303,245 research outputs found

    Dynamic Matrix-Fracture Transfer Behaviour in Dual-Porosity Models

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    Imperial Users onl

    Closed expression of the interaction kernel in the Bethe-Salpeter equation for quark-antiquark bound states

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    The interaction kernel in the Bethe-Salpeter equation for quark-antiquark bound states is derived from the Bethe-Salpeter equations satisfied by the quark-antiquark four-point Green's function. The latter equations are established based on the equations of motion obeyed by the quark and antiquark propagators, the four-point Green's function and some other kinds of Green's functions which follow directly from the QCD generating functional. The B-S kernel derived is given an exact and explicit expression which contains only a few types of Green's functions. This expression is not only convenient for perturbative calculations, but also suitable for nonperturbative investigations.Comment: 27 pages,no figure

    Classification of derivation-simple color algebras related to locally finite derivations

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    We classify the pairs (A,D)(A,D) consisting of an (ϵ,Γ)(\epsilon,\Gamma)-olor-commutative associative algebra AA with an identity element over an algebraically closed field FF of characteristic zero and a finite dimensional subspace DD of (ϵ,Γ)(\epsilon,\Gamma)-color-commutative locally finite color-derivations of AA such that AA is Γ\Gamma-graded DD-simple and the eigenspaces for elements of DD are Γ\Gamma-graded. Such pairs are the important ingredients in constructing some simple Lie color algebras which are in general not finitely-graded. As some applications, using such pairs, we construct new explicit simple Lie color algebras of generalized Witt type, Weyl type.Comment: 15 page

    Random walks on the torus with several generators

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    Our paper gives bounds for the rate of convergence for a class of random walks on the d-dimensional torus generated by a set of n vectors in R^d/Z^d. We give bounds on the discrepancy distance from Haar measure; our lower bound holds for all such walks, and if the generators arise from the rows of a "badly approximable" matrix, then there is a corresponding upper bound. The bounds are sharp for walks on the circle.Comment: 10 pages; related work at http://www.math.hmc.edu/~su/papers.htm

    Revisiting Play School: A historical case study of the BBC’s address to the pre-school audience

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    Although clearly recognised in broader institutional histories of British children’s television as a significant moment in the BBC’s address toward the pre-school child, Play School (BBC 1964-88) has not been the focus of sustained archival analysis. This arguably reflects the fact that a good deal of work on children’s television in Britain adopts either an institutional or an audience focus, and the study of programmes cultures is often more neglected. This article seeks to revisit Play School using available historical documentation – including memos, scripts and press cuttings - from the BBC Written Archive Centre, as well as early surviving episodes (principally from 1964). In doing so, it seeks to explore how it fitted into BBC’s historical address to the pre-school child, how it intersected with discourses on pre-school education, and the range of institutional and social contexts surrounding its emergence. Key Words: Play School * Pre-school television * BBC * Child audienc

    Natural evidence for garnet-spinel transition (GST) in the Earth's mantle

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    This study based on compiled world-wide garnet peridotite data confirms the GST in high P and T conditions, which was obtained from Al-free experimental system (MgO-Cr~2~O~3~-SiO~2~) by Klemme (2004). A new spinel-phase peridotite zone, garnet peridotite discontinuous zone, is defined, and another GST, although no experimental data, is principally and presumably proposed to exist. The garnet inclusion-bearing spinel harzburgite from Lashaine (Tanzania) provides the first evidence for the existence of ultra-high spinel zone and is explained as recrystallized minerals hosting the interacted residue of ancient oceanic lithosphere subducted into the great depth of more than 220km. These previously unexpected findings are generating great challenges to phase transition in extreme conditions and to our understanding of layered-structure of the Earth. In addition, coexistent five-phase peridotite is suggested to be naturally useful tool to constrain the GST

    Three Square

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