• Geophysics and Geophysical Exploration
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• v.11 no.1
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• pp.52-59
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• 2008

We have developed a new deep-towed marine DC resistivity survey system. It was designed to detect the top boundary of the methane hydrate zone, which is not imaged well by seismic reflection surveys. Our system, with a transmitter and a 160-m-long tail with eight source electrodes and a receiver dipole, is towed from a research vessel near the seafloor. Numerical calculations show that our marine DC resistivity survey system can effectively image the top surface of the methane hydrate layer. A survey was carried out off Joetsu, in the Japan Sea, where outcrops of methane hydrate are observed. We successfully obtained DC resistivity data along a profile ${\sim}3.5\;km$ long, and detected relatively high apparent resistivity values. Particularly in areas with methane hydrate exposure, anomalously high apparent resistivity was observed, and we interpret these high apparent resistivities to be due to the methane hydrate zone below the seafloor. Marine DC resistivity surveys will be a new tool to image sub-seafloor structures within methane hydrate zones.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.6
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• pp.434-449
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• 2019

In this study, we develop a new cross-shore sediment module which takes the effect of infra-gravity waves of bound mode, and boundary layer streaming on the sediment transport into account besides the well-known asymmetry and under-tow. In doing so, the effect of individual random waves occurring during the unit observation period of 1 hr on sediment transport is also fully taken into account. To demonstrate how the individual random waves would affect the sediment transport, we numerically simulate the non-linear shoaling process of random wavers over the beach of uniform slope. Numerical results show that with the consistent frequency Boussinesq Eq. the application of which is lately extended to surf zone, we could simulate the saw-tooth profile observed without exception over the surf zone, infra-gravity waves of bound mode, and boundary-layer streaming accurately enough. It is also shown that when yearly highest random waves are modeled by the equivalent nonlinear uniform waves, the maximum cross-shore transport rate well exceeds the one where the randomness is fully taken into account as much as three times. Besides, in order to optimize the free parameter K involved in the long-shore sediment module, we carry out the numerical simulation to trace the yearly shoreline change of Mang-Bang beach from 2017.4.26 to 2018.4.20 as well, and proceeds to optimize the K by comparing the traced shoreline change with the measured one. Numerical results show that the optimized K for Mang-Bang beach would be 0.17. With K = 0.17, via yearly grand circulation process comprising severe erosion by consecutively occurring yearly highest waves at the end of October, and gradual recovery over the winter and spring by swell, the advance of shore-line at the northern and southern ends of Mang-Bang beach by 18 m, and the retreat of shore-line by 2.4 m at the middle of Mang-Bang beach can be successfully duplicated in the numerical simulation.

• Economic and Environmental Geology
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• v.39 no.1 s.176
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• pp.27-38
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• 2006

To understand the geologic and hydrogeochemical controls on the occurrence of high fluoride concentrations in bedrock groundwaters of South Korea, we examined a total of 367 hydrochemistry data obtained from deep groundwater wells (avg. depth=600 m) that were drilled fur exploitation of hot springs. The fluoride concentrations were generally very high (avg. 5.65mg/L) and exceeded the Drinking Water Standard (1.5 mg/L) in $72\%$ of the samples. A significant geologic control of fluoride concentrations was observed: the highest concentrations occur in the areas of granitoids and granitic gneiss, while the lowest concentrations in the areas of volcanic and sedimentary rocks. In relation to the hydrochemical facies, alkaline $Na-HCO_3$ type waters had remarkably higher F concentrations than circum-neutral to slightly alkaline $Ca-HCO_3$ type waters. The prolonged water-rock interaction occurring during the deep circulation of groundwater in the areas of granitoids and granitic gneiss is considered most important for the generation of high F concentrations. Under such condition, fluoride-rich groundwaters are likely formed through hydrogeochemical processes consisting of the removal of Ca from groundwater via calcite precipitation and/or cation exchange and the successive dissolution of plagioclase and F-bearing hydroxyl minerals (esp. biotite). Thus, groundwaters with high pH and very high Na/Ca ratio within granitoids and granitic gneiss are likely most vulnerable to the water supply problem related to enriched fluorine.

