• Journal of The Korean Society of Agricultural Engineers
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• v.66 no.2
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• pp.25-34
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• 2024

The long-term monitoring of the Soyang Lake's water quality, covering 25% of the North Han River watershed, is crucial for effective management of both lake water quality and pollution sources in the broader region. This study utilized continuous monitoring data from the front of the Soyang Dam spanning 2003 to 2022, aiming to analyze trends and provide foundational insights for water quality management. Results revealed a slightly poor grade (IV) for total nitrogen (T-N) in both surface and mid-depth layers, indicating a need for concentrated T-N management. Trend analyses using the Mann-Kendall test and Sen's Slope depicted a decreasing trend in total phosphorus (T-P) for both layers, attributed to non-point source pollution reduction projects initiated after the Soyang Lake's designation as a pollution control area in 2007. The LOWESS analysis showed a T-P increase until 2006, followed by a decrease, influenced by the impact of Typhoon Ewiniar in that year. This 20-year overview establishes a comprehensive understanding of the Soyang Lake's water quality and trends, allowing for a seasonal and periodical analysis of water quality changes. The findings underscore the importance of continued monitoring and management strategies to address evolving water quality issues in the Soyang Lake over time.

• Korean Journal of Ecology and Environment
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• v.46 no.1
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• pp.128-134
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• 2013

In the summer season (June~August) during the study period of Lake Doam, average concentrations of major water quality parameters, COD, SS, TN, and TP were 4.0, 16.2, 3.129 and $0.077mg\;L^{-1}$, respectively, and Chl-a was $11.8mg\;m^{-3}$. The result has indicated that Lake Doam was a meso-eutrotrophic lake. Lake Doam data from the summer season (June~August), precipitation from 2001 to 2012, and water quality (COD, SS, TN, TP, Chl-a etc.) of seven years (2001, 2002, 2004 and 2009~2012), were statistically analyzed for long-term trends by Mann-Kendall test and Sen's slope estimator methods. The statistical results showed that precipitation, SD, COD, TN, $NO_3-N$, $NH_3-N$ and Chl-a had decreasing trends, and EC, turbidity, SS, TP and DIP had increasing trends. Suspended solids and total phosphorus were directly affected by precipitation. In the case of suspended solids, more aggressive and constructive plans need to be implemented than the current turbidity reduction project to achieve the targeted water quality ($5mg\;L^{-1}$ of SS) in Lake Doam. In particular, we need to specify a project that considers the steep topographic characteristics of high, land farming areas and precipitation conditions of the Lake Doam watershed, which can increase the efficiency of a turbidity reduction project.

• Journal of Korean Society for Atmospheric Environment
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• v.13 no.4
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• pp.249-256
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• 1997

To identify the long-term influence of acid rain treatment on tree growth, acid rain of various composition (pH 2.0, pH 4.0 and pH 5.6 as control) was applied to several landscape trees for five months (April through August, 1991). Tree height, pH values and $Al^{3+}$ concentration in soil were investigated. Acid rain treatments seemed to promote height growth in the first year (1991), but have become an inhibiting factor over five years. All of coniferous species and most broad-leaved species, except Acer ginnala, showed opposite trends in height responses to acid rain treatments between the first (1991) and last (1996) year. In contrast, Acer ginnala showed similar trends to acid rain treatments in the height growth between 1991 and 1996. This result suggested that Acer ginnala has a characteristic adapability to acid rain stress. pH values of surface soil were lower than those of 30 cm soil depth. This fact suggested that acid rain treatments made surface soil acidic condition. In addition, physiological characteristics (photosynthesis, stomatal condition and biomass) have to be investigated to identify the relationship between long-term effects of $AL^{3+}$ concentration and growth.

• Smart Structures and Systems
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• v.14 no.2
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• pp.209-224
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• 2014

With more and more built long-term structural health monitoring (SHM) systems, it has been considered to apply monitored data to learn the reliability of bridges. In this paper, based on a long-term SHM system, especially in which the sensors were embedded from the beginning of the construction of the bridge, a method to calculate the localized reliability around an embedded sensor is recommended and implemented. In the reliability analysis, the probability distribution of loading can be the statistics of stress transferred from the monitored strain which covered the effects of both the live and dead loads directly, and it means that the mean value and deviation of loads are fully derived from the monitored data. The probability distribution of resistance may be the statistics of strength of the material of the bridge accordingly. With five years' monitored strains, the localized reliabilities around the monitoring sensors of a bridge were computed by the method. Further, the monitored stresses are classified into two time segments in one year period to count the loading probability distribution according to the local climate conditions, which helps us to learn the reliability in different time segments and their evolvement trends. The results show that reliabilities and their evolvement trends in different parts of the bridge are different though they are all reliable yet. The method recommended in this paper is feasible to learn the localized reliabilities revealed from monitored data of a long-term SHM system of bridges, which would help bridge engineers and managers to decide a bridge inspection or maintenance strategy.

• Korean System Dynamics Review
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• v.10 no.2
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• pp.81-102
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• 2009

Based on various employment and technology data in the cultural sector from the mid-1990s to the mid-2000s in Seoul, Korea, this research examines whether technology- and human resource-oriented programs exert significant impact on creative manpower, R&D technology level and tolerance. After briefly introducing Seoul's trends in the culture industry, it tries to explain major reinforcing and balancing loops. The stock-flow diagram of the culture industry in Seoul is applied to estimate relative effectiveness of technology- and human resource-oriented cultural programs cultural programs. Judging from a series of simulated experiments, technology-oriented cultural programs are essential to increase creative manpower and R&D technology level in the short term. For the first half of research period, this research finds that human resource-oriented cultural programs put forth minimal impact, if they even exist at all. The trends, however, are reversed in the long term: Both size of creative manpower and R&D technology level absolutely depend on human resource-oriented cultural programs in the second half.

