• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.2
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• pp.143-150
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• 1993

Shallow sub-bottom reflection recorders are obtained using dual frequency (15/100 KHz). The main goal of this study is to enhance the resolving power and penetration for the sub-bottom reflection of the sub-marine seismic exploration. The Fresnel zones of spherical waves for the near-field are of great importance to reach the high resoluton. In case a target to detects than the Fresnel radius, a diffraction hyperbola on the recorder is observed. A larger attenuation of sand makes less penetration than the smaller attenuation of silt and clay. It is found that the selective frequency as well as the seismic energy generation is the most important factors for sub-marine exploration. This technique of using dual frequency sub-marine exploration may be applied to detect the sub-bottom sludge soil, ocean contamination and marine archaeological relics.

• The Journal of Korea Robotics Society
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• v.13 no.2
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• pp.79-85
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• 2018

This study focuses on autonomous exploration based on map expansion for an underwater robot equipped with acoustic sonars. Map expansion is applicable to large-area mapping, but it may affect localization accuracy. Thus, as the key contribution of this paper, we propose a method for underwater autonomous exploration wherein the robot determines the trade-off between map expansion ratio and position accuracy, selects which of the two has higher priority, and then moves to a mission step. An occupancy grid map is synthesized by utilizing the measurements of an acoustic range sonar that determines the probability of occupancy. This information is then used to determine a path to the frontier, which becomes the new search point. During area searching and map building, the robot revisits artificial landmarks to improve its position accuracy as based on imaging sonar-based recognition and EKF-SLAM if the position accuracy is above the predetermined threshold. Additionally, real-time experiments were conducted by using an underwater robot, yShark, to validate the proposed method, and the analysis of the results is discussed herein.

• Carbon letters
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• v.5 no.3
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• pp.108-112
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• 2004

Effect of silicon infiltration on the bend and tensile strength of 2D cross-ply carbon-carbon composites are studied. It is observed that bend strength higher than tensile strength in both types of composite is due to the different mode of fracture and loading direction. After silicon infiltrations bend and tensile strength suddenly decreases of carbon-carbon composites. This is due to the fact that, after silicon infiltration, silicon in the immediate vicinity of carbon forms the strong bond between carbon and silicon by formation silicon carbide and un-reacted silicon as free silicon. Therefore, these composites consist of three components carbon, silicon carbide and silicon. Due to mismatch between these three components secondary cracks developed and these cracks propagate from $90^{\circ}$ oriented plies to $0^{\circ}$ oriented plies by damaging the fibers (i.e., in-situ fiber damages). Hence, secondary cracks and in-situ fiber damages are responsible for degradation of mechanical properties of carbon-carbon composites after silicon infiltration which is revealed by microstructure investigation study by scanning electron microscope.

• Economic and Environmental Geology
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• v.25 no.2
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• pp.145-151
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• 1992

In order to study the optimum depth for the soil geochemical exploration in the area which is affected by agricultural activities and waste disposal of metal mine, the soil samples were sampled from the B layer of residual soil and vertical 7 layers up to 250 cm in the rice field and 3 layers up to 90 cm in the ordinary field. They were analyzed for Au, As, Cu, Pb and Zn by AAS, AAS-graphite furnace and ICP. To investigate the proper depth for the soil sampling in the contaminated area, the data were treated statistically by applying correlation coefficient, factor analysis and trend analysis. It is conclude that soil geochemical exploration method could be applied in the farm-land and a little contaminated area. The optimum depth of soil sampling is 60 cm in the ordinary field, and 150~200 cm in the rice field. Soil sampling in the area of a huge mine waste disposal is not recommendable. Plotting of geochemical map with factor scores as a input data shows a clear pattern compared with the map of indicater element such as As or Au. The second or third degree trend surface analysis is effective in inferring the continuity of vein in the area where the outcrop is invisible.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.3
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• pp.65-72
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• 2007

Fire is one of important checkpoints in crewed exploration systems, where men inhabit in space. In space, astronaut can't escape from fire out of a spacecraft and not expect any help of fire fighters, either. Accordingly, the best way to stand against fire is to prevent it. But, when fire occurs in space, flame behaviors are quite different from those observed on earth because of micro- or zero-gravity in space. The present paper introduces major research results on flame behaviors under microgravity and fire prevention, detection, and suppression in crewed exploration spacecrafts and international space station based on NASA's FPDS research program.

