• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.8
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• pp.970-976
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• 2007

This paper presents a novel polar transmitter architecture with a 2-bit sigma-delta modulator. In the proposed architecture, the 2-bit sigma-delta modulator is introduced to suppress quantization noise of conventional sigma-delta modulator. The power amplifier configuration is also modified in a binary form to accommodate the 2-bit digitized envelope signal. The Ptolemy simulation results of the proposed structure show that the spectral property is greatly improved in full transmit band of EDGE system. The fine quantization scheme of the 2-bit modulator lowers the noise level by 10dB without increasing the over-sampling ratio, which may be obtained if the over-sampling ratio increases twofold. Dynamic range is also enhanced up to 5dB owing to the new form of the power amplifier in the transmitter.

• Journal of the Korean Geophysical Society
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• v.3 no.2
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• pp.127-138
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• 2000

This study was conducted to examine the differences between dynamic and static elastic constants by use of some laboratory tests of cement mortar specimens which have different water/cement mixing ratios. Specific gravity measurement, ultrasonic velocity estimating and uniaxial compression test were adopted to acquire the dynamic and static elastic constants. Digital data acquisition and processing enhanced the accuracy of estimating the velocities of specimens drastically, Also, the method using the gradient of propagation delay time in according to increment of specimen length more enhanced the accuracy than the method using the only one specimen length over total propagation time. The correlation between density and the P and S wave velocity of specimens shows reliable positive relation and the correlation between density and the strength of uniaxial compression has the similar relationship. The dynamic Young's modulus $(E_D)$ is alway greater than the static Young's modulus $(E_S)$ and there is increasing tendency of the ratio $(E_D/E_S)$ according to the increase of density or strength of the specimens. On the other hand, there is no typical relationship between dynamic Poisson's ratio $({\nu}_D)$ and static Poisson's ratio $({\nu}_S)$ and just the ratio of ${\nu}_D/{\nu}_S$ ranges front 69 to 122 %.

• Applied Chemistry for Engineering
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• v.10 no.6
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• pp.881-884
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• 1999

We have studied the other unit which is partial element in fullerene $C_{90}$. The energy of the higher fullerene increased by 5.6 kcal/mol for each $1.0{\beta}$ of planarity for the other units and increased by 11.0 kcal/mol for each $2C_1$ other unit at RHF/AM1 method. Therefore, we have known that the stable $C_{90}$ isomer do not have $C_1$ unit in other unit and have small planarity. The confirmable $C_{90}$ isomers by experiment satisfies these two conditions.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04a
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• pp.17-20
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• 2002

The effects of relatively low lead content (0.2~0.3) on the 2223 phase formation and transport property of Bi-2223/Ag tapes have been investigated. The results show that lead contents have great impact on the phase assemblage of precursors, subsequently, on the phase formation and transport property of silver sheathed BSCCO-2223 tapes. Powders containing Pb=0.25 and Pb=0.3 resulted in the nearly identical $J_c$ values in fully processed tapes, but leaded to significant difference on the phase formation process. For the case of Pb=0.2, both low conversion fraction of 2212 to 2223 and low $J_c$ value were obtained in final reacted tape, which was probably due to lack of enough liquid phase to facilitate the phase transformation.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.226-229
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• 2003

Following the successful development of practical high temperature superconducting (HTS) wires, there has been renewed activity in the development of superconducting power equipments. HTS equipments must be operated in the coolant, such as liquid nitrogen (L$N_2$) or cooled by cooler, such as GM-cryocooler to maintain the temperature below critical temperature. In this paper, dielectric strength of some insulating materials, such as epoxy, teflon, and glass fiber reinforced plastic (GFRP) in L$N_2$was measured. Surface breakdown voltage of GFRP which is basic property in design of HTS solenoid coil was measured. Epoxy is a goof insulating material but it is fragile at cryogenic temperature. The multi-layer insulating method of current lead is suggested to compensate this fragile property. It consists of teflon tape layer and epoxy layer fixed with texture. Based on these measurements, the 6.6㎸ class HTS magnet for DC reactor type high-T$_{c}$ superconducting fault current limiter (SFCL) was successfully fabricated and tested.d.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.3
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• pp.45-54
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• 2000

Ignition transient is a. very rapid process lasting only in the order of 100 milliseconds and therefore it is difficult to measure all relevant ballistic properties. Numerical simulation is thus useful to quantify some of these hard to measure flow and ballistic properties. One-dimensional model was employed to study the effects of aging using simplified aging scenarios for both N-H sustainer and booster motors. Also the effects of newly designed igniter on the ignition of N-H sustainer was simulated. Radiation effects could be significant in terms of energy flux increase to the propellant surface and the energy exchange between the combustion gas itself. One dimension implementation of radiation showed significant effects for rear-mounted igniter. Implementation of radiation effects into 2-D axi-symmetric numerical model was completed and its effects on the N-H sustainer were examined. To have a reliable prediction of computer model on ignition transient, accurate chemical property data on the propellant and igniter gas are required. It was found that such property data on aged N-H motors are not available. Chemical aging model can be used to predict to some degree of accuracy effects of aging on chemical and mechanical properties. Such a model was developed, albeit 2-dimensional, to study migration of moisture through a representative solid rocket motor configuration.

