Environmental risk assessment of an underwater acoustic mobile network

Underwater vehicles make inspections and surveillance safer and with a lower carbon footprint than ship-based operations. However, to effectively operate them, they need robust positioning and communication systems. One solution is to use multi-modal communications, that can operate at very short (centimeters), medium (meters), and long distances (hundreds of meters). In this paper, we describe a multi-modal mobile network, whereby a simple acoustic communication and positioning protocol is used to send network control messages and positioning signals, optical point-to-point links may be used to transfer larger data files, and magnetic induction data and power transfer is used to recharge the drone and offload the data from the drone to the benthic station. In this context, we then quantify the sound exposure level and the impact radius reduction derived from using multi-modal underwater communications with respect to full acoustic approach in underwater mobile networks.acceptedVersio

Spread Spectrum Modulation with Grassmannian Constellations for Mobile Multiple Access Underwater Acoustic Channels

The objective of this study is to evaluate Grassmannian constellations combined with a spread spectrum multiple access scheme for underwater acoustic mobile multiple access communication systems. These communication systems enable the coordination of a fleet of Autonomous Underwater Vehicles (AUVs) from a surface or bottom control unit, e.g., a boat. Due to its robustness against phase rotation, the demodulator of Grassmannian constellations uses non-coherent detection, and the main advantage of such modulation lies in the spectrum efficiency gain with respect to conventional differential modulation. The communication system under study in this paper consists of (i), at the transmitter side, a Grassmannian modulation used in an orthogonal spread spectrum multiple access scheme called Multiuser Hyperbolic Frequency Modulation (MU-HFM) and (ii), at the receiver side, a non-coherent array decoder. The modulation and demodulation are presented as well as the considered spreading sequences. Finally, performances of the proposed transmission scheme are evaluated over replayed underwater acoustic channel responses collected at sea by a multi-sensor acoustic acquisition system.Spread Spectrum Modulation with Grassmannian Constellations for Mobile Multiple Access Underwater Acoustic ChannelspublishedVersio

Frequency of positive antiphospholipid antibodies in pregnant women with SARS-CoV-2 infection and impact on pregnancy outcome: A single-center prospective study on 151 pregnancies

Background: At the beginning of the SARS-CoV-2 pandemic, there was a lack of information about the infection’s impact on pregnancy and capability to induce de novo autoantibodies. It soon became clear that thrombosis was a manifestation of COVID-19, therefore the possible contribution of de novo antiphospholipid antibodies (aPL) raised research interest. We aimed at screening SARS-CoV-2 positive pregnant patients for aPL. Methods: The study included consecutive pregnant women who were hospitalized in our Obstetric Department between March 2020 and July 2021 for either a symptomatic SARS-CoV-2 infection or for other reasons (obstetric complications, labour, delivery) and found positive at the admission nasopharyngeal swab. All these women underwent the search for aPL by means of Lupus Anticoagulant (LA), IgG/IgM anti-cardiolipin (aCL), IgG/IgM anti-beta2glycoprotein I (aB2GPI). Data about comorbidities, obstetric and neonatal complications were collected. Results: 151 women were included. Sixteen (11%) were positive for aPL, mostly at low titre. Pneumonia was diagnosed in 20 women (5 with positive aPL) and 5 required ICU admission (2 with positive aPL). Obstetric complications occurred in 10/16 (63%) aPL positive and in 36/135 (27%) negative patients. The occurrence of HELLP syndrome and preeclampsia was significantly associated with positive aPL (p=0,004). One case of maternal thrombosis occurred in an aPL negative woman. aPL positivity was checked after at least 12 weeks in 7/16 women (44%): 3 had become negative; 2 were still positive (1 IgG aB2GPI + IgG aCL; 1 IgM aB2GPI); 1 remained positive for IgG aCL but became negative for aB2GPI; 1 became negative for LA but displayed a new positivity for IgG aCL at high titre. Conclusions: The frequency of positive aPL in pregnant women with SARS- CoV-2 infection was low in our cohort and similar to the one described in the general obstetric population. aPL mostly presented as single positive, low titre, transient antibodies. The rate of obstetric complications was higher in aPL positive women as compared to negative ones, particularly hypertensive disorders. Causality cannot be excluded; however, other risk factors, including a full-blown picture of COVID-19, may have elicited the pathogenic potential of aPL and contributed themselves to the development of complications

