• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1999년도 추계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.18-18
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• 1999

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1993년도 추계학술강연 및 발표대회강연 및 발표논문 초록집
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• pp.20-21
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• 1993

• Applied Microscopy
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• 제45권1호
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• pp.9-15
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• 2015

In the present study, microstructural evolution in CuCrFeNi, CuCrFeNiMn, and CuCrFeNiMnAl alloys has been investigated. The as-cast CuCrFeNi alloy consists of a single fcc phase with the lattice parameter of 0.358 nm, while the as-cast CuCrFeNiMn alloy consists of (bcc+fcc1+fcc2) phases with lattice parameters of 0.287 nm, 0.366 nm, and 0.361 nm. The heat treatment of the cast CuCrFeNiMn alloy results in the different type of microstructure depending on the heat treatment temperature. At $900^{\circ}C$ a new thermodynamically stable phase appears instead of the bcc solid solution phase, while at $1,000^{\circ}C$, the heat treated microstructure is almost same as that in the as-cast state. The addition of Al in CuCrFeNiMn alloy changes the constituent phases from (fcc1+fcc2+bcc) to (bcc1+bcc2).

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2014년도 추계학술대회 논문집
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• pp.47-51
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• 2014

In this work, a possible mechanism for grain evolution in Al-Mg alloy films during thermal annealing is suggested on the basis of the phase transition and the related residual stress. Al-Mg alloy films with compositions of 14.0 and 18.0 wt% Mg content were deposited on cold-rolled steel substrates by the direct current co-sputtering method using Al and Mg targets. After the deposition, the samples were thermally annealed at $400^{\circ}C$ for 10 min. The featureless, dense cross-sectional microstructure of the as-deposited films turned into a grainy microstructure after the thermal annealing. According to the residual stress evaluated by using the $XRD-sin2{\psi}$ technique and the phase analysis by XRD, it is likely that grains were created in order to relieve the additional accumulation of residual stress originating from the phase transition from face-centered cubic Al (${\alpha}$) to Al3Mg2 (${\beta}$) and Mg (${\delta}$) phases, suggesting interplay between the microstructure and residual stress.

• 한국재료학회지
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• 제25권6호
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• pp.293-299
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• 2015

In this study, nitrogen ions were implanted into STS 316L austenitic stainless steel by plasma immersion ion implantation (PIII) to improve the corrosion resistance. The implantation of nitrogen ions was performed with bias voltages of -5, -10, -15, and -20 kV. The implantation time was 240 min and the implantation temperature was kept at room temperature. With nitrogen implantation, the corrosion resistance of 316 L improved in comparison with that of the bare steel. The effects of nitrogen ion implantation on the electrochemical corrosion behavior of the specimen were investigated by the potentiodynamic polarization test, which was conducted in a 0.5 M $H_2SO_4$ solution at $70^{\circ}C$. The phase evolution and texture caused by the nitrogen ion implantation were analyzed by an X-ray diffractometer. It was demonstrated that the samples implanted at lower bias voltages, i.e., 5 kV and 10 kV, showed an expanded austenite phase, ${\gamma}_N$, and strong (111) texture morphology. Those samples exhibited a better corrosion resistance.

• Coupled systems mechanics
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• 제6권1호
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• pp.41-54
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• 2017

Shape-memory alloys (SMA) have interesting behaviors and important mechanical properties due to the solid-solid phase transformation. These phenomena are dominated by the evolution of microstructures. In recent years, the microstructures in SMAs have been studied extensively and modeled using molecular dynamics (MD) simulations. However, it remains difficult to identify the crystal variants in the simulation results, which consist of large numbers of atoms. In the present work, a method is developed to identify the austenite phase and the monoclinic martensite crystal variants in MD results. The transformation matrix of each lattice is calculated to determine the corresponding crystal variant. Evolution of the volume fraction of the crystal variants and the microstructure in Ni-Ti SMAs under thermal and mechanical boundary conditions are examined. The method is validated by comparing MD-simulated interface normals with theoretical solutions. In addition, the results show that, in certain cases, the interatomic potential used in the current study leads to inconsistent monoclinic lattices compared with crystallographic theory. Thus, a specific modification is applied and the applicability of the potential is discussed.

