• Bulletin of the Korean Chemical Society
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• v.35 no.6
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• pp.1713-1719
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• 2014

1FSD is a 28-residue designed protein with a ${\beta}{\beta}{\alpha}$ motif. Since this protein displays most essential features of protein structures in such a small size, this model protein can be an outstanding system for evaluating the balance in the propensity of the secondary structures and the quality of all-atom protein force fields. Particularly, this protein would be difficult to fold to its correct native structure without establishing proper balances between the secondary structure elements in all-atom energy functions. In this work, a series of the recently optimized five amber protein force fields [$ff03^*$, $f99sb^*$-ildn, ff99sb-${\phi}^{\prime}$-ildn, ff99sb-nmr1-ildn, ff99sb-${\Phi}{\Psi}$(G24, CS)-ildn] were investigated for the simulations of 1FSD using a conventional molecular dynamics (MD) and a biased-exchange meta-dynamics (BEMD) methods. Among those tested force fields, we found that ff99sb-nmr1-ildn and ff99sb-${\Phi}{\Psi}$(G24, CS)-ildn are promising in that both force fields can locate the native state of 1FSD with a high accuracy (backbone rmsd ${\leq}1.7{\AA}$) in the global free energy minimum basin with a reasonable energetics conforming to a previous circular dichroism (CD) experiment. Furthermore, both force fields led to a common set of two distinct folding pathways with a heterogeneous nature of the transition state to the folding. We anticipate that these force fields are reasonably well balanced, thereby transferable to many other protein folds.

• Carbon letters
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• v.13 no.1
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• pp.39-43
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• 2012

The size and the physical properties of graphene oxide sheets were controlled by changing the oxidation temperature of graphite. Graphite oxide (GO) samples were prepared at different oxidation temperatures of $20^{\circ}C$, $27^{\circ}C$ and $35^{\circ}C$ using a modified Hummers' method. The carbon-to-oxygen (C/O) ratio and the average size of the GO sheets varied according to the oxidation temperature: 1.26 and 12.4 ${\mu}m$ at $20^{\circ}C$, 1.24 and 10.5 ${\mu}m$ at $27^{\circ}C$, and 1.18 and 8.5 ${\mu}m$ at $35^{\circ}C$. This indicates that the C/O ratio and the average size of the graphene oxide sheets respectively increase as the oxidation temperature decreases. Moreover, it was observed that the surface charge and optical properties of the graphene oxide sheets could be tuned by changing the temperature. This study demonstrates the tunability of the physical properties of graphene oxide sheets and shows that the properties depend on the functional groups generated during the oxidation process.

• Journal of the Korean institute of surface engineering
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• v.48 no.5
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• pp.199-204
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• 2015

Recently, fuel cell is a good alternative for energy source. Separator is a important component for fuel cell. In this study, The surface of separator was modified for corrosion resistance and electric conductivity. Reduced graphene oxide (rGO) was made by Staudenmaier's method. Nickel, phosphorus and rGO were coated on 6061 aluminum alloy as a separator of proton exchange membrane fuel cell by composite electroless plating. Scanning electron microscope, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were used to examine the morphology of Ni-P-rGO. Surface images were shown that the rGO was dispersed on the surface of Ni-P electroless plating, and nickel was combined with the un-reduced oxygen functional group of rGO.

• Journal of the Korean Ceramic Society
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• v.50 no.1
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• pp.63-69
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• 2013

Negative-temperature coefficient (NTC) thermistors based on nickel manganite spinel ($NiMn_2O_4$) are widely used for many applications, such as sensors and temperature compensators, due to their good thermistor characteristics and stabilities. However, to achieve thermistors with a high NTC B constant, which is an important figure of merit pertaining to the degree of temperature sensitivity, the activation energy should be high such that high resistivity at ambient temperatures results. To obtain a high B constant and low resistivity, Al and Si modified spinel structured $Ni_{0.6}Si_{0.2}Al_{0.6}Mn_{1.6}O_4$ hybrid thick films with the conducting metal oxide of $LaNiO_3$ were fabricated on a glass substrate by aerosol deposition at room temperature (RT). The NTC-$LaNiO_3$ hybrid thick films showed resistivity as low as < $100k{\Omega}\;cm$ at $90^{\circ}C$, which is one or two orders of magnitude lower than that of the monolithic NTC films, while retaining a high B constant of $NiMn_2O_4$ of over 5500 K when 20 wt% $LaNiO_3$ was added without a post-thermal treatment. These phenomena are explained by the percolation threshold mechanism.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.159-159
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• 2013

Atomically thin graphene is the ideal model system for studying nanoscale friction due to its intrinsic two-dimensional anisotropy. Furthermore, modulating its tribological properties could be an important milestone for graphene-based micro and nano-mechanical devices. Here, we report that the tribological properties can be easily altered via simple chemical modifications of the graphene surface. Friction force microscopy measurements show that hydrogenated, fluorinated, and oxidized graphenes exhibit, 2-, 6-, and 7-fold enhanced nanoscale friction on their surfaces, respectively, compared to pristine graphene. The measured nanoscale friction should be associated with the adhesive and elastic properties of the chemically modified graphenes. Density functional theory calculations suggest that, while the adhesive properties of chemically modified graphenes are marginally reduced down to ~30%, the out-of-plane elastic properties are drastically increased up to 800%. Based on these findings, we propose that nanoscale friction on graphene surfaces is characteristically different from that on conventional solid surfaces; stiffer graphene exhibits higher friction, whereas a stiffer three-dimensional solid generally exhibits lower friction. The unusual friction mechanics of graphene is attributed to the intrinsic mechanical anisotropy of graphene, which is inherently stiff in plane, but remarkably flexible out of plane. The out-of-plane flexibility can be modulated up to an order of magnitude by chemical treatmentof the graphene surface. The correlation between the measured nanoscale friction and the calculated out-of-plane flexibility suggests that the frictional energy in graphene is mainly dissipated through the out-of-plane vibrations, or the flexural phonons of graphene.

