• 한국음향학회지
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• 제10권3호
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• pp.13-18
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• 1991

본 연구에서는 취약한 고체의 표면에 존재하는 crack에 탄성표면파를 입사 시켰을 때 발생하는 반사계수를 측정하여 파괴응력을 해석하는 방법을 연구 분석하였다. Crack이 존재하는 취약한 고체에서의 파괴응력은 임계응력확대계수와 정규화된 최대응력확대계수의 함수로써 나타나며, 이 때 정규화된 최대응력확대계수는 탄성표면파의 반사계수를 측정하여 구할 수 있었다. 실험을 위하여 Pyrex glass원판 중앙에 깊이가 0.5mm~0.9mm인 crack을 제작하였고, SAW wedge transducer를 피치캐치(pitch-catch) 모드로 구성하여 반사계수를 측정하고 파괴응력값을 산출하였으며 UTM(Universal Testing Machine)으로 측정한 값과 비교 분석하였다.

• Journal of applied mathematics & informatics
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• 제39권5_6호
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• pp.717-723
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• 2021

The purpose of the present paper is to give sufficient conditions for normalized Dini function which is the special combination of the generalized Bessel function of first kind to be in the classes k-starlike functions and k-uniformly convex functions.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1734-1737
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• 2015

Insulating characteristics of Cl₂-He mixture gases in gas discharges were analysed to evaluate ability of these gases for using in medium voltage and many industries. These are electron transport coefficients, which are the electron drift velocity, density-normalized longitudinal diffusion coefficient, and density-normalized effective ionization coefficient, in Cl₂-He mixtures. A two-term approximation of the Boltzmann equation was used to calculate the electron transport coefficients for the first time over a wide range of E/N (ratio of the electric field E to the neutral number density N). The limiting field strength values of E/N, (E/N)_lim, for these binary gas mixtures were also derived and compared with those of the pure SF₆ gas.

• 에너지공학
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• 제22권2호
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• pp.197-204
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• 2013

A cyclic variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under idling conditions. The coefficient of variation (COV) in indicated mean effective pressure (IMEP) defines the cyclic variability in indicated work per cycle, and it has been found that vehicle drivability problems usually result. For analysis of the cyclic variations in spark ignition engines at idling, the results show that cyclic variability by the COV, COV of IMEP, the lowest normalized value (LNV), and burn angles can help to design the spark ignition engine.

• Journal of Mechanical Science and Technology
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• 제14권5호
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• pp.518-529
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• 2000

A detailed and thorough parametric study of digital image correlation method is presented. A theoretical background and development of the method were introduced and the effects of various parameters on the determination of displacement outputs from the raw original and deformed image information were examined. Use of the normalized correlation coefficient, the use of 20 to 40 pixels for a searching window side, 6 variables searching, bi-cubic spline sub pixel interpolations and the use of coarse-fine search are some of the key choices among the results of parametric studies. The displacement outputs can be further processed with two dimensional curve fitting for the data noise reduction as well as displacement gradient calculation.

• Journal of Mechanical Science and Technology
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• 제14권10호
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• pp.1151-1158
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• 2000

Combustion analysis based on cylinder-pressure provides a mechanism through which a combustion researcher can understand the combustion process. The objective of this paper was to identify the most significant sources of cycle-to-cycle combustion variability in a spark ignition engine at idle. To analyse the cyclic variation in a test engine, the burn parameters are determined on a cycle-to-cycle basis through the analysis of the engine pressure data. The burn rate analysis program was used here and the burn parameters were used to determine the variations in the input parameter-i. e., fuel, air, and residual mass. In this study, we investigated the relationship of indicated mean effective pressure (IMEP), coefficient of variation (COV) of IMEP, burn angles, and lowest normalized value (LNV) in a spark ignition engine in a view of cyclic variations.

• 정보처리학회논문지B
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• 제10B권1호
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• pp.73-80
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• 2003

본 논문에서는 기준영상과 탐색영상 사이의 대응되는 특징 점을 정합 하는 알고리즘을 제안한다. 두 영상에서 특징 점을 찾기 위하여 Harris의 코너 점 검출기를 사용하였다. 기준영상의 각 특징 점에 대해, 정규상관계수가 임계치 이상인 탐색영상의 특징 점들로 후보 정합 점을 구한다. 최종적으로 동적 프로그래밍을 사용하여 후보 정합 점들 중에서 대응되는 특징 점을 구한다. 실험으로 인위적인 영상과 실제 영상에서 특징 점을 정합 하는 결과를 보였다.

• 한국지능시스템학회논문지
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• 제22권3호
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• pp.287-293
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• 2012

본 논문에서는 영상의 다차원 명암도 증감에 기반을 둔 유사도 측정에 의한 효율적인 영상정합 방법을 제안하였다. 여기서 다차원 명암도는 영상의 4방향을 고려한 유사성 판정으로 영상이 가지는 속성을 더욱 더 많이 반영하기 위함이고, 명암도 증감은 인접 픽셀간의 밝기변화를 고려함으로써 좀 더 포괄적으로 유사성을 측정하기 위함이다. 또한 측정된 4방향 각각의 명암도 증감에 대한 정규상호상관계수를 구하고, 그 각각에 바탕을 둔 전체 정규상호상관계수, 각 방향의 상관계수에 대한 산술평균과 단순 곱 및 최대값으로 정규화된 상관계수의 산술평균과 단순 곱으로 정의된 유사도 계수로 각각 정합을 측정하였다. 제안된 방법을 22개의 243*243 픽셀 얼굴영상과 9개의 500*500 픽셀 인물영상을 대상으로 각각 실험한 결과, 영상의 속성을 잘 반영한 우수한 정합성능이 있음을 확인하였다. 특히 각 방향의 상관계수에 대한 산술평균 유사도가 가장 우수한 신뢰성을 가지는 정합척도임을 알 수 있었다.

• Tribology and Lubricants
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• 제11권1호
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• pp.27-36
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• 1995

Maximum allowable PV values of oilless composite bearing materials (70% epoxy-resin/30% Graphite) were measured and compared at various types of test rigs that have different contact geometry and the operating conditions. Test results showed that material failure was mainly characterized by the sharp increase in both coefficient of friction and surface temperature, and different PV values were measured under different Contact geometry. The discrepancy in measurement of PV values was analyzed in the light of theoretical frictional heating analysis. Results show that surface temperature rise depends on its contact geometry, and PV values could be overestimated in the testing conditions of high sliding velocity. Test data of different contact geometry were normalized by using a normalized contact pressure and sliding velocity; it showed a good correlation. This work suggests that normalized PV values could be more effective in evaluating bearing materials than conventional PV values for a design parameter of journal bearings.

• 소음진동
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• 제6권4호
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• pp.475-479
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• 1996

Recently, fiber optic hydrophone is a subject which has attracted as a underwater acoustic sensor. In this paper, a length of optical fiber is bonded to an end-capped hollow cylinder of some elastic material, e. g. aluminum and glass-pyres. The normalized sensitivity is derived according to the direction of polarization. Derived sensitivity equations are simulated for two different mandrel materials. The results are also compared to the McMahon's results which calculated for an average Pockel coefficient. Based on the numerical simulation normalized sensitivity is propotional to the inner to outer diameter ratio.