• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.509-512
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• 2008

The nitrogen adsorption method was used to evaluate the change fine pore structure of concrete under high temperature. The mechanical properties and chloride ion diffusion coefficient were also measured. Two dimension FEM model for the life expectancy of RC structure was built considering the effect of high temperature. The porosity under 0.01${\mu}m$ decreased in proportion to the temperature. However, that of $0.01{\mu}m{\sim}0.1{\mu}m$ increased. The strength decreased and the chloride ion diffusion coefficient increased in the temperature range of $200{\sim}600^{\circ}C$.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.2
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• pp.319-326
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• 2020

PRNGs(Pseudorandom number generators) are essential for generating encryption keys for to secure online communication. A bitstream generated by the PRNG must be generated at high speed to encrypt the big data effectively in a symmetric key cryptosystem and should ensure the randomness of the level to pass through the several statistical tests. CA(Cellular Automata) based PRNGs are known to be easy to implement in hardware and to have better randomness than LFSR based PRNGs. In this paper, we design PRNGs based on PMLCA(Programable Maximum Length CA) that can generate effective key sequences in symmetric key cryptosystem. The proposed PRNGs generate bit streams through nonlinear control method. First, we design a PRNG based on an (m,n)-cell PMLCA ℙ with a single complement vector that produces linear sequences with the long period and analyze the period and the generating polynomial of ℙ. Next, we design an (m,n)-cell PC-MLCA based PRNG with two complement vectors that have the same period as ℙ and generate nonlinear sequences, and analyze the location of outputting the nonlinear sequence.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.11
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• pp.637-644
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• 2014

This paper investigates the detection performance of fault location using STDR(sequence time domain reflectometry) and SSTDR(spread spectrum time domain reflectometry) with various length and types of sequences, and then, proposes an improved detection technique by eliminating the injected signal in SSTDR. The detection error rates are compared and analyzed in power line channel model with various fault locations, fault types, and spreading sequences such as m-sequence, binary Barker sequence, and 4-phase Frank sequence. It is shown that the proposed technique is able to improve the detection performance obviously when the reflected signal is weak or the fault location is extremely close.

• Solar Energy
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• v.12 no.1
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• pp.95-102
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• 1992

A small scale solar collector system composed of a Fresnel lens of $0.5m^2$ area as a solar concentrator and a compact fluidized-bed solar receiver was developed. Performance and temperature distribution in the fluidized bed receiver were measured using SiC for particles and air for working fluid. The maximum gas temperature was attained up to 1250K at this moment. In this study, energy efficiency achieved by the present experiment was high for the small scale solar collector system and compact receiver.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.192-192
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• 2003

오염된 폐수를 처리하는 과정으로 다양한 방법이 사용되고 있으나, 담체를 이용하여 미생물을 배양하고, 미생물에 의해 정수하는 방법이 이용되고 있다. 이를 위해서는 미생물을 배양을 위한 담체의 조건으로 다양한 크기의 연속기공을 갖고, 젖음성과 표면거칠기가 높으며, 이들 중 초기 미생물번식의 조건을 제공하는 기체 포집용 미세기공을 보유하고, 미생물이 성장할 수 있는 수백 $\mu\textrm{m}$까지의 다양한 크기의 연속된 기공을 갖는 미생물 담체용 다공성 세라믹스의 제조를 목적으로 본 연구를 행하였다. 본 연구는 다양한 크기의 기공분포를 형성하기 위하여 첨가물로 activated carbon과 무기염, 고분자 binder를 활성알루미나 기지재료에 사용하여 수열반응에 의해 각각의 물질이 형성할 수 있는 기공의 크기를 확인하고, 수 nm에서 수백 $\mu\textrm{m}$까지의 연속된 기공이 존재하는 담체를 제조하였다. 수열조건과 첨가물의 양에 따라 수은침투가압을 이용하여 기공의 크기와 분포를 측정하고 평균기공률을 얻을 수 있었고, 압축강도를 측정하고, 기공의 형상을 주사전자현미경을 통해 확인하였다.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2005.10a
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• pp.243-247
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• 2005

