47,638 research outputs found

    Geometric phase and gauge theory structure in quantum computing

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    We discuss the presence of a geometrical phase in the evolution of a qubit state and its gauge structure. The time evolution operator is found to be the free energy operator, rather than the Hamiltonian operator.Comment: 5 pages, presented at Fifth International Workshop DICE2010: Space-Time-Matter - current issues in quantum mechanics and beyond, Castiglioncello (Tuscany), September 13-17, 201

    Hierarchical inference of disparity

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    Disparity selective cells in V1 respond to the correlated receptive fields of the left and right retinae, which do not necessarily correspond to the same object in the 3D scene, i.e., these cells respond equally to both false and correct stereo matches. On the other hand, neurons in the extrastriate visual area V2 show much stronger responses to correct visual matches [Bakin et al, 2000]. This indicates that a part of the stereo correspondence problem is solved during disparity processing in these two areas. However, the mechanisms employed by the brain to accomplish this task are not yet understood. Existing computational models are mostly based on cooperative computations in V1 [Marr and Poggio 1976, Read and Cumming 2007], without exploiting the potential benefits of the hierarchical structure between V1 and V2. Here we propose a two-layer graphical model for disparity estimation from stereo. The lower layer matches the linear responses of neurons with Gabor receptive fields across images. Nodes in the upper layer infer a sparse code of the disparity map and act as priors that help disambiguate false from correct matches. When learned on natural disparity maps, the receptive fields of the sparse code converge to oriented depth edges, which is consistent with the electrophysiological studies in macaque [von der Heydt et al, 2000]. Moreover, when such a code is used for depth inference in our two layer model, the resulting disparity map for the Tsukuba stereo pair [middlebury database] has 40% less false matches than the solution given by the first layer. Our model offers a demonstration of the hierarchical disparity computation, leading to testable predictions about V1-V2 interactions

    Approximation by the Dickman distribution and quasi-logarithmic combinatorial structures

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    Quasi-logarithmic combinatorial structures are a class of decomposable combinatorial structures which extend the logarithmic class considered by Arratia, Barbour and Tavar\'{e} (2003). In order to obtain asymptotic approximations to their component spectrum, it is necessary first to establish an approximation to the sum of an associated sequence of independent random variables in terms of the Dickman distribution. This in turn requires an argument that refines the Mineka coupling by incorporating a blocking construction, leading to exponentially sharper coupling rates for the sums in question. Applications include distributional limit theorems for the size of the largest component and for the vector of counts of the small components in a quasi-logarithmic combinatorial structure.Comment: 22 pages; replaces earlier paper [arXiv:math/0609129] with same title by Bruno Nietlispac

    A survey of visual preprocessing and shape representation techniques

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    Many recent theories and methods proposed for visual preprocessing and shape representation are summarized. The survey brings together research from the fields of biology, psychology, computer science, electrical engineering, and most recently, neural networks. It was motivated by the need to preprocess images for a sparse distributed memory (SDM), but the techniques presented may also prove useful for applying other associative memories to visual pattern recognition. The material of this survey is divided into three sections: an overview of biological visual processing; methods of preprocessing (extracting parts of shape, texture, motion, and depth); and shape representation and recognition (form invariance, primitives and structural descriptions, and theories of attention)
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