• 한국레이저가공학회지
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• 제13권2호
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• pp.10-16
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• 2010

Laser-assisted machining is dependent on absorbed energy density into workpiece. Generally, the absorptivity of laser beam is dependent on wave length of laser, materials, surface roughness, etc. Various shapes and energy densities for beam irradiation can be used to laser-assisted machining. In this thesis, efficient method of heat source modeling was developed and designed by using one fundamental experimental trials. And then, laser-assisted machining of rod-shaped cast iron was simulated by using commercial FEM code MARC. Simulations and experiments with various conditions were carried out to determine suitable condition of pre-heating for laser-assisted turning process. Temperature distribution of cutting zone could be predicted by simulation.

• Steel and Composite Structures
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• 제21권2호
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• pp.267-287
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• 2016

The seismic performance of the ordinary steel reinforced concrete (SRC) columns has no significant improvement compared to the reinforced concrete (RC) columns mainly because I, H or core cross-shaped steel cannot provide sufficient confinement for core concrete. Two improved SRC columns by constructing with new-type shaped steel were put forward on this background, and they were named as enlarging cross-shaped steel and diagonal cross-shaped steel for short. The seismic behavior and carrying capacity of new-type SRC columns have been researched theoretically and experimentally, while the shear behavior remains unclear when the new-type columns are joined onto SRC beams. This paper presents an experimental study to investigate the shear capacity of new-type SRC joints. For this purpose, four new-type and one ordinary SRC joints under low reversed cyclic loading were tested, and the failure patterns, load-displacement hysteretic curves, joint shear deformation and steel strain were also observed. The ultimate shear force of joint specimens was calculated according to the beam-end counterforce, and effects of steel shape, load angel and structural measures on shear capacity of joints were analyzed. The test results indicate that: (1) the new-type SRC joints display shear failure pattern and has higher shear capacity than the ordinary one; (2) the oblique specimens have good bearing capacity if designed reasonably; and (3) the two proposed construction measures have little effect on the shear capacity of SRC joints embedded with diagonal cross-shaped steel. Based on the mechanism observed from the test, the formulas for calculating ultimate shear capacity considering the main factors (steel web, stirrup and axial compression ratio) were derived, and the calculated results agreed well with the experimental and simulated data.

• Restorative Dentistry and Endodontics
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• 제37권3호
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• pp.175-179
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• 2012

The aim of this study was to present a method for endodontic management of a maxillary first molar with unusual C-shaped morphology of the buccal root verified by cone-beam computed tomography (CBCT) images. This rare anatomical variation was confirmed using CBCT, and nonsurgical endodontic treatment was performed by meticulous evaluation of the pulpal floor. Posttreatment image revealed 3 independent canals in the buccal root obturated efficiently to the accepted lengths in all 3 canals. Our study describes a unique C-shaped variation of the root canal system in a maxillary first molar, involving the 3 buccal canals. In addition, our study highlights the usefulness of CBCT imaging for accurate diagnosis and management of this unusual canal morphology.

• Steel and Composite Structures
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• 제26권4호
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• pp.439-452
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• 2018

This paper presents experimental and numerical study on buckling behaviors and hysteretic performance of Class 1 H-shaped steel beam subjected to cyclic pure bending within the scope of ultra-low cycle fatigue (ULCF). A loading device was designed to achieve the pure bending loading condition and 4 H-shaped specimens with a small width-to-thickness ratio were tested under 4 different loading histories. The emphasis of this work is on the impacts induced by local buckling and subsequent ductile fracture. The experimental and numerical results indicate that the specimen failure is mainly induced by elasto-plastic local buckling, and is closely correlated with the plastic straining history. Compared with monotonic loading, the elasto-plastic local buckling can occur at a much smaller displacement amplitude due to a number of preceding plastic reversals with relative small strain amplitudes, which is mainly correlated with decreasing tangent modulus of the material under cyclic straining. Ductile fracture is found to be a secondary factor leading to deterioration of the load-carrying capacity. In addition, a new ULCF life evaluation method is proposed for the specimens using the concept of energy decomposition, where the cumulative plastic energy is classified into two categories as isotropic hardening and kinematic hardening correlated. A linear correlation between the two energies is found and formulated, which compares well with the experimental results.

