• 한국음향학회지
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• 제41권5호
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• pp.507-517
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• 2022

광음향 현미경은 높은 공간 해상도와 높은 대조도를 갖는 영상을 제공할 수 있어 생명과학 연구와 의료응용에 있어 유용하다. 광음향 현미경은 레이저 펄스 송신 후 생체조직에서 발생하는 광음향 신호를 수신하여 영상을 구성한다. 일반적으로 광음향 신호의 크기는 작기 때문에, 고품질의 광음향 현미경 영상을 얻기 위해서는 고성능의 광학 및 음향 모듈과 더불어 신호 수신용 고성능 시스템이 필요하다. 그러나 대부분의 광음향 현미경 시스템은 광음향 신호의 수신, 증폭, 품질향상, 디지털화를 위해 여러 상용 장비의 조합으로 구성된다. 이러한 이유로 광음향 현미경은 부피가 클 수밖에 없으며, 최적의 성능을 제공하기 어렵다. 본 논문에서는 향상된 신호 대 잡음비와 대조도를 제공할 수 있는 광음향 수신 시스템의 구조를 제안하고 성능 평가 결과를 제시한다. 개발한 저잡음 광대역 광음향 신호 수신 시스템은 두개의 저잡음 증폭기, 두 개의 가변 이득 증폭기, 아날로그 필터, 아날로그 디지털 변환기, 그리고 디지털 제어 로직으로 구성되어 있다. 개발된 시스템의 영상 성능은 생체 모사 혈관 팬텀, 와이어 타겟 팬텀 영상 실험을 통하여 상용 신호수신 시스템의 성능과 비교하여 평가하였다. 영상 비교 실험을 통해 개발한 광음향 현미경 시스템이 상용 장비 보다 신호 대 잡음비는 6.7 dB 이상 높았고, 영상의 대조도는 3 dB 이상 높다는 것을 확인하였다.

• 대한의생명과학회지
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• 제11권1호
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• pp.23-29
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• 2005

Molecular imaging with targeted contrast agents enables tissues to be distinguished by detecting specific cell-surface receptors. In the present study, a ligand-targeted acoustic nanoparticle system is used to identify angioplasty-induced expression of tissue factor by smooth muscle cell within carotid arteries. Pig carotid arteries were overstretched with balloon catheters, treated with tissue factor-targeted or a control nanoparticle system, and imaged with intravascular ultrasound before and after treatment. Tissue factor-targeted emulsion bound and increased the echogenicity and gray-scale levels of overstretched smooth muscle cell within the tunica media, versus no change in contralateral control arteries. Expression of stretch-induced tissue factor in carotid artery media was confirmed by immunohistochemistry. The potential for abnormal thrombogenicity of balloon-injured arteries, as reflected by smooth muscle expression of tissue factor, was imaged using a novel, targeted, nanoparticulate ultrasonic contrast agent.

• 음성과학
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• 제7권3호
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• pp.53-68
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• 2000

Although Korean stops and affricates show a three-way contrast of phonemes into lax, tense and aspirated, Korean fricatives have only two types, so-called 'lax' and tense. Considering that all the other obstruents maintain a three-way distinction but fricatives, it might be interesting to investigate whether the lax fricatives are really 'lax' in their phonetic and phonological realizations, as assumed. From an acoustic analysis, I found that Korean lax fricatives had a heavy aspiration along with a high pitch for the following vowel, being more comparable to the aspirated category. By contrast, their durational properties were found to be short, or lax-like. In other words, Korean lax fricatives are phonetically neither lax nor aspirated, but both. This dual nature of the lax fricatives takes a better account of the fact that why lax fricatives are subject to tensification, but not aspiration phonologically. Is that simply because there is no aspirated fricative in Korean? I suggest that Korean lax fricatives undergo tensification because of their being short in duration, and that they are not subject to the aspiration rule because they are indeed aspirated sounds.

• 말소리와 음성과학
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• 제12권4호
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• pp.57-61
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• 2020

Previous research has indicated that the patterns of phonetic modulations induced by prominence are not consistent across languages but are conditioned by sound systems specific to a given language. Most studies examining the prominence effects in Korean have been restricted to segments in word-initial and phrase-initial positions. The present study, thus, set out to explore the prominence effects for Korean stop consonants in word-medial intervocalic positions. A total of 16 speakers of Seoul Korean (8 males, 8 females) produced word-medial intervocalic lenis and aspirated stops with and without prominence. The prominence was induced by contrast focus on the phonation-type contrast, that is, lenis vs. aspirated stops. Our results showed that F0 of vowels following both lenis and aspirated stops became higher when the target stops received focus than when they did not, whereas voice onset time (VOT) and voicing during stop closure for both lenis and aspirated stops did not differ between the focus and no-focus conditions. The findings add to our understanding of diverse patterns of prominence-induced strengthening on the acoustic realizations of segments.

