44,966 research outputs found

    A covariant formalism of spin precession with respect to a reference congruence

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    We derive an effectively three-dimensional relativistic spin precession formalism. The formalism is applicable to any spacetime where an arbitrary timelike reference congruence of worldlines is specified. We employ what we call a stopped spin vector which is the spin vector that we would get if we momentarily make a pure boost of the spin vector to stop it relative to the congruence. Starting from the Fermi transport equation for the standard spin vector we derive a corresponding transport equation for the stopped spin vector. Employing a spacetime transport equation for a vector along a worldline, corresponding to spatial parallel transport with respect to the congruence, we can write down a precession formula for a gyroscope relative to the local spatial geometry defined by the congruence. This general approach has already been pursued by Jantzen et. al. (see e.g. Jantzen, Carini and Bini, Ann. Phys. 215 (1997) 1), but the algebraic form of our respective expressions differ. We are also applying the formalism to a novel type of spatial parallel transport introduced in Jonsson (Class. Quantum Grav. 23 (2006) 1), as well as verifying the validity of the intuitive approach of a forthcoming paper (Jonsson, Am. Journ. Phys. 75 (2007) 463) where gyroscope precession is explained entirely as a double Thomas type of effect. We also present the resulting formalism in explicit three-dimensional form (using the boldface vector notation), and give examples of applications.Comment: 27 pages, 8 figure

    On the width of handles in two-dimensional quantum gravity

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    We discuss the average length l of the shortest non-contractible loop on surfaces in the two-dimensional pure quantum gravity ensemble. The value of Îłstr\gamma_{str} and the explicit form of the loop functions indicate that l diverges at the critical point. Scaling arguments suggest that the critical exponent of l is 1/2. We show that this value of the critical exponent is also obtained for branched polymers where the calculation is straightforward.Comment: 7 pages, 1 ps figure, late

    Trends and possible future developments in global forest-product markets - implications for the Swedish forest sector

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    This paper analyzes trends and possible future developments in global wood-product markets and discusses implications for the Swedish forest sector. Four possible futures, or scenarios, are considered, based on qualitative scenario analysis. The scenarios are distinguished principally by divergent futures with respect to two highly influential factors driving change in global wood-product markets, whose future development is unpredictable. These so-called critical uncertainties were found to be degrees to which: (i) current patterns of globalization will continue, or be replaced by regionalism, and (ii) concern about the environment, particularly climate change, related policy initiatives and customer preferences, will materialize. The overall future of the Swedish solid wood-product industry looks bright, irrespective of which of the four possible futures occurs, provided it accommodates the expected growth in demand for factory-made, energy-efficient construction components. The prospects for the pulp and paper industry in Sweden appear more ambiguous. Globalization is increasingly shifting production and consumption to the Southern hemisphere, adversely affecting employment and forest owners in Sweden. Further, technical progress in information and communication technology (ICT) is expected to lead to drastic reductions in demand for newsprint and printing paper. Chemical pulp producers may profit from a growing bio-energy industry, since they could manufacture new, high-value products in integrated bio-refineries. Mechanical pulp producers cannot do this, however, and might suffer from higher prices for raw materials and electricity

    Nanophotonics with the scanning electron microscope

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    Physical size and power consumption are both increasingly important issues in increasing the data throughput of future optical interconnects, switches and ultimately even optical memory elements. In this respect, phase-change memories have proven to be strong candidates, with data recording done by switching the material between amorphous and crystalline phases, much in line with today's DVD/DVR technology. However, polymorphic systems exist in which crystalline-to-crystalline transitions can provide for higher-base logics as well. In particular, by coding each distinct optical characteristic by a unique label, the different optical cross-sections of absorption and scattering of the crystalline phases of a single nanoparticle can be used as a logical element

    Real and Virtual Photon Structure

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    The structure of real and virtual photons has been studied in electron-proton scattering processes producing di-jet events at HERA by the H1 and ZEUS collaborations. Data have been compared to next-to-leading order QCD calculations and to the predictions of Monte Carlo generators based on the DGLAP and CCFM formalisms for describing the parton dynamicsComment: Proceedings 'QCD and High Energy Hadronic Interactions', Recontres de Morion