Browsing by Subject "Computation theory"

Now showing 1 - 19 of 19

Open Access
Block SOR for Kronecker structured representations
(Elsevier, 2004) Buchholz, P.; Dayar, Tuğrul
The Kronecker structure of a hierarchical Markovian model (HMM) induces nested block partitionings in the transition matrix of its underlying Markov chain. This paper shows how sparse real Schur factors of certain diagonal blocks of a given partitioning induced by the Kronecker structure can be constructed from smaller component matrices and their real Schur factors. Furthermore, it shows how the column approximate minimum degree (COLAMD) ordering algorithm can be used to reduce fill-in of the remaining diagonal blocks that are sparse LU factorized. Combining these ideas, the paper proposes three-level block successive over-relaxation (BSOR) as a competitive steady state solver for HMMs. Finally, on a set of numerical experiments it demonstrates how these ideas reduce storage required by the factors of the diagonal blocks and improve solution time compared to an all LU factorization implementation of the BSOR solver. © 2004 Elsevier Inc. All rights reserved.
Open Access
Coherent energetic interfaces accounting for in-plane degradation
(Springer Netherlands, 2016) Esmaeili, A.; Javili, A.; Steinmann, P.
Interfaces can play a dominant role in the overall response of a body. The importance of interfaces is particularly appreciated at small length scales due to large area to volume ratios. From the mechanical point of view, this scale dependent characteristic can be captured by endowing a coherent interface with its own elastic resistance as proposed by the interface elasticity theory. This theory proves to be an extremely powerful tool to explain size effects and to predict the behavior of nano-materials. To date, interface elasticity theory only accounts for the elastic response of coherent interfaces and obviously lacks an explanation for inelastic interface behavior such as damage or plasticity. The objective of this contribution is to extend interface elasticity theory to account for damage of coherent interfaces. To this end, a thermodynamically consistent interface elasticity theory with damage is proposed. A local damage model for the interface is presented and is extended towards a non-local damage model. The non-linear governing equations and the weak forms thereof are derived. The numerical implementation is carried out using the finite element method and consistent tangents are listed. The computational algorithms are given in detail. Finally, a series of numerical examples is studied to provide further insight into the problem and to carefully elucidate key features of the proposed theory. © 2016, Springer Science+Business Media Dordrecht.
Open Access
Consensus as a Nash equilibrium of a dynamic game
(IEEE, 2016) Niazi, Muhammad Umar B.; Özgüler, Arif Bülent; Yıldız, Aykut
Consensus formation in a social network is modeled by a dynamic game of a prescribed duration played by members of the network. Each member independently minimizes a cost function that represents his/her motive. An integral cost function penalizes a member's differences of opinion from the others as well as from his/her own initial opinion, weighted by influence and stubbornness parameters. Each member uses its rate of change of opinion as a control input. This defines a dynamic non-cooperative game that turns out to have a unique Nash equilibrium. Analytic explicit expressions are derived for the opinion trajectory of each member for two representative cases obtained by suitable assumptions on the graph topology of the network. These trajectories are then examined under different assumptions on the relative sizes of the influence and stubbornness parameters that appear in the cost functions.
Open Access
Design and fabrication of CSWAP gate based on nano-electromechanical systems
(Springer, Cham, 2016) Yüksel, Mert; Erbil, Selçuk Oğuz; Arı, Atakan B.; Hanay, M. Selim
In order to reduce undesired heat dissipation, reversible logic offers a promising solution where the erasure of information can be avoided to overcome the Landauer limit. Among the reversible logic gates, Fredkin (CSWAP) gate can be used to compute any Boolean function in a reversible manner. To realize reversible computation gates, Nano-electromechanical Systems (NEMS) offer a viable platform, since NEMS can be produced en masse using microfabrication technology and controlled electronically at high-speeds. In this work-in-progress paper, design and fabrication of a NEMS-based implementation of a CSWAP gate is presented. In the design, the binary information is stored by the buckling direction of nanomechanical beams and CSWAP operation is accomplished through a mechanism which can selectively allow/block the forces from input stages to the output stages. The gate design is realized by fabricating NEMS devices on a Silicon-on-Insulator substrate. © Springer International Publishing Switzerland 2016.
