• Journal of the Korean Society of Combustion
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• v.9 no.3
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• pp.27-35
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• 2004

Diode laser absorption sensors are advantageous because they may provide fast, sensitive, absolute, and selective measurements of species concentration. These systems are very attractive for practical applications owing to its compactness, resonable cost, robustness, and ease of use. In addition, diode lasers are fiber-optic compatible and thus enable simultaneous measurements of multiple species along a line-of-sight. Recent advances of room-temperature, near-IR and visible diode laser sources for telecommunication, optical data storage applications make it possible to be applied for combustion diagnostics based on diode laser absorption spectroscopy. Therefore, combined with fiber-optics and high sensitive detection strategies, compact and portable sensor systems are now appearing for variety of applications. The objectives of this research are to develope a new gas sensing system and to verify feasibility of this system. Wavelength and power characteristics as a function of injection current and temperature are experimentally found out. Direct absorption spectroscopy has been demonstrated in these experiments and has a bright prospect to this diode laser system.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3276-3281
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• 2007

A novel oxy-fuel burner for a boiler has been devised and composed into a 50 kW class boiler system. A series of test has been conducted to show the characteristics of combustion, exhaust gas and the boiler. Numerical simulations have been also performed and validated against the experimental data to discuss detailed physics. The oxy-fuel burner can effectively heat the combustion chamber with the significantly reduced combustion gas, which enables to realize the compactness of the system. The composition of exhaust gas reveals that the sealing of the system is crucial to achieve high $CO_2$ concentration and low $NO_X$ emission.

• Journal of the Korean Mathematical Society
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• v.47 no.3
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• pp.547-572
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• 2010

We study existence of positive solutions of the classical nonlinear Schr$\ddot{o}$dinger equation $-{\Delta}u\;+\;V(x)u\;-\;f(x,\;u)\;-\;H(x)u^{2*-1}\;=\;0$, u > 0 in $\mathbb{R}^n$ $u\;{\rightarrow}\;0\;as\;|x|\;{\rightarrow}\;{\infty}$. In fact, we consider the following more general quasi-linear Schr$\ddot{o}$odinger equation $-div(|{\nabla}u|^{m-2}{\nabla}u)\;+\;V(x)u^{m-1}$ $-f(x,\;u)\;-\;H(x)u^{m^*-1}\;=\;0$, u > 0 in $\mathbb{R}^n$ $u\;{\rightarrow}\;0\;as\;|x|\;{\rightarrow}\;{\infty}$, where m $\in$ (1, n) is a positive number and $m^*\;:=\;\frac{mn}{n-m}\;>\;0$, is the corresponding critical Sobolev embedding number in $\mathbb{R}^n$. Under appropriate conditions on the functions V(x), f(x, u) and H(x), existence and non-existence results of positive solutions have been established.

• Journal of applied mathematics & informatics
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• v.32 no.1_2
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• pp.137-152
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• 2014

In this paper, we prove, in the spirit of [3, 12, 20, 22, 23], the existence of infinitely many small solutions to the following quasilinear elliptic equation $-{\Delta}_{p(x)}u+{\mid}u{\mid}^{p(x)-2}u={\mid}u{\mid}^{q(x)-2}u+{\lambda}f(x,u)$ in a smooth bounded domain ${\Omega}$ of ${\mathbb{R}}^N$. We also assume that $\{q(x)=p^*(x)\}{\neq}{\emptyset}$, where $p^*(x)$ = Np(x)/(N - p(x)) is the critical Sobolev exponent for variable exponents. The proof is based on a new version of the symmetric mountainpass lemma due to Kajikiya [22], and property of these solutions are also obtained.

• Membrane and Water Treatment
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• v.9 no.1
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• pp.33-42
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• 2018

Microscopic examination of the activated sludge and morphological characterization of the flocs provides detailed information about the treatment process. The aim of this study is to investigate the morphological parameters of flocs obtained from a thermophilic jet loop membrane bioreactor (JLMBR) in different sludge retention times (SRTs), considering EPS and SMP concentration, hydrophobicity, zeta potential. The results showed that irregularity decreased with the increasing SRT. The compactness value was calculated to be less than 1 for all SRTs. However, the sludge had a more compact structure when the SRT increased. Zeta potential increased whereas hydrophobicity and floc size reduced, with increasing SRT. Furthermore, 2-D porosity calculated using the hole ratio was higher at greater SRTs. Hence, there was a significant correlation between the results obtained using the imaging technique and operation conditions of thermophilic JLMBR.

