Finite-Element Discretization of Static Hamilton-Jacobi Equations Based on a Local Variational Principle

We propose a linear finite-element discretization of Dirichlet problems for static Hamilton-Jacobi equations on unstructured triangulations. The discretization is based on simplified localized Dirichlet problems that are solved by a local variational principle. It generalizes several approaches known in the literature and allows for a simple and transparent convergence theory. In this paper the resulting system of nonlinear equations is solved by an adaptive Gauss-Seidel iteration that is easily implemented and quite effective as a couple of numerical experiments show.Comment: 19 page

Glider observations of enhanced deep water upwelling at a shelf break canyon: a mechanism for cross-slope carbon and nutrient exchange

Using underwater gliders we have identified canyon driven upwelling across the Celtic Sea shelf-break, in the vicinity of Whittard Canyon. The presence of this upwelling appears to be tied to the direction and strength of the local slope current, which is in itself highly variable. During typical summer time equatorward flow, an unbalanced pressure gradient force and the resulting disruption of geostrophic flow can lead to upwelling along the main axis of two small shelf break canyons. As the slope current reverts to poleward flow, the upwelling stops and the remnants of the upwelled features are mixed into the local shelf water or advected away from the region. The upwelled features are identified by the presence of sub-pycnocline high salinity water on the shelf, and are upwelled from a depth of 300 m on the slope, thus providing a mechanism for the transport of nutrients across the shelf break onto the shelf

Structure of self-organized Fe clusters grown on Au(111) analyzed by Grazing Incidence X-Ray Diffraction

We report a detailed investigation of the first stages of the growth of self-organized Fe clusters on the reconstructed Au(111) surface by grazing incidence X-ray diffraction. Below one monolayer coverage, the Fe clusters are in "local epitaxy" whereas the subsequent layers adopt first a strained fcc lattice and then a partly relaxed bcc(110) phase in a Kurdjumov-Sachs epitaxial relationship. The structural evolution is discussed in relation with the magnetic properties of the Fe clusters.Comment: 7 pages, 6 figures, submitted to Physical Review B September 200

Counting BPS states on the Enriques Calabi-Yau

We study topological string amplitudes for the FHSV model using various techniques. This model has a type II realization involving a Calabi-Yau threefold with Enriques fibres, which we call the Enriques Calabi-Yau. By applying heterotic/type IIA duality, we compute the topological amplitudes in the fibre to all genera. It turns out that there are two different ways to do the computation that lead to topological couplings with different BPS content. One of them leads to the standard D0-D2 counting amplitudes, and from the other one we obtain information about bound states of D0-D4-D2 branes on the Enriques fibre. We also study the model using mirror symmetry and the holomorphic anomaly equations. We verify in this way the heterotic results for the D0-D2 generating functional for low genera and find closed expressions for the topological amplitudes on the total space in terms of modular forms, and up to genus four. This model turns out to be much simpler than the generic B-model and might be exactly solvable.Comment: 62 pages, v3: some results at genus 3 corrected, more typos correcte

Flavor SU(3) breaking effects in the chiral unitary model for meson-baryon scatterings

We examine flavor SU(3) breaking effects on meson-baryon scattering amplitudes in the chiral unitary model. It turns out that the SU(3) breaking, which appears in the leading quark mass term in the chiral expansion, can not explain the channel dependence of the subtraction parameters of the model, which are crucial to reproduce the observed scattering amplitudes and resonance properties.Comment: RevTeX4, 4 pages, 3 figures, 2 table

On the background in the γp→ω(π0γ)p\gamma p \to \omega(\pi^0\gamma) p reaction and mixed event simulation

In this paper we evaluate sources of background for the $\gamma p \to \omega p$, with the $\omega$ detected through its $\pi^0 \gamma$ decay channel, to compare with the experiment carried out at ELSA. We find background from $\gamma p \to \pi^0 \pi^0 p$ followed by decay of a $\pi^0$ into two $\gamma$, recombining one $\pi^0$ and one $\gamma$, and from the $\gamma p \to \pi^0 \eta p$ reaction with subsequent decay of the $\eta$ into two photons. This background accounts for the data at $\pi^0 \gamma$ invariant masses beyond 700 MeV, but strength is missing at lower invariant masses which was attributed to photon misidentification events, which we simulate to get a good reproduction of the experimental background. Once this is done, we perform an event mixing simulation to reproduce the calculated background and we find that the method provides a good description of the background at low $\pi^0 \gamma$ invariant masses but fakes the background at high invariant masses, making background events at low invariant masses, which are due to $\gamma$ misidentification events, responsible for the background at high invariant masses which is due to the $\gamma p \to \pi^0 \pi^0 p$ and $\gamma p \to \pi^0 \eta p$ reactions.Comment: 10 pages, 5 figure

Large scale numerical investigation of excited states in poly(phenylene)

A density matrix renormalisation group scheme is developed, allowing for the first time essentially exact numerical solutions for the important excited states of a realistic semi-empirical model for oligo-phenylenes. By monitoring the evolution of the energies with chain length and comparing them to the experimental absorption peaks of oligomers and thin films, we assign the four characteristic absorption peaks of phenyl-based polymers. We also determine the position and nature of the nonlinear optical states in this model.Comment: RevTeX, 10 pages, 4 eps figures included using eps

Active Galaxies in the UV

In this article we present different aspects of AGN studies demonstrating the importance of the UV spectral range. Most important diagnostic lines for studying the general physical conditions as well as the metalicities in the central broad line region in AGN are emitted in the UV. The UV/FUV continuum in AGN excites not only the emission lines in the immediate surrounding but it is responsible for the ionization of the intergalactic medium in the early stages of the universe. Variability studies of the emission line profiles of AGN in the UV give us information on the structure and kinematics of the immediate surrounding of the central supermassive black hole as well as on its mass itself.Comment: 29 pages, 13 figures, Ap&SS in pres

Meaning and Dialogue Coherence: A Proof-theoretic Investigation

This paper presents a novel proof-theoretic account of dialogue coherence. It focuses on an abstract class of cooperative information-oriented dialogues and describes how their structure can be accounted for in terms of a multi-agent hybrid inference system that combines natural deduction with information transfer and observation. We show how certain dialogue structures arise out of the interplay between the inferential roles of logical connectives (i.e., sentence semantics), a rule for transferring information between agents, and a rule for information flow between agents and their environment. The order of explanation is opposite in direction to that adopted in game-theoretic semantics, where sentence semantics (or a notion of valid inference) is derived from winning dialogue strategies. That approach and the current one may, however, be reconcilable, since we focus on cooperative dialogue, whereas the game-theoretic tradition concentrates on adversarial dialogue

On Physical Equivalence between Nonlinear Gravity Theories

We argue that in a nonlinear gravity theory, which according to well-known results is dynamically equivalent to a self-gravitating scalar field in General Relativity, the true physical variables are exactly those which describe the equivalent general-relativistic model (these variables are known as Einstein frame). Whenever such variables cannot be defined, there are strong indications that the original theory is unphysical. We explicitly show how to map, in the presence of matter, the Jordan frame to the Einstein one and backwards. We study energetics for asymptotically flat solutions. This is based on the second-order dynamics obtained, without changing the metric, by the use of a Helmholtz Lagrangian. We prove for a large class of these Lagrangians that the ADM energy is positive for solutions close to flat space. The proof of this Positive Energy Theorem relies on the existence of the Einstein frame, since in the (Helmholtz--)Jordan frame the Dominant Energy Condition does not hold and the field variables are unrelated to the total energy of the system.Comment: 37 pp., TO-JLL-P 3/93 Dec 199