• The Journal of the Acoustical Society of Korea
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• 제43권4호
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• pp.466-475
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• 2024

Matched-Field Processing (MFP) is a model-based approach that requires accurate knowledge of the ocean environment and array geometry (e.g., array tilt) to localize underwater acoustic sources. Consequently, it is inherently sensitive to model mismatches. In contrast, the waveguide invariant-based approach (also known as array invariant) offers a simple and robust means for source-range estimation in shallow waters. This approach solely exploits the beam angles and travel times of multiple arrivals separated in the beam-time domain, requiring no modeling of the acoustic fields, unlike MFP. This paper extends the waveguide invariant-based approach to shallow water environments featuring a shallow pit, where the waveguide invariant is not defined due to the complex bathymetry. An in-depth performance analysis is conducted using experimental data and numerical simulations.

• Phonetics and Speech Sciences
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• 제8권1호
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• pp.37-44
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• 2016

The goal of the current study is to investigate how the sound change is reflected in production or in perception, and what the effect of lexical frequency is on the loss of sound contrasts. Specifically, the current study examined whether the vowel length contrasts are retained in Korean speakers' productions, and whether Korean listeners can distinguish vowel length minimal pairs in their perception. Two production experiments and two perception experiments investigated this. For production tests, twelve Korean native speakers in their 20s and 40s completed a read-aloud task as well as a map-task. The results showed that, regardless of their age group, all Korean speakers produced vowel length contrasts with a small but significant differences in the read-aloud test. Interestingly, the difference between long and short vowels has disappeared in the map task, indicating that the speech mode affects producing vowel length contrasts. For perception tests, thirty-three Korean listeners completed a discrimination and a forced-choice identification test. The results showed that Korean listeners still have a perceptual sensitivity to distinguish lexical meaning of the vowel length minimal pair. We also found that the identification accuracy was affected by the word frequency, showing a higher identification accuracy in high- and mid- frequency words than low frequency words. Taken together, the current study demonstrated that the speech mode (read-aloud vs. spontaneous) affects the production of the sound undergoing a language change; and word frequency affects the sound change in speech perception.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제18권7호
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• pp.269-274
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• 2017

This study aimed to investigate the acoustic differences that occur in diverse sections of sustained vowel phonation, which is often used in an objective speech analysis of voice disorder patients. The subjects included 17 voice disorder patients (vocal nodules) and 12 normal individuals without any voice disorder. The participants' sustained vowel phonation of /a/ was divided into onset, middle, and offset, and the jitter, shimmer, and NHR in each section were analyzed using the MDVP(Multi-Dimensional Voice Program). The Friedman test and post hoc analysis were used. In the vocal nodules group, the jitter, shimmer and NHR were significantly higher in the off section of sustained vowel phonation than in the middle section, and there were no significant differences between the beginning and middle sections. In contrast, in the group of normal individuals, there were no significant differences between any of the sections. The values of the acoustic parameters according to the section of analysis in the sustained vowel phonation are different and the vocal in the end section is significantly more unstable than that in the middle section. The results of this study will be useful for selecting the sections to be analyzed in sustained vowel phonation and interpreting the results of the analysis.

• Clinical and Experimental Reproductive Medicine
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• 제25권2호
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• pp.153-160
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• 1998

The objective of this retrospective study was to evaluate whether the transvaginal ultrasonographic analysis of endometrial pattern and thickness could predict the stage of menstrual cycle. Endometrial pattern and thickness were observed in those patients receiving infertility work up from April, 1994 to July, 1998 at Seoul National University Hospital. The study group was 185 patients with normal regular menstrual cycles. Among them, 44 patients received endometrial biopsy, and the date of endometrium was compared with the observed endometrial pattern and thickness. The observed endometrial pattern was presence or absence of central cavity echogenicity, triple line sign, endometrial hypoechogenicity, ring sign, endometrial hyperechogenicity and posterior acoustic sonic enhancement. The results were as follows; Central cavity echogenicity was seen throughout menstrual cycle. Triple line sign was observed in 81.1% of patients during early secretory phase. However, in mid to late secretory phase, triple line sign was appeared in only 6.8%. The percentage of positive endometrial hypoechogenicity was highest in early secretory phase. In contrast to hypoechogenicity, positive endometrial hyperechogenicty was highest in mid to late secretory phase. Ring sign was observed in 73.5% of the patients during early secretory phase with peak incidence. Posterior acoustic enhancement was seen in 72.7% of the patients during late secretory phase. The sensitivity and specificity of being a secretory phase if the patients showed hyperechogenic endometrium, were 84.2%, 83.3% respectively. The sensitivity and specificity of being a secretory phase if the patients showed posterior acoustic enhancement were 93.8%, 58.3% respectively. Endometrial thickness was not correlated with endometrial dating. In conclusion, transvaginal ultrasonographical delineation of the endometrial pattern might be useful tool in predicting endometrial status during normal menstrual cycle. But, endometrial thickness could not predict the endometrial dating.

• Phonetics and Speech Sciences
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• 제13권2호
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• pp.91-101
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• 2021

The purpose of this study was to investigate laryngeal characteristics in children with autism spectrum disorders (ASD). A total of 50 children participated, including eight children aged 2 to 4 years old diagnosed with ASD and 42 normal controls at the same age. All children recorded X-ray images of the midsagittal plane of the cervical spine and larynx, and compared the laryngeal positions of ASD and control. In addition, samples of children with vowel prolongation were collected and analyzed for acoustic parameters. X-rays showed that the height of the hyoid bone in the normal group was the lowest at 3 years of age, and ascended at 4 years of age. Nevertheless, the distance from the external acoustic meatus to the hyoid bone was longest at age 4. 4-year-olds with explosive language development showed laryngeal height elevation and anteriorization. In contrast, the hyoid height of the ASD group of all ages was lower than that of the control group, and there was no difference in the hyoid position between the ages. As a result of acoustic evaluation, PFR, vFo, and vAm were significantly higher ASD than control. Low laryngeal height of ASD children may be associated with delayed language development. PFR, vFo, and vAm seem to be voice markers showing the difference between normal and ASD children.

