The glass forming ability was investigated in the codoped Er3+/Yb3+ ternary system NaPO3-WO3-PbF2 with increasing amounts of PbF2. It has been found that glass samples can be obtained for PbF2 contents ranging from 0 mole% to 50 mole% for the codoped samples and an undoped sample containing 60% of lead fluoride could also be vitrified. Thermal properties of the most PbF2 concentrated glasses exhibit strong dependence of the composition with a decrease of the glass transition temperatures and thermal stabilities against devitrification with increasing the lead fluoride content. These glass samples were heat-treated near the crystallization peaks and the X-ray diffraction measurements pointed out that the dominant phase which precipitates from the glass samples containing 40% and 50% of PbF2 is the lead fluorophosphate phase Pb5F(PO4)3 whereas the sample containing 60% of PbF2 exhibits a preferential bulk crystallization of cubic lead fluoride β-PbF2.

Existe a necessidade de garantia de um fluxo constante de madeira com potencial comercial para a viabilidade da pequena propriedade, porém nem sempre isto é possível, pelo fato de os talhões serem pequenos e, principalmente, a distribuição das espécies de interesse na floresta nativa ser irregular, por serem os ecossistemas heterogêneos e pela variedade de tipologias florestais que formam um complexo mosaico. Este trabalho teve como finalidade principal apresentar um modelo matemático que auxilie no planejamento e na distribuição dos talhões em uma pequena propriedade da floresta tropical. O modelo matemático resultou em um novo conceito de talhão. Com base no inventário pré-exploratório, os talhões foram subdivididos em compartimentos, onde foram consideradas características diferenciais como: espécie, volume por espécie, abundância, possibilidade de mercado e, principalmente, valor final de cada subtalhão. Para definição do modelo matemático utilizou-se a PM (programação por metas), que se faz necessária na seleção dos subtalhões, combinando-os e unindo-os em uma área equivalente ou menor que a do compartimento anual original. Este modelo, ao mesmo tempo que organiza novos talhões, determina a taxa de extração anual e sua possível renda, além de limitar a área do compartimento a ser explorado, o que se faz necessário para garantia da regeneração do compartimento no ciclo de corte previsto. Como resultado, o modelo proposto mostrou-se bastante superior ao formal e garantiu sobremaneira o equilíbrio do rendimento anual para o pequeno proprietário.

There is a need to ensure an even flow of timber with commercial potential to make forest management viable on small farms; however, this need is not always met, due to the fact that compartments are small and especially due to the irregular distribution of the species of interest in the native forest because of the heterogeneous ecosystems and forest typologies that form a complex mosaic. The main purpose of this work was to develop a mathematical model to help with the planning and distribution of stands in a small tropical forest farm. The mathematical model resulted in a new concept of stand. Based on the pre-exploratory forest inventory, the compartments were divided into sub compartments with their different values being calculated according to market timber prices. Since the annual logging rate allowed had already been defined based on local and regional studies, the goal was to guarantee that this rate, transformed in monetary value can really be reached annually. The mathematical model GP (Goal programming) was utilized in the selection of the sub compartments by grouping them into a final compartment with size similar to that of the original annual compartment. The proposed stand model was compared with the type of stand normally used in tropical forests and was proved rather superior to the conventional one, thus guaranteeing small farmers a balanced annual income.