8,964 research outputs found

    Note on massless bosonic states in two-dimensional field theories

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    In a wide class of GL×GRG_L\times G_R invariant two-dimensional super-renormalizable field theories, the parity-odd part of the two-point function of global currents is completely determined by a fermion one-loop diagram. For any non-trivial fermion content, the two-point function possesses a massless pole which corresponds to massless bosonic physical states. As an application, we show that two-dimensional N=(2,2)\mathcal{N}=(2,2) supersymmetric gauge theory without a superpotential possesses U(1)L×U(1)RU(1)_L\times U(1)_R symmetry and contains one massless bosonic state per fixed spatial momentum. The N=(4,4)\mathcal{N}=(4,4) supersymmetric pure Yang-Mills theory possesses SU(2)L×SU(2)RSU(2)_L\times SU(2)_R symmetry, and there exist at least three massless bosonic states.Comment: 17pages, 4 figures, uses PTPTeX.cls and feynMF, added an appendi

    Environmental test chamber for the support of learning and teaching in intelligent control

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    The paper describes the utility of a low cost, 1 m2 by 2 m forced ventilation, micro-climate test chamber, for the support of research and teaching in mechatronics. Initially developed for the evaluation of a new ventilation rate controller, the fully instrumented chamber now provides numerous learning opportunities and individual projects for both undergraduate and postgraduate research students

    Unitarity constraints on chiral perturbative amplitudes

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    Low lying scalar resonances emerge as a necessary part to adjust chiral perturbation theory to experimental data once unitarity constraint is taken into consideration. I review recent progress made in this direction in a model independent approach. Also I briefly review studies on the odd physical properties of these low lying scalar resonances, including in the γγ→π+π−,π0π0\gamma\gamma\to\pi^+\pi^-, \pi^0\pi^0 processes.Comment: Talk given at: International Workshop on Effective Field Theories: from the pion to the upsilon, February 2-6 2009, Valencia, Spai

    Multi-Objective Robust H-infinity Control of Spacecraft Rendezvous

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    Based on the relative motion dynamic model illustrated by C-W equations, the problem of robust Hinfin control for a class of spacecraft rendezvous systems is investigated, which contains parametric uncertainties, external disturbances and input constraints. An Hinfin state-feedback controller is designed via a Lyapunov approach, which guarantees the closed-loop system to meet the multi-objective design requirements. The existence conditions for admissible controllers are formulated in the form of linear matrix inequalities (LMIs), and the controller design is cast into a convex optimization problem subject to LMI constraints. An illustrative example is provided to show the effectiveness of the proposed control design method

    Robust scheduled control of longitudinal flight with handling quality satisfaction

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    Classic flight control systems are still widely used in the industry because of acquired experience and good understanding of their structure. Nevertheless, with more stringent constraints, it becomes difficult to easily fulfil all the criteria with these classic control laws. On the other hand, modern methods can handle many constraints but fail to produce low order controllers. The following methodology proposed in this paper addresses both classic and modern flight control issues, to offer a solution that leverages the strengths of both approaches. First, an H∞ synthesis is performed in order to get controllers which satisfy handling qualities and are robust withrespect to mass and centre of gravity variations. These controllers are then reduced and structured by using robust modal control techniques. In conclusion, a self-scheduling technique is described that will schedule these controllers over the entire flight envelope
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