1,393 research outputs found

    Rehabilitation of timber bridge piles using a wrapping system

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    The majority of the thousands of timber bridges around Australia are more than 50 years old and strengthen-ing and rehabilitation of deteriorated timber bridges is a strong financial commitment. Therefore it is a timely concern to investigate the rehabilitation process involved. The maintenance cost of timber bridges are affect-ed significantly by a number of deterioration mechanisms, which require a systematic approach for diagnosis and treatment. The techniques used to rehabilitate timber bridges vary depending on the deterioration mecha-nism and location. This research aims at investigating the techniques used in timber pile rehabilitation. The main deterioration mechanism studied in this research is the splitting. An experimental program was carried out to investigate the strength enhancement due to a FRP wrapping system combined with two types of filler material, Crane Rail Grout (CRG) and Underwater Cementitious Grout (UCG). Hardwood timber of grade F27 with 150 mm diameter and 300 mm high samples were used in the testing program. Three levels of dam-age were introduced to the total height, samples were wrapped with FRP system and tested for compression. Load and displacement curves were developed based on the experimental results

    Unification of gravity and electromagnetism revisited

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    Within the context of a 5D5D space-time, we construct a unified theory of gravity and electromagnetism from which the Einstein field equations and Maxwell equations emerge, with homogenous Maxwell equations appearing naturally. We also introduce a well-defined five dimensional energy-momentum tensor consistent with our unification scheme. A correction term appears in Maxwell equations which can be used to explain the recently discovered galactic magnetic fields.Comment: 10 page

    Brane f(R)f(\cal R) gravity

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    We consider a brane world scenario in which the bulk action is assumed to have the form of a generic function of the Ricci scalar f(R)f(\mathcal{R}) and derive the resulting Einstein field equations on the brane. In a constant curvature bulk a conserved geometric quantity appears in the field equations which can be associated with matter. We present cosmological and spherically symmetric solutions by assuming specific forms for f(R)f(\mathcal{R}) and show that the former can explain an accelerated expanding universe while the latter may account for galaxy rotation curves.Comment: 8 pages, 2 figures, to appear in EP

    Lifshitz-type Quantum Field Theories in Particle Physics

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    This introduction to Lifshitz-type field theories reviews some of its aspects in Particle Physics. Attractive features of these models are described with different examples, as the improvement of graphs convergence, the introduction of new renormalizable interactions, dynamical mass generation, asymptotic freedom, and other features related to more specific models. On the other hand, problems with the expected emergence of Lorentz symmetry in the IR are discussed, related to the different effective light cones seen by different particles when they interact.Comment: 26 pages, comments and references adde

    Detailed balance condition and ultraviolet stability of scalar field in Horava-Lifshitz gravity

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    Detailed balance and projectability conditions are two main assumptions when Horava recently formulated his theory of quantum gravity - the Horava-Lifshitz (HL) theory. While the latter represents an important ingredient, the former often believed needs to be abandoned, in order to obtain an ultraviolet stable scalar field, among other things. In this paper, because of several attractive features of this condition, we revisit it, and show that the scalar field can be stabilized, if the detailed balance condition is allowed to be softly broken. Although this is done explicitly in the non-relativistic general covariant setup of Horava-Melby-Thompson with an arbitrary coupling constant λ\lambda, generalized lately by da Silva, it is also true in other versions of the HL theory. With the detailed balance condition softly breaking, the number of independent coupling constants can be still significantly reduced. It is remarkable to note that, unlike other setups, in this da Silva generalization, there exists a master equation for the linear perturbations of the scalar field in the flat Friedmann-Robertson-Walker background.Comment: Some typos are corrected. To appear in JCA

    Effective potential for Lifshitz type z=3 gauge theories

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    We consider the one-loop effective potential at zero temperature in field theories with anisotropic space-time scaling, with critical exponent z=3z=3, including scalar, fermion and gauge fields. The fermion determinant generates a symmetry breaking term at one loop in the effective potential and a local minimum appears, for non zero scalar field, for every value of the Yukawa coupling. Depending on the relative strength of the coupling constants for the scalar and the gauge field, we find a second symmetry breaking local minimum in the effective potential for a bigger value of the scalar field.Comment: 12 pages, 3 figures. Minor corrections in the text, results unchange

    f(R) theories

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    Over the past decade, f(R) theories have been extensively studied as one of the simplest modifications to General Relativity. In this article we review various applications of f(R) theories to cosmology and gravity - such as inflation, dark energy, local gravity constraints, cosmological perturbations, and spherically symmetric solutions in weak and strong gravitational backgrounds. We present a number of ways to distinguish those theories from General Relativity observationally and experimentally. We also discuss the extension to other modified gravity theories such as Brans-Dicke theory and Gauss-Bonnet gravity, and address models that can satisfy both cosmological and local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in Relativity, Published version, Comments are welcom

    Coherent J/psi photoproduction in ultra-peripheral PbPb collisions at root s(NN)=2.76 TeV with the CMS experiment

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    Cross section measurement of t-channel single top quark production in pp collisions at root s=13 TeV

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