• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.2
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• pp.108-115
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• 2003

Two types of one-dimensional dispersion-correction scheme are developed to take into account the dispersion effects for the simulation of tsunami propagation using ADCIRC finite element model based on shallow-water equations The first is an implicit scheme, and the dispersion-correction is accomplished by controlling the weighting factor assigned to each spatial derivative term of different time levels. The other scheme is explicit and the dispersion is considered by adjusting the element size. The validity of the dispersion-correction scheme proposed in this study is confirmed through the comparison of numerical solutions calculated using the new schemes with analytical ones considering dispersion effect of waves.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.2
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• pp.126-133
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• 2013

This paper presents a study on the dispersion effect of the X-Ray diffraction, glass transition and DMA properties of organic modifier clay/epoxy nanocomposites produced in a homogenizer. Several experiments were conducted including different types of dispersion condition with varying processing conditions such as homogenizer rotor speed and applied time of homogenizer. The effects of these variables on the dispersion properties of nanocomposites were then studied. In order to fully understand the experimental results, a X-ray diffraction, DSC and DMA were used to investigate the effect of above mentioned variables on microstructure and intercalation/exfoliation of organic modifier clay/epoxy nanocomposites. The results from this work could be used to determine the best processing condition to obtain appropriate levels of d-spacing, glasss transition temperature and storage modulus in organic modifier clay/epoxy nanocomposites.

• Geomechanics and Engineering
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• v.13 no.5
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• pp.775-791
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• 2017

Surface wave techniques are widely used as non-invasive method for geotechnical site characterization. Field surface wave data are collected and analyzed using different processing techniques to generate the dispersion curves, which are further used to extract the shear wave velocity profile by inverse problem solution. Characteristics of a dispersion curve depend on the subsurface layering information of a vertically heterogeneous medium. Sometimes soft layer can be found between two stiff layers in the vertically heterogeneous media, and it can affect the wave propagation dramatically. Now most of the surface wave techniques use the fundamental mode Rayleigh wave propagation during the inversion, but this may not be the actual scenario when a soft layer is present in a vertically layered medium. This paper presents a detailed and comprehensive study using finite element method to examine the effect of soft layers which sometimes get trapped between two high velocity layers. Determination of the presence of a soft layer is quite important for proper mechanical characterization of a soil deposit. Present analysis shows that the thickness and position of the trapped soft layer highly influence the dispersion of Rayleigh waves while the higher modes also contribute in the resulting wave propagation.

• Particle and aerosol research
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• v.13 no.3
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• pp.133-139
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• 2017

In this paper, we proposed an emulsification method without using an emulsifier and investigated the effects of particle size distribution in fluids on dispersion stability. Surfactant-free oil in water emulsion was prepared with 1 % (w/w) of olive oil by using high speed agitation, high pressure and ultrasonic dispersion methods. The particle size, microscopic observation, and dispersion stability of each sample were evaluated and dispersion stability according to various dispersion methods was compared. As a result, the emulsion dispersed by the ultrasonic dispersion method showed the smallest particle size and uniform distribution of $0.07{\sim} 0.3{\mu}m$ and was the most stable in a 7 days stability evaluation. In the above experiment, four olive oil emulsions having different particle sizes were prepared using ultrasonic dispersion technology that was capable of producing stable emulsions. The dispersion stability of each samples with oil droplet sizes of (A) 0.1 to $0.5{\mu}m$, (B) 0.3 to $4{\mu}m$, (C) 1 to $10.5{\mu}m$ and (D) 2 to $120{\mu}m$, was observed for 7 days, and the relationship between the stability and performance was studied. Emulsion (A) with particle size less than $0.5{\mu}m$ displayed the dispersion stability showing below 5 % change in a 7 days stability evaluation. In the case of (B), (C), and (D) that had larger particle than $0.5{\mu}m$, the changes of dispersion stability were 10 %, 13 % and 35 % respectively. From these results, it was proved that dispersion stability of emulsion with uniform particle size of $0.5{\mu}m$ or less was confirmed to be very stable.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.1011-1016
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• 2001

The purpose of this study is to find out the effect of polymer glass transition temperature on mechanical properties of polymer latex-modified mortars in comparison with ordinary cement mortar. The Polymer latex-modified mortars are prepared with 5, 10, 15 and 20% of polymer cement ratio respectively, and properties of modified mortars such as air content, compressive, flexural and tensile strengths are tested. The test results indicate that the types of polymer dispersion and the polymer-cement ratio are very important factors to characterize the properties of polymer-modified mortars, and also the glass transition temperature of polymer dispersions has an important effect on the performance of polymer-modified mortars. The modifying effects of two kinds of polymer dispersion, St/BA-1 and SBR, are evaluated.

