8,250 research outputs found
Modified Nonlinear Integral Sliding Mode Control for Satellite Attitude Stabilization Using Magnetically Suspended Gimbaled Momentum Wheel
This paper treats the attitude stabilization problem for satellite using only one MSGMW (Magnetically Suspended Gimbaled Momentum Wheel). To start, the coupled dynamic model of satellite and MSGMW is defined and simplified based on the fact that the attitude errors are small during the mission mode that the MSGMW services. In order to improve the dynamic performance, reduce the steady state error and avoid the chattering phenomenon, a modified integral chattering-free sliding mode controller with a nonlinear integral function and a saturation function is introduced. Lyapunov theory is employed to prove the convergence characteristic outside the boundary layer and the terminal convergence characteristic inside the boundary layer. A numerical simulation example is employed to show the effectiveness and suitability of the proposed controller
Study on stability and rotating speed stable region of magnetically suspended rigid rotors using extended Nyquist criterion and gain-stable region theory
This paper presents a novel and simple method to analyze the absolute stability and the rotor speed stable region of a magnetically suspended rotor (MSR). At the beginning of the paper, a complex variable is introduced to describe the movement of the MSR and a complex coefficient transfer function is obtained accordingly. The equivalent stability relationship between this new variable and the two traditional deflection angles is also demonstrated in a simple way. The detailed characteristics of the open-loop MSR system with time delay are studied carefully based on the characteristics of its Nyquist curve. A sufficient and necessary condition of absolute stability is then deduced by using an extended complex Nyquist stability criterion for MSRs. Based on the relationship between the rotor speed and gain-stable region proposed in this paper, the rotor speed stable region can be solved simply and directly. The usefulness and effectiveness of the proposed approaches are validated by examples and simulations
Novel accelerating Einstein vacua and smooth inhomogeneous Riemannian manifolds
A novel class of Einstein vacua is presented, which possess non-vanishing
cosmological constant and accelerating horizon with the topology of
fibration over . After Euclideanization, the solution describes a
conformally distorted fibration over , which is smooth, compact
and inhomogeneous, and can be regarded as analogue of Don Page's gravitational
instanton.Comment: 14 pages. v2: Reference adde
Production of charged heavy quarkonium-like states at the LHC and the Tevatron
We study prompt hadroproduction of the charged bottomonium-like states
and , and the charged charmonium-like states
and , at the Tevatron and the LHC, provided
that these states are -wave hadronic molecules. Using two Monte Carlo event
generators, Herwig and Pythia, to simulate the production of heavy meson pairs,
we derive an order-of-magnitude estimate of the production rates for these four
particles. Our estimates yield a cross section at the nb level for the
and . The results for the and
are larger by a factor of 20-30. These cross sections are large enough to be
observed, and measurements at hadron colliders in the future will supplement
the study using electron-positron collisions, and therefore allow to explore
the mysterious nature of these exotic states.Comment: 5 pages, 1 figur
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