No abstract

We investigate classical planetesimal accretion in a binary star system of separation a b ≤50 AU by numerical simulations, with particular focus on the region at a distance of 1 AU from the primary. The planetesimals orbit the primary, are perturbed by the companion and are in addition subjected to a gas drag force. We concentrate on the problem of relative velocities ∆v among planetesimals of different sizes. For various stellar mass ratios and binary orbital parameters we determine regions where ∆v exceed planetesimal escape velocities v esc (thus preventing runaway accretion) or even the threshold velocity v ero for which erosion dominates accretion. Gaseous friction has two crucial effects on the velocity distribution: it damps secular perturbations by forcing periastron alignment of orbits, but at the same time the size-dependence of this orbital alignment induces a significant ∆v increase between bodies of different sizes. This differential phasing effect proves very efficient and almost always increases ∆v to values preventing runaway accretion, except in a narrow e b ≃ 0 domain. The erosion threshold ∆v > v ero is reached in a wide (a b , e b ) space for small < 10 km planetesimals, but in a much more limited region for bigger ≃ 50 km objects. In the intermediate v esc < ∆v < v ero domain, a possible growth mode would be the type II runaway growth identified by Kortenkamp et al. (2001).

Part 3: Open Government and TransformationInternational audienceThis study presents the first results of an analysis primarily based on semi-structured interviews with government officials and managers who are responsible for smart city initiatives in four North American cities—Philadelphia and Seattle in the United States, Quebec City in Canada, and Mexico City in Mexico. With the reference to the Smart City Initiatives Framework that we suggested in our previous research, this study aims to build a new understanding of smart city initiatives. Main findings are categorized into eight aspects including technology, management and organization, policy context, governance, people and communities, economy, built infrastructure, and natural environment

No abstract