Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Interventions invitées (5 hrs) dans le cadre de l’école thématique internationale Speciation and Bioavailability of Metals, Organics, and Nanoparticles : ‘Assessing electrostatic determinants of nanoparticles-cell interactions’ & ‘Whole cell metal-responsive biosensors: description and possibilities''

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Séries de cours-conférences invitées (17 hrs) au National Institute of Technology de Patna (Inde) dans le cadre du programme international Global Initiative of Academic Networks (GIAN)

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Metal partitioning at (bio)interfaces: going beyond the thermodynamic paradigm for evaluation of biouptake and toxicity

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Dynamics of metal uptake by charged soft biointerphases: impacts of depletion, internalisation, adsorption and excretion

International audienceA comprehensive theory is elaborated for the dynamics of metal ion uptake by charged spherical microorganisms. The formalism integrates the interplay over time between bulk metal depletion, metal adsorption, metal excretion (efflux) and transport of metals by conductive diffusion toward the metal-consuming biomembrane. The model further involves the basic physicochemical features of the microbial interphase in terms of size, distribution of electrostatic charges and thickness of peripheral soft surface appendage. A generalization of the Best equation is proposed and leads to the expression of the time-dependent concentration of metal ions at the active membrane surface as a function of bulk metal concentration. Combination of this equation with the metal conservation condition over the sample volume allows a full evaluation of bulk metal depletion kinetics and the accompanying time-dependent uptake and excretion fluxes as a function of metal-microorganism electrostatic interaction, microbe concentration and relevant biophysicochemical features of the interphase. Practically tractable expressions are derived in the limit where the Biotic Ligand Model (BLM) is obeyed and in situations where conductive diffusion transport of metals significantly determines the rate of biouptake. In particular, the plateau value reached at sufficiently long times by bulk metal concentration is rigorously expressed in terms of the key parameters pertaining to the adsorption process and to the kinetics of metal uptake and excretion. The theory extends and unifies previous approximate models where the impacts of extracellular metal transport and/or metal efflux on the overall rate of uptake were ignored

Coupling between Electroosmotically Driven Flow and Bipolar Faradaic Depolarization Processes in Electron-Conducting Microchannels

A quantitative theory is proposed for the analysis of steady electroosmotically driven flows within conducting cylindrical microchannels. Beyond a threshold value of the electric field applied in the electrolyte solution and parallel to the conducting surface, electrochemical oxidation and reduction reactions take place at the two extremities of the substrate. The spatial distribution of the corresponding local faradaic currents along the bipolar electrode is intrinsically coupled to that of the electric field in solution. The nonuniform distribution of the electric field alters the double layer composition, and in particular the zeta-potential value, along the conducting surface via the occurrence of concomitant electronic and ionic double layer charging processes. The combined spatial dependencies of the lateral electric field and electrokinetic potential considerably affects the distribution of the electroosmotic velocity field in the directions parallel and perpendicular to the surface depolarized by faradaic processes. In this paper, the coupling between bipolar electrodic behavior and electroosmosis is explicitly investigated for the case of irreversible—that is, kinetically controlled—electron transfer reactions. Typical simulation results are presented and illustrate the possibility of controlling and optimizing electroosmotic flows in conducting channels by electrochemical means

Electrostatics and electrophoresis of engineered nanoparticles and particulate environmental contaminants: Beyond zeta potential-based formulation

International audienceColloidal nano/micro-(bio)particles carry an electrostatic charge in aqueous media, and this charge is critical in defining their stability, (bio)adhesion properties, or toxicity toward humans and biota. Determination of interfacial electrostatics of these particles is often performed from zeta potential estimation using the electrophoresis theory by Smoluchowski. The latter, however, strictly applies to the ideal case of hard particles defined by a surface charge distribution under the strict conditions of particle impermeability to electrolyte ions and to flow. Herein, we review sound theoretical alternatives for capturing electrokinetic and therewith electrostatic features of soft colloids of practical interest defined by a 3D distribution of their structural charges and by a finite permeability to ions and/ or flow (e.g., bacteria, viruses, nanoplastics, (bio)functionalized particles or engineered nanoparticles). Reasons for the inadequacy of commonly adopted hard particle electrophoresis models when applied to soft particulate materials are motivated, and analytical expressions that properly capture their electrophoretic response are comprehensively reviewed

Modulation of Electroosmotic Flows in Electron-Conducting Microchannels by Coupled Quasi-Reversible Faradaic and Adsorption-Mediated Depolarization

A theoretical model is proposed for the description of steady electroosmotic flows within a cylindrical electron-conducting microchannel that is depolarized by faradaic and adsorption-mediated processes. The bipolar electron-transfer (e.t.) reactions are examined in the general situation where the electrolyte contains a quasi-reversible redox couple. The rate of the e.t. reactions is governed by transversal convective diffusion of the electroactive species to/from the surface and a position-dependent degree of reversibility. The nonuniform distribution of the electric field in solution, that is intimately coupled to that of the local faradaic current density, alters the double layer composition along the conducting surface via the occurrence of simultaneous electronic and ionic double layer charging processes. This in turn generates a nonlinear distribution of the zeta potential, which affects the electroosmotic flow. The highly coupled spatial profiles for the concentrations of the electroactive species, the faradaic current density, the electrokinetic potential, the electric field and the electroosmotic velocity in/along the metallic channel are solved by consistent numerical analysis of (i) the convective-diffusion equation, (ii) the generalized Butler–Volmer expression that includes mass transport and electron-transfer kinetic contributions, (iii) the continuity and Navier–Stokes equations, and (iv) the Poisson equation for finite currents. The results reported as a function of the surface properties of the channel and the kinetic characteristics of the e.t. reaction illustrate the deviations of the electroosmotic flow profiles as compared to the typical pluglike distribution predicted by Smoluchowski\u27s equation and encountered for homogeneous and dielectric channels. Manipulation of the flow patterns by bipolar electrochemical means is a promising way to control and optimize the local detection and separation of electroactive molecules or molecules dyed with electroactive elements