6,666 research outputs found

    New high order sufficient conditions for configuration tracking

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    In this paper, we propose new conditions guaranteeing that the trajectories of a mechanical control system can track any curve on the configuration manifold. We focus on systems that can be represented as forced affine connection control systems and we generalize the sufficient conditions for tracking known in the literature. The new results are proved by a combination of averaging procedures by highly oscillating controls with the notion of kinematic reduction.Comment: arXiv admin note: text overlap with arXiv:0911.536

    Digital Architecture of the New ATLAS Pixel Chip FE-I4

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    With the high hit rate foreseen for the innermost layers at an upgraded LHC, the current ATLAS Front-End pixel chip FE-I3 would start being inefficient. The main source of inefficiency comes from the copying mechanism of the pixel hits from the pixel array to the end of column buffers. A new ATLAS pixel chip FE-I4 is being developed in a 130 nm technology for use both in the framework of the Insertable B-Layer (IBL) project and for the outer layers of Super-LHC. FE-I4 is 80×336 pixels wide and features a reduced pixel size of 50×250 μm2. In the current design, a new digital architecture is introduced in which hit memories are distributed across the entire chip and the pixels organized in regions. Additional features include neighbor hit checking which allows a timewalk-less hit recording

    BF Actions for the Husain-Kuchar Model

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    We show that the Husain-Kuchar model can be described in the framework of BF theories. This is a first step towards its quantization by standard perturbative QFT techniques or the spin-foam formalism introduced in the space-time description of General Relativity and other diff-invariant theories. The actions that we will consider are similar to the ones describing the BF-Yang-Mills model and some mass generating mechanisms for gauge fields. We will also discuss the role of diffeomorphisms in the new formulations that we propose.Comment: 21 pages (in DIN A4 format), minor typos corrected; to appear in Phys. Rev.

    SO(4,C)-covariant Ashtekar-Barbero gravity and the Immirzi parameter

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    An so(4,C)-covariant hamiltonian formulation of a family of generalized Hilbert-Palatini actions depending on a parameter (the so called Immirzi parameter) is developed. It encompasses the Ashtekar-Barbero gravity which serves as a basis of quantum loop gravity. Dirac quantization of this system is constructed. Next we study dependence of the quantum system on the Immirzi parameter. The path integral quantization shows no dependence on it. A way to modify the loop approach in the accordance with the formalism developed here is briefly outlined.Comment: 14 pages, LATEX; minor changes; misprints corrected; commutator of two secondary second class constraints correcte
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