Atomic clocks: new prospects in metrology and geodesy

We present the latest developments in the field of atomic clocks and their applications in metrology and fundamental physics. In the light of recent advents in the accuracy of optical clocks, we present an introduction to the relativistic modelization of frequency transfer and a detailed review of chronometric geodesy.Comment: Proceedings of the Workshop "Relativistic Positioning Systems and their Scientific Applications" held in Brdo near Kranj, Slovenia, 19-21 September 2012. To appear in Acta Futura (http://www.esa.int/gsp/ACT/publications/ActaFutura/

Charactérisation à haute fréquence d'un jet balayant

International audienceSweeping jets are an emerging type of actuators that have gained interest due to their potential use in flow control applications. The working principle of these devices is based on the bi-stable attachment of a jet to adjacent walls. They are able to produce unsteady blowing within a wide range of operating frequencies. Nevertheless, the state of art shows a lack of space-time characterization of these actuators for high sweeping frequencies. This paper resents a conditional approach that reconstructs the spatial dynamic response of sweeping jets for sweeping frequencies above 500 Hz. The time-dependent velocity is measured with two single-hot-wire sensors: a reference one placed at the edge of the exit nozzle, and a flying one. The method is then tested to characterize the flow at the exit nozzle of an in-house sweeping jet actuator with 1mm space resolution, and 50 µs time resolution. These measurements are performed with a sweeping frequency of 639 Hz. Overall this paper demonstrates that the conditional approach is very useful for understanding the physics of flow control actuators.Les jets balayants sont des actionneurs fluidiques en pleine extension dans le domaine du contrôle actif des écoulements de par leur large gamme de fréquences et de vitesses. Ils se basent sur le phénomène de bi-stabilité de détachement de l'écoulement sur les parois interne de l'actionneur. Cependant la littérature montre une faiblesse pour la caractérisation expérimentale à haute fréquence de l'écoulement en sortie d'actionneur. Ce papier présente une méthode de reconstruction résolue en espace et en temps, basée sur une approche conditionnelle permettant de reconstruire l'écoulement pour des fréquence de balayage supérieures à 500Hz. Les signaux de vitesse résolus en temps sont mesurés à l'aide de deux fils chauds : un fixe pour le signal de synchronisation et un mobile, se déplaçant sur un maillage de finesse 1mm. Cette méthode est ensuite appliquée à un actionneur de jet balayant fonctionnant a une fréquence de 639Hz, avec un signal de vitesse de résolution temporelle de 50 micro secondes. Ce papier démontre ainsi que l'approche conditionnelle peut être utilisable pour comprendre la physique des écoulements en sortie d'actionneurs fluidiques

Pulsed air injection system characterization for stall margin improvement in an axial compressor

This paper presents the design and the characterization of a pulsed air injection system on a single stage axial compressor. The goal of this system is to delay the rotating stall onset and to extend the compressor operating range. The proposed control system consists in 20 injection blocks of 2 injectors, allowing to adjust some of the fluidic and geometrical parameters of the injected perturbations. Velocity, flow rate and momentum can be varied on a large range and the injectors can be rotated by 15° steps or replaced to change the yaw angle and the outlet section.The present work was supported by the ANR project NUMERICCS (ANR-15-CE06-0009), and this project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 886352

Small-width wall-attached Coandǎ jets for flow control

The flow dynamics of small-width wall-attached jets generated by a Coand-effect nozzle is investigated by unsteady Reynolds-averaged Navier–Stokes simulations. The data are validated by comparison with hot-wire velocity measurements performed on the same flow configurations. The jets exhibit a complex topology strongly influenced not only by the spanwise vorticity (as usually observed in wall jets) but also by a vorticity component normal to the wall and induced by the shear layer developing on the jet sides. This results in an original U-shaped jet whose characteristics are studied in detail for three different mass flow rates. The robustness of the flow topology on a larger range of injected mass flow rates is finally presented and discussed in terms of the injected momentum near the wall. The resulting flow profiles point out that our injector is expected to be a promising candidate for active flow control in gas-turbine compressors for aeronautical and energy applications

