• Journal of Korean Society for Atmospheric Environment
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• v.30 no.6
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• pp.577-585
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• 2014

A series of experiments using atmospheric-pressure non-thermal plasma coupled with transition metal catalysts were performed to remove ethylene from agricultural storage facilities. The non-thermal plasma was created by dielectric barrier discharge, which was in direct contact with the catalyst pellets. The transition metals such as Ag and $V_2O_5$ were supported on ${\gamma}-Al_2O_3$. The effect of catalyst type, specific input energy (SIE) and oxygen content on the removal of ethylene was examined to understand the behavior of the hybrid plasma-catalytic reactor system. With the other parameters kept constant, the plasma-catalytic activity for the removal of ethylene was in order of $V_2O_5/{\gamma}-Al_2O_3$ > $Ag/{\gamma}-Al_2O_3$ > ${\gamma}-Al_2O_3$ from high to low. Interestingly, the rate of plasma-catalytic ozone generation was in order of $V_2O_5/{\gamma}-Al_2O_3$ > ${\gamma}-Al_2O_3$ > $Ag/{\gamma}-Al_2O_3$, implying that the catalyst activation mechanisms by plasma are different for different catalysts. The results obtained by varying the oxygen content indicated that nitrogen-derived reactive species dominated the removal of ethylene under oxygen-lean condition, while ozone and oxygen atoms were mainly involved in the removal under oxygen-rich condition. When the plasma was coupled with $V_2O_5/{\gamma}-Al_2O_3$, nearly complete removal of ethylene was achieved at oxygen contents higher than 5% by volume (inlet ethylene: 250 ppm; gas flow rate: $1.0Lmin^{-1}$; SIE: ${\sim}355JL^{-1}$).

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.458-465
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• 2009

In general, ultrasonic guided wave techniques that used for an evaluation of the internal defect have been applied without considering energy loss. It can be found out that the significant attenuation is observed in the signal of structure with defect by the scattering and absorption. Even in the signal acquired from defect-free structure, this attenuation can be also significant. Therefore, it is very essential to determine the Lamb wave propagation characteristics depending on modes because the dispersibility of Lamb wave can be easily influenced by the attenuation effect with frequency and thickness. For this reason, changing the propagation distance, attenuation coefficient of each Lamb wave mode needs to be investigated by the contact pitch-catch method with PZT(piezoelectric) sensors. In this paper, the experimental attenuation coefficient is measured by choosing the following three different variables; mode, thickness and plate materials. As a result, experimental attenuation coefficient is obtained as the function of variables.

• Tribology and Lubricants
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• v.36 no.1
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• pp.39-46
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• 2020

Air stages are usually applied to precision engineering in sectors such as the semiconductor industry owing to their excellent performance and extremely low friction. Since the productivity of a semiconductor depends on the acceleration and deceleration performance of the air stage, many attempts have been made to improve the speed of the stage. Even during sudden start or stop sequences, the stage should maintain an air film to avoid direct contact between pad and the rail. The purpose of this study is to quantitatively predict the dynamic behavior of the air stage when acceleration and deceleration occur. The air stage is composed of two parts; the stage and the guide-way. The stage transports objects to the guideway, which is supported by an externally pressurized gas bearing. In this study, we use COMSOL Multiphysics to calculate the pressure of the air film between the stage and the guide-way and solve the two-degree-of-freedom equations of motion of the stage. Based on the specified velocity conditions such as the acceleration time and the maximum velocity of stage, we calculate the eccentricity and tilting angle of the stage. The result shows that the stiffness and damping of the gas bearing have non-linear characteristics. Hence, we should consider the operating conditions in the design process of an air stage system because the dynamic behavior of the stage becomes unstable depending on the maximum velocity and the acceleration time.

