Miracle-dz/UniFAR-FTUs huggingface dataset:
Functional renormalisation group for turbulence

Abstract Turbulence is a complex nonlinear and multi-scale phenomenon. Although the fundamental underlying equations, the Navier–Stokes equations, have been known for two centuries, it remains extremely challenging to extract from them the statistical properties of turbulence. Therefore, for practical purposes, a sustained effort has been devoted to obtaining an effective description of turbulence, that we may call turbulence modelling, or statistical theory of turbulence. In this respect, the renormalisation group (RG) appears as a tool of choice, since it is precisely designed to provide effective theories from fundamental equations by performing in a systematic way the average over fluctuations. However, for Navier–Stokes turbulence, a suitable framework for the RG, allowing in particular for non-perturbative approximations, has been missing, which has thwarted RG applications for a long time. This framework is provided by the modern formulation of the RG called the functional renormalisation group (FRG). The use of the FRG has enabled important progress in the theoretical understanding of homogeneous and isotropic turbulence. The major one is the rigorous derivation, from the Navier–Stokes equations, of an analytical expression for any Eulerian multi-point multi-time correlation function, which is exact in the limit of large wavenumbers. We propose in this JFM Perspectives article a survey of the FRG method for turbulence. We provide a basic introduction to the FRG and emphasise how the field-theoretical framework allows one to systematically and profoundly exploit the symmetries. We stress that the FRG enables one to describe fully developed turbulence forced at large scales, which was not accessible by perturbative means. We show that it yields the energy spectrum and second-order structure function with accurate estimates of the related constants, and also the behaviour of the spectrum in the near-dissipative range. Finally, we expound the derivation of the spatio-temporal behaviour of $n$-point correlation functions, and largely illustrate these results through the analysis of data from experiments and direct numerical simulations.
SUPERSONIC LINE BROADENING WITHIN YOUNG AND MASSIVE SUPER STAR CLUSTERS

The origin of supersonic infrared and radio recombination nebular lines often detected in young and massive superstar clusters is discussed. We suggest that these arise from a collection of repressurizing shocks (RSs), acting effectively to re-establish pressure balance within the cluster volume and from the cluster wind which leads to an even broader although much weaker component. The supersonic lines here are shown to occur in clusters that undergo a bimodal hydrodynamic solution, that is within clusters that are above the threshold line in the mechanical luminosity or cluster mass versus the size of the cluster plane. A plethora of RSs is due to frequent and recurrent thermal instabilities that take place within the matter reinserted by stellar winds and supernovae. We show that the maximum speed of the RSs and of the cluster wind are both functions of the temperature reached at the stagnation radius. This temperature depends only on the cluster heating efficiency (η). Based on our two-dimensional simulations we calculate the line profiles that result from several models and confirm our analytical predictions. From a comparison between the predicted and observed values of the half-width zero intensity of the two line components, we conclude that the thermalization efficiency in young super star clusters above the threshold line must be lower than 20%.
Open Research Online Geographical trends in academic conferences: An analysis of authors’ aﬃliations

In the last decade, the research literature has reached an enormous volume with an unprecedented current annual increase of 1.5 million new publications. As research gets ever more global and new countries and institutions, either from academia or corporate environments, start to contribute, it is important to monitor this complex phenomenon and understand its dynamics and equilibria. We present a study on a conference proceedings dataset extracted from Springer Nature SciGraph that illustrates insightful geographical trends and highlights the unbalanced growth of competitive research institutions worldwide in the 1996–2016 period. The main contribution of this work is fourfold. In the ﬁrst instance, we found that the distributions of institutions and publications among countries follow a power law, consistently with previous literature, i.e., very few countries keep producing most of the papers accepted by high-tier conferences. Secondly, we show how the turnover rate of country rankings is extremely low and steadily declines over time, suggesting an alarmingly static landscape in which new entries struggle to emerge. We also performed an analysis of the venue locations and their effect on the distribution of countries involved in the publications, underlining the central role of Europe and China as knowledge hubs. Finally, we evidence the presence of an increasing gap between the number of institutions initiating and overseeing research endeavours (i.e. ﬁrst and last authors’ afﬁliations) and the total number of institutions participating in research. The paper also discusses our experience in working with authors’ afﬁliations: an utterly simple matter at ﬁrst glance, that is instead revealed to be a complex research and technical challenge.
Sculpting Andromeda – made-to-measure models for M31’s bar and composite bulge: dynamics, stellar and dark matter mass

