• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.975-979
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• 2012

Structure and Dynamics of dilute two-dimensional (2D) ring polymer solutions are investigated by using discontinuous molecular dynamics simulations. A ring polymer and solvent molecules are modeled as a tangent-hard disc chain and hard discs, respectively. Some of solvent molecules are confined inside the 2D ring polymer unlike in 2D linear polymer solutions or three-dimensional polymer solutions. The structure and the dynamics of the 2D ring polymers change significantly with the number ($N_{in}$) of such solvent molecules inside the 2D ring polymers. The mean-squared radius of gyration ($R^2$) increases with $N_{in}$ and scales as $R{\sim}N^{\nu}$ with the scaling exponent $\nu$ that depends on $N_{in}$. When $N_{in}$ is large enough, ${\nu}{\approx}1$, which is consistent with experiments. Meanwhile, for a small $N_{in}{\approx}0.66$ and the 2D ring polymers show unexpected structure. The diffusion coefficient (D) and the rotational relaxation time ($\tau_{rot}$) are also sensitive to $N_{in}$: D decreases and $\tau$ increases sharply with $N_{in}$. D of 2D ring polymers shows a strong size-dependency, i.e., D ~ ln(L), where L is the simulation cell dimension. But the rotational diffusion and its relaxation time ($\tau_{rot}$) are not-size dependent. More interestingly, the scaling behavior of $\tau_{rot}$ also changes with $N_{in}$; for a large $N_{in}$ $\tau_{rot}{\sim}N^{2.46}$ but for a small $N_{in}$ $\tau_{rot}{\sim}N^{1.43}$.

• Nuclear Engineering and Technology
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• 제52권8호
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• pp.1611-1625
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• 2020

We propose a scaled-down experimental model of vertical air-natural convection channels by applying the modified Ishii-Kataoka scaling method with the assistance of numerical analyses to the Reactor Vault Cooling System (RVCS) of the Proto-type Gen-IV Sodium-cooled fast reactor (PGSFR) being developed in Korea. Two major non-dimensional numbers (modified Richardson and Friction number) from the momentum equation and Stanton number from the energy balance equation were identified to design the scaled-down experimental model to assimilate thermal-hydraulic behaviors of the natural convective air-cooling channel of RVCS. The ratios of the design parameters in the PGSFR RVCS between the prototype and the scaled-down model were determined by setting Richardson and Stanton number to be unity. The friction number which cannot be determined by the Ishii-Kataoka method was estimated by numerical analyses using the MARS-KS system code. The numerical analyses showed that the friction number with the form loss coefficient of 2.0 in the scale-down model would result in an acceptable prediction of the thermal-hydraulic behavior in RVCS. We also performed experimental benchmarking using the scaled-down model with the MARS-KS simulations to verify the appropriateness of the scale-down model, which demonstrated that the temperature rises and the average air flow velocity measured in the scale-down model.

• 방송공학회논문지
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• 제8권4호
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• pp.473-480
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• 2003

본 논문에서는 차영상(differential image)에 대해 효율적으로 양자화 하기 위해 기존 쿼드 트리(Quadtree) 부호화의 단점을 개선한 새로운 쿼드트리 부호화 기법을 제안하였다. 제안된 기법에서는 실제 표준화되고 있는 영상의 크기에 대응하면서, 기존의 쿼드트리와 제로트리 기반의 앙자화기보다 계산량을 줄여 부호화 및 복호화 처리 시간을 줄이고, 영상의 화질을 높일 수 있다. 실제 동영상 코덱에 적용 가능하도록 차영상의 특징을 분석하였고, 임의의 크기를 갖는 영상을 처리할 수 있도록 블록단위로 처리하는 기존의 쿼드트리 부호화의 기능을 개선하였다. 또한 웨이블릿 변환된 차영상의 계수값을 스케일링(scaling)하여 화질을 향상시킬 수 있었다. 제안한 기법을 기존의 쿼드트리와 SPIHT 기법과 비교한 결과 부호화 시간 및 복호화 시간의 손실 없이 영상의 화질을 향상시킬 수 있었다.

