1,118 research outputs found
Dynamic resource allocation scheme for distributed heterogeneous computer systems
This invention relates to a resource allocation in computer systems, and more particularly, to a method and associated apparatus for shortening response time and improving efficiency of a heterogeneous distributed networked computer system by reallocating the jobs queued up for busy nodes to idle, or less-busy nodes. In accordance with the algorithm (SIDA for short), the load-sharing is initiated by the server device in a manner such that extra overhead in not imposed on the system during heavily-loaded conditions. The algorithm employed in the present invention uses a dual-mode, server-initiated approach. Jobs are transferred from heavily burdened nodes (i.e., over a high threshold limit) to low burdened nodes at the initiation of the receiving node when: (1) a job finishes at a node which is burdened below a pre-established threshold level, or (2) a node is idle for a period of time as established by a wakeup timer at the node. The invention uses a combination of the local queue length and the local service rate ratio at each node as the workload indicator
Stokes IQUV mapping of CVn & other Ap stars using ESPaDOnS and NARVAL
New spectral line polarisation observations of 7 bright Ap stars have been
obtained with the ESPaDOnS and Narval high resolution spectropolarimeters
(Silvester et al. 2012). The aim of this data set is produce a series of
surface magnetic field and surface chemistry maps for these Ap stars. We
present new magnetic maps for the Ap star CVn using these new data
and the MDI inversion code INVERS10. CVn is the first Ap star to be
observed during two separate epochs using high resolution phase resolved
spectropolarimetric observations and as such allows us an insight into
how stable the surface magnetic structure is over a decade timescale. We show
that the new maps give a magnetic field structure consistent with the previous
maps obtained by Kochukhov and Wade (2010) from lower quality MuSiCoS spectra
taken a decade ago and that the field topology cannot be described by a dipolar
or quadrupolar field.Comment: 6 pages, 3 figures. Proceedings of New advances in stellar physics:
from microscopic to macroscopic processes (Roscoff 2013
The magnetic field topology and chemical abundance distributions of the Ap star HD 32633
Previous observations of the Ap star HD 32633 indicated that its magnetic
field was unusually complex in nature and could not be characterised by a
simple dipolar structure. Here we derive magnetic field maps and chemical
abundance distributions for this star using full Stokes vector (Stokes )
high-resolution observations obtained with the ESPaDOnS and Narval
spectropolarimeters. Our maps, produced using the Invers10 magnetic Doppler
imaging (MDI) code, show that HD 32633 has a strong magnetic field which
features two large regions of opposite polarity but deviates significantly from
a pure dipole field. We use a spherical harmonic expansion to characterise the
magnetic field and find that the harmonic energy is predominately in the
and poloidal modes with a small toroidal component. At the
same time, we demonstrate that the observed Stokes parameter profiles of HD
32633 cannot be fully described by either a dipolar or dipolar plus quadrupolar
field geometry. We compare the magnetic field topology of HD 32633 with other
early-type stars for which MDI analyses have been performed, supporting a trend
of increasing field complexity with stellar mass. We then compare the magnetic
field topology of HD 32633 with derived chemical abundance maps for the
elements Mg, Si, Ti, Cr, Fe, Ni and Nd. We find that the iron-peak elements
show similar distributions, but we are unable to find a clear correlation
between the location of local chemical enhancements or depletions and the
magnetic field structure.Comment: 15 pages, 11 figures, accepted for publication in MNRA
Adaptive time-stepping for incompressible flow. Part II: Navier-Stokes equations
We outline a new class of robust and efficient methods for solving the Navier- Stokes equations. We describe a general solution strategy that has two basic building blocks: an implicit time integrator using a stabilized trapezoid rule with an explicit Adams-Bashforth method for error control, and a robust Krylov subspace solver for the spatially discretized system. We present numerical experiments illustrating the potential of our approach. © 2010 Society for Industrial and Applied Mathematics
A preconditioner for the 3D Oseen equations
We describe a preconditioner for the linearised incompressible Navier-Stokes equations (the Oseen equations) which requires as components only a preconditioner/solver for each of a discrete Laplacian and a discrete advection-diffusion operator. With this preconditioner, convergence of an iterative method such as GMRES is independent of the mesh size and depends only mildly on the viscosity parameter (the inverse Reynolds number). Thus when the component preconditioner/solvers are effective on their respective subproblems (as one expects with an appropriate multigrid cycle for instance) a fast Oseen solver results
- …