• Journal of Korean Society on Water Environment
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• v.28 no.4
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• pp.538-550
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• 2012

This study suggests a general methodology which is designed for assessing RDOC behavior at the catchment scale by coupling properly a series of steam flow and water quality simulation models and actual monitoring data set. The modified TANK model in which a river routing function is incorporated to the conventional one is applied to simulate the long-term daily stream flow data, and the simulated stream flow data is combined with the 7-parameter log-linear model coupled to the minimum variance unbiased estimator to simulate the long-term daily water quality (BOD, COD and TOC) loads. Finally, the regression analysis between the usually monitored water quality data (BOD, COD and TOC) and RDOC is combined with the simulated water quality data to manifest the spatio-temporal variability of RDOC flux behavior at the Korean TMDL catchment scale.

• Carbon letters
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• v.25
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• pp.84-88
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• 2018

At present, an important research area is the search for materials that are compatible with CMOS technology and achieve a satisfactory response rate and modulation efficiency. A strong local field of graphene surface plasmon polariton (SPP) can increase the interaction between light and graphene, reduce device size, and facilitate the integration of materials with CMOS. In this study, we design a new modulator of SPP-based cycle branch graphene waveguide. The structure comprises a primary waveguide of graphene-$LiNbO_3$-graphene, and a secondary cycle branch waveguide is etched on the surface of $LiNbO_3$. Part of the incident light in the primary waveguide enters the secondary waveguide, thus leading to a phase difference with the primary waveguide as reflected at the end of the branch and interaction coupling to enhance output light intensity. Through feature analysis, we discover that the area of the secondary waveguide shows significant localized fields and SPPs. Moreover, the cycle branch graphene waveguide can realize gain compensation, reduce transmission loss, and increase transmission distance. Numerical simulations show that the minimum effective mode field area is about $0.0130{\lambda}^2$, the gain coefficient is about $700cm^{-1}$, and the quality factor can reach 150. The structure can realize the mode field limits of deep subwavelength and achieve a good comprehensive performance.

• Smart Structures and Systems
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• v.18 no.4
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• pp.787-800
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• 2016

The aim of the paper is to analyze nonlinear transverse vibration of an embedded piezoelectric plate reinforced with single walled carbon nanotubes (SWCNTs). The system in rested in a Pasternak foundation. The micro-electro-mechanical model is employed to calculate mechanical and electrical properties of nanocomposite. Using nonlinear strain-displacement relations and considering charge equation for coupling between electrical and mechanical fields, the motion equations are derived based on energy method and Hamilton's principle. These equations can't be solved analytically due to their nonlinear terms. Hence, differential quadrature method (DQM) is employed to solve the governing differential equations for the case when all four ends are clamped supported and free electrical boundary condition. The influences of the elastic medium, volume fraction and orientation angle of the SWCNTs reinforcement and aspect ratio are shown on frequency of structure. The results indicate that with increasing volume fraction of SWCNTs, the frequency increases. This study might be useful for the design and smart control of nano/micro devices such as MEMS and NEMS.

• Journal of the Korean Society of Safety
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• v.31 no.1
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• pp.66-73
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• 2016

Lyocell fibers were used as a precursor in order to improve yield and strength of cellulose-based precursor while manufacturing activated carbon fiber(ACF). Lyocell fibers as a precursor for the preparation of ACF were surface-modified by reaction with 3-aminopropyltriethoxysilane(APTES) and pre-treated with KOH and H3PO4. Using aforementioned precursor, ACFs were prepared by a series of stabilization, carbonization and activation process at high temperatures. On each process, FT-IR, TGA, UTM and SEM were used to observe fibers' physical properties including structure and porous surfaces. FT-IR results proved that surface modification was achieved during stabilization, carbonization and activation process. TGA results during carbonization process found that surface modified fibers with APTES 0.02 mol(A2) showed higher thermostability, and extended pre-treatment increased yield. Especially, yield was found to have an increase of 10~20 wt% with surface modification during activation process. UTM results showed that tensile strength has the same order of concentration of APTES after surface modification, however, was found to show lower tensile strength than lyocell fibers after stabilization process. SEM results revealed that more homogeneous porosity control could be proceed after modifying the surface for the effective removal of hazardous substances.

• Journal of Microbiology and Biotechnology
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• v.15 no.2
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• pp.234-238
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• 2005

Glucose oxidase was immobilized on the carboxylated multi-wall carbon nanotubes (MWNT-COOHs) in the presence of a coulping reagent, 1-ethy1-3-(3-dimethylaminopropy1) carbodiimide. Significant amounts of glucose oxidase were also immobilized on MWNT-COOHs without the coupling reagent. Various conditions for the immobilization of glucose oxidase were optimized. Optimal pH for the maximal activity of the immobilized glucose oxidase shifted to 7 from the optimal pH of 6 for the maximal activity of free enzyme due to the carboxy1 groups on the surface of MWNT-COOHs. An electrode of graphite rod with a diameter of 6 mm was fabricated using the immobilized glucose oxidase. The cyclic voltammetry study of the enzyme electrode revealed that the oxidation of glucose and subsequent transfer of electrons from the oxidation of glucose to the electrode were possible by the immobilized glucose oxidase without a mediator, implying that the enzyme electrode can be utilized for the development of biofuel cells.

