• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.11
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• pp.1349-1354
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• 2013

Sealing structure to prevent flowing hot gas into the driving device, located between the driving shaft and the liner of On-Off valve for controlling the hot gas flow path was studied. Wear occurs due to the constant movement of the driving shaft controlled by actuator on graphite as the sealing material. In this paper, the dynamic wear behavior in high temperature of graphite(HK-6) to be used as sealing material was evaluated. Reciprocating wear test was carried out for the graphite(HK-6) to the relative motion between shaft materials(W-25Re). The results of friction coefficient and specific wear rate according to contact load, sliding speed at room temperature and $485^{\circ}C$ considering the actual operating environment were evaluated. Through the SEM analysis of the worn surface, third body as lubricant films were observed and lubricant effect of third body was considered.

• The Journal of the Petrological Society of Korea
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• v.24 no.1
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• pp.1-10
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• 2015

Neulgeori prehistoric site is located at Joong-ri Kwanin-myon Pocheon-si, Gyeonggi-do, where lots of stone artefacts were excavated. We investigated the petrological features of the artefacts through petrographical observation and modal analysis. In addition we estimated the provenance of the artefacts by means of the geological survey. The twelve stone artefacts used in this study are identified as ash tuff, lapilli tuff, granite porphyry, andesite and diorite porphyry. Various rocks were used for making flakes, whereas blades and debris were from the tuffaceous rocks. Lapilli tuff is considered to have been delivered from the Dongmakgol tuff in the Cheolwon basin, granite porphyry from the Cretaceous granite porphyry stocks cropped out at the southeastern Oksan-ri and eastern Yeoncheon areas. Andesite artefact would have been originated from the outcrops located at the northern part of the site, and diorite porphyry artefact from the southern part of the site. The stone artefacts investigated are estimated to have been transported from the area within 15 kilometers from the site.

• Journal of Korean Society of Forest Science
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• v.104 no.4
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• pp.588-597
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• 2015

This study was carried out to identify the reasons of the landslide by land creeping in South Korea in order to provide basic information for establishing the management plan for prevention. Total 29 sites of landslide areas caused by land creeping were observed in South Korea. Among them, the soil-composition of most frequent landslide areas occurred by land creeping was colluvium landslide as 75.9% (22 sites), followed by clay soil landslide as 10.3% (3 sites), bedrock landslide as 6.9% (2 sites), and weathered rock landslide as 6.9% (2 sites). According to the types of parental rocks, the investigated landslide areas were divided into 3 types: 1) metamorphic rocks including schist, phylite, migmatitic gneiss, quartz schist, pophyroblastic gneiss, leucocratic granite, mica schst, banded gneiss and granitic gneiss, 2) sedimentary rocks including limestone, sandstone or shale and mudstone, 3) igneous rocks such as granite, andesite, rhyolite and masanite. As a result, it was noticed that the landslides occurred mostly at the metamorphic rocks areas (13 sites; 44.8%), followed by sedimentary rock areas (12 sites; 41.4%), and igneous rock areas (4 sites; 13.8%). Looking at the direct causes of the landslide, the anthropological activities (71%) such as cut slopes for quarrying, construction of country house, plant, and road, farming of mountain top, and reservoir construction were the biggest causes of the landslides, followed by the land creeping landslides (22%) caused by geological or naturally occurred (22%), and cliff erosions (7%) by caving of rivers and valleys.

• Journal of Korean Society of Forest Science
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• v.108 no.4
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• pp.552-561
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• 2019

In korea, debris-flow disasters are induced by typhoon and localized torrential rainfall annually. These disasters are particularly severe in the Korean national park due to its geomorphological characteristics. This study was conducted to analyze the landslide characteristics and forest environmental factors of landslide areas located in rugged mountain range in the Korean national park (Mt. Seorak, Mt. Jiri, and Mt. Sobaek). Overall, landslides occurred at 474 sites. The average area of the landslide scar among these sites was 1,212 ㎡. The average landslide sediment was 1,389 ㎥, average landslide length was 75 m, and the average width was 12.9 m. The landslides frequently occurred in regions with igneous rock and coniferous forest. In addition, slope gradient degree (31°-40°), slope gradient direction (N), vertical slope (concave), cross slope (concave), altitude (401-800 m), position (middle), stream order (first order), forest type (mixed), parent rock (igneous), and soil depth (<46 cm). The relationship between landslide soil volume and environmental factors showed positive correlation. The variables of vertical slope (complex), altitude (<1,201 m), and soil depth (<46 cm) correlated significantly at 1 % level.

