• Journal of Astronomy and Space Sciences
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• v.28 no.2
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• pp.117-122
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• 2011

In this paper, the anisotropic nature of the magnetic turbulence associated with magnetic dipolarizations in the Earth's plasma sheet is examined. Specifically, we determine the power spectral indices for the perpendicular and parallel components of the fluctuating magnetic field with respect to the background magnetic field, and compare them in order to identify possible anisotropic features. For this study, we identify a total of 47 dipolarization events in February 2008 using the magnetic field data observed by the THEMIS A, D and E satellites when they are situated near the neutral sheet in the near-Earth tail. For the identified events, we estimate the spectral indices for the frequency range from 1.3 mHz to 42 mHz. The results show that the degree of anisotropy, as defined by the ratio of the spectral index of the perpendicular components to that of the parallel component, can range from ~0.2 to ~2.6, and there are more events associated with the ratio greater than unity (i.e., the perpendicular index being greater than the parallel index) than those which are anisotropic in the opposite sense. This implies that the dipolarization-associated turbulence of the magnetic field is often anisotropic, to some non-negligible degree. We then discuss how this result differs from what the theory of homogeneous, anisotropic, magnetohydrodynamic turbulence would predict.

• Journal of Powder Materials
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• v.24 no.5
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• pp.357-363
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• 2017

In this study, Bi-Sb-Te thermoelectric materials are produced by mechanical alloying (MA) and spark plasma sintering (SPS). To examine the influence of the milling atmosphere on the microstructure and thermo-electric (TE) properties, a p-type Bi-Sb-Te composite powder is mechanically alloyed in the presence of argon and air atmospheres. The oxygen content increases to 55% when the powder is milled in the air atmosphere, compared with argon. All grains are similar in size and uniformly, distributed in both atmospheric sintered samples. The Seebeck coefficient is higher, while the electrical conductivity is lower in the MA (Air) sample due to a low carrier concentration compared to the MA (Ar) sintered sample. The maximum figure of merit (ZT) is 0.91 and 0.82 at 350 K for the MA (Ar) and MA (Air) sintered samples, respectively. The slight enhancement in the ZT value is due to the decrease in the oxygen content during the MA (Ar) process. Moreover, the combination of mechanical alloying and SPS process shows a higher hardness and density values for the sintered samples.

• Journal of the Korean Applied Science and Technology
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• v.36 no.1
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• pp.153-164
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• 2019

To develop a high performance SCR catalyst which has better specific surface area, lightness of weight and fast temperature response than those of existing commercial SCR catalyst, metal foam type SCR catalysts were prepared by washcoating with vanadium, tungsten and binder. The de-NOx performance test of the prepared catalysts was carried out on atmospheric micro-test unit at lab. scale according to space velocity variation and temperature change, and the characteristics of them were analyzed by Porosimeter, SEM(scanning electron microscope), EDX(energy dispersive x-ray spectrometer), ICP(inductively coupled plasma) and Stereomicroscope. The NOx reduction performance decreased as the space velocity increased and was found to be the best at 3.5 wt.% contents of the vanadium and tungsten. It was found that the larger amount of binder was added, the worse the NOx reduction performance was, which was considered to be that the number of active sites of the prepared catalyst surface was occupied by the binder. We found that the amount of binder to be added to prepare the catalyst should be properly controlled by the condition of coated catalyt surface.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.4
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• pp.151-157
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• 2014

The degradation mechanisms of thermal barrier coatings (TBCs) were investigated in different thermal fatigue condition in terms of microstructural analyses. The isothermal and cyclic oxidation tests were conducted to atmospheric plasma sprayed-TBCs on NIMONIC 263 substrates. The delamination occurred by the oxide layer formation at the interface, the Ni/Cr-based oxide was formed after Al-based oxide layer grew up to ${\sim}10{\mu}m$ in the isothermal condition. In the cyclic oxidation with dwell time, the failure occurred earlier (500 hr) than in the isothermal oxidation (900 hr) at same temperature. The thickness of Al-based oxide layer of the delaminated specimen in the cyclic condition was ${\sim}4{\mu}m$ and the interfacial cracks were observed. The acoustic emission method revealed that the cracks generated during the cooling step. It was considered that the specimens were prevented from the formation of the Al-based oxide by cooling treatment, and the degradation mode in the cyclic test was dominantly interfacial cracking by the difference of thermal expansion coefficients of the coating layers.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.194.2-194.2
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• 2016

저주파 (수십 kHz)와 고주파 (13.56 MHz)로 구동되는 대기압 플라즈마 젯을 발생시키고, 인가전압 (혹은 인가전력)과 기체 유량에 따른 대기압 플라즈마의 특성을 비교하였다. 고주파에서 발생된 플라즈마는 저주파의 경우보다 안정적이었으며, 인가전압 (혹은 인가전력)이 증가함에 따라 플라즈마 기체온도는 상승하였고, 고주파 젯의 기체온도는 저주파 젯 보다 높았으나 330 K이하인 것을 확인하였다. Optical Emission Spectroscopy (OES)를 이용하여 저주파와 고주파의 광 방출 특성을 측정하였다. 저주파에서는 $N_2{^+}$ (391.4 nm)의 intensity 증가가 두드러지게 나타났지만 고주파 젯에서는 $N_2$, $N_2{^+}$의 intensity는 감소하였으며, OH, NO, $H_{\alpha}$, O와 같은 활성 산소 종 (Reactive Oxygen Species)이 저주파 젯 보다 높게 측정되었다. Boltzmann plot method를 이용한 분석을 통해 저주파와 고주파 영역에서의 플라즈마 전자 여기 온도를 측정하였다. 또한 자외선 흡수분광법을 이용하여 플라즈마-액체 계면에서의 OH이 입자밀도를 측정하여 OES방법으로 측정한 OH 밀도와 비교하였다. 그리고 화학적 측정법 (terephtalic acid solution)을 이용하여 액체 내의 OH의 농도를 측정하였다.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.307-310
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• 2005

