• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.111-114
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• 2012

The ignition behavior of single coal particles of five kindes of coal with different ranks (low volatile bituminous, low volatile sub-bituminous, high volatile bituminous, lignite) with particle size of $150-200{\mu}m$ was investigated at high heating rate condition. Particles were injected into a laminar flow reactor and the ignition behavior was observed with high speed cinematography. Sub-bituminous were observed to ignite homogeneously; however, low volatile bituminous coal and lignite undergo fragmentation prior to igntion. The observation was analyzed with previous work.

• Structural Engineering and Mechanics
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• 제82권6호
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• pp.713-724
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• 2022

Effects of coal tensile strength and plow configuration on the coal fragmentation process was modeled by two-dimensional particles flow code (PFC2D). Three tensile strength values, 0.5, 1,5 and 3.5 MPa were considered in this numerical study. The cutters of plow penetrated in the coal for 4 mm at a rate of 0.016 m/s. According to the PFC manual, the local damping factor was 0.7. Three failure mechanism of coal during the fragmentation process by plow were modelled. The coal material beneath the cutters showed the elastic, plastic and fracturing behaviors in this analysis. In all the models, the plastic zone was fractured and some micro-cracks were induced but the elastic zone remained undamaged. It was observed that the tensile strength affected the failure mechanism of coal significantly and as it increased the extent of the fractured zone underneath the plow cutter decreased during the fragmentation process.

• Geomechanics and Engineering
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• 제18권2호
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• pp.111-119
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• 2019

Due to certain geological characteristics (high thickness, rocky properties), some underground coal mines require the use of explosives. This paper explores the effects of fragmentation of different decks detonated simultaneously in a single borehole with the use of numerical analysis. ANSYS/LS-DYNA code was used for the implementation of the models. The models include an erosion criterion to simulate the cracks generated by the explosion. As expected, the near-borehole area was damaged by compression stresses, while far zones and the free surface of the boundary were subjected to tensile damage. With the increase of the number of decks in the borehole, different changes in the fracture pattern were observed, and the superposition effects of the stress wave became evident, affecting the fragmentation results. The superposition effect is more evident in close distances to the borehole, and its effect attenuates when the distance to the borehole increase.

• Geomechanics and Engineering
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• 제24권3호
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• pp.205-213
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• 2021

Water infusion has long been taken as an effective way to eliminate coal burst risk as coal properties can be loosen and soften by water infusion. However, not all industrial trials of water infusion for coal burst prevention have been necessarily effective in all situations as the effectiveness of this method can be affected by water infusion time, coal properties and the parameters of water injection. Hence, some fundamental issues including the effects of water infusion time on burst propensity and energy evolution need to be further discussed. In this paper, four groups of coal specimens with 0 day, 5 days, 10 days, and 15 days water saturation time are tested under uniaxial compression load with the application of AE monitoring. To comprehensively compare the burst behavior of coal specimens under different water saturation time, stress-strain curves, AE counts, fragmentation characteristics and burst propensity of these groups are analyzed. It was found by this research that sufficient water saturation can mitigate the burst behavior of coal samples while insufficient water infusion might cannot reach the burst mitigation aims.

• Geomechanics and Engineering
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• 제30권5호
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• pp.401-411
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• 2022

To obtain the dynamic mechanical properties, fracture modes, energy and brittleness characteristics of Furong Baijiao coal rock, the dynamic impact compression tests under 0, 4, 8 and 12 MPa confining pressure were carried out using the split Hopkinson pressure bar. The results show that failure mode of coal rock in uniaxial state is axial splitting failure, while it is mainly compression-shear failure with tensile failure in triaxial state. With strain rate and confining pressure increasing, compressive strength and peak strain increase, average fragmentation increases and fractal dimension decreases. Based on energy dissipation theory, the dissipated energy density of coal rock increases gradually with growing confining pressure, but it has little correlation with strain rate. Considering progressive destruction process of coal rock, damage variable was defined as the ratio of dissipated energy density to total absorbed energy density. The maximum damage rate was obtained by deriving damage variable to reflect its maximum failure severity, then a brittleness index BD was established based on the maximum damage rate. BD value declined gradually as confining pressure and strain rate increase, indicating the decrease of brittleness and destruction degree. When confining pressure rises to 12 MPa, brittleness index and average fragmentation gradually stabilize, which shows confining pressure growing cannot cause continuous damage. Finally, integrating dynamic deformation and destruction process of coal rock and according to its final failure characteristics under different confining pressures, BD value is used to classify the brittleness into four grades.

• Geomechanics and Engineering
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• 제16권1호
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• pp.85-95
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• 2018

Water affects the mechanical properties of coal and stress wave propagation. To comprehensively investigate the effect of water content on the properties of coal, laboratory tests including X-Ray Diffraction (XRD) analysis, P-wave test, S-wave test, static and dynamic compression test with different water contents were conducted. The compressive strength, elastic modulus and failure strain and their mechanism of coal specimen under coupled static-dynamic load with the increased water content were observed. Meanwhile, energy transmission and dissipation characteristics of a stress wave in coal specimens with different water contents under dynamic load and its relation with the failure features, such as fragmentation and fractal dimension, of coal was analyzed. Furthermore, the dynamic interpretation of water infusion to prevent coal burst based on water infusion model of coal seam roadway was provided.

