• Journal of Convergence for Information Technology
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• v.12 no.3
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• pp.151-157
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• 2022

The purpose of this study was to investigate the frequency characteristics of forced vibration considering the vehicle progress. And the vibration characteristics in frequency domain that occur, when vehicle passes the bump, were analyzed. The responses such as displacement, velocity and acceleration were obtained through numerical analysis, and FFT processing was performed to analyze the frequency response function(FRF) characteristics. In particular, the location of vehicle eigenmodes and external excitation modes was clearly shown and analyzed. In the forced vibration model by external force, the behavior of the eigenmode in power spectrum and real and imaginary parts were also analyzed. The mode characteristics were also analyzed in each FRF. It was approximated by assuming total excitation force by considering the exciting frequency using impulse and sine wave forces, which can give the amplitude and frequencies. The response characteristics of forced oscillations having different mass, damping and stiffness have been systematically discussed.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.174-183
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• 2022

Acoustic radiation from a submerged elastic shell with an internal fluid surrounded by the bubble layer is studied with the modal theory. An omni-directional point source located on the center of the internal fluid is used as acoustic noise source. The unknown coefficients of modal solutions are solved using the interface conditions between media. To preserve the stability of the modal solution over wide frequency ranges, the scaled technique of modal solution is used. The bubble layer is modeled with four kinds of bubble distribution; uni-modal distribution, uniform distribution, normal distribution, and power-law distribution, based on the effective medium theory of Commander and Prosperetti. For each bubble distribution, the insertion losses are mainly calculated for the frequency. In addition, the numerical simulations are performed depending in the bubble void fraction, the material property of elastic shell, and the gap between the bubble layer and the elastic shell.

• Journal of the Korean BIBLIA Society for library and Information Science
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• v.20 no.1
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• pp.137-150
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• 2009

This study has introduced folksonomy to general patterns of folksonomy tags for the university libraries that have practically implemented Library 2.0. From the results, we can see that average about 1.35 tag is used for one content. Typical pattern of the tags follow a power function that frequency of use decreases as No. of uses increases, 79.51% of tags are expressing topic of contents, and 84.61% of tags are tag of social motivation. The results of analysis on increase/decrease rate for tags divided into 4 quarters said that A university library has big differences from quarters while B university library has similar data between quarters. The users have used average 5.25 tags. Trends of the users can be divided into 3 groups according to tagging patterns of the users.

• The Journal of the Acoustical Society of Korea
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• v.29 no.7
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• pp.411-421
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• 2010

A time-reversal mirror (TRM) is useful in diverse areas, such as reverberation ing, target echo enhancement and underwater communication. In underwater communication, the bit error rate has been improved significantly due to the increased signal-to-noise ratio by spatio-temporal focusing. This paper deals with two issues. First, the optimal number of array elements for a given environment was investigated based on the exploitation of spatial diversity. Second, an algorithm was developed to determine the optimal location of the given number of array elements. The formulation is based on a genetic algorithm maximizing the contrast between the foci and area of interest as an objective function. In addition, the developed algorithm was applied to the matched field processing with ocean experimental data for verification. The sea-going data and simulation showed almost 3 dB improvement in the output power at the foci when the array elements were optimally distributed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.4
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• pp.48-54
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• 2024

NPP (Nuclear power plant) structures have been constructed near to the sea shore line for cooling water and exposed to steel corrosion due to chloride attack. Regarding NPP structures built in the UAE, chloride transport may be more rapid than those in the other regions since the temperature near to the coast is high. In this study, concrete samples with 5,000psi (35MPa) design strength grade were manufactured with the materials and mix proportions, which were the same as used in the UAE NPP structures, then chloride diffusion coefficients were evaluated considering temperature and curing age. The compressive strength and the diffusion coefficient were evaluated and analyzed for the samples with 28 and 91 curing days. In addition, chloride diffusion tests for 91-day-cured condition were carried out in the range of 20℃ to 50℃. The activation energy was obtained through converting the temperature slope to a logarithmic function and it was compared with the previous studies. The proposed activation energy can be useful for a reasonable durability design by using actual temperature-dependent chloride diffusion coefficient.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.1
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• pp.139-148
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• 2006

