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Theoretical, numerical and experimental study of geometrical parameters that affect anisotropy measurements in polarization-resolved SHG microscopy.
No full textInternational audiencePolarization-resolved second harmonic generation (P-SHG) microscopy is an efficient imaging modality for in situ observation of biopolymers structure in tissues, providing information about their mean in-plane orientation and their molecular structure and 3D distribution. Nevertheless, P-SHG signal build-up in a strongly focused regime is not throroughly understood yet, preventing reliable and reproducible measurements. In this study, theoretical analysis, vectorial numerical simulations and experiments are performed to understand how geometrical parameters, such as excitation and collection numerical apertures and detection direction, affect P-SHG imaging in homogeneous collagen tissues. A good agreement is obtained in tendon and cornea, showing that detection geometry significantly affects the SHG anisotropy measurements, but not the measurements of collagen in-plane orientation
The POLARCAT Model Intercomparison Project (POLMIP): overview and evaluation with observations
No full textInternational audienceA model intercomparison activity was inspired by the large suite of atmospheric chemistry observations made during the International Polar Year (2008) in the Arctic. Nine global and two regional chemical transport models have performed simulations for 2008 using a common emissions inventory to quantify the differences in model chemistry and transport schemes. This paper summarizes the models and compares their simulations of ozone and its precursors, and presents an evaluation of the simulations using a variety of surface, balloon, aircraft and satellite observations. Despite using the same emissions, large differences are seen among the models. Differences in a number of model parameters are identified as contributing to differences in the modelled chemical species, including cloud fields and photolysis rates. The largest differences among models, and between models and observations, are in NOy partitioning (PAN vs. HNO3) and in oxygenated volatile organic compounds (VOCs) such as acetaldehyde and acetone. Comparisons to surface site measurements of ethane and propane indicate that the emissions of these species are significantly underestimated. While limited in spatial and temporal coverage, the aircraft measurements provide a simultaneous evaluation of many species. Satellite observations of NO2 from OMI have been used to evaluate the models over source regions, indicating anthropogenic emissions are underestimated in East Asia, but fire emissions are generally overestimated. The emission factors for wildfires in Canada are evaluated using the correlations of VOCs to CO in the model output in comparison to enhancement factors derived from aircraft observations, showing reasonable agreement for methanol and acetaldehyde, but underestimate of ethanol, propane and acetone, while overestimating ethane emission factors
Quarkonium suppression from coherent energy loss in fixed-target experiments using LHC beams
No full text7 pages, 2 figuresInternational audienceQuarkonium production in proton-nucleus collisions is a powerful tool to disentangle cold nuclear matter effects. A model based on coherent energy loss is able to explain the available quarkonium suppression data in a broad range of rapidities, from fixed-target to collider energies, suggesting cold energy loss to be the dominant effect in quarkonium suppression in p-A collisions. This could be further tested in a high-energy fixed-target experiment using a proton or nucleus beam. The nuclear modification factors of J/ and as a function of rapidity are computed in p-A collisions at GeV, and in p-Pb and Pb-Pb collisions at GeV. These center-of-mass energies correspond to the collision on fixed-target nuclei of 7 TeV protons and 2.76 TeV lead nuclei available at the LHC
Compact Sobolev embeddings and torsion functions
No full textFor a general open set, we characterize the compactness of the embedding W 1,p 0 → L q in terms of the summability of its torsion function. In particular, for 1 ≤ q < p we obtain that the embedding is continuous if and only if it is compact. The proofs crucially exploit a torsional Hardy inequality that we investigate in details
Learning the intensity of time events with change-points
No full textInternational audienceWe consider the problem of learning the inhomogeneous intensity of a counting process, under a sparse segmentation assumption. We introduce a weighted total-variation penalization, using data-driven weights that correctly scale the penalization along the observation interval. We prove that this leads to a sharp tuning of the convex relaxation of the segmentation prior, by stating oracle inequalities with fast rates of convergence, and consistency for change-points detection. This provides first theoretical guarantees for segmentation with a convex proxy beyond the standard i.i.d signal + white noise setting. We introduce a fast algorithm to solve this convex problem. Numerical experiments illustrate our approach on simulated and on a high-frequency genomics dataset
