Direction-Dependent Polarised Primary Beams in Wide-Field Synthesis Imaging

The process of wide-field synthesis imaging is explored, with the aim of understanding the implications of variable, polarised primary beams for forthcoming Epoch of Reionisation experiments. These experiments seek to detect weak signatures from redshifted 21cm emission in deep residual datasets, after suppression and subtraction of foreground emission. Many subtraction algorithms benefit from low side-lobes and polarisation leakage at the outset, and both of these are intimately linked to how the polarised primary beams are handled. Building on previous contributions from a number of authors, in which direction-dependent corrections are incorporated into visibility gridding kernels, we consider the special characteristics of arrays of fixed dipole antennas operating around 100-200 MHz, looking towards instruments such as the Square Kilometre Array (SKA) and the Hydrogen Epoch of Reionization Arrays (HERA). We show that integrating snapshots in the image domain can help to produce compact gridding kernels, and also reduce the need to make complicated polarised leakage corrections during gridding. We also investigate an alternative form for the gridding kernel that can suppress variations in the direction-dependent weighting of gridded visibilities by 10s of dB, while maintaining compact support.Comment: 15 pages, 4 figures. Accepted for publication in JA

Water fragmentation by bare and dressed light ions with MeV energies: Fragment-ion-energy and time-of-flight distributions

The energy and time-of-flight distributions of water ionic fragments produced by impact of fast atoms and bare and dressed ions; namely, H+, Li0-3+, C1+, and C2+ are reported in this work. Fragment species as a function of emission energy and time-of-flight were recorded by using an electrostatic spectrometer and a time-of-flight mass spectrometer, respectively. An improved Coulomb explosion model coupled to a classical trajectory Monte Carlo (CTMC) simulation gave the energy centroids of the fragments for the dissociation channels resulting from the removal of two to five electrons from the water molecule. For the energy distribution ranging up to 50 eV, both the experiment and model reveal an isotropic production of multiple charged oxygen ions, as well as hydrogen ions. From the ion energy distribution, relative yields of the dissociation resulting from multiple ionization were obtained as a function of the charge state, as well as for several projectile energies. Multiple-ionization yields with charge state up to 4+, were extracted from the measurements of the time-of-flight spectra, focused on the production of single and multiple charged oxygen ions. The measurements were compared to ion-water collision experiments investigated at the keV energy range available in the literature, revealing differences and similarities in the fragment-ion energy distribution.Fil: Wolff, W.. Universidade Federal do Rio de Janeiro; BrasilFil: Luna, H.. Universidade Federal do Rio de Janeiro; BrasilFil: Schuch, R.. Alba Nova University Center; SueciaFil: Cariatore, Nelson Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Otranto, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Turco, Federico. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Fregenal, Daniel Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Bernardi, Guillermo Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Suárez, S.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentin

In situ differentiation processes in Plio-Pleistocene basaltic flows of Southern Payenia, Provinces of Mendoza and La Pampa

En este trabajo se presentan los resultados obtenidos de estudios petrológicos realizados en estructuras de segregación alojadas en lavas basálticas emplazadas al sur de la Provincia Volcánica de Payenia. Se analizaron cuatro tipos morfológicos de estructuras: mantos, láminas y cilindros de vesículas y vesículas de segregación. El líquido residual que les dio origen fue segregado durante la cristalización del núcleo de la colada y migró a través de una malla cristalina gracias al mecanismo de gas filter-pressing. De acuerdo a un estudio previo, las estructuras aquí analizadas clasifican texturalmente en tres categorías: afíricas de grano grueso (subtipo A), afíricas de grano fino (subtipo B) y seriadas (subtipo C). Los datos obtenidos de los análisis puntuales de las principales fases minerales de las estructuras de segregación indican que las mismas presentan composiciones más diferenciadas que sus basaltos hospedantes. Esto se evidencia a partir del enriquecimiento en Si, Fe, Na y K y el empobrecimiento de Al, Ca y Mg en la mineralogía de las estructuras en relación a la del basalto, lo cual se interpreta como el resultado de un proceso de cristalización fraccionada in situ. Los cálculos geotermométricos arrojaron una temperatura de erupción del basalto hospedante de 1195 ± 71 ºC y de entre 996 y 1001 ± 71 ºC para la temperatura del liquidus del vidrio que compone la vesícula de segregación.In situ differentiation processes in Plio-Pleistocene basaltic flows of Southern Payenia, Provinces of Mendoza and La Pampa In this paper are presented the petrologic studies made on segregation structures found in basaltic lava flows from southern Payenia Volcanic Province. Four morphological types of structures were identified: thick vesicle sheets, thin vesicle sheets, vesicle cylinders and segregation vesicles. The residual liquid migrated through a crystal network driven by the gas filter-pressing mechanism. In agree with a previous work the segregation structures classified according to their texture as aphyric coarse-grained textured (A-subtype), aphyric fine-grained textured (B-subtype) and seriate textured (C-subtype). The chemical data obtained from the individual analyzes of main mineral phases of the segregation structures indicate that they present more differentiated compositions than their host basalts. This is mainly evidenced by the enrichment in Si, Fe, Na and K and the drop of Al, Ca and Mg values in the mineral association of the structures with regard to the mineral chemistry of the basalt, which is interpreted as the result of an in situ crystal fractionation process. From thermometric calculations it was estimated that the eruption temperature of the host basalt was 1195 ± 71 ºC. The liquidus temperature estimated for the glass that constitutes the segregation vesicle groundmass was between 996 and 1001 ± 71 °C.Fil: Bernardi, Mauro Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; ArgentinaFil: Bertotto, Gustavo Walter. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; ArgentinaFil: Ponce, Alexis Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentin

