• 한국진공학회지
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• 제5권1호
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• pp.39-47
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• 1996

The segregation of S in electrotransport-purified polycrystaline $\alpha$-Ti and Ti-aluminide alloys has been studied by Auger electron spectroscopy(AES), Ion scattering spectroscopy(ISS) and Secondary ion mass spectrometry(SIMS) in the temperature range extending from 20 to $1000^{\circ}C$. The chemisorbed oxygen and carbon on Ti were observed to disappear at T>$400^{\circ}C$ after which the S signal increased to levels approaching 0.5 monolayer. At lower temperatures the presence of the surface oxygen and carbon appeared to inhibit the segregation, presumably because there were no available surfaces sites for the S emerging from the bulk. The activation energy for the S segregation in pure polycrystaline Ti was determined to be 16.7 kcal/mol, which, when compared to S segretation from single-crystal Ti, is quite small and suggests grain boundary or defect diffusion segregation kinetics. In the Ti-aluminide alloys, the presence of Al appeared to enhance the retention of surface oxygen which, in turn, substantially reduced the S segretation. The $\gamma$ alloy, with its high Al content, exhibited the greatest retention of surface oxygen and the smallest quantity of the S segregation(T$\simeq1000^{\circ}C$).

• Nuclear Engineering and Technology
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• 제52권1호
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• pp.148-154
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• 2020

The radiation induced segregation of Cr at grain boundaries (GBs) in Ferritic/Martensitic steels was modeled assuming vacancy and interstitialcy diffusion mechanisms. In particular, the dependence of segregation on temperature and grain boundary misorientation angle was analyzed. It is found that Cr enriches at grain boundaries at low temperatures primarily through the interstitialcy mechanism while depletes at high temperatures predominantly through the vacancy mechanism. There is a crossover from Cr enrichment to depletion at an intermediate temperature where the Cr:Fe vacancy and interstitialcy diffusion coefficient ratios intersect. The bell-shape Cr enrichment response is attributed to the decreasing void sinks inside the grains as temperature rises. It is also shown that low angle grain boundaries (LAGBs) and special Σ coincidence-site lattice (CSL) grain boundaries exhibit suppressed radiation induced segregation (RIS) response while high angle grain boundaries (HAGBs) have high RIS segregation. This different behavior is attributed to the variations in dislocation density at different grain boundaries.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 고액공존금속의 성형기술 심포지엄(III) SYMPOSIUM ON SEMISOLID FORMING TECHNOLOGY(III)
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• pp.15-32
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• 1999

A relationship between stress and stain is very important to design a die to avoid defects of products during semi-solid forming process. Since the liquid will be of eutectic composition in alloys liquid segregation will result in significant or undesirable situation. The materials used in this experiment are A 357. A390, Al2024 alloys that is fabricated by the electro-magnetic stirring process from Pechiney in France. The compression test was performed by induction heating equipment and MTS. In order to prevent the liquid segregation these measured temperature would be useful to control of strain rate during compression test. The liquid segregation is controlled as change of the strain rate and solid fraction during the compression process, The characteristics of flow between solid and liquid phase considering liquid segregation is examined through the above experiments. In the case of medium and high volume fractions of solid the distribution of strain rate is calculated by using compression test data of semi-solid materials (SSM). The thixoforming experiments with the designed die are carried out successfully. The die filling patterns of SSM for variation of die temperature and pressing force have been investigated. The hardness of the thixoformed scroll products is evaluated in terms of the microstructure for each position.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.60-60
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• 2015

Nanosheets of graphene and related 2D materials have attracted much attention due to excellent physical, chemical and mechanical properties. Single-layer graphene (SLG) was first synthesized by Blakely et al in 1974 [1]. Following his achievements, we initiated the growth and characterization of graphene and h-BN on metal substrates using surface segregation and precipitation in 1980s [2,3]. There are three important steps for nanosheet growth; surface segregation of dopants, surface reaction for monolayer phase, and subsequent 3-D growth (surface precipitation). Surface phase transition was clearly demonstrated on C-doped Ni(111) by in situ XPS at elevated temperatures [4]. The growth mode was clarified by inelastic background analysis [5]. The surface segregation approach has been applied to C-doped Pt(111) and Pd(111), and controllable growth of SLG has been demonstrated successfully [6]. Recently we proposed a promising method for producing SLG fully covering an entire substrate using Ni films deposited on graphite substrates [7]. A universal method for layer counting has been proposed [8]. In this paper, we will focus on the effect of competitive surface-site occupation between carbon and other surface-active impurities on the graphene growth. It is known that S is a typical impurity of metals and the most surface-active element. The surface sites shall be occupied by S through surface segregation. In the case of Ni(110), it is confirmed by AES and STM that the available surface sites is nearly occupied by S with a centered $2{\times}2$ arrangement. When Ni(110) is doped with C, surface segregation of C may be interfered by surface active elements like S. In this case, nanoscopic characterization has discovered a preferred directional growth of SLG, exhibiting a square-like shape (Fig. 1). Also the detailed characterization methodologies for graphene and h-BN nanosheets, including AFM, STM, KPFM, AES, HIM and XPS shall be discussed.

