• Korean Journal of Materials Research
• /
• v.22 no.4
• /
• pp.207-210
• /
• 2012

The preparation of $Sm_2O_3$ doped $CeO_2$ in Igepal CO-520/cyclohexane reverse micelle solutions has been studied. In the present work, we synthesized nanosized $Sm_2O_3$ doped $CeO_2$ powders by reverse micelle process using aqueous ammonia as the precipitant; hydroxide precursor was obtained from nitrate solutions dispersed in the nanosized aqueous domains of a micro emulsion consisting of cyclohexane as the oil phase, and poly (xoyethylene) nonylphenylether (Igepal CO-520) as the non-ionic surfactant. The synthesized and calcined powders were characterized by Thermogravimetry-differential thermal analysis (TGA-DTA), X-ray diffraction analysis (XRD), and Transmission electron microscopy (TEM). The crystallite size was found to increase with increase in water to surfactant (R) molar ratio. Average particle size and distribution of the synthesized $Sm_2O_3$ doped $CeO_2$ were below 10 nm and narrow, respectively. TG-DTA analysis shows that phase of $Sm_2O_3$ doped $CeO_2$ nanoparticles changed from monoclinic to tetragonal at approximately $560^{\circ}C$. The phase of the synthesized $Sm_2O_3$ doped $CeO_2$ with heating to $600^{\circ}C$ for 30 min was tetragonal $CeO_2$. This study revealed that the particle formation process in reverse micelles is based on a two step model. The rapid first step is the complete reduction of the metal to the zero valence state. The second step is growth, via reagent exchanges between micelles through the inter-micellar exchange.

• Proceedings of the Korean Environmental Health Society Conference
• /
• 2004.06a
• /
• pp.193-196
• /
• 2004

To evaluate the acute effects of fine particles on pulmonary function, a longitudinal study was conducted. This study was carried out for the schoolchildren (3rd and 6th grades) living in Beijing, China. Children were asked to record their daily levels of peak expiratory flow rate using portable peak flow meter (mini-Wright) for 40 days. The relationship between daily PEFR and fine particle levels was analyzed using a mixed linear regression models including gender, height, the presence of respiratory symptoms, and daily average temperature and relative humidity as extraneous variables. The total number of students participating in this longitudinal study was 87. Daily measured PEFR was in the range of $253{\sim}501L/min$. On the daily basis, a PEFR measured in the morning was shown to be lower than that measured in the evening (or afternoon). The daily mean concentrations of $PM_{10}$ and $PM_{2.5}$ over the study period were $180.2\;{\mu}g/m^3$ and $103.2\;{\mu}g/m^3$, respectively. The IQR (inter-quartile range) of $PM_{10}$ and $PM_{2.5}$ were $91.8\;{\mu}g/m^3$ and $58.0\;{\mu}g/m^3$. Daily mean PEFR was regressed with the 24-hour average $PM_{10}$ (or $PM_{2.5}$) levels, weather information such as air temperature and relative humidity, and individual characteristics including gender, height, and respiratory symptoms. The analysis showed that the increase of fine particle concentrations was negatively associated with the variability in PEFR. The IQR increments of $PM_{10}$ or $PM_{2.5}$ (at 1-day time lag) were also shown to be related with 1.54L/min (95% Confidence intervals -2.14, -0.94) and 1.56L/min (95% CI -2.16, -0.95) decline in PEFR.

• Particle and aerosol research
• /
• v.5 no.2
• /
• pp.53-62
• /
• 2009

In this study, the continuous monitoring of the concentration of PM-10 atmospheric particulate matter using beta ray attenuation method was compared with gravimetric method from September, 2006 to August, 2007. On the effects of the PM-10 concentration and mass difference by relative humidity and precipitation were considered. The result showed that the measurement error between beta ray method and gravimetric method are within -3~6% in average, which means PM-10 concentration data with beta ray method are relatively comparable. The current study also shows that the high PM-10 concentration events are mainly due to haze, Asian dust, and high relative humidity and the PM-10 mass concentration is closely related with relative humidity and precipitation events. Based on daily mean data, the PM-10 increases as relative humidity increases up to 70~80%, then decreases over 80% due to the precipitation. However, the distinct measurement discrepancy was not shown between beta ray method and gravimetric method based on current results. Consequently, this study shows that the collocated measurement in different instrument is essential in order to quantify the accuracy of PM-10. Furthermore, the more comprehensive and spatially distributed comparison is needed and this is remained for future study.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2008.10a
• /
• pp.394-397
• /
• 2008

