• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 C
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• pp.1860-1862
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• 2004

It is widely known that the ultra high frequency (UHF) method that detects the electromagnetic wave of the PD pulses in the gas insulated space is one of the most competitive methods for its high sensitivity. From the above point of view, this paper describes the characteristics of GIS PD signals measured with ultra wide band (UWB) GIS PD detecting system in which PD signals are detected into the dual UHF band. The UWB PD detection system consists of the UWB UHF coupler, the UWB low noise amplifier (LNA) and the oscilloscope. The dual bands for PD signals are 0.5-2GHz(full band) and 1-2GHz(high band). As results, it was found that the partial discharges of each defect have their own characteristic pattern and the ratio of High band to Full band increases with gas pressure.

• 한국지리정보학회지
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• 제12권4호
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• pp.125-135
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• 2009

FIHS(Fast Intensity Hue Saturation) 융합은 빠른 계산 능력 때문에 널리 이용되고 있으나 IHS(Intensity Hue Saturation) 융합과 마찬가지로 분광정보 왜곡 현상이 나타난다. 본 논문에서는 각 분광 대역의 비율을 이용하여 분광정보 왜곡을 줄일 수 있는 융합법(FIHS-BR)과 공간정보 및 분광 대역의 비율을 활용한 적응 FIHS 융합법(FIHS-SABR)을 제안하였다. 제안한 FIHS-BR 융합은 각 분광 대역의 비율을 이용하여 구한 분광 대역별로 서로 다른 공간 해상도 개선 값을 더하여 분광정보 왜곡을 줄일 수 있도록 하였으며, FIHS-SABR 융합은 국부 영상의 공간정보 특성에 따라 적응적으로 결정된 공간 해상도 개선 값을 각 분광 대역의 비율에 따라 분광 대역별로 재조정하여 분광 정보 왜곡을 더 많이 줄일 수 있도록 하였다. 제안한 FIHS-BR 융합과 FIHS-SABR 융합의 성능을 확인하기 위하여 IKONOS 위성 영상에 대하여 컴퓨터 시뮬레이션을 수행하였으며, 실험 결과 제안 방법들이 기존 융합 영상에서 색상 왜곡이 심하게 나타나는 삼림지역 등에서 색상 왜곡 현상이 적게 나타남을 확인할 수 있었으며, 융합 영상의 분광정보 특성 평가 결과도 가장 우수함을 확인할 수 있었다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.1-3
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• 2003

In this study, spectroradiometer data were coupled with fluorometer data to find out the best suited bands ratio to monitor the chlorophyll a concentration for inland water. Remote sensing reflectance measurements were used to evaluate the performance of several default ocean color chlorophyll algorithms for SeaWiFS data. This study shows that the chlorophyll a concentration from fluorometer and reflectance from spectroradiometer lies in exploiting the signal provided by the chlorophyll a red absorption peak near 670nm. Two-band ratio based on a ratio of reflectance 670 and 700nm provided a good correlation for a linear model, compare with blue-green two band ratio.

• 한국음향학회지
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• 제35권2호
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• pp.102-109
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• 2016

본 논문은 밀접한 간격의 두 개의 마이크 배열 환경에서 SNR(Signal-to-Noise Ratio) 추정을 통한 잡음 억제 방법을 제안한다. 기존의 방법은 전 밴드에서 간섭 함수 기반의 SNR 추정을 통해 이득 함수를 얻는 잡음 억제 방법을 사용한다. 그러나 이 방법은 잡음으로 인한 손상이 모든 특징 벡터 성분에 영향을 미쳐 성능을 저하시키는 문제점을 가지고 있다. 따라서 주파수 영역의 신호를 N개의 다중 주파수 밴드로 구분하고 각 밴드별로 간섭 함수 기반의 SNR 추정을 통한 이득 함수를 얻는 잡음 억제 방법을 제안한다. 제안하는 방법의 성능평가는 ITU-T(International Telecommunications Union Telecommunication)에서 제공되는 객관적인 품질 평가 방법인 PESQ(Perceptual Evaluation of Speech Quality)로 비교하여 나타내었다.