• Science of Emotion and Sensibility
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• v.13 no.4
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• pp.613-620
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• 2010

The purpose of this study was to quantitatively evaluate the effects of the secondary task while simulated driving using the variable indicating control of vehicle and smoothness of motion. Fifteen healthy adults having 1~2years driving experience were participated. 9 markers were attached on the subjects' upper(shoulder, elbow, Wrist) and lower(knee, ankle, toe) limbs and all subjects were instructed to keep the 30m distance with the front vehicle running at 80km/hr speed. Sending text message(STM) and searching navigation(SN) were selected as the secondary task. Experiment consisted of driving alone for 1 min and driving with secondary task for 1 min, and was defined driving and cognition blocks respectively. To indicate the effects of secondary task, coefficient of variation of distance between vehicles and lane keeping(APCV and MLCV) and jerk-cost function(JC) were analyzed. APCV was increased by 222.1% in SN block. MLCV was increased by 318.2% in STM and 308.4% in SN. JC were increased at the drivers' elbow, knee, ankle and toe, especially the total mean JC of lower limbs were increased by 218.2% in STM and 294.7% in SN. Conclusively, Performing secondary tasks while driving decreased the smoothness of motion with increased JC and disturbed the control of vehicle with increased APCV and MLCV.

• Journal of Environmental Policy
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• v.10 no.1
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• pp.49-70
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• 2011

The numerous efforts have been made in understanding generation and transportation mechanism of nonpoint source pollutants from agricultural areas. Also, the water quality degradation has been exacerbated over the years in many parts of Korea as well as other countries. Nonpoint source pollutants are transported into waterbodies with direct runoff and baseflow. It has been generally thought that groundwater quality is not that severe compared with surface water quality. However its impacts on groundwater in the vicinity of stream quality is not negligible in agricultural areas. The SWAT model has been widely used in hydrology and water quality studies worldwide because of its flexibilities and accuracies. The spatial property of each HRU, which is the basic computational element, is not presented. Thus, the SWAT HRU mapping module was developed in this study and was applied to the study watershed to evaluate recharge rate and $NO_3-N$ loads in groundwater. The $NO_3-N$ loads in groundwater on agricultural fields were higher than on forests because of commercial fertilizers and manure applied in agricultural fields. The $NO_3-N$ loads were different among various crops because of differences in crop nutrient uptake, amount of fertilizer applied, soil properties in the field. As shown in this study, the SWAT HRU mapping module can be efficiently used to evaluate the pollutant contribution via baseflow in agricultural watershed.

• Journal of the Korean Geotechnical Society
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• v.21 no.2
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• pp.113-120
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• 2005

An understanding of soil-structure interaction is the key to rational and economical design for laterally loaded drilled shafts. It is very difficult to formulate the ultimate lateral capacity into a general equation because of the inherent soil nonlincarity, nonhomogeneity, and complexity enhanced by the three dimensional and asymmetric nature of the problem though extensive research works on the behavior of deep foundations subjected to lateral loads have been conducted for several decades. This study reviews the four most well known methods (i.e., Reese, Broms, Hansen, and Davidson) among many design methods according to the specific site conditions, the drilled shaft geometric characteristics (D/B ratios), and the loading conditions. And the hyperbolic lateral capacities (H$_h$) interpreted by the hyperbolic transformation of the load-displacement curves obtained from model tests carried out as a part of this research have been compared with the ultimate lateral capacities (Hu) predicted by the four methods. The H$_u$ / H$_h$ ratios from Reese's and Hansen's methods are 0.966 and 1.015, respectively, which shows both the two methods yield results very close to the test results. Whereas the H$_u$ predicted by Davidson's method is larger than H$_h$ by about $30\%$, the C.0.V. of the predicted lateral capacities by Davidson is the smallest among the four. Broms' method, the simplest among the few methods, gives H$_u$ / H$_h$ : 0.896, which estimates the ultimate lateral capacity smaller than the others because some other resisting sources against lateral loading are neglected in this method. But it results in one of the most reliable methods with the smallest S.D. in predicting the ultimate lateral capacity. Conclusively, none of the four can be superior to the others in a sense of the accuracy of predicting the ultimate lateral capacity. Also, regardless of how sophisticated or complicated the calculating procedures are, the reliability in the lateral capacity predictions seems to be a different issue.

