• International Journal of Concrete Structures and Materials
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• 제7권4호
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• pp.287-293
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• 2013

Strength and some durability properties of concrete containing rice husk ash (RHA) predominantly composed of amorphous silica at a specific surface of 235 $m^2/kg$ produced using a charcoal incinerator were determined. The maximum ordinary Portland cement (OPC) replacement with the RHA increased with increase in water/binder (w/b) ratio of the concrete mixes. The results show that 15 % OPC could be substituted by the RHAwithout strength loss at w/b ratio of 0.50. The split tensile strength generally increased with increase in RHA content for the mixes.

• Clinical and Experimental Pediatrics
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• 제60권12호
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• pp.395-402
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• 2017

Purpose: The potential effect of gonadotropin-releasing hormone agonist (GnRHa) treatment on the weight of girls with central precocious puberty (CPP) remains a controversy. We investigated anthropometric changes during and after GnRHa treatment among girls with CPP. Methods: This retrospective study evaluated data from 127 girls with CPP who received GnRHa treatment for ${\geq}2years$. Height, weight, and body mass index (BMI) values were compared at the baseline (visit 1), after 1 year of GnRHa treatment (visit 2), the end of GnRHa treatment (visit 3), and 6-12 months after GnRHa discontinuation (visit 4). Results: The height z score for chronological age (CA) increased continuously between visit 1 and visit 4. No significant differences were observed in BMI z score for CA between visits 1 and 4. However, an increasing trend in the BMI z score for bone age (BA) was observed between visits 1 and 4. The numbers of participants who were of normal weight, overweight, and obese were 97, 22, and 8, respectively, at visit 1, compared to 100, 16, and 11, respectively, at visit 4 (P=0.48). Conclusion: Among girls with CPP, the overall BMI z score for CA did not change significantly during or after GnRHa treatment discontinuation, regardless of their BMI status at visit 1. However, the BMI z score for BA showed an increasing trend during GnRHa treatment and a decreasing trend after discontinuation. Therefore, long-term follow-up of BMI changes among girls with CPP is required until they attain adult height.

• 한국구조물진단유지관리공학회 논문집
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• 제19권2호
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• pp.117-124
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• 2015

건설분야에서 이산화탄소를 저감하기 위해 최근들어 친환경 혼화재료가 많이 사용되고 있다. 또한 콘크리트의 취성파괴를 보완하기 위해 다양한 섬유재의 사용이 고려되고 있다. 본 연구에서는 Rice Ash Husk를 10% 및 20% 치환한 콘크리트를 제조하였으며, 천연섬유 (코코넛 섬유)를 0.125%, 0.250%, 0.375% 혼입하면서 역학적 특성을 평가하였다. 평가를 위해 압축강도, 쪼갬인장강도, 휨강도, 내충격성, 부착강도 등이 평가되었으며, 휨부재의 하중에 따른 균열 및 변위를 분석하였다. RHA를 첨가한 콘크리트는 압축강도를 효과적으로 개선하였으며, 섬유재를 0.125%를 첨가하였을 때, 인장강도, 연성증가 그리고 균열저항성 등이 뚜렷하게 개선되었다. RHA 및 첨연섬유는 자원의 재활용 뿐 아니라 콘크리트의 성능도 개선할 수 있으므로 효과적인 건설재료라고 판단된다.

• 한국지반공학회논문집
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• 제33권12호
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• pp.45-58
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• 2017

최근 들어 시설물별 내진설계기준이 성능기반 내진설계로 전환됨에 따라, 신뢰성있는 비선형 응답이력해석(Response-history analysis, RHA)에 대한 요구가 높아지고 있다. 그러나, 부지응답해석 분야에 있어서는 1970년대 이후 등가선형 해석이 표준절차로 자리잡고 있음에 따라, 이를 대체하기 위해서는 비선형 응답이력해석의 신뢰성이 확보되어야 한다. 본 논문에서는 1989년 미국 Loma Prieta 지진기록을 바탕으로 다층지반에 대해서 비선형 RHA를 이용한 부지응답해석 결과의 신뢰성을 검증하였다. 이를 위하여, 비선형 RHA를 위한 비선형 지반모델의 선정방법과 3차원 해석시 요구되는 기반암 경계조건의 영향을 평가 하였다. 평가 결과, 제한된 조건하에서 가장 정확한 비선형 지반모델과 경계조건을 적용 시 비선형 RHA의 결과는 등가선형 해석결과와 유의미한 차이는 발생하지 않음을 알 수 있었다. 또한, 3차원 해석을 시행하는 경우, 전체 모델의 회전운동을 제어하기 위하여 최 하단부 흡수 경계조건을 적용해야 함을 알 수 있었다.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제17권3호
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• pp.239-252
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• 1995

The present study was aimed to evaluate the effect of demineralized freeze-dried bone (DFDB) and resorbable hydroxyapatite (RHA) on bone formation in the extracted socket. The lower left and right 2nd and 3rd premolar were extracted in adult dogs. The one group was grafted with DFDB into the extracted socket, and the other group grafted with RHA. The extracted socket was sutured without any graft materials as control. The animals were killed on the 1st, 2nd, 4th, and 8th week after the graft for macroscopic and microscopic examination. Results obtained were as follows : 1. Macroscopically, nor infection of the graft site and dislodgement of the grafted material were noted in any animals used. 2. Young trabeculae of osteoid were formed in the socket wall in control group at 2 weeks after the graft. Osteoid tissue was formed in DFDB group at 1 week after graft, and a fine osteoid tissue was grown through the RHA particles in RHA group at 2 weeks graft. 3. The grafted groups showed more rapid bone formation than the control. Between the grafted groups, DFDB group showed more rapid formation than RHA group, DFDB group showed osteoinductive bone formation and RHA group showed osteoconductive bone formation. These results suggest that DFDB and RHA are useful to preserve the alveolar bone and to improve new bone formation by immediate grafting into the extraction sockets.

