• Structural Engineering and Mechanics
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• 제42권6호
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• pp.831-847
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• 2012

Impact from water-borne debris during tsunami and flood events pose a potential threat to structures. Debris impact forces specified by current codes and standards are based on rigid body dynamics, leading to forces that are dependent on total debris mass. However, shipping containers and other debris are unlikely to be rigid compared to the walls, columns and other structures that they impact. The application of a simple one-dimensional model to obtain impact force magnitude and duration, based on acoustic wave propagation in a flexible projectile, is explored. The focus herein is on in-air impact. Based on small-scale experiments, the applicability of the model to predict actual impact forces is investigated. The tests show that the force and duration are reasonably well represented by the simple model, but they also show how actual impact differs from the ideal model. A more detailed three-dimensional finite element model is also developed to understand more clearly the physical phenomena involved in the experimental tests. The tests and the FE results reveal important characteristics of actual impact, knowledge of which can be used to guide larger scale experiments and detailed modeling. The one-dimensional model is extended to consider water-driven debris as well. When fluid is used to propel the 1-D model, an estimate of the 'added mass' effect is possible. In this extended model the debris impact force depends on the wave propagation in the two media, and the conditions under which the fluid increases the impact force are discussed.

• 한국지리정보학회지
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• 제20권3호
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• pp.42-51
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• 2017

대설은 우리나라의 법적 자연재해 중 하나이다. 최근 기상현상에 의한 사회경제적 영향력을 함께 예보하는 영향예보가 부각되고 있으며, 이를 위해서는 먼저 각 지역의 기후적 특징을 분석할 필요가 있다. 본 연구에서는 영향예보의 기반마련을 위해 자기조직화지도를 활용하여 적설동질지역을 구분하여 지역별 적설 특징을 분석했다. 연구결과 적설동질지역은 7개 군집으로 나타났으며, 강설량 및 관측일수, 최대강설량을 이용하여 각 그룹의 특징을 구분했다. 대관령, 강릉시, 정읍시는 강설량이 많은 지역으로, 경상도는 강설량이 적은 지역으로 구분되었다. 선행연구와 비교결과 대표적인 지역이 잘 구분되었으나 강설의 특징은 차이가 있는 것으로 나타났다. 본 연구의 결과는 각 지역의 영향예보를 위한 정책결정에 기초자료로 활용될 수 있다.

• 대한원격탐사학회지
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• 제33권5_3호
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• pp.799-807
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• 2017

환경영향평가는 개발사업의 해로운 환경영향 감소를 위해 시행되는 규제적 성격의 제도이다. 그러나 환경가치는 계량화가 어렵고 불확실성이 따르기 때문에 제도 운영의 객관성 및 신뢰성 저하 문제가 지속적으로 지적되어 온 실정이다. 따라서 데이터 기반 환경영향평가제도의 필요성이 점차 높아지고 있는데, 특히 환경영향평가는 특정 지역의 개발에 대한 내용을 담기 때문에 공간정보의 비중이 높아 환경공간정보의 활용 가능성이 높은 분야이다. 또한 사후환경관리제도의 도입에 따라 환경정보의 시계열적 제공 및 활용체계가 요구되고 있다. 본 연구에서는 환경영향평가의 제도적 특징을 통해 정보제공체계의 필요성을 도출하고 기존 환경정보 활용체계를 분석하였다. 그리고 이를 토대로 공신력 있는 환경공간정보 제공방안을 제시하여 환경영향평가제도의 한계점 개선을 위한 정책적 함의를 찾고자 하였다.

• 대한금속재료학회지
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• 제48권10호
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• pp.875-883
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• 2010

This study assessed the Charpy impact properties of the heat-affected zones (HAZs) of API X80 linepipe steels containing complex oxides. Three types of steel were fabricated by adding Mg and $O_2$ to form complex oxides and their microstructures and Charpy impact properties were investigated. The number of complex oxides increased with the amount of excess Mg and $O_2$ that was included in the steels. Simulated HAZs containing a number of oxides showed a high volume fraction of acicular ferrite (AF) because the oxides acted as nucleation sites for AF, thereby leading to an improvement in the Charpy impact properties. According to a correlation study between the heat input, the volume fraction of the AF, and the Charpy impact properties, ductile fractures occurred predominantly when the fraction of the AF was 20% or higher; moreover, the Charpy absorbed energy was excellent at more than 100 J. These findings suggest that the improvement of the Charpy impact properties of the HAZs was associated with the active nucleation of AF in the oxide-containing steel HAZs.

• 대한금속재료학회지
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• 제47권3호
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• pp.155-168
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• 2009

In this study, microstructural investigation was conducted on the separation phenomenon occurring during Charpy impact tests of API X80 linepipe steels. Particular emphasis was placed on the role of microstructural phases present in the API X80 steels such as acicular ferrite, bainite, and hard secondary phases. Detailed microstructural analysis of fractured impact specimens showed that highly elongated bainite worked as prior initiation sites for separations, and that the number and length of separations increased with increasing volume fraction of bainite. In the steels having high work hardenability, tearing-shaped separations were found because the hammer-impacted region was seriously hardened during the impact test, which led to the reduction in the impact toughness. As the test temperature decreased, the tendency of separations increased, but separations were not observed when the cleavage fracture prevailed at very low temperatures. Thus, the minimization of the formation of bainite and secondary phases in the steels would be beneficial for preventing or minimizing separations because separations deteriorated low-temperature impact toughness.

