Three-body Casimir-Polder interactions

As part of our program to develop the description of three-body effects in quantum vacuum phenomena, we study the three-body interaction of two anisotropically polarizable atoms with a perfect electrically conducting plate, a generalization of earlier work. Three- and four-scattering effects are important, and lead to nonmonotonic behavior.Comment: 10 pages, 5 figures, for the proceedings of the conference Mathematical Structures in Quantum Systems, Benasque, Spain, July 2012, to be published in Nuovo Ciment

PT-Symmetric Quantum Electrodynamics and Unitarity

More than 15 years ago, a new approach to quantum mechanics was suggested, in which Hermiticity of the Hamiltonian was to be replaced by invariance under a discrete symmetry, the product of parity and time-reversal symmetry, $\mathcal{PT}$. It was shown that if $\mathcal{PT}$ is unbroken, energies were, in fact, positive, and unitarity was satisifed. Since quantum mechanics is quantum field theory in 1 dimension, time, it was natural to extend this idea to higher-dimensional field theory, and in fact an apparently viable version of $\mathcal{PT}$-invariant quantum electrodynamics was proposed. However, it has proved difficult to establish that the unitarity of the scattering matrix, for example, the K\"all\'en spectral representation for the photon propagator, can be maintained in this theory. This has led to questions of whether, in fact, even quantum mechanical systems are consistent with probability conservation when Green's functions are examined, since the latter have to possess physical requirements of analyticity. The status of $\mathcal{PT}$QED will be reviewed in this report, as well as the general issue of unitarity.Comment: 13 pages, 2 figures. Revised version includes new evidence for the violation of unitarit

Repulsive Casimir and Casimir-Polder Forces

Casimir and Casimir-Polder repulsion have been known for more than 50 years. The general "Lifshitz" configuration of parallel semi-infinite dielectric slabs permits repulsion if they are separated by a dielectric fluid that has a value of permittivity that is intermediate between those of the dielectric slabs. This was indirectly confirmed in the 1970s, and more directly by Capasso's group recently. It has also been known for many years that electrically and magnetically polarizable bodies can experience a repulsive quantum vacuum force. More amenable to practical application are situations where repulsion could be achieved between ordinary conducting and dielectric bodies in vacuum. The status of the field of Casimir repulsion with emphasis on recent developments will be surveyed. Here, stress will be placed on analytic developments, especially of Casimir-Polder (CP) interactions between anisotropically polarizable atoms, and CP interactions between anisotropic atoms and bodies that also exhibit anisotropy, either because of anisotropic constituents, or because of geometry. Repulsion occurs for wedge-shaped and cylindrical conductors, provided the geometry is sufficiently asymmetric, that is, either the wedge is sufficiently sharp or the atom is sufficiently far from the cylinder.Comment: 24 pages, 14 figures, contribution to the special issue of J. Phys. A honoring Stuart Dowker. This revision corrects typos and adds additional references and discussio

Analysis of the Evans and Baranyai variational principle in dilute gases

A variational principle for thermostated nonequilibrium steady states recently proposed by Evans and Baranyai [Phys. Rev. Lett. 67, 2597 (1991)] is analyzed by means of a model kinetic equation for dilute gases. It is shown that the principle does not apply exactly, although deviations from it are small, especially when the gradients are not very largeDirección General de Investigaciones Científicas y Técnicas PB89-0618 y PB91-031

Impacts Des Technologies De l’Information Et De La Communication (TIC) Sur Les Rendements Scolaires Des Apprenants De La Ville De Dassa-Zoumé Dans Le Département Des Collines Au Bénin

L’usage des TIC consiste à l’accès et à l’utilisation des technologies de l’information et de la communication dans l’éducation. L’objectif global de cette recherche est de montrer les répercutions socio-éducatives des usages des TIC sur le rendement des apprenants des établissements publics de Dassa-Zoumé. L’approche méthodologique adoptée se subdivise en trois points à savoir : la recherche documentaire, la collecte de données, le traitement des informations et l’analyse des résultats.Les résultats obtenus sur le terrain ont révélé que 37 % des enseignants ont estimé que les TIC facilitent les recherches et 65 % de ceux-ci pensent que cela contribue à l’amélioration des résultats scolaires. L’usage des TIC pour des recherches documentaires est adopté par 65 % des enquêtés. 14 % ont affirmé que cela affaiblit le niveau scolaire des apprenants parce qu’ils l’utilisent pour des fins peu orthodoxes. Malgré les multiples avantages que procurent l’usage des TIC en milieu scolaire, des défis restent à relever à savoir : la non-maîtrise des outils informatiques, le coût d’accès élevés, l’éloignement des lieux d’accès et la privation formelle de l’usage des smartphones par les parents. Enfin 18 % ont énuméré l’indisponibilité des services offerts par les TIC