Center for the Study of Complex Systems

Siena, Italy

Center for the Study of Complex Systems

Siena, Italy
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Bravi M.,Polo Universitario Colle Of Val Delsa | Parisi M.L.,University of Siena | Tiezzi E.,Polo Universitario Colle Of Val Delsa | Tiezzi E.,University of Siena | And 3 more authors.
Energy | Year: 2011

In this paper the results from a in-depth life cycle analysis of production and use of a novel grid-connected photovoltaic micromorph system are presented and compared to other thin film and traditional crystalline silicon photovoltaic technologies. Among the new thin film technologies, the micromorph tandem junction appears to be one of the most promising devices from the industrial point of view. The analysis was based on actual production data given to the authors directly from the PRAMAC Swiss Company and it is consistent with the recommendations provided by the ISO norms and updates. The gross energy requirement, green house gas emissions and energy pay-back time have been calculated for the electric energy output virtually generated by the studied system in a lifetime period of 20 years. A comparative framework is also provided, wherein results obtained for the case study are compared with data from literature previously obtained for the best commercially available competing photovoltaic technologies. Results clearly show a significant decrease in gross energy requirement, in green house gas emissions and also a shorter energy pay-back time for the micromorph technology. © 2011 Elsevier Ltd.

Riolo M.A.,Center for the Study of Complex Systems | Riolo M.A.,University of Michigan | King A.A.,Center for the Study of Complex Systems | King A.A.,University of Michigan | And 4 more authors.
Vaccine | Year: 2013

Pertussis incidence has been rising in some countries, including the UK, despite sustained high vaccine coverage. We questioned whether it is possible to explain the resurgence without recourse to complex hypotheses about pathogen evolution, subclinical infections, or trends in surveillance efficiency. In particular, we investigated the possibility that the resurgence is a consequence of the legacy of incomplete pediatric immunization, in the context of cohort structure and age-dependent transmission. We constructed a model of pertussis transmission in England and Wales based on data on age-specific contact rates and historical vaccine coverage estimates. We evaluated the agreement between model-predicted and observed patterns of age-specific pertussis incidence under a variety of assumptions regarding the duration of immunity. Under the assumption that infection-derived immunity is complete and lifelong, and regardless of the duration of vaccine-induced immunity, the model consistently predicts a resurgence of pertussis incidence comparable to that which has been observed. Interestingly, no resurgence is predicted when infection- and vaccine-derived immunities wane at the same rate. These results were qualitatively insensitive to rates of primary vaccine failure. We conclude that the alarming resurgence of pertussis among adults and adolescents in Britain and elsewhere may simply be a legacy of historically inadequate coverage employing imperfect vaccines. Indeed, we argue that the absence of resurgence at this late date would be more surprising. Our analysis shows that careful accounting for age dependence in contact rates and susceptibility is prerequisite to the identification of which features of pertussis epidemiology want additional explanation. © 2013 Elsevier Ltd.

Souza A.N.,University of Michigan | Doering C.R.,University of Michigan | Doering C.R.,Center for the Study of Complex Systems
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2015

We derive rigorous upper bounds on the transport 〈XY〉 where 〉 indicates time average, for solutions of the Lorenz equations without assuming statistical stationarity. The bounds are saturated by nontrivial steady (albeit often unstable) states, and hence they are sharp. Moreover, using an optimal control formulation we prove that no other flow protocol of the same strength, i.e., no other function of time X(t) driving the Y(t) and Z(t) variables while satisfying the basic balance 〈X2〉=〈XY〉, produces higher transport. © 2014 Elsevier B.V.

Squartini T.,Leiden University | Squartini T.,University of Siena | Squartini T.,Center for the Study of Complex Systems | Garlaschelli D.,Leiden University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

In self-organizing networks, topology and dynamics coevolve in a continuous feedback, without exogenous driving. The World Trade Network (WTN) is one of the few empirically well documented examples of self-organizing networks: its topology depends on the GDP of world countries, which in turn depends on the structure of trade. Therefore, understanding the WTN topological properties deviating from randomness provides direct empirical information about the structural effects of self-organization. Here, using an analytical pattern-detection method we have recently proposed, we study the occurrence of triadic ‘motifs’ (three-vertices subgraphs) in the WTN between 1950 and 2000. We find that motifs are not explained by only the in- and out-degree sequences, but they are completely explained if also the numbers of reciprocal edges are taken into account. This implies that the self-organization process underlying the evolution of the WTN is almost completely encoded into the dyadic structure, which strongly depends on reciprocity. © IFIP International Federation for Information Processing 2012.

Bravi M.,Polo Universitario Colle Of Val Delsa | Parisi M.L.,University of Siena | Tiezzi E.,Polo Universitario Colle Of Val Delsa | Tiezzi E.,University of Siena | And 4 more authors.
International Journal of Heat and Technology | Year: 2010

The study, developed through a detailed analysis of available data in the international literature, aims to better understand the nature and the extent of risks related to all stages of photovoltaic panels life cycle, produced by the most advanced technologies. For example, the CdTe (Cadmium Telluride) thin film photovoltaic technology is very promising from an economic and energetic point of view, but it shows challenges and risks related to the presence of a potentially very dangerous heavy metal, whose utilization has been actually banned in many products. Currently, CdTe photovoltaic panels arc not included in European regulations limiting elements considered dangerous and regulating their disposal. In terms of environmental impact, previous studies showed that the CdTe modules have similar or less impact than other photovoltaic technologies and have a lower energy consumption relative to the production stage. Indeed, these studies are developed on the only energetic return and EPBT (Energy Pay-Back Time) basis, and they do not take into account the effects related to heavy metals pollution. In this context, the CIGS (Copper Indium Gallium di-Selenide) and amorphous/micromorph MCPH thin-film silicon technologies showed to have an environmental impact comparable to that of CdTe and in some cases even less. The lack of ascertained data on the extent of risks associated with production, use and disposal stages of these panels and the fast technological progress of solar technologies make difficult, but necessary to outline a reliable framework and to assess a balance between risks and benefits in the use photovoltaic modules on a largescale. It is also urgent to implement an efficient action for the recovery and recycling based on the precautionary principle.

Parisi M.L.,University of Siena | Sinicropi A.,University of Siena | Basosi R.,University of Siena | Basosi R.,Center for the Study of Complex Systems
International Journal of Heat and Technology | Year: 2011

In the context of a constant energy demand growth, the interest of the scientific community is progressively moving towards renewable energy sources. Among these, photovoltaics has a prominent role. With the aim of overcoming the limits of silicon production, research turned itself to the development of new photovoltaic technologies based on alternative materials, such as organic compounds. The Dye Sensitized Solar Cells, also known as Grätzel-type cells, have attracted much interest, especially in the last decade. This is due to their potentially lower economic and environmental costs compared with traditional silicon-based cells even though they are not efficient enough yet to be industrially competitive. In this study we present the preliminary results obtained through a multidisciplinary project for the design and synthesis of new organic sensitizers for solar cells together with a life cycle assessment of a Grätzel-type panel production. The life cycle analysis has been developed based on preliminary and estimated production data along all the project stages in order to evaluate environmental impacts and energy consumption associated with the production process. This analysis will be pivotal in understanding the environmental dynamics, the benefits and drawbacks associated with the production of dye sensitized solar cells in comparison with other competitor photovoltaic technologies.

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