• Journal of Mechanical Science and Technology
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• 제20권11호
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• pp.1891-1897
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• 2006

In this study, a new model to predict the effective elastic constants of composites with spherical fillers is proposed. The original Eshelby model is extended to a finite filler volume fraction without using Mori-Tanaka's mean field approach. When single filler is embedded in the matrix, the effective elastic constants of the composite are computed. The composite is in turn considered as a new matrix, where new single filler is again embedded in the matrix. The predicted results by the present model with a series of embedding procedures are compared with those by Mori-Tanaka, self-consistent, and generalized self-consistent models. It is revealed through parametric studies such as stiffness ratio of the filler to the matrix and filler volume fraction that the present model gives more accurate predictions than Mori-Tanaka model without using the complicated numerical scheme used in self-consistent and generalized self-consistent models.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1163-1167
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• 2003

Effective properties of ceramic matrix plain woven textile composites were calculated using finite element analysis. The considered geometry is a unit cell of plain weave and the analysis was performed by commercial finite element program, ANSYS. The materials for analysis are 3 types for matrix, 1 type for fiber with various volume fraction. The result indicates that the effective properties of ceramic matrix composites can be controlled by the volume fraction. The result can be used for numerical analysis using ceramic matrix composites.

• 청정기술
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• 제24권4호
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• pp.287-292
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• 2018

효율적으로 이산화탄소를 처리할 수 있는 활성탄을 제조하기 위하여 활성탄의 물리적 특성이 이산화탄소 흡착에 미치는 영향을 조사하였다. 소나무 톱밥과 석탄이 활성탄의 원료로 사용되었고, 제조된 활성탄의 비표면적, 미세기공 부피, 중기공 부피를 분석하였다. 제조된 활성탄은 열중량 분석기를 이용하여 이산화탄소 흡착량을 결정하였다. 그리고 이산화탄소 흡착량 결과를 활성탄의 비표면적, 미세기공 부피, 중기공 부피에 따라 분석하였다. 실험 결과, 소나무 톱밥 활성탄과 석탄 활성탄의 비표면적과 미세기공 부피는 이산화탄소 흡착량과 높은 연관성을 보인 반면에 중기공 부피는 이산화탄소 흡착에 거의 영향을 미치지 않았다. 따라서 활성탄의 비표면적과 미세기공 부피를 극대화하는 것이 효율적인 이산화탄소 처리를 위해 매우 중요한 요소로 나타났다.

• 한국식품영양학회지
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• 제14권4호
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• pp.311-316
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• 2001

This study was designed to investigate the effective ratio of healthy bread wish green tea powder. The weight. volume, and colon difference of bread with various contents of green tea powder were measured. And the picture of bread and the panel test were taken. To avoid the decrease of volume, the experiment was taken with active gluten. The weight to bread was increased and the volume was decreased significantly according to increase of green tea powder ratio. But, the volume of the group with active gluten(3%+ and 4%+) was higher than that of the group with green tea powder 2%. That is which the correction of the volute was taken by active gluten in green tea powder bread. In the result of panel test and volume measurement. addition of 3% green tea powder was appropriate, and the addition of active gluten corrected the decrease of volume. Therefore. using the green tea powder, the diversity of bread by functionality, nutritional composition. taste, color. flavor of green tea powder can be developed. This result will support the background the development of green tea bread of good quality.

