Strong Isotopic Effect in Phase II of Dense Solid Hydrogen and Deuterium

Quantum nuclear zero-point motions in solid H$_2$ and D$_2$ under pressure are investigated at 80 K up to 160 GPa by first-principles path-integral molecular dynamics calculations. Molecular orientations are well-defined in phase II of D$_2$, while solid H$_2$ exhibits large and very asymmetric angular quantum fluctuations in this phase, with possible rotation in the (bc) plane, making it difficult to associate a well-identified single classical structure. The mechanism for the transition to phase III is also described. Existing structural data support this microscopic interpretation.Comment: 5 pages, 3 figure

Convective and absolute Eckhaus instability leading to modulated waves in a finite box

We report experimental study of the secondary modulational instability of a one-dimensional non-linear traveling wave in a long bounded channel. Two qualitatively different instability regimes involving fronts of spatio-temporal defects are linked to the convective and absolute nature of the instability. Both transitions appear to be subcritical. The spatio-temporal defects control the global mode structure.Comment: 5 pages, 7 figures (ReVTeX 4 and amsmath.sty), final versio

Large scale ab initio calculations based on three levels of parallelization

We suggest and implement a parallelization scheme based on an efficient multiband eigenvalue solver, called the locally optimal block preconditioned conjugate gradient LOBPCG method, and using an optimized three-dimensional (3D) fast Fourier transform (FFT) in the ab initio}plane-wave code ABINIT. In addition to the standard data partitioning over processors corresponding to different k-points, we introduce data partitioning with respect to blocks of bands as well as spatial partitioning in the Fourier space of coefficients over the plane waves basis set used in ABINIT. This k-points-multiband-FFT parallelization avoids any collective communications on the whole set of processors relying instead on one-dimensional communications only. For a single k-point, super-linear scaling is achieved for up to 100 processors due to an extensive use of hardware optimized BLAS, LAPACK, and SCALAPACK routines, mainly in the LOBPCG routine. We observe good performance up to 200 processors. With 10 k-points our three-way data partitioning results in linear scaling up to 1000 processors for a practical system used for testing.Comment: 8 pages, 5 figures. Accepted to Computational Material Scienc

Nonlinear dynamics of waves and modulated waves in 1D thermocapillary flows. II: Convective/absolute transitions

We present experimental results on hydrothermal waves in long and narrow 1D channels. In a bounded channel, we describe the primary and secondary instabilities leading to waves and modulated waves in terms of convective/absolute transitions. Because of on the combined effect of finite group velocity and of the presence of boundaries, the wave-patterns are non-uniform in space. We also investigate non-uniform wave-patterns observed in an annular channel in the presence of sources and sinks of hydrothermal waves. We connect our observations with the complex Ginzburg-Landau model equation in the very same way as in the first part of the paper (nlin.PS/0208029).Comment: 37 pages, 23 figures (elsart.cls + AMS extensions). Accepted in Physica D. See also companion paper "Nonlinear dynamics of waves and modulated waves in 1D thermocapillary flows. I: General presentation and periodic solutions" (nlin.PS/0208029). A version with high resolution figures is available on N.G. webpag

Cell-to-Cell Stochastic Variation in Gene Expression Is a Complex Genetic Trait

The genetic control of common traits is rarely deterministic, with many genes contributing only to the chance of developing a given phenotype. This incomplete penetrance is poorly understood and is usually attributed to interactions between genes or interactions between genes and environmental conditions. Because many traits such as cancer can emerge from rare events happening in one or very few cells, we speculate an alternative and complementary possibility where some genotypes could facilitate these events by increasing stochastic cell-to-cell variations (or ‘noise’). As a very first step towards investigating this possibility, we studied how natural genetic variation influences the level of noise in the expression of a single gene using the yeast S. cerevisiae as a model system. Reproducible differences in noise were observed between divergent genetic backgrounds. We found that noise was highly heritable and placed under a complex genetic control. Scanning the genome, we mapped three Quantitative Trait Loci (QTL) of noise, one locus being explained by an increase in noise when transcriptional elongation was impaired. Our results suggest that the level of stochasticity in particular molecular regulations may differ between multicellular individuals depending on their genotypic background. The complex genetic architecture of noise buffering couples genetic to non-genetic robustness and provides a molecular basis to the probabilistic nature of complex traits

