• KSCE Journal of Civil and Environmental Engineering Research
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• 제26권3C호
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• pp.143-155
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• 2006

SPT-Uphole tomography method was introduced for the evaluation of near subsurface shear wave velocity (Vs) distribution map. In SPT-Uphole method, SPT (Standard Penetration Test) which is common in geotechnical site investigation was used as a source and several surface geophones in line were used as receivers. Vs distribution map which is the triangular shape around the boring point can be developed by tomography inversion. To obtain the exact travel time information of shear wave component, a procedure using the magnitude summation of vertical and horizontal components was used based on the evaluation of particle motion at the surface. It was verified that proposed method could give reliable Vs distribution map through the numerical study using the FEM (Finite Element Method) model. Finally, SPT-Uphole tomography method was performed at the weathered soil site where several boring data with SPT-N values are available, and the feasibility of proposed method was verified in the field.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• 제28권4호
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• pp.143-157
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• 2023

This study confirmed the characteristics of macrobenthic community due to anthropogenic environmental changes in the Boryeong Jugyo tidal flat, where the habitat of manila clam (Ruditapes philippinarum) and mud shrimp (Upogebia major) is separated. The total number of occurring species was 55 during the study period with an average habitat density of 338 ind./m² and a biomass of 212.2 gWWt/m². The number of occuring species increased from 27 species at the upper flat to 37 species at the lower flat, and the dominant species differed by tide levels (Upper: Leonnates persica, Middle: Heteromastus filiformis, Lower: R. philippinarum). The macro-benthic community sturctures of the top 10 species using cluster analysis and nMDS were divided into two groups, focusing on Manila clam culture farm of lower flats and middle flats with high habitat density, reflecting the influence of specific species. The sediment composition of the U. major habitat space fluctuated highly, but it was maintained annually, and the sorting coefficient was 2.1 𝜑, and the proportion of the same particle size was increased. In particular, because the middle flat has a dense anthropogenic impact, a dominant species, H. filiformis dominated and revealed a relationship with the density of burrow holes of U. major, which is considered to be a biological interaction between these two macrofauna in this tidal flat.

• Journal of the Korean Geosynthetics Society
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• 제22권4호
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• pp.43-49
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• 2023

This study described the test results to evaluate the effect of fines content on the wettability of sandy soil composed of hydrophobic soil particles. Wettability was evaluated using the contact angle obtained from the water drop test results for Jumunjin standard sand and sandy soil containing fines content. The test results showed that the wettability of sandy soil composed of sand and fine-grained soil changed depending on the hydrophobic level and fines content. The influence of fines content on the wettability of sandy soil was analyzed. It was found that 1% and 3% hydrophobic sandy soil with 5% fines content decreased by 94.4% and 32.4%, respectively, compared to the contact angle of standard sand. In addition, the contact angle reduction ratio for sandy soil with a 5% hydrophobic level and a fines content of 5% and 10% were 24.4% and 37.3%, respectively. In other words, the wettability of the soils should be evaluated considering the fines content to predict the behavior of contaminants, because the fines content has a significant impact on the value and increase/decrease ratio of the contact angle of sandy soil

• Korean Journal of Agricultural and Forest Meteorology
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• 제25권4호
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• pp.415-426
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• 2023

In this study, the horizontal and vertical structure of wind speed and wind direction were analyzed at the origin of migratory insect pests in China. Wind rose analysis was carried out using the Land-Atmosphere Modeling Package (LAMP) - WRF data, which has the spatiotemporal resolution of about 20 km and 1 hour intervals. Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) was employed for backward trajectory analysis between South Korea and Southeastern China with Global Data Assimilation System (GDAS). The research interest date is July 16, when rice planthopper and leafhopper were observed at the same time. In order to examine where a jet stream occurs in the vertical in source regions and South Korea during the period (July 8 to July 17 in 2021), three-dimensional wind information was extracted and analyzed using the east-west, north-south, and vertical component wind data of the LAM P. The vertical distribution of wind showed that the wind changed in favor of the inflow of migratory insect pests during the period. As a result of analyzing the wind rose, about 30% or more of the wind at a point close to South Korea was classified into the low-level jet stream. In addition, majority of the wind directions for the low-level jet streams (rather than high-level jet streams) at the five origin sites were heading toward South Korea and even Japan, and this was supported by the HYSPLIT-based backward trajectory analysis.

