Staurosira patagonica sp. nov., a new diatom (Bacillariophyta) from southern Argentina, with a discussion on the genus Staurosira Ehrenberg

We present a detailed morphological analysis by light and scanning electron microscopy of Staurosira patagonica sp. nov. from quaternary sediments of Maar Magallanes and recent sediments of the shallow lake Laguna Toro, both in Santa Cruz Province, Argentinian Patagonia. While the valve outline of this new taxon resembles Staurosira incerta, S. construens and Pseudostaurosira pseudoconstruens, it presents features (e.g., fl at valve surface, bifurcate volae and radiate striae) that set it apart from them. Staurosira patagonica sp. nov. is smaller than other small fragilarioids species. We also discuss the main characteristics of Staurosira, we provide a list of species currently included in it, and we propose several new combinations accordingly with current concepts of araphid diatom genera.Fil: García, María Luján. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Maidana, Nora Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; ArgentinaFil: Ector, L.. Luxembourg Institute of Science and Technology; LuxemburgoFil: Morales, E.A.. Universidade de Évora; Portuga

Teaching friction at university level through an experiment with images

The experiment with images described here contributes to the scarce literature about the experimental approach to the classical problem of oblique launching on the surface of an inclined plane. It is directed at an intermediate physics course, with the aim of contextualizing the teaching of the laws of friction and empirical modeling in Classical Mechanics. We used a video of a two-dimensional real motion of a coin sliding on an inclined plane, a case where the net force varies continuously. The video frames were separated and each one was assigned a time code by a computational process. The resulting set of images was used to analyze the dynamical evolution of the system, by recording the coin positions at known instants. All the images and laboratory manuals can be accessed at http://www.fep.if.usp.br/∼fisfoto/translacao/planoInclinado/index.php. Realizing that the resistive force can be interpreted as the kinetic friction force, according to Amontons’ laws, it is possible to build a theoretical model able to predict the trajectory through a first order numerical method, and then fit its parameters to the observed trajectory. This proposal reconciles the laboratory with Information and Communication Digital Technologies (ICDT). It also favors a deeper discussion about the role of laws, models and hypotheses in the physical sciences, which could be particularly interesting in the case of teacher education.Fil: Leite, Marcos L.. Universidade de Sao Paulo; BrasilFil: Maidana, Nora L.. Universidade de Sao Paulo; BrasilFil: Fonseca, Monaliza. Universidade de Sao Paulo; BrasilFil: Barros, Suelen F.. Universidade de Sao Paulo; Brasil. Instituto Federal de Educação, Ciência e Tecnologia de São Paulo; BrasilFil: Aduriz Bravo, Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Formación e Investigación en Enseñanza de las Ciencias; ArgentinaFil: Vanin, Vito R.. Universidade de Sao Paulo; Brasi

Triple- and quadruple-escape peaks in HPGe detectors: Experimental observation and Monte Carlo simulation

The triple- and quadruple-escape peaks of 6.128 MeV photons from the (19)F(p,alpha gamma)(16)O nuclear reaction were observed in an HPGe detector. The experimental peak areas, measured in spectra projected with a restriction function that allows quantitative comparison of data from different multiplicities, are in reasonably good agreement with those predicted by Monte Carlo simulations done with the general-purpose radiation-transport code PENELOPE. The behaviour of the escape intensities was simulated for some gamma-ray energies and detector dimensions; the results obtained can be extended to other energies using an empirical function and statistical properties related to the phenomenon. (C) 2010 Elsevier B.V. All rights reserved.Ministerio de Ciencia e InnovacionMinisterio de Ciencia e Innovacion[PHB2007-0059-TA]Ministerio de Ciencia e Innovacion[FPA2006-12066]Ministerio de Ciencia e InnovacionFEDERFondo Europeo de Desarrollo Regional (FEDER)Coordenacao de Aperfeicoamento de Pessoal de Nivel SuperiorCoordenacao de Aperfeicoamento de Pessoal de Nivel Superior[CAPES-DGU 176/08]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Comissão Nacional de Energia Nuclear (CNEN)Comissao Nacional de Energia Nuclear (CNEN

A freshwater diatom perspective on the evolution of the southern westerlies for the past ∼14,000 years in southwestern Patagonia

