• Korean Journal of Materials Research
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• v.2 no.3
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• pp.220-227
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• 1992

Electrorheological(ER) fluid's storage shear modulus(G') and loss factor(${\eta}$) have been directly measured using small amplitude forced oscillating rheometer as a function of oscillating frequency, strain amplitude and applied electric field. Two types of experiment were performed , (a) frequency sweep and (b) amplitude sweep. Two kinds of sample were employed for this experiment ; cornstarch particles in corn oil and zeolite particles in silicone oil. The storage shear modulus was a strong function of driving frequency. Generally, the modulus increased with driving frequency. On the other hand, the loss factor was not well behaved as storage modulus, but as the driving frequency increases the loss factor slightly decreases was the trend of the material's characteristics. Also the modulus was a strong function of strain amplitude. Generally, modulus decreased with increasing strain, but loss factor increases slightly with increasing strain amplitude. For G', cornstarch in corn oil ER fluid has higher values than zeolite based fluid as we increased applied electric field. On the other hand, zeolite based fluid has higher values for ${\eta}$. There is a reasonable agreement between theoretical calculation and experiment.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.1 s.34
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• pp.21-26
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• 2005

The field effect transistors (FETs) were fabricated ell $Y_2O_3/Si(100)$ substrates by the conventional memory processes and sol-gel process using $(Bi,La)Ti_3O_{12}(BLT)$ ferroelectric gate materials. The remnant polarization ($2Pr = Pr^+-Pr^-$) int Pt/BLT/Pt/Si capacitors increased from $22 {\mu}C/cm^2$ to $30{\mu}C/ cm^2$ at 5V as the annealing temperature increased from $700^{\circ}C$ to $750^{\circ}C$. There was no drastic degradation in the polarization values after applying the retention read pulse for $10^{5.5}$ seconds. The capacitance-voltage data of $Pt/BLT/Y_2O_3/Si$ capacitors at 5V input voltage showed that the memory window voltage decreased from 1.4V to 0.6V as the annealing temperature increased from $700^{\circ}C$ to $750^{\circ}C$. The leakage current of the $Pt/BLT/Y_2O_3/Si$ capacitors annealed at $750^{\circ}C$ was about $510^{-8}A/cm^2$ at 5V. From the drain currents versus gate voltages ($V_G$) for $Pt/BLT/Y_2O_3/Si(100)$ FET devices, the memory window voltages increased from 0.3V to 0.8V with increasing tile $V_G$ from 3V to 5V.

• Korean Chemical Engineering Research
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• v.50 no.6
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• pp.1064-1067
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• 2012

Recently, there is a growing interest in vegetable oils, cheap and abundant renewable natural resources. Vegetable oils can be used as raw materials for ecofriendly biodegradable polymer materials. In this study, poly(${\beta}$-amino esters) were synthesized by polymerization reaction of acrylated epoxidized soybean oil (AESO) and 2-aminoethanol. Various polymer films were prepared by changing the molar ratio of AESO to 2-aminoethanol. The formation of C-N bonds in poly(${\beta}$-amino ester) was confirmed using FT-IR. Gel contents higher than 98% confirmed the synthesis of crosslinked polymer networks. Tensile strengths and elongation at breaks of polymer films ranged from 0.3 to 1.3 MPa and 32 to 55%, respectively. Polymer films degraded 2 to 7% of the initial weight in 35 days in phosphate buffer solution (pH 7.2) containing lipase enzyme.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.3
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• pp.463-470
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• 1996

Ceramic membrane consisting of an ${\alpha}-Al_{2}O_{3}$ support and Fe doped $TiO_{2}$ top layer was prepared by the sol-gel method. The supported Fe doped $TiO_{2}$ top layer was made by dip coating the support in a mixed sol. The microstructure of the composite membranes was studied by SEM after calcination at $550~850^{\circ}C$. After sintering at $650^{\circ}C$ for 1 hr., the average particle diameter of the Fe doped $TiO_{2}$ top layer was ~40 nm. The supported Fe doped $TiO_{2}$ composite membranes exhibited much higher heat resistance than the $TiO_{2}$ membrane. The Fe doped $TiO_{2}$ composite membrane retained a crack-free microstructure and narrow particle size distribution even after calcination up to $650^{\circ}C$.

• Journal of Magnetics
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• v.20 no.3
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• pp.229-240
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• 2015

In this study, nanocrystalline ferrite powders with the composition $Ni_{0.5}Zn_{0.5}Fe_2O_4$ were prepared by the autocombustion method. The obtained powders were sintered at $800^{\circ}C$, $900^{\circ}C$ and $1,000^{\circ}C$ for 4 h in air atmosphere. The as-prepared and the sintered powders were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and magnetization studies. An increase in the crystallite size and a slight decrease in the lattice constant with sintering temperature were observed, whereas microstrain was observed to be negative for all the samples. Two significant absorption bands in the wave number range of the $400cm^{-1}$ to $600cm^{-1}$ have been observed in the FT-IR spectra for all samples which is the distinctive feature of the spinel ferrites. The force constants were found to vary with sintering temperature, suggesting a cation redistribution and modification in the unit cell of the spinel. The M-H loops indicate smaller coercivity, which is the typical nature of the soft ferrites. The observed variation in the saturation magnetization and coercivity with sintering temperature has been attributed to the role of surface, inhomogeneous cation distribution, and increase in the crystallite size.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.221-225
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• 2003