• 한국전자파학회논문지
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• 제19권8호
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• pp.826-831
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• 2008

본 논문은 이동 위성 통신을 위한 성형 반사판 기반의 하이브리드 안테나 설계에 대하여 서술한다. 하이브리드 안테나는 성형 반사판과 $1{\times}8$ 배열의 선형 위상 배열 안테나로 이루어진 급전부로 구성되며, 최소의 개구면으로 안테나에 요구되는 최적의 성능을 구현하기 위하여, 반사판 성형화 기법이 적용되었다. 또한, 급전부 설계에 있어서, 능동 배열의 수를 최적화함으로써 전체적인 안테나의 제작 단가를 최소화 할 수 있다는 장점을 갖는다. Ka-대역에서 설계된 본 안테나는 앙각 방향 $+45^{\circ}$를 기준으로 ${\pm}3^{\circ}$ 범위에서 빔 패턴을 전기적으로 제어할 수 있으며, 부엽 레벨을 포함한 안테나 빔 패턴에 대해서는 ITU-R S.465-5에 만족하도록 설계되었다.

• 한국강구조학회 논문집
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• 제15권6호통권67호
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• pp.639-648
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• 2003

연구의 목적은 H형강보에 작용하는 매달림 하중 중 면내 및 면외 모멘트를 그 대상으로 구조설계시 적용되는 설계하중에 대하여 면내 및 면외 모멘트가 스터드 커넥터를 통하여 슬래브를 전달되는 하중전달 경로와 그 성능을 파악하는데 있다. 이를 위하여 면내 및 면외 모멘트를 받는 경우에 대하여 각각 2개의 실험체를 대상으로 가력실험 및 수치해석을 수행하였다. 실험의 변수로는 H형강보의 크기가 적용되었다. 면내 및 면의 모멘트 가력실험결과 현행 강구조계산기준을 따라 설계하면 스터드 커넥터에 의한 H형강보의 모멘트 전달성능을 설계하중을 만족하고 있음을 확인하였다.

• Applied Microscopy
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• 제51권
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• pp.1.1-1.2
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• 2021

We demonstrate a fabrication of an atomically controlled single-crystal heart-shaped nanostructure using a convergent electron beam in a scanning transmission electron microscope. The delicately controlled e-beam enable epitaxial crystallization of perovskite oxide LaAlO₃ grown out of the relative conductive interface (i.e. 2 dimensional electron gas) between amorphous LaAlO₃/crystalline SrTiO₃.

• Steel and Composite Structures
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• 제45권2호
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• pp.293-303
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• 2022

In order to improve the seismic resilience of coupled wall structure, coupling beam with fuse has been developed to reduce the post-earthquake damage. However, the fuses often have a build-up I-shaped section and are relatively heavy to be replaced. Moreover, the fuse and the beam segments are usually connected by bolts and it is time-consuming to replace the damaged fuse. For reducing the repair time and cost, a novel quickly replaceable coupling beam with buckling-restrained energy dissipaters is developed. The fuse of the proposed coupling beam consists of two chord members and bar-typed energy dissipaters placed at the corners of the fuse. In this way, the weight of the energy dissipater can be greatly reduced. The energy dissipaters and the chords are connected with hinge and it is convenient to take down the damaged energy dissipater. The influence of ratio of the length of coupling beam to the length of fuse on the seismic performance of the structure is also studied. The seismic performance of the coupled wall system with the proposed coupling beam is compared with the system with reinforced concrete coupling beams. Results indicated that the weight and post-earthquake repair cost of the proposed fuse can be reduced compared with the typical I-shaped fuse. With the increase of the ratio of the beam length to the fuse length, the interstory drift of the structure is reduced while the residual fuse chord rotation is increased.

• Journal of Advanced Marine Engineering and Technology
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• 제31권8호
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• pp.961-969
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• 2007

The laser material processing has replaced a conventional material processing such as a welding, cutting, drilling and surface modification and so on. LTH(Laser Transformation Hardening) is one branch of the laser surface modification process. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power intensity comparatively. The absorptivity of the laser energy with respect to material depends on the wave length of a beam. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser(HPDL) whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

• 한국진공학회지
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• 제12권3호
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• pp.182-192
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• 2003

밀리미터파 대역용 고속 PHEMT 소자 제작 및 개발을 위하여 다층 리지스트 및 다원자 기판 구조에서 전자빔 리소그래피 공정을 분석할 수 있는 새로운 몬테 카를로 시뮬레이션 모델을 개발하였다. 전자빔에 의해 다층 다원자 타겟 기판 구조에 전이되는 에너지를 정확하고 효율적으로 계산하기 위하여 다층 리지스트 및 다층 다원자 기판 구조에서 시뮬레이션 가능하도록 새로이 모델링하였다. 본 논문에서 제안 개발된 모델을 사용하여 PHEMT 소자의 전자빔 리소그래피에 의한 T-게이트 형성 공정을 시뮬레이션하고 SEM측정 결과와 비교 분석하여 타당성을 검증하였다.