• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.129-139
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• 2002

Dielectric constant measurement has drawn much attention in the investigation of the properties and contaminations of subsurface. In this study, by varying the frequency from 75 kHz to 12 MHz, dielectric constant was measured for the weathered granite soil and Jumunjin sand having different water contents and dry density. The dielectric constant of sand showed the dispersive behavior indicating that dielectric constant decreased with frequency of an electric field. And the dielectric constant of soil increased as water content and/or dry density increased due to the decrease of air portion and/or the increase of amount of water molecules which could contribute to the development of orientation polarization. The dielectric constant of sand showed a linear relationship with the moisture density, considering both water content and dry density. At low frequency, the dielectric constants calculated by Maxwell's, Topp's and CRIM equation deviated from measured values. It could be explained by the fact that those equations did not consider dispersive behavior of dielectric constant with the frequency.

• Proceedings of the Korean Society of Crop Science Conference
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• 2022.10a
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• pp.108-108
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• 2022

In this study, multispectral images of wheat according to soil water state were collected, compared, and analyzed to measure the physiological response of crops to environmental stress at the individual level. CMS-V multi-spectral camera(Silios Technologies) was used for image acquisition. The camera lens consists of eight spectral bands between 550nm and 830nm. Light Reflective information collected in each band sensor and stored in digital values, and it is converted into a reflectance for calculating the vegetation index and used. According to the camera manual, the NDVI(Normalized Difference vegetation index) value was calculated using 628 nm and 752 nm bands. Image measurement was conducted under natural light conditions, and reflectance standards(Labsphere) were captured with plants for reflectance calculation. The wheat variety used Gosomil, and the wheat grown in the field was transplanted into a pot after heading date and measured. Three treatments were performed so that the soil volumetric water content of the pot was 13~17%, 20~23%, and 25%, and the growth response of wheat according to each treatment was compared using the NDVI value. In the first measurement after port transplantation, the difference in NDVI value according to treatment was not significant, but in the subsequent measurement, the NDVI value of the treatment with a water content of 13 to 17% was lowest and was the highest at 20 to 23%. The NDVI values decreased compared to the first measurement in all treatment, and the decrease was the largest at 13-17% water content and the smallest at 20-23%. Although the difference in NDVI values could be confirmed, it would be difficult to directly relate it to the water stress of plants, and further research on the response of crops to environmental stress and the analysis of multi-spectral image will be needed.

• Korean Journal of Soil Science and Fertilizer
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• v.43 no.6
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• pp.804-811
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• 2010

The lower portion of sloping paddy fields normally contains excessive moisture and the higher water table caused by the inflow of ground water from the upper part of the field resulting in non-uniform water content distribution. Four drainage methods namely Open Ditch, Vinyl Barrier, Pipe Drainage and Tube Bundle for multiple land use were installed within 1-m position from the lower edge of the upper embankment of sloping alluvial paddy fields. Knowledge of the spatial variability of soil water properties is of primary importance for management of agricultural lands. This study was conducted to evaluate the effect of drainage in the soil on spatial variability of soil water content using the geostatistical analysis. The soil water content was collected by a TDR (Time Domain Reflectometry) sensor after the installation of subsurface drainage on regular square grid of 80 m at 20 m paddy field located at Oesan-ri, Buk-myeon, Changwon-si in alluvial slopping paddy fields ($35^{\circ}22^{\prime}$ N, $128^{\circ}35^{\prime}$). In order to obtain the most accurate field information, the sampling grid was divided 3 m by 3 m unit mesh by four drainage types. The results showed that spatial variance of soil water content by subsurface drainage was reduced, though yield of soybean showed the same trends. Value of "sill" of soil water content with semivariogram was 9.7 in Pipe Drainage, 86.2 in Open Ditch, and 66.8 in Vinyl Barrier and 15.7 in Tube Bundle.

• Korean Journal of Agricultural Science
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• v.43 no.4
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• pp.547-559
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• 2016

The objectives of this study were to investigate the effects of excessive soil-water on crop growth and to predict decrease of yields caused by excessive soil-water. The following five crops were selected for investigation: foxtail millet, proso millet, sorghum, adzuki bean, and sesame. These were planted in pots and a soil-water table was set to 10cm for 10 days. Crop susceptibility (CS) factors and stress-day indexes (SDI) were calculated for each crop to estimate effects of excessive soil-water. SDI models were calculated using CS and SDI data for each crop and predicted the yields of crops cultivated in paddy fields. All crops were cultivated in paddy fields with different soil water contents to evaluate the yield-SDI models. Results showed that yields decreased most when crops were affected by excessive soil-water at the early development stage. Decrease of yields was the greatest when the excessive soil-water treatment was applied at early growth stage. In the field experiment, crops from soils with the greatest soil-water content had the smallest yield, while ones from soils with the smallest soil water contents showed the greatest yields. Observed yields from the field and predicted yields from SDI models showed the least correlation for proso millet, foxtail millet, and adzuki bean and the greatest correlation for sesame. In conclusion, proso millet, foxtail millet, and adzuki bean were more susceptible to soil water than other crops, while sorghum and sesame were more suitable to cultivation in paddy fields.

• Economic and Environmental Geology
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• v.53 no.1
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• pp.71-85
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• 2020

To understand behavior of fault cores in the field of geotechnical and geological engineering, we present an investigation of the physical properties (breccia and clay contents, unit weight, porosity, and water content) and friction characteristics (internal friction angle and cohesion) of fault cores, in granitic, sedimentary, and volcanic rocks in South Korea. The breccia contents in the fault cores are positively correlated with unit weight and negatively correlated with clay content, porosity, and water content. The inter-quartile ranges of internal friction angles and cohesion calculated from direct shear tests are 16.7-38.1° and 2.5-25.3 kPa, respectively. The influence of physical properties on the friction characteristics of the fault cores was analyzed and showed that in all three rock types the internal friction angles are positively correlated with breccia content and unit weight, and negatively correlated with clay content, porosity, and water content. In contrast, the cohesions of the fault cores are negatively correlated with breccia content and unit weight, and positively correlated with clay content, porosity, and water content.

