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The present work follows a series of investigations of ours aimed at understanding whether longrange intermolecular electrodynamic forces could play a role in accelerating the encounter of the cognate partners of biochemical reactions in living matter and by which experimental methods and available techniques these forces could be detected. After the experimental detection of collective intramolecular oscillations of protein molecules [that we reported in Phys. Rev.X8, 031061 (2018)] the possibility of observing the mentioned electrodynamic interactions appears more realistic and thus deserving a deeper theoretical investigation of possible experimental detection of these forces with new data at hand.

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International audience; Early number skills are critical predictors of academic achievement, which is why focusing on their instruction from the very beginning of education is recommended. Young children’s number knowledge is also strongly influenced by home numeracy practices. This 12-week quasi-experimental study tested whether early number skills could be enhanced by a play-based intervention implemented at kindergarten (aged 4–6 years) by the teachers and whether providing numerical games to families delivered added value. A total of 569 children from 46 kindergarten classes were assigned either to the first treatment condition in which games were played only at kindergarten, or to the second treatment condition in which games were played at kindergarten and at home, or to the business-as-usual control condition. Measures of numerical ability were collected at pretest and posttest and analyzed through item response theory and multilevel modeling. Results indicated that playing the games at kindergarten allowed children with average and above-average initial performance to make more progress than children in the control group, while providing the games at home allowed low achievers from various backgrounds to progress more than in the other conditions. Implications for early mathematics instruction and for home-based intervention studies are discussed.

International audience; The preschool pupils’ numeracy competencies are predictive of their later academic and socio-professional success, and students who enter primary school with low numeracy skills tend to lag behind their peers mathematically later in school. Evidence shows that early numeracy skills are influenced by family background as well as family numeracy practices. However, few studies have attempted to understand precisely these relationships. Using data from Luxembourg, Switzerland, Belgium and France on the numeracy skills of 644 children aged 4 to 6 years and 388 parental questionnaires, this study aims at better identifying parental educational practices and family background characteristics that are associated with kindergarten children's numeracy skills. On one hand, our results show that the frequency of informal activities at home seems to be conducive to the development of early numeracy competencies, and this beyond the age of the children and the socio-economic and cultural level of the parents. On the other hand, it appears that parents seek to move closer to school when their child presents learning difficulties in mathematics. The implications of these various findings are discussed in terms of possible school interventions.; Les compétences en numératie des jeunes élèves sont prédictives de leur réussite scolaire et socio-professionnelle ultérieure, et les élèves qui entrent à l’école primaire avec de faibles connaissances sur le nombre ont tendance à rester en retard mathématique par rapport à leurs pairs plus tard dans leur scolarité. Les données disponibles montrent que les premières compétences numériques sont influencées par le background familial ainsi que par les pratiques familiales en matière de numératie. Toutefois, les études ayant cherché à comprendre précisément ces liens sont peu nombreuses. Au départ de données luxembourgeoises, suisses, belges et françaises sur les compétences numériques de 644 enfants de 4 à 6 ans et de 388 questionnaires parentaux, la présente étude vise à mieux identifier les pratiques éducatives parentales et les caractéristiques du background familial qui sont associées aux compétences en numératie des jeunes enfants. D’une part, les résultats mettent en évidence que la fréquence des activités informelles à domicile semble propice au développement des premières compétences mathématiques, et ce quel que soient l’âge des enfants et le niveau socio-économique et culturel des parents. D’autre part, il ressort que les parents cherchent à se rapprocher de l’école lorsque leur enfant présente des difficultés d’apprentissage en mathématiques. Les implications de ces différents constats sont discutées en termes d’interventions scolaires possibles.