본 연구에서는 화력발전소 바닥재를 중금속 흡착제로 활용하기 위한 기초연구로서 수열합성법에 의해 제올라이트를 합성하였다. 화력발전소 바닥재를 분쇄하여 반응온도$(80{\sim}150^{\circ}C)$ 및 NaOH 농도$(1{\sim}5M)$를 변화시키면서 알칼리 수열합성법으로 반응시킨 결과, NaP1, hydrxoy-sodalite, tobermorite 등이 생성되었으며, 양이온 교환 능력이 높은 NaP1은 $120^{\circ}C$ 이하의 온도와 2M 이하의 NaOH 농도에서 주로 합성되었다.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.11a
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• pp.1088-1091
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• 2011

최근 대중화된 무선 유비쿼터스 환경으로 출퇴근, 점심시간, 여가 시간 등 자투리 시간을 활용하여 소셜 네트워크, 게임, 동영상 시청, 쇼핑, 학습, 필요한 정보 등 다양한 콘텐츠들을 모바일기기를 이용하여 즐기는 사용자가 급증하고 있다. 본 논문은 모바일 환경에서의 수열 문제 풀이에 대한 학습 효과를 검증하기 위해 여러 종류의 수열 문제들로 구성된 기능성 게임을 아이폰과 안드로이드 기반으로 설계 및 구현하였다. 또한 저장된 수열 게임 이용자의 기록 데이터베이스 내용을 대상으로 사용자들의 분포와 이에 따른 학습 효과를 분석하였다.

• Korean Journal of Crystallography
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• v.12 no.2
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• pp.97-101
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• 2001

Phillipsite-type zeolite powders were synthesized from domestic coal fly ash by hydrothermal reaction with 2.0 M-3.5M NaOH solution at $80^{\circ}C{\sim}120^{\circ}C$ for 24 h. The properties of zeolite were investigated by XRD, SEM and IR spectroscopy. The effects of chemical composition of fly ash, reaction temperature and NaOH concentration on the zeolite synthesis were well appeared on IR spectra. It is found that the $TO_4$(T=Si, Al) tetrahedra have a well ordered structure as the $SiO_2$ content, synthesis temperature and NaOH concentration become high.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.4
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• pp.154-159
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• 2001

(Li,Al)$MnO_2(OH)_2$:Co compound was synthesized by hydrothermal method. $MnO_2$, LiOH.$H_2$O, $Co_3O_4$ and $Al(OH)_3$ were used as starting materials and the optimum conditions for synthesis of monolithic (Li,Al)$MnO_2(OH)_2$:Co compound were as follows : reaction temperature; $200^{\circ}C$, reaction time; 3 days, hydrothermal solvent; 3M-KOH solution, reaction apparatus; seesaw type, atomic ratio of Li:Al:Mn;Co = 1:2.1:2.5~2:0.5~1. Monolithic(Li,Al)$MnO_2(HO)_2$:Co compound synthesized in this work had a god crystallinity and excellent color forming effect as a blue pigment compatible with natural mineral. The particles of the synthesized (Li,Al)$MnO_2(OH)_2$:Co compound have hexagonal plate shape with the size of 0.5~1 $\mu\textrm{m}$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.2
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• pp.129-140
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• 1996

In this study, we have prepared corundum ($\alpha$-Al_{2}O_{3}$) single crystals from aluminum hydroxides by hydrothermal growing process and have investigated the reaction conditions. The hydrothermal conditions were mainly affected by reaction temperature, seed crystal and reaction time. Especially, seed crystal has strong effects on the particle size and crystallity of products. By adding seed crystal in Japanese gibbsite solution as the nutrient, hydrothermal reaction was performed for 2 hours at the reaction temperature of $460^{\circ}C$, to produce corundum powders which had weight mean particle diameter of $11\;\mu\textrm{m}$ with hexagonal crystal, Without adding seed crystal in Russian gibbstite solution, corundum powders that have weight mean particle diameter of $6\;\mu\textrm{m}$ with hexagonal crystals were also formed after 2 hours operation at the reaction temperature of $420^{\circ}C$.