Lifshitz transition driven by spin fluctuations and spin-orbit renormalization in NaOsO3_3

In systems where electrons form both dispersive bands and small local spins, we show that changes of the spin configuration can tune the bands through a Lifshitz transition, resulting in a continuous metal-insulator transition associated with a progressive change of the Fermi surface topology. In contrast to a Mott-Hubbard and Slater pictures, this spin-driven Lifshitz transition appears in systems with small electron-electron correlation and large hybridization. We show that this situation is realized in 5$d$ distorted perovskites with an half-filled $t_{2g}$ bands such as NaOsO$_3$, where the strong $p-d$ hybridization reduces the local moment, and spin-orbit coupling causes a large renormalization of the electronic mobility. This weakens the role of electronic correlations and drives the system towards an itinerant magnetic regime which enables spin-fluctuations

Studio sperimentale delle prestazioni di un'applicazione di beaconing per reti veicolari multihop

1 Introduzione 1.1 Descrizione della Tesi 1.2 Obiettivi della Tesi 1.3 Stato dell'arte 1.4 Organizzazione della Tesi 2 Le tecnologie utilizzate 2.1 Le reti veicolari 2.1.1 La struttura delle VANET6 2.1.2 L'architettura a livelli delle VANET 2.2 Il canale radio 2.2.1 Lo standard IEEE 802.11p per sistemi WAVE 2.3 I protocolli di routing 2.3.1 Il Beaconing 2.3.2 Applicazioni basate su beaconing 3 Gli esperimenti 3.1 Il setup fisico 3.1.1 Le LinkBird-MX 3.1.2 Gli altri componenti 3.2 I report finali 3.2.1 Singlehop/Multihop 3.2.2 LineOfSight (LOS)/NonLineOfSight (NLOS) 3.2.3 Le misure calcolate 4 Il software realizzato 4.1 L'applicazione di beaconing 4.2 Il programma di Post-Processing 5 I risultati generali 5.1 La raccolta dei dati 5.2 I tipi di report 5.3 L'analisi dei risultati 5.4 Conclusioni 6 Le analisi nel dettaglio 6.1 Confronto tra i report dei tre viaggi 7 Conclusioni 7.1 Lavori futuri 7.2 Esperienze acquisite Bibliograph

The importance of live binary evolution in numerical simulations of binaries embedded in circumbinary discs

The shrinking of a binary orbit driven by the interaction with a gaseous circumbinary disc, initially advocated as a potential way to catalyze the binary merger, has been recently debated in the case of geometrically thick (i.e. with $H/R\gtrsim 0.1$) discs. However, a clear consensus is still missing mainly owing to numerical limitations, such as fixed orbit binaries or lack of resolution inside the cavity carved by the binary in its circumbinary disc. In this work, we asses the importance of evolving the binary orbit by means of hydrodynamic simulations performed with the code {\sc gizmo} in meshless-finite-mass mode. In order to model the interaction between equal mass circular binaries and their locally isothermal circumbinary discs, we enforce hyper-Lagrangian resolution inside the cavity. We find that fixing the binary orbit ultimately leads to an overestimate of the gravitational torque that the gas exerts on the binary, and in an underestimate of the torque due to the accretion of material onto the binary components. Furthermore, we find that the modulation of the accretion rate on the binary orbital period is strongly suppressed in the fixed orbit simulation, while it is clearly present in the live binary simulations. This has potential implications for the prediction of the observable periodicities in massive black hole binary candidates.Comment: 7 pages, 8 figures, accepted for publication in MNRA

Understanding Vehicle-to-Vehicle IEEE 802.11p Beaconing Performance in Real-World Highway Scenarios

Periodic exchange of situational information (beacons) is at the basis of most active safety applications in vehicular environments. Despite its fundamental role in raising the level of "situational awareness" onboard vehicles, very little is known to date on beaconing performance in a real vehicular environment. This paper analyzes the results of two measurement campaigns that have been designed with the purpose of disclosing beaconing performance in a variety of vehicular links, for what concerns vehicle configuration (tall/short), line-of-sight conditions (LOS/NLOS), as well as single-hop or two-hop propagation of the information reported in the beacons. For the first time, beaconing performance is characterized in terms of not only the packet (beacon) delivery rate (PDR), but also in terms of the packet (beacon) inter-reception (PIR) time. The latter metric has been suggested in the literature as more accurately measuring the level of "situation awareness" onboard vehicles than the traditional PDR metric. This paper also presents a simulation-based analysis aimed at estimating the benefit of multi-hop propagation of situational information beyond the second hop of communication. The analysis of the data collected in the measurement campaigns as well as the simulation-based analysis disclose a number of interesting insights which might prove useful in the design of active safety applications. Finally, another major contribution of this paper is promoting the Gilbert-Elliot model, previously proposed to model bit-error bursts in packet switched networks, as a very accurate model of beacon reception behavior observed in real-world scenarios

