• Elastomers and Composites
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• v.37 no.2
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• pp.79-85
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• 2002

Ethyl-branched polyethylene [PE(2)] containing 2mole% ethyl branch and three ethylene-propylene rubbers (EPR's) having the same ethylene(E)-propylene(P) molar ratio(E/P=50/50) with different stereoregularity, that is, random EPR (r-EPR), alternating-EPR (alt-EPR) and isotactic-alternating-EPR (iso-alt-EPR) were mixed for the investigation or their properties depending on the stereoregularity. Crystallinity of the prepared blends decreased with increasing content of amorphous EPR because of a decrease in both the degree of annealing and kinetics of diffusion of the crystallizable polymer content. With blend composition, crystallinity was reduced with the stereoregularity in EPR. The thermodynamic interaction parameter(x) for the three blend systems approximately equals to zero near the melting point. These systems were determined to be miscible on a molecular scale near or above the crystalline melting point or the crystalline PE(2). From the measurement of $T_m$ vs. $T_c$, the behavior of PE(2) is mainly due to a diluent effect of EPR component. The spherulite size measured by small angle light scattering (SALS) technique depended upon blend composition, and stereoregularity of EPR. The size of spherulite was enlarged with the content of rubbery EPR and the decrease of stereoregularity in EPR.

• Journal of the Korean Institute of Gas
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• v.27 no.3
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• pp.59-71
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• 2023

Carbon capture, and storage (CCS) is important for the reduction of greenhouse gases and achieving carbon neutrality. CCS focuses on storing captured CO₂ permanently in underground reservoirs. CO₂-enhanced oil recovery (CO₂-EOR) is one form of CCS, where CO₂ is injected into the underground to enhance oil recovery. CO₂-EOR not only aids in the extraction of residual oil but also contributes to carbon neutrality by storing CO₂ underground continuously. CO₂-EOR can be classified into miscible and immiscible methods, with the CO₂-water alternating gas (CO₂-WAG) technique being a representative approach within the miscible method. In CO₂-WAG, water and CO₂ are alternately injected into the reservoir, enabling oil production and CO₂ storage. The WAG method allows for controlling the breakthrough of injection fluids, providing advantages in oil recovery. It also induces hysteresis in relative permeability during the injection and production process, expanding the amount of trapped CO₂. In this study, the effects of enhancing oil recovery and storing CO₂ underground during CO₂-EOR were presented. Additionally, cases of CO₂-EOR application in relation to CCS were introduced.

• Progress in Medical Physics
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• v.24 no.2
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• pp.108-118
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• 2013

Currently, an arterial spin labeling (ASL) magnetic resonance imaging (MRI) technique does not routinely used in clinical studies to measure perfusion in brain because optimization of imaging protocol is required to obtain optimal perfusion signals. Therefore, the objective of this study was to investigate changes of perfusion-weighed signal intensities with varying several parameters on a pulsed arterial spin labeling MRI technique obtained from a 3T MRI system. We especially evaluated alternations of ASL-MRI signal intensities on special brain areas, including in brain tissues and lobes. The signal targeting with alternating radiofrequency (STAR) pulsed ASL method was scanned on five normal subjects (mean age: 36 years, range: 29~41 years) on a 3T MRI system. Four parameters were evaluated with varying: 1) the labeling gap, 2) the labeling delay time, 3) the labeling thickness, and 4) the slice scan order. Signal intensities were obtained from the perfusion-weighted imaging on the gray and white matters and brain lobes of the frontal, parietal, temporal, and occipital areas. The results of this study were summarized: 1) Perfusion-weighted signal intensities were decreased with increasing the labeling gap in the bilateral gray matter areas and were least affected on the parietal lobe, but most affected on the occipital lobe. 2) Perfusion-weighted signal intensities were decreased with increasing the labeling delay time until 400 ms, but increased up to 1,000 ms in the bilateral gray matter areas. 3) Perfusion-weighted signal intensities were increased with increasing the labeling thickness until 120 mm in both the gray and white matter. 4) Perfusion-weighted signal intensities were higher descending scans than asending scans in both the gray and white matter. We investigated changes of perfusion-weighted signal intensities with varying several parameters in the STAR ASL method. It should require having protocol optimization processing before applying in patients. It has limitations to apply the ASL method in the white matter on a 3T MRI system.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.54-61
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• 2000

