93 research outputs found
Monotone and boolean unitary Brownian motions
The additive monotone (resp. boolean) unitary Brownian motion is a
non-commutative stochastic process with monotone (resp. boolean) independent
and stationary increments which are distributed according to the arcsine law
(resp. Bernoulli law) . We introduce the monotone and booleen unitary Brownian
motions and we derive a closed formula for their associated moments. This
provides a description of their spectral measures. We prove that, in the
monotone case, the multiplicative analog of the arcsine distribution is
absolutely continuous with respect to the Haar measure on the unit circle,
whereas in the boolean case the multiplicative analog of the Bernoulli
distribution is discrete. Finally, we use quantum stochastic calculus to
provide a realization of these processes as the stochastic exponential of the
correspending additive Brownian motions.Comment: 19 page
Stochastic analysis for obtuse random walks
We present a construction of the basic operators of stochastic analysis
(gradient and divergence) for a class of discrete-time normal martingales
called obtuse random walks. The approach is based on the chaos representation
property and discrete multiple stochastic integrals. We show that these
operators satisfy similar identities as in the case of the Bernoulli randoms
walks. We prove a Clark-Ocone-type predictable representation formula, obtain
two covariance identities and derive a deviation inequality. We close the
exposition by an application to option hedging in discrete time.Comment: 26 page
Summing free unitary Brownian motions with applications to quantum information
Motivated by quantum information theory, we introduce a dynamical random
state built out of the sum of independent unitary Brownian motions.
In the large size limit, its spectral distribution equals, up to a normalising
factor, that of the free Jacobi process associated with a single self-adjoint
projection with trace . Using free stochastic calculus, we extend this
equality to the radial part of the free average of free unitary Brownian
motions and to the free Jacobi process associated with two self-adjoint
projections with trace , provided the initial distributions coincide. In
the single projection case, we derive a binomial-type expansion of the moments
of the free Jacobi process which extends to any the one derived in
\cite {DHH} in the special case . Doing so give rise to a non normal
(except for ) operator arising from the splitting of a self-adjoint
projection into the convex sum of unitary operators. This binomial
expansion is then used to derive a pde for the moment generating function of
this non normal operator and for which we determine the corresponding
characteristic curves.Comment: The characteristic curves are determine
The Hermitian Jacobi process: simplified formula for the moments and application to optical fibers MIMO channels
Using a change of basis in the algebra of symmetric functions, we compute the
moments of the Hermitian Jacobi process. After a careful arrangement of the
terms and the evaluation of the determinant of an `almost upper-triangular'
matrix, we end up with a moment formula which is considerably simpler than the
one derived in \cite{Del-Dem}. As an application, we propose the Hermitian
Jacobi process as a dynamical model for optical fibers MIMO channels and
compute its Shannon capacity for small enough power at the transmitter.
Moreover, when the size of the Hermitian Jacobi process is larger than the
moment order, our moment formula may be written as a linear combination of
balanced terminating -series evaluated at unit argument.Comment: Accepted for publication in Funct. Anal. Appl
The quantum mechanics canonically associated to free probability Part I: Free momentum and associated kinetic energy
After a short review of the quantum mechanics canonically associated with a
classical real valued random variable with all moments, we begin to study the
quantum mechanics canonically associated to the \textbf{standard semi--circle
random variable} , characterized by the fact that its probability
distribution is the semi--circle law on . We prove that, in the
identification of with the --mode interacting Fock space
, defined by the orthogonal polynomial gradation of , is
mapped into position operator and its canonically associated momentum operator
into times the --Hilbert transform on .
In the first part of the present paper, after briefly describing the simpler
case of the --harmonic oscillator, we find an explicit expression for the
action, on the --orthogonal polynomials, of the semi--circle analogue of
the translation group and of the semi--circle analogue of the free
evolution respectively in terms of Bessel functions of the first
kind and of confluent hyper--geometric series. These results require the
solution of the \textit{inverse normal order problem} on the quantum algebra
canonically associated to the classical semi--circle random variable and are
derived in the second part of the present paper. Since the problem to
determine, with purely analytic techniques, the explicit form of the action of
and on the --orthogonal polynomials
is difficult, % aaa ask T if it is solved the above mentioned results show the
power of the combination of these techniques with those developed within the
algebraic approach to the theory of orthogonal polynomials.Comment: 28 page
Analyse expérimentale, par PIV, de la corrélation entre la dynamique tourbillonnaire d'un jet heurtant une plaque fendue et le champ acoustique généré
International audienceLors de l’impact entre un jet et une plaque fendue, des nuisances sonores peuvent être générées. Réellement,au niveau de la fente, l’obstacle peut interagir avec l’écoulement, sous certaines conditions, pour donner naissance à des perturbations de la dynamique tourbillonnaire de l’écoulement et peut contrôler le détachement tourbillonnaire dès sa naissance. Ces perturbations dynamiques mettent en relief le transfert d’énergie du champ aérodynamique vers le champ acoustique ainsi généré. Afin de visualiser la partie tourbillonnaire de l’écoulement et de mettre en exergue les mécanismes responsables des nuisances sonores, une métrologie laser a été appliquée : la PIV (vélocimétrie par images de particules). Cette méthode de mesures est basée sur l’ensemencement de l’écoulement avec des traceurs appropriés dans l’écoulement, et à la génération de plans lumineux, à l’aide d’un laser pulsé à deux têtes, afin de matérialiser les plans étudiés. Une caméra rapide phantom V711 est utilisée pour enregistrer les paires d’images ainsi réalisées. Un logiciel dédié à laPIV « DaVis » permet de réaliser les calculs de champs cinématiques en fonction du temps. Dans cette étude,on met en évidence les corrélations qui existent entre les pics acoustiques observés dans certaines configurations et la dynamique tourbillonnaire de l’écoulement. Pour cela des microphones Brüel & Kjær et une centrale d’acquisition équipée d’une carte NI PXI – 4472 ont été utilisés pour la partie acoustique, et un suivi spécifique des structures tourbillonnaires a été réalisé
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