• 한국정보통신학회논문지
• /
• 제18권8호
• /
• pp.1818-1826
• /
• 2014

해면 상태의 변화는 수중 음향 통신 수신 신호에 전방 산란 및 도플러 확산을 야기하여 수신 신호의 진폭, 주파수 및 위상은 시간적으로 변화한다. 따라서 통신채널의 일관성 대역폭과 페이딩 변화에 의해 고속 동기식 디지털 통신 성능은 장애를 받게 된다. 본 논문에서는 2가지의 해면 상태에서 QPSK의 성능을 평가하였다. 해면 산란이 성능에 미치는 영향은 LFM 신호를 이용하여 구한 채널의 임펄스 응답과 시간 일관성을 기반으로 해석하였다. 잔잔한 해면보다 거친 해면 상태의 임펄스 응답은 불안정하고 일관성 시간은 짧다. 이러한 결과와 수신 신호의 포락선, 진폭 및 위상과의 관계를 해석하여 QPSK의 비트 오류율이 해면 상태와 직접적으로 관계되는 것을 확인하였다.

• Journal of Oral Medicine and Pain
• /
• 제48권4호
• /
• pp.159-168
• /
• 2023

Purpose: Coordinated activity between the jaw and neck muscles is important in oral motor tasks such as chewing. This study examined coherence between the jaw and neck muscles during chewing in healthy adults. Methods: A total of 12 healthy adults underwent electromyography (EMG) of the jaw and neck muscles during right-sided chewing at a frequency of 1 Hz. Surface electrodes were placed over the temporalis (TA), masseter (MS), anterior digastric (DA), and sternocleidomastoid (SM) muscles on the right side. EMG signals were processed for coherence and phase analysis using advanced signal processing techniques. Results: The MS and TA muscle pair exhibited high synchronization when chewing (median coherence=0.992). Contrarily, the coherence values between the MS and DA, as well as the MS and SM muscle pairs, were relatively low (median coherence=0.848 and 0.957, respectively). Phase analysis revealed minimal temporal differences between the MS and TA muscle pair and the MS and SM muscle pair, whereas substantial phase shifts were observed between the MS and DA muscle pair. Conclusions: During chewing in healthy adults, the TA muscle works synergistically whereas the DA muscle antagonistically with the MS muscle, and the SM muscle supports the activity of the MS muscle. The observed synchrony and coordination provide insights into the intricate interplay among these muscles during oral motor tasks.

• 대기
• /
• 제20권4호
• /
• pp.495-503
• /
• 2010

Satellite data have an intrinsic problem due to a number of various physical parameters, which can have a similar effect on measured radiance. Most evaluations of satellite performance have relied on comparisons with limited spatial and temporal resolution of ground-based measurements such as soundings and in-situ measurements. In order to overcome this problem, a new way of satellite data evaluation is suggested with statistical tools such as empirical orthogonal function(EOF), and singular value decomposition(SVD). The EOF analyses with OMI and OMI HCHO over northeast Asia show that the spatial pattern show high correlation with population density. This suggests that human activity is a major source of as well as HCHO over this region. However, this analysis is contradictory to the previous finding with GOME HCHO that biogenic activity is the main driving mechanism(Fu et al., 2007). To verify the source of HCHO over this region, we performed the EOF analyses with vegetation and HCHO distribution. The results showed no coherence in the spatial and temporal pattern between two factors. Rather, the additional SVD analysis between $NO_2$ and HCHO shows consistency in spatial and temporal coherence. This outcome suggests that the anthropogenic emission is the main source of HCHO over the region. We speculate that the previous study appears to be due to low temporal and spatial resolution of GOME measurements or uncertainty in model input data.

• 한국정밀공학회지
• /
• 제23권9호
• /
• pp.102-110
• /
• 2006

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

• 정보저장시스템학회논문집
• /
• 제10권2호
• /
• pp.55-60
• /
• 2014

Laser projector has many advantages of high brightness, high resolution and small size, but the huge drawback of image degradation called speckle which generated by coherence of laser and roughness of surface interrupts their general use. There are many methods to reduce speckle pattern, but they need effective optical systems to realize display to the far field with huge volume. We designed speckle reduction element by using microlens with controlled curvature to reduce spatial coherence. Vibration element was also applied to reduce temporal coherence which considered response time of eye. Designed element was fabricated by simple reflow method and imprinting method. From the results, the fabricated element performed 48.33% of speckle reduction efficiency and 41.29% of optical efficiency with a single doublet lens.

