Quantum Electrodynamics vacuum polarization solver

The self-consistent modeling of vacuum polarization due to virtual electron-positron fluctuations is of relevance for many near term experiments associated with high intensity radiation sources and represents a milestone in describing scenarios of extreme energy density. We present a generalized finite-difference time-domain solver that can incorporate the modifications to Maxwell's equations due to vacuum polarization. Our multidimensional solver reproduced in one dimensional configurations the results for which an analytic treatment is possible, yielding vacuum harmonic generation and birefringence. The solver has also been tested for two-dimensional scenarios where finite laser beam spot sizes must be taken into account. We employ this solver to explore different types of counter-propagating configurations that can be relevant for future planned experiments aiming to detect quantum vacuum dynamics at ultra-high electromagnetic field intensities

Non-singular inflation with vacuum decay

On the basis of a semi-classical analysis of vacuum energy in an expanding spacetime, we describe a non-singular cosmological model in which the vacuum density decays with time, with a concomitant production of matter. During an infinitely long period we have an empty, inflationary universe, with H \approx 1. This primordial era ends in a fast phase transition, during which H and \Lambda decrease to nearly zero in a few Planck times, with release of a huge amount of radiation. The late-time scenario is similar to the standard model, with the radiation phase followed by a long dust era, which tends asymptotically to a de Sitter universe, with vacuum dominating again. An analysis of the redshift-distance relation for supernovas Ia leads to cosmological parameters in agreement with other current estimations.Comment: Work presented at IRGAC 2006, Barcelona, July 11-15 2006. To appear in a special issue of Journal of Physics

Avaliação do potencial alelopático de três espécies de Eucalyptus na germinação de espécies cultivadas e nativas do cerrado.

Realizaram-se ensaios de germinação com sementes de Lactuca sativa L. (alface) cv. Aurélia, sorgo cv. BR 304, Anadenanthera peregrina (L.) Speg. (angico) e Enterolobium contortisiliquum (Vell.) (tamboril), com o objetivo de avaliar o potencial alelopático de extratos aquosos foliares de três espécies de Eucalyptus. Prepararam-se os extratos colocando as folhas senescentes, secas e moídas de E. camaldulensis Dehnh (EC), E. grandis W.Hill ex Maien (EG) e E. urophylla S.T.Blake (EU) em água destilada na concentração 5% (p/v). Após agitados e centrifugados, obtiveram-se extratos a 100% (v/v), com os quais diluiram-se para 75, 50, 25, 12,5, 0% (v/v) e medidos o pH e o potencial osmótico em cada concentração. As sementes foram colocadas para germinar em placas gerbox, forradas com papel de filtro e umedecidas com os extratos, numa amostragem de 100 sementes por tratamento (4x25). As placas foram colocadas em câmara germinadora a 25°C, na presença de luz. A germinação foi verificada a cada 48h, durante 7 dias, sendo o critério germinativo a emergência radicular. O pH dos extratos das três espécies de Eucalyptus diminuiu com o aumento da concentração, porém, não afetou a germinação das espécies receptoras testadas. Os extratos aquosos de folhas de EC, EG e EU não interferiram na germinação das sementes de angico, tamboril e sorgo, porém inibiram a germinação das sementes de alface. Eucalyptus camaldulensis; E; grandis; E; urophyll