Spatial variability of methane emissions from Swiss alpine fens

Wetland ecosystems are a major natural source of the important greenhouse gas methane (CH4). Among these ecosystems, fens have been shown to release high quantities of CH4. Data on CH4 emissions from alpine fens are scarce and mainly limited to the United States and China. Therefore, static chambers were used to quantify CH4 emissions from 14 fens located in the Swiss Alps. The aims of this study were to determine the spatial variability of the emissions and to identify potential key factors which influence CH4 turnover. The fens were located at altitudes between 1,800 and 2,600m a.s.l., the pore water varied from acidic to slightly acidic (pH 4.5-6.4) and the vegetation was dominated by plants of the genus Carex. In addition, the underlying bedrock was either siliceous or calcareous. Methane emissions ranged from 74±43 to 711±212mg CH4 m−2day−1. The type of bedrock, the plant biomass above the water table and the CH4 pore water concentrations at depths from 0 to 20cm were the main factors influencing CH4 emissions. Detailed measurements in three selected fens suggested that more than 98% of the total CH4 emissions are due to plant-mediated transport

ODINet - Online Data Integration Network

Along with the expansion of Open Data and according to the latest EU directives for open access, the attention of public administration, research bodies and business is on web publishing of data in open format. However, a specialized search engine on the datasets, with similar role to that of Google for web pages, is not yet widespread. This article presents the Online Data Integration Network (ODINet) project, which aims to define a new technological framework for access to and online dissemination of structured and heterogeneous data through innovative methods of cataloging, searching and display of data on the web. In this article, we focus on the semantic component of our platform, emphasizing how we built and used ontologies. We further describe the Social Network Analysis (SNA) techniques we exploited to analyze it and to retrieve the required information. The testing phase of the project, that is still in progress, has already demonstrated the validity of the ODINet approach

Tunable ferroelectric polarization and its interplay with spin-orbit coupling in tin iodide perovskites.

Ferroelectricity is a potentially crucial issue in halide perovskites, breakthrough materials in photovoltaic research. Using density functional theory simulations and symmetry analysis, we show that the lead-free perovskite iodide (FA) SnI3, containing the planar formamidinium cation FA, (NH2CHNH2)(+), is ferroelectric. In fact, the perpendicular arrangement of FA planes, leading to a 'weak' polarization, is energetically more stable than parallel arrangements of FA planes, being either antiferroelectric or 'strong' ferroelectric. Moreover, we show that the 'weak' and 'strong' ferroelectric states with the polar axis along different crystallographic directions are energetically competing. Therefore, at least at low temperatures, an electric field could stabilize different states with the polarization rotated by pi/4, resulting in a highly tunable ferroelectricity appealing for multistate logic. Intriguingly, the relatively strong spin-orbit coupling in noncentrosymmetric (FA)SnI3 gives rise to a co-existence of Rashba and Dresselhaus effects and to a spin texture that can be induced, tuned and switched by an electric field controlling the ferroelectric state

Majorization-Minimization for sparse SVMs

Several decades ago, Support Vector Machines (SVMs) were introduced for performing binary classification tasks, under a supervised framework. Nowadays, they often outperform other supervised methods and remain one of the most popular approaches in the machine learning arena. In this work, we investigate the training of SVMs through a smooth sparse-promoting-regularized squared hinge loss minimization. This choice paves the way to the application of quick training methods built on majorization-minimization approaches, benefiting from the Lipschitz differentiabililty of the loss function. Moreover, the proposed approach allows us to handle sparsity-preserving regularizers promoting the selection of the most significant features, so enhancing the performance. Numerical tests and comparisons conducted on three different datasets demonstrate the good performance of the proposed methodology in terms of qualitative metrics (accuracy, precision, recall, and F 1 score) as well as computational cost

ODINet un framework innovativo per l\u27accesso e la diffusione on-line di dati strutturati ed eterogenei

ODINet is a research and development project, approved as part of the Regional Operational Programme through the European Regional Development Fund 2007-2013. The project involves the construction of a semantic search engine prototype able to catalog the data in a ontological graph, to extract the most relevant information depending on user requests and return them in a highly usable way. The application domain concerns the social, economic and health, in order to cover most of the data held by public bodies in the national context. The focus of this report is in the first place the description of the semantic components of the platform, emphasizing how the ontologies have been used to build an index in the form of graph. We also present a description of our semantic searches and finally an analysis of the results obtained in the final stage of the ODINEt prototype testing