• Journal of the Korean Ceramic Society
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• v.26 no.1
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• pp.37-42
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• 1989

Periodic layered domain structures in doped LiNbO3 crystals grown by Czochralski method were obtained by thermal fluctuation and crystal rotation with inhomogeneous radial temprature distribution. The stressinduced domain formation mechanism model was suggested and discussed.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.27-29
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• 1996

We describe the formation of large-scale inhomogeneous structure of expa-nding Universe on the basic of two components system-usual nonrelativistic particles and dark matter, with taking into account their interaction.

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.37-38
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• 2007

• Bulletin of the Korean Space Science Society
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• 2004.10b
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• pp.90-90
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• 2004

• Proceedings of the Optical Society of Korea Conference
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• 1997.08a
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• pp.89-89
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• 1997

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.2
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• pp.1-8
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• 2004

A cylindrical constant volume combustion chamber was used to investigate the exhaust emission characteristics of homogeneous charge, stratified pattern and inhomogeneous charge under various conditions using gas chromatography. In the case of homogeneous charge condition, the $CO_2$ concentration is proportional to excess air ratio and overall charge pressure, the $CO_2$ concentration is proportional to excess air ratio and the UHC concentration is inversely proportional to ignition time and overall charge pressure. In the case of stratified pattern, the RI(rich injection) condition shows better exhaust emission characteristics, especially $CO_2$, than that of HI (homogeneous injection) or LI (lean injection) conditions. In inhomogeneous charge conditions, when initial charge pressure is increased, $CO_2$ and UHC concentration is reduced but $O_2$ concentration is increased. And when the excess air ratio of initial charge mixture is 3.0, UHC and $CO_2$concentration show lowest values.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.3 no.1
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• pp.33-41
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• 1992

In this paper the propagation problems of waves nomally incident upon an anisotropic medium with arbitrary permittivity tensors are analyzed through the variational finite element method. First, a variational equation is derived from the new approach basd on the induction theorm, reactions, and reciprocity. Next, by using the finite element method, the propagation problems are solved from the obtained functional. Specially, the reflection and transmission coefficient and axis ratio are obtained on the case of normally incident upon a homogeneous and inhomogeneous anisotropic medium such as cold mgnetoplasma slab and showed agreement with those of the previous method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.12
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• pp.1933-1943
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• 2001

A micromechanical model is presented for superplasticity in which heterogeneous microstructures are coupled with deformation behavior. The effects of initial distributions of grain size, and their evolutions on the mechanical properties can be predicted by the model. Alternative stress rate models such as Jaumann rate and rotation incremental rate have been employed to analyze uniaxial loading and simple shear problems and the appropriate modeling was studied on the basis of hypoelasticity and elasto-viscoplasticity. The model has been implemented into finite element software so that full process simulation can be carried out. Tests have been conducted on Ti-6Al-4V alloy and the microstructural features such as grain size, distributions of grain size, and volume fraction of each phase were examined for the materials that were tested at different strain rates. The experimentally observed stress-strain behavior on a range of initial grain size distributions has been shown to be correctly predicted. In addition, the effect of volume fraction of the phases and concurrent grain growth were analyzed. The dependence of failure strain on strain rate has been explained in terms of the change in mechanism of grain growth that occurs with changing strain rate.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.3
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• pp.231-238
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• 2007

Ultrasonic inspection of austenitic steel weldments is a truly difficult task due to complicated wave propagation phenomena such as beam skewing, splitting and distortion. In order to understand these phenomena and design proper inspection procedures, simulation is increasingly paid more attention to. This article addresses a ray tracing based approach to determine incident angle and position of optimal wave mode ultrasonic beam for flaw detection in anisotropic and inhomogeneous austenitic steel weldments. Specially, the optimal mode of ultrasonic wave wave is selected by ray tracing simulation, and an optimization approach based on ray tracing and bi-section search is proposed in order to find the ray path connecting two given points in weldments. With help of this approach, the optimal incident angle and position of ultrasonic beam can be determined for a given flaw position.

• Journal of electromagnetic engineering and science
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• v.18 no.1
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• pp.52-57
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• 2018

Surface dielectric barrier discharge (SDBD), which is widely used to control turbulence in aerodynamics, has a significant effect on the radar cross-section (RCS). A four-way linearly synthesized SDBD air plasma actuator is designed to bolster the plasma effects on electromagnetic waves. The diffraction angle is calculated to predict the RCS because of the periodic structure of staggered electrodes. The simplified plasma modeling is utilized to calculate the inhomogeneous surface plasma distribution. Monostatic RCS shows the diffraction in the plane perpendicular to the electrode array and the notable distortion by plasma. In comparison, the overall pattern is maintained in the parallel plane with minor plasma effects. The trends also appear in the bistatic RCS, which has a significant difference in the observation plane perpendicular to the electrodes. The peaks by Bragg's diffraction are shown, and the RCS is reduced by 10 dB in a certain range by the plasma effect. The diffraction caused by the actuator and the inhomogeneous air plasma should be considered in designing an SDBD actuator for a wide range of application.