• Journal of Korean Society on Water Environment
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• v.20 no.2
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• pp.145-150
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• 2004

This study investigated the effect of chlorine dose and chlorine reaction time for the formation of haloacetic acids (HAAs). According to the results, HAA formation was highly affected by chlorine dose and chlorine reaction time. HAA formation reached a plateau value at 30 mg/L of chlorine dose and 24 hr of chlorine reaction time. For the speciation of formed HAAs in the test water, the concentration of brominated-HAAs was significantly lower than that of chlorinated-HAAs because of low level of bromide ion concentration in the test water. It also investigated the removal efficiency of HAA precursors by several unit processes, such as ozone alone, UV alone, and combined ozone/UV system. Of them, ozone/UV system was proved as the best process to control the HAAs formation. The increase of the brominated-HAAs was observed during ozonation with and without UV irradiation showing the slight increase of total HAA concentrations.

• Journal of Environmental Science International
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• v.23 no.9
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• pp.1635-1642
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• 2014

Haloacetic acids (HAAs) concentrations have been observed to decreased at drinking water distribution system extremities. This decrease is associated with microbiological degradation by pipe wall biofilm. The objective of this study was to evaluate HAAs degradation in a drinking water system in the presence of a biofilm and to identify the factors that influence this degradation. Degradation of monochloroacetic acid (MCAA), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) was observed in a simulated distribution system. The results obtained showed that different parameters came into play simultaneously in the degradation of HAAs, including retention time, water temperature, biomass, and composition of organic matter. Seasonal variations had a major effect on HAAs degradation and biomass quantity (ATP concentration) was lower by 25% in the winter compared with the summer.

• Journal of the Korean Vacuum Society
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• v.10 no.2
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• pp.262-266
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• 2001

We have presented the electrical properties of the quantum wire fabricated by split gate on GaAs/AlGaAs heterostructures by using the Shubnikov de Haas oscillation and quantum Hall effect measurements. We observed the 1D properties of the sample as increasing gate voltage. The misfit between quantum Hall plateau and minima in Shubnikov do Haas oscillations are interpreted as Landauer-B$"{u}$ tikker formula based on the edge state transport.port.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.4
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• pp.303-307
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• 2007

This paper investigated the effect of the pad buffing process on the material removal characteristics and pad stabilization during silicon chemical mechanical polishing. The pads surface were controlled by the buffing process using a buffer made by the sandpaper. The buffing process is based on abrasive machining by using a high speed sandpaper. The controlled pad by the buffing process show less deformation deviation and stable material removal rate during the CMP process. In addition, the controlled pad ensure better uniformity of removal rate than comparative pads. As a result of monitoring, the controlled pad by the buffing process demonstrated constant and stable friction force signals from initial polishing stage. Therefore, the tufting process could control the pad surface to be uniform and improve the performance of the polishing pad.

• Korean Journal of Materials Research
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• v.18 no.2
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• pp.103-106
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• 2008

The magneto-transport properties of an individual single crystalline Bi nanowire grown by a spontaneous growth method are reported. A four-terminal device based on an individual 400-nm-diameter nanowire was successfully fabricated using a plasma etching technique that removed an oxide layer that had formed on the surface of the nanowire. Large transverse ordinary magnetoresistance (1401%) and negative longitudinal ordinary magnetoresistance (-38%) were measured at 2 K. It was observed that the period of Shubnikov-de Haas oscillations in transverse geometry was $0.074^{T-1}$, $0.16^{T-1}$ and $0.77^{T-1}$, which is in good agreement with those of bulk Bi. However, it was found that the period of SdH oscillation in longitudinal geometry is $0.24^{T-1}$, which is larger than the value of $0.16^{T-1}$ reported for bulk Bi. The deviation is attributable to the spatial confinement arising from scattering at the nanowire surface boundary.

