• Journal of the Korean Society for Railway
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• v.16 no.4
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• pp.253-261
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• 2013

According to the measured results of KTX brake squeal noise in this study, high level brake noise occurred in a wide frequency range, 100~18,000Hz. To identify the sources of the brake squeal noise, unstable vibration modes due to brake disc/pad interaction were analyzed under various conditions by the finite element method. Complex eigenvalues for a brake unit with a disc and four pads were obtained. It was found that the real parts of the complex eigenvalues, that is, unstable vibration modes, were closely related to friction coefficients, pressure on the brake cylinders, elastic moduli of the components, and other conditions.

• Communications of Mathematical Education
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• v.31 no.1
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• pp.71-84
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• 2017

Taylor series has a complicated structure comprising of various concepts in college major mathematics. This subject is a strong tool which has usefulness and applications not only in calculus, analysis, and complex analysis but also in physics, engineering etc., and other study. However, students have difficulties in understanding mathematical structure of Taylor series convergence correctly. In this study, after classifying students' mathematical characteristic into three categories, we use structural image of Taylor series convergence which associated with mathematical structure and operation acted on that structure. Thus, we try to analyze the understanding of Taylor series convergence and present the results of this study.

• Journal of Broadcast Engineering
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• v.26 no.2
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• pp.143-154
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• 2021

In this paper, we propose a method of compressing digital hologram standardized data provided by JPEG Pleno. In numerical reconstruction of digital holograms, the addition of random phases for visualization reduces speckle noise due to interference and doubles the compression efficiency of holograms. Holograms are composed of completely complex floating point data, and due to ultra-high resolution and speckle noise, it is essential to develop a compression technology tailored to the characteristics of the hologram. First, frequency characteristics of hologram data are analyzed using various wavelet filters to analyze energy concentration according to filter types. Second, we introduce the subband selection algorithm using energy concentration. Finally, the JPEG2000, SPIHT, H.264 results using the Daubechies 9/7 wavelet filter of JPEG2000 and the proposed method are used to compress and restore, and the efficiency is analyzed through quantitative quality evaluation compared to the compression rate.

• Composites Research
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• v.34 no.3
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• pp.143-147
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• 2021

Full width half maximum (FWHM) analysis of superimposed terahertz (THz) signals in the glass fiber reinforced polymer (GFRP) was studied to detect fine delamination inside GFRP. The THz signals were measured for each fine delamination size inside the GFRP using the reflection mode of the terahertz time domain spectroscopy (THz-TDS) system. Then, the FWHM of the superimposed THz signal reflected at the fine delamination was extracted. Thereafter, the complex refractive index of the GFRP was measured using transmission mode of the THzTDS system. Based on this, the FWHM of the superimposed THz signal at the fine delamination were calculated and compared with respect to the fine delamination size. From the theoretically calculated superimposed signals, the relationship between the fine delamination size and the FWHM in the superimposed THz signal was derived. Consequently, the fine delamination size could be predicted through the analysis of the FWHM extracted from the THz signal at the fine delamination.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.11
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• pp.10-22
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• 1998

In this paper, as a way of improving the availability and spectral efficiency of radio relay system, a co-channel radio relay system based upon the synchronous digital hierarchy is developed and its performance measured by 64-QAM with a never-seen multi-purpose ASIC chip is illustrated. This system provides a couple of transmission capacity compared with alternative channel arrangement. By adopting a powerful complex 13-tap adaptive time domain equalizer and cross-pol interference canceller, improvement of more than 1.5 ~ 2.0 dB in signature is obtained in comparison to 9 or 11-tap adaptive time domain equalizer, and about 22.5 dB in improvement factor of cross-pol interference canceller is achieved at C/N of 24.5 dB. In addition, digital filter makes it possible to optimize the occupied bandwidth by selecting an appropriate roll-off factor externally. It is expected that co-channel radio relay system with the powerful multi-purpose ASIC chip plays a key role in creating a value-added product, reliability, and reducing the outage time.

