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Measurements of t t-bar charge asymmetry using dilepton final states in pp collisions at sqrt(s) = 8 TeV
No full textSubmitted to Phys. Lett. B ; see paper for full list of authorsInternational audienceThe charge asymmetry in t t-bar events is measured using dilepton final states produced in pp collisions at the LHC at sqrt(s)=8 TeV. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 19.5 inverse femtobarns. The measurements are performed using events with two oppositely charged leptons (electrons or muons) and two or more jets, where at least one of the jets is identified as originating from a bottom quark. The charge asymmetry is measured from differences in kinematic distributions, unfolded to the parton level, of positively and negatively charged top quarks and leptons. The t t-bar and leptonic charge asymmetries are found to be 0.011 +/- 0.011 (stat) +/- 0.007 (syst) and 0.003 +/- 0.006 (stat) +/- 0.003 (syst), respectively. These results, as well as charge asymmetry measurements made as a function of t t-bar system kinematic properties, are in agreement with predictions of the standard model
Pathogens trigger top-down climate forcing on ecosystem dynamics
No full textInternational audienceEvaluating the effects of climate variation on ecosystems is of paramount importance for our ability to forecast and mitigate the consequences of global change. However, the ways in which complex food webs respond to climate variations remain poorly understood. Here, we use long-term time series to investigate the effects of temperature variation on the intraguild-predation (IGP) system of Windermere (UK), a lake where pike (Esox lucius, top predator) feed on small-sized perch (Perca fluviatilis) but compete with large-sized perch for the same food sources. Spectral analyses of time series reveal that pike recruitment dynamics are temperature controlled. In 1976, expansion of a size-truncating perch pathogen into the lake severely impacted large perch and favoured pike as the IGP-dominant species. This pathogen-induced regime shift to a pike-dominated IGP apparently triggered a temperature-controlled trophic cascade passing through pike down to dissolved nutrients. In simple food chains, warming is predicted to strengthen top–down control by accelerating metabolic rates in ectothermic consumers, while pathogens of top consumers are predicted to dampen this top–down control. In contrast, the local IGP structure in Windermere made warming and pathogens synergistic in their top–down effects on ecosystem functioning. More generally, our results point to top predators as major mediators of community response to global change, and show that size-selective agents (e.g. pathogens, fishers or hunters) may change the topological architecture of food webs and alter whole ecosystem sensitivity to climate variation
Impact of the New South Wales fires during October 2013 on regional air quality in eastern Australia
No full textInternational audienceSmoke plumes from fires contain atmospheric pollutants that can be transported to populated areas and effect regional air quality. In this paper, the characteristics and impact of the fire plumes from a major fire event that occurred in October 2013 (17–26) in the New South Wales (NSW) in Australia, near the populated areas of Sydney and Wollongong, are studied. Measurements from the Fourier Transform InfraRed (FTIR) spectrometer located at the University of Wollongong allowed a calculation of specific emission factors (EFs) in terms of grams per kilogram of dry fuel burned: 1640 g kg−1 of carbon dioxide; 107 g kg−1 of carbon monoxide; 7.8 g kg−1 of methane; and 0.16 g kg−1 of nitrous oxide. These EFs have then been used to calculate daily fire emissions for the NSW fire event using the APIFLAME emissions' model, leading to an increase of 54% of CO emitted compared to calculations with EFs from Akagi et al. (2011), widely used in the literature
Evaluation of spectroscopic databases through radiative transfer simulations compared to observations. Application to the validation of GEISA 2015 with IASI and TCCON
No full textInternational audienceThe quality of spectroscopic parameters that serve as input to forward radiative transfer models are essential to fully exploit remote sensing of Earth atmosphere. However, the process of updating spectroscopic databases in order to provide the users with a database that insures an optimal characterization of spectral properties of molecular absorption for radiative transfer modelling is challenging. The evaluation of the databases content and the underlying choices made by the managing team is thus a crucial step. Here, we introduce an original and powerful approach for evaluating spectroscopic parameters: the Spectroscopic Parameters And Radiative Transfer Evaluation (SPARTE) chain. The SPARTE chain relies on the comparison between forward radiative transfer simulations made by the 4A radiative transfer model and observations of spectra made from various observations collocated over several thousands of well-characterized atmospheric situations. Averaging the resulting ‘calculated-observed spectral’ residuals minimizes the random errors coming from both the radiometric noise of the instruments and the imperfect description of the atmospheric state. The SPARTE chain can be used to evaluate any spectroscopic databases, from the visible to the microwave, using any type of remote sensing observations (ground-based, airborne or space-borne). We show that the comparison of the shape of the residuals enables: (i) identifying incorrect line parameters (line position, intensity, width, pressure shift, …), even for molecules for which interferences between the lines have to be taken into account; (ii) proposing revised values, in cooperation with contributing teams; (iii) validating the final updated parameters. In particular, we show that the simultaneous availability of two databases such as GEISA and HITRAN helps identifying remaining issues in each database. The SPARTE chain has been here applied to the validation of the update of GEISA-2015 in 2 spectral regions of particular interest for several currently exploited or planned Earth space missions: the thermal infrared domain and the short-wave infrared domain, for which observations from the space-borne IASI instrument and from the ground-based FTS instruments at the Parkfalls TCCON site are used respectively. Main results include: (i) the validation of the positions and intensities of line parameters, with overall significantly lower residuals for GEISA-2015 than for GEISA-2011; (iii) the validation of the choice made on the parameters (such as pressure shift and air-broadened width) which has not been given by the provider but completed by ourselves. For example, comparisons between residuals obtained with GEISA-2015 and HITRAN-2012 have highlighted a specific issue with some HWHM values in the latter that can be clearly identified on the ‘calculated-observed’ residuals
