Bergson, Einstein, Coimbra e o problema do tempo

Texto publicado publicado num volume de actas de homenagem a Leonardo Coimbr

Dos núcleos aos agregados atómicos : campo médio e movimentos colectivos

Director: E. Glendon Gabbard Set Design: Edward Pisoni Costume Design: Douglas Koertgehttps://thekeep.eiu.edu/productions_1960s/1038/thumbnail.jp

Equivalence of thermodynamical fundamental equations

The Gibbs function, which depends on the intensive variables T and P , is easier to obtain experimentally than any other thermodynamical potential. However, textbooks usually first introduce the internal energy, as a function of the extensive variables V and S, and then proceed, by Legendre transformations, to obtain the Gibbs function. Here, taking liquid water as an example, we show how to obtain the internal energy from the Gibbs function. The two fundamental equations (Gibbs function and internal energy) are examined and their output compared. In both cases complete thermodynamical information is obtained and shown to be practically the same, emphasizing the equivalence of the two equations. The formalism of the Gibbs function is entirely analytical, while that based on the internal energy is, in this case, numerical. Although it is well known that all thermodynamic potentials contain the same information, usually only the ideal gas is given as an example. The study of real systems, such as liquid water, using numerical methods, may help students to obtain a deeper insight into thermodynamic

Thermodynamics at work : on the pressure derivative of the specific heat

Thermodynamics relates measurable quantities such as thermal coefficients and specific heats. The first law, which implies that the enthalpy is a function of state, yields a relation for the pressure derivative of the specific heat cP . The second law gives a simpler and well-known relation for this pressure derivative. We compare the values of the pressure derivative of cP obtained from the first and second laws to the values obtained from measurements for water at different pressures. The comparison illustrates the scope and methodology of thermodynamics

Fission of metallic clusters in the liquid drop model

Using the liquid drop model and the jellium model, we calculate fission barrier heights as a function of charge and mass asymmetry for a family of shapes consisting of two spheres connected by a quadratic surface. We find the fissibility for which a mass asymmetric splitting gives place to the symmetric one (Bussinaro-Gallone point) and evaluate the size of charged clusters of alkali metals for which the fission barrier height is equal to the evaporation energy (critical sizes). The results for the critical sizes agree very well with experimen

Experiments with the drinking bird

We made some experiments with the drinking bird oriented by a quantitative model for its period of oscillation. The effect of humidity on the motion was studied, concluding that there are two evaporation regimes. We made a computer simulation which describes well the drinking bird dynamic

Ciência e tecnologia em Portugal : métricas e impacto (1995-2011)

Apresenta-se um retrato do sistema científico-tecnológico nacional, com base na sua evolução de 1995 até 2011. Contextualiza-se a ciência e a tecnologia nacionais usando alguns países de referência e discutimos o desempenho português nos programas europeus. São dadas respostas às seguintes questões: Que ciência se faz em Portugal? Que áreas são mais dinâmicas e que resultados se destacam? Que resultados surgiram do investimento realizado nesse período? Quais as forças e as fraquezas do nosso sistema científico