• Journal of Korean Society of Coastal and Ocean Engineers
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• v.1 no.1
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• pp.22-30
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• 1989

Wave propagation is changed by the effect of shoaling, current-depth refraction and shelter-ing etc. To solve these problems. numerous models have been developed. In the present study, a coordinate system is proposed based on the wave ray equation with the wave number equation including diffraction effects . The governing equation for the study was derived from the mild slope wave equation in non-steady state, including current effects (Kirby, 1986a) and trans-formed into an orthogonal curvilinear coordinate system on the basis of the wave ray equation. To obtain a numerical solution, an explicit finite difference scheme was used, and solved by the relaxation method. This model was tested for various cases: Firstly a submersed circular shoal and a constant unit depth. Secondly a submerged elliptic shoal on a slope, and finally a breakwater harbour with obliquely incident waves on a slope. The model was found to simulate the experimental results and other theoretical results in wave height and wave angle fairy well, and the applicability of the model around an arbitrary shaped coastal structure was also verified. To demonstrate the general usefullness of the present approach , the model is to be applied to a field situation with a complex bed topography.

• Journal of the Institute of Convergence Signal Processing
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• v.8 no.1
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• pp.78-83
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• 2007

Robot collects surrounding information to recognize tile unknown environment by using various sensors such as visual, infrared ray and ultra sonic sensors. Although visual sensor is the most popular one, it has some difficulties in collecting data in dark or too bright environment due to sensitivity of the light. It also requests significant amount of calculation on collecting data from certain images with marked, straight and curved ones. As an alternative, ultra sonic sensor can simply overcome this visual sensing system's flaw and easily be used. It is easier than visual system, especially in case of collecting data on object and distance in dark environment. Ultra sonic sensor can replace the expensive visual sensing system not only in avoiding obstacles but also in reaching to the target area smoothly. The purpose of this paper is to develop the algorithm to optimize the environmental recognition, path planning and free-ranging by minimizing errors caused by inaccurate information and by considering characteristics of the ultra sonic rays such as refraction and diffusion. This paper also realizes the system that can recognize the environment and make the appropriate path planning by applying the algorithm on this moving robot.

• Journal of Adhesion and Interface
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• v.14 no.2
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• pp.57-67
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• 2013

The incompletion of TIR (Total Internal Reflection) in FTIR (Frustrated Total Internal Reflection) touch screen has been investigated as follows. Assuming a 3 layer thin film of medium1 ($n_1$)-medium2 ($n_2$)-medium3 ($n_3$) with refraction indices of $n_1=n_3{\neq}n_2$, it was theoretically proven that FTIR or OT (ordinary transmission) phenomena might happen through medium2 from medium1 to medium3 relying on relative difference in $n_1(=n_3)$ and $n_2$, and that the formulae for FTIR and OT could be transformed into each other depending on the number state (imaginary or real) of the light wave phase. In parallel to the theoretical analysis, the incompletion of TIR in acrylate due to external contacts was also elucidated from the experimental and phenomenological viewpoints. On the basis of this considerate work, we explained how to improve the touching performance for better FTIR touch screen.

• Geophysics and Geophysical Exploration
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• v.7 no.1
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• pp.14-18
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• 2004

High levels of ambient noise and safety factors often limit the use of 'active-source' seismic methods for geotechnical investigations in urban environments. As an alternative, shear-wave velocity-depth profiles can be obtained by treating the background microtremor wave field as a stochastic process, rather than adopting the traditional approach of calculating velocity based on ray path geometry from a known source. A recent field test in Melbourne demonstrates the ability of the microtremor method, using only Rayleigh waves, to resolve a velocity inversion resulting from the presence of a hard, 12 m thick basalt flow overlying 25 m of softer alluvial sediments and weathered mudstone. Normally the presence of the weaker underlying sediments would lead to an ambiguous or incorrect interpretation with conventional seismic refraction methods. However, this layer of sediments is resolved by the microtremor method, and its inclusion is required in one-dimensional layered-earth modelling in order to reproduce the Rayleigh-wave coherency spectra computed from observed seismic noise records. Nearby borehole data provided both a guide for interpretation and a confirmation of the usefulness of the passive Rayleigh-wave microtremor method. Sensitivity analyses of resolvable modelling parameters demonstrate that estimates of shear velocities and layer thicknesses are accurate to within approximately $10\%\;to\;20\%$ using the spatial autocorrelation (SPAC) technique. Improved accuracy can be obtained by constraining shear velocities and/or layer thicknesses using independent site knowledge. Although there exists potential for ambiguity due to velocity-thickness equivalence, the microtremor method has significant potential as a site investigation tool in situations where the use of traditional seismic methods is limited.

