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Looking for observational signatures of early binary black hole systems
No full textInternational audienceContext. A lot of recent studies have focused on the observables associated with near merger binary black-holes (BBHs) embedded in a circumbinary disk (CBD) but we still we lack knowledge of observables of BBHs in their early stage. In that stage the separation between the two black holes is so large that both black holes could potentially retain their individual accretion disk existing before the creation of the BBH. For such early BBH systems, it is interesting to look for observables originating in those individual disks whose structure is likely to differ from mini-disks often observed in simulations of later stages of BBHs. Aims. In a companion paper we presented a set of hydrodynamical simulations of an individual disk surrounding a primary black hole while being impacted by the presence of a secondary black-hole in an early BBH system, leading to the creation of three well-known characteristic features in the disk's structure. Here we explore the imprints of these three features on the observables associated with the thermal emission of the pre-existing black hole disk. The aim is two-fold, first to see which observables are best suited for detecting those early systems and, secondly, what could be extrapolated about these systems from observations. Methods. We used general relativistic ray-tracing in order to produce synthetic observations of the thermal emission emitted by early BBHs with different mass ratio and separations in order to search for distinctive observational features of early systems. Results. We found that in the case of early BBH with pre-existing disk(s) a necessary, although not unique, observational feature is the truncation of their disk(s). Conclusions. Such observable could be used for automated search of potential BBHs and discriminate some existing candidates
Zoo: A Framework for the Verification of Concurrent OCaml 5 Programs using Separation Logic
No full textInternational audienceThe release of Ocaml 5, which introduced parallelism in the OCaml runtime, drove the need for safe and efficient concurrent data structures. New libraries like Saturn address this need. This is an opportunity to apply and further state-of-the-art program verification techniques. We present Zoo, a framework for verifying fine-grained concurrent OCaml 5 algorithms. Following a pragmatic approach, we defined a limited but sufficient fragment of the language to faithfully express these algorithms: ZooLang. We formalized its semantics carefully via a deep embedding in the Rocq proof assistant, uncovering subtle aspects of physical equality. We provide a tool to translate source OCaml programs into ZooLang syntax embedded inside Rocq, where they can be specified and verified using the Iris concurrent separation logic. To illustrate the applicability of Zoo, we verified a subset of the standard library and a collection of fined-grained concurrent data structures from the Saturn and Eio libraries. In the process, we also extended OCaml to more efficiently express certain concurrent programs
Biophysics of organoids
No full textInternational audienceOrganoids, 3D in vitro structures derived from embryonic or adult stem cells, offer powerful models for studying tissue patterning, development, morphogenesis, organ physiology and disease. These systems replicate biological processes, such as cell differentiation, symmetry breaking, and tissue organization, while revealing species-specific developmental variations. Biophysical factors, such as extracellular matrix composition, fluid dynamics, and tissue stiffness, interact with biochemical signals to drive organoid formation, revealing a complex multiscale phenomenon during growth, patterning and homeostasis. Physics-based approaches provide a framework to understand these processes from first principles. In recent years, a growing community of researchers has been exploring what can be termed the "biophysics of organoids." This review covers a broad range of approaches-mechanical, kinetic, information-based, statistical, and AI-driven-to study organoid development, offering insights into organogenesis, disease modeling, and regenerative medicine
Precision Measurements of Atom-Dimer Interactions in a Uniform Planar Bose Gas
No full textCold quantum gases, when acted upon by electromagnetic fields, can give rise to samples where isolated atoms coexist with dimers or trimers, which raises the question of the interactions between these various constituents. Here we perform microwave photoassociation in a degenerate gas of Rb atoms to create weakly-bound dimers in their electronic ground state. From the density-induced shift of the photoassociation line, we measure the atom-dimer scattering length for the two least-bound states of the molecular potential. We also determine the complete energy diagram of one hyperfine manifold of the least-bound state, which we accurately reproduce with a simple model
Councils, local power and social mobility at the turn of the third millennium BC
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Feedback-induced attitudinal changes in risk preferences
