Interlaced spin grating for optical wave filtering

Interlaced Spin Grating is a scheme for the preparation of spectro-spatial periodic absorption gratings in a inhomogeneously broadened absorption profile. It relies on the optical pumping of atoms in a nearby long-lived ground state sublevel. The scheme takes advantage of the sublevel proximity to build large contrast gratings with unlimited bandwidth and preserved average optical depth. It is particularly suited to Tm-doped crystals in the context of classical and quantum signal processing. In this paper, we study the optical pumping dynamics at play in an Interlaced Spin Grating and describe the corresponding absorption profile shape in an optically thick atomic ensemble. We show that, in Tm:YAG, the diffraction efficiency of such a grating can reach 18.3% in the small angle, and 11.6% in the large angle configuration when the excitation is made of simple pulse pairs, considerably outperforming conventional gratings.Comment: 11 pages, 13 figures in Physical Review A, 201

Test generation from recursive tiles systems

International audienceIn this paper we explore test generation for Recursive Tile Systems (RTS) in the framework of the classical ioco testing theory. The RTS model al- lows the description of reactive systems with recursion, and is very similar to other models like Pushdown Automata, Hyperedge Replacement Grammars or Recursive State Machines. We first present an off-line test generation algorithm for Weighted RTS, a determinizable sub-class of RTS, and second, an on-line test generation algorithm for the full RTS model. Both algorithms use test purposes to guide test selection through targeted behaviours

Diagnostic, opacité et test de conformité pour des systèmes récursifs

L'une des façons les plus efficace de s'assurer du bon fonctionnement d'un système informatique est de les représenter par des modèles mathématiques. De nombreux travaux ont été réalisés en utilisant des automates finis comme modèles, nous essayons ici d'étendre ces travaux à des modèles infinis. Dans cette thèse, nous nous intéressons à quelques problèmes dans lesquels un système est observé de façon incomplète. Dans ce cas, il est impossible d'accéder à certaines informations internes. La diagnosticabilité d'une propriété donnée consiste à vérifier qu'à l'exécution du système, un observateur sera en mesure de déterminer avec certitude que la propriété est vérifiée par le système. L'opacité consiste, réciproquement, à déterminer qu'un doute existera toujours. Une autre application concerne la génération de cas de test. Une fois encore, on considère qu'un observateur n'accède qu'à une partie des événements se produisant dans le système (en général les entrées et les sorties). À partir d'une spécification, on produit automatiquement des cas de test, qui ont pour but de détecter des non-conformités (elles même formalisées de façon précise). Ces trois problèmes ont été étudiés pour des modèles finis. Dans cette thèse, nous étendons leur étude aux modèles récursifs, pour cela nous avons introduit notre propre modèle, les RTS, qui sont une généralisation des automates à pile, et d'autres modèles de la récursivité. Nous adaptons ensuite les techniques utilisées sur des modèles finis, qui servent à résoudre les problèmes qui nous intéressent.An effective way to ensure the proper functioning of a computer system is to represent it by using mathematical models . Many studies have been conducted using finite automata as models, in this thesis we try to extend these works to infinite models. We focus on three problems in which a system is partially observed. In this case, it is impossible to access certain internal informations. Diagnosability of a given property consist in checking, that, during the execution of the system, an observer will be able to determine with certainty that the property is verified by the system. Conversely, the opacity consists in determining if a doubt will always exist. Another application is the generation of test cases. Once again, we consider that an observer accesses only some events of the system (typically the inputs and outputs): from a specification, we automatically generate test cases, which are designed to detect non-conformance. These three problems have been studied for finite models. In this thesis, we extend their study to recursive models. For this purpose, we have introduced a new model, the RTS, which are a generalization of pushdown automata and other models of recursion. In order to solve problems of interest, we adapt the techniques used in finite models.RENNES1-Bibl. électronique (352382106) / SudocSudocFranceF

Simulation de la faisabilité d'un plan d'épandage de lisier de porc et conséquences sur les émissions gazeusesau stockage et à l'épandage

