A unified electrostatic and cavitation model for first-principles molecular dynamics in solution

The electrostatic continuum solvent model developed by [Fattebert and Gygi J. Comput. Chem. 23, 662 (2002); Int. J. Quantum Chem. 93, 139 (2003)] is combined with a first-principles formulation of the cavitation energy based on a natural quantum-mechanical definition for the surface of a solute. Despite its simplicity, the cavitation contribution calculated by this approach is found to be in remarkable agreement with that obtained by more complex algorithms relying on a large set of parameters. Our model allows for very efficient Car-Parrinello simulations of finite or extended systems in solution and demonstrates a level of accuracy as good as that of established quantum-chemistry continuum solvent methods. We apply this approach to the study of tetracyanoethylene dimers in dichloromethane, providing valuable structural and dynamical insights on the dimerization phenomenon.     

Preparation process and upconversion luminescence of Er3+-Doped glass ceramics containing Ba2LaF7 nanocrystals

The preparation process and upconversion luminescence of the Er(3+)-doped glass ceramics containing Ba(2)LaF(7) nanocrystals were investigated. The formation of Ba(2)LaF(7) nanocrystals in the glass ceramics was confirmed by X-ray diffraction. Er(3+)-doped glass ceramics containing Ba(2)LaF(7) nanocrystals exhibited highly efficient upconversion luminescence in comparison with glasses. With the increase of heat treatment temperature the upconversion luminescence intensity increased gradually. The composition of glasses was also found to have significant influence on the crystallization process of glass ceramics. The mixture of Ba(2)LaF(7) and La(2)O(3) nanocrystals and the mixture of La(2)F(3) and La(2)O(3) nanocrystals in the glass ceramics could be obtained by controlling different compositions of glasses. The upconversion luminescence intensity also varied significantly with different nanocrystals in the glass ceramics.     

Descent distribution on Catalan words avoiding a pattern of length at most three

Catalan words are particular growth-restricted words over the set of non-negative integers, and they represent still another combinatorial class counted by the Catalan numbers. We study the distribution of descents on the sets of Catalan words avoiding a pattern of length at most three: for each such a pattern $p$ we provide a bivariate generating function where the coefficient of $x^n{y}^k$ in its series expansion is the number of length $n$$p$-avoiding Catalan words with $k$ descents. As a byproduct, we enumerate the set of Catalan words avoiding $p$, and we provide the popularity of descents on this set.     

Hydrogenation of β-N-substituted enaminoesters in the presence of ruthenium catalysts

β-Aminoesters were prepared in two simple steps from β-ketoesters derivatives and primary amines under mild conditions. Their hydrogenation was performed at 50 °C in the presence of several organometallic catalysts under acidic conditions. The new β-N-substituted aminoesters were isolated in moderate to good yields.     

Photooxidation of polypropylene/layered double hydroxide nanocomposites: Influence of intralamellar cations

The influence of layered double hydroxides (LDHs) on the photooxidation of polypropylene (PP)/LDH nanocomposites was studied under irradiation at long wavelengths (λ > 300 nm, 60 °C and in the presence of oxygen). The influence of hybrid LDHs containing different divalent cations (Mg, Zn or both Mg and Zn) on the photooxidation mechanism of PP and on the rates of oxidation of the matrix was characterised based on infrared analysis. The presence of LDHs modifies the photoproducts accumulating in the PP and the rates of oxidation of PP were changed depending on the divalent cations in the LDH layers. Whereas natural clays, such as montmorillonite (MMt), can lead to a faster degradation of the materials, LDHs (Zn₂-Al-DS, for example) appear to have no inductive effect on polymer oxidation.     

Metal-free Brønsted acids catalyzed synthesis of functional 1,4-dihydropyridines

Brønsted acids catalyze the addition of β-enaminoacrylates to α,β-unsaturated aldehydes leading to substituted dihydropyridines in moderate to good yields under mild conditions. The first example of an enantioselective synthesis of a dihydropyridine is also reported.     

A new class of fractional step techniques for the incompressible Navier–Stokes equations using direction splitting

A new direction-splitting-based fractional time stepping is introduced for solving the incompressible Navier–Stokes equations. The main originality of the method is that the pressure correction is computed by solving a sequence of one-dimensional elliptic problems in each spatial direction. The method is very simple to program in parallel, very fast, and has exactly the same stability and convergence properties as the Poisson-based pressure-correction technique, either in standard or rotational form.     

Photoageing behaviour of epoxy nanocomposites: Comparison between spherical and lamellar nanofillers

The photochemical behaviour of a nanofilled epoxy resin has been studied. It has been shown that the filler content increases at the surface with irradiation time. Qualitative stiffness and adhesion measurements compare the surface properties of the filled and unfilled samples upon ageing. Depth profiling has been achieved by AFM nanoindentation and micro-FTIR. These two techniques allowed comparing stiffness and photooxidation of the aged samples. Both techniques showed an influence of nanofillers on thickness profiles. The relationship between the oxidation process and its consequences on the physical properties is explained taking into account oxygen permeability and light diffusion. Additionally, it has been shown that, whatever the content (5-10 wt%), the nature (silica or different organo-modified montmorillonites) or the shape of the filler (spherical or lamellar), the photoproducts were formed in comparable proportions and at similar rates as in the pristine matrix.     

Transient elastography in anisotropic medium: application to the measurement of slow and fast shear wave speeds in muscles

From the measurement of a low frequency (50-150 Hz) shear wave speed, transient elastography evaluates the Young's modulus in isotropic soft tissues. In this paper, it is shown that a rod source can generate a low frequency polarized shear strain waves. Consequently this technique allows to study anisotropic medium such as muscle. The evidence of the polarization of low frequency shear strain waves is supported by both numeric simulations and experiments. The numeric simulations are based on theoretical Green's functions in isotropic and anisotropic media (hexagonal system). The experiments in vitro led on beef muscle proves the pertinent of this simple anisotropic pattern. Results in vivo on man biceps shows the existence of slow and fast shear waves as predicted by theory.