• Journal of Korean Ophthalmic Optics Society
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• v.15 no.2
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• pp.123-130
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• 2010

Purpose: The study was conducted to compare the values of auto-refraction, manifest refraction and cycloplegic refraction in school-aged children. Methods: One hundred five myopic school children ranged from 6 to 14 years old (210 eyes, $10.28{\pm}1.59$ years old) were recruited and noncycloplegic auto-refraction (AR) and manifest refraction (MR) were conducted and then underwent cycloplegia and refractive status (CR) again with the auto-refractometer. Results: Refractive powers measured by AR, MR, and CR were highly correlated. However, spherical and cylindrical powers of the subjects measured by AR were measured higher negative power than in CR (p<0.001). From 210 eyes, the discrepancy rate in the spherical and cylindrical powers were 40 eyes (19%) and 19 eyes (9%) of the total subjects, respectively and the differences between noncycloplegic and cycloplegic refractions were higher with the spherical and cylindrical powers increasing. Conclusions: The use of the autorefractometer in children with negative spherical power without cycloplegia may overestimate the actual myopia that subjective refraction is the most important in prescription for the eyeglasses and regression equations would be used to prognose the cycloplegic refraction from the auto-refraction as the basic data for the subjective refraction.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.4
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• pp.425-431
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• 2011

Purpose: For better understanding refractive error in Korean children and teenagers, a follow-up study on the changes of refractive error was performed in 1~13-year-old subjects for ten years. Methods: Among the people who had visited an ophthalmologic hospital in Seoul to examine the visual acuity and to correct refractive error from 2000 to 2010 years, 223 subjects (364 eyes) having the corrected visual acuity over 0.7 had been investigated the changes of spherical equivalent power of the cycloplegic clinical refraction and manifest clinical refraction from the accumulated medical record data for ten years. Results: The changes of spherical equivalent power for ten years in 1 to 13 years old were shown the highest change at 7-year-old. And annual change of spherical equivalent power was shown the highest change at from 9-year-old to 10-year-old (-0.64${\pm}$0.64 D) followed by from 8-year-old to 9-year-old (-0.64${\pm}$0.81 D). Conclusions: The changes of refractive error for Korean children and teenagers aged 1 to 13 years in an optometric practice were shown the tendency to proceeding to myopia with age, especially the largest increase at from 7-year-old to 10-year-old, and this period is important for vision care.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.1
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• pp.34-43
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• 2007

As a method to improve the poor torque capacity on the continuously variable transmission(CVT), power splitted devices(PSD) reducing the power entering into the transmission has been considered. But this kind of PSD requires for the variator to be a large coverage of the speed ratio (CSR) Since the CSRs of the well-known push belt or the toroidal ones are not enough large, the power splitted CVTs (PSCVTs) using them should be made with multiple modes. inevitably adding the do9 clutches and the associated accessories. In this paper a PSCVT with single mode is conceptually designed A new continuously variable unit (CVU) consisting of the paired inner and outer spherical rotors is used. The CVU has large CSR and excellent compactness. As a PSD. a variable bridge (VB) using the Planetary gear units (PGUs) is considered because it has an upper bound on the power ratio. An optimal design to minimize the effective efficiency of the PSCVT is carried out. Through the performance analysis on the designed model, good expectation on the practicability in the heavy vehicle system is shown.

• Structural Engineering and Mechanics
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• v.64 no.1
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• pp.93-107
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• 2017

The article presents the vibration and acoustic responses of un-baffled doubly curved laminated composite panel structure under the excitation of a harmonic point load. The structural responses are obtained using a simulation model via ANSYS including the effect various geometries (cylindrical, elliptical, spherical and hyperboloid). Initially, the model has been established by solving adequate number of available examples to show the convergence and comparison behaviour of the natural frequencies. Further, the acoustic responses are obtained using an indirect boundary element approach for the coupled fluid-structure analysis in LMS Virtual.lab by importing the natural frequency values. Subsequently, the values for the sound power level are computed using the present numerical model and compared with that of the available published results and in-house experimentally obtained data. Further, the acoustic responses (mean-square velocity, radiation efficiency and sound power level) of the doubly curved layered structures are evaluated using the current simulation model via several numerical experimentations for different structural parameters and corresponding discussions are provided in detail.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.31-32
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• 2007

