Pierre-and-Marie-Curie University

About: Pierre-and-Marie-Curie University is a education organization based out in Paris, France. It is known for research contribution in the topics: Population & Raman spectroscopy. The organization has 34448 authors who have published 56139 publications receiving 2392398 citations.

Synthesis and Characterization of Mesostructured Titania-Based Materials through Evaporation-Induced Self-Assembly

Abstract: Mesostructured TiO2−hexadecyltrimethylammonium bromide hybrid powders, displaying a bidimensional hexagonal pattern (p6m), have been synthesized by an evaporation-induced self-assembly (EISA) method, in ethanol/HCl/H2O media. Thermal treatment of these “titaniatropic” hybrid phases leads to phosphorus-free, high surface area (280−370 m2 g-1) mesoporous titania, with 20−25 A pores. The role of the synthesis parameters (surfactant and acid concentrations and temperature) is thoroughly discussed to understand their influence on the hybrid mesostructures. It is suggested that hydrophilic Ti-oxo nanometric building blocks formed in the acidic synthesis conditions self-assembly upon solvent evaporation to produce organized structures.

Elastic properties of single-walled carbon nanotubes

Abstract: Analytical expressions for the velocities of the longitudinal and the torsional sound waves in single-walled carbon nanotubes are derived using Born's perturbation technique within a lattice-dynamical model. These expressions are compared to the formulas for the velocities of the sound waves in an elastic hollow cylinder from the theory of elasticity to obtain analytical expressions for the Young's and shear moduli of nanotubes. The calculated elastic moduli for different chiral and achiral ~armchair and zigzag! nanotubes using force constants of the valence force field type are compared to the existing experimental and theoretical data. vibration amplitude of several isolated MWNT's was ana- lyzed in a transmission electron microscope to eventually obtain 1.8 TPa for the average Young's modulus. Later on, this technique was applied to measure Young's modulus of isolated SWNT's in the diameter range 1.0 21.5 nm and an average value ^Y&51.2520.35/10.45 TPa was derived. 7 In another experimental approach 8 the MWNT's were pinned to a substrate by conventional lithography and the force was measured at different distances from the pinned point by atomic force microscope ~ATM!. The average Young's modulus for different MWNT's with diameters from 26 to 76 nm was found to be 1.2860.59 TPa. Recently, Young's and shear moduli of ropes of SWNT's were measured by sus- pending the ropes over the pores of a membrane and using ATM to determine directly the resulting deflection of the rope. 9 The theoretical estimation of the elastic moduli was accomplished exclusively by numerical second derivatives of the energy of the strained nanotubes. In the calculation of the elastic moduli of various SWNT's within a simple force- constant model 10 it was found that the moduli were insensi- tive to tube size and helicity and had the average values of ^Y&50.97 TPa and ^G&50.45 TPa. In several works, molecular-dynamics ~MD! simulation algorithms using the Tersoff-Brenner potential for the carbon-carbon interactions were implemented to relax the strained nanotubes and calcu- late their energy. 11-13 For tubes of diameter of 1 nm values for Y of 5.5 TPa ~Ref. 12! and 0.8 TPa ~Ref. 13! were ob- tained. A non-orthogonal tight-binding ~TB! scheme was ap- plied to calculate Young's modulus of several chiral and achiral SWNT's yielding an average value of 1.24 TPa. 14 Recently, the second derivative of the strain energy with re- spect to the axial strain, calculated with a pseudopotential density-functional-theory ~DFT! model for a number of SWNT's, 15 was found to vary slightly with the tube type and to have the average value of 56 eV. In this paper, we choose a different approach to the cal- culation of the elastic properties of SWNT's. Namely, we derive analytical expressions for the elastic ~Young's and shear! moduli of SWNT's using a perturbation technique due to Born 16 within a lattice-dynamical model for nanotubes. 17 This scheme has the advantage that the elastic moduli are consistent with the lattice dynamics of the nanotubes and that each of these moduli is obtained in one calculational step only. The essential features of a model of the lattice dynamics of SWNT's based on the explicit accounting for the helical symmetry of the tubes 17 are summarized in Sec. II A. This model is applied to study of the long-wavelength vibrations in nanotubes using Born's perturbation technique 16 and to obtain analytical expressions for the velocities of the longi- tudinal and the torsional sound waves in SWNT's ~see Sec. II B!. The comparison of these expressions with the formulas from the theory of elasticity for the velocities of these waves in an elastic hollow cylinder allows one to determine the Young's and shear moduli of the nanotubes. The calculated phonon dispersion of a (10,10) nanotube and elastic moduli for various chiral and achiral ~armchair and zigzag! nano- tubes using force constants of the valence force field ~VFF! type 18 are presented in Sec. III and discussed in comparison with the existing experimental and theoretical data.

