• 한국음향학회지
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• 제6권3호
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• pp.23-30
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• 1987

본 논문에서는 반사형 음향 현미경의 반사응답 특성인 V(z)현상을 고찰하고 이 현미경을 이용한 새로운 형태의 비파괴 검사 기술을 제시한다. 10원 주화, 알루미늄, 집적회로 소자, 그리고 kevlar-epoxy 등을 샘플로서 선택하고 중심주파수 3 MHz의 음향 현미경을 focused mode 및 defocused mode에서 동작시켜 실험하였다. 이 과정에서 음향 현미경의 분해능은 $500\mu m$로 나타났고 샘플의 표면 및 그 내부에 존재하는 결함은 검출되어 이를 영상화하였으며 샘플에 대한 영상의 콘트라스트 변화는 V(z)현상과 잘 일치함을 보였다.

• 말소리와 음성과학
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• 제2권3호
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• pp.65-73
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• 2010

No systematic study has examined the relationship between acoustic variability and /w/-deletion in Korean. Most previous studies on /w/-deletion have described /w/-variants in categorical terms, i.e., /w/-deletion or a full glide (Silva 1991; Kang 1997; Yun 2005). These studies are based either on impressionistic judgements without a systematic acoustic analysis or on an exclusive examination of internal acoustic variability of /w/ such as F2, without examining the availability of external acoustic cues such as voice onset time (VOT) of a consonant. However, given the important influence of the adjacent sounds for segmental realizations, it is necessary to examine possible acoustic variability in the differentiation of /w/-variants. The present study aims to address this issue by evaluating the acoustic properties of /CwV/, including VOT and formant transitions. In the analysis, 432 tokens in word-initial position (216 /CwV/ words and 216 /CV/ words) were examined. The results indicated that /w/ exhibits four different variants. Firstly, /w/ is realized as a full glide. Such a variant is characterized by a VOT difference and significant differences in F1 and F2 at voicing onset compared with /CwV/ and /CV/. Secondly, /w/ can be maintained but coarticulated with the following vowel. Such a variant is demonstrated by differences in VOT and F2. Thirdly, /w/ is categorically deleted, which is indicated by the absence of any differences in VOT, F1, and F2. Fourthly, /w/ overlaps a consonant. The F2 difference without VOT difference is manifested in the variant. In contrast to VOT, F1, and F2 differences, pitch plays little role in determining /w/-variants in Korean. These findings suggest that allophones can be produced along a gradient continuum of acoustic cues, exhibiting sounds intermediate between the full realization of a given category and its deletion. Furthermore, each variant can be cued by a set of internal and external acoustic cues.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1993년도 제18회 학술대회 초록집
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• pp.77-84
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• 1993

Systems with journal bearings generally operate in large scale and under severe loading conditions such as steam generator turbines and internal combustion engines, in contrast to the machineries using rolling element bearings. Failure of the bearings in these machineries can result in the system breakdown. To avoid the time consuming repair and considerable economic loss, the detection of incipient failure in journal bearings becomes very important. In this experimental approach, acoustic emission monitoring is employed to the detection of incipient failure caused by intervention of foreign particles most probable in the journal bearing systems. It has been known that the intervention of foreign materials, insufficient lubrication and misassembly etc. are principal factors to cause bearing failure and distress. The experiment was conducted under such designed conditions as inserting alumina particles to the lubrication layer in the simulated journal bearing system. The results showed that acoustic emission could be an effective tool to detect the incipient failure in journal bearings.

• 말소리와 음성과학
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• 제8권3호
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• pp.31-38
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• 2016

Speech inversion (acoustic-to-articulatory mapping) is not a trivial problem, despite the importance, due to the highly non-linear and non-unique nature. This study aimed to investigate the performance of Deep Neural Network (DNN) compared to that of traditional Artificial Neural Network (ANN) to address the problem. The Wisconsin X-ray Microbeam Database was employed and the acoustic signal and articulatory pellet information were the input and output in the models. Results showed that the performance of ANN deteriorated as the number of hidden layers increased. In contrast, DNN showed lower and more stable RMS even up to 10 deep hidden layers, suggesting that DNN is capable of learning acoustic-articulatory inversion mapping more efficiently than ANN.

• 말소리와 음성과학
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• 제4권1호
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• pp.67-74
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• 2012

The neutralization of /$s^h$/ and /$s^*$/ in Gyeongsang dialects is a culturally salient stereotype that has received relatively little attention in the phonetic literature. The current study is a more extensive acoustic comparison of the sibilant fricative productions of Seoul and Gyeongsang dialect speakers. The data presented here suggest that, at least for young Seoul and Daegu speakers, there are few inter-dialectal differences in sibilant fricative production. These conclusions are supported by the output of mixed effects logistic regression models that used aspiration duration, spectral mean of the frication noise, and H1-H2 of the following vowel to predict fricative type in each dialect. The clearest dialect difference was that Daegu speakers' /$s^h$/ and /$s^*$/ productions had overall shorter aspiration durations than those of Seoul speakers, suggesting the opposite of the traditional "/$s^*$/ produced as [$s^h$]" stereotype of Gyeongsang dialects. Further work is needed to investigate whether /$s^h/-/s^*$/ neutralization in Daegu is perceptual rather than acoustic in nature.

