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The diameter of type associahedra and the non-leaving-face property
No full textInternational audienceGeneralized associahedra were introduced by S. Fomin and A. Zelevinsky in connection to finite type cluster algebras. Following recent work of L. Pournin in types and , this paper focuses on geodesic properties of generalized associahedra. We prove that the graph diameter of the -dimensional associahedron of type is precisely for all greater than . Furthermore, we show that all type associahedra have the non-leaving-face property , that is, any geodesic connecting two vertices in the graph of the polytope stays in the minimal face containing both. This property was already proven by D. Sleator, R. Tarjan and W. Thurston for associahedra of type . In contrast, we present relevant examples related to the associahedron that do not always satisfy this property
Magnesium stent scaffolds: DREAMS become reality
No full textInternational audienceWhy are bioresorbable scaffolds so exciting? Simply because they fulfil the task of scaffolding the artery wall during the healing period, and thereafter vanish. In other words, their lifetime is adjusted to the healing process, thus avoiding any risk of causing a new disease (eg, late thrombosis, in-stent restenosis, or neoatherosclerosis) as can happen with permanent stents. Permanent stents do a perfect scaffolding job, but remain in place when they are no longer necessary, leading to a foreign body reaction with complications
Filamentation and light bullet formation dynamics in solid-state dielectric media with weak, moderate and strong anomalous group velocity dispersion
No full textInternational audienceWe present a series of measurements, which characterize filamentation dynamics of intense ultrashort laser pulses in the space–time domain, as captured by means of three-dimensional imaging technique in sapphire and fused silica, in the wavelength range of 1.45–2.25 μm, accessing the regimes of weak, moderate and strong anomalous group velocity dispersion (GVD). In the regime of weak anomalous GVD (at 1.45 μm), pulse splitting into two sub-pulses producing a pair of light bullets with spectrally shifted carrier frequencies in both nonlinear media is observed. In contrast, in the regimes of moderate (at 1.8 μm) and strong (at 2.25 μm) anomalous GVD we observe notably different transient dynamics, which however lead to the formation of a single self-compressed quasistationary light bullet with an universal spatiotemporal shape comprised of an extended ring-shaped periphery and a localized intense core that carries the self-compressed pulse
A bijection for nonorientable general maps
No full textInternational audienceWe give a different presentation of a recent bijection due to Chapuy and Dołega for nonorientable bipartite quadrangulations and we extend it to the case of nonorientable general maps. This can be seen as a Bouttier–Di Francesco–Guitter-like generalization of the Cori–Vauquelin– Schaeffer bijection in the context of general nonorientable surfaces. In the particular case of triangulations, the encoding objects take a particularly simple form and this allows us to recover a famous asymptotic enumeration formula found by Gao
Plankton networks driving carbon export in the oligotrophic ocean
No full textInternational audienceThe biological carbon pump is the process by which CO2 is transformed to organic carbon via photosynthesis, exported through sinking particles, and finally sequestered in the deep ocean. While the intensity of the pump correlates with plankton community composition, the underlying ecosystem structure driving the process remains largely uncharacterized. Here we use environmental and metagenomic data gathered during the Tara Oceans expedition to improve our understanding of carbon export in the oligotrophic ocean. We show that specific plankton communities, from the surface and deep chlorophyll maximum, correlate with carbon export at 150 m and highlight unexpected taxa such as Radiolaria and alveolate parasites, as well as Synechococcus and their phages, as lineages most strongly associated with carbon export in the subtropical, nutrient-depleted, oligotrophic ocean. Additionally, we show that the relative abundance of a few bacterial and viral genes can predict a significant fraction of the variability in carbon export in these regions
Measurement of dijet azimuthal decorrelation in pp collisions at sqrt(s) = 8 TeV
