• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.170-175
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• 2003

A control algorithm is developed for highly efficient operation of auxiliary power unit (APU) that consists of a diesel engine and a directly coupled induction generator in series hybrid electric Bus (SHEB). In a series hybrid configuration the APU supplies the electric power needed for maintaining the state of charge (SOC) of the battery unit in various conditions of vehicle operation. As the rotational speed of generator does not depend on the vehicle speed, an optimized operation of engine-generator unit based on the efficiency map of each component can be achieved. The output torque of diesel engine can be controlled by the amount of fuel injection, and the power converted from mechanical to electrical energy can be adjusted by generate control unit (GCU) using the decoupling vector control of torque and flux. As for the given reference of the generating power, the multiply of speed and torque, many combinations of operating speed and torque are possible. The algorithm decides the new operating point based on the engine efficiency map and generator characteristic curve. During the transition of operating points, the speed controller saturation is avoided using variable limit and filtering of generator torque reference. A test rig and SHEB consist of a 1.5L diesel engine and a 30kw induction generator are constructed by Hyundai Motor Company.

• Bulletin of the Korean Chemical Society
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• v.17 no.9
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• pp.820-826
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• 1996

The p2H dependence of the NMR chemical shifts of the proton signals of heme methyl groups and ionizable groups in the vicinity of the heme were investigated. The p2H titration of heme methyl signals in four macroscopic oxidation states by saturation tranfer method was performed in the range between p2H 5.2 and 9.0. While the p2H dependence of the heme methyl resonance in fully oxidized state was small, most resonances in the intermediate oxidation states showed certain shifts. Particularly, methyl resonances of heme 1 (sequential heme numbering) exhibited sharp p2H dependence in acidic range. β-CH2 of the propionate of hemes 1 and 4 were titrated in the range of p2H 4.5-9.0. Only the 6-propionate group of heme 1 was protonated in this p2H range and its titration curve was similar to those of methyl resonances of heme 1 in intermediate oxidation states. Analysis of the microscopic redox potentials showed that they change depending on p2H. The ionizable groups responsible for the p2H dependence of these potentials are 6-propionate of heme 1 in acidic range and His 67 in basic range.

• Journal of Magnetics
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• v.21 no.4
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• pp.622-628
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• 2016

Magnetization property is a critical factor for magnetorheological fluids (MRFs) to achieve the liquid-solid transition. The main focus of this study is on exploring the influence factors on magnetization properties of MRFs. In this paper, a theoretical analysis is performed to discuss the magnetization characteristics of MRFs firstly. Then, a method for the preparation of carbonyl iron-based MRFs is illustrated and five MRFs samples with various material parameters are prepared. It is succeeded by a series of experiments on testing the hysteresis loop and the magnetization curve of each sample and the influence factors are compared and analyzed. Experimental results indicate that there is basically no hysteresis phenomenon on MRFs which exhibits superparamagnetic behavior at room temperature. A surfactant coating on magnetic particles can slightly improve the MRFs magnetization. Additionally, the magnetic susceptibility and the saturation magnetization both increase with the particle concentration, whereas the influence of particle diameter is relatively very small. Moreover, as the temperature increases, the magnetization decreases and the declining rate accelerates gradually.

• Journal of the Korean Physical Society
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• v.73 no.9
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• pp.1334-1339
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• 2018

Spherical nickel ferrite nanoparticles were synthesized using the thermal decomposition method and coated with cetyl trimethyl ammonium bromide (CTAB) after the synthesis. Transmission electron microscopy images showed that the average diameter of the particles was 9.40 nm. The status of the CTAB-coating on the surface of the particles was checked using Fourier-transform infrared spectroscopy. Their hysteresis curve showed that the particles exhibited a superparamagnetic behavior. The $T_1$ and the $T_2$ relaxations of the nuclear spins were observed in aqueous solutions of the particles with different particles concentrations by using a magnetic resonance imaging (MRI) scanner, which showed that the $T_1$ and the $T_2$ relaxivities of the particles in water were $0.57mM^{-1}{\cdot}s^{-1}$ and $10.42mM^{-1}{\cdot}s^{-1}$, respectively. In addition, using an induction heating system, we evaluated their potentials for magnetic hyperthermia applications. The aqueous solution of the particles with a moderate concentration (smaller than 6.5 mg/mL) showed a saturation temperature larger than the hyperthermia target temperature of $42^{\circ}C$. These findings show that the CTAB-coated nickel ferrite particles are suitable for applications as $T_2$ contrast agents in MRI and heat generators in magnetic hyperthermia.

