64,137 research outputs found
PQCD Analysis of Parton-Hadron Duality
We propose an extraction of the running coupling constant of QCD in the
infrared region from experimental data on deep inelastic inclusive scattering
at Bjorken x -> 1. We first attempt a perturbative fit of the data that extends
NLO PQCD evolution to large x values and final state invariant mass, W, in the
resonance region. We include both target mass corrections and large x
resummation effects. These effects are of order O(1/Q^2), and they improve the
agreement with the Q^2 dependence of the data. Standard analyses require the
presence of additional power corrections, or dynamical higher twists, to
achieve a fully quantitative fit. Our analysis, however, is regulated by the
value of the strong coupling in the infrared region that enters through large x
resummation effects, and that can suppress, or absorb, higher twist effects.
Large x data therefore indirectly provide a measurement of this quantity that
can be compared to extractions from other observables.Comment: 10 pages, 3 figure
Multibody Interplanetary Swingby Trajectories /MIST-1/
Computer program incorporates new isolation procedure to determine interplanetary trajectories which utilize a maximum of three flybys. Program also computes singe planet flybys and direct transfer trajectories. The three principle systems employed in MIST-1 use as their fundamental plane the mean plane of the earth's orbit around the sun
General tooth boundary conditions for equation free modelling
We are developing a framework for multiscale computation which enables models
at a ``microscopic'' level of description, for example Lattice Boltzmann, Monte
Carlo or Molecular Dynamics simulators, to perform modelling tasks at
``macroscopic'' length scales of interest. The plan is to use the microscopic
rules restricted to small "patches" of the domain, the "teeth'', using
interpolation to bridge the "gaps". Here we explore general boundary conditions
coupling the widely separated ``teeth'' of the microscopic simulation that
achieve high order accuracy over the macroscale. We present the simplest case
when the microscopic simulator is the quintessential example of a partial
differential equation. We argue that classic high-order interpolation of the
macroscopic field provides the correct forcing in whatever boundary condition
is required by the microsimulator. Such interpolation leads to Tooth Boundary
Conditions which achieve arbitrarily high-order consistency. The high-order
consistency is demonstrated on a class of linear partial differential equations
in two ways: firstly through the eigenvalues of the scheme for selected
numerical problems; and secondly using the dynamical systems approach of
holistic discretisation on a general class of linear \textsc{pde}s. Analytic
modelling shows that, for a wide class of microscopic systems, the subgrid
fields and the effective macroscopic model are largely independent of the tooth
size and the particular tooth boundary conditions. When applied to patches of
microscopic simulations these tooth boundary conditions promise efficient
macroscale simulation. We expect the same approach will also accurately couple
patch simulations in higher spatial dimensions.Comment: 22 page
Symmetries and reversing symmetries of polynomial automorphisms of the plane
The polynomial automorphisms of the affine plane over a field K form a group
which has the structure of an amalgamated free product. This well-known
algebraic structure can be used to determine some key results about the
symmetry and reversing symmetry groups of a given polynomial automorphism.Comment: 27 pages, AMS-Late
The structure of reversing symmetry groups
We present some of the group theoretic properties of reversing symmetry
groups, and classify their structure in simple cases that occur frequently in
several well-known groups of dynamical systems.Comment: 12 page
The prevalence and properties of cold gas inflows and outflows around galaxies in the local Universe
We perform a stacking analysis of the neutral
\nad\,5889,5895\,\AA\ ISM doublet using the SDSS DR7
spectroscopic data set to probe the prevalence and characteristics of cold
(T\,\,10\,K) galactic-scale gas flows in local (0.0250.1) inactive and AGN-host galaxies across the SFR-M plane. We
find low-velocity outflows to be prevalent in regions of high SFRs and stellar
masses (10 log M/M 11.5), however we do
not find any detections in the low mass (log M/M 10)
regime. We also find tentative detections of inflowing gas in high mass
galaxies across the star-forming population. We derive mass outflow rates in
the range of 0.14-1.74\,Myr and upper limits on inflow rates
<1\,Myr, allowing us to place constraints on the mass loading
factor (=/SFR) for use in simulations of the local
Universe. We discuss the fate of the outflows by comparing the force provided
by the starburst to the critical force needed to push the outflow outward, and
find the vast majority of the outflows unlikely to escape the host system.
Finally, as outflow detection rates and central velocities do not vary strongly
with the presence of a (weak) active supermassive black hole, we determine that
star formation appears to be the primary driver of outflows at 0.Comment: Accepted in MNRAS. 36 pages, 15 figure
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