ABINIT: Overview and focus on selected capabilities

Paper published as part of the special topic on Electronic Structure SoftwareABINIT is probably the first electronic-structure package to have been released under an open-source license about 20 years ago. It implements density functional theory, density-functional perturbation theory (DFPT), many-body perturbation theory (GW approximation and Bethe–Salpeter equation), and more specific or advanced formalisms, such as dynamical mean-field theory (DMFT) and the “temperaturedependent effective potential” approach for anharmonic effects. Relying on planewaves for the representation of wavefunctions, density, and other space-dependent quantities, with pseudopotentials or projector-augmented waves (PAWs), it is well suited for the study of periodic materials, although nanostructures and molecules can be treated with the supercell technique. The present article starts with a brief description of the project, a summary of the theories upon which ABINIT relies, and a list of the associated capabilities. It then focuses on selected capabilities that might not be present in the majority of electronic structure packages either among planewave codes or, in general, treatment of strongly correlated materials using DMFT; materials under finite electric fields; properties at nuclei (electric field gradient, Mössbauer shifts, and orbital magnetization); positron annihilation; Raman intensities and electro-optic effect; and DFPT calculations of response to strain perturbation (elastic constants and piezoelectricity), spatial dispersion (flexoelectricity), electronic mobility, temperature dependence of the gap, and spin-magnetic-field perturbation. The ABINIT DFPT implementation is very general, including systems with van der Waals interaction or with noncollinear magnetism. Community projects are also described: generation of pseudopotential and PAW datasets, high-throughput calculations (databases of phonon band structure, second-harmonic generation, and GW computations of bandgaps), and the library LIBPAW. ABINIT has strong links with many other software projects that are briefly mentioned.This work (A.H.R.) was supported by the DMREF-NSF Grant No. 1434897, National Science Foundation OAC-1740111, and U.S. Department of Energy DE-SC0016176 and DE-SC0019491 projects. N.A.P. and M.J.V. gratefully acknowledge funding from the Belgian Fonds National de la Recherche Scientifique (FNRS) under Grant No. PDR T.1077.15-1/7. M.J.V. also acknowledges a sabbatical “OUT” grant at ICN2 Barcelona as well as ULiège and the Communauté Française de Belgique (Grant No. ARC AIMED G.A. 15/19-09). X.G. and M.J.V. acknowledge funding from the FNRS under Grant No. T.0103.19-ALPS. X.G. and G.-M. R. acknowledge support from the Communauté française de Belgique through the SURFASCOPE Project (No. ARC 19/24-057). X.G. acknowledges the hospitality of the CEA DAM-DIF during the year 2017. G.H. acknowledges support from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 (Materials Project Program No. KC23MP). The Belgian authors acknowledge computational resources from supercomputing facilities of the University of Liège, the Consortium des Equipements de Calcul Intensif (Grant No. FRS-FNRS G.A. 2.5020.11), and Zenobe/CENAERO funded by the Walloon Region under Grant No. G.A. 1117545. M.C. and O.G. acknowledge support from the Fonds de Recherche du Québec Nature et Technologie (FRQ-NT), Canada, and the Natural Sciences and Engineering Research Council of Canada (NSERC) under Grant No. RGPIN-2016-06666. The implementation of the libpaw library (M.T., T.R., and D.C.) was supported by the ANR NEWCASTLE project (Grant No. ANR-2010-COSI-005-01) of the French National Research Agency. M.R. and M.S. acknowledge funding from Ministerio de Economia, Industria y Competitividad (MINECO-Spain) (Grants Nos. MAT2016-77100-C2-2-P and SEV-2015-0496) and Generalitat de Catalunya (Grant No. 2017 SGR1506). This work has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation program (Grant Agreement No. 724529). P.G. acknowledges support from FNRS Belgium through PDR (Grant No. HiT4FiT), ULiège and the Communauté française de Belgique through the ARC project AIMED, the EU and FNRS through M.ERA.NET project SIOX, and the European Funds for Regional Developments (FEDER) and the Walloon Region in the framework of the operational program “Wallonie-2020.EU” through the project Multifunctional thin films/LoCoTED. The Flatiron Institute is a division of the Simons Foundation. A large part of the data presented in this paper is available directly from the Abinit Web page www.abinit.org. Any other data not appearing in this web page can be provided by the corresponding author upon reasonable request.Peer reviewe

