• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.4
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• pp.85-90
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• 2018

The objective of this paper is to observe effects of ignition position and time on ignition transition. A gaseous oxygen and liquid kerosene mixture is used as propellant with a shear-coaxial injector. In order to study the ignition delay time and combustion instability intensity, the pressure transducer was used. Sequences, excepting igniter operation time, were fixed to compare the ignition time only. Initial pressure peak and ignition delay time increased as the ignition time was delayed. Additionally, an unstable flame development zone was detected when the igniter was away from the injector.

• Journal of the Korean Geotechnical Society
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• v.23 no.4
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• pp.133-147
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• 2007

Downhole seismic method is very economic and easy of operation because it uses only one borehole and simple surface source to obtain the shear wave velocity ($V_s$) profile of a site. Even though it is widely used by the site investigation companies, universities and institutes, however, the $V_s$ profile determined by downhole seismic method has often low reliability due to employment of wrong combinations of field losing equipment and interpretation method and deficiency of experience. Round robin test was performed and testing equipment and procedure were compared. Adequate downhole seismic testing equipment was constructed based on the comparison and verification study of the round robin test. The data acquisition and software interpretation were also developed for automation and quick test in field. Finally, the effectiveness and applicability were verified through the field test by using the constructed testing system.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.824-827
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• 2002

12inch 이상의 웨이퍼 성장에는 실리콘 용탕의 대류를 억제하여 웨이퍼의 순도를 높이기 위해 자기장 특히, 웨이퍼의 성장방향에 수직인 '수평자장'을 인가하는 방법이 사용된다. 현재 '자기장인가 방식', 특히 초전도를 사용한 자장인가 방식이 직경 1600mm에 이르는 용탕의 용액을 제어하는 유일한 방법으로 받아들여지고 있다. 본 논문에서는 12inch 실리콘 웨이퍼 성장용 초전도 마그네트 개발의 전단계로 개발중인 8inch 웨이퍼 성장용 수평자장형 초전도마그네트의 제작과정과 성능평가 결과에 대해 다루었다. 본 연구를 통해 액체헬륨의 증발을 최소화하기 위한 재응축형 극저온 용기에 대한 기술이 개발 되었으며, diode를 이용한 ��치보호부, HTS 전류리드의 ��치 protection부 등의 부속기술이 개발되었다. 초전도 마그네트는 내경 1400mm의 saddle type으로 이의 제작에 있어 많은 기술적 난재들을 경험해야 했다. 전체 시스템에 대한 성능평가 결과, 극저온용기 및 부속장치에 대한 결과는 만족스러웠으나, 코일부의 성능은 계획한 목표에 미치지 못했다.

• Journal of the Korea Concrete Institute
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• v.26 no.1
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• pp.79-86
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• 2014

In this paper, a stress transfer mechanism between near surface-mounted (NSM) fiber reinforced polymer (FRP) plate and concrete was investigated and a reliable analytical procedure for it was presented by using bilinear bond-slip model simulating the bond behavior of NSM FRP plate. As a result, critical values in the bi-linear model such as maximum shear strength, slip at that time and failure slip at the initiation of softening de-bonding were suggested for being used in the differential equation considering he interfacial characteristic between NSM FRP and concrete. Also, it was found that the bond-slip behavior could be suitably redicted by using the proposed procedure even in the case of various bond lengths from the comparison with bond test result.

• Journal of Biomedical Engineering Research
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• v.25 no.3
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• pp.217-225
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• 2004

In this paper, a new automatic classification method for the normal EEC and schizophrenia EEC using hidden Markov model(HMM) is proposed. We used the feature parameters which are the variance for statistical stationary interval of the EEC and power spectrum ratio of the alpha, beta, and theta wave. The results were shown that high classification accuracy of 90.9％ in the case of normal person, and 90.5％ in the case of schizophrenia patient. It seems that proposed classification system is more efficient than the system using complicate signal processing process. Hence, the proposed method can be used at analysis and classification for complicated biosignal such as EEC and is expected to give considerable assistance to clinical diagnosis.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2005.05a
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• pp.933-937
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• 2005