• Journal of the Korean Electrochemical Society
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• v.12 no.3
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• pp.263-270
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• 2009

Carbon felt surface was modified by heat or acid treatment in order to use for the electrode of a redox-flow battery. Polymers on the surface of carbon felt was removed and oxygen-containing functional group was attached after the thermal treatment of carbon felt. Thermal treatment was better for the stability of the carbon structure than the acid treatment. Oxygen-containing functional group on the thermally treated carbon felt at 500$^{\circ}C$ was confirmed by XPS and elementary analysis. BET surface area was increased from nearly zero to 96 $m^2/g$. Thermally treated carbon felt at 500$^{\circ}C$ showed lower activation polarization than the thermally treated carbon felt at 400$^{\circ}C$ and the acid-treated carbon felt in the cyclicvoltammetry and polarization experiments. The thermally treated carbon felts at 400$^{\circ}C$ and 500$^{\circ}C$ and the acid-treated carbon felt was applied for the electrode to prepare vanadium redox flow battery. Voltage efficiencies of charge/discharge were 86.6%, 89.6%, and 96.9% for the thermally treated carbon felts at 400$^{\circ}C$ and 500$^{\circ}C$ and the acid-treated carbon felt, respectively.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.4 s.316
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• pp.86-92
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• 2007

A discrete dynamic model for tracking feature points in 2D images is developed. Conventional snake approaches deform a contour to lock onto features of interest within an image by finding a minimum of its energy functional, composed of internal and external forces. The neighborhood around center snaxel is a space matrix, typically rectangular. The structure of the model proposed in this paper is a set of connected vertices. Energy model is designed for its local minima to comprise the set of alternative solutions available to active process. Block on tracking is one dimension, line type. Initial starting points are defined to the satisfaction of indent states, which is then automatically modified by an energy minimizing process. The track is influenced by curvature constraints, ascent/descent or upper/lower points. The advantages and effectiveness of this layer approach may also be applied to feature points tracking of digital image whose pixels have one directional properties with high autocorrelation between adjacent data lines, vertically or horizontally. The test image is the ultrasonic carotid artery image of human body, and we have verified its effect on intima/adventitia starting points tracking.

• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.455-461
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• 2015

Porous ceramics with tailored pore size and shape are promising materials for the realization of a number of functional and structural properties. A novel method has been reported for the investigation of the role of SiC in the formation of $SiO_2$ foams by colloidal wet processing. Within a suitable pH range of 9.9 ~ 10.5 $SiO_2$, particles were partially hydrophobized using hexylamine as an amphiphile. Different mole ratios of the SiC solution were added to the surface modified $SiO_2$ suspension. The contact angle was found to be around $73^{\circ}$, with an adsorption free energy $6.8{\times}10^{-12}J$. The Laplace pressure of about 1.25 ~ 1.6 mPa was found to correspond to a wet foam stability of about 80 ~ 85%. The mechanical and thermal properties were analyzed for the sintered ceramics, with the highest compressive load observed at the mole ratio of 1:1.75. Hertzian indentations are used to evaluate the damage behavior under constrained loading conditions of $SiO_2$-SiC porous ceramics.

• Elastomers and Composites
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• v.35 no.2
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• pp.98-105
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• 2000

Using FT-IR and contact angle measurements it is observed that the chemical surface treatments on virgin carbon blacks lead to a change of the surface properties, including surface functionality and surface free energy It is found that the developments of surface functional groups on acidically and basically treated (ACB and BCB in this study, respectively) carbon blacks are largely correlated with the specific component of surface free energy of the carbon blacks. However, a significant advantage of compounding composites is gained by BCB or NCB (nonpolar chemical treatment) specimens, resulting in improving the hardness, elongation at break, and tensile strength. Particularly, it is seen that the tensile strength of the composites are greatly depended on the London dispersive component of surface free energy determined from the contact angle measurements. It is then concluded that the London dispersion component of carbon blacks plays an important role in an organic rubbers-based compounding composite system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.533-538
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• 2003

It has been shown that ion implantation produces remarkable improvements in surface-sensitive physical and chemical properties as well as other mechanical properties, in polymers. In this study, ion implantation was performed onto polymer, PC(polycarbonate), in order to investigate surface hydrophilic property through contact angle measurement using distilled water. PC was irradiated with N, Ar, Xe ions at the irradiation energy of $20\;{\sim}\;50keV$ and the dose range of $5{\times}10^{15},\;1{\times}10^{16},\;7{\times}10^{16}\;ions/cm^2$. The contact angle of water has been reduced with increasing fluence and ion mass but increased with increasing implanted energy. The changes of chemical and structural property are discussed in view of infrared spectroscopy and FT-IR, XPS, which shows increasing C-O bonding and C-C bonding. The root mean square of surface roughness examined by means of AFM changed smoothly from 0.387nm to 0.207nm and the change of wettability was discussed with respect to elastic and inelastic collisions obtained as results of TRIM simulation. It was found that wettability of the modified PC surface was affected on change of functional group and nuclear stopping or linear energy transfer(LET, energy deposited per unit track length per ion) that causes chain scission by displacing atom from polymer chains, but was not greatly dependant on surface morphology.