The MFIS-FET(Field Effect Transistor) devices using $BLT/Y_2O_3$ buffer layer on p-Si(100) substrates were fabricated by the Sol-Gel method and conventional memory processes. The crystal structure, morphologies and electrical properties of prepared devices were investigated by using various measuring techniques. From the C-V(capacitance-voltage) data at 5V, the memory window voltage of the $Pt/BLT/Y_2O_3/si$ structure decreased from 1.4V to 0.6V with increasing the annealing temperature from $700^{\circ}C\;to\;750^{\circ}C$. The drain current (Ic) as a function of gate voltages $(V_G)$ for the $MFIS(Pt/BLT/Y_2O_3/Si(100))-FET$ devices at gate voltages $(V_G)$ of 3V, 4V and 5V, the memory window voltages increased from 0.3V to 0.8V as $V_G$ increased from 3V to 5V.

• Membrane Journal
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• v.16 no.2
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• pp.106-114
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• 2006

This study is concerned with preparation of chlorine resistant (CR) thin layer composite (TFC) membranes. The novel method for making CR membranes from commercially available RO membranes is based on sol-gel condensation of trialkoxyalkylsilane derivatives. The silane coupling agents used in this study have different number of alkyl carbon chain group (methyltriethoxysilane; METES and octyltriethoxysilane; OCTES). The OCTES composite membranes have a significant tolerance to chlorine compared to commercial polyamide RO membrane or METES composite membranes. The surface properties of membranes were examined to explain a significant difference of chlorine tolerance between OCTES composite membrane and the other two membranes. In this study, we tried several surface analyses to explain difference of chlorine tolerance. The element composition results of surface analysis by EDX confirmed that both silane fixed on polyamide firmly, The surface roughness and contact angle results showed long chain alkyl group of OCTES enhancing hydrophobicity considerably than METES. The hydrophobicity plays an important role in chlorine resistance of membrane.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.281-281
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• 2010

Very low refractive index (<1.4) materials have been proved to be the key factor improving the performance of various optical components, such as reflectors, filters, photonic crystals, LEDs, and solar cell. Highly porous SiO2 are logically designed for ultralow refractive index materials because of the direct relation between porosity and index of refraction. Among them, ordered macroporous SiO2 is of potential material since their theoretically low refractive index ~1.10. However, in the conventional synthesis of ordered macroporous SiO2, the time required for the crystallization of organic nanoparticles, such as polystyrene (PS), from colloidal solution into well ordered template is typical long (several days for 1 cm substrate) due to the low interaction between particles and particle - substrate. In this study, polystyrene - polyacrylic acid (PS-AA) nanoparticles synthesized by miniemulsion polymerization method have hydrophilic polyacrylic acid tails on the surface of particles which increase the interaction between particle and with substrate giving rise to the formation of PS-AA film by simply spin - coating method. Less ordered with controlled thickness films of PS-AA on silicon wafer were successfully fabricated by changing the spinning speed or concentration of colloidal solution, as confirmed by FE-SEM. Based on these template films, a series of macroporous SiO2 films whose thicknesses varied from 300nm to ~1000nm were fabricated either by conventional sol - gel infiltration or gas phase deposition followed by thermal removal of organic template. Formations of SiO2 films consist of interconnected air balls with size ~100 nm were confirmed by FE-SEM and TEM. These highly porous SiO2 show very low refractive indices (<1.18) over a wide range of wavelength (from 200 to 1000nm) as shown by SE measurement. Refraction indices of SiO2 films at 633nm reported here are of ~1.10 which, to our best knowledge, are among the lowest values having been announced.

• Korean Journal of Food Science and Technology
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• v.25 no.5
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• pp.456-460
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• 1993

The present study was conducted to investigate Angiotensin I-converting enzyme(ACE) inhibition activity of the components of traditional tea materials in Korea. Angiotensin I-converting enzyme(ACE) inhibition activity of water soluble fractions obtained from the samples were strong in Zingiberis rhizoma, Acantopanacis cortex, Schizandrae fructus, Perilla semen, Cassiae torae semen, Zizyphy fructus in order. ACE inhibition activity of fractions obtained from methanol extract of Cassiae torae semen were strong in ethyl acetate fraction, ethyl ether fraction, water fraction, chloroform fraction in order. Compound C showed the strongest ACE inhibition activity among compound A, B, C, D separated from Cassiae torae semen, but Compound C separated from Cassiae torae semen was lower than bradykinin in the ACE inhibition activity.

• Korean Journal of Food Science and Technology
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• v.35 no.6
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• pp.1221-1225
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• 2003

As an effort to select powerful anti-cariogenic materials from natural resources, various plant extracts were examined for their anti-S. mutans and anti-glucosyltransferase (GTase) activities. The ethanol extracts of licorice bark, which was produced after water extraction of licorice, showed the most powerful anti-S. mutans as well as anti-GTase activities. When licorice bark was consecutively fractionated with n-hexane, chloroform, ethylacetate, and butanol, the chloroform fraction exhibited the strongest anti-S. mutans activites. This fraction was further fractionated into 4 fractions through a silica gel column, and according to HPLC analysis, anti-S. mutant activities seemed to come mostly from relatively hydrophobic materials.