Descripción: Perturbing the Navier-Stokes equation in the ionospheric F-region, the dispersion relation and the unstable regions in wavenumber space are derived as a function of two control parameters, the colatitude θ and the slow time evolution for tidal modes τ. Our results satisfy the internal gravity wave (IGW) dispersion relation and are in good agreement with observational data. Also, we obtained a nice prediction for the excitation regions of these modes in the parameter space (θ, τ). The distribution of IGW excitations, in this parameter space is in very good agreement with observational data distributed along the day. An alternative explanation to the disappearence of IGW near the equator is given. Our model predicts an interesting latitude dependence, which needs to be tested by new observational data.

Descripción: We study improper mixtures from a quantum logical and geometrical point of view. Taking into account the fact that improper mixtures do not admit an ignorance interpretation and must be considered as states in their own right, we do not follow the standard approach which considers improper mixtures as measures over the algebra of projections. Instead of it, we use the convex set of states in order to construct a new lattice whose atoms are all physical states: pure states and improper mixtures. This is done in order to overcome one of the problems which appear in the standard quantum logical formalism, namely, that for a subsystem of a larger system in an entangled state, the conjunction of all actual properties of the subsystem does not yield its actual state. In fact, its state is an improper mixture and cannot be represented in the von Neumann lattice as a minimal property which determines all other properties as is the case for pure states or classical systems. The new lattice also contains all propositions of the von Neumann lattice. We argue that this extension expresses in an algebraic form the fact that-alike the classical case-quantum interactions produce nontrivial correlations between the systems. Finally, we study the maps which can be defined between the extended lattice of a compound system and the lattices of its subsystems. © 2010 American Institute of Physics.

Descripción: The complete set of concomitants is given of the metric, a scalar function, and their derivatives in six dimensions without imposing conditions on the order of the derivatives and their properties are studied under conformal transformations. These results are useful in several physical problems, like finding φ2ren and Τμν ren in any geometry. © 1992 American Institute of Physics.

Descripción: Weyl's theorem is extended making use of the theory of concomitants to obtain a Lagrangian density for the massless bosonic fields without dimensional constants. It turns out to be quadratic in the gravitational field and encompasses all the theories that usually appear in the literature. It is shown that the gauge invariance of the Lagrangian follows from the invariance of the field equations. © 1987 American Institute of Physics.

Descripción: Applying the doublet representation we analyze the solutions of a Hamiltonian system which has eigenstates with complex eigenvalues. The example of the Friedrichs model allows us to show how the appearance of solutions with non-Hilbert initial conditions is linked to the energy degeneration of the Hamiltonian spectrum. We discuss the difficulties of giving a physical meaning to the growing or decaying non-Hilbert solutions. We also suggest a way to circumvent the problem of the anomalous probabilities related to both complex energy eigenvalues and degeneration of the spectrum. © 1998 American Institute of Physics.