858 research outputs found
Computations for Coxeter arrangements and Solomon's descent algebra III: Groups of rank seven and eight
In this paper we extend the computations in parts I and II of this series of
papers and complete the proof of a conjecture of Lehrer and Solomon expressing
the character of a finite Coxeter group W acting on the pth graded component of
its Orlik-Solomon algebra as a sum of characters induced from linear characters
of centralizers of elements of W for groups of rank seven and eight. For
classical Coxeter groups, these characters are given using a formula that is
expected to hold in all ranks.Comment: Minor changes; final versio
Computations for Coxeter arrangements and Solomon's descent algebra II: Groups of rank five and six
In recent papers we have refined a conjecture of Lehrer and Solomon
expressing the character of a finite Coxeter group acting on the th
graded component of its Orlik-Solomon algebra as a sum of characters induced
from linear characters of centralizers of elements of . Our refined
conjecture relates the character above to a component of a decomposition of the
regular character of related to Solomon's descent algebra of . The
refined conjecture has been proved for symmetric and dihedral groups, as well
as finite Coxeter groups of rank three and four.
In this paper, the second in a series of three dealing with groups of rank up
to eight (and in particular, all exceptional Coxeter groups), we prove the
conjecture for finite Coxeter groups of rank five and six, further developing
the algorithmic tools described in the previous article. The techniques
developed and implemented in this paper provide previously unknown
decompositions of the regular and Orlik-Solomon characters of the groups
considered.Comment: Final Version. 17 page
Accuracy of numerical relativity waveforms from binary neutron star mergers and their comparison with post-Newtonian waveforms
We present numerical relativity simulations of nine-orbit equal-mass binary
neutron star covering the quasicircular late inspiral and merger. The extracted
gravitational waveforms are analyzed for convergence and accuracy. Second order
convergence is observed up to contact, i.e. about 3-4 cycles to merger; error
estimates can be made up to this point. The uncertainties on the phase and the
amplitude are dominated by truncation errors and can be minimized to 0.13 rad
and less then 1%, respectively, by using several simulations and extrapolating
in resolution. In the latter case finite-radius extraction uncertainties become
a source of error of the same order and have to be taken into account. The
waveforms are tested against accuracy standards for data analysis. The
uncertainties on the waveforms are such that accuracy standards are generically
not met for signal-to-noise ratios relevant for detection, except for some best
cases using extrapolation from several runs. A detailed analysis of the errors
is thus imperative for the use of numerical relativity waveforms from binary
neutron stars in quantitative studies. The waveforms are compared with the
post-Newtonian Taylor T4 approximants both for point-particle and including the
analytically known tidal corrections. The T4 approximants accumulate
significant phase differences of 2 rad at contact and 4 rad at merger,
underestimating the influence of finite size effects. Tidal signatures in the
waveforms are thus important at least during the last six orbits of the merger
process.Comment: Physical Review D (Vol.85, No.10) 201
Computations for Coxeter arrangements and Solomon's descent algebra: Groups of rank three and four
In recent papers we have refined a conjecture of Lehrer and Solomon
expressing the characters of a finite Coxeter group afforded by the
homogeneous components of its Orlik-Solomon algebra as sums of characters
induced from linear characters of centralizers of elements of . Our refined
conjecture also relates the Orlik-Solomon characters above to the terms of a
decomposition of the regular character of related to the descent algebra of
. A consequence of our conjecture is that both the regular character of
and the character of the Orlik-Solomon algebra have parallel, graded
decompositions as sums of characters induced from linear characters of
centralizers of elements of , one for each conjugacy class of elements of
. The refined conjecture has been proved for symmetric and dihedral groups.
