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Anomalous spectral laws in differential models of turbulence
No full textInternational audienceDifferential models for hydrodynamic, passive-scalar and wave turbulence given by nonlinear first- and second-order evolution equations for the energy spectrum in the -space were analysed.Both types of models predict formation an anomalous transient power-law spectra.The second-order models were analysed in terms of self-similar solutions of the second kind, and a phenomenological formula for the anomalous spectrum exponent was constructed using numerics for a broad range of parameters covering all known physical examples. The first-order models were examined analytically, including finding an analytical prediction for the anomalous exponent of the transient spectrum and description of formation of the Kolmogorov-type spectrum as a reflection wave from the dissipative scale back into the inertial range. The latter behaviour was linked to pre-shock/shock singularities similar to the ones arising in the Burgers equation.Existence of the transient anomalous scaling and the reflection-wave scenario are argued to be a robust feature common to the finite-capacity turbulence systems. The anomalous exponent is independent of the initial conditions but varies for for different models of the same physical system
Variabilite des nuages en Europe: utilisation combinee CALIPSO/simulation régionale WRF/MedCordex
No full textInternational audienceVariabilité des nuages en Europe: utilisation combinée CALIPSO/simulation régionale WRF/MedCordex. Liens/rétroactions entre la variabilité climatique régionale et les nuages. Représentation de la variabilité saisonnière/interannuelle de la structure verticale des nuages en Europ
Multi-model study of chemical and physical controls on transport of anthropogenic and biomass burning pollution to the Arctic
No full textUsing observations from aircraft, surface stations and satellite, we comprehensively evaluate multi-model simulations of carbon monoxide (CO) and ozone (O3) in the Arctic and over lower latitude emission regions, as part of the POLARCAT Model Inter-comparison Project (POLMIP). Evaluation of eleven atmospheric models with chemistry shows that they generally underestimate CO throughout the Arctic troposphere, with the largest biases found during winter and spring. Negative CO biases are also found throughout the Northern Hemisphere, with multi-model mean gross errors (9-12%) suggesting models perform similarly over Asia, North America and Europe. A multi-model annual mean tropospheric OH (10.8 ± 0.6 × 105 molec cm−3) is found to be slightly higher than previous estimates of OH constrained by methyl chloroform, suggesting negative CO biases in models may be improved through better constraints on OH. Models that have lower Arctic OH do not always show a substantial improvement in their negative CO biases, suggesting that Arctic OH is not the dominant factor controlling the Arctic CO burden in these models. In addition to these general biases, models do not capture the magnitude of CO enhancements observed in the Arctic free troposphere in summer, suggesting model errors in the simulation of plumes that are transported from anthropogenic and biomass burning sources at lower latitudes. O3 in the Arctic is also generally underestimated, particularly at the surface and in the upper troposphere. Summer O3 comparisons over lower latitudes show several models overestimate upper tropospheric concentrations. Simulated CO, O3 and OH all demonstrate a substantial degree of inter-model variability. Idealised CO-like tracers are used to quantitatively compare the impact of inter-model differences in transport and OH on CO in the Arctic troposphere. The tracers show that model differences in transport from Europe in winter and from Asia throughout the year are important sources of model variability at the Barrow. Unlike transport, inter-model variability in OH similarly affects all regional tracers at Barrow. Comparisons of fixed lifetime and OH-loss idealised CO-like tracers throughout the Arctic troposphere show that OH differences are a much larger source of inter-model variability than transport differences. The concentration of OH in the models is found to be correlated with inter-model differences in H2O, suggesting it to be an important driver of differences in simulated concentrations of CO and OH at high latitudes in these simulations. Despite inter-model differences in transport and OH, the relative contributions from the different source regions (North America, Europe and Asia) and different source types (anthropogenic and biomass burning) are comparable across the models. Fire emissions from the boreal regions in 2008 contribute 33, 43 and 19% to the total Arctic CO-like tracer in spring, summer and autumn, respectively, highlighting the importance of boreal fire emissions in controlling pollutant burdens in the Arctic
Measurements of the ZZ production cross sections in the 2 l 2 nu channel in proton-proton collisions at sqrt(s) = 7 and 8 TeV and combined constraints on triple gauge couplings
No full textSubmitted to EPJC - see paper for full list of authorsInternational audienceMeasurements of the ZZ production cross sections in proton-proton collisions at center-of-mass energies of 7 and 8 TeV are presented. Candidate events for the leptonic decay mode ZZ to 2 l 2 nu, where l denotes an electron or a muon, are reconstructed and selected from data corresponding to an integrated luminosity of 5.1 (19.6) inverse femtobarns at 7 (8) TeV collected with the CMS experiment. The measured cross sections, sigma(pp to ZZ) = 5.2 -1.4 +1.5 (stat) -1.1 +1.4 (syst) +/- 0.2 (lumi) pb at 7 TeV, and 6.9 -0.8 +0.8 (stat.) -1.4 +1.8 (syst) +/- 0.3 (lumi) pb at 8 TeV, are in good agreement with the standard model predictions with next-to-leading-order accuracy. The selected data are analyzed to search for anomalous triple gauge couplings involving the ZZ final state. In the absence of any deviation from the standard model predictions, limits are set on the relevant parameters. These limits are then combined with the previously published CMS results for ZZ in 4 l final states, yielding the most stringent constraints on the anomalous couplings
Characterization and mapping of surface physical properties of Mars from CRISM multi-angular data : application to Gusev Crater and Meridiani Planum
