• Journal of the Korean Vacuum Society
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• v.18 no.1
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• pp.1-8
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• 2009

Hydrophilic Surface modification of Polysarene (PS) was performed by Atmospheric Pressure Plasma (APP). Air or 0, gases were used for carrier gases and RF power was changed from 150 to 350 W. We controlled the treatment time as 1 time to 4 time passing through the plasma region. when the carrier gas was air, the water contact angle on the PS surface was decreased from $91^{\circ}$ to $20^{\circ}$. And the surface energy increased from 45.74 dyne/cm to 68.48 dyne/cm. In case of the $O_2$ plasma treatment, at 300 W of RF power and 4 times treatment, the water contact angle on the PS. Surface was decreased from $91^{\circ}$ to $17^{\circ}$ and the surface energy was increased from 45.74 dyne/cm to 69.73 dyne/cm. The surface energy was increased by polar force not by dispersion force. Improvement of surface properties can be explained by the formation of new hydrophilic groups which is identified as C-O, C=O by XPS analysis. The contact angle of APP treated PS surface kept in air was increased with time elapse, but maintained same value when it was kept in water. We treated the PS surface by APP and deposited Cu as $4,000\;{\AA}$ and $8,000\;{\AA}$ by thermal evaporation. The adhesion between sample and Cu thin film improvement of treated PS surface against untreated sample. could be verifiable by Tape test (ASTM D3359)

• Corrosion Science and Technology
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• v.18 no.2
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• pp.49-54
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• 2019

The purpose of this paper is to present failure analysis, of the heat exchanger tube in a district heating system. SS304 stainless steel is used, as material for the heat exchanger tube. The heat exchanger operates in a soft water environment containing a small amount of chloride ions, and regularly repeats operation and standstill period. This causes concentration of chloride ions on the outer surface of the tube, as well as repeat of thermal expansion, and shrinkage of the tube. As a result of microscopic examination, cracks showed transgranular as well as branched propagation, and many pits were present, at the initiation point of each crack. Energy disperstive spectroscopy analysis showed Fe and O peak, as well as Cl peak, meaning that cracks were affected by Cl ion. Failure of the tube was caused by chloride-induced stress corrosion cracking by thermal stress, high temperature, and localized enrichment of chloride ions.

• Journal of environmental and Sanitary engineering
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• v.10 no.1
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• pp.1-11
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• 1995

We had passed through a serious water pollution with a rapid urbanization and industrialization in the 1960's. Seoul Chunggyechun Sewage Disposal System set uP in 1966 and finished in 1976, as the first sewage disposal system in Korea, had covered only 4 percentage of the sewage disposal system per capita for 10 years. Through holding the Asian Games in 1986 and the Olympic Games in 1988, we expanded the sewage disposal system so that it became increased 18 percentage of the population in 1986. Finally, we have installed about 60 sewage disposal system by 1994 for a large environmental investment which was critically caused by "Phenol Accident in Nakdong River" . Now, the sewage disposal system per capita covers 42 percentage and the activity for water quality improvement is going on rapidly. The method of sewage disposal is mainly "activated sludge process" . However, the technical ability for the sewage disposal has largely developed since 1991 so the "extended aeration process" is used in Po$\v{u}$n, Tangyang, Mun$\v{u}$i, "rotating biological contact process" in Onch$\v{u}$ng, Pukok, and "oxidation ditch process" in K$\v{o}$ch'ana.