• 한국산학기술학회논문지
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• 제12권7호
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• pp.2931-2938
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• 2011

2상 복합재에 적용되어오던 수정된 Eshelby 모델(MEM)을 두 종류의 구형 입자를 포함하는 3상 복합재로 확장하여 복합재의 등가열전도계수를 간단히 양함수 형태로 표시한다. 이의 유효성 검증을 위해 이 결과를 미소등가물모델(DEMM)로 구한 결과와 비교하고, 또 참고문헌의 2상 및 3상 복합재의 실험결과와 비교한다. 2상 복합재의 경우 MEM이 충전재의 체적비 0.5 미만에서는 DEMM보다 잘 예측한다. 3상 복합재의 경우 모재 대비 큰 열전도계수비를 갖는 충전재의 체적비가 적은 경우 MEM이 잘 예측하나, 체적비가 증가할수록 DEMM이 잘 예측한다. 이 체적비가 두 모델의 예측결과에 결정적 영향을 주는 인자임이 변수들의 영향 연구를 통해 밝혀졌으며, Molina 등이 제안한 3상 복합재에 대해 MEM과 DEMM은 동등한 예측 수준을 보였다.

• 터널과지하공간
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• 제8권4호
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• pp.275-286
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• 1998

균열연결망 모델에서의 투수계수 텐서, 주 투수계수 그리고 주 투수계수 방향들에 대한 인자에 근거해서 유효투수계수와 대표요소체적을 구하였다. 전체브록에 대한 소블록의 투수계수의 계산을 통해서 유효투수계수는 조화평균과 산술평균 사이의 범위임을 알 수 있었다. 정육면체 모델에서 체적의 증가에 따른 유량의 변화계산에 대한 수치실험으로부터 유량의 변화는 모델의 체적이 대표요소체적에 접근함에 따라 감소함을 보여 주어ST다. 터널로의 지하수 유입량은 대표요소체적 개념보다는 터널길이대 모델크기의 비에 더 큰 영향을 받는다고 볼 수 있다. 그리고 균열연결망 모델과 등가다공성 모델에서의 지하수 유입량은 정확히 일치하지 않았으며 특히 모델크기에 대한 터널길이가 작을수록 그 차이가 크게 발생하였다.

• 대한핵의학회지
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• 제17권2호
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• pp.1-17
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• 1983

The purpose of this study is to investigate the effects of thyroid hormone on the left ventricular(LV) volume arid function in man with untreated hyperthyroidism and to determine the effects of successful therapy for thyrotoxicosis on the ventricular pathophysiology. In the present study, equilibrium radionuclide cardiac angiography was performed and LV volume index, ejection phase indexes of LV performance, serum thyroid hormone levels and other hemodynamic parameters were measured in 28 normal subjects and 39 patients with hyperthyroidism before treatment and again every 4 weeks for the first 2 months after the initiation of effective therapy. The results obtained were as follows; 1) In the untreated hyperthyroid state heart rate, blood volume, cardiac index and stroke volume index($97{\pm}14$ beats/min, $73.5{\pm}11.8ml/kg,\;6.9{\pm}1.4\;l/min/m^2$ and $77.6{\pm}13.8ml/m^2$, respectively) were increased significantly compared to those in normal control($74{\pm}12beats/min$, $66.6{\pm}14.8ml/kg,\;3.8{\pm}1.2\;l/min/m^2$ and $56.6{\pm}13.2ml/m^2$ respectively). $(Mean{\pm}SD)$ 2) There was a significant increase in LV end-diastolic volume index in patients with hyperthyroidism ($30.5{\pm}7.5$ for hyperthyroid group compared to a normal control of $22.2{\pm}6.5$; p<0.001), whereas end-systolic volume index remained unchanged $9.6{\pm}3.6\;and\;8.8{\pm}3.3$ respectively).3) In patients with hyperthyroidism, LV ejection fraction was $70.0{\pm}5.6%$, fractional shortening $32.9{\pm}5.1%$, mean velocity of circumferential fiber shortening(mean Vcf) $1.34{\pm}0.31$ circ/sec and maximum ejection rate $3.47{\pm}0.80$. All the ejection phase indexes were significantly greater than those in normal control($65.2{\pm}5.7%,\;28.8{\pm}3.2%,\;0.88{\pm}0.37$ circ/see and $2.27{\pm}0.50$, respectively; p<0.001). 4) Effective therapy produced significant decrease in all the values of serum thyroid hormone concentrations(p<0.00l), hemodynamic parameters(p<0.001), end-diastolic volume index(p<0.01) and ejection phase indexes of LV contractility in patients with hyperthyroidism and after one to two months, when the patients were euthyroid, these measurements were in the range of normal. 5) A significant linear correlation between mean Vcf and serum thyroxine level(r=0.63, p<0.001) as well as between mean Vcf and serum triiodothyronine level(r=0.62, p<0.001) was found. The lesser degree of correlation was also noted between other ejection phase indexes and serum thyroid hormone concentrations. The results indicate that the major effects of excess thyroid hormone on the LV in human beings with hyperthyroidism are an enhancement of LV function and an increase in LV enddiastolic volume and that these effects cause predictable reversible cardiac alteration which are changed dramatically and immediately after effective therapy.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.341-348
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• 2001

