• Environmental Engineering Research
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• v.20 no.3
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• pp.223-229
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• 2015

The application of coagulation for feed water pretreatment prior to microfiltration (MF) process has been widely adopted to alleviate fouling due to particles and organic matters in feed water. However, the efficiency of coagulation pretreatment for MF is sensitive to its operation conditions such as pH and coagulant dose. Moreover, the optimum coagulation condition for MF process is different from that for rapid sand filtration in conventional drinking water treatment. In this study, the use of response surface methodology (RSM) was attempted to determine coagulation conditions optimized for pretreatment of MF. The center-united experimental design was used to quantify the effects of coagulant dose and pH on the control of fouling control as well as the removal organic matters. A MF membrane (SDI Samsung, Korea) made of polyvinylidene fluoride (PVDF) was used for the filtration experiments. Poly aluminum chloride (PAC) was used as the coagulant and a series of jar tests were conducted under various conditions. The flux was $90L/m^2-h$ and the fouling rate were calculated in each condition. As a result of this study, an empirical model was derived to explore the optimized conditions for coagulant dose and pH for minimization of the fouling rate. This model also allowed the prediction of the efficiency of the coagulation efficiency. The experimental results were in good agreement with the predictions, suggesting that RSM has potential as a practical method for modeling the coagulation pretreatment for MF.

• Journal of Environmental Health Sciences
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• v.29 no.2
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• pp.69-76
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• 2003

Hexavalent chromium may reduce on polyvinyl chloride (PVC) filter during sampling and storage of sample. Recently, new or modified filters for preventing Cr(VI) from the reduction has been introduced. Thus, this study was performed to compare the reduction behaviors of Cr(VI) on several sampling filters and to find the most appropriate filter for airborne Cr(VI) sampling in plating operation. The results were as follows. 1. There were statistically significant differences among PVC, polytetrafluoroethylene (PTFE). glass fiber (GF) and polyvinylidene fluoride (PVDF) filters in recovery rates of spiked Cr(VI) samples by storage time(p<0.05). There was no significant difference between PVC and PTFE filters(p>0.05). The PVC and PTFE filters showed higher recoveries than GF and PVDF filters(p<0.05). 2. The quartz fiber(QF) filter treated with an alkali solution(2% NaOH/3% Na$_2$CO$_3$, 1% NaOH) showed a significantly higher recovery of Cr(VI) by storage time than other filters(GF and QF filter)(p<0.05). There was no difference in recovery of Cr(VI) between alkali-treated and untreated GF it filters(p>0.05). But the QF filters treated with two alkali solution showed a significantly higher recovery than the untreated QF filter(p<0.05). There was no significant difference in recovery of Cr(VI) between QF filters treated with 1% NaOH and 2% NaOH/3% Na$_2$CO$_3$(p>0.05). In conclusion, treatment of QF fillers with alkali solution was most effective in protecting from the reduction of Cr(VI).

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.5
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• pp.91-97
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• 2012

Recently, the performances of electrical and electronic devices are improving while the sizes are becoming smaller. As sound-generating systems, the two-dimensional speakers have been developed in place of conventional three-dimensional ones. Piezoelectric materials show the mechanical vibrations due to the voltage applied from outside the materials. The early film speakers had a limitations of output power in that it was not easy to make the conducting macromolecular films on the surfaces of the materials due to the internal chemical properties of materials. We have adopted the corona surface treatment in order to improve the output characteristics by increasing the adhesion of the coating material on to the surface of the center material of piezo film. The results showed the improvement of output power in the wider range of operating frequencies.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.1
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• pp.47-53
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• 2012

As one of the methods for recycling the FRP from the waste ships, separation of roving layer from the mat has some merits in a sense of the eco-friendly and economical recycling process. Similar characteristics, however, between the roving and the mat even with different ratio of the resin and the glass and the thickness of the roving, much thinner than the mat, make the mechanically automatic differentiation difficult. In this study spectrochemical differentiation between the two layers has been made using boiling concentrated sulfuric acid, methanol and isopropanol solution saturated with KOH, or hydrogen fluoride (HF) solution. Furthermore efficiently coloring water-soluble dye following the HF treatment makes the roving layer more distinguishable photophysically. The layer differentiation and the automatic layer distraction move up the date of simple and automatic separation process for the waste FRP.

