• 한국결정성장학회지
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• 제13권1호
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• pp.15-18
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• 2003

High purity single crystalline calcium fluoride ($CaF_2$) has excellent optical transmission characteristics down to deep UV and is therefore selected as the main optical material for the next generation of lithography apparatus operating at wavelength of 157 nm. The growth of large sized $CaF_2$ single crystals with the required properties for this optical application can be achieved only by optimizing the crystal growth process by the aid of numerical simulation. This needs especially a precise calculation of the heat transport and temperature distribution in the solid and liquid $CaF_2$ under crystal growth conditions. As $CaF_2$ is considered to be semitransparent, the internal radiative heat transfer in $CaF_2$ plays an decisive role in the simulation of the heat transport. On the other hand it is very difficult to obtain quantitative experimental data for evaluating numerical models as $CaF_2$ is extremely corrosive at high temperatures. In this work we present a newly developed experimental technique to perform temperature measurements in $CaF_2$-crystal as well as in the melt under conditions of crystal growth process. These experimental results are compared to calculated temperature data, which were obtained by using different numerical models concerning the internal heat transfer in semitransparent $CaF_2$. It will be shown, that an advanced model, which was developed by the authors, gives a much better agreement with experimental data as a standard model, which was taken from the literature.

• Restorative Dentistry and Endodontics
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• 제29권5호
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• pp.454-461
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• 2004

The purpose of this study is to compare and to evaluate the effects of the degree of saturation on the progression of artificial root caries lesion. A total of 8 human premolars without any defects and cracks selected and the cementum were removed and the teeth were cleaned with ultrasonic device and pumice without fluoride. Each tooth was sectioned into 6 pieces and they were ground with #800 sandpaper until they had a thickness of 200pm. Specimens were applied with nail vanish except for the 2-3 mm window area after application of bonding agent. Under the constant pH, the specimens were divided into 6 groups (degree of saturation: 0.1415, 0.1503, 0.1597, 0.1676, 0.1771. 0.1977). Each group was immersed in acid buffer solution for 1. 2, 3, 5 days under controlled temperature ($25^{\circ}C$) and imbibed in water and examined using the polarizing microscope. The results were as follows 1. Although the degree of saturation of demineralization solution decreased, the depth of penetration in the dentin was constant. 2. Erosion was observed on the surface of all the teeth in the group I, II. In the group III, IV, V, surfaces were not changed. The teeth in the group VI showed the more mineralized surface but not the shape of the dentinal tubules distinctively. 3. In all groups, the lesion progressed rapidly at the first day of the experiment, but increased gradually as time elapsed.

• 대한치과기공학회지
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• 제13권1호
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• pp.61-78
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• 1991

Dental caries is one of the main factors to cause the teeth to be lost. Diet is the important factor in the development of dental caries. Today, Dental plaque control, Fluoride to pical application, Fissure sealing and Diet control are used to prevent dental caries. By the five day diet diary, the author surveyed the food in take of 600 infants aged from 10 to 12 in the subures of Seoul. Using the cariogenic food intake analysis form, the detergent food intake analysis form and the basic food intake analysis form, the data were collected, analysed and discussed. After discussing the results, the author concluded as follows : 1. The intake frequency of meals per day was 4.91 times, of which 2.74 times taken at meals and 2.17 times at between meals. Girls(5.00) had taken more times than boys(4.69) at meals an between meals. 2. The intake frequency of cariogenic food per day was 1.93 times, Liquid cariogenic food was taken 0.05 times at meals, and 0.58 times at between meals. Solid cariogenic food was taken 0.05 times at meals, and 0.08 times at between meals. Girls(1.67) had taken cariogenic food more times than boys(1.46). 3. The percentage of intake without detergent food of each intake time per head per day was 71.62% at meals, and 85.7% at between meals. The highest percentage was at evening meals. Boys(44.00%) had taken more detergent food than girls(56.71%). 4. Both boys and girls had the basic food intake taken enough only in 2nd group of basic food, lacking in the other 4 groups. Girls had taken the basic food comparatively more times than boys.

