149 research outputs found
External field effect of modified Newtonian dynamics in the Solar system
The Modified Newtonian Dynamics (MOND) has been formulated as a modification
of the Poisson equation for the Newtonian gravitational field. This theory
generically predicts a violation of the strong version of the equivalence
principle, and as a result the gravitational dynamics of a system depends on
the external gravitational field in which the system is embedded. This
so-called external field effect has been recently shown to imply the existence
of an anomalous quadrupolar correction, along the direction of the external
Galactic field, in the gravitational potential felt by planets in the Solar
System. In this paper we confirm the existence of this effect by a numerical
integration of the MOND equation in the presence of an external field, and
compute the secular precession of the perihelion of planets induced by this
effect. We find that the precession effect is rather large for outer gaseous
planets, and in the case of Saturn is comparable to published residuals of
precession obtained by Saturn range tracking data. The effect is much smaller
for inner planets, but in the case of the Earth it appears to be in conflict
for most of the MOND functions with the very good constraint on the
perihelion precession obtained from Jupiter VLBI data. The MOND functions that
are compatible with this constraint appear to have a very rapid transition from
the MONDian regime to the Newtonian one.Comment: 15 pages, 8 figures, accepted for publication in MNRA
Testing MOND in the Solar System
The Modified Newtonian Dynamics (MOND) generically predicts a violation of
the strong version of the equivalence principle. As a result the gravitational
dynamics of a system depends on the external gravitational field in which the
system is embedded. This so-called external field effect is shown to imply the
existence of an anomalous quadrupolar correction, along the direction of the
external galactic field, in the gravitational potential felt by planets in the
Solar System. We compute this effect by a numerical integration of the MOND
equation in the presence of an external field, and deduce the secular
precession of the perihelion of planets induced by this effect. We find that
the precession effect is rather large for outer gaseous planets, and in the
case of Saturn is comparable to, and in some cases marginally excluded by
published residuals of precession permitted by the best planetary ephemerides.Comment: 8 pages, two figures, to appear in the proceedings of the "46th
Rencontres de Moriond and GPhyS Colloquium on Gravitational Waves and
Experimental Gravity", la Thuile, March 20-27, 201
A new spectral apparent horizon finder for 3D numerical relativity
We present a new spectral-method-based algorithm for finding apparent
horizons in three-dimensional space-like hypersurfaces without symmetries.
While there are already a wide variety of algorithms for finding apparent
horizons, our new algorithm does not suffer from the same weakness as previous
spectral apparent horizon finders: namely the monopolar coefficient (
in terms of the spherical harmonics decomposition) needed to be determined by a
root-finding procedure. Hence, this leads to a much faster and more robust
spectral apparent horizon finder. The finder is tested with the Kerr-Schild and
Brill-Lindquist data. Our finder is accurate and is as efficient as the
currently fastest methods developed recently by Schnetter (2003 Class. Quantum
Grav. {\bf 20}, 4719) and Thornburg (2004 Class. Quantum Grav. {\bf 21}, 743).
At typical resolutions it takes only 0.5 second to find the apparent horizon of
a Kerr-Schild black hole with to the accuracy for the
fractional error in the horizon's location on a 2 GHz processor.Comment: Minor changes and references added. Published in Class. Quantum Gra
Influence of pions and hyperons on stellar black hole formation
We present numerical simulations of stellar core-collapse with spherically
symmetric, general relativistic hydrodynamics up to black hole formation. Using
the CoCoNuT code, with a newly developed grey leakage scheme for the neutrino
treatment, we investigate the effects of including pions and \Lambda-hyperons
into the equation of state at high densities and temperatures on the black hole
formation process. Results show non-negligible differences between the models
with reference equation of state without any additional particles and models
with the extended ones. For the latter, the maximum masses supported by the
proto-neutron star are smaller and the collapse to a black hole occurs earlier.
