• Journal of Korean Ophthalmic Optics Society
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• v.11 no.4
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• pp.293-298
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• 2006

For this study, Clinical evaluation of the diverse Autorefractors was performed to examine validity and repeatability compared with subjective refraction. Measurements of refractive error were performed on 212 eyes of 106 subjects subjectivly noncycloplegic. Intersession repeatability of the Autorefractors were also assessed on all 106 subjects together with intersession repeatability on 7 to 14 days intervals. Spherical powers of subjective refraction and autorefractions by Autorefractors were analyzed by paired T-test.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.2
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• pp.50-59
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• 2010

In this paper, two kind of free-form progressive addition lenses (PALs) were designed with Zernike polynomial surface and anatomically accurate finite presbyopic schematic eyes which have aspheric cornea, aspheric GRIN crystalline lens, aspheric retina, and Gaussian apodization factor. Geometrical and diffraction MTFs were used for the optimization process in sequence. 5th orders of Zernike polynomials were used for the evaluation of progression zones of the two examples. The target MTF was set as 0.22 at 100 lp/mm which satisfies the standard visual resolution. These examples were fabricated with a CNC diamond turning machine controlled by slow tool servo (STS). After polishing process, the wavefront aberrations were measured with a laser interferometer on the ten test points across the progression zones and then compared with three current commercially available PALs on the optical performance. Astigmatic aberrations of the examples are very lower than the three selected PALs and have more increased stabilized progressive intermediate zones and near zones. It is expected to give better clear and comfortable distance, intermediate and near visions than other conventional PALs and to improve the adaptability of presbyopic patients to PALs.

• The Journal of Engineering Geology
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• v.17 no.4
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• pp.615-621
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• 2007

Seismic refraction survey which is assumed to be effective for investigating of the amount of bed sediment was applied to two sites having different soil types. The ten lines of seismic surveys were carried out in the areas of the levee near the Wolchon Bridge, Yongin and the Damam levee, Yecheon. At the same time, two borehole data were obtained to be used in classifying geological formations on the inverted seismic sections. As the results of interpolating the depths of geological formations and the surface elevation values, it is possible to estimate the volume of the bed sediments at $24,000m^3\;and\;56,000m^3$ in Yongin and Yecheon, respectively.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.12a
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• pp.43-51
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• 2007

In order to investigate the velocity structure of the southern part of the Korean peninsula, exploded seismic signals were recorded for 120 s along a 294-km WNW-ESE line and 150 s along a 335-km NNW-SSE line in 2002 and 2004, respectively. Velocity tomograms were derived from inverting P-wave and S-wave first arrival times. The raypaths indicate several midcrust interfaces. The shallowest one is at the approximate depth of $2{\sim}3\;km$ with refraction velocities of approximately Vp=6.0 and Vs=3.5 km/s, respectively. The second one of $15{\sim}17\;km$ depth has refraction velocities of approximately Vp=7.1 and Vs=3.7 km/s, respectively. The deepest significant interface varies in depth from 30.8 km to 36.1 km. The critically refracting Vp of $7.8{\sim}8.1\;km/s$ and Vs of $4.2{\sim}4.6\;km/s$ along this interface which may correspond to the Moho discontinuity. The velocity tomograms show (1) existence of a low-velocity zone centered at $6{\sim}7\;km$ depth under the Okchon fold belt and the Yeongnam massif, (2) extension of the Yeongdon fault down to greater than 10 km, and (3) existence of high-velocity materials under the Gyeongsan basin less than 4.2 km thick.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.12
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• pp.24-28
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• 2000

This paper reports a new calculation method of three dimensional deposeition rate by level set method. To model an advancement of the surface efficiently, we have developed a new iteration method to re-initialize the level set function. For calculating etching and deposition rate by direct flow, we have developed a visibility test module and a refraction and re-sputtering model. Sputter deposition rate with shadow effect and surface refraction is calculated. We report that difference of profiles in cases that sticking coefficient are 1.0 and 0.3. We report that the difference of the deposition rate on bottom of the hole is caused by a difference of visible angle by the shadowing effect.

• Journal of the Korea Computer Graphics Society
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• v.13 no.1
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• pp.7-14
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• 2007

In this paper we present an illumination model for rendering realistic stained glass. This techniques simulates the phenomenon of stained glass in real world by applying important optical component of the stained glass to the rendering algorithm. The optics for stained glass involves three basic physical mechanisms. First, diffuse light and highlight contribute to the brightness of stained glass which is typically white and changes along with the light source and the view position. Next, Fresnel refraction dominates the amount of refracted (transmitted) light. Finally, we express volume absorption occurs in all stained glass. Then, the rendered stained glass images achieve excellent realism.

