• Journal of Information Processing Systems
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• 제14권6호
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• pp.1445-1456
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• 2018

Environment perception and three-dimensional (3D) reconstruction tasks are used to provide unmanned ground vehicle (UGV) with driving awareness interfaces. The speed of obstacle segmentation and surrounding terrain reconstruction crucially influences decision making in UGVs. To increase the processing speed of environment information analysis, we develop a CPU-GPU hybrid system of automatic environment perception and 3D terrain reconstruction based on the integration of multiple sensors. The system consists of three functional modules, namely, multi-sensor data collection and pre-processing, environment perception, and 3D reconstruction. To integrate individual datasets collected from different sensors, the pre-processing function registers the sensed LiDAR (light detection and ranging) point clouds, video sequences, and motion information into a global terrain model after filtering redundant and noise data according to the redundancy removal principle. In the environment perception module, the registered discrete points are clustered into ground surface and individual objects by using a ground segmentation method and a connected component labeling algorithm. The estimated ground surface and non-ground objects indicate the terrain to be traversed and obstacles in the environment, thus creating driving awareness. The 3D reconstruction module calibrates the projection matrix between the mounted LiDAR and cameras to map the local point clouds onto the captured video images. Texture meshes and color particle models are used to reconstruct the ground surface and objects of the 3D terrain model, respectively. To accelerate the proposed system, we apply the GPU parallel computation method to implement the applied computer graphics and image processing algorithms in parallel.

• Advances in concrete construction
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• 제13권1호
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• pp.83-99
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• 2022

The two, NBD and SCB tests using gypsum circular discs each containing a single notch have been experimentally accomplished in a rock mechanics laboratory. These specimens have also been numerically modelled by a two-dimensional particle flow which is based on Discrete Element Method (DEM). Each testing specimen had a thickness of 5 cm with 10 cm in diameter. The specimens' lengths varied as 2, 3, and 4 cm; and the specimens' notch angles varied as 0°, 45° and 90°. Similar semi-circular gypsum specimens were also prepared each contained one edge notch with angles 0° or 45°. The uniaxial testing machine was used to perform the experimental tests for both NBD and SCB gypsum specimens. At the same time, the numerical simulation of these tests were performed by PFC2D. The experimental results showed that the failure mechanism of rocks is mainly affected by the orientations of joints with respect to the loading directions. The failure mechanism and fracturing patterns of the gypsum specimens are directly related to the final failure loading. It has been shown that the number of induced tensile cracks showing the specimens' tensile behavior, and increases by decreasing the length and angle of joints. It should be noted that the fracture toughness of rocks' specimens obtained by NBD tests was higher than that of the SCB tests. The fracture toughness of rocks usually increases with the increasing of joints' angles but increasing the joints' lengths do not change the fracture toughness. The numerical solutions and the experimental results for both NDB and SCB tests give nearly similar fracture patterns during the loading process.

• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1416-1428
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• 2021

Pebble flow characteristics can be significantly affected by the configuration of pebble bed, especially for HTGR pebble beds. How to achieve a desired uniform flow pattern without stagnation is the top priority for reactor design. Pebbles flows inside some specially designed pebble bed with arc-shaped contraction configurations at the bottom, including both concave-inward and convex-outward shapes are explored based on discrete element method. Flow characteristics including pebble retention, residence-time frequency density, flow uniformity as well as axial velocity are investigated. The results show that the traditionally designed pebble bed with cone-shape bottom is not the most preferred structure with respect to flow pattern for reactor design. By improving the contraction configuration, the flow performance can be significantly enhanced. The flow in the convex-shape configuration featured by uniformity, consistency and less stagnation, is much more desirable for pebble bed design. In contrast, when the shape is from convex-forward to concave-inward, the flow shows more nonuniformity and stagnation in the corner although the average cross-section axial velocity is the largest due to the dominant middle pebbles.

• Geomechanics and Engineering
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• 제34권5호
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• pp.577-595
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• 2023

A dynamic triaxial discrete element numerical model of lightweight soil was established using the discrete element method to study the microscopic mechanism of expanded polystyrene (EPS) particles in the soil under cyclic loading. The microscopic parameters of the discrete element model of the lightweight soil were calibrated depending on the dynamic triaxial test hysteresis curves. Based on the calibration results, the effects of the EPS particles volume ratio and amplitude on the contact force, displacement field, and velocity field of the lightweight soil under different accumulated strains were studied. The results showed that the hysteresis curves of lightweight soil exhibit nonlinearity, hysteresis, and strain accumulation. The strain accumulated in remolded soil is mainly tensile strain, and that in lightweight soil is mainly compressive strain. As the volume ratio of EPS particles increased, the contact force first increased and then decreased, and the displacement and velocity of the particles increased accordingly. With an increase in amplitude, the dynamic stress of the particle system increased, and the accumulation rate of the dynamic strain of the samples also increased. At 5% compressive strain, the contact force of the particles changed significantly and the number of particles deflected in the direction of velocity also increased considerably. These results indicated that the cemented structure of the lightweight soil began to fail at a compressive strain of 5%. Thus, a compressive strain of 5% is more reasonable than the dynamic strength failure standard of lightweight soil.

