• 한국세라믹학회지
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• 제29권5호
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• pp.347-356
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• 1992

Various kaolin samples with different alumina content were prepared from calcined admixture of kaolin and ammonium sulfate by varying the treatment time in sulfuric acid. Samples were nitridated under N2 or N2-H2 atmosphere with changing the amount of added carbon, the reaction time and temperature. As the alumina content lowered, the size of kaolin particles decreased and the specific surface area increased. XRD analysis indicated that ${\alpha}$-quartz remained by decomposition of halloysite and meta-halloysite. Experimental results of nitridation behavior are summerized as follows; 1) Nitridation under N2 atmosphere. With the increase of C/SiO2 ratio and with the decrease of Al2O3 content, disappearance of XRD pattern peaks of mullite, ${\alpha}$-quartz and ${\alpha}$-Al2O3 were accelerated at 1300$^{\circ}C$. SiC was the main phase in the reaction product of acid-treated kaolin samples nitridated at 1300$^{\circ}C$ for 10 hours regardless of C/SiO2 ratio. But the XRD peak intensities of ${\beta}$-Si3N4, ${\beta}$-sialon and SiC did not show much difference when untreated raw kaolin was fired at the same condition. When the ratio of C/SiO2 was 3.5, ${\beta}$-sialon and ${\beta}$-Si3N4 existed in the reaction product of about 22% alumina containing kaolin sample fired at 1350$^{\circ}C$ for 7 hours. Only ${\beta}$-sialon existed in the same sample fired at 1400$^{\circ}C$ for 10 hours. ${\beta}$-sialon was obtained from all of the acid-treated kaolin samples fired at 1400$^{\circ}C$ for 40 hours, but AlN and SiC remained in the untreated kaolin sample. Z value of the ${\beta}$-sialon obtained from the 22% alumina containing kaolin sample fired at 1400$^{\circ}C$ for 40 hours was about 1.3(XRD) and 1.5(EDS). 2) Nitridation under 80N2+2OH2 mixed gas atmosphere with the C/SiO2 ratio of 1 Mullite was not found, but ${\alpha}$-Si3N4, and ${\beta}$-sialon were present in the reaction product of about 22% alumina containing kaolin sample fired at 1300$^{\circ}C$ for 10 hours. When untreated kaolin sample was nitridated at the same condition, mullite remained. AlN and SiC were not found in the reaction product of about 22% alumina containing kaolin sample fired at 1350$^{\circ}C$ for 5 hours. On the other hand, AlN and SiC remained in the product of untreated kaolin fired at the same condition.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.113-114
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• 2009

Silicon carbide is one of the most attractive and promising wide band-gap semiconductor material with excellent physical properties and huge potential for electronic applications. Up to now, the most successful method for growth of large SiC crystals with high quality is the physical vapor transport (PVT) method [1, 2]. Since further reduction of defect densities in larger crystal are needed for the true implementation of SiC devices, many researchers are focusing to improve the quality of SiC single crystal through the process modifications for SiC bulk growth or new material implementations [3, 4]. It is well known that for getting high quality SiC crystal, source materials with high purity must be used in PVT method. Among various source materials in PVT method, a SiC powder is considered to take an important role because it would influence on crystal quality of SiC crystal as well as optimum temperature of single crystal growth, the growth rate and doping characteristics. In reality, the effect of powder on SiC crystal could definitely exhibit the complicated correlation. Therefore, the present research was focused to investigate the quality difference of SiC crystal grown by conventional PVT method with using various SiC powders. As shown in Fig. 1, we used three SiC powders with different particles size. The 6H-SiC crystals were grown by conventional PVT process and the SiC seeds and the high purity SiC source materials are placed on opposite side in a sealed graphite crucible which is surrounded by graphite insulation[5, 6]. The bulk SiC crystal was grown at $2300^{\circ}C$ of the growth temperature and 50mbar of an argon pressure. The axial thermal gradient across the SiC crystal during the growth is estimated in the range of $15\sim20^{\circ}C/cm$. The chemical etch in molten KOH maintained at $450^{\circ}C$ for 10 min was used for defect observation with a polarizing microscope in Nomarski mode. Electrical properties of bulk SiC materials were measured by Hall effect using van der Pauw geometry and a UV/VIS spectrophotometer. Fig. 2 shows optical photographs of SiC crystal ingot grown by PVT method and Table 1 shows electrical properties of SiC crystals. The electrical properties as well as crystal quality of SiC crystals were systematically investigated.