No full textInternational audienceThe analysis of particle physical properties (grain size, shape and internal structure) and its organization (surface porosity, roughness, and grain size distribution) provides information about the geological processes which formed and modified planetary surfaces. CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) multi-angular observations (varied emission angles) allow for the characterization of the surface scattering behavior, which depends on the composition and on the material physical properties such as the grain size, shape, internal structure, and the surface roughness. After an atmospheric correction (compensating mineral aerosol effects) by the Multi-angle Approach for Retrieval of the Surface Reflectance from CRISM Observations (MARS-ReCO), the surface reflectances at different geometries were analyzed by inverting the Hapke photometric model depending on six parameters: single scattering albedo, 2 phase function terms, macroscopic roughness and 2 opposition effects terms. In this work, surface photometric maps are created to observe the spatial variations of surface scattering properties as a function of geological units. Information regarding the single scattering albedo, the particle phase function and the macroscopic roughness are provided at the CRISM spatial resolution (200m/pixel). This article describes the application of this methodology to the data covering the Mars Exploration Rover (MER) landing sites located at Gusev Crater and Meridiani Planum where orbital and in situ observations are available. Complementary orbital observations (e.g., CRISM spectra, THermal EMission Imaging System (THEMIS), High Resolution Imaging Science Experiment, (HiRISE) images) were used for interpreting the modeled Hapke photometric parameters in terms of physical properties which can be used to constrain the geological processes. Available MER in situ observations were used as ground truth to validate the interpretations of the Hapke parameters. Varied scattering properties were observed within a CRISM observation (5x10km) suggesting that the surfaces are controlled by local geological processes (e.g., volcanic resurfacing, aeolian and impact processes) rather than regional or global processes. Results are consistent with the in situ observations, thus validating the approach and the use of photometry for the characterization of Martian surface physical properties
Peru-Chile upwelling dynamics under climate change
No full textInternational audienceThe consequences of global warming on the Peru-Chile Current System (PCCS) ocean circulation are examined with a high-resolution, eddy-resolving regional oceanic model. We performed a dynami-cal downscaling of climate scenarios from the IPSL-CM4 Coupled General Circulation Model (CGCM), corresponding to various levels of CO2 concentrations in the atmosphere. High-resolution atmospheric forcing for the regional ocean model are obtained from the IPSL atmospheric model run on a stretched grid with increased horizontal resolution in the PCCS region. When comparing future scenarios to preindustrial (PI) conditions, the circulation along the Peru and Chile coasts is strongly modified by changes in surface winds and increased stratification caused by the regional warming. While the coastal poleward undercurrent is intensified, the surface equatorial coastal jet shoals and the nearshore mesoscale activity are reinforced. Reduction in alongshore wind stress and nearshore wind stress curl drive a year-round reduction in upwelling intensity off Peru. Modifications in geostrophic circulation mitigate this upwelling decrease in late austral summer. The depth of the upwelling source waters becomes shallower in warmer conditions, which may have a major impact on the system's biological productivity
Constraints on the pMSSM, AMSB model and on other models from the search for long-lived charged particles in proton-proton collisions at sqrt(s) = 8 TeV
No full textsee paper for full list of authorsInternational audienceStringent limits are set on the long-lived lepton-like sector of the phenomenological minimal supersymmetric standard model (pMSSM) and the anomaly-mediated supersymmetry breaking (AMSB) model. The limits are derived from the results presented in a recent search for long-lived charged particles in proton-proton collisions, based on data collected by the CMS detector at a centre-of-mass energy of 8 TeV at the Large Hadron Collider. In the pMSSM parameter sub-space considered, 95.9% of the points predicting charginos with a lifetime of at least 10 ns are excluded. These constraints on the pMSSM are the first obtained at the LHC. Charginos with a lifetime greater than 100 ns and masses up to about 800 GeV in the AMSB model are also excluded. The method described can also be used to set constraints on other models
Geo-indistinguishability: A Principled Approach to Location Privacy
No full textInternational audienceIn this paper we report on our ongoing project aimed at protecting the privacy of the user when dealing with location-based services. The starting point of our approach is the principle of geo-indistinguishability, a formal notion of privacy that protects the user’s exact location, while allowing approximate information – typically needed to obtain a certain desired service – to be released. We then present two mechanisms for achieving geo-indistinguishability, one generic to sanitize locations in any setting with reasonable utility, the other custom-built for a limited set of locations but providing optimal utility. Finally we extend our mechanisms to the case of location traces, where the user releases his location repeatedly along the day and we provide a method to limit the degradation of the privacy guarantees due to the correlation between the points. All the mechanisms were tested on real datasets and compared both among themselves and with respect to the state of the art in the field
HIGHER CODIMENSION ISOPERIMETRIC PROBLEMS
No full textWe consider a variational problem for submanifolds Q ⊂ M with nonempty boundary ∂Q = K. We propose the definition that the boundary K of any critical point Q have constant mean curvature, which seems to be a new perspective when dim Q < dim M . We then construct small nearly-spherical solutions of this higher codimension CMC prob-lem; these concentrate near the critical points of a certain curvature function
