Ciências e Tecnologia / Sciences and Technology
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- Dependência do tempo de vida da fluorescência do 9-antroato de metilo na presença de águaPublication . Costa, Fernando Pestana da; Melo, Eurico C.; Costa, Sílvia B.; Fareleira, João M. N. A.; Maçanita, António L.
- The 9-antroate chromophore as a fluorescence probe for waterPublication . Costa, Fernando Pestana da; Costa, Sílvia B.; Melo, Eurico C.; Prieto, Manuel; Maçanita, António L.
- Mutual diffusivity in n-Heptane + n-Hexane isomersPublication . Lopes, M. L. Matos; Castro, C. A. Nieto de; Oliveira, Carla Padrel deA preliminary study of the effect of branching in the binary diffusion of hexane isomer + n-heptane systems is presented. Measurements have been performed with an instrument modeled for the Taylor dispersion technique, at several compositions, at 297 K, for the n-hexane + n-heptane and 2,2-dimethylbutane + n-heptane binary mixtures. The accuracy is estimated to be 1%. The influence of branching is discussed. It was found that the rough hard sphere model for binary diffusion can reproduce the experimental data within 6%. This model was used to predict the binary diffusion coefficients in the 2-methylpentane + n-heptane and 3-methylpentane + n-heptane mixtures, with an estimated accuracy of 5%.
- Mutual diffusivity in binary mixtures of n-heptane with n-hexane isomersPublication . Oliveira, Carla Padrel de; Fareleira, João M. N. A.; Castro, C. A. Nieto deThis paper presents a study of the influence of branching in the binary diffusion coefficients of n-heptane+n-hexane isomers, in the liquid state. The measurements have been made with the Taylor dispersion technique, at several compositions, at 283 and 298 K, for the X+n-heptane mixtures, where X=n-hexane, 3-methylpentane, 2, 3-dimethylbutane, and 2, 2-dimethylbutane. The results show a very interesting behavior of the composition dependence of the binary diffusion coefficients, presenting a maximum, for compositions about a molar fraction of n-heptane of 0.5, which increases with the increase in the degree of branching, suggesting the possibility of order~tisorder effects caused by stereochemically favored packing in the liquid phase and energetically favored segment interaction in the liquid mixtures. An attempt to apply the van der Waals model to these data could not predict the experimental binary diffusion coefficients of these systems within the experimental accuracy.
- The 9-Anthroate chromophore as a fluorescent probe for waterPublication . Costa, Fernando Pestana da; Maçanita, António L.; Costa, Sílvia B.; Melo, Eurico C.; Santos, HelenaWater quenches the fluorescence of methyl 9-anthroate with a rate constant showing little dependence on solvent viscosity or polarity. In dioxane, at 20ºC the value of the rate constant is 9.6 X 10^6 M^(-1) s^(-1) , and the activation energy found for the process is 14.1 kJ mol^(-1). The quenching process is entropy-controlled and is likely to involve a hydrogen-bonded complex as an intermediate. Since the fluorescence lifetime of methyl 9-anthroate does not depend on the solvent properties other than its hydrogen-bonding ability, the concentration of nearby water can be estimated directly. Values of 3, 54, and 14 M were obtained for the solubilization site of methyl 9-anthroate in micelles of Triton X-100, sodium dodecyl sulfate (SDS), and dodecyltrimethylammonium chloride (DTAC), respectively. From the ring current effect of the anthroate group on the 'H NMR chemical shifts of the surfactant protons, it is concluded that the anthroate fluorescent probe is preferentially located in the surface region of the SDS and DTAC micelles; however, in Triton X-100, it resides in the micelle interior near the phenoxy groups of the surfactant molecule.
- Artes de pesca no Rio Tejo: diversidade actual e passadaPublication . Moreira, Francisco; Seixas, Sónia; Dias, SusanaPretende-se com o presente trabalho conhecer um pouco da diversidade das artes de pesca usadas no rio Tejo, procurando-se também comparar a sua riqueza actual com a de tempos que só os velhos pescadores lembram. Para isso deslocámo-nos a algumas localidades existentes ao longo do rio, cobrindo o troço desde o estuário até às barragens de Belver, Castelo de Bode, Maranhão e Montargil, e tentámos descobrir artes de pesca presentes e passadas, usadas nas várias zonas. Factos a salientar nos resultados obtidos são o desaparecimento de muitas das grandes artes de arrasto, como a varina, a influência das barragens na alteração do tipo de artes usadas, a relação entre a existência de determinada espécie piscícola e a presença de uma arte dedicada essencialmente à sua captura e a existência de «artes novas», não referidas nos documentos antigos. Um facto inegável é a diminuição da riqueza etnográfica da pesca, tornando-se cada velho pescador um verdadeiro museu de diferentes e variadas recordações que conviria não perder.
- Didáctica da física : experiência em movimento de translaçãoPublication . Ferreira, Victor; Valadares, Jorge; Azedo, Artur; Leão, HelenaExperiência, em estúdio, pelo professor Victor Ferreira, da Escola Secundária Machado de Castro. Disciplina “Didáctica da Física e da Química”, do Curso de Profissionalização em Exercício.
- Vibrating-wire viscometry on liquid hydrocarbons at high pressurePublication . Oliveira, Carla Padrel de; Assael, Marc J.; Papadaki, Maria; Richardson, Stephen M.; Wakeham, William A.A vibrating-wire viscometer for the measurement of the viscosity of liquids at elevated pressures is described. The instrument is one of a pair, developed collaboratively in different laboratories, that operate in a relative manner according to a complete theory of the instrument. The instrument described here has been used for measurements at pressures up to 80 MPa in toluene, and in n-heptane along two isotherms.
- Didáctica da física : a física na Feira PopularPublication . Valadares, Jorge; Azedo, Artur; Leão, HelenaA atividade lúdica e a aprendizagem da física. Visita à Feira Popular de Lisboa, guiada pelo professor Jorge Valadares. Disciplina “Didáctica da Física e da Química“, do Curso de Profissionalização em Exercício.