Superradiant scattering in fluids of light

We theoretically investigate the scattering process of Bogoliubov excitations on a rotating photon-fluid. Using the language of Noether currents we demonstrate the occurrence of a resonant amplification phenomenon, which reduces to the standard superradiance in the hydrodynamic limit. We make use of a time-domain formulation where superradiance emerges as a transient effect encoded in the amplitudes and phases of propagating localised wavepackets. Our findings generalize previous studies in quantum fluids to the case of a non-negligible quantum pressure and can be readily applied also to other physical systems, in particular atomic Bose-Einstein condensates. Finally we discuss ongoing experiments to observe superradiance in photon fluids, and how our time domain analysis can be used to characterise superradiant scattering in non-ideal experimental conditions.Comment: 11 pages, 6 figures Version 2: Updated first author affiliation, fixed grammatical typo

Saturating linear sets of minimal rank

Saturating sets are combinatorial objects in projective spaces over finite fields that have been intensively investigated in the last three decades. They are related to the so-called covering problem of codes in the Hamming metric. In this paper, we consider the recently introduced linear version of such sets, which is, in turn, related to the covering problem in the rank metric. The main questions in this context are how small the rank of a saturating linear set can be and how to construct saturating linear sets of small rank. Recently, Bonini, Borello, and Byrne provided a lower bound on the rank of saturating linear sets in a given projective space, which is shown to be tight in some cases. In this paper, we provide construction of saturating linear sets meeting the lower bound and we develop a link between the saturating property and the scatteredness of linear sets. The last part of the paper is devoted to show some parameters for which the bound is not tight.Comment: 26 page

New insights into pathogenesis and treatment of anca-associated vasculitis. autoantibodies and beyond

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis is a group of rare systemic diseases affecting small-caliber vessels. The damage caused by AAV mainly involves the lung and kidneys. AAV includes three different types: granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Although the different phenotypic forms of AAV share common features, recent studies have shown that there are significant differences in terms of pathogenetic mechanisms involving both the adaptive and innate immune systems. Advances in our understanding of pathogenesis have enabled the development of immuno-targeted therapies. This review illustrates the characteristics of the various forms of AAV and the new therapies available for this disease that can have lethal consequences if left untreated

Illegal pedestrian crossing at a traffic light: a study on tourist behaviour

Illegal pedestrian crossing situations at signalized intersections are observed worldwide. The main goal of this study was to observe attributes and determine the proportion and type of pedestrian violations and dangerous crossing situations at a traffic light located in a recreational tourist urban environment, i.e. the beach town of Viareggio on the coast of Tuscany, Italy. A large signalized intersection placed close to the beach was observed for some days in Summer 2015, for several hours, both in the morning and in the afternoon, to collect data. The main aim was to identify the illegal pedestrian crossing behaviour with red traffic light. Pedestrian crossing data were recorded with a video camera. Then, the video data were processed using a semi-automated software self-written in MATLAB to extract information on different pedestrian factors. Some factors, identified in the current literature as having an influence on the proportion of violations, such as age, sex and group size, were analysed. Furthermore, the impact of the amber length time on the proportion of dangerous performed crossings was studied. The obtained results highlight that pedestrians in a recreational tourist environment are generally more in compliance with traffic light than those in a weekday urban context. It is also important to pay particular attention to pedestrian yellow time (amber steady man) in order to avoid dangerous legal crossings. In fact it was often observed that pedestrians start to cross on the green walking man but end under the red light

Experimental characterization of nonlocal photon fluids

Quantum gases of atoms and exciton-polaritons are now well-established theoretical and experimental tools for fundamental studies of quantum many-body physics and suggest promising applications to quantum computing. Given their technological complexity, it is of paramount interest to devise other systems where such quantum many-body physics can be investigated at lesser technological expense. Here we examine a relatively well-known system of laser light propagating through thermo-optical defocusing media: based on a hydrodynamic description of light as a quantum fluid of interacting photons, we investigate such systems as a valid room-temperature alternative to atomic or exciton–polariton condensates for studies of many-body physics. First, we show that by using a technique traditionally used in oceanography it is possible to perform a direct measurement of the single-particle part of the dispersion relation of the elementary excitations on top of the photon fluid and to detect its global flow. Then, using a pump-and-probe setup, we investigate the dispersion of excitation modes of the fluid: for very long wavelengths, a sonic, dispersionless propagation is observed that we interpret as a signature of superfluid behavior

Exceptional scattered sequences

The concept of scattered polynomials is generalized to those of exceptional scattered sequences which are shown to be the natural algebraic counterpart of $\mathbb{F}_{q^n}$-linear MRD codes. The first infinite family in the first nontrivial case is also provided and equivalence issues are considered. As a byproduct, a new infinite family of MRD codes is obtained.Comment: 32 page