No full textSubmitted to EPJC ; see paper for full list of authorsInternational audienceA measurement of the decorrelation of azimuthal angles between the two jets with the largest transverse momenta is presented for seven regions of leading jet transverse momentum up to 2.2 TeV. The analysis is based on the proton-proton collision data collected with the CMS experiment at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 inverse femtobarns. The dijet azimuthal decorrelation is caused by the radiation of additional jets and probes the dynamics of multijet production. The results are compared to fixed-order predictions of perturbative quantum chromodynamics (QCD), and to simulations using Monte Carlo event generators that include parton showers, hadronization, and multiparton interactions. Event generators with only two outgoing high transverse momentum partons fail to describe the measurement, even when supplemented with next-to-leading-order QCD corrections and parton showers. Much better agreement is achieved when at least three outgoing partons are complemented through either next-to-leading-order predictions or parton showers. This observation emphasizes the need to improve predictions for multijet production
Combined search for anomalous pseudoscalar HVV couplings in VH production and H to VV decay
No full textSubmitted to Phys. Lett. B ; see paper for full list of authorsInternational audienceA search for anomalous pseudoscalar couplings of the Higgs boson H to electroweak vector bosons V (= W or Z) in a sample of proton-proton collision events corresponding to an integrated luminosity of 18.9 inverse-femtobarns at a center-of-mass energy of 8 TeV is presented. Events consistent with the topology of associated VH production, where the Higgs boson decays to a pair of bottom quarks and the vector boson decays leptonically, are analyzed. The consistency of data with a potential pseudoscalar contribution to the HVV interaction, expressed by the effective pseudoscalar cross section fractions f[a3], is assessed by means of profile likelihood scans. Results are given for the VH channels alone and for a combined analysis of the VH and previously published H to VV channels. Assuming the standard model ratio of the coupling strengths of the Higgs boson to top and bottom quarks, f[a3](ZZ) > 0.0034 is excluded at 95% confidence level in the combination. Scenarios in which these assumptions are relaxed are also considered
A backward dual representation for the quantile hedging of Bermudan options
No full textInternational audienceWithin a Markovian complete financial market, we consider the problem of hedging a Bermudan option with a given probability. Using stochastic target and duality arguments, we derive a backward numerical scheme for the Fenchel transform of the pricing function. This algorithm is similar to the usual American backward induction, except that it requires two additional Fenchel transformations at each exercise date. We provide numerical illustrations
Search for massive WH resonances decaying into the l nu b anti-b final state at sqrt(s)=8 TeV
No full textSubmitted to Eur. Phys. J. C ; see paper for full list of authorsInternational audienceA search for a massive resonance W' decaying into a W and a Higgs boson in the l nu b anti-b (l = e, mu) final state is presented. Results are based on data corresponding to an integrated luminosity of 19.7 inverse femtobarns of proton-proton collisions at sqrt(s)=8 TeV, collected using the CMS detector at the LHC. For a high-mass (>~1 TeV) resonance, the two bottom quarks coming from the Higgs boson decay are reconstructed as a single jet, which can be tagged by placing requirements on its substructure and flavour. Exclusion limits at 95% confidence level are set on the production cross section of a narrow resonance decaying into WH, as a function of its mass. In the context of a little Higgs model, a lower limit on the W' mass of 1.4 TeV is set. In a heavy vector triplet model that mimics the properties of composite Higgs models, a lower limit on the W' mass of 1.5 TeV is set. In the context of this model, the results are combined with related searches to obtain a lower limit on the W' mass of 1.8 TeV, the most restrictive to date for decays to a pair of standard model bosons
What do we mean by identifiability in mixed effects models?
No full textWe discuss the question of model identifiability within the context of nonlinear mixed effects models. Although there has been extensive research in the area of fixed effects models, much less attention has been paid to random effects models. In this context we distinguish between theoretical identifiability, in which different parameter values lead to non-identical probability distributions , structural identifiability which concerns the algebraic properties of the structural model, and practical identifiability, whereby the model may be theoretically identifiable but the design of the experiment may make parameter estimation difficult and imprecise. We explore a number of pharmacokinetic models which are known to be non-identifiable at an individual level but can become identifiable at the population level if a number of specific assumptions on the probabilistic model hold. Essentially if the probabilistic models are different, even though the structural models are non-identifiable, then they will lead to different likelihoods. The findings are supported through simulations