• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7A
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• pp.657-665
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• 2007

In this paper, it is investigated that the limitation due to the asymmetry of optical power and chromatic dispersion with respect to optical phase conjugator (OPC) for compensating optical signal distortion of WDM channels in mid-span spectral inversion (MSSI) technique is overcame by using OPC position offset and optimal dispersion coefficients of fiber sections, which depend on OPC position offset. It is confirmed that overall WDM channels are efficiently compensated by applying the optimal parameter values obtained from the proposed method into 24 channels ${\times}\;40\;Gbps$ WDM system with non zero - dispersion shifted fiber (NZ-DSF) of 1,000 km, such as power penalties of inter-channel are reduce to almost 3.5 dB from the infinite value. It is also confirmed that the flexible design of WDM system with OPC is possible by using the optimal parameters, in which OPC is placed at ${\pm}15\;km$ from 500 km for efficiently compensating overall channels.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.10
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• pp.1854-1862
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• 2006

The numerical methods of finding out the optimal position of optical phase conjugator (OPC) and the optimal fiber dispersions are prosed, which are able to effectively compensate overall channels in $8{\times}40Gbps$Gbps WDM system with non zero - dispersion shifted fiber (NZ-DSF) as an optical fiber. And BER characteristics in the system with two induced optimal parameters are compared with those in the system with the currently used mid-span spectral inversion (MSSI) in order to confirm the availability of the proposed methods. It is confirmed that the applying two induced optimal parameters into WDM system contribute to reduce power penalty to 4 times than that of WDM system with the conventional MSSI. Thus, the methods proposed in this research will be expected to alternate with the method of making a symmetrical distribution of power and local dispersion in real optical link which generates a serious problem if it was not made but it is the condition in the case of applying the OPC into multi-channels WDM system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.5A
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• pp.473-483
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• 2004

In this paper, we numerically investigated the optimum pump light power best compensating for pulse distortion due to both chromatic dispersion and self phase modulation (SPM) as a function of channel input power in 8 channel ${\times}$ 40 Gbps wavelength division multiplexing (WDM systems. Also we investigated the allowable maximum channel input power dependence on modulation format and fiber dispersion coefficient in the various pump light power of OPC. The considered WDM transmission system is based on path-averaged intensity approximation (PAIA) mid-span spectral inversion (MSSI) compensation method, which has highly-nonlinear dispersion shifted fiber (HNL-SDF) as nonlinear medium of optical phase conjugator (OPC) in the mid-way of total transmission line. We confirmed that optimal pump light power of HNL-DSF OPC depend on modulation format, initial channel input power, total transmission length and fiber dispersion. But optimal pump light power of HNL-DSF OPC must be selected to make power conversion ratio to almost unity. And we confirmed that, if we allow a 1 dB eye opening penalty (EOP), the tolerable maximum channel input power is increased by using RZ than NRZ as modulation format when pump light power of HNL-DSF OPC is not optimal value but another values.

• Journal of the Korean earth science society
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• v.28 no.7
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• pp.903-913
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• 2007

In this study, the researchers compared the S-wave velocity structures obtained by two kinds of dispersion curves: phase and group dispersions from a tidal flat located in the SW coast of the Korean peninsula. The ${\tau}-p$ stacking method was used for the phase velocity and two different methods (multiple filtering technique: MFT and continuous wavelet transform: CWT) for the phase velocity. It was difficult to separate higher modes from the fundamental mode phase velocities using the ${\tau}-p$ method, whereas the separation of different modes of group velocity were easily achieved by both MFT and CWT. Of the two methods, CWT was found to be more efficient than MFT. The spatial resolutions for the inversion results of the fundamental mode for both phase and group velocities were good for only a very shallow depth of ${\sim}1.5m$. On the other hand, the spatial resolutions were good up to ${\sim}4m$ when both the fundamental and the 1st higher mode poop velocities obtained by CWT were used for S-wave inversion. This implies that the 1st higher mode Rayleigh waves contain more information on the S-wave velocity in deeper subsurface. The researchers applied the CWT method to obtain the fundamental and the 1st higher mode poop velocities of the S-wave velocity structure of a tidal flat located in SW coast of the Korean peninsula. Thea the S-wave velocity structures were compared with the borehole description of the study area.

• Journal of Environmental Science International
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• v.7 no.6
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• pp.875-881
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• 1998

Microemulsion is prepared by the method of phase inversion emulsification with d-limonene that is environmental friendly substance and nontoxic to human body as dispersed phase. Emulsifier used for preparation of microemulsion is nonionic surfactants, polyoxyethylene nonylphenyl ether. Stability of prepared microemulsion was estimated by the various method of ξ-potential, hydrodynamic diameter and electric conductivity. When d-limonene is emulsified by NP series, microemulsion is most stable and narrowly distributed at HLB value of 12.3(either one emulsifier or mixed emulsifiers). Stability of microemulsion is increased as the amount of emulsifiers is increased at same HLB value of 12.3. In the case of using the same amount of emulsifiers, number of produced micelle are relatively large as hydrodynamic diameter is small. Therefore, the state of microemulsion is stable and the electric conductivity is increased. One can determine that higher electric conductivity value means that microemulsion has more micelles and is more stable.