• Health Policy and Management
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• v.12 no.4
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• pp.1-17
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• 2002

This study was attempted to identify the liquidity trends and determinants of private hospitals in Korea different. Data used in this study were collected from 98 hospitals with complete general data of present conditions as well as financial statements(balance sheets, income statements). They were chosen from hospitals that passed the standardization audit undertaken by the Korean Hospital Association from 1996 to 2000 for the purpose of accrediting training hospitals. The dependent variables in this study were used current ration and quick ratio as a proxy indicator for liquidity. The independent variables were ownership type, hospital type, location, bed size, period of establishment, short-term liabilities to total assets, long-term liabilities to total assets, borrowings to total assets, fixed asset ration, net profit to total assets, operating margin to gross revenue, growth rate of net worth to total assets, total asset turnover, and business risk(volatility of profit). The major findings of this study were as follows. Trends of liquidity(current ratio, quick ratio) had been continuously decreased. Especially, There were very distinct decreasing trends of personal hospitals and less than 300beds, which weakened liquidity. The factors had significant effect on current ratio were short-term debt to total assets(-), fixed asset ratio(-), business risk(+). High short-term debt to total assets, high fixed asset ratio and high business risk significantly decreased in liquidity. The factors that significantly affected on quick ratio were short-term debt to total assets(-), borrowings to total assets(+), fixed asset ratio(-), business risk(+).

• Atmosphere
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• v.19 no.3
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• pp.243-253
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• 2009

In other to interpret the long-term variations of sunshine duration, cloud lifetime, and precipitation intensity observed in and around Seoul and Busan for the period from 1986 to 2005, aerosol indirect effect was employed and applied. For the identification of long-term trend of aerosol concentration, observed visibility and AOT of AERONET sunphotometer data were also used over the same regions. The result showed that the time series of visibility was decreased and those of AOT increased, especially trends were remarkable in 2000s. In both regions, occurrence frequencies of observed cloudiness (cloud amount ${\leq}6/10$) and strong precipitation (rain rate > $0.5mmhour^{-1}$) have been steadily increased while those of cloudiness (cloud amount > 7/10) and weak precipitation (rain rate ${\leq}0.2mmhour^{-1}$) decreased. These results are corresponding to the trend of both visibility and AERONET data, implying the aerosol indirect effect that makes size of cloud droplet reduce, cloud life-time longer and precipitation efficiency decreased. Our findings demonstrate that, although these phenomena are not highly significant, weather and climate system over Korean urban area have been changed toward longer lifetime of small cloudiness and increasing precipitation intensity as a result of increased aerosol indirect effect.

• Journal of Labour Economics
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• v.43 no.2
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• pp.75-107
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• 2020

Using the data from 1980 to 2017, I show the long-term trends in the gender wage gap in Korea and analyze factors using decomposition method. It tended to decline until the 1990s, but gradually slowed after the 2000s. Gelbach(2016)'s decomposition method is used as an alternative rather than Blinder-Oaxaca decomposition. The results show that the proportion of explanation of traditional factors, such as age, education, firm size, industry and occupation, are continuously decreasing in explaining the gender wage gap. Expecially, the proportion of explanation of age and that of education have decreased, and that of industry tended to decrease in the 1990s but to increase after the 2000s.

• The Korean Journal of Archival Studies
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• no.10
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• pp.27-62
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• 2004

As the penetration of information technology into everyday life is accelerated day by day, virtually all kinds of human representation of knowledge and arts are produced and distributed in the digital form. It is problematic, however, because digital objects are so volatile that it is not easy to keep them in fixed form. The fatal fragility makes it extremely tricky to preserve the digital heritage of our time for the next generation. The present paper aims to introduce current endeavors made at the international and the national levels and to provide with suggestions for Korean national strategy of digital preservation. It starts with reviewing the global trends of digital archiving and long-term preservation, focusing on standardization, preservation strategies and current experiments and projects being conducted for preserving various digital objects. It then sketches national strategies of several leading countries. Based on the sketch, twofold suggestions for Korean national strategy are proposed: establishing a central coordinating agency and accommodating the digital preservation issue in the legislative and regulatory framework for the information society. The paper concludes with the necessity of cooperation among heritage organizations, including libraries, archives, museums. They should cooperate with each other because they have traditionally been trusted with the custodianship of collective memory of humankind and the digital heritage cannot be passed onto the next generation without their endeavor. They should also work together because any single institution, or any single nation could cover what it takes to complete the task of long-term preservation of our digital heritage.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.195-196
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• 2022

Insulation material absorption rate is closely related to thermal conductivity. In Korea, there is no study on the change of insulation material in a long-term continuous exposure environment. In this study, basic data on the long-term durability of insulation materials were obtained by measuring the absorption rate of insulation materials over time. For the purpose of providing, as a result of the measurement, PIR class2 No.2 and PIR noncombustible show similar absorption rate trends, which is thought to be due to the fact that both are made of rigid urethane foam, and flame retardant EPS has the highest absorption rate except for PF. This is thought to be because there is a space for absorption between the beads and the beads. In the case of XPS, it is thought that the reason for showing the lowest absorption rate is that because it is produced by extrusion, it has a high density and thus has less space for moisture to penetrate.