• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.6
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• pp.65-71
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• 2002

Characteristics of corona discharge of the different types of the plasma reactors which are cone-hole and cone-plate is investigated experimentally. The discharge starts at lower voltage for the cathode corona than the anode corona and spark occurs at higher voltage for the cathode corona. And the cathode corona makes more stable discharge than the anode corona. The effect of the base gas in corona discharge for different O$_2$/N$_2$ concentrations is related with the gas molecular weight. The discharge for the smaller molecular weight gas occurs easier than for the high molecular weight gas. The discharge current decreases with the increase of oxygen concentration and it increases more sharply for anode corona than for cathode corona as discharge voltage increases after corona onset voltage. NO-NO$_2$ conversion increases with the energy density of corona discharge and the addition of O$_2$ in a base N$_2$ gas.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.11
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• pp.1246-1251
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• 2004

This paper is investigated about the effect of carrier gas type and the humidity for generating hydrogen gas. The vibration of the water surface is more powerful with increasing applied voltage. In this experimental reactor which is made of multi-needle and plate, the maximum acquired hydrogen production rate is about 3500 ppm. In the experimental result of generating hydrogen gas by non-thermal plasma reactor, the rate of generating hydrogen gas is different with what kind of carrier gas is. We used two types of carrier gas, such as $N_2$ and He. $N_2$ as carrier gas is more efficient to generate hydrogen gas than He because $N_2$ is reacted with $O_2$, which is made from water dissociation. In comparison with water droplet by humidifier and without water droplet by humidifier, the generation of hydrogen gas is decreased in case of water droplet by humidifier. That is the result that the energy for water dissociation is reduced on water surface because a part of plasma energy is absorbed at the small water molecular produced from humidifier.

• Journal of Astronomy and Space Sciences
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• v.33 no.2
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• pp.109-117
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• 2016

We explain the results of Yu et al. (2015b) of the novel sharpness angle measurement to a large number of spectra obtained from the Fermi gamma-ray burst monitor. The sharpness angle is compared to the values obtained from various representative emission models: blackbody, single-electron synchrotron, synchrotron emission from a Maxwellian or power-law electron distribution. It is found that more than 91% of the high temporally and spectrally resolved spectra are inconsistent with any kind of optically thin synchrotron emission model alone. It is also found that the limiting case, a single temperature Maxwellian synchrotron function, can only contribute up to 58⁺²³₋₁₈% of the peak flux. These results show that even the sharpest but non-realistic case, the single-electron synchrotron function, cannot explain a large fraction of the observed spectra. Since any combination of physically possible synchrotron spectra added together will always further broaden the spectrum, emission mechanisms other than optically thin synchrotron radiation are likely required in a full explanation of the spectral peaks or breaks of the GRB prompt emission phase.

• Composites Research
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• v.36 no.4
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• pp.241-245
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• 2023

Aluminum (Al) and copper(Cu) are non-ferrous alloys with excellent electrical and thermal conductivity but have relatively lower mechanical properties than iron alloys. Stainless steel(STS), an iron alloy, is a high-strength industrial material due to its excellent mechanical properties and corrosion resistance compared to non-ferrous Al and Cu. In this research combined Al, Cu, and STS to fabricate as a functionally graded material (FGM) through a powder metallurgical process. The produced FGM exhibited lightweight and excellent surface hardness compared to copper and iron alloys and also showed higher thermal conductivity than single Al and STS materials.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.67.3-68
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• 2016

An X1.6 flare occurred in AR 12192 on 2014 October 22 around 14:06 UT and was observed by Hinode, IRIS, SDO and RHESSI. We analyze a bright kernel which produces a white light flare (WLF) with continuum enhancement and a hard X-ray (HXR) peak. Taking advantage of the spectroscopic observations of IRIS and EIS, we measure the temporal variation of the plasma properties in the bright kernel in the chromosphere and corona. We found that explosive evaporation was observed when the WLF occurred, even though the intensity enhancement in hotter lines is quite weak. The temporal correlation of the WLF, HXR peak, and evaporation flows indicates that the WLF was produced by accelerated electrons. To understand the white light emission processes, we calculated the deposited energy flux from the non-thermal electrons observed by RHESSI and compared it to the dissipated energy estimated from the chromospheric lines (Mg II triplet) observed by IRIS. The deposited energy flux from the non-thermal electrons is about $3.1{\times}10^{10}erg\;cm^{-2}s^{-1}$ when we assume a cut-off energy of 20 keV. The estimated energy flux from the temperature changes in the chromosphere measured from the Mg II subordinate line is about $4.6-6.7{\times}10^9erg\;cm^{-2}s^{-1}$, 15 - 22 % of the deposited energy. By comparison of these estimated energy fluxes we conclude that the continuum enhancement was directly produced by the non-thermal electrons.

