• The korean journal of orthodontics
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• v.26 no.5 s.58
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• pp.497-507
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• 1996

The aim of present study in vitro was to evaluate and compare the effects of different washing times of enamels etched with low phosphoric acid solution which makes unsoluble salts and etched but contaminated with saliva on shear bond strength of an orthodontic adhesive to enamel, and to observe the washing effect on the etched enamel surface by scanning electron microscope. All brackets were bonded with Mono-$Lok2^{TM)}$) on the labial surface of extracted human bicuspids after etching with $20w/w\%\;and\;37w/w$ and phosphoric acid solution for 60seconds and then washing for 0,5,10 and 20seconds respectedly. After etching with $37w/w\%$ phosphoric acid solution and contaminating with saliva for 30seconds and then washing for 0,5,20 and 30seconds and re-etching for 10seconds. After 24hours passed in the $37^{\circ}C$ water bath, the shear bond strengths were measured on Universal Test Machine. The data were evaluated and tested by ANOVA and Duncan's multiple range test, and those results were as follows. 1. There was no significant differences between (p>0.05) shear bond strength of bonded brackets with 5, 10, 20seconds washing etched enamel using $37{\%}w/w{\%}$ phosphoric acid solution. 2. The shear bond strength of bonded brackets with $20w/w\%$ phosphoric acid and then washing for 5seconds showed bonded strength durable to occlusal force but its coefficiency score was high and etched surface was not cleaned completely and therefore it was assumed that its clinical application is not applicable. 3. There was no significant differences between (p>0.05) shear bond strengths of bonded brckets with washing for 5seconds etched enamel using $37w/w\%$ phosphoric acid solution and 10,20 seconds washing etched enamel using $20w/w\%$ phosphoric acid solution. 4. The shear bond strength of washing for 5seconds etched enamel which was contaminated with saliva showed sufficient bonded strength durable to occlusal force but its coefficiency score was high and therefore its clinical application was not applicable. 5. After etching, the sample contaminated with saliva showed the sufficient shear bond strength even washing 20seconds without re-etching.

• The korean journal of orthodontics
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• v.32 no.2 s.91
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• pp.129-142
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• 2002

The purpose of this study was to evaluate the effects of caffeine and calcium on the activities of the osteoblastic cell from mouse calvaria. The author cultured osteoblastic cells obtained from the mouse calvaria and were divided into three groups : the caffeine-treated, the calcium-treated and the combine-treated group. In caffeine-treated group, the cell toxicity was measured by MTT assay at 1, 2 and 4 days after treatment of caffeine. In all groups, the densities of the mineralized bone nodules were measured by imaging analyzer after Von Kossa staining. The alkaline phosphotase (ALP) activities were measured at 2, 7, 14, 21 and 28 days and the interleukin-1 ${\beta}$ activities at 48 hours after treatment of caffeine and calcium. The measurements were statistically executed with ANOVA test and the results were as follows. 1. The cellular toxicity of the caffeine increased with the concentration of caffeine during the incubation period. 2. The maximum densities of mineralization were observed at 0.2 mM caffeine-treated group, 1.2 mM calcium-treated group, 0.1 mM caffeine and 1.8 mM calcium-treated group. 3. The activities of ALP were peaked at 14 days at calcium-treated group as no-treated. But, the activities of ALP increased with concentrations of caffeine at caffeine-treated group. At combine-treated group, the act of ALP were peaked at 24 days at 1.2 mM, 1.8 mM calcium-treated group, But decreased at 2.5 mM calcium-treated group. 4. The activites of the IL-1 ${\beta}$ were increased significantly at 0.2 mM caffeine-treated group, 1.8 mM calcium-treated group and 0.1 mM caffeine and 1.8 mM calcium-treated group. But, they were decreased at all groups of high concentration.

