• Journal of Hydrogen and New Energy
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• v.17 no.2
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• pp.149-157
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• 2006

Hydrogen as new energy sources is highly efficient and have very low environmental emissions. The proton exchange membrane fuel cell (PEMFC) is an emerging technology that can meet these demands. Therefore, the preparation of stable polymeric membranes with good proton conductivity and durability are very important for hydrogen production via water electrolysis with PEM at medium temperature above $80^{\circ}C$. Currently Nafion of Dupont and Aciflex of Asahi, etc., solid polymer electrolytes of perfluorosulfonic acid membrane, are the best performing commercially available polymer electrolytes. However, these membrane have several flaws including its high cost, and its limited operational temperature above $80^{\circ}C$. Because of this, significant research efforts have been devoted to the development of newer and cheaper membranes. In order to make up for the weak points and to improve the mechanical characteristics with cross -linking, acid-base complexes were prepared by the combination PSf-co-PPSS-$NH_2$ with PEEK-$SO_3H$. The results showed that the proton conductivity decreased in 17.6% and 40% but tensile strength increased in 78% and 98%, about $20.65\;{\times}\;10^6N/m^2$, in comparison with SBPSf/HPA and SPEEK/HPA complex membrane.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.8A
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• pp.613-619
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• 2003

Bluetooth is a communication technology enabling short-range devices to be wirelessly connected. A master and one or more slave devices are connected to form a piconet, and piconets are joined to form a scatternet. The units participating in two or more piconets in a scatternet, is called bridge or gateway nodes. In order to operate the scatternet efficiently, both piconet scheduling for the master and slaves of a piconet, and scatternet scheduling for the bridge nodes are playing important roles. In this paper, we propose a traffic-adaptive dynamic scatternet scheduling algorithm based on rendezvous points and rendezvous windows. The performance of the proposed algorithm is compared and analyzed with that of a static scheduling algorithm via simulations. Simulation results show that our algorithm can distribute wireless resources efficiently to bridge nodes depending on the traffic characteristics.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.1113-1116
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• 2005

Using COMSAT which provides multi-beam switching function, the optimal transmission channel environment which provides the high data rate communication are proposed in this paper. Also the link budget for communication transponder of COMSAT is designed. Based on the channel modeling for group delay, non-linear and gain flatness characteristics, the system performances which provide various data rate services were analyzed in Ka-band satellite channel. As the transmission data rate is increased, the degradation due to these channel characteristics is severely increased. The linear component of group delay and the AM-AM component of non-linear characteristics severely affect the system performance. To efficiently provide the various service via the same transmission system it is necessary to equalize the primary impairment factors. The optimum operating points of HDR satellite transmission system are implemented and operated by considering the analyzed results on channel characteristics.

• Tribology and Lubricants
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• v.30 no.6
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• pp.323-329
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• 2014

The friction-reducing properties of lubricants containing ionic liquids based on ammonium dithiocarbamate are studied. The ionic liquids are produced through the following two steps: the synthesis of sodium alkyl dithiocarbamates via the substitution reaction of dialkylamine and carbon disulfide and their subsequent conversion into ammonium dithiocarbamate-based ionic liquids through an ion-exchange reaction with a quaternary alkyl ammonium halide salt. The structures of the ionic liquids are characterized by NMR spectroscopy and Fourier transform infrared spectroscopy. The isolated yields of the ionic liquids, which are viscous and pale yellow, are approximately 92%. The Brookfield viscosities and pour points of the ionic liquids are determined. Further, their wear resistances are measured through the four-ball wear test and the Schwingung Reibung Ver-schleiss (oscillation, friction, wear) test. The wear scar diameter of the lubricants containing 1 wt of the quaternary alkyl ammonium dithiocarbamate-based ionic liquids (0.475-0.631 mm) is significantly lower than that of the base oil (0.825 mm), proving that the ammonium dithiocarbamate-based ionic liquids have good friction-reducing characteristics. However, these friction-reducing characteristics fade significantly after long-term storage, owing to the degradation of the ionic liquids.

