595 research outputs found
B Physics on the Lattice: , , , , mixing, \fb and all that
We present a short review of our most recent high statistics lattice
determinations in the HQET of the following important parameters in B physics:
the B--meson binding energy, and the kinetic energy of the
b quark in the B meson, , which due to the presence of power
divergences require a non--perturbative renormalization to be defined; the
running mass of the b quark,
; the -- mass splitting, whose
value in the HQET is determined by the matrix element of the chromo--magnetic
operator between B meson states, ; the B parameter of the
-- mixing, , and the decay constant of the B meson,
. All these quantities have been computed using a sample of gauge
field configurations on a lattice at . For
and , we obtain our
estimates by combining results from three independent lattice simulations at
, and on the same volume.Comment: 3 latex pages, uses espcrc2.sty (included). Talk presented at
LATTICE96(heavy quarks
DEPENDENCE OF THE CURRENT RENORMALISATION CONSTANTS ON THE QUARK MASS
We study the behaviour of the vector and axial current renormalisation
constants and as a function of the quark mass, . We show that
sizeable and systematic effects are present in the
Wilson and Clover cases respectively. We find that the prescription of
Kronfeld, Lepage and Mackenzie for correcting these artefacts is not always
successful.Comment: Contribution to Lattice'94, 3 pages PostScript, uuencoded compressed
Semileptonic Decays of Heavy Mesons: A Status Report
We present intermediate results on our ongoing investigation concerning
semileptonic decays of heavy pseudoscalar mesons into pseudoscalar and vector
mesons. The corresponding formfactors are evaluated at several momenta and
appropriate combinations of four light and four heavy quarks, which are chosen
to allow for an extrapolation into the B Meson region. In order to obtain clear
groundstate signals we apply gauge invariant ``Wuppertal'' smearing to the
quarks. The analysis is based on 32 quenched gauge configurations of size at , with Wilson fermions.Comment: 3 pages, uuencoded, contribution to Lat 9
Non-perturbative Renormalization of the Complete Basis of Four-fermion Operators and B-parameters
We present results on the B-parameters , and , at
, with the tree-level Clover action. The renormalization of the
complete basis of dimension-six four-fermion operators has been performed
non-perturbatively. Our results for and are in reasonable
agreement with those obtained with the (unimproved) Wilson action. This is not
the case for . We also discuss some subtleties arising from a
recently proposed modified definition of the B-parameters.Comment: Talk presented at Lattice '97, Edinburgh (UK), July 1997. LaTeX 3
pages, uses espcrc
Theoretical and experimental analysis of dissipative buckling restrained barces
Buckling restrained braces are passive energy dissipators used for seismic protection of building
frames; such devices consist of slender steel bars connected usually to the frame to be protected
either like conventional (concentric) diagonal braces or like chevron braces. Under horizontal
seismic motions, the interstory drifts generate axial strains in the steel bars beyond their yielding
points; such tension-compression cycles constitute the hysteresis loops. The buckling of the steel
bars (core) is prevented by embedding them in a stockiest encasing; it consists usually of a steel
tube filled with mortar. A crucial issue is to allow sliding between the core and the encasing to
prevent relevant shear stress transfer.
This work aims to contribute to a better understanding of the behavior of buckling restrained
braces; the final objective is to foster its mass use in developing countries (in earthquake prone
regions), particularly for reinforced concrete building frames. The research approach consists of
designing, producing and testing (in Argentina) five reduced scale dissipators (about 400 mm
long) and of taking profit of the gained experience to design, to produce and to test (in Spain) four
full size (near 3000 mm long) prototype devices. All these tests are individual, i.e. no
subassemblies (accounting for the building frames) are considered.
The main conclusion is that it is possible to obtain a reasonably cheap (about 1000 US$ per unit;
this amount corresponds to production in Spain (summer 2006) without optimizing the
fabrication process), efficient, robust, low maintenance and durable prototype device requiring
only a low-tech production process (suitable for developing countries). Moreover, the results
show that the fatigue life of buckling restrained braces, even highly uncertain, can be significantly
bigger than expected (according to some previously published results); it might allow extending
the life of these devices after a number of strong seismic inputs.
