Browsing by Subject "Computation time"
Now showing 1 - 7 of 7
Results Per Page
Sort Options
Item Open Access Effect of the off-focus shift of the feed on the radiation characteristics of a 2-D parabolic reflector antenna(IEEE, 2010) Oğuzer, T.; Altıntaş, A.; Nosich, AlexanderThe parabolic reflector antennas are widely used in the telecommunication systems and generally have large aperture sizes like 50λ to 80λ and larger. Their reliable full-wave analysis with the conventional Method of Moments (MoM) or with the other numerical methods is difficult because of inaccessible speed and accuracy. This statement is valid both for 3D and 2D reflector antennas in both polarizations. The Method of Analytical Regularization (MAR) constitutes an alternative solution compared to the ordinary MoM, which can provide only 1-2 digit accuracy. It provides finer accuracy within a reasonable computation time because the computational error can be decreased simply by increasing the matrix size in MAR. We have previously developed this method for the accurate simulation of the arbitrary conical section profile 2D reflector antennas, and the corresponding codes have provided us with accurate benchmark data. Here we study a similar problem however with the feed simulated by Complex Source Point (CSP) source located at an off-focus point on the symmetry axis of a front-fed reflector antenna. The numerical results are presented for the radiation characteristics including the forward and backward directivities and the radiation patterns in all directions. © 2010 IEEE.Item Open Access Histogram of oriented rectangles: a new pose descriptor for human action recognition(Elsevier BV, 2009-09-02) İkizler, N.; Duygulu, P.Most of the approaches to human action recognition tend to form complex models which require lots of parameter estimation and computation time. In this study, we show that, human actions can be simply represented by pose without dealing with the complex representation of dynamics. Based on this idea, we propose a novel pose descriptor which we name as Histogram-of-Oriented-Rectangles (HOR) for representing and recognizing human actions in videos. We represent each human pose in an action sequence by oriented rectangular patches extracted over the human silhouette. We then form spatial oriented histograms to represent the distribution of these rectangular patches. We make use of several matching strategies to carry the information from the spatial domain described by the HOR descriptor to temporal domain. These are (i) nearest neighbor classification, which recognizes the actions by matching the descriptors of each frame, (ii) global histogramming, which extends the idea of Motion Energy Image proposed by Bobick and Davis to rectangular patches, (iii) a classifier-based approach using Support Vector Machines, and (iv) adaptation of Dynamic Time Warping on the temporal representation of the HOR descriptor. For the cases when pose descriptor is not sufficiently strong alone, such as to differentiate actions "jogging" and "running", we also incorporate a simple velocity descriptor as a prior to the pose based classification step. We test our system with different configurations and experiment on two commonly used action datasets: the Weizmann dataset and the KTH dataset. Results show that our method is superior to other methods on Weizmann dataset with a perfect accuracy rate of 100%, and is comparable to the other methods on KTH dataset with a very high success rate close to 90%. These results prove that with a simple and compact representation, we can achieve robust recognition of human actions, compared to complex representations. © 2009 Elsevier B.V. All rights reserved.Item Open Access An ILP formulation for application mapping onto Network-on-Chips(IEEE, 2009) Tosun, S.; Öztürk, Özcan; Ozen, M.Ever shrinking technologies in VLSI era made it possible to place several modules onto a single die. However, the need for the new communication methods has also increased dramatically since traditional bus-based systems suffer from signal propagation delays, signal integrity, and scalability. Network-on-Chip (NoC) is the biggest step towards the communication bottleneck of System-on-Chip (SoC) architectures. In this paper, we present an Integer Linear Programming (ILP) formulation for application mapping onto mesh based Network-on-Chips to minimize the energy consumption of the system. The proposed method obtains optimal or close to optimal results within the given computation time limit. We also experimentally investigate the impact of the size of the mesh architecture on the application mapping and total communication. ©2009 IEEE.Item Open Access Investigation of load balancing scalability in space plasma simulations(Springer, Berlin, Heidelberg, 2013) Türk, Ata; Demirci, Gündüz