• Earthquakes and Structures
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• 제1권2호
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• pp.147-162
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• 2010

The ground acceleration measured at a point on the earth's surface is composed of several waves that have different phase velocities, arrival times, amplitudes, and frequency contents. For instance, body waves contain primary and secondary waves that have high frequency content and reach the site first. Surface waves are composed of Rayleigh and Love waves that have lower phase velocity, lower frequency content and reach the site next. Some of these waves could be of more damage to the structure depending on their frequency content and associated amplitude. This paper models critical earthquake loads for single-degree-of-freedom (SDOF) inelastic structures considering evolution of the seismic waves in time and frequency. The ground acceleration is represented as combination of seismic waves with different characteristics. Each seismic wave represents the energy of the ground motion in certain frequency band and time interval. The amplitudes and phase angles of these waves are optimized to produce the highest damage in the structure subject to explicit constraints on the energy and the peak ground acceleration and implicit constraints on the frequency content and the arrival time of the seismic waves. The material nonlinearity is modeled using bilinear inelastic law. The study explores also the influence of the properties of the seismic waves on the energy demand and damage state of the structure. Numerical illustrations on modeling critical earthquake excitations for one-storey inelastic frame structures are provided.

• 기술혁신연구
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• 제18권2호
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• pp.253-288
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• 2010

본 연구는 기업의 지속적 생존과 성장이 변화하는 환경에 대응할 수 있는 지속적인 제품혁신에 있음에 초점을 두고, 산업 진화과정이 기업의 제품혁신 유형에 어떤 영향을 미치고 있는지와 인지, 기회구현, 변형의 세 가지 동태적 역량이 제품혁신에 미치는 영향을 분석하였다. 연구분석을 위해 1999년부터 2008년까지 산업의 도입기부터 성장기, 성숙기, 쇠퇴기를 모두 경험함으로써 종단적 분석에 적합한 한국 무선인터넷 산업의 7개 상장 기업에 대한 인터뷰와 문헌조사를 통한 사례연구를 수행하였다. 본 연구의 분석을 통하여 발견된 주요 결과는 다음과 같다. 첫째, 산업의 성장률이 둔화되는 성숙기 또는 쇠퇴기에는 제품혁신의 경로종속성은 낮아지고, 산업진화 과정의 외생적 변수가 중요해진다. 둘째, 기업의 인지활동은 상위 수준의 전략에 영향을 많이 받으며, 인지활동 범위와 제품혁신의 유형과는 밀접한 관계가 있다. 따라서 지속적인 성장을 위해서는 다양한 영역의 인지활동이 필요하다. 셋째, 기회구현역량은 제품혁신의 성공가능성에 영향을 미치며, 궁극적으로 기업의 재무적 성과에 기여하게 된다. 특히 경로종속성이 높은 제품혁신을 선택했을 때 높은 성과를 얻을 수 있으며, 적절한 비즈니스 모델의 개발과 필요한 자원 및 역량의 조달이 병행될 때 가능성은 높아진다. 넷째, 변형역량이 강한 기업이 그렇지 못한 기업에 비해 기존 역량을 활용할 수 있는 점진적 유형의 제품혁신을 선택할 확률이 크다. 결론적으로 기업이 성공적인 제품혁신을 추진하기 위해서는 산업 진화과정의 고려와 함께 균형적인 동태적 역량의 개발이 반드시 필요하며 이것이 기업의 지속적인 생존과 성장에 중요한 영향을 미친다고 할 수 있다.

• 천문학회지
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• 제38권2호
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• pp.207-210
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• 2005

We study the influence of rotation on the dynamical evolution of collisional single-mass stellar clusters up to core-collapse by using N-body simulations. Rotating King models which are characterized by dimensionless central potential parameter $W_o$ and the rotation parameter $W_o$ are used as initial models. Our results show that inner shells slowly contract until core-collapse phase is reached, followed by a slow expansion. Angular momentum is transported outward, while the core is rotating even faster than before, as predicted by gravogyro catastrophe theory. We confirm that rotation plays an important role in accelerating the dynamical evolution of stellar cluster, in particular in accelerating the core collapse.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 추계학술대회논문집
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• pp.149-152
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• 1999

The effect of initial orientation on the microstructure and texture evolution of two ferritic stainless steels was investigated. the columnar and equiaxed crystal specimens which were prepared from continuous casting slab were hot rolled annealed cold rolled and annealed respectively. The rolling and recrystallization textures at each process stage were examined by orientation distribution function (ODF) and electron back-scattered diffraction (EBSD); The observation showed that the orientation density of the $\alpha$-fibre of hot rolled band of columnar crystal specimen was more pronounced than that of the equaxed one at the center layer. Nevertheless the cold rolled textures of Type 430 steel have demonstrated a rather similar development . Compared to Type 430 steel the development of the $\alpha$-fibre in the center layer of Type 409L steel was much more pronounced. The relation between texture evolution and ridging behaviour has been discussed.