• The Journal of the Acoustical Society of Korea
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• 제24권1E호
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• pp.28-33
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• 2005

This study was designed to suggest an assessment tool for analyzing the characteristics of Korean phonetic contrast intelligibility among dysarthric individuals. The intelligibility deficit factors of phonetic contrast in Korean dysarthric patients were analyzed through stepwise regression analysis. The 19 acoustic-phonetic contrasts proposed by Kent et al. (1999) have been claimed to be useful for clinical assessment and research on dysarthria. However, the test cannot be directly applied to Korean patients due to linguistic differences between English and Korean. Thus, it is necessary to devise a Korean word intelligibility test that reflects the distinct characteristics of the Korean language. To identify the speech error characteristics of a Korean dysarthric group, a Korean word list was audio-recorded by 3 spastic, 4 flaccid, and 5 mixed type of dysarthric patients. The word list consisted of monosyllabic consonant-vowel-consonant (CVC) real word pairs. Stimulus words included 41 phonemic contrast pairs and six triplets. The results showed that the percentage of errors in final position contrast was higher than in any other position. Unlike the results of previous studies, the initial-position contrasts were crucial in predicting the overall intelligibility among Korean patients.

• Ocean and Polar Research
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• 제37권4호
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• pp.333-340
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• 2015

The contrast (fish body to medium ratio) of density and sound speed were measured to estimate acoustic scattering from small juvenile cod (Gadus macrocephalus) with the Kirchhoff-Ray Mode backscatter model. The density contrast was measured by the density-bottle method and the sound speed contrast was estimated by the time of flight method. The results revealed that the measured density contrasts of juvenile cod varied between 1.003 and 1.029 (mean = 1.014, S.D. = 0.01). On the other hand, sound speed contrasts varied between 1.039 and 1.041 (mean = 1.041, S.D. = 0.001). The relationship between averaged target strength (TS) and total length (TL) established by the model were <$TS_{38kHz}$> = 20log(TL) - 68.8 and <$TS_{38kHz}$> = 20log(TL) - 69.4, respectively.

• 말소리와 음성과학
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• 제10권2호
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• pp.15-24
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• 2018

Earlier studies reported that the /o/ and /u/ phonemes of Seoul Korean were currently merging in the F1/F2 space. However, studies on perception tests have shown that rates of correctness were high, even in cases where the two vowels overlapped. This study explores whether there is another acoustic parameter that differentiates /o/ from /u/, besides the F1/F2 contrast. Seventy-five native speakers of Seoul Korean, born between 1953 and 1999, participated in a production test. The data collected were analyzed in terms of F1 and F2, H1-H2, and F0. The result shows that the /o/ and /u/ of female speakers almost overlap in the F1/F2 space for all ages, while H1-H2 values are significantly different between the two vowels regardless of age. On the other hand, the /o/ and /u/ of male speakers are largely well separated in the F1/F2 space, while the H1-H2 values between the two vowels are very close at all ages. F0 effect is relatively small for both male and female speakers, even though there is a statistically significant difference. The result of this study provides evidence that female speakers use phonation differences to distinguish /o/ from /u/, and that the F1/F2 contrast has been replaced by H1-H2 values.

• 한국음향학회지
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• 제18권3호
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• pp.55-61
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• 1999

본 연구에서는 쿼드러춰 방식의 초음파현미경을 구성하고 미세한 높이변화를 갖는 표면결함에 대한 진폭영상과 위상영상을 복원하여 상대적인 영상 강도의 변화와 영상의 질을 비교 분석하였다. 본 실험에서는 중심주파수가 3㎒인 focused 변환기를 사용하여 초음파현미경을 구성하고 알루미늄 재료를 선택하여 하나는 직경이 2㎜이고 깊이가 100㎛인 원형결함을 갖도록 하였고 다른 하나는 직경이 4㎜이고 깊이가 5㎜인 원형결함을 갖도록 시편을 제작하였으며 이들에 대한 진폭과 위상영상을 복원하였다. 결함 깊이가 100㎛인 원형결함이 존재하는 시편에 대한 라인 스캔(line scan) 결과 상대적인 영상강도의 진폭 변동율은 7%로 미약한 반면에 위상 변동율은 89%로 커다란 변화를 나타내므로 결함에 대해서 위상영상이 우수한 콘트라스트를 보였다. 이에 비하여 결함의 깊이가 5㎜인 시편에 대해서 진폭영상은 위상영상에 비하여 우수한 콘트라스트를 보이므로서 결함 깊이가 한 파장을 기준으로하여 위상영상과 진폭영상은 큰 차이를 나타내었다. 따라서 쿼드러춰 검출방식의 초음파현미경은 진폭만을 검출하는 포락선 검출기에 비해 한 파장보다 작은 높이변화를 갖는 결함의 탐상시 위상영상을 진폭영상의 상호보완적인 관계로 사용하므로서 결함의 미세 높이 변동을 효율적으로 평가 할 수 있다.

• 설비공학논문집
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• 제9권2호
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• pp.221-228
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• 1997

A strong combustion-driven sound from a surface burner made of a perforated metal fiber plate for premixed gas was investigated to clarify the physical mechanism of its generation. A simple model was developed for the acoustic power generation in terms of the heat transfer response function and the acoustic impedance of the burner. The acoustic impedance of the perforated metal fiber placed on the open exit was measured and the heat release response of the burner to the oscillating flow associated with the acoustic disturbance was expressed in terms of a response function. It was found that the power is generated by the heat release in response to the downstream particle velocity, in contrast to the upstream velocity in the case of the Rijke oscillation driven by a heater placed in the lower half of a columm with upstream flow. The measured frequencies of the oscillation were in agreement with the estimated resonance frequencies and their excitation was varied with the combustion conditions. For the same fuel rate, the excited frequency increases with the air ratio if it is low but decreases with the ratio if not so low. Such frequency characteristics were explained by assuming a heat release response function with a time constant and it was shown that the excited frequency decreases as the time constant increases.