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  • Mathematics  (49)
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  • Articles  (49)
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  • 1
    Publication Date: 2015-08-21
    Description: Smoothing splines provide flexible nonparametric regression estimators. However, the high computational cost of smoothing splines for large datasets has hindered their wide application. In this article, we develop a new method, named adaptive basis sampling, for efficient computation of smoothing splines in super-large samples. Except for the univariate case where the Reinsch algorithm is applicable, a smoothing spline for a regression problem with sample size n can be expressed as a linear combination of n basis functions and its computational complexity is generally O ( n 3 ). We achieve a more scalable computation in the multivariate case by evaluating the smoothing spline using a smaller set of basis functions, obtained by an adaptive sampling scheme that uses values of the response variable. Our asymptotic analysis shows that smoothing splines computed via adaptive basis sampling converge to the true function at the same rate as full basis smoothing splines. Using simulation studies and a large-scale deep earth core-mantle boundary imaging study, we show that the proposed method outperforms a sampling method that does not use the values of response variables.
    Print ISSN: 0006-3444
    Electronic ISSN: 1464-3510
    Topics: Biology , Mathematics , Medicine
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  • 2
    Publication Date: 2015-09-15
    Description: This paper deals with the distributed robust output regulation problem for the multi-agent systems with general nonlinear dynamics and uncertainty parameters. Assume that the information of active leaders or environmental disturbances cannot be completely measurable for all other agents. By employing the centre manifold theory and characteristics of the agents’ communication, the nonlinear distributed dynamic feedback controllers are designed to make the agents asymptotically track the references or reject the disturbance signals, which are generated by the exosystem. Two numerical examples are provided to show the effectiveness of the main results.
    Print ISSN: 0265-0754
    Electronic ISSN: 1471-6887
    Topics: Mathematics
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  • 3
    Publication Date: 2016-01-10
    Description: As known from the theory of centre manifolds, it is important to approximate invariant manifolds when discussing high order terms of the reduced systems in the investigation of bifurcations. In this paper, we give a method to approximate invariant manifolds which are obtained under pseudo-hyperbolicity. This method enables us to avoid the trouble of increasing dimension of the so-called approximate inertial manifold for smaller thickness of attractive neighbourhood. Unlike centre manifolds, exponential expansion and contraction may exist on such manifolds. Consequently, the technique of the contraction principle cannot be used directly. We not only overcome the difficulty so as to approximate such $C^{1}$ manifolds at a possibly higher order but also estimate, for non-local bifurcations, the lower bound of their locality radius such that the approximation is valid. Our approximation is demonstrated by examples of a wave equation and an ordinary differential equation.
    Print ISSN: 0272-4960
    Electronic ISSN: 1464-3634
    Topics: Mathematics
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  • 4
    Publication Date: 2015-07-16
    Description: This paper is concerned with the spatial dynamics of a time-delayed reaction and diffusion malaria model. We first analyse the well-posedness of the initial-boundary value problem of the model. Then, we study the global stability of the disease-free or endemic steady state for the system by structuring two Lyapunov functionals. Moreover, by applying Schauder fixed-point theorem, we establish the existence of travelling wave solutions connecting the two steady states: the disease-free steady state and the endemic steady state if the basic reproduction ratio $\mathcal {R}_0 〉 1$ , and show the non-existence of travelling wave solutions connecting the disease-free steady state to itself if $\mathcal {R}_0 〈 1$ . Our analytic results show that $\mathcal {R}_0$ is a threshold value for global dynamics and the existence of travelling wave solutions to the malaria model.
