The properties of woody fuels during the combustion can complement the interpretation of the modes of acquisition and use of firewood by groups of the past. The experimental method allows to deepen about the properties of different plant species as fuel, but more importantly allows the reconstruction of the processes that have generated the archaeobotanical remains recovered. This paper has two objectives. For one determine the combustion properties of four woody species (austrocedrus, fitzroya cupressoides, nothofagus and nothofagus antarctica dombeyi) and understand their behavior in the combustion process. Furthermore, explore whether shrinkage cracks present in the charcoal respond to water content the firewood (green-dry). The performance of 16 experimental combustions and the study of the charcoal produced during combustion show differences between woody species studied. The results allow, in some cases, to discriminate the use of dry wood and green wood as fuel. The results obtained allow on one hand, discriminate the use of dry wood and green wood as fuel. On the other, deepen the identification and interpretation of the alterations present in the archaeological charcoals and complement the archaeobotanical analysis of the different sites patagonia.

Conocer las propiedades combustibles de las especies leñosas permite complementar el análisis e interpretación de las modalidades de adquisición y uso del material leñoso por parte de grupos del pasado. El método experimental permite profundizar en las propiedades que las distintas especies vegetales poseen como combustible, pero más importante aun posibilita la reconstrucción de los procesos que han generado el conjunto de restos recuperados. Este trabajo presenta dos objetivos. Por un lado determinar las cualidades que poseen como combustible cuatro especies leñosas (austrocedrus chilensis, fitzroya cupressoides, nothofagus antarctica y nothofagus dombeyi) y comprender su comportamiento en el proceso de combustión. Por otro lado, explorar si las grietas de contracción presentes en los carbones responden al estado de la madera puesta al fuego (verde-seco). La realización de 16 fuegos experimentales y el estudio de sus carbones evidencian diferencias entre las especies leñosas estudiadas. Los resultados obtenidos permiten por un lado, discriminar la utilización de madera seca y madera verde como combustible. Por otro, profundizar en la identificación e interpretación de las alteraciones presentes en los carbones arqueológicos y complementar el análisis arqueobotánico de los distintos sitios patagónicos.

Neste artigo discute-se a importância de se explorar o conceito de simetria no programa de física básica do ensino médio. A partir do exame de um conjunto significativo de livros didáticos de física, constata-se que nenhuma alusão é feita à idéia de simetria e ao papel deste conceito no desenvolvimento da ciência. Argumenta-se que, do ponto de vista pedagógico, não há qualquer tipo de impedimento a que se fale de simetria para alunos do ensino médio. Discute-se, a partir daí, a importância do ensino do conceito geral de simetria nesse nível de escolaridade e apresentam-se três situações, como proposta de uma primeira abordagem concreta do problema, envolvendo a relação entre o movimento retilíneo uniforme e a simetria de translação, vista sob vários aspectos.

In this paper the relevance of exploring the concept of symmetry in a high school physics course is stressed. A review of a significative set of Brazilian teaching books led to the conclusion that there is no reference to the idea of symmetry and its rôle in science development. It is argued that there is no psico-pedagogical constraint of any type that prohibit to talk about symmetry to students at this level. Then, it is discussed how teaching the general concept of symmetry at this school level is important and a first specific proposal is made: the relation between uniform rectilinear mouvement and translation symmetry.

A Density Functional Theory (DFT) analysis of the mixed phosphine complexes Au(PPh3)(Ph2P(CH2)3PPh2)X shows a clear trend in the metal geometry as the anion X- is varied: the softer the anion, the more it is tetrahedral, or alternatively, the more ionic the complex, the more the complex geometry approaches trigonal planar. A strong (soft) donor as cyanide (X- = CN-) penetrates markedly the coordination sphere and establishes the most tetrahedral geometry. In the antitumor compound Au(PPh3)(Ph2P(CH2)3PPh2)Cl (X- = Cl-), the weaker donor chloride is slightly displaced from the coordination sphere with consequent strengthening of Au-P bonds, thus stabilizing a more pyramidal geometry. If the anion is completely out of the coordination sphere, the cation [Au(PPh3)(Ph2P(CH2)3PPh2)]+ shows further strengthening of Au-P bonds and a geometry very close to the trigonal planar "AuP3" system. X-ray and DFT data for Au(PPh3)(Ph2P(CH2)3PPh2)Cl show generally good agreement; however, in the crystal the Au-Cl bond appears lengthened with consequent strong Au-P bonds. This is probably due to packing effects; nevertheless, the X-ray structure agrees with the trend mentioned above as well.

El análisis estructural teórico (Density Functional Theory, DFT) de los complejos de coordinación Au(PPh3)(Ph2P(CH2)3PPh2)X muestra diferentes propiedades al variar el anion X-. Para aniones "blandos", por ejemplo X- = CN-, la geometria es tetraédrica y el anión está fuertemente unido al metal. En cambio para un anión fuera de la esfera de coordinación, el catión[Au(PPh3)(Ph2P(CH2)3PPh2)]+ posee las uniones Au-P más fuertes y la geometria alrededor del metal es trigonal planar. Una configuración intermedia se verifica en el complejo antitumoral Au(PPh3)(Ph2P(CH2)3PPh2)Cl(X = Cl-), debido a que el Cl- es menos "blando" que el CN-. Los datos estructurales de difracción de rayos X y DFT del Au(PPh3)(Ph2P(CH2)3PPh2)Cl muestran buen acuerdo, a pesar de un alargamiento de la unión Au-Cl y el reforzamiento de las uniones Au-P en el cristal. La estructura cristalográfica también sigue la tendencia descripta por los datos de DFT.