• 한국정밀공학회지
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• 제20권10호
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• pp.183-190
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• 2003

Major device failures such as die cracking, interfacial delamination and warpage in flip chip packages are due to excessive heat and thermal gradients- There have been significant researches toward understanding the thermal performance of electronic packages, but the majority of these studies do not take into account the combined effects of thermo-mechanical interactions of the different package constituents. This paper investigates the thermo-mechanical performance of flip chip package constituents based on the finite element method with thermo-mechanically coupled elements. Delaminations with different lengths between the silicon die and underfill resin interfaces were introduced to simulate the defects induced during the assembly processes. The temperature gradient fields and the corresponding stress distributions were analyzed and the results were compared with isothermal case. Parametric studies have been conducted with varying thermal conductivities of the package components, substrate board configurations. Compared with the uniform temperature distribution model, the model considering the temperature gradients provided more accurate stress profiles in the solder interconnections and underfill fillet. The packages with prescribed delaminations resulted in significant changes in stress in the solder. From the parametric study, the coefficients of thermal expansion and the package configurations played significant roles in determining the stress level over the entire package, although they showed little influence on stresses profile within the individual components. These observations have been implemented to the multi-board layer chip scale packages (CSP), and its results are discussed.

• 천문학회지
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• 제31권1호
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• pp.51-65
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• 1998

We present B VRI CCD surface photometry for the central $(6'.35\times6'.35)$ regions of the dwarf elliptical galaxies NGC 185 and NGC 205 in the Local Group. Surface brightness profiles of NGC 185 (R<225') and NGC 205 (R<186') show excess components in the central regions. The colors of NGC 185 get bluer inward at R<25', while they remain constant at $R\geq25'$. The colors of NGC 205 get bluer inward at 1'$\approx10^5\; L_\bigodot$. Distributions of dust clouds in the central regions of the two galaxies are also investigated.

• 한국작물학회지
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• 제44권1호
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• pp.78-85
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• 1999

To investigate kernel hardness, a compression test which is widely used to measure the hardness of individual kernels as a physical testing method was made simultaneously with the measurement of friabilin (15KDa) which is strongly associated with kernel hardness and was recently developed as a biochemical marker for evaluating kernel hardness in 79 Korean wheat varieties and experimental lines. With the scattered diagram based on the principal component analysis from the parameters of the compression test, 79 Korean wheat varieties were classified into three groups based on the principal component analysis. Since conventional methods required large amount of flour samples for analysis of friabilin due to the relatively small amount of friabilin in wheat kernels, those methods had limitations for quality prediction in wheat breeding programs. An extraction of friabilin from the starch of a single kernel through cesium chloride gradient centrifugation was successful in this experiment. Among 79 Korean wheat varieties and experimental lines 50 lines (63.3%) exhibited a friabilin band and 29 lines (36.7%) did not show a friabilin band. In this study, lines that contained high maximum force and the lower ratio of minimum force to maximum force showed the absence of the friabilin band. Identification of friabilin, which is the product of a major gene, could be applied in the screening procedures of kernel hardness. The single kernel analysis system for friabilin was found to be an easy, simple and effective screening method for early generation materials in a wheat breeding program for quality improvement.

• Tribology and Lubricants
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• 제36권5호
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• pp.290-296
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• 2020

When two layers of carbon nanotube (CNT) arrays are loaded to mate, the free ends of individual CNTs come into contact at the interface of the two layers. This leads to a higher contact resistance due to a smaller contact region. However, when the free CNT ends of one array penetrate into the mating array, the contact region increases, effectively lowering the contact resistance. To explore the penetration of mating CNTs, we perform molecular dynamic simulations of a simple unit cell model, incorporating four CNTs in the lower array layer coupled with a single moving CNT on the upper layer. The interaction with neighboring CNTs is modelled by long-range carbon bond order potential (LCBOP I). The model structure is optimized by energy minimization through the conjugate gradient method. A NVT ensemble is used for maintain a room temperature during simulation. The time integration is performed through the velocity-Verlet algorithm. A significant vibrational motion of CNTs is captured when penetration is not available, resulting in a specific vibration mode with a high frequency. Due to this vibrational behavior, the random behaviors of CNT motion for predicting the penetration are confirmed under the specific gap distances between CNTs. Thus, the probability of penetration is examined according to the gap distance between CNTs in the lower array and the aspect ratio of CNTs. The penetration is significantly affected by the vibration mode due to the van der Waals forces between CNTs.

• 천문학회지
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• 제39권4호
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• pp.115-123
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• 2006

We present $JHK_S$ near-infrared CCD photometric study for the Galactic open clusters NGC 1641 and NGC 2394. These clusters have never been studied before, and we provide, for the first time the cluster parameters; reddening, distance, metallicity and age. NGC 1641 is an old open cluster with age $1.6{\pm}0.2$ Gyr, metallicity $[Fe/H]=0.0{\pm}0.2$ dex, distance modulus$(m-M)_0=10.4{\pm}0.3\;mag(d=1.2{\pm}02\;kpc)$, and reddening $E(B-V)=0.10{\pm}0.05$ mag. The parameters for the other old open cluster NGC 2394 are estimated to be $age=1.1{\pm}0.2$ Gyr, $[Fe/H]=0.0{\pm}0.2$ dex, $(m-M)_0=9.1{\pm}0.4\;mag(d=660{\pm}120\;pc)$, and $E(B-V)=0.05{\pm}0.10$ mag. The metallicities and distance values for these two old open clusters are consistent with the relation between the metallicities and the Galactocentric distances of other old open clusters. We find the metallicity gradient of 53 old open clusters including NGC 1641 and NGC 2394 to be ${\Delta}[Fe/H]/{\Delta}R_{gc}=-0.067{\pm}0.009\;dex\;kpc^{-1}$.

