1,447 research outputs found
A Perturbative Approach to Neutron Stars in Gravity
We derive a Tolman-Oppenheimer-Volkoff equation in neutron star systems
within the modified -gravity class of models using a
perturbative approach. In our approach -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 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 -gravity.Comment: arXiv admin note: text overlap with arXiv:1701.0476
Quark Stars in Gravity
We derive a working model for the Tolman-Oppenheimer-Volkoff equation for
quark star systems within the modified -gravity class of
models. We consider -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 parameter parameter, namely taking and investigate the behavior of a linear
energy-momentum tensor trace, . We also outline the restrictions
which modified -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 -gravity
Bayesian Model Search for Nonstationary Periodic Time Series
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
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
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 âguiding centerâ 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 Foucaultâs pendulum. In this sense, a particle trapped in the symmetric rotating saddle trap is, effectively, a Foucaultâs pendulum, but in the inertial frame
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