Green buildings and design for adaptation: strategies for renovation of the built environment

The recent EU Directives 2010/31 and 2012/27 provide standards of nearly zero energy buildings for new constructions, aiming at a better quality of the built environment through the adoption of high-performance solutions. In the near future, cities are expected to be the main engine of development while bearing the impact of population growth: new challenges such as increasing energy efficiency, reducing maintenance costs of buildings and infrastructures, facing the effects of climate change and adjusting on-going and future impacts, require smart and sustainable approaches. To improve the capability of adaptation to dynamics of transformation, buildings and districts have to increase their resilience, assumed as ‘the capacity to adapt to changing conditions and to maintain or regain functionality and vitality in the face of stress or disturbance’ (Wilson A., Building Resilience in Boston, Boston Society of Architects, 2013). This paper describes the research methodology, developed by the Department of Architecture, a research unit of Technology for Architecture, to perform the assessment of resilience of existing buildings, as well as the outcomes of its application within Bologna urban context. This methodology focuses on the design for adaptation of social housing buildings, aiming at predicting their expected main impacts (energy consumption, emissions, efficiency, urban quality and environmental sustainability) and at developing models for renovation

Is LaO1−x_{1-x}Fx_xFeAs an electron-phonon superconductor ?

In this paper we calculate the electron-phonon coupling of the newly-discovered superconductor LaO$_{1-x}$F$_x$FeAs from first-principles, using Density Functional Perturbation Theory. For pure LaOFeAs, the calculated electron-phonon coupling constant $\lambda=0.21$ and logarithmic-averaged frequency $\omega_{ln}=206 K$, give a maximum $T_c$ of 0.8 K, using the standard Migdal-Eliashberg theory. For the $F-$doped compounds, we predict even smaller coupling constants, due to the strong suppression of the electronic Density of States at the Fermi level. To reproduce the experimental $T_c=26 K$, a 5-6 times larger coupling constant would be needed. Our results indicate that electron-phonon coupling is not sufficient to explain superconductivity in the newly-discovered LaO$_{1-x}$F$_x$FeAs superconductor, probably due to the importance of strong correlation effects

Experimental tests to recover the photovoltaic power by battery system

The uncertainty and variability of the Renewable Energy Sources (RES) power plants within the power grid is an open issue. The present study focuses on the use of batteries to overcome the limitations associated with the photovoltaic inverter operation, trying to maximize the global energy produced. A set of switches, was placed between a few photovoltaic modules and a commercial inverter, capable to change configuration of the plant dynamically. Such system stores the power that the inverter is not able to let into the grid inside batteries. At the base of this optimization, there is the achievement of two main configurations in which the batteries and the photovoltaic modules are electrically connected in an appropriate manner as a function of inverter efficiency and thus solar radiation. A control board and the relative program, to change the configuration, was designed and implemented, based on the value of the measured radiation, current, batteries voltage, and calculated inverter efficiency. Finally from the cost and impact analysis we can say that, today the technology of lithium batteries, for this application, is still too expensive in comparison with lead-acid batteries

Five minutes with Tito Boeri: “We don’t just need a welfare state in Europe, we also need a welfare union”

Are Europe’s welfare states fit to meet the demands brought on by the financial crisis? In an interview with EUROPP’s Managing Editor Stuart Brown, Tito Boeri discusses the need for a ‘stress test’ of the European welfare state, why citizens in southern European countries have been much more susceptible to poverty during the crisis, and the role that EU cooperation should play in providing a more effective safety net for European citizens

Functional renormalization group study of an eight-band model for the iron arsenides

We investigate the superconducting pairing instabilities of eight-band models for the iron arsenides. Using a functional renormalization group treatment, we determine how the critical energy scale for superconductivity depends on the electronic band structure. Most importantly, if we vary the parameters from values corresponding to LaFeAsO to SmFeAsO, the pairing scale is strongly enhanced, in accordance with the experimental observation. We analyze the reasons for this trend and compare the results of the eight-band approach to those found using five-band models.Comment: 11 pages, 10 figure

