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Mars in the Glacial Ages of The Past Millions of Years: Modeling a Planet Partially Mantled by Dust and Ice
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Fluctuations and Entanglement spectrum in quantum Hall states
No full textFinal Version. Invited Article, for Special Issue of JSTAT on "Quantum Entanglement in Condensed Matter Physics"International audienceThe measurement of quantum entanglement in many-body systems remains challenging. One experimentally relevant fact about quantum entanglement is that in systems whose degrees of freedom map to free fermions with conserved total particle number, exact relations hold relating the Full Counting Statistics associated with the bipartite charge fluctuations and the sequence of R\' enyi entropies. We draw a correspondence between the bipartite charge fluctuations and the entanglement spectrum, mediated by the R\' enyi entropies. In the case of the integer quantum Hall effect, we show that it is possible to reproduce the generic features of the entanglement spectrum from a measurement of the second charge cumulant only. Additionally, asking whether it is possible to extend the free fermion result to the fractional quantum Hall case, we provide numerical evidence that the answer is negative in general. We further address the problem of quantum Hall edge states described by a Luttinger liquid, and derive expressions for the spectral functions of the real space entanglement spectrum at a quantum point contact realized in a quantum Hall sample
Polymorphic copper iodide clusters: insights into the mechanochromic luminescence properties.
No full textInternational audienceAn in-depth study of mechanochromic and thermochromic luminescent copper iodide clusters exhibiting structural polymorphism is reported and gives new insights into the origin of the mechanochromic luminescence properties. The two different crystalline polymorphs exhibit distinct luminescence properties with one being green emissive and the other one being yellow emissive. Upon mechanical grinding, only one of the polymorphs exhibits great modification of its emission from green to yellow. Interestingly, the photophysical properties of the resulting partially amorphous crushed compound are closed to those of the other yellow polymorph. Comparative structural and optical analyses of the different phases including a solution of clusters permit us to establish a correlation between the Cu-Cu bond distances and the luminescence properties. In addition, the local structure of the [Cu4I4P4] cluster cores has been probed by (31)P and (65)Cu solid-state NMR analysis, which readily indicates that the grinding process modifies the phosphorus and copper atoms environments. The mechanochromic phenomenon is thus explained by the disruption of the crystal packing within intermolecular interactions inducing shortening of the Cu-Cu bond distances in the [Cu4I4] cluster core and eventually modification of the emissive state. These results definitely establish the role of cuprophilic interactions in the mechanochromism of copper iodide clusters. More generally, this study constitutes a step further into the understanding of the mechanism involved in the mechanochromic luminescent properties of metal-based compounds
Direct Synthesis and Integration of Individual, Diameter-Controlled Single-Walled Nanotubes (SWNTs)
No full textWe present a robust and versatile approach for the reproducible and controllable growth of single-walled carbon nanotubes (SWNTs) through a self-assembled mono-layer (SAM) technique coupled with an atomic hydrogen (Hat) pretreatment to control the catalytic metallic nanoparticles size and density. The nanoparticles are obtained from a self-assembled monolayer of metal complexes or salts on a SiO2 substrate using a two-step strategy. The oxide is first functionalized by silanization with a coordinating ligand leading to the formation of an anchoring SAM on the substrate. Then, metallic complexes such as ruthenium porphyrin (RuTPP) or metallic salts (FeCl3, RuCl3) are assembled by coordination bonds on the preformed organic SAM. Pyrolysis under radical hydrogen atmosphere of the as-prepared SAM yields metallic nanoparticles whose size and density are controlled and tuned. Using the as-formed nanoparticles as catalysts, SWNTs are grown by double hot-filament-assisted chemical vapor deposition (d-HFCVD). They exhibit a remarkably good crystalline quality, with a diameter (and type) strongly dependent on the nature of the initial catalyst precursor and its preparation. Field-effect transistors (FETs) with excellent characteristics were obtained using such in-place grown SWNTs. The electronic properties of the SWNTs can be tuned: the transistors obtained from Ru(TPP) and FeCl3 exhibit ION/IOFF current ratio up to ∼109, indicative of the direct growth of a high proportion of semiconducting nanotubes over than 98%. Such elevated values have been reported essentially for CNT-FETs devices based on individual semiconducting SWNTs. By contrast, devices obtained from the RuCl3 salt display ION/IOFF current ratio well below 102, indicating the direct growth of SWNTs highly enriched in metallic specimens