• Journal of Bio-Environment Control
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• v.19 no.4
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• pp.251-256
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• 2010

Objective of this research was to investigate the influence of $NH_4^+$ and $NO_3^-$ ratios in liquid feeding on the growth of snapdragon 'Potomac Red' and changes in medium chemical properties. The seeds were sown into 200 plug trays and fertigated once a week with nutrient solution containing various ratios of $NH_4^+$ and $NO_3^-$ such as 0 : 100, 27 : 73, 50 : 50, 73 : 27, and 100 : 0. The total N concentrations were adjusted to 50, 100 and $150\;mg{\cdot}L^{-1}$ in plug stages of 2, 3, and 4, respectively. Determination of seedling growth and analysis of plant tissue and root medum were conducted at 56 days after sowing. The treatment of 27 : 73 ($NH_4^+:NO_3^-$) had the greatest plant height, fresh weight, and dry weight. The N and P contents in 27 : 73 ($NH_4^+:NO_3^-$) treatment based on the above ground plant tissues were 2.39 and 0.39%, respectively, which were the greatest among treatments. The elevation of $NH_4^+$ ratio in fertigation solution decreased tissue Ca and Mg contents, but that did not influence tissue K content. The variations in $NH_4^+:NO_3^-$ ratios impacted the soil solution pH and the difference among treatments had been severe since three weeks after sowing. Elevation of $NH_4^+$ ratios in fertigation solution increased electrical conductivity and concentrations of K, Ca, and Mg in soil solution of root medum. The $NH_4^+$ and $NO_3^-$ concentrations in the soil solution were high in weeks 2, 3, and 4, then decreased gradually as the biomass of seedlings increased. Medium P concentration decreased gradually as seedlings grew, but statistical differences were not observed among treatments.

• Korean Journal of Soil Science and Fertilizer
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• v.41 no.4
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• pp.260-266
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• 2008

Small lysimeter experiment under rain shelter plastic film house was conducted to investigate the effect of soil characteristics on the leaching and soil solution concentration of nitrate and phosphate. Three soils were obtained from different agricultural sites of Korea: Soil A (mesic family of Typic Dystrudepts), Soil B (mixed, mesic family of Typic Udifluvents), and Soil C (artificially disturbed soils under greenhouse). Organic-C contents were in the order of Soil C ($32.4g\;kg^{-1}$) > Soil B ($15.0g\;kg^{-1}$) > Soil A ($8.1g\;kg^{-1}$). Inorganic-N concentration also differed significantly among soils, decreasing in the order of Soil B > Soil C > Soil A. Degree of P saturation (DPS) of Soil C was 178%, about three and fifteen times of Soil B (38%) and Soil A (6%). Prior to treatment, soils in lysimeters (dia. 300 mm, soil length 450 mm) were tabilized by repeated drying and wetting procedures for two weeks. After urea at $150kg\;N\;ha^{-1}$ and $KH_2PO_4$ at $100kg\;P_2O_5\;ha^{-1}$ were applied on the surface of each soil, total volume of irrigation was 213 mm at seven occasions for 65 days. At 13, 25, 35, 37, and 65 days after treatment, soil solution was sampled using rhizosampler at 10, 20, and 30 cm depth and leachate was sampled by free drain out of lysimeter. The volume of leachate was the highest in Soil C, and followed by the order of Soils A and B, whereas the amount of leached nitrate had a reverse trend, i.e. Soil B > Soil A > Soil C. Soil A and B had a significant increase of the nitrate concentration of soil solution at depth of 10 cm after urea-N treatment, but Soil C did not. High nitrate mobility of Soil B, compared to other soils, is presumably due to relatively high clay content, which could induce high extraction of nitrate of soil matrix by anion exclusion effect and slow rate of water flow. Contrary to Soil B, high organic matter content of Soil C could be responsible for its low mobility of nitrate, inducing preferential flow by water-repellency and rapid immobilization of nitrate by a microbial community. Leached phosphate was detected in Soil C only, and continuously increased with increasing amount of leachate. The phosphate concentration of soil solution in Soil B was much lower than in Soil C, and Soil A was below detection limit ($0.01mg\;L^{-1}$), overall similar to the order of degree of P saturation of soils. Phosphate mobility, therefore, could be largely influenced by degree of P saturation of soils but connect with apparent leaching loss only more than any threshold of P accumulation.

