• Bulletin of the Korean Chemical Society
• /
• v.19 no.6
• /
• pp.661-666
• /
• 1998

Active reaction sites and electrochemical O2 reduction kinetics on La_{1-x}Sr_xMnO_{3+{\delta}} (x=0.1-0.4)/YSZ (yttria-stabilized zirconia) electrodes are investigated in the temperature range of 700-900 ℃ at $Po_2=10^{-3}$-0.21 atm. Results of the steady-state polarization measurements, which are formulated into the Butler-Volmer formalism to extract transfer coefficient values, lead us to conclude that the two-electron charge transfer step to atomically adsorbed oxygen is rate-limiting. The same conclusion is drawn from the $Po_2$-dependent ac impedance measurements, where the exponent m in the relationship of $I_o$ (exchange current density) ∝ $P_{o_{2}}^m$ is analyzed. Chemical analysis is performed on the quenched Mn perovskites to estimate their oxygen stoichiometry factors (δ) at the operating temperature (700-900 ℃). Here, the observed δ turns out to become smaller as both the Sr-doping contents (x) and the measured temperature increase. A comparison between the 8 values and cathodic activity of Mn perovskites reveals that the cathodic transfer coefficients $({\alpha}_c)$ for oxygen reduction reaction are inversely proportional to δ whereas the anodic ones $({\alpha}_a)$ show the opposite trend, reflecting that the surface oxygen vacancies on Mn perovskites actively participate in the $O_2$ reduction reaction. Among the samples of x= 0.1-0.4, the manganite with x=0.4 exhibits the smallest 8 value (even negative), and consistently this electrode shows the highest ${\alpha}_c$ and the best cathodic activity for the oxygen reduction reaction.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.21 no.7
• /
• pp.585-593
• /
• 2008

In this work, we report several experimental data capable of evaluating the phase transformation characteristics of GeSbTe pseudobinary thin films comprehensively utilized as phase change materials. The phase transformation of the GeSbTe thin films was confirmed by XRD measurement from amorphous to hexagonal structure via fee structure except for $Ge_8Sb_2Te_{11}$. In addition, X-ray photoelectron spectra analysis revealed to weaken Ge-Te bond for $Ge_2Sb_2Te_5$ and to strengthen the bonds of all elements for $Ge_8Sb_2Te_{11}$ during the amorphous to crystalline transition. The values of optical energy gap $(E_{OP})$ were around 0.71 and 0.50 eV and the slopes of absorption in extended region (B) were ${\sim}5.1{\times}10^5$ and ${\sim}10{\times}10^5cm^{-1}{\cdot}V^{-1}$ for the amorphous and fcc-crystalline structures, respectively. Finally, the kinetics of amorphous-to-crystalline phase change on the GeSbTe films was characterized using a nano-pulse scanner with 658-nm laser diode (power; $1{\sim}17$ mW, pulse duration; $10{\sim}460$ ns).

• Analytical Science and Technology
• /
• v.15 no.1
• /
• pp.15-19
• /
• 2002

The pretreatment of tungsten added $BaTiO_x$ ceramics was performed to improve the recovery of Ba, Ti and W. $BaTiO_x$ ceramics were digested with HF : HCl ( 1 : 2 ) mixture in an acid digestion bomb at $220^{\circ}C$ for 3 hrs. The concentration of Ba, Ti and W were determined by ICP-AES. Recoveries of Ba, Ti and W were 99.6%, 99.8% and 99.2%, respectively. And their C.V. values were 1.02%, 0.73% and 1.79%. Using this method, the analytical results of Ba, Ti and W for a real sample were obainted to be 25.9% (w/w), 38.8% (w/w) and 3.31% (w/w), respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.27 no.1
• /
• pp.20-26
• /
• 2016

This paper presents an X-band two-stage power amplifier using GaN-HEMT. Two-stage structure was adopted to take its high gain and simple inter-stage matching network. Based on a 3D EM simulation, the bond-wire inductance and the parasitic capacitance were predicted. By reducing bond-wire inductance, Q of the matching network is decreased and the bandwidth is improved. The implemented two-stage PA shows a power gain of more than 16 dB, saturated output power of more than 42.5 dBm, and a efficiency of more than 35 % in frequency range of 8.1~8.5 GHz with an operating voltage of 40 V.

