• Journal of Environmental Science International
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• v.21 no.8
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• pp.989-996
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• 2012

Nitrate contamination of water environments can create serious problems such as eutrophication of rivers. Conventional biological processes for nitrate removal by heterotrophic denitrification often need additional organic substrates as carbon sources and electron donors. We tried to accelerate biological denitrification by using bioelectrochemical reactor (BER) in which electrode works as an electron donor. Denitrification activity of 8 environmental samples from various sediments, soils, groundwaters, and sludges were tested to establish an efficient enrichment culture for BER. The established enrichment culture from a soil sample showed stable denitrification activity without any nitrite accumulation. Microbial community analysis by using PCR-DGGE method revealed that dominant denitrifiers in the enrichment culture were Pantoea sp., Cronobacter sakazakii, and Castellaniella defragrans. Denitrification rate ($0.08kg/m^3{\cdot}day$) of the enrichment culture in BER with electrode poised at -0.5 V (vs Ag/AgCl) was higher than that ($2.1{\times}10^{-2}kg/m^3{\cdot}day$) of BER without any poised potential. This results suggested that biological denitrification would be improved by supplying potential throughout electrode in BER. Further research using BER without any organic substrate addition is needed to apply this system for bioremediation of water and wastewater contaminated by nitrate.

• Journal of Microbiology and Biotechnology
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• v.13 no.2
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• pp.225-229
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• 2003

Each oxidoreductase activity of the aerobic respiratory chain-linked NADH oxidase system in the marine bacterium Pseudomonas nautica was stimulated by monovalent cations including $Na^+,\;Li^+,\;and\;K^+$. In the presence of NADH or deamino-NADH as electron donors, $GH_2$ formation was approximately 1.3-fold higher in the presense of 0.08 M of $Na^+\;than\;K^+$, Whereas the other reductase activities were not significantly higher in $Na^+\;than\;K^+$. The optimal pH of NADH (or deamino-NADH):ubiquinone-1 oxidoreductase was 9.0 in the presence of 0.08 M NaCl. The activity of NADH (or deamino-NADH):ubiquinone-1 oxidoreductase was inhibited by about 33% with $60{\mu}M$ 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO). The activity of NADH (deamino-NADH): ubiquinone-1 oxidoreductase was inhibited by about 32 to 38% with $80{\mu}M$ rotenone, whereas the activity was highly resistant to capsaicin. On the other hand, electron transfer from NADH or deamino-NADH to ubiquinone-1 generated a membrane potential (${\Delta}{\psi}$) which was larger in the presence of $Na^+$ than that observed in the absence of $Na^+$. The ${\Delta}{\psi}$ was almost completely collapsed by $5{\mu}M$ carbonylcyanide m-chlorophenylhydrazone(CCCP), and approximately 50% inhibited by $100{\mu}M$ rotenone, or $60{\mu}M$ 2-heptyl-4-hydroxyquinoline (HQNO). Also, HQNO made the ${\Delta}{\psi}$ very unstable. The results suggest that the enzymatic and energetic properties of the NADH:ubiquinone oxidoreductase of P. nautica are quite different, compared with those of other marine halophilic bacteria.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.304.2-304.2
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• 2014

