• Structural Engineering and Mechanics
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• 제63권6호
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• pp.725-734
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• 2017

This paper investigated the effects of rebar corrosion on bond performance between rebar and two different concrete mixes (compressive strengths of 20.7 MPa and 44.4 MPa). The specimen was designed as a rebar centrally embedded in a 200 mm concrete cube, with two stirrups around the rebar to supply confinement. An electrochemical accelerated corrosion technique was applied to corrode the rebar. 120 specimens of two different concrete mixes with various reinforcing steel corrosion levels were manufactured. The corrosion crack opening width and length were recorded in detail during and after the corrosion process. Three different loading schemes: monotonic pull-out load, 10 cycles of constant slip loading followed by pull-out and varied slip loading followed by pull-out, were carried out on the specimens. The effects of rebar corrosion with two different concrete mixes on corrosion crack opening, bond strength and corresponding slip value, initial slope of bond-slip curve, residual bond stress, mechanical interaction stress, and energy dissipation, were discussed in detail. The mean value and coefficient of variation of these parameters were also derived. It was found that the coefficient of variation of the parameters of the corroded specimens was larger than those with intact rebar. There is also obvious difference in the two different concrete mixes for the effects of rebar corrosion on bond-slip parameters.

• The Korean Journal of Physiology
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• 제14권1호
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• pp.7-13
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• 1980

In the previous experiment, authors have shown that during the latter half of estrous cycle there was an increase in plasma testosterone level in the rats stimulated with hCG. To determine the physiologic significance of elevated plasma testosterone, changes of the plasma concentrations of TeBG and testosterone following hCG stimulation were analyzed in the rats having a regular 5 day cycle. The rats were divided into three groups; the control, the rats stimulated with single hCG on the day of proestrus and stimulated with hCG throughout the entire cycle. Blood samples were obtained once a day for an estrous cycle and analyzed for the binding capacity of TeBG using ammonium sulphate precipitation method and testosterone concentration by means of radioimmunoassay. Followings were the results; 1) There was no significant variation in the binding capacity of TeBG in peripheral blood during the estrous cycle of the control rats. 2) No cyclic variation in the binding capacity of TeBG was observed in the rats stimulated with single hCG on proestrus. although the levels tended to be higher in the rats with stimulation than in the control rats. 3) Continual stimulation of hCG produced a marked increase in the binding capacity of TeBG especially on the day of metaestrus. 4) The changes in the plasma level of testosterone followed the same basic pattern seen in the TeBG binding capacity. 5) From above results, the followings were suggested. a. hCG related increase of the binding capacity of TeBG is probably secondary to a modest increase in estrogen as well. b. hCG related increase of plasma testosterone in female rats is not entirely due to excess production rather in part due to decreased metabolism induced by the rise in TeBG. c. It seems likely that most of elevated testosterone shown in the rat stimulated with hCG is bound to TeBG and only small portion is unbound form which influence cellular activity. It is rather possible that an increase in TeBG could augment estrogen activity.

• 한국대기환경학회지
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• 제33권2호
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• pp.174-183
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• 2017

The background level and timely variation characteristics of atmospheric $^{222}Rn$ concentrations have been evaluated by the real time monitoring at Gosan site of Jeju Island, Korea, during 2008~2015. The average concentration of atmospheric radon was $2,480mBq\;m^{-3}$ for the study period. The cyclic seasonality of radon was characterized such as winter maximum and summer minimum, consistent with the reduction in terrestrial fetch going to summer. On monthly variations of radon, the mean concentration in October was the highest as $3,041mBq\;m^{-3}$, almost twice as that in July ($1,481mBq\;m^{-3}$). The diurnal radon concentrations increased throughout the nighttime approaching to the maximum ($2,819mBq\;m^{-3}$) at around 7 a.m., and then gradually decreased throughout the daytime by the minimum ($2,069mBq\;m^{-3}$) at around 3 p.m. The diurnal radon cycle in winter showed comparatively small amplitude due to little variability in atmospheric mixing depth, conversely, large amplitude was observed in summer due to relatively a big change in atmospheric mixing depth. The cluster back-trajectories of air masses showed that the high radon events occurred by the predominant continental fetch over through Asia continent, and the radon concentrations from China continent were about 1.9 times higher on the whole than those from the North Pacific Ocean. The concentrations of $PM_{10}$ also increased in proportion to the high radon concentrations, showing a good linear correlation between $PM_{10}$ and radon concentrations.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 C
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• pp.2410-2412
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• 2005