• Korean Journal of Materials Research
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• v.22 no.10
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• pp.562-568
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• 2012

Metal nanowires can be coated on various substrates to create transparent conducting films that can potentially replace the dominant transparent conductor, indium tin oxide, in displays, solar cells, organic light-emitting diodes, and electrochromic windows. One issue with these metal nanowire based transparent conductive films is that the resistance between the nanowires is still high because of their low aspect ratio. Here, we demonstrate high-performance transparent conductive films with silver nanofiber networks synthesized by a low-cost and scalable electrospinning process followed by two-step sequential thermal treatments. First, the PVP/$AgNO_3$ precursor nanofibers, which have an average diameter of 208 nm and are several thousands of micrometers in length, were synthesized by the electrospinning process. The thermal behavior and the phase and morphology evolution in the thermal treatment processes were systematically investigated to determine the thermal treatment atmosphere and temperature. PVP/$AgNO_3$ nanofibers were transformed stepwise into PVP/Ag and Ag nanofibers by two-step sequential thermal treatments (i.e., $150^{\circ}C$ in $H_2$ for 0.5 h and $300^{\circ}C$ in Ar for 3 h); however, the fibrous shape was perfectly maintained. The silver nanofibers have ultrahigh aspect ratios of up to 10000 and a small average diameter of 142 nm; they also have fused crossing points with ultra-low junction resistances, which result in high transmittance at low sheet resistance.

• Molecules and Cells
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• v.38 no.1
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• pp.20-25
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• 2015

TGF-${\beta}$ regulates pleiotropic cellular responses including cell growth, differentiation, migration, apoptosis, extracellular matrix production, and many other biological processes. Although non-Smad signaling pathways are being increasingly reported to play many roles in TGF-${\beta}$-mediated biological processes, Smads, especially receptor-regulated Smads (R-Smads), still play a central mediatory role in TGF-${\beta}$ signaling for epithelial-mesenchymal transition. Thus, the biological activities of R-Smads are tightly regulated at multiple points. Inhibitory Smad (I-Smad also called Smad7) acts as a critical endogenous negative feedback regulator of Smad-signaling pathways by inhibiting R-Smad phosphorylation and by inducing activated type I TGF-${\beta}$ receptor degradation. Roles played by Smad7 in health and disease are being increasingly reported, but the molecular mechanisms that regulate Smad7 are not well understood. In this study, we show that E3 ubiquitin ligase Itch acts as a positive regulator of TGF-${\beta}$ signaling and of subsequent EMT-related gene expression. Interestingly, the Itch-mediated positive regulation of TGF-${\beta}$ signaling was found to be dependent on Smad7 ubiquitination and its subsequent degradation. Further study revealed Itch acts as an E3 ubiquitin ligase for Smad7 polyubiquitination, and thus, that Itch is an important regulator of Smad7 activity and a positive regulator of TGF-${\beta}$ signaling and of TGF-${\beta}$-mediated biological processes. Accordingly, the study uncovers a novel regulatory mechanism whereby Smad7 is controlled by Itch.

• Korean Journal of Geomatics
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• v.2 no.1
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• pp.37-46
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• 2002

Accurate classification of water area is an preliminary step to accurately analyze the flooded area and damages caused by flood. This step is especially useful for monitoring the region where annually repeating flood is a problem. The accurate estimation of flooded area can ultimately be utilized as a primary source of information for the policy decision. Although SAR (Synthetic Aperture Radar) imagery with its own energy source is sensitive to the water area, its shadow effect similar to the reflectance signature of the water area should be carefully checked before accurate classification. Especially when we want to identify small flood area with mountainous environment, the step for removing shadow effect turns out to be essential in order to accurately classify the water area from the SAR imagery. In this paper, the flood area was classified and monitored using multi-temporal RADARSAT SAR images of Ok-Chun and Bo-Eun located in Chung-Book Province taken in 12th (during the flood) and 19th (after the flood) of August, 1998. We applied several steps of geometric and radiometric calculations to the SAR imagery. First we reduced the speckle noise of two SAR images and then calculated the radar backscattering coefficient $(\sigma^0)$. After that we performed the ortho-rectification via satellite orbit modeling developed in this study using the ephemeris information of the satellite images and ground control points. We also corrected radiometric distortion caused by the terrain relief. Finally, the water area was identified from two images and the flood area is calculated accordingly. The identified flood area is analyzed by overlapping with the existing land use map.