• Geophysics and Geophysical Exploration
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• v.13 no.4
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• pp.323-329
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• 2010

Three deconvolution methods were applied to stacked seismic data obtained to investigate gas-hydrates in the Ulleung Basin, East Sea: (1) minimum-phase spiking deconvolution, (2) minimum-phase spiking deconvolution using an averaged wavelet from all traces, and (3) deterministic deconvolution using a wavelet with phases computed from well-logs. We analyzed the resolving property of these methods for lithological boundaries. The first deconvolution method increases temporal resolution but decreases lateral continuity. The second method shows, in an overall sense, similar results to the spiking deconvolution using a minimum phase wavelet for each trace; however, it results in a more consistent and continuous bottom-simulating reflector (BSR) and better resolved sub-BSR reflectors. The results from the third method reveal more detailed internal structures of debris-flow deposits and increased continuity of reflectors; in addition, the seafloor reflection and the BSR appear to have changed to a zero-phase waveform. These properties help more precisely estimate the distribution and reserves of gas hydrates in the exploration area by improving analysis of facies and amplitude of the BSR.

• Elastomers and Composites
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• v.46 no.1
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• pp.70-77
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• 2011

A new piece of test equipment, the slurry wear tester (SWT), was proposed in this study to evaluate the wear behavior of rubber vulcanizate in environmental contact with slurry. Natural rubber (NR) and chloroprene rubber (CR) were chosen as the basic matrices to test the slurry wear. The fluids used to fill the chamber of the SWT were 35% HCl and NaCl solution. The Akron abrasion test was used for comparison with SWT. According to the results of the Akron abrasion test, CR vulcanizate abraded more rapidly than NR vulcanizate under same test condition. It was found that the hysteresis of rubber was key factor contribute to the wear behavior. However, the slurry wear rate of the NR and CR vulcanizates did not change significantly, even with changes in the concentration of acid and the immersion time in both HCl and NaCl solutions; the fluid decreased the friction between the abrasive paper and the specimen. It also reduced the heat generated from repeated deformation and wear debris at the surface of the SWT's abrasion arm. Thus, these phenomena affected the wear behavior of rubber vulcanizate and caused different results in the conventional Akron abrasion test. This outcome could have resulted in an incorrect analysis if the slurry wear behavior of the rubber vulcanizate was estimated by the conventional abrasion tests, which are operated under dry conditions.

• The Korean Journal of Mycology
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• v.34 no.2
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• pp.92-97
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• 2006

The liquid culture extract of Coriolus versicolor was prepared by directly boiling the whole culture broth 7 days after incubation in 12% citrus extract medium. After removal of mycelial debris through filtration, this extract was further extracted with equal volume of ethyl acetate (1 : 1, v/v). The ethyl acetate extracts showed significant antibacterial activities against Stapylococcus aureus CCARM3230 and Psudomonas aeruginosa CCARM2171, which are resistant to several antibiotics. The most active fraction was eluted from a silica gel column with a mixture of dichloromethane and methanol (9 : 1, v/v) and the purity of this active substance was confirmed by HPLC analysis. The results suggest that the purified active substance could be a good source for the development of a new antimicrobial agent, especially for the treatment of antibiotic resistant bacteria.

