• Korean Journal of Materials Research
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• v.29 no.4
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• pp.233-240
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• 2019

This study analyzes the mechanical properties, including the attrition rate, of $50{\mu}m$ size yttria-stabilized zirconia (YSZ) beads with different microstructures and high-energy milling conditions. The yttria distribution in the grain and grain-boundary of the fully sintered beads relates closely to Vickers hardness and the attrition rate of the YSZ beads. Grain size, fractured surfaces, and yttrium distribution are analyzed by electronic microscopes. For standardization and a reliable comparison of the attrition rate of zirconia beads with different conditions, Zr content in milled ceramic powder is analyzed and calculated by X-ray Fluorescence Spectrometer(XRF) instead of directly measuring the weight change of milled YSZ beads. The beads with small grain sizes sintered at lower temperature exhibit a higher Vickers hardness and lower attrition rate. The attrition rate of $50{\mu}m$ YSZ beads is measured and compared with the various materials properties of ceramic powders used for high-energy milling. The attrition rate of beads appears to be closely related to the Vickers hardness of ceramic materials used for milling, and demonstrates more than a 10 times higher attrition rate with Alumina(Hv ~1650) powder than $BaTiO_3$ powder (Hv ~315).

• Journal of Sensor Science and Technology
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• v.31 no.6
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• pp.455-460
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• 2022

Brush-like ZnO hierarchical nanostructures decorated with MgxZn1-xO (x = 0.1, 0.2, 0.3, 0.4, and 0.5) were fabricated and examined for application to a gas sensor. They were synthesized using vapor phase growth (VPG) on indium tin oxide (ITO) substrates. To generate electronic accumulation at ZnO surface, MgZnO nanoparticles were prepared by sol-gel method, and the ratio of Mg and Zn was adjusted to optimize the device for NO₂ gas detection. As the electrons in the accumulation layer generated by the heterojunction reacted faster and more frequently with the gas, the sensitivity and speed improved. When tested as sensing materials for gas sensors at 100 ppm NO₂ at 300℃, these MgZnO decorated ZnO nanostructures exhibited an improvement from 165 to 514 times compared to pristine ZnO. The response and recovery time of the MgZnO decorated ZnO samples were shorter than those of the pristine ZnO. Various analyzing techniques, including field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD) were employed to confirm the growth morphology, atomic composition, and crystalline information of the samples, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.207-207
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• 2011

Amorphous transparent oxide semiconductors (a-TOS) have been widely studied for many optoelectronic devices such as AM-OLED (active-matrix organic light emitting diodes). Recently, Nomura et al. demonstrated high performance amorphous IGZO (In-Ga-Zn-O) TFTs.1 Despite the amorphous structure, due to the conduction band minimum (CBM) that made of spherically extended s-orbitals of the constituent metals, an a-IGZO TFT shows high mobility.2,3 But IGZO films contain high cost rare metals. Therefore, we need to investigate the alternatives. Because Aluminum has a high bond enthalpy with oxygen atom and Alumina has a high lattice energy, we try to replace Gallium with Aluminum that is high reserve low cost material. In this study, we focused on the electrical properties of IZO:Al thin films as a channel layer of TFTs. IZO:Al were deposited on unheated non-alkali glass substrates (5 cm ${\times}$ 5 cm) by magnetron co-sputtering system with two cathodes equipped with IZO target and Al target, respectively. The sintered ceramic IZO disc (3 inch ${\phi}$, 5 mm t) and metal Al target (3 inch ${\phi}$, 5 mm t) are used for deposition. The O2 gas was used as the reactive gas to control carrier concentration and mobility. Deposition was carried out under various sputtering conditions to investigate the effect of sputtering process on the characteristics of IZO:Al thin films. Correlation between sputtering factors and electronic properties of the film will be discussed in detail.

