• The Journal of the Acoustical Society of Korea
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• v.41 no.4
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• pp.375-388
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• 2022

This paper deals with the process of obtaining sound transmission loss of a cylindrical silencer lined with multi-layered poroelastic sound absorbing materials. The Biot model and the Johnson-Champoux-Allard-Lafarge (JCAL) model were used to deal with waves propagating in multi-layered poroelastic materials. The boundary conditions required for analysis of the silencer were obtained and the numerical process of finding modes was explained. A numerical experiment was conducted on the 2-layered silencer using the modes and the transmission loss converged with the first 12 modes. Finally, the mode matching method proposed in this research was validated by being compared with the results calculated from Finite Element Method (FEM) about different kinds of sound absorbing materials.

• Communications for Statistical Applications and Methods
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• v.16 no.6
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• pp.891-901
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• 2009

In this paper, we investigate the approach to estimate VaR under the transformed GARCH model. The time series are transformed to approximate to the underlying distribution of error terms and then the parameters and the one-sided prediction interval are estimated with the transformed data. The back-transformation is applied to compute the VaR in the original data scale. The analyses on the asset returns of KOSPI and KOSDAQ are presented to verify the accuracy of the coverage probabilities of the proposed VaR.

• The Journal of Fisheries Business Administration
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• v.30 no.2
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• pp.79-89
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• 1999

This study is conducted to apply the insight of Johnson and Libecap(1982) to Korea's coastal vessel fishing. According to Johnson and Libecap(1982) the differences in fishing ability are largely attributed to acquired knowledge and innate skills. Since those skills are unlikely to be readily transferable assets, economic rents exist in the fishery, even under open access conditions. Therefore the paper tries to examine whether the acquired information from fishing experience and innate skill could also have an effect on catch variation of coastal vessel fishing in Kyung-Nam province. To do so, the paper is performing the analysis by establishing econometric model. Results show us that the acquired information from fishing experience have a significant effect on catch variation, but the innate skill does not.

• The Korean Journal of Applied Statistics
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• v.25 no.6
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• pp.889-896
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• 2012

In this paper, we propose a statistic to measure investor sentiment. It is a usual phenomenon that an asymmetric volatility (referred to as the leverage effect) is observed in financial time series and is more sensitive to bad news rather than good news. In a bubble state, investors tend to continuously speculate on financial instruments because of optimism about the future; subsequently, prices tend to abnormally increase for a long time. Estimators of the transformation parameter and the skewness based on Yeo-Johnson transformed GARCH models are employed to check whether a bubble or abnormality exist. We verify the appropriacy of the proposed interpretation through analyses of KOSPI and NIKKEI.

• International Journal of Automotive Technology
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• v.1 no.1
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• pp.35-41
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• 2000

The crashworthiness of vehicles with finite element methods depends on the geometry modeling and the material properties. The vehicle body structures are generally composed of various members such as frames, stamped panels and deep-drawn parts from sheet metals. In order to ensure the impact characteristics of auto-body structures, the dynamic behavior of sheet metals must be examined to provide the appropriate constitutive relation. In this paper, high strain-rate tensile tests have been carried out with a tension type split Hopkinson bar apparatus specially designed for sheet metals. Experimental results from both static and dynamic tests with the tension split Hopkinson bar apparatus are interpolated to construct the Johnson-Cook and a modified Johnson-Cook equation as the constitutive relation, that should be applied to simulation of the dynamic behavior of auto-body structures. Simulation of auto-body structures has been carried out with an elasto-plastic finite element method with explicit time integration. The stress integration scheme with the plastic predictor-elastic corrector method is adopted in order to accurately keep track of the stress-strain relation for the rate-dependent model accurately. The crashworthiness of the structure with quasi-static constitutive relation is compared to the one with the rate-dependent constitutive model. Numerical simulation has been carried out for frontal frames and a hood of an automobile. Deformed shapes and the Impact energy absorption of the structure are investigated with the variation of the strain rate.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.1
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• pp.103-108
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• 2012

