• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.6
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• pp.520-530
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• 2007

Combination of the parametric and the wavelet analyses of acoustic emission (AE) signals was applied to identify the failure modes in carbon fiber reinforced plastic (CFRP) composite laminates during tensile testing. AE signals detected by surface mounted lead-zirconate-titanate (PZT) and polyvinylidene fluoride (PVDF) sensors were analyzed by parametric analysis based on the time of occurrence which classifies AE signals corresponding to failure modes. The frequency band level-energy analysis can distinguish the dominant frequency band for each failure mode. It was observed that the same type of failure mechanism produced signals with different characteristics depending on the stacking sequences and the type of sensors. This indicates that the proposed method can identify the failure modes of the signals if the stacking sequences and the sensors used are known.

• International journal of advanced smart convergence
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• v.8 no.2
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• pp.126-131
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• 2019

This study investigated the relationship between depressive symptoms and interests of workers in their 30s to 40s. This study recruited 49 workers who fit the selection criteria. Descriptive, frequency, and regression analyses were performed. To describe participant characteristics and the classification of depression and interest, descriptive and frequency analyses were used. The effect of interest patterns on depressive symptoms was analyzed using a multiple regression analysis, specifying the significance level at 0.05. The results of this study showed that half of the respondents, who were in their 30s and 40s, experienced depression. In addition, this study indicated that interest of workers in their 30s to 40s in daily, cognitive, physical, and social activities in the present was lower than that in the past. This interest level affected depression in past and present interest (p<0.05). This study investigated the relationship between interest and depression of workers in their 30s to 40s and suggest that interest in various areas may help prevent depression.

• Proceedings of the Korean Institute of Interior Design Conference
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• 2001.05a
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• pp.121-127
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• 2001

An unified measure of user interface efficiency and aesthetics for cyber museum is proposed. First, general structure of cyber museum is discussed and hierarchical analyses are done for sample sites. Usability tests based on the hierarchical analyses yield statistics of user access frequency and persistency for each page, on which access probability is deduced. Second, visual occupancy, a measure of efficiency of user interface element based on access probability is defined. The hierarchical statistics of visual occupancy can be an index for characterization and classification of cyber museums. Examples are provided.

• International Journal of Safety
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• v.6 no.1
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• pp.22-25
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• 2007

Damping out high frequency low amplitude structural vibrations using PZT bimorph is presented. Static and Dynamic analyses of the piezoelectric bimorph bender were performed. Three layer piezoelectric actuators were modeled with SOLID5 coupled-field elements using ANSYS. Static deflection and modal analyses of the piezoelectric bimorph bender are presented. Proper tuning of the values of the resistor and inductor in the shunt circuit is required for maximum vibration suppression.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.10a
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• pp.247-252
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• 2000

In this paper, we discuss frequency allocation and sharing for high speed radio access network in domestic 5㎓ the band. In order to evaluate the possibility of frequency sharing between meterological radar and high speed radio access network we analyses radio interference of meterological radar by means of minimum coupling loss method and Monte Carlo simulation And simulations show that it is necessary to use DFS(Dynamic Frequency Selection) scheme for frequency sharing between meterological radar and high speed radio access network.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.4
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• pp.751-758
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• 2000

In this paper, we discuss frequency allocation and sharing for high speed radio access network in domestic 5GHz the band. In order to evaluate the possibility of frequency sharing between meteorological radar and high speed radio access network, we analyses radio interference of meteorological radar by means of minimum coupling loss method and Monte Carlo simulation. And simulations show that it is necessary to use DFS(Dynamic Frequency Selection) scheme for frequency sharing between meteorological radar and high speed radio access network.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.7
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• pp.654-661
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• 2013

The dynamic characteristics of a free-piston stirling engine(FPSE) with regard to the working frequency is investigated from theoretical and experimental studies. The FPSE is modeled as a two degree-of-freedom linear vibration system. A theoretical expression on the working frequency is derived from the instability condition for self-excitation based on the linear vibration model. A ${\gamma}$-type free-piston stirling engine is fabricated for experimental studies, and its working frequency is measured on various heater temperatures. Comparisons between the theoretical and experimental results reveal that the working frequency of the test FPSE depends on both the temperature of the compression space and the temperature difference between the expansion and compression spaces.

• Journal of Ocean Engineering and Technology
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• v.34 no.6
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• pp.428-435
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• 2020

Energy flow analysis (EFA) has been used to predict the frequency-averaged vibrational responses of built-up structures at high frequencies. In this study, the frequency-averaged exact energetics of the in-plane motions of the plate were derived for the first time by solving coupled partial differential equations. To verify the EFA for the in-plane waves of the plate, numerical analyses were performed on various coupled plate structures. The prediction results of the EFA for coupled plate structures were shown to be accurate approximations of the frequency-averaged exact energetics, which were obtained from classical displacement solutions. The accuracy of the results predicted via the EFA increased with an increase in the modal density, regardless of various structural parameters. Therefore, EFA is an effective technique for predicting the frequency-averaged vibrational responses of built-up structures in the high frequency range.

• Educational Technology International
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• v.24 no.2
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• pp.331-358
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• 2023

This paper explores the impact of mobile device usage frequency in the classroom on students' perceptions of their use. To assess this, we created a survey that measured students' perceived frequency, usefulness, and convenience of using mobile devices, using a reversed Technology Acceptance Model. Through the analysis of responses from 781 Korean students, utilizing confirmatory item factor analyses and a structural equation mixture model, we found that the effect of frequent mobile device use on students' positive perceptions is non-linear. As the frequency reaches to a certain level, the effect sizes of the frequency in the positive perceptions diminishes. Additionally, students who used mobile devices less frequently in class reported higher levels of difficulties in using the devices. This study introduces a tool for evaluating multiple aspects of students' perceptions regarding mobile device use and offers a framework for understanding the relationship between usage frequency, usefulness, and convenience.

• The Journal of Advanced Prosthodontics
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• v.2 no.3
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• pp.71-76
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• 2010

PURPOSE. The purpose of this study was to compare men with women in terms of speech intelligibility, to investigate the validity of objective acoustic parameters related with speech intelligibility, and to try to set up the standard data for the future study in various field in prosthodontics. MATERIALS AND METHODS. Twenty men and women were served as subjects in the present study. After recording of sample sounds, speech intelligibility tests by three speech pathologists and acoustic analyses were performed. Comparison of the speech intelligibility test scores and acoustic parameters such as fundamental frequency, fundamental frequency range, formant frequency, formant ranges, vowel working space area, and vowel dispersion were done between men and women. In addition, the correlations between the speech intelligibility values and acoustic variables were analyzed. RESULTS. Women showed significantly higher speech intelligibility scores than men and there were significant difference between men and women in most of acoustic parameters used in the present study. However, the correlations between the speech intelligibility scores and acoustic parameters were low. CONCLUSION. Speech intelligibility test and acoustic parameters used in the present study were effective in differentiating male voice from female voice and their values might be used in the future studies related patients involved with maxillofacial prosthodontics. However, further studies are needed on the correlation between speech intelligibility tests and objective acoustic parameters.