• Journal of Korean Ophthalmic Optics Society
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• v.16 no.2
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• pp.167-170
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• 2011

Purpose: This study was tried whether expectation of astigmatism from spherical equivalent visual acuity was possible. Methods: For 54 men and women (108 eyes) corrected to emmetropia, average age of 23.3, changes of visual acuity (5m) were measured with an increasing the powers at every ${\pm}$0.25D when the (-) axis of cross cylinder is $180^{\circ}$, $90^{\circ}$, and $45^{\circ}$, respectively. Results: As the power of cross cylinder was increased, visual acuity was decreased. When the powers of cross cylinder were ${\pm}$2.50D ($180^{\circ}$ and $90^{\circ}$) and ${\pm}$2.25D ($45^{\circ}$), visual acuity was 0.05 which is the minimum measurement possible. Conclusions: The diagram on astigmatism dealing with each spherical equivalent visual acuity was able to tabulate.

• Journal of Korean Ophthalmic Optics Society
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• v.6 no.2
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• pp.115-119
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• 2001

To research the refractive error of the eyes on the 30's employees, 510 eyes were tested by the object and subject methods. The results were as follows. 1. Among the 510 eyes, myopia is 74.4%, hyperopia is 0.9% and emmetropia is 24.7%, respectively. 2. In test, the low myopia (-0.50Dt < Spherical Equivalent ${\leq}$ -2.00Dt) is 24.1%, the middle myopia(-2.00Dt < Spherical Equivalent ${\leq}$ -6.00Dt) is 51.4%, the high myopia(-6.00Dt < Spherical Equivalent) is 14.8% and the low hyperopia(+0.50Dt < Spherical Equivalent ${\leq}$ +2.00Dt) is 1.2%, respectively. 3. In test of astigmatism, the amount of astigmatism with-the rule is 58.5%, the amount of astigmatism against-the rule is 22.6% and the amount of astigmatism with oblique is 18.9%, respectively.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.3
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• pp.707-715
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• 1994

This study presents thickness optimization for the pressure vessel domes subject to internal pressure and axial force simultaneously. The considered typical pressure vessel domes are ellipsoidal and tori-spherical domes with skirt and nozzle part. These pressure vessel domes under loading have higher stress concentration on geometric discontinuity parts. Therefore, thickness optimization of axi-symmetric pressure vessel domes is essentially concerned on minimizing this stress concentration. The objective function is minimization of weight of pressure vessel dome. The design variable is thickness of dome and cylinder. Considered constraint is Von Mises equivalent stress. In the optimization procedure, ANSYS code is used. The equivalent and hoop stress of original shape domes are compared with those of optimal shape domes. And optimal thicknesses for pressure vessel domes are presented.

• Journal of Korean Clinical Health Science
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• v.1 no.3
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• pp.33-37
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• 2013

Purpose. In this study, we divided elementary school students into two investigated groups. The A group is the lower graders(boys 9, girls 18), and the B group is the higher graders(boys 10, girls 13). The myopia progression has been compared with to each group and it has been investigated for variable terms. Methods. We have analyzed the refraction inspection record of 50 students(boys 19, girls 31) who visited optical shops and more than two times in one year. Results. The subject of study were 50 students(boys 19, girls 31). 1. The distribution of spherical equivalent power with ages : boys A group -2.42D, girls A group -2.53D, boys B group -2.63D, girls B group -2.78D. boys B group -2.63D, girls B group -2.78D. 2. The monthly variation of spherical equivalent power : -0.055D(A), -0.04D(B) in boys, and -0.065D(A), -0.07D(B) in girls. Conclusions. Considering monthly variations and Supposing that the time of changing spectacles degrees were the time of refracting inspection. The result : 3.8 month for A group, 4.5 month for B group in boys, and 3.5 month for A group, 5.2 month for B group in girls.

• Journal of Korean Ophthalmic Optics Society
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• v.14 no.1
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• pp.39-45
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• 2009

Purpose: The purpose of this study is to compare the visual performance by contrast sensitivity (CS) and disability glare (DG) in low astigmatic eyes corrected with toric soft lenses and other optical corrections. Methods: Twenty university students with myopia (-1.00 to -6.50D Sph. with astigmatism up to 1.50 cyl) were enrolled and corrected by five different methods: 1) soft toric lenses; 2) spherical soft contact lenses; 3) RGP lenses; 4) best spectacle corrected visual acuity; 5) spherical equivalent spectacles. All subjects had corrected vision acuity of 20/20 or better. Contrast sensitivity and disability glare were measured using the OPTEC 6500 contrast sensitivity view-in tester included the EyeView Functional Vision Analysis software at photopic or mesopic conditions with glare. Results: At photopic condition, best corrected spectacle wearers had the highest monocular contrast sensitivity at all spatial frequency followed by soft toric lenses, RGP lenses, spherical equivalent spectacles, and spherical soft contact lenses. However, all of them were in normal contrast sensitivity value at photopic condition. At mesopic condition with glare, toric soft lenses were the highest and followed by RGP lenses, spherical equivalent spectacles, best spectacle corrected visual acuity and spherical soft contact lenses. It was observed that spherical soft contact lens wearers demonstrated lower range than normal contrast sensitivity value at mesopic condition with glare. Conclusion: Toric soft lenses gave better visual performance than spherical soft lenses in low astigmatic eyes. Subjects requiring the use of contact lenses under mesophic conditions could benefit from toric soft lenses.

