• 재활복지공학회논문지
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• 제5권1호
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• pp.41-46
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• 2011

감각신경성 난청의 원인 중 하나는 내이에 존재하는 와우(cochlea)의 기능적 이상 때문이다. 와우에서 내유모세포(inner hair cell, IHC)나 신경의 기능적 이상이 있는 곳을 'dead region'이라고 한다. 보청기에서 dead region에 속하는 주파수 영역의 증폭은 효과가 미약한 것으로 알려져 있다. 본 논문에서는 dead region의 위치에 따른 음성신호의 인지 능력 비교와 dead region이 존재할 때 보청기의 효과적인 이득값을 알아보기 위해 WRS 검사와 선호도 조사를 실시하였다. WRS(Word Recognition Score)검사와 선호도 조사를 위해 정상 청력 능력을 지닌 성인 남녀 8명을 대상으로, white noise와 babble noise를 이용하여 신호 대 잡음비(SNR) 0dB의 조건으로 검사음과 혼합하였으며, dead region의 영역을 세 가지로 분류하였다. 주파수 영역에 따라 low-frequency, mid-frequency, high-frequency dead region으로 나누고, 각 dead region에 따라 14.5 dB, 11.5 dB, 6 dB의 증폭 이득을 다르게 하여 결과를 비교하였다. dead region의 위치에 따른 검사 결과는 각 영역별로 차이가 있었다. WRS 검사결과 low-frequency dead region일 때 보다, mid-frequency dead region나 high-frequency dead region일 때의 WRS점수와 선호도 평가가 높게 나왔으며, 증폭 이득값의 차이를 비교해 보았을 때, 14.5 dB의 이득에 비해 낮은 이득을 주었을 때 WRS 검사 결과값이 더 높게 나왔으며, 높은 이득일수록 선호도 조사에서 낮은 점수를 받았다.

• 한국해양공학회지
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• 제36권1호
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• pp.61-81
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• 2022

The available underwater acoustic spectrum is limited. Therefore, it is imperative to avoid frequency interference from overlapping frequencies of underwater acoustic equipment (UAE) for the co-existence of the UAE. Cognitive technology that senses idle spectrum and actively avoids frequency interference is an efficient method to facilitate the collision-free operation of multiple UAE with overlapping frequencies. Cognitive technology is adopted to identify the frequency usage of UAE to apply cognitive technology. To this end, we investigated two principle underwater acoustic sources: UAE and marine animals. The UAE is classified into five types: underwater acoustic modem, acoustic positioning system, multi-beam echo-sounder, side-scan sonar, and sub-bottom profiler. We analyzed the parameters of the frequency band, directivity, range, and depth, which play a critical role in the design of underwater acoustic cognitive technology. Moreover, the frequency band of several marine species was also examined. The mid-frequency band from 10 - 40 kHz was found to be the busiest. Lastly, this study provides useful insights into the design of underwater acoustic cognitive technologies, where it is essential to avoid interference among the UAE in this mid-frequency band.

• 해양환경안전학회지
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• 제26권3호
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• pp.297-307
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• 2020

In the study, energy flow analysis is performed to predict the performance of silencers. To date, deterministic approaches such as finite element method have been widely used for silencer analysis. However, they have limitations in analyzing large structures and mid-high frequency ranges due to unreasonable computational costs and errors. However, silencers used for ships and off-shore plants are much larger than those used in other engineering fields. Hence, energy governing equation, which is significantly efficient for systems with high modal density, is solved for silencers in ships and off-shore plants. The silencer is divided into two different acoustic media, air and absorption materials. The discontinuity of energy density at interfaces is solved via hypersingular integrals for the 3-D modified Helmholtz equation to analyze multi-domain problems with the energy flow boundary element method. The method is verified by comparing the measurements and analysis results for ship silencers over mid-high frequency ranges. The comparisons confirm good agreement between the measurement and analysis results. We confirm that the applied analysis method is useful for large silencers in mid-high frequency ranges. With the proven procedures, energy flow analysis can be performed for various types of silencer used in ships and off-shore plants in the first stage of the design.

