QCD Corrections to QED Vacuum Polarization

We compute QCD corrections to QED calculations for vacuum polarization in background magnetic fields. Formally, the diagram for virtual $e\bar{e}$ loops is identical to the one for virtual $q\bar{q}$ loops. However due to confinement, or to the growth of $\alpha_s$ as $p^2$ decreases, a direct calculation of the diagram is not allowed. At large $p^2$ we consider the virtual $q\bar{q}$ diagram, in the intermediate region we discuss the role of the contribution of quark condensates \left and at the low-energy limit we consider the $\pi^0$, as well as charged pion $\pi^+\pi^-$ loops. Although these effects seem to be out of the measurement accuracy of photon-photon laboratory experiments they may be relevant for $\gamma$-ray burst propagation. In particular, for emissions from the center of the galaxy (8.5 kpc), we show that the mixing between the neutral pseudo-scalar pion $\pi_0$ and photons renders a deviation from the power-law spectrum in the $TeV$ range. As for scalar quark condensates \left and virtual $q\bar{q}$ loops are relevant only for very high radiation density $\sim 300 MeV/fm^3$ and very strong magnetic fields of order $\sim 10^{14} T$.Comment: 15 pages, 4 figures; Final versio

‘No memory, no desire’: psychoanalysis in Brazil during repressive times

Until recently, the growth and significance of Brazilian psychoanalysis has been neglected in histories of psychoanalysis. Not only is this history long and rich in its professional and cultural dimensions, but there was an especially important ‘event’ – the so-called ‘Cabernite-Lobo affair’ – that took place during the period of the military dictatorship, which can be seen as dramatising some of the issues concerning the erasure of memory in psychoanalysis, especially in connection with political difficulties. In this paper, we provide an outline of the origins and dissemination of psychoanalysis in Brazil before looking again at the Cabernite-Lobo affair in order to examine in a situated way how psychoanalysis engages with political extremism, and particularly to explore the consequences of an unthinking generalisation of the idea of ‘neutrality’ from the consulting room to the institutional setting. We draw especially on Brazilian papers in Portuguese, which have not been accessible in the English-language psychoanalytic literature

Ladder Dyson-Schwinger calculation of the anomalous gamma-3pi form factor

The anomalous processes, \gamma \to 3 \pi and \gamma \pi \to \pi\pi, are investigated within the Dyson-Schwinger framework using the rainbow-ladder approximation. Calculations reveal that a complete set of ladder diagrams beyond the impulse approximation are necessary to reproduce the fundamental low-energy theorem for the anomalous form factor. Higher momentum calculations also agree with the limited form factor data and exhibit the same resonance behavior as the phenomenological vector meson dominance model.Comment: 9 pages, 8 .eps figures, Revte

Estrutura da comunidade de Chlorococcales sensu lato (Chlorophyceae) em diferentes hábitats aquáticos e hidroperíodos Structure of the Chlorococcales sensu lato (Chlorophyceae) community in different aquatic habitats and hydroperiods

