• 한국분말재료학회지
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• 제16권1호
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• pp.9-15
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• 2009

Amorphization and crystallization behaviors of $Ti_{50}Cu_{50}Ni_{20}Al_{10}$ powders during high-energy ball milling and subsequent heat treatment were studied. Full amorphization obtained after milling for 30 h was confirmed by X-ray diffraction and transmission electron microscope. The morphology of powders prepared using different milling times was observed by field-emission scanning electron microscope. The powders developed a fine, layered, homogeneous structure with prolonged milling. The crystallization behavior showed that the glass transition, $T_g$, onset crystallization, $T_x$, and super cooled liquid range ${\Delta}T=T_x-T_g$ were 691,771 and 80 K, respectively. The isothermal transformation kinetics was analyzed by the John-Mehn-Avrami equation. The Avrami exponent was close to 2.5, which corresponds to the transformation process with a diffusion-controlled type at nearly constant nucleation rate. The activation energy of crystallization for the alloy in the isothermal annealing process calculated using an Arrhenius plot was 345 kJ/mol.

• 물과 미래
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• 제27권2호
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• pp.73-83
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• 1994

확산현상, 표사유동 및 인간의 여러 활동이 실제 연안해역에서 일어나므로 연안해역 해수운동의 물리적 특성을 파악하고 해석하는 것은 중요한 의미를 지닌다. 본 연구에서는 연안해역에서의 파랑변형과 평균해수위 변동 그리고 연안유속 분포양상에 대해 여러 인자들이 미치는 영향을 2차원 유한차분 모형(ADI, Up-wind)을 이용하여 분석하였다. 계산결과로는 수치모형을 해저경사가 일정한 2차원 지형에 적용하여 해저경사, 입사파고, 파향각, 파주기, 마찰계수 및 수평확산계수가 연안해역 특히 쇄파대내에서 파랑변형, 평균해수위 변동 및 연안유속 분포에 미치는 영향을 분석하였다.

• 대한금속재료학회지
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• 제47권8호
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• pp.488-493
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• 2009

Direct syntheses of bulk $Ti_3Al$ via electro-discharge-sintering (EDS) of a stoichiometric elemental powder mixture were investigated. A capacitor bank of $450{\mu}F$ was charged with three input energies, 0.5, 1.0, and 1.5 kJ. The charged capacitor bank was then instantaneously discharged through 0.3 g of a Ti-25.0 at.%Al powder mixture for consolidation. Complete phase transformation occurred in less than $200{\mu}sec$ by the discharge and a bulk $Ti_3Al$ compact was obtained. Compared with consolidated samples fabricated by conventional methods such as high vacuum sintering and casting, the electro-discharge-sintered $Ti_3Al$ compact shows a very fine microstructure with a hardness value of 425 Hv. Electro-discharge-sintering under a $N_2$ atmosphere successfully modified the surface Ti oxide of the $Ti_3Al$ compact into Ti nitride, which concurred with the synthesis and consolidation of $Ti_3Al$. Complete conversion yielding a single phase $Ti_3Al$ is primarily dominated by the fast solid state diffusion reaction.

• 한국재료학회지
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• 제11권12호
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• pp.1057-1062
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• 2001

We investigated the change of mechanical properties for TiNi shape memory alloy by heat treatment. 6061Al matrix composites with TiNi shape memory alloy as reinforcement were fabricated by vacuum casting. TiNi alloy has the maximum tensile strength at 673K treated and there is no change of tensile strength and hardness at 448K treated. The composites, prepared by vacuum casting, showed good interface bonding by vacuum casting. It was about 3$\mu\textrm{m}$ of thickness of the diffusion layer. Tensile strength of the composite was in higher than that of 6061Al alloy as increased value of about 70MPa at room temperature and about 110MPa at 363K. We thought that the increase of the tensile strength at 363K was due to reverse transformation of the TiNi shape memory alloy.

• 대한기계학회논문집
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• 제12권2호
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• pp.338-348
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• 1988

본 연구는 환상휜에서 휜 바탕의 온도가 조기적으로 변화할 때, 휜 바탕의 온도가 주기적으로 변화할 때, 휜 주변 뿐만 아니라 휜 선단에서의 대류현상을 고려한 과도 전열에 대한 해석이다.

