• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.369.2-369.2
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• 2014

Diamond-like Carbon(DLC) films doping Si were deposited by linear ion source(LIS)-physical vapor deposition method on Si wafer. We have studied the effects of Si content on friction and wear properties of DLC films and the characteristics of the films were investigated using Nano-indentation, Micro raman spectroscopy, Field Emission-Scanning Electron Microscope (FM-SEM) and X-ray Photoelectron Spectroscopy (XPS). The films has been various low-friction and low-stress by varying the flow rates of silane gas. Under the about 2% of Si doping is very suitable for improving the adhesion of films and reducing internal stress while maintaining the surfaces hardness of DLC films. Linear ion source (LIS)를 사용하여 Si wafer위에 Si 이온이 첨가된 DLC 박막을 증착하였다. 참가된Si 이온의 양에 따라 DLC 박막에 미치는 영향을 분석하기 위하여 마찰 계수 및 경도를 비교하였고, Micro raman spectroscopy, Field Emission-Scanning Electron Microscope (FM-SEM) and X-ray Photoelectron Spectroscopy (XPS)를 통하여 표면 상태를 분석하였다. 천체 주입된 가스량의 약 2%까지 Si 이온 주입이 늘어날수록 DLC 박막의 마찰계수는 낮아졌고, 경도는 Si 이온이 주입되지 않았을 경우와 비슷한 값(약 20~23 GPa)을 가졌다. 2% 이상의 주입량에서는 마찰계수는 주입량이 늘어날수록 높아졌으며 경도는 떨어지는 경향을 보였다. 이는 Si이온이 2%이하로 첨가되었을 경우, DLC 박막의 생성시 탄소 이온들의 결합 Stress를 줄여 마찰계수가 줄어든다고 볼 수 있으며, 그 양이 2%이상이 되면 오히려 불순물로 작용하여 DLC 박막의 Stress는 급격히 증가하고 마찰계수도 높아짐을 알 수 있다.

• Microbiology and Biotechnology Letters
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• v.31 no.1
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• pp.1-12
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• 2003

Myxobacteria are soil bacteria that move by gliding and have a complicated life cycle. In the research over the 25 years the myxobacteria have been shown to be a rich source of potentially useful bioactive substances. So far about 80 different basic compounds and 450 structural variants have been characterized. It is remarkable that myxobacteria produce the substance has special mechanisms. 26 new electron transport inhibitors,5 inhibitors of nucleic acid polymerases, 10 substances that act on the cytoskeleton, and 1 inhibitor of fungal acetyl-CoA carboxylase have been found. Presently, large-scale technical process was not fully established. But one of the compounds from myxobacteria is able to pass the many thresholds, which are on the road to application.

• Bulletin of the Korean Chemical Society
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• v.28 no.4
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• pp.533-537
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• 2007

This paper describes the heteroepitaxial growth of single-crystalline 3C-SiC (cubic silicon carbide) thin films on Si (100) wafers by atmospheric pressure chemical vapor deposition (APCVD) at 1350 oC for micro/nanoelectromechanical system (M/NEMS) applications, in which hexamethyldisilane (HMDS, Si2(CH3)6) was used as a safe organosilane single-source precursor. The HMDS flow rate was 0.5 sccm and the H2 carrier gas flow rate was 2.5 slm. The HMDS flow rate was important in obtaing a mirror-like crystalline surface. The growth rate of the 3C-SiC film in this work was 4.3 μm/h. A 3C-SiC epitaxial film grown on the Si (100) substrate was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Raman scattering, respectively. These results show that the main chemical components of the grown film were single-crystalline 3C-SiC layers. The 3C-SiC film had a very good crystal quality without twins, defects or dislocations, and a very low residual stress.

• Journal of the Korean institute of surface engineering
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• v.37 no.4
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• pp.220-225
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• 2004

A new ion beam extraction system is designed using a simple ion mass filter and a micro mass balance and a QMS based detecting system. A quadrupole Mass Filter is used for selective ion beam formation from inductively coupled high density plasma sources with appropriate electrostatic lens and final analyzing QMS. Also a quartz crystal microbalance is set between a QMF and a QMS to measure the etching and polymerization rate of the mass selected ion beam. An inductively coupled plasma was used as a ion/radical source which had an electron temperature of 4-8 eV and electron density of $4${\times}$10^{11}$＃/㎤. A computer interfaced system through 12bit AD-DA board can control the pass ion mass of the qmf by setting RF/DC voltage ratio applied to the quadrupoles so that time modulation of pass ion's mass is possible. So the direct measurements of ion - surface chemistry can be possible in a resolution of $1\AA$/sec based on the qcm's sensitivity. A full set of driving software and hardware setting is successfully carried out to get fundamental plasma information of the ICP source and analysed $Ar^{+}$ beam was detected at the $2^{nd}$ QMS.

