• Korean Journal of Environmental Biology
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• v.36 no.4
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• pp.439-455
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• 2018

Hanon made in the largest maar crater in Korea, is the only paddy field ecosystem in Jeju Island that has been conducting rice farming, for the past 500 years. Flora surveys were conducted eight times, 2015-2018, to understand floristic characteristics and a restoration plan of the study area. As a result, vascular plants of Hanon paddy fields were listed 225 taxa that consist of 55 families, 151 genera, 194 species, 1 subspecies, 25 varieties, and 4 forms. The taxonomic group including the most species, was Gramineae (36 taxa). The next families were Compositae (29 taxa), Cyperaceae (20), Leguminosae (13), and Polygonaceae (11). Biological type of the Hanon was $Th-R_5-D_4-t$ type. The rare plants revealed 3 taxa; Ottelia alismoides(L.) Pers., Acorus calamus L., Pseudoraphis ukishiba Ohwi. Endemic plant revealed 1 taxon; Saururus chinensis(Lour.) Baill. Forty three taxa were naturalized plants composed of 15 families, 24 genera, 41 species, and 2 varieties. The urbanization index and naturalized index were 13.3% and 16.9%, respectively. The Hanon has high plant diversity, including endemic plant and rare plants, and is the only rice paddy in Jeju Island. So, the Hanon has sufficient values in ecological and socio-cultural aspects, so it should be maintained continuously in the future.

• Explosives and Blasting
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• v.36 no.4
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• pp.35-47
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• 2018

In this study, several concrete-block blast tests and AUTODYN numerical analyses were conducted to analyze the effects of different stemming and coupling materials on explosion results. Air, sand, and polymer gel were used as both the stemming and coupling materials. The stemming and coupling effects of these materials were compared with those of the full-charge condition. Soil-covered or buried concrete blocks were used for field crater tests. It was found from the concrete block tests and numerical analyses that both the crater size and the peak pressure around the blast hole were higher when the polymer gel was used than when the sand and the decoupling condition were used. The numerical analyses revealed the same trend as those of the field tests. Pressure peaks in concrete block models were calculated to be 37, 30, and 16 MPa, respectively, for the cases of the polymer gel, sand, and no stemming and decoupling condition. The pressure peak was 52 MPa in the case of full-charge condition, which was the highest pressure. But the damage area for the case was smaller than that obtained from the use of polymer gel. Full-charge was also used as a reference test.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.1
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• pp.85-96
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• 2016

A series of tests were conducted to examine the filled tube shape with respect to the filling module type used and to investigate cone resistance properties of a dredged-soil-filled geotextile tube under water and drained conditions. Results based on the filling observation showed that the distribution of the accumulated fills inside the acrylic cell and vinyl tubes differs with respect to the type of filling modules. A crater formation around the inlet area was found during the test using I-type filling module and a horizontal sediment distribution was found during the test using inverse T-Type filling module. The dredged fill material was obtained from the Saemangeum area. The geotextile tube deformation of each filling stage was almost converged when the tube was fully drained. The cone resistance of the dredged fill in the geotextile tube under drained condition is large and is approximately 2~6 times that of the tube under water condition.

• Journal of the Korean earth science society
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• v.28 no.4
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• pp.462-477
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• 2007

The purpose of this study is to determine the petrology of basalt and the volcanic process in the Seondol cinder cone, Seobjikoji area, eastern Jeju Island. The Seondol cinder cone is mainly composed of spatters in the lower part, pyroclastic deposits including reddish brown blocks, ashes with volcanic bombs in the middle part, and dark black scoria deposits in the upper part. The volcanic sequences suggest volcanic processes that progress through Strombolian eruption and end with Hawaiian lava effusion which breached the cinder cone northwestward and extended over northwestward as lava delta and basalt emplaced as a volcanic neck in the central part of crater in the cinder cone. The age of basalt lava flows is about $95\;{\pm}\;3\;ka$. The basalts belong to transitional basalt and show products of fractional crystallization of clinopyroxene and olivine from a parental basalt magma on the basis of variation diagram of major, trace and rare earth elements. Basalts in the region of this study are plotted at the region of within plate basalt.

