• The Journal of the Acoustical Society of Korea
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• v.28 no.5
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• pp.424-431
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• 2009

This study investigates the difference of sound velocity (compressional wave velocity) between gas hydrate-bearing sediments and nongas hydrate-bearing sediments in the Ulleung Basin, East Sea. We use a dataset measured from one site in the central part of the Ulleung Basin. Sound velocity for gas hydrate-bearing sediment shows the range from 1600 m/s to 2200 m/s. However, the value for nongas hydrate-bearing sediment is mostly around 1500 m/s, being less than 1400 m/s below 140 m subbottom depth. This trend is probably due to the presence of free gas below BSR (Bottom Simulating Reflector). Gas hydrate-bearing sediments show high value (maximum 150 Ohm-m) of resistivity. The physical properties between gas hydrate-bearing sediment and nongas hydrate-bearing sediment are characterized by the different patterns due to the presence of gas hydrate in comparison with those of marine unconsolidated sediments. Therefore, in order to investigate acoustic and physical properties for gas hydrate-bearing sediments, the study for the occurrence type and the amount of gas hydrates should be conducted simultaneously.

• The Journal of the Acoustical Society of Korea
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• v.28 no.6
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• pp.542-547
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• 2009

In this in vivo study, correlations of lumbar and femoral bone mineral densities (BMDs) with calcaneal speed of sound (SOS) were investigated in 36 osteoporotic women. Areal BMDs of the L2-L4 lumbar spine and the right femoral neck were measured by using dual energy X-ray absorptiometry (DEXA). SOS of the right calcaneus was measured by using ultrasound bone densitometry. Pearson's correlation coefficient (r) and level of significance (p) were used to evaluate the correlations between measurements. Lumbar BMD was highly correlated with femoral BMD (r=0.81). Lumbar and femoral BMDs exhibited similar comparable negative correlations with age (r=-0.52 and r=-0.55). A moderate negative correlation was found between calcaneal SOS and age (r=-0.45). Calcaneal SOS was significantly correlated with lumbar and femoral BMDs, with a higher correlation with femoral BMD rather than with lumbar BMD (r=0.54 and r=0.62). However, calcaneal SOS may not be an optimum index for the estimation of BMD of the most important fracture sites, such as the lumbar and the femur, because it showed lower correlations with lumbar and femoral BMDs compared to that with calcaneal BMD. Therefore, the development of a quantitative ultrasound technology for the direct measurement of acoustic properties at the lumbar and the femur is required to estimate BMD of these sites more accurately.

• The Journal of the Acoustical Society of Korea
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• v.28 no.8
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• pp.781-789
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• 2009

The absorption coefficients of the materials used in a 1:50 scale model multipurpose hall were measured based on ISO 354 and related laws. The shape and materials for the scale model were evaluated based on reflective surfaces, variable acoustic elements and sound-absorbing quality (125Hz-1kHz average) of seats. The measured average absorption coefficients of audience seats, audience and orchestra were 0.64, 0.74 and 0,45, respectively, which were simulated with the combination of wood, absorption materials and foam board. Various mounting methods for absorption curtain and banner were considered according to the installation methods. The average absorption coefficient was measured as 0.42, 0.47 and 0.45 in the conditions of Type A mounting, E mounting with 0.9 m backing air cavity, and Type G mounting which is suspended at the ceiling, respectively. It was confirmed that the absorption coefficient was increased at low frequency by backing air gap. The finishing material of stage house was an absorption material covered with thin fabric, which aimed average absorption coefficient of 0.68 by using fiber glass board. Each part of the real materials was compared with those of 1:50 scale model and it was found that the absorption characteristics of both cases were similar.

• Advances in nano research
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• v.16 no.6
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• pp.565-577
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• 2024

