• Mass Spectrometry Letters
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• v.14 no.3
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• pp.104-109
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• 2023

Anabolic-androgenic steroids (AAS) are used illegally to enhance muscle development and increase strength and power. In this study, a reliable, and sensitive quantitative method was developed and validated using heptafluorobutyric acid anhydride (HFPA) derivatives for the simultaneous detection of prohibited AAS (testosterone [TS], boldenone [BD], 5α-estrane-3β,17α-diol [EAD]) using gas chromatography-tandem mass spectrometry (GC-MS/MS). For processing the samples, solid phase extraction, methanolic hydrolysis, and liquid-liquid extraction were used. For detection using mass spectrometry, the multiple reaction monitoring (MRM) mode was used with the electron ionization (EI) positive mode. The method was evaluated for selectivity, linearity, lower limit of quantification, intra- and inter-day precision, accuracy, and stability. The results showed that the method was accurate and reproducible for the quantitation of the three steroids. The developed method was finally applied to the analysis of a suspect gelding urine sample received from the Asian Quality Assurance Program (AQAP).

• Journal of the Korean Applied Science and Technology
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• v.26 no.3
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• pp.279-287
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• 2009

Fisher-Tropsch synthesis for the production of hydrocarbon from syngas was investigated on 20% cobalt-based catalysts (20% Co/HSA, 20% Co/Si-MMS), which were prepared by home-made supports with high surface areas such as high surface alumina (HSA) and silica mesopores molecular sieve (Si-MMS). In the gas phase reaction by syngas only, 20% Co/Si-MMS catalyst was shown in higher CO conversion and lower carbon dioxide formation than 20% Co/HSA, whereas the olefin selectivity was higher in 20% Co/HSA than in 20% Co/Si-MMS. In the effect of n-hexane added in syngas, the selectivities of $C_{5+}$ and olefin were increased by comparing the supercritical phase reaction with the gas phase reaction in addition to reduce unexpected methane and carbon dioxide.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.374-377
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• 2009

The operating temperature of Proton Exchange Membrane Fuel Cell (PEMFC) usually has to be limited under $100^{\circ}C$ to maintain the proper ionic conductivity. Therefore, the only product from reaction, water, is in the liquid phase. Two-phase flow makes the flow phenomenon in the channel difficult to understand and predict. Water blocking in the PEMFC channel or the pore of Gas Diffusion Layer (GDL), called flooding, is known as the main effect of PEMFC degradation. To analyze two-phase flow, the PEMFC with transparent acrylic plate was used. Two-phase flow patterns were observed by varying the current density. When the PEMFC is mounted horizontally, water in the cathode is mainly transported on the interface between the channel and GDL.

• Applied Chemistry for Engineering
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• v.5 no.3
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• pp.509-516
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• 1994

Liquid phase hydrogenation come into use for the removal process of unsaturated hydrocarbon such as croton aldehyde. The croton aldehyde is generated in a very small amount as by-product in the ethanol production, and it is converted into n-butanol through hydrogenation. Liquid phase hydrogenation is low energy consumption process as compared with gas phase hydrogenation. The nickel catalyst is selected with respect to the economic aspect such as durability and cost. The analysis of the conversion were performed by method of the PMT(permangante time) test. The PMT was sharply decreased as the initial concentrations of croton aldehyde in the ethanol solution were increased. The hydrogenation of croton aldehyde to n-butanol was carried out in sequence after the saturation of the carbon-carbon double bond. The formation of both butyraldehyde and n-butanol followed zero order kinetics. Within expermental conditions the PMT gets longer as reaction temperature goes higer and as LHSV becomes slower, while the reaction pressure has almost no relation with PMT.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.102-102
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• 2016

Water, which is most abundant in Earth surface and very closely related to all forms of living organisms, has a simple molecular structure but exhibits very unique physical and chemical properties. Even though tremendous effort has been paid to understand this nature's core substance, there amazingly still lefts much room for scientist to explore its novel behaviors. Especially, as the scale goes down to nano-regime, water shows extraordinary properties that are not observable in bulk state. One of such interesting features is the formation of nanoscale bubbles showing unusual long-term stability. Nanobubbles can be spontaneously formed in water on hydrophobic surface or by decompression of gas-saturated liquid. In addition, the nanobubbles can be generated during electrochemical reaction at normal hydrogen electrode (NHE), which possibly distorts the standard reduction potential at NHE as the surface nanobubble screens the reaction with electrolyte solution. However, the real-time evolution of these nanobubbles has been hardly studied owing to the lack of proper imaging tools in liquid phase at nanoscale. Here we demonstrate, for the first time, that the behaviors of nanobubbles can be visualized by in situ transmission electron microscope (TEM), utilizing graphene as liquid cell membrane. The results indicate that there is a critical radius that determines the long-term stability of nanobubbles. In addition, we find two different pathways of nanobubble growth: i) Ostwald ripening of large and small nanobubbles and ii) coalescence of similar-sized nanobubbles. We also observe that the nucleation and growth of nanoparticles and the self-assembly of biomolecules are catalyzed at the nanobubble interface. Our finding is expected to provide a deeper insight to understand unusual chemical, biological and environmental phenomena where nanoscale gas-state is involved.

