Entropy-based randomisation of rating networks

In the last years, due to the great diffusion of e-commerce, online rating platforms quickly became a common tool for purchase recommendations. However, instruments for their analysis did not evolve at the same speed. Indeed, interesting information about users' habits and tastes can be recovered just considering the bipartite network of users and products, in which links have different weights due to the score assigned to items. With respect to other weighted bipartite networks, in these systems we observe a maximum possible weight per link, that limits the variability of the outcomes. In the present article we propose an entropy-based randomisation of (bipartite) rating networks by extending the Configuration Model framework: the randomised network satisfies the constraints of the degree per rating, i.e. the number of given ratings received by the specified product or assigned by the single user. We first show that such a null model is able to reproduce several non-trivial features of the real network better than other null models. Then, using it as a benchmark, we project the information contained in the real system on one of the layers, showing, for instance, the division in communities of music albums due to the taste of customers, or, in movies due the audience.Comment: 12 pages, 30 figure

Collaboration and followership: A stochastic model for activities in social networks

In this work we investigate how future actions are influenced by the previous ones, in the specific contexts of scientific collaborations and friendships on social networks. We describe the activity of the agents, providing a model for the formation of the bipartite network of actions and their features. Therefore we only require to know the chronological order in which the actions are performed, and not the order in which the agents are observed. Moreover, the total number of possible features is not specified a priori but is allowed to increase along time, and new actions can independently show some new-entry features or exhibit some of the old ones. The choice of the old features is driven by a degree-fitness method: indeed, the probability that a new action shows one of the old features does not solely depend on the popularity of that feature (i.e. the number of previous actions showing it), but it is also affected by some individual traits of the agents or the features themselves, synthesized in certain quantities, called fitnesses or weights, that can have different forms and different meaning according to the specific setting considered. We show some theoretical properties of the model and provide statistical tools for the parameters' estimation. The model has been tested on three different datasets and the numerical results are provided and discussed

Brevi trattamenti in post raccolta con elicitori gassosi e cambiamenti metabolici in uva da vino sottoposta a parziale disidratazione

La disidratazione post raccolta è un processo tecnologico utilizzato per la produzione di vini da dessert o rinforzati: in questo contesto produttivo l' appassimento delle uve è un passaggio cruciale che può essere condotto sotto diverse condizioni ambientali che possono modulare il tasso di disidratazione e, conseguentemente, il metabolismo dell’acino di uva. Strutture dedicate all'appassimento possono essere anche utilizzate per l'applicazione di specifici trattamenti con elicitori al fine di modificare alcuni processi metabolici delle uve. Trattamenti post raccolta controllati, sono stati effettuati applicando etilene (1000 ppm) o CO2 (30-100%) su uve da vino (cv Trebbiano e Sangiovese) sottoposte a disidratazione più o meno intensa, per studiarne gli effetti sul metabolismo primario e secondario delle bacche e, possibilmente, migliorare alcune caratteristiche qualitative del vino. I trattamenti post raccolta con etilene gassoso (1000 ppm) sull’uva a bacca rossa (cv Sangiovese) sono stati efficaci nell’indurre alcuni cambiamenti nella composizione dei metaboliti della buccia, che è risultato il tessuto del frutto più influenzato dal trattamento. La diminuzione del contenuto in antocianine, che di norma avviene durante la disidratazione post raccolta, è stata ridotta, ed il contenuto di alcuni composti stilbenici è risultato maggiore dopo l’applicazione di etilene. L’etilene ha indotto anche l’aumento dell’attività di enzimi responsabili del rammollimento delle pareti cellulari, come le poligalatturonasi e pectin metil esterasi, insieme alle ßglucosidasi, coinvolte anche nel rilascio di composti aromatici dalle molecole di zucchero. Il contenuto di norisoprenoidi glicosidati rilevato in uva Sangiovese è infatti diminuito in seguito al trattamento, come quello di carotenoidi, clorofilla e la maggior parte delle xantofille. L’attività di enzimi coinvolti in processi di ossidazione (polifenolo ossidasi e perossidasi) non ha mostrato nessuna variazione significativa. I cambiamenti indotti dall’etilene nell’uva sono risultati in una modifica della composizione chimica del vino, dove il contenuto di polifenoli e composti aromatici è aumentato significativamente: ciò potrebbe essere il risultato dell’aumento dell’estraibilità dovuto alla maggiore attività degli enzimi responabili delle modifiche a carico della architettura e composizione delle pareti cellulari. Il trattamento con CO2 è stato effettuato in postraccolta a diverse concentrazioni per tempi differenti (da uno a tre giorni, 30-100%) su uva Trebbiano ed è stata seguita da un periodo di disidratazione più o meno prolungato. In generale, gli effetti della CO2 sono stati visibili per la durata del trattamento, e per pochi giorni a seguire. In particolare la breve applicazione di CO2 ha modulato la sintesi e la polimerizzazione dei flavan-3-oli e ha ridotto la degradazione dei composti lipofili nella buccia dell’uva. L’attività degli enzimi coinvolti in processi ossidativi (polifenolo ossidasi e perossidasi) e delle poligalatturonasi è risultata minore nell’uva trattata rispetto a quella di controllo. Rispetto al controllo, il Vin Santo ottenuto con l’uva Trebbiano trattata con CO2 era caratterizzato da un minore contenuto di composti aromatici percepibili (acidi, norisoprenoidi, esteri, fenoli), ma da un maggiore contenuto di norisoprenoidi e terpeni glicosilati, che possono essere considerati una riserva di aromi potenziali durante l’invecchiamento del Vin Santo

