Implication de la théorie algébrique des graphes dans les algorithmes de calibration de phase en synthèse d'ouverture

Nous présentons une nouvelle classe d'algorithmes de calibration de phase. L'originalité des ces algorithmes, ainsi que leur efficacité, résulte de certaines structures particulières dont l'analyse relève de la théorie algébrique des graphes. Le processus d'optimisation correspondant, qui est fondé sur le principe des méthodes de région de confiance, s'avère être très bien adapté à ces structures particulières. Les premières retombées de notre approche concernent l'imagerie à clôture de phase en imagerie radio et en interférométrie optique

Semigrupos e o Teorema de Gorenstein para singularidades de curvas algébricas planas

O objetivo central desta dissertação é apresentar o Teorema de Gorenstein para singularidades de curvas algébricas planas. Consideramos os dois casos: primeiramente o caso local onde a singularidade da curva tem apenas um ramo e depois o caso em que a singularidade tem vários ramos. O caso local é quando a equação local é dada por uma série irredutível em k[[X; Y ]] e o caso semi-local e quando a equação local e dada por um produto de séries irredutíveis não associadas duas a duas. Uma equação local dada por uma tal série de potências f é chamada curva plana algebróide. Associados a uma curva plana algebróide estão o seu anel local O = O(f), o fecho inteiro ~O de O em seu anel total de frações e o ideal condutor de ~O em O. Podemos dizer que estes dados codi-cam as informações algébrico/geométricas da curva algebróide (f). O Teorema de Gorenstein, demonstrado por D. Gorenstein em [Go] a-rma que em ambos os casos (local e semi-local), a codimensão (como k-espacos vetoriais) do ideal condutor no anel O e igual a codimensão do anel O em ~O. Isto nos fornece uma certa simetria que e reetida nosemigrupo associado a curva algebróide (f). Assim estudamos também esta simetria de semigrupos dos naturais e a relacionamos com a simetria do anel O no caso local

Compressed sensing imaging techniques for radio interferometry

Radio interferometry probes astrophysical signals through incomplete and noisy Fourier measurements. The theory of compressed sensing demonstrates that such measurements may actually suffice for accurate reconstruction of sparse or compressible signals. We propose new generic imaging techniques based on convex optimization for global minimization problems defined in this context. The versatility of the framework notably allows introduction of specific prior information on the signals, which offers the possibility of significant improvements of reconstruction relative to the standard local matching pursuit algorithm CLEAN used in radio astronomy. We illustrate the potential of the approach by studying reconstruction performances on simulations of two different kinds of signals observed with very generic interferometric configurations. The first kind is an intensity field of compact astrophysical objects. The second kind is the imprint of cosmic strings in the temperature field of the cosmic microwave background radiation, of particular interest for cosmology.Comment: 10 pages, 1 figure. Version 2 matches version accepted for publication in MNRAS. Changes includes: writing corrections, clarifications of arguments, figure update, and a new subsection 4.1 commenting on the exact compliance of radio interferometric measurements with compressed sensin

The Camassa-Holm equation as the long-wave limit of the improved Boussinesq equation and of a class of nonlocal wave equations

In the present study we prove rigorously that in the long-wave limit, the unidirectional solutions of a class of nonlocal wave equations to which the improved Boussinesq equation belongs are well approximated by the solutions of the Camassa-Holm equation over a long time scale. This general class of nonlocal wave equations model bidirectional wave propagation in a nonlocally and nonlinearly elastic medium whose constitutive equation is given by a convolution integral. To justify the Camassa-Holm approximation we show that approximation errors remain small over a long time interval. To be more precise, we obtain error estimates in terms of two independent, small, positive parameters $\epsilon$ and $\delta$ measuring the effect of nonlinearity and dispersion, respectively. We further show that similar conclusions are also valid for the lower order approximations: the Benjamin-Bona-Mahony approximation and the Korteweg-de Vries approximation.Comment: 24 pages, to appear in Discrete and Continuous Dynamical System

Asymptotic models for the generation of internal waves by a moving ship, and the dead-water phenomenon

