345 research outputs found
Geodesic properties in terms of multipole moments in scalar-tensor theories of gravity
The formalism for describing a metric and the corresponding scalar in terms
of multipole moments has recently been developed for scalar-tensor theories. We
take advantage of this formalism in order to obtain expressions for the
observables that characterise geodesics in terms of the moments. These
expressions provide some insight into how the structure of a scalarized compact
object affects observables. They can also be used to understand how deviations
from general relativity are imprinted on the observables.Comment: 16 page
Multipole moments in scalar-tensor theory of gravity
Stationary, asymptotically flat spacetimes in general relativity can be
characterized by their multipole moments. The moments have proved to be very
useful tools for extracting information about the spacetime from various
observables and, more recently, for establishing universalities in the
structure of neutron stars. As a first step toward extending these methods
beyond general relativity, we develop the formalism that allows one to define
and calculate the multipole moments in scalar-tensor theories of gravity.Comment: 12 pages, references added, accepted for publication as a Regular
Article in Physical Review
Matching of analytical and numerical solutions for neutron stars of arbitrary rotation
We demonstrate the results of an attempt to match the two-soliton analytical
solution with the numerically produced solutions of the Einstein field
equations, that describe the spacetime exterior of rotating neutron stars, for
arbitrary rotation. The matching procedure is performed by equating the first
four multipole moments of the analytical solution to the multipole moments of
the numerical one. We then argue that in order to check the effectiveness of
the matching of the analytical with the numerical solution we should compare
the metric components, the radius of the innermost stable circular orbit
(), the rotation frequency and the
epicyclic frequencies . Finally we present some
results of the comparison.Comment: Contribution at the 13th Conference on Recent Developments in Gravity
(NEB XIII), corrected typo in of eq. 5 of the published versio
Alleviation of Chronic Cancer Pain by Adrenal Medullary Transplants in the Spinal Subarachnoid Space
Energy-Aware, Collision-Free Information Gathering for Heterogeneous Robot Teams
This paper considers the problem of safely coordinating a team of
sensor-equipped robots to reduce uncertainty about a dynamical process, where
the objective trades off information gain and energy cost. Optimizing this
trade-off is desirable, but leads to a non-monotone objective function in the
set of robot trajectories. Therefore, common multi-robot planners based on
coordinate descent lose their performance guarantees. Furthermore, methods that
handle non-monotonicity lose their performance guarantees when subject to
inter-robot collision avoidance constraints. As it is desirable to retain both
the performance guarantee and safety guarantee, this work proposes a
hierarchical approach with a distributed planner that uses local search with a
worst-case performance guarantees and a decentralized controller based on
control barrier functions that ensures safety and encourages timely arrival at
sensing locations. Via extensive simulations, hardware-in-the-loop tests and
hardware experiments, we demonstrate that the proposed approach achieves a
better trade-off between sensing and energy cost than coordinate-descent-based
algorithms.Comment: To appear in Transactions on Robotics; 18 pages and 16 figures. arXiv
admin note: text overlap with arXiv:2101.1109
Comparison of Branching Ratio and Sum-Rule Analyses of Magnetic Circular Dichroism in X-Ray-Absorption Spectroscopy
Two localized picture methods of analyzing the magnetic circular dichroism in x-ray absorption will be applied to experimental results: the branching ratio (BR) and sum rule (SR) approaches. A derivation of the BR formulas and detailed comparison to the SR expressions will be made, including error estimations. The BR approach will be seen to be a limiting case form of the SR spin-moment expression and provide a simple picture of the underlying physics in magnetic x-ray circular dichroism absorption in 3d magnetic materials
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