A Hamiltonian functional for the linearized Einstein vacuum field equations

By considering the Einstein vacuum field equations linearized about the Minkowski metric, the evolution equations for the gauge-invariant quantities characterizing the gravitational field are written in a Hamiltonian form by using a conserved functional as Hamiltonian; this Hamiltonian is not the analog of the energy of the field. A Poisson bracket between functionals of the field, compatible with the constraints satisfied by the field variables, is obtained. The generator of spatial translations associated with such bracket is also obtained.Comment: 5 pages, accepted in J. Phys.: Conf. Serie

Local continuity laws on the phase space of Einstein equations with sources

Local continuity equations involving background fields and variantions of the fields, are obtained for a restricted class of solutions of the Einstein-Maxwell and Einstein-Weyl theories using a new approach based on the concept of the adjoint of a differential operator. Such covariant conservation laws are generated by means of decoupled equations and their adjoints in such a way that the corresponding covariantly conserved currents possess some gauge-invariant properties and are expressed in terms of Debye potentials. These continuity laws lead to both a covariant description of bilinear forms on the phase space and the existence of conserved quantities. Differences and similarities with other approaches and extensions of our results are discussed.Comment: LaTeX, 13 page

Diffusive transport and self-consistent dynamics in coupled maps

The study of diffusion in Hamiltonian systems has been a problem of interest for a number of years. In this paper we explore the influence of self-consistency on the diffusion properties of systems described by coupled symplectic maps. Self-consistency, i.e. the back-influence of the transported quantity on the velocity field of the driving flow, despite of its critical importance, is usually overlooked in the description of realistic systems, for example in plasma physics. We propose a class of self-consistent models consisting of an ensemble of maps globally coupled through a mean field. Depending on the kind of coupling, two different general types of self-consistent maps are considered: maps coupled to the field only through the phase, and fully coupled maps, i.e. through the phase and the amplitude of the external field. The analogies and differences of the diffusion properties of these two kinds of maps are discussed in detail.Comment: 13 pages, 14 figure

Social networks as tools for the prevention and promotion of health among youth

The emergence of information and communication technologies (ICT) has generated a number of research questions, related to their use and potential risk, but also potentials for prevention or health promotion. Online social networks have become an important source of information for users as well as a tool for social relations. As traditional social networks, they can act as vehicles to improve the health of adolescents and youth, as well as play a key role in an educational context. The aim of this work is then to explore the theoretical relevance of ICT, particularly on online social networks, on disease prevention and health promotion of communicable diseases. Literature review points out the role of online social networks, particularly in the field of sexual health, body image, especially eating habits and overweight, as well as smoking and alcohol dependence. Data allow us to understand how online social network behavior and interaction is related to their burden and interventions developed in sexual health and addiction show positive results. More efforts in body image are needed in order to use these tools for prevention and promotion of health from early age.This research was supported by Instituto de Investigación de Drogodependencias, Universidad Miguel Hernández, and Fundação para a Ciência e a Tecnologia (strategic projects PEst-OE/FIL/UI0683/2014)

Personal and psychossocial determinants of tobacco and alcohol use in adolescence

Substance use in adolescence continues to be one of major concerns in public health. Its implications in personal and social terms motivate the search for determinants of consumption in order to develop effective preventive responses. Method: this study aims to explore personal determinants of tobacco and alcohol among a sample of 323 adolescents, 199 of them were girls (61.6%), aged between 15 and 19 years (M = 16.79, SD = 1.096) who attended Portuguese public high schools. For data collection, it was used a sociodemographic and consumption questionnaire, the Proactive Attitude Scale, the Proactive Coping Scale, the General Self-Efficacy Scale, the Berlin Social Support Scales and the Scales of Attitudes Toward Tobacco and Alcohol to evaluate psychosocial determinants. Results: The results allow us to verify the determinant role of attitudes on the experience of tobacco use, being higher among those who have tried and with a positive correlation with the intensity of consumption. Nevertheless, the onset age of cigarette smoking correlates only with the perception of emotional support. Also on alcohol consumption, there was a more favorable attitude among those who have tried and a negative correlation with the age of first experience. In addition, differences in attitudes were verified depending on the pattern of consumption, with more favorable attitudes according with binge drinking frequency and drunkenness episodes. Is also noticed a lower perception of demand and need for social support between adolescents that relate more drunkenness episodes. Conclusions: The study suggests the central role of attitudes towards consumption, although depending on the specific substances, findings that should be explored in future studies.These data are discussed according the existing literature and implications to prevention and further studies are presented.info:eu-repo/semantics/publishedVersio

The Myth of the Declining Reference Statistic: Revealing Dynamic Reference Services through Digital Analytics

It seems customary practice now that there is a need for libraries to “justify” their relevance, impact, contributions, and more. Traditionally, we do this by looking at some basics - how many people walk through our doors, how many classes/workshops are we teaching, and how many people did we help at the reference desk? It is hard to deny when looking at these statistics that there are some obvious trends. In the reference realm, this traditionally translates to decreasing statistics - but are these statistics telling the whole story? Are our reference desk statistics really going down? Are there other statistics/analytics that can be brought into the discussion to provide a more accurate picture? FIU Libraries has invested heavily in online content creation, online services, and the development of point-of-need unmediated services and resources. Those investments resulted in a whole new body of potential data points poised to statistically overtake our traditional reference services. This chapter shows the process of identifying other tools, platforms or sites that could be offered as expansions of reference service offerings. It presents a new holistic definition of reference services analytics and offers real-life projects (solutions) that resulted from this strategic approach. Reference offerings were broadened and diversified and now include virtual reference services and services to online students, a robust and varied library of LibGuides, and even strategically hired positions to concentrate on virtual learning, digital technologies, web services and development, and user experience

Symplectic quantization, inequivalent quantum theories, and Heisenberg's principle of uncertainty

We analyze the quantum dynamics of the non-relativistic two-dimensional isotropic harmonic oscillator in Heisenberg's picture. Such a system is taken as toy model to analyze some of the various quantum theories that can be built from the application of Dirac's quantization rule to the various symplectic structures recently reported for this classical system. It is pointed out that that these quantum theories are inequivalent in the sense that the mean values for the operators (observables) associated with the same physical classical observable do not agree with each other. The inequivalence does not arise from ambiguities in the ordering of operators but from the fact of having several symplectic structures defined with respect to the same set of coordinates. It is also shown that the uncertainty relations between the fundamental observables depend on the particular quantum theory chosen. It is important to emphasize that these (somehow paradoxical) results emerge from the combination of two paradigms: Dirac's quantization rule and the usual Copenhagen interpretation of quantum mechanics.Comment: 8 pages, LaTex file, no figures. Accepted for publication in Phys. Rev.