This paper deals with the dead-water phenomenon, which occurs when a ship sails in a stratified fluid, and experiences an important drag due to waves below the surface. More generally, we study the generation of internal waves by a disturbance moving at constant speed on top of two layers of fluids of different densities. Starting from the full Euler equations, we present several nonlinear asymptotic models, in the long wave regime. These models are rigorously justified by consistency or convergence results. A careful theoretical and numerical analysis is then provided, in order to predict the behavior of the flow and in which situations the dead-water effect appears.Comment: To appear in Nonlinearit

Multiphase weakly nonlinear geometric optics for Schrodinger equations

We describe and rigorously justify the nonlinear interaction of highly oscillatory waves in nonlinear Schrodinger equations, posed on Euclidean space or on the torus. Our scaling corresponds to a weakly nonlinear regime where the nonlinearity affects the leading order amplitude of the solution, but does not alter the rapid oscillations. We consider initial states which are superpositions of slowly modulated plane waves, and use the framework of Wiener algebras. A detailed analysis of the corresponding nonlinear wave mixing phenomena is given, including a geometric interpretation on the resonance structure for cubic nonlinearities. As an application, we recover and extend some instability results for the nonlinear Schrodinger equation on the torus in negative order Sobolev spaces.Comment: 29 page

Simple blood fibrosis tests reduce unnecessary referrals for specialized evaluations of liver fibrosis in NAFLD and ALD patients

BACKGROUND: Liver fibrosis evaluation is mandatory in non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) to decide the patient management. Patients with these diseases are usually under the care of non-liver specialists who refer them to specialized centers where the most accurate fibrosis tests are available. We aimed to evaluate whether simple blood fibrosis tests available to all physicians help to reduce the rate of unnecessary referral of NAFLD and ALD patients without advanced fibrosis. METHODS: NAFLD and/or ALD patients newly referred to our center for a non-invasive evaluation of liver fibrosis were retrospectively included. The FibroMeter (FM, combination of blood markers and Fibroscan results) was defined as the reference test for specialized evaluation of liver fibrosis. A FM result <0.384 indicated the absence of advanced fibrosis and thus an "unnecessary referral". RESULTS: 558 patients were included (NAFLD: 283, ALD: 156, mixed NAFLD+ALD: 119). FM was <0.384 (unnecessary referral) in 58.8% of patients. FIB4 was <1.30 in 45.2% and eLIFT <8 in 47.7% of the patients. 84.9% of patients with FIB4 <1.30 and 85.3% of patients with eLIFT <8 had also FM <0.384. Therefore, using FIB4 or eLIFT as first-line evaluation of liver fibrosis decreased by three-fold the rate of unnecessary referral. The negative predictive value of FIB4 and eLIFT was >80% whatever the underlying cause of chronic liver disease. CONCLUSION: The use of eLIFT by non-liver specialists for NAFLD and ALD patients can improve the relevance of referrals for specialized evaluation of liver fibrosis

Using nutritional geometry to define the fundamental macronutrient niche of the widespread invasive ant <i>Monomorium pharaonis</i>

The emerging field of nutritional geometry (NG) provides powerful new approaches to test whether and how organisms prioritize specific nutritional blends when consuming chemically complex foods. NG approaches can thus help move beyond food-level estimates of diet breadth to predict invasive success, for instance by revealing narrow nutritional niches if broad diets are actually composed of nutritionally similar foods. We used two NG paradigms to provide different, but complementary insights into nutrient regulation strategies and test a hypothesis of extreme nutritional generalism in colony propagules of the globally distributed invasive ant Monomorium pharaonis. First, in two dimensions (protein:carbohydrates; P:C), M. pharaonis colonies consistently defended a slightly carbohydrate-biased intake target, while using a generalist equal-distance strategy of collectively overharvesting both protein and carbohydrates to reach this target when confined to imbalanced P:C diets. Second, a recently developed right-angled mixture triangle method enabled us to define the fundamental niche breadth in three dimensions (protein:carbohydrates:lipid, P:C:L). We found that colonies navigated the P:C:L landscape, in part, to mediate a tradeoff between worker survival (maximized on high-carbohydrate diets) and brood production (maximized on high-protein diets). Colonies further appeared unable to avoid this tradeoff by consuming extra lipids when the other nutrients were limiting. Colonies also did not rely on nutrient regulation inside their nests, as they did not hoard or scatter fractions of harvested diets to adjust the nutritional blends they consumed. These complementary NG approaches highlight that even the most successful invasive species with broad fundamental macronutrient niches must navigate complex multidimensional nutritional landscapes to acquire limiting macronutrients and overcome developmental constraints as small propagules

