15,794 research outputs found

    Hydrodynamic squeeze-film bearings for gyroscopes

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    Experimental tests are conducted on squeeze-film bearings by applying electricity to piezoelectric ceramics, causing vibrations at thousands or millions of Hz that are amplified and transmitted to the bearing. Rotor operation through 24,000 rpm without whirl instability proved bearing ability to support rotor weight without hydrodynamic action

    On Error Torques of Squeeze-film Cylindrical Journal Bearings

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    Error torques of squeeze film cylindrical journal bearing

    Viscous dissipative effects in isotropic brane cosmology

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    We consider the dynamics of a viscous cosmological fluid in the generalized Randall-Sundrum model for an isotropic brane. To describe the dissipative effects we use the Israel-Hiscock-Stewart full causal thermodynamic theory. In the limiting case of a stiff cosmological fluid with pressure equal to the energy density, the general solution of the field equations can be obtained in an exact parametric form for a cosmological fluid with constant bulk viscosity and with a bulk viscosity coefficient proportional to the square root of the energy density, respectively. The obtained solutions describe generally non-inflationary brane worlds, starting from a singular state. During this phase of evolution the comoving entropy of the Universe is an increasing function of time, and thus a large amount of entropy is created in the brane world due to viscous dissipative processes.Comment: 15 pages, 11 figure

    Spherical squeeze-film hybrid bearing with small steady-state radial displacement

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    Spherical squeeze-film hybrid bearing with small steady-state radial displacement analysi

    Study of BK()+B\to K^{(*)} \ell^+\ell^- Decays in the Family Non-universal ZZ' Models

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    In a combined investigation of the BK()+B\to K^{(*)}\ell^+\ell^- decays, constraints on the related couplings in family non-universal ZZ^{\prime} models are derived. We find that within the allowed parameter space, the recently observed forward-backward asymmetry in the BK+B\to K^*\ell^+\ell^- decay can be explained, by flipping the signs of the Wilson coefficients C9effC_9^{\rm eff} and C10C_{10}. With the obtained constraints, we also calculate the branching ratio of the Bsμ+μB_s\to\mu^+\mu^- decay. The upper bound of our prediction is near the upper bound given by CDF Collaboration recently.Comment: 19 pages, 4 figures, some errors corrected; Journal versio

    On the slowly time dependent problem of squeeze film bearings

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    Time dependency of spherical squeeze-film bearing for use in suspension of precision gyroscope outpu

    Cosmological and Solar-System Tests of f(R) Modified Gravity

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    We investigate the cosmological and the local tests of the f(R) theory of modified gravity via the observations of (1) the cosmic expansion and (2) the cosmic structures and via (3) the solar-system experiments. To fit the possible cosmic expansion histories under consideration, for each of them we reconstruct f(R), known as "designer f(R)". We then test the designer f(R) via the cosmic-structure constraints on the metric perturbation ratio Psi/Phi and the effective gravitational coupling G_eff and via the solar-system constraints on the Brans-Dicke theory with the chameleon mechanism. We find that among the designer f(R) models specified by the CPL effective equation of state w_eff, only the model closely mimicking general relativity with a cosmological constant (LambdaCDM) can survive all the tests. Accordingly, these tests rule out the frequently studied "w_eff = -1" designer f(R) models which are distinct in cosmic structures from LambdaCDM. When considering only the cosmological tests, we find that the surviving designer f(R) models, although exist for a variety of w_eff, entail fine-tuning.Comment: 22 pages, 9 figures, LaTe
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