The first decades of Doppler-free two-photon spectroscopy
Publication date: Available online 16 May 2019Source: Comptes Rendus PhysiqueAuthor(s): François BirabenAbstractThis paper gives a review of the Doppler-free two-photon experiments performed since the beginning of the 1970s until the end of the 1990s. The Doppler-free two-photon method was first tested on the sodium atom, then used extensively to study the hydrogen atom and measure the Rydberg constant and the Lamb shifts.RésuméCet article présente une revue des expériences de spectroscopie à deux photons sans effet Doppler, réalisées depuis le début des années 1970 jusqu'à la fin des années 1990. La méthode d...
Source: Comptes Rendus Physique - May 18, 2019 Category: Physics Source Type: research
A new test of gravitational redshift using Galileo satellites: The GREAT experiment
We present the result of the analysis of the GREAT (Galileo gravitational Redshift test with Eccentric sATellites) experiment. An elliptic orbit induces a periodic modulation of the fractional frequency difference between a ground clock and the satellite clock, partly due to the gravitational redshift, while the good stability of Galileo clocks allows one to test this periodic modulation to a high level of accuracy. GSAT0201 and GSAT0202, with their large eccentricity and on-board H-maser clocks, are perfect candidates to perform this test. Satellite laser ranging data allows us to partly decorrelate the orbit perturbation...
Source: Comptes Rendus Physique - May 10, 2019 Category: Physics Source Type: research
A new dual system for the fundamental units including and going beyond the newly revised SI
Publication date: Available online 6 May 2019Source: Comptes Rendus PhysiqueAuthor(s): Pierre FayetAbstractWe propose a new system for the fundamental units, which includes and goes beyond the present redefinition of the SI, by choosing also c=ħ=1. By fixing c=c∘ m/s=1, ħ=ħ∘ J s = 1 and μ∘_=μ∘ N/A=21, it allows us to define the metre, the joule, and the ampere as equal to (1/ 299 792 458) s, (1/ħ∘=.948...×1034)s−1 and μ∘N=μ∘c∘/ħ∘s−1=1.890...×1018s−1. It presents at the same time the advantages and elegance of a system with ħ=c=μ∘_=ϵ∘_=k=NA=1, where the vacuum m...
Source: Comptes Rendus Physique - May 7, 2019 Category: Physics Source Type: research
The ampere and the electrical units in the quantum era
Publication date: Available online 6 May 2019Source: Comptes Rendus PhysiqueAuthor(s): Wilfrid Poirier, Sophie Djordjevic, Félicien Schopfer, Olivier ThévenotAbstractBy fixing two fundamental constants from quantum mechanics, the Planck constant h and the elementary charge e, the revised “Système international” (SI) of units endorses explicitly quantum mechanics. This evolution also highlights the importance of this theory that underpins the most accurate realizations of the units. From 20 May 2019 onwards, the new definitions of the kilogram and of the ampere, based on fixed values of h and e, respectively, will pa...
Source: Comptes Rendus Physique - May 7, 2019 Category: Physics Source Type: research
State of the art in the determination of the fine-structure constant and the ratio h/mu
Publication date: Available online 12 April 2019Source: Comptes Rendus PhysiqueAuthor(s): Pierre Cladé, François Nez, François Biraben, Saïda Guellati-KhelifaAbstractThe fine structure constant α and the ratio h/mu between the Planck constant and the unified atomic mass are keystone constants for the determination of other fundamental physical constants, especially the ones involved in the framework of the future International System of units. This paper presents how these two constants, which can be deduced from one another, are measured. We will present in detail the measurement of h/mRb performed by atomic interfer...
Source: Comptes Rendus Physique - April 14, 2019 Category: Physics Source Type: research
Evaluation of the effect of a phase-change material on the thermal response of a bizone building under the climatic conditions of Tunisia
Publication date: Available online 10 April 2019Source: Comptes Rendus PhysiqueAuthor(s): Nour Ben Taher, Nour Lajimi, Noureddine BoukadidaAbstractThis paper extends the thermoelectric analogy method to study the thermal behavior of a concrete envelope of a dual-zone building containing microencapsulated phase-change material (PCM) and subjected to realistic climatic conditions based on weather data for a typical summer day in Tunisia. This work deals with a numerical study based on the nodal method to predict the effect of phase change on the thermal response as well as the energy flux reduction associated with the compos...
Source: Comptes Rendus Physique - April 11, 2019 Category: Physics Source Type: research
André Guinier: Local order in condensed matter
Publication date: Available online 9 April 2019Source: Comptes Rendus PhysiqueAuthor(s): Jean-Paul Pouget, Anne-Marie Levelut, Jean-François SadocAbstractThis contribution is a tribute to André Guinier and to the scientific school he created. We show how his thesis work allowed one to develop new X-ray scattering techniques of investigation of matter both at small and large scattering Bragg angles. In parallel to his pioneering experimental work, André Guinier introduced a well-adapted formalism allowing a precise characterization of various types of local order in the matter. These findings, which have been extended by...
