• Journal of Korea Technology Innovation Society
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• v.3 no.3
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• pp.85-101
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• 2000

The purpose of this study is to test whether prices of personal computers reflect their varying degrees of non-marketable characteristics including after-sales service. This purpose is carried out using the hedonic price model. In this paper, we estimated 74 functional forms of hedonic price model using the quadratic Box-Cox transformation function and selected one based on the three criteria: expected signs, the statistical significance of estimated coefficients, and goodness of fit in terms of root-mean-square-percentage-error. In this study, we found hat as the after-sales service level increases the price of the personal computer increases. This result is consistent with the hypothesis that the less after-sales service offered with a personal computer, the less consumers are willing to pay for the personal computer, when all else remain constant. This finding shows that since the market works indirectly to influence pricing, the need to rely on consumer protection legislation to guarantee after-sales service is lessened. This study also found that after-sales service supported by each personal computer producer is not a free service, thus produces have a profit incentive for providing after-sales service.

• Ocean Systems Engineering
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• v.3 no.4
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• pp.327-348
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• 2013

An Oscillating Water Column (OWC) is a relatively practical and convenient device that converts wave energy to a usable form, which is electricity. The OWC is kept inside a fixed truncated vertical cylinder, which is a hollow structure with one open end submerged in the water and with an air turbine at the top. This research adopts potential theory and Galerkin methods to solve the fluid motion inside the OWC. Using an air-water interaction model, OWC design for energy extraction from regular wave is also explored. The hydrodynamic coefficients of the scattering and radiation potentials are solved for using the Galerkin approximation. The numerical results for the free surface elevation have been verified by a series of experiments conducted in the University of New Orleans towing tank. The effect of varying geometric parameters on the response amplitude operator (RAO) of the OWC is studied and modification of the equation for evaluating the natural frequency of the OWC is made. Using the model of air-water interaction under certain wave parameters and OWC geometric parameters, a computer program is developed to calculate the energy output from the system.

• Journal of Microbiology and Biotechnology
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• v.19 no.3
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• pp.291-298
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• 2009

The carbon metabolism of newly isolated Clostridium tyrobutyricum JM1 was investigated at varying initial glucose concentrations (27.8-333.6mM). Because an understanding of metabolic regulations was required to provide guidance for further effective metabolic design or optimization, in this case, maximizing hydrogen production, carbon and energy balances by C. tyrobutyricum JM1 were determined and applied in anaerobic glucose metabolism. The overall carbon distribution suggested that initial glucose concentrations had strong influence on the stoichiometric coefficients of products and the molar production of ATP on the formation of biomass. C. tyrobutyricum JM1 had a high capacity for hydrogen production at the initial glucose concentration of 222.4 mM with high concentrations of acetate and butyrate.

• Journal of Microbiology and Biotechnology
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• v.19 no.12
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• pp.1565-1568
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• 2009

Purified Helicobacter pylori urease displayed a sigmoid curve in the plot of velocity versus [S] at urea concentrations less than 0.1mM. Under conditions where preservatives, glycerol, or polyethylene glycol (PEG) were added to the enzyme reaction, the substrate hydrolysis was consistent with Michaelis-Menten kinetics, with a $K_m$ of $0.21\;{\pm}\;0.06\;mM$ and a $V_{max}$ of $1,200\;{\pm}\;300\;{\mu}mol\;min^{-1}\;mg^{-1}$. However, at saturating substrate concentrations, the kinetic parameters of H. pylori urease were unaffected by the presence of the preservatives, and enzyme catalysis conformed to Michaelis-Menten kinetics. The Hill coefficients of the enzyme-catalyzed urea hydrolysis in the presence and absence of PEG were 1 and 2, respectively. Based on these findings, we suggest that H. pylori urease may exist in aggregated and dissociated forms, each with intact function but differing kinetics that may be of importance in maximizing urea breakdown at varying urea concentrations in vivo.

• Advances in concrete construction
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• v.6 no.3
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• pp.297-309
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• 2018

The objective of this study was to evaluate the influence of silica fume (SF) on the hydration heat and compressive strength of concrete. Portland cement with w/(c+sf) ratios varying between 0.25 to 0.45 was substituted by 10%, 20% and 30% of SF by mass. A superplasticizer was used to maintain a fluid consistency of the concrete. The heat of hydration was monitored continuously by a semi-adiabatic calorimetric method for 10 days at $20^{\circ}C$. Compressive strengths are tested for each mixture until age of 180 days. The results show that silica fume considerably influences the evolution and the ultimate values of the compressive strengths as well as the hydration heat especially for 10% rate. The w/b ratio has a considerable effect where its decrease modifies compressive strength and hydration heat more than silica fume. The correlation of the obtained results allows deducing of ultimate properties as well as the ages to reach half of their values. The correlation coefficients are close to unity and reflect the judicious choice of these relationships to be used to predict compressive strength and hydration heat.

