Observation of the stray field of thin film magnetic tips using electron holography

The stray field around thin film ferromagnetic tips employed for magnetic force microscopy has been revealed using electron holography. The experimental phase difference maps are in good agreement with simulations. Quantitative flux measurements of the leakage field are obtained

Averaged number of visits

International audienceWe introduce a new indicator for dynamical systems, namely the averaged number of visits, to estimate the frequency of visits in small regions when a map is iterated up to the inverse of the measure of this region. We compute this quantity analytically and numerically for various systems and we show that it depends on the ergodic properties of the systems and on their topological properties, such as the presence of periodic points

Wearable Computing per Realtà Aumentata e Internet of Things: Stato dell'Arte e considerazioni sulla Sicurezza

La rapida innovazione in ambito tecnologico degli ultimi decenni ha portato, oggigiorno, alla disponibilità sul mercato di dispositivi ICT di varia natura, la cui efficienza, ben si adatta alle nuove e molteplici esigenze legate allo sviluppo del software a supporto della quotidianità. Prestazioni, design e comfort hanno fatto sì che le persone potessero migliorare significativamente le loro attività, puntando a raggiungere una sempre più stretta interazione con questi dispositivi, fino ad arrivare a permettere agli utenti di indossare i propri device, definiti wearable. Il mondo del Wearable Computing si sta sempre più integrando a quello dell'Internet of Things, portando alla realizzazione di Smart Environment, mediante il quale l'utente può interagire con gli oggetti anche con semplici gesti. Lo sviluppo e la diffusione dei wearable, inoltre, sta contribuendo ad aumentare la percezione della realtà dell'utente che li indossa. A tal proposito si può quindi dire che il mondo dell'Augmented Reality (AR) si sta evolvendo sempre di più, appoggiandosi a dispositivi che possono essere indossati. Di fronte a queste realtà, l'obiettivo di questa tesi, è presentare come i dispositivi del Wearable Computing hanno contribuito e espanderanno in futuro concretamente gli scenari di AR e di IoT, che attualmente costituiscono le 2 realtà dove più facilmente i wearable si sono sviluppati. L'evoluzione rapida del Wearable Computing e la diffusione celere dei sistemi che ne fanno parte negli ambienti di IoT e AR, ha provocato (e provocherà in futuro) la diffusione di molte informazioni personali degli utenti che li usano, che devono essere tutelate il più possibile da efficaci sistemi di sicurezza. Per questo motivo, si è ritenuto opportuno sviluppare un approfondimento relativo ai rischi a cui possono essere soggetti i dati che percepiamo con i wearable e alle misure di sicurezza per preservarne l'integrità, la riservatezza e la disponibilità

Visible light communication with efficient far-red/near-infrared polymer light-emitting diodes

Visible light communication (VLC) is a wireless technology that relies on optical intensity modulation and is potentially a game changer for internet-of-things (IoT) connectivity. However, VLC is hindered by the low penetration depth of visible light in non-transparent media. One solution is to extend operation into the “nearly (in)visible” near-infrared (NIR, 700–1000 nm) region, thus also enabling VLC in photonic bio-applications, considering the biological tissue NIR semitransparency, while conveniently retaining vestigial red emission to help check the link operativity by simple eye inspection. Here, we report new far-red/NIR organic light-emitting diodes (OLEDs) with a 650–800 nm emission range and external quantum efficiencies among the highest reported in this spectral range (>2.7%, with maximum radiance and luminance of 3.5 mW/cm2 and 260 cd/m2, respectively). With these OLEDs, we then demonstrate a “real-time” VLC setup achieving a data rate of 2.2 Mb/s, which satisfies the requirements for IoT and biosensing applications. These are the highest rates ever reported for an online unequalised VLC link based on solution-processed OLEDs

A computer code for forward calculation and inversion of the H/V spectral ratio under the diffuse field assumption

During a quarter of a century, the main characteristics of the horizontal-to-vertical spectral ratio of ambient noise HVSRN have been extensively used for site effect assessment. In spite of the uncertainties about the optimum theoretical model to describe these observations, several schemes for inversion of the full HVSRN curve for near surface surveying have been developed over the last decade. In this work, a computer code for forward calculation of H/V spectra based on the diffuse field assumption (DFA) is presented and tested.It takes advantage of the recently stated connection between the HVSRN and the elastodynamic Green's function which arises from the ambient noise interferometry theory. The algorithm allows for (1) a natural calculation of the Green's functions imaginary parts by using suitable contour integrals in the complex wavenumber plane, and (2) separate calculation of the contributions of Rayleigh, Love, P-SV and SH waves as well. The stability of the algorithm at high frequencies is preserved by means of an adaptation of the Wang's orthonormalization method to the calculation of dispersion curves, surface-waves medium responses and contributions of body waves. This code has been combined with a variety of inversion methods to make up a powerful tool for passive seismic surveying.Comment: Published in Computers & Geosciences 97, 67-7

Towards efficient near-infrared fluorescent organic light-emitting diodes

The energy gap law (EG-law) and aggregation quenching are the main limitations to overcome in the design of near-infrared (NIR) organic emitters. Here, we achieve unprecedented results by synergistically addressing both of these limitations. First, we propose porphyrin oligomers with increasing length to attenuate the effects of the EG -law by suppressing the non-radiative rate growth, and to increase the radiative rate via enhancement of the oscillator strength. Second, we design side chains to suppress aggregation quenching. We find that the logarithmic rate of variation in the non-radiative rate vs. EG is suppressed by an order of magnitude with respect to previous studies, and we complement this breakthrough by demonstrating organic light-emitting diodes with an average external quantum efficiency of ~1.1%, which is very promising for a heavy-metal-free 850 nm emitter. We also present a novel quantitative model of the internal quantum efficiency for active layers supporting triplet-to-singlet conversion. These results provide a general strategy for designing high-luminance NIR emitters

Guidelines for the good practice of surface wave analysis: a product of the InterPACIFIC project

Surface wave methods gained in the past decades a primary role in many seismic projects. Specifically, they are often used to retrieve a 1D shear wave velocity model or to estimate the VS,30 at a site. The complexity of the interpretation process and the variety of possible approaches to surface wave analysis make it very hard to set a fixed standard to assure quality and reliability of the results. The present guidelines provide practical information on the acquisition and analysis of surface wave data by giving some basic principles and specific suggestions related to the most common situations. They are primarily targeted to non-expert users approaching surface wave testing, but can be useful to specialists in the field as a general reference. The guidelines are based on the experience gained within the InterPACIFIC project and on the expertise of the participants in acquisition and analysis of surface wave data.Published2367-24205T. Sismologia, geofisica e geologia per l'ingegneria sismicaJCR Journa

a review and some new issues on the theory of the h v technique for ambient vibrations

In spite of the Horizontal-to-Vertical Spectral Ratio (HVSR or H/V) technique obtained by the ambient vibrations is a very popular tool, a full theoretical explanation of it has been not reached yet. A short excursus is here presented on the theoretical models explaining the H/V spectral ratio that have been development in last decades. It leads to the present two main research lines: one aims at describing the H/V curve by taking in account the whole ambient-vibration wavefield, and another just studies the Rayleigh ellipticity. For the first theoretical branch, a comparison between the most recent two models of the ambient-vibration wavefield is presented, which are the Distributed Surface Sources (DSS) one and the Diffuse Field Approach (DFA). A mention is done of the current developments of these models and of the use of the DSS for comparing the H/V spectral ratio definitions present in literature. For the second research branch, some insights about the connection between the so-called osculation points of the Rayleigh dispersion curves and the behaviour of the H/V curve are discussed