982 research outputs found
Finite Schur filtration dimension for modules over an algebra with Schur filtration
Let G be GL_N or SL_N as reductive linear algebraic group over a field k of
positive characteristic p. We prove several results that were previously
established only when N 2^N. Let G act rationally on a finitely
generated commutative k-algebra A. Assume that A as a G-module has a good
filtration or a Schur filtration. Let M be a noetherian A-module with
compatible G action. Then M has finite good/Schur filtration dimension, so that
there are at most finitely many nonzero H^i(G,M). Moreover these H^i(G,M) are
noetherian modules over the ring of invariants A^G. Our main tool is a
resolution involving Schur functors of the ideal of the diagonal in a product
of Grassmannians.Comment: 22 pages; final versio
Producing valid statistics when legislation, culture, and medical practices differ for births at or before the threshold of survival: Report of a European workshop
To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked Downloa
Two-Loop Polarization Contributions to Radiative-Recoil Corrections to Hyperfine Splitting in Muonium
We calculate radiative-recoil corrections of order
to hyperfine splitting in muonium generated by the
diagrams with electron and muon polarization loops. These corrections are
enhanced by the large logarithm of the electron-muon mass ratio. The leading
logarithm cubed and logarithm squared contributions were obtained a long time
ago. The single-logarithmic and nonlogarithmic contributions calculated here
improve the theory of hyperfine splitting, and affect the value of the
electron-muon mass ratio extracted from the experimental data on the muonium
hyperfine splitting.Comment: 15 pages, 11 figure
5-dim Superconformal Index with Enhanced En Global Symmetry
The five-dimensional supersymmetric gauge theory with Sp(N)
gauge group and SO(2N_f) flavor symmetry describes the physics on N D4-branes
with D8-branes on top of a single O8 orientifold plane in Type I' theory.
This theory is known to be superconformal at the strong coupling limit with the
enhanced global symmetry for . In this work we calculate
the superconformal index on for the Sp(1) gauge theory by the
localization method and confirm such enhancement of the global symmetry at the
superconformal limit for to a few leading orders in the chemical
potential. Both perturbative and (anti)instanton contributions are present in
this calculation. For cases some issues related the pole structure of
the instanton calculation could not be resolved and here we could provide only
some suggestive answer for the leading contributions to the index. For the
Sp(N) case, similar issues related to the pole structure appear.Comment: 70 pages, references added, published versio
Single-Spin Observables and Orbital Structures in Hadronic Distributions
Within the light-quark sector of the standard model, P-odd observables are
generated from point-like electroweak processes while A_t- odd observables
(neglecting quark mass parameters) come from dynamic spin-orbit correlations
within hadrons or within larger composite systems, such as nuclei. The effects
of A_t-odd dynamics can be inserted into transverse-momentum dependent
constituent distribution functions and, in this paper, we construct the
contribution from an orbital quark to the A_t odd quark parton distribution.
Using this distribution, we examine the crucial role of initial- and
final-state interactions in the observation of the scattering asymmetries in
different hard-scattering processes. This construction provides a geometrical
and dynamical interpretation of the Collins conjugation relation between
single-spin asymmetries in semi-inclusive deep inelastic scattering and the
asymmetries in Drell-Yan production. Finally, our construction allows us to
display a significant difference between the calculation of a spin asymmetry
generated by a hard scattering mechanism involving color-singlet exchange (such
as a photon) and a calculation of an asymmetry with a hard-scattering exchange
involving gluons. This leads to an appreciation of the process dependence
inherent in measurements of single-spin observables.Comment: 35 pages, 6 figure
Twistors, Harmonics and Holomorphic Chern-Simons
We show that the off-shell N=3 action of N=4 super Yang-Mills can be written
as a holomorphic Chern-Simons action whose Dolbeault operator is constructed
from a complex-real (CR) structure of harmonic space. We also show that the
local space-time operators can be written as a Penrose transform on the coset
SU(3)/(U(1) \times U(1)). We observe a strong similarity to ambitwistor space
constructions.Comment: 34 pages, 3 figures, v2: replaced with published version, v3: Added
referenc
The compositional and evolutionary logic of metabolism
Metabolism displays striking and robust regularities in the forms of
modularity and hierarchy, whose composition may be compactly described. This
renders metabolic architecture comprehensible as a system, and suggests the
order in which layers of that system emerged. Metabolism also serves as the
foundation in other hierarchies, at least up to cellular integration including
bioenergetics and molecular replication, and trophic ecology. The
recapitulation of patterns first seen in metabolism, in these higher levels,
suggests metabolism as a source of causation or constraint on many forms of
organization in the biosphere.
We identify as modules widely reused subsets of chemicals, reactions, or
functions, each with a conserved internal structure. At the small molecule
substrate level, module boundaries are generally associated with the most
complex reaction mechanisms and the most conserved enzymes. Cofactors form a
structurally and functionally distinctive control layer over the small-molecule
substrate. Complex cofactors are often used at module boundaries of the
substrate level, while simpler ones participate in widely used reactions.