The dynamic characteristics of a bridge deduced by using the modeling techniques depend on its stiffness and mass calculated from its geometric model. This research develops the FE modeling techniques for a steel plate girder bridge with composite section. and proves their validity by comparing the results with those from actual measurement. The FE modeling techniques are divided into two categories--a simplified one and two-dimensional model and a detailed three-dimensional model. In the meantime, the dynamic responses of the bridge tested for this research were measured by the ambient vibration some of accelerometers were been attached to its upper slab girder under normal traffic load. The Cross Power Spectrum obtained from the measurement was used to analyze the dynamic characteristics by natural excitation techniques. The analytic results are compared to those of each FE modeling, and thereby the modeling techniques were proved to be valid.

• The Journal of the Petrological Society of Korea
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• v.24 no.3
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• pp.165-180
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• 2015

Jurassic granite from Geochang was analysed with respect to the characteristics of the rock cleavage. The phases of distribution of microcracks were well evidenced from the enlarged photomicrographs(${\times}6.7$) of the thin section. In this study, the length - cumulative frequency diagrams were used for expressing the distribution characteristics of microcrack. The diagrams for the six directions were arranged in the magnitude of density(${\rho}$). These diagrams show an order of H2 < H1 < G2 < G1 < R2 < R1 from the related chart. Among six diagrams, the diagram for hardway 2(H2) occupies the lowermost region on the left. On the contrary, the diagram for rift 1(R1) occupies the uppermost region on the right. Curve patterns of the two diagrams change from uniform to exponential distribution type in accordance with the increased density. The overall distribution characteristics of the diagrams were well evidenced from the magnitude of the exponent(${\lambda}$) and length of line oa related to the exponential straight line. The magnitude of exponent governing the values of slope(${\theta}$) is inversely proportional to the values of microcrack parameters such as number(N), length(L) and density. On the contrary, length of line oa is directly proportional to the values of the above three parameters. Above microcrack parameters related to the order of arrangement of diagrams show an order of hardway(H1 + H2) < grain(G1 + G2) < rift(R1 + R2). The distribution characteristics of progressive variation are found among the six diagrams. The order of arrangement of the diagrams indicates a relative magnitude of the rock cleavage. Meanwhile, the parameters such as slope, exponent, density and length of line oa were arranged in an order of H2 < H1 < G2 < G1 < R2 < R1. The variation curves of a smooth quadratic function are shown from the related chart. From the correlation chart between density and the above parameters, a common regularity following power-law correlation function was derived. Finally, the analysis for the rock cleavage was conducted through the combination between the diagram and microcrack parameter. This type of combination contribute to the progressivity in evaluation for the rock cleavage.

• Journal of Preventive Medicine and Public Health
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• v.31 no.3 s.62
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• pp.490-502
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• 1998

This study purports to find the predictor of hospital bankruptcy in Korea and to examine the predictive power of the discriminant function model of hospital bankruptcy. Data on 17 financial and 4 non-financial indicators of 31 bankrupt and 31 profitable hospitals of 1, 2, and 3 years before bankruptcy were obtained from the hospital performance databank of Korea Institute of Health Services Management. Significant variables were identified through mean comparison of each indicator between bankrupt and profitable hospitals, and the discriminant function model of hospital bankruptcy was developed. The major findings are as follows 1. As for profitability indicators, net worth to total assets, operating profit to total capital, operating profit ratio to gross revenues, normal profit to total assets, normal profit to gross revenues, net profit to total assets were significantly different in mean comparison test in 1, 2, and 3 years before hospital bankruptcy. With regard to liquidity indicators, current ratio and quick ratio were significant in 1 year before bankruptcy. For activity indicators, patients receivable turnover was significant in 2 and 3 years before bankruptcy and added value per adjusted inpatient days was significant in 3 years before bankruptcy. 2. The discriminant function in 1, 2, and 3 years before bankruptcy were; $Z=-0.0166{\times}quick$ ratio-$0.1356{\times}normal$ profit to total assets-$1.545{\times}total$ assets turnrounds in 1 year before bankruptcy, $Z=-0.0119{\times}quick$ ratio-$0.1433{\times}operating$ profit to total assets-$0.0227{\times}value$ added to total assets in 2 years before bankruptcy, and $Z=-0.3533{\times}net$ profit to total assets-$0.1336{\times}patients$ receivables turn-rounds-$0.04301{\times}added$ value per adjusted $patient+0.00119{\times}average$ daily inpatient census in 3 years before bankruptcy. 3. The discriminant function's discriminant power in 1, 2, and 3 years before bankruptcy was 77.42, 79.03, 82.25% respectively.