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

• ETRI Journal
• /
• 제35권6호
• /
• pp.980-989
• /
• 2013

The important requirements for stereo video retargeting are threefold: keeping temporal coherence, preventing depth distortion, and minimizing shape distortions of the retargeted video. To meet these requirements, the left and right video sequences are divided into groups of frames (GoFs), where the GoF is a basic unit for the seam carving and we assign a set of fixed seams for all frames within the GoF. To determine the fixed seams for each GoF, we need to find the GoF boundary in the video first. Then, the representative frame for each GoF is generated by considering the spatial saliency and temporal coherence. Also, the confidence of the stereoscopic correspondence between the left and right frames is considered to prevent depth distortion.

• 대한의용생체공학회:의공학회지
• /
• 제27권4호
• /
• pp.170-179
• /
• 2006

The purpose of this study was to investigate the spatiotemporal cortical activation pattern and functional connectivity during visual perception of words. 61 channel recordings of electroencephalogram were obtained from 15 subjects while they were judging the meaning of Korean, English, and Chinese words with concrete meanings. We examined event-related potentials (ERP) and applied independent component analysis (ICA) to find and separate simultaneously activated neural sources. Spectral analysis was also performed to investigate the gamma-band activity (GBA, 30-50 Hz) which is known to reflect feature binding. Five significant ERP components were identified and left hemispheric dominance was observed for most sites. Meaningful differences of amplitudes and latencies among languages were observed. It seemed that familiarity with each language and orthographic characteristics affected the characteristics of ERP components. ICA helped confirm several prominent sources corresponding to some ERP components. The results of spectral and time-frequency analyses showed distinct GBAs at prefrontal, frontal, and temporal sites. The GBAs at prefrontal and temporal sites were significantly correlated with the LPC amplitude and response time. The differences in spatiotemporal patterns of GBA among languages were not prominent compared to the inter-individual differences. The gamma-band coherence revealed short-range connectivity within frontal region and long-range connectivity between frontal, posterior, and temporal sites.

• 한국정보과학회논문지:시스템및이론
• /
• 제27권1호
• /
• pp.13-22
• /
• 2000

이 논문에서는 시점이 고정된 경우 프레임간의 시간 일관성을 이용해서 z-버퍼 알고리즘의 렌더링 속도를 향상시키는 방법을 제안한다. z-버퍼 알고리즘은 일단의 다각형들을 렌더링하는 동안 각 화소의 깊이 값을 저장해서 나머지 다각형들을 렌더링할 때 이들의 가시성을 판별하는데 사용한다. 만약 일부 다각형들에 해당하는 색상과 깊이 정보를 렌더링을 하지 않고도 얻어 낼 수 있다면, 나머지 다각형들만을 렌더링해서 동일한 화상을 얻을 수 있다. 화면의 갱신주기가 짧은 경우 연속된 두 프레임에서 움직임이 없는 다각형들의 집합은 상당히 큰 일관성을 가진다. 이러한 시간 일관성을 이용하면 연속한 프레임에서 움직임이 없는 다각형들의 색상과 깊이 정보를 새롭게 계산할 필요가 없다. 이를 위해 고정된 다각형들의 색상과 깊이 정보를 따로 저장해두었다가 재사용하는 방법을 제안한다. 이 방법은 복잡한 자료구조를 사용하거나 기존 z-버퍼 알고리즘 자체를 바꾼 것이 아니므로 구현이 쉽고 하드웨어로 구현하기도 용이하다.

• 한국광학회지
• /
• 제3권3호
• /
• pp.161-166
• /
• 1992

회전하는 거친금속표면에 s-편극된 레이저광을 $-30^{\circ}$로 입시시켜 생긴 후방산란파중 입사광과 동일한 편극을 가지는 후방산란파에 대하여 세기의 시간상관함수 $g_{s}^{(2)}(\tau)$를 측정하였다. 이 과정에서 광전신호로부터 $g_{s}^{(2)}(0)$의 측정을 할 때 수반되는 shot noise의 영향을 제하여 줌으로써 정확한 $g_{s}^{(2)}(0)$ 값을 얻었다. 각 산란각$\theta_{s}$에서$g_{s}^{(2)}(\tau)$는 {1+exp($-\tau^2/\tau_0^2$)}함수와 거의 일치하였는데, 이는 등속으로 회전하는 간유리를 투과하여 형성된 레이저 스펙클의 경우와 같은 결과이다. 또한, 산란각에 따른 $\tau_0$의 분포에서는 $\theta_s=34^{\circ}$에서 예리하게 최대값을 가지는 것이 관찰되었다. 이 연구에서, 다중산란이 10%를 넘는 금속판산란과 다중산란이 무시될 수 있는 간유리판산란이 같은 함수꼴의 세기의 시간상관함수를 갖는다는 사실이 확인되었다.