• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.20 no.6
• /
• pp.583-588
• /
• 2008

Swell data observed in the East Sea in February, 2008 were analyzed using wavelet method. The wavelet analyzed results show detailed time series variation of wave group, peak frequency and spectrum. The comparison of time averaged wavelet spectrum with fourier spectrum turn out to be very similar in terms of spectrum shape and peak frequency evolution but the peak frequency wave energy and the significant wave height show discrepancies. Wavelet analysis can detect the change of spectrum in time as well as in frequency and very efficient to study transient and irregular phenomena such as freak waves and abnormal swells in the ocean. More analysis with more wave data are needed for future application.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.8C
• /
• pp.713-719
• /
• 2010

Collaborative spectrum sensing has been found to be an effective means for detecting the activity of primary users in a fading environment. Most previous works on collaborative spectrum sensing are based on the assumption that the local spectrum sensing decisions of secondary users are statistically independent. However, it may not hold in some practical situations. In this paper, we consider a cognitive radio network where the local spectrum sensing decisions of secondary users are statistically correlated with the same level of correlation if they are next to each other in location and statistically independent, otherwise. Then, for the system, we analyzed the performance of the collaborative spectrum sensing with the AND and the OR fusion rules and found that the scheme with the AND fusion rule performs better than the one with OR fusion rule when the degree of correlation is significant.

• Journal of the Korean Society of Radiology
• /
• v.7 no.1
• /
• pp.51-55
• /
• 2013

When the X-ray energy is high, the X-ray penetrates the object and decrease the contrast of imaging, and when the X-ray energy is low, the X-ray increases the contrast of imaging but it is to be absorbed into the object, which in the long run increases patient's radiation exposure level. Therefore, appropriate X-ray energy is an essential element affecting the imaging quality and radiation exposure level. This study simulated the energy spectrums according to the target materials of mammography, and compared qualities of phantom imaging for the management of radiolographic quality and patient's radiation exposure level with the introduction of the mammography that employs diversified radiation quality by using new anode materials.

• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.2
• /
• pp.58.1-58.1
• /
• 2010

Telescope Array (TA) experiment in Utah, USA, observes ultrahigh-energy cosmic rays (UHECRs); UHECRs refer cosmic rays with energy above $10^{18}eV$. Using COSMOS and CORSIKA, we have produced a library of over 1000 thinned extensive air shower (EAS) simulations with the primary energies ranging from $10^{18.5}eV$ to $10^{20.25}eV$ and the zenith angle of primary cosmic ray particle from $0^{\circ}$ to $45^{\circ}$. Here, we present the energy spectrum of particles arriving at the ground. We have also calculated the detector response evaluated using GEANT4 simulations. Here, we discuss S(800), i.e. the signal at a distance of 800 m from the shower core, as the primary energy estimator.

• Nuclear Engineering and Technology
• /
• v.49 no.6
• /
• pp.1310-1317
• /
• 2017

GASFLOW-MPI is a widely used scalable computational fluid dynamics numerical tool to simulate the fluid turbulence behavior, combustion dynamics, and other related thermal-hydraulic phenomena in nuclear power plant containment. An efficient scalable linear solver for the large-scale pressure equation is one of the key issues to ensure the computational efficiency of GASFLOW-MPI. Several advanced Krylov subspace methods and scalable preconditioning methods are compared and analyzed to improve the computational performance. With the help of the powerful computational capability, the large eddy simulation turbulent model is used to resolve more detailed turbulent behaviors. A backward-facing step flow is performed to study the free shear layer, the recirculation region, and the boundary layer, which is widespread in many scientific and engineering applications. Numerical results are compared with the experimental data in the literature and the direct numerical simulation results by GASFLOW-MPI. Both time-averaged velocity profile and turbulent intensity are well consistent with the experimental data and direct numerical simulation result. Furthermore, the frequency spectrum is presented and a -5/3 energy decay is observed for a wide range of frequencies, satisfying the turbulent energy spectrum theory. Parallel scaling tests are also implemented on the KIT/IKET cluster and a linear scaling is realized for GASFLOW-MPI.