• Korean Journal of Agricultural and Forest Meteorology
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• v.18 no.4
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• pp.366-377
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• 2016

Water use efficiency (WUE) is considered as an important ecological indicator which may provide information on the process-structure relationships associated with energy-matter-information flows in ecosystem. The WUE at ecosystem-level can be defined as the ratio of gross primary productivity (GPP) to evapotranspiration (ET). In this study, KoFlux's long-term (2007-2015) eddy covariance measurements of $CO_2$ and water vapor fluxes were used to examine the WUE of needle fir plantation in Korea National Arboretum. Our objective is to ascertain the seasonality and inter-annual variability in WUE of this needle fir plantation so that the results may be assimilated into the development of a holistic ecological indicator for resilience assessment. Our results show that the WUE of needle fir plantation is characterized by a concave seasonal pattern with a minimum ($1.8-3.3g\;C{\cdot}(kg\;H_2O)^{-1}$) in August and a maximum ($5.1-11.4g\;C{\cdot}(kg\;H_2O)^{-1}$) in February. During the growing season (April to October), WUE was on average $3.5{\pm}0.3g\;C\;(kg\;H_2O)^{-1}$. During the dormant seasons (November to March), WUE showed more variations with a mean of $7.4{\pm}1.0g\;C{\cdot}(kg\;H_2O)^{-1}$. These values are in the upper ranges of WUE reported in the literature for coniferous forests in temperate zone. Although the growing season was defined as the period from April to October, the actual length of the growing season (GSL) varied each year and its variation explained 62% of the inter-annual variability of the growing season WUE. This is the first study to quantify long-term changes in ecosystem-level WUE in Korea and the results can be used to test models, remote-sensing algorithms and resilience of forest ecosystem.

• Bulletin of the Korean Chemical Society
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• v.32 no.10
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• pp.3712-3719
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• 2011

Confined Pt and $CoFe_2O_4$ nanoparticles (NPs) in a mesoporous core/shell silica microsphere, Pt-$CoFe_2O_4$@meso-$SiO_2$, were prepared using a bi-functional linker molecule. A large number of Pt NPs in Pt-$CoFe_2O_4$@meso-$SiO_2$, ranging from 5 to 8 nm, are embedded into the shell and some of them are in close contact with $CoFe_2O_4$ NPs. The hydrogenation of cyclohexene over the Pt-$CoFe_2O_4$@meso-$SiO_2$ microsphere at $25^{\circ}C$ and 1 atm of $H_2$ yields cyclohexane as a major product. In addition, it gives oxygenated products. Control experiments with $^{18}O$-labelled water and acetone suggest that surface-bound oxygen atoms in $CoFe_2O_4$ are associated with the formation of the oxygenated products. This oxidation reaction is operative only if $CoFe_2O_4$ and Pt NPs are in close contact. The Pt-$CoFe_2O_4$@meso-$SiO_2$ catalyst is separated simply by a magnet, which can be re-used without affecting the catalytic efficiency.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.2
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• pp.161-165
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• 2012

It is one of the most important to protect the battery over charging for stable use and to extend the life of battery which occurs with repeated charging and discharging. Various research have been studied to know the state of health, and in this paper the terminal voltage of battery is measured to calculate the state of charge simply. The circuit used comparator is designed and built not to fall under the specific voltage of battery. The designed circuit board is attached to the automatic water sanitizer device with a solar power system. The system is located in the water tank where there is not water and electric service, and confirmed that the state of working is good.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.3
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• pp.204-210
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• 2013

This study has focused on the possibility for recycling tailings from the Sangdong tungsten mine (TA) as admixture for concrete. TA has been accumulating for several decades in Sangdong, a region in Korea, and there is a growing demand for alternative uses for this hazardous substance. In particular, the use must be in accordance with the hazardous materials stipulations under the Korean waste control act. This study showed that TA presented pH of 8.0-9.3, 18.7-22.0% of water content, 2.7% of maximum ignition loss. The chemical composition of TA showed minute differences from each depth of sampling that represented approximately 50% of $SiO_2$ and 13% of both $Al_2O_3$ and $Fe_2O_3$. The chemical composition of Cd, Cu, Zn and Pb from mortar incorporating TA showed lower levels of hazardous materials which met the specifications of the waste control act in Korea. The TA mortar also appeared very effective for stabilizing/solidifying heavy metals particularly when used in conjunction with SG.

