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Jorda L.,Aix - Marseille University | Gaskell R.,Planetary Science Institute | Capanna C.,Aix - Marseille University | Hviid S.,Planetary Science Institute | And 47 more authors.
Icarus | Year: 2016

The Rosetta spacecraft reached Comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) in August 2014 at an heliocentric distance of 3.6 a.u. and was then put in orbit around its nucleus to perform detailed observations. Among the collected data are the images acquired by the OSIRIS instrument up to the perihelion passage of the comet in August 2015, which allowed us to map the entire nucleus surface at high-resolution in the visible. Stereophotoclinometry methods have been used to reconstruct a global high-resolution shape model and to monitor its rotational parameters using data collected up to perihelion.The nucleus has a conspicuous bilobate shape with overall dimensions along its principal axes of (4.34 ± 0.02) × (2.60 ± 0.02) × (2.12 ± 0.06) km. The best-fit ellipsoid dimensions of the individual lobes along their principal axes of inertia are found to be 4.10 × 3.52 × 1.63 km and 2.50 × 2.14 × 1.64 km. Their volume amounts to 66% and 27% of the total volume of the nucleus. The two lobes are connected by a "neck" whose volume has been estimated to represent ~7% of the total volume of the comet. Combining the derived volume of 18.8 ± 0.3 km3 with the mass of 9.982 ± 0.003 × 1012 kg determined by the Rosetta/RSI experiment, we obtained a bulk density of the nucleus of 532±7kgm-3. Together with the companion value of 535±35kgm-3 deduced from the stereophotogrammetry shape model of the nucleus (Preusker et al. [2015] Astron. Astrophys. 583, A33), these constitute the first reliable and most accurate determination of the density of a cometary nucleus to date. The calculated porosity is quite large, ranging approximately from 70% to 75% depending upon the assumed density of the dust grains and the dust-to-ice mass ratio. The nature of the porosity, either micro or macro or both, remains unconstrained. The coordinates of the center of gravity are not compatible with a uniform nucleus density. The direction of the offset between the center of gravity and the center of figure suggests that the big lobe has a slightly higher bulk density compared to the small one. the center of mass position cannot be explained by different, but homogenous densities in the two lobes.The initial rotational period of 12.4041 ± 0.0001 h of the nucleus persisted until October 2014. It then slightly increased to a maximum of 12.4304 h reached on 19 May 2015 and finally dropped to 12.305 h just before perihelion on August 10, 2015. A periodogram analysis of the (RA, Dec) direction of the Z-axis of the comet obtained in parallel with the shape reconstruction exhibits a highly significant minima at 11.5 ± 0.5 day clearly indicating an excited rotational state with an amplitude of 0.15 ± 0.03°. © 2016 Elsevier Inc. Source


Rahni A.,AKKA Technologies | Grolleau E.,University of Poitiers | Richard M.,University of Poitiers | Richard P.,University of Poitiers
Real-Time Systems | Year: 2012

The objective of this paper is two-fold: give a survey of response time analysis (RTA), and contribute to schedulability analysis for the real-time transaction model. The RTA is studied under fixed priority policies (FPP), while schedulability analysis assumes an optimal scheduling algorithm (like the deadline driven scheduling algorithm EDF) in a preemptive context on uniprocessor systems. We compare the transaction model to the family of multiframe models, then present the exact, and approximated methods, as well as a tunable method to compute the RTA. Finally we present a new schedulability analysis method and an efficient algorithm to speed up this test. © 2012 Springer Science+Business Media, LLC. Source


Jurik T.,School of Engineering in Information and Communication Science and Technology | Jurik T.,Brno University of Technology | Cela A.,School of Engineering in Information and Communication Science and Technology | Cela A.,Supelec | And 5 more authors.
IEEE Intelligent Transportation Systems Magazine | Year: 2014

The rapid development of Mobile Internet and Smart Devices and advent of a new generation of Intelligent Transportation Systems (ITS) increase information about present driving conditions and make its prediction possible. Real time traffic information systems (TIS) like SYTADIN help in route to destination planning and traffic state prediction. Energy-optimal routing for electric vehicles creates novel algorithmic challenges where the computation complexity and the quality of information on traffic state are the main issues. This complexity is induced by the possible negative values of edge energy as well as the variability of route and vehicle variables which render the standard algorithms unsuitable. In this paper we present an Energy Optimal Real Time Navigation System (EORTNS), implemented on Samsung Galaxy Tab, capable of calculating the route to destination based on information flow obtained from SYTADIN. As an application example we propose a real time energy management for a Hybrid Electrical Vehicle (HEV) composed of batteries and Super-Capacitors (SC). The EORTNS is not only capable of energy optimal route to destination calculation with respect to traffic state but also operates the On-Board power splitting between batteries and Super-Capacitors. © 2009-2012 IEEE. Source


Moezzi K.,AKKA Technologies | Aghdam A.G.,Concordia University at Montreal
International Journal of Robust and Nonlinear Control | Year: 2015

In this paper, sufficient conditions are provided for the stability of switched retarded and neutral time-delay systems with polytopic-type uncertainties. It is assumed that the delay in the system dynamics is time-varying and bounded. Parameter-dependent Lyapunov functionals are employed to obtain criteria for the exponential stability of the system in the form of linear matrix inequality (LMI). Free-weighting matrices are then provided to express the relationship between the system variables and the terms in the Leibniz-Newton formula. Numerical examples are presented to show the effectiveness of the results. Copyright © 2014 John Wiley & Sons, Ltd. Source


Jurik T.,School of Engineering in Information and Communication Science and Technology | Cela A.,School of Engineering in Information and Communication Science and Technology | Hamouche R.,School of Engineering in Information and Communication Science and Technology | Reama A.,School of Engineering in Information and Communication Science and Technology | And 4 more authors.
IEEE Conference on Intelligent Transportation Systems, Proceedings, ITSC | Year: 2013

Real time traffic information systems like SYTADIN[11] help in route to destination planning and traffic state prediction. Energy-optimal routing for electric vehicles creates novel algorithmic challenges where the computation complexity is the main issue. This complexity is induced by the possible negative values of edge energy as well as the variability of route and vehicle variables which render the standard algorithms unsuitable (inapplicable). In this paper we present an Energy Optimal Real Time Navigation System (EORTNS), implemented on Samsung Galaxy Tab, capable of calculating the route to destination based on a information flow obtained from SYTADIN. As an application example we propose a real time energy management for a Hybrid Electrical Vehicle (HEV) composed of batteries and Super-Capacitors (SC). The EORTNS is not only capable of energy optimal route to destination calculation with respect to traffic state but also operates the On-Board power splitting between batteries and Super-Capacitors. Based on calculated 3D energy optimal route to destination and average speeds for each road segment as well as the vehicle model the state of charge (SOC) of batteries and Super-Capacitors for each receding horizon are predicted and modified in real time. © 2013 IEEE. Source

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