9,441 research outputs found
Tools for monitoring and controlling distributed applications
The Meta system is a UNIX-based toolkit that assists in the construction of reliable reactive systems, such as distributed monitoring and debugging systems, tool integration systems and reliable distributed applications. Meta provides mechanisms for instrumenting a distributed application and the environment in which it executes, and Meta supplies a service that can be used to monitor and control such an instrumented application. The Meta toolkit is built on top of the ISIS toolkit; they can be used together in order to build fault-tolerant and adaptive, distributed applications
Accretion in giant planet circumplanetary disks
During the final growth phase of giant planets, accretion is thought to be
controlled by a surrounding circumplanetary disk. Current astrophysical
accretion disk models rely on hydromagnetic turbulence or gravitoturbulence as
the source of effective viscosity within the disk. However, the
magnetically-coupled accreting region in these models is so limited that the
disk may not support inflow at all radii, or at the required rate. Here, we
examine the conditions needed for self-consistent accretion, in which the disk
is susceptible to accretion driven by magnetic fields or gravitational
instability. We model the disk as a Shakura-Sunyaev disk and calculate
the level of ionisation, the strength of coupling between the field and disk
using Ohmic, Hall and Ambipolar diffusevities for both an MRI and vertical
field, and the strength of gravitational instability. We find that the standard
constant- disk is only coupled to the field by thermal ionisation
within with strong magnetic diffusivity prohibiting accretion through
the bulk of the midplane. In light of the failure of the constant- disk
to produce accretion consistent with its viscosity we drop the assumption of
constant- and present an alternate model in which varies
radially according to the level magnetic turbulence or gravitoturbulence. We
find that a vertical field may drive accretion across the entire disk, whereas
MRI can drive accretion out to , beyond which Toomre's and
gravitoturbulence dominates. The disks are relatively hot (K),
and consequently massive ().Comment: 19 pages, 5 figures, 2 tables; accepted for publication by MNRA
Eigenstate Thermalization in Systems with Spontaneously Broken Symmetry
A strongly non-integrable system is expected to satisfy the eigenstate
thermalization hypothesis, which states that the expectation value of an
observable in an energy eigenstate is the same as the thermal value. This must
be revised if the observable is an order parameter for a spontaneously broken
symmetry, which has multiple thermal values. We propose that in this case the
system is unstable towards forming nearby eigenstates which yield each of the
allowed thermal values. We provide strong evidence for this from a numerical
study of the 2D transverse-field quantum Ising model.Comment: 4 pages, 5 figure
Magnetic fields in gaps surrounding giant protoplanets
Giant protoplanets evacuate a gap in their host protoplanetary disc, which
gas must cross before it can be accreted. A magnetic field is likely carried
into the gap, potentially influencing the flow. Gap crossing has been simulated
with varying degrees of attention to field evolution (pure hydrodynamical,
ideal, and resistive MHD), but as yet there has been no detailed assessment of
the role of the field accounting for all three key non-ideal MHD effects: Ohmic
resistivity, ambipolar diffusion, and Hall drift. We present a detailed
investigation of gap magnetic field structure as determined by non-ideal
effects. We assess susceptibility to turbulence induced by the
magnetorotational instability, and angular momentum loss from large-scale
fields. As full non-ideal simulations are computationally expensive, we take an
a posteriori approach, estimating MHD quantities from the pure hydrodynamical
gap crossing simulation by Tanigawa et al. (2012). We calculate the ionisation
fraction and estimate field strength and geometry to determine the strength of
non-ideal effects. We find that the protoplanetary disc field would be easily
drawn into the gap and circumplanetary disc. Hall drift dominates, so that much
of the gap is conditionally MRI unstable depending on the alignment of the
field and disc rotation axes. Field alignment also influences the strong
toroidal field component permeating the gap. Large-scale magnetic forces are
small in the circumplanetary disc, indicating they cannot drive accretion
there. However, turbulence will be key during satellite growth as it affects
critical disc features, such as the location of the ice line.Comment: 14 pages, 6 figures, accepted for publication by MNRA
- …