In order to determine the mode I stress intensity factor ($K_I$) by means of the alternating current potential drop(ACPD) technique, the change in potential drop due to load for a paramagnetic material containing a two-dimensional surface crack was examined. The cause of the change in potential drop and the effects of the magnetic flux and the demagnetization on the change in potential drop were clarified by using the measuring systems with and without removing the magnetic flux from the circumference of the specimen. The change in potential drop was linearly decreased with increasing the tensile load and was caused by the change in conductivity near the crack tip. The reason of decreasing the change in potential drop with increasing the tensile load was that the increase of the conductivity near the crack tip due to the tensile load caused the decreases of the resistance and internal inductance of the specimen. The relationship between the change in potential drop and the change in $K_I$ was not affected by demagnetization and was independent of the crack length.

• Journal of Power Electronics
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• v.14 no.6
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• pp.1303-1313
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• 2014

Dynamic behavior of the harmonic detection part of an active power filter (APF) has an essential role in filter compensation performances during transient conditions. Instantaneous power (p-q) theory is extensively used to design harmonic detectors for active filters. Large overshoot of p-q theory method deteriorates filter response at a large and rapid load change. In this study the harmonic estimation of an APF during transient conditions for balanced three-phase nonlinear loads is conducted. A novel fuzzy instantaneous power (FIP) theory is proposed to improve conventional p-q theory dynamic performances during transient conditions to adapt automatically to any random and rapid nonlinear load change. Adding fuzzy rules in p-q theory improves the decomposition of the alternating current components of active and reactive power signals and develops correct reference during rapid and random current variation. Modifying p-q theory internal high-pass filter performance using fuzzy rules without any drawback is a prospect. In the simulated system using MATLAB/SIMULINK, the shunt active filter is connected to a rapidly time-varying nonlinear load. The harmonic detection parts of the shunt active filter are developed for FIP theory-based and p-q theory-based algorithms. The harmonic detector hardware is also developed using the TMS320F28335 digital signal processor and connected to a laboratory nonlinear load. The software is developed for FIP theory-based and p-q theory-based algorithms. The simulation and experimental tests results verify the ability of the new technique in harmonic detection of rapid changing nonlinear loads.

• Bulletin of the Korean Chemical Society
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• v.26 no.2
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• pp.309-311
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• 2005

Single crystals of the new pentanary thiophosphate, $K_{0.5}Ag_{0.5}Nb_2PS_{10}$ has been prepared through reactions of the elements with halide fluxes. The structure of $K_{0.5}Ag_{0.5}Nb_2PS_{10}$ has been analyzed by single crystal X-ray diffraction technique. The structure of $K_{0.5}Ag_{0.5}Nb_2PS_{10}$ is made up of one-dimensional ${^{\infty}_1}[Nb_2PS_{10}]$ chains along the [001] direction and these chains are separated from one another by $Ag^+$ and disordered $K^+$ ions. This chain is basically built up from bicapped trigonal prismatic [Nb2S12] units and tetrahedral [PS4] groups. The [$Nb_2S_{12}$] units are connected together to form the linear chain, ${^{\infty}_1}[Nb_2S_9]$ by sharing the S-S prism edge. Short (2.885(2) $\AA$ or 2.888(2) $\AA$) and long (3.743(1) $\AA$) Nb-Nb distances are alternating along the chain, and the $S_2{^2-}]\;and\;S^{2-}$anionic species are observed. The distorted octahedral coordination around the $Ag^+$ ion can be described as [2+4] bonding interaction.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.9
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• pp.838-842
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• 2006

0.03Pb$(Sb_{0.5}Nb_{0.5})O_{3}-0.03Pb(Mn{1/3}Nb{2/3)O_{3}-(0.94-x)PbTiO_{3}-xPbZrO_{3}$ ceramics doped with $CeO_{2}$ were synthesized by conventional bulk ceramic processing technique. Phases analysis, microstructures and piezoelectric properties were investigated as a function of $CeO_{2}$ content (0.03, 0.05, 0.1 0.3, 0.5 and 0.7 wt%). Microstructures and phases information were characterized using a scanning electron microscope (SEM) and an X-ray diffractometer (XRD). Mechanical quality factor ($Q_{m}$) and coupling factor(kp) were obtained from the resonance measurement method. Both $Q_{m}$ and $k_{p}$ were shown to reach to the maximum at 0.1 wt% $CeO_{2}$. In order to evaluate the stability of resonance frequency and effective electromechanical coupling factor ($K_{eff}$) as a function of $CeO_{2}$, the variation of resonance and anti-resonance frequency were also measured using a high voltage frequency response analyzer under various alternating electric fields from 10 V/mm to 80 V/mm. It was shown that the stability of resonance frequency and effective electromechanical coupling factor were increased with increasing the $CeO_{2}$ contents.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.1
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• pp.205-213
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• 2011

