• Journal of Ocean Engineering and Technology
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• v.23 no.4
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• pp.1-5
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• 2009

A dilatometer was used to investigate the effect of cure conditions, mold types and the presence of filler in an epoxy system. These studies showed shrinkage in the cured epoxy when heating it through the glass transition temperature region. The magnitude of the shrinkage, related to stress build up in the epoxy during curing, was influenced by the processing conditions, filler presence and the nature of the mold used to contain the resin. Cure and cyclic cure at a lower temperature, prior to a post cure, decreased the magnitude of observed shrinkage. Cure shrinkage decreased with the number of cyclic cures. Post cured samples outside the mold led to less shrinkage compared with samples in the mold. Sample cured in a silicon mold represented less shrinkage than sample cured in an aluminum mold. Sample containing kaolin filler showed less shrinkage than unfilled sample.

• Journal of the Korean Geotechnical Society
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• v.22 no.8
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• pp.99-106
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• 2006

In the present study, in order to clarify the effects of latent hydraulic property of granulated blast furnace slag (GBF slag) on the liquefaction, GBF slag was cured in the high temperature alkali water (adding the calcium hydroxide, pH=12, water temperature is about $30^{\circ}C$), and then the cyclic and the static tri-axial compression tests were carried out. Then the results were compared with those for Japanese standard sand of Toyoura sand and natural sand of Genkai sand. From the test results, it is clarified that the liquefaction strength of the GBF slag increases with the increase of the curing period by the hardening due to the latent hydraulic property. It is also shown that GBF slag with Dr=50% and 80% which was cured for 189 days in the fresh-water shows cohesion due to developing of latent hydraulic property. In addition, as for the liquefaction strength of GBFS during the hardening process, a linear relation between the cyclic stress ratio $R_{20}$ at the number of stress cycles Nc=20 and cohesion $C_{d}$ was observed. It is also clarified that the liquefaction strength for cured GBF slag in the high temperature alkali water is predicted by the cohesive strength or the unconfined compressive strength.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.47-56
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• 2006

The repeated loading responses of four shear-critical reinforced concrete beams with two different shear span-to-depth ratios, were studied. One series of beams was reinforced using pairs of bundled stirrups with $90^{\circ}$ standard hooks, haying free end extensions of $6d_b$. The companion beams contained shear reinforcement made with larger diameter headed bars anchored with 50mm diameter circular heads. A single headed bar had the same area as a pair of bundled stirrups and hence the two series were comparable. The test results indicate that beams containing headed bar stirrups have a superior performance to companion beams containing bundled standard stirrups with improved ductility, larger energy absorption and enhanced post-peak load carrying capability. Due to splitting of the concrete cover and local crushing, the hooks of the standard stirrups opened resulting in loss of anchorage. In contrast, the headed bar stirrups did not lose their anchorage and hence were able to develop strain hardening and also served to delay buckling of the flexural compression steel. Excellent load-deflection predictions were obtained by reducing the tension stiffening to account for repeated load effects.

• The Korean Journal of Applied Statistics
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• v.28 no.2
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• pp.201-210
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• 2015

Repeated measurements on each variables of interest often arise in bioscience or medical research. We need to account for correlations among repeated measurements to assess the correlation between two variables in the presence of replication. This paper reviews methods to estimate a correlation coefficient between two variables in repeated measurements using the variance-covariance matrix of linear mixed effect models. We analyze acoustic radiation force impulse imaging (ARFI) data to assess correlation between three shear wave velocity (SWV) measurements in liver or spleen and spleen length by ultrasonography. We present how to obtain parameter estimates for the variance-covariance matrix and correlations in mixed effects models using PROC MIXED in SAS.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.33-37
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• 2002

Recently, composites have been widely applied in the sporting goods, automobile, aerospace industry. As the use of advanced composites increase, specific techniques have been developed to repair damaged composite structures. In order to repair the damaged part, it is required that the material in the damaged area be removed first by utilizing the proper method, and prepreg be laid up in the area and cured under vacuum using the vacuum bagging materials. In curing process, either in an oven or autoclave is to be delamination can be occurred in the sound areas during and/or after the exposure to the elevated curing temperature in case that the repair process is repeated. Therefore, this study was conducted to evaluate the degree of degradation of properties of the cured parts and how it affects to the delamination phenomenon between laminated skin and honeycomb core.

• The Korean Journal of Rheology
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• v.10 no.2
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• pp.106-112
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• 1998

항공기용 소재로 개발된 에폭시/탄소섬유 복합재료가 매트릭스의 유리전이온도에 육 박하는 온도주기를 경험할 때 발생하는 복합재료의 구조 및 물성변화를 실험과 모델링을 통 하여 연구하였다. 복합재료의 표준 경화온도인 177$^{\circ}C$에서 2시간 체류시킨후 냉각시키는 바 복 열주기는 복합재료를 취약하게 하여 결국 표면에서부터 미세크랙이발생한다는 것을 알수 있었다. 이러한 열주기에 따른 미세크랙 현상은 매트릭스의 분해반응이 발생할수 있는 유효 표면적을 증가시키고 크랙을 통하여 산소의투과를 용이하게 함으로서 산화반응을 가속화하 여 복합재료시편의 무게감소를 가속화시키는 것으로 판단된다. 특히 본 연구에서는 등온과 등속도 승온조건을 주기적으로 반복하는 열주기 조건을 해석하기 위하여 열주기 조건을 특 정온도에서의 등오시간으로 전환할 수 있는 e-quivalent cycle time(ECT)를 제안하였고 이 를 이용하여 열주기에 의한 복합재료 손상의 가속/감속 현상을 규명할수있었다.

