• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.535-537
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• 2015

Interpreting ultraviolet-to-infrared (UV-to-IR) observations of galaxies in terms of constraints on physical parameters-such as stellar mass ($M_{\ast}$) and star formation rate (SFR)-requires spectral synthesis modelling. We investigate how increasing the level of sophistication of the standard simplifying assumptions of such models can improve estimates of galaxy physical parameters. To achieve this, we compile a sample of 1048 galaxies at redshifts 0.7 < z < 2.8 with accurate photometry at rest-frame UV to near-IR wavelengths from the 3D-HST Survey. We compare the spectral energy distributions of these galaxies with those from different model spectral libraries to derive estimates of the physical parameters. We find that spectral libraries including sophisticated descriptions of galaxy star formation histories (SFHs) and prescriptions for attenuation by dust and nebular emission provide a much better representation of the observations than 'classical' spectral libraries, in which galaxy SFHs are assumed to be exponentially declining functions of time, associated with a simple prescription for dust attenuation free of nebular emission. As a result, for the galaxies in our sample, $M_{\ast}$ derived using classical spectral libraries tends to be systematically overestimated and SFRs systematically underestimated relative to the values derived adopting a more realistic spectral library. We conclude that the sophisticated approach considered here is required to reliably interpret fundamental diagnostics of galaxy evolution.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.70-80
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• 2000

In order to reduce seismic hazard the characteristics of strong earthquakes are required. In the region where strong earthquakes do not happen frequently the stochastic simulation of strong motion is an alternative way to predict strong motions. this simulation required input parameters such as the quality factor the corner frequency the moment magnitude the stress drop and so on which can be obtained from analyses of records of small and intermediate earthquakes. Using those parameters obtained in the previous work the strong ground motions are predicted employing the stochastic method, . The results are compared to the two observed earthquakes-the Ulsan Offshore Earthquake and the Kyungju Earthquake. Although some deviations are found the predictions are similar to the observed data. Finally we computed attenuation equations for PGA PGV and ground accelerations for some frequencies using the results of predictions. These results can be used for earthquake engineering and more reliable results will come out as earthquake observations continue.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.487-495
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• 2005

Mechanical properties of in-service facilities are required to evaluate the integrity of power plants and chemical plants. Non-destructive technique can be used to evaluate the mechanical properties. To investigate the mechanical properties using ultrasonic technique, the four classes of thermally aged specimens were prepared using an artificially accelerated aging method. Ultrasonic tests, tensile tests, fracture toughness tests, and hardness tests were performed for the specimens. Then the mechanical properties were compared with ultrasonic parameters such as attenuation and non-linear parameter. From the investigation, we confirm that the ultrasonic parameter can be used to evaluate the mechanical properties.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.9
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• pp.1375-1380
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• 1989

Mobility reduction parameters are extracted using a method based on the exploitatiion of Id-Vg and Gm-Vg characteristics of short channel n-MOSFETs in strong inversion region at room temperature. It is found that the reduction of the maximum field effect mobility, \ulcornerFE,max, with the channel length is due to i) the difference between the threshold voltage and the gate voltage which corresponds to the maximum transconductance, and ii) the channel length dependence of the mobility attenuation coefficient, \ulcorner The low field mobility, \ulcorner, is found to be independent of the channel length down to 0.25 \ulcorner ofeffective channel length. Also, the channel length reduction, -I, the mobility attenuation coefficient, \ulcorner the threshold voltage, Vt, and the source-drain resistance, Rsd, are determined from the Id-Vg and -gm-Vg characteristics n-MOSFETs.

• Nuclear Engineering and Technology
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• v.41 no.10
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• pp.1255-1262
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• 2009

This paper introduces the status of and issues related to the PSHA (Probabilistic Seismic Hazard Analysis) of Korean Nuclear Power Plant sites. PSHA was first introduced to the nuclear industry in the mid-1980s. The Korean PSHA is based on Cornell and accommodates the modem approach for eliciting expertise and statistical treatment. Due to the low seismicity in Korea, large uncertainties exist in the PSHA database including seismic source maps, seismicity parameters of seismic sources, and attenuation formulae. Though research in seismology, geology, and earthquake engineering since the mid-1990s has significantly reduced uncertainties, a considerable amount still exists. Considering the low seismicity of the Korean Peninsula, especially the lack of strong motion data, further reduction will take several decades.

