Browsing by Subject "Matrix"

Now showing 1 - 11 of 11

Open Access
Algorithms for efficient vectorization of repeated sparse power system network computations
(IEEE, 1995) Aykanat, Cevdet; Özgü, Ö.; Güven, N.
Standard sparsity-based algorithms used in power system appllcations need to be restructured for efficient vectorization due to the extremely short vectors processed. Further, intrinsic architectural features of vector computers such as chaining and sectioning should also be exploited for utmost performance. This paper presents novel data storage schemes and vectorization alsorim that resolve the recurrence problem, exploit chaining and minimize the number of indirect element selections in the repeated solution of sparse linear system of equations widely encountered in various power system problems. The proposed schemes are also applied and experimented for the vectorization of power mismatch calculations arising in the solution phase of FDLF which involves typical repeated sparse power network computations. The relative performances of the proposed and existing vectorization schemes are evaluated, both theoretically and experimentally on IBM 3090ArF.
Open Access
Analysis of strain fields in silicon nanocrystals
(American Institute of Physics, 2009) Yilmaz, D. E.; Bulutay, C.; Çaǧın, T.
Strain has a crucial effect on the optical and electronic properties of nanostructures. We calculate the atomistic strain distribution in silicon nanocrystals up to a diameter of 3.2 nm embedded in an amorphous silicon dioxide matrix. A seemingly conflicting picture arises when the strain field is expressed in terms of bond lengths versus volumetric strain. The strain profile in either case shows uniform behavior in the core, however, it becomes nonuniform within 2-3 Å distance to the nanocrystal surface: tensile for bond lengths whereas compressive for volumetric strain. We reconcile their coexistence by an atomistic strain analysis.
Open Access
Çarpıcıdan bağımsız ortak fark matrisi kullanarak video ve görüntü işleme
(IEEE, 2009-04) Çetin, A. Enis; Duman, Kaan; Tuna, Hakan; Eryıldırım, Abdulkadir
Bu bildiride gerçel sayılar üzerinde yarı grup kuran yeni bir iletmen tanımlayarak elde edilen bir bölge betimleyicisi ile hareketli obje takibi, yüz sezimi, plaka bulma, bölge betimleme için kullanılabilecek hızlı bir algoritma sunuyoruz. Bu yeni iletmen hiçbir çarpma gerektirmez. Bu iletmeni kullanarak, imge bölgelerini nitelendiren ve ortak fark adı verilen bir matris tanımlıyoruz. Plaka bulma uygulamasında ortak fark matrislerinı plaka bölgelerinden kestirip, bunları bir veritabanında saklıyoruz. Plaka bölgelerini gerçek zamanlı videoda tanımlamak için ilk önce videodaki hareketli bölgeleri taşıyan imgeleri belirliyoruz, sonra hareketli bölgelerin içinde ya da bütün resim içinde plaka büyüklüğündeki bölgelerin ortak ayrık matrislerini veritabanındaki plaka ortak ayrık matrisleriyle karşılaştırarak bölge içinde plaka olup olmadığını belirliyoruz.
Open Access
Detection of fungal damaged popcorn using image property covariance features
(Elsevier, 2012) Yorulmaz, O.; Pearson, T. C.; Çetin, A.
Covariance-matrix-based features were applied to the detection of popcorn infected by a fungus that causes a symptom called " blue-eye" . This infection of popcorn kernels causes economic losses due to the kernels' poor appearance and the frequently disagreeable flavor of the popped kernels. Images of kernels were obtained to distinguish damaged from undamaged kernels using image-processing techniques. Features for distinguishing blue-eye-damaged from undamaged popcorn kernel images were extracted from covariance matrices computed using various image pixel properties. The covariance matrices were formed using different property vectors that consisted of the image coordinate values, their intensity values and the first and second derivatives of the vertical and horizontal directions of different color channels. Support Vector Machines (SVM) were used for classification purposes. An overall recognition rate of 96.5% was achieved using these covariance based features. Relatively low false positive values of 2.4% were obtained which is important to reduce economic loss due to healthy kernels being discarded as fungal damaged. The image processing method is not computationally expensive so that it could be implemented in real-time sorting systems to separate damaged popcorn or other grains that have textural differences.
Open Access
Direct evidence for the instability and deactivation of mixed-oxide systems: influence of surface segregation and subsurface diffusion
(2011) Emmez, E.; Vovk, E. I.; Bukhtiyarov V. I.; Ozensoy, E.
In the current contribution, we provide a direct demonstration of the thermally induced surface structural transformations of an alkaline-earth oxide/transition metal oxide interface that is detrimental to the essential catalytic functionality of such mixed-oxide systems toward particular reactants. The BaOx/TiO2/Pt(111) surface was chosen as a model interfacial system where the enrichment of the surface elemental composition with Ti atoms and the facile diffusion of Ba atoms into the underlying TiO2 matrix within 523 873 K leads to the formation of perovskite type surface species (BaTiO3/Ba2TiO4/BaxTiyOz). At elevated temperatures (T > 973 K), excessive surface segregation of Ti atoms results in an exclusively TiO2/TiOx-terminated surface which is almost free of Ba species. Although the freshly prepared BaOx/TiO2/Pt(111) surface can strongly adsorb ubiquitous catalytic adsorbates such as NO2 and CO2, a thermally deactivated surface at T > 973 K practically loses all of its NO2/CO2 adsorption capacity due to the deficiency of surface BaOx domains.
