• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.222-222
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• 2013

GaN 기반 반도체는 넓은 bandgap을 가지고 있어 가시광부터 자외선까지 다양한 광전소자에 유용하게 사용된다. 광전소자중 발광다이오드의 경우 대부분 사파이어 기판위에 성장된다. 하지만 사파이어와 GaN의 격자 불일치 및 열팽창 계수의 차이로 인해 고품질의 GaN를 성장하기가 어렵다. 특히 열팽창 계수의 차이는 GaN 성장 공정이 고온에서 이루어지기 때문에 성장후 상온으로 온도가 떨어질 때 웨이퍼의 bowing을 발생시키고 동시에 dislocation이나 crack과 같은 결함이 생성되 GaN 성장막의 품질을 떨어트린다. 웨이퍼의 크기가 커지면 커질수록 웨이퍼 bowing은 커져 이에 대한 연구는 중요하다. 본 논문에서 2인치 사파이어 기판위에 성장된 GaN의 bow특성을 알아보기 위해 먼저 simulation을 하였고 실제로 성장된 GaN 웨이퍼와 비교를 하였다. c-plane 사파이어 기판위에 성장된 c-plane GaN의 bow특성을 알아보기 위해 성장 온도 $1,100^{\circ}C$에서 GaN두께를 1 ${\mu}m$에서 10 ${\mu}m$까지 1 ${\mu}m$씩 변화시켜 가며 simulation을 하였다. GaN두께가 1 ${\mu}m$일때는 bow가 11 ${\mu}m$, 6 ${\mu}m$ 일때는 54.7 ${\mu}m$, 10 ${\mu}m$ 일때는 108 ${\mu}m$를 얻어 GaN두께가 1 ${\mu}m$씩 증가할 때 마다 bow가 약 10 ${\mu}m$씩 증가하였다. 성장온도에 대한 영향을 알아보기 위해 $700^{\circ}C$에서 $1,200^{\circ}C$까지 $100^{\circ}C$씩 증가시켜며 bow특성 simulation을 하였다. 6 ${\mu}m$성장된 GaN의 경우 성장온도가 $100^{\circ}C$ 씩 증가할 때 bow는 약 6 ${\mu}m$ 증가하였다. 실제 성장된 c-plane GaN웨이퍼와 비교하기 위해 GaN을 각각 3 ${\mu}m$와 6 ${\mu}m$를 성장시켰고 high resolution x-ray diffraction장비를 사용하여 bow를 측정한 결과 각각 28 ${\mu}m$와 61 ${\mu}m$ 였고 simulation결과는 각각 33 ${\mu}m$와 65.5 ${\mu}m$를 얻어 비슷한 결과를 보였다. c-plane 사파이어 기판위에 성장된 c-plane GaN는 방향에 무관하게 동일한 bow 특성을 가지는 반해 r-plane 사파이어 기판위에 성장된 a-plane GaN는 방향에 따라 다른 bow특성을 보인다. a-plane GaN 이방향성적인 bow 특성을 알아보기 위해 simulation을 하였다. $1,100^{\circ}C$에서 a-plane GaN을 성장할 때 두께가 1 ${\mu}m$ 증가할 때마다 bow가 c축 방향으로는 21.7 ${\mu}m$씩 증가하였고 m축 방향으로는 11.8 ${\mu}m$ 씩 증가하여 매우 큰 이방향성적인 bow 특성을 보였다. 실제 r-plane 사파이어 기판위에 성장된 a-plane GaN의 bow를 측정하였고 simulation 결과와 비교해 보았다.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1259-1265
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• 2020

