• 대한치과보철학회지
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• 제45권2호
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• pp.274-282
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• 2007

Statement of problem: Main consideration was given to the stresses at the site of implant entry into the cortical bone at the alveolar crest. As a suspectible factor affecting the occurrence of stress concentrations, the contact angle between the implant and the alveolar crest bone was addressed. Purpose: The purpose of this study is to evaluate angles between the alveolar crest bone and the implant effect on the implant crestal area induced stresses using a finite element method. Material and methods: Cylindrically shaped, standard size ITI implants entering into alveolar crest with four different contact angles of 0, 15, 30, and 45 deg. with the long axis of the implant were axisymmetrically modelled. Alterations of stresses around the implants were computed and compared at the cervical cortical bone. Results and conclusion: The results demonstrated that regardless of the difference of the implant/alveolar crest bone contact angles, stress concentration occurred at the cervical bone and the angle differences led to insignificant variations in stress level.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1098-1102
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• 2008

To increase the ink transfer rate in the micro-gravure-offset printing, the liquid transfer process between two separating plates is investigated. During the liquid transfer process, in which one plate is fixed and the other one moves vertically, a sessile droplet is separated into two droplets. The volume ratio of the two droplets depends on the contact angles of the two plates. In a numerical study of the ink transfer processes, liquid transfer between two parallel separating plates and between a trapezoidal cavity and an upward moving plate are simulated, as models of the printing of ink from the offset pad onto the substrate and the picking up of ink from the gravure plate by the offset pad, respectively. Also, in experimental study, to obtain various surface contact angles, chemical treatment, plasma treatment, and electrowetting- on-dielectric (EWOD) surface are considered. The transfer rate between two plates is calculated by analyzing the droplet images. From the results, the optimal surface contact angles of the units of the micro-gravure-offset printing can be characterized.

• Tribology and Lubricants
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• 제33권5호
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• pp.202-206
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• 2017

In this study, the hydrophobicity properties for riblet surfaces that replicate shark skin are simulated. Riblet surfaces with surface roughness on riblets are generated numerically based on the measured data of real shark skin. We assumed that a rib on a scale is hemi-elliptical surface. The surface used in the simulation for the calculation of contact angle is composed of 9 scales like checkerboard type with a roughness. The contact angle of a water droplet can be calculated using the Wenzel equation and Cassie-Baxter equation for the generated riblet surfaces. The variation of contact angles with a fractional depth of penetration for the generated shark skin surfaces without and with coatings is demonstrated in the condition of solid-air-water. The results show that the contact angle for the surface without coating decreases with an increase of the fractional depth of penetration more drastically than that for the surface with coating. We compared the experimental and simulated results. It is shown that the measured contact angles of the shark skin template and the shark skin replica are within the simulated results. Therefore the contact angle of water droplet for rough surfaces can be estimated by the developed numerical method in this study.

• 한국안광학회지
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• 제16권1호
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• pp.31-40
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• 2011

목적: 본 연구는 안경원에서의 안경용 초음파세척기를 이용한 소프트렌즈 세척 실태를 조사하고 세척용기를 달리하였을 때의 단백질 제거 효과를 비교하기 위하여 수행되었다. 방법: 서울시 소재 75개 안경원을 대상으로 소프트렌즈 세척 실태에 관한 설문조사를 실시하였다. 또한 인공누액을 사용하여 소프트렌즈에 인위적으로 단백질을 침착시킨 후 세척용기를 달리하여 안경용 초음파세척기로 세척한 후 단백질 잔존량을 측정함으로써 세척효율을 비교하였다. 또한 반복적인 초음파 세척으로 인한 소프트렌즈의 표면과 습윤성 변화를 분석하였다. 결과: 안경원에서 콘택트렌즈 세척에 안경용 초음파세척기를 이용하는 주목적은 신속함 때문임을 확인하였다. 세척용기로 플라스틱 렌즈 용기와 유리병 렌즈용기를 사용하고 안경용 초음파세척기로 소프트렌즈를 세척한 경우 유리병 렌즈용기를 사용하였을 때 세척효율이 높은 경향을 보였으나 유의성 있는 차이는 아니었다. 한편 반복적인 초음파 처리로 인하여 소프트렌즈의 표면과 습윤성의 변화가 나타남을 관찰할 수 있었다. 결론: 안경용 초음파세척기 이용 시 세척용기로 플라스틱 렌즈용기와 유리병 렌즈용기의 사용이 모두 효과적이었지만 반복적인 초음파 세척 시에는 세척용기를 사용하였다 하더라도 초음파로 인한 소프트렌즈의 변성이 우려되므로 주의를 기울여 사용하여야 것이다.

• 대한기계학회논문집B
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• 제37권6호
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• pp.559-566
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• 2013

본 연구에서는 고체의 표면조도가 나노유체 액적의 접촉각에 미치는 영향에 대해 실험적 연구를 수행하였다. 나노유체는 산화구리(CuO) 나노분말을 순수 물과 혼합하여 제조하였으며, 고체는 한 변의 길이가 10 mm 정육면체 구리시편을 실험에 사용하였다. 나노유체 액적의 접촉각은 동일한 표면조도 조건에서 순수 물 액적의 접촉각 보다 다소 낮게 측정되었으며, 구리시편의 표면조도가 증가할수록 순수 물과 나노유체 액적의 접촉각은 모두 증가하고 있음을 실험결과로부터 알 수 있었다. 또한 가열-급냉(quench) 실험을 거친 구리시편 표면에서의 접촉각은 순수 표면에서의 접촉각보다 다소 낮게 측정되었으며, 이는 구리표면의 산화에 기인하는 것으로 판단된다. 그러나 가열-급냉 실험에 있어서 냉각 액체로서 순수 물과 나노유체를 사용한 경우의 액적 접촉각 측정결과들은 큰 차이가 없는 것으로 나타났으며, 이러한 실험결과로부터 냉각과정에 있어서 나노입자가 액적의 접촉각에 영향을 미칠 정도로 구리시편의 표면상태를 변화시키지 못하는 것으로 생각된다.