• Korean Journal of Plant Resources
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• v.23 no.4
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• pp.350-359
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• 2010

The distribution of the Mankyua chejuense was restricted to the northeast region of Jeju Island. It grows in the isolated pit crater-like swamp areas of various extent and shape, where the height is lower compared to the adjacent areas, and the adjacent regions contained a evergreen broad-leaved forests, a shrubbery, and a grassland vegetation. It contained 147 taxa of 61 families, 112 genera and 147 species in the habitats. The life form of the flora showed that the habitat of M. chejuense is different from the surrounding others, in particular, the ratio of the Therophytes and the Hydrophytes appeared highly. Preservation of habitat conditions is very important for stable maintenance the flora, and the surrounding area including habitats has to be designated a protection area for habitat preservation.

• Journal of Space Technology and Applications
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• v.1 no.3
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• pp.375-395
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• 2021

Korea plans to send a pathfinder lunar orbiter to the Moon for the first time in August 2022. And according to the 3rd Basic Plan for Space Development Promotion, the plan is to send a lunar lander to the Moon before 2030. The selection of the lunar landing area can be varied depending on the lunar lander's mission, therefore preliminary research on the lunar landing sites is essential for a successful lunar exploration mission design. This paper analyzed the characteristics of major regions among 14 proposed regions using NASA's MoonTrek based on the data on the candidate areas for the major moon landing proposed sites by the NASA workshop in 2018. And we looked into what kind of future moon landing missions are suitable for these areas. We also looked at the importance of lunar Antarctica area through the recent lunar landing areas of Moon landing countries and Artemis plan.

• International Journal of Precision Engineering and Manufacturing-Green Technology
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• v.5 no.5
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• pp.583-591
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• 2018

Tool-chip adhesion impacts on cutting performance significantly, especially in finish cutting process. To promote cutting tools' anti-adhesion property, the concave micro-grooves texture (MGT) and convex volcano-like texture (VLT) were fabricated separately on lathe tools' rake faces by laser surface texturing (LST). Various orientations of MGT and different area densities (9% and 48%) and regions (partial and full) of VLT were considered in textured patterns designing. The following orthogonal cutting experiments, machining of aluminum alloy 5038, analyzed tools' performances including cutting force, cutting stability, chip shape, rake face adhesion and abrasion. It indicated that under dry finish cutting conditions, MGT contributed to cutting stability and low cutting forces, meanwhile friction and normal force reduced by around 15% and 10%, respectively with a weak correlation to the grooves' orientation. High density VLT tools, on the other hand, presented an obvious anti-adhesion property. A $5{\mu}m$ reduction of crater wear's depth can be observed on textured rake faces after long length cutting and textured rake faces presented half size of BUE regions comparing to the flat tool, however, once the texture morphologies were filled or worn, the anti-adhesion effect could be invalid. The bearing ratio curve was employed to analysis tool-chip contact and durability of textured surfaces contributing to a better understanding of anti-adhesion and enhanced durability of the textured tools.

• Korean Journal of Environment and Ecology
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• v.28 no.6
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• pp.697-704
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• 2014

Mt. Hallasan in Jejudo has been well known as a habitat for both northern and southern limited butterflies and attracts the interests of many lepidopterists. In this study, the line transect method was used to monitor the community and similarity of butterflies monthly monitoring from May to September 2013, and the results were compared with the previous data. Through monitoring, 3,397 individuals in 26 species of 5 families were found in the present study. The monitored individuals belonging to 4 species (Aphantopus hyperantus, Eumenis autono, Lethe diana and Melanargia epimede) was 2,578 (75.9%), showing the prevalent species among the butterflies observed in the grassy area of the Mt. Hallasan. The butterflies inhabiting Mt. Hallasan showed higher similarity in the area where the open grassy space and the crowns of tree layer coexist than in landscape consisting of solely the tree layer or open grassy space. The habitation of butterflies by heights showed the altitudes between 1,665 to 1,700 m, located beneath the Baekrokdam (the crater) of Mt. Hallasan, possessed the most species and individuals. And it was also observed that the species that previously inhabited the subalpine zone moved to the area of higher altitudes together with the species that previously inhabited rather lower altitudes than the subalpine zone.

