• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.43 no.5
• /
• pp.551-556
• /
• 2010

The large jellyfish Nemopilema nomurai causes serious damage to fisheries, particularly around the seas of Korea and Japan. Decreasing this damage requires knowledge of the distribution and abundance of jellyfish. Acoustic technology using quantitative echosounders is one method of studying the distribution and abundance of jellyfish. Such methods are commonly used worldwide because they have the advantage of providing substantial information about all water layers in a wide area in a short time. However, in order to conduct an acoustic survey, the acoustic characteristics of the target organism must be known. These can be altered by a number of factors, including pulsation, swimming angle, frequency and size. Accordingly, this study determined the variation in target strength according to pulsation of N. nomurai. Data were analyzed for two jellyfish with bell diameters in air of (a) was 32.0 and (b) 25.0 cm. The pulsation cycle of jellyfish (a) was 1.5~2.0 sec and the target strength (TS) cycle was 1.0~2.5 sec, while jellyfish (b) had a pulsation cycle of 1.0~1.5 sec and TS cycle of 1.0~3.0 sec. The variation width of the TS with the change in pulsation was 7.8 dB (-72.4~-64.6 dB) for jellyfish (a) and 10.3 dB (-71.6~-61.3 dB) for jellyfish (b). The variation in bell diameter was about 0.28 and 0.35, respectively. These results confirmed that the variation in bell diameter caused by pulsation is closely related to the variation in TS.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.5 no.2
• /
• pp.125-132
• /
• 2010

The authors have investigated the acoustic field analysis using the Constrained Interpolation Profile(CIP) Method recently proposed by Yabe. This study has examined the calculation accuracy of the three-dimensional(3-D) acoustic field analysis using the type C CIP method. In this paper we show phase error of type C CIP method and the dependence on the wave-propagation direction in the type C CIP acoustic field analysis, and then demonstrate that it gives less-diffusive results than conventional analysis. Moreover, in comparison between type C-1 CIP, type C-2 CIP, type M CIP and FDTD, reports the memory requirements and calculation time of each method.

• The Journal of the Acoustical Society of Korea
• /
• v.36 no.3
• /
• pp.179-185
• /
• 2017

The problem that occurred in the design/fabrication/testing of the wideband transmitting power amplifier for an embedded active SONAR (Sound Navigation and Ranging) system operating underwater was analyzed and the solution of the problem was proposed in this paper. Wideband acoustic SONAR systems had been developed in order to improve the underwater detection performance. The underwater acoustic transmission system had been also developed to achieve the wideband SONAR system. In this paper, the wideband acoustic transmission signal was generated using a 2 Level sawtooth type Class D PWM (Pulse Width Modulation) which was not complicated to implement. When the sonar signals having two or more frequencies were simultaneously generated, parasitic frequencies were added to the original signals by integer multiples of the frequency difference of the original signal. To cope with this problem, we proposed a way to remove the parasitic frequency from the source signal through modeling and simulation of the implemented power amplifier and PWM control hardware using MATLAB and Simulink.

• Journal of the Korean Solar Energy Society
• /
• v.31 no.6
• /
• pp.1-7
• /
• 2011

Sound waves and acoustic energy generated by two identical TA (ThermoAcoustic) lasers were analyzed and studied. One end of the ceramic stack was heated by a thin NiCr wire wound around that end. The other end of the stack was cooled by natural convection of atmospheric air. The wavelength of the sound waves generated by a single TA laser was four times the tube length and the amplitude of the waves increased with the heating rate. SPL (SoundPressure Level) meters and microphones were employed to measure and study the sound waves at different distances from the glass tube opening and at the focusing point of the TA laser pair for different laser position arrangements. The sound waves of the two TA lasers at the focusing point were found to be almost 180 degrees out of phase when the openings of the two lasers were very close to each other and the angle between the laser axes was small. When the two TA lasers were placed far apart, the sound wave amplitudes and the phase difference between the two laser outputs varied periodically with time. The frequencies of the sound waves changed when the openings of the two TA lasers were in close vicinity and the angle between the laser axes exceeded a certain value. In this case, the glass tube opening was no longer a pressure anti-node and the wavelength of the fundamental mode was not equal to four times the tube length.

• Phonetics and Speech Sciences
• /
• v.2 no.4
• /
• pp.185-192
• /
• 2010

The acoustic vowel space has been used as an acoustic parameter in dysarthric speech. The aim of this work was to examine mathematical formulae for acoustic vowel space and to apply these to Korean speakers with idiopathic Parkinson's disease(IPD). Five acoustic parameters were chosen from earlier works and one new parameter was proposed, the pentagonal vowel space. The six parameters included triangular vowel space (3 area), irregular quadrilateral vowel space (4 area), irregular pentagonal vowel space (5 area), vowel articulatory index (VAI), formant centralization ratio (FCR) and F2i/F1u ratio (F2 ratio). An experimental group of 32 IPD patients(male:female=16:16) and a control group of twenty healthy people (male:female=8:12) participated in the study and repeated vowels (/a-i-u-e-o/) three times. A correlation analysis was performed among the six parameters, 2-way ANOVA was done with gender and groups as independent factors, and an independent sample t-test was conducted between the male and the female group as post hoc comparison. All parameters were highly correlated with each other and only the FCR showed a high negative correlation with the others. The results of ANOVA showed a significant difference in F2 ratio, 3 area, 4 area and 5 area between gender and in 4 area and 5 area between groups. For the male members of the two groups, significant statistical differences were found in all parameters whereas no such differences were found for the female members. These findings indicated that the vowel space of the female group was wider than the vowel space of the male group. These differences may have been caused by gender-specific speech styles rather than by patho-physiological mechanisms. We also claim that the pentagonal vowel space is better than the other vowel spaces at representing the disordered speech in natural speech situations.

