1,834 research outputs found
Evidence for eta prime - pion splitting in unquenched lattice QCD
We perform an extrapolation from negative to positive flavour numbers of full
QCD lattice estimates of the mass. The extrapolations are carried out
by keeping and masses at fixed values. We find an --
splitting which shows a flavour dependence consistent with the Witten Veneziano
formula based on the anomaly. The quantitative splitting is consistent
with the estimates made in the quenched approximation.Comment: 22 pages, uuencoded latex files, text + 8 figure
Universal behaviour of the SU(2) running coupling constant in the continuum limit
We present data from the ALPHA Collaboration about lattice calculation of
SU(2) pure--gauge running coupling constant, obtained with two different
definitions of the coupling itself, which show universality of the continuum
limit and clarify the applicability of renormalized perturbation theory.Comment: 3 pages, postscript, contribution to LAT94 also available at
http://sutova.roma2.infn.it/preprints/TovApe/lat94m.ps (eq. (3) corrected
Pseudofermion observables for static heavy meson decay constants on the lattice
A method based on the Monte Carlo inversion of the Dirac operator on the
lattice provides low noise results for the correlations entering the definition
of the heavy meson decay constant in the static limit. The method is
complementary to the usual method of smeared sources, avoids the systematic
error arising from optimizing the size of the smearing volume and is more
efficient for the values of lattice parameters that we have explored.Comment: 11 pages, uuencoded ps file, 2 figures include
Statistics of finite scale local Lyapunov exponents in fully developed homogeneous isotropic turbulence
The present work analyzes the statistics of finite scale local Lyapunov
exponents of pairs of fluid particles trajectories in fully developed
incompressible homogeneous isotropic turbulence. According to the hypothesis of
fully developed chaos, this statistics is here analyzed assuming that the
entropy associated to the fluid kinematic state is maximum. The distribution of
the local Lyapunov exponents results to be an unsymmetrical uniform function in
a proper interval of variation. From this PDF, we determine the relationship
between average and maximum Lyapunov exponents, and the longitudinal velocity
correlation function. This link, which in turn leads to the closure of von
K\`arm\`an-Howarth and Corrsin equations, agrees with results of previous
works, supporting the proposed PDF calculation, at least for the purposes of
the energy cascade main effect estimation. Furthermore, through the property
that the Lyapunov vectors tend to align the direction of the maximum growth
rate of trajectories distance, we obtain the link between maximum and average
Lyapunov exponents in line with the previous results. To validate the proposed
theoretical results, we present different numerical simulations whose results
justify the hypotheses of the present analysis.Comment: Research article. arXiv admin note: text overlap with
arXiv:1706.0097
Refinement of a previous hypothesis of the Lyapunov analysis of isotropic turbulence
The purpose of this brief comunication is to improve a hypothesis of the
previous work of the author (de Divitiis, Theor Comput Fluid Dyn,
doi:10.1007/s00162-010-0211-9) dealing with the finite--scale Lyapunov analysis
of isotropic turbulence. There, the analytical expression of the structure
function of the longitudinal velocity difference is derived
through a statistical analysis of the Fourier transformed Navier-Stokes
equations, and by means of considerations regarding the scales of the velocity
fluctuations, which arise from the Kolmogorov theory. Due to these latter
considerations, this Lyapunov analysis seems to need some of the results of the
Kolmogorov theory.
This work proposes a more rigorous demonstration which leads to the same
structure function, without using the Kolmogorov scale. This proof assumes that
pair and triple longitudinal correlations are sufficient to determine the
statistics of , and adopts a reasonable canonical decomposition of
the velocity difference in terms of proper stochastic variables which are
adequate to describe the mechanism of kinetic energy cascade.Comment: 6 page
Bifurcations analysis of turbulent energy cascade
This note studies the mechanism of turbulent energy cascade through an
opportune bifurcations analysis of the Navier--Stokes equations, and furnishes
explanations on the more significant characteristics of the turbulence. A
statistical bifurcations property of the Navier--Stokes equations in fully
developed turbulence is proposed, and a spatial representation of the
bifurcations is presented, which is based on a proper definition of the fixed
points of the velocity field. The analysis first shows that the local
deformation can be much more rapid than the fluid state variables, then
explains the mechanism of energy cascade through the aforementioned property of
the bifurcations, and gives reasonable argumentation of the fact that the
bifurcations cascade can be expressed in terms of length scales. Furthermore,
the study analyzes the characteristic length scales at the transition through
global properties of the bifurcations, and estimates the order of magnitude of
the critical Taylor--scale Reynolds number and the number of bifurcations at
the onset of turbulence.Comment: 14 pages, 5 figures, available online Annals of Physics, 201
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