Tests of Sapphire Crystals Produced with Different Growth Processes for Ultra-stable Microwave Oscillators

We present the characterization of 8-12 GHz whispering gallery mode resonators machined in high-quality sapphire crystals elaborated with different growth techniques. These microwave resonators are intended to constitute the reference frequency of ultra-stable Cryogenic Sapphire Oscillators. We conducted systematic tests near 4 K on these crystals to determine the unloaded Q-factor and the turnover temperature for whispering gallery modes in the 8-12 GHz frequency range. These characterizations show that high quality sapphire crystals elaborated with the Heat Exchange or the Kyropoulos growth technique are both suitable to meet a fractional frequency stability better than 1x10-15 for 1 s to 10.000 s integration times.Comment: 7 figure

A practical inference method with several implicative gradual rules and a fuzzy input: one and two dimensions

International audienceA general approach to practical inference with gradual implicative rules and fuzzy inputs is presented. Gradual rules represent constraints restricting outputs of a fuzzy system for each input. They are tailored for interpolative reasoning. Our approach to inference relies on the use of inferential independence. It is based on fuzzy output computation under an interval-valued input. A double decomposition of fuzzy inputs is done in terms of alpha-cuts and in terms of a partitioning of these cuts according to areas where only a few rules apply. The case of one and two dimensional inputs is consideredCet article présente une méthode d'inférence avec des règles implicatives graduelles pour une entrée floue. Les règles graduelles représentent des contraintes qui restreignent l'univers de sortie pour chacune des entrées. Elles sont conçues pour réaliser des interpolations. L'algorithme que nous proposons s'appuie sur le principe de indépendance inférentielle. Il met en oeuvre une double décomposition de l'ensemble flou d'entrée, par alpha-coupes et suivant le partitionnement de l'univers des variables d'entrée. Les cas étudiés correspondent à des systèmes à une et deux dimension

A New Development Framework for Multi-Core Processor based Smart-Camera Implementations

International audienceThe exponential evolution of the smart camera processing performances is directly linked to the improvements on hardware processing elements. Nowadays, high processing performances can be reached considering hardware targets which enables a high level of task parallelism to be implemented. Highly regular tasks are good candidate for a reconfigurable logic implementation and less regular parts of the algorithm could be described on the processor. Meanwhile the prototyping time is related to the selected target and the associated development methodology. The implementation on reconfigurable logic is highly efficient in exploiting the intrinsic task parallelism nevertheless can be time consuming using traditional methodology (i.e. Hardware Language Description). Several approaches can be considered to decrease the proto-typing time and to conserve high processing performances for instance implementation based on: • heterogeneous architectures [1] that mixed reconfig-urable logic (i.e. FPGA) and embedded processor, • high-level abstraction description and the associated fast prototyping tools [2][3][4], • multi-core processor architectures such as Digital Signal Processors (DSP), Graphic Processor Units (GPU) or even Generic Purpose Processor (GPP). In this paper, we propose to focus on implementation based on GPP due to the emergence of new generation of low-cost multi-core processors which enables high processing performances to be reached and therefore to match with some constraints of complex image-processing algorithms. The key idea of this development is to be able to propose fast prototyping using a low-cost smart camera based on this kind of target. Hence, we have developed a new framework dedicated to multi-core processor associated with an image sensor. The framework aims to offer a high degree of flexibility for managing the tasks and the memory allocation. Hence, the framework enables the priority and the allocation of each task to be controlled. Each task (or binary) is independent in terms of execution nevertheless it can be linked and controlled using a higher hierarchy level binary. The image acquisition task can be completely independent from the other processing tasks. One processor's core can even be dedicated to the acquisition task to guarantee a constant input data-flow to the image processing tasks. The data exchange is defined in POSIX, each binary can be therefore coded differently (for instance in C or C++, or in another languages) and offer a relative Operating System (OS) compatibility. The memory management enables a sequence of images to be automatically stored and a simultaneous access to be granted for several processings. The framework includes an interface dedicated to the management of the tasks: the user can add or suppress a binary during the runtime, logs or processing results can be visualised for each task

A Low Power Cryogenic Sapphire Oscillator with better than 10-15 short term frequency stability

