• Proceedings of the Korean Geotechical Society Conference
• /
• 2007.09a
• /
• pp.481-501
• /
• 2007

Excessive rainfalls due to climatic changes can trigger an increase in rainfall-induced slope failures that pose real threats to both lives and properties. Many high slopes in residual soils could stand at a steep angle, but failed during or after rainfall. Commonly, these slopes have a deep groundwater table and negative pore-water pressures in the unsaturated zone above the groundwater table contribute to the shear strength of soil and consequently to factor of safety of the slope. Stability assessment of slope under rainfall requires information on rate of rainwater infiltration in the unsaturated zone and the resulting changes in pore-water pressure and shear strength of soil. This paper describes the application of unsaturated soil mechanics principles and theories in the assessment of rainfall effect on stability of slope through proper characterization of soil properties, measurement of negative pore-water pressures, seepage and slope stability analyses involving unsaturated and saturated soils. Factors controlling the rate of changes in factor of safety during rainfall and a preventive method to minimize infiltration are highlighted in this paper.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.12 no.5
• /
• pp.355-363
• /
• 2007

In this paper, the transformerless three-phase line-connected PV PCS (photovoltaic power conditioning system) is proposed. An improved P&O (perturb and observe) MPPT (maximum power point tracking) algorithm that prevents local maximum power point tracking is proposed. By controlling the three-phase line-connected voltage source inverter using outer DC-link voltage controller, inner current controller and microcontroller friendly simplified space vector modulation (SVM) method, a unity power factor is achieved. An algorithm is suggested to control the DC-link voltage faster and more correctly for the increase system stability and power factor. All algorithms and controllers are implemented on a single-chip microcontroller and the superiority of the proposed algorithms and controllers is proved by experiments.

• Journal of Institute of Control, Robotics and Systems
• /
• v.21 no.3
• /
• pp.283-289
• /
• 2015

In this paper, a GNSS interference detection algorithm based on an adaptive fading Kalman filter is proposed to detect a spoofing signal which is one of the threatening GNSS intentional interferences. To detect and mitigate the spoofing signal, the fading factor of the filter is used as a detection parameter. For simulation, the effect of the spoofing signal is modeled by the ramp type bias error of the pseudorange to emulate a smart spoofer and the change of the fading factor value according to ramp type bias error is quantitatively analyzed. In addition, the detection threshold is established to detect the spoofing signal by analyzing the change of the error covariance and the effect of spoofing is mitigated by controlling the Kalman gain of the filter. To verify the performance analysis of the proposed algorithm, various simulations are implemented. Through the results of simulations, we confirmed that the proposed algorithm works well.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
• /
• 2004.09a
• /
• pp.450-452
• /
• 2004

Using factor analysis and bivariate comparisons of major components in ground water, three geochemical processes were identified as controlling factors of ground water chemistry; 1) natural mineralization by water rock interactions, 2) effect of seawater which includes salinization by seawater near seashores and deposition of sea salt, and 3) nitrate contamination by N fertilization. Contribution of rainfall was also estimated from the measured composition of wet deposition. The geochemical processes were separated using total alkalinity as an indicator for natural mineralization, Cl for effect of seawater, and nitrate for N fertilization. Relatively high correlation of major components with nitrate suggests that nitrification of nitrogenous fertilizers significantly affects ground water chemistry. Total cations derived from nitrate sources have good linearity for nitrate in equivalent basis with a slope of 1.8, which is a mean of proton production coefficients in nitrification of two major compounds in nitrogenous fertilizers, ammonium and urea. Contribution of nitrate sources to base cations, Cl, and SO$_4$ in ground water was determined considering maximum contribution of natural mineralization to estimate a threshold of the effect of N fertilization for ground water chemistry, which shows W fertilization has a greatest effect than any other processes in ground water with nitrate concentration greater than 50 mg/L for Ca, Mg, Na and with concentration greater than 30 mg/L for Cl and SO$_4$.

• Korean Journal of Health Education and Promotion
• /
• v.32 no.3
• /
• pp.109-120
• /
• 2015

Objectives: The purpose of this study was to investigate risk factors for chronic ADL, IADL disability. The study explored clinical and socio-demographic risk factors of functional status decline. Methods: Data from the Survey of Living Condition of Elderly 3-year panel study were analyzed. The study subjects were 5,928 community-dwelling people aged 65 years or older who were no disability in ADL and IADL at baseline. Predisposing factors, pathology, impairment, and functional limitations were regarded as risk factors. Logistic regression analysis was used. Results: During the 3-year study period, 3.9% participants developed chronic ADL disability, 9.4% participants were IADL disabled. After controlling for predisposing factor, the best predictors for ADL disability at 36 months were fall as a pathology factor, cognitive decline, disability judgement, lower limb functional limitation. Comorbidity, fall, cognitive decline, disability judgement, lower limb and upper limb functional limitation were risk factors for IADL disability. Conclusions: Health promotion program focusing elderly is essential to prevent ADL and IADL disability. Mobilizing physical activity should be included in health promotion program for elderly.