• The Journal of Art Theory & Practice
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• no.3
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• pp.173-192
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• 2005

Yoo Youngkuk started his career as an artist when he entered Bunkagakuin of Tokyo in 1935 he actively participated in the Japanese art scene as a young Korean artist until 1943. In his earliest works, Rhapsody and Work B, Surrealist and abstract influences are manifested as these were prevalent in Japan at the time. With the exception of Rhapsody and Work B, all works available that were executed between 1937 and 1940 are abstract, which points to the fact that Yoo intended abstraction from the beginning. Surviving works in relief suggest his early style was founded on the abstractions similar to Russian Avant-Garde, Neo-plasticism and Bauhaus simplicity. His early abstractions were not the ideational images derived in the process of the abstraction of the representational image, but they arose from the constructive attitude in composing the already stylized non-representational geometries. It is worth noting that his early emphasis was on the pure and absolute geometric abstraction, rather than the images motivated from the figurative representation. Yoo differentiates himself from Kim Whan Ki in the following aspects: one, he eliminated the subject matter i.e. human figures and the nature; two, he maintained the constructivist attitude in creating a strict and absolute abstraction; three, he experimented with different styles without combining them. He manifests direct influences from the prevalent Western art influences, such as Futurism and Russian Avant-Garde, unlike Kim who vaguely references. In both paintings and reliefs, Yoo's attempt in the realization of the pictorial depth and space seems cerebral and conceptualized compared with the other artists of the time who resolved abstraction via the constructive dimension. Uemura, a contemporary critic to the geometric abstractions in Japan, disapproves the stylistic bent in the adaptation of the abstract painting without the comprehension of its spiritual movement. As witnessed in other criticisms as well, contemporary Japanese critics' interest lie mainly in the superficial observation such as the presence of representational elements, composition and use of color. Such formal and superficial understanding of the geometric abstraction resulted in

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.4
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• pp.81-87
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• 2003

In this paper, the feasibility of using Shannon's sampling theorem to reconstruct exact mode shapes of a structural system from a limited number of sensor points and localizing damage in that structure with reconstructed mode shapes is investigated. Shannon's sampling theorem for the time domain is reviewed. The theorem is then extended to the spatial domain. To verify the usefulness of extended theorem, mode shapes of a simple beam are reconstructed from a limited amount of data and the reconstructed mode shapes are compared to the exact mode shapes. On the basis of the results, a simple rule is proposed for the optimal placement of accelerometers in modal parameter extraction experiments. Practicality of the proposed rule and the extended Shannon's theorem is demonstrated by detecting damage in laboratory beam structure with two-span via applying to mode shapes of pre and post damage states.

• Bulletin of the Korean Chemical Society
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• v.7 no.5
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• pp.395-399
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• 1986

Intramolecular proton transfer equilibria of acetamide and methyl carbamate have been studied theoretically by MNDO MO method. For both substrates, carbonyl-O protonated tautomer was found to be the most stable form, the next most stable one being N-protonated form. Gas phase proton transfers take place by the 1,3-proton rearrangement process and in all cases have prohibitively high activation barriers. When however one solvate water molecule participates in the process, the barriers are lowered substantially and the process proceeds in an intermolecular manner through the intermediacy of the water molecule via a triple-well type potential energy surface; three wells correspond to reactant(RC), intermediate(IC) and product complex(PC) of proton donor-acceptor pairs whereas two transition states(TS) have proton-bridge structure. General scheme of the process can be represented for a substrate with two basic centers(heteroatoms) of A and B as, $$ABH\limits^+\;+\;H_2O\;{\to}\;ABH\limits^+{\cdots}{\limits_{RC}}OH_2\;{\to}\;AB{\cdots}H\limits_{TS}^+{\cdots}{\limits_{1}}OH_2\;{\to}\;AB{\cdots}{\limits_{IC}}H\limits^+OH_2\;{\to}\;BA{\cdots}H\limits_{TS}^+{\cdots}{\limits_{2}}OH_2\;{\to}\;BA H\limits^+{\cdots}{\limits_{PC}}OH_2\;{\to}\;BAH\limits^+\;+\;H_2O$$ Involvement of a second solvate water had negligible effect on the relative stabilities of the tautomers but lowered barrier heights by 5∼6 Kcal/mol. It was calculated that the abundance of the methoxy-O protonated tautomer of the methyl carbamate will be negligible, since the tautomer is unfavorable thermodynamically as well as kinetically. Fully optimized stationary points are reported.