27,285 research outputs found
Nonlinear growth of zonal flows by secondary instability in general magnetic geometry
We present a theory of the nonlinear growth of zonal flows in magnetized
plasma turbulence, by the mechanism of secondary instability. The theory is
derived for general magnetic geometry, and is thus applicable to both tokamaks
and stellarators. The predicted growth rate is shown to compare favorably with
nonlinear gyrokinetic simulations, with the error scaling as expected with the
small parameter of the theory.Comment: New J. Phys. 201
Consistency in NLO analyses of inclusive and semi-inclusive polarized DIS data
We perform a detailed study of the consistency between different sets of
polarized deep inelastic scattering data and theory, from the standpoint of a
next to leading order QCD global analysis, and following the criteria proposed
by Collins and Pumplin. In face of recent suggestions that challenge the usual
assumption about parent parton spin independence of unpolarized fragmentation
functions, we specially focus on polarized semi-inclusive data.Comment: 17 pages, 5 figure
Constraints on gluon polarization in the nucleon at NLO accuracy
We compare constraints on the gluon polarization in the nucleon obtained in
next to leading order global QCD fits to polarized deep inelastic scattering
data with those coming from observables more directly linked to the gluon
polarization, such as the double spin asymmetry measured by Phenix at RHIC, and
high-pT hadron production studied by COMPASSComment: 4 pages, 3 figures, 1 tabl
Understanding nonlinear saturation in zonal-flow-dominated ion temperature gradient turbulence
We propose a quantitative model of ion temperature gradient driven turbulence
in toroidal magnetized plasmas. In this model, the turbulence is regulated by
zonal flows, i.e. mode saturation occurs by a zonal-flow-mediated energy
cascade ("shearing"), and zonal flow amplitude is controlled by nonlinear
decay. Our model is tested in detail against numerical simulations to confirm
that both its assumptions and predictions are satisfied. Key results include
(1) a sensitivity of the nonlinear zonal flow response to the energy content of
the linear instability, (2) a persistence of zonal-flow-regulated saturation at
high temperature gradients, (3) a physical explanation of the nonlinear
saturation process in terms of secondary and tertiary instabilities, and (4)
dependence of heat flux in terms of dimensionless parameters.Comment: Final journal version. Some clarifications and a new Fig.
Sea quark and gluon polarization in the nucleon at NLO accuracy
We investigate the sea quark polarization in the nucleon by means of a
combined next to leading order analysis to the recently enlarged set of
inclusive and semi-inclusive polarized deep inelastic scattering data. Using
the Lagrange multiplier method, we asses the uncertainty inherent to the
extraction of the different spin dependent parton densities in a QCD global
fit, and the impact of the increased set of semi-inclusive data now available.
We comment on future prospects at RHIC and JLAB and their potential impact in
the future determination of polarized parton densities.Comment: 15 pages, 9 figures, 3 table
Extraction of polarized parton densities from polarized DIS and SIDIS
We present results on the quark and gluon polarization in the nucleon
obtained in a combined next to leading order analysis to the available
inclusive and semi-inclusive polarized deep inelastic scattering data.Comment: Talk given at XIII International Workshop on Deep Inelastic
Scattering, April,27 - May,1, 2005, Madison, Wisconsin, USA, 4 pages, 2
figure
Tidal Torques and the Orientation of Nearby Disk Galaxies
We use numerical simulations to investigate the orientation of the angular
momentum axis of disk galaxies relative to their surrounding large scale
structure. We find that this is closely related to the spatial configuration at
turnaround of the material destined to form the galaxy, which is often part of
a coherent two-dimensional slab criss-crossed by filaments. The rotation axis
is found to align very well with the intermediate principal axis of the inertia
momentum tensor at this time. This orientation is approximately preserved
during the ensuing collapse, so that the rotation axis of the resulting disk
ends up lying on the plane traced by the protogalactic material at turnaround.
This suggests a tendency for disks to align themselves so that their rotation
axis is perpendicular to the minor axis of the structure defined by surrounding
matter. One example of this trend is provided by our own Galaxy, where the
Galactic plane is almost at right angles with the supergalactic plane (SGP)
drawn by nearby galaxies; indeed, the SGP latitude of the North Galactic Pole
is just 6 degrees. We have searched for a similar signature in catalogs of
nearby disk galaxies, and find a significant excess of edge-on spirals (for
which the orientation of the disk rotation axis may be determined
unambiguously) highly inclined relative to the SGP. This result supports the
view that disk galaxies acquire their angular momentum as a consequence of
early tidal torques acting during the expansion phase of the protogalactic
material.Comment: 5 pages, 2 figures, accepted for publication in ApJ
A Faster Implementation of Online Run-Length Burrows-Wheeler Transform
Run-length encoding Burrows-Wheeler Transformed strings, resulting in
Run-Length BWT (RLBWT), is a powerful tool for processing highly repetitive
strings. We propose a new algorithm for online RLBWT working in run-compressed
space, which runs in time and bits of space, where
is the length of input string received so far and is the number of runs
in the BWT of the reversed . We improve the state-of-the-art algorithm for
online RLBWT in terms of empirical construction time. Adopting the dynamic list
for maintaining a total order, we can replace rank queries in a dynamic wavelet
tree on a run-length compressed string by the direct comparison of labels in a
dynamic list. The empirical result for various benchmarks show the efficiency
of our algorithm, especially for highly repetitive strings.Comment: In Proc. IWOCA201
Improved Approximate String Matching and Regular Expression Matching on Ziv-Lempel Compressed Texts
We study the approximate string matching and regular expression matching
problem for the case when the text to be searched is compressed with the
Ziv-Lempel adaptive dictionary compression schemes. We present a time-space
trade-off that leads to algorithms improving the previously known complexities
for both problems. In particular, we significantly improve the space bounds,
which in practical applications are likely to be a bottleneck
Dictionary Matching with One Gap
The dictionary matching with gaps problem is to preprocess a dictionary
of gapped patterns over alphabet , where each
gapped pattern is a sequence of subpatterns separated by bounded
sequences of don't cares. Then, given a query text of length over
alphabet , the goal is to output all locations in in which a
pattern , , ends. There is a renewed current interest
in the gapped matching problem stemming from cyber security. In this paper we
solve the problem where all patterns in the dictionary have one gap with at
least and at most don't cares, where and are
given parameters. Specifically, we show that the dictionary matching with a
single gap problem can be solved in either time and
space, and query time , where is the number
of patterns found, or preprocessing time and space: , and query
time , where is the number of patterns found.
As far as we know, this is the best solution for this setting of the problem,
where many overlaps may exist in the dictionary.Comment: A preliminary version was published at CPM 201
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