• Journal of the Korean Magnetic Resonance Society
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• v.10 no.2
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• pp.141-154
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• 2006

A solid-state reaction of $V_2O_5$ with AlMCM-41 followed by calcinations generated $V^{5+}$ species in the mesoporous materials. Dehydration results in the formation of a vanadyl species, $VO^{2+}$, that can be characterized by electron spin resonance (ESR). The chemical environment of the vanadium centers in V-AlMCM-41 was investigated by XRD, EDX, diffuse reflectance UV-VIS, ESR, $^{29}Si,\;^{27}Al,\;and\;^{51}V$ NMR. It was found that the vanadium species on the wall surface and inside the wall of the hexagonal tubular wall of the V-AlMCM-41 were completely oxidized to tetrahedral $V^{5+}$ and transformed to square pyramidal by additional coordination to water molecules upon hydration. The oxidized $V^{5+}$ species on the wall surfaces and inside the wall were also reversibly reduced to $VO^{2+}$ species or lower valences by thermal process.

• Journal of the Korean Society of Industry Convergence
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• v.27 no.2_2
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• pp.397-402
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• 2024

Silicon carbide materials undergo an oxidation reaction in a high-temperature oxidizing environment and show different characteristics depending on the test temperature and time. In particular, the added oxides form a secondary phase within the sintering process and exhibit different oxidation characteristics depending on the added sintering materials. Therefore, to evaluate the oxidation characteristics, the weight of the test piece and the thickness of the oxidation layer were observed, and the structure and oxidation characteristics of the material were analyzed using SEM. SEM observation showed that an oxide layer was formed on the surface of the liquid sintered silicon carbide material after it was oxidized at 1200 ℃, 1300 ℃, and 1400 ℃ for 10 hours, respectively. Then, a bending test was performed at each temperature on the test piece with the oxidation layer formed to evaluate the change in flexural strength. The strength was 466.6 MPa at 1200 ℃, 363.1 MPa at 1300 ℃, and 350.8 MPa at 1400 ℃. Al₂O₃-SiO₂ oxidized at 1200 ℃ for 10 hours showed an increase in strength of about 21.0 MPa compared to the data before the oxidation test.

• Journal of Korean Society for Atmospheric Environment
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• v.30 no.3
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• pp.261-269
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• 2014

This study focused on the performance of the newly developed hybrid filter system to capture fine particulate matter and mercury compounds in a coal-fired power plant. The hybrid filter system combining bag-filter and electrostatic precipitator had been developed to remove fine particulate matter. However, it would have a good performance to control mercury compounds as well. In Hybrid filter capture system, the total removal efficiency of total mercury compounds consisting of particulate mercury ($Hg_p$), oxidized mercury ($Hg^{2+}$), and elemental mercury ($Hg^0$) was 66.2%. The speciation of mercury compounds at inlet and outlet of Hybrid filter capture system were 1.3% and 0% of $Hg_p$, 85.2% and 68.1% of $Hg^0$, and 13.5% and 31.9% of $Hg^{2+}$, respectively. In hybrid filter capture system injected with 100% of flue-gas, the removal efficiency of total mercury was calculated to increase to 93.5%.

• Journal of Biosystems Engineering
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• v.41 no.2
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• pp.85-92
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• 2016

Background: The same plant, Camellia sinensis, is used to produce all types of tea, and the differences among the various types arise from the different processing steps that are used. Based on the degree of fermentation, tea can be classified as black, green, white, or oolong tea. Of these, black tea is the most or fully fermented tea. The oxidized polyphenolic compounds such as theaflavins (TF) and thearubigins (TR) formed during fermentation are responsible for the color, taste, flavor, and aroma of black tea. Results: Research indicates that an optimum ratio of TF and TR (1:10) is required to ensure a quality cup of tea. The concentrations of TF and TR as well as desirable quality characteristics increase as fermentation time increases, reaching optimum levels and then degrading if the fermentation time is prolonged. It is also necessary to control the environment for oxidation. There are no established environment conditions that must be maintained during the fermentation of the ruptured tea leaves. However, in most cases, the process is performed at a temperature of $24-29^{\circ}C$ for 2-4 h or 55-110 min for orthodox tea or crush, tear, and curl (CTC) black tea, respectively, under a high relative humidity of 95-98% with an adequate amount of oxygen. Conclusion: The polyphenolic compounds in black tea such as TF and TR as well as un-oxidized catechins are responsible for the health benefits of tea consumption. Tea is rich in natural antioxidant activities and is reported to have great potential for the management of various types of cancers, oral health problems, heart disease and stroke, and diabetes and to have other health benefits such as the ability to detoxify, improve urine and blood flow, stimulate, and improve the immune system.

