1,382 research outputs found
The large-scale structure of passive scalar turbulence
We investigate the large-scale statistics of a passive scalar transported by
a turbulent velocity field. At scales larger than the characteristic
lengthscale of scalar injection, yet smaller than the correlation length of the
velocity, the advected field displays persistent long-range correlations due to
the underlying turbulent velocity. These induce significant deviations from
equilibrium statistics for high-order scalar correlations, despite the absence
of scalar flux.Comment: 4 pages, 6 figure
Scaling and universality in turbulent convection
Anomalous correlation functions of the temperature field in two-dimensional
turbulent convection are shown to be universal with respect to the choice of
external sources. Moreover, they are equal to the anomalous correlations of the
concentration field of a passive tracer advected by the convective flow itself.
The statistics of velocity differences is found to be universal, self-similar
and close to Gaussian. These results point to the conclusion that temperature
intermittency in two-dimensional turbulent convection may be traced back to the
existence of statistically preserved structures, as it is in passive scalar
turbulence.Comment: 4 pages, 6 figure
Relative dispersion in fully developed turbulence: from Eulerian to Lagrangian statistics in synthetic flows
The effect of Eulerian intermittency on the Lagrangian statistics of relative
dispersion in fully developed turbulence is investigated. A scaling range
spanning many decades is achieved by generating a multi-affine synthetic
velocity field with prescribed intermittency features. The scaling laws for the
Lagrangian statistics are found to depend on Eulerian intermittency in
agreement with a multifractal description. As a consequence of the Kolmogorov's
law, the Richardson's law for the variance of pair separation is not affected
by intermittency corrections.Comment: 4 pages RevTeX, 4 PostScript figure
The predictability problem in systems with an uncertainty in the evolution law
The problem of error growth due to the incomplete knowledge of the evolution
law which rules the dynamics of a given physical system is addressed. Major
interest is devoted to the analysis of error amplification in systems with many
characteristic times and scales. The importance of a proper parameterization of
fast scales in systems with many strongly interacting degrees of freedom is
highlighted and its consequences for the modelization of geophysical systems
are discussed.Comment: 20 pages RevTeX, 6 eps figures (included
Pair dispersion in synthetic fully developed turbulence
The Lagrangian statistics of relative dispersion in fully developed
turbulence is numerically investigated. A scaling range spanning many decades
is achieved by generating a synthetic velocity field with prescribed Eulerian
statistical features. When the velocity field obeys Kolmogorov similarity, the
Lagrangian statistics is self similar too, and in agreement with Richardson's
predictions. For an intermittent velocity field the scaling laws for the
Lagrangian statistics are found to depend on Eulerian intermittency in
agreement with a multifractal description. As a consequence of the Kolmogorov
law the Richardson law for the variance of pair separation is not affected by
intermittency corrections. A new analysis method, based on fixed scale averages
instead of usual fixed time statistics, is shown to give much wider scaling
range and should be preferred for the analysis of experimental data.Comment: 9 pages, 9 ps figures, submitted to Physics of Fluid
Monotonic Distributive Semilattices
In the study of algebras related to non-classical logics, (distributive) semilattices are always present in the background. For example, the algebraic semantic of the {→, ∧, ⊤}-fragment of intuitionistic logic is the variety of implicative meet-semilattices (Chellas 1980; Hansen 2003). In this paper we introduce and study the class of distributive meet-semilattices endowed with a monotonic modal operator m. We study the representation theory of these algebras using the theory of canonical extensions and we give a topological duality for them. Also, we show how our new duality extends to some particular subclasses.Fil: Celani, Sergio Arturo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Departamento de Matemática; ArgentinaFil: Menchón, María Paula. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Departamento de Matemática; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Mimicking a turbulent signal: sequential multiaffine processes
An efficient method for the construction of a multiaffine process, with
prescribed scaling exponents, is presented. At variance with the previous
proposals, this method is sequential and therefore it is the natural candidate
in numerical computations involving synthetic turbulence. The application to
the realization of a realistic turbulent-like signal is discussed in detail.
The method represents a first step towards the realization of a realistic
spatio-temporal turbulent field.Comment: 4 pages, 3 figures (included), RevTeX 3.
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