18 resultados para field theories in higher dimensions
Resumo:
An area's innate potential to regenerate represents a crucial factor for its conservation and management. The seed rain and seed bank are important agents in the regeneration process. Seed banks are particularly important in communities where there is a high proportion of obligate seeders. Rocky outcrops are habitats where most part of the plant species depends on their seeds to reproduce and maintain viable populations. Therefore, seed banks ought to be important in this vegetation physiognomy. We test the hypotheses that the seed bank of the rocky outcrops found in the rupestrian fields of "Serra do Cipó", Brazil, is richer in species and denser than those formed on different vegetation physiognomies neighboring the outcrops. We then compared species abundance, species richness and composition in the rocky outcrops' seed banks with those of sandy and peaty bogs, forests, gallery forests, and "cerrados". Furthermore, we report on the natural regeneration potential of these soils by assessing a greenhouse study on seedling emergence. Soil samples were collected from 0 to 5 and 5 to 10 cm of depth. Rocky outcrops had the poorest in species and less dense seed bank and showed segregation in species composition. Emergence was greater in the most superficial layer. However, soils on rocky outcrops showed the greatest proportion of endemic threatened species in their seed banks, demonstrating their importance for biodiversity conservation of the "Serra do Cipó" rupestrian fields.
Hydraulic conductivity in response to exchangeable sodium percentage and solution salt concentration
Resumo:
Hydraulic conductivity is determined in laboratory assays to estimate the flow of water in saturated soils. However, the results of this analysis, when using distilled or deionized water, may not correspond to field conditions in soils with high concentrations of soluble salts. This study therefore set out to determine the hydraulic conductivity in laboratory conditions using solutions of different electrical conductivities in six soils representative of the State of Pernambuco, with the exchangeable sodium percentage adjusted in the range of 5-30%. The results showed an increase in hydraulic conductivity with both decreasing exchangeable sodium percentage and increasing electrical conductivity in the solution. The response to the treatments was more pronounced in soils with higher proportion of more active clays. Determination of hydraulic conductivity in laboratory is routinely performed with deionized or distilled water. However, in salt affected soils, these determinations should be carried out using solutions of electrical conductivity different from 0 dS m-1, with values close to those determined in the saturation extracts.
Resumo:
An important constituent group and a key resource of higher education institutions (HEIs) is the faculty or academic staff. The centrality of the faculty role makes it a primary sculptor of institutional culture and has implications for the quality of the institution and therefore has a major role in achieving the objectives of the institution. Demand for academic staff in higher education has been increasing and may be expected to continue to increase. Moreover the performance of academic staff as teachers and researchers determines much of the student satisfaction and has an impact on student learning. There are many factors that serve to undermine the commitment of academics to their institutions and careers. Job satisfaction is important in revitalizing staff motivation and in keeping their enthusiasm alive. Well motivated academic staff can, with appropriate support, build a national and international reputation for themselves and the institution in the professional areas, in research and in publishing. This paper aims to identify the issues and their impacts on academic staff job satisfaction and motivation within Portuguese higher education institutions reporting an ongoing study financed by the European Union through the Portuguese Foundation for Science and Technology.