• 생물정신의학
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• 제21권4호
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• pp.168-174
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• 2014

Objectives Sensory gating dysfunctions in patients with schizophrenia and bipolar disorder have been investigated through two similar methods ; P50 suppression and prepulse inhibition paradigms. However, recent studies have demonstrated that the two measures are not correlated but rather constitute as distinct neural processes. Recent studies adopting spectral frequency analysis suggest that P50 suppression reflects the interaction between gamma and other frequency bands. The aim of the present study is to investigate which frequency component shows more significant interaction with gamma band. Methods A total of 108 mood disorder patients and 36 normal subjects were included in the study. The P50 responses to conditioning and test stimuli with an intra-pair interval of 500 msec were measured in the study population. According to P50 ratio (amplitude to the test stimulus/amplitude to the conditioning stimulus), the subjects with P50 ratio less than 0.2 were defined as suppressed group (SG) ; non-suppressed group (NSG) consisted of P50 ratio more than 0.8. Thirty-five and 25 subjects were included in SG and NSG, respectively. Point-to-point correlation coefficients (PPCCs) of both groups were calculated between two time-windows : the first window (S1) was defined as the time-window of one hundred millisecond after the conditioning auditory stimulus and the second window (S2) was defined as the time-window of 100 msec after the test auditory stimulus. Spectral frequency analysis was performed to investigate which frequency band results in the difference of PPCC between SG and NSG. Results Significant reduction of PPCC between S1 and S2 was observed in the SG (Pearson's r = 0.24), compared to PPCC of the NSG (r = 0.58, p < 0.05). In spectral frequency analysis, gamma band showed "phase-reset" and similar responses after the two auditory stimuli in suppressed and non-suppressed group. However in the case of alpha band, comparison showed significantly low PPCC in SG (r = -0.14) compared to NSG (r = 0.36, p < 0.05). This may be reflecting "phase-out" of alpha band against gamma band at approximately 50 msecs after the test stimulus in the SG. Conclusions Our study suggests that normal P50 suppression is caused by phase-out of alpha band against gamma band after the second auditory stimulus. Thus it is demonstrated that normal sensory gating process is constituted with attenuated alpha power, superimposed on consistent gamma response. Implications of preserved gamma and decreased alpha band in sensory gating function are discussed.

• 제어로봇시스템학회논문지
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• 제20권8호
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• pp.890-894
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• 2014

In this paper, we derive the CRLB (Cramer-Rao Lower Bound) of effective carrier-to-noise power ratio ($C/N_0$) estimation for a GPS (Global Positioning System) L1 C/A (Coarse/Acquisition) signal under band-limited white noise jamming environments. The quality of a received GPS signal is commonly described in terms of its $C/N_0$, implying that the noise is white and thus can be described by scalar noise density. However, if some intentional interference is received to a victim GPS receiver, then the $C/N_0$ is no longer the efficacious performance indicator. The correct and straightforward measurement to analyze the receiving situation is the effective $C/N_0$. In this paper, we consider a band-limited white noise jamming whose bandwidth is 2MHz and is the same as one of the first null-to-null bandwidth of the GPS L1 C/A signal.

• Carbon letters
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• 제28권
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• pp.72-80
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• 2018

In this study, an empirical relationship between the energy band gap of multi-walled carbon nanotubes (MWCNTs) and synthesis parameters in a chemical vapor deposition (CVD) reactor using factorial design of experiment was established. A bimetallic (Fe-Ni) catalyst supported on $CaCO_3$ was synthesized via wet impregnation technique and used for MWCNT growth. The effects of synthesis parameters such as temperature, time, acetylene flow rate, and argon carrier gas flow rate on the MWCNTs energy gap, yield, and aspect ratio were investigated. The as-prepared supported bimetallic catalyst and the MWCNTs were characterized for their morphologies, microstructures, elemental composition, thermal profiles and surface areas by high-resolution scanning electron microscope, high resolution transmission electron microscope, energy dispersive X-ray spectroscopy, thermal gravimetry analysis and Brunauer-Emmett-Teller. A regression model was developed to establish the relationship between band gap energy, MWCNTs yield and aspect ratio. The results revealed that the optimum conditions to obtain high yield and quality MWCNTs of 159.9% were: temperature ($700^{\circ}C$), time (55 min), argon flow rate ($230.37mL\;min^{-1}$) and acetylene flow rate ($150mL\;min^{-1}$) respectively. The developed regression models demonstrated that the estimated values for the three response variables; energy gap, yield and aspect ratio, were 0.246 eV, 557.64 and 0.82. The regression models showed that the energy band gap, yield, and aspect ratio of the MWCNTs were largely influenced by the synthesis parameters and can be controlled in a CVD reactor.

