• 한국재료학회지
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• 제20권9호
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• pp.472-477
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• 2010

$Al_2O_3$ has received wide attention with established use as a catalyst and growing application in structural or functional ceramic materials. On the other hand, the boehmite (AlO(OH)) obtained by sol-gel process has exhibited a decrease in surface area during phase transformation due to a decline in surface active site at high temperature. In this work, $Al_2O_3$-CuO/ZnO (ACZ) and $Al_2O_3$-CuO/CeO (ACC) composite materials were synthesized with aluminum isopropoxide, copper (II) nitrate hemi (pentahydrate), and cerium (III) nitrate hexahydrate or zinc (II) nitrate hexahydrate. Moreover, the Span 80 as the template block copolymer was added to the ACZ/ACC composition to make nano size particles and to keep increasing the surface area. The ACZ/ACC synthesized powders were characterized by Thermogravimetry-Differential Thermal analysis (TG/DTA), X-ray Diffractometer (XRD), Field-Emmision Scanning Electron Microscope (FE-SEM), Bruner-Emmett-Teller (BET) surface analysis and thermal electrical conductivity (ZEM-2:M8/L). An enhancement of surface area with the addition to Span 80 surfactant was observed in the ACZ powders from 105 $m^2$/g to 142 $m^2$/g, and the ACC powders from 103 $m^2$/g to 140 $m^2$/g, respectively.

• 지질공학
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• 제16권3호
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• pp.227-233
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• 2006

암반은 일반적으로 생성환경 및 지질학적 조건에 따라 균질하지 못하며, 특히 기질과 역의 성분차이가 심한 역암 또는 각력암이나 핵석 등은 복합물질로 구성된 암반에 해당된다. 이들 복합 지반물질의 역학적 특성은 역과 기질의 역학특성과 분포특성 등에 따라 달라진다. 사면과 터널 및 지하구조물의 설계를 위한 이들의 역학성 평가는 매우 중요하지만 일반적으로 행해지는 암반분류법에 의한 이들의 평가는 부적절하다. 따라서 본 연구에서는 복합지반물질의 역학성 평가를 위해 균질화법을 적용하였다. 역의 함유량, 크기, 기질의 고결도, 분급, 경사 등의 인자를 고려한 조합에 의해 총 49개의 해석모델을 작성하여 탄성해석을 실시하였다. 해석결과는 역암이나 핵석같은 복합지반물질의 역학성 계산에 적용될 수 있다.

• 한국재료학회지
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• 제23권1호
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• pp.7-12
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• 2013

The $Cu_2ZnSnS_4$ (CZTS) thin film solar cell is a candidate next generation thin film solar cell. For the application of an absorption layer in solar cells, CZTS thin films were deposited by pulsed laser deposition (PLD) at substrate temperature of $300^{\circ}C$ without post annealing process. Deposition time was carefully adjusted as the main experimental variable. Regardless of deposition time, single phase CZTS thin films are obtained with no existence of secondary phases. Irregularly-shaped grains are densely formed on the surface of CZTS thin films. With increasing deposition time, the grain size increases and the thickness of the CZTS thin films increases from 0.16 to $1{\mu}m$. The variation of the surface morphology and thickness of the CZTS thin films depends on the deposition time. The stoichiometry of all CZTS thin films shows a Cu-rich and S-poor state. Sn content gradually increases as deposition time increases. Secondary ion mass spectrometry was carried out to evaluate the elemental depth distribution in CZTS thin films. The optimal deposition time to grow CZTS thin films is 150 min. In this study, we show the effect of deposition time on the structural properties of CZTS thin film deposited on soda lime glass (SLG) substrate using PLD. We present a comprehensive evaluation of CZTS thin films.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2005년도 INTERNATIONAL SYMPOSIUM ON SOIL & GROUNDWATER ENVIRONMENT
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• pp.229-230
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• 2005

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2005년도 INTERNATIONAL SYMPOSIUM ON SOIL & GROUNDWATER ENVIRONMENT
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• pp.231-232
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• 2005

• Bulletin of the Korean Chemical Society
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• 제31권6호
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• pp.1789-1792
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• 2010

• Bulletin of the Korean Chemical Society
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• 제33권12호
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• pp.3931-3932
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• 2012

• 대한기계학회논문집 C: 기술과 교육
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• 제1권1호
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• pp.99-105
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• 2013

LNG 극저온기계기술 시험인증센터에 구축되는 LNG 선박용 펌프 및 압축기 성능시험에서 발생하는 증발가스는 안전을 위하여 전량 회수가 요구된다. 본 논문에서는 36 MTD 용량의 천연가스 재액화 시스템에 대한 기본 설계 연구를 수행하였다. 대기압, $-60^{\circ}C$, 일반적인 도시가스 조성비, 1,500 kg/hr 유량의 공급 가스를 기본 설계 조건으로 하여 공정 설계가 이루어졌고, 입구 온도 조건 및 가스 조성비에 따른 LNG 생산량 또한 계산하여 다양한 입구 설계 조건에 따른 시스템의 성능 변화를 비교, 분석하였다. 공정 설계 외에도 재액화 시스템의 핵심 기기인 송풍기, 압축기, 극저온 열교환기, 컴팬더의 제작 사양이 도출되었으며, 전력 및 냉각수의 유틸리티 요구조건 또한 기본 설계를 통해 도출되었다.

• 한국보육지원학회지
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• 제13권6호
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• pp.69-86
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• 2017

Objective: This study was conducted to investigate the effects of small-group arithmetic word problem activities with concrete materials on 5 year old children's mathematical ability and attitude. Methods: A total of 34 five-year-old children (control group 16 children, experimental group18 children) attending two kindergartens in P city participated in this study. Fifteen small-group arithmetic word problem activities with concrete materials were conducted in the classroom of the experimental group twice a week for eight weeks. Before and after the activities, all the participants individually took a basic arithmetic test, mathematical word problem solving test, and mathematical attitudes test. Results: First, we observed that the children in the experimental group achieved significantly higher scores on the mathematical ability tests, including the basic arithmetic test and mathematical word problems solving test when compared to the children in the control group. Second, we also found that children in the experimental group showed higher improvement in the mathematical attitudes test than their counterparts. Conclusion/Implications: The results of this study suggest that small-group arithmetic word problem activities with concrete materials are effective in improving children's mathematical ability and attitudes.

• 센서학회지
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• 제21권4호
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• pp.256-262
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• 2012

Hyaluronic acid(HA) hydrogels were synthesized by immersing HA microbeads in phosphate buffered saline solutions having different pH levels to assess the effect of pH on the swelling ratio of HA hydrogels for smart drug delivery systems. No beads were formed when the HA solution(below pH 9) was crosslinked with divinyl sulfone(DVS) because DVS is a basic solution. The variation regarding the size of the microbead was not significant, suggesting that the bead size is not a function of pH(10 ~ 14). However, the pore size of the microbeads decreased with increasing pH from 10 to 14, leading to the surface smoothness and dense network as a result of higher crosslinking. The swelling ratio of hydrogels increased when the pH rose from 2(acidic) to 6(neutral). Afterwards, it decreased with further increasing pH(basic). The lower swelling ratio may be due to the lack of ionization of the carboxyl groups. On the other hand, a higher swelling ratio is likely due to the increased electrostatic repulsions between negatively charged carboxyl groups on different chains. Experimental results suggested that pH-responsive HA hydrogels can be applicable to the controlled drug delivery systems.