• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.542-545
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• 2010

재료의 마이크로 스케일 해석에서 결정의 geometrically necessary dislocation (GND) 효과에 의한 소성구배(plastic gradient)를 고려하는 것은 재료의 소성 거동을 분석하는데 영향을 미친다. 본 연구에서는 먼거리(long range)에서 전위(dislocation)의 영향을 고려하는 GND의 효과를 적용하여 소성 구배의 영향을 받는 다결정(polycrystal) 고체의 거동을 유한요소해석을 이용하여 살펴보았다. 재료의 거동을 분석하기 위해 탄성(elastic)과 소성(plastic) 변형에 먼 거리 변형률(long range strain)을 고려한 항(term)이 포함된 변형 구배(deformation gradient)의 multiplicative decomposition 모델을 사용하였다. 먼 거리 변형률에 의한 영향을 고려하기 위해 구배 경화 계수(gradient hardness coefficient)와 먼 거리 변형률 길이에 대한 재료변수(parameter)가 사용되었다. 각각의 계수들이 다결정 고체의 거동에 미치는 영향을 확인하기 위해 두 변수의 적용에 따른 다결정 고체의 거동을 분석하였다. 다결정 재료의 GND 효과에 의한 소성 구배 효과를 고려해서, 고려하지 않은 경우와 비교하여 발생하는 경화(hardening)의 차이를 분석함으로서 GND에 의한 다결정 고체 거동의 영향을 확인하였다.

• Journal of Wetlands Research
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• v.21 no.spc
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• pp.61-68
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• 2019

Recently, climate indices represented by quantifying atmospheric-ocean circulation patterns have been widely used to predict hydrologic variables for considering long-term climate variability. Hydrologic forecasting models based on artificial neural networks have been developed to provide accurate and stable forecasting performance. Forecasts of hydrologic variables considering climate variability can be effectively used for long-term management of water resources and environmental preservation. Therefore, identifying significant indicators for hydrologic variables and applying forecasting models still remains as a challenge. In this study, we selected representative climate indices that have significant relationships with dam inflow time series in the Han-River basin, South Korea for applying the dam inflow forecasting model. For this purpose, the ensemble empirical mode decomposition(EEMD) method was used to identify a significance between dam inflow and climate indices and an artificial neural network(ANN) ensemble model was applied to overcome the limitation of a single ANN model. As a result, the forecasting performances showed that the mean correlation coefficient of the five dams in the training period is 0.88, and the test period is 0.68. It can be expected to come out various applications using the relationship between hydrologic variables and climate variability in South Korea.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.1
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• pp.165-174
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• 2019

As a nonstationarity is observed in hydrological data, various studies on nonstationary frequency analysis for hydraulic structure design have been actively conducted. Although the inherent diversity in the atmosphere-ocean system is known to be related to the nonstationary phenomena, a nonstationary frequency analysis is generally performed based on the linear trend. In this study, a nonstationary frequency analysis was performed using climate indices as covariates to consider the climate variability and the long-term trend of the extreme rainfall. For 11 weather stations where the trend was detected, the long-term trend within the annual maximum rainfall data was extracted using the ensemble empirical mode decomposition. Then the correlation between the extracted data and various climate indices was analyzed. As a result, autumn-averaged AMM, autumn-averaged AMO, and summer-averaged NINO4 in the previous year significantly influenced the long-term trend of the annual maximum rainfall data at almost all stations. The selected seasonal climate indices were applied to the generalized extreme value (GEV) model and the best model was selected using the AIC. Using the model diagnosis for the selected model and the nonstationary GEV model with the linear trend, we identified that the selected model could compensate the underestimation of the rainfall quantiles.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.20-29
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• 2022