• Journal of the Korean Society for Marine Environment & Energy
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• v.12 no.1
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• pp.55-59
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• 2009

As one of the methods for recycling the FRP from the small and medium waste ships, separation of roving layer from the mat has some merits in a sense of the recycling energy and the environmental effects. Similar characteristics, however, between the roving and the mat even with different ratio of the resin and the glass and the thickness of the roving, much thinner than the mat, make the mechanically automatic differentiation difficult. In this study spectrochemical differentiation between the two layers has been made using (1) boiling concentrated sulfuric acid which can dissolve the resin in the FRP layer, (2) methanol and isopropanol solution saturated with KOH which can dissolve the glass, or (3) hydrogen fluoride(HF) solution which can reacts with $SiO_2$ fragments of the glass. Furthermore coloring water-soluble dye following the HF treatment makes the roving layer more distinguishable photo-physically.

• Journal of Korean Society on Water Environment
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• v.35 no.5
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• pp.418-424
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• 2019

In this study, $TiO_2$ nanotubes with different morphologies were prepared in the electrolyte consisting of ethylene glycol, ammonium fluoride($NH_4F$), and deionized water($H_2O$) by controlling the voltage and time in the anodization method. Thicknesses and pore sizes of these $TiO_2$ nanotubes were measured to interpret the relationship between anodization conditions and $TiO_2$ nanotube morphologies. Element contents in the $TiO_2$ nanotubes were detected for further analysis of $TiO_2$ nanotube characteristics. Photoelectrolyticdecolorization efficiencies of the $TiO_2$ nanotube plates with various morphologies were tested to clarify the morphology that a highly active $TiO_2$ nanotube plate should have. Influences of applied voltage in photoelectrolysis processes and sodium sulfate($Na_2SO_4$) concentration in wastewater on the decolorization efficiency were also studied. To save the equipment investment cost in photoelectrolysis methods, a two-photoelectrode system that uses the $TiO_2$ nanotube plates as photoanode and photocathode instead of adding other counter electrodes was studied. Compared with single-photoelectrode system that uses the $TiO_2$ nanotube plate as photoanode and titanium plate as cathode on the view of the treatment of dye wastewater containing different amounts of salt. As a result, a considerably suitable voltage was strictly needed for enhancing the photoelectrolyticdecolorization effect of the two-photoelectrode system but if salts exist in wastewater, an excellent increase in the decolorization efficiency can be obtained.

• The korean journal of orthodontics
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• v.40 no.4
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• pp.260-266
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• 2010

Objective: The aim of this study was to determine whether different types of adhesive systems and enamel-protective agents will affect the tensile bond strength of lingual brackets. Methods: A total of 75 extracted mandibular incisors were randomly divided into 5 groups and lingual brackets were bonded. Group 1 specimens received Transbond XT (3M Unitek, Monrovia, CA, USA), Group 2 required the application of a fluoride-releasing resin (Ortho-coat, Pulpdent, Watertown, MA, USA) with Transbond XT, Group 3 specimens received a chlorhexidine varnish (Cervitec Plus, Ivoclar Vivadent, Schaan, Lichtenstein) with Transbond XT. In Group 4, a light-cured orthodontic adhesive (Aegis Ortho, Bosworth, Skokie, USA) was applied and in Group 5, an antimicrobial self-etching primer (Clearfil Protect Bond, Kuraray, Osaka, Japan) was used. Results: There were no significant differences in bond strength whether fluoride-releasing resin or chlorhexidine varnish were used or not. Group 5 had significantly higher bond strength and adhesive remnant index (ARI) values than other groups (p < 0.001). The application of enamel-protective products did not have an adverse affect on the bond strength of lingual brackets. Conclusions: These products might provide benefits both for the patient and the clinician, by supporting the oral hygiene during lingual orthodontic treatment. The higher ARI score may be beneficial for Clearfil Protect Bond but its excessive bond strength should be considered in clinical practice, especially where the enamel is thin.

