• Proceedings of the KIEE Conference
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• 1987.07b
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• pp.1243-1246
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• 1987

To characterize the biological tissues, the new methods to measure the frequency dependent attenuation are presented in this paper. In general, ultrasonic phase information was assumed by linear function of the frequency. But, the minimum phase function which characterizes the frequency dispersion of tissue was derived in [l]. It is very significant to measure the attenuation by using the minimum phase function to characterize the frequency dispersion of tissue. Therefore, a more efficient method measuring the frequency dependent attenuation are proposed by using the estimated sound velocity and polarity of reflected signal. To verify the algorithms, pulse reflection experiments are performed.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06a
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• pp.734-739
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• 1994

Elastic wave propagation in discrete random medium is studied to evaluate the effects of particle resonance on dispersion and attenuation of composite materials containing spherical inclusions. The frequency-dependent wave speed and attenuation coefficient can be obtained from proposed self-consistent method. It can be observed that the abrupt increase of effective wave speed and the concurrent peak of attenuation at low frequency is due to the lowest resonance of particles, whereas those in high frequency region are due to higher ones. The lowest resonance is mainly caused by the density mismatch and higher resonances by the stiffness mismatch between matrix and particles. The dispersion and attenuation of elastic waves in particulate composites are affected by the lowest resonance much than by higher ones.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.12
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• pp.1916-1924
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• 1990

In this paper attenuation effect on the measurement and the tomography of nonlinear parameter is discussed. We perform computer simulation with the method using harmonic components and the method using secondary wave components, and then estimate attenuation effect through the results and compare two measurement techniques. According to simulation result the attenuation effect is more intensive as large n and \ulcorner, and the degree of the attenuation effect is represented as error functions. In the aspect of measuremnet techniques, the method using secondary wave components is more insensitive to attenuation effect than the method using harmonic compnents. We obtain the same result in the nonlinear tomography, and show that the attenuation compensive filter is required because the whole tomogram is affected by frequency dependent attenuation(or nonlinear attenuation)

• Journal of the Korea Society of Computer and Information
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• v.19 no.5
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• pp.37-42
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• 2014

The objective of this study is the frequency of the noise source 170 dB level of impulsive sound attenuation performance by earplugs to identify, to analyze the frequency characteristics of a shape and pattern. The attenuation performance of the impulsive noise by the frequency levels on the Combat Arm and 3M Form types 1100 Earplugs were evaluated. In order to check the sound attenuation performance of the B&K head and torso simulator and sound attenuation performance of the ear simulator data was verified. Previous studies have most impact, even in the noise source and the impulse noise level is 140 dB, but this study is higher than that of the impulsive noise source features. The results of the impulse noise attenuation effect is frequency-dependent mean 28.58 dB.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.8
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• pp.1091-1098
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• 2012

This paper describes frequency response and propagation characteristics considering semiconducting screen in distribution cables. In CIGRE WG 21-05, Simplified Approach(SA) and Rigorous Approach(RA) which can revise the permittivity considering semiconducting screen propose for more detailed EMTP model and frequency dependant analysis. In this paper, the frequency dependent characteristics of complex permittivity are variously analysed by cole-cole function of RA. The attenuation, propagation velocity and surge impedance according to frequency range(1 kHz to 500 MHz) and cable length are also analysed by SA and EMTP simulation in distribution cables. The propagation velocity considering semiconducting screen is slower, and it is saturated over the range of 1 MHz. The signal is significantly attenuated as frequency range is high.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.9
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• pp.3043-3067
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• 2022

With the mobile traffic in the network increases exponentially, multi-access edge computing (MEC) develops rapidly. MEC servers are deployed geo-distribution, which serve many mobile terminals locally to improve users' QoE (Quality of Experience). When the cache space of a MEC server is full, how to replace the cached videos is an important problem. The problem is also called the cache replacement problem, which becomes more complex due to the dynamic video popularity and the varied video sizes. Therefore, we proposed a new cache replacement scheme based on local video popularity and video size to solve the cache replacement problem of MEC servers. First, we built a local video popularity model, which is composed of a popularity rise model and a popularity attenuation model. Furthermore, the popularity attenuation model incorporates a frequency-dependent attenuation model and a frequency-independent attenuation model. Second, we formulated a utility based on local video popularity and video size. Moreover, the weights of local video popularity and video size were quantitatively analyzed by using the information entropy. Finally, we conducted extensive simulation experiments based on the proposed scheme and some compared schemes. The simulation results showed that our proposed scheme performs better than the compared schemes in terms of hit rate, average delay, and server load under different network configurations.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.713-716
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• 1988

To characterize the bioloical tissues, the new methods to measure the frequency dependent attenuation are presented in this paper. In general, ultrasonic phase information was assumed by linear function of the frequency. But the minimum phase function which characterizes the frequency dispersion of tissue was derived in (2). It is very significant to measure the attenuation by using the minimum phase function to characterize the frequence dispersion of tissue. Also, we propose the phase correcting technique to take advantage of the idea that the distortion of amplitude component when the wave propagates through media.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.5
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• pp.509-517
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• 2012

In the present study, temperature and frequency dependences of ultrasonic properties such as attenuation coefficient and phase velocity was investigated for six kinds of commercial MC-Nylon polymer samples. The ultrasonic properties of the samples were measured by using a pulse transmission method in water over a broadband frequency range of 2 to 8 MHz. Water temperature was varied from 10 to $60^{\circ}C$ with the $10^{\circ}C$ interval. The attenuation coefficients of the samples increased with the frequency and the exponent n of frequency dependence ranged within 1.16 to 1.44, slightly deviating from the linear dependence (n=1). The phase velocities of the samples exhibited negative dispersion, i.e., decreasing velocity with increasing frequency, except for ivory sample at $60^{\circ}C$. The frequency-dependent phase velocities of the samples showed the decreasing tendency with increasing temperature.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.7
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• pp.1697-1704
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• 1994

Elastic wave propagation in discrete random medium studies to predict dynamic effective properties of composite materials containing spherical inclusions. A self-consistent method is proposed which is analogous to the well-known coherent potential approximation. Three conditions that must be satisfied by two effective elastic moduli and effective density are derived for the time without limit of frequency. The derived self-consistency conditions have the physical meaning that the scattering of coherent wave by the constituents in effective medium is vanished on the average. The frequency-dependent complex effective wave speed and coherent attenuation can be obtained by solving the derived self-consistency conditions numerically. The wave speed and attenuation obtained from present theory are shown to be in the better agreements with previous experimental observations than the previous theory.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.35-40
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• 1999

In order to know the characteristics of attenuation of coda wave in the Kyungsang Sedimentary Basin quality factor for coda wave or coda Q is estimated from the earthquake data recorded in the KIGAM microearthquake network. The single scattering model for coda wave generation is adopted in estimating coda Q. Coda Q appears to be largely dependent on the normalized time(a) which is the ratio of elapsed time to S-wave travel time. In the present study coda Q(Qc) is estimated in the range of a=1.5-3.Q and expressed in terms of frequency(f). The deduced function in the range of 1 to 25 Hz is Qc=36.8283 f1.15095 to represent the strong dependence of coda Q on frequency. It is found that the difference of Qc between U-D N-S and E-W components is negligible, This face supports the back-scattering theory that coda were originates from scattered waves by randomly distributed heterogeneities in the crust. On the other hand it is observed that the coda Q increases with depth.