied to various areas such as aerospace and biomedical industries. Because product characteristics can be controlled by SLM process parameters, several investigations have been conducted to clarify the relationship between process parameters and product characteristics. Melt pool, controlled by process parameters, is a suitable resource to determine the product profile accuracy and mechanical property. Two laser types, continuous wave (CW) and pulse width modulation (PWM), are typically used in SLM processes, and each has distinct advantages depending on the purpose of the process. While CW maintains its power constant, PWM presents a repeated pattern with a pulse width. Herein, the main differences in the process parameters between the two laser types and their effects on the melt pool formation during the SLM process are explained. The results demonstrate that CW and PWM are favorable for dense and fine structures, respectively.
SM45C 와 STD_(11)의 CW Nd:YAG 레이저 표면경화 특성비교
김지환,유영태,신호준,오용석 조선대학교 에너지.자원신기술연구소 2003 에너지·자원신기술연구소 논문지 Vol.25 No.1
Laser surface hardening is an effective technique used to improve the tribological properties and also to increase the service life of automobile components such as camshafts, crankshatfs, lorry brake drums and gears. High power CO_(2) lasers and Nd:YAG lasers are employed for localized hardening of materials and hence are of potential application in the automobile industries. The heat is conducted rapidly into the bulk of the specimen causing self-quenching to occur and the formation of martensitic structure In this investigation, the microstructrual features occurring in Nd:YAG laser hardening SM45C and STD_(11) steel are discussed with the use of optical microscopic and scanning electron microscopic analysis. Moreover, This paper describes the optimisation of the processing parameters for maximum hardened depth of SM54C and STD_(11) steel specimens of 4.5㎜, 10㎜ thickness by using CW Nd:YAG laser.
수용액중에서 산소에 의한 Co-Ni 공심수산화물의 산화반응 거동에 관하여 : 페라이트법에 의한 중금속 폐수처리에 관한 연구 제2보
김지환,오재현,강남기 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.12
The oxidation behaviors of Co-Ni hydroxide coprecipitates were investigated with relation to the conditions of the solution such as R value(=2〔OH^-〕 / 〔SO^(2-)₄〕), temperature and initial 〔Ni(Ⅱ)〕/〔Co(Ⅱ)〕 molar ratio. The characteristics of reaction products were examined by composition analysis, XRD, TEM and magnetic property measurement. When increasing R value, the reaction time and particle sizes were increased. And the reaction products were Co-Ni ferrite. The amount of Co incorporated into the spinel structure increased and that of Ni decreased with increasing R value and temperature. In reaction products represented by Co, Ni_yFe_(3-(x+y))O₄, the amount of (x+y) shows the ranges between 0.6 and 0.7, regardless of R value and temperature. In the conditions of R=1.5, 70℃, 〔Co(Ⅱ)+Ni(Ⅱ)〕/〔Fe(Ⅱ)〕 ratio 0.5, 〔Ni(Ⅱ)〕/〔Co(Ⅱ)〕 ratio =2.0 in the initial solution, Co and Ni incorporated with equal amounts into spinel structures and the reaction product of Co_(0.29)Ni_(0.29)Fe_(2.41)O₄ was obtained.
치과용 시멘트에 따른 주조금관의 응력 분포에 대한 고찰
김지환 高麗大學校 倂設 保健大學 保健科學硏究所 1994 保建科學硏究論集 Vol.3 No.1
The purpose of this study was to compare difference in the stress distributions of crown according to dental cements under static load. To evaluate the stresses of crown, dental cement, abutment tooth, a mandibular first molar was used and prepared to same dimension. According to the FEM modelling method, the casting gold crown was designed. The teeth and the casting gold restorations were divided into three groups and modelled on computer as natural condition, 12㎏ of static force was loaded individually each two point of crown; buccal cusp tip, central fossa. The Von Mises stresses developed in the casting gold restoration according to dental cements. The Von Mises stress as were measured at buccal and lingual slope between crown and cement and abutment. The form of crown was designed ; thickness of functional cusp - 1.5㎜, central fossa - 1.0㎜. A two dimensional stress analysis model was constructed to represent a mandibular first molar. Finite element models were created and analysed using software SUPER SAP for IBM AT 386 personal computer. The results obtained were as follows ; 1. On loading condition, there was significant difference according to dental cements. 2. There were proportional relationship between cement's strength and stress distribution. 3. On loading condition vertically, stress was distributed more favorably in zinc phosphate cement than others.