• 한국학교ㆍ지역보건교육학회지
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• 제19권2호
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• pp.53-63
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• 2018

Objectives: This study was intended to provide resources for the development and operation of the elderly's oral health education programs by comparing the difference of oral health behavior, oral health care self-efficacy and oral health levels according to their oral health education experiences and by researching the correlation of oral Health Behavior, self-efficacy, subjective oral health level and oral health education experience. Methods: An interview survey using structured questionaries was done on 180 senior citizens older than 65 years old residing in some areas of Gyeonggi-do from April 19 to May 25, 2018. The data was analyzed with Chi-square, t-test, spearman correlation coefficient with the use of SPSS 20.0. Results: 1. Those who are older than 75 years old and have higher levels of education and finance have more experiences of oral health education. 2. Those who have experiences of oral health education brush their teeth more than three times a day, use more oral health care items and get more regular preventive treatments such as oral examination and scaling. 3. As they has experiences of oral health education, their oral health behaviors, oral health care self-efficacy(tooth care, dietary control, regular checkup) and subjective oral health levels are high. Conclusion: It is necessary to try to improve the elderly's oral health levels by motivating the importance of oral health care and changing their oral health behaviors positively with the implement of oral health education on the elderly. Especially, oral health education programs that are operated on the elderly should be planned with practical programs that can cause the change of their oral health behaviors and should be processed to reinforce oral health care self-efficacy. Furthermore, preventive treatments for the elderly such as oral health education, oral examination and scaling should be implemented systematically and continuously by policy.

• Structural Engineering and Mechanics
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• 제80권5호
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• pp.503-522
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• 2021

This paper investigates experimentally and numerically the influence of drilling process on the mechanical and thermomechanical behaviors of woven glass fiber reinforced polymer (GFRP) composite plate. Through the experimental analysis, a CNC machine with cemented carbide drill (point angles 𝜙=118° and 6 mm diameter) was used to drill a woven GFRP laminated squared plate with a length of 36.6 mm and different thicknesses. A produced temperature during drilling "heat affected zone (HAZ)" was measured by two different procedures using thermal IR camera and thermocouples. A thrust force and cutting torque were measured by a Kistler 9272 dynamometer. The delamination factors were evaluated by the image processing technique. Finite element model (FEM) has been developed by using LS-Dyna to simulate the drilling processing and validate the thrust force and torque with those obtained by experimental technique. It is found that, the present finite element model has the capability to predict the force and torque efficiently at various drilling conditions. Numerical parametric analysis is presented to illustrate the influences of the speeding up, coefficient of friction, element type, and mass scaling effects on the calculated thrust force, torque and calculation's cost. It is found that, the cutting time can be adjusted by drilling parameters (feed, speed, and specimen thickness) to control the induced temperature and thus, the force, torque and delamination factor in drilling GFRP composites. The delamination of woven GFRP is accompanied with edge chipping, spalling, and uncut fibers.

• 지질공학
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• 제14권1호
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• pp.29-46
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• 2004