Cofactor functions thus act as "keys" that incorporate classes of organic
reactions within biochemistry.
The same modules that organize the compositional diversity of metabolism are
argued to have governed long-term evolution. Early evolution of core
metabolism, especially carbon-fixation, appears to have required few
innovations among a small number of conserved modules, to produce adaptations
to simple biogeochemical changes of environment. We demonstrate these features
of metabolism at several levels of hierarchy, beginning with the small-molecule
substrate and network architecture, continuing with cofactors and key conserved
reactions, and culminating in the aggregation of multiple diverse physical and
biochemical processes in cells.Comment: 56 pages, 28 figure
Male reproductive health and environmental xenoestrogens
EHP is a publication of the U.S. government. Publication of EHP lies in the public domain and is therefore without copyright.
Research articles from EHP may be used freely; however, articles from the News section of EHP may contain photographs or figures copyrighted by other commercial organizations and individuals that may not be used without obtaining prior approval from both the EHP editors and the holder of the copyright.
Use of any materials published in EHP should be acknowledged (for example, "Reproduced with permission from Environmental Health Perspectives") and a reference provided for the article from which the material was reproduced.Male reproductive health has deteriorated in many countries during the last few decades. In the 1990s, declining semen quality has been reported from Belgium, Denmark, France, and Great Britain. The incidence of testicular cancer has increased during the same time incidences of hypospadias and cryptorchidism also appear to be increasing. Similar reproductive problems occur in many wildlife species. There are marked geographic differences in the prevalence of male reproductive disorders. While the reasons for these differences are currently unknown, both clinical and laboratory research suggest that the adverse changes may be inter-related and have a common origin in fetal life or childhood. Exposure of the male fetus to supranormal levels of estrogens, such as diethlylstilbestrol, can result in the above-mentioned reproductive defects. The growing number of reports demonstrating that common environmental contaminants and natural factors possess estrogenic activity presents the working hypothesis that the adverse trends in male reproductive health may be, at least in part, associated with exposure to estrogenic or other hormonally active (e.g., antiandrogenic) environmental chemicals during fetal and childhood development. An extensive research program is needed to understand the extent of the problem, its underlying etiology, and the development of a strategy for prevention and intervention.Supported by EU Contract BMH4-CT96-0314
Learning through social spaces: migrant women and lifelong learning in post-colonial London
This article shows how migrant women engage in learning through social spaces. It argues that such spaces are little recognised, and that there are multiple ways in which migrant women construct and negotiate their informal learning through socialising with other women in different informal modes. Additionally, the article shows how learning is shaped by the socio-political, geographical and multicultural context of living in London, outlining ways in which gendered and racialised identities shape, construct and constrain participation in lifelong learning. The article shows that one way in which migrant women resist (post)colonial constructions of difference is by engaging in informal and non-formal lifelong learning, arguing that the benefits are (at least) two-fold. The women develop skills (including language skills) but also use their informal learning to develop what is referred to in this article as 'relational capital'. The article concludes that informal lifelong learning developed through social spaces can enhance a sense of belonging for migrant women
Influence of low back pain and prognostic value of MRI in sciatica patients in relation to back pain
Background: Patients with sciatica frequently complain about associated back pain. It is not known whether there are prognostic relevant differences in Magnetic Resonance Imaging (MRI) findings between sciatica patients with and without disabling back pain. Methods: The study population contained patients with sciatica who underwent a baseline MRI to assess eligibility for a randomized trial designed to compare the efficacy of early surgery with prolonged conservative care for sciatica. Two neuroradiologists and one neurosurgeon independently evaluated all MR images. The MRI readers were blinded to symptom status. The MRI findings were compared between sciatica patients with and without disabling back pain. The presence of disabling back pain at baseline was correlated with perceived recovery at one year. Results: Of 379 included sciatica patients, 158 (42%) had disabling back pain. Of the patients with both sciatica and disabling back pain 68% did reveal a herniated disc with nerve root compression on MRI, compared to 88% of patients with predominantly sciatica (P,0.001). The existence of disabling back pain in sciatica at baseline was negatively associated with perceived recovery at one year (Odds ratio [OR] 0.32, 95% Confidence Interval 0.18-0.56, P,0.001). Sciatica patients with disabling back pain in absence of nerve root compression on MRI at baseline reported less perceived recovery at one year compared to those with predominantly sciatica and nerve root compression on MRI (50% vs 91%, P,0.001). Conclusion: Sciatica patients with disabling low back pain reported an unfavorable outcome at one-year follow-up compared to those with predominantly sciatica. If additionally a clear herniated disc with nerve root compression on MRI was absent, the results were even worse. Copyright
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