On the well-posedness of uncalibrated photometric stereo under general lighting

Uncalibrated photometric stereo aims at estimating the 3D-shape of a surface, given a set of images captured from the same viewing angle, but under unknown, varying illumination. While the theoretical foundations of this inverse problem under directional lighting are well-established, there is a lack of mathematical evidence for the uniqueness of a solution under general lighting. On the other hand, stable and accurate heuristical solutions of uncalibrated photometric stereo under such general lighting have recently been proposed. The quality of the results demonstrated therein tends to indicate that the problem may actually be well-posed, but this still has to be established. The present paper addresses this theoretical issue, considering first-order spherical harmonics approximation of general lighting. Two important theoretical results are established. First, the orthographic integrability constraint ensures uniqueness of a solution up to a global concave-convex ambiguity , which had already been conjectured, yet not proven. Second, the perspective integrability constraint makes the problem well-posed, which generalizes a previous result limited to directional lighting. Eventually, a closed-form expression for the unique least-squares solution of the problem under perspective projection is provided , allowing numerical simulations on synthetic data to empirically validate our findings

Solving Uncalibrated Photometric Stereo using Total Variation

International audienceEstimating the shape and appearance of an object, given one or several images, is still an open and challenging research problem called 3D-reconstruction. Among the different techniques available, photometric stereo (PS) produces highly accurate results when the lighting conditions have been identified. When these conditions are unknown, the problem becomes the so-called uncalibrated PS problem, which is ill-posed. In this paper, we will show how total variation can be used to reduce the ambiguities of uncalibrated PS, and we will study two methods for estimating the parameters of the generalized bas-relief ambiguity. These methods will be evaluated through the 3D-reconstruction of real-world objects

Modèles ecologiques pour l'extrapolation des effets écotoxicologiques enregistrés lors de biotests in situ cheZ Gammarus

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCAInternational audienceEvaluating the effects of chemical contamination on populations and ecological communities still constitutes a challenging necessity in environmental management. However the toxic effects of contaminants are commonly measured by means of organism-level responses. Linking such effects measures with ecological models is a promising way to apprehend population-level impacts. In this way, population models are currently increasingly used in predictive risk assessment procedures, but their use in environmental diagnostic framework remains limited due to their lack of ecological realism. The present study with the crustacean amphipod Gammarus fossarum, a sentinel species in freshwater monitoring, combines a dual field and laboratory experimental approach with a population modelling framework. In this way, we developed an ecologically-relevant periodic matrix population model for Gammarus. This model allowed us to capture the population dynamics in the field, and to understand the particular pattern of demographic sensitivities induced by Gammarus life-history phenology. The model we developed provided a robust population-level assessment of in situ-based effects measures recorded during a biomonitoring program on a French watershed impacted by past mining activities. Thus, our study illustrates the potential of population modelling when seeking to decipher the role of environmental toxic contamination in ecological perturbations

The Frequency Drift of the Envelope Solitary Waves Near ωcH+ in Observations of Freja

In this paper, the ion cyclotron envelope solitary waves with a "cigar" shape observed by Freja satellite are reported and studied, especially, the drift of the frequency of the waves is contributed to the non-linear effects on the resonance frequency, which predicts that the frequency drift is directly proportional to the squaire of the amplitude of the oscillations. This result is comparable with the observations of the Freja satellite

Réalisme environnemental des modèles de populations pour l'évaluation de l'impact démographique de la toxicité des contaminants : exemple de la prise en compte de la variabilité saisonnière chez les invertébrés aquatiques

National audienceAlors que la population constitue un niveau d’intérêt pour la gestion environnementale (a priori et a posteriori), la caractérisation des effets des contaminants reste difficile directement à ce niveau. En effet, les caractéristiques populationnelles in situ présentent une variabilité naturelle forte, compliquant une lecture spécifique des effets des contaminants. L’expérimentation quant à elle se heurte à la dimension spatiale et temporelle des phénomènes à étudier. Dans les démarches prédictives, la difficulté expérimentale est aujourd’hui contournée par l’emploi de techniques de modélisation permettant le changement d’échelle entre niveaux individuel et populationnel. La paramétrisation de ces modèles de dynamique de populations s’appuie le plus souvent sur des observations de petits groupes d’individus au laboratoire. Néanmoins, le réalisme environnemental de ces modèles doit être amélioré afin de fournir une appréciation pertinente du danger encourue par les populations naturelles. Pour exemple, en couplant encagements in situ, suivis démographiques et modélisation matricielle, nous avons caractérisé la démographie de populations d’invertébrés présents dans nos rivières. Nous montrons ainsi l’importance de prendre en compte la phénologie de ces espèces dans l’extrapolation des effets des contaminants au niveau populationnel. En effet, en recourant à l’analyse de sensibilités de ces modèles, il apparaît grâce à la modélisation que la vulnérabilité démographique des populations face au stress chimique est fortement marquée par une variabilité saisonnière, pouvant remettre fortement en question les conclusions de modèles classiques construits pour appréhender la dynamique de populations au laboratoire

Influence of biotic and abiotic factors on metallothionein level in Gammarus pulex

International audienceDetection and assessment of the impact of pollution on biological resources imply increasing research on early-warning markers such as metallothioneins in metal exposure. Metallothioneins are cytosolic, low-molecular-weight proteins, involved principally in essential metal homeostasis and non-essential metal detoxication. Metallothionein synthesis could be influenced by abiotic (season) or biotic (reproduction process) factors directly or indirectly by its effect on metal bio-accumulation (i.e., sex, weight). In view of using metallothioneins as metal-exposure biomarkers in Gammarus pulex, this study attempts to define the effect of several factors (sex, weight/size and season) on the level of this protein. Metallothionein levels recorded in individuals over a large range of weights indicate a negative correlation between them. Inversely in our conditions, no difference was observed between male and female organisms. During field study, metallothionein level changes were observed with the highest levels in autumn and winter periods. The highest metallothionein levels were observed after the reproduction period, perhaps with the metabolic needs of biologically available essential metal such as zinc

