A Preliminary Formation Flying Orbit Dynamics Analysis for Leonardo-BRDF

Leonardo-BRDF is a new NASA mission concept proposed to allow the investigation of radiative transfer and its effect on the Earth's climate and atmospheric phenomenon. Enabled by the recent developments in small-satellite and formation flying technology, the mission is envisioned to be composed of an array of spacecraft in carefully designed orbits. The different perspectives provided by a distributed array of spacecraft offer a unique advantage to study the Earth's albedo. This paper presents the flight dynamics analysis performed in the context of the Leonardo-BRDF science requirements. First, the albedo integral is investigated and the effect of viewing geometry on science return is studied. The method used in this paper, based on Gauss quadrature, provides the optimal formation geometry to ensure that the value of the integral is accurately approximated. An orbit design approach is presented to achieve specific relative orbit geometries while simultaneously satisfying orbit dynamics constraints to reduce formation-keeping fuel expenditure. The relative geometry afforded by the design is discussed in terms of mission requirements. An optimal Lambert initialization scheme is presented with the required DeltaV to distribute all spacecraft from a common parking orbit into their appropriate orbits in the formation. Finally, formation-keeping strategies are developed and the associated DeltaV's are calculated to maintain the formation in the presence of perturbations

Synergistic prostaglandin E synthesis by myeloid and endothelial cells promotes fetal hematopoietic stem cell expansion in vertebrates

During development, hematopoietic stem cells (HSCs) are produced from the hemogenic endothelium and will expand in a transient hematopoietic niche. Prostaglandin E2 (PGE2) is essential during vertebrate development and HSC specification, but its precise source in the embryo remains elusive. Here, we show that in the zebrafish embryo, PGE2 synthesis genes are expressed by distinct stromal cell populations, myeloid (neutrophils, macrophages), and endothelial cells of the caudal hematopoietic tissue. Ablation of myeloid cells, which produce the PGE2 precursor prostaglandin H2 (PGH2), results in loss of HSCs in the caudal hematopoietic tissue, which could be rescued by exogeneous PGE2 or PGH2 supplementation. Endothelial cells contribute by expressing the PGH2 import transporter slco2b1 and ptges3, the enzyme converting PGH2 into PGE2. Of note, differential niche cell expression of PGE2 biosynthesis enzymes is also observed in the mouse fetal liver. Taken altogether, our data suggest that the triad composed of neutrophils, macrophages, and endothelial cells sequentially and synergistically contributes to blood stem cell expansion during vertebrate development

Set up of a methodology for participatory plant breeding in bread wheat in France

In Organic Agriculture, cultivation environments and agronomic practices are very diverse. This diversity can be handled with decentralized selection based on the knowledge of farmers and scientists. A collaborative work between associations from Réseau Semences Paysannes and the DEAP team from INRA du Moulon set up an innovative breeding approach on farm based on decentralization and participation of farmers. This approach makes it possible to (i) create new population varieties of bread wheat locally adapted (genetic innovation) (ii) set up an organizational scheme based on decentralization and co construction between actors (societal innovation) and (iii) develop experimental designs, create statistical and data management tools which stimulate these genetic and societal innovations

Geometrical checking by virtual gauge, including measurement uncertainties

International audienceFor the most part, metrology software is currently based on the calculation of distances or angles between geometrical elements. This kind of method implies series of geometrical constructions which are amplifying measurement uncertainties. Usually, the estimation of error bars is then done after the geometrical verification. Hence, uncertainties are not directly taken into account during the checking process. To avoid these impediments, a new checking method, based on virtual gauges, is proposed in this paper. Based on Gram matrix, virtual gauges permit to perform checking without any intermediate geometrical construction. Moreover, thanks to a statistical description of the specified surface, the measurement uncertainties are thus directly taken into account during the conformance test process. An example of application is presented to demonstrate the relevance of this approach

Approach to better assess Fission Gas Behaviours, applicable to Fuels with Complex Microstructures

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Approach to better assess fission gas behaviors, applicable to fuels with complex microstructures