In situ observation of the Yb2+ emission in the radiodarkening process of Yb-doped optical preform
No full textInternational audienceThis Letter relates the clear evidence of Yb2+ formation under 2.5 MeV electron irradiation in optical fiber preforms showing a darkening of the core. We thus detected by in situ photoluminescence measurements the green emission of divalent Yb2+ under the 355 nm excitation. Moreover, we showed the existence of two types of Yb2+ ion species with different stabilities. We demonstrated that the radiodarkening mechanism is based on a pair association of Yb2+ with aluminum oxygen hole center point defects
New insights into the hydrological cycle from IASI δD distributions across theglobe
No full textInternational audienceBecause they have different vapour pressures, the different isotopologues of water (H216O and HDO)preferentially evaporate or condense during phase changes, leading to a fractionation of their ratio(δD). Numerous key processes of the hydrological cycle - such as convection, re-evaporation ofhydrometeors, evapotranspiration, mixing - mark distinctly the isotopic ratio of the air masses.Observations of δD constitute therefore a useful constraint on the moistening/drying processes. IASIprovide observations of δD in the free troposphere, after inversion of the measured radiances, at anunprecedented resolution.In this presentation, we illustrate the IASI capabilities to retrieve δD in the troposphere and show firstdistributions across the globe. The interest of these distributions is presented by analyzing theinformation contained in δD. For example, we show that the height of convection gives the watervapour a particular isotopic fingerprint which is of great interest to evaluate the representation oftropospheric mixing in climate models. We also present long term (6 years) time-series in the NorthernAtlantic. The seasonal and inter-annual variations are interpreted with backward trajectory analysesand we show that the Saharan dynamic strongly influence the isotopic composition above the AtlanticOcean through the formation of the Saharan Heat Low
Search for heavy resonances decaying to two Higgs bosons in final states containing four b quarks
No full textSubmitted to EPJC ; see paper for full list of authorsInternational audienceA search is presented for narrow heavy resonances X decaying into pairs of Higgs bosons (H) in proton-proton collisions collected by the CMS experiment at the LHC at sqrt(s)=8 TeV. The data correspond to an integrated luminosity of 19.7 inverse femtobarns. The search considers HH resonances with masses between 1 and 3 TeV, having final states of two b quark pairs. Each Higgs boson is produced with large momentum, and the hadronization products of the pair of b quarks can usually be reconstructed as single large jets. The background from multijet and t-tbar events is significantly reduced by applying requirements related to the flavor of the jet, its mass, and its substructure. The signal would be identified as a peak on top of the dijet invariant mass spectrum of the remaining background events. No evidence is observed for such a signal. Upper limits obtained at 95% confidence level for the product of the production cross section and branching fraction sigma(gg to X) B(X to HH to b-bbar b-bbar) range from 10 to 1.5 fb for the mass of X from 1.15 to 2.0 TeV, significantly extending previous searches. For a warped extra dimension theory with a mass scale Lambda[R] = 1 TeV, the data exclude radion scalar masses between 1.15 and 1.55 TeV
Sub-Riemannian curvature in contact geometry
No full textInternational audienceWe compare different notions of curvature on contact sub-Riemannian manifolds. In particular we introduce canonical curvatures as the coefficients of the sub-Riemannian Jacobi equation. The main result is that all these coefficients are encoded in the asymptotic expansion of the horizontal derivatives of the sub-Riemannian distance. We explicitly compute their expressions in terms of the standard tensors of contact geometry. As an application of these results, we obtain a sub-Riemannian version of the Bonnet-Myers theorem that applies to any contact manifold
Gender and the Publication Output of Graduate Students: A Case Study
No full textInternational audienceWe examine gender differences among the six PhD student cohorts 2004–2009 at the California Institute of Technology using a new dataset that includes information on trainees and their advisors and enables us to construct detailed measures of teams at the advisor level. We focus on the relationship between graduate student publications and: (1) their gender; (2) the gender of the advisor, (3) the gender pairing between the advisor and the student and (4) the gender composition of the team. We find that female graduate students co-author on average 8.5% fewer papers than men; that students writing with female advisors publish 7.7% more. Of particular note is that gender pairing matters: male students working with female advisors publish 10.0% more than male students working with male advisors; women students working with male advisors publish 8.5% less. There is no difference between the publishing patterns of male students working with male advisors and female students working with female advisors. The results persist and are magnified when we focus on the quality of the published articles, as measured by average Impact Factor, instead of number of articles. We find no evidence that the number of publications relates to the gender composition of the team. Although the gender effects are reasonably modest, past research on processes of positive feedback and cumulative advantage suggest that the difference will grow, not shrink, over the careers of these recent cohorts
Focused and Synthetic Nested Sequents (Extended Technical Report)
No full textFocusing is a general technique for transforming a sequent proof system into one with a syntactic separation of non-deterministic choices without sacrificing completeness. This not only improves proof search, but also has the representational benefit of distilling sequent proofs into synthetic normal forms. We show how to apply the focusing technique to nested sequent calculi, a generalization of ordinary sequent calculi to tree-like instead of list-like structures. We thus improve the reach of focusing to the most commonly studied modal logics, the logics of the modal S5 cube. Among our key contributions is a focused cut-elimination theorem for focused nested sequents.This is an extended version of a paper with the same title and authors that appears in the Proceedings of the 19th International Conference on Foundations of Software Science and Computation Structures (FoSSaCS), Eindhoven, Netherlands, 2-4 April 2016. This version contains full proofs of all the important lemmas and theorems