• Journal of Bio-Environment Control
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• v.8 no.3
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• pp.152-163
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• 1999

It is required to analyze the controlled response of air temperature in greenhouse according to control techniques for precise control. In this study, a mathematical model was established for air heating of greenhouse with hot-water heating system The parameters of the model were decided by regression analysis using reference data measured at the greenhouse being heated In the simulation for the digital control of air temperature in the greenhouse, the mathematical model to evaluate the control performances was used. Tested control methods were ON-OFF contpol, p control, rl control and PID control. The mathematical model represented by inside air temperature ( T$_{i}$), hot-water temperature (T$_{w}$) in heating pipe and outside air temperature (T$_{o}$) was expressed as a following discrete time equation ; T$_{i}$($textsc{k}$＋1)＝ 0.851.T$_{i}$($textsc{k}$)＋0.055.T$_{w}$($textsc{k}$)＋0.094.T$_{o}$($textsc{k}$) Control simulations for various control methods showed the settling time, the overshoot and the steady state nor as follows; infinite time, 3.5$0^{\circ}C$, 3.5$0^{\circ}C$ for ON-OFF control : 30min 2.37$^{\circ}C$, 0.51$^{\circ}C$ for P control; 21min, 0.0$0^{\circ}C$, 0.23$^{\circ}C$ for PI control; 18min 0.0$0^{\circ}C$, 0.23$^{\circ}C$ for PID control, respectively. PI and PID controls appeared to be optimal control methods. There was no effect of differential gain on the heating process but much effect of integral gain on it.on it.

• Journal of Soil and Groundwater Environment
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• v.22 no.1
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• pp.1-12
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• 2017

Nitrate ($NO_3^-$), a common surface water and groundwater pollutant, poses a serious environmental problem in regions with intensive agricultural activities and dense population. It is thus important to identify the source of nitrate contamination to better manage water quality. Due to the distinct isotope compositions of nitrate among different origins, the dual isotope analysis (${\delta}^{15}N$ and ${\delta}^{18}O$) of nitrate has been widely applied to track contamination sources. This paper provided the underlying backgrounds in the isotope analysis of nitrate, which included typical ranges of ${\delta}^{15}N$ and ${\delta}^{18}O$ from various nitrate sources, isotope fractionation, the analytical methods used to concentrate nitrate from samples, and the potential limitations of the dual isotope analysis along with the resolutions. To enhance the applicability of the dual isotope analysis as well as increase the ability to interpret field data, this paper also introduced several case studies. Furthermore, other environmental tracers including ${\delta}^{11}B$ and $Cl^-/Br^-$ ratios were discussed to accompany the dual isotope analysis for better assignment of contamination sources even when microbial transformation of nitrate and/or mixing between contaminant plumes occur.

• Economic and Environmental Geology
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• v.46 no.6
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• pp.495-508
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• 2013

Recently, stable isotopes (${\delta}^{18}O$ and ${\delta}D$) of water are increasingly analyzed using laser-based technologies. These methods have advantages over Isotope Ratio Mass Spectrometry (IRMS) in that they can be used for in-situ measurements and require much less maintenance and preparation work. Two types of laser-based methods are currently available, which have different analytical principles; OA-ICOS (off-axis integrated cavity output spectroscopy) and WS-CRDS (wavelength-scanned cavity ring-down spectroscopy). In the WS-CRDS instrument, water is vaporized at controlled environment and transferred to an optical cavity by nitrogen carrier gas, and stable isotopic compositions of water vapor are measured using the degree of absorbance of specific wavelengths and the ratios of attenuation time of the laser intensity with the sensitivity of ppb to tens of ppt level. In this study, we introduce the principle of the WS-CRDS technology and the performance results including stability and comparisons with Isotope Ratio Mass Spectrometry (IRMS) and suggest possible applications of various topics in isotope hydrology.