• Proceedings of the Korean Society for Bio-Environment Control Conference
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• 2007.05a
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• pp.316-321
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• 2007

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2001.06a
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• pp.21-22
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• 2001

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1993.05a
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• pp.90-95
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• 1993

수력, 화력, 원자력 다음으로 제 4의 전원으로서 관심의 대상이 되고 있는 연료전지는 연료가 가지고있는 화학에너지를 직접에너지로 변환시키는 점에서 종래의 발전 기술과는 원리적으로 다르며, 카르노(Carnot)사이클에 의한 에너지 변환 효율의 제한을 받지 않기 때문에 효율이 높으며 공해가 없는 특징을 가지고 있다. 연료전지의 발전 방식은 작동 온도, 전해질 등에 의해서 분류되나 현재 실용화단계의 기술은 인산형연료전지 발전이다. 인산형 연료전지의 발전용 연료는 천연가스, 메탄올, 납사 등과 같은 탄화수소 계열의 다양한 연료를 사용할 수 있으며, 이들 연료들을 수소가 많이 함유된 가스로 변환시켜 연료전지에 공급하여야 한다. 연료전지발전시스템 개발은 주로 전력이용 측면에서 천연가스를 개질연료로 사용하는 연구가 주류를 이루었으나, 최근에는 전 세계적으로 대기 공해에 시달리고 있는 도시의 환경개선을 위하여 도심용 버스 및 대형 트럭 등에 응용하기 위한 무공해 수송용 자동차엔진의 개발, 국방용 이동전원 개발 및 100㎾ 미만의 현지설치용 및 낙도용 전원으로서 메탄올을 연료로 한 연료전지의 개발이 활발히 진행되고 있다. 한국에너지기술연구소는 한국전력 기술연구원과 공동으로 1989년부터 1992년까지 본체를 제외한 5.9㎾급 인산형 연료전지 발전시스템 즉, 메탄올 연료 개질장치, 운전자동화 시스템, 배열이용 시스템, 종합 배관 등을 설계 구성하여 발전 플랜트의 운전 특성 연구를 수행하였으며, 본 고에서는 이들 설비들의 운전 특성과 발전 플랜트로서의 효율 특성에 대한 고찰을 수행하였다. 본 시스템은 연료개질기가 연결되고 배열을 이용하는 국내최초의 종합적인 연료전지 발전 시스템으로서 개질된 연료로 운전하였을 경우 본체의 효율은 31.9%, 배열을 회수한 종합발전 플랜트의 효율은 45.2%였다.로서, 흰쥐 유선이 LH의 생성처이면서 동시에 작용처이며 유선에서 합성된 GnRH의 조절하에 국부적인 인자로 작용할 가능성을 시사한다.f variation)가 10% 내외로 만족할 만한 범위에 들었다. 본 실험 방법을 타액과 혈청내 testosterone 농도 측정에 응용하여 RIA의 결과와 비교하여 본 바 상관관계가 타액에서 r=0.969, 혈청에서 r=0.990으로 두 결과가 잘 일치하였다. 본 실험에서 측정된 한국인 여성의 타액내 testosterone농도는 107.7$\pm$12.0 pmol／l이었고, 남성의 타액내 농도는 274.2$\pm$22.1 pmol／l이었다. 이상의 결과로 보아 본 연구에서 정립된 EIA 방법은 RIA를 대신하여 소규모의 실험실에서도 활용할 수 있을 것으로 사려된다.또한 상실기 이후 배아에서 합성되며, 발생시기에 따라 그 영향이 다르고 팽창과 부화에 관여하는 것으로 사료된다. 더욱이, 조선의 ${\ulcorner}$구성교육${\lrcorner}$이 조선총독부의 관리하에서 실행되었다는 것을, 당시의 사범학교를 중심으로 한 교육조직을 기술한 문헌에 의해 규명시켰다.nd of letter design which represents -natural objects and was popular at the time of Yukjo Dynasty, and there are some documents of that period left both in Japan and Korea. "Hyojedo" in Korea is supposed to have been influenced by the letter design. Asite- is also considered to have been "Jap