In this research, the fine-structure TiO2+Ti bulks have been fabricated by the combined application of magnetic pulsed compaction (MPC) and subsequent sintering, and their densification behavior was investigated. The obtained density of $TiO_2$+Ti bulk prepared by the combined processes was increased with increasing MPC pressure from 0.7 to 1.7 GPa. Relatively higher density (88%) in the MPCed specimen at 0.7Gpa was attributed to the decreasing of the inter-particle distance of pre-compacted component. High pressure and rapid compaction by Magnetic Pulsed Compaction could reduce shrinkage rate (about 10%) of the sintered bulks compared to that of general processing (about 20%). Mixing conditions of PVA, water, Ti and $TiO_2$ nano powder for compaction of $TiO_2$ nano powder did not affect on density and shrinkage of the sintered bulks due to high pressure of MPC.

• The Journal of the Acoustical Society of Korea
• /
• v.20 no.3E
• /
• pp.3-9
• /
• 2001

This study aims to describe a prosodic pattern on the Korean subjective particles with respect to their discourse function. 4 kinds of Korean subjective particles were mainly investigated with reference to sentential location, grammatical relations that precede or follow the word including subjective particles, and prosodic phrasing. F0 and energy were gradually diminished as the particles moved down to the sentential final position. 'Ga'particle, which has been potentially regarded as having a grammatical focusing function, looks like to show relatively higher F0 in sentential medial in discourse. At sentential medial position, when the words including 'ga, eun, and neun'particles were preceded by adverbials, the acoustic variables of particles tended to be diminished by some ratio in comparison with the mean value. The duration of particles might vary with respect to style variation and especially that it tended to diminish from 150 basic, 50 separate, and finally 50 discourse successively. And there's some specific phenomenon that prosodic phrasing itself was relatively easily taken place after 'eun' and 'neun' particles. Finally, I tried to catch the prosodic characteristics (which would be established as acoustic features) of inter-word position at which specific subjective particles were intervened. These acoustic features can be made up of the duration and F0 fluctuation activated in the successive 3 syllables in which word (or prosodic) boundary was located.

• Korea-Australia Rheology Journal
• /
• v.12 no.2
• /
• pp.135-141
• /
• 2000

The linear viscoelastic behavior of acrylonitrile-butadiene-styrene (ABS) polymers with different rubber content has been investigated in the frame of a linear viscoelastic model, which takes into account the inter-connectivity of the dispersed rubber particles. The model developed in our previous work has been shown to properly predict the low frequency plateau for the storage modulus, which is generally observed in polymer blends containing core-shell-type impact modifiers. In the present study, further experiments have been carried out on ABS polymers with different rubber content to verify the validity of our linear viscoelastic model. It has been found that our model describes quite properly the rheological behavior of ABS polymers with different rubber content, especially at low frequencies. The experimental data confirm that our model describes the rheological properties of rubber-modified thermoplastic polymers with strong adhesion at the particle/matrix interface more accurately than the Palierne model.

• Biotechnology and Bioprocess Engineering:BBE
• /
• v.6 no.4
• /
• pp.269-273
• /
• 2001

This study presents a new formulation method for improving DNA transfection effi-ciency using a fusogenic peptide and polyethylene glycol-grafted polyethylenimine. Succinimidyls succinate polyethylene glycol (PEG-SSA) was conjugated with polyethylenimine(PEL). PEL is well known for a good endosomal escaping and DNA condensign agent. The positively charged syn-thetic fusogenic peptide, KALA was coated on the negatively charged PEG-g-PEI/DNA and PEI/DNA complexes. The KALA/PEI/ DNA complexes exhibited aggregation behavior at higher KALA coating amount with an effective diameter of around 1,000 nm. However, the LALA/PEG-g-PEI/DNA complexes were 100-300 nm in size with a surface zeta-potential (ζ)value of about +20mV. The conjugated PEG molecules suppressed any KALA-mediated inter-particle aggregation, and thereby improved the transfection efficiency, Consequently, the transfection efficiency of the KALA/PEG-g-PEI/DNA complexes was obtained by utilizing both the fusogenic activity of KALA and the steric repulsion effect of PEC.

