Face amplitude of spinfoam quantum gravity

The structure of the boundary Hilbert-space and the condition that amplitudes behave appropriately under compositions determine the face amplitude of a spinfoam theory. In quantum gravity the face amplitude turns out to be simpler than originally thought.Comment: 5 pages, 2 figure

A Curie-Weiss model with dissipation

We consider stochastic dynamics for a spin system with mean field interaction, in which the interaction potential is subject to noisy and dissipative stochastic evolution. We show that, in the thermodynamic limit and at sufficiently low temperature, the magnetization of the system has a time periodic behavior, despite of the fact that no periodic force is applied

Cashtag piggybacking: uncovering spam and bot activity in stock microblogs on Twitter

Microblogs are increasingly exploited for predicting prices and traded volumes of stocks in financial markets. However, it has been demonstrated that much of the content shared in microblogging platforms is created and publicized by bots and spammers. Yet, the presence (or lack thereof) and the impact of fake stock microblogs has never systematically been investigated before. Here, we study 9M tweets related to stocks of the 5 main financial markets in the US. By comparing tweets with financial data from Google Finance, we highlight important characteristics of Twitter stock microblogs. More importantly, we uncover a malicious practice - referred to as cashtag piggybacking - perpetrated by coordinated groups of bots and likely aimed at promoting low-value stocks by exploiting the popularity of high-value ones. Among the findings of our study is that as much as 71% of the authors of suspicious financial tweets are classified as bots by a state-of-the-art spambot detection algorithm. Furthermore, 37% of them were suspended by Twitter a few months after our investigation. Our results call for the adoption of spam and bot detection techniques in all studies and applications that exploit user-generated content for predicting the stock market

Oxidative responsiveness to multiple stressors in the key Antarctic species, Adamussium colbecki: interactions between temperature, acidification and cadmium exposure.

Abstract: High-latitude marine ecosystems are ranked to be among the most sensitive regions to climate change since highly stenothermal and specially adapted organisms might be seriously affected by global warming and ocean acidification. The present investigation was aimed to provide new insights on the sensitivity to such environmental stressors in the key Antarctic species, Adamussium colbecki, focussing also on their synergistic effects with cadmium exposure, naturally abundant in this area for upwelling phenomena. Scallops were exposed for 2 weeks to various combinations of Cd (0 and 40 μgL-1), pH (8.05 and 7.60) and temperature (-1 and +1°C). Beside Cd bioaccumulation, a wide panel of early warning biomarkers were analysed in digestive glands and gills including levels of metallothioneins, individual antioxidants and total oxyradical scavenging capacity, onset of oxidative cell damage like lipid peroxidation, lysosomal stability, DNA integrity and peroxisomal proliferation. Results indicated reciprocal interactions between multiple stressors and their elaboration by a quantitative hazard model based on the relevance and magnitude of effects, highlighted a different sensitivity of analysed tissues. Due to cellular adaptations to high basal Cd content, digestive gland appeared more tolerant toward other prooxidant stressors, but sensitive to variations of the metal. On the other hand, gills were more affected by various combinations of stressors occurring at higher temperatur

Phantom without phantom or how the PT symmetry saves us from the Big Rip

We consider the PT symmetric flat Friedmann model of two scalar fields with positive kinetic terms. While the potential of one ("normal") field is taken real, that of the other field is complex. We study a complex classical solution of the system of the two Klein-Gordon equations together with the Friedmann equation. The solution for the normal field is real while the solution for the second field is purely imaginary, realizing classically the "phantom" behavior. The energy density and pressure are real and the corresponding geometry is well-defined. The Lagrangian for the linear perturbations has the correct potential signs for both the fields, so that the problem of stability does not arise. The background dynamics is determined by an effective action including two real fields one normal and one "phantom". Remarkably, the phantom phase in the cosmological evolution is transient and the Big Rip never occurs. Our model is contrasted to well-known quintom models, which also include one normal and one phantom fields.Comment: revised and enlarged version, to be published in Int. J. Mod. Phys. D, the title is change

Application of a Weight of Evidence Approach for Monitoring Complex Environmental Scenarios: the Case-Study of Off-Shore Platforms

Multidisciplinary investigations based on integration of chemical and biological measurements, represent an added value to monitoring and management protocols, and their use is recommended by European Directives to evaluate the environmental status of aquatic ecosystems. However, assessing the overall significance of results obtained in different typologies of studies is often a difficult challenge. The aim of this work was to present a quantitative Weight Of Evidence (WOE) model (Sediqualsoft) to integrate huge amounts of heterogeneous data and to validate this approach in complex monitoring scenarios. Using the case-study of an off-shore platform field in the Adriatic Sea, procedures are presented to elaborate different typologies of data (lines of evidence, LOEs), including chemical characterization of sediments, bioavailability, biomarkers, ecotoxicological bioassays and benthic communities around three platforms. These data are initially evaluated by logical flowcharts and mathematical algorithms, which provide specific hazard indices for each considered LOE, before their different weighting and overall integration in an environmental risk index. The monitoring study selected for the WOE elaboration consisted on chemical analyses of trace metals, aliphatic hydrocarbons, polycyclic aromatic hydrocarbons carried out on 60 sediment samples; the same samples were also characterized for the status of benthic communities; bioavailability of metals from sediments was assessed in laboratory conditions on the polychaete Hediste diversicolor, while bioaccumulation of inorganic and organic chemicals and biomarker responses were measured in native and transplanted mussels; ecotoxicological properties of sediments were evaluated through a battery of bioassays determining algal growth of the diatom Phaeodactylum tricornutum, bioluminescence of the marine bacterium Vibrio fischeri, survival of the copepod Acartia tonsa and embryotoxicity of sea urchin Paracentrotus lividus. Overall, almost 7000 analytical results were elaborated and summarized in specific hazard indices. The WOE integration of multiple typologies of data allowed more robust and weighted conclusions compared to the use of individual LOEs, highlighting the feasibility of this procedure for multidisciplinary monitoring and risk assessment approaches. On a practical side, the WOE evidences also suggested a revision of actual monitoring procedures. Overall, the proposed WOE model appeared as a useful tool to summarize large datasets of complex data in integrative indices, and to simplify the interpretation for stakeholders and decision makers, thus supporting a more comprehensive process of "site-oriented" management decisions

Reconstruction of scalar potentials in two-field cosmological models

We study the procedure of the reconstruction of phantom-scalar field potentials in two-field cosmological models. It is shown that while in the one-field case the chosen cosmological evolution defines uniquely the form of the scalar potential, in the two-field case one has an infinite number of possibilities. The classification of a large class of possible potentials is presented and the dependence of cosmological dynamics on the choice of initial conditions is investigated qualitatively and numerically for two particular models.Comment: final version, to appear in JCA