A beta ray scanner was proposed for in-situ discrimination of beta and gamma ray radioactivity. This scanner is based on the principle that gamma and beta rays experience different changes in detection efficiency in scintillators with different geometries, especially with regard to the scintillator thickness. The ratios of the counting rates of gamma rays (R_gamma), beta rays (R_beta), and sample measurements (R_total) in a thick scintillator to those in a thin one are reported. The parameter X_thick, which represents the counting rate contributed by beta rays to the total counting rate in the thick scintillator, was derived as a function of those ratios. The values of R_gamma and R_beta for ⁶⁰Co and ⁹⁰Sr sources were estimated as 3.2 ± 0.057 and 0.99 ± 0.0049, respectively. The estimated beta ray contributions had relative standard deviations of 2.05-4.96%. The estimated range of the beta rays emitted from ⁹⁰Sr was 19 mm as per the Monte Carlo N-Particle simulation, and this value was experimentally verified. Homogeneous and surface contaminations of ⁶⁰Co and ⁹⁰Sr-⁹⁰Y were simulated for application of the proposed method. The counting rate contributed by the beta rays was derived and found to be proportional to the concentration of ⁹⁰Sr-⁹⁰Y contamination.

• Journal of Korea Multimedia Society
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• v.20 no.12
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• pp.1980-1991
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• 2017

Many stroke patients undergoing rehabilitation therapy require a quantitative indicator for the evaluation of body function in paretic and non-paretic regions. In this study, the impedance parameters were acquired to assess the physical status in the upper extremity of thirty six stroke patients with hemiplegia caused by cerebral hemorrhage (10 patients) and cerebral infarction (26 patients), using bioelectrical impedance. Prediction marker (PM), phase angle (PA), PM/PA, and resistance (R) versus reactance ($X_c$) were utilized to evaluate the functional status of the paretic and non-paretic regions. In addition, the hand grip strength (HGS) and the pinch strength (lateral, palmer, tip) were measured on the upper extremity of hemiplegic stroke patients. PM was distributed in inversely proportional to HGS, but PA was distributed in proportional to HGS. However, there were a number of patients with HGS of 0, regardless of the impedance parameters (PM, PA, R vs. $X_c$). Paretic and non-paretic status in upper extremity of these patients could not be analyzed using impedance parameters. At the rehabilitation therapist's instructions, they were unable to move the hand and fingers of the paretic upper extremity by cranial nerve damage, motor nerve damage, and severe cognitive decline.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.47 no.4
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• pp.419-427
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• 2011

Simulation technique for the fish behavior was applied to estimate fish school movement in the cage net. Individual-based fish behavior model (Huth and Wessel, 1991) was evaluated in a free area to understand the characteristics for the model, and the movement in the cage net was simulated by defining the fish reaction against the displacement of cage net. As a result, the distance to the net was not considerably changed and the space among fishes in cage net was slightly decreased by reducing the net space. Swimming area was, however, significantly affected by changing the net space and the relationship between swimming area and net displacement was theoretically estimated as y=-0.21x+1.02 ($R^2$=0.96). these results leads the conclusion that individual-based model was appropriated to describe the fish school reaction in the cage net and be able to use for evaluating the influence on cultured fish.

• Journal of the East Asian Society of Dietary Life
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• v.16 no.3
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• pp.242-250
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• 2006

The purpose of this study was to identify tourist product factor combinations which confer the highest utility to tourists and to establish the relative importance of factors in terms of their contribution to total utility across gender. Among 250 questionnaires, 230 questionnaires were utilized for the analysis. $X^2$ analysis, Conjoint model, Max. Utility model, BTL model, Logit model, K-means cluster analysis, and one-way anova analysis were used for this study. The findings from this study were as follows. First, the Pearson's R and Kendall's tau statistics showed that the model fitted the data well across gender. Second, it was found that total respondents and three clusters regarded taste price as the very important factor across gender. Third, it was found that the male and female tourists most preferred product with light red color, shaped package, and highly pungent taste sold at a cheap price in factory. Fourth, it was found that the male tourists most preferred simulation product with light red color, shaped package, and highly pungent taste sold at a cheap price in factory. The female tourists most preferred simulation product with light red color, shaped package, and mild taste sold at a cheap price in factory. Finally, the results of the study provide some insights into the types of effective product designs that can be successfully developed by marketers.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.26 no.2
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• pp.151-157
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• 2017

