55,813 research outputs found

    New Developments in Treacherous Points of Light-Front Dynamics

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    Light-front dynamics(LFD) plays an important role in hadron phenomenology. Last few years, however, it has been emphasized that treacherous points such as zero-mode contributions should be taken into account for successful LFD applications to hadron phenomenology. We discuss examples of treacherous points and present new progresses made last few years to handle them correctly.Comment: 5 pages, espcrc1.sty. proceedings of FB XVIII (August 2006, Brazil), to be published in Nucl. Phys.

    A classification of Lagrangian planes in holomorphic symplectic varieties

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    Classically, an indecomposable class RR in the cone of effective curves on a K3 surface XX is representable by a smooth rational curve if and only if R2=2R^2=-2. We prove a higher-dimensional generalization conjectured by Hassett and Tschinkel: for a holomorphic symplectic variety MM deformation equivalent to a Hilbert scheme of nn points on a K3 surface, an extremal curve class RH2(M,Z)R\in H_2(M,\mathbb{Z}) in the Mori cone is the line in a Lagrangian nn-plane PnM\mathbb{P}^n\subset M if and only if certain intersection-theoretic criteria are met. In particular, any such class satisfies (R,R)=n+32(R,R)=-\frac{n+3}{2} and the primitive such classes are all contained in a single monodromy orbit.Comment: 18 pages, comments welcome. v3: classification extended to all curve classes; some examples added. v4: to appear in J. Inst. Math. Jussie

    New technologies developed for conventional growing systems: possibilities for application in organic systems

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    The End of Epicurean Infinity: Critical Reflections on the Epicurean Infinite Universe

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    In contrast to other ancient philosophers, Epicurus and his followers famously maintained the infinity of matter, and consequently of worlds. This was inferred from the infinity of space, because they believed that a limited amount of matter would inevitably be scattered through infinite space, and hence be unable to meet and form stable compounds. By contrast, the Stoics claimed that there was only a finite amount of matter in infinite space, which stayed together because of a general centripetal tendency. The Roman Epicurean poet Lucretius tried to defend the Epicurean conception of infinity against this Stoic alternative view, but not very convincingly. One might suspect, therefore, that the Epicureans’ adherence to the infinity of matter was not so much dictated by physical arguments as it was motivated by other, mostly theological and ethical, concerns. More specifically, the infinity of atoms and worlds was used as a premise in several arguments against divine intervention in the universe. The infinity of worlds was claimed to rule out divine intervention directly, while the infinity of atoms lent plausibility to the chance formation of worlds. Moreover, the infinity of atoms and worlds was used to ensure the truth of multiple explanations, which was presented by Epicurus as the only way to ward off divine intervention in the realm of celestial phenomena. However, it will be argued that in all of these arguments the infinity of matter is either unnecessary or insufficient for reaching the desired conclusion

    Sunk costs and the dynamics of creative industries

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    This chapter examines the long-run evolution of modern entertainment industries such as the film and music industries. It investigates ways to conceptualise and quantify the subsequent waves of creative destruction, and investigates specifically how sunk costs affect the evolution of the industry through its interaction with variety, market integration, product differentiation and price discrimination, and how old entertainment formats almost never became extinct. It finds that within this framework, four economic tendencies shaped the entertainment industries evolution: first, endogenous sunk costs often led to a competitive escalation of production expenditures, which we call ‘quality races’, which increased industrial concentration. Second, the fact that marginal revenues largely equalled marginal profits led to extreme vertical integration through ownership or revenue-sharing contracts, as well as to an oversupply of variety and a dual market structure with high-concept blockbuster products and low-budget niche products. Third, entertainment’s public good characteristics led to substantial income inequality among creative inputs and business models optimising exclusion possibilities in the value chain. Finally, the project-based character of entertainment production implied large intra- and inter-industry agglomeration benefits and often led to geographical concentration. Dynamic product differentiation allowed various old formats to survive the waves of creative destruction, albeit in much smaller incarnations

    Gravitational binding in 4D dynamical triangulation

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    In the dynamical triangulation model of four dimensional euclidean quantum gravity we investigate gravitational binding. Two scalar test particles (quenched approximation) have a positive binding energy, thereby showing that the model can represent gravitational attraction.Comment: 19 pages, LaTeX2e, version as accepted by Nucl Phys