Dynamics of the radiative envelope of rapidly rotating stars: Effects of spin-down driven by mass loss

(abridged) This paper aims at deciphering the dynamics of the envelope of a rotating star when some angular momentum loss due to mass loss is present. We especially wish to know when the spin-down flow forced by the mass loss supersedes the baroclinic flows that pervade the radiative envelope of rotating stars. We consider a Boussinesq fluid enclosed in a rigid sphere whose flows are forced both by the baroclinic torque, the spin-down of an outer layer, and an outward mass flux. The spin-down forcing is idealized in two ways: either by a rigid layer that imposes its spinning down velocity at some interface or by a turbulent layer that imposes a stress at this same interface to the interior of the star. In the case where the layer is rigid and imposes its velocity, we find that, as the mass-loss rate increases, the flow inside the star shows two transitions: the meridional circulation associated with baroclinic flows is first replaced by its spin-down counterpart, while at much stronger mass-loss rates the baroclinic differential rotation is superseded by the spin-down differential rotation. In fact, we find three wind regimes: weak (or no wind), moderate, and strong. In the first case, the flow in the radiative envelope is of baroclinic origin. In the moderate case, the circulation results from the spin-down while the differential rotation may either be of baroclinic or of spin-down origin, depending on the coupling between mass and angular momentum losses. For fast rotating stars, our model says that the moderate wind regime starts when mass loss is higher than ~1e-11 Msun/yr. In the strong wind case, the flow in the radiative envelope is mainly driven by angular momentum advection. This latter transition depends on the mass and the rotation rate of the star, being around 1e-8 Msun/yr for a 3 Msun ZAMS star rotating at 200 km/s according to our model.Comment: 13 pages, 9 figures, to appear in Astronomy and Astrophysic

Low-rank Similarity Measure for Role Model Extraction

Computing meaningful clusters of nodes is crucial to analyze large networks. In this paper, we present a pairwise node similarity measure that allows to extract roles, i.e. group of nodes sharing similar flow patterns within a network. We propose a low rank iterative scheme to approximate the similarity measure for very large networks. Finally, we show that our low rank similarity score successfully extracts the different roles in random graphs and that its performances are similar to the pairwise similarity measure.Comment: 7 pages, 2 columns, 4 figures, conference paper for MTNS201

Performances of a GNSS receiver for space-based applications

Space Vehicle (SV) life span depends on its station keeping capability. Station keeping is the ability of the vehicle to maintain position and orientation. Due to external perturbations, the trajectory of the SV derives from the ideal orbit. Actual positioning systems for satellites are mainly based on ground equipment, which means heavy infrastructures. Autonomous positioning and navigation systems using Global Navigation Satellite Systems (GNSS) can then represent a great reduction in platform design and operating costs. Studies have been carried out and the first operational systems, based on GPS receivers, become available. But better availability of service could be obtained considering a receiver able to process GPS and Galileo signals. Indeed Galileo system will be compatible with the current and the modernized GPS system in terms of signals representation and navigation data. The greater availability obtained with such a receiver would allow significant increase of the number of point solutions and performance enhancement. For a mid-term perspective Thales Alenia Space finances a PhD to develop the concept of a reconfigurable receiver able to deal with both the GPS system and the future Galileo system. In this context, the aim of this paper is to assess the performances of a receiver designed for Geosynchronous Earth Orbit (GEO) applications. It is shown that high improvements are obtained with a receiver designed to track both GPS and Galileo satellites. The performance assessments have been used to define the specifications of the future satellite GNSS receiver

Chemical vapour deposition and atomic layer deposition of amorphous and nanocrystalline metallic coatings: towards deposition of multimetallic films

This paper provides a prospective insight on chemical vapour deposition (CVD) and atomic layer deposition (ALD) as dry techniques for the processing of amorphous and nanocrystalline metallic thin films. These techniques are part of major technologies in application fields such as microelectronics, energy, or protective coatings. From thermodynamic analysis, areas of investigation to generate a set of materials with the strongest propensity for amorphization as well as useful guidelines for the target phase material deposition are provided. Prospective to develop MOCVD (metalorganic chemical vapour deposition) and ALD of intermetallic films, in view of fabrication of metallic glass thin films is proposed. Examples from selected ALD and MOCVD single element metallic deposition processes will be described to illustrate the effect of deposition parameters on the physico-chemical properties of the films. This processing approach is particularly promising for metallic glass thin films

