Browsing by Subject "Periodic behavior"
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Item Open Access Contour based smoke detection in video using wavelets(IEEE, 2006-09) Töreyin, B. Uğur; Dedeoğlu, Yiğithan; Çetin, A. EnisThis paper proposes a novel method to detect smoke in video. It is assumed the camera monitoring the scene is stationary. The smoke is semi-transparent at the early stages of a fire. Therefore edges present in image frames start loosing their sharpness and this leads to a decrease in the high frequency content of the image. The background of the scene is estimated and decrease of high frequency energy of the scene is monitored using the spatial wavelet transforms of the current and the background images. Edges of the scene produce local extrema in the wavelet domain and a decrease in the energy content of these edges is an important indicator of smoke in the viewing range of the camera. Moreover, scene becomes grayish when there is smoke and this leads to a decrease in chrominance values of pixels. Periodic behavior in smoke boundaries is also analyzed using a Hidden Markov model (HMM) mimicking the temporal behavior of the smoke. In addition, boundary of smoke regions are represented in wavelet domain and high frequency nature of the boundaries of smoke regions is also used as a clue to model the smoke flicker. All these clues are combined to reach a final decision.Item Open Access Nanosprings harvest light more efficiently(OSA - The Optical Society, 2015) Khudiyev, T.; Bayındır, MehmetNanotechnology presents versatile architectural designs for the purpose of utilization as a building block of 1D optoelectronic nanodevices because current nanowire-based schemes require more effective solutions for low absorption capacity of nanoscale volumes. We report on the potential of nanospring absorbers as an alternative light-harvesting platform with significant advantages over conventional nanowires. Absorption capacity of nanospring geometry is found to be superior to cylindrical nanowire shape. Unlike nanowires, they are able to trap a larger amount of light thanks to characteristic periodic behavior that boosts light collection for the points matched with Mie resonances. Moreover, nanospring shape supplies compactness to a resulting device with area preservation as high as twofold. By considering that a nanospring array with optimal periods yields higher absorption than individual arrangements and core-shell designs, which further promote light collection due to unique antireflection features of shell layer, these nanostructures will pave the way for the development of highly efficient self-powered nanosystems.Item Open Access Wavelet based real-time smoke detection in video(IEEE, 2005-09) Töreyin, B. Uğur; Dedeoǧlu, Yiğithan; Çetin, A. EnisA method for smoke detection in video is proposed. It is assumed the camera monitoring the scene is stationary. Since the smoke is semi-transparent, edges of image frames start loosing their sharpness and this leads to a decrease in the high frequency content of the image. To determine the smoke in the field of view of the camera, the background of the scene is estimated and decrease of high frequency energy of the scene is monitored using the spatial wavelet transforms of the current and the background images. Edges of the scene are especially important because they produce local extrema in the wavelet domain. A decrease in values of local extrema is also an indicator of smoke. In addition, scene becomes grayish when there is smoke and this leads to a decrease in chrominance values of pixels. Periodic behavior in smoke boundaries and convexity of smoke regions are also analyzed. All of these clues are combined to reach a final decision.