On twisted contact groupoids and on integration of twisted Jacobi manifolds

We introduce the concept of twisted contact groupoids, as an extension either of contact groupoids or of twisted symplectic ones, and we discuss the integration of twisted Jacobi manifolds by twisted contact groupoids. We also investigate the very close relationships which link homogeneous twisted Poisson manifolds with twisted Jacobi manifolds and homogeneous twisted symplectic groupoids with twisted contact ones. Some examples for each structure are presented

'The perception of fear conditioning urban space'

The dominant metabolic system within urban environments often involves deep socio-economic inequalities, exploitative productive practices and a persistent sense of alienation among the vast majority of the population. The city itself spawns the conditions both for the development of actual criminality and, more perniciously, for the emergence of an acute perception of fear within the polis. Over the years, this perception has affected a whole array of societal elements including, quite significantly, the spatial structure of neighborhoods, urban forms and housing design. The big boom of gated communities signifies the development of social segregation and the tendency to ensure ontological security behind impenetrable walls. The development of off-center exclusive communities, parallel to the inner city impoverished neighborhoods establishes the “new ghettos trendâ€. The new gated suburbs seem to have increased safety measures such as surveillance cameras, security personnel, high fences, moat-like structures, dead-end roads etc., involving a complex defensive architecture, in order to eliminate random and unaccounted movements, to enhance a sense of security and minimize the perception of fear. This paper examines the complex inter-determinations between perceived fear of urban otherness and spatial appropriation, urban forms and housing design, aspects whose functional attributes address almost exclusively the fear factor. It also presents the results of a comparative field study of the exclusive neighborhoods of Hampstead and Psychiko, in greater London and Athens respectively, where the material manifestations of the fear – urban character inter-relationship are examined, including road plans, pedestrian areas, home security systems, housing design elements and, perhaps most revealingly, real estate values. Key words: exclusive suburbs, gated communities, perception of fear, defensive architecture, security. References: Amin A. (1994): “Post- Fordism: A Readerâ€, Blackwell Publishers Davis M. (2008): “Beyond Blade Runner: Urban control- The ecology of fearâ€, Futura Press Ellin N. (1996): “Postmodern Urbanismâ€, Princeton Architectural Press Low S. (2003): “Behind the gates: Life, security and the pursuit of happiness in fortress Americaâ€, Routledge Savage M., Warde A. (1993): “Urban Sociology, Capitalism and Modernityâ€, Palgrave Macmillan Sennett R. (1990): “The conscience of the eye: The design and social life of citiesâ€, Norton & Company

Dynamical friction and the evolution of Supermassive Black hole Binaries: the final hundred-parsec problem

The supermassive black holes originally in the nuclei of two merging galaxies will form a binary in the remnant core. The early evolution of the massive binary is driven by dynamical friction before the binary becomes "hard" and eventually reaches coalescence through gravitational wave emission. { We consider the dynamical friction evolution of massive binaries consisting of a secondary hole orbiting inside a stellar cusp dominated by a more massive central black hole.} In our treatment we include the frictional force from stars moving faster than the inspiralling object which is neglected in the standard Chandrasekhar's treatment. We show that the binary eccentricity increases if the stellar cusp density profile rises less steeply than $\rho\propto r^{-2}$. In cusps shallower than $\rho\propto r^{-1}$ the frictional timescale can become very long due to the deficit of stars moving slower than the massive body. Although including the fast stars increases the decay rate, low mass-ratio binaries ($q\lesssim 10^{-3}$) in sufficiently massive galaxies have decay timescales longer than one Hubble time. During such minor mergers the secondary hole stalls on an eccentric orbit at a distance of order one tenth the influence radius of the primary hole (i.e., $\approx 10-100\rm pc$ for massive ellipticals). We calculate the expected number of stalled satellites as a function of the host galaxy mass, and show that the brightest cluster galaxies should have $\gtrsim 1$ of such satellites orbiting within their cores. Our results could provide an explanation to a number of observations, which include multiple nuclei in core ellipticals, off-center AGNs and eccentric nuclear disks.Comment: 18 pages, 13 Figures. Accepted for publication in Ap

Analysis of science textbook pictures about energy and pupils' readings of them

This article outlines the findings of the part of the "Science Teacher Training in an Information Society" (STTIS) project concerned with describing the possible difficulties the pupils have when "reading" science textbook pictures about "energy". Six documents were selected on the basis that they had some of the textual/graphical features previously identified by the project as potentially presenting difficulties to pupils. The pupils' readings of these were investigated using a questionnaire and a follow-up interview. The analysis of three of the documents and of twelve pupils' readings of them is reported in this paper. The results confirm the hypothesis that the "reading" of science textbook pictures is not at all trivial for pupils and conclude that teachers need to spend time and effort talking through the meaning of the images with them. They also suggest that the list of textual/graphical features used in this research is a good starting point for this kind of critical examination

Probabilistic Matching: Causal Inference under Measurement Errors

The abundance of data produced daily from large variety of sources has boosted the need of novel approaches on causal inference analysis from observational data. Observational data often contain noisy or missing entries. Moreover, causal inference studies may require unobserved high-level information which needs to be inferred from other observed attributes. In such cases, inaccuracies of the applied inference methods will result in noisy outputs. In this study, we propose a novel approach for causal inference when one or more key variables are noisy. Our method utilizes the knowledge about the uncertainty of the real values of key variables in order to reduce the bias induced by noisy measurements. We evaluate our approach in comparison with existing methods both on simulated and real scenarios and we demonstrate that our method reduces the bias and avoids false causal inference conclusions in most cases.Comment: In Proceedings of International Joint Conference Of Neural Networks (IJCNN) 201

Non-Parametric Causality Detection: An Application to Social Media and Financial Data

According to behavioral finance, stock market returns are influenced by emotional, social and psychological factors. Several recent works support this theory by providing evidence of correlation between stock market prices and collective sentiment indexes measured using social media data. However, a pure correlation analysis is not sufficient to prove that stock market returns are influenced by such emotional factors since both stock market prices and collective sentiment may be driven by a third unmeasured factor. Controlling for factors that could influence the study by applying multivariate regression models is challenging given the complexity of stock market data. False assumptions about the linearity or non-linearity of the model and inaccuracies on model specification may result in misleading conclusions. In this work, we propose a novel framework for causal inference that does not require any assumption about the statistical relationships among the variables of the study and can effectively control a large number of factors. We apply our method in order to estimate the causal impact that information posted in social media may have on stock market returns of four big companies. Our results indicate that social media data not only correlate with stock market returns but also influence them.Comment: Physica A: Statistical Mechanics and its Applications 201