• Korean Journal of Materials Research
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• v.12 no.1
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• pp.27-35
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• 2002

In laser materials processing, localized heating, melting and evaporation caused by focused laser radiation forms a vapor on the material surface. The plume is generally an unstable entity, fluctuating according to its own dynamics. The beam is refracted and absorbed as it traverses the plume, thus modifying its power density on the surface of the condensed phases. This modifies material evaporation and optical properties of the plume. A laser-produced plasma plume simulation is completed using axisymmetric, high-temperature gas dynamic model including the laser radiation power absorption, refraction, and reflection. The physical properties and velocity profiles are verified using the published experimental and numerical results. The simulation results provide the effect of plasma plume fluctuations on the laser power density and quantitative beam radius changes on the material surface. It is proved that beam absorption, reflection and defocusing effects through the plume are essential to obtain appropriate mathematical simulation results. It is also found that absorption of the beam in the plume has much less direct effect on the beam power density at the material surface than defocusing does and helium gas is more efficient in reducing the beam refraction and absorption effect compared to argon gas for common laser materials processing.

• Journal of Information Processing Systems
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• v.13 no.4
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• pp.677-688
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• 2017

In order to solve the undetected probability of multiple targets in ultra-wideband (UWB) through-the-wall radar imaging (TWRI), a time-delay and amplitude modified back projection (BP) algorithm is proposed. The refraction point is found by Fermat's principle in the presence of a wall, and the time-delay is correctly compensated. On this basis, transmission loss of the electromagnetic wave, the absorption loss of the refraction wave, and the diffusion loss of the spherical wave are analyzed in detail. Amplitude compensation is deduced and tested on a model with a single-layer wall. The simulating results by finite difference time domain (FDTD) show that it is effective in increasing the scattering intensity of the targets behind the wall. Compensation for the diffusion loss in the spherical wave also plays a main role. Additionally, the two-layer wall model is simulated. Then, the calculating time and the imaging quality are compared between a single-layer wall model and a two-layer wall model. The results illustrate the performance of the time-delay and amplitude-modified BP algorithm with multiple targets and multiple-layer walls of UWB TWRI.

• Tunnel and Underground Space
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• v.17 no.2 s.67
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• pp.102-108
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• 2007

Generally, the method used most widely for rock mass classification is considering the rock strength and development of joint frequency. However, if rock bed has micro-crack and long joint, this method is not rational. Therefore, the difficulties of excavation in the rock bed with complicated geological condition are decided by combining joint frequency. indoor tests (uniaxiall compressive strength, point load test, indoor elastic wave velocity, etc.) and field seismic refraction survey, and the rock mass classification should be implemented by considering their interrelationship.

• Journal of Korean Medical Science
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• v.33 no.44
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• pp.275.1-275.15
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• 2018

Background: We compared the efficacy between trifocal and bifocal diffractive intraocular lens (IOL) implantation. Methods: Through PubMed, MEDLINE, EMBASE, and CENTRAL, we searched potentially relevant articles published from 1990 to 2018. Defocus curves, visual acuities (VAs) were measured as primary outcomes. Spectacle dependence, postoperative refraction, contrast sensitivity (CS), glare, and higher-order aberrations (HOAs) were measured as secondary outcomes. Effects were pooled using random-effects method. Results: We included 11 clinical trials, with a total of 787 eyes (395 subjects). The trifocal IOL group showed better binocular distance VA corrected with defocus levels of -0.5, -1.0, -1.5, and -2.5 diopter than the bifocal IOL group (All $P{\leq}0.004$). The trifocal IOL group showed better monocular uncorrected distance and intermediate VAs (mean difference [MD], -0.04 logarithm of the minimum angle of resolution [logMAR]; 95% confidence interval [CI], -0.07, -0.01; P = 0.006 and MD, -0.07 logMAR; 95% CI, -0.13, -0.01; P = 0.03, respectively). Postoperative refraction, glare, CS, and HOAs were not significantly different from each other. Conclusion: The overall findings indicate that trifocal diffractive IOL implantation is better than the bifocal diffractive IOL in intermediate VA, and provides similar or better in distance and near VAs without any major deterioration in the visual quality.