• Structural Engineering and Mechanics
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• 제87권3호
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• pp.221-229
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• 2023

Urbanization and industrialization have significantly increased the amount of solid waste produced in recent decades, posing considerable disposal problems and environmental burdens. The practice of waste utilization in concrete has gained popularity among construction practitioners and researchers for the efficient use of resources and the transition to the circular economy in construction. This study employed Lytag aggregate, an environmentally friendly pulverized fuel ash-based lightweight aggregate, as a substitute for natural coarse aggregate. At the same time, fly ash, an industrial by-product, was used as a partial substitute for cement. Concrete mix M20 was experimented with using fly ash and Lytag lightweight aggregate. The percentages of fly ash that make up the replacements were 5%, 10%, 15%, 20%, and 25%. The Compressive Strength (CS), Split Tensile Strength (STS), and deflection were discovered at these percentages after 56 days of testing. The concrete cube, cylinder, and beam specimens were examined in the explorations, as mentioned earlier. The results indicate that a 10% substitution of cement with fly ash and a replacement of coarse aggregate with Lytag lightweight aggregate produced concrete that performed well in terms of mechanical properties and deflection. The cementitious composites have varying characteristics as the environment changes. Therefore, understanding their mechanical properties are crucial for safety reasons. CS, STS, and deflection are the essential property of concrete. Machine learning (ML) approaches have been necessary to predict the CS of concrete. The Artificial Fish Swarm Optimization (AFSO), Particle Swarm Optimization (PSO), and Harmony Search (HS) algorithms were investigated for the prediction of outcomes. This work deftly explains the tremendous AFSO technique, which achieves the precise ideal values of the weights in the model to crown the mathematical modeling technique. This has been proved by the minimum, maximum, and sample median, and the first and third quartiles were used as the basis for a boxplot through the standardized method of showing the dataset. It graphically displays the quantitative value distribution of a field. The correlation matrix and confidence interval were represented graphically using the corrupt method.

• 한국분말재료학회지
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• 제30권5호
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• pp.394-401
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• 2023

Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) is considered to be one of the promising solid-state electrolytes owing to its excellent chemical and thermal stability, wide potential range (~5.0 V), and high ionic conductivity (~10^-4 S/cm). LATP powders are typically prepared via the sol-gel method by adding and mixing nitrate or alkoxide precursors with chelating agents. Here, the thermal properties, crystallinity, density, particle size, and distribution of LATP powders based on chelating agents (citric acid, acetylacetone, EDTA) are compared to find the optimal conditions for densely sintered LATP with high purity. In addition, the three types of LATP powders are utilized to prepare sintered solid electrolytes and observe the microstructure changes during the sintering process. The pyrolysis onset temperature and crystallization temperature of the powder samples are in the order AC-LATP > CA-LATP > ED-LATP, and the LATP powder utilizing citric acid exhibits the highest purity, as no secondary phase other than LiTi₂PO₄ phase is observed. LATP with citric acid and acetylacetone has a value close to the theoretical density (2.8 g/cm³) after sintering. In comparison, LATP with EDTA has a low sintered density (2.2 g/cm³) because of the generation of many pores after sintering.

• 한국세라믹학회지
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• 제36권2호
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• pp.203-209
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• 1999