Influence of metallic mixture exposure on subcellular metal distribution in Daphnia magna

International audienceAquatic ecosystems are constantly subjected to the introduction of anthropogenic pollutants which constitute a threat for living organisms. Metals are among the major contaminants, because of their persistence and may have short and long term deleterious effects. The whole body metal concentrations give useful information on the bioavailability of these compounds, but they are inadequate to predict their potential toxicity. As only a portion of incorporated metals is potentially toxic, the knowledge of the subcellular behaviour of metals in living organisms is fundamental. In several studies, authors show that effects were linked to the metal concentrations in the cytosolic fraction and particularly to the metal bound to low molecular weight compounds (Wang et al, 1999) or to high molecular weight compounds (Perceval et al, 2006). The aim of this project was to assess on one hand the metal distribution between cytosolic and insoluble fractions and on the other hand the cytosolic metal distribution according to three molecular mass class compounds including a fraction containing metallothionein proteins

Modèles de population chez Gammarus (Crustacé) et Potamopyrgus (Gastéopode) : compréhension de la variabilité saisonnière des sensibilités démographiques au stress toxique par analyse de sensibilité

International audienceToday there exists a large consensus that ecological models with populations rather than individuals as targets to protect have a high potential to be implemented into ecotoxicological risk assessment [1]. Indeed, they revealed particularly useful to solve the challenging issue of extrapolating toxic effects measured at the individual level towards possible contamination impacts on populations. Nevertheless, with the perspective to project or predict population answer, the environmental relevance of these models has to be improved, accounting for variability in population vulnerability and making them transferable with native species. In this way, the extrapolation process could be also used within a diagnostic framework. Our work was focused on two phylogenetically and ecologically contrasted species (the Crustacean Amphipod Gammarus fossarum and the Mollusk Gastropod Potamopyrgus antipodarum), widely present in European rivers and for which ecotoxicological (sub)individual biomarkers are available. We first developed environmentally realistic size-structured population models including both in situ caging and laboratory data, and relating individual-level demographic parameters (survival, growth, reproductive activity, fecundity, size at maturity) to the dynamics of reference native populations all along a year. Second, this methodology was coupled with in situ biotests or laboratory bioassays, in order to allow a population-level assessment of water quality or chemical compound toxicity. We showed thus the relevance to take into account the phenology of population dynamics (seasonal variability), by illustrating how it strongly controls the demographic sensitivity to toxic alteration of individual fitness traits in native species. More precisely, the poster will exemplify how sensitivity analyses of population endpoints were able to improve the comprehensive evaluation of possible contamination impacts on ecologically relevant biological levels

Mesure du taux d'alimentation in situ avec Gammarus fossarum (Crustacé) : un outil écologiquement pertinent pour l'évaluation de la qualité chimique des milieux aquatiques

National audienceDe nombreuses études au laboratoire ont montré que le taux d'alimentation des gammares pouvait être inhibé par une large gamme de contaminants chimiques. De plus, l'inhibition de l'alimentation constitue dans beaucoup de cas une des premières réponses biologiques observées dans des contextes de pollutions environnementales. Etudier les effets des contaminations chimiques sur l'alimentation est particulièrement pertinent car ces effets peuvent être reliés à des effets sur les traits d'histoire de vie tels que la croissance ou la reproduction ce qui permet d'évaluer les effets des contaminants à des niveaux d'organisation biologique supérieurs tels que la population via des modèles de dynamique de population. Notre travail, centré sur l'utilisation du crustacé Gammarus fossarum comme espèce sentinelle largement présente dans les cours d'eau européens, a pour objectif de proposer une évaluation de la qualité des milieux aquatiques à partir de la mesure in situ du taux d'alimentation et d'interpréter les impacts observés à ce niveau individuel jusqu'au niveau populationnel. Dans une première partie, nous illustrons comment la prise en compte de l'influence des facteurs biotiques (taille) et abiotiques (température et dureté de l'eau) sur le taux d'alimentation permet d'améliorer l'interprétation des mesures de taux d'alimentation in situ lors de biotests par encagement. Pour cela, nous avons mis en place une approche en 3 étapes : (i) nous avons caractérisé l'influence des facteurs confondants au laboratoire, (ii) grâce à la modélisation de ces influences, nous avons pu déterminer et valider la robustesse d'une gamme de valeurs de référence du taux d'alimentation lors d'encagements d'organismes dans des sites de référence présentant des caractéristiques physico-chimiques contrastées, (iii) enfin, nous avons souligné l'importance de prendre en compte l'influence de tels facteurs pour la quantification et l'interprétation des impacts observés lors d'encagements dans des sites contaminés. Dans une deuxième partie, nous nous sommes intéressés au lien entre les effets observés sur le taux d'alimentation et des effets sur la fécondité Nous développons ensuite des modèles matriciels de dynamique de population qui font le lien entre traits de vie (dont la fécondité) et indicateurs de fitness populationnelle. Ainsi, par le couplage des approches d'expérimentation in situ et de modélisation démographique, nous proposons une méthodologie qui vise à évaluer l'impact potentiel sur les populations, de la qualité chimique des milieux aquatiques via la perturbation de la fonction d'alimentation