• Applied Chemistry for Engineering
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• v.35 no.1
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• pp.16-22
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• 2024

Polymer electrolyte membrane fuel cells have the advantage of low operating temperatures and fast startup and response characteristics compared to others. Simulation studies are actively researched because their cost and time benefits. In this study, the resistance of water residual in the gas diffusion layer (GDL) of the unit cell was added to the existing equation to compare the actual data with the model data. The experiments were conducted with a 25 cm² unit cell, and the samples were separated into stopping times of 0, 10, and 60 minutes following primary impedance measurement, activation, and polarization curve data acquisition. This gives 0, 10, and 60 minutes for the residual water in the GDL to evaporate. Without the rest period, the magnitude of the performance improvement was not significantly different at the same potential and flow rate, but the rest period did improve the performance of the membrane electrode assembly when measuring impedance. By changing the magnitude of the resistance reduction to an overvoltage, the voltage difference between the fuel cell model with and without residual water was compared, and the error rate in the high current density region, which is dominated by concentration losses, was reduced.

• The Journal of Pediatrics of Korean Medicine
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• v.24 no.2
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• pp.99-111
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• 2010

Objectives The objectives of this study were to evaluate the correlations between the indices of obesity and percentage body fat by bioelectrical impedance analysis(BIA). Also, this study was designed to define the cut off values of percentage body fat by BIA which would represent BMI and degree of obesity in order to detect overweight and obesity in preschool children. Methods The height and weight of 683 children aged four to six years old were measured. Also, percentages of body fat were measured by BIA. Results There were high correlations between the boy's body fat percentages and degree of obesity(r=790). Also, there were high correlations between the girl's body fatpercentages and BMI(r=778). The cut off values of body fat percentage, which would correspond to those of BMI percentiles, were calculated by ROC curve analysis. To classify as an overweight, the correspondent cut off values of body fat percentage were 19.55% in boys and 22.35% in girls. For obesity, the cut off values were 28.80% in boys and 27.60% in girls. The cut off values of body fat percentage, which would correspond to degree of obesity were calculated by ROC curve analysis. To classify as an overweight, the correspondent cut off values of body fat percentage were 19.75% in boys and 22.35% in girls. For obesity, the cut off values were 29.05% in boys and 28.75% in girls. Conclusions According to the BMI criteria by the Korean pediatrics society in 2007, the most appropriate cut off values of body fat percentage in for four to six years old children were follows; for boys, 19.55% considered as overweight, and 28.80% as obese while for girls, 22.35% considered as overweight and 27.60% as obese. According to suggested degree of obesity criteria, the most appropriate cut off values of body fat percentage in for four to six old children were were follows; For boys, 19.75% was considered as overweight, and 29.05% as obesity. For girls, 22.35% was considered as overweight, and 28.75% as obese.

• Tuberculosis and Respiratory Diseases
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• v.72 no.5
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• pp.433-440
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• 2012

Background: The pulmonary function test is the most basic test method to diagnosis lung disease. The purpose of this study was to research the correlation of the body mass index (BMI), the fat percentage of the body mass (fat%), the muscle mass, the fat-free mass (FFM) and the fat-free mass index (FFMI), waist-hip ratio (WHR), on the forced expiratory volume curve. Methods: Between March and April 2009, a total of 291 subjects were enrolled. There were 152 men and 139 female (mean age, $46.3{\pm}9.92$ years), and they were measured for the following: forced vital capacity (FVC), forced expiratory volume at 1 second ($FEV_1$), and forced expiratory flow during the middle half of the FVC ($FEF_{25-75}$) from the forced expiratory volume curve by the spirometry, and the body composition by the bioelectrical impedance method. Correlation and a multiple linear regression, between the body composition and pulmonary function, were used. Results: BMI and fat% had no correlation with FVC, $FEV_1$ in male, but FFMI showed a positive correlation. In contrast, BMI and fat% had correlation with FVC, $FEV_1$ in female, but FFMI showed no correlation. Both male and female, FVC and $FEV_1$ had a negative correlation with WHR (male, FVC r=-0.327, $FEV_1$ r=-0.36; p<0.05; female, FVC r=-0.175, $FEV_1$ r=-0.213; p<0.05). In a multiple linear regression of considering the body composition of the total group, FVC explained FFM, BMI, and FFMI in order ($r^2$=0.579, 0.657, 0.663). $FEV_1$ was explained only fat% ($r^2$=0.011), and $FEF_{25-75}$ was explained muscle mass, FFMI, FFM ($r^2$=0.126, 0.138, 0.148). Conclusion: The BMI, fat%, muscle mass, FFM, FFMI, WHR have significant association with pulmonary function but $r^2$ (adjusted coefficient of determination) were not high enough for explaining lung function.

