Elastic properties of graphyne-based nanotubes

Graphyne nanotubes (GNTs) are nanostructures obtained from rolled up graphyne sheets, in the same way carbon nanotubes (CNTs) are obtained from graphene ones. Graphynes are 2D carbon-allotropes composed of atoms in sp and sp2 hybridized states. Similarly to conventional CNTs, GNTs can present different chiralities and electronic properties. Because of the acetylenic groups (triple bonds), GNTs exhibit large sidewall pores that influence their mechanical properties. In this work, we studied the mechanical response of GNTs under tensile stress using fully atomistic molecular dynamics simulations and density functional theory (DFT) calculations. Our results show that GNTs mechanical failure (fracture) occurs at larger strain values in comparison to corresponding CNTs, but paradoxically with smaller ultimate strength and Young's modulus values. This is a consequence of the combined effects of the existence of triple bonds and increased porosity/flexibility due to the presence of acetylenic groups

Produção orgânica de rabanete em plantio direto sobre cobertura morta e viva.

O objetivo deste trabalho foi avaliar o uso de plantas espontâneas e cobertura viva de amendoim forrageiro(Arachis pintoi), associado à aplicação de composto orgânico na produção orgânica do rabanete em plantio direto. O experimento foi instalado na Universidade Federal do Acre, em Rio Branco-AC, de 15/06 a 14/07/2007. O delineamento experimental utilizado foi em blocos casualizados com parcelas subdivididas 4x3, em quatro repetições. As parcelas corresponderam ao sistema de plantio direto com cobertura viva de amendoim forrageiro, cobertura viva de planta espontânea, cobertura morta de planta espontânea e sistema de plantio em canteiro com solo descoberto. As subparcelas foram compostas pelas doses de composto orgânico de 5, 10 e 15 t ha-1 (base seca). O plantio direto na palha de plantas espontâneas teve desempenho semelhante ao preparo convencional do solo, ambos superiores ao plantio sobre as coberturas vivas. A produtividade do rabanete cv. Cometo, não foi afetada pelas doses crescentes de composto orgânico, podendo aplicar-se apenas 5 t ha-1, enquanto em preparo convencional do solo, o aumento da produtividade ultrapassa o plantio direto na palha apenas na dose maior de composto (15 t ha-1)

The Role of Transformation in Learning and Education for Sustainability

Education research has acknowledged the value of transformation, which offers an opportunity for researching and rethinking how appropriate and successful educational practices may be. However, despite the role of transformation in higher education and particularly in sustainability learning, there is a paucity of studies which examine the extent to which transformation and learning on matters related to sustainable development may be integrated. Based on this perceived research need, the purpose of this article is to present how transformation in learning in education for sustainability requires the commitment of Faculty and the engament of students. To do this, a set of qualitative case studies were used in higher education institutions across seven countries (Brazil, Serbia, Latvia, South Africa, Spain, Syria, UK). The findings revealed that the concept of education for sustainable development has not been sufficiently integrated into the concept of transformation in higher education institutions. It also found that to enhance sustainability in the curricula, academics should develop collaborative approaches, and discuss how to redesign their own disciplines, and how to appreciate the epistemology and multicultural vision of sustainability, both as a topic, and as a field of education research. It was further found that reflections of the academics on their own values are crucial for developing the transformative potential of students as agents of a sustainable future. It is necessary that universities should transform to serve as models of social justice and environmental stewardship, and to foster sustainability learning

Pequi leaves incorporated into the soil reduce the initial growth of cultivated, invasive and native species

Estudos têm identificado potencial fitotóxico de tecidos vegetais de diversas espécies do Cerrado. Entretanto, a maior parte destes estudos foi conduzida em substrato inerte, ou fazendo uso de quantidades exageradas de material vegetal. Neste estudo investigamos o potencial fitotóxico de folhas de pequi adicionadas a substrato solo em quantidades compatíveis ao volume de liteira produzida por esta espécie no campo. Folhas de pequi foram trituradas e incorporadas a latossolo vermelho em proporções entre 0,75 e 3% (p/p), sendo o controle constituído por solo sem folhas. Estas misturas foram adicionadas a vasos plásticos irrigados diariamente. Sementes germinadas das espécies cultivadas sorgo e gergelim, da invasora braquiária, e da nativa ipê-roxo foram dispostas nos vasos e crescidas por cinco a sete dias a 30°C, com fotoperíodo de 12 h. Plântulas de todas as espécies apresentaram redução dose-dependente no crescimento, sendo o crescimento radicular mais afetado que o aéreo. Sinais de necrose foram observados nas raízes de sorgo, gergelim e braquária. Os efeitos fitotóxicos gerados por uma quantidade relativamente baixa de tecido vegetal, em substrato solo, e em razoável número de espécies de diferentes grupos funcionais sugerem que a liteira desta espécie possa exercer real potencial alelopático em condições de campo.Studies have identified the phytotoxicity of many native species of the Cerrado; however, most of them were conducted either in inert substrates, or using exaggerate proportions of plant material. We investigated the phytotoxicity of pequi leaves added to substrate soil in quantities compatible with the litter produced by this species. Pequi leaves were triturated and added to red latosol in concentrations of 0.75%, 1.5% and 3%; the control was constituted of leafless soil. These mixtures were added to pots and irrigated daily to keep them moist. Germinated seeds of the cultivated sorghum and sesame, of the invasive brachiaria and of the native purple ipê, were disposed in the pots to grow for five to seven days at 30°C within a photoperiod of 12 h. Seedlings of all the species presented a reduction in their initial growth in a dose-dependent way. In general, the root growth was more affected by the treatments than the shoot growth; moreover, signs of necrosis were observed in the roots of the sorghum, sesame and brachiaria. The phytotoxic effects generated by relatively small quantities of leaves, in a reasonable range of species within a soil substrate, suggest potential allelopathy of pequi leaves under natural conditions