In this paper we develop algorithmic tools to prove the conjecture
computationally for a given finite Coxeter group. We use these tools to verify
the conjecture for all finite Coxeter groups of rank three and four, thus
providing previously unknown decompositions of the regular characters and the
Orlik-Solomon characters of these groups.Comment: Final version. 20 pages, 6 tables. To appear in J. Symbolic Compu
Autumn destabilization of deep porewater CO2 store in a northern peatland driven by turbulent diffusion
The CO2 stored in deep peat porewater is viewed as a fixed component of peatland C cycling. Here, the authors reveal a hitherto unknown hydro-physical process that results in sudden losses from this CO2 store every autumn.The deep porewater of northern peatlands stores large amounts of carbon dioxide (CO2). This store is viewed as a stable feature in the peatland CO2 cycle. Here, we report large and rapid fluctuations in deep porewater CO2 concentration recurring every autumn over four consecutive years in a boreal peatland. Estimates of the vertical diffusion of heat indicate that CO2 diffusion occurs at the turbulent rather than molecular rate. The weakening of porewater thermal stratification in autumn likely increases turbulent diffusion, thus fostering a rapid diffusion of deeper porewater CO2 towards the surface where net losses occur. This phenomenon periodically decreases the peat porewater CO2 store by between 29 and 90 g C m(-2) throughout autumn, which is comparable to the peatland's annual C-sink. Our results establish the need to consider the role of turbulent diffusion in regularly destabilizing the CO2 store in peat porewater
Can Authorship Representation Learning Capture Stylistic Features?
Automatically disentangling an author's style from the content of their
writing is a longstanding and possibly insurmountable problem in computational
linguistics. At the same time, the availability of large text corpora furnished
with author labels has recently enabled learning authorship representations in
a purely data-driven manner for authorship attribution, a task that ostensibly
depends to a greater extent on encoding writing style than encoding content.
However, success on this surrogate task does not ensure that such
representations capture writing style since authorship could also be correlated
with other latent variables, such as topic. In an effort to better understand
the nature of the information these representations convey, and specifically to
validate the hypothesis that they chiefly encode writing style, we
systematically probe these representations through a series of targeted
experiments. The results of these experiments suggest that representations
learned for the surrogate authorship prediction task are indeed sensitive to
writing style. As a consequence, authorship representations may be expected to
be robust to certain kinds of data shift, such as topic drift over time.
Additionally, our findings may open the door to downstream applications that
require stylistic representations, such as style transfer.Comment: appearing at TACL 202
Wintertime phytoplankton bloom in the subarctic Pacific supported by continental margin iron
Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 20 (2006): GB1006, doi:10.1029/2005GB002557.Heightened biological activity was observed in February 1996 in the high-nutrient low-chlorophyll (HNLC) subarctic North Pacific Ocean, a region that is thought to be iron-limited. Here we provide evidence supporting the hypothesis that Ocean Station Papa (OSP) in the subarctic Pacific received a lateral supply of particulate iron from the continental margin off the Aleutian Islands in the winter, coincident with the observed biological bloom. Synchrotron X-ray analysis was used to describe the physical form, chemistry, and depth distributions of iron in size fractionated particulate matter samples. The analysis reveals that discrete micron-sized iron-rich hot spots are ubiquitous in the upper 200 m at OSP, more than 900 km from the closest coast. The specifics of the chemistry and depth profiles of the Fe hot spots trace them to the continental margins. We thus hypothesize that iron hot spots are a marker for the delivery of iron from the continental margin. We confirm the delivery of continental margin iron to the open ocean using an ocean general circulation model with an iron-like tracer source at the continental margin. We suggest that iron from the continental margin stimulated a wintertime phytoplankton bloom, partially relieving the HNLC condition.This work was
supported by the U.S. Department of Energy, Office of Science, Office of
Biological and Environmental Research (KP1202030) to J. K. B and by
NSFATM-9987457 to I. F. The Advanced Light Source is supported by the
Director, Office of Science, Office of Basic Energy Sciences, Division of
Materials Sciences and Division of Chemical Sciences, Geosciences, and
Biosciences of the U.S. Department of Energy at Lawrence Berkeley
National Laboratory under contract DE-AC03-76SF00098
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