• 한국음향학회지
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• 제38권1호
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• pp.51-55
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• 2019

본 논문에서는 잡음 환경에 강인한 음성 인식 성능을 위해 특징 보상 이득을 이용한 음성 향상 기법을 제안한다. 본 논문에서는 변분모델 생성 기법을 채용한 병렬 결합된 가우스 혼합 모델(Parallel Combined Gaussian Mixture Model, PCGMM) 기반의 특징 보상 기법으로부터 계산할 수 있는 특징 보상 이득을 이용하는 음성 향상 기술을 제안한다. 불일치 환경 음성 인식 시스템 적용 환경에서 본 논문에서 제안하는 기법이 실험 결과에서 기존의 전처리 기법 및 이전 연구에서 제안된 특징 보상 기반의 음성 향상 기법에 비해 다양한 잡음 및 SNR(Signal to Noise Ratio) 조건에서 월등한 인식 성능을 나타내는 것을 확인한다. 또한 잡음 모델 선택 기법을 적용함으로써 음성 인식 성능을 유사한 수준으로 유지하면서 계산량을 대폭적으로 감축할 수 있다.

• 한국통신학회논문지
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• 제21권12호
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• pp.3215-3226
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• 1996

In this paper a K-band harmonic oscillator competitive to ordinary Push-Push type oscillators is introduced. This oscillator is composed of two-X-band dielectric resonance circuits. To favor its harmonic generation, the load effect and the bias effect are studied to allow the maximum harmonic distortion. As results, the dielectric resonated load and the class A bias are used for the 2nd harmonic generation. analytical study for modelling of voltage controlled dielectric resonator is carried out with theoretical background. The performance of the circuit is evaluated by simulation using harmonic balanced method. The novel structure has ont only a voltage tuning circuit but also an output port at fundamental frequency as the function of prescaler for phase lockede loop application on the just single oscillation structure. In experimentation, the output freqneyc of the 2nd harmonic signal is 20.5GHz and the maximum power level of output is +5.5dBm without additional post amplifiers. the harmonic oscillator exhibits -30dBc of high fundamental frequency rejection without added extra filters. The phase noise of -90dBc/Hz at 100kHz off-carrier has been achieved under free running condition, that satisfies phase noise requirement of IESS 308. The proposed oscillator may be utilized as the clean and stable fixed local oscillator in Transmit Block Upconvertor(TBU) or Low oise Block downconvertor(LNB) for K/Ka-band digital communications and satellite broadcastings.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 추계학술대회 논문집 학회본부
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• pp.502-504
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• 1995

In video image compression, it is important to extract the exact notion information from image sequence in order to perform the data compression, the field rate conversion, and the motion compensated interpolation effectively. It is well known that the location of the smallest sum of absolute difference(SAD) does not always give the true motion vector(MV) since the MV obtained via full block search is often corrupted by noise. In this paper, we first classifies the input blocks into 3 categories : the background, the shade-motion, and the edge-motion. According to the characteristics of the classified blocks, multiple locations of relatively small SAD are searched with an adaptive search window by using the proposed method. The proposed method picks MVs among those candidates by using temporal correlation. Since temporal correlation reveals the noise level in a particular region of the video image sequence, we are able to reduce the search are very effectively.

• 한국통신학회논문지
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• 제29권12C호
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• pp.1660-1668
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• 2004

본 논문에서는 간단한 구조, 적은 계산량과 안정된 빠른 수렴속도를 가진 RBF (Radial Basis Function) 신경회로망을 이용한 이중 임계값 방식의 음성구간 검출기 알고리즘을 제안하고 시뮬레이션을 통해 유용성을 확인하였다. 음성압축기에 사용되는 CELP (Code-Excited Linear Prediction) 파라미터들을 신경회로망 입력으로 하여 잡음에 강하게 반응하게 하였고, 음성구간 검출기의 성능향상을 위해 음성구간과 침묵구간에서 다른 임계값을 사용하는 이중 임계값 방식을 적용하였다. 실험 결과 이중 임계값을 이용한 RBF 신경망 음성구간 검출기는 G.729 Annex B 음성구간 검출기 보다 우수한 성능을 보였고, 기존의 MLP (Multi Layer Perceptron) 신경회로망을 이용한 음성구간 검출기와 비교하여 음성구간에서는 비슷한 성능을 보였으나 침묵구간에서 25% 정도의 성능향상을 보였다.

