• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.99-99
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• 2013

In this talk, I will present two research works in progress, which are: i) mapping of piezoelectric polarization and associated charge density distribution in the heteroepitaxial InGaN/GaN multi-quantum well (MQW) structure of a light emitting diode (LED) by using inline electron holography and ii) in-situ observation of the polarization switching process of an ferroelectric Pb(Zr1-x,Tix)O3 (PZT) thin film capacitor under an applied electric field in transmission electron microscope (TEM). In the first part, I will show that strain as well as total charge density distributions can be mapped quantitatively across all the functional layers constituting a LED, including n-type GaN, InGaN/GaN MQWs, and p-type GaN with sub-nm spatial resolution (~0.8 nm) by using inline electron holography. The experimentally obtained strain maps were verified by comparison with finite element method simulations and confirmed that not only InGaN QWs (2.5 nm in thickness) but also GaN QBs (10 nm in thickness) in the MQW structure are strained complementary to accommodate the lattice misfit strain. Because of this complementary strain of GaN QBs, the strain gradient and also (piezoelectric) polarization gradient across the MQW changes more steeply than expected, resulting in more polarization charge density at the MQW interfaces than the typically expected value from the spontaneous polarization mismatch alone. By quantitative and comparative analysis of the total charge density map with the polarization charge map, we can clarify what extent of the polarization charges are compensated by the electrons supplied from the n-doped GaN QBs. Comparison with the simulated energy band diagrams with various screening parameters show that only 60% of the net polarization charges are compensated by the electrons from the GaN QBs, which results in the internal field of ~2.0 MV cm-1 across each pair of GaN/InGaN of the MQW structure. In the second part of my talk, I will present in-situ observations of the polarization switching process of a planar Ni/PZT/SrRuO3 capacitor using TEM. We observed the preferential, but asymmetric, nucleation and forward growth of switched c-domains at the PZT/electrode interfaces arising from the built-in electric field beneath each interface. The subsequent sideways growth was inhibited by the depolarization field due to the imperfect charge compensation at the counter electrode and preexisting a-domain walls, leading to asymmetric switching. It was found that the preexisting a-domains split into fine a- and c-domains constituting a $90^{\circ}$ stripe domain pattern during the $180^{\circ}$ polarization switching process, revealing that these domains also actively participated in the out-of-plane polarization switching. The real-time observations uncovered the origin of the switching asymmetry and further clarified the importance of charged domain walls and the interfaces with electrodes in the ferroelectric switching processes.

• The Journal of Internal Korean Medicine
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• v.22 no.3
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• pp.423-430
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• 2001

Objects: The purpose of this case-control study was done to examine the relationship between stroke prevalence and the anthropometric indices(body mass index(BMI), modified Broca's method(Broca's index), waist circumference(WC), waist-hip ratio(WHR)), dyslipidemia, past medical history(heart disease, hypertension, diabetes mellitus(DM)), life-style factors(smoking, drinking) in Korean adults. Methods : The study group consisted of neurologically confirmed 116 stroke patients as the case group and 116 non-stroke patients as control group. Obesity were defined as $BMI{\geq}25kg/m^2,\;Broca's\;index{\geq}30%$, WC >94cm in male and WC >80cm in female, $WHR{\geq}0.9$ in male and $WHR{\geq}0.8$ in female. Oyslipidemia were defined as total $cholesterol{\geq}200mg/dl,\;triglyceride{\geq}200mg/dl,\;HDL-cholesterol {\leq}35mg/dl,\;LDL-cholesterol{\geq}160mg/dl$. Information on life-style factors and past medical history was obtained from personal interview. The analysis of the data was done by means of chi-square test(Pearson's chi-square test, Fisher's exact test) and student t-test. Results: The results were as follow. In the study group: Hypertension had a 4:05 odds ratio, Broca's $index{\geq}30%$ had a 1.98 odds ratio, WC >94cm in male had a 2.17 odds ratio, WC >80cm in female had a 2.80 odds ratio, $WHR{\geq}0.9$ in male had a 4.66 odds ratio, $WHR{\geq}0.8$ in female had a 5.35 odds ratio, but heart disease, DM, life-style factors, serum lipid and 8MI had no direct relationship with odds ratio(nonsignificant). By student t-test, risk factors for stroke were found to be total cholesterol(p=0,025), LDL-cholesterol(p=0.013), WC(p=0.000) and WHR(p=0.000). Conclusions: This study suggests that people should be advised to control hyperlitension, hyperlipidemia and obesity since these carry a risk of stroke.

