• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.236-239
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• 2002

Surface states of silicone polymer treated by plasma were investigated by the analysis by x-ray photoelectron spectroscopy (XPS) and surface voltage decay. Plasma treatment causes the silica-like oxidative layer, which is confirmed with XPS, and lowers surface resistivity with increasing the plasma treatment time. Using the decay time constant of surface voltage, the calculated surface resistivity was compared with the value directly measured by a voltage-current method. A good agreement between two methods was obtained. In addition, we estimated the thermal activation energy for surface conduction, Based on our results, we could understand the relationship between surface chemical states and surface electrical properties.

• Journal of Magnetics
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• v.16 no.2
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• pp.192-195
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• 2011

The phase transition of vortex matter from solid to liquid was studied in iron-based superconductors. Based on the traditional vortex glass theory, we have examined the magnetoresistivity data of iron-based superconductors using our extended thermal activation model: $\rho(B,T)=\rho((T-T_g(B))/(T_c(0)-T_g(B)))^{v(z-1)}$. We predict that the magnetic field-dependent area S + $S_0$ which integrates $\rho$ with T is proportional to $B^{\beta}$, where ${\beta}$ is the vortex glass transition exponent. From our calculation, the vortex glass transition exponent is 0.33, close to the exponent of area $S_0$ + S is 0.31 in $SmO_{0.9}F_{0.1}FeAs$; the exponent of area S is 0.63, which is close to the irreversibility line exponent 2/3. Both of the results show the validity of our model. In addition, our model is shown to be effective in describing irreversibility behavior in layered superconductors.

• Journal of the Korean Society of Safety
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• v.16 no.3
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• pp.68-75
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• 2001

Photopolymerization, the utilization of electromagnetic radiation(or light) as the energy source for polymerization of functional monomers, oligomers is the basis of important commercial processes with broad applicability, including photoimaging and RV curing of coatings and inks. The objective of this study is to investigate the characteristics of environmental fraternitive photopolymerization of methyl methacrylate(MMA). This work is the first step to continue further research about alkyl methacrylate. The experiment was done in aqueous solution under the influence of photo-initiator concentration(0.05-0.25mol/l), light intensity (5000-9000 ${\mu}J/cm^2$) and monomer concentration(2-6mol/l). Methyl methacrylate was polymerized to high conversion ratio using hydrogen peroxide($H_2O_2$) and the kinetics model we have obtained is as follows. $R_p=k_p[S]^{0.41}[M]^{0.62}[L]^{2.45} exp(53.64/RT$). The differential method of thermogravimetric analysis(Friedman method) was used to obtain value of activation energy on decomposition reaction. The average value of it res 45.4Kca1/mol.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.8
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• pp.700-704
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• 2003

This paper describes on characteristics of 2" 3C-SiC wafer bonding using PECVD (plasma enhanced chemical vapor deposition) oxide and HF (hydrofluoride acid) for SiCOI (SiC-on-Insulator) structures and MEMS (micro-electro-mechanical system) applications. In this work, insulator layers were formed on a heteroepitaxial 3C-SiC film grown on a Si (001) wafer by thermal wet oxidation and PECVD process, successively. The pre-bonding of two polished PECVD oxide layers made the surface activation in HF and bonded under applied pressure. The bonding characteristics were evaluated by the effect of HF concentration used in the surface treatment on the roughness of the oxide and pre-bonding strength. Hydrophilic character of the oxidized 3C-SiC film surface was investigated by ATR-FTIR (attenuated total reflection Fourier transformed infrared spectroscopy). The root-mean-square suface roughness of the oxidized SiC layers was measured by AFM (atomic force microscope). The strength of the bond was measured by tensile strength meter. The bonded interface was also analyzed by IR camera and SEM (scanning electron microscope), and there are no bubbles or cavities in the bonding interface. The bonding strength initially increases with increasing HF concentration and reaches the maximum value at 2.0 ％ and then decreases. These results indicate that the 3C-SiC wafer direct bonding technique will offers significant advantages in the harsh MEMS applications.ions.

• Korean Chemical Engineering Research
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• v.46 no.1
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• pp.200-204
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• 2008

The curing kinetics of diglycidyl ether of bisphenol F (DGEBF) with an asymmetric cycloaliphatic amine curing agent were examined by thermal analysis in both isothermal and dynamic curing conditions. From the residual curing of the samples partially cured in isothermal condition and from the dynamic curing with various heating rates, it was found that there exist two kinds of reactions such as at low temperature and at high temperature regions. It was thus also found that the cure parameters obtained from the isothermal curing kinetic model hardly estimate experimental results for a degree of cure larger than 0.6. The activation energies and frequency factors of these two kinds of reactions were obtained from the dynamic curing experiments with various heating rates. From the curing analysis, it was verified that the total cure kinetics for low degrees of cure is dominated by the cure reaction in the low temperature region.

