Galilée (savant)

Résumé

Galilée (Galileo Galilei), né à Pise le et mort à Arcetri près de Florence le , est un mathématicien, géomètre, physicien et astronome italien du . Parmi ses réalisations techniques, il a perfectionné et exploité la lunette astronomique, perfectionnement de la découverte hollandaise d'une lunette d'approche, pour procéder à des observations rapides et précoces qui ont bouleversé les fondements de l'astronomie. Cet homme de sciences s'est ainsi posé en défenseur de l'approche modélisatrice copernicienne de l'Univers, proposant d'adopter l'héliocentrisme et les mouvements satellitaires. Ses observations et généralisations se sont alors heurtées aux critiques des philosophes partisans d'Aristote (proposant un géocentrisme stable, une classification des corps et des êtres, un ordre immuable des éléments et une évolution réglée des substances et des scientifiques attachés au modèle de Ptolémée), ainsi qu'à une partie des théologiens de l'Église catholique romaine et des Églises protestant

Source officielle

https://fr.wikipedia.org/wiki/Galil%C3%A9e_(savant)

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (16)

Publications associées

Chargement

Personnes associées (4)

Personnes associées

Chargement

Unités associées (3)

Unités associées

Chargement

Concepts associés (172)

Concepts associés

Chargement

Cours associés (25)

Cours associés

Chargement

Séances de cours associées (52)

Séances de cours associées

Chargement

A flexible Galileo E1 Receiver Platform for the Validation of Low Power and Rapid Acquisition Schemes

Marcel Baracchi Frei, Cyril Botteron, Frédéric Chastellain, Pierre-André Farine, Davide Manetti, Giuseppe Zamuner

With the inclusion of 406 MHz transponders on the Galileo satellites and the new search and rescue (SAR) return link message (RLM) on the open service E1B signal, the availability of distress beacons equipped with a Galileo or combined GPS/Galileo receiver will be very important in the future to take advantage of the SAR RLM, thereby facilitating the rescue operations and helping to identify and reject false alerts. Consequently, this paper provides the status of the development of a flexible Galileo L1 receiver platform as well as an analysis and comparison of acquisition schemes suitable to be implemented in 406 MHz Cospas-Sarsat distress beacons. For each considered acquisition scheme, we compare the acquisition performance that can be obtained using GPS L1 C/A or Galileo E1B or E1C signals and consider and discuss the following main constraints: a very short time to first fix (TTFF) in cold start conditions (the beacon’s GNSS receiver may not be powered on for years before it is activated in an emergency); a low energy consumption per position fix (the beacon and GNSS receiver are battery powered); a possibly long coherent integration time to achieve synchronization and tracking in harsh environments (e.g., when some or all of the satellite signals are blocked or attenuated by an obstruction); the ability to demodulate the satellites signals in the presence of a 406MHz/5W and a 121.5MHz/(up to 100mW) beacon transmitters; and a low complexity (low price).

2006

Chargement

General coordinate invariance in quantum many-body systems

Solomon G Shamsuddin Osman Endlich, Alexander Monin

We extend the notion of general coordinate invariance to many-body, not necessarily relativistic, systems. As an application, we investigate nonrelativistic general covariance in Galilei-invariant systems. The peculiar transformation rules for the background metric and gauge fields, first introduced by Son and Wingate in 2005 and refined in subsequent works, follow naturally from our framework. Our approach makes it clear that Galilei or Poincare symmetry is by no means a necessary prerequisite for making the theory invariant under coordinate diffeomorphisms. General covariance merely expresses the freedom to choose spacetime coordinates at will, whereas the true, physical symmetries of the system can be separately implemented as "internal" symmetries within the vielbein formalism. A systematic way to implement such symmetries is provided by the coset construction. We illustrate this point by applying our formalism to nonrelativistic s-wave superfluids.

Amer Physical Soc2014

Chargement

, , , ,

The current Search-and-Rescue (SAR) service, which is based on the Cospas-Sarsat system, suffers from major limitations such as poor position accuracy, long alert times and high false alarm rate. Two types of distress signals are used, the 121.5MHz/(up to 100mW) signal and the 406.8MHz/5W signal, the latter being able to carry digitally encoded data, such as the beacon’s position. As a consequence, most distress beacons available today contain a GNSS receiver in order to be able to include the position into the distress message. Galileo will importantly contribute to the improvement of the SAR system. Indeed, the Galileo satellites will include a transponder in order to re-broadcast the 406.8MHz message, which will allow a better coverage of the earth (27 Galileo satellites plus the current seven Cospas-Sarsat satellites) and also a shorter alert time. They will also include a return link message (RLM) in the Galileo E1b open service signal, which will reduce the number of false alarms. Galileo is therefore a great opportunity for the development of a new generation of beacons which will include a Galileo receiver and therefore be able to take advantage of the better coverage provided by the Galileo constellation to provide shorter alert times and of the RLM to reduce the number of false alarms. One of the major issue when designing a Galileo receiver to be operated in a distress beacon is to design a front-end that is sensitive enough to pick the very weak E1b signal in the presence of the strong distress signals. Indeed, in order to receive the RLM message, the Galileo receiver will have to track E1b while the distress signals are emitted. This paper presents a Galileo radio frequency front-end designed in order to operate in the presence of such signals.

2007

Chargement