• Geomechanics and Engineering
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• 제17권3호
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• pp.295-305
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• 2019

The bedding plane has a significant influence on the effect of blasting fragmentation and the overall performance of underground mining. This paper explores the effects of fragmentation of the bedding plane and different angles by using the numerical analysis. ANSYS/LS-DYNA code was used for the implementation of the models. The models include a dynamic compressive and tensile failure which is applied to simulate the fractures generated by the explosion. Firstly, the cracks propagation with the non-bedding plane in the coal with two boreholes detonated simultaneously is calculated and the particle velocity and maximum principal stress at different points from the borehole are also discussed. Secondly, different delay times between the two boreholes are calculated to explore its effects on the propagation of the fractures. The results indicate that the coal around the right borehole is broken more fully and the range of the cracks propagation expanded with the delay time increases. The peak particle velocity decreases first and then increases with the distance from the right borehole increasing. Thirdly, different angles between the bedding plane and the centerline of the two boreholes and the transmission coefficient of stress wave at a bedding plane are considered. The results indicated that with the angles increase, the number of the fractures decreases while the transmission coefficient increases.

• Journal of Ecology and Environment
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• 제29권3호
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• pp.191-203
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• 2006

본 연구는 중부 온대활엽수림을 대표하는 광릉 숲을 대상으로 산림성 조류가 숲의 내부와 가장자리를 어떻게 이용하는지 분석하고, 숲의 단편화로 인한 영향을 파악할 수 있도록 가장 자리 선호도에 따라 서식지 특이종을 파악하기 위해 실시되었다. 그 결과 조류의 풍부도는 숲의 내부와 가장자리에서 일관성 있는 결과를 얻지 못하였으며, 이는 숲 내부와 가장자리를 모두 이용할 수 있는 일반종의 출현 여부에 의해 크게 좌우되었다. 따라서 산림의 단편화가 산림성 조류에 미치는 영향을 파악하기 위해서는 전체 조류군집의 풍부도를 확인하는 것보다 특정 환경을 선호하는 서식지 특이종의 변화를 집중적으로 파악하는 것이 유리할 것으로 판단되었다. 선 조사법과 정점 조사법에 의해 얻어진 숲 내부와 가장자리의 서식밀도를 기준으로 서식지 특이종을 파악한 결과 숲새(U. squameiceps), 흰배 지빠귀(T. pallidus), 진박새(P. ater) 등 3 종이 숲 내부종으로 나타났으며 까치(P. pica), 꾀꼬리(O. chinensis)의 2 종은 숲 가장자리종으로 나타났다. 따라서 광릉 숲으로 대표되는 중부 온대활엽수림의 단편화에 의한 산림성 조류의 영향을 파악하기 위해서는 서식지 특이종으로 파악된 종을 대상으로 한 분포와 번식 등에 대한 모니터링이 필요하며, 특히 숲의 내부에 강한 선호도를 보이는 종에 대한 조사가 우선되어야 할 것으로 판단된다.

• 한국시뮬레이션학회논문지
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• 제29권3호
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• pp.1-8
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• 2020

적 무인기가 거대 도시지역에 침투 시 다양한 형태의 대공화기들이 넓은 지역에 배치되어 대응한다. 대공무기의 특징상 다량으로 비행체에 대해서 사격함으로 명중탄을 제외한 잔여탄은 자체 폭발 후 다양한 크기의 파편으로 낙하한다. 파편이 지상으로 낙하하면서 인명에게 피해를 줄 수 있는 임계속도, 파편질량, 파편 초기속도, 물체충돌 속도 등 4가지 요소를 도출하여 대공포와 유도무기로 구분하여 피해율을 분석하였다. 앞으로 북은 비대칭전력인 무인기를 활동하여 수도서울에 대한 침투가 예상됨으로 대응 간 인명 피해 최소화를 위해 사전 피탄지역과 사격제한지역을 설정해 둠으로서 피해를 최소화 할 수 있을 것이다.

• 생명과학회지
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• 제26권2호
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• pp.147-154
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• 2016

본 연구에서는 인간 골육종암세포주인 Saos-2 세포를 이용하여 Eucheuma cottonii 추출물(Extract of Eucheuma cottonii, EE)의 항암 활성 및 분자적 작용기전을 분석하였다. 먼저 EE가 세포증식에 미치는 영향을 WST-1^® assay를 통해 확인한 결과 EE는 인간 위암세포 AGS, 인간 간암세포 SK-Hep 1, 인간 뇌교모세포종 U87MG, 인간 정상 신장세포 HEK-293의 생존율에는 영향을 미치지 않고 Saos-2 세포주의 생존율만을 농도의존적으로 감소시킴을 확인 하였다. 또한 처리 농도가 증가함에 따라 Saos-2 세포의 외형적 변화가 나타남을 도립현미경을 통해 확인할 수 있었다. 그리고 DAPI staining을 통해 apoptosis classical hall marker라고 할 수 있는 DNA fragmentation이 EE 처리 농도 의존적으로 나타남을 관찰할 수 있었다. 이를 토대로 EE가 Saos-2 세포에서 세포 내의 어떠한 기작을 통해 apoptosis를 유도하는지 Western blot analysis를 통해 확인한 결과, Fas-Associated Death Domain(FADD)에 의한 caspase cascade signal pathway 발현이 증가하였고, apoptosis의 key protein 이라고 할 수 있는 cleaved caspase-3와 하위 인자인 cleaved PARP가 증가 함을 확인할 수 있었다. 이와 관련된 분자적 기전 분석을 위한 immunofluorescence staining과 Flow cytometry analysis를 추가로 수행한 결과, EE 처리시 caspase cascade signal pathway의 시발점인 FAS와 cleaved caspase-3의 발현증가가 실제 세포 내에서 일어남을 관찰 할 수 있었으며 apoptosis 유발군인 sub G1기가 증가 함을 알 수 있었다. 이상의 결과를 통해 EE는 인간 골육종암세포에서 FADD에 의한 caspase cascade signal pathway 발현증가가 유도되어 apoptosis를 유발시킨다는 것을 증명하였으며 새로운 골육종암 치료제로서의 개발 가능성과 기전연구를 위한 중요한 기초자료가 될 수 있음을 시사한다.