• 대한음성학회:학술대회논문집
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• 대한음성학회 2007년도 한국음성과학회 공동학술대회 발표논문집
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• pp.240-242
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• 2007

The goal of this paper is to investigate effects of three prosodic factors, such as phrasal accent (accented vs. unaccented), prosodic boundary (IP-initial vs. IP-medial) and coda voicing (e.g., bed vs. bet), on acoustic realization of English vowels (/i, $_I/$, $/{\varepsilon}$, ${\ae}/$) as produced by native (Canadian) and nonnative (Korean) speakers. The speech corpus included 16 minimal pairs (e.g., bet-bat, bet-bed) embedded in a sentence. Results show that phonological contrast between vowels are maximized when they were accented, though the contrast maximization pattern was not the same between the English and Korean speakers. However, domain-initial position do not affect the phonetic manifestation of vowels. Results also show that phonological contrast due to coda voicing is maximized only when the vowels are accented. These results propose that the phonetic realization of vowels is affected by phrasal accent only, and not by the location within prosodic position.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.322-326
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• 2008

In this paper, we have studied the images which have been reconstructed by using combination of images acquired by the variation of operating frequency. When inner images have been reconstructed, they have been superposed by the surface state effect. In this case, the images of the phase object can be enhanced by the contrast of inner images. There is a kind of specimen, one is a reference block having 1/4T, 1/2T, 3/4T side drilled holes as main run piping material of the steam generator in nuclear power plants. It has been shown that the two results of defect shapes have better than before in this processing and phase contrast grow about twice. And we have constructed the acoustic microscope by using a quadrature detector that enables to acquire the amplitude and phase of the reflected signal simultaneously. Further more we have studied the reconstruction method of the amplitude and phase images, the enhancement method of the defect images' contrast.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.126-132
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• 2006

In this paper, we aim to control the sound and vibration spatially, so that a desired physical variable is enhanced within a zone we select. This is somewhat analogous to have manipulators that can draw wave shape in any place we want. Brightness and contrast control have shown that such a manipulation is possible by controlling multiple sources[J.-W. Choi and Y.-H. Kim, J. Acoust. Soc. Am. 111(4), 2002]. In particular, the acoustic brightness control seeks a way to increase loudness of sound over a chosen area, and the contrast control aims to enhance loudness difference between two neighboring regions. This enables us to manipulate spatial distribution of sound by making two different kinds of zone ? the bright and dark zone- at the same time. The primary focus of this study is to unit the theoretical formulation of the brightness and contrast control and to find a link between these methods, as well as its relation to other conventional techniques. It is also shown that we can generate various shape of wave field by transforming the domain we consider.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.176-180
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• 2001

In this paper, we have studies the images have been reconstructed by using combination of images which has been acquired by the variation of operating frequency. When inner images has been reconstructed, inner image has been superposition by surface state effect. In this case, image enhancement the phase object and enhance the contrast of inner image. In the result of the specimen for the round defect with 2mm diameter, for the types of the depth are 1.5mm, 2mm, 2.5mm, and 3mm, it has been show that the shape of defect has better than before this processing and phase contrast grow large twice. And we have constructed the acoustic microscope by using quadrature detector that is able simultaneously to acquired the amplitude and phase of the reflected signal. Father more we have studied the reconstruction method of the amplitude and phase images and the enhancement method of the defect images' contrast.

• 음성과학
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• 제12권1호
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• pp.89-105
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• 2005

This paper is a production study of the effects of Korean prosody on two voiceless coronal fricatives /$s^h$/ and /s*/. The target segments were embedded in four prosodic positions: initial to the Intonational Phrase or the Accentual Phrase, and medial to the Accentual Phrase or to the Prosodic Word. Acoustic measurements showed that the durational differences associated with the /$s^h$/ versus /s*/ contrast vary in magnitude in different prosodic positions, confirming the proposal that segmental properties are affected by prosodic categories. This suggests that any speech synthesizer should take into consideration prosodically conditioned durational variation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.468-471
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• 2008

Sound manipulation is to control sound field using multiple sound sources for appropriate purposes. In linear acoustics, a sound can be constructed by superimposing several fundamental sound fields such as a planewave and sphere shape sound field. That is how we manipulate sound field. In this paper, we introduce the theory of sound manipulation and its applications from the examples of the generation of fundamental sound field: a circle, a ring shape sound field and a planewave field.