• Bulletin of the Korean Chemical Society
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• v.35 no.4
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• pp.983-984
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• 2014

• Applied Chemistry for Engineering
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• v.8 no.2
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• pp.211-219
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• 1997

Liquid or gas phase alkylation of isobutane with 1-butene for i-octane production was carried out over Cs- or $NH_4$-exchanged $H_3PW_{12}O_{40}$. Pretreatment temperature of the catalyst played an important role on the catalytic activity of heteropoly acids in the liquid phase alkylation. Cation-exchanged $H_3PW_{12}O_{40}$ showed a better total yield and i-octane selectivity than the mother acid in the liquid phase alkylation, and $(NH_4)_{2.5}H_{0.5}PW_{12}O_{40}$ was more efficient than $Cs_{2.5}H_{0.5}PW_{12}O_{40}$ in terms of i-octane selectivity. It was found that the acidic property (deactivation of acid sites) of the catalyst was closely related to the catalytic activity of Cs- or $NH_4$-exchanged $H_3PW_{12}O_{40}$ in the gas phase alkylation. $C_5-C_7$ were mainly formed in the early stage of gas phase alkylation due to the strong acidic property of the catalyst, whereas $C_8$ and $+C_9$ were mainly produced as the reaction proceeded due to the deactivation of acid sites. $Cs_{2.5}H_{0.5}PW_{12}O_{40}$ showed the highest total yield in the gas phase alkylation among the catalysts examined.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.104-104
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• 2015

Due to the demand of the cold neutron flux in the neutron science and beam utilization technology, the cold neutron source (CNS) has been constructed and operating in the nuclear research reactor all over the world. The majority of the heat load removal scheme in the CNS is two-phase thermosiphon using the liquid hydrogen as a moderator. The CNS moderates thermal neutrons through a cryogenic moderator, liquid hydrogen, into cold neutrons with the generation of the nuclear heat load. The liquid hydrogen in a moderator cell is evaporated for the removal of the generated heat load from the neutron moderation and flows upward into a heat exchanger, where the hydrogen gas is liquefied by the cryogenic helium gas supplied from a helium refrigeration system. The liquefied hydrogen flows down to the moderator cell. To keep the required liquid hydrogen stable in the moderator cell, the CNS consists of an in-pool assembly (IPA) connected with the hydrogen system to handle the required hydrogen gas, the vacuum system to create the thermal insulation, and the helium refrigeration system to provide the cooling capacity. If one of systems is running out of order, the operating research reactor shall be tripped because the integrity of the CNS-IPA is not secured under the full power operation of the reactor. To prevent unscheduled reactor shutdown during a long time because the research reactor has been operating with the multi-purposes, the introduction of the standby cooling system (STS) can be a solution. In this presentation, the design considerations are considered how to design the STS satisfied with the following objectives: (a) to keep the moderator cell less than 350 K during the full power operation of the reactor under loss of the vacuum, loss of the cooling power, loss of common electrical power, or loss of instrument air cases; (b) to circulate smoothly helium gas in the STS circulation loop; (c) to re-start-up the reactor within 1 hour after its trip to avoid the Xenon build-up because more than certain concentration of Xenon makes that the reactor cannot start-up again; (d) to minimize the possibility of the hydrogen-oxygen reaction in the hydrogen boundary.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.1
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• pp.24-30
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• 2004

Analysis model for the two-phase catalytic reactor is presented. With the progress in development of micro thermofluidic devices, needs fur understanding of the phenomena in two phase reaction in cm scale has been arisen. To investigate thermal and reactive performance of down scaled two phase reactor simple analysis model that is a kind of lumped flow model is proposed. Analysis model presented is based on the experiment on mm scale model reactor. Target experiment is catalytic decomposition of 70wt％ hydrogen peroxide with existence of perovskite L $a_{0.8}$S $r_{0.2}$Co $O_3$ catalyst. It is composed of balance equations of mass and energy. Each phase is considered to be a species fur the simplicity. Axial diffusion and transversal distribution of properties are neglected. Two phase catalytic reaction is modeled as successive gasification of liquid lump around catalyst and reaction in gas phase. Heat transfer is modeled by model function ofNu number. Modeled Nu is expressed as Nu=N $u_{0}$ (1＋ $a_1$( $a_2$ $T^{-}$ $a_3$)exp( $a_4$ $T^{-1}$)exp( $a_{5}$ z). Transfer coefficients are determined by the comparison of experimental results. With the model, heat transfer characteristics are investigated. Also by the mass transfer coefficient, characteristics in mass transfer is investigated. With the result basic understanding on design and analysis of mm scale two-phase reactive device is obtained. Also it can be further applied to micro scale reactive device fabricated by micromachining.ing..

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.654-657
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• 2003

We obtained amorphous calcium carbonate through the carbonation reaction of $Ca(OH)_2$, and through this reaction, observed changes in particle shape and phase by electric conductivity, XRD and TEM analysis. According to the result of the analysis, in the first declining stage of electric conductivity, amorphous calcium carbonate that has formed is coated on the surface of $Ca(OH)_2$ and obstructs its dissolution, and in the first recovery stage of electric conductivity, amorphous calcium carbonate is dissolved and re-precipitated and forms chains of fine calcite particles linearly joined. In the second decline of conductivity, viscosity increases due to the growth of chains of calcite particles, and finally the calcite particles are dissolved and separated into colloidal crystalline calcite, thereby increasing electric conductivity again.