• Journal of Ocean Engineering and Technology
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• v.28 no.1
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• pp.64-68
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• 2014

This study was conducted to investigate the durability of carbon fiber/epoxy composites (CFRP) in a saline water environment. The carbon fiber/epoxy composites were modified to use nanoparticles such as carbon nanotubes and titanum oxide. These hybrid composites were exposed to a saline water environment for a certain period. The weight gain according to the immersion time, a quasi-static tensile test, and micro-graphic characterization were used to investigate the samples exposed to the saline water environment. The weight gains increased with increasing immersion time. The weight gains of the hybrid composites were lower than that for pure CFRP throughout the entire immersion time. The tensile strengths decreased with increasing immersion time. The tensile strengths of the hybrid composites were higher than that of the pure CFRP throughout the entire immersion time. The pure CFRP was observed to be more degraded than the hybrid composites in the saline water environment. Therefore, it was concluded that the addition of nanoparticles to CFRP could lead to improved durability in a saline water environment.

• Journal of Magnetics
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• v.21 no.1
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• pp.141-147
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• 2016

Staphylococcus aureus cultures exposed to rotating magnetic field (RMF) were studied in order to analyse the possible induced changes in staphylococcal enterotoxin genes (se) expression. Liquid cultures of S. aureus strains carrying different se were exposed to the RMF of magnetic frequency 50 Hz and magnetic induction 34 mT for 10 h at $37^{\circ}C$. Three time points of bacterial growth cycle were considered for RNA extractions. Gene expression analyses were evaluated using real-time quantitative PCR method. The present study confirmed, that the RMF can stimulate the growth rate of S. aureus cultures in comparison to the unexposed controls, while the stimulation is not strain dependent. The studies have also shown, that the RMF, depending on the exposure time but regardless the bacterial strain, can influence on the expression of various se. In general, except for sea, as a result of bacterial exposure to the RMF through subsequent growth phases, the expression of se decreased, reaching the values below results recorded for unexposed controls. In the case of sea expression remained at a lower level as compared to the control, regardless the time of exposition.

• Computers and Concrete
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• v.15 no.4
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• pp.643-671
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• 2015

Chloride induced reinforcement corrosion is widely accepted to be the most frequent mechanism causing premature degradation of reinforced concrete members, whose economic and social consequences are growing up continuously. Prevention of these phenomena has a great importance in structural design, and modern Codes and Standards impose prescriptions concerning design details and concrete mix proportion for structures exposed to different external aggressive conditions, grouped in environmental classes. This paper focuses on reinforced concrete column section load carrying capacity degradation over time due to chloride induced steel pitting corrosion. The structural element is considered to be exposed to marine environment and the effects of corrosion are described by the time degradation of the axial-bending interaction diagram. Because chlorides ingress and consequent pitting corrosion propagation are both time-dependent mechanisms, the study adopts a time-variant predictive approach to evaluate residual strength of corroded reinforced concrete columns at different lifetimes. Corrosion initiation and propagation process is modelled by taking into account all the parameters, such as external environmental conditions, concrete mix proportion, concrete cover and so on, which influence the time evolution of the corrosion phenomenon and its effects on the residual strength of reinforced concrete columns sections.

• Composites Research
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• v.30 no.6
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• pp.422-428
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• 2017

The moisture absorption behavior, tensile properties, and thermal analysis properties of MWCNT embedded nanocomposites exposed to temperature and moisture were evaluated. The contents of MWCNT were 0 wt%, 1 wt%, and 2 wt%, respectively. The specimens were exposed to immersed conditions at $25^{\circ}C$ and $75^{\circ}C$ for up to 600 hours. According to the results, the apparent moisture content increased as the exposure time increased, but the difference between the maximum moisture content and the moisture content at 600 hours was almost constant. The tensile modulus decreased with increasing exposure time and the degree of decrease was increased significantly as the MWCNT content and exposure temperature increased. The tensile strength decreased with longer exposure time without MWCNT, but increased with MWCNT due to the reinforcing effect of MWCNT. The storage modulus, glass transition temperature, tan d peak magnitude were low as the exposure time increased, but tan d curves with two peaks appeared when exposed to high exposure temperature for more than 300 hours.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.989-992
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• 2008

