1,393 research outputs found

    A Perturbative Approach to Neutron Stars in f(T,T)f(T, \mathcal{T})-Gravity

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    We derive a Tolman-Oppenheimer-Volkoff equation in neutron star systems within the modified f(T,T)f(T, \mathcal{T})-gravity class of models using a perturbative approach. In our approach f(T,T)f(T, \mathcal{T})-gravity is considered to be a static spherically symmetric space-time. In this instance the metric is built from a more fundamental tetrad vierbein which can be used to relate inertial and global coordinates. A linear function f=T(r)+T(r)+χh(T,T)+O(χ2)f = T(r) + \mathcal{T}(r) + \chi h(T, \mathcal{T}) + \mathcal{O}(\chi^{2}) is taken as the Lagrangian density for the gravitational action. Finally we impose the polytropic equation of state of neutron star upon the derived equations in order to derive the mass profile and mass-central density relations of the neutron star in f(T,T)f(T, \mathcal{T})-gravity.Comment: arXiv admin note: text overlap with arXiv:1701.0476

    Quark Stars in f(T,T)f(T, \mathcal{T})-Gravity

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    We derive a working model for the Tolman-Oppenheimer-Volkoff equation for quark star systems within the modified f(T,T)f(T, \mathcal{T})-gravity class of models. We consider f(T,T)f(T, \mathcal{T})-gravity for a static spherically symmetric space-time. In this instance the metric is built from a more fundamental tetrad vierbein from which the metric tensor can be derived. We impose a linear f(T)f(T) parameter parameter, namely taking f=αT(r)+βT(r)+φf=\alpha T(r) + \beta \mathcal{T}(r) + \varphi and investigate the behavior of a linear energy-momentum tensor trace, T\mathcal{T}. We also outline the restrictions which modified f(T,T)f(T, \mathcal{T})-gravity imposes upon the coupling parameters. Finally we incorporate the MIT bag model in order to derive the mass-radius and mass-central density relations of the quark star within f(T,T)f(T, \mathcal{T})-gravity

    Bayesian Model Search for Nonstationary Periodic Time Series

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    We propose a novel Bayesian methodology for analyzing nonstationary time series that exhibit oscillatory behaviour. We approximate the time series using a piecewise oscillatory model with unknown periodicities, where our goal is to estimate the change-points while simultaneously identifying the potentially changing periodicities in the data. Our proposed methodology is based on a trans-dimensional Markov chain Monte Carlo (MCMC) algorithm that simultaneously updates the change-points and the periodicities relevant to any segment between them. We show that the proposed methodology successfully identifies time changing oscillatory behaviour in two applications which are relevant to e-Health and sleep research, namely the occurrence of ultradian oscillations in human skin temperature during the time of night rest, and the detection of instances of sleep apnea in plethysmographic respiratory traces.Comment: Received 23 Oct 2018, Accepted 12 May 201

    A Coriolis force in an inertial frame

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    Particles in rotating saddle potentials exhibit precessional motion which, up to now, has been explained by explicit computation. We show that this precession is due to a hidden Coriolis-like force which, unlike the standard Coriolis force, is present in the inertial frame. We do so by finding a hodograph-like "guiding center" transformation using the method of normal form. We also point out that the transformation cannot be of contact type in principle, thus showing that the standard (in applied literature) heuristic averaging gives the correct result but obscures the fact that the transformation of the position must involve the velocity

    Precession on a rotating saddle: a gyro force in an inertial frame

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    Particles in rotating saddle potentials exhibit precessional motion which, up to now, has been explained by explicit computation. We show that this precession is due to a hidden gyroscopic force which, unlike the standard Coriolis force, is present in the inertial frame. We do so by finding a hodograph-like “guiding center” transformation using the method of normal form, which yields a simplified equation for the guiding center of the trajectory that coincides with the equation of the Foucault’s pendulum. In this sense, a particle trapped in the symmetric rotating saddle trap is, effectively, a Foucault’s pendulum, but in the inertial frame
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