2,826 research outputs found
Tax Analysis in an Oligopoly Model
In this paper we analyze taxation using the conjectural variations model of oligopoly. We demonstrate the way in which the incidence of a tax depends upon the pattern of firm interaction. The results obtained have important implications for the controversy surrounding the question of whether a tax oncorporate income can be over-shifted. We also study normative aspects of taxation. The focus here is on the errors that can arise in excess burden calculations when incorrect assumptions on market structure are made.
Many-Task Computing and Blue Waters
This report discusses many-task computing (MTC) generically and in the
context of the proposed Blue Waters systems, which is planned to be the largest
NSF-funded supercomputer when it begins production use in 2012. The aim of this
report is to inform the BW project about MTC, including understanding aspects
of MTC applications that can be used to characterize the domain and
understanding the implications of these aspects to middleware and policies.
Many MTC applications do not neatly fit the stereotypes of high-performance
computing (HPC) or high-throughput computing (HTC) applications. Like HTC
applications, by definition MTC applications are structured as graphs of
discrete tasks, with explicit input and output dependencies forming the graph
edges. However, MTC applications have significant features that distinguish
them from typical HTC applications. In particular, different engineering
constraints for hardware and software must be met in order to support these
applications. HTC applications have traditionally run on platforms such as
grids and clusters, through either workflow systems or parallel programming
systems. MTC applications, in contrast, will often demand a short time to
solution, may be communication intensive or data intensive, and may comprise
very short tasks. Therefore, hardware and software for MTC must be engineered
to support the additional communication and I/O and must minimize task dispatch
overheads. The hardware of large-scale HPC systems, with its high degree of
parallelism and support for intensive communication, is well suited for MTC
applications. However, HPC systems often lack a dynamic resource-provisioning
feature, are not ideal for task communication via the file system, and have an
I/O system that is not optimized for MTC-style applications. Hence, additional
software support is likely to be required to gain full benefit from the HPC
hardware
White Dwarf Mergers on Adaptive Meshes I. Methodology and Code Verification
The Type Ia supernova progenitor problem is one of the most perplexing and
exciting problems in astrophysics, requiring detailed numerical modeling to
complement observations of these explosions. One possible progenitor that has
merited recent theoretical attention is the white dwarf merger scenario, which
has the potential to naturally explain many of the observed characteristics of
Type Ia supernovae. To date there have been relatively few self-consistent
simulations of merging white dwarf systems using mesh-based hydrodynamics. This
is the first paper in a series describing simulations of these systems using a
hydrodynamics code with adaptive mesh refinement. In this paper we describe our
numerical methodology and discuss our implementation in the compressible
hydrodynamics code CASTRO, which solves the Euler equations, and the Poisson
equation for self-gravity, and couples the gravitational and rotation forces to
the hydrodynamics. Standard techniques for coupling gravitation and rotation
forces to the hydrodynamics do not adequately conserve the total energy of the
system for our problem, but recent advances in the literature allow progress
and we discuss our implementation here. We present a set of test problems
demonstrating the extent to which our software sufficiently models a system
where large amounts of mass are advected on the computational domain over long
timescales. Future papers in this series will describe our treatment of the
initial conditions of these systems and will examine the early phases of the
merger to determine its viability for triggering a thermonuclear detonation.Comment: Accepted for publication in the Astrophysical Journa
Measuring the dynamical length of galactic bars
We define a physically-motivated measure for galactic bar length, called the
dynamical length. The dynamical length of the bar corresponds to the radial
extent of the orbits that are the backbone supporting the bar feature. We
propose a direct observational technique using integral field unit spectroscopy
to measure it. Identifying these orbits and using the dynamical length is a
more faithful tracer of the secular evolution and influence of the bar. We
demonstrate the success of the metric for recovering the maximal bar-parenting
orbit in a range of simulations, and to show its promise we perform its
measurement on a real galaxy. We also study the difference between
traditionally used ellipse fit approaches to determine bar length and the
dynamical length proposed here in a wide range of bar-forming N-body
simulations of a stellar disc and dark matter halo. We find that ellipse
fitting may severely overestimate measurements of the bar length by a factor of
1.5-2.5 relative to the extent of the orbits that are trapped and actually
comprise the bar. This bias leads to overestimates of both bar mass and the
ratio of corotation radius to bar length, i.e. the bar speed, affecting
inferences about the evolution of bars in the real universe.Comment: Submitted to MNRAS, comments welcome. arXiv admin note: text overlap
with arXiv:1903.0820
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