In this paper, we are presenting a case that integrates ultra high strength concrete(150MPa) with surface-exposed concrete. Ahead of the field application, we carried out laboratory experiment and B/P Test for a basic property of concrete(slump flow, air content, 50cm flow time, elapse time change and compression strength) and productivity. The next, we conducted Mock-up Test using simulation specimen to evaluate infilling, surface-finishing and hydration heat of concrete. We had satisfactory results for a basic property and hydration heat of concrete. However at the time of field application, it was occurred rupture of formwork because of high lateral pressure of concrete, and then formwork was reinforced and case-in-place time was adjusted. And regardless of low and high frequency vibration, it occurred to surface-pockmark. In case that applies ultra high strength concrete to surface-exposed concrete, we estimate that it is important of systematic management and improvement of construction.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.11
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• pp.1012-1018
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• 2016

We perform a electromagnetic analysis method for indirect effects of a high-conductive structure such as an aircraft exposed by lightning, by using the finite-difference time-domain(FDTD) method. The lightning waveform used to analyze indirect effects has low frequency spectrum and high-conductive materials such as aluminum and carbon fiber composite materials have very short skin depths, and thus, it requires large memory and long computation time using conventional three dimensional FDTD analysis method. We develop an efficient electromagnetic analysis method suitable for lightning and high-conductive structures. The developed analysis method is based on two dimensional FDTD and impedance network boundary condition(INBC) algorithms and we investigate the indirect effects on the structures exposed to lightning.

• Journal of the Korean housing association
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• v.14 no.3
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• pp.51-56
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• 2003

All the outdoor and indoor spaces are connected with each other. The human being moves toward those spaces with temperature fluctuation between the natural and artificial temperature. We conducted an experiment which subjects were wearing the data logger in urban life, and measured 24 hours' exposed temperature and thermal comfort in summer. Results were as follows. 1. Subjects controls their micro climate like this. Most of them(84.6%) get weather information. Fashion(46.2%) and weather(30.8%) are the reasons to select clothes. They spend their time in indoor environment for 84.92% hours of a day and have an air-conditioner(61.5%) in their houses. 2. Temperature fluctuation which subjects were exposed for 24 hours were from 15.6$^{\circ}C$ to 33.8$^{\circ}C$ and average fluctuation was 9.02$^{\circ}C$. The median value of experienced temperature were 26-26.5$^{\circ}C$ and average temperature was 26.18$^{\circ}C$. They experienced cold shock of 3.96 times in a day.

• Journal of information and communication convergence engineering
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• v.10 no.2
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• pp.135-140
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• 2012

Massive numbers of users of social networks share various types of information such as opinions, news, and ideas in real time. As a new form of social network, Twitter is a particularly useful information source. Studying influence can help us better understand the role of social networks. The popularity of social networks like Twitter is primarily measured by the number of followers. The number of followers in Twitter and the number of users exposed to news media are important factors in measuring influence. We chose Twitter and the New York Times as representative media to analyze the influence and present an empirical analysis of these datasets. When the correlation between the number of followers in Twitter and the number of users exposed to the New York Times is computed, the result is moderately high. The correlation between the number of users exposed to the New York Times and the number of sections including the users on it, was found to be very high. We measure the normalized influence score using our proposed expression based on the two correlation coefficients.

• Journal of the Korean Ceramic Society
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• v.37 no.2
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• pp.181-185
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• 2000

A new technique capable of accelerating the crystallization of ferrite powder at low temperature is developed. Effects of the ultrasonic waves on the crystallization were studied for ferrite powders prepared using the co-precipitation method. The crystallization of the ferrite powders exposed to the ultrasonic waves were characterized by the XRD. The amorphous ferrite powders prepared using the co-precipitation method were crystallized as a result of the exposure to the ultrasonic waves for 5h and the crystallization of the ferrite powders became more enhanced in proportion to the time exposed. The ferrite powder exposed to the ultrasonic waves for 25h had higher crystallinity a larger specific surface area than the ferrite powder calcined at 500$^{\circ}C$ for 2h.

• ALGAE
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• v.21 no.4
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• pp.471-477
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• 2006

Amphora costata W. Smith 1853 is a down thrown diatom species and also known as metal corrosive ship-fouling organism. A. costata was isolated from Alang ship breaking yard, Alang and evaluated the toxicity tolerance and growth responses of the cultures exposed to different doses of toxic and relatively accessible heavy metals, such as Fe, Mn, Cd, Co, Cu, Zn, Ni, and Pb in the constantly monitored laboratory culture conditions. The strongest toxic effect was observed on A. costata exposed to Cd even at relatively low concentrations as compared to other metals. The following trend of decreasing order of toxicity i.e. Cd>Zn>Ni>Co>Pb>Cu>Fe was observed, when they were exposed to equal concentration and expose time.