• 한국지역지리학회지
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• 제13권5호
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• pp.477-494
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• 2007

본 논문은 부산시를 대상으로 1900년대 초(구한말)부터 현재에 이르기까지 거주지역의 불평등한 현상을 거주분화의 개념을 중심으로 사회공간적으로 분석한다. 부산은 1900년대 초 조선 전통사회의 성격을 이어받아 신분사회의 계층질서에 의한 거주선택의 제한으로 불평등한 거주공간이 형성되었다. 이후 일제에 의한 신시가지의 형성으로 기존의 한국인 거주지와 분리되는 현상을 경험하였으며 일본인과 한국인, 그리고 중국인 거주지역으로 구분되는 민족별 분화 현상도 나타났다. 해방과 한국전쟁 이후 급속하게 인구가 증가함으로써 새로운 빈민거주지역이 등장하였고 이는 이후에 전개될 거주지 분화의 주요 요인으로 작용하게 된다. 빈민지역의 문제를 해소하기 위해 1960년대부터 실시한 정책이주는 제도상의 결점으로 인하여 큰 효과를 보지 못하였다. 1990년 이후 주민의 사회경제적 지위는 주택선택에 영향을 주어 주택계층에 의한 거주지역분화를 가능하게 하였다. 중간주택계층보다는 상 하위 주택계층이 거주공간의 불평등한 분포에 큰 영향을 주었다. 맥락적이고 시계열적인 접근방법을 시도하여 거주공간의 사회공간적 불평등에 관한 인과성을 파악하려고 시도한 본 연구는 미래에 전개될 거주공간패턴을 예측하고 다른 도시들의 거주공간연구에 도움을 줄 것으로 예상된다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.923-926
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• 2008

국내 외에서는 건축물들이 고유동 및 고성능 콘크리트의 사용량이 증가되고 있는 추세이다. 그러나 고유동 고성능 콘크리트는 유동성 향상을 위해 고성능 감수제를 다량으로 사용할 경우 유동성은 향상되었을 망정 재료분리가 발생하여 콘크리트 구조물에 악영향을 미치게 된다. 이러한 콘크리트의 재료분리 저항성을 판정하기 위한 방법으로 육안관찰, 굵은골재 씻기 시험, L Flow 철근사이의 통과성 시험, 점성측정에 의한 방법 등이 있는데, 이 같은 방법들은 매우 복잡하고 번거로우므로 실무적용에는 어려움이 있다. 그러므로 콘크리트의 재료분리 저항성을 보다 손쉬운 방법으로 평가하기 위한 방법으로 슬럼프플로우치를 슬럼프치로 나눈 EIS를 제안하기 위하여 기존 참고자료를 바탕으로 분석하였다. 그 결과 고유동 콘크리트의 경우 시방적 규정으로 재료분리 여부를 관리할 경우에는 EIS 값을 2.5 이하로 규정하면 타당할 것으로 사료되고, 성능적으로 EIS를 규정할 경우에는 1등급 2,2 이하, 2등급 2.2$\sim$2.4, 3등급 2.4$\sim$2.6, 2.6 이상은 재료분리로 관리하면 합리적일 것으로 사료된다.

• 생명과학회지
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• 제19권10호
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• pp.1346-1351
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• 2009

Neural crest는 신경계의 발생과정에서 생긴 특정화된 외배엽으로서 말초신경계(peripheral nervous system)의 모든 sensory cells과 peripheral cells, unipolar spinal ganglion cell, cranial sensory ganglia, peripheral nerve의 neurolemmal sheath cells, ganglia의 capsule cells, sympathetic ganglia, chromaffin cells, pigment cell 등의 자율신 경계의 대부분의 세포로 분화 한다. 최근pluripotetic neural crest cells의 운명이 이미 제한되어 있으며, 이러한 fate-restricted crest cells이 neural tube에서 emigration된다고 보고된바 있다. 또한 본 연구자는 Wnt와 Wnt의 antagonist가 neural crest cell의 specification이 일어나는 시기에 발현하여, neural crest cell의 segregation과 differentiation에 직접적으로 관여함을 밝혔다. 이를 보다 명확히 규명하기 위해, 본 연구에서는 neural tube에 Wnt-3a expressing cell의 grafting 혹은 dominant negative GSK construct의 electroporation을 통해 Wnt signaling을 modulation 하여 downstream mediator를 조사하였다. Wnt signaling의 stimulation은 neural crest cell의 melanoblast 로의 commitment를 유도하였으며, 이와 더불어 cadherin 7과 slug의 발현을 조절함을 확인하였다.

