• Journal of Korean Ophthalmic Optics Society
• /
• v.8 no.2
• /
• pp.1-11
• /
• 2003

A mathematical model was proposed to analyze the oxygen diffusion reaching the cornea through the tear layers and contact lens based on Fick's law and the principle of continuity of the diffusion flux through the each layers. The model predicts how the parameters such as the thickness of tear layer on the cornea, both the Dk and thickness of contact lenses etc., affect the oxygen tension at cornea and oxygen flux entering the cornea. It is found that either too flat or too tightly fitted contact lenses can cause the oxygen deficiency inside the periphery of the cornea because of the reduction of oxygen flux resulted from too thickened tear layer.

• Journal of Korean Ophthalmic Optics Society
• /
• v.16 no.1
• /
• pp.107-116
• /
• 2011

Purpose: The review article was written to establish an excel program that could calculate minimal Dk of contact lens without $O^2$ deficiency and actual $O^2$ concentration on cornea when contact lens were being fitted by changing lens-related factors. Methods: An excel program was formulated to calculate the thickness of post-lens lacrimal layer, Dk of contact lens and $O^2$ concentration on cornea. Results: With the excel program established, minimal $O^2$ concentration needed on cornea could be calculated when the thickness of post-lens lacrimal layer was changed by varying lens-related factors. A different route in the excel program was needed to choose based on the shape of lacrimal layer. The thickness of lacrimal layer was determined by the shape of meniscus made of tear between lens edge and cornea with flat fit. Thus, the $O^2$ concentration showing negative number in calculation decreased on peripheral cornea with flatter fitting and actual $O^2$ concentration would be zero on cornea. With tight fitting, the thickness of post-lens lacrimal layer is much thicker than lens itself thus negative number in calculation by the excel program is shown indicating zero oxygen on cornea. It can cause $O^2$ deficiency regardless of Dk of contact lens. Conclusions: The calculation of thickness of post-lens lacrimal layer and $O^2$ concentration on cornea by the established excel program is suggested to avoid $O^2$ deficiency when fitting state is varied by changing lens-related factors.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2007.11a
• /
• pp.13-13
• /
• 2007

Ni-Fe 합금을 전주성형하여 Ni용출 특성을 연구하였다. 피팅현상은 Ni용출을 가속화시키나 전주성형된 Ni-Fe 합금의 나노구조는 피팅현상을 줄임으로써 Ni용출량을 줄이는 역할을 함을 알 수 있었다. Ni 용출시험은 인공땀 용액에서 수행하였다.

• Journal of Korean Ophthalmic Optics Society
• /
• v.13 no.3
• /
• pp.35-43
• /
• 2008

Purpose: This review article was written to investigate how the various factors, such as lacrimal thickness, CL's thickness and Dk, affects the influx of $O_2$ diffusion into the cornea. Methods: A mathematical model was proposed to analyze the oxygen diffusion reaching the cornea through the tear layers and contact lens based on Fick's law and the principle of continuity of the diffusion flux through the each layers. Results: The model predicts how the parameters such as the thickness of tear layer on the cornea, both the Dk and thickness of contact lenses etc., affect the oxygen tension at cornea and oxygen flux entering the cornea. Conclusions: It is found that either too flat or too tightly fitted contact lenses can cause the oxygen deficiency at/inside the periphery of the cornea because of the reduction of oxygen flux resulted from too thickened tear layer.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.3
• /
• pp.80-88
• /
• 2010

A simple computational model for modeling of subsurface crack growth under cyclic contact loading is presented. In this model, it is assumed that the initial fatigue crack will initiate in the region of the maximum equivalent stress at certain depth under the contacting surface. The position and magnitude of the maximum equivalent stress are determined by using the equivalent contact model, which is based on the Hertzian contact conditions with frictional forces. The virtual crack extension method is used for simulation of the fatigue crack growth from the initial crack up to the formation of the surface pit due to contact fatigue. The relationships between the stress intensity factor and crack length are then determined for various combinations of equivalent contact radii and loadings.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.3
• /
• pp.1630-1638
• /
• 2015