• Journal of Dental Rehabilitation and Applied Science
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• v.25 no.4
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• pp.375-390
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• 2009

Statement of problem: Implant supported overdenture is accepted widely as a way to restore edentulous ridge providing better retention and support of dentures. Various types of attachment for overdenture have been developed. Purpose: The purpose of this study was to investigate the influence of attachment type in implant overdentures on the biomechanical stress distribution in the surrounding bone, prosthesis and interface between implant and bone. Material and methods: Finite element analysis method was used. Average CT image of mandibular body(Digital $Korea^{(R)}$, KISTI, Korea) was used to produce a mandibular model. Overdentures were placed instead of mandibular teeth and 2mm of mucosa was inserted between the overdenture and mandible. Two implants($USII^{(R)}$, Osstem, Korea) were placed at both cuspid area and 4 types of overdenture were fabricated ; ball and socket, Locator, magnet and bar type. Load was applied on the from second premolar to second molar tooth area. 6 times of finite element analyses were performed according to the direction of the force $90^{\circ}$, $45^{\circ}$, $0^{\circ}$ and unilateral or bilateral force applied. The stress at interface between implants and bone, and prosthesis and the bone around implants ware compared using von Mises stress. The results were explained with color coded graphs based on the equivalent stress to distinguish the force distribution pattern and the site of maximum stress concentration. Results: Unilateral loading showed that connection area between implant fixture and bar generated maximum stress in bar type overdentures. Bar type produced 100 Mpa which means the most among 4 types of attachments. Bilateral loading, however, showed that bar type was more stable than other implants(magnet, ball and socket). 26 Mpa of bar type was about a half of other types on overdenture under $90^{\circ}$ bilateral loading. Conclusions: In any directions of stress, bar type was proved to be the most vulnerable type in both implants and overdentures. Interface stress did not show any significant difference in stress distribution pattern.

• Journal of the Korean Geographical Society
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• v.29 no.3
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• pp.233-252
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• 1994

One of major advantages of Lumped model is its ability to simulate extended flows. A further advantage is that it requires only conventional, readily available hydrological data (rainfall, evaporation and runoff). These two advantages commend the use of this type of model for the analysis of the hydrological effects of landuse change. Experimental Catchment(K11) of Kimakia site in Kenga experienced three phases of landuse change for sixteen and half years. The Institute of Hydrology offered the hydrological data from the catchment for this research. On basis of Blackie's(l972) 9-parameter model, a new model(R1131) was reorganized in consideration of the following aspects to reflect the hydrological characteristics of the catchment: 1) The evapotranspiration necessary for the landuse hydrology, 2) high permeable soils, 3) small catchment, 4) input option for initial soil moisture deficit, and 5) othel modules for water budget analysis. The new model is constructed as a 11-parameter, 3-storage, 1-input option model. Using a number of initial conditions, the model was optimized to the data of three landuse phases. The model efficiencies were 96.78%, 97.20%, 94.62% and the errors of total flow were -1.78%, -3.36%, -5.32%. The bias of the optimized models were tested by several techniques, The extended flows were simulated in the prediction mode using the optimized model and the data set of the whole series of experimental periods. They are used to analyse the change of daily high and low-flow caused by landuse change. The relative water use ratio of the clearing and seedling phase was 60.21%, but that of the next two phases were 81.23% and 83.78% respectively. The annual peak flows of second and third phase at a 1.5-year return period were decreased by 31.3% and 31.2% compared to that of the first phase. The annual peak flow at a 50-year return period in the second phase was an increase of only 4.8%, and that in the third phase was an increase of 12.9%. The annual minimum flow at a 1.5-year return period was decreased by 34.2% in the second phase, and 34.3% in the third phase. The changes in the annual minimum flows were decreased for the larger return periods; a 20.2% decrease in the second phase and 20.9% decrease in the third phase at a 50-year return period. From the results above, two aspects could be concluded. Firstly, the flow regime in Catchment K11 was changed due to the landuse conversion from the clearing and seedling phade to the intermediate stage of pine plantation. But, The flow regime was little affected after the pine trees reached a certain height. Secondly, the effects of the pine plantation on the daily high- and low-flow were reduced with the increase in flood size and the severity of drought.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.12 no.6
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• pp.111-122
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• 2017

