• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.204-207
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• 2005

We discuss two possibilities of using femtosecond pulse lasers as a new interferometric light source fer enhanced precision surface profile metrology. First, a train of ultra-fast laser pulses yields repeated low temporal coherence, which allows performing unequal-path scanning interferometry that is not feasible with white light. Second, high spatial coherence of femtosecond pulse lasers enables to test large size optics in non-symmetric configurations with relatively small size reference surfaces. These two advantages are verified experimentally using Fizeau and Twyman-Green type scanning interferometers.

• 한국전자파학회논문지
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• 제21권8호
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• pp.851-856
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• 2010

본 논문에서는 3.5 GHz에 설계된 balanced amplifier에 DBS(Dynamic Bias Switching)를 적용하여 평균 전력에서 효율을 개선하였다. DBS는 입력 신호의 포락선 크기에 따라 전력 증폭기에 두 단계의 드레인 전압을 인가하여 효율을 개선하는 기술로써 balanced amplifier에 DBS를 적용하기 위해서 동일하게 구성된 DBS 회로를 각 단에 설치하여 실제 제작하였다. 20 MHz 대역폭과 8.5 dB의 PAR(Peak to Average Ratio)을 갖는 OFDM 신호를 사용하여 측정한 결과, 28 V 단일 드레인 전압을 사용했을 때보다 42.5 dBm에서 6 %의 PAE 개선을 나타냈다.

• 대한인간공학회지
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• 제30권6호
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• pp.689-694
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• 2011

Objective: The aim of this study is to evaluate the fluctuation of signal amplitude during repetitive dynamic contraction based on surface electromyography(EMG). Background: The most previous studies were considered isometric muscle contraction and they were difference to smoothing window length by moving average filter. In practical, the human movement is dynamic state. Dynamic EMG signal which indicated as the nonstationary pattern should be analyzed differently compared with the static EMG signal. Method: Ten male subjects participated in this experiment, and EMG signal was recorded by biceps brachii, anterior/posterior deltoid, and upper/lower trapezius muscles. The subject was performed to repetitive right horizontal lifting task during ten cycles. This study was considered three independent variables(muscle, amplitude processing technique, and smoothing window length) as the within-subject experimental design. This study was estimated muscular activation by means of the linear envelope technique(LE). The dependent variable was set coefficient of variation(CV) of LE for each cycle. Results: The ANOVA results showed that the main and interaction effects between the amplitude processing technique and smoothing window length were significant difference. The CV value of peak LE was higher than mean LE. According to increase the smoothing window length, this study shows that the CV trend of peak LE was decreased. However, the CV of mean LE was analyzed constant fluctuation trend regardless of the smoothing window length. Conclusion: Based on these results, we expected that using the mean LE and 300ms window length increased reproducibility and signal noise ratio during repetitive dynamic muscle contraction. Application: These results can be used to provide fundamental information for repetitive dynamic EMG signal processing.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2008년도 추계학술발표대회 논문집
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• pp.190-195
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• 2008

The objective of this research is to determine overall heat transfer coefficients (K-value) of exterior wall, floor, and roof of Nakseonjae, a Korean traditional residence via field measurement of transient heat flow and temperature difference across each envelope component. Heat flow sensors and T-type thermocouple were attached on the internal and the external surface of each building component, and real-time measurement data were collected for the three consecutive summer days. The K-values determined in this research showed good agreement with other results from open literature. Peak and annual thermal loads of the traditional residence estimated by a commercial energy simulation program were compared with those for a current apartment house. The traditional house showed lower annual cooling load than that of the current building. It may caused by the fact that the traditional building has less air-tight envelopes and no fenestration passing direct solar radiation into the space.

• 한국통신학회논문지
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• 제38A권6호
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• pp.512-519
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• 2013

본 논문에서는 합성 이진 옵셋 반송파를 (composite binary offset carrier: CBOC) 위한 새로운 비모호 상관함수를 제안한다. 먼저, CBOC 신호의 부반송파를 네 개의 부분 부반송파의 합으로 해석하고, 각 부분 부반송파들과 수신 신호의 부분 상관들을 생성한다. 이후 생성된 부분 상관을 재조합하여 날카로운 주 첨두를 갖는 새로운 비모호 상관함수를 생성한다. 모의실험의 결과로부터 신호 추적에 제안한 상관함수를 이용한 경우 기존 상관함수들을 이용한 경우보다 더욱 향상된 추적 오류 표준편차와 다중 경로 오류 포락선을 가짐을 확인한다.