The Andromeda galaxy (M31) contains a box/peanut bulge (BPB) entangled with a classical bulge (CB) requiring a triaxial modelling to determine the dynamics, stellar, and dark matter mass. We construct made-to-measure models fitting new VIRUS-W IFU bulge stellar kinematic observations, the IRAC-3.6 mu m photometry, and the disc's HI rotation curve. We explore the parameter space for the 3.6 mu m mass-to-light ratio ((sic)(3.6)), the bar pattern speed (Omega(p)), and the dark matter mass in the composite bulge (M-DM(B)) within 3.2 kpc. Considering Einasto dark matter profiles, we find the best models for (sic)(3.6) = 0.72 +/- 0.02 M circle dot L circle dot-1, M-DM(B) = 1.2(-0.4)(+0.2) x 10(10) M-circle dot, and Omega(p) = 40 +/- 5 km s(-1) kpc(-1). These models have a dynamical bulge mass of M-dyn(B) = 4.25(-0.29)(+0.10) x 10(10) M-circle dot including a stellar mass of M-star(B) = 3.09(-0.12)(+ 0.10) x 10(10) M-circle dot (73 per cent), of which the CB has M-star(CB) = 1.18(-0.07)(+0.06)x 10(10) M-circle dot (28 per cent) and the BPB M-star(BPB) = 1.91 +/- 0.06 x 10(10) M-circle dot (45 per cent). We also explore models with NFW haloes finding that, while the Einasto models better fit the stellar kinematics, the obtained parameters agree within the errors. The M-DM(B) values agree with adiabatically contracted cosmological NFW haloes with M31's virial mass and radius. The best model has two bulge components with completely different kinematics that only together successfully reproduce the observations (mu(3.6), upsilon(los), sigma(los), h3, h4). The modelling includes dust absorption which reproduces the observed kinematic asymmetries. Our results provide new constraints for the early formation of M31 given the lower mass found for the classical bulge and the shallow dark matter profile, as well as the secular evolution of M31 implied by the bar and its resonant interactions with the classical bulge, stellar halo and disc.
OBSERVING SIMULATED PROTOSTARS WITH OUTFLOWS: HOW ACCURATE ARE PROTOSTELLAR PROPERTIES INFERRED FROM SEDs?

The properties of unresolved protostars and their local environment are frequently inferred from spectral energy distributions (SEDs) using radiative transfer modeling. In this paper, we use synthetic observations of realistic star formation simulations to evaluate the accuracy of properties inferred from fitting model SEDs to observations. We use ORION, an adaptive mesh refinement (AMR) three-dimensional gravito-radiation-hydrodynamics code, to simulate low-mass star formation in a turbulent molecular cloud including the effects of protostellar outflows. To obtain the dust temperature distribution and SEDs of the forming protostars, we post-process the simulations using HYPERION, a state-of-the-art Monte Carlo radiative transfer code. We find that the ORION and HYPERION dust temperatures typically agree within a factor of two. We compare synthetic SEDs of embedded protostars for a range of evolutionary times, simulation resolutions, aperture sizes, and viewing angles. We demonstrate that complex, asymmetric gas morphology leads to a variety of classifications for individual objects as a function of viewing angle. We derive best-fit source parameters for each SED through comparison with a pre-computed grid of radiative transfer models. While the SED models correctly identify the evolutionary stage of the synthetic sources as embedded protostars, we show that the disk and stellar parameters can be very discrepant from the simulated values, which is expected since the disk and central source are obscured by the protostellar envelope. Parameters such as the stellar accretion rate, stellar mass, and disk mass show better agreement, but can still deviate significantly, and the agreement may in some cases be artificially good due to the limited range of parameters in the set of model SEDs. Lack of correlation between the model and simulation properties in many individual instances cautions against overinterpreting properties inferred from SEDs for unresolved protostellar sources.
Weyl metrics and wormholes

