• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.110.2-110.2
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• 2011

Nishikida et al. (2006) presented the first far-ultraviolet (FUV) em${\lambda}$ission-line images of the Vela supernova remnant (SNR) obtained with FIMS/SPEAR instrument. Those include C III ${\lambda}$977, O VI ${\lambda}{\lambda}$1032, 1038, Si IV+O IV] ${\lambda}{\lambda}$1393, 1403 (un-resolved), C IV ${\lambda}{\lambda}$1548, 1551 emission-line images. As a following work, we re-constructed these emission-line images using the new-version processed FIMS/SPEAR data. Additionally, we made N IV] ${\lambda}$1486, He II ${\lambda}$1640.5, O III] ${\lambda}{\lambda}$1661, 1666 emission-line images. The new-version images cover the whole region of the Vela SNR and show more resolved features than the old-version. We compare these FUV emission-line images with other wavelength (X-ray, optical, etc.) images obtained in previous studies.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.67.2-67.2
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• 2013

Part of mid-J CO emission detected by the Herschel/PACS observations of embedded young stellar objects (YSOs) has been attributed to the UV-heated outflow walls. We have applied our newly developed self-consistent models of Photon Dominated Region (PDR) and Non-LTE line Radiative transfer In general Grid (RIG) to the Herschel FIR CO observations. If the black body radiation of T = 15,000 K is used, the observed mid-J CO line fluxes can be produced in inner dense regions (n ${\geq}$ 106 cm-3) with -4.5 ${\leq}$ log Gdust/n ${\leq}$ -2.5, where gas temperatures are larger than 300 K and CO abundances are ${\geq}$ 10-5, along the UV-heated outflow walls. The contribution of the UV heated outflow cavity wall in Class I seems to be larger than that in Class 0.

• Proceedings of the KIEE Conference
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• 1989.11a
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• pp.142-144
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• 1989

Triggering characteristics of a trigatron spark gap have been studied by measuring self-emission UV light. By combining the measurement of the UV light with that of the trigger gap voltage and the lain discharge current, we distinguished clearly the differences between the trigatron operations in which the lain discharge occurs after the trigger discharge in the case of sale polarity between the trigger pin and the lain electrode at the opposite side, and the lain gap breakdown takes place before the formation of the trigger spark in the case of different polarity. We show the observation of UV radiation with the other electromagnetic measurements is a simple and reliable scheme to investigate the triggering properties of the trigatron spark gaps.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.28.1-28.1
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• 2010

Recent surveys have shown that many early-type galaxies have signatures of ongoing or recent star formation (RSF). These RSF galaxies show blue integrated UV-optical colours that set them aside in the NUV integrated colour-magnitude relation. Among them, NGC 4150 has been observed using the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope to inspect the galaxy with higher spatial resolution. In the WFC3 data, the galaxy reveals ubiquitous near-UV emission and remarkable dusty substructure. Our analysis shows this galaxy to lie in the near-UV green valley, and its pixel-by-pixel photometry exhibits a narrow range of UV-optical colours that are similar to those of nearby E+A (post-starburst) galaxies, and lie between those of M83 (an actively star-forming spiral) and the local quiescent early-type galaxy population. This work reaffirms our hypothesis that minor mergers play a significant role in the evolution of early-type galaxies at late epochs.

• Journal of the Korean Ceramic Society
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• v.48 no.3
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• pp.251-256
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• 2011

The luminescence properties of polycrystalline ZnO annealed in reducing ambience ($H_2/N_2$) have been studied. An effective quenching of green luminescence with enhanced UV emission from polycrystalline ZnO is observed for the reduced ZnO. The variations of the UV and green luminescence band upon reduction treatment are investigated as a function of temperature in the range between 20 and 300 K. Upon annealing treatment in reducing ambience, the optical quality of polycrystalline ZnO is improved. The UV to green intensity ratio of sintered ZnO approaches close to zero (~0.05). However, this ratio reaches more than 13 at room temperature for polycrystalline ZnO annealed at $800^{\circ}C$ in reducing ambience. Furthermore, the full width at half maximum (FWHM) of the UV band of polycrystalline ZnO is reduced compared to unannealed polycrystalline ZnO. Electron paramagnetic resonance (EPR) measurements clearly show that there is no direct correlation between the green luminescence and oxygen vacancy concentration for reduced polycrystalline ZnO.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.240-244
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• 2002

The GdOBr:Ce phosphor were prepared by solid state reaction using starting chemicals of $Gd_2O_3,\;CeO_2\;and\;NH_4Br$. Under 370nm UV excitation, GdOBr:Ce phosphors showed blue emission band with a spectral range of 410∼430nm. The maximum photoluminescence(PL) emission intensity was observed at 2mol% Ce content. In order to look for feasibility of application for low voltage filed emission display, cathodoluminescence(CL) of GdOBr:Ce phosphors were measured. CL emission spectra was found to be in the range of 410∼430nm, which is the same as PL spectra. The phosphors with 1mol% Ce concentration showed the maximum CL emission intensity. For the comparison of degradation property of the prepared phosphors with commercial ones, the electron beam was applied for 10min. From the result, GdOBr:Ce could be used as a blue phosphor for FED.