Test of special relativity using a fiber network of optical clocks

International audienc

Test of special relativity using a fiber network of optical clocks

International audienc

Chronometric Geodesy and Fundamental Physics

International audienceAtomic clocks are today essential for several daily life applications, such as the building of the International Atomic Time (TAI) or Global Navigation Satellite Systems (GNSS). With the new generation of optical clocks, they reach such accuracy and stability that they are now considered in practical applications for the measurement of gravitational potential differences, thanks to the Einstein effect, or gravitational redshift. Several projects explored the possibilities of using clocks in geodesy or geophysical applications and research. This context offers a fantastic opportunity to use atomic clocks to test fundamental physics. In this talk I will present two such studies for testing the gravitational redshift and Lorentz invariance.The first project is the "Galileo gravitational Redshift test with Eccentric sATellites" (GREAT), funded by the European Space Agency (ESA). Here we use the on-board atomic clocks of the Galileo satellites 5 and 6 to look for violations of general relativity theory. These two satellites were launched on August, 30th 2014 and, because of a technical problem, the launcher brought them on an elliptic orbit. An elliptic orbit induces a periodic modulation of the gravitational redshift while the good stability of recent GNSS clocks allows to test this periodic modulation to a very good level of accuracy. The Galileo 5 and 6 satellites, with their large eccentricity and on-board H-maser clocks, are hence perfect candidates to perform this test.In the second study we propose a test of special relativity theory using a network of distant optical lattice clocks located in France, Germany and Great-Britain. By exploiting the difference between the velocities of each clock in the inertial geocentric frame, due to their different positions on the surface of the Earth, we can test the time dilation effect. The connection between these clocks, achieved with phase-compensated optical fibers, allows for an unprecedented level of statistical resolution for the comparison of remote atomic clock, making such a test now competitive with the best Ives-Stillwell tests

Chronometric Geodesy and Fundamental Physics

International audienceAtomic clocks are today essential for several daily life applications, such as the building of the International Atomic Time (TAI) or Global Navigation Satellite Systems (GNSS). With the new generation of optical clocks, they reach such accuracy and stability that they are now considered in practical applications for the measurement of gravitational potential differences, thanks to the Einstein effect, or gravitational redshift. Several projects explored the possibilities of using clocks in geodesy or geophysical applications and research. This context offers a fantastic opportunity to use atomic clocks to test fundamental physics. In this talk I will present two such studies for testing the gravitational redshift and Lorentz invariance.The first project is the "Galileo gravitational Redshift test with Eccentric sATellites" (GREAT), funded by the European Space Agency (ESA). Here we use the on-board atomic clocks of the Galileo satellites 5 and 6 to look for violations of general relativity theory. These two satellites were launched on August, 30th 2014 and, because of a technical problem, the launcher brought them on an elliptic orbit. An elliptic orbit induces a periodic modulation of the gravitational redshift while the good stability of recent GNSS clocks allows to test this periodic modulation to a very good level of accuracy. The Galileo 5 and 6 satellites, with their large eccentricity and on-board H-maser clocks, are hence perfect candidates to perform this test.In the second study we propose a test of special relativity theory using a network of distant optical lattice clocks located in France, Germany and Great-Britain. By exploiting the difference between the velocities of each clock in the inertial geocentric frame, due to their different positions on the surface of the Earth, we can test the time dilation effect. The connection between these clocks, achieved with phase-compensated optical fibers, allows for an unprecedented level of statistical resolution for the comparison of remote atomic clock, making such a test now competitive with the best Ives-Stillwell tests

Etude du rôle de l'histone acétyltransférase MOZ dans l'hématopoïèse et la leucémogenèse