• Journal of Information Science Theory and Practice
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• v.9 no.4
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• pp.35-49
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• 2021

In a situation where there are multiple diverse datasets, it is essential to have an efficient method to provide users with the datasets they require. To address this suggestion, necessary datasets should be selected on the basis of the relationships between the datasets. In particular, in order to discover the necessary datasets for disaster resolution, we need to consider the disaster resolution stage. In this paper, in order to provide the necessary datasets for each stage of disaster resolution, we constructed a disaster type and disaster management process ontology and designed a method to determine the necessary datasets for each disaster type and disaster management process step. In addition, we introduce a method to determine relationships between datasets necessary for disaster response. We propose a method for discovering datasets based on minimal relationships such as "isA," "sameAs," and "subclassOf." To discover suitable datasets, we designed a knowledge exploration model and collected 651 disaster-related datasets for improving our method. These datasets were categorized by disaster type from the perspective of disaster management. Categorizing actual datasets into disaster types and disaster management types allows a single dataset to be classified as multiple types in both categories. We built a knowledge exploration model on the basis of disaster examples to ensure the configuration of our model.

• Journal of Astronomy and Space Sciences
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• v.36 no.3
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• pp.213-223
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• 2019

This paper analyzes delta-Vs to maintain an extremely low altitude on the Moon and investigates the possibilities of performing a CubeSat mission. To formulate the station-keeping (SK) problem at an extremely low altitude, current work has utilized real-flight performance proven software, the Systems Tool Kit Astrogator by Analytical Graphics Inc. With a high-fidelity force model, properties of SK maneuver delta-Vs to maintain an extremely low altitude are successfully derived with respect to different sets of reference orbits; of different altitudes as well as deadband limits. The effect of the degree and order selection of lunar gravitational harmonics on the overall SK maneuver strategy is also analyzed. Based on the derived SK maneuver delta-V costs, the possibilities of performing a CubeSat mission are analyzed with the expected mission lifetime by applying the current flight-proven miniaturized propulsion system performances. Moreover, the lunar surface coverage as well as the orbital characteristics of a candidate reference orbit are discussed. As a result, it is concluded that an approximately 15-kg class CubeSat could maintain an orbit (30-50 km reference altitude having ${\pm}10km$ deadband limits) around the Moon for 1-6 months and provide almost full coverage of the lunar surface.

• Journal of the Society of Disaster Information
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• v.14 no.4
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• pp.430-439
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• 2018

Purpose: The purpose of this study is to verify the effectiveness of maintenance method using GPR exploration by buried detective materials in the ground for efficient maintenance of recovered cavities. Method: EMI sheet, EMI paint, and ferronickel slag were used as the detection materials, and the experiment was conducted by varying the size and depth of the buried detectable material. Results: As a result of the exploration, Detectable influence range by GPR exploration was found depending on the size and depth of buried detectable material in all materials, and the possibility of using it as a detection material was confirmed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.12
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• pp.877-888
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• 2022

Recently, as the CAPSTONE, a precursor mission for Lunar Gateway, was launched on a small launch vehicle for the purpose of demonstrating communications and navigation technology in the NRHO, large attention was brought to this event that enabled high-impact deep space mission using dedicated small launch vehicle and small spacecraft. In this study, we introduced the concept of a dual launch operation and examined the capability of the new concept in the exploration of the Moon, Mars and asteroid. It turned out a single launch is sufficient for the lunar low orbit mission up to around 247 kg, and the dual launch option can transport 215 kg and 183 kg to nearby destinations as such as Mars and astroid Apophis respectively.

• Journal of Space Technology and Applications
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• v.3 no.1
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• pp.44-57
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• 2023

In order for a latecomer in deep-space exploration such as Korea to quickly keep pace with advanced deep-space exploration countries in the mutually-beneficial space exploration market, it is essential to derive a deep-space probe reference model that can reduce development period and cost. In this paper, concept and configuration for the deep-space probe reference model consisting of basic, lightweight, and expansion types are newly presented, which are based on commonly required designs for various deep-space probes. The proposed configuration adopts modular design so that the expandability and design/implementation efficiency are improved. In addition, the electrical system design pursuing lightweight and expandability is also described, which is applicable to the proposed three-types of deep-space probe reference model.