• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.388-388
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• 2011

Graphene, with its unique physical and structural properties, has recently become a proving ground for various physical phenomena, and is a promising candidate for a variety of electronic device and flexible display applications. The physical properties of graphene depend directly on the thickness. These properties lead to the possibility of its application in high-performance transparent conducting films (TCFs). Compared to indium tin oxide (ITO) electrodes, which have a typical sheet resistance of ~60 ${\Omega}/sq$ and ~85% transmittance in the visible range, the chemical vapor deposition (CVD) synthesized graphene electrodes have a higher transmittance in the visible to IR region and are more robust under bending. Nevertheless, the lowest sheet resistance of the currently available CVD graphene electrodes is higher than that of ITO. Here, we report an ingenious strategy, irradiation of MeV electron beam (e-beam) at room temperature under ambient condition,for obtaining size-homogeneous gold nanoparticle decorated on graphene. The nano-particlization promoted by MeV e-beam irradiation was investigated by transmission electron microscopy, electron energy loss spectroscopy elemental mapping, and energy dispersive X-ray spectroscopy. These results clearly revealed that gold nanoparticle with 10~15 nm in mean size were decorated along the surface of the graphene after 1.0 MeV-e-beam irradiation. The fabrication high-performance TCF with optimized doping condition showed a sheet resistance of ~150 ${\Omega}/sq$ at 94% transmittance. A chemical transformation and charge transfer for the metal gold nanoparticle were systematically explored by X-ray photoelectron spectroscopy and Raman spectroscopy. This approach advances the numerous applications of graphene films as transparent conducting electrodes.

• Analytical Science and Technology
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• v.14 no.3
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• pp.197-202
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• 2001

The characteristics of the electrochemically Li intercalated synthetic graphite were determined from the studies with XRD method, DSC and solid $^7Li-NMR$ spectrophotometric analysis. From the results of X-ray diffraction method, it was found that the compounds in the stage 1 structure were predominantly formed. The enthalpy and entropy changes of the compounds can be obtained from the differential scanning calorimetric analysis results. From these results, it was found that exothermic and endothermic reactions of lithium intercalated into synthetic graphite are related to thermal stability of lithium ion between carbon graphene layers. From the $^7Li-NMR$ data, scientific observation found that bands are shift toward higher frequencies with increasing lithium concentration because non-occupied electron shells of Li increased in charge carrier density. Line widths of the Li intercalated synthetic graphite compounds decreased slowly because of non-homogeneous local magnetic order and the random electron spin direction for substituted Li.

• Macromolecular Research
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• v.13 no.1
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• pp.45-53
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• 2005

In this study, a series of highly swelling hydrogels based on sodium alginate (NaAlg) and polymethacryl­amide (PMAM) was prepared through free radical polymerization. The graft copolymerization reaction was performed in a homogeneous medium and in the presence of ammonium persulfate (APS) as an initiator and N,N'-methylenebis­acrylamide (MBA) as a crosslinker. The crosslinked graft copolymer, alginate-graft-polymethacrylamide (Alg-g­PMAM), was then partially hydrolyzed by NaOH solution to yield a hydrogel, hydrolyzed alginate-graft-poly­methacrylamide (H-Alg-g-PMAM). During alkaline hydrolysis, the carboxamide groups of Alg-g-PMAM were converted into hydrophilic carboxylate anions. Either the Alg-g-PMAM or the H-Alg-g-PMAM was characterized by FTIR spectroscopy. The effects of the grafting variables (i.e., concentration of MBA, MAM, and APS) and the alkaline hydrolysis conditions (i.e., NaOH concentration, hydrolysis time, and temperature) were optimized systematically to achieve a hydrogel having the maximum swelling capacity. Measurements of the absorbency in various aqueous salt solutions indicated that the swelling capacity decreased upon increasing the ionic strength of the swelling medium. This behavior could be attributed to a charge screening effect for monovalent cations, as well as ionic cross-linking for multivalent cations. Because of the high swelling capacity in salt solutions, however, the hydrogels might be considered as anti-salt superabsorbents. The swelling behavior of the superabsorbing hydrogels was also measured in solutions having values of pH ranging from 1 to 13. Furthermore, the pH reversibility and on/off switching behavior, measured at pH 2.0 and 8.0, suggested that the synthesized hydrogels were excellent candidates for the controlled delivery of bioactive agents. Finally, we performed preliminary investigations of the swelling kinetics of the synthesized hydrogels at various particle sizes.