A deterministic approximation method in shape optimization under random uncertainties
No full textInternational audienceThis paper is concerned with the treatment of uncertainties in shape optimization. We consider uncertainties in the loadings, the material properties, the geometry and the vibration frequency, both in the parametric and geometric optimization setting. We minimize objective functions which are mean values, variances or failure probabilities of standard cost functions under random uncertainties. By assuming that the uncertainties are small and generated by a finite number N of random variables, and using first-or second-order Taylor expansions, we propose a deterministic approach to optimize approximate objective functions. The computational cost is similar to that of a multiple load problems where the number of loads is N. We demonstrate the effectiveness of our approach on various parametric and geometric optimization problems in two space dimensions
Biomass burning influence on high-latitude tropospheric ozone and reactive nitrogen in summer 2008: a multi-model analysis based on POLMIP simulations
No full textInternational audienceWe have evaluated tropospheric ozone enhancement in air dominated by biomass burning emissions at high laititudes (> 50˚ N) in July 2008, using 10 global chemical transport model simulations from the POLMIP multi-model comparison exercise. In model air masses dominated by fire emissions, Δ O3/ΔCO values ranged between 0.039 and 0.196 ppbv ppbv−1 (mean: 0.113 ppbv ppbv−1) in freshly fire-influenced air, and between 0.140 and 0.261 ppbv ppbv−1 (mean: 0.193 ppbv) in more aged fire-influenced air. These values are in broad agreement with the range of observational estimates from the literature. Model ΔPAN/ΔCO enhancement ratios show distinct groupings according to the meteorological data used to drive the models. ECMWF-forced models produce larger ΔPAN/ΔCO values (4.44–6.28 pptv ppbv−1) than GEOS5-forced models (2.02–3.02 pptv ppbv−1), which we show is likely linked to differences efficiency of vertical transport during poleward export from mid-latitude source regions. Simulations of a large plume of biomass burning and anthropogenic emissions exported from Asia towards the Arctic using a Lagrangian chemical transport model show that 4 day net ozone change in the plume is sensitive to differences in plume chemical composition and plume vertical position among the POLMIP models. In particular, Arctic ozone evolution in the plume is highly sensitive to initial concentrations of PAN, as well as oxygenated VOCs (acetone, acetaldehyde), due to their role in producing the peroxyacetyl radical PAN precursor. Vertical displacement is also important due to its effects on the stability of PAN, and subsequent effect on NOx abundance. In plumes where net ozone production is limited, we find that the lifetime of ozone in the plume is sensitive to hydrogen peroxide loading, due to the production of HO2 from peroxide photolysis, and the key role of HO2 + O3 in controlling ozone loss. Overall, our results suggest that emissions from biomass burning lead to large-scale photochemical enhancement in high latitude tropospheric ozone during summer
Measurement of the differential cross section for top quark pair production in pp collisions at sqrt(s) = 8 TeV
No full textSubmitted to EPJC ; see paper for full list of authorsInternational audienceThe normalized differential cross section for top quark pair (ttbar) production is measured in pp collisions at a centre-of-mass energy of 8 TeV at the CERN LHC using the CMS detector in data corresponding to an integrated luminosity of 19.7 inverse femtobarns. The measurements are performed in the lepton+jets (e/mu+jets) and in the dilepton (e e, mu mu, and e mu) decay channels. The ttbar cross section is measured as a function of the kinematic properties of the charged leptons, the jets associated to b quarks, the top quarks, and the ttbar system. The data are compared with several predictions from perturbative QCD up to approximate next-to-next-to-leading-order precision. No significant deviations are observed relative to the standard model predictions
Radical-based route to 2-(trifluoromethyl)-1,3,4-oxadiazoles and trifluoromethyl-substituted polycyclic 1,2,4-triazoles and dihydrofurans.
No full textInternational audienceO-Ethyl S-[5-(trifluoromethyl)-1,3,4-oxadiazol-2-yl]methyl xanthate was readily prepared on a large scale and shown to undergo very efficient intermolecular radical additions to unactivated alkenes. The products were further elaborated by exploiting both radical and ionic processes to provide a variety of trifluoromethyl-substituted derivatives, including medicinally relevant triazoles. In particular, the application of a radical allylation on the initial adducts leads to structures that are able to undergo intramolecular [4 + 2] cycloaddition reactions