• KCID journal
• /
• v.13 no.2
• /
• pp.283-292
• /
• 2006

The characteristics of nonpoint source pollutant loads in upstream of Nakdong River were studied through analysis of pollutant loads of 10 sub-watersheds divided based on administrative district. The discharge and pollutant concentration of each sub-watershed were collected from Nakdong-River Water Research Institute and Daegu Regional Environmental office, respectively. Pollution items analysed in this study were BOD, T-N and T-P. The delivery loads of the nonpoint source pollutions of each sub-watershed were calculated after analysing the concentration of the pollution of each site. Several points were found from the results. Firstly, in general, city areas including Sangju, Andong showed higher degree of nonpoint pollution than country areas including Cheongsong, Yeongyang. The sub-watersheds located upstream side, such as Yeongju, Bonghwa, Necessarily show better water quality than the sub-watersheds located downstream side, such as Mungyeong, Uiseong. This result indicates that a given pollution condition within the watershed can be more sensitive than location factor to the level of water quality. Secondly, the delivery load and area of watershed were not necessarily correlated in the sense of water quality, while the discharge was shown to be highly correlated to the delively load of pollution. Lastly, sewage and waste caused from population and livestock, as well as landuse factor, were found to significantly contribute to the water pollution. Alternative solutions for controlling pollution source, therefore, should be provided to meet target levels of water quality in these regions.

• Journal of Power Electronics
• /
• v.17 no.5
• /
• pp.1173-1185
• /
• 2017

In this paper, a new single phase multilevel inverter topology with a single DC source is presented. The proposed topology is developed based on the concepts of the L-Z source inverter and the switched capacitor multilevel inverter. The input voltage to the proposed inverter is boosted by two steps: the first step by an impedance network and the second step by switched capacitor units. Compared to other existing topologies, the presented topology can produce a higher boosted multilevel output voltage while using a smaller number of components. In addition, it provides more flexibility to control boosting factor, size, cost and complexity of the inverter. The proposed inverter possesses all the advantages of the L-Z source inverter and the switched capacitor multilevel inverter like controlling the start-up inrush current and capacitor voltage balancing using a simple switching strategy. The operating principle and general expression for the different parameters of the proposed topology are presented in detail. A phase disposition pulse width modulation strategy has been developed to switch the inverter. The effectiveness of the topology is verified by extensive simulation and experimental studies on a 7-level inverter structure.

• Korean Journal of Community Nutrition
• /
• v.2 no.2
• /
• pp.151-158
• /
• 1997

This study was conducted to observe the relationship between diet and blood pressure for Korean(kangwha) and Nepali adolescents. 542 middle school students in Korea and 159 students in Nepal in the same age(14-15yr) group were investigated as the study subjects. Data for blood pressure as well as weight and diet were collected for the analysis. multiple regression analysis was employed to identify the influencing factors among the variables considered. As the results, the mean body weight of body weight of boys and girls in Kangwha was 54.5Kg, 50.6Kg which was 17Kg and 10Kg heavier than the weight of the Nepal students. Dietary survey result showed that there was no big difference in energy intake in Kangwha and Nepal students., Mean energy intake of Kangwha boys was 2, 848kcal and that of Nepal boys was 2, 720 kcal. The similar result showed significantly lower intake in other nutreints than that of Kangwha subjects whose consumption level was close to the Korean Recommended Dietary Allowances. The result of multiple regression analysis showed that weight was the greatest influencing factor on blood pressure both in Kangwha and in Nepal subjects. Nevertheless, after controlling the weight factor, there were axxociations observed between diet and blood pressure. And the relationship was stronger in case of Nepal than in Kangwha.

• Transactions of Materials Processing
• /
• v.25 no.3
• /
• pp.182-188
• /
• 2016

Flexibly-reconfigurable roll forming (FRRF) is a novel sheet metal forming technology conducive to producing multi-curvature surfaces by controlling the strain distribution along longitudinal direction. In FRRF, a sheet metal is shaped into the desired curvature by using reconfigurable rollers and gaps between the rollers. As FRRF technology and equipment are under development, a simulation model corresponding to the physical FRRF would aid in investigating how the shape of a sheet varies with input parameters. To facilitate the investigation, the current study exploits regression analysis to construct a predictive model for the longitudinal curvature of the sheet. Variables considered as input parameters are sheet compression ratio, radius of curvature in the transverse direction, and initial blank width. Samples were generated by a three-level, three-factor full factorial design, and both convex and saddle curvatures are represented by a quadratic regression model with two-factor interactions. The fitted quadratic equations were verified numerically with R-squared values and root mean square errors.

• Transactions of Materials Processing
• /
• v.26 no.6
• /
• pp.341-347
• /
• 2017

Flexibly-reconfigurable roll forming (FRRF) is a novel sheet metal forming technology conducive to produce multi-curvature surfaces by controlling strain distribution along longitudinal direction. Reconfigurable rollers could be arranged to implement a kind of punch die set. By utilizing these reconfigurable rollers, desired curved surface can be formed. In FRRF process, three-dimensional surface is formed from two-dimensional curve. Thus, it is difficult to predict the forming result. In this study, a regression analysis was suggested to construct a predictive model for a longitudinal curvature of FRRF process. To facilitate investigation, input parameters affecting the longitudinal curvature of FRRF were determined as maximum compression value, curvature radius in the transverse direction, and initial blank width. Three-factor three-level full factorial experimental design was utilized and 27 experiments using FRRF apparatus were performed to obtain sample data of the regression model. Regression analysis was carried out using experimental results as sample data. The model used for regression analysis was a quadratic nonlinear regression model. Determination factor and root mean square root error were calculated to confirm the conformity of this model. Through goodness of fit test, this regression predictive model was verified.