Deuterium adsorption on (and desorption from) SiC(0001)-(3×3), (√3×√3)R30°, (6√3×6√3)R30° and quasi-free standing graphene obtained by hydrogen intercalation

International audienceWe present a comparative high-resolution electron energy-loss spectroscopy study on the interaction of atomic hydrogen and deuterium with various reconstructions of SiC(0 0 0 1). We first show that on both the (3 × 3) and reconstructions, deuterium atoms only bind to silicon atoms, thereby confirming the silicon-rich appellation of these reconstructions. Deuterium passivation of the (3 × 3) is only reversible when exposed to atomic deuterium at a surface temperature of 700 K since tri- and dideuterides, necessary precursors for silicon etching, are not stable. On the other hand, we show that the deuteration of the is always reversible because precursors to silicon etching are scarce on the surface. Then, we demonstrate that hydrogen (deuterium) adsorption at 300 K on both the (buffer-layer) and the quasi-free-standing graphene occurs on carbon atoms justifying their carbon-rich appellation. Comparison of the deuterium binding in the intercalation layer of quasi-free-standing graphene with the deuterated surface provides some indication on the bonding structure at the substrate intercalation layer. Finally, by measuring C-H (C-D) vibrational frequencies and hydrogen (deuterium) desorption temperatures we suggest that partial sp2-to-sp3 rehybridization occurs for the carbon atoms of the buffer-layer because of the corrugation related to covalent bonding to the SiC substrate. In contrast, on quasi-free-standing graphene hydrogen (deuterium) atoms adsorb similarly to what is observed on graphite, i.e. without preferential sticking related to the underlying SiC substrate

Investigating Gene–Gene and Gene–Environment Interactions in the Association Between Overnutrition and Obesity-Related Phenotypes

Introduction: Animal studies suggested that NFKB1, IKBKB, and SOCS3 genes could be involved in the association between overnutrition and obesity. This study aims to investigate interactions involving these genes and macronutrient intakes affecting obesity-related phenotypes.Methods: We used a traditional statistical method, logistic regression, and compared it to alternative statistical method, multifactor dimensionality reduction (MDR) and penalized logistic regression (PLR), to better detect genes/environment interactions in the Toronto Nutrigenomics and Health Study (n = 1639) using dichotomized body mass index (BMI) and waist circumference as obesity-related phenotypes. Exposure variables included genotype on 54 single nucleotide polymorphisms (NFKB1: 18, IKBKB: 9, SOCS3: 27), macronutrient (carbohydrates, protein, fat) and alcohol intakes and ethno-cultural background.Results: After correction for multiple testing, no interaction was found using logistic regression. MDR identified interactions between SOCS3 rs6501199 and rs4969172, and IKBKB rs3747811 affecting BMI in the Caucasian population; SOCS3 rs6501199 and NFKB1 rs1609798 affecting WC in the Caucasian population; and SOCS3 rs4436839 and IKBKB rs3747811 affecting WC in the South Asian population. PLR found a main effect of SOCS3 rs12944581 on BMI among the South Asian population.Conclusion: While MDR and PLR had discordant results, some models support results from previous studies. These results emphasize the need to use alternative statistical methods to investigate high-order interactions and suggest that variants in the nutrient-responsive hypothalamic IKKB/NF-kB signaling pathway may be involved in obesity pathogenesis

Enjeux théoriques et pratiques du développement régional : 30 Ans de recherche au GRIR

Le trentième anniversaire du GRIR a été souligné au printemps 2013 par un colloque regroupant plusieurs chercheurs dans le domaine du développement local et régional. Cet ouvrage est le produit de leurs réflexions tant sur le plan théorique que pratique. Ce livre est articulé autour de trois axes : 1) la présentation des divers courants en développement régional, 2) des réflexions sur le passé et le présent des Premières Nations et 3) la présentation de cas concrets sur la prise en main du développement par les différents acteurs du territoire. Cet ouvrage est un outil permettant de constater le travail accompli en développement local et régional et de dégager des pistes de réflexion sur les avenues possibles de développement

Tabletop imaging of structural evolutions in chemical reactions

The introduction of femto-chemistry has made it a primary goal to follow the nuclear and electronic evolution of a molecule in time and space as it undergoes a chemical reaction. Using Coulomb Explosion Imaging we have shot the first high-resolution molecular movie of a to and fro isomerization process in the acetylene cation. So far, this kind of phenomenon could only be observed using VUV light from a Free Electron Laser [Phys. Rev. Lett. 105, 263002 (2010)]. Here we show that 266 nm ultrashort laser pulses are capable of initiating rich dynamics through multiphoton ionization. With our generally applicable tabletop approach that can be used for other small organic molecules, we have investigated two basic chemical reactions simultaneously: proton migration and C=C bond-breaking, triggered by multiphoton ionization. The experimental results are in excellent agreement with the timescales and relaxation pathways predicted by new and definitively quantitative ab initio trajectory simulations

Comparison of Methods to Correct Survival Estimates and Survival Regression Analysis on a Large HIV African Cohort

The evaluation of HIV treatment programs is generally based on an estimation of survival among patients receiving antiretroviral treatment (ART). In large HIV programs, loss to follow-up (LFU) rates remain high despite active patient tracing, which is likely to bias survival estimates and survival regression analyses

Correcting Mortality for Loss to Follow-Up: A Nomogram Applied to Antiretroviral Treatment Programmes in Sub-Saharan Africa

Matthias Egger and colleagues present a nomogram and a web-based calculator to correct estimates of program-level mortality for loss to follow-up, for use in antiretroviral treatment programs

Inhibition of the phase conjugation of orbital angular momentum superpositions in cylindrical vector beams during stimulated Brillouin scattering

Phase conjugation with stimulated Brillouin scattering can be used to correct wavefront aberrations in high-power laser systems. Here, we consider such process with cylindrical vector lasers beams. By using a vectorial approach and a modal decomposition, we obtain a differential matrix equation that enables the calculation of the structure of Stokes vector eigenmodes and their Brillouin gain. The emphasis is put on the mode with the largest gain, which contributes the most to the Stokes beam. We show that the phase conjugation of orbital angular momentum in cylindrical vector beams is prevented from happening almost everywhere on the higher-order Poincar\'e sphere. This phenomenon is traced to the tendency of the Stokes beam to acquire a polarization structure similar to the incident pump beam, which constraints the possible combinations of topological charges of the two orbital angular momentum modes making up the Stokes cylindrical vector beams. However, near the poles of the higher-order Poincar\'e sphere, the Stokes mode with the largest gain acquires an additional helical phase factor that produces the conjugated topological charge for the stronger circularly polarized component without affecting the polarization structure. Experimental results are found to agree with our theoretical predictions