• Journal of the Korean Society for Railway
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• v.19 no.1
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• pp.1-10
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• 2016

To improve the sound insulation performance of laminated glass in high speed trains, it is beneficial to study the relationship between the characteristics of interlayer films and the acoustical performance. In addition to those of conventional PVB (polyvinyl butyral), the dynamic mechanical properties of PVB derivatives and PC (polycarbonate), which are candidates for interlayer films, were analyzed. We assumed that PVB-HEMU, which has a glass transition temperature ($T_g$) around room temperature and a large tan ${\delta}$ (loss tangent) value, can be made to damp efficiently. The damping capability was tested utilizing sound transmission loss measurement and simulation under the identical structure of laminated glass in high speed trains. We also built a database for analysis of relations between interlayer film characteristics and acoustical performance; this was followed by the determination of sound transmission loss using the intensity technique and FEA.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.2
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• pp.82-89
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• 1998

The experimental results using the X -ray technique, the position and structure of mica crystal are not observed the phase change of aging and sound specimen respectively. However, We could observe the intensity difference of crystal element in both atmospheres. The analysis of mica-epoxy materials by optical microscope are shown that the each surface of sound and aging specimens are different in both atmospheres Also, the experimental results have shown that the potassium ions of mica cristal are substituted by hydrogen ions at boundary area of mica-epoxy and/or mica-mica. On components made of mica, a potassium ion of big atomic radius, is replaced by hydrogen ion of small atomic radius. The voids are created by the difference of radius progressed by combined stresses. Through these phenomena, it has been proposed that the conductive layers made of potassium enable the voids to form and the cracks to create by high electric field.

• The Journal of the Acoustical Society of Korea
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• v.39 no.1
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• pp.47-56
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• 2020

The sound source localization technique has various application fields in the era of internet-of-things, for which the probe size becomes critical. The localization methods using the acoustic intensity vector has an advantage of downsizing the layout of the array owing to a small finite-difference error for the short distance between adjacent microphones. In this paper, the acoustic intensity vector and the Time Difference of Arrival (TDoA) method are compared in the viewpoint of the localization error in the far-field. The comparison is made according to the change of spacing between adjacent microphones of the three-dimensional microphone array arranged in a tetrahedral shape. An additional test is conducted in the reverberant field by varying the reverberation time to verify the effectiveness of the methods applied to the actual environments. For estimating the TDoA, the Generalized Cross Correlation-Phase transform (GCC-PHAT) algorithm is adopted in the computation. It is found that the mean localization error of the acoustic intensimetry is 2.9° and that of the GCC-PHAT is 7.3° for T₆₀ = 0.4 s, while the error increases as 9.9°, 13.0° for T₆₀ = 1.0 s, respectively. The data supports that a compact array employing the acoustic intensimetry can localize of the sound source in the actual environment with the moderate reflection conditions.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.200-207
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• 1999

The purpose of this research is to setup the design procedure of low noise rolling stocks. Noise sources are identified at a field test, and the contribution of noise sources to each part of car interior is ensured by sound intensity measurement technique. Added material to each section of the carbody makes it possible to identify absorption or reflection performance of each part to the anterior random noise. Such experimental tests to the exterior noise intruding through the floor represent that the best countermeasure on the floor is to implement reflecting material which can properly interfere noise. Design procedure of low noise rolling stocks is set through several experiments.

• Journal of the korean academy of Pediatric Dentistry
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• v.24 no.1
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• pp.301-312
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• 1997

The purpose of this study was to evaluate the analgesic effect on pulp induced by pulsed Nd : YAG laser according to the power density, irradiated time and the method of application (Non-contact vs contact) in vivo. Experiments were carried out on 90 volunteers who have sound 4 canines. Each canine was grouped by the intensity and the time of irradiation of pulsed Nd : YAG laser was measured. Mean EPT response(units) was measured at 5 min, 30 min, and 60 min after irradiation with various intensity(1.5-3W, 15-30Hz), irradiated time (1.5min, 3min), and application method (Non-contact and contact). The results were as follows: 1. 5 minutes after irradiation, the mean EPT response(units) was increased by 32 % in the non-contact method and by 35% in the contact method of application. Which showed significant difference in mean EPT response(units) compared to not-lased canine in each groups(P<0.05). 2. The mean EPT response(units) with irradiating condition according to the various laser intensity, and the irradiation time stastically did not show significant difference in each groups as time elapsed. 3. There was no significant difference between the non-contact and contact method in the mean EPT response(units). 4. The mean EPT response(units) returned to the baseline value within 30 miuntes. In regard to the above results, the analgesic effect on pulp induced by pulsed Nd : YAG laser resulted a slight increase of pulpal pain threshold, but it was not as high as to replace the role of drug analgesia as whole. This technique can be used for inducing pulpal analgesia as adjunct to other pain control methods and is needed to develop better analgesic effects.