A Mixed Volume and Boundary Integral Equation Method is applied for the effective analysis of plane elastostatic problems in unbounded solids containing general anisotropic inclusions and voids or isotropic inclusions. It should be noted that this newly developed numerical method does not require the Green's function for anisotropic inclusions to solve this class of problems since only Green's function for the unbounded isotropic matrix is involved in their formulation for the analysis. This new method can also be applied to general two-dimensional elastodynamic and elastostatic problems with arbitrary shapes and number of anisotropic inclusions and voids or isotropic inclusions. Through the analysis of plane elastostatic problems in unbounded isotropic matrix with orthotropic inclusions and voids or isotropic inclusions, it will be established that this new method is very accurate and effective for solving plane elastic problems in unbounded solids containing general anisotropic inclusions and voids or isotropic inclusions.

• 동력기계공학회지
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• 제10권4호
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• pp.133-138
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• 2006

Effective thermal conductivity of particulate reinforced composite has been predicted by Eshelby's equivalent inclusion method modified with Mori-Tanaka's mean field theory. The predicted results are compared with the experimental results from the literature. The model composite is polymer matrix filled with ceramic particles such as silica, alumina, and aluminum nitride. The preliminary examination by Eshelby type model shows that the predicted results are in good agreements with the experimental results for the composite with perfect spherical filler. As the shape of filler deviates from the perfect sphere, the predicted error increases. By using the aspect ratio of the filler deduced from the fixed filler volume fraction of 30%, the predicted results coincide well with the experimental results for filler volume fraction of 40% or less. Beyond this fraction, the predicted error increases rapidly. It can be finally concluded from the study that Eshelby type model can be applied to predict the thermal conductivity of the particulate composite with filler volume fraction less than 40%.

• 대한기계학회논문집A
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• 제29권1호
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• pp.67-73
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• 2005

The paper presents a single-heater microfluid injector, whose ejected droplet volume is adjusted by digital current path control for a single microheater. The previous droplet volume adjustable methods have used the digital current control for multiple heaters or the analog current control for a single heater, while the present method uses the digital current control for a single microheater. Two different microinjectors, having a rectangular heater and a circular hearter, are designed and fabricated in the chip area of $7.64\;mm{\times}5.26\;mm$. The fabricated microinjectors have been tested and characterized for the number, size, shape and lifetime of the generated bubbles as well as for the volume and velocity of the ejected droplets. The input power for the rectangular heater and the circular heater has been varied in the ranges of $8.7{\sim}24.9{\mu}W\;and\;8.1{\sim}43.8{\mu}W$, respectively. The projected area of the generated bubble has been changed in the ranges of $440{\sim}l,3600{\mu}m^2\;and\;800{\sim}3,300{\mu}m^2$ for the rectangular heater and the circular heater, respectively. The microinjector with the rectangular heater ejects three discrete levels of the droplet in the volume range of $9.4{\sim}20.7pl$ with the velocity range of $0.8{\sim}1.7m/s$, while the microinjector with the circular heater achieves five discrete levels of the droplet in the volume range of $7.4{\sim}27.4pl$ with the velocity range of $0.5{\sim}2.8m/s$.