SrTiO(3) substrates capped with a GaAs monolayer: An ab initio study

International audienceThe epitaxy of GaAs monolayers on SrTiO(3) substrates is studied by extensive first-principles simulations, considering both cleavage (100) and polar (110) orientations of SrTiO(3) with distinct terminations, and several adsorption sites for the overlayer. Large charge transfers take place for the two SrTiO(110)/GaAs and O(2)-(110)/GaAs polar heterojunctions, at variance with other substrate terminations, which are polar compensated by construction. As a function of the thermodynamic conditions, the formation of mixed compounds at the interface can be avoided. Relying on the interfacial energy, we predict that the GaAs monolayer is much more stable on (110) than on (100) surfaces, consistent with the available experimental results. Moreover, it should wet both SrTiO and Sr terminations of SrTiO(3)(110)

Les partis populistes en quête de légitimité: analyse des discours du parti du travail de Belgique et du parti populaire

Le populisme est un concept aux multiples usages qui fait l’objet de nombreux débats. Classiquement, les termes « populisme » et « populiste » sont utilisés pour critiquer un adversaire politique. Outre le champ politique, la littérature scientifique tente de mobiliser la notion à des fins de classification, visant à une meilleure compréhension de phénomènes sociopolitiques. Au-delà de la question de l’étiquette « populiste » mobilisée par les acteurs politiques et des tentatives de définition de la notion, la littérature propose une définition minimale, présentant le populisme comme un style de communication politique construit sur une opposition fondamentale entre, d’un côté, le peuple et, de l’autre, les élites. Les partis adoptant un style de communication populiste – dits partis populistes – sont considérés dans la littérature comme une menace pour la démocratie et pour les principes libéraux qui la caractérisent. En conséquence, les partis dits « traditionnels » adoptent à leur égard des mesures qui peuvent être exclusives ou inclusives. Afin d’accéder au pouvoir malgré ces difficultés qu’ils éprouvent, les partis populistes ambitionnent de renforcer leur légitimité vis-à-vis des partis traditionnels mais également vis-à-vis de l’électorat. La manière dont les partis populistes construisent cette légitimité reste une question peu étudiée de manière empirique en science politique. Pour cette raison, nous proposons d’étudier les discours de ces partis politiques afin de mieux comprendre comment s’articule leur rhétorique vis-à-vis des autres formations politiques mais également vis-à-vis des électeurs. Pour ce faire, nous proposons, dans un premier temps, de définir la notion de populisme et de mettre au jour la structure rhétorique employée par les formations populistes. Ensuite, nous définirons la notion de légitimité, particulièrement au regard de la notion de populisme. La section méthodologique présentera ensuite la sélection des cas opérée dans le cadre de ce chapitre, à savoir le Parti du Travail de Belgique (PTB) et le Parti populaire belge (PP), ainsi que la manière dont les données sont collectées puis analysées. L’analyse des discours sera opérée dans un quatrième temps. Alors que les cas à l’étude reposent sur des idéologies fondamentalement différentes, l’objectif de la recherche est de repérer les différences mais aussi les similitudes dans la manière de construire leur légitimité. Enfin, nous concluerons en répondant à la question qui structure ce chapitre : quelles sont les stratégies discursives employées par les deux formations populistes sélectionnées pour renforcer leur légitimité