We study solutions obtained via applying dualities and complexifications to the vacuum Weyl metrics generated by massive rods and by point masses. Rescaling them and extending to complex parameter values yields axially symmetric vacuum solutions containing singularities along circles that can be viewed as singular matter sources. These solutions have wormhole topology with several asymptotic regions interconnected by throats and their sources can be viewed as thin rings of negative tension encircling the throats. For a particular value of the ring tension the geometry becomes exactly flat although the topology remains non-trivial, so that the rings literally produce holes in flat space. To create a single ring wormhole of one metre radius one needs a negative energy equivalent to the mass of Jupiter. Further duality transformations dress the rings with the scalar field, either conventional or phantom. This gives rise to large classes of static, axially symmetric solutions, presumably including all previously known solutions for a gravity-coupled massless scalar field, as for example the spherically symmetric Bronnikov-Ellis wormholes with phantom scalar. The multi-wormholes contain infinite struts everywhere at the symmetry axes, apart from solutions with locally flat geometry.
M33: A Galaxy with No Supermassive Black Hole

Galaxies that contain bulges appear to contain central black holes whose masses correlate with the velocity dispersion of the bulge. We show that no corresponding relationship applies in the pure disk galaxy M33. Three-integral dynamical models fit Hubble Space Telescope WFPC2 photometry and Space Telescope Imaging Spectrograph spectroscopy best if the central black hole mass is zero. The upper limit is 1500 M⊙. This is significantly below the mass expected from the velocity dispersion of the nucleus and far below any mass predicted from the disk kinematics. Our results suggest that supermassive black holes are associated only with galaxy bulges and not with their disks.
Electrodynamic models of 2D materials: can we match thin film and single sheet approaches?

The electromagnetic properties of 2D materials are modeled either as single sheets with a surface susceptibility or conductivity, or as thin films of finite thickness with an effective permittivity. Their intrinsic anisotropy, however, has to be fully described to reliably predict the optical response of systems based on 2D materials or to unambiguously interpret experimental data. In the present work, we compare the two approaches within the transfer matrix formalism and provide analytical relations between them. We strongly emphasize the consequences of the anisotropy. In particular, we demonstrate the crucial role of the choice of the thin film’s effective thickness compared with the parameters of the single sheet approach and therefore the computed properties of the 2D material under study. Indeed, if the isotropic thin film model with very low thickness is similar to an anisotropic single sheet with no out-of-plane response, with larger thickness it matches with a single sheet with isotropic susceptibility, in the reasonable small phase condition. We illustrate our conclusions Corresponding author: Pascal.Kockaert@ulb.ac. be on extensively studied experimental quantities such as transmittance, ellipsometry and optical contrast, and we discuss similarities and discrepancies reported in the literature when using single sheet or thin film models.
Plasma Diagnostics of Coronal Dimming Events

Coronal mass ejections are often associated with coronal dimmings, i.e., transient dark regions that are most distinctly observed in Extreme Ultra-violet wavelengths. Using Atmospheric Imaging Assembly (AIA) data, we apply Differential Emission Measure diagnostics to study the plasma characteristics of six coronal dimming events. In the core dimming region, we find a steep and impulsive decrease of density with values up to 50%–70%. Five of the events also reveal an associated drop in temperature of 5%–25%. The secondary dimming regions also show a distinct decrease in density, but less strong, decreasing by 10%–45%. In both the core and the secondary dimming the density changes are much larger than the temperature changes, confirming that the dimming regions are mainly caused by plasma evacuation. In the core dimming, the plasma density reduces rapidly within the first 20–30 minutes after the flare start and does not recover for at least 10 hr later, whereas the secondary dimming tends to be more gradual and starts to replenish after 1–2 hr. The pre-event temperatures are higher in the core dimming (1.7–2.6 MK) than in the secondary dimming regions (1.6–2.0 MK). Both core and secondary dimmings are best observed in the AIA 211 and 193 Å filters. These findings suggest that the core dimming corresponds to the footpoints of the erupting flux rope rooted in the AR, while the secondary dimming represents plasma from overlying coronal structures that expand during the CME eruption.
The Warm Neptunes around HD 106315 Have Low Stellar Obliquities