• Biomolecules & Therapeutics
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• 제1권2호
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• pp.177-182
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• 1993

From 84 clinical isolates of Staphylococcus species, ten strains showing inducible resistance to MLS antibiotics were selected by disk agar diffusion method. Colony hybridization was executed using two MLS inducible resistance genes, ermA and ermC, previously identified from S. aureus as probes. S. hemolyticus 401 and S. epidermidis 542 whose genes were not homologous to those probes were finally selected. It was determined that the resistance genes of S. hemolyticus 401 and S. epidermidis 542 were not homologous to ermA, ermC and ermAM by Southern hybridization. S. epidermidis 542 had a plasmid DNA. To know if the plasmid may have genes related to inducible resistance, it was attempted to transform B. subtilis BR151 and S. aureus RN4220 with the plasmid prepared from S. epidermidis 542. It was shown that the gene related to inducible resistance to MLS antibiotics did not exist in this plasmid. These results indicate that two clinical isolates of S. hemolyticus 401 and S. epidermidis 542 had novel genes which were not homologous to MLS resistance genes identified previously. It was assumed that these genes may exist in chromosomal DNA.

• 한국재료학회지
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• 제10권1호
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• pp.29-33
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• 2000

비정질 WNx 박막이 반응성 스퍼터링법으로 제조되었다. 비정질 형성을 위한 질소의 농도범위는 10~40at%이었다. 비정질 W(sub)67N(sub)33 박막은 1273K에서 1분 동안 급속 열처리되어 저항이 낮은 등축정의 $\alpha$-텅스텐 상과 과잉의 질소로 변태되었다. 이러한 박막의 저항은 순수한 텅스텐 박막과 유사하였다. $\alpha$-텅스텐 상으로부터 방출된 과잉의 질소는 $\alpha$-텅스텐/다결정 실리콘의 계면에 편석되었다. 편석된 질소는 Si$_3$N$_4$나노 결정으로 균일한 확산 장벽층을 형성시켰고, 저항이 높은 텅스텐 실리사이드의 반응을 억제하였다.

• 한국인터넷방송통신학회논문지
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• 제13권6호
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• pp.79-85
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• 2013

이 논문에서는 먼저 디지털 하프토닝 영상을 생성하는 기존의 방법들과 DCT 변환에 대해서 설명한다. 그런후에 DCT 변환에 근간을 둔 새롭고 단순한 하프토닝 알고리즘을 제안한다. 이 논문은 제안한 알고리즘을 검정하기 위해서 실현 가능성 검증을 수행한다. 그래서 DCT 계수의 가중치를 조절하여 생성된 여러 가지 영상들을 평가하였다. 실험을 통해서 단순한 이상적인 계단 함수 형태의 가중치를 사용하는 것보다는 램프 함수 형태의 가중치를 사용하면 더 좋은 결과를 얻었다. 단순한 응용분야로서 MPEG 비디오에 제안한 알고리즘을 적용하여 하프토닝 비디오를 생성할 수 있다.

• ETRI Journal
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• 제20권1호
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• pp.55-73
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• 1998

In this paper we analyze the technological accumulation processes in the Korean semiconductor industry from the institutional approach. Institutional approach, which is closely connected with Neo-Schumpeterian tradition, has emerged as an alternative theoretical framework to neoclassical approach to understand the process of producing technological knowledge. Traditional wisdom of neoclassical approach revealed the limitation to explain the complex nature of knowledge creation and diffusion. US patent data are analyzed in terms of the increasing trend of numbers and its content to measure the rate and direction of technological capability accumulation. This analysis shows that semiconductor technologies are one of the fastest growing fields among Korean technological activities. Moreover, the analysis of patent content suggests that fabrication technologies are the most important area within the technological development of semiconductors, whilst circuit design and testing technologies are beginning to increase in significance. In addition, it is examined how private sectors and public institutions have contributed to generate technological capabilities, and the relationship between them has been changed during the development processes. It is found that Korean firms enhanced their technological capabilities from the learning and assimilation of imported technology to enhanced in-house R&D capabilities in the later stage. The support of public institution and government policy also played significant role to this successful transformation in conjunction with vigorous R&D investment of public sector.

• 대한기계학회논문집B
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• 제24권3호
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• pp.426-434
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• 2000

This paper deals with a generalized similarity solution for the one-dimensional solidification of ternary or higher-order multicomponent alloys. The present approach not only retains the existing features of binary systems such as temperature- solute coupling, shrinkage-induced flow, solid-liquid property differences, and finite back diffusion, but also is capable of handling a multicomponent alloy without restrictions on the partition coefficient and microsegregation parameter. For an alloy of N-solute species, governing equations in the mushy region reduce to (N+2) nonlinear ordinary differential equations via similarity transformation, which are to be solved along with the closed-form solutions for the solid and liquid regions. A linearized correction scheme adopted in the solution procedure facilitates to determine the solidus and liquidus positions stably. The result for a sample ternary alloy agrees excellently with the numerical prediction as well as the reported similarity solution. Additional calculations are also presented to show the utility of this study. Finally, it is concluded that the present analysis includes the previous analytical approaches as subsets.