Oil-based nanofluids are prepared by dispersing spherical and fiber-shaped $Al_2O_3$ and AlN nanoparticles in transformer oil. Two hydrophobic surface modification processes are compared in this investigation. It is obvious that the combination of nanoparticle, surfactant and surface modification process is very important for the dispersity of nanofluids. For ($Al_2O_3$+AIN) particles with 1% volume fraction, the enhancement of thermal conductivity and convective heat transfer coefficient is nearly 11% and 30%, respectively, compared to pure transformer oil. The cooling effect of ($Al_2O_3$+AlN)-oil nanofluids on the heating element and oil itself is confirmed by a natural convection test using a prototype transformer.

• Journal of Korean Ophthalmic Optics Society
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• v.14 no.2
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• pp.31-34
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• 2009

Purpose: We are to analyze optically how to affect the eye related with movement of the iris. Methods: Using the schematic eye to have the crystalline lens of the radial GRIN and the spherical GRIN forms that come to be planned in existing, the iris centre was moved 0.5 mm with nasal direction in order to be identical with the real eye. Also, considering that the iris centre move according to increase of the pupil size, the iris centre was moved 0.4 mm with temporal direction to analyze the optical performance change of the eye respectively. Results: Because of decrease in the spherical aberration, the schematic eye with nasal direction 0.5 mm eccentricity of the iris showed a different consequence plentifully compared with the performance of the real eye. Besides, the schematic eye with temporal direction 0.4 mm eccentricity of the iris showed that the spherical aberration somewhat increased. Conclusions: In case of design of the schematic eye with the similar real eye performance which the iris centre was moved 0.5 mm with nasal direction, we need to research about aspheric coefficient of optical constants of each refracting surface considering the performance change of a spherical aberration, a peripheral power error and astigmatism etc, owing to change of the real eye hence to be affected by the iris movement.

• Journal of the Korean Solar Energy Society
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• v.31 no.3
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• pp.80-88
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• 2011

Heliostat in the tower type solar thermal power plant is a sun tracking mirror system to reflect the solar energy to the receiver and the optical performance of it affects to the efficiency of whole power plant most significantly. Thus a solid understanding of heliostat's energy concentration characteristics is the most important step in designing of the heliostat field and the whole power plant. The work presented here is the analysis of energy concentration characteristics of heliostat used in 200kW solar thermal power plant, where the receiver located at 43m high in tower has $2{\times}2$m rectangular shape. The heliostat reflective surface is formed by 4 of $1{\times}1$m flat plate mirror facet and the mirror facet is mounted on the spherical frame. The direct normal incident radiation models in vernal equinox, summer solstice, autumnal equinox and winter solstice are first derived from the actually measured data. Then the intercept ratio, heat flux distribution and total energy collected at the receiver for the heliostats located in the various places of the heliostat field are investigated. Finally the effect of mirror facet installation error on the optical performance of the heliostat is analyzed.

• Nuclear Engineering and Technology
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• v.1 no.1
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• pp.5-16
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• 1969

A design of new burst cartridge detection system for gas-cooled power reactor using a spherical sampling chamber with negative electrode is presented. The results of theoretical calculation indicate that the designed system is feasible for a practical application and sensitive enough to detect a 1 $\textrm{cm}^2$ hole in the fuel clad-ding.

• 대한방사선방어학회:학술대회논문집
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• 2009.04a
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• pp.234-235
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• 2009

• Journal of Biomedical Engineering Research
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• v.22 no.5
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• pp.419-424
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• 2001

We intended to evaluate the Young's modulus of trabecular bone of a human distal femur by spherical Indentation test and CT images and to quantify relationships between the direction of load, density. and Young's modulus. The specimens were scanned at 1 mm intervals on CT scanner After scanning the bones were sectioned with diamond saw. producing 8mm cubes of trabecular bone. The tubes were mechanically tested in inferior-superior(IS), anterior-posterior(AP). and medial-lateral(ML) direction with custom-made device. After testing, the real apparent density of specimens were measured. The results of this study showed that the IS modulus was significant1y greater than both the AP and ML modulus and the AP modulus was also greater than ML modulus significantly(p〈0.01) A significant Power relationship between the apparent density and the modulus was also found.