• Journal of Environmental Science International
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• v.13 no.1
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• pp.55-59
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• 2004

The effect of ozone on the formation and the removal of disinfection byproducts(DBPs) of chlorination process was studied to elucidate the performance of water treatment process. The samples of raw water, prechlorination process, and preozonation process were analyzed quantitatively according to the Standard Methods for the Examination of drinking water. As a result, most of total trihalomethanes(THMs) which were formed in prechlorine treatment process was not removed in the preozonation process. Most of haloacetic acids(HAAs), haloacetonitriles(HANs), and chloral hydrate(CH) was removed in sedimentation and biological activated carbon(BAC) filtration processes. However, DBPs were increased more or less by postchlorine step. In particular, the formation of THMs and HAAs depends on ozone more than chlorine, but, the formation of HANs and CH depends on chlorine more than ozone. The seasonal variation of DBPs concentration for the year needs to be investigated to study the temperature effect because DBPs strongly depend on temperature among various efficient factors.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.955-959
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• 2004

The effects of conduction band offset on 2 dimensional electron gas (2DEG) in N-InAlAs(AlAsSb)/InGaAs/InAlAs (AlAsSb) metamorphic heterostructures (MMHS) are studied. A combination of the Shubnikov-deHaas oscillations and the Hall measurements is used to investigate the electron transport properties of these structures. The mobility in the second subband is higher than that in the first subband in all heterostructures. This is attributed to the fact that electrons in the first subband we, on average, closer to the interface and are therefore scattered more strongly by ionized impurities. The results suggest that intersubband scattering rate is more dominant in structures with higher conduction band offset whereas alloy scattering is found to be more dominant in the higher band offset system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.297-298
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• 2011

• Journal of Environmental Science International
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• v.14 no.10
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• pp.965-972
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• 2005

This research studied the effect of factors that are able to form disinfection by-products (DBPs) of chlorination, including natural organic matter (NOM) with sewage, bromide ions, pH and contact time. Trihalomethane (THMs) yield of $0.95{\mu}mol/mg$ was higher than other DBPs yield for the chlorinated humic acid samples. THMs yield of sewage sample was $0.14{\mu}mol/mg$ and haloacetonitriles (HANs) yield in the sewage samples were $0.13{\mu}mol/mg$ but only $0.02{\mu}mol/mg$ for the humic acid samples. As the concentration of bromide ions increased, brominated DBPs increased while chlorinated DBPs decreased, because bromide ions produce brominated DBPs. THMs were highest $(55.55{\mu}g/L)$ at a pH of 7.9 and haloacetic acids (HAAs) were highest $(34.98{\mu}g/L)$ at a pH of 5. Also THMs increased with increasing pH while HAAs decreased with increasing pH. After chlorination, the rate of THMs and HAA formation are faster at initial contact time and then reaches a nearly constant value after 24 hours. This study considers ways to reduce DBP formation by chlorination.

• Journal of Environmental Science International
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• v.21 no.9
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• pp.1031-1041
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• 2012

This study was carried out to investigate the characteristics of disinfection by-products (DBPs-trihalomethanes (THMs), haloacetic acids (HAAs) and haloacetonitriles (HANs) formation in chlorination of principal raw waters used for drinking water on Jeju Island, Korea. The domestic water supply of other area and humic acid solution (HA) were used as a reference point. The effects of chlorine contact time, solution temperature and pH on DBPs formation potential (DBPFP) were investigated for raw waters. In addition, the effect of $Br^-$ was studied for HA. The DBPFP (THMFP, HAAFP and HANFP) were increased with increasing chlorine contact time. Comparing the individual DBPFPs for raw waters, they decreased in the order of HAAFP > THMFP ${\geq}$ HANFP. As the solution temperature was increased, the THMFP, HAAFP and HANFP increased. With increasing the solution pH, the THMFP was increased, but HAAFP and HANFP were decreased. With the addition of 0.3 mg/L $Br^-$ for HA, the DBPFP was increased and the major chemical species changed: from trichloromethane to dibromochloromethane and tribromomethane for THMs; from dichloroacetic acid and trichloroacetic acid to tribromoacetic acid for HAAs; and from dichloroacetonitrile to dibromoacetonitrile for HANs.