• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.6
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• pp.1535-1541
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• 1994

The void content of carbon fiber reinforced composite laminates was determined by the ultrasonic nondestructive technique. The ultrasonic immersion, through-transmission method developed stresses the utilization of spectral analysis and frequency dependence of the attenuation due to porosity. The measured attenuation shows approximately linear behavior over the frequency range investigated. The linear relationship between the void content and the attenuation slop (d $\alpha$/df) is found to hold, but the constant of proportionality is quite different for samples with different pore morphology. The void volume fraction determined by the attenuation slope agreed very well with that obtained by the acid digestion analysis.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.40.2-40.2
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• 2016

The attenuation of starlight by dust in galactic environments is investigated through models of radiative transfer in a spherical, clumpy interstellar medium (ISM). We show that the attenuation curves are primarily determined by the wavelength dependence of absorption rather than by the underlying extinction (absorption+scattering) curve; the observationally derived attenuation curves cannot constrain a unique extinction curve unless the absorption or scattering efficiency is specified. Attenuation curves consistent with the Calzetti curve are found by assuming the silicate-carbonaceous dust model for the Milky Way (MW), but with the $2175{\AA}$ bump suppressed or absent. The discrepancy between our results and previous work that claimed the Small Magellanic Cloud dust to be the origin of the Calzetti curve is ascribed to the difference in adopted albedos; we use the theoretically calculated albedos whereas the previous ones adopted empirically derived albedos from observations of reflection nebulae. It is found that the model attenuation curves calculated with the MW dust are well represented by a modified Calzetti curve with a varying slope and UV bump strength. The strong correlation between the slope and UV bump strength, as found in star-forming galaxies at 0.5 < z < 2.0, is well reproduced if the abundance of the UV bump carriers is assumed to be 30-40% of that of the MW-dust; radiative transfer effects lead to shallower attenuation curves with weaker UV bumps as the ISM is more clumpy and dustier. We also argue that some of local starburst galaxies have a UV bump in their attenuation curves, albeit very weak.

• Journal of Biomedical Engineering Research
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• v.8 no.1
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• pp.41-48
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• 1987

In estimating the freguency-dependent attenuation coefficient, we analyzed the range-dependent ultrasonic beam and proposed the method of calculating the experimental equation of beam pattern in order to reduce the error on the influence of beam pattern. These experimental equations are divided into the spectral centroid and the spec ural standard deviation slope according to axial propagation length. These are repnesented by the first-order equation in the near field of the beam and the second- order eqLlatlon In the far field. In order to prove the validity of this method, the attenuation coefficients of the non-corrected ease and the corrected case are compared. Using the reflected signal from acryle plate, the attenuation coefficients were estimated by the spectral shift method ann the spectral difference method. The result shows attenuation coeffi talents after correction are better than attenuation coefficients before correction. And this method can be applied In vivo measurement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.6A
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• pp.782-793
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• 2000

This paper presents a simple dynamical prediction scheme of the signal level which is attenuated and varied due to rain fading in satellite communication links using above 10GHz frequency bands. The proposed prediction scheme has four functional blocks for discrete-time low-pass filtering, slope-based prediction, mean-error correction and hybrid fixed/variable prediction margin allocation. Through simulations using Ka-band attenuation data obtained from the data measured over Ku-band by frequency-scaling, it is shown that the slope-based prediction with the mean-error correction has as small standard deviation of prediction error as below 1 dB, and that the error is about 1.5 to 2.5 times as small as that without the mean-error correction. The hybrid prediction margin allocation requires smaller average margin than those of both fixed and variable methods.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.946-956
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• 2008

Acoustic emission(AE) is low-energy seismic event associated with a sudden inelastic deformation such as the sudden movement of existing fractures, the generation of new fractures or the propagation of fractures. These events rapidly increase before major failure and happen within a given rock volume and radiate detectable seismic waves. Rock slopes are usually large in scale and there are many discontinuities in rock mass. AE waves are strongly attenuated when they propagate through joints. Thus we should resolve the attenuation problem to monitor large volume. In this study, we developed waveguide which is composed of two different materials, cement mortar and stainless steel rod. And several laboratory tests on developed waveguide are performed to obtain generalized AE parameters to predict the failure stage in rock slope. Comparing field data with experimental data in laboratory tests, failure stage of rock slope can be evaluated. To verify and optimize the developed monitoring method, we are now carrying out the field application at a rock slope.

