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SPICAM on Mars Express: a 10 year in-depth survey of the Martian atmosphere
No full textInternational audienceThe SPICAM experiment onboard Mars Express has accumulated over the last decade a wealth of observations that has permitted a detailed characterization of the atmospheric composition and activity from the near-surface to above the exosphere. SPICAM is dual ultraviolet (110 to 320 nm)-infrared (1 to 1.7 µm) spectrometer specifically designed to retrieve the major and minor species abundances of the Martian atmosphere [1]. SPICAM has the distinct capability of observing with a variety of geometrical configurations; monitoring the column-integrated abundances of ozone, water vapor as well as aerosols in a nadir-looking mode, characterizing their vertical distribution in either stellar or solar occultation modes so as to constrain their presence above typically 10 km up to 140 km of altitude (for CO 2) [2,3,4]. In a dedicated limb staring mode, SPICAM can infer the density of hydrogen atoms from 200 up to 10 000 km of altitude while using the resonantly scattered solar photons at the Lyman-alpha emission line of Hydrogen [5,6].Since the beginning of its operations at Mars, SPICAM has performed several thousands of stellar and solar occultations and has provided a multi-annual tracking in nadir mode. Here, we present a synthesis of the observations collected to date in order to assemble a single, coherent picture of the Martian atmosphere specifically adressing the issue of water decomposition into its lighter component (hydrogen) that can escape to space. In doing so, we propose a different angle for the long-term evolution of water and hydrogen on Mars
Search for a standard model Higgs boson produced in association with a top-quark pair and decaying to bottom quarks using a matrix element method
No full textSubmitted to Eur. Phys. J. C ; see paper for full list of authorsInternational audienceA search for a standard model Higgs boson produced in association with a top-quark pair and decaying to bottom quarks is presented. Events with hadronic jets and one or two oppositely charged leptons are selected from a data sample corresponding to an integrated luminosity of 19.5 inverse femtobarns collected by the CMS experiment at the LHC in pp collisions at a centre-of-mass energy of 8 TeV. In order to separate the signal from the larger ttbar+jets background, this analysis uses a matrix element method that assigns a probability density value to each reconstructed event under signal or background hypotheses. The ratio between the two values is used in a maximum likelihood fit to extract the signal yield. The results are presented in terms of the measured signal strength modifier, mu, relative to the standard model prediction for a Higgs boson mass of 125 GeV. The observed (expected) exclusion limit at a 95% confidence level is mu < 4.2 (3.3), corresponding to a best fit value mu-hat = 1.2+1.6-1.5
A variable reference trajectory for model-free glycemia regulation
No full textInternational audienceThe control design of an artificial pancreas, a hot research topic in diabetology, is tackled via the newly introduced model-free control and its corresponding "intelligent" proportional controller, which were already quite successful in many concrete and diverse situations. It results in an insulin injection for type 1 diabetes which displays via constant references a good nocturnal/fasting response, but unfortunately a poor postprandial behavior due to long hyperglycemia. When a variable reference is introduced, that switches between a constant one, when glycemia is more or less normal or moderate, and an exponential decay reference path, when a high glycemia rate indicates a meal intake, the results in silico, which employ real clinical data, become excellent. We obtain a bolus-shaped insulin injection rate during postprandial phases. The hyperglycemic peaks are therefore lowered a lot
Autophoretic locomotion from geometric asymmetry
No full textInternational audienceAmong the few methods which have been proposed to create small-scale swimmers, those relying on self-phoretic mechanisms present an interesting design challenge in that chemical gradients are required to generate net propulsion. Building on recent work, we propose that asymmetries in geometry are sufficient to induce chemical gradients and swimming. We illustrate this idea using two different calculations. We first calculate exactly the self-propulsion speed of a system composed of two spheres of unequal sizes but identically chemically homogeneous. We then consider arbitrary, small-amplitude, shape deformations of a chemically homogeneous sphere, and calculate asymptotically the self-propulsion velocity induced by the shape asymmetries. Our results demonstrate how geometric asymmetries can be tuned to induce large locomotion speeds without the need of chemical patterning
Search for a Higgs boson in the mass range from 145 to 1000 GeV decaying to a pair of W or Z bosons
No full textsee paper for full list of authorsInternational audienceA search for a heavy Higgs boson in the H to WW and H to ZZ decay channels is reported. The search is based upon proton-proton collision data samples corresponding to an integrated luminosity of up to 5.1 inverse femtobarns at sqrt(s)=7 TeV and up to 19.7 inverse femtobarns at sqrt(s)=8 TeV, recorded by the CMS experiment at the CERN LHC. Several final states of the H to WW and H to ZZ decays are analyzed. The combined upper limit at the 95% confidence level on the product of the cross section and branching fraction exclude a Higgs boson with standard model-like couplings and decays in the range 145 < m[H] < 1000 GeV. We also interpret the results in the context of an electroweak singlet extension of the standard model
Importance of boundary layer mixing for the isotopic composition of surface vapor over the subtropical North Atlantic Ocean