• The Journal of the Acoustical Society of Korea
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• v.35 no.5
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• pp.340-348
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• 2016

Ray-based model for the calculation of the ocean surface-generated ambient noise coherence function has the form of double integral with respect to a range and a bearing angle. While the theoretical consideration about its numerical implementations was partly given in the past work of authors, the numerical results on the ocean environment have not been presented yet. In this paper, we perform numerical experiments for shallow and deep water environments. It is shown that the coherence function depends on the ocean sediment sound speed, and is more sensitive to the ocean sediment sound speed in the shallow water than in the deep water. Similar trend is also observed for varying the orientation of hydrophone pair. In addition, a post-processing technique is proposed in order to plot the noise intensity for the noise receiving angle. This procedure will supplement the weakness of the ray-based model about the output data type compared to the semi-analytic model of Harrison.

• Journal of Biomedical Engineering Research
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• v.36 no.5
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• pp.143-149
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• 2015

In this paper, we proposed a novel method for automatic detection for snoring and heart beat using a single piezoelectric sensor. For this study multi-rate signal processing technique was applied to detect snoring and heart beat from the single source signal. The sound event duration and intensity features were used to snore detection and heart beat was found by autocorrelation. The performance of the proposed method was evaluated on clinical database, which is the nocturnal piezoelectric snoring data of 30 patients that suffered obstructive sleep apnea. The method achieved sensitivity of 88.6%, specificity of 96.1% with accuracy of 95.6% for snoring and sensitivity of 94.1% and positive predictive value of 87.6% for heart beat, respectively. These results suggest that the proposed method can be a useful tool in sleep monitoring and sleep disordered breathing diagnosis.

• Journal of ILASS-Korea
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• v.10 no.3
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• pp.29-37
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• 2005

The spray and acoustic characteristics of a gas/liquid swirl coaxial injector are studied experimentally. The self-pulsation is defined as a pressure and flow rate oscillations by a time-delayed feedback between liquid and gas phase. Self-pulsation has strong influences on atomization and mixing processes and accompanies painful screams. So. the spray and acoustic characteristics are investigated. Spray patterns are observed by shadow photography technique in order to determine the onset of self-pulsation. And self-pulsation boundary with Injection conditions and recess length is get. To measure the frequency of the spray oscillation. oscillation of the laser intensity which passes through spray is analyzed by Fast Fourier Transform. For acoustic tests, a PULSE System was used. Acoustic characteristics of a swirl coaxial injector are investigated according to the injection conditions. such as the pressure drop or the liquid and gas phase. and injector geometries. such as recess length and gap size between the inner and outer injector. Front the experimental results. the increase of recess length leads to the rapid increase of the sound pressure level. And as the pressure drop of the liquid phase increases. the frequency of the self?pulsation shifts to the higher frequency. The frequency of spray oscillations is the same as that of the acoustic fields by self-pulsation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.228-233
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• 2004

The spray and acoustic characteristics by the self-oscillation of a swirl coaxial injector were experimentally studied. The self-oscillation of a swirl coaxial injector is defined as pressure and flowrate oscillations by a time-delayed feedback between liquid and gas phase and has strong influences on atomization and mixing processes. Hence the occurrence and effect of the self-oscillation are measured using shadow photography technique, acoustic test and PDPA. The occurrence of self-oscillation largely depends on the injection conditions, such as pressure drop of liquid phase and relative momentum ratio. From the experimental results, self-oscillation occurs when the momentum of gas phase is enough large and the smaller the pressure drop of liquid phase is, the better self-oscillation occurs at the same momentum ratio. The self-oscillation is also affected by injector geometries, increasing the recess length results in the expansion of self-oscillation region and the increase of sound pressure level. The self-oscillation of a swirl coaxial injector accompanies a high intensity scream and this scream may provide harmful disturbances to combustion processes. Self-oscillation leads to strong changes in the drop size distribution and smoothly varies the slope of radial SMD distribution.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.5
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• pp.212-221
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• 2010

The bubbles could be created from multiple source in the surface of ocean. The bubbles which are created like this affect to the intensity and the sound speed of acoustic wave which are used from the ocean. From the research, it observed Reverberation from the sea surface, using Vbeam transmission and reception equipment that was a cross-shaped Array, from 2008 July 2nd to July 3rd at 4Km from the East Sea Mookho port. It is difficult to analyze data because the received signal has ambient noise and occurrence ISI(Inter Symbol Interference) for multipath. This paper remove that ambient noise and ISI using the directions of arrival beamforming and the filter and sum beamforming. After beamforming, a following DFE(Decision Feedback Equalizer) removes the remaining multipath components. Experimental results show that the proposed technique reduce the errors caused by ISI.