• 천문학회지
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• 제45권3호
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• pp.71-84
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• 2012

We present a photometric study of the globular clusters (GCs) in the Virgo giant elliptical galaxy M86 based on Washington $CT_1$ images. The colors of the GCs in M86 show a bimodal distribution with a blue peak at ($C-T_1$) = 1.30 and a red peak at ($C-T_1$) = 1.72. The spatial distribution of the red GCs is elongated similar to that of the stellar halo, while that of the blue GCs is roughly circular. The radial number density profile of the blue GCs is more extended than that of the red GCs. The radial number density profile of the red GCs is consistent with the surface brightness profile of the M86 stellar halo. The GC system has a negative radial color gradient, which is mainly due to the number ratio of the blue GCs to the red GCs increasing as galactocentric radius increases. The bright blue GCs in the outer region of M86 show a blue tilt: the brighter they are, the redder their mean colors get. These results are discussed in comparison with other Virgo giant elliptical galaxies.

• 한국환경생태학회지
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• 제9권1호
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• pp.49-55
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• 1995

본 연구는 계룡산 국립공원과 오대산 국립공원의 9개 등산로를 대상으로 등산로의 물리적 조건이 심장박동수에 미치는 영향을 밝히기 위하여 수행되었다. 산오르기 등산은 피검자가 에르고메타를 이용하여 측정한 최대심박수의 84~96%에 해당하는 고된 신체운동이며, 동일한 코스를 내려올 때의 최대심박수는 올라갈 때의 최대심박수에 약 78~93%에 해당하는 값을 나타내었다. 등산로의 경사도는 심박수에 영향을 미치는 것으로 나타났으나, 노폭은 심박수와 무관한 것으로 판단된다. 비시설 등산로에 비하여 나무 또는 돌계단식과 같은 등산로 노면재료가 심박수의 증가에 영향을 크게 미치는 것으로 나타났다.

• 한국의류산업학회지
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• 제15권3호
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• pp.414-422
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• 2013

This study identifies the foot shapes of elderly men by classifying foot types according to the shapes of sole of foot and analyzing individual characteristics. The subjects were 269 elderly men over 60 years of age. Their right feet were measured indirectly with a 2D scanner. The anthropometric measuring items consisted of 38 items that were estimated on the right foot of each subject. The 2D scan data were analyzed by various statistical methods such as factor analysis, ANOVA and cluster analysis using the statistical program SPSS 19.0. A total of 8 factors were extracted through a factor analysis and these factors represent 77.83% of total variance. The 8 factors were: ball and lateral foot protrusion, ball gradient, medial foot protrusion, anterior and posterior foot length ratio, lateral ball length, heel size, toes breadth, and foot length, that explained 77.83% of the total variance. A total of 4 clusters (as their sole type) were categorized using 8 factor scores by cluster analysis. Type 1 was classified as H-type(toes width, foot width, heel width uniform and medial malleolus and lateral malleolus almost no protrusion). Type 2 was classified as V-type(foot width and toes width, wide and heel width narrow). Type 3 was classified as A-type(foot width and heel width, wide but toes width narrow, protruded inside). Type 4 was classified as D-type(protruded outside).

• Nuclear Engineering and Technology
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• 제15권2호
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• pp.142-148
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• 1983

핵급물질에 함유된 미량 희토류윈소인 Sm, Eu, Gd, Dy를 개별 분리하기 위해 Dowex50W$\times$8 양이온교환수지와 $\alpha$-hydroxyisobutyric acid ($\alpha$-HIBA) 사이에서 분배계수를 측정하였다. 양이온교환수지를 이용하여 우라늄매질로부터 미량희토류원소를 군분리한 후 0.40M$\alpha$-HIBA용리액의 pH를 3.40에서 3.60까지 변화시키면서 개별분리하였다. Sm, Eu, Dy은 형광분석법으로 Gd은 비색법으로 정량하였으며 실험결과를 토대로하여 magnesium diuranate(yellow cake) 중의 Sm, Eu, Gd, Dy를 각각 정량하였다

• 약학회지
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• 제36권4호
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• pp.370-378
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• 1992

A simple and sensitive high performance liquid chromatographic method to quantitate ${\alpha}-keto$ acids in serum and urine was investigated. ${\alpha}-Keto$ acids react with 1,2-diamino-4,5-methylenedioxybenzene (DMB) in the presence of 2-mercapto-ethanol and sodium hydrogen sulfite to form highly fluorescent derivatives, substituted 6,7-methylenedioxyquinoxalinol. The derivatization procedure was performed in water bath at $100^{\circ}C$, and completed within 50 min. By the use of a reversed-phase column and multi-step gradient with two solvents, a mixture containing twelve of these derivatives were efficiently resolved within 35 minutes. The optimal wavelengh of the fluorescence detector are ${\lambda}_{ex}=364\;nm$ and ${\lambda}_{em}=445\;nm$. The quantitation of the individual ${\alpha}-Keto$ acids was reproducible with relative standard deviation of $3.0{\sim}7.9%$ and had a detection limits of $10{\sim}60$ fmol, except for p-hydroxyphenylpyruvic acid (960 fmol).