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45 W average-power, high-energy deep-UV generation at 257 nm in LBO
No full textInternational audienceWe report on high average-power, high-energy picosecond fourth-harmonic generation in LBO. The first stages of a Yb:YAG laser chain operating at 1 kHz repetition rate generate few-picosecond 220 mJ chirped pulses at 1030 nm fundamental wavelength. They are frequency-converted in a cascade of three LBO crystals to generate the second-, third-, and fourth harmonics at 515 nm, 343 nm and 257 nm respectively. Crystals thicknesses and angular phase matching detuning were calculated as a function of pulse duration through broadband nonlinear optical numerical simulations. Last crystal is both conduction-cooled on edge and surface-cooled at center through forced-air flow to mitigate heating due to nonlinear absorption in the deep-UV and reduce temperature gradients. Chirped-pulse duration was experimentally adjusted to achieve stable 20% overall conversion efficiency. Near-field beam profiles were continuously recorded at 10 Hz, for all four wavelengths involved, together with corresponding energies, showing no significant beam degradation over 50 hours. Temperatures of the two last crystals were monitored and will help optimize surface cooling for future power ramping-up
Loi EGAlim : quels effets pour les consommateurs et la grande distribution ?
No full textInternational audienceThis article analyzes the effect of the EGAlim law on prices and sales of food products. The IRI data from January 2017 to February 2020 reveal a 1% inflation during the first year following the EGAlim law. However, using the causal identification method of differences-in-differences, we show that the three measures of the law, the raising in the resale below cost threshold and the supervision in volume and value of promotions, do not have any significant effect on prices in the long run on the regular stock of stores, except for the first three months on the loss leaders specifically concerned by the raising of the resale below cost threshold. Moreover, our results suggest that the supervision of promotions would play a non-negligeable role in the increase in the prices paid by consumers.Cet article étudie l’effet de la loi EGAlim sur les prix et ventes des produits alimentaires. Les données IRI de janvier 2017 à février 2020 révèlent une inflation de l’ordre de 1 % durant la première année qui a suivi l’entrée en vigueur de la loi. Cependant, grâce à la méthode d’identification causale des doubles différences, nous montrons que les trois mesures de cette loi, le relèvement du seuil de revente à perte et l’encadrement en volume et en valeur des promotions, n’ont pas eu un effet significatif à long terme sur les prix des produits composant le fond de rayon des magasins, excepté sur les trois premiers mois pour les produits d’appel ciblés par le relèvement du seuil de revente à perte. De plus, nos résultats suggèrent que l’encadrement des promotions jouerait un rôle non négligeable dans l’augmentation des prix payés par les consommateurs
Mathematical modelling and analysis of Impermanent Loss and Fees in Uniswap v3
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A Morphological Algorithm for the Detection of Linear Contrails
No full textInternational audienceThe climate impact of aviation can be separated into CO2 and non-CO2 effects, with the latter being potentially larger than the former. In thiscontext we are more specifically interested in condensation trails (hereafter contrails) and induced cirrus. Monitoring contrail formation and evolution isnecessary to understand their radiative effects and help the aviation industry to transition towards a more sustainable activity. Current research aimed atdetecting contrails is mostly based on geostationary satellite images because they allow to follow the contrail over a long period of time. However a majorshortcoming is that the formation phase of the contrails cannot be detected and larger, but older, contrails cannot always be attributed to the flightsthat produced them. To circumvent the problem that satellite images do not have a sufficient resolution to observe the contrail formation phase, weuse a ground-based hemispheric camera with a two-minute sampling rate as a complementary source of information. As a first step, we have developeda traditional morphological algorithm that will help preparing a sufficiently large labelled database as required to train a deep-learning algorithm. Ouralgorithm aims to detect whether each aircraft that passes in the field of view of the camera (as monitored from an ADSB radar) produces a contrail or not. We are thus able to relate contrail formation and evolution with aircrafttype, flight altitude and weather conditions. We start by focusing on the young linear contrails that appears just behind the aircraft. We also considerall weather conditions except completely cloudy conditions that prevents contrails to be observed. The algorithm combines various morphologicaltreatments to binarise the image and a linear Hough transform to identify straight lines in a direction close to the aircraft’s trajectory. Its performance is evaluated against a database that was manually annotated consisting of 400 images with 407 contrails. We find that our algorithm has a specificityof 97%, i.e. there are few false detections, but its sensitivity is about 55%, i.e. it is missing a significant fraction of contrail appearances. Looking inmore details, the sensitivity is 60% in clear-sky contidions but only 40% in conditions of a thin high cloud cover with superimposed contrails. Ananalysis of several years of contrail detection will be presented to determine precisely the fraction of contrail-producing flights and the associated weatherconditions with non-persistent and persistent contrails