Extracting significant signal of news consumption from social networks: the case of Twitter in Italian political elections

According to the Eurobarometer report about EU media use of May 2018, the number of European citizens who consult on-line social networks for accessing information is considerably increasing. In this work we analyse approximately 106 tweets exchanged during the last Italian elections held on March 4, 2018. Using an entropy-based null model discounting the activity of the users, we first identify potential political alliances within the group of verified accounts: if two verified users are retweeted more than expected by the non-verified ones, they are likely to be related. Then, we derive the users’ affiliation to a coalition measuring the polarisation of unverified accounts. Finally, we study the bipartite directed representation of the tweets and retweets network, in which tweets and users are collected on the two layers. Users with the highest out-degree identify the most popular ones, whereas highest out-degree posts are the most “viral”. We identify significant content spreaders with a procedure that allows to statistically validate the connections that cannot be explained by users’ tweeting activity and posts’ virality, using an entropy-based null model as benchmark. The analysis of the directed network of validated retweets reveals signals of the alliances formed after the elections, highlighting commonalities of interests before the event of the national elections

Extracting significant signal of news consumption from social networks: the case of Twitter in Italian political elections

According to the Eurobarometer report about EU media use of May 2018, the number of European citizens who consult on-line social networks for accessing information is considerably increasing. In this work we analyze approximately $10^6$ tweets exchanged during the last Italian elections. By using an entropy-based null model discounting the activity of the users, we first identify potential political alliances within the group of verified accounts: if two verified users are retweeted more than expected by the non-verified ones, they are likely to be related. Then, we derive the users' affiliation to a coalition measuring the polarization of unverified accounts. Finally, we study the bipartite directed representation of the tweets and retweets network, in which tweets and users are collected on the two layers. Users with the highest out-degree identify the most popular ones, whereas highest out-degree posts are the most "viral". We identify significant content spreaders by statistically validating the connections that cannot be explained by users' tweeting activity and posts' virality by using an entropy-based null model as benchmark. The analysis of the directed network of validated retweets reveals signals of the alliances formed after the elections, highlighting commonalities of interests before the event of the national elections

Human relaxin-2 (Serelaxin) attenuates oxidative stress in cardiac muscle cells exposed in vitro to hypoxia–reoxygenation. evidence for the involvement of reduced glutathione up-regulation