V.; Aykanat, Cevdet; Von Alfthan, S.; Honkonen I.In this study we report the load-balancing performance issues that are observed during the petascaling of a space plasma simulation code developed at the Finnish Meteorological Institute (FMI). The code models the communication pattern as a hypergraph, and partitions the computational grid using the parallel hypergraph partitioning scheme (PHG) of the Zoltan partitioning framework. The result of partitioning determines the distribution of grid cells to processors. It is observed that the initial partitioning and data distribution phases take a substantial percentage of the overall computation time. Alternative (graph-partitioning-based) schemes that provide better balance are investigated. Comparisons in terms of effect on running time and load-balancing quality are presented. Test results on Juelich BlueGene/P cluster are reported. © 2013 Springer-Verlag.Item Open Access Lumped element modeling of CMUT arrays in collapsed mode(IEEE, 2014-09) Aydoğdu, Elif; Özgürlük, A.; Atalar, Abdullah; Köymen, HayrettinThis study focuses on modeling collapsed modeoperation of CMUT arrays, and obtaining a small signal lumped element model for collapsed mode operation. Having the large signal model for single CMUT from previous studies, the mutual radiation impedance is presented for the collapsed mode, and a large signal model for a CMUT array is obtained for simulating the operation in both uncollapsed and collapsed modes. For faster computation, a small signal model for a CMUT cell is derived by linearizing the collapsed mode operation at a given bias point, and the computation time is reduced significantly. Using this model we are able to simulate a large array of collapsed CMUT cells. © 2014 IEEE.Item Open Access Synthesis of three-dimensional light fields with binary spatial light modulators(Optical Society America, 2011-05-24) Ulusoy, E.; Onural, L.; Özaktaş, Haldun M.Computation of a binary spatial light modulator (SLM) pattern that generates a desired light field is a challenging quantization problem for which several algorithms have been proposed, mainly for far-field or Fourier plane reconstructions. We study this problem assuming that the desired light field is synthesized within a volumetric region in the non-far-field range after free space propagation from the SLM plane. We use Fresnel and Rayleigh-Sommerfeld scalar diffraction theories for propagation of light. We show that, when the desired field is confined to a sufficiently narrow region of space, the ideal gray-level complex-valued SLM pattern generating it becomes sufficiently low pass (oversampled) so it can be successfully halftoned into a binary SLM pattern by solving two decoupled real-valued constrained halftoning problems. Our simulation results indicate that, when the synthesis region is considered, the binary SLM is indistinguishable from a lower resolution full complex gray-level SLM. In our approach, free space propagation related computations are done only once at the beginning, and the rest of the computation time is spent on carrying out standard image halftoning.Item Open Access Thereconstruction quality improvement of holographic stereograms via variable size segmentation(IEEE, 2010) Şahin, Erdem; Onural, Levent; Kang, HoonjongAs computer generated holograms becomes more common, the fast computation of holographic interference patterns in digital environment becomes a necessity. Since the computation time of holograms via Fresnel (or Rayleigh-Sommerfeld) diffraction models makes real time applications impossible, the holographic stereograms are developed to be a solution for this problem. Holographic stereograms divide the hologram plane into segments. In phase added stereograms the coordinates of 3D source points are used while calculating the diffraction field. And that enables to calculate the diffraction field with appropriate sized FFTs. Although the phase added stereograms are advantageous in terms of computation time, the quality of the reconstructed three dimensional images may not be satisfactory. The main reason is that the diffraction field of a given point source is approximated as a pure complex sinusuoid in each segment. To increase the reconstruction quality, we propose a method that uses variable sized segments, as opposed to previously developed holographic stereograms that use fixed sized segments. While approximating the diffraction field of a point source, higher frequency regions are covered with smaller segments and lower frequency regions with larger segments. As a result of this, we keep the total number of oscillations of pure sinusoidal waves constant in each segment. The simulations that we carried out for a point source show that we are able to obtain better quality reconstruction with our method. ©2010 IEEE.