• Advances in environmental research
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• v.3 no.3
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• pp.199-206
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• 2014

Dewatering is an extremely important step in wastewater treatment process to reduce the final sludge volume in order to minimize the cost of sludge transportation and disposal. In the present study, the effect of different sludge solids content (1, 2 and 3.8%) on the dewaterability of anaerobically digested sludge using Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans was studied. The pH reduction rate was higher during initial process in the sludge having low solids content, but after 48 h of bioleaching, similar pH of below 3 was observed with all the different solids content. Bio-oxidation rate of $Fe^{2+}$ was initially higher in sludge with low solids content, but 100% $Fe^{2+}$ was oxidized within 60 h in all the three treatment levels. Compared to the control, specific resistance to filtration was reduced by 75, 78 and 80% in the sludge with a solids content of 1, 2 and 3.8% respectively, showing improvement in dewaterability with an increase in sludge solids content. Sludge effluent quality and sludge settling rate were also improved in treatments with higher solids content after the bioleaching process.

• Journal of Korean Society for Atmospheric Environment
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• v.32 no.5
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• pp.485-500
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• 2016

We examined acidity state of inorganic aerosol and oxidation state of organic aerosol by High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) at Baengnyeong Super site from Jan 2012 to Dec 2013. Additionally, we carried out the analysis for the aerosol component group of organic matter ($C_xH_y$, $C_xH_yO_1$, $C_xH_yO_z$, $C_xH_yO_zN_p$) and elemental composition to calculate H/C, O/C, N/C, OM/OC and identify the oxidation state. The aerosol chemical composition in this study is dominated by sulfate ($SO_4{^{2-}}$), nitrate ($NO_3{^-}$) plays a smaller role in aerosol acidity. Ammonium ($NH_4{^+}$) was found in a formation of $(NH_4)_3H(SO_4)_2$. However, the binding formations of $NH_4NO_3$ and $NH_4Cl$ increase in the winter. $C_xH_yO_1$ indicating the oxidized state of $PM_{1.0}$ has the highest ratio of 41% while $C_xH_y$ indicating the non-oxidized state has a lower ratio of 36%, meaning that the oxidation level of $PM_{1.0}$ in Baengnyeong Island is high. The ratio between H/C and O/C was 1.33 and 0.78 respectively, showing the characteristic of LV-OOA (Low volatility-Oxygenated Organic Aerosol). Acidic and oxidized aerosols sampled during this field study were largely anthropogenic in origin from Chinese continent and photochemically aged.

• Journal of Korean Society for Atmospheric Environment
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• v.14 no.4
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• pp.387-392
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• 1998

Recently, among after-treatment devices which have high possibility of utility, diesel oxidation catalyst (DOC) is concerned over the world. DOC oxidizes pollutants by means of activate-reaction during by -passing in the catalyst, in doing so, conversion efficiency of PM, CO and HC is high, and this device does not have an effect on engine performance because back pressure is not nearly increased. But, as a small amount of sulfur content in fuel is oxidized, it makes sulfate, which is absorbed on the surface of catalyst. So, in this study, the experiment is carried out by means of using ordinary fuel (0.1wt%) and low sulfur fuel (0.05wt%) with DOC, and the emission gas of diesel engine is measured.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1998.11a
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• pp.189-194
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• 1998

Geochemical study was carried out to find out the distribution of metals and cyanide in soil in the vicinity of the abandoned Keum-Jung mine. Chemical analysis showed that content of As in soil around tailings exceeded 15mg/kg, Korean standard of soil contamination in the farm land. That means the contamination of soil by As is due to input of tailings. According to total decomposition of tailings, As was highly concentrated in tailings. However the water in tailings impoundment was changed to acidic and contaminated by metal and sulfate because the tailings in the top of the tailings impoundment had been oxidized. Acid mine drainage contaminated the water course in the vicinity of the paddy soils. The proper measures are required to prevent contamination of the soil and water in the vicinity of the Keum-Jung mine.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.04a
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• pp.45-48
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• 2001

The packed column experiments were conducted with a field soil, collected directly from the aquifer located at Bonchon industrial complex in K-city in order to characterize SOM reaction with ozone and to delineate the transformation of water soluble SOM after ozonation. As reaction time increased, water soluble organic matter increased, and this organic matter was in the range of 500∼1000 dalton. pH of extractants decreased with the increase of ozonation time. This Is because aromtic compounds in SOM were oxidized and carboxylic acid groups were formed. From the FT-IR spectra, the content of carboxylate increased as ozone injection time increased and hydroxyl group, which represents phenolic and alcoholic hydroxyl groups decreased. This is because oxidative ring fission formed carboxyl acid groups. This result provides a good agreement with pH decrease.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.04a
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• pp.393-396
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• 2005

The reactive transport model on the biologically mediated sequential nitrate transformation and its subsequent transport was developed and tested. This model was coded as a reaction module within the RT3D framework (Clement, 1997). Transports of the reasonable six mobile solutes (dissolved organic carbon, $O_2,\;{NO_3}^-,\;{NO_2}^-,\;N_2O,\;N_2$) and two immobile microbes were simulated. The simulation results gave a reasonable match with supposed transport pattern. For the next step, the developed model will be validated against experimental data.