• Journal of The Korean Astronomical Society
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• v.36 no.spc1
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• pp.49-54
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• 2003

We introduce the two-dimensional spectral observations of solar flares using the Solar Tower Tele-scope of Nanjing University, China. In particular, we introduce three typical events and the methods used to analyze the data. (1) The flare of November 11, 1998, which is a limb flare. We derive the temperature and density within the flaring loop using non-LTE calculations. The results show that the loop top may be hotter and denser than other parts of the loop, which may be a result of magnetic reconnect ion above the loop. (2) The flare of March 10, 2001, which is a white-light flare that shows an emission enhancement at the near infrared continuum. We propose a model of non-thermal electron beam heating plus backwarming to interpret the observations. (3) The flare of September 29, 2002, which shows unusual line asymmetries at one flare kernel. The line asymmetries are caused by an upward moving plasma that is accelerated and heated during the flare development.

• Journal of the Korean Society of Industry Convergence
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• v.6 no.1
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• pp.81-86
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• 2003

For the simultaneous removal of $SO_2$/NOx from an iron-ore sintering plant, industrial plasma experiments have been conducted with a flue gas flow rate of $5,000Nm^3/hr$. The maximum 40kW power using the magnetic pulse compression (MPC) system generates a peak value of 100-150kV pulse voltage with its risetime of 200nsec and full width at half maximum (FWHM) of 500nsec, and with a frequency <300Hz. The plasma reactor module adopts a wire-plate structure with a gap of 200-400mm ID between plates. Initial concentrations of $SO_2$ and NOx were around 100-150ppm, respectively in the presence of 15% $O_2$ and <10% $H_2O$. Various reaction parameters such as specific energy ($Whr/Nm^3$), $NH_3$ injection with corona discharge, flow rate and injection of hydrocarbons were investigated for $SO_2$/NOx removal characteristics. About 90/65% of $SO_2$/NOx were simultaneously removed with a specific energy of $3.0Whr/Nm^3$ when both $NH_3$ and hydrocarbons were injected. Practical implications that the pilot-scale plasma results provide are further discussed.

• Restorative Dentistry and Endodontics
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• v.42 no.2
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• pp.125-133
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• 2017

Objectives: This study compared the effect of hexamethyldisiloxane (HMDSO) and ammonia ($NH_3$) plasmas on the bond strength of resin cement to fiber posts with conventional treatments. Materials and Methods: Sixty-five fiber posts were divided into 5 groups: Control (no surface treatment); $H_2O_2$ (24% hydrogen peroxide for 1 min); Blasting (blasting with aluminum oxide for 30 sec); $NH_3$ ($NH_3$ plasma treatment for 3 min); HMDSO (HMDSO plasma treatment for 15 min). After the treatments, the Ambar adhesive (FGM Dental Products) was applied to the post surface (n = 10). The fiber post was inserted into a silicon matrix that was filled with the conventional resin cement Allcem Core (FGM). Afterwards, the post/cement specimens were cut into discs and subjected to a push-out bond strength (POBS) test. Additionally, 3 posts in each group were evaluated using scanning electron microscopy. The POBS data were analyzed by one-way analysis of variance and the Tukey's honest significant difference post hoc test (${\alpha}=0.05$). Results: The Blasting and $NH_3$ groups showed the highest POBS values. The HMDSO group showed intermediate POBS values, whereas the Control and $H_2O_2$ groups showed the lowest POBS values. Conclusion: Blasting and $NH_3$ plasma treatments were associated with stronger bonding of the conventional resin cement Allcem to fiber posts, in a procedure in which the Ambar adhesive was used.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.46-53
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• 2013

Impedance spectroscopy is a non-destructive evaluation (NDE) method first proposed and developed for evaluating TGO layers with compressive stress inside thermally degraded plasma-sprayed thermal barrier coatings (PS TBCs). A bode plot (phase angle (h) vs. frequency (f)) was used to investigate the TGO layer on electrical responses. In our experimental study, the phase angle of Bode plots is sensitive for detecting TGO layers while applying compressive stress on thermal barrier coatings. It is difficult to detect TGO layers in samples isothermally aged for 100 hrs and 200 hrs without compressive stress, and substantial change of phase was observed these samples with compressive stress. Also, the frequency shift of the phase angle and change of the phase angle are observed in samples isothermally aged for more than 400 hrs.

• Advances in materials Research
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• v.13 no.1
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• pp.55-62
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• 2024

Cu-based sulfides have recently emerged as promising thermoelectric (TE) materials due to their low cost, non-toxicity, and abundance. In this research, point defect structure of Cu_2-xZnSnS₄ (x=0.1, 0.2, 0.3) samples were synthesized by the mechanical alloying method. Mixed powders of Cu, Zn, Sn and S were milled using high energy ball milling at a rotation speed of 300 rpm in Ar atmosphere. The milled Cu_2-xZnSnS₄ powders were heat-treated at 723 K for 24 h, and subsequently consolidated using spark plasma sintering (SPS) under an applied pressure of 60 MPa for 15 min. The thermal conductivity of the sintered Cu_2-xZnSnS₄ samples was evaluated. A well-defined Cu_2-xZnSnS₄ powders were successfully formed after milling for 16 h, with the particle sizes mostly distributed in the range of 60-100 nm. The lattice constants of aand cdecreased with increasing composition value x. The thermal conductivity of sintered x=0.1 sample exhibited the lowest value and attained 0.93 W/m K at 673 K.