43,637 research outputs found

    Automatic fault correction system for parallel signal channels Patent

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    Error correction circuitry for binary signal channel

    Simplified circuit corrects faults in parallel binary information channels

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    Corrective circuit prevents the appearance of erroneous output signals from the possible failure of any single-channel element interconnected in parallel binary information channels. The circuit is simplified and economical because it does not use redundant channels

    Downlink beamforming for cellular mobile communications

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    A new technique for downlink transmission beamformer design in cellular mobile communications systems using an antenna array at the base station is presented. The method is based on estimation of an underlying spatial distribution associated with each source's spatial downlink channel. The algorithm isPeer ReviewedPostprint (published version

    A forward view on reliable computers for flight control

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    The requirements for fault-tolerant computers for flight control of commercial aircraft are examined; it is concluded that the reliability requirements far exceed those typically quoted for space missions. Examination of circuit technology and alternative computer architectures indicates that the desired reliability can be achieved with several different computer structures, though there are obvious advantages to those that are more economic, more reliable, and, very importantly, more certifiable as to fault tolerance. Progress in this field is expected to bring about better computer systems that are more rigorously designed and analyzed even though computational requirements are expected to increase significantly

    Stable subnorms revisited

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    Let A be a finite-dimensional, power-associative algebra over a field F, either R or C, and let S, a subset of A, be closed under scalar multiplication. A real-valued function f defined on S, shall be called a subnorm if f(a) > 0 for all 0 not equal a is an element of S, and f(alpha a) = |alpha| f(a) for all a is an element of S and alpha is an element of F. If in addition, S is closed under raising to powers, then a subnorm f shall be called stable if there exists a constant sigma > 0 so that f(a(m)) less than or equal to sigma f(a)(m) for all a is an element of S and m = 1, 2, 3.... The purpose of this paper is to provide an updated account of our study of stable subnorms on subsets of finite-dimensional, power-associative algebras over F. Our goal is to review and extend several of our results in two previous papers, dealing mostly with continuous subnorms on closed sets

    Exact Nonperturbative Unitary Amplitudes for 1->N Transitions

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    I present an extension to arbitrary N of a previously proposed field theoretic model, in which unitary amplitudes for 1>81->8 processes were obtained. The Born amplitude in this extension has the behavior A(1>N)tree = gN1 N!A(1->N)^{tree}\ =\ g^{N-1}\ N! expected in a bosonic field theory. Unitarity is violated when A(1>N)>1|A(1->N)|>1, or when N>Ncrite/g.N>\N_crit\simeq e/g. Numerical solutions of the coupled Schr\"odinger equations shows that for weak coupling and a large range of N>\ncrit, the exact unitary amplitude is reasonably fit by a factorized expression |A(1->N)| \sim (0.73 /N) \cdot \exp{(-0.025/\g2)}. The very small size of the coefficient 1/\g2 , indicative of a very weak exponential suppression, is not in accord with standard discussions based on saddle point analysis, which give a coefficient 1. \sim 1.\ The weak dependence on NN could have experimental implications in theories where the exponential suppression is weak (as in this model). Non-perturbative contributions to few-point correlation functions in this theory would arise at order $K\ \simeq\ \left((0.05/\g2)+ 2\ ln{N}\right)/ \ ln{(1/\g2)}inanexpansioninpowersof in an expansion in powers of \g2.$Comment: 11 pages, 3 figures (not included

    Galaxy-Galaxy Flexion: Weak Lensing to Second Order

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    In this paper, we develop a new gravitational lensing inversion technique. While traditional approaches assume that the lensing field varies little across a galaxy image, we note that this variation in the field can give rise to a ``Flexion'' or bending of a galaxy image, which may then be used to detect a lensing signal with increased signal to noise. Since the significance of the Flexion signal increases on small scales, this is ideally suited to galaxy-galaxy lensing. We develop an inversion technique based on the ``Shapelets'' formalism of Refregier (2003). We then demonstrate the proof of this concept by measuring a Flexion signal in the Deep Lens Survey. Assuming an intrinsically isothermal distribution, we find from the Flexion signal alone a velocity width of v_c=221\pm 12 km/s for lens galaxies of r < 21.5, subject to uncertainties in the intrinsic Flexion distribution.Comment: 11 pages, Latex, 4 figures. Accepted by ApJ, changes include revision of errors from previous draf

    Learning Convex Partitions and Computing Game-theoretic Equilibria from Best Response Queries

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    Suppose that an mm-simplex is partitioned into nn convex regions having disjoint interiors and distinct labels, and we may learn the label of any point by querying it. The learning objective is to know, for any point in the simplex, a label that occurs within some distance ϵ\epsilon from that point. We present two algorithms for this task: Constant-Dimension Generalised Binary Search (CD-GBS), which for constant mm uses poly(n,log(1ϵ))poly(n, \log \left( \frac{1}{\epsilon} \right)) queries, and Constant-Region Generalised Binary Search (CR-GBS), which uses CD-GBS as a subroutine and for constant nn uses poly(m,log(1ϵ))poly(m, \log \left( \frac{1}{\epsilon} \right)) queries. We show via Kakutani's fixed-point theorem that these algorithms provide bounds on the best-response query complexity of computing approximate well-supported equilibria of bimatrix games in which one of the players has a constant number of pure strategies. We also partially extend our results to games with multiple players, establishing further query complexity bounds for computing approximate well-supported equilibria in this setting.Comment: 38 pages, 7 figures, second version strengthens lower bound in Theorem 6, adds footnotes with additional comments and fixes typo

    Robust beamforming for interference rejection in mobile communications

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    The problem of robust beamformer design in the presence of moving sources is considered. A new technique based on a generalization of the constrained minimum variance beamformer is proposed. The method explicitly takes into account changes in the scenario due to the movement of the desired and interfering sources, requiring only estimation of the desired DOA. Computer simulations show that the resulting performance constitutes a compromise between interference and noise rejection, computational complexity, and sensitivity to source movement.Peer ReviewedPostprint (published version
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