Vibration investigation of fluid-filled functionally graded cylindrical shells with ring supports is studied here. Shell motion equations are framed first order shell theory due to Sander. These equations are partial differential equations which are usually solved by approximate technique. Robust and efficient techniques are favored to get precise results. Employment of the Rayleigh-Ritz procedure gives birth to the shell frequency equation. Use of acoustic wave equation is done to incorporate the sound pressure produced in a fluid. Hankel's functions of second kind designate the fluid influence. Mathematically the integral form of the Langrange energy functional is converted into a set of three partial differential equations. A cylindrical shell is immersed in a fluid which is a non-viscous one. These shells are stiffened by rings in the tangential direction. For isotropic materials, the physical properties are same everywhere where the laminated and functionally graded materials, they vary from point to point. Here the shell material has been taken as functionally graded material. After these, ring supports are located at various positions along the axial direction round the shell circumferential direction. The influence of the ring supports is investigated at various positions. Effect of ring supports with empty and fluid-filled shell is presented using the Rayleigh - Ritz method with simply supported condition. The frequency behavior is investigated with empty and fluid-filled cylindrical shell with ring supports versus circumferential wave number and axial wave number. Also the variations have been plotted against the locations of ring supports for length-to-radius and height-to-radius ratio. Moreover, frequency pattern is found for the various position of ring supports for empty and fluid-filled cylindrical shell. The frequency first increases and gain maximum value in the midway of the shell length and then lowers down. It is found that due to inducting the fluid term frequency result down than that of empty cylinder. It is also exhibited that the effect of frequencies is investigated by varying the surfaces with stainless steel and nickel as a constituent material. To generate the fundamental natural frequencies and for better accuracy and effectiveness, the computer software MATLAB is used.

• The Journal of the Acoustical Society of Korea
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• v.43 no.2
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• pp.214-224
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• 2024

Sonobuoys are disposable devices that utilize sound waves for information gathering, detecting engine noises, and capturing various acoustic characteristics. They play a crucial role in accurately detecting underwater targets, making them effective detection systems in anti-submarine warfare. Existing sonobuoy deployment methods in multistatic systems often rely on fixed patterns or heuristic-based rules, lacking efficiency in terms of the number of sonobuoys deployed and operational time due to the unpredictable mobility of the underwater targets. Thus, this paper proposes an optimal sonobuoy placement strategy for Unmanned Aerial Vehicles (UAVs) to overcome the limitations of conventional sonobuoy deployment methods. The proposed approach utilizes reinforcement learning in a simulation-based experimental environment that considers the movements of the underwater targets. The Unity ML-Agents framework is employed, and the Proximal Policy Optimization (PPO) algorithm is utilized for UAV learning in a virtual operational environment with real-time interactions. The reward function is designed to consider the number of sonobuoys deployed and the cost associated with sound sources and receivers, enabling effective learning. The proposed reinforcement learning-based deployment strategy compared to the conventional sonobuoy deployment methods in the same experimental environment demonstrates superior performance in terms of detection success rate, deployed sonobuoy count, and operational time.

• The Journal of the Acoustical Society of Korea
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• v.43 no.2
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• pp.243-252
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• 2024

Among the Foley sound generation models that have recently begun to be studied, a sound generation technique using the Vector Quantized-Variational AutoEncoder (VQ-VAE) structure and generation model such as Pixelsnail are one of the important research subjects. On the other hand, in the field of deep learning-based acoustic signal compression, residual vector quantization technology is reported to be more suitable than the conventional VQ-VAE structure. Therefore, in this paper, we aim to study whether residual vector quantization technology can be effectively applied to the Foley sound generation. In order to tackle the problem, this paper applies the residual vector quantization technique to the conventional VQ-VAE-based Foley sound generation model, and in particular, derives a model that is compatible with the existing models such as Pixelsnail and does not increase computational resource consumption. In order to evaluate the model, an experiment was conducted using DCASE2023 Task7 data. The results show that the proposed model enhances about 0.3 of the Fréchet audio distance. Unfortunately, the performance enhancement was limited, which is believed to be due to the decrease in the resolution of time-frequency domains in order to do not increase consumption of the computational resources.

• Phonetics and Speech Sciences
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• v.16 no.1
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• pp.33-40
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• 2024

This study investigated acoustic features in spectral moment analysis, comparing accurate articulations with distortions of alveolar fricatives such as dentalization, palatalization, and lateralization. A retrospective analysis was conducted on speech samples from 61 children (mean age: 5.6±1.5 years, 19 females, 42 males) using the Assessment of Phonology & Articulation for Children (APAC) and Urimal-test of Articulation and Phonology I (U-TAP I). Spectral moment analysis was applied to 169 speech samples. The results revealed that the center of gravity of accurate articulations was higher than that of palatalization, while palatalization was lower than dentalization. The variance of dentalization was higher than that of both accurate articulations and palatalization. The skewness of dentalization was higher than that of accurate articulations, and the skewness of palatalization was higher than that of accurate articulations. The kurtosis of palatalization was higher than that of both accurate articulations and dentalization. No significant differences were observed for the position of fricatives (initial, medial) and tense type (plain, tense) across all variables of spectral moment analysis for each distortion type. This study confirmed distinct patterns in center of gravity, variance, skewness, and kurtosis depending on the type of alveolar fricative distortion. The objective values provided in this study will serve as foundational data for diagnosing alveolar fricative distortions in children with speech sound disorders.