균열을 따른 지하수 유동은 균열 기하양상에 의해 속도와 유동형태가 결정되므로, 암반 내 지하수 유동특성 해석 시 유동경로 역할을 하는 균열의 기하양상을 정확하게 파악하는 것은 중요하다. 그러나, 실제 현장규모에서는 노두의 불연속적 분포와 지표 하 정보의 연속적 획득이 불가능하기 때문에 전체적인 균열 정보를 얻기 어렵다. 따라서, 해석대상 균열 전체양상을 표현할 수 있는 방법의 개발이 요구된다. 이 연구는 퓨리에 변환을 토대로 해석대상 균열의 전체 기하양상을 파악하는 방법을 개발하고자 새로운 접근을 시도하였다. 시추코아로부터 해석대상 균열을 따라 시료를 채취한 후, 각 시료별로 퓨리에 변환을 통해 거칠기 구성성분 중 영향력이 큰 성분을 선택하였다. 그리고, 선정된 성분들을 평균하여 평균 스펙트럼을 구하였다. 평균 스펙트럼은 각 시료의 모든 성분을 포함하고 있으므로, 해석 대상 균열의 거칠기 성분 중 대표성분을 나타낸다. Low pass filtering을 수행한 후, 퓨리에 역변환을 실시하여 평균화 된 전체 균열의 거칠기 형상을 재현하였다. 재현된 거칠기 형상 또한 각 시료의 전체 기하특성을 포함하는 해석대상 지표하 균열의 대표적 거칠기 양상을 나타내는 것이다. 또한, 이는 규모확장을 통한 균열 전체의 거칠기 양상을 의미하는 것이다. 해석대상 균열을 따른 투수계수 특성을 파악하기 위해 재현된 거칠기 양상을 바탕으로 균열모델을 구성하였다. 투수계수는 균열 기하특성을 최대한 반영하여 정확한 투수계수를 구할 수 있는 균질화 해석법을 통해 산정 하였다. 해석결과는 $10^{-4}{\;}and{\;}10^{-3}{\;}cm/sec$ 범위의 투수계수 분포를 보이는데, 이는 큰 규모의 균열을 따른 투수계수 값이라 할 수 있다. 이러한 시도는 전술한 바와 같이 제한된 단속적 균열정보를 이용해 해석대상의 균열전체에 대한 기하양상은 물론 투수계수를 산정 할 수 있는 방법이 될 것이다.도는 매립된 폐기물의 성상과 밀접한 관계를 보이며 해안가를 따라 매립되어 있는 지역의 토양 내 중금속의 용출은 주변 환경에 대한 잠재적인 환경위험을 결정 시 중요한 역할을 한다.로 제거할 수 있는 것으로 나타났다. 오염 지도에 근거하여 산출된 복원 물량에 대하여 토양세척법을 이용하는 경우 복원 비용을 산출하였으며, 이와 같은 자료는 고로폐광산 주변 오염 토양에 대한 실제 복원 공정의 설계에 중요한 자료로 활용될 수 있을 것으로 판단된다.om the sampling and analytical procedures. There is a cost involved in order to improve the precision of sampling and analytical methods so as to decrease the degree of measurement uncertainty. The economical point of compromise in an investigation planning can be achieved when the allowable degree of uncertainty has been set before-hand. The investigation can then be planned accordingly not to exceed the uncertainty limit. Furthermore, if the measurement uncertainty estimated from the preliminary investigation can be separated into sampling and analytical uncertainties, it can be used as a criterion where the resources for the investigation should be allotted cost-effectively to reinforce the weakest link of

• Journal of Advanced Marine Engineering and Technology
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• 제38권10호
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• pp.1217-1224
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• 2014

This paper provides a practical scaling method to solve an old problem for scaling and developing the speed and resistance of a model to full-scale submarine in fully submerged underwater test. In every experimental test in towing tank, water tunnel and wind tunnel, in the first step, the speed of a model should be scaled to the full-scale vessel (ship or submarine). In the second step, the obtained resistance of the model should be developed. For submarine, there are two modes of movement: surface and submerged mode. There is no matter in surface mode because, according to Froude's law, the ratio of speed of the model to the full-scale vessel is proportional to the square root of lengths (length of the model on the length of the vessel). This leads to a reasonable speed and is not so much for the model that is applicable in the laboratory. The main problem is in submerged mode (fully submerged) that there isn't surface wave effect and therefore, Froude's law couldn't be used. Reynold's similarity is actually impossible to implement because it leads to very high speeds of the model that is impossible in a laboratory and inside the water. According to Reynold's similarity, the ratio of speed of the model to the full-scale vessel is proportional to the ratio of the full-scale length to the model length that leads to a too high speed. This paper proves that there is no need for exact Reynold's similarity because after a special Reynolds, resistance coefficient remains constant. Therefore, there is not compulsion for high speeds of the model. For proving this finding, three groups of results are presented: two cases are based on CFD method, and one case is based on the model test in towing tank. All these three results are presented for three different shapes that can show; this finding is independent of the shapes and geometries. For CFD method, Flow Vision software has been used.

• KSBB Journal
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• 제24권3호
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• pp.303-311
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• 2009

Bi-staged pH process 하의 jar fermenter system에서 영지의 액체배양 시 효율적인 균사체 및 세포의 다당 생산을 위한 용존산소의 영향을 조사하고, 산소이동용량계수와 발효조 조작변수와의 상관관계를 해석하여 scale up의 조건을 검토, 확립하였다. 교반속도에 따른 용존산소의 농도변화를 살펴본 결과, hi-staged pH process에서 배양 $2{\sim}4$일에 용존 산소의 급격한 감소를 보였으나 용존 산소의 제한은 일어나지 않고, 다시 증가하는 경향을 보였으며, 교반속도가 증가할수록 감소 폭과 깊이는 증가하는 경향을 보였다. 다당 생성은 대수 증식기 이후의 용존 산소농도가 $40{\sim}80%$ 범위일 때 가장 높았으며, 이 보다 낮거나 높은 경우 다당의 생성은 저해되었다. 교반 및 통기에 따른 산소이동용량계수 ($k_La$)와 통기속도 (Vs), 교반속도 (N) 및 impeller 지름 (Di)의 자료로부터 중회귀분석한 결과, 이들 사이의 관계는 다음 식으로 표현할 수 있었다. $$k_La=0.555{\times}Vs^{0.42}{\times}(N^3{\times}Di^2)^{0.33}\;(R^2=0.925,\;p<0.05)$$ 2.6 L 발효조의 경우, 15.43 g/L의 최대 다당 생산량은 400 rpm 및 1 vvm에서 얻어졌으며, 2.6 L 발효조의 최적 산소이동용량계수 값을 적용한 20 및 75 L 발효조에서의 scale up 시험 결과는 서로 잘 일치하였다. 최대의 다당생성을 위한 산소전달계수의 감은 $85.4{\pm}26.70\;h^{-1}$이었다.

