436 research outputs found
Matching Regge Theory to the OPE
The spectra of masses and decay constants for non-strange meson resonances in
the energy range 0--2.5 GeV is analyzed. It is known from meson phenomenology
that for given quantum numbers these spectra approximately follow linear
trajectories with a universal slope. These facts can be understood in terms of
an effective string description for QCD. For light meson states the
trajectories deviate noticeably from the linear behavior. We investigate the
possible corrections to the linear trajectories by matching two-point
correlators of quark currents to the Operator Product Expansion (OPE). We find
that the allowed modifications to the linear Regge behavior must decrease
rapidly with the principal quantum number. After fitting the lightest states in
each channel and certain low-energy constants the whole spectrum for meson
masses and residues is obtained in a satisfactory agreement with phenomenology.
We briefly speculate on possible implications for the QCD effective string.Comment: 24 pages, Latex, significant changes in discussion of fits, more refs
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Flavour SU(3) Symmetry in Charmless B Decays
QCD sum rules are used to estimate the flavour SU(3)-symmetry violation in
two-body B decays to pions and kaons. In the factorizable amplitudes the
SU(3)-violation manifests itself in the ratio of the decay constants f_K/f_pi
and in the differences between the B->K, B_s->K and B->pi form factors. These
effects are calculated from the QCD two-point and light-cone sum rules,
respectively, in terms of the strange quark mass and the ratio of the strange
and nonstrange quark-condensate densities. Importantly, QCD sum rules predict
that SU(3) breaking in the heavy-to-light form factors can be substantial and
does not vanish in the heavy-quark mass limit. Furthermore, we investigate the
strange-quark mass dependence of nonfactorizable effects in the B->K pi decay
amplitudes. Taking into account these effects we estimate the accuracy of
several SU(3)-symmetry relations between charmless B-decay amplitudes.Comment: Two references added, version to be published in Phys.Rev.D, 21
pages, 12 postscript figure
Modelled agroforestry outputs at field and farm scale to support biophysical and environmental assessments
This report, comprising Deliverable 6.17, in the AGFORWARD project brings together examples of modelled outputs at field and farm scale to support the biophysical, social, and environmental assessment of the innovations selected from work-packages 2 to 5.N/
Evaluation of sesamum gum as an excipient in matrix tablets
In developing countries modern medicines are often beyond the affordability of the majority of the population. This is due to the reliance on expensive imported raw materials despite the abundance of natural resources which could provide an equivalent or even an improved function. The aim of this study was to investigate the potential of sesamum gum (SG) extracted from the leaves of Sesamum radiatum (readily cultivated in sub-Saharan Africa) as a matrix former. Directly compressed matrix tablets were prepared from the extract and compared with similar matrices of HPMC (K4M) using theophylline as a model water soluble drug. The compaction, swelling, erosion and drug release from the matrices were studied in deionized water, 0.1 N HCl (pH 1.2) and phosphate buffer (pH 6.8) using USP apparatus II. The data from the swelling, erosion and drug release studies were also fitted into the respective mathematical models. Results showed that the matrices underwent a combination of swelling and erosion, with the swelling action being controlled by the rate of hydration in the medium. SG also controlled the release of theophylline similar to the HPMC and therefore may have use as an alternative excipient in regions where Sesamum radiatum can be easily cultivated
Global data on earthworm abundance, biomass, diversity and corresponding environmental properties
14 p.Earthworms are an important soil taxon as ecosystem engineers, providing a variety of crucial ecosystem functions and services. Little is known about their diversity and distribution at large spatial scales, despite the availability of considerable amounts of local-scale data. Earthworm diversity data, obtained from the primary literature or provided directly by authors, were collated with information on site locations, including coordinates, habitat cover, and soil properties. Datasets were required, at a minimum, to include abundance or biomass of earthworms at a site. Where possible, site-level species lists were included, as well as the abundance and biomass of individual species and ecological groups. This global dataset contains 10,840 sites, with 184 species, from 60 countries and all continents except Antarctica. The data were obtained from 182 published articles, published between 1973 and 2017, and 17 unpublished datasets. Amalgamating data into a single global database will assist researchers in investigating and answering a wide variety of pressing questions, for example, jointly assessing aboveground and belowground biodiversity distributions and drivers of biodiversity change
Fine-mapping of prostate cancer susceptibility loci in a large meta-analysis identifies candidate causal variants
Prostate cancer is a polygenic disease with a large heritable component. A number of common, low-penetrance prostate cancer risk loci have been identified through GWAS. Here we apply the Bayesian multivariate variable selection algorithm JAM to fine-map 84 prostate cancer susceptibility loci, using summary data from a large European ancestry meta-analysis. We observe evidence for multiple independent signals at 12 regions and 99 risk signals overall. Only 15 original GWAS tag SNPs remain among the catalogue of candidate variants identified; the remainder are replaced by more likely candidates. Biological annotation of our credible set of variants indicates significant enrichment within promoter and enhancer elements, and transcription factor-binding sites, including AR, ERG and FOXA1. In 40 regions at least one variant is colocalised with an eQTL in prostate cancer tissue. The refined set of candidate variants substantially increase the proportion of familial relative risk explained by these known susceptibility regions, which highlights the importance of fine-mapping studies and has implications for clinical risk profiling. © 2018 The Author(s).Prostate cancer is a polygenic disease with a large heritable component. A number of common, low-penetrance prostate cancer risk loci have been identified through GWAS. Here we apply the Bayesian multivariate variable selection algorithm JAM to fine-map 84 prostate cancer susceptibility loci, using summary data from a large European ancestry meta-analysis. We observe evidence for multiple independent signals at 12 regions and 99 risk signals overall. Only 15 original GWAS tag SNPs remain among the catalogue of candidate variants identified; the remainder are replaced by more likely candidates. Biological annotation of our credible set of variants indicates significant enrichment within promoter and enhancer elements, and transcription factor-binding sites, including AR, ERG and FOXA1. In 40 regions at least one variant is colocalised with an eQTL in prostate cancer tissue. The refined set of candidate variants substantially increase the proportion of familial relative risk explained by these known susceptibility regions, which highlights the importance of fine-mapping studies and has implications for clinical risk profiling. © 2018 The Author(s).Peer reviewe
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