The finite element analysis has become an essential process to investigate the structural performance in many industry fields. In addition, the computer's performance is improving rapidly, but in large design problems, there is a limit to apply the optimal design techniques. For this, it is general to introduce a metamodel based optimization technique. The method to generate an approximate model can be classified into curve fitting and interpolation, and each representative one is response surface model and kriging interpolation method. This study proposes an ensemble model made of RSM and kriging to solve a structural design problem. The suggested method is applied to the designs of two bar and automobile outer tie rod.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.4
• /
• pp.387-393
• /
• 2012

A roller rack pinion (RRP) system, which consists of a rack-bar and a cam pinion, transforms a rotation motion into a linear one. The rack-bar has a series of roller trains, and meshes with the cam pinion. This paper first proposes the exact tooth profile of the cam pinion and the non-undercut condition to satisfy the required performance by introducing the profile shift coefficient. The paper then investigates the load stress factors under various shape design parameters to predict the gear surface fatigue limit, which was strongly related to the gear noise and vibration at the contact patch. The results show that the pitting life can be extended significantly with an increase in the profile shift coefficient.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2014.11a
• /
• pp.224-224
• /
• 2014

최근 기존의 아연 도금 강판의 성능을 향상시키기 위하여 다른 금속과의 합금 박막의 연구가 활발히 진행 중에 있다. 기존 아연 도금 강판에 비해 Mg를 함유한 Zn-Mg 합금 박막이 내식성이 우수하다고 알려져 있으며, 본 연구에서는 다양한 Mg 함량의 Zn-Mg 합금 타겟을 사용하여 Zn-Mg 박막을 합성하였다. 합성된 박막들의 내식성을 평가하기 위해서 Electrochemical Impedance Spectroscopy (EIS) 분석을 실시하였으며, 도출된 Nyquist plot 과 Bode phase angle plot 결과를 등가회로 피팅과 시뮬레이션을 실시하여 Mg 함량에 따른 Zn-Mg 박막의 내식성을 비교 분석하였다. Zn-Mg 박막은 Mg 함량이 증가할수록 내식성 또한 증가하였으며, 이는 Mg 함량에 따라 치밀해지는 미세구조에 의한 것으로 판단된다.

• Tribology and Lubricants
• /
• v.25 no.1
• /
• pp.38-42
• /
• 2009

Gear is an essential component of an automotive. Crowning is used for tooth modification of a gear. The basic concept of gear tooth crowning is to reduce the stress concentration in edge of contact area and appropriate profile modifications can help gears to resist scoring, pitting, and tooth breakage. In this study, a method to determinate spur gear tooth crowning amount to make smooth surface stress and subsurface stress distribution is proposed. This method is based on the contact analysis.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2012.05a
• /
• pp.238-239
• /
• 2012

ZnO disk는 Ar 가스의 ON/OFF 사이클을 사용한 기상 이동법으로 성장하였다. 온도 의존성 photoluminescence (PL)은 PL 스펙트럼의 quenching 동작을 관장하는 메커니즘을 연구하기 위해 조사하였다. ZnO disk의 12 K PL 스펙트럼에서 3.364, 3.315, 3.244, 3.212, 3.170, 3.139, 3.100 eV의 피크를 관측되었고, 그것은 각각 excitons bound to neutral donors ($D^{\circ}X$), A-line, first-order longitudinal optical (1LO) phonon replica of A-line (A-1LO), donor-to acceptor pair (DAP), A-2LO, DAP-1LO, A-3LO 이다. $D^{\circ}X$와 A-line 피크는 Varshni 공식에 의해서 피팅을 하였고, 도너 이온화 에너지는 40 meV 이었다. Free excitons, $D^{\circ}X$, A-line의 lifetime은 이론적으로 계산하였고, 온도가 증가함에 따라 lifetime이 증가하였다.