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나승현,강현주,송영진,송명신,Na, Seung-Hun,Kang, Hyun-Ju,Song, Young-Jin,Song, Myong-Shin 한국세라믹학회 2010 한국세라믹학회지 Vol.47 No.5
To improve concrete quality one of the most widely used chemical admixtures is polycarboxylate type superplasticizer. Unlike lignosulfonate and naphthalene-sulfonate, it has high dispersion property and excellent sustainable dispersion property for cement and concrete. Thus, polycarboxylate type superplasticizer has been widely used as a high-performance water reducing admixture together with silica fume in high-performance concrete and other applications for the dispersion of high-strength concrete over 100 MPa. However, even though there have been many studied on the dispersion of concrete by the structure of polycarboxylate type superplasticizer, there have a few studied that clarified the relationships between its rheological properties and microstructure properties in the early hydration behavior of ordinary portland cement. To investigate the correlations between the rheological properties and microstructure of cementitious materials with polycarboxylate type superplasticizer, this study experimented on the rheology, pore structure, heat evolution, and consistency in early hydration as well as on the compressive strength by early dispersion characteristics.
전자상거래 시스템에 적용 가능한 이동 에이전트 보안 메커님즘의 설계
나승현,한승조,정일용 조선대학교 전자정보통신연구소 2001 電子情報通信硏究所論文誌 Vol.4 No.1
This paper suggests the table for a mobile agent path which performs on transfer a mobile agent in security and based on which introduced the transfer protocol of a mobile agent. As the last prodceure of this, shows that how to write the closing time of a mobile transferring by using a Time stamp and keep not only preparing for the stop and attack for a receiving host but also the record of the transfer for a mobile agent. Later this paper will analyzes the security for an attack of a receiving host, a transmitting host and the third part host based on proposed system.
수율 최적화를 통한 Ku-Band용 2단 저잡음 증폭기 제작
나승현,양승인 崇實大學校 生産技術硏究所 1995 論文集 Vol.25 No.1
In this paper, we designed and fabricated a 2-stage Low Noise Amplifier(LNA) in Ku-Band using GaAs HEMT and MESFET with CAD tool "HP-EEsof Libra" of HP company. We designed the input matching network of LNA on the basis of minimum noise figure and also tried to get characteristics of constant passband gain, good impedance matching. Also, when the small inductive parasitic element becomes considerable for a source-to-ground amplifier above the X-Band, we considered it as source inductance. In this paper, we analyzed the sensitivity of each varying element in the predictable range on the overall LNA performance. It is shown that we could raise the yield from 33% to 95% through the yield optimization. As the performance of the yield optimization, we obtained the total gain 20.2dB - 20.8dB, the noise figure 0.9dB - 1.0dB at the center frequency 12.5GHz with 500MHz bandwidth. As the result of the measurement, the total gain is between 17.7dB and 20.5dB, and the noise figure is between 1.86dB and 2.74dB.
강승민,나승현,김경남,송명신,Kang, Seung-Min,Na, Seung-Hyun,Kim, Kyung-Nam,Song, Myong-Shin 한국세라믹학회 2015 한국세라믹학회지 Vol.52 No.1
Hardened cement-based materials exposed to the high temperatures of a fire are known to experience change in the pore structure as well as microstructural changes that affect their mechanical properties and tend to reduce their durability. In this experimental investigation, hardened Portland cement pastes were exposed to elevated temperatures of 200, 400, 600, 800, and $1000^{\circ}C$ for 60 minutes, and the resulting damage was studied by thermogravimetry (TG), mercury intrusion porosimetry (MIP) and density measurements. These results revealed that the residual compressive strength is increased at temperatures greater than $400^{\circ}C$ due to a small pore size of 3 nm and/or rehydration of the dehydrated cement paste. However, a loss of the residual strength occurs at temperatures exceeding 500 and $600^{\circ}C$. This can be attributed to the decomposition of hydrates such as portlandite and to an increase in the total porosity.
내구성 향상을 위하여 단열성능이 부여된 단면복구 MORTAR의 물성
강현주,나승현,송명신,정의담,서병돌,Kang, Hyun-Ju,Na, Seung-Hyun,Song, Myong-Shin,Jeong, Eui-Dam,Seo, Byung-Dol 한국세라믹학회 2010 한국세라믹학회지 Vol.47 No.5
In this study, we studied on the durability of restorative cement mortar for deteriorated concrete at complex deteriorated conditions as variation of temperature and of humidities. We made a comparison between restorative materials with insulation function and restorative materials without insulation function in items of compressive and bending strength and permeability of water, durability for carbonation, salt damage, diffusion coefficient of salt at complex deterioration conditions like change of temperature, change of humidity, For insulation, we used close-pore type Alumino-Silicate lightweight aggregate and substituted 12 wt% and 15 wt% out of original restorative cement mortar without insulation function. As a result, it was found that original restorative cement mortar without insulation function fail to meet Korean Standard on polymer modified cement mortar for maintenance in concrete structure, but restorative cement mortar with insulation function is in contentment Korean Standard to meet excellent than restorative materials without insulation function for durability at complex deteriorated conditions.