Source: Comptes Rendus Physique - April 10, 2019 Category: Physics Source Type: research
Bayesian fusion of GNSS, ITS-G5 and IR–UWB data for robust cooperative vehicular localization
Publication date: Available online 8 April 2019Source: Comptes Rendus PhysiqueAuthor(s): Gia Minh Hoang, Benoît Denis, Jérôme Härri, Dirk SlockAbstractIn the automotive domain, Cooperative Localization (CLoc) is a new promising paradigm that aims at outperforming conventional Global Navigation Satellite Systems (GNSS) in terms of positioning accuracy, robustness, and service continuity, by relying on Vehicle-to-Vehicle (V2V) communications and hybrid data fusion. However, the growing number and the variety of the sensors aboard vehicles raise unprecedented challenges, especially in the context of distributed fusion app...
Source: Comptes Rendus Physique - April 10, 2019 Category: Physics Source Type: research
Autonomous system for data collection: Location and mapping issues in post-disaster environment
Publication date: Available online 3 April 2019Source: Comptes Rendus PhysiqueAuthor(s): Tullio Joseph Tanzi, Jean IsnardAbstractDisaster relief requires many resources. Depending on the circumstances of each event, it is important to rapidly choose the suitable means to respond to the emergency intervention. A brief review of the conditions and means demonstrated the usefulness of an autonomous stand-alone machine for these missions. If many techniques and technologies exist, their relevant combination to achieve such a system presents several challenges. This communication tries to outline the possible achievement of an ...
Source: Comptes Rendus Physique - April 4, 2019 Category: Physics Source Type: research
The Kibble balance and the kilogram
This article explains the Kibble balance, its role in the redefinition of the unit of mass, and attempts an outlook of the future.RésuméBryan Kibble a inventé la balance du watt en 1975 pour améliorer la réalisation de l'unité de courant électrique, l'ampère. Après la découverte de l'effet Hall quantique en 1980 par Klaus von Klitzing, conjointement avec un autre effet quantique prédit par Josephson, cet instrument mécanique peut être utilisé pour mesurer la constante de Planck h. Quinn, Mills, Williams, Taylor et Mohr ont proposé d'utiliser la balance de Kibble pour réaliser l'unité de masse, le kilogramm...
Source: Comptes Rendus Physique - March 27, 2019 Category: Physics Source Type: research
Studies on the cold binary fragmentation of even–even 230–250U isotopes
Publication date: Available online 25 March 2019Source: Comptes Rendus PhysiqueAuthor(s): Kolathu Parambil Santhosh, Annu CyriacAbstractWithin the framework of the Coulomb and proximity potential model (CPPM), we studied the cold binary fission of even–even 230–250U isotopes using the two versions of the nuclear proximity potential, Proximity 1977 and Proximity 2000. The most favorable binary fission path is the one that has a high Q value and a minimum driving potential with respect to the mass and charge asymmetries. A nucleus with doubly-closed shell or near doubly-closed shell always appears as the heaviest nucleus...
Source: Comptes Rendus Physique - March 27, 2019 Category: Physics Source Type: research
Benefits of space-time diversity for radar
Publication date: Available online 26 March 2019Source: Comptes Rendus PhysiqueAuthor(s): François Le Chevalier, Nikita PetrovAbstractWhen designing a new radar system, standard resolution trade-offs play a major role, providing the basic parameters of the radar, such as size, update rate, and range. Besides, diversity has long been used for mitigating fading effects due to the fluctuation of targets and clutter.However, with the arrival of more flexible systems, using multiple parallel channels on transmit and receive, and wider instantaneous bandwidths, these standard trade-offs are becoming less simple—and more flexi...
Source: Comptes Rendus Physique - March 27, 2019 Category: Physics Source Type: research
Analyzing gravitational waves with general relativity
We describe these effects within a simple Newtonian model.RésuméAprès une brève revue des propriétés importantes des ondes gravitationnelles et de la nouvelle astronomie gravitationnelle, nous nous concentrons sur les aspects théoriques. Les méthodes d'approximation analytiques en relativité générale ont joué un rôle crucial dans les récentes détections d'ondes gravitationnelles. Elles sont utilisées pour créer des banques de modèles (patrons) théoriques qui servent à rechercher et analyser les signaux dans les détecteurs au sol LIGO et Virgo et dans les détecteurs dans l'espace de type LISA, dévelop...
Source: Comptes Rendus Physique - March 8, 2019 Category: Physics Source Type: research
The unit of time: Present and future directions
Publication date: Available online 26 February 2019Source: Comptes Rendus PhysiqueAuthor(s): Sébastien BizeAbstractSome 50 years ago, physicists, and after them the entire world, started to found their time reference on atomic properties instead of motions of the Earth that have been in use since the origin. Far from being an arrival point, this decision marked the beginning of an adventure characterized by an improvement by 6 orders of magnitude in the uncertainty of realization of atomic frequency and time references. Ever-progressing atomic frequency standards and time references derived from them are key resources for...
Source: Comptes Rendus Physique - February 27, 2019 Category: Physics Source Type: research
Astronomical distance scales
This article is an overview of the determination of astronomical distances from a metrological standpoint. Distances are considered from the Solar System (planetary distances) to extragalactic distances, with a special emphasis on the fundamental step of the trigonometric stellar distances and the giant leap recently experienced in this field thanks to the ESA space astrometry missions Hipparcos and Gaia.RésuméCet article donne un aperçu de la détermination des distances astronomiques d'un point de vue métrologique. Les distances sont prises en compte depuis le système solaire (distances planétaires) jusqu'aux dista...
Source: Comptes Rendus Physique - February 20, 2019 Category: Physics Source Type: research
