3,019 research outputs found
The prevalence and clinical signs and symptoms of low back pain in people with hip osteoarthritis: a cross sectional study
B -> K^* gamma from D -> K^* l nu
The B -> K^* gamma branching fraction is predicted using heavy quark spin
symmetry at large recoil to relate the tensor and (axial-)vector form factors,
using heavy quark flavor symmetry to relate the B decay form factors to the
measured D -> K^* l nu form form factors, and extrapolating the semileptonic B
decay form factors to large recoil assuming nearest pole dominance. This
prediction agrees with data surprisingly well, and we comment on its
implications for the extraction of |Vub| from B -> rho l nu.Comment: 10 page
Charm and Bottom Semileptonic Decays
We review the present status of theoretical attempts to calculate the
semileptonic charm and bottom decays and then present a calculation of these
decays in the light--front frame at the kinematic point . This allows us
to evaluate the form factors at the same value of , even though the
allowed kinematic ranges for charm and bottom decays are very different. Also,
at this kinematic point the decay is given in terms of only one form factor
. For the ratio of the decay rates given by the E653 collaboration we
show that the determination of the ratio of the Cabibbo--Kobayashi--Maskawa
(CKM) matrix elements is consistent with that obtained from the unitarity
constraint. At present, though, the unitarity method still has greater
accuracy. Since comparisons of the semileptonic decays into and either
electrons or muons will be available soon from the E791 Fermilab experiment, we
also look at the massive muon case. We show that for a range of the
symmetry breaking is small even though the contributions of the
various helicity amplitudes becomes more complicated. For decays, the decay
at involves an extra form factor
coming from the photon contribution and so is not amenable to the same kind of
analysis, leaving only the decay as a
possibility. As the mass of the decaying particle increases we note that the
symmetry becomes badly broken at .Comment: Latex, 19 pages, two figures are attached, a minor change in the
manuscript related to thi
Optical energies of AllnN epilayers
Optical energy gaps are measured for high-quality Al1−xInxN-on-GaN epilayers with a range of compositions around the lattice match point using photoluminescence and photoluminescence excitation spectroscopy. These data are combined with structural data to determine the compositional dependence of emission and absorption energies. The trend indicates a very large bowing parameter of 6 eV and differences with earlier reports are discussed. Very large Stokes' shifts of 0.4-0.8 eV are observed in the composition range 0.13<x<0.24, increasing approximately linearly with InN fraction despite the change of sign of the piezoelectric fiel
A consistent treatment for pion form factors in space-like and time-like regions
We write down some relevant matrix elements for the scattering and decay
processes of the pion by considering a quark-meson vertex function. The pion
charge and transition form factors , , and
are extracted from these matrix elements using a relativistic
quark model on the light-front. We found that, the form factors and
in the space-like region agree well with experiment.
Furthermore, the branching ratios of all observed decay modes of the neutral
pion, that are related to the form factors and
in the time-like region, are all consistent with the data as
well. Additionally, in the time-like region, which deals with the
nonvalence contribution, is also discussed.Comment: 24 pages, 6 figures, to appear in Phys. Rev.
Distributed Drug Discovery, Part 2: Global Rehearsal of Alkylating Agents for the Synthesis of Resin-Bound Unnatural Amino Acids and Virtual D3 Catalog Construction
Specifying computer-supported collaboration scripts
Collaboration scripts are activity programs which aim to foster collaborative learning by structuring interaction between learners. Computer-supported collaboration scripts generally suffer from the problem of being restrained to a specific learning platform and learning context. A standardization of collaboration scripts first requires a specification of collaboration scripts that integrates multiple perspectives from computer science, education and psychology. So far, only few and limited attempts at such specifications have been made. This paper aims to consolidate and expand these approaches in light of recent findings and to propose a generic framework for the specification of collaboration scripts. The framework enables a description of collaboration scripts using a small number of components (participants, activities, roles, resources and groups) and mechanisms (task distribution, group formation and sequencing)
Distributed Drug Discovery, Part 3: Using D3 Methodology to Synthesize Analogs of an Anti-Melanoma Compound
Potential Models for Radiative Rare B Decays
We compute the branching ratios for the radiative rare decays of B into
K-Meson states and compare them to the experimentally determined branching
ratio for inclusive decay b -> s gamma using non relativistic quark model, and
form factor definitions consistent with HQET covariant trace formalism. Such
calculations necessarily involve a potential model. In order to test the
sensitivity of calculations to potential models we have used three different
potentials, namely linear potential, screening confining potential and heavy
quark potential as it stands in QCD.We find the branching ratios relative to
the inclusive b ->s gamma decay to be (16.07\pm 5.2)% for B -> K^* (892)gamma
and (7.25\pm 3.2)% for B -> K_2^* (1430)gamma for linear potential. In the case
of the screening confining potential these values are (19.75\pm 5.3)% and
(4.74\pm 1.2)% while those for the heavy quark potential are (11.18\pm 4.6)%
and (5.09\pm 2.7)% respectively. All these values are consistent with the
corresponding present CLEO experimental values: (16.25\pm 1.21)% and (5.93\pm
0.46)%.Comment: RevTeX, 6 pages, 1 eps figur
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