Seismic evidence for a rapidly rotating core in a lower-giant-branch star observed with kepler

Abstract: Rotation is expected to have an important influence on the structure and the evolution of stars. However, the mechanisms of angular momentum transport in stars remain theoretically uncertain and very complex to take into account in stellar models. To achieve a better understanding of these processes, we desperately need observational constraints on the internal rotation of stars, which until very recently was restricted to the Sun. In this paper, we report the detection of mixed modes—i.e., modes that behave both as g modes in the core and as p modes in the envelope—in the spectrum of the early red giant KIC 7341231, which was observed during one year with the Kepler spacecraft. By performing an analysis of the oscillation spectrum of the star, we show that its non-radial modes are clearly split by stellar rotation and we are able to determine precisely the rotational splittings of 18 modes. We then find a stellar model that reproduces very well the observed atmospheric and seismic properties of the star. We use this model to perform inversions of the internal rotation profile of the star, which enables us to show that the core of the star is rotating at least five times faster than the envelope. This will shed new light on the processes of transport of angular momentum in stars. In particular, this result can be used to place constraints on the angular momentum coupling between the core and the envelope of early red giants, which could help us discriminate between the theories that have been proposed over the last few decades.

Long-range transport of Saharan dust to northern Europe : The 11-16 October 2001 outbreak observed with EARLINET

Abstract: The spread of mineral particles over southwestern, western, and central Europe resulting from a strong Saharan dust outbreak in October 2001 was observed at 10 stations of the European Aerosol Research Lidar Network (EARLINET). For the first time, an optically dense desert dust plume over Europe was characterized coherently with high vertical resolution on a continental scale. The main layer was located above the boundary layer (above 1-km height above sea level (asl)) up to 3–5-km height, and traces of dust particles reached heights of 7–8 km. The particle optical depth typically ranged from 0.1 to 0.5 above 1-km height asl at the wavelength of 532 nm, and maximum values close to 0.8 were found over northern Germany. The lidar observations are in qualitative agreement with values of optical depth derived from Total Ozone Mapping Spectrometer (TOMS) data. Ten-day backward trajectories clearly indicated the Sahara as the source region of the particles and revealed that the dust layer observed, e.g., over Belsk, Poland, crossed the EARLINET site Aberystwyth, UK, and southern Scandinavia 24–48 hours before. Lidar-derived particle depolarization ratios, backscatter- and extinction-related Angstrom exponents, and extinction-to-backscatter ratios mainly ranged from 15 to 25%, −0.5 to 0.5, and 40–80 sr, respectively, within the lofted dust plumes. A few atmospheric model calculations are presented showing the dust concentration over Europe. The simulations were found to be consistent with the network observations.

On the nucleus structure and activity of comet 67P/Churyumov-Gerasimenko

Abstract: Images from the OSIRIS scientific imaging system onboard Rosetta show that the nucleus of 67P/Churyumov-Gerasimenko consists of two lobes connected by a short neck. The nucleus has a bulk density less than half that of water. Activity at a distance from the Sun of >3 astronomical units is predominantly from the neck, where jets have been seen consistently. The nucleus rotates about the principal axis of momentum. The surface morphology suggests that the removal of larger volumes of material, possibly via explosive release of subsurface pressure or via creation of overhangs by sublimation, may be a major mass loss process. The shape raises the question of whether the two lobes represent a contact binary formed 4.5 billion years ago, or a single body where a gap has evolved via mass loss.