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) in Peaches: is it a problem?

Healthy peach fruit is not considered a preferred host for Drosophila suzukii (Matsumura); however, it becomes a more preferable host when damaged. Thus, damaged peach fruit is of importance not only in terms of economic losses, but also because it serves as a reservoir for this fly species. This work aimed to evaluate the suitability of peaches mechanically damaged or harboring the brown rot disease as hosts for D. suzukii compared to hosts for which they have a low (undamaged peach) and high (undamaged strawberry) preference. Damaged peaches were as susceptible as undamaged strawberries. Fungus infection alone did not increase the susceptibility of peaches compared to undamaged peaches. This information should be considered when an Integrated Pest Management program is defined in a scenario of different species of fruit production

Aumento de la eficiencia de un método de descomposición de dominio mediante estimaciones a posteriori

En este trabajo introducimos un método de descomposición de dominio sin solapamiento con penalización, que viene motivado a partir de un análisis del error a posteriori del método estudiado por T. Chacón y E. Chacón en [5] y [6]. Con el objetivo de mejorar la tasa de convergencia del método de [6], en este trabajo, introducimos una nueva versi´on de este método en la cual un término de penalización H 1/2 00 (Γ) reemplaza el término L 2 (Γ) del original de [6]. Usando este nuevo término, el nímero de iteraciones necesarias para alcanzar una solución con un error del mismo orden que el error de discretización, se reduce significativamente. Realizamos además un análisis de error a posteriori, que nos permite desarrollar un estrategia para determinar simultáneamente un parámetro de penalización óptimo y una malla optimal, para reducir el error por debajo de un valor prefijado. Varios test numéricos muestran los buenos resultados de nuestras aproximaciones

A posteriori error analysis for two non-overlapping domain decomposition techniques

This paper is devoted to the construction of fast solvers for penalty domain decomposition techniques, based upon a posteriori error analysis. We introduce a penalty non-overlapping domain decomposition method (ddm) motivated by the a posteriori error analysis of the method proposed by Chacón and Chacón in [T. Chacón Rebollo, E. Chacón Vera, A non-overlapping domain decomposition method for the Stokes equations via a penalty term on the interface, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 1–16]. In the new method a penalty term replaces the L2(Γ) one in the original method. The number of iterations needed by the new ddm to yield a solution with an error of the same order as the discretization error is remarkably reduced. We develop an a posteriori error analysis that we use to determine an optimal value of the penalty parameter for a given grid, and also to jointly determine an optimal grid and a penalty parameter to reduce the error below a targeted value. Several numerical tests for model problems exhibit the good performances of our approach and provide to a numerical comparison of the two penalty methods.Cet article a pour but la construction de solveurs rapides pour les techniques de décomposition de domaine avec pénalisation et repose sur une analyse a posteriori. Nous introduisons une méthode de décomposition de domaine sans recouvrement, issue de l’analyse a posteriori de la méthode proposée par Chacón et Chacón [Chacón Rebollo, T., Chacón Vera, E., A non-overlapping domain decomposition method for the Stokes equations via a penalty term on the interface. C.R. Acad. Sci. Paris, t. 334, Série I; pp. 1–16, 2002.6], où une pénalisation de type H 1/2 00 (Γ) remplace celle de type L2 (Γ) dans la première méthode. Le nombre d’itérations pour une erreur du mème ordre que l’erreur de discrétisation est considérablement réduit. Nous prouvons des estimations d’erreur a posteriori qui permettent d’optimiser le choix du paramètre de pénalisation pour une grille donnée, et aussi lors de l’adaptation de maillage. Plusieurs expériences numériques sur des problèmes académiques montrent les bonnes performances de notre approche et permettent une comparaison numérique des deux méthodes.Dirección General de Investigació