Elemental Phosphorus: structural and superconducting phase diagram under pressure

Pressure-induced superconductivity and structural phase transitions in phosphorous (P) are studied by resistivity measurements under pressures up to 170 GPa and fully $ab-initio$ crystal structure and superconductivity calculations up to 350 GPa. Two distinct superconducting transition temperature (T$_{c}$) vs. pressure ($P$) trends at low pressure have been reported more than 30 years ago, and for the first time we are able to reproduce them and devise a consistent explanation founded on thermodynamically metastable phases of black-phosphorous. Our experimental and theoretical results form a single, consistent picture which not only provides a clear understanding of elemental P under pressure but also sheds light on the long-standing and unsolved $anomalous$ superconductivity trend. Moreover, at higher pressures we predict a similar scenario of multiple metastable structures which coexist beyond their thermodynamical stability range. Metastable phases of P experimentally accessible at pressures above 240 GPa should exhibit T$_{c}$'s as high as 15 K, i.e. three times larger than the predicted value for the ground-state crystal structure. We observe that all the metastable structures systematically exhibit larger transition temperatures than the ground-state ones, indicating that the exploration of metastable phases represents a promising route to design materials with improved superconducting properties.Comment: 14 pages, 4 figure

The Redevelopment of The Heritage of Social Housing in Italy: Survey and Assessment Instruments. The Case Study of Pilastro Neighborhood in Bologna

Abstract The increasing importance of social housing in order to deal with the emergency caused by the pressing demand, places in the foreground the need to redevelop the existing public housing heritage. The paper proposes the deepening of one case study, the Pilastro neighborhood, a significant example of social housing high density settlement, situated in the outskirts of Bologna in order to brought out the technical, functional and social factors, on which the level of quality of the settlement and the phenomena of social uneasiness depend. It also highlighted some factors that may pose a resistance to the measures of improvement

A combined experimental and computational study of the pressure dependence of the vibrational spectrum of solid picene C_22H_14

We present high-quality optical data and density functional perturbation theory calculations for the vibrational spectrum of solid picene (C$_{22}$H$_{14}$) under pressure up to 8 GPa. First-principles calculations reproduce with a remarkable accuracy the pressure effects on both frequency and intensities of the phonon peaks experimentally observed . Through a detailed analysis of the phonon eigenvectors, We use the projection on molecular eigenmodes to unambiguously fit the experimental spectra, resolving complicated spectral structures, in a system with hundreds of phonon modes. With these projections, we can also quantify the loss of molecular character under pressure. Our results indicate that picene, despite a \sim 20 % compression of the unit cell, remains substantially a molecular solid up to 8 GPa, with phonon modes displaying a smooth and uniform hardening with pressure. The Grueneisen parameter of the 1380 cm^{-1} a_1 Raman peak ($\gamma_p=0.1$) is much lower than the effective value ($\gamma_d=0.8$) due to K doping. This is an indication that the phonon softening in K doped samples is mainly due to charge transfer and electron-phonon coupling.Comment: Replaced with final version (PRB

The challenge of unravelling magnetic properties in LaFeAsO

First principles calculations of magnetic and, to a lesser extent, electronic properties of the novel LaFeAsO-based superconductors show substantial apparent controversy, as opposed to most weakly or strongly correlated materials. Not only do different reports disagree about quantitative values, there is also a schism in terms of interpreting the basic physics of the magnetic interactions in this system. In this paper, we present a systematic analysis using four different first principles methods and show that while there is an unusual sensitivity to computational details, well-converged full-potential all-electron results are fully consistent among themselves. What makes results so sensitive and the system so different from simple local magnetic moments interacting via basic superexchange mechanisms is the itinerant character of the calculated magnetic ground state, where very soft magnetic moments and long-range interactions are characterized by a particular structure in the reciprocal (as opposed to real) space. Therefore, unravelling the magnetic interactions in their full richness remains a challenging, but utterly important task