323 research outputs found
Design and Experimental Validation of a Ducted Counter-rotating Axial-flow Fans System
An experimental study on the design of counter-rotating axial-flow fans was
carried out. The fans were designed using an inverse method. In particular, the
system is designed to have a pure axial discharge flow. The counter-rotating
fans operate in a ducted-flow configuration and the overall performances are
measured in a normalized test bench. The rotation rate of each fan is
independently controlled. The relative axial spacing between fans can vary from
17% to 310%. The results show that the efficiency is strongly increased
compared to a conventional rotor or to a rotor-stator stage. The effects of
varying the rotation rates ratio on the overall performances are studied and
show that the system has a very flexible use, with a large patch of high
efficient operating points in the parameter space. The increase of axial
spacing causes only a small decrease of the efficiencyComment: accepted in Journal of Fluid Engineerin
Semi-leptonic decays heavy-light to heavy light
We present results for the QCD matrix elements involved in semi-leptonic
decays of B-mesons into pseudo scalar heavy light states. The application of
NRQCD heavy quarks allows for quark masses around the physical b-quark. We
investigate the dependence of the form factors on the external momenta and
looked at the mass dependence at zero recoil. For the first time, results for
radially excited decay products are presented.Comment: 3 pages LaTeX, 5 figures, Talk given at LATTICE99(Heavy Quarks), June
29th to July 3rd, 1999, Pisa, Ital
Update: Precision D_s decay constant from full lattice QCD using very fine lattices
We update our previous determination of both the decay constant and the mass
of the meson using the Highly Improved Staggered Quark formalism. We
include additional results at two finer values of the lattice spacing along
with improved determinations of the lattice spacing and improved tuning of the
charm and strange quark masses. We obtain = 1.9691(32) GeV, in good
agreement with experiment, and = 0.2480(25) GeV. Our result for
is 1.6 lower than the most recent experimental average
determined from the leptonic decay rate and using from CKM
unitarity. Combining our with the experimental rate we obtain a
direct determination of , or alternatively using a probability distribution for statistical errors for this
quantity which vanishes above 1. We also include an accurate prediction of the
decay constant of the , = 0.3947(24) GeV, as a calibration
point for other lattice calculations.Comment: 24 pages, 20 figures. Updated to include new experimental results
from BaBar, new experimental averages from HFAG and consequent discussion of
theory/experiment comparison. Other minor typographical changes. Version
accepted by Phys. Rev.
Fast Fits for Lattice QCD Correlators
We illustrate a technique for fitting lattice QCD correlators to sums of
exponentials that is significantly faster than traditional fitting methods ---
10--40 times faster for the realistic examples we present. Our examples are
drawn from a recent analysis of the Upsilon spectrum, and another recent
analysis of the D -> pi semileptonic form factor. For single correlators, we
show how to simplify traditional effective-mass analyses.Comment: 5 pages, 4 figure
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