Reasoning By Contradiction in Dynamic Geometry

This paper addresses contributions that dynamic geometry systems (DGSs) may give in reasoning by contradiction in geometry. We present analyses of three excerpts of students’ work and use the notion of pseudo object, elaborated from previous research, to show some specificities of DGS in constructing proof by contradiction. In particular, we support the claim that a DGS can offer “guidance” in the solver’s development of an indirect argument thanks to the potential it offers of both constructing certain properties robustly, and of helping the solver perceive pseudo objects

La Medida de la sostenibilidad de la ciudad histórico-turística

Urban sustainability is a key issue in our world. The aim of the thesis is to decline this issue in relation to tourist-historic cities, analyzing the impacts of tourism on urban sustainability and defining a set of indicators for sustainability evaluation and monitoring in these cities. The thesis proposes a new classification of tourism impacts in this context identifying three basic ambits, direct tourism impacts, Public Administration Activities impacts and Carrying Capacity impacts, and two city categories, differentiated and undifferentiated cities depending on urban structure and tourism spatial organization. Indicators are used both to classify cities and to identify unsustainable dynamics. The main aspects of direct tourism impact are also aggregate in a tourism unsustainability index, which measures the aggressiveness of tourism towards historic city, according to the previous considerations. Once identified problems, the thesis suggests some possible policies to cope with unsustainable dynamics. In order to validate this new evaluation methodology, indicators are applied to a specific city, Alghero, to classify the city, calculate tourism unsustainability index, identify negative dynamics and suggest possible policies to Local Administration

Detergency and its implications for oil emulsion sieving and separation

Separating petroleum hydrocarbons from water is an important problem to address in order to mitigate the disastrous effects of hydrocarbons on aquatic ecosystems. A rational approach to address the problem of marine oil water separation is to disperse the oil with the aid of surfactants in order to minimize the formation of large slicks at the water surface and to maximize the oil-water interfacial area. Here we investigate the fundamental wetting and transport behavior of such surfactant-stabilized droplets and the flow conditions necessary to perform sieving and separation of these stabilized emulsions. We show that, for water soluble surfactants, such droplets are completely repelled by a range of materials (intrinsically underwater superoleophobic) due to the detergency effect; therefore, there is no need for surface micro/nanotexturing or chemical treatment to repel the oil and prevent fouling of the filter. We then simulate and experimentally investigate the effect of emulsion flow rate on the transport and impact behavior of such droplets on rigid meshes to identify the minimum pore opening (w) necessary to filter a droplet with a given diameter (d) in order to minimize the pressure drop across the mesh and therefore maximize the filtering efficiency, which is strongly dependent on w. We define a range of flow conditions and droplet sizes where minimum droplet deformation is to be expected and therefore find that the condition of is sufficient for efficient separation. With this new understanding, we demonstrate the use of a commercially available filter--without any additional surface engineering or functionalization--to separate oil droplets from a surfactant stabilized emulsion with a flux of 11,000 L m$^{-2}$ hr$^{-1}$ bar$^{-1}$. We believe these findings can inform the design of future oil separation materials

Energy Communities: energy and economic development laboratories in the Tortona valleys

Clean Energy for All Europeans, Green Deal and Fit for 55 at European level and the Piano Nazionale Integrato per l’Energia e il Clima have identified essential decarbonisation goals that are achievable by broadening the audience of actors involved and the ability to innovate in terms of the evolution of products/services and production processes. In this sense, decentralised energy production technologies together with Renewable Energy Communities (RECs) and bottomup initiatives play a strategic role in the establishment of local energy systems. The objective of the paper is to illustrate these dynamisms within the territorial system, and the characteristics of local initiatives and RECs as means of energy transition and economic development