72 research outputs found
The Paraldor Project
Paraldor is an experiment in bringing the power of categorical languages to
lattice QCD computations. Our target language is Aldor, which allows the
capture of the mathematical structure of physics directly in the structure of
the code using the concepts of categories, domains and their
inter-relationships in a way which is not otherwise possible with current
popular languages such as Fortran, C, C++ or Java. By writing high level
physics code portably in Aldor, and implementing switchable machine dependent
high performance back-ends in C or assembler, we gain all the power of
categorical languages such as modularity, portability, readability and
efficiency.Comment: 4 pages, 2 figures, Lattice 2002 conference proceeding
Decays of mesons with charm quarks on the lattice
We investigate mesons containing charm quarks on fine lattices with a^{-1}
\sim 5 GeV. The quenched approximation is employed using the Wilson gauge
action at \beta = 6.6 and nonperturbatively O(a) improved Wilson quarks. We
present results for decay constants using various interpolating fields and give
preliminary results for form factors of semileptonic decays of D_s mesons to
light pseudoscalar mesons.Comment: 7 pages, 3 figures, talk presented at the XXV International Symposium
on Lattice Field Theory, 30 July - 4 August 2007, Regensburg, German
Spectral Curves and Localization in Random Non-Hermitian Tridiagonal Matrices
Eigenvalues and eigenvectors of non-Hermitian tridiagonal periodic random
matrices are studied by means of the Hatano-Nelson deformation. The deformed
spectrum is annular-shaped, with inner radius measured by the complex Thouless
formula. The inner bounding circle and the annular halo are stuctures that
correspond to the two-arc and wings observed by Hatano and Nelson in deformed
Hermitian models, and are explained in terms of localization of eigenstates via
a spectral duality and the Argument principle.Comment: 5 pages, 9 figures, typographical error corrected in reference
QCD dynamics in a constant chromomagnetic field
We investigate the phase transition in full QCD with two flavors of staggered
fermions in presence of a constant abelian chromomagnetic field. We find that
the critical temperature depends on the strength of the chromomagnetic field
and that the deconfined phase extends to very low temperatures for strong
enough fields. As in the case of zero external field, a single transition is
detected, within statistical uncertainties, where both deconfinement and chiral
symmetry restoration take place. We also find that the chiral condensate
increases with the strength of the chromomagnetic field.Comment: 18 pages, 8 figures, 1 tabl
Semi-leptonic decays of heavy mesons and the Isgur-Wise function in quenched lattice QCD
The form factors for the semi-leptonic B->D and B->D* decays are evaluated in
quenched lattice QCD at two different values of the coupling, beta=6.0 and 6.2.
The action and the operators are fully O(a) non-perturbatively improved. The
slope of the Isgur-Wise function is evaluated, and found to be
rho^2=0.83^{+15+24}_{-11-1} (quoted errors are statistical and systematic
respectively). Ratios of form factors are evaluated and compared to
experimental determinations.Comment: 21 pages, 10 figure
Semileptonic form factors D , K and B , K from a fine lattice
We extract the form factors relevant for semileptonic decays of D and B mesons from a relativistic computation on a fine lattice in the quenched approximation. The lattice spacing is a = 0.04 fm (corresponding to a -1 = 4.97 GeV), which allows us to run very close to the physical B meson mass, and to reduce the systematic errors associated with the extrapolation in terms of a heavy-quark expansion. For decays of D and Ds mesons, our results for the physical form factors at \ensuremath q^2 = 0 are as follows: \ensuremath f_+^{D\rightarrow\pi}(0) = 0.74(6)(4) , \ensuremath f_+^{D \rightarrow K}(0) = 0.78(5)(4) and \ensuremath f_+^{D_s \rightarrow K} (0) = 0.68(4)(3) . Similarly, for B and Bs we find \ensuremath f_+^{B\rightarrow\pi}(0) = 0.27(7)(5) , \ensuremath f_+^{B\rightarrow K} (0) = 0.32(6)(6) and \ensuremath f_+^{B_s\rightarrow K}(0) = 0.23(5)(4) . We compare our results with other quenched and unquenched lattice calculations, as well as with light-cone sum rule predictions, finding good agreemen
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Mechanisms of airfoil noise near stall conditions
The focus of this paper is on investigating the noise produced by an airfoil at high angles of attack over a range of Reynolds number
Reâ2Ă10â”â4Ă10â”. The objective is not modeling this source of noise but rather understanding the mechanisms of generation for surface pressure fluctuations, due to a separated boundary layer, that are then scattered by the trailing edge. To this aim, we use simultaneous noise and surface pressure measurement in addition to velocimetric measurements by means of hot wire anemometry and time-resolved particle image velocimetry. Three possible mechanisms for the so-called âseparation-stall noiseâ have been identified in addition to a clear link between far-field noise, surface pressure, and velocity fields in the noise generation
Leading edge serrations for the reduction of aerofoil separation self-noise
This paper presents an experimental investigation into the use of LE serrations for the reduction of trailing edge self-noise, at least for the NACA-65 aerofoil family. It is shown that the leading edge serrations are able to reduce the self-noise in a low frequency range at small and negative angles of attack. The exact mechanism of this reduction is still not completely discovered, but the LE serrations are discovered able to modulate the mean velocity ïŹeld and turbulent velocity spectrum in that range of frequencies, as well as to dampen the eïŹect of the angle of attack on the pressure ïŹeld and to reduce its coherence. We emphasise that this paper represents work in progress and further investigations are still necessary in order to completely understand the dynamics behind this reduction
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