• Atmosphere
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• 제34권1호
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• pp.35-53
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• 2024

Under the leadership of the National Institute of Meteorological Sciences (NIMS), the first domestic autonomous flight-type weather modification experimental drone for fog and lower-level cloud seeding was developed in 2021. This drone is designed based on a multi-copter configuration with a maximum takeoff weight of approximately 25 kg, enabling the installation of up to four burning flares for seeding materials and facilitating weather observations (temperature, pressure, humidity, and wind) as well as aerosol (PM₁₀, PM_2.5, and PM_1.0) particle measurements. This research aims to introduce the construction of the drone and its recent applications over the past two years, providing insights into the experimental procedures, effectiveness verification, and improvement directions of the weather modification drone-based rain enhancement. In particular, partial confirmation of the experimental effects was obtained through the fog dissipation experiment on December 10, 2021, and the lower-level cloud seeding case study on October 5, 2022. To enhance the scope and rainfall amount of weather modification experiments using drones, various technological approaches, including adjustments to experimental altitude, seeding lines, seeding amount, and verification methods are necessary. Through this research, we aim to propose the development direction for weather modification drone technology, which will serve as foundational technology for practical application of domestic rain enhancement technology.

• The Journal of the Convergence on Culture Technology
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• 제9권5호
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• pp.523-528
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• 2023

The applicability as a material to improve solar cell performance was reviewed by synthesizing a phosphor that emits red wavelengths by a liquid synthesis method using a metal salt aqueous solution and a polymer medium as a starting material. An aqueous solution was prepared using nitrate of metals such as Ca, Zn, Al, and Eu, and a precursor impregnated with starch, a natural polymer, was sintered to synthesize CaZnAlO:Eu phosphor powder. The surface structure and composition analysis of the synthesized CaZnAlO:Eu phosphor powder were analyzed by scanning electron microscope(SEM) and energy-dispersed X-ray spectroscopy(EDS). The crystal structure of CaZnAlO:Eu phosphor particles was analyzed by an X-ray diffraction analyzer (XRD). As a result of measuring the photoluminescence(PL) characteristics of the phosphor, it was confirmed that a red phosphor with a light emitting wavelength of 650-780nm was successfully synthesized. According to SEM and EDS analysis, the synthesized Ca₁₄Zn₆Al_9.93O₃₅:Eu³⁺_0.07 phosphor powder has a uniform particle size, and Eu ions used as an activator are present. The synthesized CZA:Eu³⁺ phosphor can be used as a material that can increase the light absorption efficiency of the solar cell by converting ultraviolet or visible light down conversion into a wavelength in the near-infrared region.

• Journal of Radiation Protection and Research
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• 제48권4호
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• pp.197-203
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• 2023

Background: The thermoluminescent dosimeter (TLD) and Monte Carlo (MC) dosimetry are carried out to determine the occupational dose for personnel in the handling of ¹²⁵I seed sources. Materials and Methods: TLDs were placed in different layers of the Alderson-Rando phantom in the thyroid, lung and also eyes and skin surface. An ¹²⁵I seed source was prepared and its activity was measured using a dose calibrator and was placed at two distances of 20 and 50 cm from the Alderson-Rando phantom. In addition, the Monte Carlo N-Particle Extended (MCNPX 2.6.0) code and a computational phantom with a lattice-based geometry were used for organ dose calculations. Results and Discussion: The comparison of TLD and MC results in the thyroid and lung is consistent. Although the relative difference of MC dosimetry to TLD for the eyes was between 4% and 13% and for the skin between 19% and 23%, because of the existence of a higher uncertainty regarding TLD positioning in the eye and skin, these inaccuracies can also be acceptable. The isodose distribution was calculated in the cross-section of the head phantom when the ¹²⁵I seed was at two distances of 20 and 50 cm and it showed that the greatest dose reduction was observed for the eyes, skin, thyroid, and lungs, respectively. The results of MC dosimetry indicated that for near the head positions (distance of 20 cm) the absorbed dose rates for the eye lens, eye and skin were 78.1±2.3, 59.0±1.8, and 10.7±0.7 µGy/mCi/hr, respectively. Furthermore, we found that a 30 cm displacement for the ¹²⁵I seed reduced the eye and skin doses by at least 3- and 2-fold, respectively. Conclusion: Using a computational phantom to monitor the dose to the sensitive organs (eye and skin) for personnel involved in the handling of ¹²⁵I seed sources can be an accurate and inexpensive method.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• 제16권5호
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• pp.217-222
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• 2023