The operational modal analysis (OMA) technique, which extracts the modal parameters of a structural system using ambient vibrations, has been actively developed as a field of structural health monitoring of cable-supported bridges. In this paper, the short and long-term modal parameters of a cable-stayed bridge were evaluated using the acceleration data obtained from the two ambient vibration tests (AVTs) and three years of continuous measurements. A total of 27 vertical modes and 1 lateral mode in the range 0.1 ~ 2.5 Hz were extracted from the high-resolution AVTs which were conducted in the 6th and 19th years after its completion. Existing OMA methods such as Peak-Picking (PP), Eigensystem Realization Algorithm with Data Correlation (ERADC), Frequency Domain Decomposition (FDD) and Time Domain Decomposition (TDD) were applied for modal parameters extraction, and it was confirmed that there was no significant difference between the applied methods. From the correlation analysis between long-term natural frequencies and environmental factors, it was confirmed that temperature change is the dominant factor influencing natural frequency fluctuations. It was revealed that the decreased natural frequencies of the bridge were not due to changes in structural performance and integrity, but to the environmental effects caused by the temperature difference between the two AVTs. In addition, when the TDD technique is applied, the accuracy of extracted mode shapes is improved by adding a proposed algorithm that normalizes the sequence so that the autocorrelations at zero lag equal 1.

• Journal of Korea Trade
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• v.23 no.5
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• pp.87-101
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• 2019

Purpose - This paper examines the effectiveness of the foreign exchange risk insurance system in the promotion of SME exports in Korea. The purpose of this study is to analyze the short-term and long-term responses of SME exports to foreign exchange risk insurance support policies. Based on these empirical studies, we would like to present some operational improvements to the operation of the foreign exchange risk insurance system. Design/methodology - In order to analyze the effect of exchange risk insurance on the exports of SMEs, a VAR model consisting of foreign exchange risk insurance underwriting values, export relative price, and domestic demand pressure, including export volume, was established. The study began with tests of the stationarity of time series data. The unit root tests showed that all concerned variables were non-stationary. Accordingly, the results of the cointegration test showed that the tested variables are not cointegrated. Finally, an impulse response function and variance decomposition analysis were conducted to analyze the impulse of foreign exchange risk insurance on exports of SMEs. Findings - As a result of estimating the VAR (1) model, foreign exchange risk insurance was found to be significant at a 1% significance level for SME' export promotion. In the impulse response analysis, SMEs' export response to the impulse of foreign exchange risk insurance showed that exports gradually increased until the third quarter, and then slowed down. However, the impulse did not disappear, and appeared continuously. Originality/value - This study analyzed the effect of foreign exchange insurance on exports of SMEs by applying the VAR model. In particular, this study is the first to analyze the short-term and long-term effects of foreign exchange risk insurance on exports of SMEs. The empirical evidence in the current study have a policy implication for the policy authority to support and promote the foreign exchange risk insurance in the effect of exchange rate volatility on Korea' export SMEs.

• Journal of Digital Convergence
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• v.18 no.12
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• pp.87-95
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• 2020

The Incheon airport is a gateway to and from the Republic of Korea and has a great influence on the image of the country. Therefore, it is necessary to predict the number of airport passengers in the long term in order to maintain the quality of service at the airport. In this study, we compared the predictive performance of various time series models to predict the air passenger demand at Incheon Airport. From 2002 to 2019, passenger data include trend and seasonality. We considered the naive method, decomposition method, exponential smoothing method, SARIMA, PROPHET. In order to compare the capacity and number of passengers at Incheon Airport in the future, the short-term, mid-term, and long-term was forecasted by time series models. For the short-term forecast, the exponential smoothing model, which weighted the recent data, was excellent, and the number of annual users in 2020 will be about 73.5 million. For the medium-term forecast, the SARIMA model considering stationarity was excellent, and the annual number of air passengers in 2022 will be around 79.8 million. The PROPHET model was excellent for long-term prediction and the annual number of passengers is expected to be about 99.0 million in 2024.

• The Journal of the Convergence on Culture Technology
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• v.7 no.4
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• pp.607-612
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• 2021

This study estimated the impact of the shock of housing price increase on the total fertility rate and the contribution of each variable to changes in the TFR. This study is differentiated by estimating the contribution rate of each variable to the fertility rate through the Shapley decomposition and the panel VAR's forecast error variance decomposition, which previous studies have not attempted. The main results of this study are as follows. First, the decline in the TFR in Korea has been strongly influenced by the recent decline in the total fertility rate, and this influence is expected to continue in the future. In the case of housing costs, in the past, housing sales prices had a relatively small contribution to changes in the total fertility rate compared to the jeonse prices, but their influence is expected to increase in the long term in the future. It has been demonstrated that private education expenses other than housing sale price and Jeonse price also acted as a major cause of the decline in the total fertility rate.

