A weighted multi-attribute method for matching user-generated Points of Interest

To a large degree, the attraction of Big Data lies in the variety of its heterogeneous multi-thematic and multi-dimensional data sources and not merely its volume. To fully exploit this variety, however, requires conflation. This is a two-step process. First, one has to establish identity relations between information entities across different data sources; and second, attribute values have to be merged according to certain procedures that avoid logical contradictions. The first step, also called matching, can be thought of as a weighted combination of common attributes according to some similarity measures. In this work, we propose such a matching based on multiple attributes of Points of Interest (POI) from the Location-based Social Network Foursquare and the local directory service Yelp. While both contain overlapping attributes that can be used for matching, they have specific strengths and weaknesses that make their conflation desirable. For instance, Foursquare offers information about user check-ins to places, while Yelp specializes in user-contributed reviews. We present a weighted multi-attribute matching strategy, evaluate its performance, and discuss application areas that benefit from a successful matching. Finally, we also outline how the established POI matches can be stored as Linked Data on the Semantic Web. Our strategy can automatically match 97% of randomly selected Yelp POI to their corresponding Foursquare entities.     

Experimental studies of sublimation of highly volatile ices in relevance to the ices of the solar system

Studies of sublimation of complex ices prepared by deposition of gaseous CO, CH₄, N₂, and NH₃ molecules on a cold plate have been performed. The low pressure and low temperature system was used: 10^?9–10^?5 mbar and the lowermost temperature 10 K. Diagnostic of composition of evaporates (at an actual temperature) was done by means of the mass spectrometer. The latter allowed following simultaneously the partial pressure of five different ions or radicals escaping from the substrate. It has been found that highly volatile molecules that were used simultaneously with the low volatile ones to form the complex ices (mixtures or clathrates) present a different sublimation pattern than the sublimation of pure high-volatile ices. In particular, the high-volatile component sublimes at two or even three different temperature regimes: At low temperature that is typical for sublimation of this component, as well as at much higher temperatures. This effect seems to be important when degassing and outbursts from cometary nuclei are considered. It can be also important for modeling of cryovolcanic processes on the icy satellites.     

Accretion in Strong Gravity: from Galactic to Supermassive Black Holes

The galactic black hole binary systems give an observational template showing how the accretion flow changes as a function of increasing mass accretion rate, or L/L_Edd. These data can be synthesised with theoretical models of the accretion flow to give a coherent picture of accretion in strong gravity, in which the major hard-soft spectral transition is triggered by a change in the nature and geometry of the inner accretion flow from a hot, optically thin plasma to a cool, optically thick accretion disc. However, a straightforward application of these models to AGN gives clear discrepancies in overall spectral shape. Either the underlying accretion model is wrong, despite its success in describing the Galactic systems and/or there is additional physics which breaks the simple scaling from stellar to supermassive black holes.     

Global dynamics of the Gliese 876 planetary system

The Gliese 876 planetary system consists of two Jupiter-like planets having a nearly commensurate 2:1 orbital periods ratio. Because the semimajor axes of the planets are very small (of the order 0.1 au and 0.2 au, respectively), and the eccentricity of the inner companion is ≃0.3, the mutual perturbations are extremely large. However, many authors claim the long-term orbital stability of the system, at least over 500 Myr for initial conditions found by Rivera & Lissauer. Results of investigations of a migration of initially separated planets into the close 2:1 mean motion resonance lock from Lee & Peale also support the conclusion that the system should be stable for the lifetime of the parent star. Initial conditions of the system, found from non-linear N -body fits by Laughlin & Chambers and Rivera & Lissauer, to the radial velocity curve, formally allow for a variety of orbital configurations of the GJ 876 system, e.g. coplanar, with planetary inclinations in the range [≃30°, 90°], and with relative inclinations of orbital planes as high as 80°. Our work is devoted to the stability investigation of the systems originating from the fitted initial conditions. We study neighbourhoods of these initial states in the orbital parameter space. We found estimations of the 2:1 mean motion resonance width and dynamical limitations on the planetary masses. We also obtain a global representation of the domains of the orbital parameters space in which initial conditions leading to stable evolutions can be found. Our results can be useful in localization of the best, stable fits to the observational data. In our investigations we use the MEGNO technique (the Mean Exponential Growth factor of Nearby Orbits) invented by Cincotta & Simó. It allows us to distinguish efficiently and precisely between chaotic and regular behaviour of a planetary system.     

Evolutionary Status of Late-type Contact Binaries: Case of a 1.2+1 M ⊙ Binary

It is argued that typical W UMa-type stars are old, advanced evolutionary objects, similar to Algols, in the sense that they are past mass exchange resulting in a mass ratio inversion. Their secondaries are oversized due to depletion of hydrogen, and in many cases they possess small helium cores. An alternative evolutionary scenario leading to such a configuration is presented. Differences between the evolution of binaries with the initial mass ratio far and close to unity are discussed.     

Modelling of Shape Changes of the Nuclei of Comets C/1995 O1 Hale–Bopp and 46P/Wirtanen Caused by Water Ice Sublimation

The aim of this modelling work is to assess shape changes of cometary nuclei caused by sublimation of ices. The simplest possible model is assumed with the nucleus being initially spherical and its thermal conductivity being neglected. We have calculated the time-dependent sublimation flux versus cometographic latitude. If the rotation axis of the comet is inclined to the orbital plane, then sublimation leads to non-symmetrical changes of the nucleus shape. Calculations were performed for the nuclei of comets Hale–Bopp and Wirtanen.