${\mathrm{BaZrO}}_{3}$ is a perovskite that remains in the simple cubic phase at all temperatures, hence with no first-order Raman-active phonon mode allowed by symmetry. Yet, it exhibits an intense Raman spectrum with sharp and well-defined features. Here, we report the evolution of the Raman spectrum of ${\mathrm{BaZrO}}_{3}$ single crystals in a broad temperature range (4--1200 K) and discuss its origin with the support of detailed first-principle calculations of the lattice dynamics. Phonon calculations are performed not only for the cubic phase of ${\mathrm{BaZrO}}_{3}$, but also for the low-symmetry phases with octahedra tilts that have been suspected to exist at the nanoscale. We show that the Raman spectrum shows no direct evidence for these nanodomains, but can instead be explained by classical second-order Raman scattering. We provide an assignment of the dominant features to phonon mode combinations. In particular, we show that the high frequency range of the spectrum is dominated by overtones and shows an image of the phonon density of states corresponding to the stretching modes of the oxygen octahedra.

International audience; Ferroic materials naturally exhibit a rich number of functionalities, which often arise from thermally , chemically or mechanically induced symmetry breakings or phase transitions. Based on Density Functional Calculations, we demonstrate here that light can drive phase transitions as well in ferroelectric materials such as the perovskite oxides lead titanate and barium titanate. Phonon analysis and total energy calculations reveal that the polarization tends to vanish under illumination , to favor the emergence of non-polar phases, potentially antiferroelectric, and exhibiting a tilt of the oxygen octahedra. Strategies to tailor photo-induced phases based on phonon instabilities in the electronic ground state are also discussed.

International audience; A large number of advanced finite element shell formulations have been developed, but their adoption is hindered by complexities of transforming mathematical formulations into computer code. Furthermore, it is often not straightforward to adapt existing implementations to emerging frontier problems in thin structural mechanics including nonlinear material behaviour, complex microstructures, multi-physical couplings, or active materials. We show that by using a high-level mathematical modelling strategy and automatic code generation tools, a wide range of advanced plate and shell finite element models can be generated easily and efficiently, including: the linear and non-linear geometrically exact Naghdi shell models, the Marguerre-von Karman shallow shell model, and the Reissner-Mindlin plate model. To solve shear and membrane-locking issues, we use: a novel re-interpretation of the Mixed Interpolation of Tensorial Component (MITC) procedure as a mixed-hybridisable finite element method, and a high polynomial order Partial Selective Reduced Integration (PSRI) method. The effectiveness of these approaches and the ease of writing solvers is illustrated through a large set of verification tests and demo codes, collected in an open-source library, FEniCS-Shells, that extends the FEniCS Project finite element problem solving environment.

Ferroic domain walls could play an important role in microelectronics, given their nanometric size and often distinct functional properties. Until now, devices and device concepts were mostly based on mobile domain walls in ferromagnetic and ferroelectric materials. A less explored path is to make use of polar domain walls in nonpolar ferroelastic materials. Indeed, while the polar character of ferroelastic domain walls has been demonstrated, polarization control has been elusive. Here, we report evidence for the electrostatic signature of the domain-wall polarization in nonpolar calcium titanate (CaTiO3). Macroscopic mechanical resonances excited by an ac electric field are observed as a signature of a piezoelectric response caused by polar walls. On the microscopic scale, the polarization in domain walls modifies the local surface potential of the sample. Through imaging of surface potential variations, we show that the potential at the domain wall can be controlled by electron injection. This could enable devices based on nondestructive information readout of surface potential., Comment: 30 pages, 12 figures

