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Publication Metadata only A limited memory BFGS based unimodular sequence design algorithm for spectrum-aware sensing systems(IEEE-inst Electrical Electronics Engineers inc, 2022) N/A; Savcı, Kubilay; PhD Student; Graduate School of Sciences and Engineering; N/AUnimodular sequences with good correlation and spectral properties are desirable in numerous applications such as active remote sensing and communication systems. therefore, designing sequences with stopband and correlation sidelobe constraints has gained a lot of attention in the last few decades. in this paper, we propose a fast and efficient iterative algorithm to design unimodular and sparse frequency waveforms with low aperiodic/periodic autocorrelation sidelobes and desired stopband properties. in our approach, the bi-objective optimization problem which minimizes both the integrated sidelobe level (ISL) of the autocorrelation function and the power density in the spectral stopbands is first turned into an unconstrained single objective optimization problem and then is treated as a nonlinear large-scale problem. for the solution of the problem, we develop an algorithm based on Limited Memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) Quasi-Newton optimization method. Unlike most gradient based algorithms which employ line searches to deduce the step length, owing to L-BFGS method, unit step length is taken as a general rule to avoid the cost of computation at every iteration with very few exceptions. the calculation of gradient is based on Fast Fourier Transform and Hadamard product operations and thus the algorithm is fast and computationally efficient. Moreover, the algorithm is space efficient and its low-memory feature makes it possible to generate long sequences. Several numerical examples are presented to validate the efficacy of the proposed method and to show its superiority over other state-of-art algorithms.Publication Metadata only A volumetric fusion technique for surface reconstruction from silhouettes and range data(academic Press inc Elsevier Science, 2007) Department of Computer Engineering; N/A; N/A; Yemez, Yücel; Wetherilt, Can James; Faculty Member; Master Student; Department of Computer Engineering; College of Engineering; 107907; N/AOptical triangulation, An active reconstruction technique, is known to be an accurate method but has several shortcomings due to occlusion and laser reflectance properties of the object surface, that often lead to holes and inaccuracies on the recovered surface. Shape from silhouette, on the other hand, As a passive reconstruction technique, yields robust, hole-free reconstruction of the visual hull of the object. in this paper, A hybrid surface reconstruction method that fuses geometrical information acquired from silhouette images and optical triangulation is presented. Our motivation is to recover the geometry from silhouettes on those parts of the surface which the range data fail to capture. a volumetric octree representation is first obtained from the silhouette images and then carved by range points to amend the missing cavity information. an isolevel value on each surface cube of the carved octree structure is accumulated using local surface triangulations obtained separately from range data and silhouettes. the MARChing cubes algorithm is then applied for triangulation of the volumetric representation. the performance of the proposed technique is demonstrated on several real objects.Publication Metadata only Adaptive streaming of multi-view video over P2P networks(Elsevier, 2012) Ekmekçioğlu, Erhan; Worrall, Stewart; Kondoz, Ahmet; N/A; N/A; Department of Electrical and Electronics Engineering; Savaş, Saadet Sedef; Gürler, Cihat Göktuğ; Tekalp, Ahmet Murat; PhD Student; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 26207In this paper, we propose a novel solution for the adaptive streaming of 3D representations in the form of multi-view video by utilizing P2P overlay networks to assist the media delivery and minimize the bandwidth requirement at the server side. Adaptation to diverse network conditions is performed regarding the features of human perception to maximize the perceived 3D. We have performed subjective tests to characterize these features and determined the best adaptation method to achieve the highest possible perceived quality. Moreover, we provide a novel method for mapping from scalable video elementary stream to torrent-like data chunks for adaptive video streaming and provide an optimized windowing mechanism that ensures timely delivery of the content over yanlis gibi. The paper also describes techniques generating scalable video chunks and methods for determining system parameters such as chunk size and window length.Publication Metadata only Bi-directional 2-D mesh representation for video object rendering, editing and superresolution in the presence of occlusion(Elsevier Science Bv, 2003) Eren, P. Erhan; Department of Electrical and Electronics Engineering; Tekalp, Ahmet Murat; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 26207In this paper, we propose a new bi-directional 2-D mesh representation of video objects, which utilizes forward and backward reference frames (keyframes). This framework extends the previous uni-directional mesh representation to enable efficient rendering, editing, and superresolution of video objects in the presence of occlusion by allowing bidirectional texture mapping as in MPEG B-frames. The video object of interest is tracked between two successive keyframes (which can be automatically or interactively selected) both in forward and backward directions. Keyframes provide the texture of the video object, whereas its motion is modeled by forward and backward 2-D meshes. In addition, we employ "validity maps", associated with each 2-D mesh, which allow selective texture mapping from the keyframes. Experimental results for efficient video object editing and object-based video resolution enhancement in the presence of self-occlusion are presented to demonstrate the effectiveness of the proposed representation.Publication Metadata only Improving throat microphone speech recognition by joint analysis of throat and acoustic microphone recordings(IEEE-inst Electrical Electronics