• Applied Biological Chemistry
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• v.41 no.1
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• pp.6-12
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• 1998

To extract insoluble proteins and to improve functional properties of abolished proteins, a protease producing Aspergillus sp. MS-18 was isolated from soil. The enzyme was purified and its enzymological characteristics were investigated. It was found that production of protease reached to the maximum when the wheat brae medium containing, 3% arabinose, 0.5% polypepton, 0.1% $(NH_4)_2SO_4$ and 0.2% magnesium chloride was cultured for 3 days. Protease was purified 16.9 folds after ion exchange chromatography and gel filtration and the specific activity was 340.4 unit/mg. Purified enzyme was confirmed as a single band by the polyacrylamide gel electrophoresis. The molecular weight of protease was estimated to be 30,000. Crystalization form of purified protease was a stick shape with rounding edges. The optimum pH and temperature for the protease activity were 9.0 and $60^{\circ}C$, respectively. The enzyme was stable in pH 7.0-12.0 at $50^{\circ}C$. The activity of purified enzyme was inhibited by $Hg^{2+}$, $Cu^{2+}$, $Zn^{2+}$ and $Pb^{2+}$, whereas it was activited by $Na^+$, $Mg^{2+}$ and $Mn^{2+}$. The activity of the protease was inhibited by the treatment with ethylenediaminetetraacetic acid and phenylmethane sulfonyl fluoride. The result suggests that the purified enzyme is a serine protease with metal ion at active site. Km and Vmax of purified protease were $29.33\;{\mu}mole/L$ and $5.13\;{\mu}g/min$, respectively.

• Korean Journal of Microbiology
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• v.45 no.4
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• pp.377-384
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• 2009

Among 27 Bacillus sp. isolated from Meju, a traditional Korean soybean fermented food, a strain MJ-226 was selected due to its strong fibrinolytic activity, and it was identified to be Bacillus subtilis MJ-226 according to morphological and biochemical characterization and sugar utilization. The fibrinolytic enzyme of B. subtilis MJ-226 was maximally produced by cultivating in the Tryptic Soy Broth (TSB) for 24~26 h at $37^{\circ}C$, and the enzymes activity was promoted with adding glucose, fructose, peptone or yeast extract to TSB. The fibrinolytic enzyme was stable at the range of pH from 6.0 to 8.0, and between 35 and $40^{\circ}C$. Also, when the crude enzyme was exposed to various metal ions and chemical inhibitors for 12 h, the enzyme stability was maintained by $MnSO_4$, $CaCl_2$, KCl, and NaCl. However, the stability was destroyed by treatment with $CuSO_4$, $MgSO_4$, $ZnSO_4$, $FeSO_4$, and $BaCl_2$, and the enzyme was unstable in the presence of chemical inhibitors such as iodoacetic acid, leupeptin, phenylmethanesulphonyl fluoride (PMSF), sodium dodecyl sulfate (SDS), thiourea, trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) and ethylenediaminetetraacetic acid (EDTA).

• Journal of the Korean Electrochemical Society
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• v.22 no.4
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• pp.148-154
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• 2019

Vanadium oxide based materials have been studied as novel negative electrode materials in lithium-ion batteries (LIBs) because of their high specific capacity. In this study, potassium metavanadate ($KVO_3$) was synthesized and its electrochemical properties are evaluated as a negative electrode materials. The aqueous solution of $NH_4VO_3$ is mixed with a stoichiometric amount of KOH. The solution is boiled to remove $NH_3$ gas and dried to obtain a precipitate. The obtained $KVO_3$ powders are heat-treated at 300 and $500^{\circ}C$ for 8 h in air. As the heat treatment temperature increases, the initial reversible capacity decreases, but the cycle performance and Coulombic efficiency are improved slightly. On the contrary, the electrochemical performances of the $KVO_3$ electrodes are greatly improved when a polyacrylic acid (PAA) as binder was used instead of polyvinylidene fluoride (PVDF) and a fluoroethylene carbonate (FEC) was used as electrolyte additive. The initial reversible capacity of the $KVO_3$ is 1169 mAh/g and the Coulombic efficiency is improved to 76.3% with moderate cycle performance. The $KVO_3$ has the potential as a novel high-capacity negative electrode materials.