Propiedades reológicas de las grasas de cupuaçu y del cacao

Cocoa butter is an important ingredient in chocolate formulation as it dictates the main properties (texture, sensation in the mouth, and gloss). In the food industry, the texture of fat-containing products strongly depends on the macroscopic properties of the fat network formed within the finished product. Cupuassu ( Theobroma grandiflorum , Sterculiaceae) is an Amazonian native fruit and the seeds can be used to derive a cocoa butter like product. In general, these fats are similar to those of cocoa, although they are different in some physical properties. The objective of this study was to analyze several properties of the cupuassu fat and cocoa butter (crystal formation at 25 ° C, rheological properties, and fatty acid composition) and mixtures between the two fats (rheological properties), in order to understand the behavior of these fats for their use in chocolate products. Fat flow was described using common rheological models ( Newton , Power Law, Casson and Bingham plastic).La manteca de cacao es un ingrediente muy importante en la formulación de chocolates y es responsable de la mayor parte de sus propiedades (textura, palatibilidad y brillo). En la industria de alimentos, la textura de productos que contienen grasa depende enormemente de las propiedades macroscópicas de la red cristalina de la grasa en el producto final. El cupuaçu es una fruta nativa de la región amazónica y sus semillas pueden ser usadas para obtener una grasa semejante a la manteca de cacao. En general, esta grasa es similar a la manteca de cacao, pero difiere en algunas de sus propiedades fisicas . El objetivo de este estudio fue analizar algunas propiedades de la grasa de cupuaçu y de la manteca de cacao (formación de cristales a 25 °C, propiedades reológicas y composición en ácidos grasos) y de algunas mezclas entre las dos grasas (propiedades reológicas), a fin de conocer el comportamiento de estas grasas para ser usadas en productos de la industria del chocolate. El flujo de la grasa se ha descrito utilizando modelos reológicos comunes (Newton, ley de la potencia, Casson y plástico de Bingham)

Interacciones físicas entre grasas de cupuassu y cacao

Cupuassu (Theobroma grandiflorum, Sterculiaceae) is an Amazonian native fruit and nowadays is cultivated only in Amazonian region. The seeds that come to about 16% of the dry weight can be used to derive a cocoa butter like product and the content of fat in the seeds is about 60% dry weight. In general, these fats are similar to those of cocoa, although they show difference in some physical properties. The objective of this study was to analyse some physical and crystallization properties of the cupuassu fat, cocoa butter and some mixtures between the two fats. The analyses performed were: dropping point, solid fat content, hardness index and Jensen cooling curve. The results suggested some advantages of the use of cupuassu fat, as lower crystallization time and smoothness than cocoa butter. The mixtures showed compatibility, cocoa butter showed bigger solid fat content at room temperature than cupuassu fat and the mixtures. Cupuassu fat had a lower dropping point than cocoa butter. The possible use of cupuassu fat and the mixtures could be in fillings and cold weather chocolate productsCupuassu (Theobroma grandiflorum, Sterculiaceae) es una fruta nativa amazónica que hoy día sólo se cultiva en esta región. Las semillas con un 16%, aproximadamente, del peso seco, tienen, aproximadamente, el 60% de grasa y pueden usarse como sustituto de manteca de cacao. En general, estas grasas son similares a las del cacao, aunque muestran diferencias en algunas de sus propiedades físicas. El objetivo de este estudio fue analizar algunas propiedades físicas y de cristalización de la grasa de cupuassu, de la manteca de cacao y de mezclas de las dos grasas. Los análisis realizados fueron: punto de goteo, contenido en grasa sólida, índice de dureza y la curva de enfriamiento de Jensen. El tiempo de cristalización inferior y la mayor suavidad que muestra la grasa de cupuassu frente a la manteca de cacao, sugieren algunas ventajas del uso de la misma. Todas mezclas fueron compatibles. El contenido en grasa sólida, a temperatura ambiente, de la manteca de cacao fue superior a la de la grasa de cupuassu y las mezclas. La grasa de cupuassu mostró un punto de goteo inferior al de la manteca de cacao. Esta grasa y las mezclas estudiadas podrían usarse en los rellenos y productos del chocolate en temporada fría