Chemical functionalization of silica and alumina particles for dispersion in carbon dioxide

The steric stabilization and flocculation of modified silica and alumina particle suspensions in condensed CO(2) were studied. Silica particles (average diameters of 7 and 12 nm) were functionalized using chlorosilanes of the form C(n)F(2n+1)CH(2)CH(2)Si(CH(3))(2)Cl (n = 8, 4, or 1) to give C(n)F(2n+1)-silica. Alumina particles (diameter of 8-14 nm) were grafted with C(8)F(17)CH(2)CH(2)Si(OEt)(3) and chemically modified with perfluorononanoic acid to yield C(8)F(17)-alumina and C(8)F(17)COOH-alumina, respectively. Elemental analysis and thermogravimetric analysis on the derivatized particles were carried out, and surface coverage was calculated. The stabilization of these modified particles in condensed CO(2) was quantified using turbidimetry. Particle stability was found to increase with increasing fluorinated tail length, temperature, and CO(2) density. Unmodified particles and those modified with only -CF(3) tails were unstable in condensed CO(2). Stabilization in supercritical CO(2) is continuous up to 24 h for the C(n)F(2n+1)-silica (n >/= 4) particles and 96 h for the C(8)F(17)-alumina particles. The C(8)F(17)COOH-alumina particles gave a significantly higher graft density than the C(8)F(17)-alumina particles but are not as stable in CO(2). The C(8)F(17)-alumina particles were stable at lower CO(2) densities than the modified silica particles. This stability difference may be attributed to the precursor organosilanes being monofunctional (modified silica) versus trifunctional (modified alumina), producing different structures on the surface.     

On-line microwave-assisted digestion of solid samples for their flame atomic spectrometric analysis

A new procedure has been developed for the on-line digestion of solids in a microwave oven. The direct injection in a water carrier flow of dispersions of solid samples in concentrated nitric acid, the merging of these slurries with 30% (v/v) H(2)O(2) and the microwave-assisted digestion in a Teflon coil of 100 cm permit a fast and quantitative extraction of Cu and Mn from different solid matrices, such as vegetables, powdered dietary products and sewage sludges. The development of an appropriate interphase, in which digested samples are cooled and degassified, previous to their introduction into the nebulizer of a flame atomic absorption spectrometer, makes possible the full automatization of the digestion and measurement steps of the elemental analysis of solids and it provides a sample frequency of 180 injections per hour. The developed procedure has also been applied for Pb and Zn determination in certified sewage sludge samples, with accurate results obtained for Pb but low results found for Zn.     

Wave shaping through finite electromagnetic bandgap structure

Transmission mechanisms and wave steering under localized feeding conditions through a finite electromagnetic bandgap structure are investigated both experimentally and theoretically. The artificial propagating medium consists of a two-dimensional metallic wire structure dimensioned for millimetre wave operation. By analogy with electron propagation in semiconductor heterostructures, the signatures of ‘modal‘ and ‘fluid‘ propagation regimes are experimentally demonstrated. Data are then analysed through electric field patterns calculated by means of a three-dimensional solver of Maxwell‘s equations.     

Modeling the thermodynamic and transport properties of decahydronaphthalene/propane mixtures: Phase equilibria, density, and viscosity

The density and viscosity of propane mixed with 66/34 trans/cis-decahydronaphthalene were measured over a wide range of temperatures (323-423 K), pressures (2.5-208 bar), and compositions (0-65 mol% propane). For conditions giving two phases, the composition of the dense phase was measured in addition to the density and viscosity. The modified Sanchez-Lacombe Equation of State (MSLEOS) was used with a single linearly temperature-dependent pseudo-binary interaction parameter to correlate the phase compositions and densities. The compositions and densities of the mixtures were captured well with absolute average deviations between the model and the data of 5.3% and 2.3%, respectively. The mixture viscosities were computed from a free volume model (FVM) by using a single constant binary interaction parameter. Density predictions from the MSLEOS were used as input mixture density values required for the FVM. The FVM was found to correlate well with the mixture viscosity data with an absolute average deviation between the model and the data of 5.7%.     

Rate of convergence of Local Linearization schemes for random differential equations

Recently, two Local Linearization (LL) schemes for the numerical integration of random differential equation have been proposed, which differ with respect to the algorithm that is used for the numerical implementation of the Local Linear discretization. However, in contrast with the Local Linear discretization, the order of convergence of the LL schemes have not been studied so far. In this paper, a general theorem about this matter is presented and, on that base, additional results are derived for each particular scheme.      

