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Coherence between multi-instrument and multi-model atmospheric moisture retrievals in the framework of the HyMeX-SOP1
No full textInternational audienceAn observational effort has been established on Menorca Island to characterize the upwindmarine low-level flow during HyMeX SOP1. The ground-based Water vapour Raman Lidar(WALI), the airborne water vapour lidar LEANDRE-2 and boundary layer pressurizedballoons were implemented during the first Special Observing Period and contributed tocharacterize water vapour variability in the vicinity of the Balearic Islands, together with theexisting network of Global Positioning System receivers. Such an experimental data set is apowerful tool for checking the reliability of numerical forecast and research models. Hence anexercise of inter-comparison was carried out using the AROME-WMED and ECMWF/IFSNWP systems, and the Weather Research and Forecasting (WRF) model. We assessed theconsistency of water vapour mixing ratio (WVMR) profiles and integrated water vapourcontents (IWVC) derived from the different data sets. We use consistency indicators such asroot mean square errors, biases and correlations. Comparison between WVMR profiles fromground-based and airborne lidars (ground-based lidar and boundary layer pressurizedballoons) leads to a root mean square error lower than 1.6 g kg-1 (1.3 g kg-1) when the sameair masses are sampled. We observed a good agreement between the vertical WVMR profilesderived from WALI and the numerical models with correlations higher than 0.7 and rootmean square errors lower than 2 g kg-1. Regarding IWVCs, the models exhibit biases lessthan 2 kg m-2, root mean square errors lower than 2.3 g kg-1 and correlations higher than0.86 when compared to WALI
Aerosol forecast over the Mediterranean area during July 2013 (ADRIMED/CHARMEX)
No full textInternational audienceThe ADRIMED (Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region) project was dedicated to study the atmospheric composition during the summer 2013 in the European Mediterranean region. During its campaign experiment part, the WRF (Weather Research and Forecast Model) and CHIMERE models were used in the forecast mode in order to decide whether intensive observation periods should be triggered. Each day, a simulation of 4 days was performed, corresponding to (D-1) to (D+2) forecast leads. The goal of this study was to determine whether the model forecast spread is lower or greater than the model biases compared to observations. It is shown that the differences between observations and the model are always higher than those between the forecasts. Among all forcing types used in the chemistry-transport model, it is shown that the strong bias and other related low forecast scores are mainly due to the forecast accuracy of the wind speed, which is used both for the mineral dust emissions (a threshold process) and for the long-range transport of aerosol: the surface wind speed forecast spread can reach 50%, leading to mineral dust emission forecast spread of up to 30%. These variations are responsible for a moderate forecast spread of the surface PM10 (a few percentage points) and for a large spread (more than 50%) in the mineral dust concentration at higher altitudes, leading to a mean AOD (aerosol optical depth) forecast spread of ±10%
Multilevel comparison of large urban systems
No full textInternational audienceFor the first time the systems of cities in seven countries or regions among the largest in the world (China, India, Brazil, Europe, the Former Soviet Union (FSU), the United States and South Africa) are made comparable through the building of spatio-temporal standardised statistical databases. We first explain the concept of a generic evolutionary urban unit (“city”) and its necessary adaptations to the information provided by each national statistical system. Second, the hierarchical structure and the urban growth process are compared at macro-scale for the seven countries with reference to Zipf’s and Gibrat’s model: in agreement with an evolutionary theory of urban systems, large similarities shape the hierarchical structure and growth processes in BRICS countries as well as in Europe and United States, despite their positions at different stages in the urban transition that explain some structural peculiarities. Third, the individual trajectories of some 10,000 cities are mapped at micro-scale following a cluster analysis of their evolution over the last fifty years. A few common principles extracted from the evolutionary theory of urban systems can explain the diversity of these trajectories, including a specific pattern in their geographical repartition in the Chinese case. We conclude that the observations at macro-level when summarized as stylised facts can help in designing simulation models of urban systems whereas the urban trajectories identified at micro-level are consistent enough for constituting the basis of plausible future population projections
Fourier transform holography with high harmonic spectra for attosecond imaging applications
No full textInternational audienceWe demonstrate a method of using a Fourier holographic technique to utilize attosecond soft x-ray pulses to image nanometer-scale objects. A discrete frequency comb of laser-generated high-order harmonics, yielding a train of attosecond pulses, has been used to record spatially and spectrally resolved images. The individual wavelengths were also combined to form a single image, albeit with lower spatial resolution, demonstrating the applicability of the method to using isolated attosecond pulses with continuous bandwidths
Un Calcul des Constructions implicite avec sommes dépendantes et à inférence de type décidable.