• Applied Science and Convergence Technology
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• v.26 no.4
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• pp.79-85
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• 2017

The crack-free AlGaN template has been successfully grown by using selective area growth with triangular GaN facet. The triangular GaN stripe structure was obtained by vertical growth rate enhanced mode with low growth temperature of $950^{\circ}C$ and high growth pressure of 500 torr. The lateral growth rate enhanced mode of AlGaN for crack-free and flat surface was also investigated. Low pressure of 30 torr and high V/III ratio of 4400 were favorable for lateral growth of AlGaN. It was confirmed that the $4{\mu}m$ -thick $Al_{0.2}Ga_{0.8}N$ was crack-free over entire 2-inch wafer. The dislocation density of $Al_{0.2}Ga_{0.8}N$ was as low as ${\sim}7.6{\times}10^8/cm^2$ measured by cathodoluminescence. Based on the high quality AlGaN with low dislocation density, the ultraviolet laser diode epitaxy with cladding, waveguide and GaN/AlGaN multiple quantum well (MQW) was grown by metalorganic chemical vapor deposition. The stimulated emission at 349 nm with full width at half maximum of 1.8 nm from the MQW was observed through optical pumping experiment with 193 nm KrF laser. We also have fabricated the deep ridge type ultraviolet laser diode (UV-LD) with $5{\mu}m-wide$ and $700{\mu}m-long$ cavity for electrical properties. The turn on voltage was below 5 V and the resistance was ${\sim}55{\Omega}$ at applied voltage of 10 V. The amplified spontaneous emission spectrum of UV-LD was also observed from pulsed current injection.

• Bulletin of the Korean Chemical Society
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• v.23 no.9
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• pp.1315-1327
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• 2002

The model compounds, 8-methoxypsoralen-CH2O(CH2)n-adenine (MOPCH2OCnAd, n=2, 3, 5, 6, 8, and 10) in which 5 position of 8-methoxypsoralen (8-MOP) is linked by various lengths of polymethylene bridge to N9 of adenine. UV absorption spectra are identical with the sum of MOPCH2OC3 and adenine absorption spectra. Solvent effects on the UV absorption and fluorescence emission spectra indicate that the lowest excited singlet state is the $(\pi${\rightarrow}$\pi*)$ state. The spectral characteristics of the fluorescence of MOPCH2OCnAd are strongly dependent upon the nature of the solvents. The fluorescence emission spectra in aprotic solvents are broad and structureless due to the excimer formation through the folded conformation accelerated by hydrophobic ${\pi}-{\pi}$ stacking interaction. Increasing polarity of the protic solvents leads to higher population of unfolded conformation stabilized through favorable solvation and H-bonding, and consequently to an increase in the fluorescence intensity, fluorescence lifetime, and a shift of fluorescence maximum to longer wavelengths. The decay characteristics of the fluorescence in polar protic solvents shows two exponential decays with the lifetimes of 0.6-0.8 and 1.6-1.9 ns in 5% ethanol/water, while MOPCH2OC3 shows 0.5 and 1.7 ns fluorescence lifetimes. The long-lived component of fluorescence can be attributed to the relaxed species (i.e., the species for which the solvent reorientation (or relaxation) has occurred), while the short-lived components can be associated with the unrelaxed, or only partially relaxed, species.

• Progress in Medical Physics
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• v.16 no.4
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• pp.202-206
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• 2005

Three-dimensional thermoluminescence (TL) spectra from $MgAl_2O_4$ irradiated with UV light were measured over 300${\~}$600 K and 300${\~}$800 nm. The peak positions of TL glow curves were shifted to lower temperature with increasing the exposure time of UV light. The 476 K TL glow curve is due to the second kinetics and its activation energy and escape frequency factor are calculated to be 0.85 eV and $1.92{\times}10^6 sec^{-1}$, respectively The TL spectra were split into 530 nm and 700 nm emission bands which were associated with $V^{2+}$ and $Cr^{2+}$, respectively. The linearity range of 700 nm omission band is smaller than that of 530 nm emission band, but the saturation time of 700 nm emission band is longer than that of 530 nm omission band.

• Journal of Astronomy and Space Sciences
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• v.29 no.2
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• pp.181-189
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• 2012

To broaden the understanding of classical Cepheid structure, evolution and atmospheres, we have extended our continuing secret lives of Cepheids program by obtaining XMM/Chandra X-ray observations, and Hubble space telescope (HST) / cosmic origins spectrograph (COS) FUV-UV spectra of the bright, nearby Cepheids Polaris, ${\delta}$ Cep and ${\beta}$ Dor. Previous studies made with the international ultraviolet explorer (IUE) showed a limited number of UV emission lines in Cepheids. The well-known problem presented by scattered light contamination in IUE spectra for bright stars, along with the excellent sensitivity & resolution combination offered by HST/COS, motivated this study, and the spectra obtained were much more rich and complex than we had ever anticipated. Numerous emission lines, indicating $10^4$ K up to ${\sim}3{\times}10^5$ K plasmas, have been observed, showing Cepheids to have complex, dynamic outer atmospheres that also vary with the photospheric pulsation period. The FUV line emissions peak in the phase range ${\varphi}{\approx}0.8-1.0$ and vary by factors as large as $10{\times}$. A more complete picture of Cepheid outer atmospheres is accomplished when the HST/COS results are combined with X-ray observations that we have obtained of the same stars with XMM-Newton & Chandra. The Cepheids detected to date have X-ray luminosities of log $L_X{\approx}28.5-29.1$ ergs/sec, and plasma temperatures in the $2-8{\times}106$ K range. Given the phase-timing of the enhanced emissions, the most plausible explanation is the formation of a pulsation-induced shocks that excite (and heat) the atmospheric plasmas surrounding the photosphere. A pulsation-driven ${\alpha}^2$ equivalent dynamo mechanism is also a viable and interesting alternative. However, the tight phase-space of enhanced emission (peaking near 0.8-1.0 ${\varphi}$) favor the shock heating mechanism hypothesis.