• Asian Journal of Innovation and Policy
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• v.10 no.1
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• pp.39-67
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• 2021

This study investigated the policy instruments pertinent to the establishment of a regional innovation system in the Mekong Delta that facilitates the development of a countermeasure towards various issues of industrial and technological nature. First, we conducted the research with regard to the status and environment of the region. Second, a field visiting survey was implemented to analyze the results of international efforts and regional capacity to solve the problems attendant upon introducing technologies related to the Fourth Industrial Revolution. Third, we derived the key policy issues and challenges from the results of the field visiting survey and experts' conference with a deep focus on technological transfer and international cooperation to enhance the capability in the science and technology field. Fourth, we conducted the opinion survey of the experts from Korea and Vietnam to converge local opinions from both countries and analyzed the results. The range of research subjects is responding to climate change, managing water resources, coordinating energy and industrial structure, making a resilient Mekong regional ecosystem, smartification of local cities, and improving the life quality of citizens, and so on. The results of this study are expected to be the beginning of fundamental research in the mid to long-term view of the Mekong Delta region innovation system of Korea and Vietnam and to evaluate the master plan.

• Geomechanics and Engineering
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• v.36 no.4
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• pp.381-390
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• 2024

The introduction of bio-based materials has been recommended in the geotechnical engineering field to reduce environmental pollutants such as heavy metals and greenhouse gases. However, bio-treated soil methods face limitations in field application due to short research periods and insufficient verification of engineering performance, especially when compared to conventional materials like cement. Therefore, this study aimed to develop a machine learning model for predicting the unconfined compressive strength, a representative soil property, of biopolymer-based soil treatment (BPST). Four machine learning algorithms were compared to determine a suitable model, including linear regression (LR), support vector regression (SVR), random forest (RF), and neural network (NN). Except for LR, the SVR, RF, and NN algorithms exhibited high predictive performance with an R² value of 0.98 or higher. The permutation feature importance technique was used to identify the main factors affecting the strength enhancement of BPST. The results indicated that the unconfined compressive strength of BPST is affected by mean particle size, followed by biopolymer content and water content. With a reliable prediction model, the proposed model can present guidelines prior to laboratory testing and field application, thereby saving a significant amount of time and money.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.47 no.3
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• pp.259-262
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• 2002

Relationship between yield and palatability value measured by vice taster among 9 rice varieties was investigated to obtain basic information for production of rice with high quality in reclaimed paddy field. The rice yield showed a highly negative correlation with palatability value of milled rice (r=-0.49$^{**}$). The varieties of high palatability value tend to show low yield. The protein content of milled rice grown in reclaimed paddy field was higher than 7.5% mainly due to heavy fertilization of nitrogen and irrigation of eutrophicated water, The rice varieties such as Daeanbyeo, Jinpumbyeo and Sindongjinbyeo were recommendable only for higher yield, but in view of rice quality, Kwanganbyeo, Surabyeo and Nampyoengbyeo were more recommendable because of their lower protein content and higher palatability value.e.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.52 no.3
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• pp.259-263
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• 2007

Sowing time of barley after cultivation of rice has frequently been delayed because of rainfall or some other reasons by rice cultivation. Partial tillage direct grain seeder with eight row, which had been developed for rice sowing and showed many advantages in wet field, were tested for barley sowing. After flooding during $2{\sim}3days$, plots were designed to make wet condition. Three sowing methods were tested; high ridged broadcasting, plat drill seeding and partial tillage direct grain seeding. It were impossible to sow properly even in 27% of soil water content by high ridged broadcasting, plat drill seeding but could be possible to sow normally by partial tillage direct grain seeder in 42% of soil water content as good as in 27% of soil water content. Initial growth condition after sowing in plots of partial tillage direct grain seeder were normal even in plots sown in more than 50% of soil water content. No. of spike, which was $508/m^2$, in plot of partial tillage direct grain seeder sowed at 30% soil water content was better than plat drill seeding, $404/m^2$. Yield and yield components of plot of partial tillage direct grain seeder, were higher than plot sowed by plat drill seeder in same soil water content. Partial tillage direct grain seeding can be a good sowing way for barley especially in wet condition. However, parts of seeder have to be improved for barley sowing; 1) ridged width of partial tillage direct grain seeder should be $10{\sim}20cm$ wider than 10 cm, which is necessary for drainage during barley growing season in wet paddy field. 2) sowing width of partial tillage direct grain seeder was not same with one of drill seeder which was the best width for light interception and should be shorter than 30cm.

• Journal of the Society of Disaster Information
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• v.8 no.3
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• pp.204-212
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• 2012

Lightweight soils are very economical and environment friendly materials that are valuable in field without wasting construction materials, dredged soils and clay/ silty soils during construction. Recently, the research of lightweight soils mixed with recycled material (recycled tire powder, rice husks) have been investigated. In this study the mix design factors (i.e., weight of soil, water content, foaming agent and added water) were analyzed and optimized mix design was suggested using cement content for revealing strength. For the analysis the stress-strain behavior, strength with respect to time, and experimental strength for the component of recycled material were analyzed. Finally, target strength was determined to calculate reasonable and economical mix ratio and the optimized cement content was suggested.