• 한국공간구조학회논문집
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• 제8권3호
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• pp.53-63
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• 2008

본 연구는 개구부를 통해 음향적으로 결합된 공간에서의 잔향특성변화를 축소모형을 이용하여 살펴보았다. 대상공간의 음향적 결합은 정방형의 개구부를 통하여 이루어졌으며, 개구부의 크기, 부실의 흡음력 및 위치를 변화시켜가며 실의 음향특성변화를 측정 분석하였다. 연구결과 동일한 체적을 가진 부실을 통해 주실의 음향특성을 조절하는 경우 부실의 흡음력을 주실보다 현저하게 낮게 하는 것이 넓은 범위의 음향조절이 가능하며, 음향특성을 단계적으로 조절하고자 하는 경우 주실보다 높은 흡음력을 가진 부실을 이용하는 것이 효과적인 것으로 나타났다. 잔향부실의 경우 음원 측에 위치시키는 것이 효과적이며, 개구율이 6.25%이상일 때부터 주실의 음장특성에 중요한 영향을 미치는 것으로 분석되었다. 그러나 개구율이 25%이상으로 증가되면 개구율 증가에 따른 주실의 유의적인 음향특성변화는 더 이상 나타나지 않았다. 흡음부실이 결합되는 경우 음원으로부터 멀리 위치시키는 것이 효과적이었으며, 개구율 3.13%이상일 때부터 주실의 음장특성변화가 가능하였다.

• 천문학회지
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• 제54권4호
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• pp.129-137
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• 2021

It has been established that the acoustic mode parameters of the Sun and Sun-like stars vary over activity cycles. Since the observed variations are not consistent with an activity-related origin, even Sun-like stars showing out-of-phase changes of mode frequencies and amplitudes need to be carefully studied using other observational quantities. In order to test whether the presumed relations between the global seismic parameters are a signature of the stellar activity cycle, we analyze the photometric light curve of HD 49933 for which the first direct detection of an asteroseismic signature for activity-induced variations in a Sun-like star was made, using observations by the CoRoT space telescope. We find that the amplitude of the envelope significantly anti-correlates with both the maximum frequency of the envelope and the width of the envelope unless superflare-like events completely contaminate the light curve. However, even though the photometric proxy for stellar magnetic activity appears to show relations with the global asteroseismic parameters, they are statistically insignificant. Therefore, we conclude that the global asteroseismic parameters can be utilized in cross-checking asteroseismic detections of activity-related variations in Sun-like stars, and that it is probably less secure and effective to construct a photometric magnetic activity proxy to indirectly correlate the global asteroseismic parameters. Finally, we seismically estimate the mass of HD 49933 based on our determination of the large separation of HD 49933 with evolutionary tracks computed by the MESA code and find a value of about 1.2M_☉ and a sub-solar metallicity of Z = 0.008, which agrees with the current consensus and with asteroseismic and non-asteroseismic data.

• 비파괴검사학회지
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• 제26권6호
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• pp.390-402
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• 2006

The elastic properties and thickness of mullite environmental barrier coatings grown through chemical vapor deposition (CVD) on silicon carbide substrates were measured using frequency domain photoacoustic microscopy. In this technique, extremely narrow bandwidth surface acoustic waves are generated with an amplitude modulated laser source. A photorefractive crystal based interferometer is used to detect the resulting surface displacement. The complex displacement field is mapped as a function of source-to-receiver distance in order to extract the wavelength of the surface acoustic wave at a given excitation frequency, and the phase velocity is determined. The coatings tested exhibited spatial variations in thickness and mechanical properties. The measured surface wave dispersion curves were used to extract an effective value for the elastic modulus and the coating thickness. Nanoindentation was used to validate the measurements of the effective elastic modulus. The average elastic modulus measured through the coating thickness using nanoindentation is compared to the effective modulus found using the photoacoustic system. Optical microscopy is used to validate the thickness measurements. The results indicate that the photoacoustic microscopy technique can be used to estimate the effective elastic properties in coatings exhibiting spatial inhomogeneities, potentially providing valuable feedback for the optimization of the CVD growth process.