The purpose of this paper was to synthesize a polymer organic hard mask that simplifies the manufacturing process, reduces process time significantly, and thereby lowers manufacturing costs. The results of measuring residual metals through vapor refining showed that 9-Naphthalen-1-ylcarbazole(9-NC) measured 101.75ppb in the 4th zone, 2-Naphthol (2-NA) measured 306.98ppb in the 5th zone, and 9-Fluorenone(9-F) measured between 129.05ppb across the 4th and 5th zones. After passing through a filtration system, the synthesized organic hard mask measured residual metals in the range of 9 to 7ppb. Additionally, the thermal analysis indicated a decrease of 2.78%, a molecular weight of 942, carbon content of 89.74%, and a yield of 72.4%. The etching rate was measured at an average of 18.22Å/s, and the coating thickness deviation was averaged at 1.19. For particle sizes below 0.2㎛ in the organic hard mask, no particles were observed. By varying the coating speed at 1,000, 1,500, and 1,800rpm and measuring the resulting coating thickness, the shrinkage rate ranged from 17.9% to 20.8%. The coating results demonstrated excellent adhesion to SiON, and it was evident that the organic hard mask was uniformly applied.

• Journal of the Korean Crystal Growth and Crystal Technology
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• 제33권5호
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• pp.167-173
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• 2023

Li₃V₂(PO₄)₃ and Li₃V₂(PO₄)₃/C composite with single phase monoclinic structure for the cathode materials are successfully synthesized by direct co-precipitation method using N₂H₄·H₂O as the reducing agent and alginic acid as the carbon source, and their electrochemical properties were compared. The particles with approximately 1~2 ㎛ size and the uniform spherical-like morphology of the narrow particle size distribution were obtained. In addition, the residual carbon can also improve the electrical conductivity. The Li₃V₂(PO₄)₃/C composite has improved initial specific discharge capacity and excellent cycle characteristics to maintain capacity stably than Li₃V₂(PO₄)₃. The results indicate that the reducing agent and carbon composite can affect the good crystallinity and electrochemical performance of the cathode materials.

• Journal of the Korea institute for structural maintenance and inspection
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• 제27권6호
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• pp.62-69
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• 2023

Re-damage is frequently occurring for various reasons, including material factors, external factors, and factors caused by poor construction in concrete cross-section restoration work, so it is necessary to identify the cause and improve it. Cement-based materials are the most commonly used maintenance materials for concrete structures, and in particular, additional cross-sectional restoration work may be carried out due to re-damage such as cracks and excitement due to dry contraction of the repair material. In this study, a basic study was conducted to identify the characteristics of concrete while diversifying the maximum dimensions and assembly rate of thick aggregates to examine the effects of using thick aggregates in repair materials. As a result, the slump of concrete increased as the maximum size of thick aggregates increased, and the amount of air content was measured 1.88 to 2.35 times higher in the mixing using aggregates with a maximum aggregate size of 5 mm or more compared to the mixing group with a maximum aggregate size of 10 mm or more. It was found that compressive strength was greatly affected by the performance rate of thick aggregates. The compressive strength was measured the highest in the mixture using thick aggregates with the highest performance rate of 20 mm, and the compressive strength of the mixture with the lowest performance rate was more than 45%. As a result of the dry shrinkage measurement, the dry shrinkage was the lowest as the performance rate of the thick aggregate increased according to the change in the maximum dimensions and assembly rate of the thick aggregate, and the lowest performance rate was the largest in the mix. Through this study, it was confirmed that adjusting the particle size by diversifying the maximum dimensions and assembly rate of thick aggregates used in concrete structure repair materials can improve strength and workability and reduce dry shrinkage.