Positron annihilation lifetime spectroscopy (PALS), differential scanning calorimetry, X-ray diffraction, and polarized light optical microscopy were used to study six low molar mass poly(ethylene oxide) samples with average molar masses ranging from 1 3 10 3 to 10 3 10 3 g mol À1 . Dynamic light scattering was used to determine molar mass and polydispersity rigorously. Polymer samples with 70-95% crystallinity, which is an unusual range in PALS studies, were prepared by molten material quenching. The ortho-positronium pick-off lifetime (s 3 ) and relative fractional free volume (f v ), determined by the free volume model, correlated well with the average molar mass and crystallinity of the polymers. X-ray diffraction and polarized light optical data support the interpretation of positron annihilation results. PALS parameter, I 3, which is associated with high cavity content, remained approximately constant at 20-22% for all samples. The cavities are present as crystallite defects in the spherulitic open texture and the amorphous phase for the low crystallinity sample (e.g., for M w ¼ 1390) and at the interfaces and in interlamellar spherulite regions of the more crystalline materials.

-Nitrogen (N) is one of the nutrients that have the most significant effect on corn grain productivity increase. In order to evaluate the effect of sources of N topdressing and doses in the grown corn culture, in a conventional till system, it was installed an experiment in the city of Urutaí, Goiás, in the 2012/13 crop, in clayey textured Red Latosol. The experimental design was a randomized complete block design with four replications, with the treatments arranged in a factorial 3 x 5, consisting of three sources (coated urea, urea and ammonium sulfate) and five doses (0, 60, 120, 180 and 240 kg ha -1 ) of N, topdressing, applied in the surface and in a single dose, when the corn plants were in V 4 stage. The hybrid used was the P3646H. We evaluated the following characters: stem diameter, plant height, height of ear insertion, leaf N, number of ears per plant, ear length, number of rows per ear, number of grains per row, 100 grains mass and grain productivity. All characters have a response to nitrogen fertilization and only the height of ear insertion showed no significant difference between sources. The source coated urea showed the best results, indicating that its use may be compensatory, especially in favorable conditions for the NH 3 volatilization, as the application of high doses of N in the surface.

Submetido em 18/03/2014 e aprovado em 17/07/2015.

Positronium formation in the bimary molecular solid solutions Tb 1Àx Eu x (dpm) 3 (dpm = dipivaloylmethanate) has been investigated. A strong linear correlation between the 5 D 4 Tb(III) energy level excited state lifetime and the positronium formation probability has been observed. This correlation indicates that the ligand-to-metal charge transfer LMCT states act in both luminescence quenching and positronium formation inhibition, as previously proposed. A kinetic mechanism is proposed to explain this correlation and shows that excited electronic states have a very important role in the positronium formation mechanism.

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A soja é uma das culturas mais importantes do mundo sendo sua produtividade afetada pela deficiência do micronutriente zinco. O presente trabalho teve como objetivo avaliar o efeito de doses e épocas de aplicação de zinco nas características agronômicas da soja, cultivada em solo da região do Cerrado. O delineamento experimental utilizado foi o de blocos casualizados em esquema fatorial 2 x 5, sendo, duas épocas de aplicação (estádio V9 e R1) e cinco doses (0, 3, 6, 9 e 12 kg ha-1 de zinco), com quatro repetições. Avaliou-se teor de zinco foliar, teor relativo de clorofila, altura de planta, diâmetro do caule, altura de inserção da primeira vagem, número de vagens por planta, número de grãos por vagem, número de nós reprodutivos por planta, massa de 100 grãos e produtividade de grãos. A adubação com Zn influenciou positivamente o teor foliar de Zn, altura de plantas, diâmetro do caule, altura de inserção da primeira vagem, número de vagens por planta, número de nós reprodutivos por planta, massa de 100 grãos e produtividade de grãos. A massa de 100 grãos e a produtividade de grãos apresentaram diferença significativa entre as épocas de aplicação, com resultados superiores para as médias de V9. De acordo com estes resultados recomenda-se a adubação com Zn na cultura da soja.

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SummaryOrganic–inorganic magnetic hybrid materials (MHMs) combine a nonmagnetic and a magnetic component by means of electrostatic interactions or covalent bonds, and notable features can be achieved. Herein, we describe an application of a self-assembled material based on ferrite associated with β-cyclodextrin (Fe-Ni/Zn/βCD) at the nanoscale level. This MHM and pure ferrite (Fe-Ni/Zn) were used as an adsorbent system for Cr3+ and Cr2O7 2− ions in aqueous solutions. Prior to the adsorption studies, both ferrites were characterized in order to determine the particle size distribution, morphology and available binding sites on the surface of the materials. Microscopy analysis demonstrated that both ferrites present two different size domains, at the micro- and nanoscale level, with the latter being able to self-assemble into larger particles. Fe-Ni/Zn/βCD presented smaller particles and a more homogeneous particle size distribution. Higher porosity for this MHM compared to Fe-Ni/Zn was observed by Brunauer–Emmett–Teller isotherms and positron-annihilation-lifetime spectroscopy. Based on the pKa values, potentiometric titrations demonstrated the presence of βCD in the inorganic matrix, indicating that the lamellar structures verified by transmission electronic microscopy can be associated with βCD assembled structures. Colloidal stability was inferred as a function of time at different pH values, indicating the sedimentation rate as a function of pH. Zeta potential measurements identified an amphoteric behavior for the Fe-Ni/Zn/βCD, suggesting its better capability to remove ions (cations and anions) from aqueous solutions compared to that of Fe-Ni/Zn.