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신대규,류도형,Shin, Dae-Kyu,Riu, Doh-Hyung 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.2
Nano magnetite particles have been prepared by two step reaction consisting of urea hydrolysis and ammonia addition at certain ranges of pH. Three different concentrations of aqueous solution of ferric ($Fe^{3+}$) and ferrous ($Fe^{2+}$) chloride (0.3 M-0.6 M, and 0.9 M) were mixed with 4 M urea solution and heated to induce the urea hydrolysis. Upon reaching at a certain pre-determined pH (around 4.7), 1 M ammonia solution were poured into the heated reaction vessels. In order to understand the relationship between the concentration of the starting solution and the final size of magnetite, in-situ pH measurements and quenching experiments were simultaneous conducted. The changes in the concentration of starting solution resulted in the difference of the threshold time for pH uprise, from I hour to 3 hours, during which the akaganeite (${\beta}$-FeOOH) particles nucleated and grew. Through the quenching experiment, it was confirmed that controlling the size of ${\beta}$-FeOOH and the attaining a proper driving force for the reaction of ${\beta}$-FeOOH and $Fe^{2+}$ ion to give $Fe_3O_4$ are important process variables for the synthesis of uniform magnetite nanoparticles.
신대규(Dae-Kyu Shin),김홍근(Hong-Geun Kim) 한국정보과학회 1998 한국정보과학회 학술발표논문집 Vol.25 No.1A
웹 클라이언트에서 동작하는 브라우져에는 사용자가 설정 가능한 옵션들이 존재한다. 이들 옵션 중에는 클라이언트 컴퓨터의 보안에 영향을 미치는 항목들이 많은데, 기본으로 제공되는 디폴트 값은 보안성보다는 사용자의 편의 위주로 설정되어 있다. 또한, 웹 브라우져의 기능이 날로 확대되어 감에 따라 옵션의 설정 역시 더 많은 기술적 복잡성을 지니게 되어 일반 사용자가 쉽게 이해하고 설정하기 어렵다. 따라서 대부분의 웹 브라우져는 보안에 매우 취약한 상태로 존재한다. 본 연구에서는 컴퓨터 백신 프로그램과 같이 클라이언트 컴퓨터에서 실행되어 브라우져의 옵션 설정 내용을 점검하여 일괄적으로 보안을 강화시키도록 옵션의 설정을 자동 실행하는 도구를 개발하였다. 이 도구는 각 조직의 웹 클라이언트 보안정책의 실행에 유용하게 사용될 수 있으며, 사용자에게 기술적 상세의 이해를 요구하지 않는다. 클라이언트 컴퓨터는 윈도즈 95 환경에서 동작하는 PC이며, 넷스케이프사의 네비게이터 4.0X버전을 그 대상으로 하였다.
이대영,신대규,Lee, Dae-Young,Shin, Dae-Kyu 한국천문학회 2012 天文學會報 Vol.37 No.2
The radiation belt structure can be approximately reproduced by a form of diffusion equation, which takes into account the radial diffusion process as well as those in pitch angle and energy. The solution of the equation depends on several factors including initial and boundary conditions, diffusion coefficients, and plasmapause location. In this paper, we have attempted to determine a set of approximate functions for the energetic electron fluxes near the outer edge of the outer belt in terms of solar wind variable. We used the electron flux data from SST onboard the THEMIS spacecraft and determined its correlation with solar wind conditions in a systematic way. The functions were determined separately for different energy channels from ~30 keV up to 719 keV. Our determination of these functions allows us to predict the radial boundary condition for the electron flux, which can be implemented in a forecast model.
Observation of long-term disappearance and reappearance of the outer radiation belt
이대영,신대규,김경찬,김진희,조정희,박미영,황정아,이용희,김경호,Lee, Dae-Young,Shin, Dae-Kyu,Kim, Kyung-Chan,Kim, Jin-Hee,Cho, Jung-Hee,Park, Mi Young,Angelopoulos, Vassilis,Hwang, Junga,Lee, Yonghee,Kim, Thomas 한국천문학회 2012 天文學會報 Vol.37 No.2
In this study we have used the data of various instruments onboard the THEMIS spacecraft to study the characteristics of the outer radiation belt during the ascending phase of solar cycle 24. The most astonishing result is that we discovered four long-term (a month or so) periods during which the belt has nearly disappeared. The first disappearance started late 2008, followed by reappearance in ~a month, and three more similar events repeated until early 2010 when the belt has reappeared. This is well revealed at 719 keV electrons, which is the currently available uppermost energy channel from the THEMIS SST observation, but also seen at even lower energies. Overall consistent features were confirmed using the NOAA-POES observations. The vanished belt periods are associated with extremely weak solar wind conditions, low geomagnetic disturbances (in terms of Kp and AE/AL), greatly suppressed wave (ULF and chorus) activities, greatly reduced storm and substorm activities (little source particle supply), and expanded plasmapause locations. The direct observations of such events shed light on the fundamental question of the origin of the radiation belt, which is the main focus of our presentation.