In this study, two types of PS substrate were fabricated for sensing of chemical and biological substances. For sensing of the humidity and chemical analyzes such as $CH_3OH$ or $C_2H_5OH$, PS layers are prepared by photoelectrochemical etching of silicon wafer in aqueous hydrofluoric acid solution. To evaluate their sensitivity, we measured the resistance variation of the PS diaphragm. As the amplitude of applied voltage increases from 2 to 6Vpp at constant frequency of 5kHz, the resistance variation for humidity sensor rises from 376.3 to $784.8{\Omega}$/%RH. And the sensitivities for $CH_3OH$ and $C_2H_5OH$ were 0.068 uA/% and 0.212 uA/%, respectively. For biological sensing application, amperometric urea sensors were fabricated based on porous silicon(PS), and planar silicon(PLS) electrode substrates by the electrochemical methods. Pt thin film was sputtered on these substrates which were previously formed by electrochemical anodization. Poly (3-methylthiophene) (P3MT) were used for electron transfer matrix between urease(Urs) and the electrode phase, and Urs also was by electrochemically immobilized. Effective working area of these electrodes was determined for the first time by using $Fe(CN)_6^{3-}/Fe(CN)_6^{4-}$ redox couple in which nearly reversible cyclic voltammograms were obtained. The $i_p$ vs $v^{1/2}$ plots show that effective working electrode area of the PS-based Pt thin film electrode was 1.6 times larger than the PLS-based one and we can readily expect the enlarged surface area of PS electrode would result in increased sensitivity by ca. 1.6 times. Actually, amperometric sensitivity of the Urs/P3MT/Pt/PS electrode was ca 0.91uA/$mM{\cdot}cm^2$, and that of the Urs/P3MT/Pt/PLS electrode was ca. 0.91uA/$mM{\cdot}cm^2$ in a linear range of 1mmol/L to 100mmol/L urea concentrations

• 대한기계학회논문집A
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• 제21권7호
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• pp.1058-1072
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• 1997

A head-neck complex dummy, for measuring brain pressure and reaction force in the cervical spine was developed for experimental study related in injury mechanism. Dummy comprised aluminium-casted head with water filled cavity for simulating brain and mechanical neck assembled with six motion segments. Several kinds of experiments (compression, bending, cyclic modulus, relaxation and constant velocity profile) for the developed mechanical neck showed that this neck model is biomechanically reliable compared with in-vitro test results. As an application of developed head-neck complex dummy, shock absorbing properties of protective helmet was chosen. The experiments showed that the maximum pressure increment of brain after impact was tolerable compared with the guide line for mild brain injury pressure (25psi). Constrast to this results, the reaction force in the neck was high enough to produce failure in the cervical spine.

• 대한화학회지
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• 제58권3호
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• pp.289-296
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• 2014

Electrochemical copolymerization of o-chlorophenol (oCP) with o-hydroxyphenol (oHP) was carried out in aqueous $H_2SO_4$ by using cyclic voltammetry (CV) technique. In addition, CV was used to evaluate the differences in electrochemical characteristics of the copolymer in comparison with the corresponding homopolymers, poly(o-chlorophenol) (PoCP) and poly(o-hydroxyphenol) (PoHP). The variation of peak currents with respect to sweep rates was compared between copolymer and homopolymers, PoCP and PoHP, films. Further support for copolymer characterization was obtained by recording UV-visible, IR spectra and elemental analysis. The mechanism of the electrochemical polymerization has been discussed. The monomer reactivity ratios ($r_1$ and $r_2$) were calculated using Fineman-R$\ddot{o}$ss method and was found to be 0.4 and 1.3 repetitivelly and the copolymer structure is a block structure and more rich in oHP units.