A phase transition to hyperonic matter is observed when the progenitor allows
for a high enough accretion rate onto the proto-neutron star. Rough estimates
of neutrino luminosity from these collapses are given, too.Comment: 22 pages, 10 figures. Minor change
General relativistic neutrino transport using spectral methods
We present a new code, Lorene's Ghost (for Lorene's gravitational handling of
spectral transport) developed to treat the problem of neutrino transport in
supernovae with the use of spectral methods. First, we derive the expression
for the nonrelativistic Liouville operator in doubly spherical coordinates (r,
theta, phi, epsilon, Theta, Phi)$, and further its general relativistic
counterpart. We use the 3 + 1 formalism with the conformally flat approximation
for the spatial metric, to express the Liouville operator in the Eulerian
frame. Our formulation does not use any approximations when dealing with the
angular arguments (theta, phi, Theta, Phi), and is fully energy-dependent. This
approach is implemented in a spherical shell, using either Chebyshev
polynomials or Fourier series as decomposition bases. It is here restricted to
simplified collision terms (isoenergetic scattering) and to the case of a
static fluid. We finish this paper by presenting test results using basic
configurations, including general relativistic ones in the Schwarzschild
metric, in order to demonstrate the convergence properties, the conservation of
particle number and correct treatment of some general-relativistic effects of
our code. The use of spectral methods enables to run our test cases in a
six-dimensional setting on a single processor.Comment: match published versio
"Mariage des Maillages": A new numerical approach for 3D relativistic core collapse simulations
We present a new 3D general relativistic hydrodynamics code for simulations
of stellar core collapse to a neutron star, as well as pulsations and
instabilities of rotating relativistic stars. It uses spectral methods for
solving the metric equations, assuming the conformal flatness approximation for
the three-metric. The matter equations are solved by high-resolution
shock-capturing schemes. We demonstrate that the combination of a finite
difference grid and a spectral grid can be successfully accomplished. This
"Mariage des Maillages" (French for grid wedding) approach results in high
accuracy of the metric solver and allows for fully 3D applications using
computationally affordable resources, and ensures long term numerical stability
of the evolution. We compare our new approach to two other, finite difference
based, methods to solve the metric equations. A variety of tests in 2D and 3D
is presented, involving highly perturbed neutron star spacetimes and
(axisymmetric) stellar core collapse, demonstrating the ability to handle
spacetimes with and without symmetries in strong gravity. These tests are also
employed to assess gravitational waveform extraction, which is based on the
quadrupole formula.Comment: 29 pages, 16 figures; added more information about convergence tests
and grid setu
Conference of Microelectronic Research 1999
https://scholarworks.rit.edu/meec_archive/1008/thumbnail.jp
Interpreting Deep Learning-Based Networking Systems
While many deep learning (DL)-based networking systems have demonstrated
superior performance, the underlying Deep Neural Networks (DNNs) remain
blackboxes and stay uninterpretable for network operators. The lack of
interpretability makes DL-based networking systems prohibitive to deploy in
practice. In this paper, we propose Metis, a framework that provides
interpretability for two general categories of networking problems spanning
local and global control. Accordingly, Metis introduces two different
interpretation methods based on decision tree and hypergraph, where it converts
DNN policies to interpretable rule-based controllers and highlight critical
components based on analysis over hypergraph. We evaluate Metis over several
state-of-the-art DL-based networking systems and show that Metis provides
human-readable interpretations while preserving nearly no degradation in
performance. We further present four concrete use cases of Metis, showcasing
how Metis helps network operators to design, debug, deploy, and ad-hoc adjust
DL-based networking systems.Comment: To appear at ACM SIGCOMM 202
A Roadmap for HEP Software and Computing R&D for the 2020s
Particle physics has an ambitious and broad experimental programme for the coming decades. This programme requires large investments in detector hardware, either to build new facilities and experiments, or to upgrade existing ones. Similarly, it requires commensurate investment in the R&D of software to acquire, manage, process, and analyse the shear amounts of data to be recorded. In planning for the HL-LHC in particular, it is critical that all of the collaborating stakeholders agree on the software goals and priorities, and that the efforts complement each other. In this spirit, this white paper describes the R&D activities required to prepare for this software upgrade.Peer reviewe
- …