• 한국음향학회지
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• 제19권2호
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• pp.8-12
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• 2000

본 논문은 주위 환경인 수압 및 수온변화에 따른 맨드릴형 광-음향센서의 감도특성을 분석한 것에 관한 것이다. 음향감지부의 구조로는 실린더형, 중공 층상복합체형 및 air cavity가 삽입된 중공 층상복합체를 선정하고, 주위 수압과 수온변화에 따른 광-음향센서의 감도특성을 분석하였다. 맨드릴형 광-음향센서는 주위 정수압의 변화에 대해 0.15dB 미만의 음향감도 변화를 나타내고, 수압변화에 대해 안정적인 특성을 보유하고 있다. 주위 수온변화에 대한 음향감도의 상대적인 안정성은 air cavity가 삽입된 중공 나일론 층상복합체를 이용한 맨드릴형 광-음향센서가 가장 우수한 것으로 나타났다.

• 말소리와 음성과학
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• 제9권3호
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• pp.57-65
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• 2017

The current study explored how Korean-speaking children processed the multiple acoustic cues (VOT and f0) for the stop laryngeal contrast (/t'/, /t/, and /$t^h$/) and examined whether individual perceptual strategies could be related to a general cognitive ability performing executive functions (EF). 15 children (aged from 7 to 8) participated in the speech perception task identifying the three Korean laryngeal stops (3AFC) on listening to the auditory stimuli of C-/a/ with synthetically varying VOT and f0. They completed a series of EF tasks to measure working memory, inhibition, and cognitive shifting ability. The findings showed that children used the two cues in a highly correlated manner. While children utilized VOT consistently for the three laryngeal categories, their use of f0 was either reduced or enhanced depending on the phonetic categories. Importantly, the children's processing strategies of a f0 suppression for a tense-aspirated contrast were meaningfully associated with children's better cognitive abilities such as working memory, inhibition, and attentional shifting. As a preliminary experimental investigation, the current research demonstrated that listeners with inefficient processing strategies were poor at the EF skills, suggesting that cognitive skills might be responsible for developmental variations of processing sub-phonemic information for the linguistic contrast.

• ETRI Journal
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• 제33권3호
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• pp.423-433
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• 2011

This paper introduces an adaptive and integrated utterance verification (UV) framework using minimum verification error (MVE) training as a new set of solutions suitable for real applications. UV is traditionally considered an add-on procedure to automatic speech recognition (ASR) and thus treated separately from the ASR system model design. This traditional two-stage approach often fails to cope with a wide range of variations, such as a new speaker or a new environment which is not matched with the original speaker population or the original acoustic environment that the ASR system is trained on. In this paper, we propose an integrated solution to enhance the overall UV system performance in such real applications. The integration is accomplished by adapting and merging the target model for UV with the acoustic model for ASR based on the common MVE principle at each iteration in the recognition stage. The proposed iterative procedure for UV model adaptation also involves revision of the data segmentation and the decoded hypotheses. Under this new framework, remarkable enhancement in not only recognition performance, but also verification performance has been obtained.

• 말소리와 음성과학
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• 제4권3호
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• pp.31-41
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• 2012

Recent studies have shown that the stop system of Korean is undergoing a sound change in terms of the two acoustic parameters, voice onset time (VOT) and fundamental frequency (f0). Because of a VOT merger of a consonantal opposition and onset-f0 interaction, the relative importance of the two parameters has been changing in Korean where f0 is a primary cue and VOT is a secondary cue in distinguishing lax from aspirated stops in speech production as well as perception. In English, however, VOT is a primary cue and f0 is a secondary cue in contrasting voiced and voiceless stops. This study examines how Korean English learners use the two acoustic parameters of L1 in producing L2 English stops and whether the sound change of acoustic parameters in L1 affects L2 speech production. The data were collected from six adult Korean English learners. Results show that Korean English learners use not only VOT but also f0 to contrast L2 voiced and voiceless stops. However, unlike VOT variations among speakers, the magnitude effect of onset consonants on f0 in L2 English was steady and robust, indicating that f0 also plays an important role in contrasting the [voice] contrast in L2 English. The results suggest that the important role of f0 in contrasting lax and aspirated stops in L1 Korean is transferred to the contrast of voiced and voiceless stops in L2 English. The results imply that, for Korean English learners, f0 rather than VOT will play an important perceptual cue in contrasting voiced and voiceless stops in L2 English.