• Journal of the Korean Society of Combustion
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• v.18 no.2
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• pp.32-41
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• 2013

This study presents both experimental and numerical investigation of ignition delay time of n-heptane and n-butanol binary fuel. The $O_2$ concentration in the mixture was set to 9-10% to make high exhaust gas recirculation( EGR) rate condition which leads low NOx and soot emission. Experiments were performed using a rapid compression machine(RCM) at compressed pressure 20bar, several compressed temperature and three equivalence ratios(0.4, 1.0, 1.5). In addition, a numerical study on the ignition delay time was performed using CHEMKIN codes to validate experimental results and predict chemical species in the combustion process. The results showed that the ignition delay time increased with increasing the n-butanol fraction due to a decrease of oxidation of n-heptane at the low temperature. Moreover, all of the binary fuel mixtures showed the combustion characteristics of n-heptane such as cool flame mode at low temperature and negative-temperature-coefficient(NTC) behavior. Due to the effect of high EGR rate condition, the operating region is reduced at lean condition and the ignition delay time sharply increased compared with no EGR condition.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.17-24
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• 2004

As the environmental pollution becomes serious global problem, the regulation of emission exhausted from automobiles is strengthened. Therefore, it is very important to know how to reduce the NOx and PM simultaneously in diesel engines, which has lot of merits such as high thermal efficiency, low fuel consumption and durability. By this reason, the new concept called as Homogeneous Charge Compression Ignition(HCCI) engines are spotlighted because this concept reduced NOx and P.M. simultaneously. However, it is well known that HCCI engines increased HC and CO. Thus, the investigation of combustion characteristics which consists cool and hot flames for HCCI engines were needed to obtain the optimal combustion condition. In this study, combustion characteristics for direct injection type HCCI engine such as quantity of cool flame and hot flame, ignition timing and ignition delay were investigated to clarify the effects of these parameters on performance. The results revealed that diesel combustion showed the two-stage ignition of cool flame and hot flame, the rate of cool flame increase and hot flame decrease with increasing intake air temperature. On the other hand, the gasoline combustion is the single-stage ignition and ignition timing is near the TDC. In addition mixed fuel combustion showed different phenomenon, which depends on the ratio of gasoline component. Ignition timing of mixed fuel is retarded near the TDC and the ignition delay is increased according to ratio of gasoline.

• Bulletin of the Korean Chemical Society
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• v.19 no.1
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• pp.39-44
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• 1998

$LiCoO_2$ powder was synthesized in an aqueous solution by a sol-gel method and used as a cathode active material for a lithium ion rechargeable battery. The layered $LiCoO_2$ powders were prepared by igniting in air for 12 hrs at 600 ℃ $(600-LiCoO_2)$ and 850 ℃ $(850-LiCoO_2)$. The structure of the $LiCoO_2$ powder was assigned to the space group R bar 3 m (lattice parameters a=2.814 Å and c=14.04Å). The SEM pictures of $600-LiCoO_2$ revealed homogeneous and fine particles of about 1 μm in diameter. Cyclic voltammograms (CVs) of $600-LiCoO_2$ electrode displayed a set of redox peaks at 3.80/4.05 V due to the intercalation/deintercalation of the lithium ions into/out of the $LiCoO_2$ structure. CVs for the $850-LiCoO_2$ electrode had a major set of redox peaks at 3.88/4.13 V, and two small set of redox peaks at 4.18/4.42 V and 4.05/4.25 V due to phase transitions. The initial charge-discharge capacity was 156-132 mAh/g for the $600-LiCoO_2$ electrode and 158-131 mAh/g for the $850-LiCoO_2$ electrode at the current density of 0.2 mA/cm2. The cycleability of the cell consisting of the $600-LiCoO_2$ electrode was better than that of the $850-LiCoO_2$. The diffusion coefficient of the $Li^+$ ion in the $600-LiCoO_2$ electrode was calculated as $4.6{\times}10^{-8}\; cm^2/sec$.

• Korean Journal of Metals and Materials
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• v.56 no.12
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• pp.900-909
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• 2018

A $ZnO/TiO_2$ photocatalyst decorated with PbS quantum dots (QDs) was synthesized to achieve high photocatalytic efficiency for the decomposition of dye in aqueous media. A $TiO_2$ porous layer, as a precursor photocatalyst, was fabricated using micro-arc oxidation, and exhibited irregular porous cells with anatase and rutile crystalline structures. Then, a ZnO-deposited $TiO_2$ catalyst was fabricated using a zinc acetate solution, and PbS QDs were uniformly deposited on the surface of the $ZnO/TiO_2$ photocatalyst using the successive ionic layer adsorption and reaction (SILAR) technique. For the PbS $QDs/ZnO/TiO_2$ photocatalyst, ZnO and PbS nanoparticles are uniformly precipitated on the $TiO_2$ surface. However, the diameters of the PbS particles were very fine, and their shape and distribution were relatively more homogeneous compared to the ZnO particles on the $TiO_2$ surface. The PbS QDs on the $TiO_2$ surface can induce changes in band gap energy due to the quantum confinement effect. The effective band gap of the PbS QDs was calculated to be 1.43 eV. To evaluate their photocatalytic properties, Aniline blue decomposition tests were performed. The presence of ZnO and PbS nanoparticles on the $TiO_2$ catalysts enhanced photoactivity by improving the absorption of visible light. The PbS $QDs/ZnO/TiO_2$ heterojunction photocatalyst showed a higher Aniline blue decomposition rate and photocatalytic activity, due to the quantum size effect of the PbS nanoparticles, and the more efficient transport of charge carriers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.165-171
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• 2010

