NON-EQUILIBRIUM STUDY OF CORRELATED HONEYCOMB IRIDATES WITH STRONG SPIN-ORBIT COUPLING.

Transition-metal oxides (TMO) are one of the most studied class of materials, as a consequence of their rich and exotic physical properties, mainly determined by the strong electronic correlations of the metal d electrons. In this thesis I discuss about a particular 5d compound, sodium iridates, where spin-orbit coupling Coulomb repulsion and bandwidth are in comparable energy scales. Furthermore, these systems are Mott insulators and present a zigzag antiferromagnetic transition below TN 15 K. Here we tackle the physics of sodium iridates by adopting a nonequilibrium viewpoint based on the use of ultrafast light pulses combined in the so-called pump-probe experimental configuration. The aim is to perturb the antiferromagnetic state of the system via the excitation with a pump pulse and to observe the ultrafast recovery of the ground state by means of a second delayed probe pulse. Specifically, we will measure the dynamics of the pump-induced reflectivity variation in the zigzag antiferromagnetic and normal states as a function of the probe energy and as a function of time delay between the pump and the probe pulses

Towards Recommender Systems with Community Detection and Quantum Computing

After decades of being mainly confined to theoretical research, Quantum Computing is now becoming a useful tool for solving realistic problems. This work aims to experimentally explore the feasibility of using currently available quantum computers, based on the Quantum Annealing paradigm, to build a recommender system exploiting community detection. Community detection, by partitioning users and items into densely connected clusters, can boost the accuracy of non-personalized recommendation by assuming that users within each community share similar tastes. However, community detection is a computationally expensive process. The recent availability of Quantum Annealers as cloud-based devices, constitutes a new and promising direction to explore community detection, although effectively leveraging this new technology is a long-term path that still requires advancements in both hardware and algorithms. This work aims to begin this path by assessing the quality of community detection formulated as a Quadratic Unconstrained Binary Optimization problem on a real recommendation scenario. Results on several datasets show that the quantum solver is able to detect communities of comparable quality with respect to classical solvers, but with better speedup, and the non-personalized recommendation models built on top of these communities exhibit improved recommendation quality. The takeaway is that quantum computing, although in its early stages of maturity and applicability, shows promise in its ability to support new recommendation models and to bring improved scalability as technology evolves

Tracking local magnetic dynamics via high-energy charge excitations in a relativistic Mott insulator

We use time- and energy-resolved optical spectroscopy to investigate the coupling of electron-hole excitations to the magnetic environment in the relativistic Mott insulator Na$_2$IrO$_3$. We show that, on the picosecond timescale, the photoinjected electron-hole pairs delocalize on the hexagons of the Ir lattice via the formation of quasi-molecular orbital (QMO) excitations and the exchange of energy with the short-range-ordered zig-zag magnetic background. The possibility of mapping the magnetic dynamics, which is characterized by typical frequencies in the THz range, onto high-energy (1-2 eV) charge excitations provides a new platform to investigate, and possibly control, the dynamics of magnetic interactions in correlated materials with strong spin-orbit coupling, even in the presence of complex magnetic phases.Comment: 5 pages, 4 figures, supplementary informatio

In a state of uncertainty? Mogadishu water supply

Following twenty years of conflict, the context of stabilization and early recovery in Mogadishu has supported a strategic water supply assessment. Traditionally supplied by shallow wells, at the outbreak of civil war the program of reticulated supply development collapsed, and the town has since reverted to an un-centralized network of wells, small scale reticulated distribution systems and vendors, with limited water treatment options. Access to sufficient safe affordable water is biased disproportionately against the poorest. The trend of well expansion driven by diaspora/national investment and humanitarian/aid programs continues. Although a planning framework is coming into place to address rehabilitation of a centrally regulated system required in the future, taking account of uncertainty, purposive research has produced an inference-based analysis. A fresh problem statement underpinning national efforts to improve prospects for sustainable water supply development for Mogadishu has been framed

Rehabilitation of alternative water supply systems

Rehabilitation of alternative water supply system

Safety in Numbers: Fault Tolerance in Robot Swarms

The swarm intelligence literature frequently asserts that swarms exhibit high levels of robustness. That claim is, however, rather less frequently supported by empirical or theoretical analysis. But what do we mean by a 'robust' swarm? How would we measure the robustness or – to put it another way – fault-tolerance of a robotic swarm? These questions are not just of academic interest. If swarm robotics is to make the transition from the laboratory to real-world engineering implementation, we would need to be able to address these questions in a way that would satisfy the needs of the world of safety certification. This paper explores fault-tolerance in robot swarms through Failure Mode and Effect Analysis (FMEA) and reliability modelling. The work of this paper is illustrated by a case study of a wireless connected robot swarm, employing both simulation and real-robot laboratory experiments

Code and its image: the functions of text and visualisation in a code-based design studio

Traditionally, design learning in the architecture studio has taken place through a combination of individual work and joint projects. The introduction of code-based design practices in the design studio has altered this balance, introducing new models of joint authorship and new ways for individuals to contribute to co-authored projects. This paper presents a case study describing four design studios in a higher education setting that used code as a tool for generating architectural geometry. The format of the studios encouraged the students to reflect critically on their role as authors and to creatively address the multiple opportunities for shared authorship available with code-based production. The research question addressed in this study involved the role of code-based practices in altering the model of architectural education in the design studio, in particular the role of visual representations of a code-based design process in the production of shared knowledge

AVI as a mechanical tool for studying thin-shells based on Kirchhoff-Love constraints

Thin-shell and rod theory using discrete mechanics applied to structures in civil engineering. The aim is to apply structure preserving algorithms to concrete problems in construction. The major objectives of this interdisciplinary work is the search and the development of a practical tool to study irregular surfaces