• 한국세라믹학회지
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• 제46권3호
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• pp.330-335
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• 2009

We investigated the effects of the re-oxidation temperature and time on the positive temperature coefficient (PTC) of resistivity characteristics of Sm-doped $BaTiO_3$ sintered at $1200{\sim}1260^{\circ}C$ for 2 h in a reducing atmosphere (3% $H_2/N_2$), followed by re-oxidization processes in air, in which re-oxidization temperature and time were $600{\sim}1000^{\circ}C$ and $1{\sim}10$h, respectively. The result reveals that Smdoped (Ba,Ca)$TiO_3$ ceramics fired in a reducing atmosphere exhibit low PTC characteristics, whereas the sample re-oxidized at $800^{\circ}C$ for 1 h in air exhibit pronounced PTC characteristics. The room-temperature resistivity and jumping characteristics of resistivity (${\rho}_{max}/{\rho}25^{\circ}C$) decrease with Sm contents. The PTC characteristics with reoxidization time at $800^{\circ}C$ have improved about $2{\sim}3$ orders of magnitude whereas differed according to the sintering temperature. The 0.7 at% Sm-doped (Ba,Ca)$TiO_3$ samples reveal the best PTC characteristics in the present range of formula and processes.

• Bulletin of the Korean Chemical Society
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• 제27권9호
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• pp.1364-1370
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• 2006

New liquid-crystalline biphenyl carboxylates with an achiral swallow-tail derived from 1,3-dialkoxy-2-propanol $[(ROCH_2)_2CHOH$] where R is methyl, ethyl, propyl, butyl, $CH_2CF_3$, and $CH_2CF_2CF_3$ were prepared. These achiral liquid crystals having 1,3-dialkoxy-2-propyl moieties exhibit diverse phase sequences [I-SmA-(SmC)-(SmCalt)-Cr] depending on the substituent R group of the swallow-tail. The compounds carrying a fluorinated swallow-tail exhibit antiferroelectric-like smectic C phases, and their temperature ranges are broader than the corresponding non-fluorinated swallow-tailed ones.

• 한국조경학회지
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• 제35권2호통권121호
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• pp.37-48
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• 2007

An exhibit entitled 'Revelatory Landscapes' was held at the San Francisco Museum of Modem Art from May 5 to October 14, 2001. For this Museum's rot off-site outdoor exhibition, five outstanding design teams-Kathryn Gustafson, Hargreaves Associates, Hood Design, Tom Leader Studio, and ADOBE LA-created site-specific installations in Berkeley, Oakland, San Jose, and the San Francisco Bay Area. Each project showcased a hybridization of environmental art and landscape design. The main content revealed through revelatory landscapes were the natural, cultural, and historical palimpsest of the sites-particularly as related to the history of minorities such as Native American, African Americans and Latin Americans-as well as the every day life of ordinary people. To represent these ideas, a juxtaposition of the past and the present was broadly applied. Furthermore, the use of dramatic colors, textures, and forms in consideration of materials coupled with the revelation of natural elements such as wind and sunlight accelerated the effect of this juxtaposition. Every project of the Revelatory Landscapes exhibit requires a phenomenological experience to be appreciated. Via the five senses, these experiences cause a synesthetic experience beyond solely the visual. By examining the projects of 'Revelatory landscapes', the threshold for a new blending between environmental art and landscape design as well as new landscape design strategies that overcome the dichotomy between nature and culture will change and evolve.

• 아동학회지
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• 제31권2호
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• pp.103-117
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• 2010

The purpose of this study was to investigate the characteristics of internet usage among 5th and 6th grade of elementary school children and to elucidate the path model and the relative effects of various factors on internet addiction in the internet addiction tendency group. According to our results, the normal internet user group exhibit higher educational levels in fathers, secure attachment to mother, and warm friendship when compared to the internet addiction tendency group. At the same time, internet addiction group exhibit longer internet use time, a greater numbers of avatars in use, and higher avatars decoration costs. The research model suggested here was supported by the results. Attachment to mother appears to affect friendship which in turn affects avatars image decoration needs and avatars identification which in turn then has an impact upon internet addiction tendency. These results were then discussed in relation to previous research and theories.

• Nuclear Engineering and Technology
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• 제37권5호
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• pp.503-510
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• 2005

An instrumental neutron activation analysis was used to measure the concentrations of about 24 elements associated with airborne particulates (PM10) that were collected in the most polluted urban region of Daejeon city, Korea from 2000 to 2002. Using the measurement data for various elements, both the extent of elemental pollution in the study area and the seasonality in their distribution characteristics were examined. Examinations of their distribution patterns indicated that most elements with crustal origin tend to exhibit seasonal peaks during spring, while most elements with anthropogenic origin tend to exhibit seasonal peaks during fall or winter. In order to explain the factors regulating their mobilization properties, the data were processed by a factor analysis. Results of the factor analysis suggested competing roles of both industrial and natural source processes, despite that the study site is located at a downwind position of the industrial complex. Based on the overall results of this study, it is concluded that the site may be strongly impacted by man-made sources but the general patterns of elemental distributions in the study area inspected over a seasonal scale are quite consistent with those typically observed from natural environment.

