Experimental evidence for ultrafast electronic relaxation in molecules, mediated by diffuse states

The existence of a mediating state for the ultrafast electronic relaxation in ethylenic-like molecules has been shown by femtosecond electron imaging techniques. This state is of Rydberg character, and its high efficiency is due to its ability to link the electron distributions of the initial and final electronic states.     

Effect of Scanning Beam Profile to Fabricate Fused Fiber Tapers by CO2 Laser Irradiation Method

Beam uniformity is a crucial building block of CO2 experiments aimed at fusing and stretching optical fibers in a lossless manner. When the irradiation beam is expanded through a galvanometer mirror, ways to achieve beam uniformity are investigated.     

Borne sur l'advection et la hauteur d'eau du problème de shallow-water avec conditions aux limites de Dirichlet

Using some properties of the Hardy spaces, we give a regularity result on the advection term of the shallow-water equations and we show a $L^2$ bound holding up to the boundary on the water height with Dirichlet boundary conditions. To cite this article: F. Flori, P. Orenga, C. R. Acad. Sci. Paris, Ser. I 340 (2005).     

Sur un problème de shallow water bicouche avec conditions aux limites de Dirichlet

We present in this Note an existence result for a bi-layer shallow water problem, with Dirichlet boundary conditions. The main difficulty arises from the terms coupling the two layers. To handle these, we must couple the natural energy estimate with an estimation of the thickness in $L^2(Q)$. To obtain this $L^2$-estimate, we introduce the Stokes operator and we use results for Hardy spaces to treat the nonlinear terms. To cite this article: F. Flori et al., C. R. Acad. Sci. Paris, Ser. I 340 (2005).     

Interacting classical dimers on the square lattice

We study a model of close-packed dimers on the square lattice with a nearest neighbor interaction between parallel dimers. This model corresponds to the classical limit of quantum dimer models [D. S. Rokhsar and S. A. Kivelson, Phys. Rev. Lett. 61, 2376 (1988)]. By means of Monte Carlo and transfer matrix calculations, we show that this system undergoes a Kosterlitz-Thouless transition separating a low temperature ordered phase where dimers are aligned in columns from a high temperature critical phase with continuously varying exponents. This is understood by constructing the corresponding Coulomb gas, whose coupling constant is computed numerically. We also discuss doped models and implications on the finite-temperature phase diagram of quantum dimer models.     

Many-body perturbation theory using the density-functional concept: beyond the GW approximation

We propose an alternative formulation of many-body perturbation theory that uses the density-functional concept. Instead of the usual four-point integral equation for the polarizability, we obtain a two-point one, which leads to excellent optical absorption and energy-loss spectra. The corresponding three-point vertex function and self-energy are then simply calculated via an integration, for any level of approximation. Moreover, we show the direct impact of this formulation on the time-dependent density-functional theory. Numerical results for the band gap of bulk silicon and solid argon illustrate corrections beyond the GW approximation for the self-energy.     

Selecting the shape of supported metal nanocrystals: Pd huts, hexagons, or pyramids on SrTiO3(001)

Increasing interest in oxide supported nanoparticle science and technology is stimulating research into controlling nanocrystal shape. Pd forms nanocrystals on the surface of SrTiO3(001), and depending on the crystallographic interface of the Pd with the substrate three shapes can be created: truncated pyramids, huts, and hexagonal shaped disks. Scanning tunneling microscopy reveals that the nanocrystal shapes are determined by the substrate reconstruction and the substrate temperature during deposition. A thermodynamic model is used to show that the pyramids and huts are stable structures, and that the hexagons are trapped in a metastable state.     

[n]-Cyclo-9,9-dibutyl-2,7-fluorene (n=4, 5): Nanoring Size Influence in Carbon-Bridged Cyclo-para-phenylenes

For the last ten years, ring-shaped π-conjugated macrocycles possessing radially directed π-orbitals have been subject to intense research. The electronic properties of these rings are deeply dependent on their size. However, most studies involve the flagship family of nanorings: the cyclo-para-phenylenes. We report herein the synthesis and study of the first examples of cyclofluorenes possessing five constituting fluorene units. The structural, optical and electrochemical properties were elucidated by X-ray crystallography, UV-vis absorption and fluorescence spectroscopy, and cyclic voltammetry. By comparison with a shorter analogue, we show how the electronic properties of [5]-cyclofluorenes are drastically different from those of [4]-cyclofluorenes, highlighting the key role played by the ring size in the cyclofluorene family.     

Synthesis of Discrete CHA Zeolite Nanocrystals without Organic Templates for Selective CO2 Capture

Small-pore zeolites such as chabazite (CHA) are excellent candidates for the selective separation of CO₂; however, the current synthesis involves several steps and the use of organic structure-directing agent (OSDA), increasing their cost and energy requirements. We report the synthesis of small-pore zeolite crystals (aluminosilicate) with CHA-type framework structure by direct synthesis in a colloidal suspension containing a mixture of inorganic cations only (Na⁺, K⁺, and Cs⁺). The location of CO₂ molecules in the host structure was revealed by 3D electron diffraction (3D ED). The high sorption capacity for CO₂ (3.8 mmol g⁻¹ at 121 kPa), structural stability and regenerability of the discreate CHA zeolite nanocrystals is maintained for 10 consecutive cycles without any visible degradation. The CHA zeolite (Si:Al=2) reaches an almost perfect CO₂ storage capacity (8 CO₂ per unit cell) and high selectivity (no CH₄ was adsorbed).