The AMMA mulid network for aerosol characterization in West Africa

Three ground based portable low power consumption microlidars (MULID) have been built and deployed at three remote sites in Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) in the framework of the African Monsoon Multidisciplinary Analyses (AMMA) project for the characterization of aerosols optical properties. A description of the instrument and a discussion of the data inversion method, including a careful analysis of measurement uncertainties (systematic and statistical errors) are presented. Some case studies of typical lidar profiles observed over the Banizoumbou site during 2006 are shown and discussed with respect to the AERONET 7-day back-trajectories and the biomass burning emissions from the Combustion Emission database for the AMMA campaign

The Underwater Acoustic Channel and its Impact on Adaptive Communications Schemes and Networking Protocols

Underwater acoustic signals have been studied since the late XIXth century, when they were used to search for and localize objects, typically submarines. Nowadays, acoustic signals are also used to communicate, i.e., to convey information wirelessly from one point to another over distances of the order of kilometers. Such technology is very useful for scientific research in different fields, such as biology, oceanography, and meteorology, to name a few. It also plays an important role in anti-submarine warfare, coastal surveillance, and oil spill relief operations. Nevertheless, the underwater acoustic communications performance, measured so far, is poor under certain conditions. In this thesis, we identify those conditions, quantify their effects on the communications system and networks, and we investigate which techniques can be useful to improve communications and networking performance. In order to do so, we analyze acoustic and environmental data collected at different times and locations. Specifically, we evaluate the communications performance and the channel characteristics, measured during those different experimental trials and we quantify the dynamics of the communications performance. In order to mitigate the effects of the time-varying observed conditions, we propose adaptive techniques, which we evaluate by both analysis and simulation. This analysis is based on Markov chains so as to validate their suitability as statistical models for representing the dynamics of the channel quality. Since the proposed adaptive techniques require feedback, they give rise to longer delays, higher energy consumption and overhead. For this reason, we analyze the possibility of predicting the channel quality, so as to reduce the amount of feedback. As a consequence of these insights, we are now able to address the future directions of the research. In particular, we can identify the problems related to the employment of adaptive techniques and networking protocols requiring signals exchanges between the source and the destination. In this way, we want to investigate new solutions which are more suitable for the underwater scenario, i.e., not requiring too much message exchanges. The results presented in this thesis also lead to useful guidelines for future experimental trials, in order to collect data more effectively supporting the development of underwater acoustic communications and networks.I segnali acustici sottomarini sono stati studiati fin dalla fine del XIX secolo, quando venivano impiegati per ricercare e localizzare oggetti, tipicamente sottomarini. Oggi, i segnali acustici vengono usati anche per comunicare, ossia per trasmettere informazioni tra due punti a kilometri di distanza l'uno dall'altro senza fili. Tale tecnologia permette di condurre importanti ricerche scientifiche in svariati ambiti come biologia, oceanografia e meteorologia. Inoltre, assume un ruolo importante nella sorveglianza delle coste e nelle operazioni di bonifica in piattaforme petrolifere. Tuttavia, le prestazioni delle comunicazioni acustiche sottomarine, misurate finora, degradano quando si verificano alcune condizioni. In questa tesi, identifichiamo tali condizioni, ne quantifichiamo gli effetti sui sistemi di comunicazione e analizziamo le tecniche che possono migliorare le prestazioni delle comunicazioni e delle reti. A questo scopo, analizziamo dati acustici e ambientali che sono stati raccolti in diversi momenti e luoghi. Nello specifico, valutiamo le prestazioni delle comunicazioni e le caratteristiche di canale misurate durante diversi esperimenti e quantifichiamo le dinamiche delle prestazioni di comunicazione. Allo scopo di mitigare gli effetti delle condizioni tempo varianti osservate, proponiamo tecniche adattive, che valutiamo sia con l'analisi sia con simulazioni. Tale analisi si basa sulle catene di Markov, che vangono così validate come modelli statistici adatti a rappresentare le dinamiche della qualità del canale. Siccome le tecniche adattive proposte richiedono scambio di messaggi, esse danno luogo a ritardi più elevati, consumo maggiore di energia e aumentato overhead. Per questo motivo analizziamo la possibilità di predire la qualità del canale, così da ridurre la quantità di messaggi da scambiare. Come conseguenza dei questi studi, siamo ora capaci di identificare le direzioni future della ricerca in questo ambito. In particolare, possiamo identificare i problemi legati all'impiego di tecniche adattive e di protocolli di rete che richiedono scambi di messaggi tra la sorgente e la destinazione. In tal modo, vogliamo approfondire lo studio di soluzioni più adatte allo scenario sottomarino acustico, ossia che non richiedano molto scambio di messaggi. I risultati presentati in questa tesi, aiutano a identificare alcune linee guida per i prossimi esperimenti in mare, allo scopo di collezionare dati, in grado di sostenere lo sviluppo di tecniche di comunicazione e di protocolli di rete per lo scenario acustico sottomarino