• 한국소음진동공학회논문집
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• 제17권7호
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• pp.596-604
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• 2007

이 논문은 후판 환형 디스크의 기하학적인 형상이 래디얼 방향 진동에 의해 방사되는 소음에 미치는 영향을 연구하였다. 디스크의 내경을 고정한 상태에서 두께와 외경을 주어진 범위내에서 변경하면서 이론적인 해를 이용하여 래디얼 모드의 고유진동수와 진동모드의 변화를 검토하였다. 이 결과를 이용하여, 해당 형상을 가진 디스크의 래디얼 방향 고유진동에 의해 발생되는 원격음장, 음향파워 및 방사효율을 계산하였다. 이 결과로부터 고유진동에 의한 음향파워와 방사효율을 최소화할 수 있는 기하학적인 형상을 선택하였다. 마지막으로, 최적화된 디스크의 임의 위치에 단위 하모닉 가진을 가했을 경우에 발생되는 음향파워 및 방사효율 스펙트럼을 구하였으며, 전산해석을 통해 그 정확성을 검증하였다. 이 논문에 소개된 방법을 적용하면 주어진 제한 조건을 만족하면서 목표 주파수 범위내에서 래디얼 진동에 의해 발생되는 소음을 최소화할 수 있는 기하학적인 형상을 간편하고 논리적으로 구할 수 있다.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2009년도 학술대회 초록집
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• pp.167-173
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• 2009

2009년 국립해양조사원은 백령도 부근 해역에 대해 바다로 1호에 장착된 Simrad EM3000 다중빔 음향측심기를 이용한 수심측량조사를 실시하였으며 정확한 음속보정을 위해 1일 $7{\sim}10$회 이상의 음속을 관측하였다. 백령도 주변해역은 계절에 따라 여러 질 수괴(쿠로시오 난류, 황해 연안수 등)가 복잡하게 분포하여 여러 형태의 수온 전선이 형성되어 수층 음속 깊이가 최대 10m/s 이상의 차이를 나타냈다. 또한 난수괴 유입으로 인해 수온약층의 깊이가 지역별로 다르게 분포 하였다. 이러한 음속의 국지적 변화는 다중빔을 이용한 수심측량 자료의 정확도를 저하시키는 요인으로 작용한다. 따라서 다중빔을 이용한 수심측량 자료의 정확도를 저하시키는 요인으로 작용한다. 따라서 백령도 주변해역 수심측량 자료의 수평 수직 변화를 음선추적 이론을 이용하여 확인하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.88-93
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• 2011

The aerodynamic drag characteristics of HEMU-400X which has been being developed for the maximum speed of 430km/h were analyzed experimentally as the variations of the pantograph cover configurations to reduce the acoustic noise and the aerodynamic drag of the pantograph system. The wind tunnel tests were performed with three pantograph cover models upon 1/20 scaled 5-car model of HEMU-400X. Two kinds of wedge shapes which induce up-flow in the vicinity of the pantograph and one cone shape which reduces the whole train drag were used in order to compare the aerodynamic characteristics as the pantograph cover shape changes. The each axial force of 5 each car was measured at a time with the test velocities, 30, 40, 50, 60m/s. Through the wind tunnel test the base drag forces of HEMU-400x model and the forces by the pantograph cover on the train model were investigated and the aerodynamic drag characteristics of the train model by the pantograph cover configurations were analyzed.