• Journal of The Korean Astronomical Society
• /
• v.24 no.2
• /
• pp.129-149
• /
• 1991

An attempt has been made to examine the characteristics of acoustic and MHD waves generated in stellar convection zones($4000\;K\;{\leq}\;T_{eff}\;{\leq}\;7000\;K$, $3\;{\leq}\;\log\;g\;{\leq}\;4.5$). With the use of wave generation theories formulated for acoustic waves by Stein (1967), for MHD body waves by Musielak and Rosner (1987, 1988) and for MHD tube waves by Musielak et al.(l989a, 1989b), the energy fluxes are calculated and their dependence on effective temperature, surface gravity and megnetic field strength are analyzed by optimization techniques. In computing magneto-convection models, the effect of magnetic fields on the efficiency of convection has been taking into account by extrapolating it from Yun's sunspot models(1968; 1970). Our study shows that acoustic wave fluxes are dominant in F and G stars, while the MHD waves dominant in K and M stars, and that the MHD wave fluxes vary as $T_{eff}^4{\sim}T_{eff}^7$ in contrast to the acoustic fluxes, as $T_{eff}^{10}$. The gravity dependence, on the other hand, is found to be relatively weak; the acoustic wave fluxes ${\varpropto}\;g^{-0.5}$, the longitudinal tube wave fluxes ${\varpropto}\;g^{0.3}$ and the transverse tube wave fluxes ${\varpropto}\;g^{0.3}$. In the case of the MHD body waves their gravity dependence is found to be nearly negligible. Finally we assesed the computed energy fluxes by comparing them with the observed fluxes $F_{ob}$ of CIV(${\lambda}1549$) lines and soft X-rays for selected main sequence stars. When we scaled the corrected wave fluxes down to $F_{ob}$, it is found that these slopes are almost in line with each other.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.11 no.3
• /
• pp.35-42
• /
• 2007

Acoustic damping induced by gap width between baffled injectors is investigated numerically, which are installed to suppress pressure oscillations in a model rocket combustor. The previous work reported that the baffled injectors show larger acoustic damping with the gap width between injectors. It is simulated numerically and its mechanism is examined. Damping factors are calculated as a function of gap width and it is found that the optimum gap is 0.1 mm or so. For understanding of the improved damping induced by the gap, dissipation rate of turbulent kinetic energy and vorticity are calculated as a function of the gap. Both parameters have their maximum values at the specific gap and especially, the dissipation rate has the same profile as that of damping factor. It verifies that the improved damping made by the gap is attributed to the increased acoustic-energy dissipation.

• Journal of Practical Engineering Education
• /
• v.10 no.1
• /
• pp.41-47
• /
• 2018

Underwater acoustic sensors are mounted on unmanned underwater vehicles(UUV) and detect and process the underwater information. These underwater acoustic sensor designs are very important subject for understanding and applying engineering. Therefore, in this paper, it was designed and fabricated the acoustic sensors step by step, evaluated their performance, and then studied the suitability of such a series of design procedures and steps to apply them to the integrated design learning. The results of the questionnaire survey showed that the steps and methods of the proposed sensor design are suitable for the contents of the integrated design project, and they are easy to acquire the technology and are very interesting design topics. It is anticipated that when the design project is applied to the integrated design in the future, high educational achievement will be achieved.

• Journal of the Korean Society of Physical Medicine
• /
• v.16 no.4
• /
• pp.13-21
• /
• 2021

PURPOSE: This study examined the effects of action observational training with acoustic stimulation (AOTA) on the balance and gait ability in stroke patients. METHODS: Forty-five chronic stroke patients were divided into three groups. The AOTA group (n = 15) received training via a video that showed a normal gait with the sound of footsteps. The action observation training (AOT) group (n = 15) received AOT without acoustic stimulation. The control group (n = 15) received physical training. Each intervention was applied once per day, three times per week for six weeks. The participants in the AOTA and AOT groups had five minutes of AOT. The participants in the all group had 20 minutes of physical training. All participants were measured using the Berg Balance Scale, the Timed Up and Go Test, the Functional Reaching Test, 10 Meter Walk Test, six Minute Walk Test, and Dynamic Gait Index. The collected data were analyzed using SPSS version 20.0 for Windows. The between- and within-group comparisons were analyzed using the one-way analysis of variance (ANOVA) test and a paired t-test, respectively. For all statistical analyses, the significance level was set to .05. RESULTS: The one-way ANOVA test identified significant differences among the measurement results of the three groups (p < .05). Post hoc analyses indicated the AOTA group to undergo more significant balance and gait changes than the control group (p < .05). CONCLUSION: The gait and balance abilities could be improved effectively for patients with stroke when action observation training and acoustic stimulation were applied simultaneously.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.54 no.6
• /
• pp.1023-1029
• /
• 2021

The Japanese common squid Todarodes pacificus is one of the fish species within the total allowable catch (TAC) system which requires further investigation. In this study, the acoustic survey method was used to analyze the distribution of the Japanese common squid Todarodes pacificus across all the seas of South Korea. The sea area within Korea was investigated using the research vessels 20, 21, and 22 of the National Institute of Fisheries Science. The acoustic surveys were carried out from July to September 2019 and February to May 2020. The acoustic systems used in the survey had frequencies of 38 kHz and 120 kHz (EK60, EK80, Simrad, Norway) of the split-beam scientific echosounder. The results showed that, in spring, 277 m²/nmi² was the highest in the east sea area, and the same in the summer season 880 m²/nmi² was the highest in the east sea area. In autumn, the highest nautical area scattering coefficient (NASC) value was observed in the coastal portion of the south sea, and in winter, the NASC values were generally low in all the sea area.