• Journal of Welding and Joining
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• v.21 no.6
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• pp.33-39
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• 2003

Wavelet transform analysis results show a spectrum energy distribution of CWT along scale factors distinguish the partial, full and over penetration in a electron beam welding by analyzing the curve of spectrum energy at small scale, middle and large scale range, respectively. Two types of signals collected by Ion collector and x-ray sensors and analyzed. The acquired signals from sensors are very complicated since these signals are very closely related the dynamics of keyhole which interact the very high density energy with materials during welding. The results show the wavelet transform is more effective to diagnosis than Fourier Transform, further for the general welding defects which are not a periodic based, but a transient, non-stationary and time-varying phenomena.

• Proceedings of the KSPS conference
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• 2006.11a
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• pp.92-95
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• 2006

The purpose of this study is to find the acoustic parameters on frequency domain to distinguish the Korean nasals, /m, n, ng/ from each other. Since it is not easy to characterize the antiformant on frequency domain, we suggest the new parameters that are calculated by LTAS(Long term average spectrum). Maximum energy value and its frequency and minimum energy and its frequency of zero are obtained from the spectrum respectively. In addition, slope1, slope2, total energy value, centroid, skewness, and kurtosis are suggested as new parameters as well. The parameters that are revealed as to be statistically signigicant difference are roughly peak1_a, zero_f, slope_1, slope_2, highENG, zero_ENG, and centroid.

• Electrical & Electronic Materials
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• v.10 no.8
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• pp.763-769
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• 1997

In this study we have synthesized Zno:Eu phosphors under various sintering atmospheres and temperatures. The analysis of X-ray diffractometer measurement indicates that for Zno:EuCl$_3$ phosphors sintered in air and vacuum 뗘 exists in the host lattice as Eu$_2$O$_3$and EuOCl respectively. From the photoluminescence for the phosphors sintered in vacuum Eu removes the broad-band emission of the ZnO host consequently isolating the red emission due to Eu$^{3+}$ ion and improves the color purity of red emission. The photoluminescence excitation and time resolving spectrum measurements suggest that energy-transfer process occurres from the self-activated defect center in ZnO host the Eu$^{3+}$ ion which exist in the host lattice in the form of EuOCl.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.41.2-41.2
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• 2018

The Minkowski Functionals of the matter densityeld, as traced by galaxies, contain information regarding the nature of dark energy and the fraction of dark matter in the Universe. In particular, the genus is a statistic that provides a clean measurement of the shape of the linear matter power spectrum. As the genus is a topological quantity, it is insensitive to galaxy bias and gravitational collapse. Furthermore, as it traces the linear matter power spectrum, it is a conserved quantity with redshift. Hence the genus amplitude is a standard population that can be used to test the distance-redshift relation. In this talk, I show how we can extract the genus from galaxy catalogs, and how we can use its properties to constrain the equation of state of dark energy and the energy content of the Universe.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.11
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• pp.5203-5217
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• 2018

In order to increase the capacity and improve the spectrum efficiency of wireless communication systems, this paper proposes a rate-based two-sided many-to-one matching game algorithm for energy-harvesting small cells with non-orthogonal multiple access (NOMA) in heterogeneous cellular networks (HCN). First, we use a heuristic clustering based channel allocation algorithm to assign channels to small cells and manage the interference. Then, aiming at addressing the user access problem, this issue is modeled as a many-to-one matching game with the rate as its utility. Finally, considering externality in the matching game, we propose an algorithm that involves swap-matchings to find the optimal matching and to prove its stability. Simulation results show that this algorithm outperforms the comparing algorithm in efficiency and rate, in addition to improving the spectrum efficiency.

• Journal of Radiation Protection and Research
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• v.41 no.1
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• pp.41-47
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• 2016

Background: For the accurate dose assessment in radiation therapy, energy spectrum of the photon beam generated from the linac head is essential. The aim of this study is to develop the technique to accurately unfolding the energy spectrum with the transmission analysis method. Materials and Methods: Clinical linear accelerator and Monet Carlo method was employed to evaluate the transmission signals according to the thickness of the observer material, and then the response function of the ion chamber response was determined with the mono energy beam. Finally the energy spectrum was unfolded with HEPROW program. Elekta Synergy Flatform and Geant4 tool kits was used in this study. Results and Discussion: In the comparison between calculated and measured transmission signals using aluminum alloy as an attenuator, root mean squared error was 0.43%. In the comparison between unfolded spectrum using HEPROW program and calculated spectrum using Geant4, the difference of peak and mean energy were 0.066 and 0.03 MeV, respectively. However, for the accurate prediction of the energy spectrum, additional experiment with various type of material and improvement of the unfolding program is required. Conclusion: In this research, it is demonstrated that unfolding spectra technique could be used in megavoltage photon beam with aluminum alloy and HEPROW program.

