1,960 research outputs found

    Riemannian Geometry of Noncommutative Surfaces

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    A Riemannian geometry of noncommutative n-dimensional surfaces is developed as a first step towards the construction of a consistent noncommutative gravitational theory. Historically, as well, Riemannian geometry was recognized to be the underlying structure of Einstein's theory of general relativity and led to further developments of the latter. The notions of metric and connections on such noncommutative surfaces are introduced and it is shown that the connections are metric-compatible, giving rise to the corresponding Riemann curvature. The latter also satisfies the noncommutative analogue of the first and second Bianchi identities. As examples, noncommutative analogues of the sphere, torus and hyperboloid are studied in detail. The problem of covariance under appropriately defined general coordinate transformations is also discussed and commented on as compared with other treatments.Comment: 28 pages, some clarifications, examples and references added, version to appear in J. Math. Phy

    Deconfinement transition in protoneutron stars: analysis within the Nambu-Jona-Lasinio model

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    We study the effect of color superconductivity and neutrino trapping on the deconfinement transition of hadronic matter into quark matter in a protoneutron star. To describe the strongly interacting matter a two-phase picture is adopted. For the hadronic phase we use different parameterizations of a non-linear Walecka model which includes the whole baryon octet. For the quark matter phase we use an SU(3)fSU(3)_f Nambu-Jona-Lasinio effective model which includes color superconductivity. We impose color and flavor conservation during the transition in such a way that just deconfined quark matter is transitorily out of equilibrium with respect to weak interactions. We find that deconfinement is more difficult for small neutrino content and it is easier for lower temperatures although these effects are not too large. In addition they will tend to cancel each other as the protoneutron star cools and deleptonizes, resulting a transition density that is roughly constant along the evolution of the protoneutron star. According to these results the deconfinement transition is favored after substantial cooling and contraction of the protoneutron star

    Statistical models of mixtures with a biaxial nematic phase

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    We consider a simple Maier-Saupe statistical model with the inclusion of disorder degrees of freedom to mimic the phase diagram of a mixture of rod-like and disc-like molecules. A quenched distribution of shapes leads to the existence of a stable biaxial nematic phase, in qualitative agreement with experimental findings for some ternary lyotropic liquid mixtures. An annealed distribution, however, which is more adequate to liquid mixtures, precludes the stability of this biaxial phase. We then use a two-temperature formalism, and assume a separation of relaxation times, to show that a partial degree of annealing is already sufficient to stabilize a biaxial nematic structure.Comment: 11 pages, 2 figure

    Virtual environments to cope with anxiety situations: Two case-studies

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    Anxiety is a growing problem in modern societies. Virtual reality has been widely adopted to treat anxiety and more severe psychological problems. We have been working on an approach that involves compelling virtual environments (VE) to treat anxiety. These VE recreate a particular situation and support in real-time the intervention of the therapist. Public domain software tools and a simple projection screen have been used. This paper describes two interactive applications that simulate VE to help people coping with particular anxiety situations. One of the applications is developed in Blender and is dedicated to the fear of talking in front of an audience; the other application is developed in OpenSim and is devoted to the fear of driving inside a tunnel.info:eu-repo/semantics/acceptedVersio

    Shelf life extension of Ricotta cheese using coatings of galactomannans from nonconventional sources incorporating nisin against Listeria monocytogenes

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    Shelf life extension of Ricotta cheese was evaluated at 4 °C upon the use of edible coatings made of galactomannans from Gleditsia triacanthos incorporating nisin against Listeria monocytogenes. Three different treatments were tested in cheese: samples without coating; samples with coating without nisin; and samples with coating containing 50 IU·g−1 of nisin. To test the effectiveness of the treatments against L. monocytogenes, the surface of the cheese was inoculated with a suspension of the microorganism. Microbiological and physical−chemical analyses of the cheese samples were performed during 28 days. Results showed that the cheese coated with nisin-added galactomannan film was the treatment presenting the best results in terms of microbial growth delay (p < 0.05). The addition of nisin also affects (p < 0.05) the physical and mechanical properties of the films: O2 permeability decreased from 1.84 to 1.35 × 10−12 cm3·(Pa·s·m)−1; CO2 permeability increased from 1.96 to 6.31 × 10−12 cm3·(Pa·s·m)−1; opacity increased from 3.68 to 4.59%; tensile strength ranged from 0.84 to 1.46 MPa; and elongation at break improved from 50.93 to 68.16%. These results demonstrate that novel galactomannan-based edible coatings, when combined with nisin, may provide consumer-friendly alternatives to reduce L. monocytogenes postcontamination on cheese products during storage.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Brazil)Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/32566/2006, SFRH/BD/23897/200

