Upon revisiting the Hamiltonian structure of classical wavefunctions in Koopman–von Neumann theory, this paper addresses the long-standing problem of formulating a dynamical theory of classical–quantum coupling. The proposed model not only describes the influence of a classical system onto a quantum one, but also the reverse effect—the quantum backreaction. These interactions are described by a new Hamiltonian wave equation overcoming shortcomings of currently employed models. For example, the density matrix of the quantum subsystem is always positive definite. While the Liouville density of the classical subsystem is generally allowed to be unsigned, its sign is shown to be preserved in time for a specific infinite family of hybrid classical–quantum systems. The proposed description is illustrated and compared with previous theories using the exactly solvable model of a degenerate two-level quantum system coupled to a classical harmonic oscillator.

This paper develops the theory of affine Euler-Poincaré and affine Lie-Poisson reductions and applies these processes to various examples of complex fluids, including Yang-Mills and Hall magnetohydrodynamics for fluids and superfluids, spin glasses, microfluids, and liquid crystals. As a consequence of the Lagrangian approach, the variational formulation of the equations is determined. On the Hamiltonian side, the associated Poisson brackets are obtained by reduction of a canonical cotangent bundle. A Kelvin-Noether circulation theorem is presented and is applied to these examples.we see that the Lie-Poisson equations for h on s * are equivalent to the Euler-Poincaré equations (1.2) for l together with the advection equationȧ + aξ = 0.Links with the reduction by stages. Consider the semidirect product Lie group S = G V acting by right translation on its cotangent bundle T * S. An equivariant momentum map relative to the canonical symplectic form is given by. Since V is a closed normal subgroup of S, it also acts on T * S and has a momentum map J V : T * S → V * given by J V (α f , (u, a)) = a.Reducing T * S by V at the value a we get the first reduced space (T * S) a = J −1 V (a)/V . The isotropy subgroup G a , consisting of elements of G that leave the point a fixed, acts freely and properly on (T * S) a and has an induced equivariant momentum map J a : (T * S) a → g * a , where g a is the Lie algebra of G a . Reducing (T * S) a at the point µ a := µ|g a , we get the second reduced space ((T * S) a ) µa = J −1 a (µ a )/(G a ) µa . Using the Semidirect Product Reduction ([28]) or the Reduction by Stages Theorem ([26]), the two-stage reduced space ((T * S) a ) µa is symplectically diffeomorphic to the reduced space (T * S) (µ,a) = J −1 R (µ, a)/G (µ,a) obtained by reducing T * S by the whole group S at the point (µ, a) ∈ s * .The first symplectic reduced space ((T * S) a , Ω a ) is symplectically diffeomorphic to the canonical symplectic manifold (T * G, Ω) and the second reduced space ((T * S) a ) µa , (Ω a ) µa is symplectically diffeomorphic to the coadjoint orbit O (µ,a) , ω (µ,a) together with its orbit symplectic form. Note also that we can consider the right G-invariant Hamiltonian H :

Part I of this paper introduced a Lagrangian variational formulation for the nonequilibrium thermodynamics of discrete systems. This variational formulation extends the Hamilton principle to allow the inclusion of irreversible processes in the dynamics. The irreversibility is encoded into a nonlinear nonholonomic constraint given by the expression of entropy production associated to all the irreversible processes involved. In Part II, we develop this formulation for the case of continuum systems by extending the setting of Part I to infinite dimensional nonholonomic Lagrangian systems. The variational formulation is naturally expressed in material representation, while its spatial version is obtained via a nonholonomic Lagrangian reduction by symmetry. The theory is illustrated with the examples of a viscous heat conducting fluid and its multicomponent extension including chemical reactions and mass transfer.