    Print ISSN: 0272-4960
    Electronic ISSN: 1464-3634
    Topics: Mathematics
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  • 5
    Publication Date: 2016-03-27
    Description: In this paper, we present a model for supply chain network design (SCND) with anticipation of variable delivered price competition in markets under deterministic and price-dependent demands and with the presence of rivals. The objective is to design a new SC under a capacity constraint in order to maximize the future profit of the SC in competing markets. The structure of the network of the new SC is assumed to be set ‘once and for all’ as a strategic decision; then the price adjustment is possible throughout the course of the competition as a decision at the operation level. In this paper, a new model for oligopolistic competitive SCND is proposed for each of the following two strategies: (1) ‘single product strategy’ and (2) ‘substitutable product strategy’. Finally, we illustrate the model through several numerical examples.
    Print ISSN: 1471-678X
    Electronic ISSN: 1471-6798
    Topics: Mathematics
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  • 6
    Publication Date: 2013-03-15
    Description: This paper investigates behaviors of flows driven by tangential velocity and shear stress on their boundaries such as solid walls and water surfaces. In a steady flow between two parallel plates with one of them in motion, analytic solutions are the same when a velocity and a shear stress boundary condition are applied on the moving plate. For an unsteady, impulsively started flow, however, analysis shows that solutions for velocity profiles as well as energy transferring and dissipation are different under the two boundary conditions. In an air-water flow, if either a velocity or a stress condition is imposed at the air-water interface, the problem becomes ill-posed because it has multiple solutions. Only when both of the conditions are specified, it will have a unique solution. Numerical simulations for cavity flows are made to confirm the theoretical results; a tangential velocity and a shear stress boundary condition introduce distinct flows if one considers an unsteady flow, whereas the two conditions lead to a same solution if one simulates a steady flow. The results in this paper imply that discretion is needed on selection of boundary conditions to approximate forcing on fluid boundaries such as wind effects on surfaces of coastal ocean waters.
    Print ISSN: 1024-123X
    Electronic ISSN: 1563-5147
    Topics: Mathematics , Technology
    Published by Hindawi
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Combinatorica 12 (1992), S. 1-17 
    ISSN: 1439-6912
    Keywords: 05 A 20 ; 52 C 17 ; 05 D 05
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We determine in almost all Manhattan lattices configurations, which for specified diameter have maximal cardinality. Cases, in which those configurations are spheres, have been studied recently by Kleitman and Fellows. For Hamming spaces we present a partial result supplementing a result of Frankl and Füredi and we formulate a general conjecture.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Zeitschrift für angewandte Mathematik und Physik 49 (1998), S. 506-513 
    ISSN: 0044-2275
    Keywords: Key words. Differential equation, nonlinear, singular, draining flow.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract. A mathematical analysis is given of a boundary value problem which arises in the model for flows draining down a dry vertical wall. Questions about existence and qualitative properties of solutions are discussed. An explicit solution is found.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 38 (1995), S. 2033-2053 
    ISSN: 0029-5981
    Keywords: Gurson model ; numerical algorithms ; consistent tangent moduli ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We investigate the generalized mid-point algorithms for the integration of elastoplastic constitutive equations for the pressure-dependent Gurson-Tvergaard yield model. By exact linearization of the algorithms and decomposition of the stresses into hydrostatic and deviatoric parts, a formula for explicitly calculating the consistent tangent moduli with the generalized mid-point algorithms is derived for the Gurson-Tvergaard model. The generalized mid-point algorithms, together with the consistent tangent moduli, have been implemented into ABAQUS via the user material subroutine. An analytical solution of the Gurson-Tvergaard model for the plane strain tension case is given and the performances of the generalized mid-point algorithms have been assessed for plane strain tension and hydrostatic tension problems and compared with the exact solutions. We find that, in the two problems considered, the generalized mid-point algorithms give reasonably good accuracy even for the case using very large time increment steps, with the true mid-point algorithm (α = 0·5) the most accurate one. Considering the extra non-symmetrical property of the consistent tangent moduli of the algorithms with α 〈 1, the Euler backward algorithm (α = 1) is, perhaps, the best choice.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Publication Date: 2013-02-13
    Print ISSN: 0022-3239
    Electronic ISSN: 1573-2878
    Topics: Mathematics
    Published by Springer
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