Ma thèse a porté sur l'étude du rôle de l'histone acétyltransférase MOZ (monocytic leukaemia zinc finger protein) dans l'hématopoïèse et la leucémogenèse. Le gène MOZ est impliqué dans plusieurs translocations chromosomiques retrouvées dans des leucémies aiguës myéloïdes (LAM). Nous avons étudié l interaction potentielle entre MOZ et MLL (mixed lineage leukemia), une histone méthyltransférase dont le gène est très fréquemment réarrangé dans les leucémies aiguës humaines. Nous avons montré que MOZ et MLL interagissent au sein d un même complexe protéique et coopèrent afin d activer la transcription de certains gènes HOX dans une population cellulaire humaine (CD34+) très enrichie en cellules souches hématopoïétiques (CSH). Les gènes HOX codent des facteurs de transcription indispensables à l embryogenèse et à l hématopoïèse (en particulier pour l auto-renouvellement des CSH), et impliqués dans la leucémogenèse. Afin d étudier précisément le rôle de MOZ dans l hématopoïèse murine, nous avons généré des souris déficientes pour Moz uniquement dans les cellules hématopoïétiques. Ces souris sont viables mais présentent des anomalies de l hématopoïèse en particulier au niveau des progéniteurs hématopoïétiques et des CSH. MOZ est donc impliquée dans la régulation de l hématopoïèse murine post-natale. Concernant la leucémogenèse associée à MOZ, nous avons généré des poissons-zèbres transgéniques exprimant une protéine de fusion de MOZ humaine (MOZ-TIF2). Ces poissons développent une LAM démontrant ainsi le très grand pouvoir leucémogène de cette protéine chimérique. Ces poissons constituent le premier modèle de LAM chez le poisson-zèbre.My thesis concerns the study of the role of the histone acetyltransferase MOZ (monocytic leukaemia zinc finger protein) in haematopoiesis and leukaemogenesis. MOZ gene is implicated in several chromosomal translocations found in acute myeloid leukaemia (AML). We studied the potential interaction between MOZ and MLL (mixed lineage leukemia), a histone methyltransferase whose gene is frequently translocated in human acute leukaemia. We showed that MOZ and MLL interact within a same complex and cooperate to activate transcription of HOX genes in a human cell population (CD34+) very enriched in haematopoietic stem cells (HSCs). HOX genes encode transcription factors essential for embryogenesis and haematopoiesis (particularly in HSCs self-renewal), and are involved in leukaemogenesis. To study precisely the role of MOZ in murine haematopoiesis, we generated deficient mice for Moz only in haematopoietic cells. These mice are viable but display abnormalities in haematopoiesis, in particular regarding haematopoietic progenitors and HSCs. Hence, MOZ is implicated in the regulation of adult murine haematopoiesis. Regarding leukaemogenesis associated with MOZ, we generated transgenic zebrafishes expressing a human MOZ fusion protein (MOZ-TIF2). Some fishes develop an AML, thus demonstrating the important leukaemogenic power of this chimeric protein. These fishes represent the first model of AML in zebrafish.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Évaluation expérimentale des interactions aérodynamiques rotor/propulseur pour les hélicoptères compound

International audienceThis paper focuses on the experimental evaluation of the rotor/propeller interactions for hybrid compound configurations. Experiments are conducted in the ONERA L2 large size-low speed wind tunnel with a 1/7.7 Dauphin 365N model and a four-bladed small-scale propeller. Measurements are realized using two six-component balances, accelerometers, and blade pitch, flap and lead-lag angle sensors. PIV measurements are performed to visualize the velocity fields around the helicopter. Different flight conditions (wind speeds and propeller rotational speeds) have been tested. The comparison of the results obtained with an isolated main rotor and an isolated propeller with the complete assembly highlighted the influence of their interactions on their performances. In hover, the propeller is completely immersed in the rotor wake, and the thrust is therefore maximal. At low speed, the propeller is partially immersed and the flow on the propeller disk is highly asymmetrical. No direct interactions are measured at high speed, where the interactions increase the performances of the propeller due to the increased angle of attack of the flow on the propeller disk