• Journal of Magnetics
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• v.10 no.1
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• pp.5-9
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• 2005

Nanoparticles $Ni_{0.9}Zn_{0.1}Fe_2O_4$ is fabricated by a sol-gel method. The magnetic and structural properties of powders were investigated with XRD, SEM, Mossbauer spectroscopy, and VSM. $Ni_{0.9}Zn_{0.1}Fe_2O_4$ powders annealed at $300{^{\circ}C}$ have a spinel structure and behaved superparamagnetically. The estimated size of $Ni_{0.9}Zn_{0.1}Fe_2O_4$ nanoparticle is about 10 nm. The hyperfine fields at 13 K for the A and B patterns are found to be 533 and 507 kOe, respectively. The ZFC curves are rounded at the blocking temperature ($T_B$)and show a paramagnetic-like behavior above $T_B$. $T_B$ of $Ni_{0.9}Zn_{0.1}Fe_2O_4$ nanoparticle is about 250 K. Nanoparticles $Ni_{0.9}Zn_{0.1}Fe_2O_4$ annealed at 400 and $500{^{\circ}C}$ have a typical spinel structure and is ferrimagnetic in nature. The isomer shifts indicate that the iron ions were ferric at the tetrahedral (A) and the octahedral (B). The saturation magnetization of nanoparticles $Ni_{0.9}Zn_{0.1}Fe_2O_4$ annealed at 400 and $500{^{\circ}C}$ are 40 and 43 emu/g, respectively. The magnetic anisotropy constant of $Ni_{0.9}Zn_{0.1}Fe_2O_4$ annealed at $300{^{\circ}C}$ were calculated to be 1.6 ${\times}$ $10^6$ ergs/$cm^3$.

• Bulletin of the Korean Chemical Society
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• v.33 no.2
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• pp.519-523
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• 2012

A kinetic study is reported on nucleophilic displacement reactions of benzyl 2-pyridyl carbonate 6 with alkalimetal ethoxides, EtOM (M = Li, Na, and K), in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plots of pseudo-firstorder rate constant $k_{obsd}$ vs. [EtOM] curve upward, a typical phenomenon reported previously for alkaline ethanolysis of esters in which alkali-metal ions behave as a Lewis-acid catalyst. The kobsd value for the reaction of 6 with a fixed EtOK concentration decreases rapidly upon addition of 18-crown-6-ether (18C6), a complexing agent for $K^+$ ion up to [18C6]/[EtOK] = 1.0 and then remains constant thereafter, indicating that the catalytic effect exerted by K+ ion disappears in the presence of excess 18C6. The reactivity of EtOM towards 6 increases in the order $EtO^-$ < EtOLi < EtONa < EtOK, which is contrasting to the reactivity order reported for the corresponding reactions of 2-pyridyl benzoate 4, i.e., $EtO^-$ < EtOK < EtONa < EtOLi. Besides, 6 is 1.7 and 3.5 times more reactive than 4 towards dissociated $EtO^-$ and ion-paired EtOK, respectively. The reactivity difference and the contrasting metal-ion selectivity are discussed in terms of electronic effects and transition-state structures.

• Journal of Energy Engineering
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• v.14 no.4 s.44
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• pp.213-218
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• 2005

In order to understand the heat and mass transfer characteristics of humid airflow in frosting conditions, a flat plate of aluminum with cooling modules located in the central part of the plate was used. A microscope system (resolution of 0.05 mm) was used for the measurement of local thickness of frost at seven points along the plate in the flow direction. For the total mass of frost at each test operation, an electronic balance (resolution of 1 mg) was used. The local frost thickness distributions far various test conditions were presented along with the frost mass data measured at the given operating times. The effect of humidity and velocity of humid air on frosting were analyzed.