• Journal of the Korean Ceramic Society
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• v.28 no.8
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• pp.585-592
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• 1991

ZnO films were deposited onto Corning glass 7059 substrate in the temperature range from $200^{\circ}C$ to $450^{\circ}C$ by chemical vapor deposition technique using the hydrolysis of Diet ylzinc (DEZ). As the deposition temperature increased from $200^{\circ}C$ to $350^{\circ}C$, the deposition rate increased with the apparent activation energy of ∼23kJ/mole. Further increase of the deposition temperature above $400^{\circ}C$, however, resulted in a reduction of the rate. It was found that ZnO film grew with a strong C-axis preferred orientation at the temperature of $400^{\circ}C$. As the deposition temperature increased, the film resistivity decreased down to ∼0.2 $\Omega$cm at $450^{\circ}C$. The electrical resistivity was governed more likely by electron concentration rather than by electron mobility. Average optical transmission of the films in the optical wavelength range of 400 nm to 900 nm was over 90% and the optical energy band gap of 3.28∼3.32 eV was obtained from the direct transition.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.8
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• pp.1376-1382
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• 2016

The discharge characteristics of inductively coupled $Ar/CH_4$ plasma were investigated by fluid simulation. The inductively coupled plasma source driven by 13.56 Mhz was prepared. Properties of $Ar/CH_4$ plasma source are investigated by fluid simulation including Navier-Stokes equations. The schematics diagram of inductively coupled plasma was designed as the two dimensional axial symmetry structure. Sixty six kinds of chemical reactions were used in plasma simulation. And the Lennard Jones parameter and the ion mobility for each ion were used in the calculations. Velocity magnitude, dynamic viscosity and kinetic viscosity were investigated by using the fluid equations. $Ar/CH_4$ plasma simulation results showed that the number of hydrocarbon radical is lowest at the vicinity of gas feeding line due to high flow velocity. When the input power density was supplied as $0.07W/cm^3$, CH radical density qualitatively follows the electron density distribution. On the other hand, central region of the chamber become deficient in CH3 radical due to high dissociation rate accompanied with high electron density.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1530-1533
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• 2005

Total 12 units of high power klystron-modulator systems as microwave source is under operation for 2.5-GeV electron linear accelerator in Pohang Light Source(PLS) linac. RF power and beam power of klystron are precisely measured for the effective control of electron beam. A precise measurement and measurement equipment with good response characteristics are required for this. Input power of klystron is calculated from the applied voltage and the current on its cathode. Tiny measurement error severely effects RF output power value of klystron. Therefore, special care is needed to measure precise beam voltage. Capacitive voltage divider(CVD) unit is intended for the measurement of beam voltage of 400 kV generated from the pulsed klystron-modulator system. Main parameter to determine the standard capacitance in the high arm of CVD is dielectric constant of insulation oil. Therefore CVD should be designed to have a minimum capacitance variation due to voltage, frequency and temperature in the measurement range. This paper will discuss the analysis of capacitive voltage divider for a pulsed high-voltage measurement, and the empirical relations between capacitance and oil temperature variation.

• Journal of Astronomy and Space Sciences
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• v.35 no.4
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• pp.211-218
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• 2018

Solar microwave bursts carry information about the magnetic field in the emitting region as well as about electrons accelerated during solar flares. While this sensitivity to the coronal magnetic field must be a unique advantage of solar microwave burst observations, it also adds a complexity to spectral analysis targeted to electron diagnostics. This paper introduces a new spectral analysis procedure in which the cross-section and thickness of a microwave source are expressed as power-law functions of the magnetic field so that the degree of magnetic inhomogeneity can systematically be derived. We applied this spectral analysis tool to two contrasting events observed by the Owens Valley Solar Array: the SOL2003-04-04T20:55 flare with a steep microwave spectrum and the SOL2003-10-19T16:50 flare with a broader spectrum. Our analysis shows that the strong flare with the broader microwave spectrum occurred in a region of highly inhomogeneous magnetic field and vice versa. We further demonstrate that such source properties are consistent with the magnetic field observations from the Michelson Doppler Imager instrument onboard the Solar and Heliospheric Observatory (SOHO) spacecraft and the extreme ultraviolet imaging observations from the SOHO extreme ultraviolet imaging telescope. This spectral inversion tool is particularly useful for analyzing microwave flux spectra of strong flares from magnetically complex systems.

• Journal of Soil and Groundwater Environment
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• v.27 no.3
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• pp.41-49
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• 2022

This study utilized citric acid as a floating agent in biological denitrification process and assessed its role under different carbon supplying conditions. Several microcosm tests including citric acid active (CAA), precipitating tablet release active (PTRA) and floating tablet release active (FTRA) were conducted to evaluate nitrate denitrification efficacy. In CAA reactors, nitrate removal was accompanied by the formation of denitrification by-products such as nitrite and nitrous oxide, with the extent of nitrate removal being proportional to citric acid concentration. These results suggest that citric acid induced heterotrophic biological denitrification. PTRA reactor that incorporated CAA and the same electron donor showed a similar denitrification efficiency to CAA reactor. FTRA reactor, which contained the same amount of fumarate as PTRA, enhanced denitrification by 7% as compared to the PTRA reactor. The overall results of this work indicate that surplus citric acid can be efficiently utilized in heterotrophic denitrification.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.1994-1998
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• 2023

This study quantitatively evaluated the source term of a linear accelerator according to target thickness for a 6-20 MeV electron beam using MCNP6. The elements of the target were tungsten and copper, and a composite target and single target were simulated by setting different thickness parameters depending on energy. The accumulation of energy generated through interaction with the collided target was evaluated at 0.1-mm intervals, and F6 tally was used. The results indicated that less than 3% reference error was maintained according to the MCNP recommendations. At 6, 8, 10, 15, 18, and 20 MeV, the energy accumulation peaks identified for each target were 0.3 mm in tungsten, 1.3 mm in copper, 1.5 mm in copper, 0.5 mm in tungsten, 0.5 mm in tungsten, and 0.5 mm in tungsten. For 8 and 10 MeV in a single target consisting only of copper, the movement of electrons was confirmed at the end of the target, and the proportion of escaped electrons was 0.00011% and 0.00181%, respectively.