2,670 research outputs found
Determination of the Kobayashi-Maskawa-Cabibbo matrix element V_{us} under various flavor-symmetry-breaking models in hyperon semileptonic decays
We study the success to describe hyperon semileptonic decays of four models
that incorporate second-order SU(3) symmetry breaking corrections. The criteria
to assess their success is by determining V_{us} in each of the three relevant
hyperon semileptonic decays and comparing the values obtained with one another
and also with the one that comes from K_{l3} decays. A strong dependence on the
particular symmetry breaking model is observed. Values of V_{us} which do not
agree with the one of K_{l3} are generally obtained. However, in the context of
chiral perturbation theory, only the model whose corrections are O(m_s) and
O(m_s^{3/2}) is successful. Using its predictions for the f_1 form factors one
can quote a value of V_{us} from this model, namely, V_{us}=0.2176\pm 0.0026,
which is in excellent agreement with the K_{l3} one.Comment: Final versio
Peaks in the Hartle-Hawking Wave Function from Sums over Topologies
Recent developments in ``Einstein Dehn filling'' allow the construction of
infinitely many Einstein manifolds that have different topologies but are
geometrically close to each other. Using these results, we show that for many
spatial topologies, the Hartle-Hawking wave function for a spacetime with a
negative cosmological constant develops sharp peaks at certain calculable
geometries. The peaks we find are all centered on spatial metrics of constant
negative curvature, suggesting a new mechanism for obtaining local homogeneity
in quantum cosmology.Comment: 16 pages,LaTeX, no figures; v2: some changes coming from revision of
a math reference: wave function peaks sharp but not infinite; v3: added
paragraph in intro on interpretation of wave functio
Panel-Stiffener Debonding and Analysis Using a Shell/3D Modeling Technique
A shear loaded, stringer reinforced composite panel is analyzed to evaluate the fidelity of computational fracture mechanics analyses of complex structures. Shear loading causes the panel to buckle. The resulting out-of-plane deformations initiate skin/stringer separation at the location of an embedded defect. The panel and surrounding load fixture were modeled with shell elements. A small section of the stringer foot, web and noodle as well as the panel skin near the delamination front were modeled with a local 3D solid model. Across the width of the stringer foot, the mixed-mode strain energy release rates were calculated using the virtual crack closure technique. A failure index was calculated by correlating the results with a mixed-mode failure criterion of the graphite/epoxy material. The objective was to study the effect of the fidelity of the local 3D finite element model on the computed mixed-mode strain energy release rates and the failure index
Redshifts for 2410 Galaxies in the Century Survey Region
The `Century Survey' strip covers 102 square degrees within the limits 8.5h
\leq \alpha_{1950} \leq 16.5h, 29.0 degrees \leq \delta_{1950} \leq 30.0
degrees. The strip passes through the Corona Borealis supercluster and the
outer region of the Coma cluster.
Within the Century Survey region, we have measured 2410 redshifts which
constitute four overlapping complete redshift surveys: (1) 1728 galaxies with
Kron-Cousins R_{phot} \leq 16.13 covering the entire strip, (2) 507 galaxies
with R_{phot} \leq 16.4 in the right ascension range 8h 32m \leq \alpha_{1950}
\leq 10h 45m, (3) 1251 galaxies with absorption- and K-corrected R_{CCD, corr}
\leq 16.2 covering the right ascension range 8.5h \leq \alpha_{1950} \leq 13.5h
and (4) 1255 galaxies with absorption- and K-corrected V_{CCD, corr} \leq 16.7
also covering the right ascension range 8.5h \leq \alpha_{1950} \leq 13.5h. All
of these redshift samples are more than 98 % complete to the specified
magnitude limit.Comment: 18 pages, 9 figures, 3 tables, 2 abbreviated tables. In press, to
appear in Astronomical Journal, Dec. 2001 issu
The double torus as a 2D cosmos: groups, geometry and closed geodesics
The double torus provides a relativistic model for a closed 2D cosmos with
topology of genus 2 and constant negative curvature. Its unfolding into an
octagon extends to an octagonal tessellation of its universal covering, the
hyperbolic space H^2. The tessellation is analysed with tools from hyperbolic
crystallography. Actions on H^2 of groups/subgroups are identified for SU(1,
1), for a hyperbolic Coxeter group acting also on SU(1, 1), and for the
homotopy group \Phi_2 whose extension is normal in the Coxeter group. Closed
geodesics arise from links on H^2 between octagon centres. The direction and
length of the shortest closed geodesics is computed.Comment: Latex, 27 pages, 5 figures (late submission to arxiv.org
Mutation analysis of HIF prolyl hydroxylases (PHD/EGLN) in individuals with features of phaeochromocytoma and renal cell carcinoma susceptibility
Germline mutations in the von Hippel–Lindau disease (VHL) and succinate dehydrogenase subunit B (SDHB) genes can cause inherited phaeochromocytoma and/or renal cell carcinoma(RCC). Dysregulation of the hypoxia-inducible factor (HIF) transcription factors has been linked to VHL and SDHB-related RCC; both HIF dysregulation and disordered function of a prolyl hydroxylase domain isoform 3 (PHD3/EGLN3)-related pathway of neuronal apoptosis have been linked to the development of phaeochromocytoma. The 2-oxoglutarate-dependent prolyl hydroxylase enzymes PHD1 (EGLN2), PHD2 (EGLN1) and PHD3 (EGLN3) have a key role in regulating the stability of HIF-a subunits (and hence expression of the HIF-a transcription factors). A germline PHD2 mutation has been reported in association with congenital erythrocytosis and recurrent extra-adrenal phaeochromocytoma. We undertook mutation analysis of PHD1, PHD2 and PHD3 in two cohorts of patients with features of inherited phaeochromocytoma (nZ82) and inherited RCC (nZ64) and no evidence of germline mutations in known susceptibility genes. No confirmed pathogenic mutations were detected suggesting that mutations in these genes are not a frequent cause of inherited phaeochromocytoma or RCC
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