• Proceedings of the KIEE Conference
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• 대한전기학회 2004년도 하계학술대회 논문집 C
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• pp.1594-1596
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• 2004

Film bulk acoustic resonator (FBAR) devices which adopt a membrane-type configuration are fabricated by a novel process. In contrast to the conventional FBAR structure, the newly fabricated resonator doesn't employ any supporting layer below or above it, so that the properties of piezoelectric layer are not influenced by the bottom electrode material. FBAR devices with Mo/AlN/Metal configuration are also fabricated. The frequency response characteristics ($S_{11}$) of the devices fabricated using the proposed process are compared with those of the conventional devices. The return losses are also estimated, in terms of the kind and thickness of bottom electrode materials.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1014-1017
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• 2007

Sound focusing technologies has been studied for various purposes from early 1990s. As a result, these technologies make us possible to apply in many uses. For example, we can treat tumors using focused ultrasonic waves without surgical knife and communicate in the ocean using time reversal array. Also applications for personal audio system become issues. Recently, as technologies are developing, in some applications, needs for regional focusing become increasing because previously suggested focusing methods, such as phase conjugation, time reversal and inverse filtering, were all about a point focusing. Therefore, studies on regional focusing method are essentially needed. Regional focusing method was firstly mentioned by Choi and Kim in 2002: acoustic contrast control. However, in regional focusing, physical interpretations between control variables and results are still not easy because of its complexity. In this regard, we tried to understand the relations between control variables and results in wavenumber domain and suggested a solution method for regional focusing: wavenumber spectrum matching. We also showed how to make spatially focused sound shape using the suggested method from the simplest case: line focusing.

• Speech Sciences
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• 제15권3호
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• pp.145-156
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• 2008

The goal of this study was to investigate acoustic and physiologic characteristics of two phonation types of 'Khoomei' which is a traditional singing style of people who live around the Altai mountains or Mongolia region. It can be produced two pitches simultaneously - high melody pitch can be perceived along with a low drone pitch. Sygyt and kargyraa styles are the most popular and identifiable styles and they can be recognized as the different sounds depending on the method of voice production. Two trained Mongolians participated and have used at least 5 - 6 years. The characteristics of this voice production were measured by using flexible fiberscope, Stroboscopy, Lx Speech studio, Spead, and Doctor Speech. In Sygyt style, very high vocal fold closure (71.50%) with both true and false vocal folds contact and strong breathing support was observed. They also showed that tongue height and harmonics were increased (around 10dB) with resonance cavity movement. In contrast, it was found that Kargyraa sound had very low pitch with relaxed stomach, less laryngeal tension and lower vocal fold contact (69.50%) than hard Sygyt style sound without raising the tongue during phonation. 'Khoomei' phonation can be made by strong contact of both true and false vocal folds and by increasing the harmonics as well.

• Phonetics and Speech Sciences
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• 제5권4호
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• pp.137-143
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• 2013

Recent investigation of acoustic correlates of Korean stop manner contrasts has reported a diachronic transition in Korean stops: young Seoul speakers are relatively more dependent on the F0 characteristics of the stops than on the VOT characteristics in aspirated and lenis stop distinction. This finding has been examined against tonal dialects of Korean and the results suggested that the speakers of tonal dialects are not sharing the transition. These results also suggested that F0 function for segmental stop classification interferes with the function for lexical tone classification in their tonal speech. The current study investigated these findings in terms of perception. Perceptual behavior of Seoul and Busan speakers of Korean was examined in a comparative manner through the measurement of perceptual cue weight of F0 and VOT in particular. The results from regression and correlation analyses revealed that Busan speakers are closer to older Seoul speakers than to younger Seoul speakers in that the cue weight for VOT and F0 were comparable in the aspirated-lenis stop distinction. This result was in contrast to the perceptual behavior of younger Seoul speakers who showed clear dominance of F0 over VOT for the same distinction. These findings provided perceptual evidence of the dual function of F0 for segmental and lexical distinctions in tonal dialects of Korean.

• The Journal of Korean Physical Therapy
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• 제22권4호
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• pp.83-89
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• 2010

Purpose: The goal of this study was to investigate the feasibility for the early diagnosis of inflammatory arthritis by the reconstruction of three-dimensional photoacoustic imaging with a tissue phantom. Methods: Q-switched Nd:YAG laser (l = 532 nm) was applied to a tissue phantom to generate photoacoustic waves, and the acquired photoacoustic signals at different positions around the sample were used to recombine the distribution of the optical absorption and the images were subsequently generated through a reconstruction algorithm. Results: From the acquired photoacoustic signals, the surface andinner core of the phantom was clearly distinguished. Furthermore, the back-projection algorithm was able to reconstruct two-dimensional and three-dimensional photoacoustic images that contained the optical absorption property information of the tissue phantom. Conclusion: The results indicate that the photoacoustic imaging technique has many advantages such as high optical contrast and high acoustic resolution. The acquired images can be used for the early diagnosis of inflammatory arthritis by the structural information obtained from the region of interest.