Development of a high brightness ultrafast Transmission Electron Microscope based on a laser-driven cold field emission source

We report on the development of an ultrafast Transmission Electron Microscope based on a cold field emission source which can operate in either DC or ultrafast mode. Electron emission from a tungsten nanotip is triggered by femtosecond laser pulses which are tightly focused by optical components integrated inside a cold field emission source close to the cathode. The properties of the electron probe (brightness, angular current density, stability) are quantitatively determined. The measured brightness is the largest reported so far for UTEMs. Examples of imaging, diffraction and spectroscopy using ultrashort electron pulses are given. Finally, the potential of this instrument is illustrated by performing electron holography in the off-axis configuration using ultrashort electron pulses.Comment: 23 pages, 9 figure

COASTLINE EXTRACTION IN VHR IMAGERY USING MATHEMATICAL MORPHOLOGY WITH SPATIAL AND SPECTRAL KNOWLEDGE

In this article, we are dealing with the problem of coastline extraction in Very High Resolution (VHR) multispectral images (Quickbird) on the Normandy Coast (France). Locating precisely the coastline is a crucial task in the context of coastal resource management and planning. In VHR imagery, some details on coastal zone become visible and the coastline definition depends on the geomorphologic context. According to the type of coastal units (sandy beach, wetlands, dune, cliff), several definitions for the coastline has to be used. So in this paper we propose a new approach in two steps based on morphological tools to extract coastline according to their context. More precisely, we first perform two detections of possible coastline pixels (respectively without false positive and without false negative). To do so, we apply a recent extension to multivariate images of the hit-or-miss transform, the morphological template matching tool, and rely on expert knowledge to define the sought templates. We then combine these two results through a double thresholding procedure followed by a final marker-based watershed to locate the exact coastline. In order to assess the performance and reliability of our method, results are compared with some ground-truth given by expert visual analysis. This comparison is made both visually and quantitatively. Results show the high performance of our method and its relevance to the problem under consideration

Spatio-temporal quasi-flat zones for morphological video segmentation

International audienceIn order to face the various needs of users, user-driven seg-mentation methods are expected to provide more relevant results than fully automatic approaches. Within Mathematical Morphology, several user-driven approaches have been proposed, mostly relying on the watershed transform. Nevertheless, Soille (IEEE TPAMI, 2008) has recently suggested another solution by gathering puzzle pieces computed as Quasi-Flat Zones (QFZ) of an image. In this paper, we study more deeply this user-driven segmentation scheme in the context of video data. Thus we also introduce the concept of Spatio-Temporal QFZ and propose several methods for extracting such zones from a video sequence

A blue light receptor that mediates RNA binding and translational regulation

Sensory photoreceptor proteins underpin light-dependent adaptations in nature and enable the optogenetic control of organismal behavior and physiology. We identified the bacterial light-oxygen-voltage (LOV) photoreceptor PAL that sequence-specifically binds short RNA stem loops with around 20 nM affinity in blue light and weaker than 1 µM in darkness. A crystal structure rationalizes the unusual receptor architecture of PAL with C-terminal LOV photosensor and N-terminal effector units. The light-activated PAL–RNA interaction can be harnessed to regulate gene expression at the RNA level as a function of light in both bacteria and mammalian cells. The present results elucidate a new signal-transduction paradigm in LOV receptors and conjoin RNA biology with optogenetic regulation, thereby paving the way toward hitherto inaccessible optoribogenetic modalities

Fast Quasi-Flat Zones Filtering Using Area Threshold and Region Merging

International audienceQuasi-flat zones are morphological operators which segment the image into homogeneous regions according to certain criteria. They are used as an image simplification tool or an image segmentation pre-processing, but they induced a very important oversegmentation. Several filtering methods have been proposed to deal with this issue but they suffer from different drawbacks, e.g., loss of quality or edge deformation. In this article, we propose a new method based on existing approaches which achieves better or similar results than existing approaches, does not suffer from their drawbacks and requires less computation time. It consists of two successive steps. First, small quasi-flat zones are removed according to a minimal area threshold. They are then filled through the growth of remaining zones

Segmentation vidéo interactive par zones quasi-plates

National audienceVideo data is continuously increasing in personal databases and Web repositories. To exploit such data, a prior segmentation is often needed in order to extract the objects-of-interest to be further processed. However, the segmentation of a given video is often not unique and indeed depends on user needs. Personalized segmentation may be achieved using interactive methods but only if their computational cost stays reasonable to enable user interactivity. We address here the problem of interactive video segmentation and introduce a 2-step segmentation scheme: 1) offline processing to automatically extract quasi-flat zones from video data, and 2) online processing to interactively gather quasi-flat zones and build objects-of-interest. Our approach is able to deal with multiple objects, robust to errors introduced by the automatic presegmentation step, and does not require to perform again the whole segmentation process each time the user provides some feedback.Le volume des données vidéo ne cesse d'augmenter dans les bases de données personnelles et sur le Web. Pour exploiter ces données, une segmentation préalable est souvent nécessaire afin d'obtenir les objets d'intérêt à traiter ultérieurement. Cependant, la segmentation d'une séquence vidéo n'est pas unique et dépend des besoins de chaque utilisateur. Une segmentation personnalisée peut être réalisée en utilisant des méthodes interactives, mais seulement si leur temps de calcul reste raisonnable afin de permettre dans de bonnes conditions cette interactivité. Dans cet article, nous abordons le problème de la segmentation vidéo interactive et proposons une approche en deux étapes : 1) un traitement hors-ligne pour extraire automatiquement les zones quasi-plates à partir d'une séquence vidéo, et 2) un traitement en-ligne interactif destiné à assembler les zones quasi-plates afin de construire les objets d'intérêt. Notre approche est capable de faire face à de multiples objets, est robuste aux erreurs introduites par l'étape de présegmentation automatique et ne nécessite pas de réitérer l'ensemble du processus de segmentation à chaque correction des marqueurs par l'utilisateur

Space-time coupling of shaped ultrafast ultraviolet pulses from an acousto-optic programmable dispersive filter

A comprehensive experimental analysis of spatio-temporal coupling effects inherent to the acousto-optic programmable dispersive filter (AOPDF) is presented. Phase and amplitude measurements of the AOPDF transfer function are performed using spatially and spectrally resolved interferometry. Spatio-temporal and spatio-spectral coupling effects are presented for a range of shaped pulses that are commonly used in quantum control experiments. These effects are shown to be attributable to a single mechanism: a group-delay--dependent displacement of the shaped pulse. The physical mechanism is explained and excellent quantitative agreement between the measured and calculated coupling speed is obtained. The implications for quantum control experiments are discussed.Comment: 8 pages, 6 figures; accepted for publication within JOSA

Attosecond chirp-encoded dynamics of light nuclei Attosecond chirp-encoded dynamics of light nuclei

International audienceWe study the spectral phase of high-order harmonic emission as an observable for probing ultrafast nuclear dynamics after the ionization of a molecule. Using a strong-field approximation theory that includes nuclear dynamics, we relate the harmonic phase to the phase of the overlap integral of the nuclear wavefunctions of the initial neutral molecule and the molecular ion after an attosecond probe delay. We determine experimentally the group delay of the high harmonic emission from D 2 and H 2 molecules, which allows us to verify the relation between harmonic frequency and the attosecond delay. The small difference in the harmonic phase between H 2 and D 2 calculated theoretically is consistent with our experimental results