• BMB Reports
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• v.35 no.2
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• pp.220-227
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• 2002

Two aspartate aminoransferase (EC 2.6.1.1) isoenzymes (AAT-1 and AAT-2) from Lupinus albus L. cv Estoril were separated, purified, and characterized. The molecular weight, pI value, optimum pH, optimum temperature, and thermodynamic parameters for thermal inactivation of both isoenzymes were obtained. Studies of the kinetic mechanism, and the kinetics of product inhibition and high substrate concentration inhibition, were performed. The effect of some divalent ions and irreversible inhibitors on both AAT isoenzymes was also studied. Native PAGE showed a higher molecular weight for AAT-2 compared with AAT-1. AAT-1 appears to be more anionic than AAT-2, which was suggested by the anion exchange chromatography. SDS-PAGE showed a similar sub-unit molecular weight for both isoenzymes. The optimum pH (between 8,0 and 9.0) and temperature ($60-65^{\circ}C$) were similar for both isoenzymes. In the temperature range of $45-65^{\circ}C$, AAT-2 has higher thermostability than AAT-1. Both isoenzymes showed a high affinity for keto-acid substrates, as well as a higher affinity to aspartate than glutamate. Manganese ions induced an increase in both AAT isoenzymes activities, but no cooperative effect was detected. Among the inhibitors tested, hydroxylamine affected both isoenzymes activity by an irreversible inhibition mechanism.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2181-2186
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• 2012

Dendrimers are a novel class of nonlinear polymers and due to their extensive applications in different fields, called versatile polymers. Polyamidoamine (PAMAM) dendrimers are one of the most important dendrimers that have many applications in nanobiotechnology and industry. Generally aldehyde terminated dendrimers are prepared by activation of amine terminated dendrimers by glutaraldehyde which has two problems, toxicity and possibility of crosslink formation. In this study, novel aldehyde-terminated PAMAM dendrimer was prepared and used for covalent immobilization of trypsin by the aim of finding a special reagent which can prevent crosslinking and deactivation of the enzyme. For this purpose aminoacetaldehydedimethylacetal (AADA) was used as spacer group between aldehyde-terminated PAMAM and trypsin.The findings of this study showed that immobilization of trypsin not only resulted higher optimal temperature, but also increased the thermal stability of the immobilized enzyme in comparison to the free enzyme.

• Bulletin of the Korean Chemical Society
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• v.28 no.6
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• pp.1031-1034
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• 2007

The R- and Z-substituent effects for the gas-phase thermal decompositions of carbamates, R2NC(=O)- OCH2CH2Z, have been investigated theoretically at B3LYP level with 6-31G(d) and 6-31++G(d,p) basis sets. Both the Z- and R-substituent effects on reactivity (ΔH≠) were well consistent with experimental results, although the R-substituent effect was underestimated theoretically. No correlations were found between activation enthalpies and reaction enthalpies. The substituent effects on reactivity seemed to be complicated at a glance, but were understandable by concurrent electronic and steric factors. Variations of bond lengths at TS structures were well correlated with the Taft's σ* values and the TS structures became tighter as the Zsubstituent became a stronger electron-acceptor (δσ* > 0). However the effects of R-substituents on the TS structures were much smaller when compared to those of Z-substituents.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.473-479
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• 2000

The nanocrystalline Fe$_{84}$Zr$_{7}$B$_{6}$Cu$_{1}$ $Al_{2}$ alloy was annealed at 450 $^{\circ}C$ and 550 $^{\circ}C$ for l hour to achieve the ultra-soft magnetic properties such as large magnetoimpedence ratio(MIR), the incremental permeability ratio(PR), nearly zero coercivity, zero magnetostriction, etc. The PR and MIR of the sample were measured from 100 kHz to 10 MHz at a cryogenic chamber where the temperature can be varie from 10 K to 300 K. The increment of MIR value is proportional to increasing temperature. The maximum PR values measured at high frequency above 1 MHz remain almost same despite of the temperature variation from 10 K to 300 K except the sharpness in PR curves. However, the maximum PR values measured below 1 MHz show drastic increment at above 150K due to thermal activation of magnetic domains.s.s.

• Electrical & Electronic Materials
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• v.1 no.1
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• pp.54-61
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• 1988

This paper was a study on dielectric phenomena of the specimen, Polypropylene films which were annealled in air and quenched in liquid nitrogen after aging for 5[hr] in water of 100[.deg.C]. The specimen was measured in temperature range of 15-120[.deg.C] and in frequency range of 30-1x 10$^{6}$ [HZ]. As the results of the study, it was confirmed that the tacticity of specimen was isotactic structure, and the degree of cryatallinity of the specimens calculated by means of Natta's method from XRD (X-ray Diffraction) spectrum was 55[%]. And for dielectric relaxation, .betha. peak-the tan .delta. (spectrum around 20[.deg.C])-attributed due to amorphous regions, and .alpha. peak - the tan .delta. spectrum around 90[.deg.C]-due to crystalline regions. It was identified that the degree of crystallinity of the specimen quenched in the liquid nitrogen was increased to 55-65[%], and that of the specimen annealled in the air was decreased to 55-50[%]. And activation energy from dielectric loss spectra was obtained 34.5[kcal/mole] for .alpha. peak and 80.5[kcal/mole] for .betha. peak, respectively.