International audienceThe industrial fission gas behavior model CARACAS developed and validated for LWR-UO2 fuels in different fuel performance codes at CEA, EDF and AREVA is now being adapted to simulate the behavior of fuels with complex microstructures. In the current industrial licensed code, the description of such fuel is based on homogenization of the pellet, whereas for CEA's fuel performance code ALCYONE, this microstructure can be modelled by inclusions surrounded by a continuous matrix. The main objectives of the CARACAS fission gas model are to propose a continuous approach in both steady-state and off-normal conditions, but also to make it depend on the initial microstructure of the material. To model the fission gas behavior in such a complex microstructure, we assume that the behavior of each phase can be modeled as a homogeneous phase. First, neutron model provides CARACAS model the average local power rate, fission density and xenon/krypton production in each phase. Then, in CARACAS model, the first way of coupling between phases is done by the fission gas production mechanism, in which the recoil of fission gas atoms and their implantation from one phase to the other is taken into account. This heterogeneity of fission distribution and fission gas atoms production leads also to a heterogeneous swelling of the material, and so to a heterogeneous distribution of stress in the microstructure.It is now possible to take into account the heterogeneity of stress induced by this heterogeneous swelling and its feedback on the fission gas behavior model, thanks to the micro-mechanical behavior law. As the fission gas behavior model (particularly the gaseous swelling and the intragranular/intergranular gas distribution) depends at first order on the hydrostatic stress, the distribution of stress in the microstructure is very important. As this approach is very time-consuming, it is more dedicated to research applications or to very specific design calculations such as refined accidental initializations. For standard industrial applications, some simplifications are done. Depending on the representation of the microstructure in the fuel performance code where the model is implemented, different hypothesis are presented homogeneous or heterogeneous. Comparison of calculated results in both configurations with experimental data is also presented. An attempt of uncertainty quantification in relation to experimental conditions of the validation database is also performed

Learning Multi-Modal Dictionaries

Abstract—Real-world phenomena involve complex interactions between multiple signal modalities. As a consequence, humans are used to integrate at each instant perceptions from all their senses in order to enrich their understanding of the surrounding world. This paradigm can be also extremely useful in many signal processing and computer vision problems involving mutually related signals. The simultaneous processing of multimodal data can, in fact, reveal information that is otherwise hidden when considering the signals independently. However, in natural multimodal signals, the statistical dependencies between modalities are in general not obvious. Learning fundamental multimodal patterns could offer deep insight into the structure of such signals. In this paper, we present a novel model of multimodal signals based on their sparse decomposition over a dictionary of multimodal structures. An algorithm for iteratively learning multimodal generating functions that can be shifted at all positions in the signal is proposed, as well. The learning is defined in such a way that it can be accomplished by iteratively solving a generalized eigenvector problem, which makes the algorithm fast, flexible, and free of user-defined parameters. The proposed algorithm is applied to audiovisual sequences and it is able to discover underlying structures in the data. The detection of such audio-video patterns in audiovisual clips allows to effectively localize the sound source on the video in presence of substantial acoustic and visual distractors, outperforming state-of-the-art audiovisual localization algorithms. Index Terms—Audiovisual source localization, dictionary learning, multimodal data processing, sparse representation

A Comparison of Trajectory Optimization Methods for the Impulsive Minimum Fuel Rendezvous Problem

In this paper we present, a comparison of trajectory optimization approaches for the minimum fuel rendezvous problem. Both indirect and direct methods are compared for a variety of test cases. The indirect approach is based on primer vector theory. The direct approaches are implemented numerically and include Sequential Quadratic Programming (SQP). Quasi- Newton and Nelder-Meade Simplex. Several cost function parameterizations are considered for the direct approach. We choose one direct approach that appears to be the most flexible. Both the direct and indirect methods are applied to a variety of test cases which are chosen to demonstrate the performance of each method in different flight regimes. The first test case is a simple circular-to-circular coplanar rendezvous. The second test case is an elliptic-to-elliptic line of apsides rotation. The final test case is an orbit phasing maneuver sequence in a highly elliptic orbit. For each test case we present a comparison of the performance of all methods we consider in this paper

Corrigendum to ‘"Mediterranea massiliensis" gen. nov., sp. nov., a new human-associated bacteria isolated from the right and left colon lavage of a 58-year-old patient’

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