Generalized Pareto Regression Trees for extreme events analysis
No full textInternational audienceIn this paper, we provide finite sample results to assess the consistency of Generalized Pareto regression trees, as tools to perform extreme value regression. The results that we provide are obtained from concentration inequalities, and are valid for a finite sample size, taking into account a misspecification bias that arises from the use of a "Peaks over Threshold" approach. The properties that we derive also legitimate the pruning strategies (i.e. the model selection rules) used to select a proper tree that achieves compromise between bias and variance. The methodology is illustrated through a simulation study, and a real data application in insurance against natural disasters
Cancer-on-a-chip model shows that the adenomatous polyposis coli mutation impairs T cell engagement and killing of cancer spheroids
No full textInternational audienceEvaluating the ability of cytotoxic T lymphocytes (CTLs) to eliminate tumor cells is crucial, for instance, to predict the efficiency of cell therapy in personalized medicine. However, the destruction of a tumor by CTLs involves CTL migration in the extra-tumoral environment, accumulation on the tumor, antigen recognition, and cooperation in killing the cancer cells. Therefore, identifying the limiting steps in this complex process requires spatio-temporal measurements of different cellular events over long periods. Here, we use a cancer-on-a-chip platform to evaluate the impact of adenomatous polyposis coli (APC) mutation on CTL migration and cytotoxicity against 3D tumor spheroids. The APC mutated CTLs are found to have a reduced ability to destroy tumor spheroids compared with control cells, even though APC mutants migrate in the extra-tumoral space and accumulate on the spheroids as efficiently as control cells. Once in contact with the tumor however, mutated CTLs display reduced engagement with the cancer cells, as measured by a metric that distinguishes different modes of CTL migration. Realigning the CTL trajectories around localized killing cascades reveals that all CTLs transition to high engagement in the 2 h preceding the cascades, which confirms that the low engagement is the cause of reduced cytotoxicity. Beyond the study of APC mutations, this platform offers a robust way to compare cytotoxic cell efficiency of even closely related cell types, by relying on a multiscale cytometry approach to disentangle complex interactions and to identify the steps that limit the tumor destruction
Causality constraints on nonlinear supersymmetry
No full textInternational audienceA bstract It is well-known that gravitino propagation in standard supergravities is free of any causality problems. However, two issues related to gravitino propagation were recently uncovered in specific supergravities with nonlinear supersymmetry. One of them concerns potential acausality/superluminality, whereas the second one arises from the vanishing of the sound speed at specific points during inflation. The former is famously related to positivity constraints on specific EFT operators, derived from dispersion relations on the energy-growing part of scattering amplitudes, and indeed we show that subluminality constraints for the gravitino are related via the equivalence theorem to positivity bounds in low-energy goldstino actions. However, the former are stronger, in the sense that they apply to functions of the scalar fields not only in the ground state, but for any field values such as those scanned by time-dependent solutions, unlike bounds derived from 2 → 2 scattering amplitudes in the vacuum. We also argue that nontrivial causality constraints arise only in the case where nonlinear supersymmetry in the matter sector is encoded into superfield constraints which do not seem to arise from microscopic two-derivative lagrangians, in particular for the orthogonal constraint used to build minimal models of inflation in supergravity. This allows us to propose simple alternatives which maintain the minimality of the spectra and are causal in all points of the theory parameter space. We also discuss minimal supergravity models of inflation along these lines
An assessment study of Islamic period tiles (Timurid, Ottoman, Safavid and Qajar) from 12th to 19th centuries to trace the glaze technology
