• Journal of KSNVE
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• v.10 no.4
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• pp.584-595
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• 2000

We design a new actuator for high density optical device in order to control the radial tilting motion. The newly designed actuator makes it possible to control the tilting motion actively, while the coventional actuator compress tilting motion with passive spring. First of all, We present 3-dimensional modeling of actuator and accomplish the modal analysis and magnetic analysis of actuator. Due to these results, a new designed actuator has performance of high sensitivity and high second resonance frequency. Secondly, We present the 3-DOF dynamic modeling of the 4-wire spring type actuator. sensitivity analysis is performed to consider the assembling error, such as the difference of mass center and force center. From these results, the sensitivities of rotation due to the assembly error are revealed and design criteria of rotation is presented. And experimental results of a newly designed actuator are presented and compared with theoretical results. Finally, We propose a dynamic tilt compensation and high acceleration actuator for high density optical storage devices.

• Applied Microscopy
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• v.17 no.1
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• pp.1-15
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• 1987

Testes from the allied rock wallaby(Petrogale assimilus) have been examined by the electron microscopy in thin sections in order to examine spermiogenesis and structure of spermatozoa. The spermiogenesis can be divided into nine stages: early Golgi, late Golgi, collapsing, nuclear protrusion, condensation and flattening, nuclear shaping, rotation, nuclear ring contraction, and maturation. The acrosome has been abruptly formed following the collapse of expanded acrosomal vesicle without the cap stage described in the eutheria. The flatly condensed nucleus rotates obliquely to the axis of the axial filament complex and the folded acrosome covers the anterior third of the dorsal nuclear surface forming a wide subacrosormal space as the nuclear ring has contracted. The Sertoli cell reaction and spur are prominent during the nuclear protrusion and rotation stages. A mature spermatozoon has S-shape head which has an extended part reaching to the vicinity of the middle piece.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.11
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• pp.2723-2729
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• 1993

Moire principles are applied to the measurement of the spindle radial error motion. As opposed to conventional techniques, no master cylinder or ball is needed in the measurement so that the offset and out-of-roundness errors of the master can be inherently eliminated. Two periodic circular gratings are used, one is made on the spindle and the other is held stationary on the reference frame. When the two gratings are seen superimposed during spindle rotation, an interference fringe pattern is observed from which the information on the eccentricity between the two gratings can be extracted with high precision. The optical design and fringe analysis techniques of a prototype measurement system are described in detail with exemplary measurement results.

• Research in Mathematical Education
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• v.18 no.1
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• pp.41-54
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• 2014

This study investigated the visual-mental capability of pre-service and in-service mathematics teachers as well as academicians making a career change to mathematics teachers with regard to manipulations of two geometric shapes (from 2- to 3-dimensional). Moreover, it investigated whether there are differences between the visual-mental capability of these participant groups. Findings illustrate that most of the participants demonstrate an adequate visual capability relating to the task dealing with a cube. Conversely, very low percentage of participants manifested a visual-mental capability in a task requiring the identification of a solid resulting from rotation of a square page, whose diagonal serves as the rotation axis. The study indicates that learners' high visual view should be developed in order to enhance their visual-mental capability.

• Korean Journal of Optics and Photonics
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• v.11 no.1
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• pp.19-24
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• 2000

Optical transmission characteristics of retardation film for obliquely incident light is calculated by using extended Jones calculus and it is geometrically interpreted on Poincare sphere representation as rotational transformation. The characteristics of a retardation film is that while the rotation axis is fixed at a point on the Equator of the Poincar sphere, the rotation angle varies with the direction of incidence. This property can be compensated by using a tandem arrangement of the two optical films whose optic axes do not coincident, and this method can be used for the improvement of the viewing angle characteristics of BTN cells. cells.