• Transactions of Materials Processing
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• v.16 no.7
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• pp.521-529
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• 2007

This paper is concerned with the analysis on the surface expansion of AA 2024 and AA 1100 aluminum alloys in backward extrusion process. Due to heavy surface expansion appeared usually in the backward can extrusion process, the tribological conditions along the interface between the material and the punch land are very severe. In the present study, the surface expansion is analyzed especially under various process conditions. The main goal of this study is to investigate the influence of degree of reduction in height, geometries of punch nose, friction and hardening characteristics of different aluminum alloys on the material flow and thus on the surface expansion on the working material. Two different materials are selected for investigation as model materials and they are AA 2024 and AA 1100 aluminum alloys. The geometrical parameters employed in analysis include punch corner radius and punch nose angle. The geometry of punch follows basically the recommendation of ICFG and some variations of punch geometry are adopted to obtain quantitative information on the effect of geometrical parameters on material flow. Extensive simulation has been conducted by applying the rigid-plastic finite element method to the backward can extrusion process under different geometrical, material, and interface conditions. The simulation results are summarized in terms of surface expansion at different reduction in height, deformation patterns including pressure distributions along the interface between workpiece and punch, comparison of surface expansion between two model materials, geometrical and interfacial parametric effects on surface expansion, and load-stroke relationships.

• Journal of Korean Society of Water and Wastewater
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• v.30 no.2
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• pp.167-177
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• 2016

This work investigated the decomposition of aqueous anatoxin-a originated from cyanobacteria using an underwater dielectric barrier discharge plasma system based on a porous ceramic tube and an alternating current (AC) high voltage. Plasmatic gas generated inside the porous ceramic tube was uniformly dispersed in the form of numerous bubbles into the aqueous solution through the micro-pores of the ceramic tube, which allowed an effective contact between the plasmatic gas and the aqueous anatoxin-a solution. Effect of applied voltage, treatment time and the coexistence of nutrients such as $NO_3{^-}$, $H_2PO_4{^-}$ and glucose on the decomposition of anatoxin-a was examined. Chemical analyses of the plasma-treated anatoxin-a solution using liquid chromatography-mass spectrometry (LC-MS) and ion chromatography (IC) were performed to elucidate the mineralization mechanisms. Increasing the voltage improved the anatoxin-a decomposition efficiency due to the increased discharge power, but the energy required to remove a given amount of anatoxin-a was similar, regardless of the voltage. At an applied voltage of 17.2 kV (oxygen flow rate: $1.0L\;min^{-1}$), anatoxin-a at an initial concentration of $1mg\;L^{-1}$ (volume: 0.5 L) was successfully treated within 3 min. The chemical analyses using LC-MS and IC suggested that the intermediates with molecular weights of 123~161 produced by the attack of plasma-induced reactive species on anatoxin-a molecule were further oxidized to stable compounds such as acetic acid, formic acid and oxalic acid.

• Journal of Korean Society of Water and Wastewater
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• v.32 no.3
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• pp.243-251
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• 2018

In this study, we compared the MZVI (Microscale Zero-Valent Iron) and NZVI (Nanoscale Zero-Valent Iron) for reactivity and mobility in a column to reduce nitrate, which is a major pollutant in Korea, and investigated the effect of operational parameters on the NZVI filled column. For the comparison of MZVI and NZVI, samples were collected for 990 minutes using fractionator in the similar operation conditions (MZVI 10g, NZVI 2g). The nitrate reduction efficiency of NZVI was about 5 times higher than that of MZVI, which was about 7.45% and 38.75% when using MZVI and NZVI, respectively. In the mobility experiment, the MZVI descended due to gravity while NZVI moved up with water flow due to its small size. Furthermore, the optimum condition of NZVI filled column was determined by changing the flow rate and pH. The amount of Fe ions was increased as the pH of the nitrate solution was lowered, and the nitrate removal rate was similar due to the higher yield of hydroxyl groups. The removal rate of nitrate nitrogen was stable while flow rate was increased from 0.5 mL/min to 2.0 mL/min (empty bed contact time: 2.26 min to 0.57 min). NZVI has a high reduction rate of nitrate, but it also has a high mobility, so both of reactivity and mobility need to be considered when NZVI is applied for drinking water treatment.