Chalcogenides (Te,Se) and pnictogens(Bi,Sb) materials have been widely investigated as thermoelectric materials. Especially, Bi2Te3 (Bismuth telluride) compound thermoelectric materials in thin film and nanowires are known to have the highest thermoelectric figure of merit ZT at room temperature. Currently, the thermoelectric material research is mostly driven in two directions: (1) enhancing the Seebeck coefficient, electrical conductivity using quantum confinement effects and (2) decreasing thermal conductivity using phonon scattering effect. Herein we demonstrated influence of annealing temperature on structural and thermoelectrical properties of Bismuth-telluride-selenide ternary compound thin film. Te-rich Bismuth-telluride-selenide ternary compound thin film prepared co-deposited by thermal evaporation techniques. After annealing treatment, co-deposited thin film was transformed amorphous phase to Bi2Te3-Bi2Te2Se1 polycrystalline thin film. In the experiment, to investigate the structural and thermoelectric characteristics of Bi2Te3-i2Te2Se1 films, we measured Rutherford Backscattering spectrometry (RBS), X-ray diffraction (XRD), Raman spectroscopy, Scanning eletron microscopy (SEM), Transmission electron microscopy (TEM), Seebeck coefficient measurement and Hall measurement. After annealing treatment, electrical conductivity and Seebeck coefficient was increased by defect states dominated by selenium vacant sites. These charged selenium vacancies behave as electron donors, resulting in carrier concentration was increased. Moreover, Thermal conductivity was significantly decreased because phonon scattering was enhanced through the grain boundary in Bi2Te3-Bi2Te2Se1 polycrystalline compound. As a result, The enhancement of thermoelectric figure-of-merit could be obtained by optimal annealing treatment.

• Korean Journal of Environmental Agriculture
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• v.31 no.1
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• pp.24-29
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• 2012

BACKGROUND: In recent years, microbial fuel cells (MFCs) have emerged as a promising technology for recovering renewable energy from waste biomass, especially wastewater. In this study, the possibility of bioelectricity generation in two chambered mediator-less microbial fuel cells (MFCs) was successfully demonstrated using fermentable and non-fermentable substrates. METHODS AND RESULTS: Two different electron acceptors have been tested in the cathode chamber for the effects of reducing agent on the power generation in MFCs. The average voltages of $0.26{\pm}0.014$ V and $0.36{\pm}0.02$ V were achieved with acetate using oxygen and potassium ferricyanide as reducing agent, respectively. Similarly, with glucose the average voltages of $0.256{\pm}0.05$ V and $0.340{\pm}0.04$ V were obtained using oxygen and ferricyanide, respectively. Using potassium ferricyanide as the reducing agent, the power output increases by 39 and 43% with acetate and glucose, respectively, as compared to the dissolved oxygen. Slightly higher coulombic efficiency (CE%) was obtained in acetate as compared to MFCs operated with glucose. The maximum power densities of 124 mW/$m^2$ and 204 mW/$m^2$ were obtained using dissolved oxygen and $K_3Fe(CN)_6$, respectively. CONCLUSION(s): This study demonstrates that power generation from the MFCs can be influenced significantly by the different types of catholyte. Relatively higher CE was obtained with $K_3Fe(CN)_6$. Thus, application of $K_3Fe(CN)_6$ as the catholyte can be vital for scaling uppower generation from the MFCs forreal time applications.

• Analytical Science and Technology
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• v.5 no.2
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• pp.213-216
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• 1992

Semiinsulating GaAs crystals employing LPLEC technique should be grown from the Ga-rich melt due to a very low incorporation of unintentional impurities such as carbon (<$10^{15}cm^{-3}$). High resisitivity of this material can be derived from the balanced compensation among not only EL2 deep donors and carbon acceptors but also H1 double charge native acceptors(Ev + 77meV, Ev + 200 meV) and H2 native acceptors(Ev + 68 meV). Considering of the complicated compensation mechanism using statistical calculation of the electron occupancy of each level, SI GaAs crystal with low impurity contents(<$10^{15}cm^{-3}$) can be successfully obtained by maintaining the melt composition around 0.45 As mole fraction.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1055-1060
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• 2013

The adsorption structures of threonine on the Ge(100) surface were investigated using core-level photoemission spectroscopy (CLPES) in conjunction with density functional theory (DFT) calculations. CLPES measurements were performed to identify the experimentally preferred adsorption structure. The preferred structure indicated the relative reactivities of the carboxyl and hydroxymethyl groups as electron donors to the Ge(100) surface during adsorption. The core-level C 1s, N 1s, and O 1s CLPES spectra indicated that the carboxyl oxygen competed more strongly with the hydroxymethyl oxygen during the adsorption reaction. Three among six possible adsorption structures were identified as energetically favorable using DFT calculation methods that considered the inter- and intra-bonding configurations upon adsorption onto the Ge(100) surface. These structures were O-H dissociated N dative inter bonding, O-H dissociated N dative intra bonding, O-H dissociation bonding. One of the adsorption structures: O-H dissociated N dative inter bonding was predicted to be stable in light of the transition state energies. We thus confirmed that the most favorable adsorption structure is the O-H dissociated N dative-inter bonding structure using CLPES and DFT calculation.