No full textVersion soutenanceThis thesis presents a programming language for developingpurely computational certified programs.We present two type systems. The first one, ICC_Σ, extends Miquel'sImplicit Calculus of Constructions (ICC) with dependent sums. ICC_Σ isa Curry-style system with implicit type operators. With theseoperators, logical information may remain implicit, which makes itpossible to write purely computational certified programs. Addingdependent sums gives more expressive power to the system and is afirst step towards adding inductive types that are already built-inthe Coq proof assistant. One drawback of ICC_Σ is that type inferenceis likely to be undecidable. To solve that issue, we define a second system : the AnnotatedImplicit Calculus of Constructions, AICC_Σ. AICC_Σ is a type systemequivalent to ICC_Σ but with a bicolor Church-style syntax. Logicalinformation may appear explicitly, thus making type inferencedecidable. A built-in erasure procedure, that removes recursively theflagged parts, transforms an annotated AICC_Σ term into a purelycomputational ICC_Σ term. We prove that this procedure is correct andcomplete, which implies that valid AICC_Σ programs correspond exactlyto valid ICC_Σ ones. We also define a correct and complete type inference algorithm forAICC_Σ. This algorithm, combined with the erasure procedure makescertified programming in ICC_Σ possible.Cette thèse propose un langage permettant de développer des programmescertifiés purement calculatoires. Pour cela deux systèmes de types sont présentés. Le premier, ICC_Σ,est une extension du Calcul des Constructions Implicite de Miquel(ICC), enrichi avec des sommes dépendantes. ICC_Σ est un système à laCurry avec des opérateurs de type implicite. Ces opérateurs permettentaux indications logiques de ne pas apparaître explicitement dans lestermes, rendant possible l'écriture de programmes certifiés purementcalculatoires. L'ajout des sommes dépendantes donne plusd'expressivité au système et est un premier pas en vue de l'ajout destypes inductifs, déjà présents dans l'assistant de preuves Coq. Unelimitation de ICC_Σ est que l'inférence de type est vraisemblablementindécidable. Pour contourner ce problème, nous définisssons un deuxième système:le Calcul des Constructions Implicite Annoté avec sommes dépendantes,noté AICC_Σ. AICC_Σ est un système de types équivalent à ICC_Σ, maisavec une syntaxe bicolore à la Church. Les indications logiques desprogrammes apparaissent explicitement, rendant l'inférence de typedécidable, mais peuvent être marquées. AICC_Σ est muni d'un mécanismeinterne d'effacement qui transforme un terme de AICC_Σ avecindications logiques en un terme de ICC_Σ purement calculatoire. Nousprouvons que cet effacement est correct et complet, ce qui signifieque les programmes valides de AICC_Σ correspondent exactement à ceuxde ICC_Σ. Nous définissons également un algorithme d'inférence de type correctet complet pour AICC_Σ. La combinaison de cet algorithme et dumécanisme d'effacement rend possible la programmation certifiée dansICC_Σ
A short survey on Kantorovich-like theorems for Newton's method
No full textWe survey influential quantitative results on the convergence of the Newton iterator towards simple roots of continuously differentiable maps defined over Banach spaces. We present a general statement of Kantorovich's theorem, with a concise proof from scratch, dedicated to wide audience. From it, we quickly recover known results, and gather historical notes together with pointers to recent articles
Poly(vinylimidazole) radiografted PVDF nanospheres as alternative binder for high temperature PEMFC electrodes
No full textInternational audienceWithin the framework of high-temperature polymer fuel cells doped with phosphoric acid, we investigate the replacement of the conventional binder in the catalyst layers by functionalized solid PVDF nanospheres. Aim of this study is to develop and test an innovative binder which might create enhanced electrode porosity and acid distribution. Aqueous suspensions of PVDF nanospheres (d ~ 200 nm) are obtained by radical emulsion polymerization and are functionalized by Vinyl-Imidazole (VI) groups via in situ g-radiation. As a consequence the nanospheres can interact with H3PO4 to obtain proton conductivity. Catalyst inks are prepared mixing the nanospheres with commercial Pt/C electrocatalyst powder, solvents and phosphoric acid. Prototype electrodes are deposited by spraying and preliminary fuel cell tests are carried out at 160 C under dry H2/air. Electrodes with grafted PVDF nanospheres as solid binder are demonstrated and its understanding is in progress. Further improvements are outlined
Estimation of matrices with row sparsity
No full textInternational audienceAn increasing number of applications is concerned with recovering a sparse matrix from noisy observations. In this paper, we consider the setting where each row of the unknown matrix is sparse. We establish minimax optimal rates of convergence for estimating matrices with row sparsity. A major focus in the present paper is on the derivation of lower bounds