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Impact of bias adjustment strategy on ensemble projections of hydrological extremes
No full textInternational audienceHydrological climate change impact studies typically rely on hydrological projections generated by hydrological models driven with bias-adjusted climate simulations. Such hydrological projections are influenced by internal climate variability, which can mask the emergence of robust climate trends. To account for internal variability in climate projections, single-model initial-condition large ensembles (SMILEs) can be employed. SMILEs are generated by running a single global/regional climate model many times with slightly perturbed initial conditions. However, it remains challenging to select an appropriate bias adjustment strategy for SMILEs used in hydrological impact studies because of the relative importance of inter-variable dependence and the preservation of both climate variability and the change signal. To facilitate such selection, we here compare different bias adjustment strategies applied to SMILEs and their effect on hydrological impact assessments. Specifically, we investigate how climate and hydrological extremes change for 87 catchments in the Swiss Alps when using (a) univariate vs. bivariate, (b) ensemble vs. individual-member, and (c) change-preserving vs. non-change-preserving bias adjustment methods. To do so, we adjust the biases of a 50-member SMILE with the different adjustment methods and drive a hydrological model to simulate and project high and low flows. Our comparison shows (1) no clear benefits from using bivariate instead of univariate bias adjustment methods when the SMILE already efficiently simulates the dependence between temperature and precipitation and (2) that the choice of using ensemble vs. individual-member and change-preserving vs. non-change-preserving bias adjustments leads to large differences in the values of signal robustness indicators, including temperature, precipitation and streamflow signal-to-noise ratios and streamflow and precipitation time-of-emergence. These influences need to be considered when selecting an appropriate bias adjustment strategy for a given application. Based on our comparison, we generally recommend to apply change-preserving and ensemble bias adjustment methods in future hydrological impact studies using SMILEs. Further research is needed to improve bias adjustment methods that preserve both the signal and the variability of ensemble climate projections
Polarizable models for selected Endocrine Disrupting Chemicals and their hosts
No full textInternational audienceSteroid hormones like estradiol and progesterone bind to nuclear hormone receptors and regulate gene transcription. They compete with pollutants and Endocrine Distrupting Chemicals (EDCs) like bisphenol A. When administered as medication, estradiol and progesterone are themselves considered EDCs. To allow modeling studies, parameters for the polarizable AMOEBA force field were derived here for these three molecules, along with the host molecule cyclodextrin and two phosphorylated forms of p-cresol and tyrosine. Indeed, phosphorylation of an Estrogen Receptor tyrosine regulates estradiol action. AMOEBA-optimized molecular structures were in good agreement with quantum mechanics, and interaction energies with water or ammonium well-reproduced. Molecular dynamics simulations of crystal structures showed improved agreement with experiment over an additive force field; the mean relative error for unit cell volumes was reduced by more than two. A short MD simulation of the estradiol-estrogen receptor complex was done as a proof of principle and was structurally stable. Although additional simulations are desirable, the developed parameters should already be useful for studying hormone and EDC interactions with their hosts
Scattering from an external field in quantum chromodynamics at high energies: From foundations to interdisciplinary connections
No full textInternational audienceWe review the factorization of the S S -matrix elements in the context of particle scattering off an external field, which can serve as a model for the field of a large nucleus. The factorization takes the form of a convolution of light cone wave functions describing the physical incoming and outgoing states in terms of bare partons, and products of Wilson lines. The latter represent the interaction between the bare partons and the external field. Specializing to elastic scattering amplitudes of onia at very high energies, we introduce the color dipole model, which formulates the calculation of the modulus-squared of the wave functions in quantum chromodynamics with the help of a branching random walk, and the scattering amplitudes as observables on this classical stochastic process. Methods developed for general branching processes produce analytical formulas for the asymptotics of such observables, and thus enable one to derive exact large-rapidity expressions for onium-nucleus cross sections, from which electron-nucleus cross sections may be inferred
Modeling complex particle suspensions: Perspectives on the rigid multiblob method
No full textInternational audienceMany suspensions contain particles with complex shapes that are affected not only by hydrodynamics but also by thermal fluctuations, internal activity, kinematic constraints, and other long-range nonhydrodynamic interactions. Modeling these systems represents a significant numerical challenge due to the interplay between different effects and the need to accurately capture multiscale phenomena. In this article we review recent developments to model large suspensions of particles of arbitrary shapes and multiple couplings with controllable accuracy within the rigid multiblob framework. We discuss the governing equations, highlight key numerical developments, and illustrate applications ranging from microswimmers to complex colloidal suspensions. This review illustrates the effectiveness and versatility of the rigid multiblob method in tackling a wide range of physical problems in fluid mechanics, soft matter physics, biophysics, materials, and colloidal science
Measurement of the ratio of the B J/ and B J/ branching fractions using three-prong lepton decays
No full textInternational audienceThe ratio between the B J/ and B J/ branching fractions is measured using a data sample of proton-proton collisions collected by CMS at a center-of-mass energy of 13 TeV in the years 20162018 and corresponding to an integrated luminosity of 138 fb. The J meson is identified through its J decay and the tau lepton is reconstructed in the hadronic three-prong final state. The measured ratio of branching fractions in this tau decay mode, = 1.04, is combined with the previous analysis based on the leptonic decay channel, leading to = 0.49 0.26. As this result is consistent with the standard model prediction of 0.258 0.004, no evidence of lepton flavor universality violation is found