International audience; Appel à contributions : La recherche, objet de recherche : à propos de la réflexivité et de la distanciation critique » Titre Gymnastique épistémologique, critique et réflexive : la construction d'une recherche en « ex-Yougoslavie » face à la colonialité du savoir Abstract Cet article tente de retracer une histoire, celle de l'évolution de ma propre réflexivité durant le temps d'une thèse intitulée « Aménager les frontières des périphéries européennes. La frontière Serbie/Croatie à l'épreuve des injonctions à la coopération et à la réconciliation » (Blondel, 2016). Mon propos ici est de rendre compte d'une conviction, la nécessité de s'engager dans une démarche réflexive et critique avant, pendant et après la production de la recherche en elle-même. Cet article constitue ainsi une tentative de démonstration par l'exemple de l'intérêt d'une telle posture. Je vise d'une part à exposer comment j'ai construit mes réflexions épistémologiques, par une déconstruction progressive des cadres théoriques classiques (nationalistes, post-socialiste, post-yougoslave) choisis ou imposés. D'autre part, j'expose les aboutissements de cette réflexivité, i.e. principalement ma prise de conscience de la colonialité du savoir (et du mien en particulier). Cette gymnastique m'a permis de parfois dépasser, et de plus souvent rendre compte de, certaines limites de mon travail, mais aussi d'accepter l'indépassable lié à certains aspects de ma situation de recherche, de la manière dont je l'ai énoncée et conduite. Mener ce type d'exercice et en rendre compte contribuent alors à mieux préciser les conditions de validité scientifique de ses travaux, à mieux situer le propos et l'apport du chercheur, sa position et donc sa positionnalité. 2 Mots-clés Réflexivité, pensée décoloniale, épistémologie, nationalismes méthodologiques, post-socialisme, post-yougoslave Abstract in English This article is a story, narrating the evolution of my own reflections during my PhD

The ability to generate efficient giga–terahertz coherent acoustic phonons with femtosecond laser makes acousto-optics a promising candidate for ultrafast light processing, which faces electronic device limits intrinsic to complementary metal oxide semiconductor technology. Modern acousto-optic devices, including optical mode conversion process between ordinary and extraordinary light waves (and vice versa), remain limited to the megahertz range. Here, using coherent acoustic waves generated at tens of gigahertz frequency by a femtosecond laser pulse, we reveal the mode conversion process and show its efficiency in ferroelectric materials such as BiFeO3 and LiNbO3. Further to the experimental evidence, we provide a complete theoretical support to this all-optical ultrafast mechanism mediated by acousto-optic interaction. By allowing the manipulation of light polarization with gigahertz coherent acoustic phonons, our results provide a novel route for the development of next-generation photonic-based devices and highlight new capabilities in using ferroelectrics in modern photonics., Electrically driven acousto-optic light modulators are limited to frequencies of a few hundred megahertz and are typically no smaller than a few micrometres. Here, the authors demonstrate gigahertz acousto-optic conversion of light polarization in a region of a few nanometres using pulsed laser stimulation of a ferroelectric.

International audience; Ferroelectrics carry a switchable spontaneous electric polarization. Thispolarization is usually coupled to strain, making ferroelectrics goodpiezoelectrics. When coupled to magnetism, they become so-called multiferroicsystems, a field that has been widely investigated since 2003. Whileferroelectrics are birefringent and non-linear optically transparent materials,the coupling of polarization with optical properties has received, since 2009,renewed attention, triggered notably by low-bandgap ferroelectrics suitable forsunlight spectrum absorption and original photovoltaic effects. Consequently,power conversion efficiencies up to 8.1% were recently achieved and valuesof 19.5% were predicted, making photoferroelectrics promising photovoltaicalternatives. This article aims at providing an up-to-date review on thisemerging and rapidly progressing field by highlighting several importantissues and parameters, such as the role of domain walls, ways to tune thebandgap, consequences arising from the polarization switchability, and the roleof defects and contact electrodes, as well as the downscaling effects. Beyondphotovoltaicity, other polarization-related processes are also described, likelight-induced deformation (photostriction) or light-assisted chemical reaction(photostriction). It is hoped that this overview will encourage further avenuesto be explored and challenged and, as a byproduct, will inspire other research