Open Access
Effective early termination techniques for text similarity join operator
(Springer, Berlin, Heidelberg, 2005) Özalp, S. A.; Ulusoy, Özgür
Text similarity join operator joins two relations if their join attributes are textually similar to each other, and it has a variety of application domains including integration and querying of data from heterogeneous resources; cleansing of data; and mining of data. Although, the text similarity join operator is widely used, its processing is expensive due to the huge number of similarity computations performed. In this paper, we incorporate some short cut evaluation techniques from the Information Retrieval domain, namely Harman, quit, continue, and maximal similarity filter heuristics, into the previously proposed text similarity join algorithms to reduce the amount of similarity computations needed during the join operation. We experimentally evaluate the original and the heuristic based similarity join algorithms using real data obtained from the DBLP Bibliography database, and observe performance improvements with continue and maximal similarity filter heuristics. © Springer-Verlag Berlin Heidelberg 2005.
Open Access
Electromagnetically induced left-handedness in a dense gas of three-level atoms
(The American Physical Society, 2004) Oktel, M. Ö.; Müstecaphoǧlu, Ö. E.
Ways in which a three-level system can be used to change the frequency-dependent magnetic permeability of an atomic gas were discussed. The resulting macroscopic electrodynamics was also discussed. The two levels were separated at optical frequencies while having a nonvanishing magnetic dipole matrix element. It was found that such level splittings require large external magnetic fields.
Open Access
Fast-dissolving, prolonged release, and antibacterial cyclodextrin/limonene-inclusion complex nanofibrous webs via polymer-free electrospinning
(American Chemical Society, 2016) Aytac Z.; Yildiz, Z. I.; Kayaci-Senirmak, F.; S. Keskin, N. O.; Kusku, S. I.; Durgun, Engin; Tekinay, T.; Uyar, Tamer
We have proposed a new strategy for preparing free-standing nanofibrous webs from an inclusion complex (IC) of a well-known flavor/fragrance compound (limonene) with three modified cyclodextrins (HPβCD, MβCD, and HPγCD) via electrospinning (CD/limonene-IC-NFs) without using a polymeric matrix. The experimental and computational modeling studies proved that the stoichiometry of the complexes was 1:1 for CD/limonene systems. MβCD/limonene-IC-NF released much more limonene at 37, 50, and 75 °C than HPβCD/limonene-IC-NF and HPγCD/limonene-IC-NF because of the greater amount of preserved limonene. Moreover, MβCD/limonene-IC-NF has released only 25% (w/w) of its limonene, whereas HPβCD/limonene-IC-NF and HPγCD/limonene-IC-NF released 51 and 88% (w/w) of their limonene in 100 days, respectively. CD/limonene-IC-NFs exhibited high antibacterial activity against E. coli and S. aureus. The water solubility of limonene increased significantly and CD/limonene-IC-NFs were dissolved in water in a few seconds. In brief, CD/limonene-IC-NFs with fast-dissolving character enhanced the thermal stability and prolonged the shelf life along with antibacterial properties could be quite applicable in food and oral care applications.
Open Access
Generalised logic program transformation schemas
(Springer, 1998-07) Büyükyıldız, Halime; Flener, Pierre
Schema-based logic program transformation has proven to be an eective technique for the optimisation of programs. This paper results from the research that began by investigating the suggestions in [11] to construct a more general database of transformation schemas for optimising logic programs at the declarative level. The proposed transformation schemas fully automate accumulator introduction (also known as descending computational generalisation), tupling generalisation (a special case of structural generalisation), and duality laws (which are extensions to relational programming of the rst duality law of the fold operators in functional programming). The schemas are proven correct. A prototype schema-based transformation system is evaluated. © Springer-Verlag Berlin Heidelberg 1998.
Open Access
Heuristics for scheduling file-sharing tasks on heterogeneous systems with distributed repositories
(Academic Press, 2007) Kaya, K.; Uçar, B.; Aykanat, Cevdet
We consider the problem of scheduling an application on a computing system consisting of heterogeneous processors and data repositories. The application consists of a large number of file-sharing otherwise independent tasks. The files initially reside on the repositories. The processors and the repositories are connected through a heterogeneous interconnection network. Our aim is to assign the tasks to the processors, to schedule the file transfers from the repositories, and to schedule the executions of tasks on each processor in such a way that the turnaround time is minimized. We propose a heuristic composed of three phases: initial task assignment, task assignment refinement, and execution ordering. We experimentally compare the proposed heuristics with three well-known heuristics on a large number of problem instances. The proposed heuristic runs considerably faster than the existing heuristics and obtains 10-14% better turnaround times than the best of the three existing heuristics. © 2006 Elsevier Inc. All rights reserved.