• 한국해양환경ㆍ에너지학회지
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• 제14권4호
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• pp.239-248
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• 2011

본 연구는 각종 해역이용 개발로 인한 해양환경 및 생태계를 보전하고, 효율적으로 관리하기 위해 2008년부터 본격적으로 시행된 해역이용협의제도의 운용 현황과 실적을 분석하여 협의 유형 및 연안에서 이루어지는 개발사업의 특성을 파악하였다. 또한, 도입기를 지나 정착 발전단계에 접어든 해역이용협의 및 평가제도의 실효성을 확보하기 위해 운용상 나타난 문제점을 고려한 제도의 개선방안을 진단하였다. 2009년 및 2010년의 전체 해역이용협의 실적은 3,705건이며, 간이해역이용협의 87.0%, 일반해역이용협의 12.8%, 해역이용영향평가 0.2%로 나타났다. 일반해역이용협의의 행위유형은 공유수면매립 43.4%, 기타 23.4%, 해수 인 배수 17.5%, 준설 5.5%, 항만시설의 설치 4.6%, 어항시설의 설치 2.3% 순이었다. 환경영향평가서의 검토유형은 항만건설이 32.9%로 가장 많았으며, 그 다음으로 산업단지조성, 관광단지개발과 도로건설, 에너지개발 순으로 분석되었다. 해역이용협의가 증가하고, 개발유형 또한 다양화되고 대형화됨에 따라 제도의 실효성 및 홍보 강화, 협의기관 및 검토기관 등의 역량 강화, 그리고 해양환경영향평가의 신뢰성 제고 방안을 지속적으로 강구해야 할 것이다.

• 대한기계학회논문집A
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• 제20권10호
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• pp.3408-3414
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• 1996

This paper investigated plane strain stress intensity factors caused by thermal impact on a center-crack strip. The crack was aligned perpendicularly to the strip boundary. The problem was analysed by determining the dislocation density function in the singular integral equations formulated by the dislocation theory. Under the abrupt temperature change along the edge, the center crack behaved as a mode I crack due to the symmetric geometry. The value of maximum stress intensity factor monotonically increased until the ratio of dimensionless crack length approached to about 0.3, followed by gradual decrease. As a result, a critical corresponding crack length was determined.

• Computers and Concrete
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• 제9권4호
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• pp.293-310
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• 2012

This paper discusses a new constitutive model called the high-rate brittle microplane (HRBM) model and also presents the details of a new software package called the Virtual Materials Laboratory (VML). The VML software package was developed to address the challenges of fitting complex material models such as the HRBM model to material property test data and to study the behavior of those models under a wide variety of stress- and strain-paths. VML employs Continuous Evolutionary Algorithms (CEA) in conjunction with gradient search methods to create automatic fitting algorithms to determine constitutive model parameters. The VML code is used to fit the new HRBM model to a well-characterized conventional strength concrete called WES5000. Finally, the ability of the new HRBM model to provide high-fidelity simulations of material property experiments is demonstrated by comparing HRBM simulations to laboratory material property data.

• Asian Pacific Journal of Cancer Prevention
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• 제13권6호
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• pp.2903-2908
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• 2012

Background: Matrix metalloproteinase-9 (MMP-9) is associated with disruption of basement membranes of blood vessels and promotion of metastasis through the lymphatics. However, its prognostic value for survival in patients with gastric cancer remains controversial. Method: We therefore conducted a meta-analysis of the published literature in order to clarify the impact of MMP-9. Clinical studies were selected for further analysis if they provided an independent assessment of MMP-9 in gastric cancer and reported analysis of survival data according to MMP-9 expression. Results: A total of 11 studies, covering 1700 patients, were included for meta-analysis. A summary hazard ratio (HR) of all studies and sub-group hazard ratios were calculated. The combined HR suggested that a positive MMP-9 expression had an impact on overall survival: 1.25 (95% confidence interval 1.11-1.40) in all eligible studies; 1.13 (1.06-1.20) in 8 studies detecting MMP-9 by immunohistochemistry; 1.36 (1.12-1.65) in 7 studies from Asia. Only one study for DFS showed a significant impact on disease free survival (HR 1.73, 95%CI 1.27-2.34). Conclusions: Our findings suggested that MMP-9 protein expression might be a factor for a poor prognosis in patients with gastric cancer. However, the association was rather weak, so that more prospective studies should further explore the prognostic impact of MMP-9 mRNA and correlations between MMP-9 and clinicopathological characteristics.

• 대한금속재료학회지
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• 제46권12호
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• pp.788-799
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• 2008

This study is concerned with the effects of Mo, Cr, and V addition on tensile and Charpy impact properties of API X80 linepipe steels. Four kinds of steels were processed by varying Mo, Cr, and V additions, and their microstructures and tensile and Charpy impact properties were investigated. Since the addition of Mo and V promoted to form fine acicular ferrite and granular bainite, while prohibiting the coarsening of granular bainite, it increased the strength and upper shelf energy, and decreased the energy transition temperature. The Cr addition promoted the formation of coarse granular bainite and secondary phases such as martensite-austenite constituents, thereby leading to the increased effective grain size, energy transition temperature, and strength and to the decreased upper shelf energy. The steel containing 0.3wt.% Mo and 0.06wt.% V without Cr had the highest upper shelf energy and the lowest energy transition temperature because its microstructure was composed of fine acicular ferrite and granular bainite, together with a small amount of hard secondary phases, while its tensile properties maintained excellent.