• Transactions of Materials Processing
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• v.3 no.3
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• pp.320-334
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• 1994

A set of full size cold rolled steel sheets has been prestrained in the direction of rolling by uniform tensile elongation of 3% and 6%. Then mid-sized tensile specimens were cut from each of the full size sheets at 30, 45, 60 and 90 degrees to the rolling direction. The mid-sized tensile specimens were then prestrained again by uniform tensile elongation by 1%, 2%, 5%, 10% and 15%. finally, miniature tensile specimens were prepared from each of the mid-sized specimens at every 10 degrees to the specimen axis. From the tensile tests on miniature specimens material's hardening behavior under non-proportional loading has been investigated. There are a number of new observations which has not been known to the authors before current work. One of them is continuous reservation of orthoropic symmetry during tensile elongation of mid-sized specimens. Another is continuous rotations of orthotropy axes. Existing theories seem to fail to explain this observations. A new model is proposed in relation to the rotation of orthotropy axes.

• Interaction and multiscale mechanics
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• v.4 no.1
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• pp.1-16
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• 2011

The inverse problem about the theoretical analysis of a drill string bending in a channel of an inclined bore-hole with localized geometrical imperfections is studied. The system of ordinary differential equations is first derived based on the theory of curvilinear flexible elastic rods. One can then use these equations to investigate the quasi-static effects of the drill string bending that may occur in the process of raising, lowering and rotation of the string inside the bore-hole. The method for numerical solution of the constructed equations is described. With the proposed method, the phenomenon of the drill column movement, its contact interaction with the bore-hole surface, and the frictional seizure can be simulated for different combinations of velocities, directions of rotation and axial motion of the string. Geometrical imperfections in the shape of localized smoothed breaks of the bore-hole axis line are considered. Some numerical examples are presented to illustrate the applicability of the method proposed.

• Current Optics and Photonics
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• v.5 no.1
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• pp.72-76
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• 2021

The polarized micro-photoluminescence spectrum was analyzed to investigate the anisotropic localized states in a single GaAs quantum ring. An energy difference of ~0.1 meV was observed from the perpendicularly polarized spectrum measured by a pair of linear analyzers. Spectral dependence of the polarized emission was also characterized in terms of rotation and ellipticity angles using four Stokes parameters. While the rotation angle indicates the symmetric axis of an anisotropic quantum ring with a small variation (± 2°), the ellipticity angle varies from 7.4° down to -2.5°. We conclude that optical anisotropy and birefringence are induced by the crescent-like lateral shape of localized states.

• Journal of Web Engineering
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• v.18 no.8
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• pp.837-864
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• 2020

We introduce a new type of 3D text-based CAPTCHA, called DotCHA, which relies on human interaction and overcomes the limitations of existing 2D and 3D CAPTCHAs. DotCHA asks users to rotate a 3D text model to identify the correct letters. The 3D text model is a twisted form of sequential 3D letters around a center pivot axis, and it shows different letters depending on the rotation angle. Because each model consists of many small spheres instead of a solid letter model, DotCHA is classified as a scatter-type CAPTCHA and resists character segmentation attacks. Moreover, DotCHA is resistant to machine learning attacks because each letter is only identified in a particular direction. We demonstrate that DotCHA is resistant to existing types of attacks while maintaining usability.

• Korean Journal of Optics and Photonics
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• v.5 no.3
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• pp.411-417
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• 1994

The electro-optic polarization transmission characteristics of a liquid crystal (LC) cell is represented by a rotational transformation on the Poincare sphere, and its characteristic parameters, the angle and the axis of the rotation, are experimentally determined with respect to the voltage applied to the LC cell. From the experimental data obtained, we determine driving voltage for the LC cell to give the rotation angle near $180^{\circ}$ of the rotation for the change of the state of the LC cell from non-select to select state, which is a necessary condition for the realization of maximally bright images. The directions of the transmission axes of the polarizer and the analyzer which form a liquid crystal display panel together with the LC cell, are determined from the general characteristics of the rotaional transformation of the LC cell. cell.