International audience; Graphene flakes with giant shape anisotropy are extensively used to establish connectedness electrical percolation in various heterogeneous systems. However, the percolation behaviour of graphene flakes has been recently predicted to be far more complicated than generally anticipated on the basis of excluded volume arguments. Here we confirm experimentally that graphene flakes self-assemble into nematic liquid crystals below the onset of percolation. The competition of percolation and liquid crystal transition provides a new route towards high-k materials. Indeed, near-percolated liquid-crystalline graphene-based composites display unprecedented dielectric properties with a dielectric constant improved by 260-fold increase as compared with the polymer matrix, while maintaining the loss tangent as low as 0.4. This performance is shown to depend on the structure of monodomains of graphene liquid-crystalline phases. Insights into how the liquid crystal phase transition interferes with percolation transition and thus alters the dielectric constant are discussed.

International audience; Predictability is an important aspect in real-time and safety-critical systems, where non-functional properties – such as the timing behavior – have high impact on the system cor-rectness. As many safety-critical systems have a growing performance demand, simple, but outdated architectures are not sufficient anymore. Instead, multi-core systems are more and more popular, even in the real-time domain. To combine the performance benefits of a multi-core architecture with the required predictability, Time Division Multiple Access (TDMA) buses are often advocated. In this paper, we are interested in accesses to shared resources in such environments. Our approach uses SMT (Satisfiability Modulo Theory) to encode the semantics and execution time of the analyzed program in an environment with shared resources. We use an SMT-solver to find a solution that corresponds to the execution path with correct semantics and maximal execution time. We propose to model a shared bus with TDMA arbitration policy. Using examples, we show how the WCET estimation is enhanced by combining the semantics and the shared bus analysis in SMT.

International audience; Mixed-criticality systems integrate components of different criticality. Different criticality levels require different levels of confidence in the correct behavior of a component. One aspect of correctness is timing. Confidence in worst-case execution time (WCET) estimates depends on the process by which they have been obtained. A somewhat naive view is that static WCET analyses determines safe bounds in which we can have absolute confidence, while measurement-based approaches are inherently unreliable. In this paper, we refine this view by exploring sources of doubt in the correctness of both static and measurement-based WCET analysis.

International audience; Leapfrog development is a typical form of sprawl. This paper aims at analyzing the existence, size, and persistence of leapfrogging in a dynamic urban economic model with endogenous green amenities. We analyze whether incoming households choose to settle at the fringe of the city or to jump further away depending on their preferences and the structure of the city. We first provide an analytical treatment of the conditions and characteristics under which a first leapfrog occurs and show how the optimal choice is affected by the size of the city, income, commuting costs, as well as the size of the area where green amenities are considered. We then study how further leapfrogging and multiple urban rings may appear and be maintained in the long-run equilibrium, and how infill processes take place through time.

This review devoted to multiferroic properties of Bismuth-based perovskites falls into two parts. The first part focuses on BiFeO3 and summarizes the recent progress made in the studies of its pressure-temperature phase diagram and magnetoelectric coupling phenomena. The second part discusses in a more general way the issue of polar - and multiferroic - phases in BiBO3 perovskites and the competition between ferroelectricity and other structural instabilities, from an inventory of recently synthetized compounds., Comment: 22 pages, 7 figures, to be published in Comptes Rendus Physique

Under which conditions do the electrical transport properties of one-dimensional (1D) carbon nanotubes (CNTs) and 2D graphene become equivalent? We have performed atomistic calculations of the phonon-limited electrical mobility in graphene and in a wide range of CNTs of different types to address this issue. The theoretical study is based on a tight-binding method and a force-constant model from which all possible electron-phonon couplings are computed. The electrical resistivity of graphene is found in very good agreement with experiments performed at high carrier density. A common methodology is applied to study the transition from 1D to 2D by considering CNTs with diameter up to 16 nm. It is found that the mobility in CNTs of increasing diameter converges to the same value, the mobility in graphene. This convergence is much faster at high temperature and high carrier density. For small-diameter CNTs, the mobility strongly depends on chirality, diameter, and existence of a bandgap., 12 pages