Le passe Navigo anonyme revisité

Colloque: Les libertés à l'épreuve de l'informatiqueInternational audienceNavigo pass could be offered for free if there was no opposition between CNIL and RATP: CNIL asks for immediate anonymisation of transit data while RATP supported by STIF would like to make use of them. The example of the Dutch OV chipcard of Translink and of the German VDV chipcard shows a possible combination of anonymous card with personalised transit data. The reason for observed divergences comes from the notion of personal data which is handled differently in France and other European countries such as the Netherlands and Germany. Definition and role of trusted third party would allow to better control the link between personal and transit data with the coming of age of electronic ticketingLe passe Navigo anonyme pourrait parfaitement fonctionner gratuitement s'il n'y avait pas un blocage entre la CNIL et la RATP : la CNIL demande l'anonymisation des données de transit quasi immédiatement tandis que la RATP soutenue par le STIF voudrait pouvoir les exploiter davantage. L'exemple de la carte électronique de transport hollandaise (OV chipcard de Translink) et allemande (chipcard de la VDV) montre la combinaison possible d'une carte anonyme avec des données de transit personnalisées. La raison des divergences observées provient du fait que la notion de données personnelles est abordée de manière différente en France et dans d'autres pays européens tels que la Hollande et l'Allemagne. La définition du rôle et des responsabilités du tiers de confiance permettrait de mieux contrôler le lien entre données personnelles et données de transit avec l'arrivée des titres de transport dématérialisés

RFID Security and Privacy

The European Commission has published in May 2009 a recommendation "on the implementation of privacy and data protection principles in applications supported by radio-frequency identification", which is designed to provide "guidance to Member States on the design and operation of RFID applications in a lawful, ethical and socially and politically acceptable way, respecting the right to privacy and ensuring protection of personal data." This recommendation requires RFID operators to conduct a "Privacy and Data Protection Impact Assessment" before an RFID application is deployed, and make its results available to the competent authority. The RFID recommendation is also designed to promote "information and transparency on RFID use", in particular through the development of "a common European sign developed by European Standardisation Organisations, with the support of concerned stakeholders", designed "to inform individuals of the presence of readers". The RFID PIA (Privacy and Impact Asssessment) process aims to reach several objectives: * to favour "privacy by design" by helping data controllers to address privacy and data protection before a product or service is deployed, * to help data controllers to address privacy and data protection risks in a comprehensive manner. an opportunity to reduce legal uncertainty and avoid loss of trust from consumers, * to help data controllers and data protection authorities to gain more insight into the privacy and data protection aspects of RFID applications. The industry has proposed a RFID PIA framework which classifies a RFID application into 4 possible levels: Level 0 applications, which essentially cover RFID applications that do not process personal data and where tags are only manipulated by users, and which are rightly excluded from conducting a PIA. Level 1 applications cover applications where no personal data is processed, yet tags are carried by individuals. Level 2 applications process personal data but where tags themselves do not contain personal data. Level 3 applications where tags contain personal data. If the RFID application level is determined to be 1 or above, the RFID operator is then required to conduct a four part analysis of the application, with a level of detail that is proportionate to identified privacy and data protection implications. The first part is used to describe the RFID application. The second part allows highlighting control and security measures. The third part addresses user information and rights. The final part of the proposed PIA framework requires the RFID operator to conclude whether or not the RFID application is ready for deployment. As a result of the PIA process, the RFID operator will produce a PIA report that will be made available to the competent authority. For the industry, only levels 2 and 3 are to be submitted to a PIA because it considers that information contained in a tag at level 1 are not personal. However level 1 arises concerns of Article 29 Working Party because tagged items carried by a person contain unique identifiers that could be read remotely. In turn, these unique identifiers could be used to recognize that particular person through time. It raises the possibility that a person will be tracked without his knowledge by a third party. When a unique identifier is associated to a person, it falls in the definition of personal data set forth in Directive 95/46/EC, regardless of the fact that the "social identity" (name, address, etc.) of the person remains unknown (i.e. he is "identifiable" but not necessarily "identified"). Additionally, the unique number contained in a tag can also serve as a means to remotely identify the nature of items carried by a person, which in turn may reveal information about social status, health, or more. Thus, even in those cases where a tag contains solely a number that is unique within a particular context, and no additional personal data, care must be taken to address potential privacy and security issues if this tag is going to be carried by persons. The Working Party has urged the industry to fully address this issue, by clearly mentioning it in the framework as part of a revised risk assessment approach for level 1. This chapter will address the issue of protecting privacy of RFID tag carriers in a privacy by design model which puts them in a position to decide if they accept or not to be tracked at level 1. In case of a negative decision, tags have to be deactivated. Security measures have also to be taken to protect personal information on RFID tags against information leak which could lead to identity theft