Search results for "fréquence"
showing 10 items of 16 documents
Genomic variation in tomato, from wild ancestors to contemporary breeding accessions
2015
[EN] Background: Domestication modifies the genomic variation of species. Quantifying this variation provides insights into the domestication process, facilitates the management of resources used by breeders and germplasm centers, and enables the design of experiments to associate traits with genes. We described and analyzed the genetic diversity of 1,008 tomato accessions including Solanum lycopersicum var. lycopersicum (SLL), S. lycopersicum var. cerasiforme (SLC), and S. pimpinellifolium (SP) that were genotyped using 7,720 SNPs. Additionally, we explored the allelic frequency of six loci affecting fruit weight and shape to infer patterns of selection. Results: Our results revealed a pat…
Variations spatiales et temporelles des communautés adventices des cultures annuelles en France
2007
Although arable weed species are particularly well adapted to habitats characterised by high levels of disturbance(ploughing, harvest), the degree and rate at which agro-ecosytems have been transformed in the last 50 years in Europe(use of chemicals, changes in crop rotations) has led to profound changes in the composition and diversity of arable weedcommunities. This thesis provides an update on the composition and diversity of weed communities that can be foundacross the main crop types and regions of France. It also addresses two objectives i) applying (community) ecologytheories for the analysis and interpretation of spatial and temporal variations in weed communities and ii) using the …
Analyse et détection des électrogrammes complexes fractionnés en vue de soigner la fibrillation auriculaire à l'aide de techniques d'ablation par rad…
2013
This manuscript presents research on the analysis and the detection of Complex Fractionated Atrial Electrograms (CFAE). In the first part, following a presentation over Atrial Fibrillation (AF) mechanisms and bioelectrical signals, the most commonly used tools for analyzing CFAE are presented. Linear tools are initially applied to signals from AF ablation procedures, then nonlinear tools are shown and integrated intoa CFAE detection algorithm. This one is based on the quantification of electrogram recurrence properties. In the second part, the cell and cardiac muscle tissue are described and simulated using mathematical models. Models such as FitzHugh Nagumo, Aliev Panfilov and Courtemanche…
Echo cancellation system for iso-frequency repeaters : contribution to the development of a new generation digital repeater
2014
On-frequency repeaters are a cost-effective solution to extend coverage and enhance wireless communications, especially in shadow areas. However, coupling between the receiving antenna and the transmitting antenna, called radio frequency echo, increases modulation errors and creates oscillations in the system when the echo power is high. According to the communication standards, extremely weak echoes decrease the transmission rate, while strong echoes damage electroni ccircuits because of power peaks. This thesis aims at characterizing the echo phenomenon under different modulations, and proposing an optimized solution directly integrated to industry. We have turned to digital solutions esp…
CARACTÉRISATION ET MODÉLISATION DE PEIGNES DE FRÉQUENCES KERR DANS DES CAVITÉS LASER BRILLOUIN À FIBRE
2022
Nous étudions une cavité en anneau non réciproque simple et reconfigurable pour générer des peignes de fréquences optiques accordables. Nous démontrons que des peignes cohérents peuvent être obtenus en exploitant finement la rétrodiffusion Brillouin stimulée et le mélange à quatre ondes en cascade dans la cavité à fibre non-linéaire.
Vers des systèmes viticoles économes en pesticides
2022
L’utilisation de produits phytosanitaires (cuivre, soufre et produits de synthèses) est à ce jour le moyen de lutte le plus efficace pour garantir une vendange qualitative et quantitative (Pujol, 2017). Face aux préoccupations sociétales croissantes concernant l’impact des pesticides sur l’environnement et la santé, la viticulture se doit pourtant de réduire sa dépendance aux produits phytosanitaires. Une transition agroécologique est ainsi nécessaire et implique de changer les pratiques afin de parvenir à diminuer l’utilisation des produits phytosanitaires. Le réseau DEPHY-Ferme a été créé en 2010 afin d’initier et stimuler cette transition agroécologique et répondre aux enjeux ambitieux i…
Génération et interfaçage de lumière à photon unique et contrôle de la dynamique atomique ultra-rapide pour l’information quantique
2010
We develop a robust and realistic mechanism for the generation of indistinguishable single-photon (SP) pulses with identical frequency and polarization. They are produced on demand from a coupled double-Raman atom-cavity system driven by a sequence of laser pump pulses. This scheme features a high efficiency, the ability to produce a sequence of narrow-band SP pulses with a delay determined only by the pump repetition rate, and simplicity of the system free from complications such as repumping process and environmental dephasing. We propose and analyze a simple scheme of parametric frequency conversion for optical quantum information in cold atomic ensembles. Its remarkable properties are m…
LA NOTION DE COLLOCATION FONDAMENTALE UNE ETUDE DE CORPUS
2016
Dans cette étude les « collocations fondamentales » sont envisagées comme des unités polylexicales significatives (unies par des liens collocationnels) fréquentes (dans l'usage) ou non fréquentes (lorsqu'elles sont pertinentes pour la communication) qui représentent pour les locuteurs natifs les contextes les plus essentiels d'un mot donné. Nous avons extrait du corpus frWaC (Baroni et al. 2010) environ 20 000 associations à partir de dix mots pivots issus du Dictionnaire Fondamental de Gougenheim (1971) ; puis, au moyen de la fréquence et de mesures d'association, nous avons sélectionné un échantillon d'environ 400 associations candidates au statut de collocations fondamentales et demandé …
Sources optiques infrarouges impulsionnelles ultra-courtes et spectralement ultra-larges générées par effet Raman dans les fibres creuses
2019
Gas-filled Hollow-Core Photonic Crystal Fibers (HC-PCF) are efficient tools regarding ultra-wide and coherent optical frequency combs by Stimulated Raman Scattering (SRS). Coherence is reached thanks to highly transient regime as it allows amplification, from quantum to macroscopic level, of a unique spatial and temporal mode (TSM). This results in the generation of Stokes waves with a well-determined phase. The present work details on which time scale coherence can subsist, between two consecutive pulses. The possibility of making a new kind of mode-lock is studied. Then the extreme versatility of gas-filled HC-PCF is illustrated by presenting different kind of new laser sources, exploitin…
Syntheses of TiO2 anatase nanocrystals with controlled size distribution. Influence of the crystallites size on the Raman spectrum and investigation …
2006
The determination of the size and the size distribution of anatase TiO2 nanopowders using Raman spectroscopy is presented. Several synthesis methods (soft chemistry, water-in-oil microemulsion, continuous hydrothermal synthesis) are used in order to control the size (from 3 to 20 nm), shape, phase and size distribution. The shift and width of the anatase Eg peak are often used to obtain the nanoparticles size. Homever, this peak is also sensitive to nonstoichiometry and others parameters. Low-frequency Raman scattering does not suffer from this problem. Size distibutions obtained by Raman spectroscopy and MET micrographs are compared. Finally, in situ Raman spectroscopy is used to study the…