• Journal of Animal Science and Technology
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• 제51권3호
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• pp.249-254
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• 2009

돈분뇨 부숙과정에서의 Mg원 첨가에 따른 MAP 크리스탈 결정체 형성과 부숙과정에 미치는 영향을 조사하였다. 돈분뇨내 수용성인산 기준 1.2M비로 Mg원을 첨가하여 부숙시킨 경우와 첨가하지 않고 부숙한 경우를 비교하여 실험한 결과 Mg원 첨가에 의한 부숙과정에서의 유기물분해 저해 현상은 관찰되지 않았다. Mg원을 첨가한 경우 분뇨 내 $NH_4$와 $PO_4$가 함께 반응하여 MAP 크리스탈 결정체를 형성함에 따라 $NH_4$-N의 함량이 낮아졌으며 이는 부숙과정에서의 암모니아 가스 형태로의 질소소실을 낮추어주는 결과가 됨을 알 수 있었다. 수용성인의 함량 또한 Mg원을 첨가한 경우에 낮아져 최종 부숙퇴비의 총인중 수용성인의 비율이 감소함을 알 수 있었다. 따라서 부숙과정에서의 Mg원 첨가는 최종 부숙퇴비의 비료성분 보존과 완효도 증가효과가 있음을 알 수 있었다. 최종퇴비의 X-Ray Diffraction 시험결과 부숙과정에서 MAP 결정체가 형성됨을 알 수 있었으며 2.8 mm 이하의 입자크기에서 형성된 결정체가 많음을 알 수 있었다. 또한 입자크기별 질소와 인 성분 분포율을 비교한 결과 2.8 mm 이하의 입자크기에 질소와 인성분의 2/3 이상이 분포해 있음을 알 수 있었다.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.20-20
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• 2017

Plant genomes include heterochromatic loci that consist of repetitive sequences and transposable elements. LTR retrotransposon is the major class of transposons in advanced plants in terms of proportion in plant genome. The elements contribute not only to genome size but also to genome stability and gene expression. A number of cases have been reported transposon insertions near genic regions affect crop traits such as fruit pigments, stress tolerance, and yields. Functional LTR retrotransposons produce extrachromosomal DNA from genomic RNA by reverse transcription that takes place within virus-like-particles (VLPs). DECREASED DNA METHYLATION 1 (DDM1) plays important roles in maintaining DNA methylation of heterochromatin affecting all sequence contexts, CG, CHG, and CHH. Previous studies showed that ddm1 mutant exhibits massive transcription of retrotransposons in Arabidopsis, but only few of them were able to create new insertions into the genome. RNA-dependent RNA POLYMERASE 6 (RDR6) is known to function in restricting accumulation of transposon RNA by processing the transcripts into 21-22 nt epigenetically activated small interfering RNA (easiRNA). We purified VLPs and sequence cDNA to identify functional LTR retrotransposons in Arabidopsis ddm1 and ddm1rdr6 plants. Over 20 LTR copia and gypsy families were detected in ddm1 and ddm1rdr6 sequencing libraries and most of them were not reported for mobility. In ddm1rdr6, short fragments of ATHILA gypsy elements were detected. It suggests easiRNAs might regulate reverse transcription steps. The highest enriched element among transposon loci was previously characterized EVADE element. It has been reported that active EVADE element is more efficiently silenced through female germline than male germline. By genetic analyses, we found ddm1 and rdr6 mutation affect maternal silencing of active EVADE elements. DDM1-GFP protein accumulated in megaspore mother cell but was not found in mature egg cell. The fusion protein was also found in early embryo and maternal DDM1-GFP allele was more dominantly expressed in the embryo. We observed localization of DDM1-GFP in Arabidopsis and DDM1-YFP in maize and found the proteins accumulated in dividing zone of root tips. Currently we are looking at cell cycle dependency of DDM1 expression using maize system. Among 10 AGO proteins in Arabidopsis, AGO9 is specifically expressed in egg cell and shoot meristematic cells. In addition, mutation of AGO9 and RDR6 caused failure in maternal silencing, implying 21-22 nt easiRNA pathway is important for retrotransposon silencing in female gametophyte or/and early embryo. On the other hand, canonical 24 nt sRNA-directed DNA methylation (RdDM) pathways did not contribute to maternal silencing as confirmed by this study. Heat-activated LTR retrotransposon, ONSEN, was not silenced by DDM1 but the silencing mechanisms require RdDM pathways in somatic cells. We will propose distinct mechanisms of LTR retrotransposons in germline and somatic stages.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.97-97
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• 2017

