Regenerating Urban Spaces under Place-specific Social Contexts: a Commentary on Green Infrastructures for Landscape Conservation

This study investigates the issue of green infrastructures in contemporary cities, adopting a strategic vision for increasingly complex metropolitan regions. Green infrastructures play an important role in ecological services and biodiversity preservation, improving significantly the quality of life of residents and visitors. The social dimension of gardens and parks at local (e.g. urban district) scale and green infrastructures at larger spatial scales is also addressed, fostering the relationship between local communities and urban landscapes. With economic crisis, urban parks are increasingly considered a primary component of integrated strategies for urban regeneration with a bottom-up approach, addressing the demand for "natural landscape" in peri-urban areas. By recovering public spaces with social purposes and providing a comprehensive strategy for aesthetic improvement of common goods, the analyzed case studies give examples of specific measures for promoting environment-friendly urban regeneration strategies under place-specific social contexts

Infrared signature of active massive black holes in nearby dwarf galaxies

We investigate the possible presence of active galactic nuclei (AGN) in dwarf galaxies and other nearby galaxies to identify candidates for follow-up confirmation and dynamical mass measurements. We use the Wide-field Infrared Survey Explorer (WISE) All-Sky Release Source Catalog and examine the infrared colours of a sample of dwarf galaxies and other nearby galaxies in order to identify both unobscured and obscured candidate AGN by applying the infrared colour diagnostic. Stellar masses of galaxies are obtained using a combination of three independent methods. Black hole masses are estimated using the bolometric luminosity of the AGN candidates and computed for three cases of the bolometric-to-Eddington luminosity ratio. We identify 303 candidate AGN, of which 276 were subsequently found to have been independently identified as AGN via other methods. The remaining 9% require follow-up observations for confirmation. The activity is detected in galaxies with stellar masses from ~ 10^6 to 10^9 solar masses; assuming the candidates are AGN, the black hole masses are estimated to be ~ 10^3 - 10^6 solar masses, adopting L_bol = 0.1 L_Edd. The black hole masses probed are several orders of magnitude smaller than previously reported for centrally located massive black holes. We examine the stellar mass versus black hole mass relationship in this low galaxy mass regime. We find that it is consistent with the existing relation extending linearly (in log-log space) into the lower mass regime. These findings suggest that CMBH are present in low-mass galaxies and in the Local Universe, and provide new impetus for follow-up dynamical studies of quiescent black holes in local dwarf galaxies.Comment: 14 pages, 9 figures, 4 tables, accepted for publication in Astronomy & Astrophysics. The first version of this paper appeared on astro-ph in 2014 (arXiv:1411.3844). The new version includes 3 new tables, 1 new figure and updated discussio

Number of cliques in random scale-free network ensembles

In this paper we calculate the average number of cliques in random scale-free networks. We consider first the hidden variable ensemble and subsequently the Molloy Reed ensemble. In both cases we find that cliques, i.e. fully connected subgraphs, appear also when the average degree is finite. This is in contrast to what happens in Erd\"os and Renyi graphs in which diverging average degree is required to observe cliques of size $c>3$. Moreover we show that in random scale-free networks the clique number, i.e. the size of the largest clique present in the network diverges with the system size.Comment: (15 pages

Emergence of large cliques in random scale-free networks

In a network cliques are fully connected subgraphs that reveal which are the tight communities present in it. Cliques of size c > 3 are present in random Erdös and Renyi graphs only in the limit of diverging average connectivity. Starting from the finding that real scale free graphs have large cliques, we study the clique number in uncorrelated scale-free networks finding both upper and lower bounds. Interesting we find that in scale-free networks large cliques appear also when the average degree is finite, i.e. even for networks with power-law degree distribution exponents ! ! (2, 3). Moreover as long as ! < 3 scale-free networks have a maximal clique which diverges with the system size

Effects of degree correlations on the loop structure of scale free networks

In this paper we study the impact of degree correlations in the subgraph statistics of scalefree networks. In particular we consider loops, simple cases of network subgraphs which encode the redundancy of the paths passing through every two nodes of the network. We provide an understanding of the scaling of the clustering coefficient in modular networks in terms of the maximal eigenvector of the average adjacency matrix of the ensemble. Furthermore we show that correlations affect in a relevant way the average number of Hamiltonian paths in a three-core of real world networks. We prove our results in the two-vertex correlated hidden variable ensemble and we check the results with exact counting of small loops in real graphs

Multi-asset minority games

We study analytically and numerically Minority Games in which agents may invest in different assets (or markets), considering both the canonical and the grand-canonical versions. We find that the likelihood of agents trading in a given asset depends on the relative amount of information available in that market. More specifically, in the canonical game players play preferentially in the stock with less information. The same holds in the grand canonical game when agents have positive incentives to trade, whereas when agents payoff are solely related to their speculative ability they display a larger propensity to invest in the information-rich asset. Furthermore, in this model one finds a globally predictable phase with broken ergodicity