RESUMO A potência e a capacidade de carga das máquinas agrícolas vêm crescendo, e os efeitos da pressão imposta no solo, por meio dos pneus, ainda são pouco estudados. Com o desenvolvimento sustentável, a relação máquina-pneu-solo deve ser criteriosamente avaliada para que haja um melhor equilíbrio entre esses elementos. Este trabalho teve por objetivo avaliar quatro pneus com dois tipos construtivos: o diagonal cinturado BPAF (Baixa Pressão e Alta Flutuação) e o radial, ambos com diâmetros de aro de 572 e 673 mm, sendo determinadas as seguintes variáveis: área de contato pneu/superfície da amostra do solo, deformação elástica do pneu, recalque e resistência mecânica à penetração da amostra em caixa de solo. Foi utilizada uma prensa hidráulica que possuía um eixo de fixação para montagem dos pneumáticos e uma caixa de solo na qual o pneu foi prensado com uma carga de 53,00 kN, utilizando as pressões nominais recomendadas pelo fabricante dos pneumáticos. O pneu de construção radial, com diâmetro de aro 673 mm, obteve menores recalque e resistência à penetração, maior deformação elástica e área de contato em relação aos demais pneumáticos, enquanto BPAF, aro 572 mm, apresentou a maior resistência à penetração e a menor deformação elástica.

ABSTRACT The power consumption and load capacity of agricultural machines have grown and the effects of pressure on the soil by tires have been still little investigated. In concern with sustainable development, the relationship machine-tire-soil must be in balance to give more consistency on the best use of tires for a given load. This study aimed to evaluate four tires of two constructive types, the bias belted tires and radial tires, both with respective rim diameters of 22.5 and 26.5 inches with variables measuring the footprint, elastic deformation, sinkage and resistance to penetration. A hydraulic press with an attachment shaft for tire mounting and a box of soil in which the tire has been imposed on a load of 53.00 kN using nominal pressures recommended by the tire manufacturer. The radial construction tire with rim diameter of 26.5 inches obtained less sinkage and resistance to penetration; however, greater elastic deformation and footprint compared to other tires. The bias-belted tire with 22.5-inch rim presented the highest resistance to penetration and the lowest elastic deformation.

RESUMO O objetivo deste trabalho foi determinar a metodologia mais adequada para superação de dormência das sementes de Parkia gigantocarpa Ducke e produção de mudas. As sementes foram submetidas aos seguintes tratamentos: imersão em água fervente à temperatura de 100 ºC, por 10 minutos; escarificação ácida, com imersão em ácido sulfúrico (H2SO4) a 98 %, por 5, 10, 20, 30 e 40 minutos; escarificação mecânica, com abrasão em lixa no 80 por 15 segundos, e testemunha (sem tratamento). Também foi realizada a avaliação da qualidade das mudas através da massa seca das raízes primárias. O delineamento experimental foi inteiramente casualizado, com oito métodos de superação de dormência. Levando-se em consideração todos os parâmetros avaliados, os resultados indicaram que a escarificação ácida por 30 e 40 minutos foram os métodos mais eficientes para a superação da dormência das sementes de Parkia gigantocarpa, proporcionando maior vigor na germinação e maiores médias de massa seca para as raízes primárias.

ABSTRACT This paper aimed to determine the best dormancy overcoming methods for Parkia gigantocarpa Ducke seeds and their influence on seedlings quality. The seeds were submitted to the following methods: immersion in boiling water for 10 minutes; acid scarification, in which the seeds were immersed in sulfuric acid (H2SO4) 98 % for 5, 10, 20, 30 and 40 minutes; mechanical scarification, with sandpaper for 15 seconds, and control (no treatment). The seedling quality was evaluated through primary root dry matter. Experiment was entirely random designed, with eight methods. Evaluating all the parameters, the acid scarification, for 30 and 40 minutes, showed the best dormancy overcoming results to the species, providing better vigor into germination and greater biomass allocation mean values to primary root.

[RE(czb)3(H2O)2] complexes (where RE = Eu3+, Tb3+, Gd3+; and czb = 4-(9H-carbazol-9-yl)benzoato) have been synthesized and characterized. The Gd3+ complex was used to determine the triplet state energy of the czb ligand. Photoluminescence measurements of the complexes have been carried out under UV excitation. The Tb3+ complex exhibited a strong green luminescence indicating an efficient antenna effect, whereas the Eu3+ complex showed low red luminescence and the Gd3+ complex a blue-green luminescence from the ligand. The luminescence lifetimes and quantum yields have also been measured for the evaluation of the spectroscopic behavior of the complexes.

In this paper the evolution of the concept of aromaticity is discussed. It considers not only historical aspects of the aromaticity concept but also the different criteria (theoretical and experimental) that have appeared to explain the properties of the aromatic compounds. The topics range from the isolation of benzene by Faraday (1825) until the modern criteria based on geometries, magnetic properties, resonance energy (RE), aromatic stabilization energy (ASE), topological analyses, and others. A chronological separation of issues concerning aromaticity was made, splitting the definitions before and after the appearance of the quantum chemistry. This work reviews the concept of aromaticity.

This work describes a simple and economical experiment for the extraction and purification of chlorophyll a from Spirulina maxima. Extraction and purification of natural compounds can be considered one of the most illustrative experiments that can be performed in Organic Chemistry courses. Particularly, the chromatography of dyes and pigments allows students to have a better comprehension of the chromatography separations. These compounds represent an important class of organic pigments applied in pharmaceutical, cosmetic, detergent compositions, and various other fields and can be extracted from plants and algae. To extract, separate and purify chlorophyll a from associated pigments such as xanthophylls, carotenes, and pheophytins, very costly processes are reported. The present approach is perfectly adequate for use in Chemistry experiments for undergraduate students.

A computational quantum chemistry experiment is described of Diels-Alder reactions between 2-cycloenones and cyclopentadiene. The effects of FMO-Frontier Molecular Orbitals (HOMO-LUMO) and of the withdrawing nature of substituents at the C=C bond of cycloenones were evaluated. The calculations were made using HF/STO-3G and B3LYP/6-31+G(d,p) methods. The FMO based indexes are in agreement with the experimentally observed reactivity order. NBO - Natural Bond Orbitals - analysis was used to ascertain the effect of C=C substituents on the dienophile reactivity.