Miniestaquia de Eucalyptus benthamii x E. dunnii em substratos a base de casca de arroz carbonizada.

Objetivou-se avaliar a viabilidade técnica da utilização de diferentes granulometrias de casca de arroz carbonizada, pura ou em mistura com fibra de coco, substrato comercial a base de casca de pinus e vermiculita como componentes de substratos para produção de mudas de Eucalyptus benthamii x E. dunnii via miniestaquia. Para tanto, foram montados 14 substratos, nos quais as miniestacas foram enraizadas para produção das mudas (60 dias em casa de vegetação, 30 dias em casa de sombra e 30 dias em área de pleno sol). Avaliou-se: 1) a sobrevivência das miniestacas, número de raízes e comprimento da maior raiz na saída da casa de vegetação; 2) a sobrevivência na saída da casa de sombra e; 3) o percentual final de enraizamento após a permanência na área de pleno sol. Com base nos resultados obtidos, conclui-se que a casca de arroz carbonizada pode ser utilizada pura (granulometria de 0,5 a 1 mm e em sua forma íntegra) ou em composição com vermiculita (50%) como substrato para produção de mudas do híbrido em questão via miniestaquia

Heating in the Accreted Neutron Star Ocean: Implications for Superburst Ignition

We perform a self-consistent calculation of the thermal structure in the crust of a superbursting neutron star. In particular, we follow the nucleosynthetic evolution of an accreted fluid element from its deposition into the atmosphere down to a depth where the electron Fermi energy is 20 MeV. We include temperature-dependent continuum electron capture rates and realistic sources of heat loss by thermal neutrino emission from the crust and core. We show that, in contrast to previous calculations, electron captures to excited states and subsequent gamma-emission significantly reduce the local heat loss due to weak-interaction neutrinos. Depending on the initial composition these reactions release up to a factor of 10 times more heat at densities < 10^{11} g/cc than obtained previously. This heating reduces the ignition depth of superbursts. In particular, it reduces the discrepancy noted by Cumming et al. between the temperatures needed for unstable 12C ignition on timescales consistent with observations and the reduction in crust temperature from Cooper pair neutrino emission.Comment: 10 pages, 11 figures, the Astrophysical Journal, in press (scheduled for v. 662). Revised from v1 in response to referee's comment

The strength of nuclear shell effects at N=126 in the r-process region

We have investigated nuclear shell effects across the magic number N=126 in the region of the r-process path. Microscopic calculations have been performed using the relativistic Hartree-Bogoliubov approach within the framework of the RMF theory for isotopic chains of rare-earth nuclei in the r-process region. The Lagrangian model NL-SV1 with the inclusion of the vector self-coupling of omega meson has been employed. The RMF results show that the shell effects at N=126 remain strong and exhibit only a slight reduction in the strength in going from the r-process path to the neutron drip line. This is in striking contrast to a systematic weakening of the shell effects at N=82 in the r-process region predicted earlier in the similar approach. In comparison the shell effects with microscopic-macroscopic mass formulae show a near constancy of shell gaps leading to strong shell effects in the region of r-process path to the drip line. A recent analysis of solar-system r-process abundances in a prompt supernova explosion model using various mass formulae including the recently introduced mass tables based upon HFB approach shows that whilst mass formulae with weak shell effects at N=126 give rise to a spread and an overproduction of nuclides near the third abundance peak at A~190, mass tables with droplet models showing stronger shell effects are able to reproduce the abundance features near the third peak appropriately. In comparison, several analyses of the second r-process peak at A~130 have required weakened shell effects at N=82. Our predictions in the RMF theory with NL-SV1, which exhibit weaker shell effects at N=82 and stronger one at N=126 in the r-process region, support the conjecture that a different nature of the shell effects at the magic numbers may be at play in r-process nucleosynthesis of heavy nuclei.Comment: 14 pages, 8 figures; submitted to Physical Review C. Part of this work was presented at Nuclear Physics in Astrophysics II, 20th International Nuclear Physics Divisional Conference of the European Physical Society, at Debrecen, Hungary, May 16-20, 200

Substratos renováveis na produção de mudas de Eucalyptus benthamii.

