2,362 research outputs found

    Coherent spin-networks

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    In this paper we discuss a proposal of coherent states for Loop Quantum Gravity. These states are labeled by a point in the phase space of General Relativity as captured by a spin-network graph. They are defined as the gauge invariant projection of a product over links of Hall's heat-kernels for the cotangent bundle of SU(2). The labels of the state are written in terms of two unit-vectors, a spin and an angle for each link of the graph. The heat-kernel time is chosen to be a function of the spin. These labels are the ones used in the Spin Foam setting and admit a clear geometric interpretation. Moreover, the set of labels per link can be written as an element of SL(2,C). Therefore, these states coincide with Thiemann's coherent states with the area operator as complexifier. We study the properties of semiclassicality of these states and show that, for large spins, they reproduce a superposition over spins of spin-networks with nodes labeled by Livine-Speziale coherent intertwiners. Moreover, the weight associated to spins on links turns out to be given by a Gaussian times a phase as originally proposed by Rovelli.Comment: 15 page

    D7.3 Training materials

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    This Deliverable gives a detailed description of the comprehensive training programme and of the open educational content that the University of Padua has accomplished up to now for the project "Linked Heritage: Coordination of standard and technologies for the enrichment of Europeana" (CIP Best Practice Network). The final version of D7.3 will be released by the end of the project, when all the Learning Objects will be finished

    Il ruolo della movimentazione degli animali nella trasmissione di malattie virali.

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    Con il termine di “movimentazione” si intende lo spostamento degli animali, per “importazione” l’introduzione di animali da Paesi Terzi (controllo PIF) e per “scambi” si identificano i movimenti all’interno della comunità stessa (controllo UVAC). Le certificazioni relative a questi movimenti si avvalgono del sistema TRACES. Organizzazioni come OIE, FAO e WHO si sono sempre adoperate a tutela della salute umana, della salute animale e delle movimentazioni sicure. Con gli anni il rischio di diffusione delle malattie è diminuito, in seguito al miglioramento della salute animale ed al lavoro portato avanti dall’OIE nella definizione di norme internazionali volte a garantire la sicurezza negli scambi di animali. Tuttavia il fenomeno della globalizzazione ha comportato l’aumento dei traffici e conseguentemente il rischio che ne deriva. La movimentazione è una importante modalità per la diffusione di molte malattie infettive oltre a costituire uno stress per gran parte delle specie animali fino a comprometterne la capacità di far fronte ai patogeni. Le arbovirosi in particolare hanno destato interesse e preoccupazione negli ultimi anni in seguito all’incremento delle movimentazioni e dei cambiamenti climatici. Sarebbe dunque auspicabile lavorare per preferire la movimentazione dei prodotti piuttosto che degli animali vivi. “Trade” is animal’s transfer from one place to another. We distinguish “import” when the animals are brought from Third Countries (BIP check) and intra communitarians trade (UVAC check). Certificates concerning those trades are produced by TRACES system. Those three organizations OIE, FAO and WHO have always done their best to protect both human and animal heath and to protect safe trade. As time has passed, the risk of disease spread has decreased thank to improvement of animal heath and thanks to the OIE’s mission, which has defined internationals roles concerning animal trade safety. At the same time globalization has increased traffic and all the dangers connected to it. Trade causes a very important spread of infectious diseases and causes such a big stress for the majority of animal species making them unable to face pathogens. The arbovirus diseases have provoked interest and worries caused by trade increase and climatic changes recently. We would prefer product trade rather then alive animal trade

    Discovering Language through Corpora: the Skills Learners Need and the Difficulties they Encounter

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    Most scholars agree on considering corpora as a valuable source of linguistic information for native and non-native speakers alike. Few researchers, however, have dealt with and systematically analysed the objective difficulties encountered by students while trying to exploit corpus data. The current paper describes a quantitative study of corpus consultation by learners and aims to establish whether different corpus analysis tasks can be considered to have different degrees of intrinsic difficulty. To this end, 26 corpus project work assignments produced by two different groups of students were assessed and tagged according to specific parameters that reflect the skills needed in corpus analysis. The data were analysed applying both parametric (ANOVA) and non parametric tests (Mann-Whitney U-test), which showed that, despite clear individual and teaching/learning environment differences between the two groups of students, the students’ results in most of the tasks were due to different levels of intrinsic difficulty. This led to the creation of a General Difficulty List of Corpus Analysis Tasks

    Wine promotion on Facebook: a linguistic comparison of posts by producers from English-speaking countries

