748 research outputs found

    Service Security and Privacy as a Socio-Technical Problem: Literature review, analysis methodology and challenge domains

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    Published online September 2015 accepted: 15 September 2014Published online September 2015 accepted: 15 September 2014The security and privacy of the data that users transmit, more or less deliberately, to modern services is an open problem. It is not solely limited to the actual Internet traversal, a sub-problem vastly tackled by consolidated research in security protocol design and analysis. By contrast, it entails much broader dimensions pertaining to how users approach technology and understand the risks for the data they enter. For example, users may express cautious or distracted personas depending on the service and the point in time; further, pre-established paths of practice may lead them to neglect the intrusive privacy policy offered by a service, or the outdated protections adopted by another. The approach that sees the service security and privacy problem as a socio-technical one needs consolidation. With this motivation, the article makes a threefold contribution. It reviews the existing literature on service security and privacy, especially from the socio-technical standpoint. Further, it outlines a general research methodology aimed at layering the problem appropriately, at suggesting how to position existing findings, and ultimately at indicating where a transdisciplinary task force may fit in. The article concludes with the description of the three challenge domains of services whose security and privacy we deem open socio-technical problems, not only due to their inherent facets but also to their huge number of users

    A Discrete Four Stroke Quantum Heat Engine Exploring the Origin of Friction

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    The optimal power performance of a first principle quantum heat engine model shows friction-like phenomena when the internal fluid Hamiltonian does not commute with the external control field. The model is based on interacting two-level-systems where the external magnetic field serves as a control variable.Comment: 4 pages 3 figure

    Measuring multipole moments of Weyl metrics by means of gyroscopes

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    Using the technique of Rindler and Perlick we calculate the total precession per revolution of a gyroscope circumventing the source of Weyl metrics. We establish thereby a link between the multipole moments of the source and an ``observable'' quantity. Special attention deserves the case of the gamma-metric. As an extension of this result we also present the corresponding expressions for some stationary space-times.Comment: 18 pages Latex, To appear in J.Math.Phy

    Exact relativistic models of thin disks around static black holes in a magnetic field

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    The exact superposition of a central static black hole with surrounding thin disk in presence of a magnetic field is investigated. We consider two models of disk, one of infinite extension based on a Kuzmin-Chazy-Curzon metric and other finite based on the first Morgan-Morgan disk. We also analyze a simple model of active galactic nuclei consisting of black hole, a Kuzmin-Chazy-Curzon disk and two rods representing jets, in presence of magnetic field. To explain the stability of the disks we consider the matter of the disk made of two pressureless streams of counterrotating charged particles (counterrotating model) moving along electrogeodesic. Using the Rayleigh criterion we derivate for circular orbits the stability conditions of the particles of the streams. The influence of the magnetic field on the matter properties of the disk and on its stability are also analyzed.Comment: 17 pages, 14 figures. arXiv admin note: text overlap with arXiv:gr-qc/0409109 by other author

    Comment on "Superconducting gap anisotropy vs. doping level in high-T_c cuprates" by C. Kendziora et al, PRL 77, 727 (1996)

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    In a recent paper Kendziora et al concluded that the superconducting gap in overdoped Bi-2212 is isotropic. From data obtained from electronic Raman scattering measurements, their conclusion was based on the observation that pair breaking peaks occured at approximately the same frequency in different scattering geometries and that the normalized scattering intensity at low energies was strongly depleted. We discuss a different interpretation of the raw data and present new data which is consistent with a strongly anisotropic gap with nodes. The spectra can be successfully described by a model for Raman scattering in a d_{x^{2}-y^{2}} superconductor with spin fluctuations and impurity scattering included.Comment: 1 page revtex plus 1 postscript figur

    A source of a quasi--spherical space--time: The case for the M--Q solution

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    We present a physically reasonable source for an static, axially--symmetric solution to the Einstein equations. Arguments are provided, supporting our belief that the exterior space--time produced by such source, describing a quadrupole correction to the Schwarzschild metric, is particularly suitable (among known solutions of the Weyl family) for discussing the properties of quasi--spherical gravitational fields.Comment: 34 pages, 9 figures. To appear in GR

    Synchronisation in the prefrontal-striatal circuit tracks behavioural choice in a go no-go task in rats

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    Rodent striatum is involved in sensory-motor transformations and reward-related learning. Lesion studies suggest dorsolateral striatum, dorsomedial striatum, and nucleus accumbens underlie stimulus-response transformations, goal-directed behaviour and reward expectation respectively. In addition, prefrontal inputs likely control these functions. Here we set out to study how reward-driven behaviour is mediated by the coordinated activity of these structures in the intact brain. We implemented a discrimination task requiring rats to either respond or suppress responding on a lever after the presentation of auditory cues in order to obtain rewards. Single unit activity in the striatal subregions and prelimbic cortex was recorded using tetrode arrays. Striatal units showed strong onset responses to auditory cues paired with an opportunity to obtain reward. Cue onset responses in both striatum and cortex were significantly modulated by previous errors suggesting a role of these structures in maintaining appropriate motivation or action selection during ongoing behaviour. Furthermore, failure to respond to the reward-paired tones was associated with higher pre-trial coherence among striatal subregions and between cortex and striatum suggesting a task-negative corticostriatal network whose activity may be suppressed to enable processing of reward-predictive cues. Our findings highlight that coordinated activity in a distributed network including both prelimbic cortex and multiple striatal regions underlies reward-related decisions

    Teleparallel Energy-Momentum Distribution of Static Axially Symmetric Spacetimes

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    This paper is devoted to discuss the energy-momentum for static axially symmetric spacetimes in the framework of teleparallel theory of gravity. For this purpose, we use the teleparallel versions of Einstein, Landau-Lifshitz, Bergmann and Mo¨\ddot{o}ller prescriptions. A comparison of the results shows that the energy density is different but the momentum turns out to be constant in each prescription. This is exactly similar to the results available in literature using the framework of General Relativity. It is mentioned here that Mo¨\ddot{o}ller energy-momentum distribution is independent of the coupling constant λ\lambda. Finally, we calculate energy-momentum distribution for the Curzon metric, a special case of the above mentioned spacetime.Comment: 14 pages, accepted for publication in Mod. Phys. Lett.
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