• Restorative Dentistry and Endodontics
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• v.34 no.6
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• pp.508-514
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• 2009

The purposes of this study were to compare the efficacy of irrigation systems by removing a calcium hydroxide $(Ca(OH)_2)$ paste from the apical third of the root canal and the effect of the patency file. Sixty single rooted human teeth were used in this study. The canals were instrumented by a crown-down manner with .04 taper ProFile to ISO #35. $Ca(OH)_2$ and distilled water were mixed and placed inside the root canals. The teeth were divided into 6 groups according to the root canal irrigation system and the use of patency file as follows: group 1 - conventional method: group 2 - $EndoActivator^{(R)}$: group 3 - $EndoVac^{(R)}$; group 4 - conventional method, patency: group 4 - $EndoActivator^{(R)}$, patency; group 6 - $EndoVac^{(R)}$, patency. All teeth were irrigated with sodium hypochlorite. After the root canal irrigation, the teeth were split in bucco-lingual aspect. Percentage of the root canal surface coverage with residual $Ca(OH)_2$ until 3 mm from working length was analyzed using Image Pro Plus ver. 4.0. Statistical analysis was performed using the One-way ANOVA, t-test and Scheffe's post-hoc test. Conventional groups had significantly more $Ca(OH)_2$ debris than $EndoActivator^{(R)}$, $EndoVac^{(R)}$ groups. There was no significant difference between $EndoActivator^{(R)}$ and $EndoVac^{(R)}$ groups. Groups with patency file showed more effective in removing $Ca(OH)_2$ paste than no patency groups. but. it was no significant difference. This study showed that $EndoActivator^{(R)}$ and $EndoVac^{(R)}$ systems were more effective in removing $Ca(OH)_2$ paste from the apical third of the root canal than conventional method.

• Journal of the Korean GEO-environmental Society
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• v.16 no.7
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• pp.43-53
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• 2015

More than 70 percent of the Korean territory consists of mountain area so development of mountain district is essential to urbanize continuously. Thus, technological developments for risk factors and standards and manuals must be needed to prevent mountain disaster. Risk Management Manual should be made and operated in government legislation related to national disaster, but there is still no Emergency Management Standard Manual and Emergency Response-Practical Manual to prevent mountain disaster. This study suggests the improvement plans that are legislated but not established cleary in the field of disaster in urban area. The main items are like as 1) adaptable standard and practical manual to prevent mountain disaster in urban area, 2) reinforcement between managing department and interagency vertically and horizontally in central and local government organization, 3) Personal SOP (Standard Operating Procedure) not EOP (Emergency Operation Plan), 4) considering 13 items selected by Ministry of Public Safety and Security, 5) schematization with personal action plan, 6) check list to do in the event of mountain disaster, and 7) regular practice per quarter.

• Journal of Korean Society of Forest Science
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• v.110 no.4
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• pp.610-621
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• 2021

The soil creep, primarily caused by earthquakes and torrential rainfall events, has widely occurred across the country. The Korea Forest Service attempted to quantify the soil creep susceptible areas using a discriminant value table to prevent or mitigate casualties and/or property damages in advance. With the advent of advanced computer technologies, machine learning-based classification models have been employed for managing mountainous disasters, such as landslides and debris flows. This study aims to quantify the soil creep susceptibility using several classifiers, namely the k-Nearest Neighbor (k-NN), Naive Bayes (NB), Random Forest (RF), and Support Vector Machine (SVM) models. To develop the classification models, we downscaled 292 data from 4,618 field survey data. About 70% of the selected data were used for training, with the remaining 30% used for model testing. The developed models have the classification accuracy of 0.727 for k-NN, 0.750 for NB, 0.807 for RF, and 0.750 for SVM against test datasets representing 30% of the total data. Furthermore, we estimated Cohen's Kappa index as 0.534, 0.580, 0.673, and 0.585, with AUC values of 0.872, 0.912, 0.943, and 0.834, respectively. The machine learning-based classifications for soil creep susceptibility were RF, NB, SVM, and k-NN in that order. Our findings indicate that the machine learning classifiers can provide valuable information in establishing and implementing natural disaster management plans in mountainous areas.