111,273 research outputs found

    A connection element for modelling end-plate connections in fire

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    In this paper a robust 2-noded connection element has been developed for modelling the bolted end-plate connection between a steel beam and column at elevated temperatures. The connection element allows the element nodes to be placed at the reference plane with offset and the non-uniform temperature distributions within the connection. In this model the connection failure due to bending, axial tension, compression and vertical shear are considered. The influence of the axial tensile force of the connected beam on the connection is also taken into account. This model has the advantages of both the previous simple and component-based models. A total of 23 fire tests were used to extensively validate the model. It can be seen that the current model is robust and has a capability to predict the behaviour of a bolted end-plate connection under fire attack with reasonable accuracy. Compared to the tested results the predictions of the current model were mainly on the conservative side. Hence, the model can be used for structural fire engineering design on steel-framed composite buildings. The idea described in this paper can also easily be applied to develop other kinds of connections, such as simple connections, column based connections or hollow section connections, and so on. (c) 2010 Elsevier Ltd. All rights reserved

    Codes Cross-Correlation Impact on S-curve Bias and Data-Pilot Code Pairs Optimization for CBOC Signals

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    The aim of this paper is to analyze the impact of spreading codes cross-correlation on code tracking performance, and to optimize the data-pilot code pairs of Galileo E1 Open Service (OS) Composite Binary Offset Carrier (CBOC) signals. The distortion of the discriminator function (i.e., S-curve), due to data and pilot spreading codes cross-correlation properties, is evaluated when only the data or pilot components of CBOC signals are tracked, considering the features of the modulation schemes. Analyses show that the S-curve bias also depends on the receiver configuration (e.g., the tracking algorithm and correlator spacing). In this paper, two methods are proposed to optimize the data-pilot code pairs of Galileo E1 OS. The optimization goal is to obtain minimum average S-curve biases when tracking only the pilot components of CBOC signals for the specific correlator spacing. The S-curve biases after optimization processes are analyzed and compared with the un-optimized results. It is shown that the optimized data-pilot code pairs could significantly mitigate the intra-channel (i.e., data and pilot) codes cross-correlation,and then improve the code tracking performance of CBOC signals

    The tensor structure on the representation category of the Wp\mathcal{W}_p triplet algebra

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    We study the braided monoidal structure that the fusion product induces on the abelian category Wp\mathcal{W}_p-mod, the category of representations of the triplet WW-algebra Wp\mathcal{W}_p. The Wp\mathcal{W}_p-algebras are a family of vertex operator algebras that form the simplest known examples of symmetry algebras of logarithmic conformal field theories. We formalise the methods for computing fusion products, developed by Nahm, Gaberdiel and Kausch, that are widely used in the physics literature and illustrate a systematic approach to calculating fusion products in non-semi-simple representation categories. We apply these methods to the braided monoidal structure of Wp\mathcal{W}_p-mod, previously constructed by Huang, Lepowsky and Zhang, to prove that this braided monoidal structure is rigid. The rigidity of Wp\mathcal{W}_p-mod allows us to prove explicit formulae for the fusion product on the set of all simple and all projective Wp\mathcal{W}_p-modules, which were first conjectured by Fuchs, Hwang, Semikhatov and Tipunin; and Gaberdiel and Runkel.Comment: 58 pages; edit: added references and revisions according to referee reports. Version to appear on J. Phys.

    Open-closed field algebras

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    We introduce the notions of open-closed field algebra and open-closed field algebra over a vertex operator algebra V. In the case that V satisfies certain finiteness and reductivity conditions, we show that an open-closed field algebra over V canonically gives an algebra over a \C-extension of the Swiss-cheese partial operad. We also give a tensor categorical formulation and categorical constructions of open-closed field algebras over V.Comment: 55 pages, largely revised, an old subsection is deleted, a few references are adde

    Vertex operator algebras, the Verlinde conjecture and modular tensor categories

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    Let V be a simple vertex operator algebra satisfying the following conditions: (i) The homogeneous subspaces of V of weights less than 0 are 0, the homogeneous subspace of V of weight 0 is spanned by the vacuum and V' is isomorphic to V as a V-module. (ii) Every weak V-module gradable by nonnegative integers is completely reducible. (iii) V is C_2-cofinite. We announce a proof of the Verlinde conjecture for V, that is, of the statement that the matrices formed by the fusion rules among irreducible V-modules are diagonalized by the matrix given by the action of the modular transformation \tau\mapsto -1/\tau on the space of characters of irreducible V-modules. We discuss some consequences of the Verlinde conjecture, including the Verlinde formula for the fusion rules, a formula for the matrix given by the action of \tau\mapsto -1/\tau and the symmetry of this matrix. We also announce a proof of the rigidity and nondegeneracy property of the braided tensor category structure on the category of V-modules when V satisfies in addition the condition that irreducible V-modules not equivalent to V has no nonzero elements of weight 0. In particular, the category of V-modules has a natural structure of modular tensor category.Comment: 18 pages. To appear in the Proc. Natl. Acad. Sci. US

    Bootstrap consistency for general semiparametric MM-estimation

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    Consider MM-estimation in a semiparametric model that is characterized by a Euclidean parameter of interest and an infinite-dimensional nuisance parameter. As a general purpose approach to statistical inferences, the bootstrap has found wide applications in semiparametric MM-estimation and, because of its simplicity, provides an attractive alternative to the inference approach based on the asymptotic distribution theory. The purpose of this paper is to provide theoretical justifications for the use of bootstrap as a semiparametric inferential tool. We show that, under general conditions, the bootstrap is asymptotically consistent in estimating the distribution of the MM-estimate of Euclidean parameter; that is, the bootstrap distribution asymptotically imitates the distribution of the MM-estimate. We also show that the bootstrap confidence set has the asymptotically correct coverage probability. These general conclusions hold, in particular, when the nuisance parameter is not estimable at root-nn rate, and apply to a broad class of bootstrap methods with exchangeable bootstrap weights. This paper provides a first general theoretical study of the bootstrap in semiparametric models.Comment: Published in at http://dx.doi.org/10.1214/10-AOS809 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org