We present the obliquity of the warm Neptune HD 106315c measured via a series of spectroscopic transit observations. HD 106315c is a 4.4 REarth warm Neptune orbiting a moderately rotating late F star with a period of 21.05 days. HD 106315 also hosts a 2.5 REarth super-Earth on a 9.55 day orbit. Our Doppler tomographic analyses of four transits observed by the Magellan/MIKE, HARPS, and TRES facilities find HD 106315c to be in a low stellar obliquity orbit, consistent with being well aligned with the spin axis of the host star at . We suggest, via dynamical N-body simulations, that the two planets in the system must be coplanar, and thus are both well aligned with the host star. HD 106315 is only the fourth warm Neptune system with obliquities measured. All warm Neptune systems have been found in well aligned geometries, consistent with the interpretation that these systems are formed in situ in the inner protoplanetary disk, and also consistent with the majority of Kepler multi-planet systems that are in low obliquity orbits. With a transit depth of 1.02 mmag, HD 106315c is among the smallest planets to have been detected in transit spectroscopy, and we discuss its detection in the context of TESS and the next generations of spectrographs.
Chinese Immigration to France

Abstract:While still marginal across France as a whole, in terms of both stocks and flows, immigration from China has increased 6 times faster than that from other countries since the 1980s. This article aims to fill the quantitative knowledge gap on Chinese immigration. It begins by analysing census data to describe the main sociodemographic characteristics of Chinese immigrants with respect to those from other origins. Then, it uses administrative data to describe the inflows that have contributed to Chinese population increase in France, and to estimate outflows. These analyses produce two main findings: first, a strong residential concentration in the Paris region (Île-de-France) and in the most urbanized areas; and second, large student inflows gradually modifying the general sociodemographic profile of Chinese migrants in France.Abstract:L'immigration chinoise, bien que toujours marginale à l'échelle de la France métropolitaine, à la fois en termes de stocks et de flux, a connu depuis les années 1980 une croissance six fois plus rapide que celle en provenance des autres pays. Cet article vise à pallier la relative méconnaissance de cette immigration sur un plan quantitatif. Il analyse tout d'abord les données des recensements afin d'en décrire les principales caractéristiques sociodémographiques par comparaison aux autres immigrés. Il se fonde ensuite sur des données administratives afin d'étudier les flux alimentant la croissance de la population chinoise en France et d'estimer les flux de sortie. Deux principaux résultats ressortent des analyses : d'une part, une forte concentration résidentielle en Île-de-France et dans les zones les plus urbanisées du pays ; d'autre part, l'apport significatif de la migration étudiante, qui modifie progressivement le profil sociodémographique général des migrants chinois en France.Abstract:La inmigración china, aunque sigue siendo marginal a escala de la Francia metropolitana, tanto en términos de volumen como de flujos, ha experimentado desde los años ochenta un crecimiento seis veces más rápido que la procedente de otros países. Este artículo pretende paliar el relativo desconocimiento de esta inmigración en un plano cuantitativo. En primer lugar, analiza los datos de los censos para describir sus principales características sociodemográficas en comparación con otros inmigrantes. A partir de datos administrativos se describen entonces los flujos que alimentan el crecimiento de la población china en Francia y se estiman los flujos de salida. Se desprenden dos resultados principales: por una parte, una fuerte concentración residencial en Île-de-France y en las zonas más urbanizadas del país; por otra, la contribución significativa de la migración estudiantil, que modifica progresivamente el perfil sociodemográfico general de los migrantes chinos en Francia.
Coexisting ferroelectric and antiferroelectric phases in dipole ordered substances. Material properties and possible applications

