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Living Reviews: “Terrestrial Gravity Fluctuations” / “Grid-based Methods in RHD and RMHD”

Living Reviews in Relativity has published a new review article on “Terrestrial Gravity Fluctuations” by Jan Harms on 2 December 2015.

Living Reviews in Computational Astrophysics has published a new review article on “Grid-based Methods in Relativistic Hydrodynamics and Magnetohydrodynamics” by Jose Maria Marti and Ewald Mueller on 22 December 2015.

Please find the abstracts and further details below.

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PUB.NO. lrca-2015-3
Marti, Jose Maria and Mueller, Ewald
“Grid-based Methods in Relativistic Hydrodynamics and Magnetohydrodynamics”

ACCEPTED: 2015-12-01
PUBLISHED: 2015-12-22

FULL ARTICLE AT:
http://www.livingreviews.org/lrca-2015-3

ABSTRACT:
An overview of grid-based numerical methods used in relativistic hydrodynamics (RHD) and magnetohydrodynamics (RMHD) is presented. Special emphasis is put on a comprehensive review of the application of high-resolution shock-capturing methods. Results of a set of demanding test bench simulations obtained with different numerical methods are compared in an attempt to assess the present capabilities and limits of the various numerical strategies. Applications to three astrophysical phenomena are briefly discussed to motivate the need for and to demonstrate the success of RHD and RMHD simulations in their understanding. The review further provides FORTRAN programs to compute the exact solution of the Riemann problem in RMHD, and to simulate 1D RMHD flows in Cartesian coordinates.

UPCOMING ARTICLES AT:
http://computastrophys.livingreviews.org/Articles/upcoming.html

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PUB.NO. lrr-2015-3
Harms, Jan
“Terrestrial Gravity Fluctuations”

ACCEPTED: 2015-11-16
PUBLISHED: 2015-12-02

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2015-3

ABSTRACT:
Different forms of fluctuations of the terrestrial gravity field are observed by gravity experiments. For example, atmospheric pressure fluctuations generate a gravity-noise foreground in measurements with super-conducting gravimeters. Gravity changes caused by high-magnitude earthquakes have been detected with the satellite gravity experiment GRACE, and we expect high-frequency terrestrial gravity fluctuations produced by ambient seismic fields to limit the sensitivity of ground-based gravitational-wave (GW) detectors. Accordingly, terrestrial gravity fluctuations are considered noise and signal depending on the experiment. Here, we will focus on ground-based gravimetry. This field is rapidly progressing through the development of GW detectors. The technology is pushed to its current limits in the advanced generation of the LIGO and Virgo detectors, targeting gravity strain sensitivities better than 10^-23 Hz^-1/2 above a few tens of a Hz. Alternative designs for GW detectors evolving from traditional gravity gradiometers such as torsion bars, atom interferometers, and superconducting gradiometers are currently being developed to extend the detection band to frequencies below 1 Hz. The goal of this article is to provide the analytical framework to describe terrestrial gravity perturbations in these experiments. Models of terrestrial gravity perturbations related to seismic fields, atmospheric disturbances, and vibrating, rotating or moving objects, are derived and analyzed. The models are then used to evaluate passive and active gravity noise mitigation strategies in GW detectors, or alternatively, to describe their potential use in geophysics. The article reviews the current state of the field, and also presents new analyses especially with respect to the impact of seismic scattering on gravity perturbations, active gravity noise cancellation, and time-domain models of gravity perturbations from atmospheric and seismic point sources. Our understanding of terrestrial gravity fluctuations will have great impact on the future development of GW detectors and high-precision gravimetry in general, and many open questions need to be answered still as emphasized in this article.

UPCOMING ARTICLES AT:
http://relativity.livingreviews.org/Articles/upcoming.html