• 한국가스학회지
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• 제19권6호
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• pp.62-66
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• 2015

LNG선이나 해양플랜트 같은 설비나 구조물은 작동 조건을 고려할 때, 특히 부재마다 가지는 고유한 연성 취성천이온도(Ductile to Brittle Transition Temperature, DBTT)를 고려하여 설계되어야 한다. 본 연구에서는 해양플랜트 및 LNG선에 hull plate로 쓰이는 A-grade 연강(mild steel)에 대해 DBTT를 샤르피 V-노치(CVN) 실험을 통해 알아보았고 파괴형상을 통한 파괴거동을 살펴보았다. 그 결과 온도가 감소함에 따라 충격 흡수에너지는 감소함을 보였다. Upper shelf energy region과 lower shelf energy region이 나타나고 그 사이 구간의 천이점을 통해 DBTT가 결정되었다. 파괴형상에서는 upper shelf energy region에서 수많은 딤플이 연성파괴 형상으로 관찰되고 lower shelf energy region에서는 전형적인 취성파단형상이 관찰되었다. 이를 통해 BCC 구조를 가지는 A-grade 연강은 upper shelf energy 구역과 lower shelf energy구역을 보이고 그 사이 구간의 천이점에서 급격하게 온도가 떨어지는 DBTT구간을 뚜렷하게 보이는 특성을 알 수 있었다.

• 한국해양공학회지
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• 제1권2호
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• pp.101-112
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• 1987

Fracture toughness characterization in the transition region is examined for heat-treated and ionnitrided Ni-Cr-Mo steel. After heat treatment for the specimens of Ni-Cr-Mo steel, organizations of specimens-specimens which are heat-treated and ion-nitrided for 4 hours at 500 .deg. C and 5 torr in 25%N/dub 2/-75%H/sub 2/mixed gas-, hardness variety, and X-ray diffraction pattern of the ion-nitriding compound layer are observed. Fracture toughenss test of unloading compliance method were conducted over the regions from room trmperature to -70.deg. C. The compound layer was consisted of r'=Fe/sub 4/N phase and ion-nitrided layer's depth was 200mm from surface. The transition regions of heat-treated and ion-nitrided specimens were about -30.deg. C and -50.deg. C, respectively. The transition region of ion-nitrided specimens is estimated less than that of heat-treated one, and this is the effect of ion-nitriding.

• 한국해양학회지
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• 제30권4호
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• pp.271-278
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• 1995

한국 동남해역의 대륙붕 표층 쇄설퇴적물에 함유된 중광물 사립자의 연구를 위하 여 88 정점의 표층시료가 분석되고 해석되었다. 중광물 함량의 분포지역은 크게 4지역 으로 다음과 같이 나누어진다. 1)서부지역-자철석,석류석 및 ZTR 등의 안정한 중광물 이 크게 농축되어 분포함, 2) 한국해곡지역-안정한 중과물의 비교적 우세한 분포, 3) 동부지역-각섬석류와 풍화된 광물, 그리고 휘석류의 분포가 우세함, 4) 북동부 붕단지 역-안정한 광물이 적으면, 풍화 변질된 중광물이 우세함. 이와 같은 중광물의 함량 및 분포양상은 대륙붕 해저에 영향을 미치는 현세 해수면상승 (해침)의 과정에 따른 동력 학적 에너지 (파랑작동과 연안류 운동) 와 관련된 것으로 해석된다. 휘석류 중광물이 우세만 퇴적물은 일본의 화산암으로부터 기원된 것으로 제안된다.

• Ocean and Polar Research
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• 제30권3호
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• pp.289-301
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• 2008