• Proceedings of the Korean Society of Applied Pharmacology
• /
• 1996.04a
• /
• pp.282-282
• /
• 1996

The purpose of this study was to prepare the nifedipine dry elixir (NDE) and coated nifedipine dry elixir (CNDE) containing nifedipine ethanol solution for improving the dissolution rate and bioavailability of nifedipine. NDE containing nifedipine and ethanol in wall materials of dextrin was prepared using a spray-dryer and then NDE was coated with eudragit acrylic resin to make CNDE. Shape and size of the NDE and CNDE were monitored by scanning electron micrograph and laser particle size analyzer In vitro dissolution tests were performed in simulated gastric and intestinal fluid. Bioavailability of NDE and CNDE were compared with drug powder suspension and commercial soft capsule after oral administration of the preparations to rats. NDE and CNDE are spherical in shape. Cross-sectional view of dry elixirs indicates the large inter cavity containing ethanolic drug solution in shell. Geometric mean diameter of NDE and CNDE is about 6.64 and 8.70 $\mu\textrm{m}$, respectively. Drug dissolution rate within first 5 min from NDE increased dramatically irrespective of dissolution medium. However, CNDE showed a particularly retarded dissolution rate in pH 1.2 simulated gastric fluid compared with NDE. The bioavailability of nifedipine in the NDE was increased dramatically compared with drug powder suspension. CNDE reduced initial burst-out plasma peak compared with NDE. CNDE as a sustained release delivery system could reduce the initial burst-out plasma peak due to controlling the release rate of nifedipine from NDE and maintain the effective plasma level over a longer period within therapeutic window with enhanced bioavailability of nifedipine.

• Bulletin of the Korean Chemical Society
• /
• v.31 no.8
• /
• pp.2235-2241
• /
• 2010

A reverse-phase HPLC method with detection by mass spectrometry is described for the simultaneous determination of doxifluridine and its two active metabolites, 5-fluorouracil (5-FU) and 5-fluorouridine (5-FUrd), in beagle dog plasma. The optimal chromatographic separation was achieved on a Waters $Xterra^{(R)}$ $C_{18}$ column ($4.6{\times}250\;mm$ i.d., $5\;{\mu}m$ particle size) with a mobile phase of 0.1% formic acid in a mixture of 99% methanol and purified water (99:1, v/v). The developed method was validated in beagle dog plasma with a lowest limit of quantification of $0.05\;{\mu}g/mL$ for both doxifluridine and 5-FU, and $0.2\;{\mu}g/mL$ for 5-FUrd. Doxifluridine and its two metabolites were stable under the analysis conditions, and intra- and inter-day accuracies exceeded 92.87%, with a precision variability ${\leq}11.34%$ for each analyte. Additionally, the method for quantifying doxifluridine and its two metabolites, 5-FU and 5-FUrd, in beagle dog plasma was applied successfully to the analysis of pharmacokinetic samples.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.11a
• /
• pp.707-710
• /
• 2004

Chemical mechanical polishing (CMP) process has been widely used to planarize dielectric layers, which can be applied to the integrated circuits for sub-micron technology. Despite the increased use of CMP process, it is difficult to accomplish the global planarization of in the defect-free inter-level dielectrics (ILD). In this paper, we have investigated slurry properties and CMP performance of silicon dioxide (oxide) as a function of different temperature of slurry. Thermal effects on the silica slurry properties such as pH, particle size, conductivity and zeta potential were studied. Moreover, the relationship between the removal rate (RR) with WIWNU and slurry properties caused by changes of temperature were investigated. Therefore, the understanding of these temperature effects provides a foundation to optimize an oxide CMP Process for ULSI multi-level interconnection technology.