Modeling the clouds on Venus: model development and improvement of a nucleation parameterization
No full textAs both the clouds of Venus and aerosols in the Earth's stratosphere are composed of sulfuric acid droplets, we use the 1-D version of a model [1,4] developed for stratospheric aerosols and clouds to study the clouds on Venus. We have removed processes and compounds related to the stratospheric clouds so that the only species remaining are water and sulfuric acid, corresponding to the stratospheric sulfate aerosols, and we have added some key processes. The model describes microphysical processes including condensation/evaporation, and sedimentation. Coagulation, turbulent diffusion, and a parameterization for two-component nucleation [8] of water and sulfuric acid have been added in the model. Since the model describes explicitly the size distribution with a large number of size bins (50-500), it can handle multiple particle modes. The validity ranges of the existing nucleation parameterization [7] have been improved to cover a larger temperature range, and the very low relative humidity (RH) and high sulfuric acid concentrations found in the atmosphere of Venus. We have made several modifications to improve the 2002 nucleation parameterization [7], most notably ensuring that the two-component nucleation model behaves as predicted by the analytical studies at the one-component limit reached at extremely low RH. We have also chosen to use a self-consistent cluster distribution [9], constrained by scaling it to recent quantum chemistry calculations [3]. First tests of the cloud model have been carried out with temperature profiles from VIRA [2] and from the LMD Venus GCM [5], and with a compilation of water vapor and sulfuric acid profiles, as in [6]. The temperature and pressure profiles do not evolve with time, but the vapour profiles naturally change with the cloud. However, no chemistry is included for the moment, so the vapor concentrations are only dependent on the microphysical processes. The model has been run for several hundreds of Earth days to reach a steady state. Preliminary results are evaluated against observations. [1] Jumelet et al., JGR, 2009. [2] Kliore et al., 1986. [3] Kurtén et al., BER, 2007 [4] Larsen et al., JGR, 2000. [5] Lebonnois et al. JGR, 2010. [6] McGouldrick and Toon, Icarus 191, 2007. [7] Vehkamäki et al. JGR, 2002 [9] Wilemski and Wyslouzil, J.Chem.Phys. 1995
Three-dimensional modelling of Venus photochemistry
No full textWe have developed a new code of the Venus atmospheric chemistry based on our photochemical model already in use for Mars (e.g., Lefèvre et al., J. Geophys. Res., 2004). For Venus, the code also includes a parameterized treatment of cloud microphysics that computes the composition of sulphuric acid droplets and their number density based on a given droplet size distribution in altitude. We coupled this photochemical-microphysical package to the LMD general circulation model of Venus (Lebonnois et al., J. Geophys. Res., 2010) with a sedimentation module recently added. We will describe preliminary results obtained with this first three-dimensional model of the Venus photochemistry. The space and time distribution of key chemical species as well as the modelled clouds characteristics will be detailed and compared to observations performed from Venus Express and from the Earth (e.g. Knollenberg and Hunten, J. Geophys. Res., 1980 ; Wilquet et al., J. Geophys. Res., 2009 ; Sandor et al., Icarus, 2012)
Density measurements and structural properties of liquid and amorphous metals under high pressure
No full textInternational audienceWe have implemented an in situ X-ray diffraction analysis method suitable for the determination of pressure-volume-temperature equations of state in the critical case of liquid and amorphous materials over an extended thermodynamic range (T > 2000K and P > 40 GPa). This method is versatile, it can be applied to data obtained using various angle-dispersive X-ray diffraction high pressure apparatus and, contrary to in situ X-ray absorption techniques, is independent from the sample geometry. Further advantage is the fast data acquisition (between 10 and 300 s integration time). Information on macroscopic bulk properties (density) and local atomic arrangement (pair distribution function g(r)) can be gathered in parallel. To illustrate the method, we present studies on liquid Fe-S alloys in the Paris Edinburgh press and in laser-heated diamond anvil cell (DAC), and measurements on Ce glass in DAC at room temperatur