• 한국자동차공학회논문집
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• 제14권6호
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• pp.50-56
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• 2006

Residual gas fraction in a combustion process is very crucial to improve combustion and cyclic variations. Especially, the residual gas fraction is strongly affected by backflow of the residual gas during the valve overlap period in an idle operation. Therefore, it is one of the most interesting that valve timings can affect flow characteristics of gas exchange process, especially during idle operation. This analysis investigates residual gas fraction with respect to valve timing changes which is critical for combustion efficiency and engine performance. Flow characteristics of residual gas by changing intake and exhaust valve timing are calculated by CFD methodology during an idle operation in an SI engine. It is analyzed that retarded EVO and advanced IVO results in the increase of valve overlap period and consequently, residual gas fraction. Futhermore, changes in IVO have stronger effects on variation of residual gas fraction.

• 한국자동차공학회논문집
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• 제6권2호
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• pp.212-219
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• 1998

Unburned hydrocarbon is a key contributor to both the fuel economy and emissions of automotive engine. Cyclic variation of HC emission is of importance, especially during throttle transients. The real time measurement of hydrocarbon is particularly important to obtain a better understanding of the mechanisms for combustion and emissions, especially during cold start and throttle transient condition. This paper reports the cycle resolved measurement technique of unburned hydrocarbons to quantify rapid changes of in-cylinder concentration in the vicinity of spark plug by using the Fast Response Flame Ionization Detector(FRFID). While this instrument actually measures fuel concentration, its results can be indicative of the AFR behaviour. In order to understand the rapid change of hydrocarbons with cylinder pressure, it is necessary to study the response time delay of the system, including the time associated with gas transportation to FID. And signal from FRFID is correlated with cylinder pressure data to relate changes in mixture preparation to the classic analysis, such as indicated mean effective(IMEF) and ignition delay, etc.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1332-1336
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• 2005

It could make the LIghtweight Piezoelectric Composite Actuator (LIPCA) damageable by the cyclic large deformation. If the progressive microvoid coalescence of LIPCA interlaminar took place, the decrease of the stiffness and the weakness of stress transmission and fiber bridging effect would make the fatigue characteristics worse suddenly. Therefore, it is required to study the variation of fatigue behavior and interlaminar condition in LIPCA under resonant frequencies. These studies such as the changeable fatigue phase and interlaminar behavior of LIPCA affected by the resonant frequencies should be carried out due to the strong anisotropy of CFRP layer. Hence, these studies are as follows. 1) The residual stresses distribution of interlaminar in LIPCA using the Classical Lamination Theory (CLT). 2) Comparative analysis of interlaminar behavior for the intact LIPCA versus LIPCA containing an artificial delamination during resonant frequency.

• 한국재료학회지
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• 제26권12호
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• pp.696-703
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• 2016

In this study, we intensively investigated the effect of conductive additive amount on electrochemical performance of organic supercapacitors. For this purpose, we assembled coin-type organic supercapacitor cells with a variation of conductive additive(carbon black) amount; carbon aerogel and polyvinylidene fluoride were employed as active material and binder, respectively. Carbon aerogel, which is a highly mesoporous and ultralight material, was prepared via pyrolysis of resorcinol-formaldehyde gels synthesized from polycondensation of two starting materials using sodium carbonate as the base catalyst. Successful formation of carbon aerogel was well confirmed by Fourier-transform infrared spectroscopy and $N_2$ adsorption-desorption analysis. Electrochemical performances of the assembled organic supercapacitor cells were evaluated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements. Amount of conductive additive was found to strongly affect the charge transfer resistance of the supercapacitor electrodes, leading to a different optimal amount of conductive additive in organic supercapacitor electrodes depending on the applied charge-discharge rate. A high-rate charge-discharge process required a relatively high amount of conductive additive. Through this work, we came to conclude that determining the optimal amount of conductive additive in developing an efficient organic supercapacitor should include a significant consideration of supercapacitor end use, especially the rate employed for the charge-discharge process.