• Korean Journal of Soil Science and Fertilizer
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• v.1 no.1
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• pp.117-123
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• 1968

A simplest and best method to find out lime requirement for Korean soils is described. Twenty six top soil samples were collected from various localities and chemical characteristics were dertermined. Three different buffer curve methods were employed as the standard to find out the most reliable test for lime requirement. In addition, the lime requirement test by the Shoemaker's and Woodruff's as well as the O.R.D. kit method were compared with the most reliable buffer curve method. The results may be summarized as follows. 1. The regression equation of the most reliable lime requirement by buffer curve method, y, on percent base saturation of various soils, X, was y=9.69-0.106 X and the negative correlation coefficient r=-0.84 was statistically significant at 5% level. 2. Lime requirement test by the best, buffer curve, method was more well correlated with the sum of exchangeable hydrogen and exchangeable aluminum contents of the soil samples than the exchangeable hydrogen content only. 3. The ordinary buffer curve method for lime requirement is more reasonable than the lime requirement test by the buffer curve prepared after addition of 1 normal potassium chloride or calcium chloride solutions. 4. The lime requirement tests by the most reasonable buffer curve method, X, and by the Woodruff's, the Shoemaker's and O.R.D. kit were compared. The best method for laboratory lime requirement test was the Shoemaker's method and the O.R.D. kit method also was good enough for the field test and these two method are recommended as the unified method of lime requirement test in each soil testing laboratories throughout Korea.

• Journal of Soil and Groundwater Environment
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• v.11 no.4
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• pp.48-56
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• 2006

Using a continuous injection tracer test at a multi-soil layer deposit, the difference of hydrodynamic dispersions in unsaturated and saturated zones were analyzed through breakthrough curves of Rhodamine WT, linear regression of concentration versus time, concentration variation rates versus time, and concentration ratio according to the distance from injection well. As a result of continuous injection tracer test, the difference of the maximum concentrations of Rhodamine WT in unsaturated and saturated zones were 13-15 times after 160 hours, and the increased rate of concentration versus time in unsaturated zone was about 10 times higher than in saturated zone. The fluctuation of Rhodamine WT breakthrough curve and concentration variation rate with time in saturated zone were larger than in unsaturated zone. Rhodamine WT concentration ratio with the distance from the injection well in saturation zone was linearly decreased faster than in unsaturated zone, and the elapsed time necessary for the concentration ratio less than 2 was longer in saturation zone. The differences resulted from the lower concentration and slower hydrodynamic dispersion of Rhodamine WT at the saturation zone of the multi-soil layer deposit, in which groundwater flow significantly flow and aquifer materials have high hydraulic heterogeneity. Effective porosity, longitudinal and transverse dispersivities were estimated $10.19{\sim}10.50%,\;0.80{\sim}1.98m$ and $0.02{\sim}0.04m$, respectively. The field longitudinal dispersivity is over 12 times larger than the laboratory longitudinal dispersivity by the scale-dependent effect.

