The effect of temperature on the dynamics of a homogeneous oscillatory system operated in batch and under flow

The effect of temperature on a network of chemical reactions is not obvious, especially when compared to the effect exerted on elementary steps. There are few reports regarding the estimation of parameters such as activation energies for oscillating chemical systems. Still less investigated is the importance of the relative distance from thermodynamic equilibrium on the way in which temperature influences the oscillators' dynamics – a crucial aspect for the understanding of chemical and bio-chemical oscillating networks. In this paper we use the bromate–oxalic acid–acetone–cerium oscillatory system to study the influence of temperature under close and far-from-equilibrium regimes. The research was carried out under identical conditions for batch and flow (in a continuous flow stirred tank reactor, CSTR) regimes, and the main oscillation features were preserved, so that it was possible to isolate the effect of flow. Overall, increasing the flow results in an increase of the oscillatory frequency. The apparent oscillatory activation energy was found to decrease from 72 ± 6 kJ mol−1, for the system operated in batch, to 50 ± 2 kJ mol−1, under the flow regime. The role of the distance from the thermodynamic equilibrium on the temperature dependence is generalized and discussed in connection with other systems. Numerical simulations using the Brusselator model under batch and flow regimes further helped the discussion of the main experimental results

Educação ambiental: uma ferramenta imprescindível para a vida do homem no planeta.

A educação ambiental se constitui numa forma abrangente de educação, que se propõe atingir todos os cidadãos, através de um processo pedagógico participativo permanente que procura incutir no educando uma consciência crítica sobre a problemática ambiental, compreendendo-se como crítica a capacidade de captar a gênese e a evolução de problemas ambientais

Gauge dependenceof the order parameter anomalous dimension in the Ginzburg-Landau model and the critical fluctuations in superconductors

The critical fluctuations of superconductors are discussed in a fixed dimension scaling suited to describe the type II regime. The gauge dependence of the anomalous dimension of the scalar field is stablished exactly from the Ward-Takahashi identities. Its fixed point value gives the $\eta$ critical exponent and it is shown that $\eta$ is gauge independent, as expected on physical grounds. In the scaling considered, $\eta$ is found to be zero at 1-loop order, while $\nu\approx 0.63$. This result is just the 1-loop values for the XY model obtained in the fixed dimension renormalization group approach. It is shown that this XY behavior holds at all orders. The result $\eta=\eta_{XY}$ should be contrasted with the negative values frequently reported in the literature.Comment: EuroLaTex, 7 pages, 2 figures, reference updated; version to be published in Europhysics Letter