Serelaxin (RLX) designates the pharmaceutical form of the human natural hormone relaxin-2 that has been shown to markedly reduce tissue and cell damage induced by hypoxia and reoxygenation (HR). The evidence that RLX exerts similar protective effects on different organs and cells at relatively low, nanomolar concentrations suggests that it specifically targets a common pathogenic mechanism of HR-induced damage, namely oxidative stress. In this study we offer experimental evidence that RLX (17 nmol L-1), added to the medium of HR-exposed H9c2 rat cardiac muscle cells, significantly reduces cell oxidative damage, mitochondrial dysfunction and apoptosis. These effects appear to rely on the up-regulation of the cellular availability of reduced glutathione (GSH), a ubiquitous endogenous antioxidant metabolite. Conversely, superoxide dismutase activity was not influenced by RLX, which, however, was not endowed with chemical antioxidant properties. Taken together, these findings verify the major pharmacological role of RLX in the protection against HR-induced oxidative stress, and shed first light on its mechanisms of action

Triple Langmuir Probes Measurements of LaB6 Hollow Cathodes Plume

Lanthanum hexaboride hollow cathodes represent a viable option for high power Hall effect thruster applications, under development for the next generation of manned and robotic interplanetary missions. In this scenario, SITAEL and the University of Pisa are actively developing high current hollow cathodes capable of providing discharge current in the range 10–100 A to be coupled with high power Hall effect thrusters. The cathode design is based on an in-house theoretical model of the internal sections of the cathode, recently integrated with a simplified model of the cathode plume. Despite the application of hollow cathodes on flight and laboratory model Hall effect thrusters, many questions remain unsolved. In particular, issues related to onset of instabilities, due to plume mode or ion acoustic turbulence, are still unclear, while it is known that they can affect the overall performance of the cathode and thruster unit. This paper focuses on the experimental investigation of the cathode plume by means of measurements of the main plasma parameters, at different operating conditions and for different cathode geometry. Two cathodes were investigated, namely HC20 and HC60, designed to be coupled with SITAEL's HT5k and HT20k (5 kW- and 20 kW-class) Hall effect thrusters. The cathodes were mounted in stand-alone configuration with an auxiliary cylindrical anode. The experimental campaign was performed using triple Langmuir probes as plasma diagnostic system. The probes were mounted on scanning mechanisms to measure the plume parameters at various radial and axial distances from the keeper exit. General trends of electron temperature, plasma potential and plasma density are reported in terms of discharge current, mass flow rate and cathode orifice geometry. The results highlight that the cathode plate orifice selection affects the plume mode onset, giving the possibility to extend the stable mode of cathode operation in the current range required by the thruster

Fibroblasts to keratinocytes redox signaling: The possible role of ROS in psoriatic plaque formation

Although the role of reactive oxygen species-mediated (ROS-mediated) signalling in physiologic and pathologic skin conditions has been proven, no data exist on the skin cells ROS-mediated communication. Primary fibroblasts were obtained from lesional and non-lesional skin of psoriatic patients. ROS, superoxide anion, calcium and nitric oxide levels and lipoperoxidation markers and total antioxidant content were measured in fibroblasts. NADPH oxidase activity and NOX1, 2 and 4 expressions were assayed and NOX4 silencing was performed. Fibroblasts and healthy keratinocytes co-culture was performed. MAPK pathways activation was studied in fibroblasts and in co-cultured healthy keratinocytes. Increased intracellular calcium, •NO and ROS levels as well as an enhanced NADPH oxidase 4 (NOX4)–mediated extracellular ROS release was shown in lesional psoriatic vs. control fibroblasts. Upon co-culture with lesional fibroblasts, keratinocytes showed p38 and ERK MAPKs pathways activation, ROS, Ca2+ and •NO increase and cell cycle acceleration. Notably, NOX4 knockdown significantly reduced the observed effects of lesional fibroblasts on keratinocyte cell cycle progression. Co-culture with non-lesional psoriatic and control fibroblasts induced slight cell cycle acceleration, but notable intracellular ROS accumulation and ERK MAPK activation in keratinocytes. Collectively, our data demonstrate that NOX4 expressed in dermal fibroblasts is essential for the redox paracrine regulation of epidermal keratinocytes proliferation