• Environmental Engineering Research
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• 제20권3호
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• pp.223-229
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• 2015

The application of coagulation for feed water pretreatment prior to microfiltration (MF) process has been widely adopted to alleviate fouling due to particles and organic matters in feed water. However, the efficiency of coagulation pretreatment for MF is sensitive to its operation conditions such as pH and coagulant dose. Moreover, the optimum coagulation condition for MF process is different from that for rapid sand filtration in conventional drinking water treatment. In this study, the use of response surface methodology (RSM) was attempted to determine coagulation conditions optimized for pretreatment of MF. The center-united experimental design was used to quantify the effects of coagulant dose and pH on the control of fouling control as well as the removal organic matters. A MF membrane (SDI Samsung, Korea) made of polyvinylidene fluoride (PVDF) was used for the filtration experiments. Poly aluminum chloride (PAC) was used as the coagulant and a series of jar tests were conducted under various conditions. The flux was $90L/m^2-h$ and the fouling rate were calculated in each condition. As a result of this study, an empirical model was derived to explore the optimized conditions for coagulant dose and pH for minimization of the fouling rate. This model also allowed the prediction of the efficiency of the coagulation efficiency. The experimental results were in good agreement with the predictions, suggesting that RSM has potential as a practical method for modeling the coagulation pretreatment for MF.

• 한국융합학회논문지
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• 제6권6호
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• pp.131-137
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• 2015

본 연구는 유치원 아동들의 구강보건교육 효과를 파악하기 위해 K지역 유치원 2곳의 6-7세 아동 214명을 대상으로 2015년 7월 주 1회 4주간 구강보건교육과 설문을 실시하였다. 그 결과 구강건강관리 실태 중 정기검진을 받는 아동(p<0.05), 불소도포경험이 있는 아동(p<0.05), 치아우식증 진단을 받은 경험이 없는 아동(p<0.001), 어머니가 구강보건교육을 받은 경험이 있는 아동(p<0.05)의 구강보건행위 점수가 높아 통계적으로 유의한 차이를 보였다. 구강보건교육 후 구강보건지식은 6점 만점에 교육 전 4.96점에서 교육 후 5.54점으로 향상되었고, 구강보건행위도 11점 만점에 교육 전 7.18점에서 교육 후 7.75점으로 향상되었다(p<0.001). 따라서 아동의 올바른 구강보건행위을 이끌어 갈 수 있는 다양한 구강보건교육 프로그램의 개발과 교육 주기를 짧게 하여 체계적이고 반복적인 실천교육이 이루어져야 할 것으로 생각된다.

• 치위생과학회지
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• 제17권3호
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• pp.202-208
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• 2017

Korea has been running the community oral health program for the elderly, including topical fluoride application and scaling. The aim of this study was to compare the subjective and objective oral health status of 345 participants according to the number of participants in the program and of 37 participants before and after the 5-year program. The survey consisted of an interview questionnaire and oral examinations. Analysis of variance was used to compare the variables of the 345 participants according to the numbers of participants. Paired t-test was used to compare the oral health statuses before and after the 5-year program in 37 subjects. There was no difference in subjective oral health status according to the number of participants in the oral health program in the elderly, including subjective health status, subjective oral health status, satisfaction with oral health, concern about oral health, need of dental treatment, oral pain, tooth sensitivity, subjective periodontal health, and subjective symptoms of periodontitis. The community periodontal index (CPI) of the 1 time participants was significantly higher than that of 3 times, 4 times or 5 times participants in the upper center, lower left, lower center, and lower right areas. There was a significant improvement in CPI from $2.59{\pm}1.14$ to $1.41{\pm}1.54$ (p<0.001) and positive oral behavioral change (daily tooth brushing frequency from $2.27{\pm}0.73$ to $2.54{\pm}0.90$) before and 5 years after the program. However, the program did not prevent tooth loss as the numbers of the remaining teeth significantly reduced from $23.77{\pm}1.84$ to $21.95{\pm}2.03$ over 5 years. We showed that running the community oral health program for the elderly for more than three years might have positive effects on the periodontal health of participants.

