• Bulletin of the Korean Chemical Society
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• v.28 no.4
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• pp.533-537
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• 2007

This paper describes the heteroepitaxial growth of single-crystalline 3C-SiC (cubic silicon carbide) thin films on Si (100) wafers by atmospheric pressure chemical vapor deposition (APCVD) at 1350 oC for micro/nanoelectromechanical system (M/NEMS) applications, in which hexamethyldisilane (HMDS, Si2(CH3)6) was used as a safe organosilane single-source precursor. The HMDS flow rate was 0.5 sccm and the H2 carrier gas flow rate was 2.5 slm. The HMDS flow rate was important in obtaing a mirror-like crystalline surface. The growth rate of the 3C-SiC film in this work was 4.3 μm/h. A 3C-SiC epitaxial film grown on the Si (100) substrate was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Raman scattering, respectively. These results show that the main chemical components of the grown film were single-crystalline 3C-SiC layers. The 3C-SiC film had a very good crystal quality without twins, defects or dislocations, and a very low residual stress.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.4
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• pp.129-135
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• 1996

The area of gear vibration and noise, has recently been the focus of many studies. The proper kinematic and geometric design of gears, the mathematical modeling of gear system are essential for a good design. This work present a gear disign for reducing noise, and practical approaches used for machinery noise reduction slong with the summary of methods available for predicting gear noise in terms of the transmis- sion error, and show a comparative study with other methods. A new tooth profile modification is proposed for reducing vibration and noise of involute gears. The method is based on the use of cubic spline curves. The tooth profile is constrained to assume an involute shape during the loaded operation. Thus the new gear profile assures conjugate motion at all points along the line of action. The new profile is found to result in a more uniform static transmission error compared to not only standard involute profile but also modificated profile therby contributing to the improvement of vibration and noise characteristics of the gear.

• Applied Microscopy
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• v.39 no.4
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• pp.341-348
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• 2009

The crystal structure of nano-crystalline, $BaTiO_3$, with the average particle size of 100 nm was investigated using electron diffraction techniques. We characterized the precession electron diffraction system and then carried out the structure determination using precession electron diffraction and conventional selected area electron diffraction. As a result, it was revealed that $BaTiO_3$ nano-crystalline exist as a mixture of tetragonal structure and cubic structure by precession electron diffraction technique. In addition, it could be turned out that $BaTiO_3$ nano-crystalline is a core-shell structure consisted of a tetragonal phased core and a cubic phased surface layer by theoretical calculation. The thickness of the cubic surface layer was approximately 8.5 nm and the lattice parameters of cubic and tetragonal phases were a=3.999${\AA}$ and a=3.999${\AA}$, c=4.022${\AA}$, respectively. Finally, it is expected that precession electron diffraction is more useful technique for structure determination of complicated nano-crystalline materials because of its higher spatial resolution and minimization of dynamical scattering effect.

• Journal of the Korean Society for Advanced Composite Structures
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• v.2 no.3
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• pp.1-11
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• 2011

The typical truss-lattice material successively packed by repeated cubic symmetric unit cells consists of sub-elements (SE) proposed in this study. The representative continuum model for this truss-lattice material such as the effective strain and stress relationship can be formulated by the homogenization procedure based on the notation of averaged mechanical properties. The volume fractions of micro-scale struts have a significant influence on the effective strength as well as the relative density in the lattice plate with replicable unit cell structures. Most of the strength contribution in the lattice material is induced by axial stiffness under uniform stretching or compression responses. Therefore, continuum based constitutive models composed of homogenized member stiffness include these mechanical characteristics with respect to strength, internal stress state, material density based on the volume fraction and even failure modes. It can be also recognized that the stress state of micro-scale struts is directly associated with the continuum constitutive model. The plastic flow at the micro-scale stress can extend the envelope of the analytical stress function on the surface of macro-scale stress derived from homogenized constitutive equations. The main focus of this study is to investigate the basic topology of unit cell structures with the cubic symmetric system and to formulate the plastic models to predict pressure dependent macro-scale stress surface functions.