Anglais correct exigé : Dynamiques et enjeux de l'anglicisation dans les entreprises françaises
No full textDéposé le 7 mai 2014The object of this thesis is the increasing use of the English language in organizations (mainly private companies) in France, which we refer to as 'anglicization'. Our aim is to analyze the mechanisms of an organizational dynamic that raises major issues. The first part of the thesis deals with anglicization as a social issue. We describe the French context, marked by a controversy over "tout-anglais" - that is all-English corporate policies - where ideology plays a leading role. Stakeholders, their motivations and arguments are reviewed. A chapter is then dedicated to France's so-called Loi Toubon, which plays an essential part in the debate. In the second part, we set out to describe anglicization as a phenomenon. We propose a novel framework of analysis based on the concept of language boundaries, which we confront with a number of cases from various organizations. It appears that anglicization, far from being a managerial fad, can be analyzed as the result of mechanisms where corporate actors play an active role. The third part focuses on anglicization as a management object. We introduce a simple framework for the description of language management in companies. Two major challenges posed by anglicization are then discussed at length: foreign language training and translation. The conclusion endeavors to resolve the tension between the apparent inevitability of anglicization and the need, felt by a number of stakeholders, to defend French as a working language, introducing the concept of corporate sociolinguistic responsibility.Cette thèse prend pour objet la montée de l'usage de l'anglais dans les organisations (principalement les entreprises) en France, à travers le concept d'anglicisation. Il s'agit d'analyser les mécanismes d'une dynamique organisationnelle qui soulève des enjeux majeurs. La première partie de la thèse aborde l'anglicisation comme sujet de société. On y décrit le contexte français, marqué par une controverse sur le " tout-anglais " dans l'entreprise où l'idéologie joue un rôle de premier plan. Les acteurs de la controverse, leurs motivations et leurs arguments sont passés en revue. Puis un chapitre est consacré à la loi Toubon, qui joue un rôle essentiel dans le débat. La seconde partie est consacrée à la description de l'anglicisation comme phénomène. Un cadre d'analyse original, basé sur le concept de frontières linguistiques, est confronté à de nombreux cas issus de neuf organisations. Il en ressort que l'anglicisation, loin d'être un phénomène de mode, peut s'analyser comme le résultat de mécanismes où les acteurs de l'entreprise jouent un rôle actif. La troisième partie s'interroge sur l'anglicisation comme objet de gestion. Ayant introduit un cadre d'analyse simple pour la gestion des langues, on aborde en détails deux des principaux défis de gestion posés par l'anglicisation : la formation aux langues étrangères et la gestion de la traduction. La conclusion tente de résoudre la tension entre l'apparente inéluctabilité de l'anglicisation et le besoin, ressenti par un certain nombre d'acteurs, de défendre le français comme langue de travail, à travers le concept de responsabilité sociolinguistique de l'entreprise
A direct, versatile route to functionalized trialkoxysilanes
No full textInternational audienceThe peroxide initiated radical addition of dithiocarbonates (xanthates) to trialkoxy vinylsilanes leads to functionalized trialkoxysilanes. Prior addition of the dithiocarbonates to an alkene before reaction with the vinylsilane can be used to increase the complexity of the final product
Some new results on modified diagonals
No full textO'Grady studied recently -th modified diagonals for a smooth projective variety, generalizing the Gross-Schoen modified small diagonal. These cycles depend on a choice of reference point (or more generally a degree zero-cycle). We prove that for any , the cycle vanishes for large . We also prove the following conjecture of O'Grady: if is a double cover of and vanishes (where belongs to the branch locus), then vanishes, and we provide a generalization to higher degree finite covers. We finally prove the vanishing when , a surface, and , which was conjectured by O'Grady and proved by him for