• The KIPS Transactions:PartB
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• v.13B no.4 s.107
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• pp.369-376
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• 2006

The degradation and its inverse modeling can achieve restoration of corrupted image, caused by scaled digitization and electronic transmission. De-speckle process on the noisy document(or SAR) images is one of the basic examples. Non-linearity of the speckle noise model may hinder the inverse process. In this paper, our study is focused on investigation of the restoration methods for bi-level document image degraded by the impulse noise model. Our study shows that, on bi-level document images, the weighted-median filter and the Lee filter methods are very effective among other spatial filtering methods, but wavelet filter method is ineffective in aspect of processing speed: approximately 100 times slower. Optimal values of the weight to be used in the weighted median filter are investigated and presented in this paper.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1096_1097
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• 2009

Aluminium doped zinc oxide(ZnO:Al) thin film, which is mainly used as a transparent conducting electrode in electronic devices, has many advantages compared with conventional indium tin oxide(ITO). In this paper in order to investigate the possible application of ZnO:Al thin films as a transparent conducting electrode for flexible film-typed dye sensitized solar cell (FT-DSCs), ZnO:Al and ITO thin films were prepared on the polyethylene terephthalate (PET) substrate by r. f. magnetron sputtering method. Specially one-inched FT-DSCs using either a ZnO:Al or ITO electrode were also fabricated separately under the same manufacturing conditions. Some properties of both the FT-DSCs with ZnO:Al and ITO transparent electrodes, such as conversion efficiency, fill factor, and photocurrent were measured and compared with each other. The results showed that by doping the ZnO target with 2 wt% of $Al_2O_3$, the film deposited at discharge power of 200W resulted in the minimum resistivity of $2.2\times10^{-3}\Omega/cm$ and at ransmittance of 91.7%, which are comparable with those of commercially available ITO. Two types of FT-DSCs showed nearly the same tendency of I-V characteristics and the same value of conversion efficiencies. Efficiency of FT-DSCs using ZnO:Al electrode was around 2.6% and that of fabricated FT-DSCs using ITO was 2.5%. This means that ZnO:Al thin film can be used in FT-DSCs as a transparent conducting layer.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1425_1426
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• 2009

In this study, commercially available polyethylene terephthalate(PET), which is widely used as a substrate of flexible electronic devices, was modified by dielectric barrier discharge(DBD) method in an air condition at atmospheric pressure, and aluminium - doped zinc oxide (ZnO:Al) transparent conducting film was deposited on PET substrate by r. f. magnetron sputtering method. Surface analysis and characterization of the plasma-treated PET substrate was carried out using contact angle measurements, X-ray Photoelectron Spectroscopy(XPS) and Atomic Force Microscopy (AFM). Especially the effect of surface state of PET substrate on some important properties of ZnO:Al transparent conducting film such as electrical and morphological properties and deposition rate of the film, was studied experimentally. The results showed that the contact angle of water on PET film was reduced significantly from $62^{\circ}$ to $43^{\circ}$ by DBD surface treatment at 20 min. of treatment time. The plasma treatment also improved the deposition rate and electrical properties. The deposition rate was increased almost linearly with surface treatment time. The lowest electrical resistivity as low as $4.97{\times}10^{-3}[\Omega-cm]$ and the highest deposition rate of 234[${\AA}m$/min] were obtained in ZnO:Al film with surface treatment time of 5min. and 20min., respectively.

• Physical Therapy Rehabilitation Science
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• v.10 no.4
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• pp.421-429
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• 2021

Objective: The purpose of this study was to examine the effect of personalized complex aerobic training programs using wearable device on cardiovascular and respiratory functions in community based female elderly. Design: One group pre-post intervention study. Methods: Twenty-one older female participants lived in 'D' city were included. The personalized complex aerobic training program using wearable devices was applied to all participants for 4 weeks, 3 times a week, 30 minutes for per session. The participants' blood pressure, heart rate, oxygen saturation, respiration rate, submaximal exercise stress test, pulmonary function test and respiratory muscle strength test were evaluated before and after the complex training program. Results: After intervention, resting diastolic blood pressure, resting systolic blood pressure and the systolic blood pressure after submaximal exercise stress test were significantly decreased over time (p<0.05), and the submaximal exercise stress test duration were significantly increased over time (p<0.05). The maximal inspiratory pressure (MIP) was significantly increased compare to before the intervention (p<0.05). Conclusions: This study showed that personalized complex training program using wearable device can provide personalized exercise intensity according to cardiopulmonary function that give feedback, and these interventions have a significant effect on improving the cardiovascular and respiratory system functions of the female elderly in the community dwelling.