• Journal of Plant Biotechnology
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• v.47 no.1
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• pp.78-89
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• 2020

Tomato fruit quality is determined by the contents of various functional metabolites in addition to fruit appearance. To develop tomato cultivars with higher amounts of functional compounds, an efficient quantification method is required to identify the natural variations in the compounds in the tomato germplasm. In this study, we investigated tomato varieties, which included 23 inbred lines and 12 commercial F₁ cultivars, for their contents of seven watersoluble vitamins (vitamin C, vitamins B1, B2, B3, B5, B6, and B9) and five polyphenolic compounds (quercetin, rutin, kaempferol, myricetin, and naringenin chalcone). The results of high performance liquid chromatography and liquid chromatography-mass spectrometry showed that vitamin C and naringenin chalcone were the major water-soluble vitamins and polyphenolic compounds, respectively, and their abundance was highly variable depending on the cultivar. By contrast, the contents of vitamin B1, quercetin, and kaempferol were lowest among the cultivars. With regard to the relationship between metabolic compounds and fruit characteristics, a significant association was found in fruit size, indicating that cherry tomato varieties contain higher amounts of the compounds compared to large fresh-type varieties. However, no direct association was detected in fruit color, except for naringenin chalcone. The results of this study provide new insights on the quantification of metabolic compounds and the selection of breeding materials, which are prerequisites for the development of functional tomato varieties.

• Journal of Preventive Medicine and Public Health
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• v.39 no.1
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• pp.30-38
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• 2006

Objectives: We examined whether the neighborhood socioeconomic position predicts the smoking rates after adjusting for individual socioeconomic position indicators. Methods: Data were obtained from the 2001 Seoul Health Indicators Survey. The neighborhood socioeconomic position was the residential distribution of the high class (power elites), as measured by the location quotients (LQ) for each administrative dong (district). A high LQ denotes a high neighborhood socioeconomic status. The individual socioeconomic position included education, occupation and income. Age-adjusted smoking rates according to the LQ level were computed with the direct method. The total number of subjects in this study (26,022 men and 28,007 women) was the reference. A multilevel logistic regression analysis was conducted with the individuals at the first level and the neighborhoods at the second level to estimate the odds ratios of smoking with 95% confidence intervals. Results: For men, the age-adjusted smoking rates increased with a decrease in the LQ. For women, the relationship between the age-adjusted smoking rate and the LQ was not clear. The odds of smoking for both genders were greater among those subjects with lower incomes and lower education. The manual occupational class had greater odds of smoking than the non-manual class for the males, while the odds ratio of smoking among females with a manual occupation tended to be lower than those females with a non-manual occupation. For the males, the LQ levels independently predicted smoking after adjustment for individual income. However, this relation between the LQ and smoking in males was explained by full adjustment for the individual socioeconomic position indicators (education, occupation and income). Conclusions: A low level of neighborhood socioeconomic position was associated with higher smoking rates among the men residing in Seoul. This association between the neighborhood socioeconomic position and smoking in men was explained by the individual socioeconomic position. Anti-smoking efforts to reduce geographical inequality in smoking should be directed at reducing the smoking rates between the individuals with different socioeconomic backgrounds in the metropolitan city of Seoul, South Korea.

• Korean Journal of Social Welfare Studies
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• no.39
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• pp.395-423
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• 2008

This study investigated population characteristics that influencing treatment service use of people who are voluntarily using drug dependency treatment services by using logistic and hierarchical regression analysis. The research model of the current study was driven by the framework of the 'the Behavioral Model of Health Services Use(the Andersen model)' that has been broadly applied to study on health behavior. This study used data from a sample group of 80 adults by using purposive sampling. This study found that some predisposing factors, enabling factors and need factors have direct effects on service use. In detail, individuals who graduated from high school use drug dependency treatment utilities more than those who did not. Further, individuals who were given more support from family, peers, or others, use the treatment utilities more frequently and were more willing to use the utilities continuously. Furthermore, the greater the perceived need felt by the dependent, the greater the tendency to enter hospitals or shelters. The important implications of this study for social work practice and social policy can be summarized as follows: first, this study supports the idea that intervention for drug dependents in Korea should be focused on environment resources rather than population characteristics; and government must support drug dependent treatment systems; the present study was the first to investigate Korean drug dependents through taking a more positive view, as well as the first to apply 'the Behavioral Model of Health Services Use', and as such represents an example of how studies could be productively conducted in the future. Despite these implications, there remain some limitations in this study. These include the following: limitation in generalizability of the results; the cross-sectional nature of the study design; survey research through the questionnaire method; using foreign scales; and the difficulty of classifying treatment settings.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.119-128
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• 2018

Limit state design has been implemented in Korea since 2015; however, there exists no specification of lateral load determination on retaining wall due to the Korean standard traffic load on retaining wall's backfill surface. The lateral load from traffic depends on lane number, standard truck's axle loads and locations, loading distance from the inner wall. The concept of equivalent height of soil accounting for traffic loadings is typically used for design of retaining walls to quantify the traffic loads transmitted to the inner wall faces. Due to the different characteristics of the standard design trucks between Korea and US (AASHTO), the direct use of the guidelines from AASHTO LRFD leads to incorrect estimation of traffic load effects on retaining walls. This paper presents the results of evaluation of equivalent height of soil to reflect the Korean standard truck, based on the findings from analytical solutions using Bounessq's theory and numerical assessment using 2D finite element method. Consequently, it was found that the equivalent heights of soil from the Korean standard truck load were lower for lower retaining wall height.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.390-395
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• 2019