• Korean Journal of Soil Science and Fertilizer
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• v.39 no.6
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• pp.366-371
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• 2006

This study was done to assess the physical and chemical properties after anaerobic fermentation treatment which use rice bran or wheat bran in plastic film house soil. The results which investigates the change of soil physical property after treatment 150 days showed a dramatic difference. The physical properties of control soil were the bulk density $1.46Mg\;m^{-3}$, hardness $2.30Kg\;cm^{-3}$, hydraulic conductivity $4.8cm\;hr^{-1}$, water stable aggregate(>0.5mm) 6.7%. Of the soil which treatment the rice bran in comparison to control soil, bulk density and hardness was diminished 12% and 58%, respectively. hydraulic conductivity and water stable aggregate(>0.5mm) were increased 4.5 and 5.2 fold, respectively. And, in the soil which treatment the wheat bran, bulk density and hardness was diminished 14% and 67%, respectively. Hydraulic conductivity and water stable aggregate(>0.5mm) were increased 6.3 and 6.5 fold, respectively. $NO_3-N$ contents of the soil which treated the rice bran or wheat bran after treatment 20 days were diminished 98% in comparison to control soil. The decrease of $NO_3-N$ contents in the soil was investigated with the fact that it is caused by with increase of the soil-microbial biomass. EC of the soil which treated the rice bran were $1.48dS\;m^{-1}$ which was diminished 58% in comparison to control soil. That of soil which treated the wheat bran was increased $3.65dS\;m^{-1}$ in the early stage because of acetic and butyric acid. But it was reduced as under $2.0dS\;m^{-1}$ after treatment 30 days. As the conclusion the anaerobic fermentation treatment with rice or wheat bran was effective to the improvement of soil physical and salt accumulation of the plastic film house soil.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1994.11a
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• pp.3-7
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• 1994

In this study, to improve sintering condition, anisotropic Property(k$\_$t//k$\_$p/) of electromechanical coupling coefficients, and hydrostatic piezoelerlric constants d$\_$h/ and g$\_$h/, MnO$_2$impurity was added to the (Pb$\_$0.76/Ca$\_$0.24)[(Co$\_$$\frac{1}{2}$W$\_$$\frac{1}{2}$/)$\_$0.04/Ti$\_$0.96/]O$_3$ System ceramics for hydrophone. And the structural, electrical properties of them were investigated. As a results. tetragonality was decreased with MnO$_2$ additives and density was the highest value of 7.06(g/㎤) at H2-3 specimen. Electromechanical coupling coefficients of H2-3 specimen were k$\_$t/=49 and k$\_$p/ 0, which exibited the hightest hydrostatic piezoelectric constants of d$\_$h/=64.52[10$\^$-1/C/N] and g$\_$h/=35.92[10$\^$-3/ Vm/N].

• Bulletin of the Korean Chemical Society
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• v.30 no.7
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• pp.1573-1578
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• 2009

A computational study of the reactions between Zn-containing species, the products of the thermal decomposition of diethylzinc (DEZn) and water was investigated. The Zn-containing species – $C_2H_5)_2,\;HZnC_2H_5,\;and\;(ZnC_2H_5)_2$ – were assumed to react with water during ZnO metal organic chemical vapor deposition (MOCVD). Density functional theory (DFT) calculations at the level of B3LYP/6-311G(d) were employed for the geometry optimization and thermodynamic property evaluation. As a result dihydroxozinc, $Zn(OH)_2$, was the most probable reaction product common for all three Zn-containing species. A further clustering of $Zn(OH)_2$ was investigated to understand the initial stage of ZnO film deposition. In experiments, the reactions of DEZn and water were examined by in-situ Raman scattering in a specially designed MOCVD reactor. Although direct evidence of $Zn(OH)_2$ was not observed, some relevant reaction intermediates were successfully detected to support the validity of the gas phase reaction pathways proposed in the computational study.

• Journal of the Korean Society of Radiology
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• v.9 no.1
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• pp.39-45
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• 2015

$La_2W_3O_{12}:Eu^{3+}$ phosphors were prepared by solid state reaction method. The crystal structure was characterized by XRD pattern and ICSD card (78180). Luminescence properties of $La_2W_3O_{12}:Eu^{3+}$ are investigated by optical and laser-excitation spectroscopy in which emission and excitation spectra and time-resolved spectra are measured. The 1 mol % $Eu^{3+}$-doped $La_2W_3O_{12}$ phosphor exhibits broad excitation band peaking at 286 nm due to the ligand-to-metal charge transfer transition. The excitation lines due to the $^7F_0{\rightarrow}{^5D_4},{^5D_4},{^5L_6},{^5G_4},{^5D_3},{^5D_2}$ transitions of $Eu^{3+}$ are observed in the wavelength region 350-500 nm. The strong line emission is observed at 618 nm corresponding to the due to the $^5D_0{\rightarrow}^7F_2$ transition. The lifetime of 618 nm emission decreases with increasing temperature as 7 K ($114{\mu}s$), 100 K ($94{\mu}s$), 200 K ($10{\mu}s$) and 300 K ($0.5{\mu}s$).