• Polymer(Korea)
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• v.27 no.4
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• pp.377-384
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• 2003

High impact polystyrene/organically modified layered silicate (HIPS/OLS) nanocomposites by in situ polymerization were synthesized to investigate the effect of clay on the particle size and properties of rubber. In the OLS, the montmorillonite having benzyl group showed best dispersion in polystyrene phase. With the addition of clay, the intercalated peak from XRB was confirmed, but the peak gradually shifted to lower angle as rubber concentration increased. Thus, it is speculated that the organoclay disperses better in rubber phase than in polystyrene phase. The average rubber particle size increased and the particle size distribution widened as the amount of clay increased, which may be caused by the increase of the viscosity ratio of rubber to polystyrene phases and the unstable dispersion. The materials having clay showed improved thermal properties from thermogravimetric analysis. Rheological properties such as complex viscosity and storage modulus increased as the amount of clay increased.

• Conservation Science in Museum
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• v.9
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• pp.1-15
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• 2008

We observed the section and microstructure by Scanning Electron Mirrorscope (SEM) for 4 'Bowls, white porcelain with impressed floral design and sliver bound rim' and 1 'Dish, white porcelain with sliver bound rim', which was manufactured by reverse firing and metal bound rim was wrapped to the part of not being spread glaze at inlet, in Jingdezhen white porcelains, the relics dug from the seabed of Shinan conserved in National Museum of Korea, and found that the ingredient of metal rim was not silver but tin as a result of measuring by BEI of Energy Dispersive Spectroscopy (EDS). And as a result of survey with Fourier transform infrared spectroscopy(FT-IR) for checking the method of joining metal rim of mouth part, it was found that joining was made with materials made of lacquer.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.6
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• pp.400-407
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• 2003

In this paper an optical encryption system, which can decrypt the original image by using the autocorrelation terms of a JTC, is proposed. Unlike the classical JTC, the joint input plane of the proposed system is composed in a frequency domain not a spatial domain, thus it needs only one Fourier transformation. To use like this, the phase component appeared in the output plane of JTC should be considered. We presents the effect of phase and provides the solution. An original image is encrypted to a complex-valued random image. The original image is reconstructed using the autocorrelation terms which is the main drawback of JTC, therefore the proposed system is more suitable for JTC and real time processing. By computer simulation and optical experiment, the analysis for the phase effect and the performance of the proposed system are confirmed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12C
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• pp.983-990
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• 2008

In communication systems, initial acquisition is required for the reliable transmission performance, and the analysis of the acquisition performance over various communication environments including different signal-to-noise ratios plays an important role in communication system design. Usage of differential correlation methods in initial synchronization procedure is desired when frequency offsets exist, and additional performance improvement can be achieved through proper modifications of conventional correlation schemes. In this paper, we derive the error probability of the initial acquisition and express it in terms of the Marcum Q-function, via statistical modeling of the differential correlator output. The result is generalized to the error probabilities of the extended differential correlation methods using the complex- and magnitude-sum of the correlator outputs. The derived probabilities can be applied for the acquisition performance verification of various communication systems including the DVB-S2 standard.

• Journal of the Korean GEO-environmental Society
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• v.17 no.3
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• pp.21-26
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• 2016

Soil particle shape analysis was conducted with sands from Jumujun, Korea and Ras Al Khair, Saudi Arabia. Two hundred times enlarged digital images of the particles of those two sands were obtained with an optical microscope. The resolution of the digital images was $640{\times}320$. By conducting digital image processing, the coordinates of the soil particle boundary were extracted. After mapping those coordinates to the complex space, Fourier transformation was performed and the coefficients of each trigonometry term were computed. The coefficients reflect the shape characteristics of the sand grains and are invariant to translation. To evaluate the shape itself excluding the size of the soil particle, the coefficient was normalized by the equivalent radius of soil particle; this is called Fourier descriptor. After analyzing the Fourier descriptors, it was found that the major characteristics of Jumunjin and Ras Al Khair sands were elongation and asymmetry. Furthermore, it was found that the particle shapes reflect the self-similar, fractal nature of the textural features. The effects of resolution on soil particle shape analysis was also studied. Regarding this, it was found that the significant Fourier descriptors were not significantly affected by the image resolution investigated in this study, but the descriptors associated with textural features were affected.