Hydrogymnastics so that sufficient exercise effect can be obtained using the resistance of water has a positive effect on patients who have to receive arthritis or rehabilitation treatment. However, the studies on the effect are insufficient, and the main cause of their effects has not been unclear yet. In this study, in order to identify the main cause of the effects of Hydrogymnastics, conducted Unsteady fluid flow simulation under the same conditions as the actual environment. The analysis model based on real hands, and the pressure fluctuation applied to the knuckle was analyzed by the computational fluid method. During the underwater movement of the hands, Various sizes of vortices were generated between fingers due to skin surface velocity and flow resistance. Pressure of about -500 Pa to +500 Pa is applied by the vortex flow. Also It was confirmed that the positive pressure and the negative pressure were continuously repeated up to maximum + 2000 Pa at the minimum of -2000 Pa at the portion where the direction was changed. Pressure fluctuations with a frequency of 20 Hz to 70 Hz were added continuously for each knuckle. These continuous pressure fluctuations provide a direct massage effect on the knuckles, an It is judged that the blood circulation at the relevant part is positively affected.

• Journal of Korea Water Resources Association
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• v.52 no.3
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• pp.187-194
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• 2019

Intake ratio from river constitutes about 31% (8/26) that beings to "water stress country" as "Medium ~ High" with China, India, Italy, South Africa, etc. Therefore, the present study on a dam that is the most effective and direct for securing water resources has been performed. First of all, climate change scenarios were investigated and analyzed. RCP 4.5 and 8.5 with 12.5 km grid resolution presented in the IPCC (Intergovernmental Panel on Climate Change) 5th Assessment Report (AR5) were applied to study watershed using SWAT (Soil and Water Assessment Tool) and HEC-ResSim models that carried out co-operation. Based on the results of dam simulation, the reduction effects of floods and droughts were quantitatively presented. The procedures of dam projects of the USA, Japan and Korea were investigated. As a result, there are no estimating quantitative criteria, calculating methods or formulas. In the present study, therefore, indexes for selecting suitable dam site through literature investigation and analyzing dam watersheds were determined, Expert questionnaire for various indexes were performed. Based on the above mentioned investigation and expert questionnaire, a methodology assigning weight using AHP method were proposed. The function of suitable dam (FSDS) site was calibrated and verified for four medium-sized watersheds. Finally, automated model for suitable dam site was developed using FSDS and 'Model builder' of GIS tool.

• Korean Journal of Remote Sensing
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• v.34 no.6_4
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• pp.1519-1529
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• 2018

The volcanic ash can spread out over hundreds of kilometers in case of large volcanic eruption. The deposition of volcanic ash may induce damages in urban area and transportation facilities. In order to respond volcanic hazard, it is necessary to estimate efficiently the diffusion area of volcanic ash. The purpose of this study is to compare in-situ volcanic deposition and satellite images of the volcanic eruption case. In this study, we used Near-Infrared (NIR) channels 7 and 8 of Geostationary Ocean Color Imager (GOCI) images for Mt. Aso eruption in 16:40 (UTC) on October 7, 2016. To estimate deposit area clearly, we applied Principal Component Analysis (PCA) and a series of morphology filtering (Eroded, Opening, Dilation, and Closing), respectively. In addition, we compared the field data from the Japan Meteorological Agency (JMA) report about Aso volcano eruption in 2016. From the results, we could extract volcanic ash deposition area of about $380km^2$. In the traditional method, ash deposition area was estimated by human activity such as direct measurement and hearsay evidence, which are inefficient and time consuming effort. Our results inferred that satellite imagery is one of the powerful tools for surface change mapping in case of large volcanic eruption.

• Journal of Korea Water Resources Association
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• v.52 no.9
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• pp.615-626
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• 2019

Soil moisture and runoff have very close relationship. Especially the water retention capacity and drainage characteristics of the soil are determined by various factors of the soil. In this study, a total of 40 rainfall events were identified from the entire rainfall events of Sulma basin in 2016 and 2017. For each selected events, the constant-K method was used to separate direct runoff and baseflow from total flow and calculate the runoff coefficient which shows positive exponential curve with Antecedent Soil Moisture (ASM). In addition to that, the threshold of soil moisture was determined at the point where the runoff coefficient starts increasing dramatically. The threshold of soil moisture shows great correlation with runoff and depth to water table. It was founded that not only ASM but also various factors, such as Initial Soil Moisture (ISM), storage capacity of soil and precipitation, affect the results of runoff response. Furthermore, wet condition and dry condition are separated by ASM threshold and the start and peak response are analyzed. And the results show that the response under wet condition occurred more quickly than that of dry condition. In most events occurred in dry condition, factors reached peak in order of soil moisture, depth to water table and runoff. However, in wet condition, they reached peak in order of depth to water table, runoff and soil moisture. These results will help identify the interaction among factors which affect the runoff, and it will help establish the relationship between various soil conditions and runoff.