• Communications of the Korean Mathematical Society
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• v.12 no.2
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• pp.221-236
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• 1997

In this paper we investigate the multiplicity of positive solutions to a quasilinear Neumann problem; $$ {\varepsilon^m div($\mid$\bigtriangledown_u$\mid$^{m-2}\bigtriangledown_u) - u$\mid$u$\mid$^{m-2} + u$\mid$u$\mid$^{m-2} + u$\mid$u$\mid$^{p-2} = 0 in \omega $$ $$ \frac{\partial u}{\partial \nu} = 0 on \partial \omega, $$ making use of Ljusternik Schnirelmann category theory.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.5
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• pp.405-410
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• 2006

We fabricated gas sensors using carbon nanotubes (CNTs) as electron emitters for the purpose of detecting inert gases. By using the silicon-glass anodic bonding and glass patterning technologies with the typical Si process, we improved the compactness of the sensors and the reliability in process. The proposed sensor, based on, an electrical discharge theory known as Paschen's law in principle, works by figuring the variation of the discharge current depending on gas concentration. In the experiment, the initial breakdown characteristics were measured for air and Ar as a function of gas pressure. As the result, even though it should be realized that there are many other factors which have an effect on the breakdown of a gap, the sensors led to similar result as predicted by Paschen's law, and they showed a possibility as gas sensors which enable to detect the gas density ranged to the vacuum pressure from 1 to $10^{-3}$ Torr.

• Journal of Electrochemical Science and Technology
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• v.11 no.4
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• pp.368-378
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• 2020

In the paper, corrosion behavior of T91 steel in different concentrations of NaHSO₃ solution was studied in combination with scanning electron microscope (SEM) and electrochemical measurements. The results showed that the steel exhibited active anodic dissolution characteristics in the solution, and NaHSO₃ concentration affected both cathodic and anodic behaviors. The steel surface was covered by intact corrosion products in the solutions, but the compactness and mechanical properties of the corrosion products degraded with the increase of NaHSO₃ concentration. In low-concentration NaHSO₃ solution the steel tended to undergo uniform corrosion with slight corrosion pits, but its corrosion mode gradually transited to localized corrosion as the NaHSO₃ concentration increased. The mechanical property degradation of the corrosion products caused by sulfur compounds and the pH decrease of the solution are the important factors to accelerating its corrosion process.

• Journal of the Korean Chemical Society
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• v.37 no.9
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• pp.781-786
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• 1993

In the presence of $Mg^{2+}$, the interaction of nonionic surfactants, $nonylphenol-(ethylene oxide)_n$[NP-nEO; n = 12, 40, 100] with iodine in aqueous solution were investigated by UV-visible spectrophotometer. CMC (critical micelle concentration) was decreased with increasing $Mg^{2+}$ concentration, and those effects depend upon EO (ethylene oxide) numbers. Above CMC, the intensity of interaction peaks by the addition of $Mg^{2+}$ increased and then decreased. The increase in the intensity of the interaction peaks were attributed to the compactness of micelle in the presence of $Mg^{2+}$. These phenomena may be explained by the fact that the linear ethylene oxide chains, to be free configuration in aqueous solution, could form a psuedo-crown ether structures capable of forming complex with $Mg^{2+}$.

• Journal of Korean Society on Water Environment
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• v.21 no.3
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• pp.242-247
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• 2005

In this study, we investigated the removal efficiencies of pollutants and permeate fluxes depending on chemistry of feed water, various molecular weight cut-offs (MWCOs) and materials of membrane, operating pressure. We used seven MWCO membranes of YC0.5, YM1, YM3, YM10, YM30, YM100 and PM30, humic acid solution and surface water as feed water, and examined variation in permeate flux. Results of TOC removal experiment demonstrate that MWCO lower 1,000daltons could remove humic acid effectively. As increasing solution pH and decreasing divalent cations ($Ca^{2+}$) concentration, TOC removal increased. But $UV_{254}$ removal efficiency increased with higher divalent cation concentration and solution pH. Membrane fouling increased with increasing electrolyte (NaCl), divalent cation concentration and decreasing solution pH. In spite of initial permeate flux of the hydrophobic membrane (PM30) was higher than that of the hydrophilic membrane (YM30), flux decline of PM30 was significant during operation. At higher operating pressure, compactness of the cake layer on the membrane surface increased, resulting in gradual increase in hydraulic resistance.