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.1
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• pp.67-73
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• 2019

We carried out basic research to evaluate covering material for improving and managing contaminated benthic environments in coastal areas. Changes in nutrient concentration such as phosphate, hydrogen sulfide of contaminated sediment, and pH, Oxidation Reduction Potential (ORP) were investigated through mesocosm experiments for 6 months by covering contaminated sediment with granulated coal ash. Calcium oxide eluted from the granulated coal ash was confirmed to neutralize acidified sediment by increasing pH through hydrolysis. Also, calcium oxide and silica eluted from the granulated coal ash adsorbed and precipitated with phosphate in the sediment. The concentration of phosphate in the sediment investigated decreased by ca. 84.31 %. Similarly, the concentration of hydrogen sulfide decreased by 133.5 mg/L in one month. The hydrogen sulfide is considered to have reacted with substances such as manganese oxide which were eluted from the granulated coal ash and precipitated. Also, it was concluded that the hydrogen sulfide was reduced since anaerobic conditions in the sediment weakened. According to the results of these mesocosm experiments, granulated coal ash was found to be effective to remediate and manage benthic environments by covering the surface layer of sediment.

• Resources Recycling
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• v.28 no.3
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• pp.15-20
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• 2019

The recovery of struvite using nitrogen and phosphorus in wastewaters is useful for prevention of eutrophication and use as fertilizer, but there are theoretical and technical issues to be resolved. Through the detailed literature review, this study discusses the possible reasonable prediction of struvite formation reaction by setting a feasible reaction equation with some theoretical considerations. In a technical aspect, the purity of struvite in solid precipitates can be promoted by excluding Ca in an effective way. As for the struvite reaction prediction issue, selection of proper equilibrium reaction as well as its reaction equilibrium coefficient is significant in the neutral and basic pH regions. The equilibrium reaction agrees well with the experimental batch test results. Considering the charge balance of the ions, the pH drop along struvite formation in a diluted solution can be predicted. Also, improvement of struvite purity through elimination of Ca can be expected by providing a highly concentrated ${NH_4}^+-N$ relative to ${HPO_4}^{2-}-P$ because ${NH_4}^+$ can enhance the thermodynamic driving force toward favorable struvite formation. Even though the phosphate reacts rapidly with Ca to form a solid precipitate, the thermodynamic driving force due to the high ${NH_4}^+$ activity can dissociate the phosphate-calcium precipitates and produce struvite.

• The Journal of the Korea Contents Association
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• v.8 no.8
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• pp.285-292
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• 2008

This study was initiated to evaluate the Phosphorus(P) leaching potential in the putting green soils and P uptake by the turfgrass in the golf course using the P fertilizers. The turfgrass, Floradwarf bermudagrass(Cynodon dactylon L. PERS,) was planted and grown in the mixture of sand and peat moss in this lysimeter study. Five representative P fertilizers, such as, ammonium polyphosphate (APP), monopotassium phosphate (MKP), MAP(monoammonium phosphate), 0-20-20(liquid), and concentrated superphosphate(CSP, solid) were used in this study. Based on the total P quantity of leachate collected during the whole 12 weeks, MKP and APP are the first group of P fertilizers contributing to the leaching of P, then MAP and 0-20-20 are the second group of P fertilizers causing the P leaching. Finally, CSP is the third group of P fertilizer resulting in the P leaching. However, most of P applied and collected in the lysimeter were leached during the first period of two and four weeks, compared to that of P leached during the second period of six, eight, ten, and twelve weeks. Applications of MAP, APP and CSP, MKP and 0-20-20 in order produced the largest amount of total dry matter. However, APP, MKP and MAP, CSP and 0-20-20 in order showed the largest amount of P uptake. Therefore, based on the data of P leaching, dry matter production, and plant P uptake, it appears that CSP, 0-20-20, and MAP are the environmentally sound fertilizers recommended in the turfgrass putting green soil of golf course.