4f-intermediate valence in an ytterbium–bipyridine coordination solid
No full textInternational audienceWe report the first structurally characterised coordination solids based on decamethylytterbocene, using bipyridine linkers to form YbCp*2(bipy) and YbCp*2(Me2bipy). Analogous to their mononuclear cousins known for intermediate valence, spectroscopic evidence suggests that YbCp*2(bipy) features a multiconfigurational ground state, composed of a superposition of an open-shell ligand non-innocent 4f13(π*)1 state and a closed-shell 4f14 state. Our findings mark a first step toward increasing electronic correlations in lanthanide–organic frameworks, with the aim of realising materials with coexisting electronic transport and emergent magnetic properties
Trends in relativistic laser–matter interaction: the promises of structured light
No full textInternational audienceTime and space envelope, frequency and wavelength distributions, polarization, and phase are quantities that define the properties of laser light. Controlling them opens up strategies for manipulating the properties of atoms in various media. At relativistic intensity, matter is rapidly transformed into a plasma state, which is modifying the laser’s propagation, its absorption enabling the generation of intense magnetic and electric fields. In this context, structured light presents exciting, promising, and challenging opportunities for research. This review article aims to explain the concepts of structured light, their applications to real experiments at relativistic intensities, practical considerations, and some scientific perspectives
The SCM instrument for the ESA Plasma Observatory mission
No full textInternational audienceThe proposal of the Plasma Observatory mission was selected for a competitive phase A with two other missions in the framework of the seventh call for medium mission (M7) organized by ESA. The mission selection is planned in 2026 for a launch in 2037. Its main objectives are to unveil how are particles energized in space plasma and which processes dominate energy transport and drive coupling between the different regions of the terrestrial magnetospheric system? The mission consists of seven satellites, a main platform (mothercraft, MSC) and six smaller identical satellites (daughtercraft) evolving along an equatorial elliptical orbit with an apogee ~17 and a perigee ~8 Earth radii. The seven satellites will fly forming two tetraedra and allowing simultaneous measurements at both fluid and ion scales. The mission will include three key science regions: dayside (solar wind, bow shock, magnetosheath, magnetopause), nightside transition region (quasidipolar region, transient near-Earth current sheet, field-aligned currents, braking flow region) and the medium magnetotail (near-Earth reconnection region, fast flow formation region). Plasma Observatory mission is the next logical step after the four satellite magnetospheric missions Cluster and MMS. The search-coil magnetometer (SCM), strongly inherited of the SCM designed for the ESA JUICE mission, is only included in the Fields instrument suite of the MSC. SCM will be delivered by LPP and LPC2E and will provide the three components of the magnetic field fluctuations in the [0.1Hz-8kHz] frequency range, after digitization by the Low frequency Receiver (LFR) within the Field and Wave Processor (FWP), relevant for the three Key science regions. It will be mounted on a 6m boom and will allow to reach the following sensitivities [10-3, 1.5x10-6, 5x10-9, 10-10, 5x10-10] nT2/Hz at [1, 10, 100, 1000, 8000] Hz. Associated with the electric field instrument (EFI), SCM will allow to fully characterize the wave polarization and estimate the direction of propagation of the wave energy. These measurements are crucial to understand the role of electromagnetic waves in the energy conversion processes, the plasma and energy transport, the acceleration and the heating of the plasma.
Concentration and excess risk bounds for imbalanced classification with synthetic oversampling
No full textInternational audienceSynthetic oversampling of minority examples using SMOTE and its variants is a leading strategy for addressing imbalanced classification problems. Despite the success of this approach in practice, its theoretical foundations remain underexplored. We develop a theoretical framework to analyze the behavior of SMOTE and related methods when classifiers are trained on synthetic data. We first derive a uniform concentration bound on the discrepancy between the empirical risk over synthetic minority samples and the population risk on the true minority distribution. We then provide a nonparametric excess risk guarantee for kernel-based classifiers trained using such synthetic data. These results lead to practical guidelines for better parameter tuning of both SMOTE and the downstream learning algorithm. Numerical experiments are provided to illustrate and support the theoretical findings
Discovery of suppressed charged-particle production in ultrarelativistic oxygen-oxygen collisions
No full textInternational audienceA hot and dense state of nuclear matter, known as the quark-gluon plasma, is created in collisions of ultrarelativistic heavy nuclei. Highly energetic quarks and gluons, collectively referred to as partons, lose energy as they travel through this matter, leading to suppressed production of particles with large transverse momenta (). Conversely, high- particle suppression has not been seen in proton-lead collisions, raising questions regarding the minimum system size required to observe parton energy loss. Oxygen-oxygen (OO) collisions examine a region of effective system size that lies between these two extreme cases. The CMS detector at the CERN LHC has been used to quantify charged-particle production in inclusive OO collisions for the first time via measurements of the nuclear modification factor (). The is derived by comparing particle production to expectations based on proton-proton (pp) data and has a value of unity in the absence of nuclear effects. The data for OO and pp collisions at a nucleon-nucleon center-of-mass energy = 5.36 TeV correspond to integrated luminosities of 6.1 nb and 1.02 pb, respectively. The is below unity with a minimum of 0.69 0.04 around = 6 GeV. The data exhibit better agreement with theoretical models incorporating parton energy loss as compared to baseline models without energy loss