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    Facebook can be considered one of the main social marketing tools used by companies who decide to advertise their products online and who aim to keep in touch with customers quickly and effectively. Social media in general and Facebook in particular are characterised by a high level of interactivity, and visual, textual and linguistic features are strategically used to attract and involve potential customers and to get their feedback, thus enhancing the company’s visibility on the market as well as the company’s knowledge of the market. This paper analyses the language used to advertise wine and wine events through Facebook posts by producers from New Zealand, South Africa and the UK. Method-wise, this study applies the same analytical methods used by Manca (2021) in her analysis of the interactive and interactional strategies employed by Australian and US wine companies to advertise their products and activities on Facebook, and also some of the analytical methods used by Bianchi (2017a, 2017b) in her studies on Facebook posts written by travel agencies to advertise their destinations. Besides describing the metadiscursive features which are mostly used on Facebook by wineries (Hyland 2005), this paper aims to establish whether the forms of interaction and the positioning of the writers depend on cultural factors, on the medium used or on other variables

    Small Sample Properties of Copula-GARCH Modelling: A Monte Carlo Study

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    Copula-GARCH models have been recently proposed in the financial literature as a statistical tool to build flexible multivariate distributions. Our extensive simulation studies investigate the small sample properties of these models and examine how misspecification in the marginals may affect the estimation of the dependence function represented by the copula. We show that the use of normal marginals when the true Data Generating Process is leptokurtic or asymmetric, produces negatively biased estimates of the normal copula correlations. A striking result is that these biases reach their highest value when correlations are strongly negative, and viceversa. This result remains unchanged with both positively skewed and negatively skewed data, while no biases are found if the variables are uncorrelated. Besides, the effect of marginals asymmetry on correlations is smaller than that of leptokurtosis. We finally analyse the performance of these models in terms of numerical convergence and positive definiteness of the estimated copula correlation matrix.Copulas, Copula-GARCH models, Maximum Likelihood, Simulation, Small Sample Properties.

    A Copula-VAR-X Approach for Industrial Production Modelling and Forecasting

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    World economies, and especially European ones, have become strongly interconnected in the last decades and a joint modelling is required. We propose here the use of Copulas to build flexible multivariate distributions, since they allow for a rich dependence structure and more flexible marginal distributions that better fit the features of empirical data, such as leptokurtosis. We use our approach to forecast industrial production series in the core EMU countries and we provide evidence that the copula-VAR model outperforms or at worst compares similarly to normal VAR models, keeping the same computational tractability of the latter approach.Forecasting, Industrial Production, Copulas, VAR models.

    A GPU Simulation Tool for Training and Optimisation in 2D Digital X-Ray Imaging

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    Conventional radiology is performed by means of digital detectors, with various types of technology and different performance in terms of efficiency and image quality. Following the arrival of a new digital detector in a radiology department, all the staff involved should adapt the procedure parameters to the properties of the detector, in order to achieve an optimal result in terms of correct diagnostic information and minimum radiation risks for the patient. The aim of this study was to develop and validate a software capable of simulating a digital X-ray imaging system, using graphics processing unit computing. All radiological image components were implemented in this application: an X-ray tube with primary beam, a virtual patient, noise, scatter radiation, a grid and a digital detector. Three different digital detectors (two digital radiography and a computed radiography systems) were implemented. In order to validate the software, we carried out a quantitative comparison of geometrical and anthropomorphic phantom simulated images with those acquired. In terms of average pixel values, the maximum differences were below 15%, while the noise values were in agreement with a maximum difference of 20%. The relative trends of contrast to noise ratio versus beam energy and intensity were well simulated. Total calculation times were below 3 seconds for clinical images with pixel size of actual dimensions less than 0.2 mm. The application proved to be efficient and realistic. Short calculation times and the accuracy of the results obtained make this software a useful tool for training operators and dose optimisation studies

    Inorganic mercury sequestration by a poly(ethylene imine) dendrimer in aqueous solution

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    The interaction of the G-2 poly(ethylene imine) dendrimer L, derived from ammonia as initiating core, with Hg(II) and HgCl42− was studied in aqueous solution by means of potentiometric (pH-metric) measurements. Speciation of these complex systems showed that L is able to form a wide variety of complexes including 1:1, 2:1, 3:1 and 3:2 metal-to-ligand species, of different protonation states, as well as the anion complexes [(H7L)HgCl4]5+ and [(H8L)HgCl4]6+. The stability of the metal complexes is very high, making L an excellent sequestering agent for Hg(II), over a large pH range, and a promising ligand for the preparation of functionalized activated carbons to be employed in the remediation and the prevention of environmental problems

    LQG propagator from the new spin foams

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    We compute metric correlations in loop quantum gravity with the dynamics defined by the new spin foam models. The analysis is done at the lowest order in a vertex expansion and at the leading order in a large spin expansion. The result is compared to the graviton propagator of perturbative quantum gravity.Comment: 28 page
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