• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1245-1247
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• 1995

In this paper, Analyzed structual property using SEM and XRD. The longer distance between substrate and target enhance crystalographic orientation of (110)plane, but inhibit growth of (002)plane. Also, deposited ZnO thin film on electrode layer inhibit crystalographic orientation of (002)plane, expecially Al electrode inhibit stronger than Pt layer. And using fabricated transducer, analyzed eletric and frequency characteristics.

• MALSORI
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• no.52
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• pp.133-144
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• 2004

The quality of narrowband speech can be enhanced by the bandwidth extension technology. This paper proposes a mixed excitation and an energy compensation method based on Gaussian Mixture Model (GMM). First, we employ the mixed excitation model having both periodic and aperiodic characteristics in frequency domain. We use a filter bank to extract the periodicity features from the filtered signals and model them based on GMM to estimate the mixed excitation. Second, we separate the acoustic space into the voiced and unvoiced parts of speech to compensate for the energy difference between narrowband speech and reconstructed highband, or lowband speech, more accurately. Objective and subjective evaluations show that the quality of wideband speech reconstructed by the proposed method is superior to that by the conventional bandwidth extension method.

• MALSORI
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• no.52
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• pp.61-84
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• 2004

This study investigates the Korean native speakers' English liquid perception and production. Perception and production experiments were each conducted twice before and after a short period of explicit learning process of phonetic characteristics of English liquids. The results showed that correlation between perception and production varied depending on factors. In both perception and production, word-final position was the most difficult, and cluster position was the easiest. A considerable improvement was observed in word-initial and medial positions in production, whereas no improvement was achieved in word-final position, especially in production. This study is also concerned with the formant structures of Korean native speakers' production of English liquids in order to see what acoustic features are highly correlated with Korean native speakers' production accuracy of English liquids. The results showed that F2 did not show a high correlation while F3 was a strong correlate of the production accuracy.

• MALSORI
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• no.62
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• pp.1-17
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• 2007

The purpose of this study was to investigate and quantitatively describe the acoustic characteristics of current Korean monophthongs. Recordings were made of 33 men and 27 women producing the vowels /i, e, ${\epsilon}$, a, ${\partial}$, o, u, i/ in a carrier phrase "This character is ___." A listening test was conducted in which 19 participants judged each vowel. F1, F2, and F3 were measured from the vowels judged as intended vowels by more than 17 people from the listening test. Analysis of formant data shows some interesting results including the undeniable confirmation of the 7-vowel system in modern Korean. It turns out that quite different sounding Korean vowels and English vowels happen to have very similar formant measurements. Also the difference between "citation-form reading" vs. "natural utterance reading" is discussed.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.150-157
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• 2011

Nowadays, high speed train has settled down as a fast and convenient environment-friendly transportation and it's need is gradually increasing. However increased train speed leads to increased aerodynamic noise, which causes critically affects comfortability of passengers. Especially, the pantograph of high speed train is protruded out of train body, which is the main factor for increased aerodynamic noise. Since aerodynamic noise caused pantograph should be measured in high speed, it is difficult to measure it and to analysis aerodynamic noise characteristics due to the various types of pantograph. In this research, aerodynamic noise of pantograph is predicted by CFD (Computational Fluid Dynamic) and FW-H (Ffowcs Williams-Hawkings) equation. Also, Wind tunnel test results and numerical simulation results were compared. As a result, Simulation results predicting sound pressure level is very similar with wind tunnel test result. This research will draw major factor in aerodynamic noise of pantograph and will be utilized for predict sound pressure level of pantograph.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.83.4-84
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• 2015

We report that a strong downflow event caused three-minute oscillations in the solar atmosphere. Our observations were carried out by using the Fast Imaging Solar Spectrograph (FISS) of the 1.6 meter New Solar Telescope (NST) and the Interface Region Imaging Spectrograph (IRIS). Our main findings are as follows: (1) The strong downflow was seen at the $H{\alpha}$ absorption line at first, and then appeared at the Si IV and C II emission lines. It seems that the characteristics of the downflow are consistent with a coronal rain event. (2) After the event, oscillations of velocity were identified in the chromospheric lines and transition region lines. (3) The amplitudes of oscillations were 2km/s at Mg II line and 3km/s at C II and Si IV lines and decreased with time. (4) The period of the oscillation was 2.67 minutes at first, but gradually increased with time. Our findings are in agreement with Chae & Goode (2015)'s theory that of acoustic waves generated by a disturbance in a gravitationally-stratified medium.

• Journal of the Korean Society of Combustion
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• v.18 no.1
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• pp.1-6
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• 2013

Authors' previous works on thermoacoustic(TA) model development showed good results in predicting combustion instability characteristics in a gas turbine combustor. However, they also suggested there were some limitations in growth rate estimation, which might be related with over-simplification of flame structure. As a first trial for improving the model accuracy, the current paper introduces the modified TA model considering the actual flame location in the combustor. The combustor is divided into the unburned and the burned area before and after the flame location, and then acoustic equations are re-organized. The modified TA model results show a better accuracy in predicting the growth rate of instabilities comparing with the previous results. However, obtained results still overestimate the conditions where the combustor goes unstable. Further researches considering heat release distribution through flames are required.

• Tribology and Lubricants
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• v.27 no.5
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• pp.249-255
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• 2011

Recently the demand for a fast and precise actuator in semiconductor industries is growing larger. A SAW motor is now expected as a new friction-drive actuator to meet such demand. However, its friction and wear properties are almost unknown and its low stability and reliability still remain to be solved. In this research the tests of SAW motor were carried out and its durability was discussed. The effect of wear caused by friction on the driving force and driving speed were clarified.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.05a
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• pp.22-25
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• 1995

In this paper, the physical characteristics of piezoelectric transducer which generates acoustic weve at microwave frequency were theoretically analized. We found that increasing electrode thickness is showed large distorthion on bandwidth. ZnO thin film were desposited by RF magnetron sputtering method. considering the sputtering parameters. Thickness of the desposited ZnO was 3.9 $\mu\textrm{m}$. In this experiment, we get that resistivity is 12.196${\times}$109 [cm$\Omega$], that resonance frequency is 827.47MHz Measuring insertion loss, we ascertained to possibility of transducer application for microwave frequency.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.6
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• pp.133-143
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• 1996

The need of comfortable car and the efforts to overcoming the noise regulations on passenger cars bring about a series of studies on the ruduction of exhaust noises. In this study, acoustic characteristics of various components that compose mufflers of automobiles were analyzed theoretically, and the program which predicts the performance of mufflers was developed by the transfer matrix approach. The simulations were verified by the experiments on a real muffler. By using the developed simulation program, we investigate the effects of each component on the entire muffler system and the energy loss coefficient on absorption materials in the front muffler. Finally, we proposed two designs to improve the performance of a muffler and verified the improved performance by the experiments and simulations.