Il flusso di coscienza in William Faulkner

Il flusso di coscienza è stato definito "tecnica dell'insignificanza". Il mio assunto è che invece esso non disconnetta le menti, bensì le connetta a qualcosa che possiamo chiamare "totalità". Dopo aver analizzato vari esempi del romanzo dello stream of consciousness, la mia attenzione si è spostata sul capolavoro di Faulkner "The Sound and the Fury", in cui maggiormente possiamo trovare la potenza evocativa della tecnica dello stream

On the predictability of underwater acoustic communications performance a case study

In this paper, we analyze the predictability of the communications performance of an adaptive modulation system for underwater acoustic communications. As a case study, we consider the KAM11 data set, which has been collected off the coast of Kauai Island during July 2011. We measure the signal to noise ratio at the output of the equalizer and we observe slow fluctuations over time intervals of up to six minutes. Based on an analytical model and using the estimated time correlation coefficient of subsequent values of the signal to noise ratio (SNR), we compute the communications performance as a function of the feedback delay for an adaptive modulation system, and we evaluate its predictability. We show that it is possible to know in advance the trend of the performance over intervals of three to four minutes

A Study on the Wide-Sense Stationarity of the Underwater Acoustic Channel for Coherent Communication Systems

In this paper, we test the wide sense stationarity of the estimation error achieved by an exponentially weighted least squares algorithm, used to estimate the channel impulse response. We choose to study the stationarity of this process because it is closely tied to the bit error rate performance of adaptive equalizers used for symbol estimation. The predictability of this error process is therefore closely related to the predictability of the quality of the communications channel and will be important in the development of link quality predictors in underwater acoustic communications networks. Most adaptive estimators are based upon estimated channel statistics which assume that the process is wide sense stationary. We analyze the SPACE08 data set, which has been collected near Martha's Vineyard Island during October 2008. In this data set the environmental conditions such as the height of the waves and the wind direction vary significantly in time, causing non-stationarity to the channel impulsive response. We choose to use a stationarity test based on an analysis of the frequency-time properties, which uses surrogates and doesn't assume any model on how the data has been generated. Understanding the time interval of stationarity for the error process of the channel estimation algorithm is important to set the adaptation rate of the parameters of the channel quality estimator. In particular this study aims at investigating the possibility of developing some predictor of the communications performance in order to trigger adaptive algorithms in the upper layers. Moreover these results are useful to estimate the channel statistics for coherent communications systems and develop better channel model for shallow water, in particular we search for correlations between the environmental data and variabilities and the acoustic fluctuations

On the spatial correlation in shallow water and its impact on networking protocols

In this paper, we study the spatial correlation of the communications performance in a static scenario, by using the SPACE08 experimental data set. Specifically we estimate the channel quality in terms of Signal to Interference and Noise Ratio (SINR) at the output of the equalizer, at four receiving stations, which were deployed at different distances and orientations, and we compute their cross correlation both in time and in space. This experimental study on the spatial distribution of the channel quality among nodes allows us to provide insight on the performance of networking protocols. As an example, we consider three routing policies, which we compare in terms of throughput, latency and link utilization. Results show that the policy that minimizes the number of hops is optimal in this scenario