• Korean Journal of Soil Science and Fertilizer
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• v.39 no.6
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• pp.329-333
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• 2006

Most of volcanic ash soils in South Korea are distributed in Jeju province which is an island placed on southern part of Korea and has steep slope mountain area. There are many soils containing high contents of organic matter (OM) derived from volcanic ash in Jejudo, also. Therefore, irrigation and drainage in volcanic ash soil different with general soil which has low OM content have to be applied with another management way, but studies searching appropriate methods for them are set on insufficient situation because the area of volcanic ash soil in South Korea is only 1.3% (130,000ha). This study was conducted for analysis of soil water content and irrigation quantity appropriate for crops cultivated in volcanic ash soil with high OM content. Although soils with different soil color have the same soil texture, soil water characteristics curve by soil color showed the difference of water retention capability by OM content. But, this characteristics classified with soil color could be unified by scaling technique with similitude analysis method which get dimensionless water content using a present water content, a residual water content and saturated water content (or water content at 10kPa). A relation of gravimetric soil water content (GSWC) and dimensionless water content by the results showed a form of power function. The dimensionless water content (DWC) express a relative saturation degree of present water content. This was also expressed by van Genuchten model which describe the relation between relative saturation degrees and matric potentials. These results on soil water characteristics curve (SWCC) of volcanic ash soil will be the basic of irrigation plan in area having high organic contents into soil.

• Korean Chemical Engineering Research
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• v.46 no.3
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• pp.626-632
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• 2008

The purpose of this study was to enhance gas exchange by producing hemosome, a hemoglobin microencapsulated with phospholipid of egg, and perfluorocarbone(PFC) emulsion solution. In the experiment, stable emulsion solution with 437 nm of mean particle size could be produced by Flusol-DA sonication, and shortening of emulsion time could be attained with higher stability as well. $0.8{\mu}m$ sized hemosome could be produced by microencapsulation of hemoglobin with phospholipid extracted from egg yolk. The pattern of oxygen saturation curve of hemosome was S shape, which is similar to that found in normal blood, and $P_{50}$ was measured to be 24 mmHg. The oxygen saturation in the mixed solution of hemosome and blood in 1:4(V/V%) ratio was similar to that of normal blood, and the same result was found in the mixed solution of PFC emulsion and blood in 1:4(V/V%) ratio.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.6
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• pp.24-33
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• 2000

Switching behaviour of the ferroelectric thin film and device characteristics of the MFSFET(Metal-Ferroelectric-Semiconductor FET) are simulated with taking into account the accumulation of oxygen vacancies near interface between the ferroelectric thin film and the bottom electrode caused by the progress of fatigue. In our switching model, relative switched charge is 0.74 nC before fatigue, but after the progress of fatigue it reduces to 0.15 nC with the generation of oxygen vacancies. It indicates that the generation of oxygen vacancies strongly suppresses polarization reversal. $C-V_G\;and\;I_D-V_G$ curves in our MFSFET device model exhibit the memory window of 2 V and show the accumulation, the depletion and the inversion regions in capacitance characteristic clearly. The difference of saturation drain current of the device before fatigue in shown by the dual threshold voltages in $I_D-V_G$ curve as 6nA/$cm^2$ and decreases as much as 50% after fatigue. Decrease of the difference of saturation drain currents by fatigue implies that the accumulation of oxygen vacancies with the fatigue should be avoided in the device application. Our simulation model is expected to play an important role in estimation of the behavior of MFSFET device with various ferroelectric thin films.

• Journal of the Mineralogical Society of Korea
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• v.15 no.2
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• pp.114-121
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• 2002

Buffer capacities for two Bo horizon soils or Andisols developed from different parent materials have been investigated. The titration curves from column leaching experiment show that buffering occurred at pH 4.0 and 6.0. The buffer intensity or soil developed from pyroclastic materials (P-soil) is higher than that from basalts (B-soil). From batch test we have found that proto-imogolite and/or imogolite may control Al solubility as well as $Al(OH) _3$in the moderate acid condition. The buffer intensities ($\beta$) of P-soils were plotted on the theoretical buffering curve of $Al(OH)_3$, while $\beta$ of B-soils approached to that of proto-imogolite, which shows the solubility of short-range-order materials in P-soil control the buffer capacity. Buffering at pH 6.0 is thought to be the result of dissolution of some silicate clays and exchange reactions between $H^{+ }$and base-forming cations. Considering the amount of annual acid precipitation, aluminum solubility of Andisols, and the low BS (Base Saturation percentage), it can be predicted that prolonged acid precipitation will reduce the buffer capacity of soils and lead to soil acidification.