A Thermodynamic Measure of Sustainability

A novel thermodynamic approach to the quantification of the “degree of sustainability” is proposed and discussed. The method includes a rigorous -and innovative- conversion procedure of the so-called externalities that leads to their expression in terms of the exergy of their equivalent primary resources consumption. Such a thermodynamic approach suggests a detailed re-evaluation of the concept of sustainability because it is well-known that the Second Law strictly negates the possibility for any open and evolving system to maintain itself in a “sustainable” state without availing itself of a continuous supply of low-entropy (i.e., high specific exergy) input. If a human society is modeled as an open system, its capacity to “grow sustainably” depends not only on how it uses non-renewable resources, but also on the rate at which it exploits the renewable ones. The necessary inclusion of different forms of energy- and material flows in such an analysis constitutes per se an argument in favor of a resource-based exergy metrics. While it is true that the thermodynamically oriented approach proposed here neglects all of the non-thermodynamic attributes of a “sustainable system” (in the Bruntland sense), it is also clear that it constitutes a rigorous basis on which different physically possible scenarios can be rigorously evaluated. Non-thermodynamic indicators can be still used at a “second level analysis” and maintain their usefulness to indicate which one of the “thermodynamically least unsustainable” scenarios is most convenient from an ethical or socio-economic perspective for the considered community or for the society as a whole. The proposed indicator is known as “Exergy Footprint,” and the advantages of its systematic application to the identification of “sustainable growth paths” is discussed in the Conclusions.

A Predictive Energy Landscape Model of Metamorphic Protein Conformational Specificity

'Metamorphic' proteins challenge state-of-the-art structure prediction methods reliant on amino acid similarity. Unfortunately, this obviates a more effective thermodynamic approach necessary to properly evaluate the impact of amino acid changes on the stability of two different folds. A vital capability of such a thermodynamic approach would be the quantification of the free energy differences between 1) the energy landscape minima of each native fold, and 2) each fold and the denatured state. Here we develop an energetic framework for conformational specificity, based on an ensemble description of protein thermodynamics. This energetic framework was able to successfully recapitulate the structures of high-identity engineered sequences experimentally shown to adopt either Streptococcus protein GA or GB folds, demonstrating that this approach indeed reflected the energetic determinants of fold. Residue-level decomposition of the conformational specificity suggested several testable hypotheses, notably among them that fold-switching could be affected by local de-stabilization of the populated fold at positions sensitive to equilibrium perturbation. Since this ensemble-based compatibility framework is applicable to any structure and any sequence, it may be practically useful for the future targeted design, or large-scale proteomic detection, of novel metamorphic proteins.

METODOLOGIA TERMODINÂMICA PARA CÁLCULO DE EFICIÊNCIA EXERGÉTICA EM CIDADES CONTEMPORÂNEAS / THERMODYNAMIC APPROACH FOR EVALUATION OF EXERGETIC EFFICIENCY OF CONTEMPORARY CITIES

O crescente interesse por sustentabilidade energética induz a procura por ferramentas teóricas concisas para o cálculo e comparação de parâmetros de interesse. O cálculo de eficiência termodinâmica para avaliação das cidades e sua analogia com máquinas térmicas é indicado para o estudo de cidades sustentáveis. No entanto, o cálculo de eficiência termodinâmica de máquinas térmicas aplicados a cidades tem uma dificuldade principal: a definição formal de fluxo de produção das cidades em termos de propriedades termodinâmicas, e que seja aplicável para qualquer cidade independente de sua formação histórica, localização, clima, cultura, economia, etc. Este artigo visa estabelecer o arcabouço teórico para cálculo da produção das cidades através de propriedades termodinâmicas, a dinâmica de consumo e transformação de massa e energia dentro das cidades, geração de irreversibilidades e a aplicação da propriedade exergia como parâmetro universal de análise termodinâmica das cidades. Para exemplificar, apresentam-se valores obtidos para eficiência exergética de cinco cidades da América Latina, apresentados em seminário acadêmico sobre eficiência das cidades dentro do escopo de avaliação de disciplinas optativas do curso de engenharia de energia da UNILA.