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권태환(Kwoen TaeHwan),양천모(Yang ChunMo),박영구(Park YoungGoo),조영구(Cho YoungKoo),임병오(Rim ByungO) 한국유화학회 2003 한국응용과학기술학회지 Vol.20 No.1
LiMn2O4 catalyst for CO2 decomposition was synthesized by oxidation method for 30 min at 600^{circ}C in an electric furnace under air condition using manganese(II) nitrate (Mn(NO3)2{cdot}6H2O), Lithium nitrate (LiNO3) and Urea (CO(NH2)2). The synthesized catalyst was reduced by H2 at various temperatures for 3 hr. The reduction degree of the reduced catalysts were measured using the TGA. And then CO2 decomposition rate was measured using the reduced catalysts. Phase-transitions of the catalysts were observed after CO2 decomposition reaction at an optimal decomposition temperature. As the result of X-ray powder diffraction analysis, the synthesized catalyst was confirmed that the catalyst has the spinel structure, and also confirmed that when it was reduced by H2, the phase of LiMn2O4 catalyst was transformed into Li2MnO3 and Li{1-2{delta}}Mn{2-{delta}}O{4-3{delta}-{delta} of tetragonal spinel phase. After CO2 decomposition reaction, it was confirmed that the peak of LiMn2O4 of spinel phase. The optimal reduction temperature of the catalyst with H2 was confirmed to be 450^{circ}C(maximum weight-increasing ratio 9.47%) in the case of LiMn2O4 through the TGA analysis. Decomposition rate(%) using the LiMn2O4 catalyst showed the 67%. The crystal structure of the synthesized LiMn2O4 observed with a scanning electron microscope(SEM) shows cubic form. After reduction, LiMn2O4 catalyst became condensed each other to form interface. It was confirmed that after CO2 decomposition, crystal structure of LiMn2O4 catalyst showed that its particle grew up more than that of reduction. Phase-transition by reduction and CO2 decomposition ; Li2MnO3 and Li{1-2{delta}}Mn{2-{delta}}O{4-3{delta}-{delta} of tetragonal spinel phase at the first time of CO2 decomposition appear like the same as the above contents. Phase-transition at 2{sim}5 time ; Li2MnO3 and Li{1-2{delta}}Mn{2-{delta}}O{4-3{delta}-{delta} of tetragonal spinel phase by reduction and LiMn2O4 of spinel phase after CO2 decomposition appear like the same as the first time case. The result of the TGA analysis by catalyst reduction ; The first time, weight of reduced catalyst increased by 9.47%, for 2{sim}5 times, weight of reduced catalyst increased by average 2.3% But, in any time, there is little difference in the decomposition ratio of CO2. That is to say, at the first time, it showed 67% in CO2 decomposition rate and after 5 times reaction of CO2 decomposition, it showed 67% nearly the same as the first time.
Research on mathematics teachers' knowledge
이중권(Joong Kwoen Lee),김용기(Yong Ki Kim) 대한수학교육학회 1999 수학교육학연구 Vol.9 No.1
수학 교사의 지식은 교과내용 지식, 일반 교육학 지식, 교육학 내용 지식, 교육과정 지식, 학습자에 대한 지식, 교육적 내용에 관한 지식, 수학 교육 목표, 목적, 가치에 대한 지식으로 분류될 수 있다. 지금까지 이러한 수학 교사에 대한 지식 종류에 대한 학문적 연구는 뚜렷하게 체계적으로 연구 되어지지 못하고 주로 저학년 학생 및 학습자 위주로 산발적인 연구가 진행되어 왔다. 수학교사가 지녀야할 지식은 수학 학습자인 학생들을 어떻게 효과적으로 가르치느냐에 가장 직접적인 영향을 미치는 것이므로 이에 따른 구체적인 조사 연구가 필요할 뿐만 아니라 교사교육 프로그램에 반영되어 효과적으로 능력있는 교사를 양성할 수 있도록 하여야 겠다.
The use of acellular allogenic dermal matrix in soft tissue management around the implants
Min-Jeong Kwoen,Sang-Yun Kim,Yong-Hoon Choi,Young-Kyun Kim 대한치과이식임플란트학회 2019 The Korean Academy of Implant Dentistry Vol.38 No.1
Purpose: The purpose of this study was to introduce various strategies to deal with soft tissue using an acellular allogenic dermal matrix and to evaluate postoperative complications and implant prognosis (success rate, survival rate, failure, and marginal bone loss). Materials and Methods: This retrospective study investigated 28 patients who had intraoral surgery using an acellular allogenic dermal matrix (Megaderm, L & C BIO Inc, Seoul, Korea) from May 2013 to December 2017. Vestibuloplasty, increasing keratinized mucosa, soft tissue augmentation, and barrier membrane for bone graft were used as surgical methods in 32 cases. Megaderm was applied to nine cases for barrier membrane after guided bone regeneration and 22 cases for soft tissue treatment. One case was used for bone graft and soft tissue treatment. A total of 48 implants were placed. Results: Among the 48 implants, 25 were counted to measure the success rate because more than a year has passed since the placement of prosthetic devices, and radiographic examination was performed. Three implants had peri-implantitis and was classified as failures. Of the 25 implants, 22 (88%) were successful. As none of implants were removed from the placement site, the survival rate was 100%. Conclusions: Megaderm is a biocompatible material which maintains its collagen structure after the manufacturing process. As a result, it acts as a membrane and graft soft tissue material properly in the intraoral environment.