Le transfert de lisier hors zone d'excédent structurel et son épandage collectif sont envisagés pour gérer les excédents des exploitations porcines dépassant les seuils réglementaires. La substitution d'engrais chimique permise réduit les impacts sur l'environnement. Cependant, ce transfert nécessite des moyens logistiques en adéquation avec les contraintes de sols, cultures, climat et organisation. Le modèle COMET (COllective Management model of Effluents on a Territory scale) simule la réalisation de plans d'épandage soumis à ces contraintes. Le cas étudié concerne le transfert de lisier de porcs charcutiers de 11 élevages vers 22 exploitations situées à une distance moyenne de 44 km : 57,6 t d'azote sont épandues sur des céréales d'hiver, du maïs, du colza et des prairies. Pour réaliser ce transfert, 4 camions de 25 m3, un stockage intermédiaire de 200 m3 et un épandeur avec enfouisseur (débit de 60 m3 h-1) sont nécessaires. En comparant une fin d'hiver humide (2001) et sèche (2002), les simulations montrent que ces moyens sont insuffisants pour épandre la quantité prévue sur les céréales (83 % réalisé). En conditions de sol médiocres (hydromorphie), le taux de réalisation est inférieur à 50 %. Il en est de même si l'épandeur est peu disponible (3 vs 5 jours par semaine). Le cumul des 2 situations réduit la réalisation au tiers de la prévision, l'épandage sur maïs étant également affecté. Davantage de colza dans l'assolement permet de mieux satisfaire le plan sauf en année humide sur sol hydromorphe. Les émissions gazeuses résultant sont également discutées

Rate equation reformulation including coherent excitation: application to periodic protocols based on spectral hole-burning

International audienceA large number of signal-processing protocols are based on recording a spectral pattern via spectral hole-burning in an inhomogeneously broadened absorption profile. We present a simulation method specifically designed for periodic excitation sequences leading to the creation of a spectral pattern. This method is applicable to any multi-level atomic structure. The atomic variables' coherent dynamics are solved for a single temporal excitation step. The result is expressed as an equivalent population transfer rate. This way, the whole sequence is described as a matrix product and the steady state of the system under periodic excitation is easily derived. The propagation through the atomic medium is fully decoupled from the temporal evolution. We apply this method to the engraving of a spectral grating in a large-absorption Tm:YAG sample for wideband spectral analysis

20 GHz instantaneous bandwidth RF spectrum analyzer with high time-resolution

International audienceWe report on the experimental demonstration of a multi-gigahertz bandwidth RF spectrum analyzer exhibiting a resolution below 20 MHz, based on spectral hole burning in a rare-earth ion-doped crystal. To be compatible with demanding real-time spectrum monitoring applications, our demonstrator is designed to reach a high time resolution. For this purpose, we implemented the so-called "rainbow" architecture in which the spectral components of the incoming signal are angularly separated by the crystal, and are then acquired with a pixelated photodetector. The Tm 3+ :YAG crystal is programmed with a semiconductor DFB laser which frequency scan is servo-controlled and synchronized with the angular scan of a resonant galvanometric mirror, while a high-speed camera is used to acquire the spectra. In the perspective of future implementation within a system, the crystal is cooled below 4 K with a closed-cycle cryostat. With this setup, we have been able to monitor and record the spectrum of complex microwave signals over an instantaneous bandwidth above 20 GHz, with a time resolution below 100 µs, 400 resolvable frequency components and a probability of intercept of 100 %

U–Th and ¹⁰Be constraints on sediment recycling in proglacial settings, Lago Buenos Aires, Patagonia

International audienceThe estimation of sediment transfer times remains a challenge to our understanding of sediment budgets and the relationships between erosion and climate. Uranium (U) and thorium (Th) isotope disequilibria offer a means of more robustly constraining sediment transfer times. Here, we present new uranium and tho-rium disequilibrium data for a series of nested moraines around Lago Buenos Aires in Argentine Patagonia. The glacial chronology for the area is constrained using in situ cosmogenic 10 Be analysis of glacial outwash. Sediment transfer times within the periglacial domain were estimated by comparing the deposition ages of moraines to the theoretical age of sediment production, i.e., the comminution age inferred from U disequilibrium data and recoil loss factor estimates. Our data show first that the classical comminution age approach must include weathering processes accounted for by measuring Th disequilibrium. Second, our combined data suggest that the pre-deposition history of the moraine sediments is not negligible, as evidenced by the large disequilibrium of the youngest moraines despite the equilibrium of the corresponding glacial flour. Monte Carlo simulations suggest that weathering was more intense before the deposition of the moraines and that the transfer time of the fine sediments to the moraines was on the order of 100-200 kyr. Long transfer times could result from a combination of long sediment residence times in the proglacial lake (recurrence time of a glacial cycle) and the remobilization of sediments from moraines deposited during previous glacial cycles. 10 Be data suggest that some glacial cycles are absent from the preserved moraine record (seemingly every second cycle), supporting a model of reworking moraines and/or fluctuations in the extent of glacial advances. The chronological pattern is consistent with the U-Th disequilibrium data and the 100-200 kyr transfer time. This long transfer time raises the question of the proportion of freshly eroded sediments that escape (or not) the proglacial environments during glacial periods