Conflicting, even opposite interpretations on the evolution of the Southern Westerly Winds (SWW) are evident in paleoenvironmental records from southwestern Patagonia since the last ice age. These divergences call for new approaches utilizing different, ideally independent indicators of paleoenvironmental/paleoclimatic change from sensitive sites in climatically relevant locations. Here we present a multidecadally resolved diatom record from Lago Cipreses (51°S), a small closed-basin lake located in a bedrock depression along the eastern foothills of the southern Patagonian Andes. The hydrological balance evolution of this isolated lake affords a direct tie with SWW intensity in a mountainous sector where zonal wind strength and local precipitation are highly correlated. We detect cold-tolerant diatoms (small fragilarioids) between ∼14-11.9 cal. ka BP followed by a shift to planktonic assemblages (Discostella pseudostelligera, Aulacoseira spp.) under warmer Holocene conditions. Diatom assemblages indicative of stratified water-column conditions (Discostella pseudostelligera, Achnanthidium aff tepidaricola, Achnanthidium sieminskae) reached their maximum stability between ∼9.1-7.4 cal. ka BP. Stronger water-column mixing is evident by an abrupt species turnover to Aulacoseira spp. between ∼7.4-3.1 cal. ka BP, superimposed on centennial-scale alternations between assemblages since ∼6.1 cal. ka BP. Cold-tolerant diatoms resurge at ∼3.1 cal. ka BP and persist until the present. Our record offers assemblage-based evidence we interpret as sub-centennial to multimillennial scale changes in hydroclimate indicative of: (i) strong SWW influence between ∼14-11.9 cal. ka BP, (ii) a transition between ∼11.9-11.3 cal. ka BP to weak SWW influence between ∼11.3-6.5 cal. ka BP, with a SWW minimum between ∼9.1-7.4 cal. ka BP, and (iii) strong SWW influence since ∼6.5 cal. ka BP, with a Holocene SWW maximum since ∼3.1 cal. ka BP. We posit that enhanced hydroclimate variability since ∼6.1 cal. ka BP attests to the onset of Southern Annular Mode-like changes at centennial-to sub-centennial timescales. We detect a remarkably coherent and synchronous response of terrestrial and aquatic ecosystems at local scale since ∼14 cal. ka BP, highlighting the overriding importance of variations in SWW influence in terrestrial and aquatic environments at multiple timescales.Fil: Villacís, L. A.. Universidad de Chile; ChileFil: Moreno, P. I.. Universidad de Chile; ChileFil: Vilanova, Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Henríquez, C. A.. Universidad de Chile; ChileFil: Henríquez, W. I.. University of Melbourne; AustraliaFil: Villa Martínez, R. P.. Universidad de Magallanes; ChileFil: Sepúlveda Zúñiga, E. A.. Pontificia Universidad Católica de Chile; ChileFil: Maidana, Nora Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentin

Observation of double electron-positron pair production by gamma rays reexamined

An experiment was conducted to observe triple- and quadruple-escape peaks, at a photon energy equal to 6.128 MeV, in the spectra recorded with a high-purity Ge detector working in coincidence with six bismuth germanate detectors. The peak intensities may be explained having recourse to only the bremsstrahlung cascade process of consecutive electron-positron pair creation; i.e., the contribution of simultaneous double pair formation (and other cascade effects) is much smaller. The experimental peak areas are in reasonably good agreement with those predicted by Monte Carlo simulations done with the general-purpose radiation-tran sport code PENELOPE.Ministerio de Educacion[PHB2007-0059-TA]Ministerio de Educacion[FPA2006-12066]CQordenacao de Aperfeicoamento de Pessoal de Nivel Superior[CAPES-DGU 176/08]Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Comissao Nacional de Energia Nuclea

Monte Carlo Semi-Empirical Model for Si(Li) X-Ray Detector: Differences between Nominal\ud and Fitted Parameters.

A detailed characterization of a X-ray Si(Li) detector was performed to obtain the\ud energy dependence of efficiency in the photon energy range of 6.4 - 59.5 keV. which was measured and reproduced by Monte Carlo (MC) simulations. Significant discrepancies between MC and experimental values were found when lhe manufacturer parameters of lhe detector were used in lhe simulation. A complete Computerized Tomagraphy (CT) detector scan allowed to find the correct crystal dimensions and position inside the capsule. The computed efficiencies\ud with the resulting detector model differed with the measured values no more than 10% in most of the energy range