Hydraulic equipment have been traditionally used for constructing machines with high power density and durability. In particular, pumps and motors are considered essential equipment, and are consistently investigated to find suitable methods for optimal utilization of their characteristics. A kinematic analysis of a swash-plate-type piston motor model using the hydraulic analysis program SimulationX$^{(R)}$ to model a nine-piston motor and simulate a swash-plate angle with a low-pulsation and high-efficiency performance of the motor has been provided in this paper. Finally, along with the theoretical consideration of the stroke, the effect of changing strokes and notch shape (V, U, non-type) on the pulsation is simulated to analyze and determine the effects of reduction in pulsation. The optimal swash-plate angle and stroke thus obtained will reduce the trial and error in future design.

• Journal of Korea Foundry Society
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• v.28 no.5
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• pp.231-236
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• 2008

H-NCM(Hong-Nanocast Method)has several benefits such as a lower porosity defect and high quality casting comparing to conventional die casting. Influence of casting parameters of hybrid-lower arm in rheocasting process on the slurry flow and the amount of porosity defect was investigated using experimental and simulation methods. In the present study, the Carreau model was adopted to simulate the pattern of rheological flow. Optimal casting paremeters such as injection speed and stroke variations were established. Sound products with integral microstructure and sound shape of joinning different materials of Al and steel pipe without deforming the steel pipe were obtained by the H-NCM slurry and X-ray analysis also showed integral condition throughout the entire parts.

• Fashion & Textile Research Journal
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• v.23 no.2
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• pp.237-246
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• 2021

This study aims to analyze short sleeve cycling tops from three brands for a change in garment fit and pressure depending on the static and cycling postures. To this end, it used a 3D virtual garment system to virtualize the garments. Further, a cross-section of the 3D virtual garment data was obtained, and the space length was measured in the design-X program to prove the objectivity of the 3D virtual garment. The results indicated that three brands had a large space length at the front than the back because of the bent posture in cycling. Therefore, appropriate ease was required for the waist and abdomen. Although there were various cutting lines of the bodice panel by brand, the design of the cutting lines should consider the changes in the surface to reflect the bent posture in cycling. The results of this experiment confirmed that the wrinkles present in the 3D virtual garment were reflected in the cross-section and that the space length was small in the high-stress area, as shown in red. Therefore, it was proven the stress of the 3D virtual garment could be used for 3D virtual garment evaluation.

• Journal of the Korean Statistical Society
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• v.30 no.3
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• pp.347-366
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• 2001

Robust analogues of the likelihood ratio test are considered for testing of hypotheses involving multiple discrete distributions. The test statistics are generalizations of the Hellinger deviance test of Simpson(1989) and disparity tests of Lindsay(1994), obtained by looking at a 'penalized' version of the distances; harris and Basu (1994) suggest that the penalty be based on reweighting the empty cells. The results show that often the tests based on the ordinary and penalized distances enjoy better robustness properties than the likelihood ratio test. Also, the tests based on the penalized distances are improvements over those based on the ordinary distances in that they are much closer to the likelihood ratio tests at the null and their convergence to the x$^2$ distribution appears to be dramatically faster; extensive simulation results show that the improvement in performance of the tests due to the penalty is often substantial in small samples.

• Communications for Statistical Applications and Methods
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• v.17 no.4
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• pp.493-505
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• 2010

Developing a test for independence of random variables X and Y against the alternative has an important role in statistical inference. Kochar and Gupta (1987) proposed a class of tests in view of Block and Basu (1974) model and compared the powers for sample sizes n = 8, 12. In this paper, we evaluate Kochar and Gupta (1987) class of tests for testing independence against quadrant dependence in absolutely continuous bivariate Farlie-Gambel-Morgenstern distribution, via a simulation study for sample sizes n = 6, 8, 10, 12, 16 and 20. Furthermore, we compare the power of the tests with that proposed by G$\ddot{u}$uven and Kotz (2008) based on the asymptotic distribution of the test statistics.