Open Access
Hypersolver: a graphical tool for commonsense set theory
(Elsevier, 1995) Pakkan, M.; Akman, V.
This paper investigates an alternative set theory (due to Aczel) called the Hyperset Theory. Aczel uses a graphical representation for sets and thereby allows the representation of non-well-founded sets. A program, called hypersolver, which can solve systems of equations defined in terms of sets in the universe of this new theory is presented. This may be a useful tool for commonsense reasoning. © 1995.
Open Access
Joint mixability of some integer matrices
(Elsevier B.V., 2016) Bellini, F.; Karaşan, O. E.; Pınar, M. Ç.
We study the problem of permuting each column of a given matrix to achieve minimum maximal row sum or maximum minimal row sum, a problem of interest in probability theory and quantitative finance where quantiles of a random variable expressed as the sum of several random variables with unknown dependence structure are estimated. If the minimum maximal row sum is equal to the maximum minimal row sum the matrix has been termed jointly mixable (see e.g. Haus (2015), Wang and Wang (2015), Wang et al. (2013)). We show that the lack of joint mixability (the joint mixability gap) is not significant, i.e., the gap between the minimum maximal row sum and the maximum minimal row sum is either zero or one for a class of integer matrices including binary and complete consecutive integers matrices. For integer matrices where all entries are drawn from a given set of discrete values, we show that the gap can be as large as the difference between the maximal and minimal elements of the discrete set. The aforementioned result also leads to a polynomial-time approximation algorithm for matrices with restricted domain. Computing the gap for a {0,1,2}-matrix is proved to be equivalent to finding column permutations minimizing the difference between the maximum and minimum row sums. A polynomial procedure for computing the optimum difference by solving the maximum flow problem on an appropriate graph is given. © 2016 Elsevier B.V. All rights reserved.
Open Access
Local current distribution at large quantum dots (QDs): A self-consistent screening model
(Elsevier B.V., 2008) Krishna, P. M.; Siddiki, A.; Güven, K.; Hakioǧlu T.
We report the implementation of the self-consistent Thomas-Fermi screening theory, together with the local Ohm's law to a quantum dot system in order to obtain local current distribution within the dot and at the leads. We consider a large dot (size > 700 nm) defined by split gates, and coupled to the leads. Numerical calculations show that the non-dissipative current is confined to the incompressible strips. Due to the non-linear screening properties of the 2DES at low temperatures, this distribution is highly sensitive to external magnetic field. Our findings support the phenomenological models provided by the experimental studies so far, where the formation of the (direct) edge channels dominate the transport.
Open Access
On Lempel-Ziv complexity of sequences
(Springer, Berlin, Heidelberg, 2006) Doǧanaksoy, A.; Göloǧlu, Faruk
We derive recurrences for counting the number a(n, r) of sequences of length n with Lempel-Ziv complexity r, which has important applications, for instance testing randomness of binary sequences. We also give algorithms to compute these recurrences. We employed these algorithms to compute a(n, r) and expected value. EPn, of number of patterns of a sequence of length n, for relatively large n. We offer a randomness test based on the algorithms to be used for testing randomness of binary sequences. We give outputs of the algorithms for some n. We also provide results of the proposed test applied to the outputs of contestant stream ciphers of ECRYPT's eSTREAM. © Springer-Verlag Berlin Heidelberg 2006.
Open Access
Polyhedral analysis for concentrator location problems
(Springer, 2006) Labbé, M.; Yaman, H.
The concentrator location problem is to choose a subset of a given terminal set to install concentrators and to assign each remaining terminal node to a concentrator to minimize the cost of installation and assignment. The concentrators may have capacity constraints. We study the polyhedral properties of concentrator location problems with different capacity structures. We develop a branch and cut algorithm and present computational results.
Open Access
Some asymptotics for extremal polynomials
(Springer, 2016) Alpan, Gökalp; Goncharov, Alexander; Hatinoğlu, B.
We review some asymptotics for Chebyshev polynomials and orthogonal polynomials. Our main interest is in the behaviour of Widom factors for the Chebyshev and the Hilbert norms on small sets such as generalized Julia sets.
