• Journal of ILASS-Korea
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• v.20 no.1
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• pp.53-58
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• 2015

In this study, we prepare the Ag nanofluids synthesized by the chemical reduction method and measure the extinction coefficient of those nanofluids at a wavelength of 632.8 nm. The Ag nanofluids are synthesized by the chemical reduction method using silver nitrate ($AgNO_3$) and sodium borohydride ($NaBH_4$) in water and ethylene glycol (EG). For stable dispersion of Ag particles in the base liquids, polyvinyl pyrrolidone (PVP) is added as a surfactant. The extinction coefficient of manufactured Ag nanofluids is measured by an in-house developed measurement system at the wavelength of 632.8 nm. The results show that the extinction coefficient of water-based and EG-based Ag nanofluids is linearly increased with respect to the particle loadings. Moreover, it is shown that the extinction coefficient of EG-based Ag nanofludis is higher than that of water-based Ag nanofluids. Finally we compare the experimental results with both the Maxwell-Garnett model and Rayleigh scattering approximation model, and they demonstrate that the Rayleigh scattering approximation model is reasonably predict the extinction coefficient of Ag nanofluids using hydraulic diameter of silver nanoparticle.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.10 no.1
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• pp.18-31
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• 2000

A stack must be designed to 1) reduce or eliminate rainfall or snowfall into a industrial exhaust system, 2) minimize a resistance to flow, 3) maximize the vertical dispersion of the contaminated air and 4) minimize maintenance. The weather cone stacks and the elbow-type stacks are very popular in Korea. But they add some resistance to the exhaust system resulting in reduction of air flow rate, but also deflect the noxious contaminants downward in undiluted form. To solve these problems, ACGIH (American Conference of Governmental Industrial Hygienists) suggested the vertical discharge stack with concentric space between the upper stack with larger diameter and the lower stack with smaller diameter. The preliminary test showed that the vertical discharge stacks did not have the good rainfall protection. The reversed cone were newly devised to satisfy the requirements for the good stack. Subsequently, the amount of rain being penetrated through the stacks was measured while the stacks were simultaneously and naturally exposed to rain in the same area outside. Test results indicate that none of the stacks tested completely exclude rain. The efficiency of rainfall protection and the pressure loss coefficient were compared. The temporary conclusion was reached to the point that the reversed cone stack is the best one. Further research is underway.

• Journal of Korean Society for Atmospheric Environment
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• v.5 no.1
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• pp.1-10
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• 1989

The sensitivity analysis is a method to quantify to what extent the output of a model changes with the values of input parameters. This will lead to increase model accuracy through measurement validation. Three line source air quality models, HIWAY 2, PAL, and CALINE 3 were selected for this study. The input parameters analysed included wind speed, wind direction, stability, emission rate, mixing height, receptor distance, initial dispersion coefficient, surface roughness, and averaging time. It turned out that PAL model generally showed higher concentration than other two models, and that between CALINE 3 and HIWAY 2, CALINE 3 showed higher concentration than HIWAY 2 model near the line sources, but beyond a certain downwind distances HIWAY 2 model showed higher concentration. The modesl were very sensitive to wind speed especially in the range of 0 $\sim$ 1 m/s and to wind direction near the parallel wind to streets. In case of emission rate, the output concentration was directly proportional to these input parameters. And the sensitivity of the input parameters such as stability, mixing height, initial dispersion coefficient, surface roughness, and averaging time were not very significant.

• Biotechnology and Bioprocess Engineering:BBE
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• v.7 no.1
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• pp.16-20
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• 2002

Parameter estimations were made for the reversed-phase adsorption of perillyl alcohol (POH), a potent anti-cancer agent, on octadecylsilyl-silica gel (ODS). The average particle diameter of ODS was about $15\;{\mu}m$, and the particles were packed in the column $(3.9\;\times\;300mm)$. The mobile phase used was a mixture of acetonitrile and water, in which the acetonitrile ranged between 50 and $70\;(v/v\;\%)$. The first absolute moment and the second central moment were determined from the chromatographic elution curves by moment analysis. Experiments were carried out using POH solutions within the linear adsorption range. The fluid-to-particle mass transfer coefficient was estimated using the Wilson-Geankoplis equation. The axial dispersion coefficient and the intra particle diffusivity were determined from the slope and intercept of a plot of H vs $1/u_0$, respectively. The contributions of each mass-transfer step were axial dispersion, fluid-to-particle mass transfer, and intraparticle diffusion.

• Solar Energy
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• v.14 no.2
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• pp.29-37
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• 1994

Radiative charaacteristics of glass windows and porous absorbing media which can be used for a solar air heater are determined through the measurements of spectral transmittances. Those in the visible range are measured by the UV-IR spectrometer. Refractive index of glass are obtained by the comparison of the measured transmittances and the correlations derived from the electromagnetic theory and are compared to the theoretical ones calculated from the classical dispersion theory. Absorption and back-scattering coefficients of 15-mesh stainless wire screens are calcuated by the comparison of the measured transmittances and the correlations derived from the two flux model.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.363-369
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• 2016

Enhancing mechanical strength of concrete has been fascinated using carbon-based nanomaterials such as CNT and graphene. The key to improving strength is a dispersion of nanomaterials. A novel method is required to investigate the dispersion inner concrete nondestructively. In this study, the optical optical properties such as refractive index and absorption coefficient are measured in nano-cement mortar specimens containing MWCNT and GO using THz electro-magnetic waves. From the results, the properties of nano-cement mortar are confirmed to be 1.0% to 2.5% higher in refractive index, and -14% to 28% higher in absorption coefficient than those of cement mortar at the average values. Using these characteristics, visualizing the dispersion of nano-concrete structures seems possible in future.

