Surface Modification of Porous Silica with Bi-thiophene Tripodal Ligand and Aplication to Adsorption of Toxic Metal Cations

The immobilization of a thiophene-based tripodal ligand, with a donor sulfur, on the surface of an epoxide group containing a silica gel phase for the synthesis of a newly functionalized material based on porous silica-bound bi-thiophene tripodal ligand (SGBT) is described. The modified silica surface was characterized by ¹³C NMR of a solid sample, elemental analysis, and infrared spectra. This new material was also studied and evaluated by determination of the surface area using the BET equation, the adsorption and desorption capability using the isotherm of nitrogen and BJH pore sizes, respectively. The target material exhibits good thermal stability as determined by thermogravimetry curves. The synthesized material was utilized in column and batch methods for adsorption of Hg²⁺, Cd²⁺, Pb²⁺, Cu²⁺, Zn²⁺, K⁺, Na⁺, and Li⁺, and the material exhibits an affinity only towards toxic heavy metals.     

A spectral approach for the exact observability of infinite-dimensional systems with skew-adjoint generator

Let A be a possibly unbounded skew-adjoint operator on the Hilbert space X with compact resolvent. Let C be a bounded operator from D(A) to another Hilbert space Y. We consider the system governed by the state equation with the output y(t)=Cz(t). We characterize the exact observability of this system only in terms of C and of the spectral elements of the operator A. The starting point in the proof of this result is a Hautus-type test, recently obtained in Burq and Zworski (J. Amer. Soc. 17 (2004) 443-471) and Miller (J. Funct. Anal. 218 (2) (2005) 425-444). We then apply this result to various systems governed by partial differential equations with observation on the boundary of the domain. The Schrödinger equation, the Bernoulli-Euler plate equation and the wave equation in a square are considered. For the plate and Schrödinger equations, the main novelty brought in by our results is that we prove the exact boundary observability for an arbitrarily small observed part of the boundary. This is done by combining our spectral observability test to a theorem of Beurling on nonharmonic Fourier series and to a new number theoretic result on shifted squares.     

Orientation de la réaction d'alkylation des pyrazoles dans des conditions neutres et en catalyse par transfert de phase

The n-butylation and N-benzylation of nine pyrazoles bearing different substituents in positions 3 and 5 have been studied in neutral and basic medium (phase transfert catalysis). The orientation of the reaction depends strongly on the method used when the position 3 (or 5) of the starting pyrazole bears a substituent with a lone pair in ortho position (pyrazolyl or pyridyl). The different products have been identified by proton nmr.     

Unusual valences and fast electron exchange in MoFe2O4

The distribution of d electrons over the cations in MoFe₂O₄, which is represented by the formal valence assignment, is shown to be complicated by the equilibrium reactionsFe²⁺_B+Fe³⁺_A+Mo³⁺Fe³⁺_B+Fe²⁺_A+Mo⁴⁺We have used thermal treatment to confirm that the Mo are primarily on octahedral sites; Fe_A[Mo_BFe_B]O₄. K-shell absorption and Mössbauer data at T = 423 K > T_c demonstrate that the iron has an average valence near 2.5+ with fast electron transfer (τ_h < 10⁻⁸ sec) on both octahedral and tetrahedral sites. Paramagnetic susceptibility data give a Curie constant C_M = 7.95 ± 0.2 emu/mole and a Weiss constant θ_p = −445 K; magnetometer measurements confirm a compensation point near 160 K. Transport data give a surprisingly high electronic conductivity, but also give an activated mobility similar to that found in AlFe₂O₄ and CrFe₂O₄ where mixed Fe^3+/2+ valences on both A and B sites have been demonstrated. However, a positive Seebeck coefficient and a preexponential factor one order of magnitude higher in MoFe₂O₄ point to involvement of a fraction of the Mo atoms in electronic transport, which would be consistent with the observation of a τ_h < 10⁻⁸ sec on the A sites of a spinel. An energy diagram consistent with these data and other information about the relative redox potentials of these ions in oxides are proposed for this system.     

Facile synthesis of Cu-LDH with different Cu/Al molar ratios: application as antibacterial inhibitors

Research on Chemical Intermediates - A range of Cu-LDHs has been synthesized by co-precipitation using metal nitrate precursors and sodium carbonate under varying molar ratios Cu/Al...     

