• Phonetics and Speech Sciences
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• v.5 no.2
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• pp.25-31
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• 2013

This study examined cross-generational changes in the vowel system of Seoul Korean. Acoustic analyses of the vowel formants of /o/ and /u/, and their Euclidean distances in the vowel space were undertaken to explore an on-going merger of these two vowels as proposed in previous acoustic studies and a phonological analysis by Chae (1999). A robust cross-generational change of /o/ and /u/ was found, more evident for female speakers than for male speakers. For female speakers, with each successive generation, /o/ became increasingly approximated with /u/, regardless of the syllable positions that the target vowels were posited, whereas the cross-generational differences in the Euclidean distances were only shown in the second syllable position for the male speakers. These results demonstrate that 1) women are more advanced than men in the on-going approximation of /o/ and /u/; 2) the approximation of /o/ and /u/ is common in the non-initial position. Taken together, the merger of /o/ and /u/ appears to be in progress in Seoul Korean.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.11
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• pp.550-554
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• 1997

Acoustic or sound noise due to gradient pulsing has been one of the problems in MRI, both in patient scanning as well as in many areas of psychiatric and neuroscience research, such as unctional MRI (fMRI). Our recent observations in MRI or the visual and motor cortex show very different results with sound noise in comparison with the results obtained without sound noise. Although a number of ideas has been suggested in the literature about the possible elimination or reduction of sound noise, progress has been slow due to the basic role of gradient pulsing in MR imaging. Therefore, we report on some typical behavior of sound noise observed from MRI scanners and the analyses of their characteristics. Data are obtained both from a commercial MRI scanner (GE Signa 1.5-T EPI system).

• Phonetics and Speech Sciences
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• v.1 no.3
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• pp.133-144
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• 2009

Pharyngeal flap surgery changes the space and shape of the oral cavity and vocal tract, and these changing conditions bring resonance change. The purpose of this study was to determine the most reliable and valuable parameters for evaluating hypernasality to distinguish two patients before and after pharyngeal flap surgery. Each patient was asked to clearly speak the vowels /a/, /i/, /u/, /e/, /o/ for voice recording. There were nine parameters: Formant (F1, F2, F3), Bandwidth (BW1, BW2, BW3), LPC energy slope ($\Delta$ |A2-A1/F2-F1|), and Band Energy (0-500 Hz, 500-1000 Hz) by each vowel. From the results of discrimination analyses on acoustic parameters, the vowels /a/, /e/ appeared to be insignificant but vowels /i/, /u/, /o/ appeared to be efficient in the separation. A 95%, 100%, and 100% recognition score could be reached when vowels /i/, /u/, and /o/ were analyzed. The results showed that F2, BW3, and LPC slope are more important parameters than the others. Finally, there is a relation between perceptual evaluation score and LPC energy slope of acoustic parameters by least square slope.

• Journal of the Korean Society of Marine Environment & Safety
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• v.3 no.2
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• pp.23-31
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• 1997

The results of high speed photography, acoustic emission detection and plasma UV radiation intensity measurement during CO2 laser welding of stainless steel 304 are presented. Video images with high spatial and temporal resolution allowed to observe the melt dynamics and keyhole evolution. The existence of a high speed melt flow which originated from the part of weld pool and flowed along the sides wall of keyhole was confirmed by the slag motion on the weld pool. the characteristic frequencies of flow instability and keyhole fluctuations at different welding speed were measured and compared with the results of Fourier analyses of temporal acoustic emission (AE) and light emission (LE) spectra. The experimental results were compared with the newly developed numerical model of keyhole dynamics. (The model is based on the assumption that the propagation of front part of keyhole into material is due to the melt ejection driven by laser induced surface evaporation.) The calculations predict that a high speed melt flow is induced at the front part of keyhole when the sample travel speed exceeds several 10mm/s. The numerical analysis also shows the hump formation on the front keyhole wall surface. Experimentally observed melt behavior and transformation of the AE and LE spectra with variation of welding speed are qualitatively in good agreement with the model predictions.

• Nuclear Engineering and Technology
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• v.50 no.6
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• pp.890-898
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• 2018

Nondestructive inspection (NDI) is an integral part of structural integrity analyses of dry storage casks that house spent nuclear fuel. One significant concern for the structural integrity is stress corrosion cracking in the heat-affected zone of welds in the stainless steel canister that confines the spent fuel. In situ NDI methodology for detection of stress corrosion cracking is investigated, where the inspection uses a delivery robot because of the presence of the harsh environment and geometric constrains inside the cask protecting the canister. Shear horizontal (SH) guided waves that are sensitive to cracks oriented either perpendicular or parallel to the wave vector are used to locate welds and to detect cracks. SH waves are excited and received by electromagnetic acoustic transducers (EMATs) using noncontact ultrasonic transduction and pulse-echo mode. A laboratory-scale canister mock-up is fabricated and inspected using the proposed methodology to evaluate the ability of EMATs to excite and receive SH waves and to locate welds. The EMAT's capability to detect notches from various distances is evaluated on a plate containing 25%-through-thickness surface-breaking notches. Based on the results of the distances at which notch reflections are detectable, NDI coverage for spent nuclear fuel storage canisters is determined.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.2
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• pp.14-22
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• 2007