• Earthquakes and Structures
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• v.14 no.4
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• pp.313-322
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• 2018

The present study is dedicated to investigate the SH body-as well as Love-waves propagation effects in porous media with uncertain porosity and permeability. A unified formulation of the governing equations for one-dimensional (1-D) wave propagation in anisotropic porous layered media is presented deterministically. The uncertainties around the above two cited parameters are taken into account by random fields with the help of Monte Carlo Simulations (MCS). Random samples of the porosity and the permeability are generated according to the normal and lognormal distribution functions, respectively, with a mean value and a coefficient of variation for each one of the two parameters. After performing several thousands of samples, the mathematical expectation (mean) of the solution of the wave propagation equations in terms of amplification functions for SH waves and in terms of dispersion equation for Love-waves are obtained. The limits of the Love wave velocity in a porous soil layer overlaying a homogeneous half-space are obtained where it is found that random variations of porosity change the zeros of the wave equation. Also, the increase of uncertainties in the porosity (high coefficient of variation) decreases the mean amplification function amplitudes and shifts the fundamental frequencies. However, no effects are observed on both Love wave dispersion and amplification function for random variations of permeability. Lastly, the present approach is applied to a case study in the Adapazari town basin so that to estimate ground motion accelerations lacked in the fast-growing during the main shock of the damaging 1999 Kocaeli earthquake.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.3
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• pp.55-61
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• 2013

This paper compare the performance of S-MMA(Sliced-MultiModulus Algorithm) adaptive equalization algorithm by effect of slice weighting value for the minimization of the distortion and noise in the communication channel.. In the traditional MMA algorithm, the output signal of equalizer and the dispersion constant of transmitting signal is used for calculating the equalizer coefficient, but in S-MMA, the output of equalizer and dispersion constant and the considering the output of decision device by the power of slice constant are used in order to simultaneously compensate the distortion of amplitude and phase distortion. It is confirmed by computer simulation that the slice weighting value affects the performance of adaptive equalization algorithm. The performance index includes the output signal constellation, the residual isi and maximum distortion and MSE that is for the convergence characteristics, the SER according to the signal and noise power ratio at the channel is used. As a result of simulation, the residual isi, maximum distortion and MSE performances are better in the small weighting values. But in SER performance is better in the large weighting values.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.7
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• pp.1157-1166
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• 2001

In this paper, we investigated the degree of compensation for optical pulse shape distortion due to both chromatic dispersion and SPM(self phase modulation) in high speed optical transmission system with dispersion shift fiber. We adopted the power symmetric MSSI(mid-span spectral inversion) as compensation method. We used EOP(eye-opening penalty) parameter in order to evaluate the compensation efficiency of distorted optical pulse. We evaluated input signal power range being able to maintain stable reception performance in the case of various chirp parameter of modulated optical pulse. And, in order to verify the applicable to wideband WDM system, we evaluated the wavelength range being able to maintain stable reception performance through the EOP calculation of various dispersion coefficient of first fiber D$\_$11/. We showed that proposed MSSI is effective compensation method to down chirped optical pulse transmission rather than up chirped optical pulse transmission in anomalous dispersion range. And we showed that this method have possibility of relative high power transmission and wideband transmission in WDM system.

• Current Optics and Photonics
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• v.5 no.3
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• pp.250-260
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• 2021

A tapered As₂S₃ photonic crystal fiber (PCF) with four layers of air holes in a hexagonal array around the core is designed in this paper. Numerical simulation shows that the dispersion D decreases and the nonlinearity coefficient γ increases from the thick to the thin end along the tapered PCF. We simulate the midinfrared pulse compression in the tapered As₂S₃ PCF using the adaptive split-step Fourier method. Initial Gaussian pulses of 4.4 ps and a central wavelength of 2.5 ㎛ propagating in the tapered PCF are located in the anomalous dispersion region. With an average power of assumed input pulses at 3 mW and a repetition frequency of 81.0 MHz, we theoretically obtain a pulse duration of 56 fs and a compression factor of 78 when the pulse propagates from the thick end to the thin end of the tapered PCF. When confinement loss in the tapered PCF is included in the simulation, the minimum pulse duration reaches 72 fs; correspondingly, the maximum compression factor reaches 61. The results show that in the anomalous-dispersion region, midinfrared pulses can be efficiently compressed in a dispersion-decreasing and nonlinearity-increasing tapered As₂S₃ PCF. Due to confinement loss in the tapered fiber, the efficiency of pulse compression is suppressed.