A necessidade premente de aumento no número de mudas plantadas anualmente, bem como a menor disponibilidade de matérias-primas tradicionais para composição de substratos têm levado à necessidade de desenvolvimento de estudos que visem à avaliação e disponibilização de novos materiais para composição de substratos, técnica e economicamente eficientes. Com base nisso, o presente estudo objetivou avaliar a viabilidade técnica da utilização de componentes renováveis a base de fibra de coco (FC), casca de arroz carbonizada (CAC) em diferentes granulometrias, biossólido (BIO) e casca de pinus semidecomposta na composição de substratos para a produção de mudas de Eucalyptus benthamii, bem como, avaliar a correlação entre as propriedades físicas e químicas dos substratos formulados com a qualidade das mudas produzidas. Para tanto, foram formulados 41 tratamentos, os quais tiveram suas propriedades físicas e químicas avaliadas, sendo a semeadura realizada em tubetes de 55 cm³. Foram avaliadas a altura da parte aérea e o diâmetro de colo a cada 30 dias, bem como, a biomassa seca da parte aérea e radicial, a facilidade de retirada do tubete e a agregação das raízes ao substrato aos 90 dias. Verificou-se que todos os materiais renováveis analisados foram adequados para a produção de mudas, no entanto o peneiramento da CAC não se justifica, quando comparado com a CAC na sua forma íntegra. Mensurações de altura e diâmetro anteriores à avaliação final não são confiáveis para predição do resultado final. O BIO e as diferentes granulometrias de CAC apresentaram baixa agregação das raízes ao substrato. Os altos níveis de salinidade, condutividade elétrica e pH não prejudicaram o crescimento das mudas. Quanto às propriedades físicas, observou-se que os substratos com maiores densidades e microporosidade proporcionaram menor agregação das raízes ao substrato e os com maior macroporosidade proporcionaram maior crescimento da parte aérea e radicial

On the Origin of the Early Solar System Radioactivities. Problems with the AGB and Massive Star Scenarios

Recent improvements in stellar models for intermediate-mass and massive stars are recalled, together with their expectations for the synthesis of radioactive nuclei of lifetime $\tau \lesssim 25$ Myr, in order to re-examine the origins of now extinct radioactivities, which were alive in the solar nebula. The Galactic inheritance broadly explains most of them, especially if $r$-process nuclei are produced by neutron star merging according to recent models. Instead, $^{26}$Al, $^{41}$Ca, $^{135}$Cs and possibly $^{60}$Fe require nucleosynthesis events close to the solar formation. We outline the persisting difficulties to account for these nuclei by Intermediate Mass Stars (2 $\lesssim$ M/M$_\odot \lesssim 7 - 8$). Models of their final stages now predict the ubiquitous formation of a $^{13}$C reservoir as a neutron capture source; hence, even in presence of $^{26}$Al production from Deep Mixing or Hot Bottom Burning, the ratio $^{26}$Al/$^{107}$Pd remains incompatible with measured data, with a large excess in $^{107}$Pd. This is shown for two recent approaches to Deep Mixing. Even a late contamination by a Massive Star meets problems. In fact, inhomogeneous addition of Supernova debris predicts non-measured excesses on stable isotopes. Revisions invoking specific low-mass supernovae and/or the sequential contamination of the pre-solar molecular cloud might be affected by similar problems, although our conclusions here are weakened by our schematic approach to the addition of SN ejecta. The limited parameter space remaining to be explored for solving this puzzle is discussed.Comment: Accepted for publication on Ap

Two-body correlation functions in nuclear matter with npnp condensate

The density, spin and isospin correlation functions in nuclear matter with a neutron-proton ($np$) condensate are calculated to study the possible signatures of the BEC-BCS crossover in the low-density region. It is shown that the criterion of the crossover (Phys. Rev. Lett. {\bf 95}, 090402 (2005)), consisting in the change of the sign of the density correlation function at low momentum transfer, fails to describe correctly the density-driven BEC-BCS transition at finite isospin asymmetry or finite temperature. As an unambiguous signature of the BEC-BCS transition, there can be used the presence (BCS regime) or absence (BEC regime) of the singularity in the momentum distribution of the quasiparticle density of states.Comment: Prepared with RevTeX4, 5p., 4 figure

First decay study of the very neutron-rich isotope Br-93

The decay of the mass-separated, very neutron-rich isotope Br-93 has been studied by gamma-spectroscopy. A level scheme of its daughter Kr-93 has been constructed. Level energies, gamma-ray branching ratios and multipolarities suggest spins and parities which are in accord with a smooth systematics of the N=57 isotones for Z less-equal 40, suggesting the N=56 shell closure still to be effective in Kr isotopes. So far, there is no indication of a progressive onset of deformation in neutron-rich Kr isotopes.Comment: 17 pages, 3 figures, Phys. Rev. C, in prin