Este estudo visa avaliar a riqueza, a densidade, a diversidade específica e a distribuição da comunidade de Chlorococcales s.l. em zonas pelágicas e litorâneas de diferentes hábitats aquáticos (lagoas isoladas, lagoas interligadas, banhados, açudes e arroios) em dois hidroperíodos (águas altas e baixas) em região subtropical no sul do Brasil. As amostragens de fitoplâncton foram realizadas em duas áreas, situadas entre as coordenadas 30(0)40´ - 30(0)10´ S e 50(0)30´ - 51(0)31´W no ano de 2003, com a obtenção simultânea de dados de temperatura, condutividade, pH, transparência e profundidade da água. Os resultados revelaram que as médias de riqueza e de diversidade específica foram maiores na zona litorânea e significativamente maiores (p<0,02) nos banhados, em relação aos outros hábitats. As médias de densidade foram também significativamente maiores nos banhados (p<0,03), no período de águas baixas (p<0,04) e em mais altas temperaturas de água (>24°C). Dentre os táxons observados, Desmodesmus heteracanthus (Guerr.) Hentschke et Torgan, D. lunatus (W. et G. S. West) Hegew. e Monoraphidium griffithii (Berk.) Kom-Legn., mostraram-se indicadoras de hábitats e D. armatus (Chod.) Hegew., D. denticulatus (Lagerh.) An, Friedl et Hegew. e D. lunatus foram indicadoras de hidroperíodo. Este estudo demonstra a importância do hábitat e do hidroperíodo, na estrutura da comunidade de Chlorococcales s.l.<br>This study aims to evaluate richness, density specific diversity and distribution of the Chlorococcales s.l. community in pelagic and littoral zones of different aquatic habitats (isolated lagoons, interlinked lagoons, swamps, reservoirs and streams) during two hydroperiods (high and low water) in a subtropical region in Southern Brazil. Phytoplankton sampling was carried out in two areas, situated within the coordinates 30(0)40´ - 30(0)10´ S and 50(0)30´ - 51(0)31´ W, in 2003 with simultaneous information on temperature, conductivity, pH, transparency and depth of water. The results showed that richness and specific diversity averages were higher in the littoral zone and significantly higher (p<0.02) in swamps in contrast to other habitats. Density averages were also significantly higher in swamps (p<0.03), during low water periods (p<0.04) and at warmer water temperatures (>24°C). Among the observed taxa Desmodesmus heteracanthus (Guerr.) Hentschke & Torgan, D. lunatus (W. et G. S. West) Hegew. and Monoraphidium griffithii (Berk.) Kom-Legn. were habitat indicators and D. armatus (Chod.) Hegew., D. denticulatus (Lagerh.) An, Friedl et Hegew. and D. lunatus were hydroperiod indicators. This study shows the importance of habitats and hydroperiods for Chlorococcales s.l. community structure

Brazilian Flora 2020: Leveraging the power of a collaborative scientific network

International audienceThe shortage of reliable primary taxonomic data limits the description of biological taxa and the understanding of biodiversity patterns and processes, complicating biogeographical, ecological, and evolutionary studies. This deficit creates a significant taxonomic impediment to biodiversity research and conservation planning. The taxonomic impediment and the biodiversity crisis are widely recognized, highlighting the urgent need for reliable taxonomic data. Over the past decade, numerous countries worldwide have devoted considerable effort to Target 1 of the Global Strategy for Plant Conservation (GSPC), which called for the preparation of a working list of all known plant species by 2010 and an online world Flora by 2020. Brazil is a megadiverse country, home to more of the world's known plant species than any other country. Despite that, Flora Brasiliensis, concluded in 1906, was the last comprehensive treatment of the Brazilian flora. The lack of accurate estimates of the number of species of algae, fungi, and plants occurring in Brazil contributes to the prevailing taxonomic impediment and delays progress towards the GSPC targets. Over the past 12 years, a legion of taxonomists motivated to meet Target 1 of the GSPC, worked together to gather and integrate knowledge on the algal, plant, and fungal diversity of Brazil. Overall, a team of about 980 taxonomists joined efforts in a highly collaborative project that used cybertaxonomy to prepare an updated Flora of Brazil, showing the power of scientific collaboration to reach ambitious goals. This paper presents an overview of the Brazilian Flora 2020 and provides taxonomic and spatial updates on the algae, fungi, and plants found in one of the world's most biodiverse countries. We further identify collection gaps and summarize future goals that extend beyond 2020. Our results show that Brazil is home to 46,975 native species of algae, fungi, and plants, of which 19,669 are endemic to the country. The data compiled to date suggests that the Atlantic Rainforest might be the most diverse Brazilian domain for all plant groups except gymnosperms, which are most diverse in the Amazon. However, scientific knowledge of Brazilian diversity is still unequally distributed, with the Atlantic Rainforest and the Cerrado being the most intensively sampled and studied biomes in the country. In times of “scientific reductionism”, with botanical and mycological sciences suffering pervasive depreciation in recent decades, the first online Flora of Brazil 2020 significantly enhanced the quality and quantity of taxonomic data available for algae, fungi, and plants from Brazil. This project also made all the information freely available online, providing a firm foundation for future research and for the management, conservation, and sustainable use of the Brazilian funga and flora