• Smart Structures and Systems
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• 제20권2호
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• pp.197-205
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• 2017

The dynamic performance of railway bridges under high-speed trains draws the attention of bridge engineers. The vibration issue for long-span bridges under high-speed trains is still not well understood due to lack of validations through structural health monitoring (SHM) data. This paper investigates the correlation between bridge acceleration and train speed based on structural dynamics theory and SHM system from three foci. Firstly, the calculated formula of acceleration response under a series of moving load is deduced for the situation that train length is near the length of the bridge span, the correlation between train speed and acceleration amplitude is analyzed. Secondly, the correlation scatterplots of the speed-acceleration is presented and discussed based on the transverse and vertical acceleration response data of Dashengguan Yangtze River Bridge SHM system. Thirdly, the warning indexes of the bridge performance for correlation scatterplots of speed-acceleration are established. The main conclusions are: (1) The resonance between trains and the bridge is unlikely to happen for long-span bridge, but a multimodal correlation curve between train speed and acceleration amplitude exists after the resonance speed; (2) Based on SHM data, multimodal correlation scatterplots of speed-acceleration exist and they have similar trends with the calculated formula; (3) An envelope line of polylines can be used as early warning indicators of the changes of bridge performance due to the changes of slope of envelope line and peak speed of amplitude. This work also gives several suggestions which lay a foundation for the better design, maintenance and long-term monitoring of a long-span high-speed bridge.

• Journal of electromagnetic engineering and science
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• 제7권4호
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• pp.147-153
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• 2007

This paper represents an analog predistortion linearizer for the high power amplifier with low memory effect. The high power amplifier is implemented using a 90-W peak envelope power(PEP) LDMOSFET at 2.14-GHz and an envelope short matching topology is applied at the active ports to minimize the memory effect. The analog predistortion circuit comprises the fundamental path and the cuber and quintic generating circuits, whose amplitudes and phases can be controlled independently. The predistortion circuit is tested for two-tone and wide-band code division multiple access(WCDMA) 4FA signals. For the WCDMA signal, the adjacent channel leakage ratios(ACLRs) at 5 MHz offset are improved by 12.4 dB at average output powers of 36 dBm and 42 dBm.

• Wind and Structures
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• 제5권2_3_4호
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• pp.337-346
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• 2002

Wind tunnel pressure measurements and numerical simulations based on the Reynolds Stress Model (RSM) are compared with full and model scale data in the flow area of impingement, separation and wake for $60^{\circ}$ and $90^{\circ}$ wind azimuth angles. The phase averaged fluctuating pressures simulated by the RSM model are combined with modelling of the small scale, random pressure field to produce the total, instantaneous pressures. Time averaged, rsm and peak pressure coefficients are consequently calculated. This numerical approach predicts slightly better the pressure field on the roof of the TTU (Texas Tech University) building when compared to the wind tunnel experimental results. However, it shows a deviation from both experimental data sets in the impingement and wake regions. The limitations of the RSM model in resolving the intermittent flow field associated with the corner vortex formation are discussed. Also, correlations between the largest roof suctions and the corner vortex "switching phenomena" are observed. It is inferred that the intermittency and short duration of this vortex switching might be related to both the wind tunnel and numerical simulation under-prediction of the peak roof suctions for oblique wind directions.

• Journal of Communications and Networks
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• 제12권6호
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• pp.544-557
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• 2010

This paper addresses the problem of controlling the envelope's power peak of single carrier modulated signals, band limited by root-raised cosine (RRC) pulse shaping filters, in order to reduce power amplifier back-off for very small aperture terminals ground stations. Magnitude modulation (MM) is presented as a very efficient solution to the peak-to-average power ratio problem. This paper gives a detailed description of the MM concept and its recent evolutions. It starts by extending the look-up-table (LUT) based approach of the MM concept to M-ary constellations with M ${\leq}$ 16. The constellation and RRC symmetries are explored, allowing considerable reduction on LUT computation complexity and storage requirements. An effective multistage polyphase (MPMM) approach for the MM concept is then proposed. As opposed to traditional LUT-MM solutions, MM coefficients are computed in real-time by a low complexity multirate filter system. The back-off from high-power amplifier saturation is almost eliminated (reduction is greater than 95%) with just a 2-stage MPMM system even for very demanding roll-off cases (e.g., ${\alpha}$ = 0,1). Also, the MPMM is independent of modulation in use, allowing its easy application to constellations with M > 16.

• 한국광학회지
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• 제12권5호
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• pp.362-370
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• 2001

간섭계의 수차는 물체광과 기준광이 서로 상쇄하는 것으로 알려져 있지만, 물체가 기울어진 경우 완벽한 상쇄가 이루어지지 않아 간섭무늬에 영향을 준다. 본 논문에서는 수치 해석을 통해 이 현상이 백색광 주사 간섭무늬의 두 정점 중, 위상 정점에 직접적인 영향을 주어 오차로 작용함을 보인다. 위상 정점은 가시도 정점에 비하여 높은 분해능과 외란에 대해 강인한 반면, 광학계의 수차에 의해 차수 계산의 부정확함이 유발되고, 측정 정밀도가 떨어지는 단점을 갖는다. 두 정점의 차이 값 계산을 실험한 결과, 위상 정점은 100nm 수준의 오차를 갖고, 특히 그 오차가 광학계의 정렬 오차에 기인함을 보인다.