Open Access
Effective preconditioners for large integral-equation problems
(IET, 2007-11) Malas, Tahir; Ergül, Özgür; Gürel, Levent
We consider effective preconditioning schemes for the iterative solution of integral-equation methods. For parallel implementations, the sparse approximate inverse or the iterative solution of the near-field system enables fast convergence up to certain problem sizes. However, for very large problems, the near-field matrix itself becomes too crude approximation to the dense system matrix and preconditioners generated from the near-field interactions cannot be effective. Therefore, we propose an approximation strategy to the multilevel fast multipole algorithm (MLFMA) to be used as a preconditioner. Our numerical experiments reveal that this scheme significantly outperforms other preconditioners. With the combined effort of effective preconditioners and an efficiently parallelized MLFMA, we are able to solve targets with tens of millions of unknowns in a few hours.
Open Access
Experimental and theoretical investigations of electronic and atomic structure of Si-nanocrystals formed in sapphire by ion implantation
(IOP, 2008) Wainstein, D.; Kovalev, A.; Tetelbaum, D.; Mikhailov, A.; Bulutay, Ceyhun; Aydınlı, Atilla
The semiconductor nanocomposites based on Si nanocrystals in dielectric matrices attract a great amount of attention due to their ability for luminescence in visible and near-IR part of the electromagnetic spectrum. Si nanocrystals in sapphire matrix were formed by Si+ ion implantation with doses from 5×1016 to 3×1017 cm -2 at an accelerating voltage 100 kV and post-implantation annealing at 500-1100 d̀C for 2 hours. Depth distribution of lattice defects, impurities and Si nanocrystals, the peculiarities of interband electronic transitions were investigated by XPS and HREELS. The molecular orbitals and local electronic structure of the Al2O3 matrix with Si nanocrystals was calculated using an atomistic pseudopotential technique. The electronic structure of Si nanocrystals as determined from HREELS measurements is in good agreement with the theoretically calculated electronic structure for Si nanocrystals.
Open Access
Integrable discrete systems on R and related dispersionless systems
(American Institute of Physics, 2008) Blaszak, M.; Gurses, M.; Silindir, B.; Szablikowski, B. M.
A general framework for integrable discrete systems on ℝ, in particular, containing lattice soliton systems and their q-deformed analogs, is presented. The concept of regular grain structures on R, generated by discrete one-parameter groups of diffeomorphisms, in terms of which one can define algebra of shift operators is introduced. Two integrable hierarchies of discrete chains together with bi-Hamiltonian structures and their continuous limits are constructed. The inverse problem based on the deformation quantization scheme is considered. © 2008 American Institute of Physics.
Open Access
Maximum likelihood estimation of Gaussian mixture models using particle swarm optimization
(IEEE, 2010-08) Arı, Çağlar; Aksoy, Selim
We present solutions to two problems that prevent the effective use of population-based algorithms in clustering problems. The first solution presents a new representation for arbitrary covariance matrices that allows independent updating of individual parameters while retaining the validity of the matrix. The second solution involves an optimization formulation for finding correspondences between different parameter orderings of candidate solutions. The effectiveness of the proposed solutions are demonstrated on a novel clustering algorithm based on particle swarm optimization for the estimation of Gaussian mixture models. © 2010 IEEE.
Open Access
Photopatterning of PMMA films with gold nanoparticles: diffusion of AuCl4-ions
(2010) Yilmaz, E.; Ertas, G.; Bengu, E.; Süzer, Şefik
Photopatterning of poly(methyl methacrylate) (PMMA) films is performed by UV irradiation of the polymer films containing uniformly distributed AuCl 4 - ions. The process reduces the gold ions and leads to production of Au nanoparticles in the irradiated regions at room temperature (RT). Resulting films are investigated with scanning electron microscopy, which revealed, in addition to regions with gold nanoparticles, the presence of "ion-depleted regions". These regions are formed at RT and within the rigid polymer matrix by diffusion of gold ions toward the irradiated regions, ending up with no or very little gold moieties, which are important for prevention of delayed processes for postgeneration of unwanted features, if and when such materials are utilized for device production. Further investigations performed by fluorescence and Raman measurements and XPS mapping give additional evidence supporting the existence of such regions. Similar regions are also observed within the poly(vinyl alcohol) (PVAL) films. The ion-depleted regions are about 10 μm wide, which is a significant length for the metal ions to travel through a rigid matrix like PMMA (or PVAL) at room temperature and raises important questions as to the diffusion mechanism(s) of the metal ions and to the nature of the driving force(s).
Open Access
Signal processing problems and algorithms in display side of 3DTV
(IEEE, 2006-10) Ulusoy, E.; Esmer, Gökhan Bora; Özaktaş, Haldun M.; Onural, Levent; Gotchev, A.; Uzunov, V.
Two important signal processing problems in the display side of a holographic 3DTV are the computation of the diffraction field of a 3D object from its abstract representation, and determination of the best display configuration to synthesize some intended light distribution. To solve the former problem, we worked on the computation of ID diffraction patterns from discrete data distributed over 2D space. The problem is solved using matrix pseudo-inversion which dominates the computational complexity. Then, the light field synthesis problem by a deflectable mirror array device (DMAD) is posed as a constrained linear optimization problem. The formulation makes direct application of common optimization algorithms quite easy. The simulations indicate that developed methods are promising. ©2006 IEEE.