• Journal of Satellite, Information and Communications
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• v.10 no.3
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• pp.6-10
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• 2015

RF energy harvesting technology is a promising technology for generating the electrical power from ambient RF signal to operate low-power consumption devices(eg. sensor) in wireless communication networks. This paper, motivated by this and building upon existing CR(Cognitive Radio) network model, proposes a optimal control policy for RF energy harvesting CR networks model where secondary users that have low power consumption harvest ambient RF energy from transmission by nearby active primary users, while periodically sensing and opportunistically accessing the licensed spectrum to the primary user's network. We consider that primary users and secondary users are distributed as Poisson point processes and contact with their intended receivers at fixed distances. Finally we can derive the optimal frame duration, transmission power and density of secondary user from the proposed model that can maximize the secondary users's throughput under the given several conditions and suggest future directions of research.

• Journal of the Korean Society of Radiology
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• v.11 no.4
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• pp.197-203
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• 2017

This study purpose is propose the basic data for selecting the optimal target material by analyzing the photon characteristics of various materials which was located in the head of medical linear accelerator. In this study, energy spectrum of 6, 15 MV photon beams were compared and analyzed for 13 target materials using MCNPX of Monte Carlo method. The mean energy for the 6 MV energy spectrum was 1.69 ~ 1.84 MeV and that for the 15 MV was 3.38 ~ 3.56 MeV, according to the target material. The flux for the 6 MV energy spectrum was $1.64{\times}10^{-5}{\sim}1.80{\times}10^{-5}{\sharp}/cm^2/e$ and that for the 15 MV was $1.76{\times}10^{-4}{\sim}1.85{\times}10^{-4}{\sharp}/cm^2/e$. The analysis shows that the average energy and flux increase with higher atomic number of the target material. Based on this study, it is possible to present the basic data about the physical characteristics of the photon, and it will be possible to select the target later considering economic, efficiency and physical aspect.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.4
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• pp.254-262
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• 2015

Parametric study on submerged body shape of an oscillating hemisphere point absorber was conducted to predict the optimal relation between radius and draft of the body. As an additional damping due to power takeoff system, the optimal damping same as wave radiation damping was applied to the PTO system to produce the maximum wave power. Body response spectrum and power spectrum were obtained for various peak frequencies on wave spectra. It was found that the maximum power can be generated when the peak frequency of available wave power was 20% greater than that of wave spectrum.

• Journal of the Earthquake Engineering Society of Korea
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• v.17 no.2
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• pp.71-77
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• 2013

The uniform hazard spectra for seven major cities in Korea, Seoul, Daejeon, Daegu, Busan, Gwangju, Ulsan, and Inchon are suggested. Probabilistic seismic hazard analyses were performed using the attenuation equations derived from seismology research in Korea since 2000 and the seismotectonic models selected by expert assessment. For the estimation of the uniform hazard spectra, the seismic hazard curves for several frequencies and PGAs were calculated by using the spectral attenuation equations. The seismic hazards (annual exceedance probability) calculated for the 7 metropolises ranged from about $1.4305{\times}0^{-4}/yr$ to $1.7523{\times}10^{-4}/yr$ and averaged out at about $1.5902{\times}10^{-4}/yr$ with a log standard deviation of about 0.085 at 0.2 g. The uniform hazard spectra with recurrence intervals of 500, 1000, and 2500 years estimated by using the calculated mean seismic hazard on the frequencies presented peak values at 10.0 Hz, and the log standard deviations of the difference between metropolises ranged from about 0.013 to 0.209. In view of the insignificant difference between the estimated uniform hazard spectra obtained for the considered metropolises, the mean uniform hazard spectrum was estimated. This mean uniform hazard spectrum is expected to be used as input seismic response spectrum for rock sites in Korea.