International audience; Cette contribution retrace les grandes lignes et les grands enjeux de l'évolution de l'appareil policier en Belgique, depuis l'indépendance du pays. Elle en dresse une synthèse à partir de l'historiographie la plus récente

International audience; What is the on-line echo of the commemoration of the centenary of the 1st World War ? What is the behavior of Memorial/Heritage Institutions about the 1st World War on Twitter ? How do they pass information about the Centenary ? Is there an effect of the English predominance on Twitter about the Centenary on the way non-English twitter accounts are considering the 1st World War? Those questions are to be answered by a research project that is to be presented in this poster, which aims at harvesting tweets containing hashtags linked to the Centenary since April 2014.

We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties with Dirac bands. Using atomistic tight-binding calculations, we show that both the atomic lattice and the overall geometry influence the band structure, revealing materials with unusual electronic properties. In rocksalt Pb chalcogenides, the expected Dirac-type features are clouded by a complex band structure. However, in the case of zinc-blende Cd-chalcogenide semiconductors, the honeycomb nanogeometry leads to rich band structures, including, in the conduction band, Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has S-orbital character and is equivalent to the pi-pi* band of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their P-orbital character. We show that the width of the Dirac bands varies between tens and hundreds of meV. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. Recent advancements in colloidal chemistry indicate that these materials can be synthesized from semiconductor nanocrystals., 12 pages, 12 figures

It is known how to transform certain canonical three-pass identification schemes into signature schemes via the Fiat---Shamir transform. Pointcheval and Stern showed that those schemes are existentially unforgeable in the random-oracle model leveraging the, at that time, novel forking lemma. Recently, a number of 5-pass identification protocols have been proposed. Extending the above technique to capture 5-pass identification schemes would allow to obtain novel unforgeable signature schemes. In this paper, we provide an extension of the forking lemma (and the Fiat---Shamir transform) in order to assess the security of what we call $$n$$n-generic signature schemes. These include signature schemes that are derived from certain $$(2n+1)$$(2n+1)-pass identification schemes. In doing so, we put forward a generic methodology for proving the security of a number of signature schemes derived from $$(2n+1)$$(2n+1)-pass identification schemes for $$n\ge 2$$n?2. As an application of this methodology, we obtain two new code-based existentially-unforgeable signature schemes, along with a security reduction. In particular, we solve an open problem in multivariate cryptography posed by Sakumoto, Shirai and Hiwatari at CRYPTO 2011.

International audience; While most recent analyses stress a shift of psychiatric forensics from issues of responsibility to dangerousness, this survey offers a different view on the question based on a study on psychiatric expert work before criminal courts. Experts still assess responsibility, not merely in its penal dimension but mainly in other forms such as factual or moral responsibility. Experts do not anymore withdraw mentally ill criminals from court proceedings but they delineate personalities of criminals and circumstances of crime. Their reports enable to assess the risk for society the accused represents. They are not asked to determine whether "criminals" should be neutralized but to assess the accused's motivation and sincerity concerning his/her commitment in a cure process and for amendment.; Alors que des analystes font état du passage d'une expertise de responsabilité à une expertise de dangerosité, une recherche sur le rôle de l'expertise psychiatrique dans les juridictions criminelles permet de nuancer ce constat, et ce, de deux façons. On remarque d'abord que les experts psychiatres participent encore et toujours à établir la responsabilité, non pas strictement pénale mais sous d'autres formes comme la responsabilité objective ou morale. Le rôle des experts ne consiste donc plus à soustraire les « fous » à la justice, mais à identifier les « criminels » et à établir les circonstances du crime. Leur discours permet aussi de savoir si l'accusé représente un risque pour la société. Les experts ne sont pas mobilisés afin de savoir s'il faut ou non neutraliser les « criminels », mais davantage afin de mesurer leur motivation et de s'assurer de la sincérité de leur engagement dans une démarche de soins où l'accusé a la responsabilité de travailler sur lui et de s'amender.

International audience