International audienceIn the field of Time and Frequency metrology, the most stable frequency source is based on a microwave whispering gallery mode sapphire resonator cooled near 6 K. Provided the resonator environment is sufficiently free of vibration and temperature fluctuation, the Cryogenic Sapphire Oscillator (CSO) presents a short term fractional frequency stability of better than 1 x 10-15. The recent demonstration of a low maintenance CSO based on a pulse-tube cryocooler paves the way for its deployment in real field applications. The main drawback which limits the deployment of the CSO technology is the large electrical consumption (three-phase 8 kW peak / 6 kW stable operation) of the current system. In this paper, we describe an optimized cryostat designed to operate with a low consumption cryocooler requiring only 3 kW single phase of input power to cool down to 4 K a sapphire resonator.We demonstrate that the proposed design is compatible with reaching a state-of-the-art frequency stabilit

Ultra-stable microwave generation with a diode-pumped solid-state laser in the 1.5-µm range

We demonstrate the first ultra-stable microwave generation based on a 1.5-µm diode-pumped solid-state laser (DPSSL) frequency comb. Our system relies on optical-to-microwave frequency division from a planar-waveguide external cavity laser referenced to an ultra-stable Fabry–Perot cavity. The evaluation of the microwave signal at ~10 GHz uses the transportable ultra-low-instability signal source ULISS®, which employs a cryo-cooled sapphire oscillator. With the DPSSL comb, we measured −125 dBc/Hz phase noise at 1 kHz offset frequency, likely limited by the photo-detection shot-noise or by the noise floor of the reference cryo-cooled sapphire oscillator. For comparison, we also generated low-noise microwave using a commercial Er:fiber comb stabilized in similar conditions and observed &gt20 dB lower phase noise in the microwave generated from the DPSSL comb. Our results confirm the high potential of the DPSSL technology for low-noise comb applications

Cerebrospinal fluid biomarkers in the differential diagnosis of Alzheimer's disease from cortical dementias

International audienceBackground: Considering that most of semantic dementia (SD) and frontotemporal dementia (FTD) patients show no postmortem Alzheimer's disease (AD) pathology, cerebrospinal fluid (CSF) biomarkers may be of value for distinguishing these patients from those with AD. Additionally, biomarkers may be useful for identifying patients with atypical phenotypic presentations of AD, such as posterior cortical atrophy (PCA) and primary progressive non-fluent or logopenic aphasia (PNFLA). Methods: We investigated CSF biomarkers (beta-amyloid 1-42 (Aβ42), total tau (T-tau), and phosphorylated tau [P-tau]) in 164 patients with AD (n=60), PCA (n=15), behavioral variant FTD (n=27), SD (n=19), (PNFLA) (n=26) and functional cognitive disorders (FCD, n=17). We then examined the diagnostic value of these CSF biomarkers in distinguishing the patients from those with AD. Results: The P-Tau/Aβ42 ratio was found to be the best biomarker for discriminating AD from FTD and SD, with a sensitivity of 91.7% and 98.3%, respectively, and a specificity of 92.6% and 84.2%, respectively. As expected, biomarkers were less effective in differentiating AD from PNFLA and PCA, as significant proportions of PCA and PNFLA patients (60% and 61.5%, respectively) had concurrent alterations of both T-tau/Aβ42 and P-Tau/Aβ42 ratios. None of the FCD patients had a typical AD CSF profile or abnormal T-tau/Aβ42 or P-Tau/Aβ42 ratios. Conclusion: The P-Tau/Aβ42 ratio is a useful tool to discriminate AD from both FTD and SD, which are known to involve pathological processes distinct from AD. Biomarkers could be useful for identifying patients with an atypical AD phenotype that includes PNFLA and PCA

Modes de Kovásznay dans la stabilité d'écoulements d'ablation en fusion par confinement inertiel

Une approche possible pour l'étude de la stabilité d'écoulements d'ablation en fusion par confinement inertiel consiste à considérer les solutions exactes autosemblables de l'hydrodynamique avec conduction thermique non linéaire pour des gaz parfaits en milieu semi-infini. Ces solutions autosemblables et leurs perturbations sont calculées à l'aide d'une méthode spectrale de Tchebyshev multidomaine avec adaptation dynamique de maillage. Pour des non-uniformités du flux laser, nous obtenons les évolutions spatio-temporelles des perturbations de l'écoulement pour une large gamme de nombres d'onde. Ici nous poursuivons cette approche en analysant les perturbations à l'aide des modes de Kov\'asznay. Ainsi, dans un premier temps, l'équation exacte de propagation des perturbations acoustiques a été établie, puis des équations de propagation approchées pour chaque zone de l'écoulement sont obtenues après une analyse des termes sources