No full textInternational audienceDuring the summer 2012, we carried out continuous measurements of the isotopic composition (δ) of water vapor over the near-surface subtropical North Atlantic Ocean (STRASSE cruise). In this region of excess evaporation, we investigate the control of evaporation and mixing with a lower troposphere-derived, isotopically depleted air mass on the near-surface δ. We use a simple model to simulate the near-surface δ as the result of a two end-member mixing of the evaporative flux with free tropospheric air. The evaporative flux δ was estimated by the Craig and Gordon equation while the δ of the lower troposphere was taken from the LMDZ-iso global atmospheric circulation model. This simulation considers instantaneous mixing of lower tropospheric air with the evaporated flux and neglects lateral advection. Despite these simplifications, the simulations allow to identify the controls on the near-surface δ. The d-excess variability is largely a consequence of varying kinetic effects during evaporation, even during a convection event when the input of tropospheric vapor was strong. Kinetic effects and mixing processes affect simultaneously the near-surface δ and result in the vapor occupying distinct domains in the δ18O-δD space. The relative humidity-d-excess relationship shows that the closure assumption overestimates the d-excess variability at short time scales (less than a day). We interpret this as due to an effect of the residence time of the near-surface water vapor on the d-excess. Finally, we highlight the importance of reproducing mixing processes in models simulating isotopes over the subtropical North Atlantic Ocean and propose an extension of the closure assumption for use in initial conditions of distillation calculations
On the transition to turbulence of wall-bounded flows in general, and plane Couette flow in particular
No full textInternational audienceThe main part of this contribution to the special issue of EJM-B/Fluids dedicated to Patrick Huerre outlines the problem of the subcritical transition to turbulence in wall-bounded flows in its historical perspective with emphasis on plane Couette flow, the flow generated between counter-translating parallel planes. Subcritical here means discontinuous and direct, with strong hysteresis. This is due to the existence of nontrivial flow regimes between the global stability threshold Re_g, the upper bound for unconditional return to the base flow, and the linear instability threshold Re_c characterized by unconditional departure from the base flow. The transitional range around Re_g is first discussed from an empirical viewpoint ({\S}1). The recent determination of Re_g for pipe flow by Avila et al. (2011) is recalled. Plane Couette flow is next examined. In laboratory conditions, its transitional range displays an oblique pattern made of alternately laminar and turbulent bands, up to a third threshold Re_t beyond which turbulence is uniform. Our current theoretical understanding of the problem is next reviewed ({\S}2): linear theory and non-normal amplification of perturbations; nonlinear approaches and dynamical systems, basin boundaries and chaotic transients in minimal flow units; spatiotemporal chaos in extended systems and the use of concepts from statistical physics, spatiotemporal intermittency and directed percolation, large deviations and extreme values. Two appendices present some recent personal results obtained in plane Couette flow about patterning from numerical simulations and modeling attempts
Search for decays of stopped long-lived particles produced in proton-proton collisions at sqrt(s) = 8 TeV
No full textSubmitted to Eur. Phys. J. C - see paper for full list of authorsInternational audienceA search has been performed for long-lived particles that could have come to rest within the CMS detector, using the time intervals between LHC beam crossings. The existence of such particles could be deduced from observation of their decays via energy deposits in the CMS calorimeter appearing at times that are well separated from any proton-proton collisions. Using a data set corresponding to an integrated luminosity of 18.6 inverse femtobarns of 8 TeV proton-proton collisions, and a search interval corresponding to 281 hours of trigger livetime, 10 events are observed, with a background prediction of 13.2+3.6-2.5 events. Limits are presented at 95% confidence level on gluino and top squark production, for over 13 orders of magnitude in the mean proper lifetime of the stopped particle. Assuming a cloud model of R-hadron interactions, a gluino with mass <1000 GeV and a top squark with mass <525 GeV are excluded, for lifetimes between 1 microsecond and 1000 s. These results are the most stringent constraints on stopped particles to date
Formulas for phase recovering from phaseless scattering data at fixed frequency
No full textInternational audienceWe consider quantum and acoustic wave propagation at fixed frequency for compactly supported scatterers in dimension d ≥ 2. In these framework we give explicit formulas for phase recovering from appropriate phaseless scattering data. As a corollary, we give global uniqueness results for quantum and acoustic inverse scattering at fixed frequency without phase information
Identifying defects in an unknown background usingdifferential measurements
No full textInternational audienceWe present a new qualitative imaging method capable of selecting defects incomplex and unknown background from differential measurements of farfieldoperators: i.e. far measurements of scattered waves in the cases with andwithout defects. Indeed, the main difficulty is that the background physicalproperties are unknown. Our approach is based on a new exact characterizationof a scatterer domain in terms of the far field operator range and the linkwith solutions to so-called interior transmission problems. We present thetheoretical foundations of the method and some validating numerical experimentsin a two dimensional setting