Computing multiple integrals involving matrix exponentials

In this paper, a generalization of a formula proposed by Van Loan [Computing integrals involving the matrix exponential, IEEE Trans. Automat. Control 23 (1978) 395–404] for the computation of multiple integrals of exponential matrices is introduced. In this way, the numerical evaluation of such integrals is reduced to the use of a conventional algorithm to compute matrix exponentials. The formula is applied for evaluating some kinds of integrals that frequently emerge in a number classical mathematical subjects in the framework of differential equations, numerical methods and control engineering applications.     

Activating multistep charge-transfer processes in fullerene-subphthalocyanine-ferrocene molecular hybrids as a function of π-π orbital overlap

We have synthesized two different fullerene-subphthalocyanine-ferrocene conjugates. The molecules were designed so that the ferrocene unit is linked at the subphthalocyanine axial position through a phenoxy spacer while the C(60) is rigidly held close to the concave face of the macrocycle via a 3-fold C(3)-symmetrical anchoring. The Bingel trisaddition reaction leading to the final products proceeded with very high regioselectivities and full diastereoselectivity. The only difference between both systems is the length of the triple tether employed, which finely regulates the regioselectivity of the trisaddition reaction and the distance between the subphthalocyanine and the C(60) complementary π-π surfaces. Thus, when the tether is connected to the subphthalocyanine through a direct C-C bond, a short π-π distance of 3.25-3.30 ? was calculated. In contrast, when it is connected through a slightly longer C-O-C bond, the distance increases to 3.5-3.6 ?. This π-π distance has a strong influence on the ground-state electronic interactions between the subphthalocyanine and the C(60), as determined from electronic absorption and cyclic voltammetry measurements. In addition, fluorescence and time-resolved transient absorption experiments demonstrated that different mechanisms operate in the two systems after photoexcitation. Despite the similar HOMO-LUMO gaps, only when the two complementary π-π surfaces of the subphthalocyanine and the C(60) are held at a close distance, therefore showing a high degree of orbital overlap, is a multistep electron transfer process triggered, ultimately leading to the long-lived, spatially separated C(60) radical anion and ferrocenium radical cation pair. A full account of the synthesis, characterization, and studies of the ground- and excited-state electronic interactions occurring in these conjugates, as well as in their reference C(60)-subphthalocyanine and subphthalocyanine-ferrocene dyads, is presented in this article.     

Photocatalytic activity of structured mesoporous TiO2 materials

Starting from colloidal TiO2 nanoparticles in combination with tetraethyl orthosilicate using neutral Pluronic or cationic cetyltrimethylammonium as templates, a series of structured mesoporous silicas has been obtained. The structure of the mesoporous titania was confirmed by isothermal gas adsorption, transmission electron microscopy, and X-ray diffraction. The pore diameter ranged between 3.8 and 10.9 nm, and the BET surface area varied from 99 to 584 m2 g(-1). The photocatalytic activity of these samples for the degradation of phenol in aqueous solution has been compared with that of standard P-25 TiO2. Even though the activity of these new mesostructured materials is lower that those found for P-25 TiO2, the turnover frequency of the photocatalytic activity (moles of phenol degraded per Ti atom present at initial reaction time) is much higher for the mesoporous titania, particularly with low titanium contents for those materials (mpTiO2-5 and TiO2SBA15-5).     

Solving the Bethe-Salpeter equation for two fermions in Minkowski space

The method of solving the Bethe-Salpeter equation in Minkowski space, developed previously for spinless particles (V.A. Karmanov, J. Carbonell, Eur. Phys. J. A 27, 1 (2006)), is extended to a system of two fermions. The method is based on the Nakanishi integral representation of the amplitude and on projecting the equation on the light-front plane. The singularities in the projected two-fermion kernel are regularized without modifying the original BS amplitudes. The numerical solutions for the J = 0 bound state with the scalar, pseudoscalar and massless vector exchange kernels are found. The stability of the scalar and positronium states without vertex form factor is discussed. Binding energies are in close agreement with the Euclidean results. Corresponding amplitudes in Minkowski space are obtained.     

Faddeev calculations in configuration space with Cartesian coordinates

The Faddeev-Noyes equations are solved in their natural Cartesian Jacobi coordinates for scattering below break-up threshold and for bound states. This approach is particularly well adapted to deal with strongly varying interactions. The method is proved to be successful in the three-nucleon system. First results concerning the⁴He trimer in configuration space are presented and further generalizations are suggested.Deceased