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.60-71
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• 2024

The present study aims to investigate the level difference of floor impact noises of composite floor structure using EVA resilient materials. In order to this, four different types of resilient materials were designed combining PET, PP sheet and EVA mount including Flat type, Deck type, Cavity type and Mount type. Totally 9 different samples were made for acoustic measurements which were carried out twice with bang-machine and impact ball as the heavy-weight floor impact noise sources. All the floor impact noise measurements were undertaken at the authentication institution. As a result, concerning Flat and Cavity types, it was found that 2 dB ~ 5 dB of heavy-weight floor impact noise was reduced supplementally when PET was added, while floor impact noise larger than 50 dB was acquired when single resilient material was used. Especially, most high performance was obtained for Mount type with 1st grade of light-weight floor impact noise and 2nd grade of heavy-weight floor impact noise. This is because of material property with low dense PET sound absorption materials which fill all around EVA mounts. Also, it was considered that this results are due to the sound impact absorption by the both EVA mounts and the air cavity between EVA mount and PP sheet. Also, it was found that at least 36 EVA mounts per 1m2 area of resilient panel make more noise reduction of heavy-weight floor impact noises.

• Journal of Music and Human Behavior
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• v.21 no.2
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• pp.107-134
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• 2024

This study aims to classify the semantic words commonly used to evaluate sound quality and to analyze their differences in reflecting the level of musical stimuli. Participants were thirty-one music majors in their 20s and 30s, with an average of 9.4 years of professional training. Each participant listened to nine pieces of music with variations in texture and instrument type and evaluated them using 18 pairs of semantic words describing sound quality. A factor analysis was conducted to group words influenced by the same latent factor, and a multivariate ANOVA determined the differences in ratings based on texture and instrument type. Radar charts were also drawn based on the identified sets of semantic words. The results showed that four factors were identified, and the word pairs 'soft-hard,' 'dull-sharp,' 'muddy-clean' and 'low-high' showed significant differences based on the level of musical stimuli. The radar charts effectively distinguished the sound quality evaluations for each music. These results indicate that developing Korean semantic words for sound quality evaluation requires a structure different from the previous categories used in Western countries and that linguistic and cultural factors are crucial. This study will provide foundational data for developing a verbal sound quality evaluation framework suited to the Korean context, while reflecting acoustic attributes in music listening.

• Journal of Korea Water Resources Association
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• v.48 no.7
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• pp.553-566
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• 2015

Acoustic Doppler Current Profilers(ADCPs) have capability to concurrently capitalize three-dimensional velocity vector and bathymetry with highly efficient and rapid manner, and thereby enabling ADCPs to document the hydrodynamic and morphologic data in very high spatial and temporal resolution better than other contemporary instruments. However, ADCPs are also limited in terms of the inevitable unmeasured regions near bottom, surface, and edges of a given cross-section. The velocity in those unmeasured regions are usually extrapolated or assumed for calculating flow discharge, which definitely affects the accuracy in the discharge assessment. This study aimed at scrutinizing a conventional extrapolation method(i.e., the 1/6 power law) for estimating the unmeasured regions to figure out the accuracy in ADCP discharge measurements. For the comparative analysis, we collected spatially dense velocity data using ADV as well as stationary ADCP in a real-scale straight river channel, and applied the 1/6 power law for testing its applicability in conjunction with the logarithmic law which is another representative velocity law. As results, the logarithmic law fitted better with actual velocity measurement than the 1/6 power law. In particular, the 1/6 power law showed a tendency to underestimate the velocity in the near surface region and overestimate in the near bottom region. This finding indicated that the 1/6 power law could be unsatisfactory to follow actual flow regime, thus that resulted discharge estimates in both unmeasured top and bottom region can give rise to discharge bias. Therefore, the logarithmic law should be considered as an alternative especially for the stationary ADCP discharge measurement. In addition, it was found that ADCP should be operated in at least more than 0.6 m of water depth in the left and right edges for better estimate edge discharges. In the future, similar comparative analysis might be required for the moving boat ADCP discharge measurement method, which has been more widely used in the field.