1,877 research outputs found
Radon needlet thresholding
We provide a new algorithm for the treatment of the noisy inversion of the
Radon transform using an appropriate thresholding technique adapted to a
well-chosen new localized basis. We establish minimax results and prove their
optimality. In particular, we prove that the procedures provided here are able
to attain minimax bounds for any loss. It s important to notice
that most of the minimax bounds obtained here are new to our knowledge. It is
also important to emphasize the adaptation properties of our procedures with
respect to the regularity (sparsity) of the object to recover and to
inhomogeneous smoothness. We perform a numerical study that is of importance
since we especially have to discuss the cubature problems and propose an
averaging procedure that is mostly in the spirit of the cycle spinning
performed for periodic signals
Inversion of noisy Radon transform by SVD based needlet
A linear method for inverting noisy observations of the Radon transform is
developed based on decomposition systems (needlets) with rapidly decaying
elements induced by the Radon transform SVD basis. Upper bounds of the risk of
the estimator are established in () norms for functions
with Besov space smoothness. A practical implementation of the method is given
and several examples are discussed
Sources d'archives publiques conservées aux Archives nationales: quelques jalons de recontextualisation critique de la réforme de l'enseignement en 1968
Présentation des fonds d'archives les plus significatifs pour écrire l'histoire de la réforme des universités et de la loi Faure du 12 novembre 1968
Parthenogenetic activation decreases the polyphosphoinositide content of frog eggs
AbstractPolyphosphoinositides were quantified in metaphase II-arrested eggs of the amphibian Xenopuslaevis, and 8–10 min later in eggs activated by pricking. The content of phosphatidylinositol 4,5-biphosphate (PIP2) was remarkably high in metaphase II-arrested eggs with respect to that of phosphatidylinositol 4-phosphate (PIP). It was found to drop dramatically at activation. In contrast PIP content did not change significantly
LOOM, an algorithm for finding local optima of expensive functions
http://www.emse.fr/~picard/publications/riviere13loom.pdfInternational audienceEngineering optimization often involves one or many computationally intensive softwares that must be called to calculate the performance of candidate solutions. Despite the calculation cost, it is useful to characterize the global and the local optima. A new algorithm is described here that searches for all the local optima in a reduced number of calls to the true performance functions. The algorithm is based on repeated local searches on metamodels of the true performance functions and called LOOM (LOcal Optima through Metamodels). The local optima are identified as an output of the search. The search distributes computational resources equally among the basins of attraction. This article presents the algorithm and describes a first series of tests in two dimensions where a kriging metamodel is used
The C(3P) + NH3 reaction in interstellar chemistry: II. Low temperature rate constants and modeling of NH, NH2 and NH3 abundances in dense interstellar clouds
A continuous supersonic flow reactor has been used to measure rate constants
for the C + NH3 reaction over the temperature range 50 to 296 K. C atoms were
created by the pulsed laser photolysis of CBr4. The kinetics of the title
reaction were followed directly by vacuum ultra-violet laser induced
fluorescence (VUV LIF) of C loss and through H formation. The experiments show
unambiguously that the reaction is rapid at 296 K, becoming faster at lower
temperatures, reaching a value of 1.8 10-10 cm3 molecule-1 s-1 at 50 K. As this
reaction is not currently included in astrochemical networks, its influence on
interstellar nitrogen hydride abundances is tested through a dense cloud model
including gas-grain interactions. In particular, the effect of the
ortho-to-para ratio of H2 which plays a crucial role in interstellar NH3
synthesis is examined
Self-organized space partitioning for multi-agent optimization
In conjunction with AAMAS 2013. http://www.emse.fr/~picard/publications/vplh13optmas.pdfInternational audienceIn this paper we explore the use of multi-agent systems to tackle optimization problems in which each point is expensive to get and there are multiple local optima. The proposed strategy dynamically partitions the search space between several agents that use different surrogates to approximate their subregion landscape. Agents coordinate by exchanging points to compute their surrogate and by modifying the boundaries of their subregions. Through a self-organized process of creation and deletion, agents adapt the partition as to exploit potential local optima and explore unknown regions. The overarching goal of this technique is to all local optima rather than just the global one. The rationale behind this is to assign adequate surrogate to each subregion so that (i) optimization is cheaper, (ii) the overall optimization process is not only global in scope but also stabilizes on local optima and (iii) the final partitioning provides a better understanding of the optimization problem