• Korean Journal of Crystallography
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• v.16 no.2
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• pp.141-148
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• 2005

It is well known that the general metals have a lot of grain boundaries. The grain boundaries play a negative role to increase the resistivity and to decrease the conductivity. The small resistivity and the large conductivity have been a goal of the material scientists, and no signal noise, perfect signal transfer, and the realization of the real sound are the dream of electronic engineers and audio manias. Generally, oxygen free copper (OFC) and Ohno continuous casting (OCC) copper cables have been used for the purpose of the precise signal transfer and low noise. However they still include a lot of grain boundaries. In our study, we have grown the single crystal by the Czochralski method and succeeded to produce single crystal wires from the crystal in the dimension of $0.5{\times}0.5{\times}2500mm$. The produced wire still possesses very good single crystal properties. We observed the structure of the wire, and measured the resistance and impedance. Glow Discharge Spectrometer (GDS) was used for analyzing the compositions of copper single crystals and commercial copper. Current-Voltage curve, resistance, total harmonic distortion and speaker frequency response were measured for comparing electrical and acoustic properties of two samples.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.308-308
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• 2013

본 연구에 염료감응형 태양전지(Dye Sensitized Solar Cells; DSSCs)의 광전변환효율을 높이기 위해 작업전극에 새로운 구조의 광투과층 및 산란층을 도입하였다. DSSCs 작업전극의 빛을 투과시키는 투과층에 크기가 10 nm 이하의 nanoparticle $TiO_2$를 적용하고, 투과된 빛이 산란되어 많은 전자가 여기 될 수 있도록 기존의 큰 입자 사이즈였던 산란층을 이용하는 대신 $TiO_2$ nanorod 및 nanotube 형태의 구조를 도입하여 기존의 작업전극과 비교하였다. 산란층에서 방향성을 가지는 rutile 상의 $TiO_2$는 저온에서 안정적인 anatase 상의 $TiO_2$보다 화학적으로 안정하며, 높은 산란율을 가지고, 광에 의해 여기된 전자를 직접적으로 집전전극에 전달해 줌으로서 소자의 효율을 증가시킨다고 보고되고 있다. Rutile 상의 $TiO_2$ 층 제작 시 수열합성법을 이용하면 nanorod 모양의 $TiO_2$층을 형성할 수 있고, 이와 같은 방법으로 성장시킨 산란층에 전기영동법의 식각 효과를 사용하면 nanotube 모양의 $TiO_2$층을 성장시킬 수 있어 산란효과의 극대화 및 전극의 표면적을 넓히는 장점이 있다. 각각의 방법을 이용하여 만든 구조 위에 입자 크기 10 nm의 $TiO_2$를 Dr blade 방법으로 도포하여 double layer (산란층+흡수층)로 구성된 작업 전극을 이용한 DSSCs를 제작한 후 I-V curve와 EIS (Electrochemical Impedance Spectroscopy)를 측정하여 효율 및 전기화학적 특성을 분석하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.12
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• pp.6098-6105
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• 2013

In the present study, the characteristics of corrosion and thermal conductivity of thermal spray coatings for seawater heat exchangers were examined experimentally. The coating types of theZn and Al thermal spray coatings with additional epoxy and silicone sealers were tested. To examine the corrosion characteristics of the thermal spray coating, the cyclic voltamogram curve was measured followed by SEM imaging for surface characterization. The laser flash method was usedto measure the thermal conductivity of the specimen. The conductivity test results showed that thermal conductivity decreased by3 ~ 4% with the silicone sealer and decreased by 70 ~ 75% with the epoxy sealer.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.4
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• pp.103-109
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• 2010