A numerical analysis of the buckling behavior of these devices is performed; it allows
formulating some design recommendations. Further research needs are identified
Theoretical and experimental analysis of dissipative buckling restrained braces
Buckling restrained braces are passive energy dissipators used for seismic protection of building frames; such devices consist of slender steel bars connected usually to the frame to be protected either like conventional (concentric) diagonal braces or like chevron braces. Under horizontal seismic motions, the interstory drifts generate axial strains in the steel bars beyond their yielding points, such tension-compresssion cycles constitute the hysteresis loops. Thebuckling of the steel bars (core) is prevented by embedding them in a stockiest encasing; it consists usually of a steel tube filled with mortar. A crucial issue is to allow sliding between the core and the encasing to prevent relevant shear stress transfer. This work aims to contribute to a better understanding of the behavior of buckling restrained braces, the final objective is to foster its mass use in developing countries (in earthquake prone regions), particulary for reinforced concrete building frames. The research approach consists of designing, producing and testing (in Argentina) five reduced scale dissipators (about 400 mm long) and of taking profit of the gained experience to design, to produce and to test (in Spain) four full size (near 3000 mm long) prototype devices. All these tests are a individual, i.e. no subassemblies (accounting for the building frames) are considered. The main conclusion is that it is possible to obtain a reasonably cheap (about 1000 US$ per unit; this amount corresponds to production in Spain (summer 2006) without optimizing the fabrication process), efficient, robust, low maintenance and durable prototype device requiring only a low-tech production process (suitable for developing countries). Moreover, the results show that the fatigue life of buckling restrained braces, even highly uncertain, can be significantly bigger than expected (according to some previously published results); it might allow extending the life of these devices after a number of strong seismic inputs. A numerical analysis of the buckling behavior of these devices is performed; it allows formulating some design recommendations. Further research needs are identified.Postprint (published version
RESULTS FOR THE B-MESON DECAY CONSTANT FROM THE APE COLLABORATION
The decay constant for the B-meson in the static limit is calculated using
the Wilson and clover actions at various lattice spacings. We show that both
the contamination of our results by excited states and the effects finite
lattice spacing are at most the order of the statistical uncertainties. A
comparison is made of our results and those obtained in other studies. Values
for and are also given.Comment: Contribution to Lattice'94, 3 pages PostScript, uuencoded compresse
Non-perturbative renormalization in kaon decays
We discuss the application of the MPSTV non-perturbative method \cite{NPM} to
the operators relevant to kaon decays. This enables us to reappraise the
long-standing question of the rule, which involves
power-divergent subtractions that cannot be evaluated in perturbation theory.
We also study the mixing with dimension-six operators and discuss its
implications to the chiral behaviour of the parameter.Comment: Talk presented at LATTICE96(improvement), LaTeX 3 pages, uses
espcrc2, 2 postscript figure
Do Patients with Bronchiectasis Have an Increased Risk of Developing Lung Cancer? A Systematic Review
Background: Initial evidence supports the hypothesis that patients with non-cystic fibrosis bronchiectasis (NCFB) have a higher risk of lung cancer. We systematically reviewed the available literature to define the characteristics of lung malignancies in patients with bronchiectasis and the characteristics of patients who develop bronchiectasis-associated lung cancer. Method: This study was performed based on the PRISMA guidelines. The review protocol was registered in PROSPERO. Results: The frequency rates of lung cancer in patients with NCFB ranged from 0.93% to 8.0%. The incidence rate was 3.96. Cancer more frequently occurred in the elderly and males. Three studies found an overall higher risk of developing lung cancer in the NCFB population compared to the non-bronchiectasis one, and adenocarcinoma was the most frequently reported histological type. The effect of the co-existence of NCFB and COPD was unclear. Conclusions: NCFB is associated with a higher risk of developing lung cancer than individuals without NCFB. This risk is higher for males, the elderly, and smokers, whereas concomitant COPDâs effect is unclear
Computation of the b-quark Mass with Perturbative Matching at the Next-to-Next-to-Leading Order
We compute the two-loop term in the perturbation series for the quark-mass in
the lattice Heavy Quark Effective Theory. This is an ingredient in the matching
factor required to obtain the -quark mass from lattice simulations of the
HQET. Combining our calculations with numerical results from the APE
collaboration, we find, at two-loop order, GeV. It was expected that
the two-loop term would have a significant effect and this is indeed what we
find. Depending on the choice of "reasonable" coupling constant in the one-loop
estimates the result for can change by several hundred MeV when the
two-loop terms are included.Comment: 24 Pages, 1 Figur
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