In this paper, we present a Lagrangian variational formulation for nonequilibrium thermodynamics. This formulation is an extension of the Hamilton principle in classical mechanics that allows the inclusion of irreversible phenomena. The irreversibility is encoded into a nonlinear phenomenological constraint given by the expression of entropy production associated to all the irreversible processes involved. Hence from a mathematical point of view, our variational formulation may be regarded as a generalization of the Lagrange-d'Alembert principle used in nonlinear nonholonomic mechanics to the nonequilibrium thermodynamics, where the conventional Lagrange-d'Alembert principle cannot be applied since the nonlinear phenomenological constraint and its associated variational constraint must be separately treated. In our approach, to deal with the nonlinear nonholonomic constraint, we introduce a variable called the thermodynamic displacement associated to each irreversible process. This allows us systematically to define the corresponding variational constraint. In Part I, our variational theory is illustrated with various examples of discrete systems such as mechanical systems with friction, matter transfer, electric circuits, chemical reactions, and diffusion across membranes. In Part II of the present paper, we will extend our variational theory of discrete systems to the case of of continuum systems. Contents 1 Introduction 2 2 Some preliminaries 5 3 Variational formulation for nonequilibrium thermodynamics of simple systems 9 3.

International audienceWe investigate higher-order geometric k-splines for template matching on Lie groups. This is motivated by the need to apply diffeomorphic template matching to a series of images, e. g., in longitudinal studies of Computational Anatomy. Our approach formulates Euler-Poincaré theory in higher-order tangent spaces on Lie groups. In particular, we develop the Euler-Poincaré formalism for higher-order variational problems that are invariant under Lie group transformations. The theory is then applied to higher-order template matching and the corresponding curves on the Lie group of transformations are shown to satisfy higher-order Euler-Poincaré equations. The example of SO(3) for template matching on the sphere is presented explicitly. Various cotangent bundle momentum maps emerge naturally that help organize the formulas. We also present Hamiltonian and Hamilton-Ostrogradsky Lie-Poisson formulations of the higher-order Euler-Poincaré theory for applications on the Hamiltonian side. © 2011 Springer-Verlag

This paper extends the Madelung–Bohm formulation of quantum mechanics to describe the time-reversible interaction of classical and quantum systems. The symplectic geometry of the Madelung transform leads to identifying hybrid quantum–classical Lagrangian paths extending the Bohmian trajectories from standard quantum theory. As the classical symplectic form is no longer preserved, the nontrivial evolution of the Poincaré integral is presented explicitly. Nevertheless, the classical phase-space components of the hybrid Bohmian trajectory identify a Hamiltonian flow parameterized by the quantum coordinate and this flow is associated to the motion of the classical subsystem. In addition, the continuity equation of the joint quantum–classical density is presented explicitly. While the von Neumann density operator of the quantum subsystem is always positive-definite by construction, the hybrid density is generally allowed to be unsigned. However, the paper concludes by presenting an infinite family of hybrid Hamiltonians whose corresponding evolution preserves the sign of the probability density for the classical subsystem.

This paper discusses the mathematical framework for designing methods of large deformation matching (LDM) for image registration in computational anatomy. After reviewing the geometrical framework of LDM image registration methods, a theorem is proved showing that these methods may be designed by using the actions of diffeomorphisms on the image data structure to define their associated momentum representations as (cotangent lift) momentum maps. To illustrate its use, the momentum map theorem is shown to recover the known algorithms for matching landmarks, scalar images and vector fields. After briefly discussing the use of this approach for Diffusion Tensor (DT) images, we explain how to use momentum maps in the design of registration algorithms for more general data structures. For example, we extend our methods to determine the corresponding momentum map for registration using semidirect product groups, for the purpose of matching images at two different length scales. Finally, we discuss the use of momentum maps in the design of image registration algorithms when the image data is defined on manifolds instead of vector spaces.

This paper presents a geometric variational discretization of compressible fluid dynamics. The numerical scheme is obtained by discretizing, in a structure preserving way, the Lie group formulation of fluid dynamics on diffeomorphism groups and the associated variational principles. Our framework applies to irregular mesh discretizations in 2D and 3D. It systematically extends work previously made for incompressible fluids to the compressible case. We consider in detail the numerical scheme on 2D irregular simplicial meshes and evaluate the scheme numerically for the rotating shallow water equations. In particular, we investigate whether the scheme conserves stationary solutions, represents well the nonlinear dynamics, and approximates well the frequency relations of the continuous equations, while preserving conservation laws such as mass and total energy.