Afterglow calculation in the electromagnetic model for gamma-ray bursts

Original article can be found at: http://www.aanda.org/--Copyright The European Southern Observatory (ESO) DOI : 10.1051/0004-6361:20065322We compute the afterglow of gamma-ray bursts produced by purely electromagnetic outflows to see if it shows characteristic signatures differing from those obtained with the standard internal/external shock model. Methods. Using a simple approach for the injection of electromagnetic energy to the forward shock we obtain the afterglow evolution both during the period of activity of the central source and after. Our method equally applies to a variable source. Results. Afterglow light curves in the visible and X-ray bands are computed both for a uniform medium and a stellar wind environment. They are brighter at early times than afterglows obtained with the internal/external shock model but relying only on these differences to discriminate between models is not sufficient.Peer reviewe

Photometric support for future astonomical research

The I.A.P.P.P. is described and how that organization can provide photometric support for future astronomical research projects such as the 1982-1984 eclipse of epsilon Aurigae discussed at this workshop. I.A.P.P.P., International Amateur-Professional Photoelectric Photometry, is an organization founded in Fairborn, Ohio by the authors in 1980. Its purpose is to encourage contact between amateur and professional astronomers interested in photoelectric photometry, for their mutual benefit and for the benefit of astronomical research. Aspects dealt with include instrumentation, electronics, computer hardware and software, observing techniques, data reduction, and observing programs. Starting with the June 1980 issue, I.A.P.P.P. has published the quarterly I.A.P.P.P. Communications. The Communications contain articles dealing with all the above aspects of photoelectric photometry, although it does not publish observational results as such. Photoelectric photometry obtained by amateurs is published in the same journals which publish photometry obtained by professionals

Casimir torque between nanostructured plates

We investigate in detail the Casimir torque induced by quantum vacuum fluctuations between two nanostructured plates. Our calculations are based on the scattering approach and take into account the coupling between different modes induced by the shape of the surface which are neglected in any sort of proximity approximation or effective medium approach. We then present an experimental setup aiming at measuring this torque.Comment: 7 pages, 7 figure

Verifying Temporal Regular Properties of Abstractions of Term Rewriting Systems

The tree automaton completion is an algorithm used for proving safety properties of systems that can be modeled by a term rewriting system. This representation and verification technique works well for proving properties of infinite systems like cryptographic protocols or more recently on Java Bytecode programs. This algorithm computes a tree automaton which represents a (regular) over approximation of the set of reachable terms by rewriting initial terms. This approach is limited by the lack of information about rewriting relation between terms. Actually, terms in relation by rewriting are in the same equivalence class: there are recognized by the same state in the tree automaton. Our objective is to produce an automaton embedding an abstraction of the rewriting relation sufficient to prove temporal properties of the term rewriting system. We propose to extend the algorithm to produce an automaton having more equivalence classes to distinguish a term or a subterm from its successors w.r.t. rewriting. While ground transitions are used to recognize equivalence classes of terms, epsilon-transitions represent the rewriting relation between terms. From the completed automaton, it is possible to automatically build a Kripke structure abstracting the rewriting sequence. States of the Kripke structure are states of the tree automaton and the transition relation is given by the set of epsilon-transitions. States of the Kripke structure are labelled by the set of terms recognized using ground transitions. On this Kripke structure, we define the Regular Linear Temporal Logic (R-LTL) for expressing properties. Such properties can then be checked using standard model checking algorithms. The only difference between LTL and R-LTL is that predicates are replaced by regular sets of acceptable terms

Spatial correlations of vacuum fluctuations and the Casimir-Polder potential

We calculate the Casimir-Polder intermolecular potential using an effective Hamiltonian recently introduced. We show that the potential can be expressed in terms of the dynamical polarizabilities of the two atoms and the equal-time spatial correlation of the electric field in the vacuum state. This gives support to an interesting physical model recently proposed in the literature, where the potential is obtained from the classical interaction between the instantaneous atomic dipoles induced and correlated by the vacuum fluctuations. Also, the results obtained suggest a more general validity of this intuitive model, for example when external boundaries or thermal fields are present.Comment: 7 page

Casimir energy and geometry : beyond the Proximity Force Approximation

We review the relation between Casimir effect and geometry, emphasizing deviations from the commonly used Proximity Force Approximation (PFA). We use to this aim the scattering formalism which is nowadays the best tool available for accurate and reliable theory-experiment comparisons. We first recall the main lines of this formalism when the mirrors can be considered to obey specular reflection. We then discuss the more general case where non planar mirrors give rise to non-specular reflection with wavevectors and field polarisations mixed. The general formalism has already been fruitfully used for evaluating the effect of roughness on the Casimir force as well as the lateral Casimir force or Casimir torque appearing between corrugated surfaces. In this short review, we focus our attention on the case of the lateral force which should make possible in the future an experimental demonstration of the nontrivial (i.e. beyond PFA) interplay of geometry and Casimir effect.Comment: corrected typos, added references, QFEXT'07 special issue in J. Phys.

Development of a protocol for standardized use of a water-soluble contrast agent with polyethylene glycol in post-mortem CT angiography.

Computed tomography angiography (PMCTA) is increasingly used in postmortem cases. Standardized validated protocols permit to compare different PMCTA images and make it more easily to defend a case in court. In addition to the well-known technique by Grabherr et al. (2011) which is using paraffin oil as a carrier substance, water-soluble polyethylene glycol 200 (PEG200) can be used in combination with the contrast agent Accupaque® 300. As to date, there exists no standardized protocol for the use of this contrast agent mixture, the aim of this study was to develop a protocol using it. Between 2012 and 2022, 23 PMCTA with PEG200 and Accupaque®300 were performed at the University Centre of Legal Medicine Lausanne (Switzerland) and the Institute of Forensic Medicine Munich (Germany). The images obtained were evaluated regarding the opacification of the vessels and possible artefacts. The best image quality was obtained with a mixing ratio of 1:15 (Accupaque®300:PEG200) and a perfusion volume of 1000 ml in the arterial, 1400 ml in the venous and 350 ml in the dynamic phase. The infusion rates described by Grabherr et al. were confirmed for the three phases. Overall, the opacification of the vessels was diagnostically sufficient. In 13 cases no opacification of the right coronary artery was observed due to a stratification artefact. By using the PMCTA protocol with PEG200 as a carrier, a good overall image quality can be achieved. This protocol offers the possibility to standardize PMCTA with PEG200