No full textAccording to the normative standpoint, decision-making under risk, as it is traditionally instantiated in choice among fully described probabilistic lotteries, should not be affected by the disclosure of outcomes (feedback). Yet, contrary to this normative prescription, empirical studies have repeatedly reported that risk preferences are affected by immediate presentation of choice outcomes. The consensual and intuitive hypothesis is that feedback affects risk preferences via a learning process, whereby experienced outcomes alter the representation of subjective values. However, despite a relatively large body of published studies, available evidence does not allow robustly establishing the direction and the impact of feedback on key decision variables, namely risk propensity and expected value maximization, limiting our ability to establish a clear cognitive mechanism. Here, we ran seven behavioral experiments, tailored to address this gap and found that the presence of feedback consistently increases risk-taking, without any detectable impact on expected value maximization. Crucially, fine-grained analyses of the temporal dynamics of the effect of feedback directly falsified one of the currently most influential models of the role of experience in decisions under risk, and challenges any instantiation of the learning hypotheses. These results rather favor of an attitudinal effect, induced by the anticipation of feedback information. Epistemic curiosity and regret avoidance may drive this effect in partial and complete feedback conditions, respectively
A Dual Approach To Combat Alzheimer's Disease through Concomitant hBChE Inhibition and S1R Activation
No full textInternational audienceAlzheimer's disease (AD) remains an incurable neurodegenerative disorder, requiring novel therapeutic strategies. We developed multitarget ligands designed to inhibit human butyrylcholinesterase (hBChE) and activate the sigma-1 receptor (S1R), addressing both cholinergic dysfunction and neuroinflammation, the latter being reduced through action on both targets. The (pseudo)-irreversible carbamate 18c emerged as the most promising compound, exhibiting potent and selective hBChE inhibition (IC 50 = 3.3 nM, 45-fold selectivity over human acetylcholinesterase) and strong S1R agonistic activity (IC 50 = 25 nM, EC 50 = 99 nM) determined in a radioligand binding assay and by S1R-BiP dissociation. Its cleavage product 14c (after carbamate hydrolysis by hBChE) retained dual activity (IC 50 (hBChE) = 269 nM, IC 50 (S1R) = 20 nM, and EC 50 (S1R) = 279 nM). Both compounds reduced lipopolysaccharide (LPS)-induced pro-inflammatory activation profile in the microglial N9 cells while preserving anti-inflammatory marker expression, thereby indicating an overall immunomodulatory effect. In vivo, inhibitor 18c improved cognitive deficits in a mouse model with Aβ 25-35 -induced neurotoxicity, enhancing short-and long-term memory in Y-maze and passive avoidance tests at dosages as low as 0.1-1 mg/kg. These findings highlight the potential of dual-targeting hBChE/S1R strategies for AD therapy
H.E.S.S. detection and multi-wavelength study of the 1 blazar PKS 034627
No full textInternational audiencePKS 0346-27 is a Low Synchrotron Peaked (LSP) blazar at redshift 0.991. The very-high-energy (VHE, E > 100 GeV) spectra of blazars are always affected by absorption by the Extragalactic Background Light (EBL) and subsequently, no blazars have been detected in VHE -rays at redshifts exceeding 1. Extending the redshift range of VHE-detected blazars to will yield insights into the cosmological evolution of both the VHE blazar population and the EBL. This is the goal of a target-of-opportunity (ToO) programme by H.E.S.S. to observe flaring high-redshift () blazars. We report on H.E.S.S. ToO and multi-wavelength observations of the blazar PKS 034627. Along with H.E.S.S., simultaneous data from {\it Fermi}-LAT, {\it Swift} (XRT and UVOT), and ATOM have been analysed and modelled using single-zone leptonic and hadronic models. PKS~0346-27 has been detected by H.E.S.S at a significance of 6.3 during one night, on 3 November 2021, while for other nights before and after this day, upper limits on the VHE flux are determined. No evidence for intra-night -ray variability has been found. A flare in high-energy (HE, ~MeV) -rays detected by {\it Fermi}-LAT preceded the H.E.S.S. detection by 2 days. A fit with a single-zone emission model to the contemporaneous spectral energy distribution during the detection night was possible with a proton-synchrotron-dominated hadronic model, requiring a proton-kinetic-energy-dominated jet power temporarily exceeding the source's Eddington limit, although alternative (e.g. multi-zone) models can not be ruled out. A one-zone leptonic model is, in principle, also able to fit the flare-state SED, however, requiring implausible parameter choices, in particular, extreme Doppler and bulk Lorentz factors of
The SKAO Pulsar Timing Array
No full textInternational audiencePulsar timing arrays (PTAs) are ensembles of millisecond pulsars observed for years to decades. The primary goal of PTAs is to study gravitational-wave astronomy at nanohertz frequencies, with secondary goals of undertaking other fundamental tests of physics and astronomy. Recently, compelling evidence has emerged in established PTA experiments for the presence of a gravitational-wave background. To accelerate a confident detection of such a signal and then study gravitational-wave emitting sources, it is necessary to observe a larger number of millisecond pulsars to greater timing precision. The SKAO telescopes, which will be a factor of three to four greater in sensitivity compared to any other southern hemisphere facility, are poised to make such an impact. In this chapter, we motivate an SKAO pulsar timing array (SKAO PTA) experiment. We discuss the classes of gravitational waves present in PTA observations and how an SKAO PTA can detect and study them. We then describe the sources that can produce these signals. We discuss the astrophysical noise sources that must be mitigated to undertake the most sensitive searches. We then describe a realistic PTA experiment implemented with the SKA and place it in context alongside other PTA experiments likely ongoing in the 2030s. We describe the techniques necessary to search for gravitational waves in the SKAO PTA and motivate how very long baseline interferometry can improve the sensitivity of an SKAO PTA. The SKAO PTA will provide a view of the Universe complementary to those of the other large facilities of the 2030s