This study analyzes the current state of entrepreneurship education and start-up foundations by country in order to find ways to improve the domestic entrepreneurial environment and to promote the recognition of desirable entrepreneurship practices. It also investigates the relationship between entrepreneurship, entrepreneurial will, and the level of opportunity-based entrepreneurships, by using data from the 2016 Global Entrepreneurship Trend Report (GETR). First, the results show the urgent need for the expansion of entrepreneurship education in Korea. In the GETR category of 'experience of entrepreneurship education in elementary, middle and high schools', Korea was ranked very low (19th place), among the 20 countries. In the 'college' and 'lifelong entrepreneurship education' categories, it procured a mid-level ranking (15th). While entrepreneurship education for all ages is being promoted globally, entrepreneurship education for middle-aged individuals in Korea is relatively weak. This implies that the expansion of entrepreneurship education to lifelong education and education for employees and retirees is required. Second, the individual's entrepreneurial intention in Korea was 3.8 points, implying a mid-level ranking (15th), and it ranked the lowest in terms of opportunity-based entrepreneurship (20th). In comparison to China (4.55) and the United States (4.01), the entrepreneurial intention of Koreans was found to be low. The level of opportunity-driven entrepreneurship was also found to be very low, compared to China (4.35), Japan (4.04) and the United States (4.59). In general, the proportion of the level in opportunity-driven entrepreneurship, increases from the factor-driven and efficiency-driven, to the innovation-driven type. In Korea, the percentage of entrepreneurial ventures centered around involuntary entrepreneurship and small businesses is high. It is also interpreted that opportunity-based entrepreneurships are low in number because of this high proportion of involuntary start-up and small businesses. Last, the entrepreneurial intention in all types (factor-driven, efficiency-driven, and innovation-driven) was exceptionally high. It has been confirmed that exposure to all entrepreneurship education (elementary, junior high, university, and lifelong education) in innovation-driven countries, greatly increases entrepreneurial intention. In the case of Korea, which is an innovation-driven country, qualitative improvement based on quantitative expansion of entrepreneurship education is expected to be a major driving force for individuals' entrepreneurial intention to obtain a mid-level ranking (15th).

• Journal of Korean Society of Forest Science
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• v.87 no.3
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• pp.328-333
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• 1998

To obtain basic information for establishing a pest control strategy for insect pest management system, changes in the population densities of the black-tipped sawfly(Acantholyda posticalis posticalis Matsumura) and damage patterns in tree growth were investigated in national forests in Hoigok-ri, Kapyung-gun, Kyunggi-do, where the pest control measures were taken. The results obtained were as follows ; 1. The larval density in the soil of the forests where the insecticides were applied have been kept below economic threshold for about 7 years. The density was the highest in the middle of slopes and similar to the level of the early stage of the insect outbreak. 2. After the pest control by insecticides, reduction in tree height and diameter growth lasted for 2-3 years in trees defoliated by over 70%. 3. The diameter growth of the trees damaged by black-tipped sawfly recovered faster in upper stem than in the lower. 4. volume growth of the trees defoliated over 70% by the insect decreased for three to four years. The volume loss of trees defoliated by 70% and 90% was 19.6% and 54.0%, respectively. 5. Maintaining the rate of defoliation below 50%, which is the economic threshold, by chemical control measures had an effect of reducing the tree volume loss by $40m^2/ha$ as compared with a stand defoliated by 90%.