• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.12
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• pp.1101-1105
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• 2005

We have investigated the optical properties of Erbium (Er)-implanted GaN by photoluminescence (PL). Various doses of Er ion were implanted on GaN epilayers by ion implantation. Visible green emission lines due to inner 4f shell transitions for $Er^{3+}$ were observed from the PL spectrum of Er-implanted GaN. The emission spectrum consists of two narrow green lines at 537 and 558 nm. The green emission lines are identified as $Er^{3+}$ transitions from the $^{5}H_{11/2}$ and $^{4}S_{3/2}$ levels to the $^{4}I_{15/2}$ ground state. The stronger peaks in the case with the dose of $5{\times}10^{14}cm^{-2}$, together with the relatively higher intensity of the $Er^{3+}$ luminescence in the lower doped sample. It implies that some damage remains in the case with the dose of $1{\times}10^{16}cm^{-2}$. The peak positions of emission lines due to inner 4f shell transitions for $Er^{3+}$ do not change with increasing temperature. It indicates that $Er^{3+}$ related emission depends very little on the ambient temperature.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.1
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• pp.26-32
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• 2014

In this study, DC (Direct current) type steam plasma igniter is developed for effective ignition of high-energy density metal aluminum and gas temperature is measured by emission spectrum of OH radical. Because of the ultra-high gas temperature, the DC plasma jet is measured by Boltzmann plot method which is the non-contact optical technique and spectrum comparison-analysis. And both methods were applied to experiment after accurate verification. As a result, we could identify that plasma jet temperature is 2900 K ~ 5800 K in the 30 mm range from the nozzle tip.

• Structural Monitoring and Maintenance
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• v.7 no.1
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• pp.13-25
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• 2020

One of the most important aspects in structural health monitoring is the detection of fatigue damage. Structural components such as heavy-duty bolts work under high dynamic loads, and thus are prone to accumulate fatigue damage and cracks may originate. Those heavy-duty bolts are used, for example, in wind power generation and mining equipment. Therefore, the investigation of new and more effective monitoring technologies attracts a great interest. In this study the acoustic emission (AE) technology was employed to detect incipient damage during fatigue testing of a M36 bolt. Initial results showed that the AE signals have a high level of background noise due to how the load is applied by the fatigue testing machine. Thus, an advanced signal processing method in the time-frequency domain, the Hilbert-Huang Spectrum (HHS), was applied to reveal AE components buried in background noise in form of high-frequency peaks that can be associated with damage progression. Accordingly, the main contribution of the present study is providing insights regarding the detection of incipient damage during fatigue testing using AE signals and providing recommendations for further research.

• International Journal of Internet, Broadcasting and Communication
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• v.7 no.2
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• pp.130-136
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• 2015

In this paper, we analyzed the adjacent channel interference of the LTE band 40 defined by 3GPP on the WLAN system based on the Monte-Carlo method, and found the guard band required for compatibility between the two systems. This study have a difference compared to the previous studies about cell radius was determined using Extended Hata Model considering practical environment, interference protection distance related to guard band, and the spectrum emission mask improvement effect for minimizing the interference. Simulation results, for no channel interference compatibility of LTE and WLAN for mobile satellite wireless package system, we can find the need 15MHz guard band at specified spectrum emission mask and 10MHz guard band at assumed spectrum emission mask.

• Journal of radiological science and technology
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• v.39 no.4
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• pp.637-642
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• 2016

In this study, we prepared and characterized a acrylate based UV-curable plastic scintillator. It was used co-polymers TMPTA, DHPA and Ultima $Gold^{TM}$ LLT organic scintillator. The emission spectrum of the plastic scintillator was located in the range of 380~520 nm, peaking at 423 nm. And the scintillator is more than 50% transparent in the range of 400~800 nm. The emission spectrum is well match to the quantum efficiency of photo-multiplier tube and the fast decay time of the scintillation is 12 ns, approximately. This scintillation material provides the possibility of combining 3D printing technology, and then the applications of the plastic scintillator may be expected in human dosimetry etc.