Community structure of heterotrophic protists and their grazing impact on phytoplankton were studied in Northwest Pacific Ocean during October, 2007. The study area was divided into four regions based on physical properties (temperature and salinity) and chlorophyll-a distribution. They were Region I of North Equatorial Currents, Region II of Kuroshio waters, Region III of shelf mixed water, and Region IV of Tsushima warm current from East China Sea. The distribution of chlorophyll-a concentrations and community structure of heterotrophic protists were significantly affected by physical properties of the water column. The lowest concentration of chlorophyll-a was identified in Region I and II, where pico-sized chlorophyll-a was most dominant (>80% of total chlorophyll-a). Biomass of heterotrophic protists was also low in Region I and II. However, Region III was characterized by low salinity and temperature and high chlorophyll-a concentration, with relatively lower pico-sized chlorophyll-a dominance. The Highest biomass of heterotrophic protists appeared in Region III, along with the relatively less important nanoprotists. In Region I, II and IV, heterotrophic dinoflagellates were dominant among the protists, while ciliates were dominant in Region III. Community structure varied with physical(salinity and temperature) and biological (chlorophyll-a) properties. Biomass of heterotrophic protists correlated well with chlorophyll-a concentration in the study area ($r^2=0.66$, p<0.0001). The potential effect of grazing activity on phytoplankton is relatively high in Region I and II. Our result suggest that biomass and size structure of heterotrophic protists might be significantly influenced by phytoplankton size and concentration.

• 한국환경과학회지
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• 제17권1호
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• pp.85-95
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• 2008

Temporal and spatial variabilities of chlorophyll a (Chl-a) in the northern East China Sea (ECS) are described, using both 8-day composite images of the SeaWiFS (Sea-viewing Wide Field-of-view Sensor) and in-situ data investigated in August and September during 2000-2005. Ocean color imagery showed that Chl-a concentrations on the continental shelf within the 50 m depth in the ECS were above 10 times higher than those of the Kuroshio area throughout the year. Higher concentrations (above $5mg/m^3$) of yearly mean Chl-a were observed along the western part of the shelf near the coast of China. The standard deviation also showed the characteristics of the spatial variability near $122-124^{\circ}E$, where the western region of the East China Sea was grater than that of the eastern region. Particularly the significant concentration of Chl-a, up to $9mg/m^3$, was found at the western part of $125^{\circ}E$ in the in-situ data of 2002. The higher Chl-a concentrations of in-situ data were consistent with low salinity waters of below 30 psu. It means that there were the close relationship between the horizontal distribution of Chl-a and low salinity water.

• 소성∙가공
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• 제15권8호
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• pp.581-585
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• 2006

Effects of V on both the formation of Ti-Nb-V carbonitrides and mechanical properties of Ti-Nb bearing low carbon HSLA steels were investigated. Hot rolling process was simulated by using Gleeble 3500 system with the steels containing three different levels of V ($0{\sim}0.1wt.%$). Vanadium precipitated as Ti-Nb-V carbonitrides at austenite region but it did not precipitate as VC during austenite to acicular ferrite or bainitic ferrite phase transformation. As V content increased, the amount of Nb precipitates was decreased but the average size of Ti-Nb-V carbonitrides was increased due to larger diffusivity of V than that of Nb. Coarsened Ti-Nb-V carbonitrides could act as heterogeneous nucleation site during ${\gamma}{\rightarrow}{\alpha}$ phase transformation, thus, acicular ferrite transformation was promoted as V content increased, resulting in increase of upper shelf energy.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.618-620
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• 2003

Harmonics of sea surface temperature (SST) in the East Sea and their possible causes are examined by analyzing NOAA/AVHRR data, SSM/I wind speeds, NSCAT wind vectors, and NCEP heat flux data. Detailed spatial structures of amplitudes and phases of the seasonal cycles and their contributions to the total variance of SST have quantitatively. The Subpolar front serves as a boundary between regions of high annual amplitudes (${\geq}$10$^{\circ}$C) in the cold continental region and low amplitudes (${\leq}$10$^{\circ}$C) in the Tsushima Warm Current region. The low phase center of annual cycle is located over a seamount at 132.2$^{\circ}$E, 41.7$^{\circ}$N south of Vladivostok. Semi-annual amplitudes are significantly large leaching over 20% of the annual amplitudes in the Tatarskiy Strait and along the continental shelf off Russian coast in fall and spring, but its forcings are substantially annual. We have shown that fall cooling is attributed by direct and local wind forcing, while spring cooling is remotely forced by cold waters from sea ices in the Tatarskiy Strait.