• Economic and Environmental Geology
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• v.52 no.6
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• pp.561-571
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• 2019

The Hupo Basin, continental marginal basin, of the East Sea extends to Uljin-gun and Yeongdeok-gun. The Hupo Bank, a terrain that is higher than the surrounding seabed, is located at the eastern boundary of the Hupo Basin. KIOST(Korea Institute of Ocean Science and Technology) conducted detailed bathymetry surveys in the northern, central and southern areas of the Hupo Basin from 2011 to 2013. The Hupo Basin, bounded by steep slopes of the Hupo Bank, is deepened from the west coast to the east and deepest to a maximum depth of about 250 m. A narrow seafloor channel appears in the northern, central, and southern areas with the deepest depths. Numerous pockmarks appear on the seafloor at depths of about 150 ~ 250 m in all the three areas of the detailed bathymetry surveys. These pockmarks generally have diameters of about 20 to 50 m and depths of about 4 to 6 m, with craterlike submarine topography of various sizes. Seafloor sediments in the pockmark areas consist of fine silt. Comparing the shape and size of the pockmark of the Hupo Basin with that of other regions of the world, it is considered to be classified as a normal pockmark. There are about 7 pockmarks/1 ㎢ in the northern part of the three areas and about 8 pockmarks/1 ㎢ in the central part. The southern part has about 5 pockmarks/1 ㎢. If the area with the possibility of pockmarks is extended to the depth area of about 150 ~ 250 m in the entire Hupo Basin, the number of pockmarks is estimated to be more than about 4800. The pockmark of the Hupo Basin is more likely to be generated by a fluid such as a liquid than a gas. But it is necessary to scrutinize the cause and continuously monitor the pockmark.

• Journal of Periodontal and Implant Science
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• v.27 no.3
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• pp.495-514
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• 1997

The purpose of this study was to evaluate the in vitro effects of Nd:YAG laser irradiation on removal of a root surface smear layer after root planing in comparison with Tetracycline HCl. The 60 extracted human teeth due to severe periodontal disease were vigorously scaled and root planed with Gracey curet. Thirty specimen($5{\times}5{\times}2mm$) were obtained from root planed surface of 30 human teeth and assigned randomly to one of three groups : root planed group(5 specimen), Tetracycline HCI group(5 specimen, burnished for 5 minutes), and Nd:YAG laser group(25 specimen, German Dental Laser, Fotona Twinlight). Nd:YAG laser group was divided into 4 subgroups according to power of 1W, 1.5W, 2W, 3W at frequency to 10Hz. The specimen were then fixed, and examed by Scanning electron microscopic study. 30 of 60 human teeth used to measurement of the intrapulpal temperature rise during laser irradiation. Laser-irradiated surface exhibited various surface texture from relative flat surface to irregular surface with patent dentinal tubules of various shape and size. In some area, the root surface alteration which are carbonization, pit and crater formation and melting and resolidification were observed. The number of exposed dentinal tubules per unit($100_{\mu}m^2$) on tetracycline HCI group was more than that in the laser group below 1.5W of power(150mJ/pulse) and was significantly less than that in laser group above 2W of power(200mJ/pulse)(P<0.OOl). As power increased the intrapulpal temperature rise also increased. The result suggested that the parameter which effectively remove root surface smear layer than tetracycline HCI may cause thermal damage to pulp and root surface alteration result from laser exposure would indicate need for additional instrumentation. Thus, Nd:YAG laser irradiation in these parameter may not be appropriate for clinical use as adjunct to conventional periodontal therapy.