• 한국수자원학회논문집
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• 제51권9호
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• pp.769-782
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• 2018

설계홍수량 산정은 일반적으로 수자원설계 목적을 위해 요구되며 수자원 관련 계획, 안정성 그리고 수공구조물의 위험도를 평가하기 위해 추정된다. 그러나 설계목적을 위한 국내의 유량자료는 매우 제한적이며, 강우자료와 비교해 봤을 때 상대적으로 관측년수가 상당히 적은 실정이다. 이러한 점에서 본 연구에서는 기 수립된 하천의 재현기간에 따른 설계홍수량 및 유역특성인자(면적, 유역경사)로부터, 설계홍수량을 멱함수 형태로 지역화하여 미계측 유역에서 설계홍수량 산정이 가능한 모형을 개발하였다. 제안된 설계홍수량 지역화 모형의 매개변수 산정과 불확실성을 정량적으로 평가하기 위해 계층적 Bayesian 모형을 활용하였으며, 최종적으로 교차검증 관점에서 모형의 적합성을 검정하였다. 모형 적용 결과, 기존 면적기반의 홍수량 산정식에 비해 약 0.3 이상 높은 상관성을 가지며 홍수량을 추정하는 결과를 확인하였다. 본 연구를 통해 제안된 모형은 검증과정과 도출된 결과를 통해 유역특성에 따른 재현기간별 설계홍수량을 효과적으로 재현하는데 유리할 뿐만 아니라, 동시에 모형의 매개변수 및 결과에 대한 불확실성 정보를 제공함으로써 미계측 유역의 홍수량을 평가하는 기초자료로써 활용 가능할 것으로 판단된다.

• 한국치위생학회지
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• 제6권2호
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• pp.129-141
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• 2006

This study attempts to provide basic information that is necessary to establish the direction of oral health education process abd to develop effective oral health promoting programs for college students by analyzing the modifying factors that may affect their oral health behaviors and their cognitive and perceptive factors. Data for this study are collected by the questionnaire method from college students who attend colleges located Chungchong and Busan province for the period between June 20, 2006 and July 30, 2006. The respondents were chosen from Dental department and Non-Dental department. After omitting the responses with insufficient information, 409 valid responses are used for this analysis. The major finding of the present study are as follows: 1. Oral health behaviors factor is higher rate dental department than non-dental department, dental department than non-dental department appear significant the oral health education, the lasted year round oral examination, the used of oral hygiene supplies, oral prevention treatment. 2. Oral health behaviors and perception-awareness factor is higher score dental department than non-dental department and self efficiency is similar. Oral health behaviors is higher score dental department, the barriers to oral health behaviors is similar. The benefits of oral health behavior is higher score dental department. 3. The oral health behavior is higher dental department. In dental department the overall average score for oral health behaviors question is the correct teeth-brushing, self-restraint of liquor and cigarettes. Non dental department the overall average score for oral health behaviors question is the correct teeth brushing, good nutrition. The lower average score is scaling and periodic oral examination. 4. The correlation coefficient analysis between oral health behaviors and perception-awareness factors, variables which appear significant correlation coefficient by the self-efficiency are the control of oral health, the benefits of oral health behaviors, behavior of oral health, variables which appear significant correlation coefficient by the control of oral health are the benefits of oral health behaviors, the knowledge of oral health, behavior of oral health. And variables which appear significant correlation coefficient by the barriers to oral health behaviors is the benefits of oral health behaviors, variables which appear significant correlation coefficient by the knowledge of oral health is oral health behaviors.