In this paper, the acoustic emission(AE) behaviors were investigated with single-and 2-spot resistance spot welded SPCC specimens. Test specimens were welded horizontally and/or vertically according to the rolling direction of base netal in 2-spot welding. In the case of 2-spot welding, when tensile-shear test has below amplitudes: crack initiation $50{\sim}60dB;$ tear fracture $40{\sim}50dB$. And when cross tensile test has below amplitudes: early stage $75{\sim}85dB;$ yielding point $65{\sim}75dB;$ post yielding $40{\sim}60dB;$ plug fracture $70{\sim}80dB\;or\;90{\sim}100dB$. Also, from the b-value that is slope of AE amplitude, we knew that there are lots of low amplitudes if b-value is big(i.e., tensile-shear $specimen{\rightarrow}tear$ fracture or shear fracture), and there are lots of high amplitudes if b-value is small(i.e.. cross tensile $specimen{\rightarrow}plug$ fracture). As the results of fiacture mechanism analyses through AE amplitude distributions, change of the b-value represented fracture patterns of materials. Correspondingly, low amplitude signals appeared in crack initiation, and high amplitude signals appeared in base metal fracture. We confirmed that these amplitude distributions represented the change or degradation of materials.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.331-337
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• 2009

Space launch vehicles require highly reliable, lightweight structures. It is thus important to monitor the structural health of these components with nondestructive inspections. In this paper, we studied an example of a nondestructive inspection that was partially applied to the manufacture and inspection of a launch vehicle. Ultrasonic tests, X-rays, tapping, and acoustic emissions comprised the inspection method. A payload fairing, high pressure tank, fastener part, and bonding part were used as hardware to be inspected. We proposed a quantitative standard for debonding inspection of the payload fairing and acoustic emission data for the proof test of the high pressure tank. We analyzed the fracture mode of the sandwich fastener part according to frequency changes. We also proposed a standard specimen for ultrasonic inspection of bonds of different materials. The present analyses and results provide data for evaluation of the launch operation sequence to ensure launch vehicles afford high reliability.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.285-290
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• 2006

To access the volume of sediments deposited after construction of the Soyang Dan and to understand their distribution in the Soyang lake, acoustic profiling using a 10-20 kHz system was conducted along profiles of 227 km length. Profile intervals are approximately 50 and 500 m for longitudinal and cross lines, respectively. The data were gain-controlled and then migrated using the f-k algorithm. After digitization of boundaries of the sediments, the acoustic interpretation was verified through correlating with 38 core samples. Thickness of the sediments averages 0.25 m and reaches to 8.25 m at maximum. Estimated total volume of the sediments based on anisotropic models in geostatistical methods is approximately $5.9{\times}10^6\;m^3$, which is more than twice greater than the earlier estimation based on an isotropic model.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.3 s.108
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• pp.291-297
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• 2006

The BVI(blade vortex interaction) noise Prediction has been one of the most challenging acoustic analyses in helicopter aeromechanical Phenomenon. It is well known high resolution airloads data with accurate tip vortex positions are necessary for the accurate prediction of this phenomenon. The truly unsteady time-marching free-wake method, which is able to capture the tip vortices instability in hover and axial flights, is expanded with the rotor flapping motion and trim routine to predict unsteady airloads in forward and descent flights. And Farassat formulation 1-A based on the FW-H equation is applied for the noise prediction considering the blade flapping motion. Main objective of this study is to validate the newly developed prediction code. To achieve the objective, the descent flight condition of AH-1 OLS(operational loads survey) configuration is analyzed using present code. The predicted sectional thrust distribution and sectional airloads time histories show the present scheme is able to capture well the unsteady airloads caused by a parallel BVI. Finally, the predicted noise data, observed in two different positions where are 3.44 times of rotor radius far from the hub center, are quite reasonable agreements with the experimental data compared to the other analysis results.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.8 no.2
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• pp.166-172
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• 1997

Background : For example, aerodynamic study, vibratory study, acoustic study, neuro-muscular test and psychoacoustic evaluation, a number of objective methods are now available for assessing pathologic voice change. They help to differentiate pathologic condition from normal condition and to monitor pathologic and aging change. These laboratory analyses are used commonly to monitor speech therapy and to follow a patient's recovery after surgery. Objectives : We investigated the values of jitter, shimmer and NNE of normal person and hoarseness patients in Korea. The values of Jitter and shimmer might be meaningful parameters distinguishing pathologic vibration from normal and recovery after surgery. Materials and Methods : Statistical significance between normal control and 48 subjects taken microlaryngeal surgery were compared with Dr. speech science program that is computerized system for acoustic analysis of voice production employed to determine vocal characteristics of pitch perturbation(jitter) and amplitude perturbation(shimmer). Results : The mean normal values of jitter and shimmer were 0.226${\pm}$0.110(%), 2.200${\pm}$0.421(%) in male and 0.164${\pm}$0.060(%), 2.063 ${\pm}$0.575(%) in female. In patients with vocal nodule, the preoperative and postoperative values of jitter and shimmer were valueless. In patients with vocal polyps, the preoperative and postoperative values of jitter and shimmer were valuable. Conclusion : Dr. speech science program was effective to monitor laryngeal disease and aging changes.