• 대한원격탐사학회지
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• 제22권4호
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• pp.275-284
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• 2006

Hyperion 영상의 노이즈는 주로 대기 효과와 센서의 기계오류, 신호변환 때문이다. 보정되지 않은 밴드, 중복 밴드, 모든 대기흡수에 영향을 많이 받는 밴드가 모두 제거되어도, 여전히 노이즈 밴드가 존재한다. 영상처리에 사용할 선명하고 안정된 밴드를 선택하기 위해 육안으로 영상을 간단하게 검사할 수 있지만, 이는 수동으로 이루어지는 비효율적이고 주관적인 방법이다 본 논문에서 우리는 노이즈 추정과 자동 밴드 선택을 위해 극단화소비 사용을 제안한다. 이를 위해 기존에 사용되던 SNR, 엔트로피와 극단화소비를 비교하였다. 첫째, 상대적으로 노이즈가 적은 ALI 영상에 Gaussian 노이즈, salt & pepper 노이즈, Speckle 노이즈를 부가하여 노이즈량과 각 통계량 사이의 관계를 살펴보았다. 둘째, Hyperion 영상에서 추출된 세 개 통계량에 대해 기대최대화 분석을 수행하여 자동으로 밴드를 선택하였다. Hyperion 데이터는 시각적 평가에 의해 5단계로 구분되어 평가자료로 사용되었다. 실험 결과에서 극단화소비가 Hyperion 영상의 밴드 선택에 효과적으로 사용될 수 있었다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.67.1-67.1
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• 2010

Triple junction solar cell을 위한 a-SiGe middle cell의 조건별 광학적 특성에 관한 연구를 실시하였다. a-SiGe I층은 GeH4 유량, 압력, H2 dilution ratio를 변화시켜 제조하였으며 전기적, 광학적 특성을 비교하여 최종적으로 선택된 조건을 triple junction solar cell에 적용하였다. a-SiGe I층은 Ge contents가 증가함에 따라 band gap은 감소하고 45% 이상의 조건에서는 700nm 전후 파장의 투과율이 감소하며, 압력이 감소함에 따라 band gap은 소폭 감소하나 700nm 전후 파장의 투과율은 증가하였다. 그리고 H2 ratio가 증가함에 따라 band gap은 소폭 감소하나 투과율에는 큰 변화가 없었다. 상기 결과를 바탕으로 최종적으로 선택된 조건에서 triple-junction solar cell을 제작하여 평가한 결과 초기 변환효율 9%의 결과를 얻었다.

• 한국측량학회:학술대회논문집
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• 한국측량학회 2006년도 춘계학술발표회 논문집
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• pp.193-198
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• 2006

Among 242 Hyperion bands, there are 46 bands that contain completely no information and some other bands with various kinds of noise. It is mainly due to the atmosphenc absorption and the low signal-to-noise ratio. The visual inspection for selecting clean and stable bands is a simple practice, but is a manual, inefficient, and subjective Process. Though uncalibrated, overlapping, and all deep water absorption bands are removed, there still exist noisy bands. In this paper, we propose that the extrema ratio be measured for noise estimation and the unsupervised band selection be performed using the Expectation-Maximization algorithm. The Hyperion data were classified into 5 categories according to the image quality by visual inspection, and used as the reference data. The accuracy of the proposed method was compared with signal-to-noise ranking and entropy ranking. As a result, the proposed mettled was effective as preprocessing step for band selection.