Plant genomes include heterochromatic loci that consist of repetitive sequences and transposable elements. LTR retrotransposon is the major class of transposons in advanced plants in terms of proportion in plant genome. The elements contribute not only to genome size but also to genome stability and gene expression. A number of cases have been reported transposon insertions near genic regions affect crop traits such as fruit pigments, stress tolerance, and yields. Functional LTR retrotransposons produce extrachromosomal DNA from genomic RNA by reverse transcription that takes place within virus-like-particles (VLPs). DECREASED DNA METHYLATION 1 (DDM1) plays important roles in maintaining DNA methylation of heterochromatin affecting all sequence contexts, CG, CHG, and CHH. Previous studies showed that ddm1 mutant exhibits massive transcription of retrotransposons in Arabidopsis, but only few of them were able to create new insertions into the genome. RNA-dependent RNA POLYMERASE 6 (RDR6) is known to function in restricting accumulation of transposon RNA by processing the transcripts into 21-22 nt epigenetically activated small interfering RNA (easiRNA). We purified VLPs and sequence cDNA to identify functional LTR retrotransposons in Arabidopsis ddm1 and ddm1rdr6 plants. Over 20 LTR copia and gypsy families were detected in ddm1 and ddm1rdr6 sequencing libraries and most of them were not reported for mobility. In ddm1rdr6, short fragments of ATHILA gypsy elements were detected. It suggests easiRNAs might regulate reverse transcription steps. The highest enriched element among transposon loci was previously characterized EVADE element. It has been reported that active EVADE element is more efficiently silenced through female germline than male germline. By genetic analyses, we found ddm1 and rdr6 mutation affect maternal silencing of active EVADE elements. DDM1-GFP protein accumulated in megaspore mother cell but was not found in mature egg cell. The fusion protein was also found in early embryo and maternal DDM1-GFP allele was more dominantly expressed in the embryo. We observed localization of DDM1-GFP in Arabidopsis and DDM1-YFP in maize and found the proteins accumulated in dividing zone of root tips. Currently we are looking at cell cycle dependency of DDM1 expression using maize system. Among 10 AGO proteins in Arabidopsis, AGO9 is specifically expressed in egg cell and shoot meristematic cells. In addition, mutation of AGO9 and RDR6 caused failure in maternal silencing, implying 21-22 nt easiRNA pathway is important for retrotransposon silencing in female gametophyte or/and early embryo. On the other hand, canonical 24 nt sRNA-directed DNA methylation (RdDM) pathways did not contribute to maternal silencing as confirmed by this study. Heat-activated LTR retrotransposon, ONSEN, was not silenced by DDM1 but the silencing mechanisms require RdDM pathways in somatic cells. We will propose distinct mechanisms of LTR retrotransposons in germline and somatic stages.