• Journal of the Korean Society of Radiology
• /
• v.17 no.3
• /
• pp.351-357
• /
• 2023

This Study Rreceived Subjective Evaluation ROC Evaluation from five projection. of projection. at a University Hospital to Obtain and Diagnose Sharp images of apophyseal joints and Vertral arch of Thoracic vertebrae from thoracic X-ray projection. In the Subjective evaluation, the highest Score was obtained by raising the phantom from Supine to LAO by 70° and scoring 20 points at 5° with the X-ray Tube facing the head. In addition, he scored the highest score of 19 points at 8° with the Prone Phantom standing 60° with RAO and the X-ray Tube facing the head. For Objective Evaluation, the Signal-to-noise ratio, was calculated. ROI was set at 1,564 mm2 to obtain the image signal average value (Mean value) and the Standard deviation (SD value). Objective Evaluation The signal-to-noise ratio, was the highest at 5° toward the head in the LPO 70° position of the phantom in the lying position of the Thoracic spine projection, and the Thoracic Spine was the highest at 8° toward the head of the RAO posture of 5,645.

• Korean Journal of Metals and Materials
• /
• v.60 no.4
• /
• pp.329-339
• /
• 2022

The effect of Cu content on the microstructure and mechanical properties of Al-8.0Zn-2.5Mg-xCu (x: 0, 1, 2, 3) aluminum alloys manufactured by the twin-roll casting process was investigated. The Al-8.0Zn-2.5Mg-xCu alloy showed an increase in surface defects with increasing Cu content. This is because the amount of residual liquid in the final solidification region increased from 9.6 wt.% to 18.3 wt.% as the Cu content increased from 0Cu to 3 Cu alloy. For the 3Cu alloy, as the amount of residual liquid in the final solidification region exceeded the critical point, a large number of surface defects and internal shrinkage defect were observed. The main secondary phases of the four alloys were the T(Mg₃₂(Al, Zn)₄₉) and η(MgZn₂) phases, and their fraction increased with Cu content. These secondary phases mainly existed in the center segregation band, and a fine η(MgZn₂) phase was additionally observed. In terms of mechanical properties, as the Cu content increased, the hardness of the center matrix, secondary phase, and overall hardness increased respectively. Although the yield strength increased, the tensile strength and elongation decreased because the center segregation band was widened from 684 ㎛ to 790 ㎛ with increasing Cu content.

• Journal of the Korean Dietetic Association
• /
• v.12 no.2
• /
• pp.172-184
• /
• 2006

This study was aimed to provide safety management guidance by evaluating the microbial quality of cooked dried-seafoods in school foodservice operations. Nineteen seafood items were collected from six elementary schools, those were dried-anchovy, dried-seaweed and dried-fish, which were classified as cooking process. The temperatures at receiving and after cooking were measured and the analyses of cooking processes and microbial quality were performed. The temperatures of all foods after cooking were higher than the temperature limit of $74\^circC$. The number of total aerobic bacteria and S. aureus in dried-anchovy over the limit of $10^5$ and even the level of S. aureus was found to be unsatisfactory. The count of total aerobic bacteria was 2.1x$10^8$ CFU/g and the number of total aerobic bacteria after cooking was over the limit in one school. The level of E. coli (3.1x$10^3$ CFU/g) was over the limit at one school and the number of S. aureus (1.2×$10^4$ CFU/g) was considered as unacceptable. Dried- tangle and green laver were contaminated with total aerobic bacteria showing the over the limit. The numbers of total aerobic bacteria in dried- filefish, pollack and squid were 4.3x$10^6$, 3.4x$10^6$-3.9x$10^7$ and 4.6x$10^5$-4.1x$10^7$ CFU/g, respectively, which were in acceptable or unsatisfactory level. The E. coli in dried- filefish and pollack were over the limit. The total aerobic bacteria levels, 4.6x$10^5$-1.5x$10^6$ CFU/g in dried-pollack and 8.0x$10^5$-2.2x$10^7$ CFU/g in dried-squid, were over the limit after cooking except dried-filefish. The E. coli levels, 4.3x$10^3$ CFU/g in dried-filefish and 2.5x$10^2$ CFU/g in dried-pollack, were over the limit of $10^2$ CFU/g. The numbers of Enterobacteriaceae were either acceptable (3.3x$10^3$ CFU/g) or unsatisfactory (1.6x$10^4$ CFU/g) level in dried-pollack. S. aureus was unsatisfactory level (6.5x$10^4$ CFU/g) in dried-filefish while unacceptable in dried-pollack both before and after cooking. Unacceptable levels of S. aureus, 2.4x$10^4$ and 1.3x$10^5$ CFU/g were found from two schools, respectively. These results suggest that the contamination of raw materials and the seasonings added after cooking should be controlled to manage the microbial safety of cooked dried-seafoods.