The Long Term Evolution (LTE) system is designed to provide a high quality data service for fast moving mobile users. It is based on the Orthogonal Frequency Division Multiplexing (OFDM) and relies its channel estimation on the training samples which are systematically built within the transmitting data. Either a preamble or a lattice type is used for the distribution of training samples and the latter suits better for the multipath fading channel environment whose channel frequency response (CFR) fluctuates rapidly with time. In the lattice-type structure, the estimation of the CFR makes use of the least squares estimate (LSE) for each pilot samples, followed by an interpolation both in time-and in frequency-domain to fill up the channel estimates for subcarriers corresponding to data samples. All interpolation schemes should rely on the pilot estimates only, and thus, their performances are bounded by the quality of pilot estimates. However, the additive noise give rise to high fluctuation on the pilot estimates, especially in a communication environment with low signal-to-noise ratio. These high fluctuations could be monitored in the alternating high values of the first forward differences (FFD) between pilot estimates. In this paper, we analyzed statistically those FFD values and propose a postprocessing algorithm to suppress high fluctuations in the noisy pilot estimates. The proposed method is based on a localized adaptive moving-average filtering. The performance of the proposed technique is verified on a multipath environment suggested on a 3GPP LTE specification. It is shown that the mean-squared error (MSE) between the actual CFR and pilot estimates could be reduced up to 68% from the noisy pilot estimates.

• Korean Journal of Materials Research
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• v.19 no.12
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• pp.637-643
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• 2009

In this study, we analyzed the effect of silicon oxynitride matrix on the optical properties of Au nanoparticles dispersed on composite film and explored the effectiveness of the silicon in fine tuning the refractive index of the composite film for applications in optical waveguide devices. The atomic fraction of nitrogen in $SiO_xN_y$ films was controlled by varying the relative flow ratio of nitrogen gas in reactive sputtering and was evaluated optically using an effective medium theory with Bruggeman geometry consisting of a random mixture between $SiO_2$ and $Si_3N_4$. The Au nanoparticles were embedded in the $SiO_xN_y$ matrix by employing the alternating deposition technique and clearly showed an absorption peak due to the excitation of surface plasmon. With increasing nitrogen atomic fraction in the matrix, the surface plasmon resonance wavelength shifted to a longer wavelength (a red-shift) with an enhanced resonance absorption. These characteristics were interpreted using the Maxwell-Garnett effective medium theory. The formation of a guided mode in a slab waveguide consisting of 3 $\mu$m thick Au:$SiO_xN_y$ nanocomposite film was confirmed at the telecommunication wavelength of 1550 nm by prism coupler method and compared with the case of using $SiO_2$ matrix. The use of $SiO_xN_y$ matrix provides an effective way of controlling the mode confinement while maintaining or even enhancing the surface plasmon resonance properties.

• Korean Journal of Materials Research
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• v.14 no.2
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• pp.141-145
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• 2004

Silicon nitride thin films were deposited by atomic layer deposition (ALD) technique in a batch-type reactor by alternating exposures of precursors. XJAKO200414714156408$_4$ or$ SiH_2$$Cl_2$ was used as the Si precursor, $NH_3$ was used as the N precursor, and the deposited films were characterized comparatively. The thickness of the film linearly increased with the number of deposition cycles, so that the thickness of the film can be precisely controlled by adjusting the number of cycles. As compared with the deposition using$ SiCl_4$, the deposition using $SiH_2$$Cl_2$ exhibited larger deposition rate at lower precursor exposures, and the deposited films using $SiH_2$$Cl_2$ had lower wet etch rate in a diluted HF solution. Silicon nitride films with the Si:N ratio of approximately 1:1 were obtained using either Si precursors at $500^{\circ}C$, however, the films deposited using $SiH_2$$Cl_2$ exhibited higher concentration of H as compared with those of the $SiC_4$ case. Silicon nitride thin films deposited by ALD showed similar physical properties, such as composition or integrity, with the silicon nitride films deposited by low-pressure chemical vapor deposition, lowering deposition temperature by more than $200^{\circ}C$.