• Journal of Radiation Protection and Research
• /
• v.46 no.4
• /
• pp.160-169
• /
• 2021

Background: Dual-energy X-ray images (DEI) can distinguish or improve materials of interest in a two-dimensional radiographic image, by combining two images obtained from separate low and high energies. The concepts of DEI performance describing the performance of double-exposure DEI systems in the Fourier domain been previously introduced, however, the performance of double-exposure DEI itself in terms of various parameters, has not been reported. Materials and Methods: To investigate the DEI performance, signal-difference-to-noise ratio, modulation transfer function, noise power spectrum, and noise equivalent quanta were used. Low- and high-energy were 60 and 130 kVp with 0.01-0.09 mGy, respectively. The energy-separation filter material and its thicknesses were tin (Sn) and 0.0-1.0 mm, respectively. Noise-reduction (NR) filtering used the Gaussian-filter NR, median-filter NR, and anti-correlated NR. Results and Discussion: DEI performance was affected by Sn-filter thickness, weighting factor, and dose allocation. All NR filtering successfully reduced noise, when compared with the dual-energy (DE) images without any NR filtering. Conclusion: The results indicated the significance of investigating, and evaluating suitable DEI performance, for DE images in chest radiography applications. Additionally, all the NR filtering methods were effective at reducing noise in the resultant DE images.

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1984.12a
• /
• pp.27-32
• /
• 1984

When chopped light inpinges on some condenced matters such as HgS, HgI2 and GaSe semiconductors, in an enclosed cell, the acoustic signals are produced within the cell. These acoustic signals were detected by using a gas-phase microphone in order to investigate the physical properties of the samples. In order to carry out investigation, PA-cell was first designed and made so as to produce higher sensitivity to acoustic signals. Second, an analysis of the photoacoustic spectrum of the various compounds was carried out to obtain the intensity of the PA-signal in terms of light wavelength and to calculate the energy band gaps occuring according to energy transitions. The agreement between the results obtained by this conventional PAS technique and the results obtained by the optical spectrum method was good. In additional analysis conducted on the basis of the R-G theory and the Sze theory are capable of determining the characteristics of energy transition of semiconductors.

• New & Renewable Energy
• /
• v.1 no.1 s.1
• /
• pp.32-36
• /
• 2005

We studied the optoelectronic properties of hybrid solar cells formed by mixing cadmium sulfide [CdS] nanorods with a conjugated polymer, poly-2-methoxy, 5-[2'-ethy[hexyloxy]-1,4-p-phenylenevinylene[MEH-PPV]. CdS nanorods were grown vertically on Ti substrates by electrochemical deposition through a porous alumina template. Absorption spectrum of the composite layer was the same as the superposition of the absorption spectrum of each individual layer. The photoluminescence signal from MEH-PPV film was reduced as a result of the mixing. The energy conversion efficiency of MEH-PPV improved from $0.0012\%$ to about $0.60\%$ when combined with the vertically aligned CdS nanorods.

• Journal of radiological science and technology
• /
• v.1 no.1
• /
• pp.31-35
• /
• 1978

X-rays contribute to electron emission from material surfaces primarily through photoelectric interaction. A simple model is described for predicting the yield and energy spectrum of photon and Auger electrons emitted from materials exposed to X-ray with low energy. In this paper, We have calculated the yield of primary, Auger, and secondary, electrons. The results of the photoelectric yield model developed here suggests that. I) The angular distribution of emitted electrons(Per unit angle) is proportional to $sin{\theta}\;cos{\theta}$ for all electron energies and all components(Primary, Auger, or Secondary) II) The shape of the energy spectrum of the photoelectric yield is independent of angle. III) For this targets the forward and backward photoelectric yields are indentical.

• Journal of The Korean Astronomical Society
• /
• v.29 no.spc1
• /
• pp.271-272
• /
• 1996

Assuming that particles can be accelerated to high energies via diffusive shock acceleration process at the accretion shocks formed by the infalling flow toward the clusters of galaxies, we have calculated the expected spectrum of high-energy protons from the cosmological ensemble of the cluster accretion shocks. The model with Jokipii diffusion limit could explain the observed cosmic ray spectrum near $10^{19}eV$ with reasonable parameters and models if about $10^{-4}$ of the infalling kinetic energy can be injected into the intergalactic space as the high energy particles.