• 멤브레인
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• 제27권5호
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• pp.458-467
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• 2017

본 연구는 열유도 상분리법(thermally induced phase separation, TIPS)을 사용하여, 수처리 분리막에 적용하기 위해, 응고조의 열용량의 변화를 위해 서로 다른 두 용액의 함량을 조절하였다. 또한, 온도의 변화를 통해 분리막의 구조 변화에 대하여 관찰하였다. 분리막을 제조하기 위한 소재로는 수처리 분리막에 주로 이용되는 기계적 물성과 내화학성이 우수한 poly (vinylidene fluoride)(PVDF)를 사용하였고, 첨가제로 실리카를 이용하였다. 희석제는 PVDF와 호환성이 좋은 dioctyl phthalate (DOP), dibutyl phthalate (DBP)를 사용하였다. 응고액의 함량 변화에 따른 열용량 변화에 따라 제조된 분리막의 구조를 관찰하기 위해 SEM 이미지를 촬영하였다. 열용량이 증가할수록 PVDF의 결정화 속도가 느려져 큰 기공을 나타내며 열용량이 작을수록 결정화 속도가 증가하여 작은 기공이 생기는 것을 확인하였다.

• 한국표면공학회지
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• 제42권3호
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• pp.109-115
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• 2009

Magnesium is one of the lightest metals, and magnesium alloys have excellent physical and mechanical properties such as high stiffness/weight ratios, good castability, good vibration and shock absorption. However their poor corrosion resistance, wear resistance, hardness and so on, have limited their application. To improve these defects, many techniques are developed. Micro arc oxidation(MAO) is a one of the surface treatments under anodic oxidation in which ceramic coating is directly formed on the surface of magnesium alloy. In this study, the characteristics of anodic film were examined after coating the AZ31B magnesium alloy through the MAO process. MAO was carried out in potassium hydroxide, potassium fluoride, and various concentration of sodium silicate in electrolyte. The morphology and chemical composition of the coating layer were characterized by SEM, XRD, EPMA and EDS. The hardness of anodic films was measured by micro-vickers hardness tester. As a result, the morphology and composition of anodic film were changed by concentration of sodium silicate. Thickness and Si composition of anodic film was increased with increasing concentration of sodium silicate in electrolyte. The hardness of anodic film was highly increased when the concentration of sodium silicate was above 40 g/l in electrolyte.

• 대한치과기공학회지
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• 제39권1호
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• pp.55-65
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• 2017

Purpose: The study has been undertaken on several factors that may influence on the orthodontic treatment satisfaction with the subject of male and female university students who have experience in receiving the orthodontic treatment by visiting orthodontic clinic. Methods: This study has implemented questionnaire survey for 350 male and female university students who have experience in receiving the orthodontic treatment by visiting orthodontic clinic due to the mall occlusion, From the 350 questionnaires collected, a total of 291 copies (83.1%) excluding the questionnaires that have inconclusive response or erroneous response is used as the research analysis data Results: The orthodontic treatment satisfaction is significantly higher for students in large cities and mid- to small sized cities than students in rural area, and it was higher for students with mid-economic class that students of upper class and lower class. It is shown for a student that began the orthodontic treatment from the elementary school, a student that had 5 times or more of brushing teeth for each day had significantly higher level of satisfaction that students that are not. In addition, a student that knows well of the oral hygiene management method, a student that had the fluoride application treatment during the orthodontic treatment period and a student that used the toothbrush for orthodontic service had significantly higher level of satisfaction that students that are not. Conclusion: Factors influencing on the orthodontic treatment satisfaction are very diverse and it is considered that it requires effort to improve the quality of medical service and sufficient understanding on several factors to improve the orthodontic treatment satisfaction for patients as well as the encouragement for orthodontic treatment patients of the relevant people in orthodontic clinics that provide the orthodontic clinic service.

• 대한소아치과학회지
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• 제25권3호
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• pp.598-603
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• 1998

본병원 소아치과에 내원한 유치와 영구치 모두에 법랑질 형성 부전증을 가지고 있는 환자에 대해 교합면의 마모를 방지하여 교합고경을 유지하기 위해 유구치부 stainless steel crown 및 맹출 중인 제 1 대구치에 sealant, 전치아에 걸쳐서 주기적인 불소도포를 이용해 치료하여 양호한 결과를 얻었다.