• The Journal of the Acoustical Society of Korea
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• v.29 no.2E
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• pp.64-72
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• 2010

Osteoporosis is a skeletal disease characterized by two factors: reduced bone mass and microstructure disruption of bone tissue. These symptoms increase bone fragility and can contribute to eventual fracture. In recent years, quantitative ultrasound (QUS) technologies have played a growing role in the diagnosis of osteoporosis. Most of the commercial bone sonometers measure speed of sound and/or broadband ultrasound attenuation at peripheral skeletal sites. However, QUS parameters are purely empirical measures that have not yet been firmly linked to physical parameters, such as bone strength or porosity, and the underlying physics for their variations in cancellous bone is not well understood yet. This paper reviews the QUS technologies for the diagnosis of osteoporosis and also addresses several theoretical models, such as the Biot model, the scattering model, the stratified model, and the modified Biot-Attenborough model, for ultrasonic wave propagation in bone.

• Journal of Power System Engineering
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• v.10 no.1
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• pp.77-82
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• 2006

In this study, dissimilar friction welding were produced using 15mm diameter solid bar in chrome molybedenum steel(SCM440) to carbon steel(S45C) to investigate their mechanical properties and the relationship between the weld parameters and the nondestructive coefficients, such as AE counts and ultrasonic attenuation coefficient. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, Vickers hardness surveys of the bond of area and heat affected zone. The specimens were tested as-welded and post weld heat treated(PWHT). The tensile strength of the friction welded steel bars was increased up to 100％ of the S45C base metal under the condition of all heating time. The ductility of PWHT specimens is higher than as-welded.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.3 s.118
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• pp.334-340
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• 2007

The prediction for vegetation attenuation using the RET model recommended in the ITU-R requires six RET input parameters. Among these, 4 parameters are related to the scattering characteristics of vegetation. To extract these parameters, two methods can be used. One is to extract the parameters by curve fitting of the measured vegetation-attenuation curve with the RET prediction model, and the other is to use the additional phase function measurement data. In the former method, fitting is quite complex and it does not result in the unique results in some cases. In addition, the extracted parameters lack the physical meaning as well. Thus, in this paper, the measurement method of phase function, and the method of extracting the RET model parameters which lead to more accurate and physically more meaningful results are presented. The extracted RET model parameters are also presented. The RET modeling method, measurement data, and the extracted RET model parameters presented in this paper were submitted to the ITU-R meeting in 2006, and adapted for ITU-R report and recommendation P.833.

• Journal of the Optical Society of Korea
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• v.18 no.3
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• pp.261-273
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• 2014

In this paper, metal insulator metal (MIM) plasmonic slot cavity narrow band-pass filters (NBPFs) are studied. The metal and dielectric of the structures are silver (Ag) and air, respectively. To improve the quality factor and attenuation range, two novel NBPFs based on tapered structures and double cavity systems are proposed and numerically analyzed by using the two-dimensional (2-D) finite difference time domain (FDTD) method. The impact of different parameters on the transmission spectrum is scrutinized. We have shown that increasing the cavities' lengths increases the resonance wavelength in a linear relationship, and also increases the quality factor, and simultaneously the attenuation of the wave transmitted through the cavities. Furthermore, increasing the slope of tapers of the input and output waveguides decreases attenuation of the wave transmitted through the waveguide, but simultaneously decreases the quality factor, hence there should be a trade-off between loss and quality factor. However, the idea of adding tapers to the waveguides' discontinuities of the simple structure helps us to improve the device total performance, such as quality factor for the single cavity and attenuation range for the double cavity. According to the proposed NBPFs, two, three, and four-port power splitters functioning at 1320 nm and novel ultra-compact two-wavelength and triple-wavelength demultiplexers in the range of 1300-1550 nm are proposed and the impacts of different parameters on their performances are numerically investigated. The idea of using tapered waveguides at the structure discontinuities facilitates the design of ultra-compact demultiplexers and splitters.

• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.321-324
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• 2004

In this paper, attenuation characteristics of silica-based variable optical attenuator (VOA) with heat insulating structures are investigated by variations of structural parameters and heating power at wavelength 1.55${\mu}m$. The characteristics of power dissipation and attenuation at this VOA was optimized in terms of heating insulating width, under-cladding height and over-cladding height. The optimized maximum attenuation of this VOA was achieved about 31dB at heating power 150mW.