• Computers and Concrete
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• 제5권1호
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• pp.75-88
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• 2008

This paper presents a mathematical model for strength and porosity of mortars made with ternary blends of ordinary Portland cement (OPC), ground rice husk ash (RHA) and classified fly ash (FA). The mortar mixtures were made with Portland cement Type I containing 0-40% FA and RHA. FA and RHA with 1-3% by weight retained on a sieve No. 325 were used. Compressive strength and porosity of the blended cement mortar at the age of 7, 28 and 90 days were determined. The use of ternary blended cements of RHA and FA produced mixes with good strength and low porosity of mortar. A mathematical analysis and two-parameter polynomial model were presented for the strength and porosity estimation with FA and RHA contents as parameters. The computer graphics of strength and porosity of the ternary blend were also constructed to aid the understanding and the proportioning of the blended system.

• Corrosion Science and Technology
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• 제6권1호
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• pp.12-17
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• 2007

Portland cement incorporating supplementary cementing material develops excellent mechanical properties and long term durability characteristics. India is a leading rice producing country and rice husk is considered as waste in the rice milling industries. In this present work, the rice husk ash (RHA) was added to concrete as cement replacement from 0 to 30%. Corrosion performance of reinforcing steel embedded in RHA blended concretes was studied using linear polarization, AC impedance and gravimetric methods. The corrosion rate of steel bars embedded in RHA concretes were compared with control concrete. The results clearly indicate that the corrosion rate of reinforcing steel embedded in concrete is significantly reduced with the incorporation of RHA. A good correlation among gravimetric method and electrochemical methods was observed. Electrochemical impedance study showed 98 percentage reduction in corrosion rate to the RHA blended concrete with 15% replacement than control concrete.

• Geomechanics and Engineering
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• 제8권2호
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• pp.173-186
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• 2015

The rapid urbanization in Pakistan is creating a shortage of sustainable construction sites with good soil conditions. Attempts have been made to use rice husk ash (RHA) in concrete industry of Pakistan, however, limited literature is available on its potential to improve local soils. This paper presents an experimental study on engineering properties of low and high plastic cohesive soils blended with 0-20% RHA by dry weight of soil. The decrease in plasticity index and shrinkage ratio indicates a reduction in swell potential of RHA treated cohesive soils which is beneficial for problems related to placing pavements and footings on such soils. It is also observed that the increased formation of pozzolanic products within the pore spaces of soil from physicochemical changes transforms RHA treated soils to a compact mass which decreases both total settlement and rate of settlement. A notable increase in friction angle with increase in RHA up to 16% was also observed in direct shear tests. It is concluded that RHA treatment is a cost-effective and sustainable alternate to deal with problematic local cohesive soils in agro-based developing countries like Pakistan.

• Advances in concrete construction
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• 제5권4호
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• pp.345-358
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• 2017

This paper describes the experimental investigation carried out to develop geopolymer concrete using rice husk ash (RHA) along with alccofine. The study reports the fresh and hardened properties of the geopolymer concrete (GPC) activated using alkaline solution. GPC were prepared using different RHA content (350, 375 and $400kg/m^3$), the molarity of the NaOH (8, 12 and 16M). The specimens were cured at $27^{\circ}C$ and $90^{\circ}C$. GPC was activated using NaOH, $Na_2SiO_3$, and alccofine. Prepared GPC samples were tested for compressive and splitting tensile strengths after 3, 7 and 28 days. RHA was suitable to produce geopolymer concrete. Results indicate that behavior of GPC prepared with RHA is similar to fly ash based GPC. Workability and strength can be improved by incorporating the alccofine. Further, alccofine and heat curing improve the early age properties of the GPC. Heat curing is responsible for the initial polymerization of GPC which leads to high workability and improved mechanical properties of the GPC. High strength can be achieved by using the high concentration alkaline solution in terms of molarity and at elevated heat curing. Further, RHA based geopolymer concrete has tremendous potential as a substitute for ordinary concrete.

• 한국양식학회지
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• 제18권4호
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• pp.293-298
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• 2005

RT-PCR을 이용하여 감성돔의 뇌하수체에서 발현하는 FSH$\beta$와 LH$\beta$ cDNA를 각각 cloning하였다. GenBank를 이용하여 FSH$\beta$와 LH$\beta$ 아미노산 배열과 상동성을 비교한 결과, 감성돔 FSH$\beta$는 참돔 FSH$\beta$와 $83.3\%$, snakehead fish FSH$\beta$와 $79.2\%$ 및 striped bass FSH$\beta$와 $76.0\%$의 상동성이 나타났으며 , 감성돔 LH$\beta$는 yellowfin seabream LH$\beta$와 $97.7\%$, 참돔 LH$\beta$와 $96.2\%$의 높은 상동성을 보였다. 또한, 본 연구에서는 1년생 수컷 감성돔에 GnRHa를 처리한 후, 뇌하수체에서 발현하는 GTH subunit mRNA의 농도와 혈중 T및 혈중 $E_2$ 농도의 변화를 조사하였다. GnRHa를 체중 g당 $0.2\;{\mu}g$으로 복강 주사한 후 0, 6, 12, 24 및 48시간제에 뇌하수체와 혈액을 샘플링한 결과, 호르몬 처리 후 6시간째에 FSH$\beta$ mRNA가 유의적으로 증가하였으나, LH$\beta$ mRNA 발현에는 유의적인 차이가 없었다. 또한 혈중 T와 혈중 $E_2$ 농도는 GnRHa처리 후 24시간째 유의적으로 증가하였다.