• Journal of Navigation and Port Research
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• v.32 no.5
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• pp.341-347
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• 2008

Recently, it has been widely recognized that water-front and coastal vegetations may have great value in supporting fisheries, protecting from wave attack, stabilizing the sea bed and maintaining good scenery. Hydrodynamic factors playa major role in the functions of water quality and ecosystems. However, the studies on numerical and analytical process of wave propagation are few and far behind compared to those on the hydrodynamic roles of water-front vegetations. In this study, in order to express wave attenuation into water-front vegetation, a numerical model based on the unsteady mild slope equation is developed. This result is compared with an analytical model for describing the wave attenuation by assumed simple long wave condition. Based on both the analytical and numerical results, the physical properties of the wave attenuation are examined under various wave, geometric and vegetation conditions. Through comparisons between the analytical and numerical results, the effects of the vegetation properties, wave properties and model parameters such as the momentum exchange coefficient have been clarified.

• Journal of Environmental Impact Assessment
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• v.25 no.5
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• pp.333-344
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• 2016

In this study, the efficiency of natural attenuation was evaluated through the hydrogeological characteristics such as monitoring and analyses, tracer tests, chemical composition analysis of the groundwater at a military site contaminated by petroleum hydrocarbon in korea. Also, based on the results, the natural attenuation rate by distance and the expressed biodegradation capacity(EBC) was evaluated. The regression slope of -0.0248($K/V_x$) and bulk attenuation rate of $1.7{\times}10^{-3}/day$ were calculated respectively. The range of total expressed biodegradation capacity(EBC) of BTEX was shown from 9.1 mg/L to 10.0 mg/L(average 9.7 mg/L). It was confirmed that the denitrification which was expressed about 63.6% in the total EBC is the largest influence redox process. Consequently, the biodegradation capacity is considered to be sufficient for remediation in the BTEX average concentration of 1.326 mg/L.

• Journal of Korean Society of Forest Science
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• v.83 no.3
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• pp.400-409
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• 1994

To investigate the noise attenuation effects of various vegetation configurations, noise levels on 6 study sites along relatively heavy traffic roads were measured. The differences between noise level measures at 1m and 10m spots from the road range from 10 to 15dB depending upon the attributes of the vegetation. When flat grass land was set to control plot, the maximum noise attenuation at 10m spot was measured at the densely planted shrubs with 5dB difference. The areas on upward slope from the road showed the least attenuation effects. Based on the study results, an appropriate setting for low level residential area noise buffer belt would be densely planted shrubs with at least 3m width and 2m height. To be effective, 3m width soft areas covered with grasses are needed at the front and behind sides of the belt. More than 15dB of the noise level caused by the road traffic would be attenuated with the prescription.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.3
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• pp.483-488
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• 2019

The propagation prediction model of the earth-space communication link used as an international standard was used to calculate and analyze the total losses on the communication path. The standard definition and scope of ITU-R Rec. were analyzed for each parameter(rain, scintillation, atmospheric gas, clouds) used to calculate the total loss. The total losses were calculated using the standard model for each parameter and the statistical data provided by ITU-R, and the results were analyzed using the validation examples data. The rain losses were calculated using long-term local rainfall attenuation statistics data measured in the region, and compared with the calculation results using a rainfall map in the ITU-R Recommendation. The data of Cheollian satellites for the L-Band and Ka-Band were used to calculate the rainfall attenuation. In the range of 0.01% to 0.1%, it was found to have a greater attenuation slope when using local data than attenuation by the model of ITU-R.

• Journal of Ocean Engineering and Technology
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• v.20 no.1 s.68
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• pp.63-68
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• 2006

Recently, it has been widely recognized that coastal vegetations may have great value in supporting fisheries, protecting from wave attack, stabilizing the sea bed and maintaining good scenery. Hydrodynamic factors play a major role in the functions of water quality and ecosystems. However, the studies on physical and numerical process of wave propagation are few and far behind compared to those on the hydrodynamic roles of coastal vegetations. In general, Vegetation flourishing along the coastal areas attenuates the incident waves, through momentum exchange between stagnated water mass in the vegetated area and rapid mass in the un-vegetated area. This study develops a numerical model for describing the wave attenuation rate in the complex topography with the vegetation area. Based on the numerical results, the physical properties of the wave attenuation are examined under various wave, geometric and vegetation conditions. Through the comparisons of these results, the effects of the vegetation properties, wave properties and model parameters such ac the momentum exchange coefficient have been clarified.