• Asian-Australasian Journal of Animal Sciences
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• 제33권12호
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• pp.1965-1974
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• 2020

Objective: This study consisted of two stages; the first was to determine the effect of extrusion and sieving treatments on the chemical properties of palm kernel cake (PKC), and accordingly, a follow-up experiment (second stage) was conducted to determine and compare the apparent metabolizable energy (AME), and protein and amino acid digestibility of extruded and sieved PKC. Methods: Two physical treatments, namely extrusion (using temperature profiles of 90℃/100℃/100℃, 90℃/100℃/110℃, and 90℃/100℃/120℃) and sieving (to 8 particles sizes ranging from >8.00 to 0.15 mm) were carried out to determine their effects on chemical properties, primarily crude protein (CP) and fiber contents of PKC. Based on the results from the above study, PKC that extruded with temperature profile 90/100/110℃ and of sieved size between 1.5 to 0.15 mm (which made up of near 60% of total samples) were used to determine treatments effect on AME and CP and amino acid digestibility. The second stage experiment was conducted using 64 male Cobb 500 chickens randomly assigned to 16 cages (4 cages [or replicates] per treatment) to the following four dietary groups: i) basal (control) diet, ii) basal diet containing 20% untreated PKC, iii) basal diet containing 20% extruded PKC (EPKC), and iv) basal diet containing 20% sieved PKC (SPKC). Results: Extrusion and sieving had no effect on CP and ash contents of PKC, however, both treatments reduced (p<0.05) crude fiber by 21% and 19%, respectively. Overall, extrusion and sieving reduced content of most of the amino acids except for aspartate, glutamate, alanine and lysine which increased, while serine, cysteine and tryptophan remained unchanged. Extrusion resulted in 6% increase (p<0.05) in AME and enhanced CP digestibility (p<0.05) by 32%, as compared to the untreated PKC while sieving had no effect on AME but improved CP digestibility by 39% which was not significantly different from that by extrusion. Conclusion: Extrusion is more effective than sieving and serves as a practical method to enhance AME and digestibility of CP and several amino acids in broiler chickens.

• 공업화학
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• 제10권6호
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• pp.843-847
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• 1999

본 연구에서는 유동층-화학증기침투에 의해 이염화이메틸규소(DDS)와 수소로부터 생성된 탄화규소를 활성탄에 증착시킨 세라믹 탄소/탄화규소복합체가 제조되었다. 4~12, 12~20, 20~40 mesh의 활성탄이 사용되었다. 증착 후 반응물인 이염화이메틸규소의 농도, 활성탄의 크기, 반응압력, 반응시간에 따른 반응후 각 시료의 표면적과 증착량 및 증착양상을 관찰하였다. 실험결과 DDS의 농도가 낮고 반응압력이 작을수록 시료 기공내에 고른 증착을 갖는 것을 알 수 있었다. 또한 기공직경과 표면적들이 어떠한 시점에서 최소값을 갖는 것으로 기공내부 증착에서 입자외부 표면 증착으로 바뀜을 알 수 있었다. DDS의 농도가 낮고 반응압력이 낮을 때 작은 탄화규소입자가 활성탄 표면에 더욱 고르게 증착되었다. 이 결과들은 SEM, TGA, 기공도측정장치, BET에 의해 확인되었다.