No full textInternational audienceRaw materials determine the final composition and properties of a fired ceramic. Distinctive minor (Ca, K, Al, Mg, etc.) and trace elements (Bi, Rb, Sr, Zr, etc.) of the geological context, which give significant signal, permit distinguishing the provenance and the phases characteristic of the firing procedures, thus differentiating different productions of tiles. In many cases, the most sophisticated part of the process is the formulation and fabrication of the glaze, especially the colored areas. Complete tiles, which are coming from identified historic buildings and exhibited in the museum showrooms are better documented concerning their origins rather than the unregistered fragmentary sherds. Therefore, a detailed analytical examination is required for these undefined tiles to identify where they are produced. Systematic studies with spectroscopic methods will lead to a statistical work in addition to the material culture and art historical research in the Islamic period (focused on the 12th and 19th centuries) ceramic art. In this study, three techniques, Raman, portable X-ray fluorescence (pXRF) and scanning electron microscopy-energy dispersive (SEM-EDS) spectrometry were applied to reveal the technological characteristics of the glazes and pigments. Raman analysis which characterizes micro-and nanostructures of colored and transparent glazes, opacified or not, was applied to sherds mostly collected before the 1960s, preserved currently at the Louvre Museum 1. These tiles were originated in Anatolia, the Caucasus, Iran, and Central Asia, which are, for most of them, characterized by the application of black lines to separate coloured areas. Similar fragmented sherds which are preserved in the reserves of Topkapi Palace Museum in Istanbul were also analysed with Raman spectroscopy if either they were produced in the Ottoman territory or if outside 2,3. Chemical analysis of glazes and colored areas were performed with pXRF for the sherds of the Louvre Museum (29 samples) and SEM-EDS for the Topkapi Palace fragments (4 samples). Figure 1 shows the similar sherds from Louvre Museum and Topkapi Palace Museum analysed for comparison. The reliability of pXRF measurements was formerly revealed when compared with the results carried out with SEM-EDS 4. Raman measurements of the collection of Musée du Louvre were carried out in the laboratory with a blue laser excitation and/or on the conservation site with a mobile device equipped with green laser 1. The samples from Topkapi Palace Museum were analysed only with green laser in the laboratory 2,3. Comparison with XRF, SEM-EDS and IB composition measurement is made 5. Three types of glazes were identified (Fig.2a): (i) a lead-rich glaze analogous to that of Byzantine, Zirid to Hafsid and al-Andalus productions, (ii) a lead-alkali glaze typical of the Ottoman productions of Iznik-Kütahya, and (iii) a mixed (poor lead/lead-free)-alkali glaze typical of Safavid productions. Further comparison is made with the data collected with a different mobile XRF instrument on Edirne Mosque tiles 6 (Edirne was the first Ottoman capital) and with those recorded on sherds excavated from Ottoman Iznik kilns 7 (Fig.2b)
Interaction-enhanced nesting in Spin-Fermion and Fermi-Hubbard models
No full text5 pages, 4 figuresInternational audienceThe spin-fermion (SF) model postulates that the dominant coupling between low-energy fermions in near critical metals is mediated by collective spin fluctuations (paramagnons) peaked at the N\'{e}el wave vector, , connecting hot spots on opposite sides of the Fermi surface. It has been argued that strong correlations at hot spots lead to a Fermi surface deformation (FSD) featuring flat regions and increased nesting. This conjecture was confirmed in the perturbative self-consistent calculations when the paramagnon propagator dependence on momentum deviation from is given by . Using diagrammatic Monte Carlo (diagMC) technique we show that such a dependence holds only at temperatures orders of magnitude smaller than any other energy scale in the problem, indicating that a different mechanism may be at play. Instead, we find that a dependence yields a robust finite- scenario for achieving FSD. To link phenomenological and microscopic descriptions, we applied the connected determinant diagMC method to the Hubbard model and found that in this case: (i) the FSD is not very pronounced, and, instead, it is the lines of zeros of the renormalized dispersion relation that deform towards nesting; (ii) this phenomenon appears at large U/t>5.5 before the formation of electron and hole pockets; (iii) the static spin susceptibility is well described by . Flat FS regions yield a non-trivial scenario for realizing a non-Fermi liquid state
Initialisation from lattice Boltzmann to multi-step Finite Difference methods: Modified equations and discrete observability
No full textInternational audienceLatitude on the choice of initialisation is a shared feature between one-step extended state-space and multi-step methods. The paper focuses on lattice Boltzmann schemes, which can be interpreted as examples of both previous categories of numerical schemes. We propose a modified equation analysis of the initialisation schemes for lattice Boltzmann methods, determined by the choice of initial data. These modified equations provide guidelines to devise and analyze the initialisation in terms of order of consistency with respect to the target Cauchy problem and time smoothness of the numerical solution. In detail, the larger the number of matched terms between modified equations for initialisation and bulk methods, the smoother the obtained numerical solution. This is particularly manifest for numerical dissipation. Starting from the constraints to achieve time smoothness, which can quickly become prohibitive for they have to take the parasitic modes into consideration, we explain how the distinct lack of observability for certain lattice Boltzmann schemes---seen as dynamical systems on a commutative ring---can yield rather simple conditions and be easily studied as far as their initialisation is concerned. This comes from the reduced number of initialisation schemes at the fully discrete level. These theoretical results are successfully assessed on several lattice Boltzmann methods