Drop deformation under surfactants adsorption

The movements of free liquid drops, resulting from unbalanced surface tension gradients, in our case the adsorption of a surfactant, constitute important surface phenomena (Marangoni effect). The aim of this paper is to correlate the effect of pressure forces on the drop, with the surface coverage degree, namely with the extent to which the drop surface is covered by the surfactant. Our model shows that for a covered degree less then about 68°, these forces are negative. This means that these forces exerted by the external liquid upon the drop are oriented towards the negative direction of the normal to the drop surface, acting like a hammer. Some numerical data are given. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

SiO2-Iron Oxide Composites Obtained by Sol-Gel Method

Composite SiO₂-iron oxide materials were prepared by three experimental procedures. In the first case (1), the iron oxides were precipitated during the sol-gel process. In the second case (2), the SiO₂ matrix was initially obtained, and the iron oxides were formed by thermal treatment after impregnation of a soluble Fe²⁺ salt in the previously processed matrix. In the third method (3), ferrite powders, prepared by wet chemical method, were embedded into a SiO₂ based sol-gel matrix. Two type of precursors (tetraethoxysilane (TEOS) or methyltriethoxysilane (MTEOS) were used as SiO₂ sources. Various properties versus both type of precursor and on the method of preparation were noticed. Materials with high porosity and nano-sized iron oxide content could be prepared using the mentioned above methods.     

Electronic properties of furyl substituents at phosphorus and their influence on 31P NMR chemical shifts

The electronic properties of 2-furyl and 3-furyl substituents attached to phosphanes and phosphonium salts were studied by means of IR spectroscopy and experimental and computational (31)P NMR spectroscopy. The heteroaromatic systems proved to be electron withdrawing with respect to phenyl substituents. However, phosphorus atoms with attached furyl substituents are strongly shielded in NMR. The reason for this phenomenon was studied by solid state (31)P MAS NMR experiments. The chemical shift tensor was extracted, and the orientation within the molecules was determined. The tensor component sigma(33), which is effected the most by furyl systems, is oriented perpendicular to the P-C bonds of the substituents. P-furyl bonds are shorter than P-phenyl bonds. We assume therefore a lower ground-state energy of the molecules, because of the electron withdrawing properties of the 2-furyl systems. The sigma(para) component of the (31)P NMR magnetic shielding is therefore smaller, which results in an overall increase of the magnetic shielding.     

A continuous Lagrangian sensitivity equation method for incompressible flow

A continuous Lagrangian sensitivity equation method (CLSEM) is presented as a cost effective alternative to the continuous (Eulerian) sensitivity equation method (CESEM) in the case of shape parameters. Boundary conditions for the CLSEM are simpler than those of the CESEM. However a mapping must be introduced to relate the undeformed and deformed configurations thus making the PDEs more complicated. We propose the use of pseudo-elasticity equations to provide a general framework to generate this mapping for unstructured meshes on complex geometries. The methodology is presented in details for the incompressible Navier–Stokes and sensitivity equations in variational form. The PDEs are solved with an adaptive FEM. Sensitivity data obtained with both approaches for a flow around a NACA 4512 are used to obtain estimates of flows around nearby geometries. Results indicate that the CLSEM produces significant improvements in terms of both accuracy and CPU time.     

Two-dimensional almost-Riemannian structures with tangency points

Two-dimensional almost-Riemannian structures are generalized Riemannian structures on surfaces for which a local orthonormal frame is given by a Lie bracket generating pair of vector fields that can become collinear. We study the relation between the topological invariants of an almost-Riemannian structure on a compact oriented surface and the rank-two vector bundle over the surface which defines the structure. We analyse the generic case including the presence of tangency points, i.e. points where two generators of the distribution and their Lie bracket are linearly dependent. The main result of the paper provides a classification of oriented almost-Riemannian structures on compact oriented surfaces in terms of the Euler number of the vector bundle corresponding to the structure. Moreover, we present a Gauss–Bonnet formula for almost-Riemannian structures with tangency points.     

Automatic chemiluminescence-based determination of carbaryl in various types of matrices

Carbaryl, a modern pesticide widely used for both agricultural and non-agricultural purposes, was determined from the chemiluminescence produced in its reaction with Ce(IV) in a nitric acid medium containing rhodamine 6G as sensitizer, using flow-injection techniques. A straightforward automatic method based on measurements peak height and peak area, which are directly proportional to the carbaryl concentration, was thus developed. Calibration graphs are linear over the concentration range from 50 to 2000 ng mL⁻¹. The limit of detection, as determined according to Clayton, is 45.6 and 28.7 ng mL⁻¹ for peak height and peak area measurements, respectively. The relative standard deviation for 10 samples was less than 1.4% with both types of measurements. Two commercial formulations containing carbaryl were analysed using both types of measurements, which provided acceptable recovery values. Solid-phase extraction was used to concentrate and separate the analyte from the matrix. The method was successfully applied to the analysis of spiked water samples as well as in soil and grain samples. The proposed method exhibited a high selectivity no other pesticide containing the naphthalene group such as antu, napropamide or naftalam, etc., was found to interfere with the determination of carbaryl.     

Decrease of luminol chemiluminescence upon exposure of human blood serum to 50 Hz electric fields

The chemiluminescence of luminol, after 1 and 2h in vitro exposure of human serum to 50 Hz electric fields of different intensities, decreases as compared to the controls. This indicates a field-induced decrease in the concentration of the free radicals. The report is limited to the key kinetic and field data, inviting independent kinetic analysis of the data in terms of reaction moments or reaction susceptibilities for the various normal modes indicated by the data.     

High‐order time integrators for front‐tracking finite‐element analysis of viscous free‐surface flows

This paper proposes implicit Runge–Kutta (IRK) time integrators to improve the accuracy of a front‐tracking finite‐element method for viscous free‐surface flow predictions. In the front‐tracking approach, the modeling equations must be solved on a moving domain, which is usually performed using an arbitrary Lagrangian–Eulerian (ALE) frame of reference. One of the main difficulties associated with the ALE formulation is related to the accuracy of the time integration procedure. Indeed, most formulations reported in the literature are limited to second‐order accurate time integrators at best. In this paper, we present a finite‐element ALE formulation in which a consistent evaluation of the mesh velocity and its divergence guarantees satisfaction of the discrete geometrical conservation law. More importantly, it also ensures that the high‐order fixed mesh temporal accuracy of time integrators is preserved on deforming grids. It is combined with the use of a family of L‐stable IRK time integrators for the incompressible Navier–Stokes equations to yield high‐order time‐accurate free‐surface simulations. This is demonstrated in the paper using the method of manufactured solution in space and time as recommended in Verification and Validation. In particular, we report up to fifth‐order accuracy in time. The proposed free‐surface front‐tracking approach is then validated against cases of practical interest such as sloshing in a tank, solitary waves propagation, and coupled interaction between a wave and a submerged cylinder. Copyright © 2015 John Wiley & Sons, Ltd.