• Journal of Advanced Navigation Technology
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• v.26 no.1
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• pp.22-28
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• 2022

In order to install ultra wide band and ultra long-haul transmission link based on standard single mode fiber, optical signal distortion due to chromatic dispersion and nonlinear Kerr effect must to be compensated. In this paper, optical link consisted of dispersion management and optical phase conjugation is proposed for compensation of the distorted wavelength division multiplexed (WDM) channels. Dispersion map profile in the proposed dispersion-managed link is configured by periodic repetitive shape, and optical phase conjugator is placed at various position including the midway of total transmission length. It is confirmed from simulation results that when the residual dispersion per span (RDPS) selected in the proposed dispersion-managed link to be large, the compensation of distorted WDM channels in the non-midway OPC system is more improved than the conventional dispersion-managed link.

• Journal of Advanced Navigation Technology
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• v.25 no.6
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• pp.517-522
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• 2021

Optical dispersion-managed link combined with optical phase conjugation for compensating of the distorted optical signals due to chromatic dispersion and nonlinear effects, which is required to implement long-haul wavelength division multiplexed system, is proposed and assessed in viewpoint of network topology flexibility. Optical phase conjugator capable to compensate for the distorted optical signal due to nonlinear effects is placed non-midway of total transmission distance. And, in dispersion-managed link, residual dispersion per span (RDPS) of each fiber spans in former half section and latter half section with respect to optical phase conjugator are different to each other. Simulation results show when the RDPS of each fiber sections in one half section makes it's own net residual dispersion slight different from another half section's net residual dispersion, the compensation effect in the proposed link configuration is more increased.

• Journal of Advanced Navigation Technology
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• v.27 no.6
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• pp.855-860
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• 2023

Long-haul transmission of multiple transmission signals, such as wavelength division multiplexed (WDM), has became possible, because the signal distortion caused by chromatic dispersion and nonlinearity can be compensated by applying dispersion management, optical phase conjugation and combination of the two methods into the transmission link. The biggest obstacle to applying optical phase conjugation to an optical link is that the optical phase conjugator (OPC) must be located only in the middle of the entire transmission line. This paper shows that the location constraints of OPC can be overcome through the application of an asymmetric dispersion map. The location of the OPC considered in this paper exists between the 8th and 9th fiber spans out of a total of 48 fiber spans. Additionally, the dispersion map has an asymmetric cumulative dispersion profile with respect to the OPC. As a result of the simulation, it was confirmed that the distortion compensation effect of the WDM channel can be increased compared to the link to which the traditional dispersion map is applied, depending on the overall shape of the cumulative dispersion profile distribution of the proposed asymmetric dispersion map and the selection of the profile slope.

• Journal of the Korean Ceramic Society
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• v.13 no.3
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• pp.37-42
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• 1976

Although the water mixed into the concrete plays the role of hydration and acquiring the necessary workability, the more portion of water acts to obtain the substantial workability rather than to complete the hydration. However, the excess amount of water causes the poor quality of concrete, therefore it is useful to add the minimum amount of water as required as to acquire the proper workability. There have been the considerable numbers of investigations in which the dispersion phenomena of strong eletrolytic high polymer compounds such as lignosulfate and some of surface activation agents were studied to utilize as the dispersion agent of concrete. In the present study, Na-lignate, dispersion properties of which has not been studied yet, were investigated with the purpose of utilizing as a dispersion agent of concrete. The microscopic observations showed a great improvement in the dispersion of cement particles, also the fluidity and compressive strength of concrete were remarkably increased with the addition of Na-lignate: The addition of Na-lignate by 0.02% showed the increase of 1.76 times and 1.27 times of slump value and flow value respectively, and the compressive strength was increased by 1.07 times.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1627-1632
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• 2003

The effect of (1) phonon dispersion in thermal conductivity model and (2) the differentiation of group velocity and phase velocity for Ge is examined. The results show drastic change of thermal conductivity regardless of using same relaxation time model. Also the contribution of transverse acoustic (TA) phonon and longitudinal acoustic (LA) phonon is changed by considering more rigorous dispersion model. Holland model underestimates the scattering rate for high frequency TA, so misleading conclusion, i.e. TA is dominant heat transfer mode at high temperature. But the actual reduction of thermal conductivity is much larger than the estimation by Holland model and high frequency TA is no more dominant heat transfer mode. Another heat transfer mechanism may exist for high temperature. Two possible explanations are (1) high frequency LA by Umklapp scattering and (2) optical phonon.