• Journal of Sensor Science and Technology
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• v.20 no.1
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• pp.35-39
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• 2011

A disposable electrochemical immunosensor system has been developed for the detection of herbicide in aqueous samples. Disposable screen printed carbon electrodes(SPCE) were used as basic electrodes and an enzyme, horseradish peroxidase (HRP), and anti-herbicide antibodies was immobilised on to the working electrode of SPCE by using avidin-biotin coupling reactions. An herbicide-glucose oxidase conjugates have been used for the competitive immunoreaction with sample herbicides. The enzymatic reaction between the conjugated glucose oxidase and glucose added generates hydrogen peroxide, which was reduced by the peroxidase immobilised. The latter process caused an electrical current change, due to direct re-reduction of peroxidase by a direct electron transfer mechanism, which was measured to determine the herbicides in the sample. The optimal operational condition was found to be: $20\;{\mu}gl-1$ deglycosylated avidin loading to the working electrode and working potential +50 mV vs. Ag/AgCl. The total assay time was 15 min after sample addition. The detection limits for herbicides, atrazine and simazine, were found to be 3 ppb and 10 ppb, respectively.

• Steel and Composite Structures
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• v.19 no.3
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• pp.713-733
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• 2015

In this paper, viscous fluid induced nonlinear free vibration and instability analysis of a functionally graded carbon nanotube-reinforced composite (CNTRC) cylindrical shell integrated with two uniformly distributed piezoelectric layers on the top and bottom surfaces of the cylindrical shell are presented. Single-walled carbon nanotubes (SWCNTs) are selected as reinforcement and effective material properties of FG-CNTRC cylindrical shell are assumed to be graded through the thickness direction and are estimated through the rule of mixture. The elastic foundation is modeled by temperature-dependent orthotropic Pasternak medium. Considering coupling of mechanical and electrical fields, Mindlin shell theory and Hamilton's principle, the motion equations are derived. Nonlinear frequency and critical fluid velocity of sandwich structure are calculated based on differential quadrature method (DQM). The effects of different parameters such as distribution type of SWCNTs, volume fractions of SWCNTs, elastic medium and temperature gradient are discussed on the vibration and instability behavior of the sandwich structure. Results indicate that considering elastic foundation increases frequency and critical fluid velocity of system.

• Bulletin of the Korean Chemical Society
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• v.24 no.9
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• pp.1276-1280
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• 2003

Thermal behavior of bromphenols was investigated by direct pyrolysis at high temperature. The thermal degradation products formed by the pyrolysis of mono-bromophenols (o-, m-, and p-) were identified by gas chromatography-mass spectrometry. During the pyrolysis reactions, several kinds of dioxins and furans were produced, and the relative ratio of pyro-products was dependent on the substituted position of bromine in phenolic structure due to the effect of symmetry and steric hindrance. The formation of dioxins can be explained by the phenoxy radical addition and Br atom elimination at an ortho-carbon site on phenolic structure. On the other hand, the formation of furans can be explained by the ortho-ortho carbon coupling of phenoxy radicals at unsubstituted sites to form o, o'-dihydroxydiphenyl intermediate via its keto-tautomer, followed by $H_2O$ elimination. The pyrolysis temperature has also a substantial effect on the dimerized products quantities but little effect on the type of pyro-products. Moreover, the formation mechanism of pyro-products was suggested on the basis of products identified.

• Bulletin of the Korean Chemical Society
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• v.30 no.2
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• pp.405-408
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• 2009

In this work multiwalled carbon nanotube (MWCNT)/fibrin hybrid structures were synthesized via the transglutaminase- catalyzed polymerization of fibrinogen (FBG). Specifically, FBG was tethered onto oxidized MWCNTs by amide coupling, and the in situ polymerization of FBG to fibrin was performed by plasma transglutaminase (Factor XIIIa) in the presence of thrombin. The attached FBG was found to be biologically active and was polymerized to fibrin by thrombin and Factor XIIIa. MWCNT-FBG and MWCNT-Fibrin structures were characterized by FT-IR spectroscopy, transmission electron microscopy, and energy-dispersive X-ray (EDX) spectroscopy.

• Korean Journal of Ecology and Environment
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• v.39 no.4 s.118
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• pp.435-444
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• 2006

A suite of extracellular enzyme activities involved in organic carbon decomposition were determined in three northern peatlands (a bog, a fen, and a swamp) over a 12 month period along with trace gas ($CO_2$ and $N_2O$) flux and DOC dynamics in the wetlands. The activities varied $0.008-0.066\;{\mu}mole\;g^{-1}\;min^{-1}$, $0.003-0.021\;{\mu}mole\;g^{-1}\;min^{-1}$, $0.003-0.016\;{\mu}mole\;g^{-1}\;min^{-1}$, $0.004-0.047\;{\mu}mole\;g^{-1}\;min^{-1}$, for ${\beta}-glucosidase$, cellobiohydrolase, ${\beta}-xylosidase$, and N-acetylglucosaminidase, respectively. In general, the activities were highest in the forested swamp followed by the fen and the bog. When the data from three wetlands are combined, the enzyme activities exhibited significant positive correlations with trace gas emission and available carbon. Further, the average activity of 4 enzymes explained about 20-40% of the variations of trace gas emssion and available carbon. The results indicate that enzymes related to the mineralization of organic carbon may play an important role in trace gas flux and DOC dynamics in northern peatlands.