In this paper, breakdown characteristics of soil in a coaxial cylindrical electrode system stressed by impulse currents were experimentally investigated. The breakdown voltage and current waveforms for 4 types of soils were measured, and the threshold electric field intensity, the time-lag to breakdown and the voltage-current (V-I) curves were analyzed and discussed. As a result, the breakdown voltage and current waveforms are strongly dependent on the grain size of soil, and the voltage and current waveforms for gravel and sand differ from those for silt and loess. The threshold electric field intensity Ec is increased in the order of gravel, sand, loess and silt. The V-I curves for all test samples show a 'cross-closed loop' of ${\infty}$-shape. Also, the time-lag to breakdown for gravel and sand are longer than those for silt and loess. It is expected that the results presented in this paper will provide useful information on the design of improving transient performance of a grounding electrode system subjected to lightning current considering the soil ionization.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.9
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• pp.740-753
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• 2008

The conventional Split Hopkinson Pressure Bar (C-SHPB) technique with aluminum pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials such as hot temperature degraded POM (Poly Oxy Methylene) and PP (Poly Propylene) to obtain more distinguishable experimental signals is used to obtain a dynamic behavior of material deformation under a high strain rate loading condition. An experimental modification with Pulse shaper is introduced to reduce the nonequilibrium on the dynamic material response during a short test period to increase the rise time of the incident pulse for two polymeric materials. For the dynamic stress strain curve obtained from SHPB experiment under high strain rate, the Johnson-Cook model is applied as a constitutive equation, and we verify the applicability of this constitutive equation to the probabilistic reliability estimation method. The methodology to estimate the reliability using the probabilistic method such as the FORM and the SORM has been proposed, after compose the limit state function using Johnson-Cook model. It is found that the failure probability estimated by using the SORM is more reliable than those of the FORM, and the failure probability increases with the increase of applied stress. Moreover, it is noted that the parameters of Johnson-Cook model such as A and n, and applied stress affect the failure probability more than the other random variables according to the sensitivity analysis.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.4
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• pp.286-297
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• 2017

This paper is a study of 6~18 GHz wideband high power amplifier which is composed of 10 single amplifier and coaxial type spatial power combiner. The property of this spatial power combiner is on a similar principle to antipodal antenna radiation mechanism. Therefore, the key structure of proposed spatial power combiner is the antipodal finline PCB board and the finline curve shape is numerically synthesized by using Klopfensein's optimum impedance taper. The measured CW output power of spatial combined high power amplifier is nearly 50 W. In conclusion we prove the good combining performance between the spatial power combiner and 10 single amplifier over 6~18 GHz frequency ranges. Also, we developed the key component PA and MFC MMIC which controls the phase and gain of the each amplifier, The main characteristic of MFC MMIC is to maximize combining efficiency of power amplifier.

• Journal of the Korean Electrochemical Society
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• v.23 no.3
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• pp.73-80
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• 2020

Fenton oxidation method using hydrogen peroxide is an eco-friendly oxidation method used in water treatment and soil restoration. When removing pollutants by this method, it is quite important to properly regulate the concentration of hydrogen peroxide according to the concentration of the contaminants. In this study, electrochemical biosensors using HRP (horseradish peroxidase) enzymes were manufactured and studies were conducted on the activity of enzymes and the detection characteristics of hydrogen peroxide. HRP were electro deposited with chitosan and AuNP on the working electrode surface of the SPCE (Screen Printed Carbon Electrode). Then, the fixation of enzymes was confirmed using the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The activity of HRP enzymes was also identified from chronoamperometry (CA) and UV spectroscopy. After immersing the biosensor in PBS solution the current generated from electrodes by titrating hydrogen peroxide was measured from CA analysis. The generated current increased linearly for the concentration of hydrogen peroxide, and a calibration curve was derived that could predict the concentration of hydrogen peroxide from the current.