• 대한기계학회논문집A
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• 제32권5호
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• pp.424-429
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• 2008

Surface wettability in terms of the size of the micro nano structures has been examined. To evaluate the influence of the nano structures on the contact angles, we fabricated two different kinds of structures: squarepillar-type microstructure with nano-protrusions and without nano-protrusions. Microstructure and nanostructure arrays were fabricated by deep reactive ion etching (DRIE) and reactive ion etching (RIE) processes, respectively. And plasma polymerized fluorocarbon (PPFC) was finally deposited onto the fabricated structures. Average value of the measured contact angles from microstructures with nanoprotrusions was $6.37^{\circ}$ higher than that from microstructures without nano-protrusions. This result indicates that the nano-protrusions give a crucial effect to increase the contact angle.

• Korean Membrane Journal
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• 제4권1호
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• pp.20-24
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• 2002

The surface of polysulfone membranes has been modified using the fluorine chemicals, ITFE (2-iodo-1,1,1-trifluoro-ethane F.W.=209.94) and PFPI (1H,1H-pentafluoro-n-propyl iodide F.W.=259.95), and PFI (1H,1H,2H,2H-perfluorohexyl iodide, F.W.=373.99) based on Friedel-Crafts reaction mechanism with varying reaction temperatures, reaction time, and catalysis types. The resulting membranes were characterized through mainly the contact angle measurement and pure water permeability. The smaller reactant shows the larger contact angles. FeBr$_3$ catalyst is more effective than AlCl$_3$. Typically, the PS film treated with ITFE at $25^{\circ}C$ under FeBr$_3$ catalyst showed the contact angle 78.5$^{\circ}C$ which indicated 10% over the value of unreacted PS films. More than 50% of pure water flux 8.0 g/$m^2$hr, reduced at reaction time 10 min relative to the original flux, 3.49 g/$m^2$hr.

• Advances in concrete construction
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• 제11권4호
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• pp.323-333
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• 2021

The main objective of this study is to characterize and evaluate the hydrophobic performance of polymer-based water-repellent coatings on cementitious mortar surfaces. Different concentrations of poly(vinyl acetate) (PVAc) and poly(1,4-butylene adipate) (PBA) were prepared in the laboratory and their applicability and performance was tested experimentally by water absorption test and analysis of surface contact angles of cementitious mortar specimens. According to the results of this study, it can be stated that incorporation of nano polymer particles on the surface of cementitious mortar specimens can enhance contact angles and reduce water absorption by increasing hydrophobicity. However, a dosage limit exists for polymer materials in coating, and observed hydrophobic improvements decreases when polymer dosage reached beyond the limit. Additionally, it is observed that water absorption of polymer coated cementitious mortars is closely related with the results of surface contact angle.

• 한국정밀공학회지
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• 제31권2호
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• pp.171-178
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• 2014

In this study, the apparent contact angle on the hydrophilic/hydrophobic surfaces with micropillars was studied. The previous researches showed that the Wenzel equation and the Cassie-Baxter equation were thermodynamically derived for the rough hydrophilic/hydrophobic surfaces and generally referenced on the field of wetting phenomena. For the verification of both equations, the apparent contact angle on the hydrophilic/hydrophobic surfaces with micro-pillars was measured. In the comparison between the measured and estimated apparent contact angles with the equations, the differences between the apparent contact angles were analyzed. Conclusively, the available range and limitation of theoretical equations were investigated and further researches about the apparent contact angle on the rough surfaces were proposed.

• 대한족부족관절학회지
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• 제14권1호
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• pp.5-10
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• 2010

Purpose: This study was performed to compare the contact area between three different correcting angles after the proximal crescentic and Ludloff osteotomies of the first metatarsal. Materials and Methods: We used the two sawbone models. Proximal crescentic (PCO) and Ludloff osteotomies (LO) were performed and secured using K-wires under the correcting intermetatarsal angle (IMA) $5^{\circ}$, $10^{\circ}$, and $15^{\circ}$. Then each 6 osteotomized model was scanned five times and measured the contact area using the calculating program. We excluded the highest and lowest values. Results: The mean area of cutting surface was 189 $mm^2$ in PCO, 863 $mm^2$ in LO. The mean contact area (contact ratio; contact area $\times$100/area of cutting surface) of PCO was 149 $mm^2$ (79%) in $5^{\circ}$, 139.5 $mm^2$ (74%) in $10^{\circ}$, 107 $mm^2$ (57%) in $15^{\circ}$ IMA. The mean contact area (contact ratio) of LO was 711 $mm^2$ (82%) in $5^{\circ}$, 535.5 $mm^2$ (62%) in $10^{\circ}$, 330 $mm^2$ (38%) in $15^{\circ}$ IMA. Conclusion: A significant decrease in the contact area and contact ratio according to increase in correcting IMA was noticed in LO. We recommend the PCO rather than LO, when the IMA is needed to correct over $15^{\circ}$.