• Clean Technology
• /
• v.21 no.4
• /
• pp.271-277
• /
• 2015

A photocatalyst which mixed by the commercialized P25-TiO₂ and a synthesized Ag_xO was used in an appropriate weight ratio to effectively produce hydrogen gas in this study. The Ag_xOs were synthesized with the conventional sol-gel method, and tetramethylammonium hydroxides were added at the synthesis process in order to stabilize the solutions, and then the solutions were heat-treated at the temperatures of -5, 25, and 50 ℃, resulted to obtain the three types of silver oxides. Physicochemical properties of the synthesized Ag_xOs were identified through X-ray diffraction analysis (XRD), scanning emission microscopy (SEM), ultraviolet-visible spectroscopy, and X-ray photoelectron spectroscopy (XPS). In the photolysis results of water/methanol (weight ratio 1:1) solution, the mixture of P25-TiO₂/Ag_xO exhibited a significantly higher hydrogen gases evolution, compared to that of pure P25-TiO₂. Additionally, the addition of H₂O₂ as an supplement oxidant and in Ag_xO synthesized at 50 ℃ improved the hydrogen production efficiency. In particular, the emitted hydrogen gases reached to 13,000 μmol during 8 hours when a mixed catalyst, Ag_xO of 0.1 g and P25-TiO₂ of 0.9 g, were used.

• ETRI Journal
• /
• v.27 no.1
• /
• pp.75-80
• /
• 2005

This paper addresses a fully-integrated low phase noise X-band oscillator fabricated using a carbon-doped InGaP heterojunction bipolar transistor (HBT) GaAs process with a cutoff frequency of 53.2 GHz and maximum oscillation frequency of 70 GHz. The oscillator circuit consists of a negative resistance generating circuit with a base inductor, a resonating emitter circuit with a microstrip line, and a buffering resistive collector circuit with a tuning diode. The oscillator exhibits 4.33 dBm output power and achieves -127.8 dBc/Hz phase noise at 100 kHz away from a 10.39 GHz oscillating frequency, which benchmarks the lowest reported phase noise achieved for a monolithic X-band oscillator. The oscillator draws a 36 mA current from a 6.19 V supply with 47.1 MHz of frequency tuning range using a 4 V change. It occupies a $0.8mm{\times}0.8mm$ die area.

• Electrical & Electronic Materials
• /
• v.9 no.8
• /
• pp.836-850
• /
• 1996

In this study, we have analyzed structural analysis and measured ferroelectric characteristics of PZT thin films prepared by sol gel process with different sintering conditions and different Zr/Ti mot%. When the Zr mot% of PZT thin film was increased, it was found that the remanent. polarization and coercive field were decreased and increased, respectively. Also, the maxium dielectric constant of PZT(50/50) thin film was 786.8. We got double hysteresis(anti-fcrroelectric) curve from PbZrO$_{3}$ thin film. As heating rate goes up, pyrochlore phase of PZT thin film was decreased and dielectric and ferroelectric characteristics were improved. As a result of variation of sintering temperature and time 500.deg. C-800.deg. C and 5 sec.-8 hours, respectively, we got optimal sintering temperature and time. The optimium sintering temperature and time of conventional furnace method and rapid thermal processing method were 650.deg. C-700.deg. C for 30-60 minutes and 700.deg. C/20 seconds-2 minutes, respectively.