• 한국태양에너지학회:학술대회논문집
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• 2011.11a
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• pp.154-157
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• 2011

Hydrogenated silicon nitride deposited by LF-PECVD is commonly used for anti-reflection coating and passivation in silicon solar cell fabrication. The deposition of the optimized silicon nitride on the surface is elemental in crystalline silicon solar cell. In this work, the carrier lifetimes were measured while the thicknesses of $SiN_x$ were changed from 700 ${\AA}$ to 1150 ${\AA}$ with the gas flow of $SiH_4$ as 40 sccm and $NH_3$ as 120 sccm,. The carrier lifetime enhanced as the thickness of $SiN_x$ increased due to improved passivation effect. To study the characteristics of $SiN_x$ with various gas ratios, the gas flow of $NH_3$ was changed from 40 sccm to 200 sccm with intervals of 40 sccm. The thickness of $SiN_x$ was fixed as 1000 ${\AA}$ and the gas flow of $SiH_4$ as 40 sccm. The refractive index of SiNx and the carrier lifetime were measured before and after heat treating at $650^{\circ}C$ to investigate their change by the firing process in solar cell fabrication. The index of refraction of SiNx decreased as the gas ratios increased and the longest carrier lifetime was measured with the gas ratio $NH_3/SiH_4$ of 3.

• Journal of Korean Ophthalmic Optics Society
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• v.11 no.2
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• pp.151-157
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• 2006

We researched distant & near horizontal heterophoria of myope using von graefe method on full correction condition for young people 49 subjects(98eyes) with myopia after testing the objective refraction. Among the whole subjects, we got the results as Orthophoria 51.00%, Exophoria 38.75%, Esophoria 10.25% and Heterophoria 49.00% at a long distant. At a short distant, they showed Orthophoria 22.45%, Exophoria 67.35, Esophoria 10.20%, and Heterophoria 77.55%, Orthophoria 22.45. At a long distant they showed Orthophoria 4.08%, Exophoria 8.16%, Esophoria 0% on high myopia, Orthophoria 18.37%, Exophoria 12.25%, Esophoria 0% on middle myopia and Orthophoria 28.57%, Exophoria 18.37%, Esophoria 10.20% on low myopia.

• Journal of Korean Ophthalmic Optics Society
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• v.11 no.2
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• pp.131-135
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• 2006

The purposes of this study is examining a wearing tendency of a progressive multifocal lens. We measured refractive error values using subjective and objective refraction method with subjects in 40-65 ages. Also, we investigated and analyzed distribution of addition power and wearing tendency of progressive multifocal lens. Detected addition powers were ranged of +0.75D - +3.00D. In case of average addition, they were detected with +1.18D in 40's, +1.55D - +1.97D in 50's and +2.38D in above 61's age. The distributions of visual ability at a distant were measured that the hyperopia and hyperopic astigmatism 43%, the myopia and myopic astigmatism characteristic astigmatism 7% appeared highly with 36%. The male who uses the interior aspect multi focal lens with the short-range work were appeared the male 20%, the woman 19%.

• Journal of Korean Ophthalmic Optics Society
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• v.11 no.2
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• pp.109-114
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• 2006

We evaluated the contour using corneal asphericity of the myopic cornea in Korea and investigated the relationship between refractive error and other ocular dimensions in Korean myopia, including anterior chamber depth and asphericity. The monoocular asphericity value of 50 myopes with $-4.83{\pm}2.38$ D between early 20 age and early 30 age in adult was included. Cycloplegic refraction, corneal asphericity and anterior chamber depth using corneal topography were examined. The mean asphericity values were$-0.27{\pm}0.13$ and the corneas of 96.0% were prolate ellipse. Refractive error was related to asphericity and anterior chamber depth among myopes. However, asphericity only were significant difference in high and low myopia group. Corneal configuration on the contact lens fits are discussed. We think that the longitudinal study for myopia and asphericity was required.

• Journal of Korean Ophthalmic Optics Society
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• v.11 no.2
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• pp.77-83
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• 2006

We have studied the astigmatism according to the bevel position and the tilting(pantoscopic) angle of decentered spectacle lens for prism prescription. For prism prescription, generally we make a general spectacle lens into decentered spectacle lens. At this time the bevel position of decentered lens is a important matter, because the difference between optic axis and visual axis occur aberrations. Using the calculation we find that the case that the axis of bevel rotation band passes the front curvature center of (+) lens has a smaller astigmatism than the case that the axis of bevel rotation band passes the rear curvature center of (+) lens and that the case that the axis of bevel rotation band passes the rear curvature center of (-) lens has a smaller astigmatism than the case that the axis of bevel rotation band passes the front curvature center of (-) lens. We find the lens with higher refraction index has a smaller astigmatism.

• Journal of Korean Ophthalmic Optics Society
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• v.20 no.2
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• pp.211-218
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• 2015

Purpose: The aim of this study was to compare the differences among prism settings of the von Graefe technique for phoria measurement. Methods: Thirty eight healthy subjects (mean age $22.35{\pm}2.72years$) were tested with eye examination by interview, cover test, and refraction. Phorias were measured in a random order using four prism settings for the von Graefe method: base-in (BI) and base-up (BU), BI and base-down (BD), BU and BI, and BD and BI over the right and left eye, respectively. Results: Among the four prism settings in measurements of lateral and vertical phoria, there were not significant differences at distance, whereas there were significant at near. The reliability of near lateral phoria (ICC: 0.95) was good, but that of near vertical phoria was less reliable (ICC: 0.83). In comparisons of the paired t-test, the 95% limits of agreement, and mean difference between prism settings, BU had more useful than other prism settings at near phoria. Conclusions: Results from this study suggest that the von Graefe test with BU or BU including other setting prisms have useful methods, especially for near phoria measurements.