Si 기판위에 Ba2YCu3O7-$\delta$ 고온초전도체를 응용하기 위해 요구되는 buffer층으로 유망한 재료인 LaAlO3 단일상 분말을 고상반응법과 자발착한 연소반응법으로 제조하였다. 제조된 LaAlO3 분말의 입자형태와 결정상태는 scanning electron microscope (SEM)과 X-ray diffractometer (XRD)를 이용하여 분석하였다. 분말의 비표면적과 소결특성은 각각 Brunauer-Emmett-Teller(BET) 방법과 dilatometer를 측정하였다. 고상반응법으로 LaAlO3 분말을 제조할 때에는 하소온도를 150$0^{\circ}C$까지 높게 하여도 단일상을 얻는 것이 어려웠으나 자발착한 연소반응법에 의한 분말제조는 $650^{\circ}C$의 저온에서 하소하여도 쉽게 얻을 수 있었다. Dilatometer 측정을 통하여 분석해 보면, 고상반응법에 의한 분말보다 자발착한 연소반응법에 의한 분말로 제조된 소결체가 고상반응법에 의한 소결체에 비해 1.4배나 큰 소멸밀도(98.87%)를 가졌다. 이렇게 소결밀도에서 큰 차이가 나는 것은 자발착한 연소방법에 의한 분말의 평균 입자크기가 nano crystal size이고 비표면적 값(56.54 $m^2$/g)이 매우 크기 때문이다. 두가지 방법으로 제조된 분말을 이용, LaAlO3 layer를 스크린 프린팅과 소결법으로 Si 기판상에 제조하였으며 자발착한 연소합성법으로 제조된 분말은 110$0^{\circ}C$에서 우수한 소결특성을 나타내었다.

• 한국지반공학회논문집
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• 제29권3호
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• pp.51-60
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• 2013

말뚝 시공 시 선단 부분에 쌓이는 슬라임은 현장타설말뚝의 선단지지력을 감소시켜 구조물의 안정성에 큰 영향을 미친다. 슬라임의 존재 유무는 주로 다짐추 혹은 철근을 낙하시켜 판정하고 있으며, 이와 같은 방법은 주관적인 판단결과로 신뢰성에 한계가 있다. 본 논문에서는 물리탐사기법 중 하나인 전기비저항 특성을 활용하여 슬라임층의 존재 여부와 두께를 과학적이고 객관적으로 평가하는 방법을 제시하고자 한다. 슬라임층의 전기비저항 특성을 평가하기 위하여 기존에 개발된 온도보상형 전기비저항 프로브(TRP)를 활용하였으며, TRP의 형상은 원뿔형태로 직경은 표준콘 관입실험 장비와 동일하게 35.7mm이다. 현장타설말뚝 공법 중 P.R.D(Percusion Rotary Drill) 방법을 적용하고 있는 현장에서 실험을 수행하였으며 전기비저항의 결과를 이용하여 슬라임층의 두께를 평가하였다. 신뢰성 높은 분석을 도모하고자 현장 슬라임층을 이용하여 케이싱 효과, 시간경과 그리고 상대밀도에 따른 실내 실험도 추가적으로 수행하였다. 본 연구에서는 전기비저항을 이용하여 슬라임층 두께를 산정하는 방법이 합리적임을 보여주며, 추후 다양한 지층과 말뚝 시공 공법에 적용성이 기대된다.

• 한국지리정보학회지
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• 제8권3호
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• pp.65-73
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• 2005

임하호 유역의 지질은 점토질 및 셰일층으로 구성되어 있기 때문에 강우발생시 흙탕물의 형태로 많은 토립자가 호소로 유입되므로 호소내 탁도관측자료는 유역내 토사유실을 평가하는 간접지표가 될 수 있다. 본 연구에서는 GIS 기반토사유실모델을 활용하여 연토사유실량을 평가하였으며 월별로 토사유실량을 배분하기 위해 시우량자료를 이용한 강우가중치 기법을 적용하였다. 2003년도 탁도자료를 볼때, 강우가중치에 의한 월별토사유실량 방법이 강우량자료에 의한 월별토사유실량 보다 더 효과적임을 알 수 있었다.

• 한국수자원학회논문집
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• 제53권1호
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• pp.29-43
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• 2020

본 연구의 목적은 하천복원에 스텝-풀 연속체를 적용하기 위해 기존 연구결과에서 스텝-풀의 기하구조, 형성 과정, 수리 기능, 복원 및 생태 기능과 관련된 사항을 검토하여 설계기준 및 세부설계 모델을 제시하는 것이다. 분석 및 검토결과를 바탕으로 스텝 간격과 하폭의 비, 단위스텝경사와 하상경사의 비, 및 스텝 높이와 입경 비로서 스텝-풀의 구조 및 규모에 대한 설계기준을 제시하였고, 스텝의 구조적 안정성 확보를 위해서는 키스톤 이론을 근거로 전도에 대한 안정성 해석방법을 설계기준으로 제시하였다. 세부설계 개념으로서 스텝-풀의 평면, 종단 및 횡단 구성에 키스톤과 아치스톤에 대한 겹침구조를 적용한 배치 모델을 제안하였다.