The Homogeneous Charge Compression Ignition (HCCI) engine concept allows for both NOx and particulate matter to be reduced simultaneously, and it is a promising way to meet the next environmental challenges. Unfortunately, HCCI combustion often increases CO and HC emissions. The development of oxidation catalyst (OC) requires high conversion efficiency for CO and HC at low temperature. Conventional oxidation catalyst technologies may not be able to convert these emissions because of the saturation of active catalytic sites. The OC used in this study was 600 cpsi cordierite. Three kinds of OC with different amounts of Pt and Pd were used. The influence of the space velocity (SV), $H_2O$ and $O_2$ concentration was also studied. All types of OCs were found to have over 90% CO conversion efficiencies at $170^{\circ}C$. When in the presence of water vapor, CO conversion was increased, but $C_3H_8$ conversion was decreased. The performance of the OC was not influenced by initial the HC concentration. The 2Pt/Pd catalyst was better in terms of thermal aging than the Pt-only catalyst. The $LOT_{50}$ of both fresh and aged OC was increased with increasing SV and with the presence of $H_2O$.

• The Journal of Fisheries Business Administration
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• v.29 no.2
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• pp.77-96
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• 1998

Fisheries products in Korea generally go through three markets, namely the wholesale market at production site (Market A), the wholesale market at consumption site (Market B), and the retail market (Market C), from producers to end consumers. As the products move from Market A through Market B to Market C, the marginal gap of prices asked in these markets demonstrates an apparent relationship. The producers, middlemen, consumers, and governmental departments concerned may influence the marketing prices of fisheries products. This study employing the cointegration theory tries to investigate whether causality of the price-setting among these markets exists and, if any, what it is. The authors have focused their attention on fisheries markets in Pusan, analyzing the long-run equilibrium relationship and causality between the prices of hairtail and squid among markets at different levels. Data used in this study cover the period f개m August 1984 to December 1997 fer hairtail, and the period from May 1989 to December 1997 for squid. The main findings of the study may be summarized as follows: First, regardless of the price time-series of hairtail and squid in individual market, the first difference is necessary fur satisfying the stationary conditions since each time-series is a first integration. This means homogeneous integration of time-series, which is a requirement of the long-run equilibrium of prices at different markets, is satisfied. Second, the study of the long-run equilibrium relationship between the prices at Market A and Market B shows that a long-run equilibrium relationship does exist for selling prices of the two species at Market A and Market B. Third, the ECM (error correction model ) used here to describe the long- and short-run dynamics of price change demonstrates that, in the case of squid, the price change in Market A will lead to a corresponding price change in Market B in the long-run period. In the short-run, however, the price at Market H is not only influenced by the price change in Market A but influence the price at Market A as well, that is, the Prices between Market A and Market B have a feedback effect. It should be stressed that the limitation in data collection, which cover only two species of hairtail and squid, is likely to cause a sampling bias. Nonetheless, we may conclude that a dynamic relation in the formation of prices does exist in view of the transaction amount of species at different markets. It is believed that the conclusion drawn from this study would not only contribute to a long-lasted debate on the direction of causality of price-setting among academic circle and fishing community, but would provide a useful standard for the policy makers in charge of the price-setting of fisheries products as well.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.11
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• pp.1005-1013
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• 2010

This study was conducted to assess the spray control of flash boiling with mixed fuel in consideration of HCCI (Homogeneous Charge Compression Ignition) engine condition. Mixed fuel existing in two phase regions can control the process of mixture formation under low temperature and density by using the spray resulting from flash boiling which is able to induce rapid evaporation of fuel spray as well as the evaporation of high boiling point component. Because HCCI engine injects the fuel early under ambient conditions, it can facilitate the chemical control of ignition combustion and physical control such as breakup and atomization of liquid fuel by flash boiling of mixed fuel which consists of highly ignitable light oil and highly volatile gasoline. This study was conducted by performing video processing after selected composition and molar fraction of the mixed fuel as major parameters and photographed Schlieren image and Mie scattered light corresponding to the flash boiling phenomenon of the fuel spray that was injected inside a constant volume vessel. It was found that flash boiling causes significant changes in the spray structure under relatively low temperature and density. Thus, we analyzed that the flash boiling spray can be used for HCCI combustion by controlling the mixture formation at the early fuel injection timing.