Comprehensive review of investigations of substances with a small difference in the energies of the ferroelectric and antiferroelectric types of dipole ordering is presented. Detailed analysis of the stability of homogeneous phases and conditions for existence of the inhomogeneous state of the substance containing domains of the coexisting ferroelectric and antiferroelectric phases is presented. It is shown that the interaction of locally separated domains of the ferroelectric and antiferroelectric phases stabilizes an inhomogeneous state of these materials. The analysis of physical phenomena caused by the presence of domains of the coexisting ferroelectric and antiferroelectric phases in different dipole ordered substances is presented. Peculiarities of behavior of the systems with the inhomogeneous state of coexisting phases under the action of changing external thermodynamic parameters (temperature, pressure, electric field, and chemical composition) are analyzed and their importance for applications of these materials is discussed.
Bridging the gap between presynaptic hair cell function and neural sound encoding

Neural diversity can expand the encoding capacity of a circuitry. A striking example of diverse structure and function is presented by the afferent synapses between inner hair cells (IHCs) and spiral ganglion neurons (SGNs) in the cochlea. Presynaptic active zones at the pillar IHC side activate at lower IHC potentials than those of the modiolar side that have more presynaptic Ca2+- channels. The postsynaptic SGNs differ in their spontaneous firing rates, sound thresholds and operating ranges. While a causal relationship between synaptic heterogeneity and neural response diversity seems likely, experimental evidence linking synaptic and SGN physiology has remained difficult to obtain. Here, we aimed at bridging this gap by ex vivo paired recordings of IHCs and postsynaptic SGN boutons with stimuli and conditions aimed to mimic those of in vivo SGN-characterization. Synapses with high spontaneous rate of release (SR) were found predominantly on the pillar side of the IHC. These high SR synapses had larger and more compact spontaneous EPSCs, lower voltage-thresholds, tighter coupling of Ca2+ channels and vesicular release sites, shorter response latencies and higher initial release rates. This study indicates that synaptic heterogeneity in IHCs directly contributes to the diversity of spontaneous and sound-evoked firing of SGNs. Significance Statement Sound encoding relies on spiral ganglion neurons (SGNs) with diverse spontaneous firing, sound thresholds of firing and sound-intensity range over which SGN firing rate changes. Such functional SGN diversity might originate from different input from afferent synapses with inner hair cells (IHCs). The present study addresses this hypothesis by using recordings from individual IHC-SGN synapses of hearing mice under ex vivo conditions aimed to mimic cochlear physiology. The results provide evidence that synaptic heterogeneity in IHCs contributes to SGN firing diversity. Thus, the cochlea employs heterogeneous synapses to decompose sound information into different neural pathways that collectively inform the brain about sound intensity.
Noncanonical CDK4 signaling rescues diabetes in a mouse model by promoting β cell differentiation

Expanding beta cell mass is a critical goal in the fight against diabetes. CDK4, an extensively characterized cell cycle activator, is required to establish and maintain beta cell number. Beta cell failure in the IRS2-deletion mouse type 2 diabetes model is in part due to loss of CDK4 regulator Cyclin D2. We set out to determine whether replacement of endogenous CDK4 with the inhibitor-resistant mutant CDK4-R24C rescued the loss of beta cell mass in Irs2-deficient mice. Surprisingly, not only beta cell mass but also beta cell dedifferentiation status was effectively rescued, despite no improvement in insulin sensitivity. Ex vivo studies in primary islet cells revealed a novel mechanism in which CDK4 intervened downstream in the insulin signaling pathway to prevent FOXO1-mediated transcriptional repression of critical beta cell transcription factor Pdx1. FOXO1 inhibition was not related to E2F1 activity, to FOXO1 phosphorylation, or even to FOXO1 subcellular localization, but rather was related to deacetylation of FOXO1 and reduced FOXO1 abundance. Taken together, these results demonstrate a novel differentiation-promoting activity of the classical cell cycle activator CDK4 and support the concept that beta cell mass can be expanded without compromising function.