31,293 research outputs found
Unleashing the Power of Distributed CPU/GPU Architectures: Massive Astronomical Data Analysis and Visualization case study
Upcoming and future astronomy research facilities will systematically
generate terabyte-sized data sets moving astronomy into the Petascale data era.
While such facilities will provide astronomers with unprecedented levels of
accuracy and coverage, the increases in dataset size and dimensionality will
pose serious computational challenges for many current astronomy data analysis
and visualization tools. With such data sizes, even simple data analysis tasks
(e.g. calculating a histogram or computing data minimum/maximum) may not be
achievable without access to a supercomputing facility.
To effectively handle such dataset sizes, which exceed today's single machine
memory and processing limits, we present a framework that exploits the
distributed power of GPUs and many-core CPUs, with a goal of providing data
analysis and visualizing tasks as a service for astronomers. By mixing shared
and distributed memory architectures, our framework effectively utilizes the
underlying hardware infrastructure handling both batched and real-time data
analysis and visualization tasks. Offering such functionality as a service in a
"software as a service" manner will reduce the total cost of ownership, provide
an easy to use tool to the wider astronomical community, and enable a more
optimized utilization of the underlying hardware infrastructure.Comment: 4 Pages, 1 figures, To appear in the proceedings of ADASS XXI, ed.
P.Ballester and D.Egret, ASP Conf. Serie
The development of direct payments in the UK: implications for social justice
Direct payments have been heralded by the disability movement as an important means to
achieving independent living and hence greater social justice for disabled people through
enhanced recognition as well as financial redistribution. Drawing on data from the ESRC
funded project Disabled People and Direct Payments: A UK Comparative Perspective,
this paper presents an analysis of policy and official statistics on use of direct payments
across the UK. It is argued that the potential of direct payments has only partly been
realised as a result of very low and uneven uptake within and between different parts
of the UK. This is accounted for in part by resistance from some Labour-controlled local
authorities, which regard direct payments as a threat to public sector jobs. In addition,
access to direct payments has been uneven across impairment groups. However, from a
very low base there has been a rapid expansion in the use of direct payments over the
past three years. The extent to which direct payments are able to facilitate the ultimate
goal of independent living for disabled people requires careful monitoring
Helioseismology of Pre-Emerging Active Regions II: Average Emergence Properties
We report on average subsurface properties of pre-emerging active regions as
compared to areas where no active region emergence was detected. Helioseismic
holography is applied to samples of the two populations (pre-emergence and
without emergence), each sample having over 100 members, which were selected to
minimize systematic bias, as described in Leka et al. We find that there are
statistically significant signatures (i.e., difference in the means of more
than a few standard errors) in the average subsurface flows and the apparent
wave speed that precede the formation of an active region. The measurements
here rule out spatially extended flows of more than about 15 m/s in the top 20
Mm below the photosphere over the course of the day preceding the start of
visible emergence. These measurements place strong constraints on models of
active region formation.Comment: 15 pages, 10 figures, ApJ (published
Nonlinear phase mixing and phase-space cascade of entropy in gyrokinetic plasma turbulence
Electrostatic turbulence in weakly collisional, magnetized plasma can be
interpreted as a cascade of entropy in phase space, which is proposed as a
universal mechanism for dissipation of energy in magnetized plasma turbulence.
When the nonlinear decorrelation time at the scale of the thermal Larmor radius
is shorter than the collision time, a broad spectrum of fluctuations at
sub-Larmor scales is numerically found in velocity and position space, with
theoretically predicted scalings. The results are important because they
identify what is probably a universal Kolmogorov-like regime for kinetic
turbulence; and because any physical process that produces fluctuations of the
gyrophase-independent part of the distribution function may, via the entropy
cascade, result in turbulent heating at a rate that increases with the
fluctuation amplitude, but is independent of the collision frequency.Comment: Revtex, 4 pages, 3 figures; replaced to match published versio
Multiscale Gyrokinetics for Rotating Tokamak Plasmas: Fluctuations, Transport and Energy Flows
This paper presents a complete theoretical framework for plasma turbulence
and transport in tokamak plasmas. The fundamental scale separations present in
plasma turbulence are codified as an asymptotic expansion in the ratio of the
gyroradius to the equilibrium scale length. Proceeding order-by-order in this
expansion, a framework for plasma turbulence is developed. It comprises an
instantaneous equilibrium, the fluctuations driven by gradients in the
equilibrium quantities, and the transport-timescale evolution of mean profiles
of these quantities driven by the fluctuations. The equilibrium distribution
functions are local Maxwellians with each flux surface rotating toroidally as a
rigid body. The magnetic equillibrium is obtained from the Grad-Shafranov
equation for a rotating plasma and the slow (resistive) evolution of the
magnetic field is given by an evolution equation for the safety factor q.
Large-scale deviations of the distribution function from a Maxwellian are given
by neoclassical theory. The fluctuations are determined by the high-flow
gyrokinetic equation, from which we derive the governing principle for
gyrokinetic turbulence in tokamaks: the conservation and local cascade of free
energy. Transport equations for the evolution of the mean density, temperature
and flow velocity profiles are derived. These transport equations show how the
neoclassical corrections and the fluctuations act back upon the mean profiles
through fluxes and heating. The energy and entropy conservation laws for the
mean profiles are derived. Total energy is conserved and there is no net
turbulent heating. Entropy is produced by the action of fluxes flattening
gradients, Ohmic heating, and the equilibration of mean temperatures. Finally,
this framework is condensed, in the low-Mach-number limit, to a concise set of
equations suitable for numerical implementation.Comment: 113 pages, 3 figure
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