• 한국지구과학회:학술대회논문집
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• 한국지구과학회 2005년도 추계학술발표회 논문집
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• pp.292-302
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• 2005

과학관은 학생들이 학교 과학 수업 이외에 과학을 경험할 수 있는 대표적인 학교밖 과학활동이다. 이에 본 연구에서는 제7차 교육과정에서 제시한 중학교 지구과학내용체계와 영역별 성취기준을 근거로 과학관 패널전시물을 분석하였다. 그 결과 교육과정에서 제시한 성취수준과 전시의 연계성이 미흡하였고, 지질영역 전시에 편중됨을 파악하였다. 따라서 교육과정을 고려한 전시물이 요구된다. 차후 이 연구의 결과는 과학관의 전시 및 교육의 방향과 개선 방안을 위한 기초 자료를 제공한다.

• East Asian Economic Review
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• 제21권4호
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• pp.385-432
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• 2017

This paper investigates how firm age, size and ownership are related with job creation and destruction, and how these patterns differ across transition and non-transition economies. The analysis finds that age is inversely related with gross job creation and net job creation in the two samples. This finding is consistent with the theory of the learning effect. The relationship between age and job destruction is indifferent in non-transition economies. On the contrary, old firms in transition economies destroy more jobs than young ones. The paper further establishes an inverse relationship between size and gross job creation in the two groups. However, there is divergence between the two samples; small firms in non-transition economies also exhibit a higher gross job destruction rate. Consequently large firms have a higher net job creation rate. In transition economies, small and large firms exhibit similar rates of job destruction. But small firms retain a higher net job creation rate. A more intriguing finding is that state owned firms do not underperform domestic private ones. This means these countries may be using soft budget constraint which allows state owned firms to overstaff. Finally, crowding out of SMEs by foreign owned firms is not evident in transition economies.

• Journal of Mechanical Science and Technology
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• 제16권9호
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• pp.1093-1101
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• 2002

Continuous fiber ceramic composites (CFCCs) have advantages over monolithic ceramics : Silicon Nitride composites are not well used for application because of their low fracture toughness and fracture strength, but CFCCs exhibit increased toughness for damage tolerance, and relatively high stiffness in spite of low specific weight. Thus it is important to characterize the fracture resistance and properties of new CFCCs materials. Tensile and flexural tests were carried out for mechanical properties and the fracture resistance behavior of a SCS6 fiber reinforced Si$_3$N$_4$ matrix CFCC was evaluated. The results indicated that CFCC composite exhibit a rising R curve behavior in flexural test. The fracture toughness was about 4.8 MPa$.$m$\^$1/2 , which resulted in a higher value of the fracture toughness because of fiber bridging. Mechanical properties as like the elastic modulus, proportional limit and the ultimate strength in a flexural test are greater than those in a tensile test. Also a numerical modeling of failure process was accomplished for a flexural test. This numerical results provided a good simulation of the cumulative fracture process of the fiber and matrix in CFCCs.

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
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• 제15권3호
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• pp.167-177
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• 2009

본 논문은 MyGuide라는 컨텍스트 인지 전시물 안내 시스템에 Simtext 개발 방법론을 적용한 개발 사례를 소개한다. 특히, 개발과정에서 컨텍스트와 관련되어서 고려할 사항, 문제를 해결한 방법 등을 소개한다. MyGuide 개발의 요구사항 도출단계에서는 비즈니스 로직과 컨텍스트 서비스를 위한 요구사항을 분리해서 도출함으로써 시스템의 복잡도를 줄일 수 있었다. 설계 단계에서는 컨텍스트 모델링, 아키덱처 설계, 클래스 및 데이타베이스 설계를 순차적으로 수행하였다. 특히 컨텍스트 모델링은 시스템의 요구 사항에 부합하도록 하였으며, 컨텍스트 모델에 따라 클래스와 데이타베이스를 설계하였다.

• Nuclear Engineering and Technology
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• 제13권4호
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• pp.245-253
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• 1981

고분자피복재 중 polyethylene은 전기적 절연성 및 내방사선성이 좋으나 난연성이 결여되어 있으므로 이 단점을 개질하였다. 방사선을 이용하여 polyethylene에 여러 종류의 난연제를 고착시켰는데 grafting 방법과 blending후 crosslinking 방법을 사용하였다. 일반적으로 grafting시키는 경우 시료에 난연제가 고착되는 량은 방사선선량이 증가할수록 증가하였다. Grafting 방법으로 polyethylene에 난연제를 고착시킬 때 시료를 팽윤(swelling)시켜서 난연제를 grafting시켜야 한다. Blending 한 후 crosslinking시킨 경우 시료와 난연제의 량을 자유롭게 조절하여 blending하여 crosslinking시킬 수 있는 이질이 있다. 난연제를 고착시키는 2가지 방법중 blending후 crosslinking 시키는 방법이 가장 바람직하다.