• Journal of Astronomy and Space Sciences
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• v.15 no.1
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• pp.59-64
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• 1998

Kim & Beuermann (1995, 1996)have developed a model for the propagation of X-rays from the accreting white dwarfthrough the infalling material and the re-emission of the energy deposited by photo-absorption in the optical (and UV) spectral range. By using this model, we calculate the profiles of the $H_{\gamma}$ emission-line spectrum of intermediate polars. Photoabsorption of X-ray by the infalling material is the dominant process in forming the observed energy-dependent rotational modulation of the X-ray flux. X-ray and optical modulations are sensitive to model parameters in different ways. In principle, these dependencies allow us to obtain improved insight into the accretion geometry of the intermediate polars. We present results of our calculations and compare them with the $H{\beta}$ line spectrum(Kim & Beuermann 1996).

• Journal of the Korean Ceramic Society
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• v.36 no.5
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• pp.478-482
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• 1999

SrTiO3 :Al, Pr phosphor as an oxide compound phosphor is expect to be applied for a field emission display(FED). In this phosphor the excitation spectrum shows a different tendency according to an addition Al3+ and Pr3+ In this excitation spectrum the main peak at 359 nm represent excitation level of Pr3+(1S0longrightarrow1D2 transition) and the absorption characteristic according to Ti/Sr molar ratio is influenced by the structure symmetry. The emission spectrum exhibits the red luminescence with the radiative decay of the 1D2 states(1D2 longrightarrow3H4 transition) The concentration quenching phenomena at 1D2 state shows up as Al3+ and Pr3+ ion concentration increases.

• Journal of The Korean Astronomical Society
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• v.37 no.2
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• pp.87-90
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• 2004

Spectrophotometry of the night sky over Mount Bohyun is presented for the nearly entire visible wavelengths of $3600{\~}$8600{\AA}$. The data was obtained under moonless clear sky in February 2004 with the 1.8-m telescope and the long slit spectrograph. The sky spectrum shows a number of strong emission lines originated from light pollution, especially due to high pressure sodium lamps. When compared to the night sky of Kitt Peak, our sky continuum is 1 to 2 magnitude brighter at all wavelengths, the worst being around the broad emission region near 6000${\AA}$. The night sky spectrum presented here with almost complete line identifications is a useful reference for arc-independent wavelength calibrations to check the gravity flexure of the spectrograph and the wavelength shift between FeNeArHe arc frames and science frames.

• Korean Journal of Materials Research
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• v.22 no.5
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• pp.215-219
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• 2012

Red phosphors $Ca_{1-1.5x}WO_4:{Eu_x}^{3+}$ were synthesized with different concentrations of $Eu^{3+}$ ions by using a solid-state reaction method. The crystal structure of the red phosphors was found to be a tetragonal system. X-ray diffraction (XRD) results showed the (112) main diffraction peak centered at $2{\theta}=28.71^{\circ}$, and the size of crystalline particles exhibited an overall decreasing tendency according to the concentration of $Eu^{3+}$ ions. The excitation spectra of all the phosphors were composed of a broad band centered at 275 nm in the range of 230-310 nm due to $O^{2-}{\rightarrow}W^{6+}$ and a narrow band having a peak at 307 nm caused by $O^{2-}{\rightarrow}Eu^{3+}$. Also, the excitation spectrum presents several strong lines in the range of 305-420 nm, which are assigned to the 4f-4f transitions of the $Eu^{3+}$ ion. In the case of the emission spectrum, all the phosphor powders, irrespective of $Eu^{3+}$ ion concentration, indicated an orange emission peak at 594 nm and a strong red emission spectrum centered at 615 nm, with two weak lines at 648 and 700 nm. The highest red emission intensity occurred at x = 0.10 mol of Eu3+ ion concentration with an asymmetry ratio of 12.5. Especially, the presence of $Eu^{3+}$ in the $Ca_{1-1.5x}WO_4:{Eu_x}^{3+}$ shows very effective use of excitation energy in the range of 305-420 nm, and finally yields a strong emission of red light.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.360-364
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• 2004

The objective of this study is to estimate the feasibility of acoustic emission method Jar the internal leak from the valves in nuclear power plants. The acoustic emission method was applied to the valves at the site, and the background noise was measured for the abnormal plant condition. From the comparison of background noise data with the experimental results as to relation between leak flow and acoustic signal, the minimum leak flow rates that am be detected by acoustic signal was suggested. When the background noise level are higher than the acoustic signal, the method described below was considered that the analysis the remainder among the background noise frequency spectrum and the acoustic signal spectrum.