• Journal of the Korean Mathematical Society
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• v.37 no.2
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• pp.285-295
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• 2000

It is well-known that there is no analogue to the Riemann mapping theorem in the higher dimensional case. Therefore, it would be an interesting question to find sufficient conditionsl for domains to be biholomorphically equivalent to the unit bal. In this paper, we investigate this questionin the case where the given domains are generalized complex ellipsoids with spherical boundary points.

• The Journal of the Acoustical Society of Korea
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• v.23 no.1
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• pp.40-46
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• 2004

The equivalent source method (ESM) uses two groups of equivalent source positions. One group includes the first order images of the sound source inside the enclosure. The positions of the other group are usually on a spherical surface some distance outside the enclosure. A proper selection of the positions for the far field sources could greatly improve the performance of the modeling accuracy and reduce the number of the sources to achieve the required accuracy. This study uses optimally distributed far field source positions on the surface of enlarged version of the rectangular enclosure instead of using typical spherical distribution. Simulations using various sizes of the box shaped distribution are executed and optimal positions are searched using an optimization technique from the larger number of candidate positions. The results of using these far field source positions are compared and analyzed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.8
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• pp.1362-1370
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• 2008

This paper describes the design and characteristic analysis of a novel 3-DOF(Degree of Freedom) spherical motor. For multi DOF actuating, several numbers of motors have been used. By the using of normal motors they connected each other in single joint, is necessary to a several type of complex power transmission devices. The 3-DOF spherical motor can drive roll, pitch, and yaw motion in only one unit and it is not necessary to use additional gears and links parts. Therefore the using of 3-DOF spherical motor can eliminate; combined effects of inertia, backlash, non-linear friction, and elastic deformation of gears. In this paper, we propose the novel structured 3-DOF spherical motor and derive its principles of operation. Firstly, we designed concept model of novel structured 3-DOF spherical motor. Next, we derive the control method by calculating the currents. Also, to have intuitive driving control, we express the rotor position in equivalent angle-axis system and determine the exciting period of currents from the calculation result of the currents. To verify the control method, we calculated the currents by the position of rotor. and then we analyzed the characteristics by 3D Finite Element Method when the calculated currents are excited.

• Journal of Korean Clinical Health Science
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• v.1 no.1
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• pp.1-7
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• 2013

Purpose. To analysis the prevalence of the myopia and corneal astigmatism in Korea women university students. Methods. From August 2011 to December 2012, one hundreds subjects were performed in refraction test using the Auto-Keratometry. Results. The mean age of the 100 subjects (200 eyes) was $21.23{\pm}2.34$. The mean spherical refractive power was -$1.78{\pm}1.65$(OD) and -$1.83{\pm}1.67$(OS) Diopter. The mean astigmatism power was $1.22{\pm}0.96$ (OD) and $1.27{\pm}0.91$ (OS). The mean corneal astigmatism was $1.44{\pm}0.81$(OD) and $1.55{\pm}0.93$(OS). Corneal astigmatism was between 0.25 D and 1.25 D in 67.7% of eyes, 1.25 D or higher in 27.5% eyes, and less than 0.25 D in 4.8% of eyes. Astigmatism was with the rule in 65%, against the rule in 31.5%, and oblique in 3.5%. There was a statistical significance between right eye and left eye in the spherical equivalent power(p=0.002). Also there was a statistical significance between spherical power and refractive astigmatism in OD(p=0.006) and OS(0.003) and a statistical significance between corneal astigmatism and refractive astigmatism in OS(p=0.0003). However, there was not a statistical significance between spherical power and corneal astigmatism in OD(p=0.08) and OS(0.1) and a statistical significance between corneal astigmatism and refractive astigmatism in OS(p=0.48). Conclusions. In this study, these results suggested that the analysis of the refractive myopia and corneal astigmatism can provide the visual correct and useful diagnosis information for the eyewear dispensing, contact lens fitting and corneal refraction surgery.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.11
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• pp.1187-1194
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• 2009

During the last decade, possibility of flaw occurrences has been rapidly increased world-widely as the increase of operating times of petro-chemical facilities. For instance, from a recent in-service inspection, three different sized surface cracks were detected in welding parts of a spherical oxygen holder in Korea. While API579 code provides corresponding engineering assessment procedures to determine crack driving forces, in the present work, numerical analyses are carried out for the cracked oxygen holder to investigate effects of complex geometry, analysis model and residual stress. With regard to the detailed finite element analysis, stress intensity factors are determined from both the full three-dimensional model and equivalent plate model. Also, as an alternative, stress intensity factors are calculated for equivalent plate model by employing the noted influence stress function technique. Finally, parametric structural integrity evaluation of the cracked oxygen holder is conducted in use of failure assessment diagram method, J/T method and DPFAD method. Effects of the geometry and so forth are examined and key findings from the simulations are fully discussed, which enables to determine practical safety margins of spherical components containing a defect.