The effect of 1′,3,5,5′-tetramethyl-1′<Emphasis Type="Italic">H</Emphasis>-1,3′-bipyrazole on the corrosion of steel in 1.0 <Emphasis Type="SmallCaps">M</Emphasis> hydrochloric acid

The effect of some prepared compounds, namely 3,5-dimethyl-1H-pyrazole (P1), 3(5)-amino-5(3)-methylpyrazole (P2), and 1′,3,5,5′-tetramethyl-1′H-1,3′-bipyrazole (P3), on the corrosion behaviour of steel in 1.0 M hydrochloric acid solution as corrosive medium has been investigated at 308 K using weight-loss measurement, potentiodynamic polarisation, linear polarisation, and impedance spectroscopy (EIS). Generally, inhibition efficiency of the investigated compounds was found to depend on the concentration and nature of the inhibitor. P3 was a better inhibitor than P1 and P2, and its inhibition efficiency increased with increasing concentration of inhibitor, attaining 94% above 10⁻³  M. Potentiodynamic polarisation studies clearly reveal that P3 acts essentially as a cathodic inhibitor. E (%) values obtained from different methods are in reasonably good agreement. EIS measurements show an increase of transfer resistance with inhibitor concentration. Partial π-charge on atoms was calculated. Correlation between the highest occupied molecular orbital energy E _HOMO and inhibition efficiencies was sought. The temperature effect on the corrosion behaviour of steel in 1.0 M HCl without and with different concentrations of inhibitor P3 was studied in the temperature range 308 to 343 K. Thermodynamic data, for example heat of adsorption ( \Updelta H_\textads^° \Updelta H_{\text{ads}}^{^\circ } ), entropy of adsorption ( \Updelta S_\textads^° \Updelta S_{\text{ads}}^{^\circ } ) and free energy of adsorption ( \Updelta G_\textads^° \Updelta G_{\text{ads}}^{^\circ } ) were calculated by use of thermodynamic equations. Kinetic activation data, for example E _a, ΔH*, ΔS* and pre-exponential factor, were calculated, and are discussed. The inhibiting action of P3 on the corrosion of steel in 1–10 M hydrochloric acid was also studied by weight-loss measurement. The rate constant and reaction constant were calculated for the corrosion reactions. Adsorption of P3 on the steel surface in 1.0 M HCl follows the Langmuir isotherm model.     

Detecting high-dimensional determinism in time series with application to human movement data

We numerically investigate the ability of a statistic to detect determinism in time series generated by high-dimensional continuous chaotic systems. This recently introduced statistic (denoted V_E2) is derived from the averaged false nearest neighbors method for analyzing data. Using surrogate data tests, we show that the proposed statistic is able to discriminate high-dimensional chaotic data from their stochastic counterparts. By analyzing the effect of the length of the available data, we show that the proposed criterion is efficient for relatively short time series. Finally, we apply the method to real-world data from biomechanics, namely postural sway time series. In this case, the results led us to exclude the hypothesis of nonlinear deterministic underlying dynamics for the observed phenomena.     

On the numerical approximation of high-frequency acoustic multiple scattering problems by circular cylinders

The aim of this paper is to propose a numerical strategy for computing the solution of two-dimensional time-harmonic acoustic multiple scattering problems at high-frequency. The scatterers are assumed to be circular, leading therefore to semi-analytical representation formulae of the scattered field through the solution of a large linear system of equations. Taking advantage of the special block Toeplitz structure of the matrix of the linear system, a fast iterative and preconditioned numerical method yielding large memory savings is proposed. Several numerical experiments for general configurations are presented to show the efficiency of the numerical method.     

Computing reachable sets for uncertain nonlinear monotone systems

We address nonlinear reachability computation for uncertain monotone systems, those for which flows preserve a suitable partial orderings on initial conditions. In a previous work Ramdani (2008) [22], we introduced a nonlinear hybridization approach to nonlinear continuous reachability computation. By analysing the signs of off-diagonal elements of system’s Jacobian matrix, a hybrid automaton can be obtained, which yields component-wise bounds for the reachable sets. One shortcoming of the method is induced by the need to use whole sets for addressing mode switching. In this paper, we improve this method and show that for the broad class of monotone dynamical systems, component-wise bounds can be obtained for the reachable set in a separate manner. As a consequence, mode switching no longer needs to use whole solution sets. We give examples which show the potentials of the new approach.