The Solar-B is the third Japanese spacecraft dedicated for solar physics to be launched in summer of 2006. The spacecraft carries a coordinated set of optical, EUV and X-ray instruments that will allow a systematic study of the interaction between the Sun's magnetic field and its high temperature, ionized atmosphere. The Solar Optical Telescope (SOT) consists of a 50cm aperture diffraction limited Gregorian telescope and a focal plane package, and provides quantitative measurements of full vector magnetic fields at the photosphere with spatial resolution of 0.2-0.3 arcsec in a condition free from terrestrial atmospheric seeing. The X-ray telescope (XRT) images the high temperature (0.5 to 10 MK) corona with improved spatial resolution of approximately 1 arcsec. The Extreme Ultraviolet Imaging Spectrometer (EIS) aims to determine velocity fields and other plasma parameters in the corona and the transition region. The Solar-B telescopes, as a whole, will enable us to explore the origins of the outer solar atmosphere, the corona, and the coupling between the fine magnetic structure at the photosphere and the dynamic processes occurring in the corona. The mission instruments (SOT/EIS/XRT) are joint effort of Japan (JAXA/NAO), the United States (NASA), and the United Kingdom (PPARC). An overview of the spacecraft and its mission instruments are presented.

• Nuclear Engineering and Technology
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• v.6 no.4
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• pp.253-259
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• 1974

The output signal voltage of the pulsed ionization chamber (PIC) was measured for a range of electron density (10$^{13}$ -10$^{17}$ m$^{-3}$ ) of the 3He plasmas. This experimental data was in excellent agreement with the theory including space charge effects. As an application of the PIC techniques, two-body recombination coefficients were obtained with electron densities measured from output signal voltage of the PIC. These values as a function of pressure were in good agreement with theoretical predictions and ranged from 5$\times$10$^{-14}$ to 3$\times$10$^{-13}$ (㎥/sec) at 300$^{\circ}$K for 1 to 10 atmospheric $^3$He plasma.

• Journal of the Korean Institute of Telematics and Electronics
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• v.22 no.2
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• pp.90-96
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• 1985

The properties of plasma-enhanced CVD phosphorous silicate glass (PECVD PSG) for passivation layer are studied . Phosphorous contentration was analyzed with X-ray fluores-cence. As a result, PECVD PSG has a limiting phosphors concentration of about 8 mole%. Curves relating to etcll rate, infrared absorption ratio, and sheet resistivity were adapted to monitor phosphorous concentration indirectly Dielectric properties, step coverage, crack resistance, and gettering effect are discussed in both of atmospheric pressure CVD (APCVO) and PECVD oxide. PECVD SiO2 film have density of about 2.4 g/㎤ at deposition rate of 450$\AA$/min, refractive index of about 1.53, and breakdown at fields of II-13 MV/cm. Crack resistance of PECVD oxide is greater than APCVD oxide. PECVD PSG films contained with 2 mole % phosphorous show good step coverage and gettering ability. The obtained results show more advantages in PECVD PSG than in APCVD PSG for device passivation.

• Laser Solutions
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• v.17 no.4
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• pp.7-13
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• 2014

In this work, the application of laser induced breakdown spectroscopy (LIBS) for the composition analysis of thin $Cu(In,Ga)Se_2$ (CIGS) solar cell films ($1-2{\mu}m$ thickness) is reported. For the ablation of CIGS films, femtosecond (fs) laser (wavelength = 343nm, pulse width = 500fs) and nanosecond (ns) laser (wavelength = 266nm, pulse width = 5ns) were used under atmospheric environment. The emission spectra were detected with an intensified charge coupled device (ICCD) spectrometer and multichannel CCD spectrometer for fs-LIBS and ns-LIBS, respectively. The calibration curves for fs-LIBS and ns-LIBS intensity ratios of Ga/Cu, In/Cu, and Ga/In were generated with respect to the concentration ratios measured by inductively coupled plasma optical emission spectrometry (ICP-OES).

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1350-1351
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• 2008

대기압 플라즈마를 발생시키는 것은 종래의 저기압 플라즈마를 발생시키는 것 보다 대단히 어렵다. 하지만, 대기압 플라즈마는 진공장치가 필요 없고, 제작방식이 비교적 간편하며 살균, 의료, 표면처리 등 다양한 응용이 가능해서 그 잠재력이 매우 크다. 본 연구에서는 유전체가 없는 두 전극사이에서 대기압 저온 마이크로 플라즈마를 발생시켰으며, submicrosecond pulse 파형으로 glow discharge를 유지할 수 있었다. 플라즈마 소스의 전극 간격은 200[${\mu}m$]이고 방전개시전압은 약 450${\sim}$600[V]이다. 플라즈마를 발생시키기 위한 feeding gas는 He 100%이다. 본 연구에서 개발된 대기압 플라즈마는 소비전력이 2[W]미만으로 온도는 조건에 따라 40$^{\circ}C$미만으로 발생 가능하다. 또한 스펙트럼 분석 시 777nm인 산소원자의 peak이 다른 원자 혹은 분자들의 peak보다 월등히 높다.