• 대한환경공학회지
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• 제37권5호
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• pp.277-284
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• 2015

대청호의 추소수역과 추동수역에서 채취한 퇴적물의 오염도를 평가하기 위하여, 퇴적물의 입도, 유기물 및 영양염류의 농도와 인의 성상별 분석을 수행하였다. 소옥천의 영향을 받는 추소수역의 상류에 비해 추소수역에서 본류로 유입되는 지점과 추동수역의 퇴적물에서 실트 크기 입자의 평균 비율이 92%로 매우 높았다. 추소수역과 추동수역에서 퇴적물 중 총인의 농도는 각각 999 (${\pm}98$)과 1,123 (${\pm}119$) mg/kg sediment로 추동수역에서 상대적으로 높았다. 퇴적물 중 인의 성상분석 결과 외부 기원성 인보다 환경 조건 변화에 의해 쉽게 용출이 되는 것으로 알려진 내부 기원성 인의 비율이 높게 측정되어 이들 지점의 부영양화에 내부부하가 중요한 것으로 판단되었다. 퇴적물 중 총질소의 농도는 모든 시료에서 환경부의 하천 호소 퇴적물 오염평가 기준인 5,600 mg/kg sediment를 초과하여, 퇴적물의 총질소 오염도가 심각한 것으로 판단되었다. 이러한 결과로부터 대청호의 수질 개선을 위해 퇴적물에 대한 관리 대책이 필요한 것으로 판단된다.

• Korean Chemical Engineering Research
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• 제51권5호
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• pp.531-535
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• 2013

철 이온을 담지시킨 BEA 제올라이트에서 $N_2O$가 분해되는 반응을 조사하여 열처리 온도가 촉매의 활성에 미치는 영향을 고찰하였다. $N_2O$ 분해 반응 실험 결과, Fe/BEA 촉매에 대한 열처리 온도가 증가함에 따라 $N_2O$ 분해 활성이 현저히 줄어들었다. 열처리 온도의 증가에 따른 Fe/BEA 촉매의 입자모양 및 크기의 변화는 크지 않았지만, 열처리 온도 증가에 따라 비표면적이 크게 줄어들었다. 또한 열처리온도가 증가함에 따라 ${\beta}$ 구조의 결정성이 크게 낮아지는 것을 확인하였고, 열처리 온도가 높아질수록 SiO 구조는 증가하거나 크게 변화가 없는 반면, Fe가 골격구조와 결합된 구조는 감소하는 것으로 판단되었다. 이와 같은 결과로 열처리 온도의 증가에 따라 알루미늄과 Fe가 결합된 ${\beta}$ 구조가 붕괴되어 $N_2O$ 분해활성이 크게 저하되는 것으로 사료된다.

• Korean Chemical Engineering Research
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• 제48권2호
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• pp.218-223
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• 2010

본 연구에서는 반도체식 가스센서 재료로서 활용 가능한 ZnO 박막을 Continuous Flow Reaction(CFR) 방법으로 실리콘 기판 위에 성장시켰다. 또한 전구물질로 사용한 zinc acetate의 농도에 따른 산화아연 박막의 성장특성과 이들의 전기적 특성이 조사되었다. 산화아연 박막 제조는 0.005~0.02 M의 zinc acetate 농도에서 수행되었다. 산화아연 박막을 구성하고 있는 ZnO의 입자크기는 농도가 증가할수록 증가되었으며, 박막의 두께도 함께 증가되었다. CFR 법에 의한 산화아연 박막의 성장속도는 전구물질의 농도에 비례적으로 의존되는 것을 확인하였으며, 균일한 박막을 제조하기 위한 전구물질의 최적 농도는 0.01 M이였다. 한편, 전구물질의 농도를 달리하여 제조된 산화아연 박막의 전압에 대한 전류를 I-V 측정기로 측정한 결과, 박막의 두께가 증가될수록 높은 전류가 흘렀다. 그러므로 산화아연 박막의 전류를 전구물질의 농도변화로 조절할 수 있다. 또한 산화아연 박막을 $300^{\circ}C$에서 5 min 동안 $500ppmv\;H_2S$에 노출시킨 결과, 전압에 대한 전류값이 낮아졌다. 이와 같이 산화아연의 전기적 특성은 가스센서로 응용할 수 있는 가능성을 확인시켜 주는 결과라 할 수 있다.