The impact of laser field statistics in determination of temperature and concentration by multiplex USED CARS

Experiments have been performed which demonstrate that the ratio of resonant to nonresonant third-order susceptibilities measured in multiplex USED CARS are affected by the time correlation of the pump fields. Comparing the resonant to nonresonant signal ratio obtained with decorrelated fields to the ratio obtained with correlated fields, a relative increase of 2.5 was measured for the nitrogen Q-branch, whereas a corresponding increase of 1.9 was observed for the hydrogen Q(1)-line. To compare our experimental results with theoretical calculations of the spectral shapes, the nonresonant third-order susceptibilities of a number of gases were re-evaluated by calibrating to the nonresonant susceptibility of argon.     

Inviscid flow modelling using asymmetric implicit finite difference schemes

Asymmetric spatial implicit high‐order schemes are introduced and, based on Fourier analysis, the dispersion and damping are calculated depending on the asymmetry parameter. The derived schemes are then applied to a number of inviscid problems. For incompressible convection problems the proposed asymmetric schemes (applied as upwind schemes) lead to stable and accurate results. To extend the applicability of the proposed schemes to compressible problems acoustic upwinding is used. In a two‐dimensional compressible flow example acoustic and conventional upwinding are combined. Evaluation of all presented results leads to the conclusion that, of the studied schemes, the implicit fifth order upwinding scheme with an asymmetry parameter of about 0.5 leads to the optimal results. Copyright © 2005 John Wiley & Sons, Ltd.     

Slow motions of a solid spherical particle close to a viscous interface

In order to investigate the hydrodynamic interaction between an interface and a spherical particle and its dependence on the type of interface, it is essential to compute the drag and torque exerted on the sphere in the vicinity of the interface. In this paper, the problem of all slow elementary motions (relative translation and rotation) and stationary movement of a spherical particle next to a solid, viscous or free interface is considered. For low capillary numbers and different values of surface dilatational and shear viscosities in a curvilinear co-ordinate system of revolution with bicylindrical co-ordinates in meridian planes, the problem reduces from three to two dimensions. The model equations and boundary conditions, which contain second-order derivatives of the velocities, transform to an equivalent well-defined system of second-order partial differential equations which is solved numerically for medium and small values of the dimensionless distance to the interface. Very good agreement with the asymptotic equation for a translating sphere close to a solid interface could be achieved. The numerical results reveal in all cases the strong influence of the surface viscosity on the motion of the solid sphere. For small distances from the interface, the drag and torque coefficients change significantly depending on the surface viscosity.     

Terahertz split-ring metamaterials as transducers for chemical sensors based on conducting polymers: a feasibility study with sensing of acidic and basic gases using polyaniline chemosensitive layer

We report on the first application of terahertz metamaterials acting as transducers for chemical sensors based on conducting polymers. In our feasibility study aimed at sensing of gaseous hydrochloric and ammonia, a two-dimensional sensor metamaterial consisting of an array of split-ring resonators on the surface of undoped silicon wafer was prepared. The surface of the resonator was coated with a 150-μm layer of polyaniline. Binding of hydrogen chloride to polyaniline leads to distinct changes in the resonance frequency of the metamaterial. Measurements can be performed both in the reflection and transmission mode. A numerical simulation of the response revealed an increase of both the real and the imaginary components of the dielectric function of the polyaniline film. These changes are attributed to the transition from emaraldine base to emeraldine salt. The results demonstrate a new approach for formation of highly sensitive transducers for chemical sensors.

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Adsorption behavior of 4-methoxypyridine on gold nanoparticles

We demonstrate a phase transfer method to create stable colloidal solutions of Au nanoparticles with 4-methoxypyridine ligands. We then investigate the adsorption behavior of 4-methoxypyridine onto gold surfaces by Raman spectroscopy, DFT calculations, and (1)H NMR. In contrast to unsubstituted pyridine and the frequently used (N,N-dimethylamino)pyridine (DMAP), a flat adsorption of 4-methoxypyridine on gold was found.     

A novel class of organo- (hydro-) gelators based on ascorbic acid

A library of novel, lipid-modified derivatives of ascorbic acid was shown to exhibit highly attractive properties as surfactants, emulsifiers, oil soluble antioxidants, and highly effective gelators in organic solvents and especially water. In these systems, intermolecular hydrogen bonding and van der Waals forces act synergistically to induce gelation as confirmed by spectroscopic studies. The morphology of the formed gel has been characterized by scanning electron microscopy.