FCBGA가 마더보드에 실장된 후 솔더 조인트에 균열이 생기면 단선이 발생한다. 솔더 조인트의 신뢰성을 평가하기 위한 방법 중 전단강도시험(shear test)은 약한 솔더 조인트를 판별하기 어려워 양품 로트와 불량 로트를 구별할 수 없으며, 인장강도시험(pull test)은 솔더 볼의 위치별 산포가 크고, peel test는 품질을 정량적으로 나타낼 수 없는 등의 문제가 있다. 새로운 시험 방법은 Area Pull Test(이하 APT)라 명명했으며 peel test와 pull test를 합한 개념으로서, 시험 샘플을 만드는 과정은 peel test와 동일하다. 솔더 조인트의 인장강도 측정은 지그를 만들어서 FCBGA 전체를 당겨서 측정하였다. 샘플은 Ni도금 두께를 3, 5, 8 ${\mu}m$로 제작하여 불량(3${\mu}m$), 양품으로 구분하였고, 양품 또한 품질 수준을 두가지(5,8${\mu}m$)로 나누었다. 그 결과 peel test 기준에 의거한 불량, 양품을 정량적인 수치(인장강도)로 판별할 수 있었으며, 솔더 조인트의 파괴모드별 인장강도를 구분 할 수 있었다.

• Composites Research
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• v.13 no.2
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• pp.1-7
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• 2000

A new ultrasonic test method is proposed to obtain elastic constants of unidirectional composite materials nondestructively. In the proposed test method, only longitudinal transducers are used to measure wave velocities by through-transmission method. An aluminum wedge and a flat aluminum rectangular block are placed on each side of the test specimen. Oblique incident longitudinal wave is transmitted from a wedge to the specimen and the mode conversions are occurred sequentially at two interfaces between the specimen and aluminium. Measuring wave velocities converted to longitudinal waves in the rectangular block give all information to determine elastic constants of the composites. In order to determine shear stiffness coefficients, transverse wave velocity is measured indirectly from received longitudinal wave. Effects of anisotropy on waves are also considered in this study.

• Composites Research
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• v.12 no.4
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• pp.17-24
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• 1999

Finite element analysis and experiment are performed to investigate residual deformation induced by the repair of composite shell structures using a prepreg patch method. The finite element program is developed on the basis of a three-dimensional degenerated shell element and the first order shear deformation theory. The results analyzed for the laminated shell with free boundary conditions are compared with strains measured during the prepreg patch repair. Final residual stresses occur greatly near the patch when the laminated shell with all edges clamped is repaired using the prepreg patch. Stacking sequences of the laminated shell and patch affect significantly the residual stresses which occur even if they are the same.

• Economic and Environmental Geology
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• v.27 no.3
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• pp.247-261
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• 1994

Honam Shear Zone is a mylonite zone approximately parallel to the NE-SW trend located southern part of Korea peninsula. Geologic ages and petrogenesis of foliated granites in this zone are as follows: Igneous rocks of this zone are composed of granite gneiss, Paleozoic granites, Songrim granites, Jurassic granites and Cretaceous granites. Foliated granites show deformed phase of Paleozoic and Songrim granites during Daebo Orogeny. And isotopic ages obtained from foliated granites are early Permian to late Triassic period (276~200 Ma). Most of foliated granite masses are igneous complex consisting of a series of differential product of cogenetic magma. The individual rock mass of foliated granites plotted on Harker diagram shows mostly similar trend of calc-alkali series. REE diagram indicates that LREE amount of foliated granites are more enriched than HREE and negative Eu anomalies of them are weaker than those of the other granites. From these data, we suggest the rocks are generated from continental margin under syntectonic environment. Original magma type of foliated granites correspond to I-type, syn-collision type and Hercyano type. In compressive stress field between Ogcheon folded belt and Youngnam massif, foliated granites had formed due to mylonitic deformation. Those facts indicate that magma of foliated granites would had been generated by melting in lower crust or contamination in upper mantle.

• Journal of the Korean Society for Railway
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• v.17 no.1
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• pp.14-18
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• 2014

Wheel/rail contact is a significant problem in railway dynamics. In this paper, the wheel/rail contact is examined analytically and numerically as a contact problem between two cylinders where torque and friction have effect. Furthermore, the contact of a real wheel and rail is investigated numerically where the normal and shear force act. This study demonstrates that the wheel/rail contact is a process that generates traction force through creep where rolling and sliding occurs simultaneously depending on the shape of the wheel and rail, and the friction coefficient between them.