• Journal of Technology Innovation
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• v.19 no.1
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• pp.203-228
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• 2011

본 연구는 소프트웨어적인 기술인 경영정보시스템(MIS)의 발전과정을 기술추격 관점에서 분석한다. 분석사례로는 창업 당시 후발업체로 선진국 기업을 모방하였지만 현재는 MIS 분야에서 선도적인 위치에 서게 된 POSCO를 선정하였다. 기술추격과정 분석을 위해 김인수의 기술혁신단계모델, Henderson and Clark의 유동기 진입이론, Doering and Parayre의 불확실한 기술에 대한 의사결정이론, Nolan의 MIS 발전단계모델 등 네 가지 모델을 활용하였다. 연구결과, POSCO의 MIS기술 발전과정은 기술후진국이 밟는 전형적인 기술추격과정, 즉 경화기${\rightarrow}$과도기${\rightarrow}$유동기로 이행하면서 모방에서 혁신으로 그 위상이 바뀐 것으로 분석되었다. 또한 장치산업이라는 철강산업의 산업적 특성으로 제조기술 및 MIS기술이 커다란 기술패러다임의 변화 없이 유동기로 진입하였으며, MIS 분야에 대한 기업경영자의 역할이 기술추격의 주요 성공요인으로 나타났다. 마지막으로 POSCO는 MIS분야에서 착수${\rightarrow}$확장${\rightarrow}$공식화${\rightarrow}$통합의 단계를 거쳐 왔을 뿐만 아니라, 반복적인 피드백 혹은 반복학습을 통하여 MIS 기술능력을 축적한 결과 기술 추종적 위치에서 기술 선도적 위치로 전환된 것으로 분석되었다. 이는 기업의 기술혁신전략 수립 시에 기술혁신의 진행경로, 산업기술의 특성, 의사결정자의 역할, 반복학습 및 피이드백의 중요성 등이 고려될 필요가 있음을 시사한다.

• Journal of the Korean Society for Railway
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• v.15 no.2
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• pp.141-146
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• 2012

The rail surface defects which are generated on repeated rolling contact fatigue are getting increased according to high speed, high density, and minimum weight. In addition, Increasing noise and vibration are affected by these also impact load generated as well. Because of this phenomenon, more serious and critical damages were occurred. In fact, in order to control them, the rail grinding amount in Korea. This study evaluated how depth of hardening on rail surface is formed and suggested optimal rail grinding amount by RCF(rolling contact fatigue) test with generated contact pressure between KTX wheel and UIC60 rail by applying FEM analysis. Therefore, the amount was generated approximately 0.2mm/20MGT to maintain integrity of rail surface by getting rid of depth of hardening on rail according to rail accumulated passing tonnage.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.38 no.7
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• pp.511-523
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• 1989

This paper investigates physical properties, the electrical and mechanical characteristics of the epoxy resin with different curing methods and postcuring conditions at room temperature or cryogenic temperature (LN2). According to the results in this paper, first, it is found that the physical properties, electrical and mechanical characteristics of the epoxy resin are largely affected by the interior reaction temperature on the curing. Thus, in the fabrication of the sample, several excellent characteristics of the sample are obtained by controlling the interior reaction temperature of the epoxy resin. Second, the sample having optimal electrical and mechanical characteristics is obtained for the repetitive post-curing method at 100c in view point of the post-curing conditions of the epoxy resin. Third, it appears that tan and characteristics at LN2 temperature are about half of those at room temperature. Fourth, it appears that the dielectric strength of the epoxy resin at LN2 temperature is higher by about 0.6-1.0 MV/cm than that at room temperature. The heat-aging of the epoxy resin due to the micro-defect and excess fever-movement have been noticed to affect dielectric strength at LN2 temperature more significantly than at room temperature.

• Tuberculosis and Respiratory Diseases
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• v.39 no.6
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• pp.542-547
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• 1992

Tuberous sclerosis is an autosomal dominant disorder characterized by mental retardation, epilepsy, and adenoma sebaceum. Associated lesions include retinal phacomata, shagreen patches, subungal fibromata, and benign visceral tumors such as pulmonary lymphangioleiomyomatosis. Lymphangioleiomyomatosis occurs exclusively in women, usually during the child-bearing years, and is characterized by proliferation of smooth muscle along the lymphatic vessels of the lung, thorax, abdomen. Proliferation of smooth muscle results in interstitial and obstructive lung disease, recurrent pneumothorax, and chylous pleural effusions. We saw two cases of pulmonary lymphangioleiomyomatosis associated with tuberous sclerosis in women of reproductive age. We report the cases with a brief review of the literatures.