Origin of renal myofibroblasts in the model of unilateral ureter obstruction in the rat
Tubulo-interstitial fibrosis is a constant feature of chronic renal failure and it is suspected to contribute importantly to the deterioration of renal function. In the fibrotic kidney there exists, besides normal fibroblasts, a large population of myofibroblasts, which are supposedly responsible for the increased production of intercellular matrix. It has been proposed that myofibroblasts in chronic renal failure originate from the transformation of tubular cells via epithelial-mesenchymal transition (EMT) or from infiltration by bone marrow-derived precursors. Little attention has been paid to the possibility of a transformation of resident fibroblasts into myofibroblasts in renal fibrosis. Therefore we examined the fate of resident fibroblasts in the initial phase of renal fibrosis in the classical model of unilateral ureter obstruction (UUO) in the rat. Rats were perfusion-fixed on days 1, 2, 3 and 4 after ligature of the right ureter. Starting from 1day of UUO an increasing expression of alpha-smooth muscle actin (αSMA) in resident fibroblasts was revealed by immunofluorescence and confirmed by the observation of bundles of microfilaments and webs of intermediate filaments in the electron microscope. Inversely, there was a decreased expression of 5′-nucleotidase (5′NT), a marker of renal cortical fibroblasts. The RER became more voluminous, suggesting an increased synthesis of matrix. Intercellular junctions, a characteristic feature of myofibroblasts, became more frequent. The mitotic activity in fibroblasts was strongly increased. Renal tubules underwent severe regressive changes but the cells retained their epithelial characteristics and there was no sign of EMT. In conclusion, after ureter ligature, resident peritubular fibroblasts proliferated and they showed progressive alterations, suggesting a transformation in myofibroblasts. Thus the resident fibroblasts likely play a central role in fibrosis in that mode
Extraction of Uranium from Seawater: Design and Testing of a Symbiotic System
Uranium present in low concentration in ocean water has the potential to greatly augment the current fuel reserve for nuclear power generation, but the challenge of extracting it economically remains. Two new designs of seawater uranium extraction systems are proposed in this paper—a stationary system and a continuous system—both of which utilize a braided polymer adsorbent. The stationary system simplifies the recovery procedure, and it is predicted to produce uranium at 403/kg of uranium.MIT Energy InitiativeS. D. Bechtel, Jr. Foundatio
Origin of renal myofibroblasts in the model of unilateral ureter obstruction in the rat
Tubulo-interstitial fibrosis is a constant feature of chronic renal failure and it is suspected to contribute importantly to the deterioration of renal function. In the fibrotic kidney there exists, besides normal fibroblasts, a large population of myofibroblasts, which are supposedly responsible for the increased production of intercellular matrix. It has been proposed that myofibroblasts in chronic renal failure originate from the transformation of tubular cells via epithelial–mesenchymal transition (EMT) or from infiltration by bone marrow-derived precursors. Little attention has been paid to the possibility of a transformation of resident fibroblasts into myofibroblasts in renal fibrosis. Therefore we examined the fate of resident fibroblasts in the initial phase of renal fibrosis in the classical model of unilateral ureter obstruction (UUO) in the rat. Rats were perfusion-fixed on days 1, 2, 3 and 4 after ligature of the right ureter. Starting from 1 day of UUO an increasing expression of alpha-smooth muscle actin (αSMA) in resident fibroblasts was revealed by immunofluorescence and confirmed by the observation of bundles of microfilaments and webs of intermediate filaments in the electron microscope. Inversely, there was a decreased expression of 5′-nucleotidase (5′NT), a marker of renal cortical fibroblasts. The RER became more voluminous, suggesting an increased synthesis of matrix. Intercellular junctions, a characteristic feature of myofibroblasts, became more frequent. The mitotic activity in fibroblasts was strongly increased. Renal tubules underwent severe regressive changes but the cells retained their epithelial characteristics and there was no sign of EMT. In conclusion, after ureter ligature, resident peritubular fibroblasts proliferated and they showed progressive alterations, suggesting a transformation in myofibroblasts. Thus the resident fibroblasts likely play a central role in fibrosis in that model
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