• Journal of the Korean GEO-environmental Society
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• v.13 no.9
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• pp.5-16
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• 2012

In the case of using the soil materials created by cutting in-situ ground directly without adjusting particle size, it is recommendable to seek the compaction property or material constant required for filling design or density control through indoor test, and many studies on this subject have been carried out during that time. The researches conducted during that time, however, were focused on the mixed materials with different diameters that exist in a natural condition. There has been no study conducted using coal fly ash that is by-product of the thermal power plant that is actively considered as the building materials. Therefore, this study was aimed at implementing compaction test and examining the basic engineering property in order to explore the influence of crushing the particles through compacting the admixture of crushed stone and coal fly ash produced from thermal power plant on its engineering property, and then the impact of the admixture volume of each material on compaction property and material property by conducting the One-Dimensional Compression Test. As result of compaction test, the optimum moisture ratio of coal fly ash was shown to be approx. 23%. As result of compaction test in accordance with the mixed ratio of coal fly ash and crushed stone under the same compaction energy and moisture ratio, dry unit weight tended to drop when the mixed ratio of coal fly ash exceeded 30%, while it reached approx. $1.81gf/cm^3$ when the mixed ratio was 30%. As result of One-Dimensional Compression Test in accordance with the mixed ratio of crushed stone and coal fly ash, the change in void ratio by particle crushing was at the highest level in the case of coal fly ash 100%, while the lowest level in the case of crushed stone 100%. In the case of mixed materials of crushed stone and coal fly ash, compression index was at the lowest level in case of coal fly ash 30%, and therefore this ratio of mixed material was judged to be the most stable from an engineering aspect.

• Journal of Service Research and Studies
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• v.6 no.1
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• pp.83-95
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• 2016

We examine the information transmission between the Service Industrial Production Index and the Service Industrial Wholesale and Retail Index, based on the returns data offered by the Korea Bank. The data includes daily return data from January 2000 to September 2015. Utilizing a dynamic analytical tool-the VAR model, Granger Causality test, Impulse Response Function and Variance Decomposition have been implemented. The results of the analysis are as follows. Firstly, results of Granger Causality test suggests the existence of mutual causality the Service Industrial Production Index precede and have explanatory power the Service Industrial Wholesale and Retail Index However the results also identified a greater causality and explanatory power of the Service Industrial Wholesale and Retail Index over the Service Industrial Production Index. Secondly, the results of impulse response function suggest that the Service Industrial Production Index show immediate response to the Service Industrial Wholesale and Retail Index and are influenced by till time 5 From time 2, the impact gradually disappears. Also the Service Industrial Wholesale and Retail Index show immediate response to the Service Industrial Production Index and are influenced by till time 2.5, the impact gradually disappears. Lastly, the variance decomposition analysis shows that the changes of return of Service Industrial Production Index are dependent on those of the Service Industrial Wholesale and Retail Index. This implies that returns on the Service Industrial Production Index have a significant influence over returns on the Service Industrial Wholesale and Retail Index. It contributes to the understanding of market price formation function through analysis of detached the Service Industrial Production Index and Service Industrial Wholesale and Retail Index. Finally, our results can be used as a guide by the Korea Bank and Republic of Korea and as well as Statistics Korea.