• Membrane Journal
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• v.19 no.1
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• pp.25-33
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• 2009

PES (polyethersulfone) membranes with highly enhanced their asymmetry were prepared by phase inversion process. The membranes were prepared by using PES/DMF (N,N-dimethylformamide)/TSA (p-toluenesulfonic acid)/PVP (polyvinylpyrrolidone) casting solution and water coagulant. The pre-coagulation of membrane surface which was induced by an addition of TSA as a demixing agent and PVP as a swelling polymer in the PES solution and humid exposure time, played a crucial role in determining morphological properties and the PWP (pure water permeation) performance. The PES solution was coated on polyester film under condition of 80% humidity for a while ($72{\sim}144$ sec) before immersing in a coagulation bath. The characterization of membranes was carried out by a capillary flow porometer, a FE-SEM and a permeation test apparatus. As the thickness of the smallest pore size layer (SPL) decreased, the asymmetry of membrane increased under conditions of 20 wt% of TSA and 10 wt% of PVP in 11 wt% of PES solution during longer humid contact time. As a result, the membranes showed a remarkable increase of PWP.

• Korean Journal of Microbiology
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• v.28 no.1
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• pp.76-82
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• 1990

In samples taken from mouth of the Nakdong River, mercury-resistant bacteria grown on the media supplemented with over 20 ppm of mercuric chlorice were below 0.3% of all aerobic heterotrophs. Among them, seven strains grown over 100 ppm of mercuric chloride were isolated and all were identified as Pseudomonas. The toxic effect of mercury on the growth of the most resistant strain N14 was influenced by the organic compounds and concentration. The growth and physiological activity to N14 strain were affected by toxic mercury in the early stage: The viable count and glucose turn over rate of N14 strain dropped to the lowest level as soon as the bacteria came into contact with mercury. During the extended lag period, however, bacteria accommodated to the stress and the viable count and glucose turnover rate increased. After the lag period, bacteria began to proliferate and their growth reached similar level to that of control. In crude extracts of N14 strain grown in nutrient browth containing. $10{\mu}M$ $HgCl_{2}$, a mercuric ion dependent oxidation of NADPH was demonstrated. Therefore the mechanism of mercury-resistance of the N14 strain involved the elimination of the mercury from growth media. In the N14 strain which a wide range of resistance to antibiotics was observed in, four multiple plasmids were detected. As a result, the supposition that N14 strain has a plasmid-encoded enzyme system may be quite within the realms of possobility.

• Polymer(Korea)
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• v.29 no.2
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• pp.172-176
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• 2005

Environmentally friendly water dispersion polyurethanes containing fluorine were prepared with a fluorinated polyol having $62\%$ of fluorine $(Fluorolink^{(R)}\;M_n\;1000)$. In order to control the fluorine contents of the synthesized polyurethanes polytetramethylene glycol (PTMG2000) and $Fluorolink^{(R)}$ were mixed at assigned ratios and reacted with isophorone diisocyanate (IPDI) as a diisocyanate used. Introducing hydrophilic anion to the polymer chain was achieved by applying dimethyl propionic acid (DMPA). The ionic groups were neutralized with triethyl amine (TEA) before dispersion into water. Chain extension was executed by adding ethylene diamine at the final stage. Mechanical properties of the polymers showed that modulus increased with increasing $Fluorolink^{(R)}$ content. Surface energy values obtained from contact angle measurement decreased with increasing $Fluorolink^{(R)}$ content up to $20\%$. We expect that the synthesized polyurethanes present reliable effect from the fluorine atoms incorporated even at a small amount of $Fluorolink^{(R)}$.

• Journal of agricultural medicine and community health
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• v.35 no.1
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• pp.46-55
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• 2010

Objectives: The aim of this study was to investigate the association of social support and quality of life of stroke patients. Methods: Stroke patients were interviewed by a direct contact survey among 160 person. A structured questionnaire was configured about demographic features, social support and health related quality of life(SF12). Data were collected from July to August 2009. Results: Among social support, satisfaction of dependable when you need help is the highest score(5.3) and console you when you are very upset is the lowest(4.0). Vitality among health related quality of life(HRQOL) is the higest score(55.9) and general health score is the the lowest(17.4). Physical component score(PCS) is lower than mental component. The results of multiple regression analysis about the factors affecting the PCS and MCS score, disability grade and feel better variable gave effect HRQOL. Conclusions: For improvement of HRQOL, among stroke patients, community social support, specially, when patients feeling generally down-in-the dumps, the rely on to help feel better was needed.