Networked volunteering during the 2013 Sardinian floods

The article describes how ordinary citizens used Twitter as an emergency-management tool during the heavy floods that occurred in Sardinia, Italy, in November 2013. The case study constitutes an example of digital volunteering in the aftermath of a disaster event. The article applies the connective action framework (Bennet & Segerberg, 2012) for a deeper understanding of the dynamics of self-organized disaster communication activities on social media. Utilizing a dataset of 93,091 tweets that used the hashtag #allertameteoSAR (weather alert in Sardinia), the analysis focuses on: 1) the roles and patterns of influence among the main actors; and 2) the strategies for a peer ‘curation’ and sharing of a disaster-recovery oriented communication. The article highlights the role of Twitter celebrities and engaged ordinary users as digital volunteers and explains how they succeeded in activating bottom-up disaster-relief oriented communication

Exploring the ferromagnetic behaviour of a repulsive Fermi gas via spin dynamics

Ferromagnetism is a manifestation of strong repulsive interactions between itinerant fermions in condensed matter. Whether short-ranged repulsion alone is sufficient to stabilize ferromagnetic correlations in the absence of other effects, like peculiar band dispersions or orbital couplings, is however unclear. Here, we investigate ferromagnetism in the minimal framework of an ultracold Fermi gas with short-range repulsive interactions tuned via a Feshbach resonance. While fermion pairing characterises the ground state, our experiments provide signatures suggestive of a metastable Stoner-like ferromagnetic phase supported by strong repulsion in excited scattering states. We probe the collective spin response of a two-spin mixture engineered in a magnetic domain-wall-like configuration, and reveal a substantial increase of spin susceptibility while approaching a critical repulsion strength. Beyond this value, we observe the emergence of a time-window of domain immiscibility, indicating the metastability of the initial ferromagnetic state. Our findings establish an important connection between dynamical and equilibrium properties of strongly-correlated Fermi gases, pointing to the existence of a ferromagnetic instability.Comment: 8 + 17 pages, 4 + 8 figures, 44 + 19 reference

Connecting dissipation and phase slips in a Josephson junction between fermionic superfluids

We study the emergence of dissipation in an atomic Josephson junction between weakly-coupled superfluid Fermi gases. We find that vortex-induced phase slippage is the dominant microscopic source of dissipation across the BEC-BCS crossover. We explore different dynamical regimes by tuning the bias chemical potential between the two superfluid reservoirs. For small excitations, we observe dissipation and phase coherence to coexist, with a resistive current followed by well-defined Josephson oscillations. We link the junction transport properties to the phase-slippage mechanism, finding that vortex nucleation is primarily responsible for the observed trends of conductance and critical current. For large excitations, we observe the irreversible loss of coherence between the two superfluids, and transport cannot be described only within an uncorrelated phase-slip picture. Our findings open new directions for investigating the interplay between dissipative and superfluid transport in strongly correlated Fermi systems, and general concepts in out-of-equlibrium quantum systems.Comment: 6 pages, 4 figures + Supplemental Materia

Out of equilibrium correlation functions of quantum anisotropic XY models: one-particle excitations

We calculate exactly matrix elements between states that are not eigenstates of the quantum XY model for general anisotropy. Such quantities therefore describe non equilibrium properties of the system; the Hamiltonian does not contain any time dependence. These matrix elements are expressed as a sum of Pfaffians. For single particle excitations on the ground state the Pfaffians in the sum simplify to determinants.Comment: 11 pages, no figures; revtex. Minor changes in the text; list of refs. modifie

Agrivoltaic System: a Case Study of PV Production and Olive Cultivation in Southern Italy

The double use of the land in the AgriVoltaic (AV) sites allows to "doubly harvest from the sun", increasing the land use exploitation with lower environmental impact. This effect strongly depends on the system configuration for both the PV and agricultural sides. The choice is between a high-density PV module arrangement, with high PV production and low agricultural harvesting, or a highly spaced arrangement with lower PV production. The present work presents a case study in Southern Italy: the simulated PV plant can have two different layouts (rated power of 7.13 MW or 5.68 MW), and each hectare can include the plantation of about 900 Arbequina olive trees

Low-frequency internal friction in silica glass

Precise low-frequency internal friction measurements on vitreous silica, taken over a wide temperature (4 K160 K the loss angle develops a distinct step-like structure followed by a plateau, both independent of ν, thus signalling the onset of a competing relaxation mechanism with much higher an activation energy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58117/2/epl_80_5_50008.pd

Mesoscopic BCS pairing in the repulsive 1d-Hubbard model

We study mesoscopic pairing in the one dimensional repulsive Hubbard model and its interplay with the BCS model in the canonical ensemble. The key tool is comparing the Bethe ansatz equations of the two models in the limit of small Coulomb repulsion. For the ordinary Hubbard interaction the BCS Bethe equations with infinite pairing coupling are recovered; a finite pairing is obtained by considering a further density-dependent phase-correlation in the hopping amplitude of the Hubbard model. We find that spin degrees of freedom in the Hubbard ground state are arranged in a state of the BCS type, where the Cooper-pairs form an un-condensed liquid on a ``lattice'' of single particle energies provided by the Hubbard charge degrees of freedom; the condensation in the BCS ground state corresponds to Hubbard excitations constituted by a sea of spin singlets.Comment: 15 pages, 6 figures. To be published on Physical Review

Nanocellulose filled biobased polyurethane foams.

In this paper, nanocellulose (NC) dispersed in glycerin was incorporated into polyurethane (PU) biobased foams, using castor oil and glycerin, in a ratio of 3:1, as a biopolyol, produced by free-rise pouring method. Firstly, the morphologicals properties, measureds by scanning electronic microscopy (SEM) images, were investigated and, after, the apparent density and compressives properties were measureds. The results indicated efficience in the preparation method for the biofoams and the filled foams presented a decrease in the cellular anisotropy and linear cell density and an increase in cell diameter, with a more homogenous cell structure. These morphologicals properties justify the modifications caused by the fillers in the biofoams, a larger cell, with less orientation, caused a decrease in the values of the apparent density and consequently lower values in compressive mechanical properties