Restenosis symptom, which is well known as a problem of stents, is due to the recoil and expansion pressure depending on shapes of stent. In order to reduce the effect of recoil problem, study on pattern and shape for the stent is required and the expansion pressure and recoil should be evaluated. This paper aims at evaluating mechanical characteristics of stent used in surgery for vessel stenosis. The expansion process of coronary artery stent in vessel for two models including the Cypher$^{(R)}$ from Johnson & Johnson$^{TM}$ and a suggested model were simulated using the Finite Element Analysis. Comparison of the directional recoil simulation results was made. The issues in the deformed shape of vessel and recoil of Cypher$^{(R)}$ were partially resolved in the suggested model. Therefore, the shape design suggested in this paper was able to reduce the restenosis symptom.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.2
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• pp.164-171
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• 2003

The side impact behavior has been investigated when the high strength steel 60TRIP(Transformation Induced Plasticity) is replaced for the conventional low-carbon steel for weight reduction of an auto-body. The side impact analysis was carried out as specified in US-SINCAP with the center pillar and the side sill of the conventional steel or 60TRIP. For accurate impact analyses, the dynamic material properties are adopted with the Johnson-Cook model. The analysis results demonstrate that the penetration of the side members is remarkably reduced when 60TRIP is employed for the center pillar and the side sill replacing the conventional steel. The crashworthiness in the side impact is considerably improved with less penetration of the side members and less acceleration of the opposite floor.

• International Journal of Automotive Technology
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• v.4 no.3
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• pp.149-156
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• 2003

This paper is concerned with the energy absorption efficiency of auto-body side structures for the conventional steel and 60TRIP high strength steel. In order to evaluate the energy absorption efficiency, the dynamic crash analysis is carried out with the regulation of US-SINCAP. The analysis adopts the Johnson-Cook model for the dynamic material properties, which have been obtained from dynamic material tests. For the sake of the dynamic material properties, the analysis has been accurately peformed for the crashworthiness assesment. The analysis result provides deformed shapes, amounts of penetration and accelerations at several important points during crash. The result confirms that 60TRIP greatly improves the crashworthiness of the side members without sacrificing the weight and thus can be used for the light-weight design of an auto-body.

• Asia Marketing Journal
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• v.22 no.3
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• pp.1-28
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• 2020

With the development of information and communication technology and spread of smart devices, online information exchange has become a daily routine. Accordingly, the management and utilization of online word of mouth (WOM) has become an important issue for companies. Numerous studies have examined the impact of online WOM on firm performance. This study analyzes the impact of negative word of mouth (NWOM) on firm value, considering the influence of corporate social responsibility (CSR) activity and research and development (R&D) investment. Using a hierarchical linear model, we find that 1) NWOM has a negative impact on firm value, 2) CSR activities do not significantly influence this impact, and 3) R&D investment reduces this negative impact. This study contributes by demonstrating the effect of NWOM on firm value, examining the influence of CSR activities and R&D investment on the impact of NWOM, and confirming that the hierarchical linear model can be applied effectively to panel data in empirical studies. As a practical implication, companies must prevent and manage NWOM, whose impact, when caused by an unavoidable incident, can be alleviated by proactively announcing that the company is striving for competitiveness, for instance, by investing in R&D.

• Transactions of Materials Processing
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• v.33 no.3
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• pp.208-213
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• 2024

Ni-based superalloys have exceptional performance in high-temperature strength, corrosion resistance, etc, and it has been widely used in various applications that require corrosion resistance at high-temperature operations. However, the relatively expensive cost of the Ni-based superalloys is one of the major hurdles. The corrosion-resisted alloy(CRA) clad materials can be a cost-effective solution. In this study, finite element analysis of the hot rolling process for manufacturing of the Alloy 625/API X65 steel CRA clad plates is conducted. The stress-strain curves of the two materials are measured in compressive tests for various temperature and strain rate conditions, using the Gleeble tester. Then, strain hardening behavior is modeled following the modified Johnson-Cook model. Finite element analysis of the hot rolled cladding process is performed using this strain rate and temperature dependent hardening model. Finally, the thickness ratio of the CRA and base material is predicted and compared with experimental values.