• Journal of the Korean Chemical Society
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• v.37 no.3
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• pp.335-343
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• 1993

The maximum absorption wavelengths of charge-transfer complexes of naphthalene, ${\alpha}-and{\beta}-methyl$ naphthalene and 1,2-, 2,3-and 2,6-dimethyl naphthalene with chloranil have been measured with a UV spectrophotometer in ethylene chloride, methylene chloride, and chloroform at 10, 15, 20, and 25$^{\circ}C$. This absorption band was interpreted as the charge transfer band of a 1 : 1 molecular complex, and the maximum absorption wavelength was changed as a function of solvent and temperature. Their formation constants (K$_f$) were decreased with the polarity of solvent and the increase of temperature. Thus, the influences of solvent and temperature on the formation constant have been discussed as consideration of thermodynamic properties, and the electronic and steric effects of electron donors on formation constant have been also discussed.

• Korean Journal of Materials Research
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• v.16 no.6
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• pp.377-381
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• 2006

Skutterudite $CoSb_3$ doped with nickel was prepared by encapsulated induction melting, and its doping effects on thermoelectric properties were investigated. Single phase ${\delta}-CoSb_3$ was successfully obtained by encapsulated induction melting and subsequent heat treatment at 773 K for 24 h. Nickel atoms acted as electron donors by substituting cobalt atoms. Thermoelectric properties were remarkably improved by appropriate heat treatment and doping, and they were closely related to phase transitions and dopant activation. The maximum ZT(dimensionless figure of merit) was achieved as 0.2 at 600 K for the $Co_{0.93}Ni_{0.07}Sb_3$ specimen.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.83-84
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• 2007

Sn-filled and Ni-doped $CoSb_3$ skutterudites were prepared by encapsulated induction melting, and their filling and doping effects on thermoelectric properties were investigated. Single phase ${\delta}-CoSb_3$ was successfully obtained by encapsulated induction melting and subsequent heat treatment at 823K for 5 days. Nickel atoms acted as electron donors by substituting cobalt atoms. Thermoelectric properties were remarkably improved by Sn filling and Ni doping.

• Journal of the Korean Society of Food Science and Nutrition
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• v.22 no.2
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• pp.246-252
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• 1993

Melanoidins, as brown colored polymers, are formed through the diversified reaction systems of Maillard type and other reactions. Melanoidins are important components in relation to food quality and also are known to have antioxidative, mutagenic and antimutagenic activities. Since these aspects have been extensively reviwed elsewhere, only the recent studies regarding to their antioxidative and antimutagenic activities are discussed in this review. Even though their mechanisms are not clearly identified, melanoidins or specific fractions isolated from their mixtures have shown varied antioxidative activities depending on the reaction systems and reaction conditions. Those activities presumely are derived from the complex functional properties of hydrogen / electron donors and metal chelating power, which are originated from their reductone structure and others. It is considered that pyrolysate and other mutagens are formed by the given conditions in some cases during browning reaction, whereas melanoidins and their fractions have antimutagenic effects on chemical and other mutagens. There are positive correlationship among the color intensity, antioxidative activity and antimutagenicity of melanoidins or their fractions. These suggest that the antimutagenicity of melanoidins could be attributed to their antioxidative properties, however, it might also be due to other factors, because the relevant responses for antimutagenicity are very complicate and not clear. Accordingly, further studies are required to determine the actual acitivities and mechanisms involved in antioxidation and (anti)mutagenicity of melanoidins by reaction systems / conditions and by the isolated fractions. And also, additional studies are needed to evaluate the applications of melanoidins and their relevant effects to food and human health.