• Journal of Microbiology and Biotechnology
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• v.22 no.10
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• pp.1330-1335
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• 2012

Foot and mouth disease (FMD) is one of the acute infectious diseases in hoofed and even-toed mammals, including pigs, and it occurs via acute infection by Aphthovirus. When FMD is suspected, animals around the location of origin are typically slaughtered and buried. Other methods such as rendering, composting, and incineration have not been verified in practice in Korea. After the FMD incident, the regular monitoring of the microbial community is required, as microorganisms greatly modify the characteristics of the ecosystem in which they live. This is the result of their metabolic activities causing chemical changes to take place in the surrounding environment. In this study, we investigated changes in the microbial community during a 24 week period with DNA extracts from leachate, formed by the decomposition of buried pigs at a laboratory test site, using denaturing gradient gel electrophoresis (DGGE) with a genomic DNA. Our results revealed that Bacteroides coprosuis, which is common in pig excreta, and Sporanaerobacter acetigenes, which is a sulfur-reduced microbe, were continuously observed. During the early stages (0~2 weeks) of tissue decomposition, Clostridium cochlearium, Fusobacterium ulcerans, and Fusobacterium sp., which are involved in skin decomposition, were also observed. In addition, various microbes such as Turicibacter sanguinis, Clostridium haemolyticum, Bacteroides propionicifaciens, and Comamonas sp. were seen during the later stages (16~24 weeks). In particular, the number of existing microbial species gradually increased during the early stages, including the exponential phase, decreased during the middle stages, and then increased again during the later stages. Therefore, these results indicate that the decomposition of pigs continues for a long period of time and leachate is created continuously during this process. It is known that leachate can easily flow into the neighboring environment, so a long-term management plan is needed in burial locations for FMD-infected animals.

• Proceedings of the Korea Society of Environmental Biology Conference
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• 2004.05a
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• pp.26-26
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• 2004

This study was conducted to evaluate the characteristics of dissolved orgamc matters based on their origins. The dissolved organic carbon(DOC) represents an index for dissolved organic matter and basically regarded as a source of organic pollution. The monthly variations and vertical profiles of dissolved organic carbon(DOC) in Kumoh reservoir were surveyed from May 2001 to April 2002. In addition, other areas such as river, reservoir, sewage and industrial wastewater were also surveyed in summer 2001. Kumoh reservoir was divided with depth into three layers .: epilimnion, metalimnion and hypolimnion. The proportion of total DOC(T-DOC) was classified by labile DOC(L-DOC) and refractory DOC(R-DOC) on the basis of long-term incubation. DOC of freshwater and Kumoh reservoir was ranged to be 1.6~4.1 mgC/L and 2.1~4.0 mgC/L, respectively. L-DOC accounted for 3~30% of DOC from watershed. Therefore, refractory dissolved organic carbon(R-DOC) was major component of DOC in the watershed. The decomposition rate(k) ranged from 0.008 $d^{-1}$ to 0.083 $d^{-1}$ in Kumoh reservoir. The highest decomposition rate(k) was observed at River Hoein III freshwater. Therefore, modified total organic carbon analyzer is needed to be applied for effective management of dissolved organic matter.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.18 no.3
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• pp.407-414
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• 2020

Thermal decomposition of the uranyl phosphate mineral phase meta-ankoleite (KUO₂PO₄·3H₂O) has been considered in relation to high temperature thermal sintering for the immobilisation of a uranyl phosphate containing waste. Meta-ankoleite thermal decomposition was studied across the temperature range 25 - 1200℃ under an inert N₂ atmosphere at 1 atm. It is shown that the meta-ankoleite mineral phase undergoes a double de-hydration event at 56.90 and 125.85℃. Subsequently, synthetically produced pure meta-ankoleite remains stable until at least 1150℃ exhibiting no apparent phase changes. In contrast, when present in a mixed waste the meta-ankoleite phase is not identifiable after thermal treatment indicating incorporation within the bulk waste either as an amorphous phase and/or as uranium oxide. Visual inspection of the waste post thermal treatment showed evidence of self-sintering owing to the presence of glass former materials, namely, silica (SiO₂) and antimony(V) oxide (Sb₂O₅). Therefore, incorporation of the uranium phase into the waste as part of waste sentencing and immobilisation via high temperature sintering for the purpose of long-term disposal is deemed feasible.