276 research outputs found
The 2015 Countershock and the Prospects for a Low-carbon Energy Transition
In this short essay we discuss the possible consequences of the recent downfall in oilprices for the prospects of the transition towards a low-carbon economy. Based on recent data and on a comparison with the oil price countershock of 1986, we reach the conclusion that, while the fall in oil prices is not necessarily good news for the prospectsof the energy transition, political and cultural variables can counterbalance purely economic ones and play a bigger role than oil prices over both the intermediate and long term.
The role of distances in the World Trade Web
In the economic literature, geographic distances are considered fundamental
factors to be included in any theoretical model whose aim is the quantification
of the trade between countries. Quantitatively, distances enter into the
so-called gravity models that successfully predict the weight of non-zero trade
flows. However, it has been recently shown that gravity models fail to
reproduce the binary topology of the World Trade Web. In this paper a different
approach is presented: the formalism of exponential random graphs is used and
the distances are treated as constraints, to be imposed on a previously chosen
ensemble of graphs. Then, the information encoded in the geographical distances
is used to explain the binary structure of the World Trade Web, by testing it
on the degree-degree correlations and the reciprocity structure. This leads to
the definition of a novel null model that combines spatial and non-spatial
effects. The effectiveness of spatial constraints is compared to that of
nonspatial ones by means of the Akaike Information Criterion and the Bayesian
Information Criterion. Even if it is commonly believed that the World Trade Web
is strongly dependent on the distances, what emerges from our analysis is that
distances do not play a crucial role in shaping the World Trade Web binary
structure and that the information encoded into the reciprocity is far more
useful in explaining the observed patterns.Comment: Preprint, accepted for SITIS 2012 (http://www.sitis-conf.org/). Final
version to be published by IEEE Computer Society as conference proceeding
Integrating urban metabolism and life cycle assessment to analyse urban sustainability
In recent decades, the close correlation between urban development and the concept of sustainability has become increasingly evident and important. This is demonstrated by European Union policies concerning EU cities and the United Nations 2030 Agenda for Sustainable Development, including sustainable development goal (SDG) 11: Sustainable cities and communities. In the context of increasing urbanization, it is essential to find innovative methods to manage urban living systems and to establish a standard method for assessing the environmental performance of cities and their infrastructures. A unified and complete methodology for assessing policies for urban sustainability that takes into consideration urban complexity is currently lacking. In this paper, we integrate the Urban Metabolism and Lice Cycle Assessment approach to assess urban sustainability by developing a multi-dimensional measure framework applied to cities. Our aim is to provide a holistic view of the city and unveiling the interconnections among a set of urban dimensions identified by means of an approach based on complex systems science and complex networks. We also propose a specific survey to investigate the city in a multi-dimensional perspective and suggest key indicators based on network centrality measures for investigating and comparing the interconnections among a set of urban dimensions specifically identified (e.g. energy, material, transport). Finally, a case study based on Beijing is considered to show potential applications
The critical issue of using lead for sustainable massive production of perovskite solar cells: a review of relevant literature
This work aims to review the most significant studies dealing with the environmental issues of the use of lead in perovskite solar cells (PSCs). A careful discussion and rationalization of the environmental and human health toxicity impacts, evaluated by life cycle assessment and risk assessment studies, is presented. The results of this analysis are prospectively related to the possible future massive production of PSC technology. © 2021 Maranghi S et al
Complex Networks and Symmetry I: A Review
In this review we establish various connections between complex networks and
symmetry. While special types of symmetries (e.g., automorphisms) are studied
in detail within discrete mathematics for particular classes of deterministic
graphs, the analysis of more general symmetries in real complex networks is far
less developed. We argue that real networks, as any entity characterized by
imperfections or errors, necessarily require a stochastic notion of invariance.
We therefore propose a definition of stochastic symmetry based on graph
ensembles and use it to review the main results of network theory from an
unusual perspective. The results discussed here and in a companion paper show
that stochastic symmetry highlights the most informative topological properties
of real networks, even in noisy situations unaccessible to exact techniques.Comment: Final accepted versio
Spatial effects in real networks: measures, null models, and applications
Spatially embedded networks are shaped by a combination of purely topological
(space-independent) and space-dependent formation rules. While it is quite easy
to artificially generate networks where the relative importance of these two
factors can be varied arbitrarily, it is much more difficult to disentangle
these two architectural effects in real networks. Here we propose a solution to
the problem by introducing global and local measures of spatial effects that,
through a comparison with adequate null models, effectively filter out the
spurious contribution of non-spatial constraints. Our filtering allows us to
consistently compare different embedded networks or different historical
snapshots of the same network. As a challenging application we analyse the
World Trade Web, whose topology is expected to depend on geographic distances
but is also strongly determined by non-spatial constraints (degree sequence or
GDP). Remarkably, we are able to detect weak but significant spatial effects
both locally and globally in the network, showing that our method succeeds in
retrieving spatial information even when non-spatial factors dominate. We
finally relate our results to the economic literature on gravity models and
trade globalization
Effects Of The Protein Environment On The Spectral Properties Of Tryptophan Radicals In Pseudomonas Aeruginosa Azurin
Many biological electron-transfer reactions involve short-lived tryptophan radicals as key reactive intermediates. While these species are difficult to investigate, the recent photogeneration of a long-lived neutral tryptophan radical in two Pseudomonas aeruginosa azurin mutants (Az48W and ReAz108W) made it possible to characterize the electronic, vibrational, and magnetic properties of such species and their sensitivity to the molecular environment. Indeed, in Az48W the radical is embedded in the hydrophobic core while, in ReAz108W it is solvent-exposed. Here we use density functional theory and multiconfigurational perturbation theory to construct quantum-mechanics/molecular-mechanics models of Az48W* and ReAz108W* capable of reproducing specific features of their observed UV-vis, resonance Raman, and electron paramagnetic resonance spectra. The results show that the models can correctly replicate the spectral changes imposed by the two contrasting hydrophobic and hydrophilic environments. Most importantly, the same models can be employed to disentangle the molecular-level interactions responsible for such changes. It is found that the control of the hydrogen bonding between the tryptophan radical and a single specific surface water molecule in ReAz108W\u27 represents an effective means of spectral modulation. Similarly, a specific electrostatic interaction between the radical moiety and a Val residue is found to control the Az48W* excitation energy. These modulations appear to be mediated by the increase in nitrogen negative charge (and consequent increase in hydrogen bonding) of the spectroscopic D-2 state with respect to the D-0 state of the chromophore. Finally, the same protein models are used to predict the relaxed Az481Ar* and ReAz108W* D-2 structures, showing that the effect of the environment on the corresponding fluorescence maxima must parallel that of Do absorption spectra
Complex Networks and Symmetry II: Reciprocity and Evolution of World Trade
We exploit the symmetry concepts developed in the companion review of this
article to introduce a stochastic version of link reversal symmetry, which
leads to an improved understanding of the reciprocity of directed networks. We
apply our formalism to the international trade network and show that a strong
embedding in economic space determines particular symmetries of the network,
while the observed evolution of reciprocity is consistent with a symmetry
breaking taking place in production space. Our results show that networks can
be strongly affected by symmetry-breaking phenomena occurring in embedding
spaces, and that stochastic network symmetries can successfully suggest, or
rule out, possible underlying mechanisms.Comment: Final accepted versio
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