• 한국해양학회지
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• 제23권4호
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• pp.169-183
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• 1989

한국(韓國) 동남해역(東南海域)의 대륙란(大陸爛)에 서식(棲息)하는 다모류군집(多毛類群集)의 종류를 파악(把握)하고, 또한 이들 군집(群集)이 서식지(棲息地) 환경(環境)에 어떻게 적응, 서식하는가를 밝히고자 하였다. 총80개 조사정점에서 채집된 다모류(多毛類)의 종류와 개체수의 자료로부터 집괴분석(集塊分析)을 실시한 결과 본 연구해역은 크게 연안역(沿岸域)과 외해역(外海域)으로 양분되었고, 8개의 다모류(多毛類) 군집(群集)이 구별되었다. 이질(泥質) 퇴적물(堆積物)이 우세한 연안역(沿岸域)에서는 Nothria holobranchiata 군집(群集)이 포항 근해역에, Magelona-Maldane 군집(群集), Ophelina acuminata 군집(群集), Nothria conchylega 군집(群集)이 연안해역의 남북방향으로 존재(存在)하였다. 이들 연안역(沿岸域)의 군집(群集)들은 종수가 적고 종다양성 지수도 낮았다. 외해역(外海域)에서는 이질퇴적물(泥質堆積物)로 구성된 대륙붕단에 Terebellides-Aglaophamus 군집(群集)이 존재(存在)하였고, 이사질(泥砂質)과 사질(砂質)이 우세한 지역에서는 Myriochele oculata 군집(群集), Spiophanes kroyeri 군집(群集) 및 Ninoe palmata 군집(群集)이 존재(存在)하였다. 외해역(外海域)의 군집(群集)들은 연안역(沿岸域)에 비해 종수나 종다양성이 높았으나, 평균서식밀도는 낮았다. 대부분의 우점종들은 그들의 식이형(食餌型)과 내장의 내용물로부터 특정 퇴적물(堆積物)에 높은 선호도를 보임을 알 수 있었다. 동일 퇴적물(堆積物)에서의 다양한 군집(群集)의 존재(存在)는 수심과 수온이 저서(底棲) 다모류(多毛類)의 분포와 관계가 있음을 시사하였다. 따라서 연구해역의 다모류군집(多毛類群集)은 퇴적물(堆積物)의 특성과 수심(水深) 또는 수온(水溫)에 따라 결정됨을 보여준다.

• 대한금속재료학회지
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• 제48권7호
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• pp.615-624
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• 2010

This study is concerned with tensile and Charpy impact properties of high-strength bainitic steels fabricated by controlled rolling process. Six kinds of steels were fabricated by varying finish rolling temperature, start cooling temperature, and cooling rate, and their microstructures and tensile and Charpy impact properties were investigated. Their effective grain sizes were also characterized by the electron backscatter diffraction analysis. The microstructures of the steels rolled in the single phase region were most similar to those of the steels rolled in the two phase region. The steels cooled from $700{^{\circ}C}$ were composed mainly of granular bainites, while those cooled from $600{^{\circ}C}$ contained a number of bainitic ferrites, which resulted in the decrease in ductility and upper shelf energy in spite of the increase in strength. In the steels cooling from $600^{\circ}C$, fine acicular ferrites were well formed when the cooling rate was slow, which led to the best combination of high ductility, high upper shelf energy, and low energy transition temperature according to the decrease in the overall effective grain size due to the presence of acicular ferrites having smaller effective grain size.

• 한국재료학회지
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• 제23권9호
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• pp.525-530
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• 2013

This study investigated the continuous cooling transformation, microstructure, and mechanical properties of highstrength low-alloy steels containing B and Cu. Continuous cooling transformation diagrams under non-deformed and deformed conditions were constructed by means of dilatometry, metallographic methods, and hardness data. Based on the continuous cooling transformation behaviors, six kinds of steel specimens with different B and Cu contents were fabricated by a thermomechanical control process comprising controlled rolling and accelerated cooling. Then, tensile and Charpy impact tests were conducted to examine the correlation of the microstructure with mechanical properties. Deformation in the austenite region promoted the formation of quasi-polygonal ferrite and granular bainite with a significant increase in transformation start temperatures. The mechanical test results indicate that the B-added steel specimens had higher strength and lower upper-shelf energy than the B-free steel specimens without deterioration in low-temperature toughness because their microstructures were mostly composed of lower bainite and lath martensite with a small amount of degenerate upper bainite. On the other hand, the increase of Cu content from 0.5 wt.% to 1.5 wt.% noticeably increased yield and tensile strengths by 100 MPa without loss of ductility, which may be attributed to the enhanced solid solution hardening and precipitation hardening resulting from veryfine Cu precipitates formed during accelerated cooling.