11 research outputs found
Robust Integrals
In decision analysis and especially in multiple criteria decision analysis,
several non additive integrals have been introduced in the last years. Among
them, we remember the Choquet integral, the Shilkret integral and the Sugeno
integral. In the context of multiple criteria decision analysis, these
integrals are used to aggregate the evaluations of possible choice
alternatives, with respect to several criteria, into a single overall
evaluation. These integrals request the starting evaluations to be expressed in
terms of exact-evaluations. In this paper we present the robust Choquet,
Shilkret and Sugeno integrals, computed with respect to an interval capacity.
These are quite natural generalizations of the Choquet, Shilkret and Sugeno
integrals, useful to aggregate interval-evaluations of choice alternatives into
a single overall evaluation. We show that, when the interval-evaluations
collapse into exact-evaluations, our definitions of robust integrals collapse
into the previous definitions. We also provide an axiomatic characterization of
the robust Choquet integral.Comment: 24 page
Generalized thermodynamics and Fokker-Planck equations. Applications to stellar dynamics, two-dimensional turbulence and Jupiter's great red spot
We introduce a new set of generalized Fokker-Planck equations that conserve
energy and mass and increase a generalized entropy until a maximum entropy
state is reached. The concept of generalized entropies is rigorously justified
for continuous Hamiltonian systems undergoing violent relaxation. Tsallis
entropies are just a special case of this generalized thermodynamics.
Application of these results to stellar dynamics, vortex dynamics and Jupiter's
great red spot are proposed. Our prime result is a novel relaxation equation
that should offer an easily implementable parametrization of geophysical
turbulence. This relaxation equation depends on a single key parameter related
to the skewness of the fine-grained vorticity distribution. Usual
parametrizations (including a single turbulent viscosity) correspond to the
infinite temperature limit of our model. They forget a fundamental systematic
drift that acts against diffusion as in Brownian theory. Our generalized
Fokker-Planck equations may have applications in other fields of physics such
as chemotaxis for bacterial populations. We propose the idea of a
classification of generalized entropies in classes of equivalence and provide
an aesthetic connexion between topics (vortices, stars, bacteries,...) which
were previously disconnected.Comment: Submitted to Phys. Rev.
Bayesian Updating, Model Class Selection and Robust Stochastic Predictions of Structural Response
A fundamental issue when predicting structural response by using mathematical models is how to treat both modeling and excitation uncertainty. A general framework for this is presented which uses probability as a multi-valued
conditional logic for quantitative plausible reasoning in the presence of uncertainty due to incomplete information. The
fundamental probability models that represent the structureâs uncertain behavior are specified by the choice of a stochastic
system model class: a set of input-output probability models for the structure and a prior probability distribution over this set
that quantifies the relative plausibility of each model. A model class can be constructed from a parameterized deterministic
structural model by stochastic embedding utilizing Jaynesâ Principle of Maximum Information Entropy. Robust predictive
analyses use the entire model class with the probabilistic predictions of each model being weighted by its prior probability, or if
structural response data is available, by its posterior probability from Bayesâ Theorem for the model class. Additional robustness
to modeling uncertainty comes from combining the robust predictions of each model class in a set of competing candidates
weighted by the prior or posterior probability of the model class, the latter being computed from Bayesâ Theorem. This higherlevel application of Bayesâ Theorem automatically applies a quantitative Ockham razor that penalizes the data-fit of more
complex model classes that extract more information from the data. Robust predictive analyses involve integrals over highdimensional spaces that usually must be evaluated numerically. Published applications have used Laplace's method of
asymptotic approximation or Markov Chain Monte Carlo algorithms
Coarse-grained distributions and superstatistics
We show an interesting connexion between the coarse-grained distribution
function arising in the theory of violent relaxation for collisionless stellar
systems (Lynden-Bell 1967) and the notion of superstatistics introduced
recently by Beck & Cohen (2003). We also discuss the analogies and differences
between the statistical equilibrium state of a multi-components
self-gravitating system and the metaequilibrium state of a collisionless
stellar system. Finally, we stress the important distinction between mixing
entropies, generalized entropies, H-functions, generalized mixing entropies and
relative entropies
Brownian theory of 2D turbulence and generalized thermodynamics
We propose a new parametrization of 2D turbulence based on generalized
thermodynamics and Brownian theory. Explicit relaxation equations are obtained
that should be easily implementable in numerical simulations for three typical
types of turbulent flows. Our parametrization is related to previous ones but
it removes their defects and offers attractive new perspectives.Comment: Submitted to Phys. Rev. Let
Statistical mechanics of Fofonoff flows in an oceanic basin
We study the minimization of potential enstrophy at fixed circulation and
energy in an oceanic basin with arbitrary topography. For illustration, we
consider a rectangular basin and a linear topography h=by which represents
either a real bottom topography or the beta-effect appropriate to oceanic
situations. Our minimum enstrophy principle is motivated by different arguments
of statistical mechanics reviewed in the article. It leads to steady states of
the quasigeostrophic (QG) equations characterized by a linear relationship
between potential vorticity q and stream function psi. For low values of the
energy, we recover Fofonoff flows [J. Mar. Res. 13, 254 (1954)] that display a
strong westward jet. For large values of the energy, we obtain geometry induced
phase transitions between monopoles and dipoles similar to those found by
Chavanis and Sommeria [J. Fluid Mech. 314, 267 (1996)] in the absence of
topography. In the presence of topography, we recover and confirm the results
obtained by Venaille and Bouchet [Phys. Rev. Lett. 102, 104501 (2009)] using a
different formalism. In addition, we introduce relaxation equations towards
minimum potential enstrophy states and perform numerical simulations to
illustrate the phase transitions in a rectangular oceanic basin with linear
topography (or beta-effect).Comment: 26 pages, 28 figure
Statistical mechanics of two-dimensional Euler flows and minimum enstrophy states
A simplified thermodynamic approach of the incompressible 2D Euler equation
is considered based on the conservation of energy, circulation and microscopic
enstrophy. Statistical equilibrium states are obtained by maximizing the
Miller-Robert-Sommeria (MRS) entropy under these sole constraints. The
vorticity fluctuations are Gaussian while the mean flow is characterized by a
linear relationship. Furthermore, the maximization of
entropy at fixed energy, circulation and microscopic enstrophy is equivalent to
the minimization of macroscopic enstrophy at fixed energy and circulation. This
provides a justification of the minimum enstrophy principle from statistical
mechanics when only the microscopic enstrophy is conserved among the infinite
class of Casimir constraints. A new class of relaxation equations towards the
statistical equilibrium state is derived. These equations can provide an
effective description of the dynamics towards equilibrium or serve as numerical
algorithms to determine maximum entropy or minimum enstrophy states. We use
these relaxation equations to study geometry induced phase transitions in
rectangular domains. In particular, we illustrate with the relaxation equations
the transition between monopoles and dipoles predicted by Chavanis and Sommeria
[J. Fluid. Mech. 314, 267 (1996)]. We take into account stable as well as
metastable states and show that metastable states are robust and have negative
specific heats. This is the first evidence of negative specific heats in that
context. We also argue that saddle points of entropy can be long-lived and play
a role in the dynamics because the system may not spontaneously generate the
perturbations that destabilize them.Comment: 26 pages, 10 figure