• Asian-Australasian Journal of Animal Sciences
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• 제18권8호
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• pp.1088-1097
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• 2005

Main objectives of this study were to investigate accuracy, bias and power of linear and threshold model segregation analysis methods for detection of major genes in categorical traits in farm animals. Maximum Likelihood Linear Model (MLLM), Bayesian Linear Model (BALM) and Bayesian Threshold Model (BATM) were applied to simulated data on normal, categorical and binary scales as well as to disease data in pigs. Simulated data on the underlying normally distributed liability (NDL) were used to create categorical and binary data. MLLM method was applied to data on all scales (Normal, categorical and binary) and BATM method was developed and applied only to binary data. The MLLM analyses underestimated parameters for binary as well as categorical traits compared to normal traits; with the bias being very severe for binary traits. The accuracy of major gene and polygene parameter estimates was also very low for binary data compared with those for categorical data; the later gave results similar to normal data. When disease incidence (on binary scale) is close to 50%, segregation analysis has more accuracy and lesser bias, compared to diseases with rare incidences. NDL data were always better than categorical data. Under the MLLM method, the test statistics for categorical and binary data were consistently unusually very high (while the opposite is expected due to loss of information in categorical data), indicating high false discovery rates of major genes if linear models are applied to categorical traits. With Bayesian segregation analysis, 95% highest probability density regions of major gene variances were checked if they included the value of zero (boundary parameter); by nature of this difference between likelihood and Bayesian approaches, the Bayesian methods are likely to be more reliable for categorical data. The BATM segregation analysis of binary data also showed a significant advantage over MLLM in terms of higher accuracy. Based on the results, threshold models are recommended when the trait distributions are discontinuous. Further, segregation analysis could be used in an initial scan of the data for evidence of major genes before embarking on molecular genome mapping.

• 대한토목학회논문집
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• 제40권6호
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• pp.633-641
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• 2020

단지형 주거지 개발은 공동체 의식 촉진과 편의성 확보 등의 장점이 있지만, 폐쇄성이란 단점이 있다. 특히 1,000세대 이상의 대규모 아파트단지는 출입구에 입주민 전용 출입 시스템을 설치하는 등 물리적으로 단절된 형태들이 도시 공간을 더욱 폐쇄적으로 만들고 있다. 그러나 폐쇄적인 도시 공간은 소득·인종 등의 사회적 계층의 분화와 주거지 분리를 야기한다. 따라서 대규모 아파트단지가 주거지 분리와 관련 있다는 연구 가설을 제시한다. 가설 검정을 위해 먼저, 상이지수와 델타지수로 국내 광역시 주거지 격리의 추이를 살펴본다. 그 후, 주거지 분리와 대규모 아파트 단지와의 상관관계는 스피어만 상관분석으로 진행한다.

• 콘크리트학회논문집
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• 제11권4호
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• pp.95-105
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• 1999

When superplasticizer is added to manufacture flowing concrete, the base concrete usually needs the adjustment to assure the sufficient fines contained to obtain flowable consistency without excessive bleeding or segregation. However, this may not only increase the cost, but also cause inconvenience in producing the base concrete. In this paper, the experiments are performed on normal base concrete to achieve a segregation-reducing flowing concrete by adding superplasticizer mixed with viscosity agents and AE admixtures. Three kinds of superplasticizer and two kinds of viscosity agent are selected. According to the results, with regard to the performance and cost of the admixtures, melamine type superplasticizer combined with the PEO viscosity agent and AE admixtures at the ratio 1:0.28:0.001 can acquire good quality and reduce the cost in producing the flowing concrete. With proper addition of combined superplasticizer, even though water to cement ratios of the base concrete are different, the segregation-reducing flowing concrete could be also achieved without reproportioning of the base concrete. However, it would be more desirable if the superplasticizer could be adjusted, before it is put into the practical use in order not to cause some other problems, such as rapid rate of slump loss and retarding of setting time.