On the Tremadoc-Arenig and Lower-Upper Tremadoc boundries in the Bell Island Group, Conception Bay, eastern Newfoundland

The Cambro-Ordovlcian ichnostratigraphic paradigm developed in England and Wales and successfully applied to coaval sequences in southwest Europe and the Mediterranean region is applied to the Ordoviclan Bell Island Group, Conception Bay, eastern Newfoundland. Its application enables a more accurate definition of the Tremadoc-Arenig boundary than previous studies have permitted and is the first attempt to define the Lower-Upper Tremadoc boundary within the Bell Island Group. It is suggested that both boundaries fall within the Beach Formation, the former at 1200 m within the succession and the latter at 1020 m. R᳧SUM᳧ On applique au Groupe de Bell Island (Ordovicien, Bale de Conception) le modᳺle ichnostratigraphique d᳻velopp᳻ pour le Cambro-Ordoviclen d'Angleterre et du Pays de Galles et utilis᳻ avec succᳺs sur des s᳻quences contemptraines d'Europe du sudouest et de la r᳻gion m᳻diterran᳻ans. Ceci per-met de d᳻finir la frontlire entre le Tr᳻madoc et l'Arenlg de fa᳹on plus exacte que lors d'᳻tudes ant᳻rieures. On tente aussi de d᳻finir pour la premiᳺre fois la frontiᳺre sᳺparant le Tr᳻madoc inf᳻rieur du Tr᳻madoc sup᳻rieur ᳲ l'int᳻rieur du Groupe de Bell Island. On suggᳺre que les deux llmites se trouvent dans la Formation de Beach, la premiᳺre ᳻tant situ᳻e ᳲ 1200 m dans la succession et la seconde ᳲ 1020 m. [Traduit par le journal

Resonantly enhanced pair production in a simple diatomic model

A new mechanism for the production of electron-positron pairs from the interaction of a laser field and a fully stripped diatomic molecule in the tunneling regime is presented. When the laser field is turned off, the Dirac operator has resonances in both the positive and the negative energy continua while bound states are in the mass gap. When this system is immersed in a strong laser field, the resonances move in the complex energy plane: the negative energy resonances are pushed to higher energies while the bound states are Stark shifted. It is argued here that there is a pair production enhancement at the crossing of resonances by looking at a simple 1-D model: the nuclei are modeled simply by Dirac delta potential wells while the laser field is assumed to be static and of finite spatial extent. The average rate for the number of electron-positron pairs produced is evaluated and the results are compared to the single nucleus and to the free cases. It is shown that positrons are produced by the Resonantly Enhanced Pair Production (REPP) mechanism, which is analogous to the resonantly enhanced ionization of molecular physics. This phenomenon could be used to increase the number of pairs produced at low field strength, allowing the study of the Dirac vacuum.Comment: 11 pages, 4 figure

SlicerAstro: a 3-D interactive visual analytics tool for HI data

SKA precursors are capable of detecting hundreds of galaxies in HI in a single 12 hours pointing. In deeper surveys one will probe more easily faint HI structures, typically located in the vicinity of galaxies, such as tails, filaments, and extraplanar gas. The importance of interactive visualization has proven to be fundamental for the exploration of such data as it helps users to receive immediate feedback when manipulating the data. We have developed SlicerAstro, a 3-D interactive viewer with new analysis capabilities, based on traditional 2-D input/output hardware. These capabilities enhance the data inspection, allowing faster analysis of complex sources than with traditional tools. SlicerAstro is an open-source extension of 3DSlicer, a multi-platform open source software package for visualization and medical image processing. We demonstrate the capabilities of the current stable binary release of SlicerAstro, which offers the following features: i) handling of FITS files and astronomical coordinate systems; ii) coupled 2-D/3-D visualization; iii) interactive filtering; iv) interactive 3-D masking; v) and interactive 3-D modeling. In addition, SlicerAstro has been designed with a strong, stable and modular C++ core, and its classes are also accessible via Python scripting, allowing great flexibility for user-customized visualization and analysis tasks.Comment: 18 pages, 11 figures, Accepted by Astronomy and Computing. SlicerAstro link: https://github.com/Punzo/SlicerAstro/wiki#get-slicerastr