• Computers and Concrete
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• v.22 no.3
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• pp.319-326
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• 2018

RC (Reinforced Concrete) members are always subjected to loading conditions and have construction joints when constructed on a big scale. Service life for RC structure exposed to chloride attack is usually estimated through chloride diffusion test in sound concrete, however the test is performed without consideration of effect of loading and joint. In the present work, chloride diffusion coefficient is measured in concrete cured for 1 year. In order to evaluate the effect of applied load, cold joint, and mineral admixtures, OPC (Ordinary Portland Cement) and 40%-replaced GGBFS (Ground Granulated Blast Furnace Slag) concrete are prepared. The diffusion test is performed under loading conditions for concrete containing cold joint. Investigating the previous test results for 91 days-cured condition and the present work, changing diffusion coefficients with applied stress are normalized considering material type and cold joint. For evaluation of service life in RC continuous beam with 2 spans, non-linear analytical model is adopted, and service life in each location is evaluated considering the effects of applied stress, cold joint, and GGBFS. From the work, varying service life is simulated under various loading conditions, and the reduced results due to cold joint and tensile zone are quantitatively evaluated. The effect of various conditions on diffusion can provide more quantitative evaluation of chloride behavior and the related service life.

• The Journal of the Acoustical Society of Korea
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• v.21 no.2E
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• pp.81-90
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• 2002

Single absorbing materials and Helmholtz resonators have limited absorption characteristics over limited frequency ranges due to their structures and properties. Porous materials are highly absorptive for mid and high frequency ranges, while they have little sound absorption for low frequency sounds. Helmholtz resonators are generally used to absorb sound energy for a specified frequency range. Hence they have limited capability in controlling the overall acoustic properties of a space. Not much has been known about useful finishing materials which have enough rigidity and absorption over broad frequency range, in spite of wide demands from acoustic designers and consultants. The present work measured and analyzed absorption characteristics of a slit absorber by varying surface materials, depths of air gap, dimensions of slat and slit widths. It was found that the narrower the slit width, the larger the absorptions over the wide frequency ranges and the pattern was dependent on the presence of porous material. Narrower slat's width tend to increase the slit absorber's absorption more or less. Absorption coefficients at low frequency ranges were dramatically improved (from 0.23 to 0.56) by increasing air gap when porous materials were present.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.2
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• pp.331-337
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• 1994

The scatting problem by E-polarized plane wave with obique incidence on a tapered resistive strip grating with zero resistivity(perfectly conducting) at strip-edges is analyzed by the method of moments in the spectral domain. Then the induced surface current density on the strip is expanded in a series of Chebyshev polynomials of the second kind. The expasion coefficients are calculated numerically in the spectral domain, the numerical results of the geometric-optical reflection coefficient for the tapered resistivity in this paper are compared with those for the existing uniform resistivity. And the position of sharp variation points in the magnitude of the geometric-optical reflection coefficient can be moved by varying the incident angle and the strip spacing, It is found out that these sparp variation points are due to the transition of higher mode between the propagation mode and the evanescent mode.

• Journal of Korean Society of Steel Construction
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• v.20 no.2
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• pp.347-354
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• 2008

Steel plate-concrete (SC) structure has recently been used in nuclear power structure because of its construction efficiency. In this study, experimental and analytical study to investigate the behavior of the SC structure's wall slab connection was carried out. Experiments were performed for typical SC and RC connections in order to examine the basic difference between each structure. Finite element analysis was performed and the result of the analysis was found to closely reflect the experimental result. By varying the thickness of the shear plate and friction coefficients and the distance of applied load from the wall, the influence of the parameters on the joint strength and failure modes were examined. Finally, it was confirmed that the joint strength formula proposed in th this research gives conservative results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.1A
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• pp.38-47
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• 2006

In this paper, we propose a velocity-adaptive channel estimation scheme using the simple zero-forcing technique in the frequency domain. Channel estimation is performed by removing frequency components that are higher than the maximum Doppler frequency in the received signal. The proposed scheme can be extended to the combined estimation scheme for channel coefficients and mobile velocity using one FFT/IFFT module. Simulation results show that the proposed scheme outperforms conventional schemes for a wide range of mobile velocities($3{\sim}300\;Km/h$). Finally, the MSE for the proposed channel estimation scheme is analyzed.