• 천문학회보
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• 제39권2호
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• pp.109.1-109.1
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• 2014

다이아몬드 선삭 기계(DTM)를 이용한 렌즈 및 반사경 가공은 제작시간 단축 및 비용 절감의 장점을 가지고 있다. 그러나 알루미늄과 같은 무른 금속을 가공하여 반사경을 제작하는 경우에는 반사경 표면에 가공오차가 발생한다. 오차는 크기에 따라 고주파 오차(High Frequency Error, HFE), 중주파 오차(Mid Frequency Error, MFE), 저주파 오차(Low Frequency Error, LFE)로 분류 할 수 있다. LFE는 가공한 반사경 표면이 설계된 형상과 얼마나 다른지를 표현하는 값으로 광학 수차와 같이 해상도를 저하시킨다. MFE는 반사경 표면에 수십 마이크로미터 크기로 나타난다. 회전하는 반사경 시료에 다이아몬드 툴의 홈이 동심원으로 생기면서 회절격자와 같이 회절 및 간섭 현상을 만든다. HFE는 표면의 거친 정도를 나타내며 반사율과 관련되고 수 나노미터 크기로 나타난다. 본 연구에서는 광학 레이저를 사용하여 MFE가 광학 성능에 미치는 영향을 분석하였다. 유리 반사경과 MFE를 제거한 반사경, 제거하지 않은 반사경에 대하여 실험을 진행하였다. 본 실험 결과는 반사경 가공 표면을 평가할 수 있는 유용한 자료가 될 것이다.

• 대한수학회논문집
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• 제9권4호
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• pp.881-889
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• 1994

Let ($X, \Beta, \mu$) be a measure space with the $\sigma$-algebra $\Beta$ and the probability measure $\mu$. Throughouth this article set equalities and inclusions are understood as being so modulo measure zero sets. A transformation T defined on a probability space X is said to be measure preserving if $\mu(T^{-1}E) = \mu(E)$ for $E \in B$. It is said to be ergodic if $\mu(E) = 0$ or i whenever $T^{-1}E = E$ for $E \in B$. Consider the sequence ${x, Tx, T^2x,...}$ for $x \in X$. One may ask the following questions: What is the relative frequency of the points $T^nx$ which visit the set E\ulcorner Birkhoff Ergodic Theorem states that for an ergodic transformation T the time average $lim_{n \to \infty}(1/N)\sum^{N-1}_{n=0}{f(T^nx)}$ equals for almost every x the space average $(1/\mu(X)) \int_X f(x)d\mu(x)$. In the special case when f is the characteristic function $\chi E$ of a set E and T is ergodic we have the following formula for the frequency of visits of T-iterates to E : $$ lim_{N \to \infty} \frac{$\mid${n : T^n x \in E, 0 \leq n $\mid$}{N} = \mu(E) $$ for almost all $x \in X$ where $$\mid$\cdot$\mid$$ denotes cardinality of a set. For the details, see [8], [10].

• 설비공학논문집
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• 제2권3호
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• pp.188-198
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• 1990

Turbulent characteristics of turbulent pulsating flows were studied experimentally in a square duct. Velocity waveforms, velocity profiles, and turbulent intensity of turbulent pulsating flow were investigated by using a hot-wire anemometer with data acquisition and a processing system in a square duct with a ratio of 1 ($40mm{\times}40mm$) to 4,000mm long. Turbulent components were shown to be larger in decelerating than in accelerating regions and also larger for a large phase of velocity and U'rms distribution of turbulent flow. The effect of velocity amplitude ratio does not exist for specified time [${\theta}(z^{\prime})$], amplitude ratio (${\mid}U^{\prime}_{rms.os.1}{\mid}/{\mid}U_{m.os.1}{\mid}$), and phase difference (${\Delta}U^{\prime}_{rms.os.1}-{\Delta}U_{m.os.1}$) in either turbulent oscillating or cross-sectional mean velocity components. The effect of dimensionless angular frequency for specified time [${\theta}(z^{\prime})$] can be disregarded because the dimensionless angular frequency does not affect the specified time. The velocity distributions of turbulent pulsating flows for various time-averaged Reynolds numbers are in approximate agreement with the velocity distributions for equivalent Reynolds numbers and 1/7th power law of steady flow.