수요체계모형을 이용한 우리나라의 1차 에너지 수요 추정 연구
김지환,김윤경 재단법인 에너지경제연구원 2024 에너지경제연구 Vol.23 No.1
2021년 기준으로 94.8%의 에너지수입의존도를 갖는 우리나라는 과거 30여년간 계속 이 수준을 유지하고 있다. 이에 본 연구에서는 1차에너지에 대한 수요 양상이 바뀌고 있다는 점을 밝히고자 1차 에너지원을 대상으로 2단계 수요체계 모형을 이용해 석탄, 원유, 천연가스를 포함한 에너지원과 노동, 기타투입재 간의 수요체계를 추정하였다. 추정결과에 따르면 1998년 이전 기간에서는 모든 재화에 대해 자기가격탄력성이 유의한 양의 값으로 나타났으며, 총산출에 대해서도 모두 양의 값을 보였다. 1999년 이후 기간에서는 모든 재화의 자기가격 탄력성이 음의 값을 보이며, 총산출에 대해서는 양의 값을 갖는 것으로 나타났다. 1차 에너지원에 대한 추정 결과를 보면, 연료용 석유를 전력으로 대체하면서 기저전원을 담당하는 석탄과 원유간의 교차가격탄력성이 유의한 양의 값으로 나타났다. 일반적으로 에너지에 대한 수요는 전력이나 석유제품과 같은 전환에너지를 대상으로 하므로 전환에너지를 생산하기 위한 1차 에너지의 가격 변동을 체감하기는 쉽지 않다. 우리나라와 같이 에너지수입의존도가 높은 나라에게 1차 에너지의 가격 변동은 정부의 정책 노력으로 완화시키기 어려우므로 더 큰 위험으로 나타나게 된다. 이에 시기에 따라서 바뀌고 있는 1차 에너지에 대한 수요체계를 검토하면서 위험을 완화할 수 있는 대책을 마련하는 것이 필요하다. Korea’s energy import dependency is 94.8% as of 2021, has maintained this level for the past 30 years. In this study, the demand system between energy sources including coal, crude oil, and natural gas, labor, and other inputs was estimated using a two-stage demand system model to reveal that the demand pattern for primary energy is changing. According to the estimation results, in the period before 1998, self-price elasticity was a positive value for all goods. All of them showed positive values for total output. In the period after 1999, the self-price elasticity of all goods showed negative values. It was found to have a positive value for the total output. According to the estimation results for the primary energy, the cross-price elasticity between coal and crude oil, which are in charge of base power while substitute fuel oil with electricity, was found to be a significant positive value. It is not very often to experience price change of primary energy to produce conversion energy because the price of electricity and petroleum products are regulated in Korea. However, for countries with a high energy import dependency, such as Korea, price change of primary energy are exposed to greater risks because they are induced from international energy market. Therefore it is necessary to examine the demand response to primary energy that is changing over time.
김지환 한국자원공학회 2019 한국자원공학회지 Vol.56 No.2
Subsoil assets statistics, now published, began in 2007 as part of the National Asset Statistics in accordance with 93SNA (System of National Accounts) standards. It was applied as an indirect estimation method. Subsoil assets are proven resources that are economically available based on present technology and relative prices, and subsoil assets statistics describes the data representing the estimated value of subsoil assets. This article explains how to estimate subsoil assets value, and suggests some ideas to improve current valuing methods, based on changes in recent laws and systems. 현재 공표되는 지하자산 통계는, 국가자산통계의 항목으로, 93SNA(System of National Accounts) 기준에 따라 2007년부터 간접추계방식으로 시작되었다. 지하자산은 현재기술과 상대가격에서 경제적으로 이용 가능한 확정광량을 대상으로 하며, 지하자산 통계는 지하자산의 가치를 추계하는 것이다. 본고는 SNA가 제안하는 지하자산 추계에의 제안사항을 설명하고 주요 선행사례들을 검토한 후 현행 우리나라의 지하자산 추계방법을 설명한다. 그리고 최근의 법, 제도 등 추계여건변화에 따라 개선해 나아갈 방향에 관해 제시한다.