• ETRI Journal
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• v.35 no.6
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• pp.1048-1057
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• 2013

In recent years, augmented reality (AR) technologies have been the subject of great interest among many communities. In education applications, old-fashioned materials (or textbooks) are still used, despite remarkable AR developments in the industrial area. We present an AR system for education. Our system consists of an authoring tool that can be used to create educational content, a viewer that plays that content, and an engine to manage the tool and viewer. In our system, a marker unit recognizes a marker printed on a plane or a cubic plane by adaptively adjusting the threshold to have an excellent recognition rate in diverse environments and acquires corresponding data of the marker. Based on the system, we test 142 elementary school students for increased educational benefits using our system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.281-286
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• 2003

A Suspension system of a car is composed of dampers and springs. The dampers and springs usually have nonlinear characteristics. However, the nonlinear characteristics of the springs and dampers through analytical model cannot agree with the experimental results. Therefore, the nonlinearity of the suing and damper should be known from the experimental results. In this study, the methods of system identification for nonlinear dynamic system in time domain are discussed and the nonlinear parameter estimation lot experimental data of an EF-SONATA car was done. The results show that a cubic and a coupled term should be considered to model the suspension system.

• Proceedings of the Korean Information Science Society Conference
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• 1999.10b
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• pp.562-564
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• 1999

래디오시티 렌더링 시스템에 적합한 모델링을 하는데 있어서 수작업을 비롯한 기존의 여러 방법을 적용해 본 결과, 제작하고자 하는 환경 설정에 많은 어려움을 겪었다. 본 논문은 이러한 문제를 해결하기 위해, 인크리먼털 컨벡스 헐 모델링 기법을 응용하여 시스템을 개발하였다. 이 시스템은 기본 데이터 정보를 입력하면 자동적으로 패치와 엘리먼트가 생성되는 프로그램으로, 물체가 많은 환경이나 곡면을 비교적 쉽고, 고속으로 표현할 수 있었다. 그리고 인크리먼털 컨벡스 헐 알고리즘으로 생성된 환경에, 폼 팩터의 대표적인 세 가지 알고리즘들을 비교.평가 해본 결과 Cubic-Tetrahedron 알고리즘이 가장 효율적이었음을 알 수 있었다.

• International Journal of Reliability and Applications
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• v.1 no.1
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• pp.81-87
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• 2000

One of the most important quantities in reliability theory is the expected number of renewals of a system during a given interval. This quantity, the renewal function, is used to determine the optimal preventive maintenance policy and to estimate the cost of a warranty. In this paper we study a parametric approach for a renewal function. The simulation study is presented to compare the relative performance of the introduced estimators of a renewal function. And we show that the proposed parametric estimator performs well.

• Journal of the Optical Society of Korea
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• v.6 no.2
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• pp.21-26
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• 2002

Interferometric metrology with a null CGH(computer-generated hologram) is presented for measuring highly aspheric surfaces used in a large screen projection television system with high accuracy. The cubic spline surface model which works in a single-pass configuration with a refractive index of object space 0 is used for designing a null CGH. A hybrid null corrector with plano-concave lens in front of a CGH is presented to make the CGH easier to fabricate. Experimental results are presented to demonstrate the validity of the proposed technique.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1609-1614
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• 2003

In this study, a practical holographic interferometric tomography system, which is instantaneous and non-contact for measuring three dimensional flow field, was developed. The system consists of holographic recording/reconstruction system, fringe analysis code and computational tomography code and it is developed with Gill environment for general users. The developed system was applied to three-dimensional natural convection from a discrete flush-mounted circular heat source on the bottom of a cubic enclosure. The heat source was located at the off-center of the bottom plate so that three-dimensional temperature field can be achieved. A set of multi-directional holographic interferograms was recorded by employing a double-reference beam, double-exposure holographic technique. Optical pathlength data were extracted from the recorded interferometric data and finally three dimensional temperature field inside the cube was reconstructed.