Engineers inc, 2009) Department of Computer Engineering; Erzin, Engin; Faculty Member; Department of Computer Engineering; College of Engineering; 34503We present a new framework for joint analysis of throat and acoustic microphone (TaM) recordings to improve throat microphone only speech recognition. the proposed analysis framework aims to learn joint sub-phone patterns of throat and acoustic microphone recordings through a parallel branch HMM structure. the joint sub-phone patterns define temporally correlated neighborhoods, in which a linear prediction filter estimates a spectrally rich acoustic feature vector from throat feature vectors. Multimodal speech recognition with throat and throat-driven acoustic features significantly improves throat-only speech recognition performance. Experimental evaluations on a parallel TaM database yield benchmark phoneme recognition rates for throat-only and multimodal TaM speech recognition systems as 46.81% and 60.69%, respectively. the proposed throat-driven multimodal speech recognition system improves phoneme recognition rate to 52.58%, A significant relative improvement with respect to the throat-only speech recognition benchmark system.Publication Metadata only Lifetime analysis of wireless sensor nodes in different smart grid environments(Springer, 2014) Eriş, Çiğdem; Güngör, Vehbi Çağrı; Fadel, Etimad; Akyıldız, Ian F.; Saimler, Merve; PhD Student; Graduate School of Sciences and Engineering; N/AWireless sensor networks (WSNs) can help the realization of low-cost power grid automation systems where multi-functional sensor nodes can be used to monitor the critical parameters of smart grid components. The WSN-based smart grid applications include but not limited to load control, power system monitoring and control, fault diagnostics, power fraud detection, demand response, and distribution automation. However, the design and implementation of WSNs are constrained by energy resources. Sensor nodes have limited battery energy supply and accordingly, power aware communication protocols have been developed in order to address the energy consumption and prolong their lifetime. In this paper, the lifetime of wireless sensor nodes has been analyzed under different smart grid radio propagation environments, such as 500 kV substation, main power control room, and underground network transformer vaults. In particular, the effects of smart grid channel characteristics and radio parameters, such as path loss, shadowing, frame length and distance, on a wireless sensor node lifetime have been evaluated. Overall, the main objective of this paper is to help network designers quantifying the impact of the smart grid propagation environment and sensor radio characteristics on node lifetime in harsh smart grid environments.Publication Metadata only Monolithic fabrication of silicon nanowires bridging thick silicon structures(IEEE-Inst Electrical Electronics Engineers Inc, 2018) Peric, Oliver; Sacchetto, Davide; Fantner, Georg Ernest; Leblebici, Yusuf; N/A; Department of Mechanical Engineering; Taşdemir, Zuhal; Alaca, Burhanettin Erdem; PhD Student; Faculty Member; Department of Mechanical Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Engineering; N/A; 115108A monolithic process is developed for the fabrication of Si nanowires within thick Si substrates. A combination of anisotropic etch and sidewall passivation is utilized to protect and release Si lines during the subsequent deep etch. An etch depth of 10 mu m is demonstrated with a future prospect for 50 mu m opening up new possibilities for the deterministic integration of nanowires with microsystems. Nanowires with in-plane dimensions as low as 20 nm and aspect ratios up to 150 are obtained. Nanomechanical characterization through bending tests further confirms structural integrity of the connection between nanowires and anchoring Si microstructures.Publication Metadata only Reclaimer scheduling in dry bulk terminals(IEEE-inst Electrical Electronics Engineers inc, 2020) Ünsal, Özgür; PhD Student; Graduate School of Sciences and Engineering; N/AThis paper studies a complex parallel scheduling problem with non-crossing constraint, sequence dependent setup times, eligibility restrictions, and precedence relationships motivated by reclaimer scheduling in dry bulk terminals. in a stockyard of any dry bulk terminal, stockpiles are handled by reclaimers. therefore, improving the operational efficiency of reclaimers is critical for the overall performance of these terminals which are struggling with increasing workload. We study the variants of this problem with and without stacking operations. for each variant, we present a lower and an upper bound. a strong lower bound is obtained by relaxing the non-crossing constraint and solving the resulting problem to the optimality. While this relaxation still addresses a challenging scheduling problem, proposed arc-time-indexed formulation copes with the instances of practical size. We develop a novel constraint programming formulation to provide an upper bound for the problem. Computational experiments show this robust approach is able to generate near-optimal schedules for different stockyard configurations within a minute.Publication Metadata only Transmission characteristics of metallodielectric photonic crystals and resonators(IEEE-Inst Electrical Electronics Engineers Inc, 2002) Department of Physics; Serpengüzel, Ali; Faculty Member; Department of Physics; College of Sciences; 27855K-u band Fabry-Perot type resonances have been observed in the stop band of a metallodielectric photonic crystal by transmission measurements at microwave frequencies. The metallodielectric photonic crystal has a face centered cubic Bravais lattice structure with a lattice constant of 15 mm. Metallic spheres with 6.35 mm diameter are placed at the lattice sites. The metallodielectric photonic crystal displayed a directional bandgap with a lower band edge of 13.0 GHz, an upper band edge of 21.5 GHz and a center frequency of 17.25 GHz, corresponding to a stop bandwidth center frequency ratio of 50%. The maximum rejection at the band center is 35 dB, corresponding to a 7 dB per unit cell rejection ratio. The Fabry-Perot type resonance in the K-u band has a quality factor of 200, with a maximum transmission peak of -5 dB.