• 대한기계학회논문집
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• 제16권3호
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• pp.547-554
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• 1992

본 연구에서는 Climet사의 백색광원 OPC인 CI226와 PMS사의 laser 광원 OPC인 LAS-X 및 HS-LAS의 응답특성을 측정하여 제작사가 제시한 응답특성과 비교하여 그 정 확성을 논하였으며 아울러 고유량(high flow rate) Clean Room용 OPC인 Climet CI- 7300, Met One 200, Hiac/Royco5120 등 3가지 장치에 관한 오계수의 원인을 박히고자 하였다.

• Journal of Yeungnam Medical Science
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• 제36권1호
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• pp.20-25
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• 2019

Background: The aim of this study was to evaluate the awareness of occupational hazards and personal protective equipment use among dental hygienists (DHs). Methods: A total of 271 self-administered questionnaires were obtained from 280 DHs working at dental hospitals or clinics in Daegu and Gyeongsangbuk-do, Korea. Results: The occupational hazards included work involving dust (94.1%), volatile substances (86.0%), noise (97.0%), and light-curing units (96.7%). The proportion of dental hygiene tasks that participants perceived as harmful were 42.4%, 51.7%, 9.2%, and 31.4% in the same order as above. The proportion of participants who used dust-proof masks during work involving dust was 1.1%. Those who wore gas-proof masks and gloves for work using volatile substances were 0.7% and 31.2%, respectively. Participants who used goggles for work involving light-curing units were 31.0%. None of the participants used ear plugs for work involving noise. A total of 22.9% of the participants recognized the Material Safety Data Sheet, while 79.7% had never been educated about harmful work environments. Conclusion: When compared to exposure status and perception of occupational hazards, the level of protective equipment use was very low. Extra measures to increase DHs' use of personal protective equipment are necessary.

• 한국대기환경학회지
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• 제17권5호
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• pp.385-393
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• 2001

We have developed a Differential Absortion LIDAR (DIAL) method for the measurement of lower tropospheric ozone concentration. We used two laser beams from quadrupled Nd:YAG (266 nm) for the resonance wavelength and dye lasers (299.5 nm) for non -resonance wavelength. Aerosol extinction coefficients in the lower troposphere was computed by both Klett and Slope methods. To correct the SIN (Signal -Induced Noise) effect caused by photo detector, we subtracted a new-fitted baseline on the background part of a LIDAR signal, after the subtraction of the DC level. This is because SIN can be treated as an exponentially decaying tail. Using theme results, ozone profiles were obtained approximately 2km at daytime and 3km at nighttime. We compared the results derided by the Slope method with those measured by UV spectrometer. The computed results are in mostly good agreement with experimental results. In the measurement of the vertical layer, we observed the variation of the ozone profiles around the top mixed layer.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.839-842
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• 2002

Some open jet wind tunnels have been operating under limitations due to large pressure fluctuations at some wind tunnel speeds. The Hyundai Aero-acoustic full scale Wind Tunnel (HAWT), which was completed in 1999, shows that most of the specifications were fulfilled but wind tunnel pulsations at some wind speeds were observed. Hyundai Motor Company started the wind tunnel modification in order to solve this problem in 2001. After the modification work the amplitude of pressure fluctuation was reduced and below required level over full wind speed range. Aero-acoustic performance, e.g. background noise, as well as aerodynamic performance were improved after this work.

• Ocean Systems Engineering
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• 제3권1호
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• pp.71-77
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• 2013

The effective tracking area of ultra short baseline (USBL) systems strongly relates to the safety of autonomous underwater vehicles (AUVs). This problem has not been studied previously. A method for determining the effective tracking area using acoustic theory is proposed. Ray acoustic equations are used to draw rays which ascertain the effective space. The sonar equation is established in order to discover the available range of the USBL system and the background noise level using sonar characteristics. The available range defines a hemisphere like enclosure. The overlap of the effective space with the hemisphere is the effective area for USBL systems tracking AUVs. Lake and sea trials show the proposed method's validity.

• 동력기계공학회지
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• 제11권1호
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• pp.39-44
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• 2007

The purpose of this study is to verify availability of the acoustic emission in-situ monitoring method to the internal leak and operating conditions of the major valves at nuclear power plants. In this study, acoustic emission tests are performed when the pressurized temperature water and steam flowed through glove valve(main steam dump valve) and check valve(main steam outlet pump check valve) on the normal size of 12 and 18". The valve internal leak monitoring system for practical field was designed. The acoustic emission method was applied to the valves at the site, and the background noise was measured for the abnormal plant condition. To improve the reliability, a judgment of leak on the system was used various factors which are AE parameters, trend analysis, frequency analysis, voltage analysis and amplitude analysis of acoustic signal emitted from the valve operating condition internal leak.