    Effect of the application of a galactomannan coating incorporating nisin on the growth of Listeria monocytogenes on Ricotta cheese

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    Antimicrobial packaging, besides protecting the product from the external environment, inhibits or delays microorganism growth in foods and meets the actual demand of consumers for healthier foods, containing less additives (Lopez‐Rubio, Gavara, & Lagaron, 2006). Cheese is a ready‐to‐eat type of food that has been associated with foodborne listeriosis. Listeria monocytogenes is an important ubiquitous foodborne pathogen which may contaminate foods at pre‐ and post‐harvest stages of production. To overcome this problem bacteriocins could be entrapped in a suitable edible coating applied to food. Nisin is an antimicrobial peptide produced by Lactococcus lactis subsp. lactis. and research studies have revealed its ability to inhibit the growth of some pathogenic bacteria (Sobrino‐López, & Martín‐Belloso, 2008). The aim of this study was to evaluate the antimicrobial activity of coatings of galactomannans from Gleditsia triacanthos incorporating nisin against L. monocytogenes during storage of Ricotta cheese at 4 °C. Three different treatments were tested: a control with no coating; a sample with coating containing no nisin and a coating with 50 IU.g‐1 of nisin. Samples of cheese (20 g) were immersed in 0.5 % w/v galactomannan solution containing glycerol (as plasticizer) (1.5 % v/v). To test the effectiveness of the treatments Ricotta cheese samples were surface‐inoculated with a solution containing approximately 1×106 CFU.ml‐1 of L. monocytogenes. Microbiological and physicalchemical parameters (color change, pH, moisture content and weight loss) were monitored over 28 days for cheese stored at 4 ºC. Among the three treatments, the combination of coating and nisin showed the best results, followed by the coating containing no nisin. Counts of L. monocytogenes were lower (p<0.05) in nisin‐containing coating that in no‐coated cheese. The nisin‐containing coating presented a reduction from 5.1 to 4.4 log CFU.g‐1 after 2 days of storage. For samples coated with nisin, reductions of 2.2 log CFU.g‐1 were achieved for samples after 7 days of storage. These results suggest that the application of these coatings could be a potential food packaging solution for the release of nisin in view of the control of L. monocytogenes spoilage in cheese

    Volume Fractions of the Kinematic "Near-Critical" Sets of the Quantum Ensemble Control Landscape

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    An estimate is derived for the volume fraction of a subset CϵP={U:gradJ(U)ϵ}U(N)C_{\epsilon}^{P} = \{U : ||grad J(U)|\leq {\epsilon}\}\subset\mathrm{U}(N) in the neighborhood of the critical set CPU(n)PU(m)C^{P}\simeq\mathrm{U}(\mathbf{n})P\mathrm{U}(\mathbf{m}) of the kinematic quantum ensemble control landscape J(U) = Tr(U\rho U' O), where UU represents the unitary time evolution operator, {\rho} is the initial density matrix of the ensemble, and O is an observable operator. This estimate is based on the Hilbert-Schmidt geometry for the unitary group and a first-order approximation of gradJ(U)2||grad J(U)||^2. An upper bound on these near-critical volumes is conjectured and supported by numerical simulation, leading to an asymptotic analysis as the dimension NN of the quantum system rises in which the volume fractions of these "near-critical" sets decrease to zero as NN increases. This result helps explain the apparent lack of influence exerted by the many saddles of JJ over the gradient flow.Comment: 27 pages, 1 figur

    A serious game-based solution to prevent bullying

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    This paper presents a Serious Game with the main purpose of inducing attitude changes as a way to prevent bullying, in a target audience of young people between 10 and 12 years old. The rationale for prevention is: first, to help victims of these aggressive episodes to acquire or improve competencies in avoiding or dealing with future real bullying situations; and, second, to promote empathy towards the victims in bystanders. A back office application complements the game, providing substantial assistance to psychologists while using the game with patients in therapy or in research work. Both components, the game and the back office, were evaluated with volunteers. The user study lead us to the conclusion that the current version of the game holds good potential in bullying prevention: the young people that played the game in a continuous time span, at the end of this testing process have expressed improvements in their bullying prevention strategies. The back office application was positively assessed by the psychologists who tested it. The game deals with strong social features, such as number of friends and invitations to social events (e.g. a birthday party), to which young people give much importance. Additionally, it offers a variability of scenarios and consequences of actions, taking into account the user's performance in the game. The main factors that make the presented solution stand out in comparison with other similar bullying prevention solutions are mainly the following: it includes a back office application to assist therapists with data management features; the role of the player in the game can be chosen accordingly to his own profile; it is possible to play even outside a therapy session (e.g. at home) and it is a portable solution.info:eu-repo/semantics/acceptedVersio
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