Open Access
A unified approach to universal prediction: Generalized upper and lower bounds
(Institute of Electrical and Electronics Engineers Inc., 2015) Vanli, N. D.; Kozat, S. S.
We study sequential prediction of real-valued, arbitrary, and unknown sequences under the squared error loss as well as the best parametric predictor out of a large, continuous class of predictors. Inspired by recent results from computational learning theory, we refrain from any statistical assumptions and define the performance with respect to the class of general parametric predictors. In particular, we present generic lower and upper bounds on this relative performance by transforming the prediction task into a parameter learning problem. We first introduce the lower bounds on this relative performance in the mixture of experts framework, where we show that for any sequential algorithm, there always exists a sequence for which the performance of the sequential algorithm is lower bounded by zero. We then introduce a sequential learning algorithm to predict such arbitrary and unknown sequences, and calculate upper bounds on its total squared prediction error for every bounded sequence. We further show that in some scenarios, we achieve matching lower and upper bounds, demonstrating that our algorithms are optimal in a strong minimax sense such that their performances cannot be improved further. As an interesting result, we also prove that for the worst case scenario, the performance of randomized output algorithms can be achieved by sequential algorithms so that randomized output algorithms do not improve the performance. © 2012 IEEE.
Open Access
V. Lifschitz, ed., formalizing common sense: papers by John McCarthy
(Elsevier BV, 1995) Akman, V.
A review is presented of Lifschitz's collection of seventeen papers written by McCarthy on the subject of common sense. The book opens with a fine overview of McCarthy's research in artificial intelligence (AI). Lifschitz offers an admirably succinct account of the development of McCarthy's ideas on common sense from the early days of AI to his current work. Lifschitz's introduction is especially useful in appreciating the dramatically original and permanently influential nature of McCarthy's work. While McCarthy's papers collected in this volume were written over the span of almost three decades, Lifschitz correctly observes that the underlying concern has always been the same: to understand and model the intellectual ability realized by human common sense.
Open Access
Watermarking based on discrete wavelet transform and q-deformed chaotic map
(Elsevier Ltd, 2017) Behnia, Sohrab; Yahyavi, Mohammad; Habibpourbisafar, Reza
Hierarchy of one-dimensional ergodic chaotic maps with Tsallis type of q-deformation are studied. We find that in the chaotic region, these maps with q-deformation are ergodic as the Birkhoff ergodic theorem predicts. q-deformed maps are defined as ratios of polynomials of degree N. Hence, by using the Stieltjes transform approach (STA), invariant measure is proposed. In addition, considering Sinai-Ruelle-Bowen (SRB) measure, Kolmogorov-Sinai (KS) entropy for q-deformed maps is calculated analytically. The new q-deformed scheme have ability to keep previous significant properties such as ergodicity, sensitivity to initial condition. By adding q-parameter to the hierarchy in order increase the randomness and one-way computation, we present a new scheme for watermarking. The introduced algorithm tries to improve the problem of failure of encryption such as small key space, encryption speed and level of security. To illustrate the effectiveness of the proposed scheme, some security analyses are presented. By considering the obtained results, it can be concluded that, this scheme have a high potential to be adopted for watermarking. It can be concluded that, the proposed novel watermarking scheme for image authentication can be applied for practical applications. © 2017 Elsevier Ltd
Open Access
A web-site-based partitioning technique for reducing preprocessing overhead of parallel PageRank computation
(Springer, Berlin, Heidelberg, 2007) Cevahir, Ali; Aykanat, Cevdet; Turk, Ata; Cambazoğlu, B. Barla
A power method formulation, which efficiently handles the problem of dangling pages, is investigated for parallelization of PageRank computation. Hypergraph-partitioning-based sparse matrix partitioning methods can be successfully used for efficient parallelization. However, the preprocessing overhead due to hypergraph partitioning, which must be repeated often due to the evolving nature of the Web, is quite significant compared to the duration of the PageRank computation. To alleviate this problem, we utilize the information that sites form a natural clustering on pages to propose a site-based hypergraph-partitioning technique, which does not degrade the quality of the parallelization. We also propose an efficient parallelization scheme for matrix-vector multiplies in order to avoid possible communication due to the pages without in-links. Experimental results on realistic datasets validate the effectiveness of the proposed models. © Springer-Verlag Berlin Heidelberg 2007.