• Proceedings of the Membrane Society of Korea Conference
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• 1998.04a
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• pp.22-24
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• 1998

1. INTRODUCTION : The phase inversion method is widely used to prepare a variety of polymeric membranes ranging from micro-filtration to gas separation. The final morphology obtained by immersion precipitation strongly reflects the thermodynamics and kinetics of the system involved. The equilibrium thermodynamics of the ternary system of polymer/solvent/ nonsolvent is still very important to understand and predict membrane structure. Polysulfone (PSf) and polyethersulfone (PES) are important polymers as membrane materials due to the chemical resistance, mechanical strength, thermal stability and transport properies. There are several reports on the experimental phase diagrams in ternary mixtures of PSf/solvent/nonsolvent, and PES/solvent/nonsolvent. It would be interesting to investigate the solution thermodynamics containing these two polymers since PES is slightly less hyclrophobic than PSf.

• Proceedings of the Membrane Society of Korea Conference
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• 1998.10a
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• pp.91-92
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• 1998

1. 서론 : 고분자를 소재로 하는 중공사막의 제막은 일반적으로 상전환법(phase inversion method)에 의하여 제조된다. 이 방법에 의한 비대칭막의 생성은 용매가 고분자용액을 빠져나가는 속도와 응결액이 고분자쪽으로 침투되는 속도의 차이에 의해서 막의 1차구조가 형성된다. 그러므로 이 속도를 첨가제 등을 사용하여 조절하므로서 막의 특성을 변화시킬 수 있다. 본 연구에서는 polyetherimide(PEI) 중공사막의 첨가제로서 dioxane 등 9종류를 사용하여 중공사막의 생성 구조에 미치는 영향을 검토하였다.

• Proceedings of the KSEEG Conference
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• 1999.04a
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• pp.90-93
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• 1999

We present a high frequency electromagnetic (EM) inversion scheme for detecting and characterizing a fracture using single-hole data. At high frequencies, say above tens of mega-hertz, since displacement currents cannot be ignored, electrical permittivity as well as electrical conductivity is to be considered together for analyzing the EM scattering data. In this paper, we have developed a three-step inversion scheme to map the fracture and to evaluate its electrical conductivity and permittivity. We performed EM profiling along the z-axis using three-component receivers for each source. The model was excited by a vertical magnetic dipole and the resistant magnetic fields were inverted using the non-linear least-squares method. Background resistivity and permittivity were easily obtained using vertical magnetic fields below 1 MHz and above 10 MHz, respectively. Both the vertical and dipping sheets were successfully mapped using the phase difference between 40 and 41 MHz. The electrical property of the sheet was well resolved using the information obtained in the previous two steps and secondary magnetic fields. Our study shows the potential of imaging the fracture in single-hole survey environment using the high frequency EM method.

• Journal of Advanced Navigation Technology
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• v.10 no.2
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• pp.103-113
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• 2006

The numerical methods of finding the optimal position of optical phase conjugator (OPC) and the optimal fiber dispersions are proposed, which are able to effectively compensate overall channels in $8{\times}40$ Gbps WDM system with non zero-dispersion shifted fiber (NZ-DSF) as an optical fiber. And BER characteristics in the system with two induced optimal parameters are compared with those in the system with the currently used mid-span spectral inversion (MSSI) in order to confirm the availability of the proposed methods. It is confirmed that two optimal parameters depend on each other, but less related with the searching procedure. The methods proposed in this research will be expected to alternate with the method of making a symmetrical distribution of power and local dispersion in real optical link which is a serious problem but the condition in the case of applying the OPC into multi-channels WDM system.

• Membrane Journal
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• v.24 no.6
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• pp.472-483
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• 2014

This study is preparation of microporous membranes by using macrocyclic metal ion complexes and extended cage complexes. It is a more favorable way to existing methods because polymer and metal ion-ligand complex system provides a fine control over the phase transition behavior. Chemical functionalization of the polar surface can be obtained. Metal-templated condensation of cyclohexanedione dioxime, hydroxyphenylboronic acid in the presence of metal salts proceeds cleanly in methanol to furnish the metal clathrochelate complexes. Organic/inorganic hybrid membranes were prepared with polyethersulfone (PES), polyvinylpyrrolidone (PVP), ethyleneglycol butyl ether (BE), metal clathrochelate s and DMF by using nonsolvent induced phase inversion method. The structure of membranes was characterized with scanning electron microscopy (SEM) and microflow permporometer. The addition of Fe(II) clathrochelate complex with p-hydroxyphenyl group leads to changes of membrane morphology such as narrow mean pore size distribution, increase of surface pore density and decrease of the largest pore size.