• 대한기계학회논문집
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• 제16권5호
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• pp.910-923
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• 1992

본 연구에서는 가장 응용 빈도가 큰 크랭크-레버 4절 기구를 제작하고 강성과 유연성 두가지 베어링을 사용하여 연결봉과 레버의 중점의 변형률을 스트레인 게이지 로 측정하여 앞의 이론 논문에서 수행한 수치해석의 결과와 비교 검토하였다.

• Journal of Audiology & Otology
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• 제23권4호
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• pp.187-192
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• 2019

Background and Objectives: Clear speech is an effective communication strategy used in difficult listening situations that draws on techniques such as accurate articulation, a slow speech rate, and the inclusion of pauses. Although too slow speech and improperly amplified spectral information can deteriorate overall speech intelligibility, certain amplitude of increments of the mid-frequency bands (1 to 3 dB) and around 50% slower speech rates of clear speech, when compared to those in conversational speech, were reported as factors that can improve speech intelligibility positively. The purpose of this study was to identify whether amplitude increments of mid-frequency areas and slower speech rates were evident in Korean clear speech as they were in English clear speech. Subjects and Methods: To compare the acoustic characteristics of the two methods of speech production, the voices of 60 participants were recorded during conversational speech and then again during clear speech using a standardized sentence material. Results: The speech rate and longterm average speech spectrum (LTASS) were analyzed and compared. Speech rates for clear speech were slower than those for conversational speech. Increased amplitudes in the mid-frequency bands were evident for the LTASS of clear speech. Conclusions:The observed differences in the acoustic characteristics between the two types of speech production suggest that Korean clear speech can be an effective communication strategy to improve speech intelligibility.

• Corrosion Science and Technology
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• 제22권6호
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• pp.393-398
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• 2023

Properties of hafnium nitride (HfN) coatings are affected by deposition conditions, most often by the sputtering technique. Appropriate use of different magnetron sputtering modes allows control of the structural development of the film, thereby enabling adjustment of its properties. This study compared properties of HfN coatings deposited by direct current magnetron sputtering (dcMS), mid-frequency direct current magnetron sputtering (mfMS), and inductively coupled plasma-assisted magnetron sputtering (ICPMS) systems. The microstructure, crystalline, and mechanical properties of these HfN coatings were investigated by field emission electron microscopy, X-ray diffraction, atomic force microscopy, and nanoindentation measurements. HfN coatings deposited using ICPMS showed smooth and highly dense microstructures, whereas those deposited by dcMS showed rough and columnar structures. Crystalline structures of HfN coatings deposited using ICPMS showed a single δ-HfN phase, whereas those deposited using dcMS and mfMS showed a mixed δ-HfN and HfN_0.4 phases. Their performance were increased in the order of dcMS < mfMS < ICPMS, with ICPMS achieving a value of 47.0 GPa, surpassing previously reported results.

• 한국음향학회지
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• 제25권8호
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• pp.389-394
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• 2006

중주파수 양상태 잔향음 준위는 음선이론을 사용하여 산출되었다. 제안된 알고리즘은 음파전달 경로 내 전방/후방 산란의 상호작용을 가정한다. 해양환경 (지형. 해저면 산란, 해수면 산란 등)은 거리 독립 해양환경으로 가정되었고 중주 파수 산란 모델이 사용되었다. 해상실험 자료를 사용한 알고리즘 검증 결과 양상태 잔향음 모델 알고리즘이 관측 해역의 양상태 잔향음 특성을 잘 반영하고 있음을 확인하였다.